Adult Neoneurogenesis and Oligodendrogenesis in Multiple Sclerosis: A Systematic Review of Human and Animal Studies

Introduction: The subventricular zone promotes remyelination through activation differentiation of oligodendroglial precursor cells (OPCs) and neural stem cells (NSCs) into mature oligodendrocytes and thus in the adult brain. In Multiple Sclerosis (MS) this regenerative capability in halted resulting in neurodegeneration. We aimed to systematically search and synthesize evidence on mechanisms and phenomena associated with SVZ dysfunction in MS. Materials and Methods: Our systematic review was reported according to the PRISMA-ScR statement. MEDLINE, SCOPUS, ProQuest and Google Scholar were searched using the terms "subventricular zone" and "multiple sclerosis", including English-written in vivo and post-mortem studies. Results: 20 studies were included. Thirteen studies on models of experimental autoimmune encephalomyelitis (EAE) reported among others strong stathmin immunoreactivity in the SVZ of EAE models, the role of MOG immunization in neurogenesis impairment, the effect of parenchymal OPCs and NSCs in myelin repair and the importance of ependymal cells (E1/E2) and ciliated B1 cells in SVZ stem cell signalling. CXCR4 signaling and, transcriptional profiles of SVZ microglia, Gli1 pathway, galactin-3 were also explored. Studies in humans demonstrated microstructural SVZ damage in progressive MS and the persistence of black holes near the SVZ, whereas post-mortem confirmed generation of PSA-NCAM and NG2-positive progenitors through SVZ activation, SVZ stathmin immunoreactivity, Shh pathway and Gal-3 upregulation. Discussion: Oligodendrogenesis defects translate to reduced remyelination, a hallmark of MS, that determines its end-phenotype and disease course. Conclusion: The role of inflammation and subsequent SVZ microenvironment disruption is evident in MS pathology.