Schizophrenia Research Forum - A Catalyst for Creative Thinking

Schizophrenia Genetics 5: From Genes to Biology…and Therapies

In SRF's schizophrenia genetics overview, writer Pat McCaffrey surveys the range of experimentation and opinion in the field in a five-part series.

See Part 1, Linkage; Part 2, GWAS, Part 3, CNVs, Part 4, Bigger Genetics. Read a PDF of the entire series.


25 March 2010. The genetic evidence amassed to date points to the conclusion that schizophrenia arises from a mixture of common variants of small effect and rarer variants of large or small effect. From linkage to candidate studies to genomewide association and copy number variant studies, dozens of suspects have arisen. Names have been named, and the debate will continue over the strength of the evidence for particular genes and how to best catalog the full spectrum of genetic variation in people with schizophrenia (you can follow the scoring for common variants at SZGene). But there are enough genes of interest now that the questions increasingly on researchers’ minds go to the next step: how can that information lead us toward understanding the biology of schizophrenia, and, ultimately, to new therapies?

Endophenotypes: bridging genes and disease
“Genes do not encode for complex behaviors,” said Daniel Weinberger of the National Institute of Mental Health, Bethesda, Maryland. They do not encode for hallucinations or delusions, panic attacks or sadness. “Genes encode for simple molecules in cells. And ultimately, those simple molecules in cells affect the element of brain circuits and systems.”

In fact, Weinberger writes in a recent editorial in Nature, “Finding specific genes for mental illness now seems a pipe dream. A more realistic endeavor for the next 10 years is to look for genes that code for basic cellular and brain functions that modulate our responses to the environment and that come together in particular ways in individuals at increased risk.”

Those basic cellular and brain functions are what Weinberger calls intermediate phenotypes and others commonly refer to as endophenotypes (for more, see SRF Live Discussion led by Irving Gottesman and Mayada Akil). Rather than behavioral readouts, intermediate phenotypes are heritable traits of brain biology that are under direct genetic control. Thus, instead of psychosis, an intermediate phenotype would be activation of brain networks during a memory task. The phenotype can be a biochemical measure, such as dopamine levels, an imaging readout, such as the size of a brain structure or a functional MRI measure. The goal of studying intermediate phenotypes is to allow researchers to define the proximal action of genetic variation on the brain and to eventually understand how that variation contributes to the development of schizophrenia.

Because endophenotypes are allegedly closer to gene function than the disease diagnosis, they should show a stronger association with genotypes. Proposed examples of this notion include the association of variants in dopamine-regulating COMT and MTHFR genes with activation of the dorsolateral prefrontal cortex during memory tasks (e.g., see SRF related news story). In newer findings, a schizophrenia-associated polymorphism in the ZNF804A gene was associated with altered functional connectivity in the brains of healthy people (see SRF related news story and Walter et al., 2010). Those studies found significant associations of the SNP with brain function in a sample of just more than 100 people.

Not everyone agrees with the endophenotype approach. Some argue that the proposed intermediate phenotypes themselves are genetically complex, perhaps no less so than schizophrenia itself. Furthermore, the links between genes and endophenotypes may be hard to discern. For example, Mike Owen makes this critique of the ZNF804A study: “They looked at three tests of cognition, but shouldn't they have looked at more before drawing conclusions? Who knows what other associated endophenotypes they might find?” Finally, there is yet no evidence that places endophenotypes on the causal path to disease. They could simply be indexing disease risk, Owen said.

Weinberger disagrees. “Many studies have shown that cortical cognitive dysfunctions are present before the emergence of the diagnostic symptoms of schizophrenia, suggesting that they are on the path, just as high cholesterol levels are risk factors on the path to cardiovascular disease. The same is true for [velo-cardio-facial syndrome], in which cognitive deficits precede the emergence of psychosis in early adolescence and clearly are linked to the chromosomal hemi-deletion.”

The question for Weinberger is not whether intermediate phenotypes are a worthwhile strategy. “They are a critical strategy,” he said. “The real debate is about how we identify intermediate biological traits that will be maximally informative in understanding the mechanisms of these genes.”

New dimensions
Another question related to the value of intermediate phenotypes is whether genetics may be more strongly correlated with different behavioral or cognitive manifestations of schizophrenia. The disease is not a monolith—patients display a varying mixture of symptoms ranging from psychosis to cognitive symptoms, negative symptoms, and mood disorders. These symptom domains could be another way to break patients into subgroups that may more strongly associate with particular genes. “There are many ways to sub-classify samples using different methods at the clinical level or at the phenotype level to identify much stronger contributions to the genotype in specific individuals,” said Markus Nöthen, Bonn University, Germany.

Those kinds of studies require not only many subjects, but also much clinical detail on each subject. Nöthen pointed out that one aim of the Psychiatric GWAS Consortium is to carry out genomewide association studies in a more detailed way with symptom dimensions. “But the problem is whether all of the samples included in the study have this information available. Probably the common information will be rather crude, for example, age at onset, or so on. Still it might be very important information, and we hope that these will actually lead to new loci,” he said.

“There will be many and much more detailed studies to come,” Nöthen said. “We have been extremely interested in the different phenotype dimension for many years, and Marcella Rietschel at the Institute of Mental Health in Mannheim has set up databases for all of our patients, which incorporate more than 2,000 items per patient on a lifetime basis. We are actually very much looking forward to correlating this with the genes identified, and I think it will be extremely interesting to see if symptom dimensions or symptom clusters are associated with specific genes.”

David Porteous, University of Edinburgh, United Kingdom, likes the idea of drilling down into existing datasets to mine the genetic heterogeneity for clues to biology. While it is clear there is no single gene for schizophrenia or bipolar disorder with a large population effect, it could be that only a very small handful of the long list of possible candidates are important and relevant to any one individual. “That question has not yet been addressed and should be before we move on. Going for ever-bigger numbers of samples just adds more ‘noise’ to the analysis,” he said.

Phenotypic parcellation could also lead to better modeling in animals, Nöthen said. “Symptom dimensions might be much more appropriate actually to model in a mouse than schizophrenia. Establishing genotype correlations is extremely important to guide neurobiology studies using other systems.”

