24 May 2013. Clues to schizophrenia may lie right under, er, inside, the nose, according to several presentations featuring the olfactory system at the International Congress of Schizophrenia Research held in Orlando, Florida, 21-25 April. Originally coming to the attention of schizophrenia research by olfactory deficits reported in schizophrenia (Hurwitz et al., 1988), the olfactory system has recently garnered more interest because of the ability to access and keep alive the primary sensory neurons that receive odorant messages within the nose. With a five-minute procedure under local anesthetic, olfactory epithelium cells may be extracted and neurons obtained for study in a dish. These cells may be useful proxies for the brain and reveal biomarkers for schizophrenia that can help diagnose the diverse spectrum of behaviors with which psychiatrists currently work. Other researchers are taking a more holistic approach by testing whether the olfactory abilities of people either with schizophrenia or at risk for developing it may predict their outcomes in the future.
Smells like psychosis?
A poster symposium on Wednesday, 24 April, highlighted ongoing studies of olfactory perception and how it relates to schizophrenia. Using a relatively inexpensive, scratch-and-sniff-style test called the UPSIT (for University of Pennsylvania Smell Inventory Test) that takes only 10 minutes to administer, Lili Kopala of the University of British Columbia reported that olfactory deficits may portend a worse course of illness. She found that people with schizophrenia who showed an olfactory impairment at their first episode of psychosis had significantly worse negative symptoms six months later when compared to those with a normal sense of smell. Similarly, those who were treatment resistant after six months of antipsychotic medication had significantly worse olfactory abilities.
An impaired sense of smell might also be an early indicator of oncoming psychosis, according to preliminary data presented by Larry Seidman of Harvard University. Giving the UPSIT to people showing early signs of psychosis when they enrolled in the North American Prodrome Longitudinal Study (NAPLS-2), Seidman reported that those who went on to develop full-blown psychosis had significantly worse olfactory discrimination than those who didn’t. This deficit was stable, in that it didn’t worsen when tested one year later, and it was similar in magnitude to that found in people at their first episode of psychosis and in patients who had been ill for a long time. Though only based on data from half the NAPLS-2 sample, the results suggest that olfactory discrimination may be one of many features, such as blood biomarkers (see SRF related news story), that can be used to quantitatively weigh the chance that a person at high clinical risk for developing psychosis will, in fact, do so.
If these olfactory deficits strike you as kind of wacky, Bruce Turetsky of the University of Pennsylvania provided some anatomical reasons for why they may travel with schizophrenia. Building on his previous work showing that the size of the nasal cavity, as measured by a sonar device, is related to schizophrenia (Turetsky et al., 2007), Turetsky reported that the size of the nasal cavity is smaller than usual in people with schizophrenia, as well as those clinically at risk for developing psychosis. Using structural magnetic resonance imaging (MRI), he also reported that these two groups had reduced olfactory bulb volumes compared to controls. In addition, the typical asymmetry found in the depth of the olfactory sulcus (the right one runs deeper than the left one) was lost in the schizophrenia group and the clinical at-risk group. Turetsky said that these oddities may point to disrupted embryonic development, because these structures emerge between the first and second trimesters of pregnancy.
The extent to which these anatomical anomalies index schizophrenia or a generic olfactory deficit is unclear. Though olfactory deficits have been reported in other psychiatric illnesses such as bipolar disorder, Turetsky said that the underlying biology behind the deficit in one disorder may differ from another. If so, these anatomical anomalies could provide another biomarker for schizophrenia that could be used in a high-risk screening tool.
Molecular profiling cells in a dish
Other researchers have set about characterizing neurons taken from the nasal epithelium of people with schizophrenia, which could provide some insight into what is happening to neurons in the brain. On Tuesday, 23 April, Noam Shomron of Tel Aviv University in Israel presented, via Skype, his work finding that a pattern of gene expression in these neurons differentiated between schizophrenia and control samples (Mor et al., 2013). Shomron focused on microRNAs because of their powerful control of the expression of many different genes (see SRF related news story). Using neurons dissected from the nasal epithelium, Shomron reported that miRNA-382 was upregulated in schizophrenia compared to controls, consistent with postmortem findings (Santarelli et al., 2011). In addition, expression of two of miRNA-382’s targets, FGFR1 and SPRY4, were downregulated. Experiments in neuroblastoma cells showed that miRNA-382 binds directly to these two genes to suppress their expression. FGFR1 and SPRY4 are involved in fibroblast growth factor (FGF) signaling and may signal a derailed developmental program in schizophrenia. Shomron suggested that these two genes could add to a panel of biomarkers that together could diagnose schizophrenia. Interestingly, miRNA-382 went undetected in blood samples, meaning that gene expression patterns found there will not necessarily match those found in neurons.
On Thursday, 24 April, a session on cell biology and cognition included research based in part on olfactory neurons. Working from her finding that the phosphorylation state of DISC1, a schizophrenia risk gene, controls whether neurons proliferate or migrate in the developing mouse brain (see SRF related news story), Koko Ishizuka of Johns Hopkins University explored whether this was also true in human cells. Nasal and skin biopsies were taken from individuals in two cohorts, each comprising people with schizophrenia and controls. Ishizuka reported that in both cohorts, phosphorylation of the S713 site of DISC1—the human equivalent of the mouse S170—was reduced in schizophrenia relative to controls, suggesting that the schizophrenia neurons were stuck in the early, cell-proliferating state of development. Consistent with this, induced pluripotent stem cells (iPSCs) derived from skin cells showed that the schizophrenia cells did not increase their phosphorylation levels over 14 days in culture, as did the control cells. These control cells differentiated into neurons, whereas this process seemed delayed in schizophrenia. Transfecting the iPSCs with a phosphorylated form of S713 DISC1 reduced the abnormal proliferation in the schizophrenia cells. Ishizuka said that the olfactory neurons are cheaper and take less time to establish than iPSCs.
To make a link with cognition, Ishizuka also assessed neuropsychological measures of individuals in these cohorts and found that the level of S713 phosphorylation in their olfactory neurons correlated with attention, with lower levels associated with worse performance. This suggests that defects in the phosphorylation-induced switch from proliferation to migration in the developing brain may give rise to subtle changes in the cortex that may be detected as cognitive deficits. Other aspects of cognition, however, did not correlate with phosphorylation, including tests of processing speed, executive function, fluency, and verbal and visual learning and memory.
Could distinguishing cases of schizophrenia be as easy as sending biopsied cells through a machine? Akira Sawa of Johns Hopkins University explored this idea in his talk given on behalf of his graduate student Chi-Ying Lin which was focused on whether autofluorescence—usually a nuisance for microscopists—could be a biomarker for schizophrenia. Using a fluorescence-activated cell sorting (FACS) machine, which shines light onto cells and measures the amount of light reflected back, Sawa reported that lymphoblast cells from people with schizophrenia had a slight, but significant increase in autofluorescence compared to controls in two separate cohorts (n = 14 and n = 26). Autofluorescence levels correlated with positive symptoms and might reflect something inherent to the disorder: the increased autofluorescence was apparent in first-episode patients before they had received medication, then decreased after a year of treatment.
What about neurons? In olfactory neurons taken from a pilot cohort of people chronically ill with schizophrenia, Sawa reported finding the same heightened autofluorescence relative to controls (1.3 vs. 1.0). Future experiments will have to work out why this is so, but Sawa suggested that autofluorescence may be a sign of cells dealing with increased oxidative stress.—Michele Solis.