Bridging integrator 1 (BIN1) isoforms expression in oligodendrocytes and their putative role in cell cycle regulation in sporadic Alzheimer’s disease

Bridging Investigator 1 is a known c-Myc inhibitor highly enriched in oligodendrocytes (OL), and its genetic variant confers a strong risk for sporadic Alzheimer’s disease (AD). BIN1 expression is tightly regulated by the alternative splicing of 20 exons, resulting in twelve protein isoforms. In human brain, as a nucleocytoplasmic protein, BIN1 regulates tau endocytosis, but its canonical nuclear function as a cell cycle regulator remains unknown. We aim to characterize BIN1 expression in the OL population of AD brains. To investigate, BIN1 expression was examined in two cohorts of post-mortem human frontal cortex tissues(NIH-NeuroBioBank, healthy control, dementia, and AD, n=24; University of Pittsburgh-ADRC Neuropathology Core, Braak stage 0–IV, n=27) using immunoblotting and immunohistochemistry with six commercial antibodies. Such OL-specific BIN1 expression and cell cycle-related function were confirmed on primary OL cultures of mouse origin (C57BL/6). Four different antibodies against the MBD and SH3 domains showed that the neuronal isoform of BIN1(BIN1:H, 95kDa) was significantly reduced in AD (P<0.0001), but the OL-specific isoform (BIN1:L, 70kDa) detectable by antibody 2F11 was increased (P=0.0349). Histologically, the axon-like BIN1-immunoreactivity was significantly reduced with the progression of Braak stages, and such a pattern was distinct from OL-specific BIN1 antibody (2F11). Remarkably, nuclear OL-specific BIN1 was commonly identified by antibodies against the N-BAR, MBD, and SH3 domains. In OL culture, we confirmed that BIN1 was predominantly expressed in mature OL, but not the NG2+ progenitors. Together, OL-specific BIN1 expression may maintain the post-mitotic status of myelinating cells and its dysfunction may implicate AD pathogenesis.