Among other big questions yet to be approached comprehensively are gene-gene interactions (epistasis), gene-environment interactions, and the question of epigenetics, or heritable changes in the genome that are not necessarily reflected in the DNA sequence. All of these may contribute to the risk of schizophrenia, and with the exception of a handful of studies on epistasis and gene-environment interactions, these areas are still largely unexplored.

New therapies?
In any case, gene discovery will lead to new therapies, according to Nicholas Brandon at Pfizer Neuroscience, Princeton, New Jersey. Starting at Merck and then at Wyeth (now Pfizer), Brandon has been a long-time collaborator of Porteous, working on the DISC1 pathway. Brandon points out that DISC1 came with a high level of biological plausibility, because of strong genetic evidence that it segregates with mental illness in an extended family. That helped the field move quickly from genes to biology, and studies of DISC1’s partners, starting with PDE4 (see SRF related news story), and lately GSK3 and others (see SRF related news story and SfN 2009 meeting coverage) have yielded several potential drug targets.

Brandon’s main job is target validation, the assessment of whether or not a particular protein will make a plausible drug target. And that critical analysis is something he sees lacking so far in the wake of the large genomewide association studies and copy number variant discoveries.

“I’m thinking beyond that new genetic hit and the first excitement and asking if something has the legs to carry on through to discovery,” Brandon said. “That’s where I think a lot of discussion has to be had now, how much effort you want to sink into these immediately.” For example, there are issues common to all drugs, such as potential side effects, and others unique to psychiatric illness, such as, Will a target affect positive or negative symptoms?

Compared to the DISC1 experience, Brandon has found the genomewide association results a bit thin so far. “A lot of money has been spent on these studies, and the output so far has been fairly limited,” he said. “I’m sure there will be a lot of meta-analyses of all the datasets, and perhaps we’ll parse out some other important findings. But I have a feeling we’ll end up with maybe one or two new candidates, and mostly we’ll end up with molecules which are part of pathways we’ve already identified using more ’old-school’ techniques. I’d love to be proved wrong, and I’d love to see some of the new findings really open up areas of biology we haven’t thought about before.”

Even though the crop of genes so far has not been overwhelming, Brandon said, they will prove to be a key platform for moving the field forward. One area where genetics will help considerably will be to define populations of patients that may benefit from differential therapy. For example, Brandon hypothesized, some patients may respond best to glutamate-based therapies, others to dopamine-targeting drugs, or even to GSK3-pathway interventions. “I think that’s where the industry’s moving now, trying to classify, at the genetic level, responders, non-responders. I think the current wave of studies, even though they may not be bringing up potentially new targets, can be providing new critical information for their part of the discovery process,” he said.

It all comes down to the details, Brandon stressed. “At the end of the day it’s still going to be people taking forward distinct pathways, whether it’s a DISC1 pathway or the neuregulin pathway, and exploring the biology in a great detail. That takes time, and that’s where I think the major breakthroughs will come.”

Optimism rules the day
To a person, all the researchers SRF spoke with professed optimism for the next five to 10 years. Whether geneticists or biologists, high-throughput proponents or those enamored of cell-based approaches, all see the next few years as a time of great opportunity to go from genes to pathways, from pathways to biology, and from biology to interventions.

We hope that another series of genetics articles circa 2015 will justify that optimism, but we humbly recognize that the puzzle of schizophrenia has resisted solution for more than a century. To paraphrase Winston Churchill, who spoke of a different battle, closing in on the genetics of schizophrenia will not be the end. It will not even be the beginning of the end. But maybe it will be the end of the beginning.—Pat McCaffrey.

See Part 1, Linkage; Part 2, GWAS, Part 3, CNVs, Part 4, Bigger Genetics. Read a PDF of the entire series.

Comments on Related News


Related News: Messing with DISC1 Protein Disturbs Development, and More

Comment by:  Anil Malhotra, SRF Advisor
Submitted 21 November 2005
Posted 21 November 2005

The relationship between DISC1 and neuropsychiatric disorders, including schizophrenia, schizoaffective disorder, and bipolar disorder, has now been observed in several studies. Moreover, a number of studies have demonstrated that DISC1 appears to impact neurocognitive function. Nevertheless, the molecular mechanisms by which DISC1 could contribute to impaired CNS function are unclear, and these two papers shed light on this critical issue.

Millar et al. (2005) have followed the same strategy that they so successfully utilized in their initial DISC1 studies, identifying a translocation that associated with a psychotic illness. In contrast to DISC1, in which a pedigree was identified with a number of translocation carriers, this manuscript is based upon the identification of a single translocation carrier, who appears to manifest classic signs of schizophrenia, without evidence of mood dysregulation. Two genes are disrupted by this translocation: cadherin 8 and phosphodiesterase 4B (PDE4B). The researchers' elegant set of experiments provides compelling biological evidence that PDE4B interacts with DISC1 and suggests a mechanism mediated by cAMP for DISC1/PDE4B effects on basic molecular processes underlying learning, memory, and perhaps psychosis. It remains possible that PDE4B (and DISC1) are proteins fundamentally involved in cognitive processes, and that the observed relationship to psychotic illnesses represents a final common pathway of neurocognitive impairment. This would be consistent with data from our group (Lencz et al., in press) demonstrating that verbal memory impairment specifically predicts onset of psychosis in at-risk subjects. Similarly, Burdick et al. (2005) found that our DISC1 risk genotypes (Hodgkinson et al., 2004) were associated with impaired verbal working memory. Finally, Callicott et al. (2005) found that a DISC1 risk SNP, Ser704Cys, predicted hippocampal dysfunction, an SNP which we (DeRosse et al., unpublished data) have also found to link with the primary psychotic symptoms (persecutory delusions) manifested by the patient in the Millar et al. study. This body of evidence supports the notion that these proteins play fundamental roles in the key clinical manifestations of schizophrenia.

Kamiya et al. (2005) provide another potential mechanism for these effects, suggesting that a DISC1 mutation may disrupt cerebral cortical development, hinting that studies examining the role of DISC1 genotypes on brain structure and function in the at-risk schizophrenia pediatric patients may be fruitful.

