23 Apr 2015
As part of our ongoing coverage of the 2015 International Congress on Schizophrenia Research (ICOSR), held March 29 through April 1 in Colorado Springs, we bring you session summaries from some of the participants in the Young Investigator program. We are, as always, grateful for the gracious assistance of conference directors Carol Tamminga and Chuck Schulz, as well as meeting staff Cristan Tamminga and Dorothy Denton. For this report, we thank Sarah Canetta of Columbia University in New York City.
April 24, 2015. The overall goal of this session was to investigate molecular mechanisms of schizophrenia using either patient-derived cells or animal models. The session's moderators, Doug Meinecke and David Panchision, both of the U.S. National Institute of Health in Rockville, Maryland, began the session by introducing induced pluripotent stem cells (iPSCs), the subject of three of the four subsequent talks, as well as providing an overview of the NIH's perspective on iPSC research. To that effect, NIH views iPSC technology as a platform for trying to understand the biological basis of psychiatric disorders.
The first speaker was Kristen Brennand of Mount Sinai Medical School of Medicine in New York City, whose lab uses iPSCs derived from fibroblasts from controls and patients with schizophrenia. Brennand reiterated the process by which fibroblasts are first differentiated into iPSCs, then into neural progenitor cells (NPCs), and then into neurons. Interestingly, NPCs and neurons derived from these fibroblasts have been found to be most similar to early fetal forebrain neurons, based on comparison of expression data from these NPCs and neurons to data from the Allen Brain Atlas. While this could be seen as a limitation of this technology, it could also be seen as an advantage, as it makes them particularly appropriate for studying disease risk.
Brennand showed that the neurons derived from patient fibroblasts had fewer neurites and less PSD95. NPCs derived from patient fibroblasts showed differences in neuronal differentiation and migration, and increased markers of oxidative stress (see SRF related news report; SRF related conference report). Finally, preliminary data indicated that patient-derived cells might have an increase in ribosomal proteins involved in protein translation and total protein. These results suggest that patient-derived cells can be used to verify phenotypes seen in postmortem studies, as well as to identify novel phenotypes.
The second speaker was Koko Ishizuka of Johns Hopkins University in Baltimore, Maryland, whose talk also demonstrated the applications of using patient-derived cells to understand molecular and cellular changes occurring in schizophrenia. The discovery that phosphorylation of the S713 site of the schizophrenia risk gene DISC1 is important for mediating the switch between proliferation and migration of neurons in the cortex. Ishizuka's group examined S713 phosphorylation in olfactory cells (OCs) as well as iPSC-derived neurons taken from schizophrenia patients with a DISC1 mutation and from controls; OCs are transcriptionally similar to iPSCs but don't require reprogramming. The researchers found that S713 phosphorylation was decreased in OCs and iPSC-derived neurons from patients with the DISC1 mutation. In keeping with a role for DISC1 S713 phosphorylation in neuronal differentiation, Ishizuka's group found that the NPCs were compromised in their ability to differentiate into neurons. This was true both in culture and when the cells were injected into embryonic (E13) mouse brain and allowed to differentiate in vivo (see SRF related news report and SRF related conference report).
The third speaker, Guo-Li Ming, also of Johns Hopkins, provided another example of the use of patient-derived cells for the study of the molecular and cellular consequences of DISC1 mutation. Echoing the other speakers, she emphasized that because schizophrenia is highly genetic and neurodevelopmental, using these patient-derived neurons that represent extremely young cells is an appropriate way to look at early neurodevelopmental alterations on a background of genetic risk. Her group has developed a method of deriving forebrain-specific NPCs that could be differentiated into 99 percent pure cultures of cortical neurons (90 percent glutamatergic and 10 percent GABAergic). They did this for fibroblasts taken from schizophrenia patients from an American family with a unique DISC1 mutation and non-affected family member controls, and found that the neurons derived from patients with the DISC1 mutation displayed decreases in the synaptic vesicle marker SV2, as well as functional changes consistent with decreased presynaptic release (measured via electrophysiology and FM dye unloading experiments). Using viral manipulations to alter DISC1 expression in healthy cells or to rescue DISC1 expression in patient cells, they proved that the mutated version of DISC1 is sufficient and required to produce the decreased release probability phenotype (see SRF related news report).
In the final talk of the session, Kim Do of University Hospital of Lausanne in Switzerland departed from the iPSC theme, though her results intersect with the oxidative stress data from Brennand's work. She presented evidence from animal models that redox dysregulation may be a common pathway by which multiple risk factors act on macro- and microcircuitry, leading to abnormal behaviors. In particular, she demonstrated that manipulation of glutathione levels had consequences for oligodendrocytes and myelination as well as for increasing the vulnerability of PV cells to oxidative stress. She provided additional evidence to suggest that PV cells are particularly vulnerable to redox manipulations early in development (P10-20 or P30-40), and that N-acetyl-cysteine treatment could prevent redox damage of PV cells and accompanying alterations in behavior.
Altogether, this session provided insight into the strengths and weaknesses of using patient-derived cells or animal models to identify potential cellular and molecular mechanisms occurring in schizophrenia. Where findings from these two strategies converge—such as redox dysregulation—may prove particularly fruitful avenues of research.—Sarah Canetta.