Exploring Fate of Myelin After Subarachnoid Hemorrhage

Introduction: Subarachnoid hemorrhage (SAH) survivors have seen improved survival rates, but they often face long-term cognitive impairments. Up to 95% of SAH survivors experience learning and memory deficits, hindering their return to work. Currently, the mechanisms behind these cognitive impairments remain unclear. Our laboratory used transcriptomics analysis of the hippocampus in a mouse model replicating SAH-induced cognitive damage observed in humans. We identified a downregulation of genes related to myelin and axons. In this study, we aimed to validate these findings using fluorescent hybridization in situ (FISH) at 24 hours.

Methods: We conducted RNAscope FISH for Mbp (Myelin basic protein) and Mog (myelin oligodendrocyte glycoprotein) in naïve mice and performed Mbp and PDGFRα (pre-myelinating oligodendrocyte marker) immunostaining in SAH and Sham mice, on frozen brain tissue. SAH was induced by endovascular perforation of the circle of Willis, while Sham mice underwent identical surgery without perforation. Naïve brains were processed as per the manufacturer's instructions, whereas SHAM and SAH brains were further processed for immunohistochemistry.

Results: In the cortex (Cx), Mbp messenger staining appeared perinuclear and filament-like, while in the hippocampus (Hpc), it was mostly perinuclear. Of note, Allen Brain atlas doesn’t indicate differences in staining in Cx and Hpc, and others reported that Mbp localized in the end terminal, near assembly sites. Colocalization of Mbp and Mog was observed in naïve mice. Notably, Mbp and PDGFRα colocalization was detected only in SAH mice. Quantitative analysis revealed a decrease in Mbp intensity, confirming our RNAseq data. However, quality control showed reduced Mbp intensity in Sham FISH and Sham FISH + IHC compared to naive, indicating variations based on brain processing.

Conclusion : This study demonstrated differences in Mbp expression following SAH, depending on brain structure and treatment. Our results underscore the unique patterns observed after SAH, emphasizing the importance of studying myelination processes in its aftermath.