Taken together, these papers add considerable new data suggesting that DISC1 plays a key role in the etiology of schizophrenia, and places DISC1 at the forefront of the rapidly growing body of schizophrenia candidate genes.

References:
Burdick KE, Hodgkinson CA, Szeszko PR, Lencz T, Ekholm JM, Kane JM, Goldman D, Malhotra AK. DISC1 and neurocognitive function in schizophrenia. Neuroreport 2005; 16(12):1399-1402. Abstract

Callicott JH, Straub RE, Pezawas L, Egan MF, Mattay VS, Hariri AR, Verchinski BA, Meyer-Lindenberg A, Balkissoon R, Kolachana B, Goldberg TE, Weinberger DR. Variation in DISC1 affects hippocampal structure and function and increases risk for schizophrenia. Proc Natl Acad Sci USA 2005; 102(24): 8627-8632. Abstract

Hodgkinson CA, Goldman D, Jaeger J, Persaud S, Kane JM, Lipsky RH, Malhotra AK. Disrupted in Schizophrenia (DISC1): Association with schizophrenia, schizoaffective disorder, and bipolar disorder. Am J Hum Genet 2004; 75:862-872. Abstract

Lencz T, Smith CW, McLaughlin D, Auther A, Nakayama E, Hovey L, Cornblatt BA. Generalized and specific neurocognitive deficits in prodromal schizophrenia. Biological Psychiatry (in press).

View all comments by Anil Malhotra

Related News: Messing with DISC1 Protein Disturbs Development, and More

Comment by:  Angus Nairn
Submitted 29 December 2005
Posted 31 December 2005
  I recommend the Primary Papers

This study describes an interesting genetic link between PDE4B (phosphodiesterase 4B) and schizophrenia that may be related to a physical interaction with DISC1 (disrupted in schizophrenia 1), another gene associated with the psychiatric disorder. The study is highly suggestive of a role for the PDE4B/DISC1 complex in schizophrenia. However, the mechanistic model suggested by the authors whereby DISC1 sequesters PDE4B in an inactive state seems overly speculative, given the results presented in this paper and in prior studies that have examined the regulation of PDE4B by phosphorylation in the absence of DISC1.

View all comments by Angus Nairn

Related News: Messing with DISC1 Protein Disturbs Development, and More

Comment by:  Patricia Estani
Submitted 2 January 2006
Posted 2 January 2006
  I recommend the Primary Papers

Related News: Messing with DISC1 Protein Disturbs Development, and More

Comment by:  Ali Mohammad Foroughmand
Submitted 16 December 2006
Posted 16 December 2006
  I recommend the Primary Papers

Related News: MTHFR, COMT Genes Work Together to Bring Down Cortical Activation in Schizophrenia

Comment by:  Jennifer Barnett (Disclosure)
Submitted 19 December 2008
Posted 19 December 2008

The recent studies of Prata and colleagues and Roffman and colleagues shed considerable further light on the ongoing mysteries of the catechol-O-methyltransferase Val158Met polymorphism and its effects on the proposed “inverted-U” shape of cortical dopamine function. Both study teams should be congratulated on these high-quality studies using what are, for neuroimaging experiments, impressive numbers of both patients and controls.

Our understanding of the effects of the COMT Val/Met polymorphism in humans remains incomplete despite no shortage of elegant studies and intriguing results. In their landmark 2001 paper, Egan and colleagues reported that Val carriers showed poorer cognitive function, a higher risk for schizophrenia, and reduced prefrontal efficiency when compared with Met carriers. These associations, along with a multitude of other psychological and psychiatric phenotypes, have since been tested in labs across the world. Meta-analyses of the available data have concluded that there is little influence of the Val/Met polymorphism on risk for schizophrenia (Allen et al., 2008; Fan et al., 2005; Munafo et al., 2005) or cognitive function (Barnett et al., 2008). Perhaps because of the increased cost and difficulty of collecting imaging data compared with cognitive or disease status, rather fewer studies have been published testing the hypothesis that Val/Met affects prefrontal cortical efficiency, but those few (e.g., Ho et al., 2005) do appear consistent with the original report .

Prata et al. (2008) studied the effects of Val/Met on cortical activation during a verbal fluency task and report an interesting, if somewhat unintuitive result: that there are opposite effects of genotype on task performance and cortical activation in patients with schizophrenia, compared with those seen in healthy controls. In patients, Val alleles were associated with poorer task performance, while in controls, there was no significant difference between genotype groups. The trend, however, was for better task performance among Val-carrying controls, and the group x genotype interaction term was significant. These results were interestingly reflected in regional activation patterns, where in the right peri-Sylvian region Val alleles were associated with increased activation in patients, and decreased activation in controls. Further analyses suggested that these group x genotype interactions may partly reflect genetically driven differences in functional connectivity. Explanations for these opposite effects in patients and controls are consistent with an inverted-U shape of dopaminergic function where patients lie on the left-hand side of the U (suboptimal dopamine) and controls lie somewhat to the right of the center, such that increased cortical dopamine (as experienced by Met carriers) is slightly disadvantageous. Interestingly, we found the same pattern when comparing the effect of Val/Met genotype on N-back performance in patients and controls (Barnett et al., 2008); it is good to see these non-linear behavioral results supported by structural and functional imaging data.

The Val/Met polymorphism is certainly not the only determinant of COMT function, and we now know that other SNPs within the gene greatly affect the amount of COMT expressed (Nackley et al., 2006). Moreover, in affecting cortical dopamine and norepinephrine, COMT does not operate alone. Roffman and colleagues’ study (Roffman et al., 2008) very nicely demonstrates how much we have still to learn about potential gene-gene interaction (epistatic) effects. They studied brain activation during a working memory task and analyzed the combined effects of Val/Met and a functional polymorphism in MTHFR, a gene with plausible biological interactions with COMT. In this study, COMT genotype alone did not predict variation in activation in dorsolateral prefrontal cortex. There was a three-way interaction, however, between COMT and MTHFR genotypes and diagnostic group, such that MTHFR genotype appeared to modulate prefrontal activation most in Val/Val patients (who would be expected to have the lowest prefrontal dopamine), and among Met/Met controls (who would be expected to have the highest prefrontal dopamine, potentially putting them beyond the optimal level in the inverted-U model).

