Oligodendrocyte Progenitor Cell Dysfunction in Familial Schizophrenia

Background and Aim: While schizophrenia is highly heritable, itsunderlying pathophysiology is yet to be fully understood. The strongestknown determinant for developing schizophrenia is family history.Recent genetic and induced pluripotent stem cell (iPSC)-based studieshave converged on a model by which neuronal function, and in particularsynaptic transmission, is a major pathophysiological mechanism ofschizophrenia. However, functional neuronal alterations may ariseeither by direct cell-type autonomous changes to neurons themselves, orindirectly through a primary pathophysiological influence on other celltypes that influence neuronal function.Methods: We implemented a family-based approach for geneticdiscovery in schizophrenia combined with functional analysis usinginduced pluripotent stem cells (iPSCs). Genetic analysis: Linkage andCopy Number Analysis was performed with Illumina HumanCytoSNP-12v2 chip arrays using an affected-only model with an assumption of99.9% penetrance. Whole-genome exome sequencing was performedtwice: initially at 40x, and again at 90x coverage. Exome variants wereconsidered for additional validation if they were rare (MAF < 0.001),predicted to alter coding sequence (missense, nonsense, frameshift,essential splice site), and occurred within the regions of suggestivelinkage. Cellular studies: Human iPSCs were differentiated to NPCs andneurons by embryoid body neural differentiation. Electrophysiology wasperformed in whole cell patch-clamp configuration after 8-10 weeksof differentiation. iPSC-derived OPCs were differentiated according to Monaco et alwith modifications. Biotinylation of cell surface proteinswas adapted from Huang et al. OPC viability was assessed by quantitativefluorometric monitoring of resazurin conversion to resorufin. Myelinationassay was performed using ex vivo organotypic cerebral cortex slices ofShiverer mice. We observed familial segregation of two rare missense mutationsin Chondroitin Sulfate Proteoglycan 4 (CSPG4) (c.391G> A [p.A131T],MAF 7.79 ×10-5and c.2702T> G [p.V901G], MAF 2.51 × 10-3). TheCSPG4A131Tmutation was absent from the Swedish Schizophrenia ExomeSequencing Study (2536 cases, 2543 controls), while the CSPG4V901Gmutation was nominally enriched in cases (11 cases vs. 3 controls,P = 0.026, OR 3.77, 95% CI 1.05-13.52). CSPG4/NG2 is a hallmarkprotein of oligodendrocyte progenitor cells (OPCs). IPSC-derived OPCsfrom CSPG4A131Tmutation carriers exhibited abnormal post-translationalprocessing (P=0.029), subcellular localization of mutant NG2 (P=0.007),as well as aberrant cellular morphology (P=3.0 ×10-8), viability (P=8.9×10-7), and myelination potential (P=0.038). Moreover, transfection ofhealthy non- carrier sibling OPCs confirmed a pathogenic effect oncell survival of both the CSPG4A131T(P=0.006) and CSPG4 V901G(P=3.4×10-4) mutations. Finally, in vivo diffusion tensor imaging of CSPG4A131Tmutation carriers demonstrated a reduction of brain white matter integritycompared to unaffected sibling and matched general population controls(P=2.2 ×10-5).Conclusion: The results obtained in this study revealed a greatconsistency with the growing body of evidence, which implicate theintegrity of white matter in schizophrenia neuropathology. In fact,recent findings demonstrating the myelination of parvalbumin-positiveGABAergic interneurons, which are arguably the most well-establishedneuronal cell type implicated in the pathophysiology of schizophrenia,may raise an intriguing possibility that schizophrenia might be initiatedby neurodevelopmental alterations of PV interneuron myelination.Taken all, these results provide a convergence of genetic and functionalevidence to implicate OPC dysfunction as a candidate pathophysiologicalmechanism of familial schizophrenia.

کلیدواژه ها:

Schizophrenia ، Induced pluripotent stem cells ، Genetics ، Exome sequencing ، Oligodendrocyte progenitor cells ، Myelination