Despite considerable interest in gene-gene and gene-environment interactions among schizophrenia researchers, replications of such interactions have been relatively few and far between. While it is notoriously difficult to demonstrate biological interaction from statistical data alone, Roffman’s study provides us with hope that a really good hypothesis may still give us reason to try and do so.

References:

Allen NC, Bagade S, McQueen MB, Ioannidis JP, Kavvoura FK, Khoury MJ, Tanzi RE, Bertram L. Systematic meta-analyses and field synopsis of genetic association studies in schizophrenia: the SzGene database. Nat Genet. 2008 Jul 1;40(7):827-34. Abstract

Barnett JH, Scoriels L, Munafò MR. Meta-analysis of the cognitive effects of the catechol-O-methyltransferase gene Val158/108Met polymorphism. Biol Psychiatry. 2008 Jul 15;64(2):137-44. Abstract

Fan JB, Zhang CS, Gu NF, Li XW, Sun WW, Wang HY, Feng GY, St Clair D, He L. Catechol-O-methyltransferase gene Val/Met functional polymorphism and risk of schizophrenia: a large-scale association study plus meta-analysis. Biol Psychiatry. 2005 Jan 15;57(2):139-44. Abstract

Ho BC, Wassink TH, O'Leary DS, Sheffield VC, Andreasen NC. Catechol-O-methyl transferase Val158Met gene polymorphism in schizophrenia: working memory, frontal lobe MRI morphology and frontal cerebral blood flow. Mol Psychiatry. 2005 Mar 1;10(3):229, 287-98. Abstract

Munafò MR, Bowes L, Clark TG, Flint J. Lack of association of the COMT (Val158/108 Met) gene and schizophrenia: a meta-analysis of case-control studies. Mol Psychiatry. 2005 Aug 1;10(8):765-70. Abstract

Nackley AG, Shabalina SA, Tchivileva IE, Satterfield K, Korchynskyi O, Makarov SS, Maixner W, Diatchenko L. Human catechol-O-methyltransferase haplotypes modulate protein expression by altering mRNA secondary structure. Science. 2006 Dec 22;314(5807):1930-3. Abstract

Prata DP, Mechelli A, Fu CH, Picchioni M, Kane F, Kalidindi S, McDonald C, Howes O, Kravariti E, Demjaha A, Toulopoulou T, Diforti M, Murray RM, Collier DA, McGuire PK. Opposite Effects of Catechol-O-Methyltransferase Val158Met on Cortical Function in Healthy Subjects and Patients with Schizophrenia. Biol Psychiatry. 2008 Dec 1; Abstract

Roffman JL, Gollub RL, Calhoun VD, Wassink TH, Weiss AP, Ho BC, White T, Clark VP, Fries J, Andreasen NC, Goff DC, Manoach DS. MTHFR 677C --> T genotype disrupts prefrontal function in schizophrenia through an interaction with COMT 158Val --> Met. Proc Natl Acad Sci U S A. 2008 Nov 11;105(45):17573-8. Abstract

View all comments by Jennifer Barnett

Related News: MTHFR, COMT Genes Work Together to Bring Down Cortical Activation in Schizophrenia

Comment by:  S.H. Lin
Submitted 15 January 2009
Posted 19 January 2009
  I recommend the Primary Papers

The “inverted-U” shape of cortical dopamine function with regard to the COMT Val158Met polymorphism is an interesting issue worthy of discussion. The COMT enzyme may modulate the balance of tonic and phasic dopamine function depending on the area-specific neurochemical environment (Bilder et al., 2004). There is thought to be a complex nonlinear relationship between dopamine availability and brain function (Williams et al., 2007).

Our study (Liao et al., 2008) examined the relationships of three COMT SNPs—rs737865 in intro 1, rs4680 in exon 4 (Val158Met), and downstream rs165599—to schizophrenia and its related deficits in neurocognitive function in families of patients with schizophrenia in Taiwan. The study results indicated that the Val allele was associated with better performance on the WCST (i.e., greater Categories Achieved and Conceptual Level Response and fewer Perseverative Errors) or CPT (i.e., greater d'), which might be explained by an “inverted U” shaped relationship between dopamine levels and prefrontal cortex function (Cools and Robbins 2004; Mattay et al., 2003). This model reveals that an optimal functioning occurs within a narrow range of dopamine level, and both excessive and insufficient dopamine levels impair working memory performance. Our results indicate that the genetic variants in COMT might be involved in modulation of neurocognitive functions, hence conferring increased risk to schizophrenia.

References:

Bilder, R.M., Volavka, J., Lachman, H.M. & Grace, A.A. (2004) The catechol-O-methyltransferase polymorphism: relations to the tonic-phasic dopamine hypothesis and neuropsychiatric pheno-types. Neuropsychopharmacology 29, 1943–1961. Abstract

Cools, R. and Robbins, T.W. (2004) Chemistry of the adaptive mind. Philos Transact A Math Phys Eng Sci 362, 2871–2888. Abstract

Liao S.Y., Lin S.H., Liu C.M., Hsieh M.H., Hwang T.J., Liu S.K., Guo S.C., Hwu, H.G., Chen W.J. (2008): Genetic variants in COMT and neurocognitive impairment in families of patients with schizophrenia. Genes, Brain and Behavior. Abstract

Mattay, V.S., Goldberg, T.E., Fera, F., Hariri, A.R., Tessitore, A., Egan, M.F., Kolachana, B., Callicott, J.H. and Weinberger, D.R. (2003) Catechol O-methyltransferase val158-met genotype and individual variation in the brain response to amphetamine. Proc Natl Acad Sci USA 100, 6186–6191. Abstract

Williams, H.J., Owen, M.J. and O‘Donovan, M.C. (2007) Is COMT a susceptibility gene for schizophrenia? Schizophr Bull 33, 635–641. Abstract

View all comments by S.H. Lin

Related News: DISC1: A Matter of Life or Death for Neural Progenitors

Comment by:  Khaled Rahman
Submitted 26 March 2009
Posted 26 March 2009

Mao and colleagues present an impressive body of work implicating GSK3β/β-catenin signaling in the function of Disc1. However, several key experimental controls are missing that detract from the impact of their study, and it is unclear whether this function of Disc1 among its many others is the critical link between the t(1;11) translocation and psychopathology in the Scottish family.

The results of Mao et al. suggest that acute knockdown of Disc1 in embryonic brain causes premature exit from the proliferative cell cycle and premature differentiation into neurons. In fact, they observe fewer GFP+ cells in the VZ/SVZ and greater GFP+ cells within the cortical plate. This is in contrast to the study by Kamiya et al. (2005), in which they find that knocking down Disc1 caused greater retention of cells in the VZ/SVZ and fewer in the cortical plate, suggesting retarded migration. Although the timing of electroporation (E13 vs. E14.5) and examination (E15 vs. P2) differed between the two studies, these results are not easily reconciled.

The authors also suggest that they can rescue the deficits in proliferation by overexpressing human wild-type DISC1, stabilizing β-catenin expression, or inhibiting GSK3β activity, and thus conclude that Disc1 is acting through this pathway. This conclusion, however, rests on an error in logic. If increasing X causes an increase in Y, and decreasing Z causes a decrease in Y, this does not mean that X and Z are operating via the same mechanism. In fact, overexpressing WT-DISC1, stabilizing β-catenin, or inhibiting GSK3β activity all increase proliferation in control cells. Thus, the fact that these manipulations also work in progenitors with Disc1 silenced only tells us that these effects are independent or downstream of Disc1. What are needed are studies that show a differential sensitivity of Disc1-silenced cells to manipulations of β-catenin or GSK3β. In other words, is there a shift in the dose response curves? This is what is to be expected given that Mao et al. show changes in β-catenin levels and changes in the phosphorylation of GSK3β substrates in Disc1 silenced cells.

Furthermore, it is surprising that a restricted silencing of Disc1 in the adult dentate gyrus produces changes in affective behaviors, when total ablation of dentate neurogenesis in the adult produces little effects on depression-related behaviors (Santarelli et al., 2003; Airen et al., 2007). The fact that inhibiting GSK3β increases proliferation in both control and Disc1 knockdown animals to a similar degree suggests that the “rescue” of any behavioral deficits is independent of the drug’s effects on proliferation. Correlating measures of proliferation with behavioral performance would help address this issue.

How this study will lead to new or improved therapeutic interventions is also an open question. Lithium is well known for its mood-stabilizing properties, and this study may point to better, more efficient ways to address these symptoms. However, it is also known that lithium does little for, if not worsens, cognitive symptoms in patients (Pachet and Wisniewski, 2003), and it is this symptom domain that is in dire need of drug development.

It is also important to keep in mind that acute silencing of Disc1 in a restricted set of cells will not necessarily recapitulate the pathogenetic process of a disease-associated mutation. It remains to be seen if similar results are obtained in animal models of the Disc1 mutation (Clapcote et al., 2007; Hikida et al., 2007; Li et al., 2007).

References:

Kamiya A, Kubo K, Tomoda T, Takaki M, Youn R, Ozeki Y, Sawamura N, Park U, Kudo C, Okawa M, Ross CA, Hatten ME, Nakajima K, Sawa A. A schizophrenia-associated mutation of DISC1 perturbs cerebral cortex development. Nat Cell Biol. 2005 Dec 1;7(12):1167-78. Abstract

Santarelli, L. et al. Requirement of hippocampal neurogenesis for the behavioral effects of antidepressants. Science 301, 805–809 (2003). Abstract

Airan, R.D. et al. High-speed imaging reveals neurophysiological links to behavior in an animal model of depression. Science 317, 819-23 (2007). Abstract

Pachet AK, Wisniewski AM. The effects of lithium on cognition: an updated review. Psychopharmacology (Berl). 2003 Nov;170(3):225-34. Review. Abstract

Clapcote SJ, Lipina TV, Millar JK, Mackie S, Christie S, et al. (2007) Behavioral phenotypes of Disc1 missense mutations in mice. Neuron 54: 387–402. Abstract

Hikida T, Jaaro-Peled H, Seshadri S, Oishi K, Hookway C, et al. (2007) Dominant-negative DISC1 transgenic mice display schizophrenia-associated phenotypes detected by measures translatable to humans. Proc Natl Acad Sci U S A 104: 14501–14506. Abstract

Li W, Zhou Y, Jentsch JD, Brown RA, Tian X, et al. (2007) Specific developmental disruption of disrupted-in-schizophrenia-1 function results in schizophrenia-related phenotypes in mice. Proc Natl Acad Sci U S A 104: 18280–18285. Abstract

View all comments by Khaled Rahman

Related News: DISC1: A Matter of Life or Death for Neural Progenitors

Comment by:  Simon Lovestone
Submitted 27 March 2009
Posted 27 March 2009

This is an intriguing paper that builds on a growing body of evidence implicating wnt regulation of GSK3 signaling in psychotic illness (Lovestone et al., 2007).

It is interesting that the authors report that binding of DISC1 to GSK3 results in no change in the inhibitory Ser9 phosphorylation site of GSK3 but a change in Y216 activation site and that this resulted in effects on some but not all GSK3 substrates. This poses a challenge both in terms of understanding the role of GSK3 signaling in schizophrenia and other psychotic disorders and in drug discovery.

The authors cite some of the other evidence for regulation of GSK3 signaling in psychosis, including, for example, the evidence for a role of AKT signaling alteration in schizophrenia and lithium, an inhibitor of GSK3, as a treatment for bipolar disorder. But in both cases, AKT (Cross et al., 1995) and lithium (Jope, 2003), the effect on GSK3 is predominantly via Ser9 phosphorylation and not via Y216. The unstated implication is at least two, possibly three, mechanisms for regulation of GSK3 are all involved in psychotic illness—the auto-phosphorylation at Y216, the exogenous signal transduction regulated Ser9 site inhibition and, if the association of schizophrenia with the wnt inhibitor DKK4 we reported is true (Proitsi et al., 2008), also via the wnt signaling effects on disruption of the macromolecular complex that brings GSK3 together with β-catenin. On the one hand, this might be taken as positive evidence of a role for GSK3 in psychosis—all of its regulatory mechanisms have been implicated; therefore, the case is stronger. On the other hand, GSK3 lies at the intersection point of very many signaling pathways and so is likely to be implicated in many disorders (as it is), and the fact that in cellular and animal models related to psychosis there is no consistent effect on the enzyme is troublesome.

From a drug discovery perspective, those with GSK3 inhibitors in the pipeline will be watching this space carefully. However, it is worth noting that Mao et al. find very selective effects of DISC1 on GSK3 substrates. Despite convincing evidence of an increase in Y216 phosphorylation, which one would expect to increase activity of GSK3 against all substrates, the authors find no evidence of effects on phosphorylation of the GSK3 substrates Ngn2 or C/EBPα. This is somewhat puzzling and merits further attention, especially as in vitro direct binding of a DISC1 fragment to GSK3 inhibited the action of GSK3 on a range of substrates. Might there be more to the direct interaction of DISC1 with GSK3 than a regulation of Y216 autophosphorylation and activation? If, however, GSK3 regulation turns out to be part of the mechanism of schizophrenia or bipolar disorder, then identifying which of the substrates and which of the many activities of GSK3, including on plasticity and hence cognition (Peineau et al., 2007; Hooper et al., 2007), are important in disease will become the critical task.

References:

Lovestone S, Killick R, Di Forti M, Murray R. Schizophrenia as a GSK-3 dysregulation disorder. Trends Neurosci. 2007 Apr 1 ; 30(4):142-9. Abstract

Cross DA, Alessi DR, Cohen P, Andjelkovich M, Hemmings BA. Inhibition of glycogen synthase kinase-3 by insulin mediated by protein kinase B. Nature . 1995 Dec 21-28 ; 378(6559):785-9. Abstract

Jope RS. Lithium and GSK-3: one inhibitor, two inhibitory actions, multiple outcomes. Trends Pharmacol Sci . 2003 Sep 1 ; 24(9):441-3. Abstract

Proitsi P, Li T, Hamilton G, Di Forti M, Collier D, Killick R, Chen R, Sham P, Murray R, Powell J, Lovestone S. Positional pathway screen of wnt signaling genes in schizophrenia: association with DKK4. Biol Psychiatry . 2008 Jan 1 ; 63(1):13-6. Abstract

Peineau S, Taghibiglou C, Bradley C, Wong TP, Liu L, Lu J, Lo E, Wu D, Saule E, Bouschet T, Matthews P, Isaac JT, Bortolotto ZA, Wang YT, Collingridge GL. LTP inhibits LTD in the hippocampus via regulation of GSK3beta. Neuron . 2007 Mar 1 ; 53(5):703-17. Abstract

Hooper C, Markevich V, Plattner F, Killick R, Schofield E, Engel T, Hernandez F, Anderton B, Rosenblum K, Bliss T, Cooke SF, Avila J, Lucas JJ, Giese KP, Stephenson J, Lovestone S. Glycogen synthase kinase-3 inhibition is integral to long-term potentiation. Eur J Neurosci . 2007 Jan 1 ; 25(1):81-6. Abstract

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Related News: DISC1: A Matter of Life or Death for Neural Progenitors

Comment by:  Nick Brandon (Disclosure)
Submitted 27 March 2009
Posted 30 March 2009
  I recommend the Primary Papers

Li-huei Tsai and colleagues have identified another pathway in which the candidate gene DISC1 looks to have a critical regulatory role, namely the wnt signaling pathway, in progenitor cell proliferation. In recent years we have seen that DISC1 has a vital role at the centrosome (Kamiya et al., 2005), in cAMP signaling (Millar et al., 2005), and in multiple steps of adult hippocampal neurogenesis (Duan et al., 2007). They have shown a pivotal role for DISC1 in neural progenitor cell proliferation through regulation of GSK3 signaling using a spectacular combination of cellular and in utero manipulations with shRNAs and GSK3 inhibitor compounds. These findings clearly implicate DISC1 in another “druggable” pathway but at this stage do not really identify new approach/targets, except perhaps to confirm that manipulating adult neurogenesis and the wnt pathway holds much potential hope for therapeutics. Perhaps understanding the mechanism of inhibition of GSK3 by DISC1 in more detail might reveal more novel approaches or encourage more innovative work around this pathway. In addition, I have read the other comment (by Rahman), and though I agree that this work still leaves many questions to be answered, the paper is much more significant and likely reconcilable with previous papers than appreciated. The commentary from Lovestone was very insightful and brings up additional gaps and issues with the present work. Additional experimentation I am sure will tease out more key facets of the DISC1-wnt interaction in the near future.

There are many avenues now to proceed with this work. In particular, from the DISC1-centric view, a GSK3 binding site on DISC1 overlaps with one of the critical core PDE4 binding site. Mao et al. show that residues 211 to 225 are a core part of a GSK3 binding site. Previously, Miles Houslay had shown very elegantly that residues 191-230 form a common binding site (known as common site 1) for both PDE4B and 4D families (Murdoch et al., 2007). It will be important to understand the relationship between GSK3 and PDE4 related signaling in reference to the activity of DISC1 starting at whether a trimolecular complex among DISC1-PDE4-GSK3 can form. Then it will be critical to understand the regulatory interplay among these molecules. For example, it is known that PKA can regulate GSK3 activity (Torii et al., 2008) and the interaction between DISC1 and PDE4, while both GSK3 and PKA can phosphorylate β-catenin (Taurin et al., 2006). The output of these relationships on progenitor proliferation will further deepen insights into the role of DISC1 complexes in neuronal processes. This type of situation is not really surprising for a molecule (DISC1) which has been shown to interact with >100 proteins (Camargo et al., 2007). The context of these interactions in both normal development and disease is likely to be critical to allow understanding of its complete functional repertoire.

Another area where these new findings need to be exploited is in the study of additional animal models. Though the two behavioral endpoint models used in the paper (amphetamine hyperactivity and forced swim test) provide a tantalizing glimpse of the behavioral importance of the complex, it would be critical to look in additional models relevant for schizophrenia and mood disorders. Furthermore, it will be very interesting to look at the effects of GSK3β inhibitors in some of the DISC1 animal models already available and to see if they can reverse all or a subset of reported behaviors. In reviewing a summary of the phenotypes available to date (Shen et al., 2008) there is clearly a number of lines which share the properties with mice injected with DISC1 shRNA into the dentate gyrus and would be of value to look at.

A very exciting paper which I am sure will drive additional research into understanding the role of DISC1 in psychiatry and hopefully encourage drug discovery efforts around this molecular pathway (Wang et al., 2008).

References:

1. Kamiya A, Kubo K, Tomoda T, Takaki M, Youn R, Ozeki Y, Sawamura N, Park U, Kudo C, Okawa M, Ross CA, Hatten ME, Nakajima K, Sawa A. A schizophrenia-associated mutation of DISC1 perturbs cerebral cortex development. Nat Cell Biol . 2005 Dec 1 ; 7(12):1167-78. Abstract

2. Millar JK, Pickard BS, Mackie S, James R, Christie S, Buchanan SR, Malloy MP, Chubb JE, Huston E, Baillie GS, Thomson PA, Hill EV, Brandon NJ, Rain JC, Camargo LM, Whiting PJ, Houslay MD, Blackwood DH, Muir WJ, Porteous DJ. DISC1 and PDE4B are interacting genetic factors in schizophrenia that regulate cAMP signaling. Science . 2005 Nov 18 ; 310(5751):1187-91. Abstract

3. Duan X, Chang JH, Ge S, Faulkner RL, Kim JY, Kitabatake Y, Liu XB, Yang CH, Jordan JD, Ma DK, Liu CY, Ganesan S, Cheng HJ, Ming GL, Lu B, Song H. Disrupted-In-Schizophrenia 1 regulates integration of newly generated neurons in the adult brain. Cell . 2007 Sep 21 ; 130(6):1146-58. Abstract

4. Murdoch H, Mackie S, Collins DM, Hill EV, Bolger GB, Klussmann E, Porteous DJ, Millar JK, Houslay MD. Isoform-selective susceptibility of DISC1/phosphodiesterase-4 complexes to dissociation by elevated intracellular cAMP levels. J Neurosci . 2007 Aug 29 ; 27(35):9513-24. Abstract

5. Torii K, Nishizawa K, Kawasaki A, Yamashita Y, Katada M, Ito M, Nishimoto I, Terashita K, Aiso S, Matsuoka M. Anti-apoptotic action of Wnt5a in dermal fibroblasts is mediated by the PKA signaling pathways. Cell Signal . 2008 Jul 1 ; 20(7):1256-66. Abstract

6. Taurin S, Sandbo N, Qin Y, Browning D, Dulin NO. Phosphorylation of beta-catenin by cyclic AMP-dependent protein kinase. J Biol Chem . 2006 Apr 14 ; 281(15):9971-6. Abstract

7. Camargo LM, Collura V, Rain JC, Mizuguchi K, Hermjakob H, Kerrien S, Bonnert TP, Whiting PJ, Brandon NJ. Disrupted in Schizophrenia 1 Interactome: evidence for the close connectivity of risk genes and a potential synaptic basis for schizophrenia. Mol Psychiatry . 2007 Jan 1 ; 12(1):74-86. Abstract

8. Shen S, Lang B, Nakamoto C, Zhang F, Pu J, Kuan SL, Chatzi C, He S, Mackie I, Brandon NJ, Marquis KL, Day M, Hurko O, McCaig CD, Riedel G, St Clair D. Schizophrenia-related neural and behavioral phenotypes in transgenic mice expressing truncated Disc1. J Neurosci . 2008 Oct 22 ; 28(43):10893-904. Abstract

9. Wang Q, Jaaro-Peled H, Sawa A, Brandon NJ. How has DISC1 enabled drug discovery? Mol Cell Neurosci . 2008 Feb 1 ; 37(2):187-95. Abstract

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Related News: DISC1: A Matter of Life or Death for Neural Progenitors

Comment by:  Akira Sawa, SRF Advisor
Submitted 8 April 2009
Posted 8 April 2009

Mao and colleagues’ present outstanding work sheds light on a novel function of DISC1. Because DISC1 is a multifunctional protein, the addition of new functions is not surprising. Thus, for the past several years, the field has focused on how DISC1 can have distinct functions in different cell contexts (for example, progenitor cells vs. postmitotic neurons, or developing cortex vs. adult dentate gyrus). In addition to Mao and colleagues, I understand that several groups, including ours, have obtained preliminary, unpublished evidence that DISC1 regulates progenitor cell proliferation, at least in part via GSK3β. Thus, I am very supportive of this new observation.

If there might be a missing point in this paper, it is unclear whether suppression of GSK3β occurs in several different biological contexts in brain in vivo. In other words, it is uncertain whether DISC1’s actions on GSK3β are constitutive or context-dependent. How can we reconcile differential roles for DISC1 in progenitor cells in contrast to postmitotic neurons? We have already obtained a preliminary promising answer to this question, which is currently being validated very intensively. These two phenotypes (progenitor cell control and postmitotic migration) may compensate for each other in cortical development; thus, overall cortical pathology looks milder in adults, at least in our preliminary unpublished data using DISC1 knockout mice. We are not sure how this novel function of DISC1 may account for the pathology of Scottish cases. Although I have great respect for the Scottish pioneers of DISC1 study, such as St. Clair, Blackwood, and Muir (I believe that the St. Clair et al., 1990 Lancet paper is one of the best publications in psychiatry), now is the time to pay more and more attention to the question of the molecular pathway(s) involving DISC1 in general schizophrenia (see 2009 SRF roundtable discussion). Unlike the role of APP in Alzheimer’s disease, DISC1 is not a key biological target in general schizophrenia, instead being an entry point to explore much more important targets for schizophrenia. There may be no more need to stick to DISC1 itself in the unique Scottish cases in schizophrenia research. In sum, although there may still be key missing points in this study, I wish to congratulate the authors on their outstanding work.

References:

St Clair D, Blackwood D, Muir W, Carothers A, Walker M, Spowart G, Gosden C, Evans HJ. Association within a family of a balanced autosomal translocation with major mental illness. Lancet . 1990 Jul 7 ; 336(8706):13-6. Abstract

View all comments by Akira Sawa

Related News: Schizophrenia-associated Variant in ZNF804A Gene Affects Brain Connectivity

Comment by:  James WaltersMichael Owen (SRF Advisor)
Submitted 3 June 2009
Posted 3 June 2009

Andreas Meyer-Lindenberg’s group examine the association between a single nucleotide polymorphism (SNP), rs1344706 in gene ZNF804A, recently identified as a risk factor for schizophrenia in a genome-wide association study (GWAS) (O'Donovan et al., 2008) and functional connectivity as measured by fMRI. The attraction of this polymorphism for a study of this kind is twofold. First, statistically speaking it is the most robust SNP association with schizophrenia reported to date. Second, because a single variant shows strong evidence for association, which is not the case for other reported associations, it is possible to specify a priori for the gene in question directional hypotheses in relation to potential neurocognitive correlates. This militates against the generation of false positives through the testing of multiple SNPs and haplotypes which has rendered problematic the interpretation of at least some previous genetic imaging studies (Walters and Owen, 2007). The function of ZNF804A is unknown but the fact that it contains a zinc finger domain suggests that it may be a transcription factor. It is hoped that the characterization of the actions of SNPs identified by GWAS will identify new pathogenic mechanisms of psychosis. One way in which this can be achieved is via approaches such as that taken in this article.

Esslinger et al. report variations in functional connectivity in 115 healthy individuals according to rs1344706 risk variant status. Given the association of ZNF804A with both schizophrenia and bipolar disorder they employed two fMRI tasks thought to be sensitive to altered function in these disorders: the N Back (2back) task is sensitive to deficits of dorsolateral prefrontal cortex (DLPFC) function in schizophrenia and an emotional face-matching task is linked with amygdala function and thought to be relevant to mood disorder. They compared the activity in these regions and functional connectivity (using time-series correlation) between the three rs1344706 genotype groups.

No differences between genotype groups were found for activation, but the authors did identify altered connectivity with the most activated DLPFC locale. Risk-allele carriers were shown to exhibit a lack of uncoupling of activity (increased functional connectivity) between the right DLPFC and left hippocampus during the 2-back task as well as decreased connectivity within right DLPFC and between right and left DLPFC. Risk variant carriers also showed wide ranging increased connectivity between right amygdala and other anatomical regions. The majority of these findings showed a risk allele dose effect.

The increased DLPFC/hippocampus functional connectivity in carriers of the risk allele is potentially the most interesting finding given that Meyer-Lindenberg’s group has previously shown that those with schizophrenia show increased functional connectivity between DLPFC and hippocampus during working memory (Meyer-Lindenberg et al., 2005). Notes of caution in this regard are that 1) the biological, anatomical or functional significance of fMRI determined functional connectivity is yet to be established and 2) other functional connectivity studies in schizophrenia have produced conflicting results Lawrie et al., 2002. Nonetheless, it is interesting that rs1344706 may affect co-ordination of activity between these two brain regions given their seeming importance in psychotic conditions. The significance of these findings to cognitive deficits and other symptom domains needs further investigation particularly as others have postulated dysconnectivity has more relevance to first rank psychotic symptoms (Stephan et al., 2009).

It is likely that genome-wide association approaches will continue to identify genes with unknown neural function and so approaches such as this are likely to be a valuable way of identifying the biological/neural pathways that involve these genes. It is also imperative that as in this study methodology is employed to allow for multiple testing and also that negative findings are reported. We would also suggest caution until these findings are replicated. As well as such approaches in humans, it is also important to investigate the effects of identified variants at other levels of analysis from gene expression to behavioural genetics work. Finally we find it reassuring that GWAS approaches seem to be successful in identifying risk variants whose functions can be investigated using methods such as that taken by Esslinger et al.

References:

O'Donovan MC, Craddock N, Norton N, et al. Identification of loci associated with schizophrenia by genome-wide association and follow-up. Nature Genetics. 2008;40(9):1053-1055. Abstract

Walters JT, Owen MJ. Endophenotypes in psychiatric genetics. Mol Psychiatry. 2007;12(10):886-890. Abstract

Meyer-Lindenberg AS, Olsen RK, Kohn PD, et al. Regionally Specific Disturbance of Dorsolateral Prefrontal-Hippocampal Functional Connectivity in Schizophrenia. Archives of General Psychiatry. 2005;62(4):379-386. Abstract

Lawrie SM, Buechel C, Whalley HC, Frith CD, Friston KJ, Johnstone EC. Reduced frontotemporal functional connectivity in schizophrenia associated with auditory hallucinations. Biological Psychiatry. 2002;51(12):1008-1011. Abstract

Stephan KE, Friston KJ, Frith CD. Dysconnection in Schizophrenia: From Abnormal Synaptic Plasticity to Failures of Self-monitoring. Schizophr Bull. 2009;35(3):509-527. Abstract

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Related News: Schizophrenia Genetics 2: The Rise of GWAS

Comment by:  Chris Carter
Submitted 7 April 2010
Posted 8 April 2010

I wonder whether the relative lack of success in schizophrenia GWAS may be because the origin of schizophrenia may lie not so much in the genetic make-up of people with schizophrenia themselves, but in their prenatal experience, and possibly with the genes of the mother rather than with those of the offspring. Famine, rubella, influenza, herpes (HSV1 and HSV2), and poliovirus infection as well as high fever during pregnancy have all been listed as risk factors for the offspring developing schizophrenia in later life, as have maternal preeclampsia and obstetric complications. (See page at Polygenic Pathways for the many references.)

Maternal resistance to these effects is likely to be gene-dependent. Is it worth considering GWAS in the mothers rather than in the offspring?

View all comments by Chris Carter