AβPP-overexpression and proteasome inhibition increase αB-crystallin in cultured human muscle: Relevance to inclusion-body myositis

Amyloid-β precursor protein (AβPP) and its fragment amyloid-β (Aβ) are increased in s-IBM muscle fibers and appear to play an important role in the pathogenic cascade. αB-Crystallin (αBC) was shown immunohistochemically to be accumulated in s-IBM muscle fibers, but the stressor(s) influencing αBC accumulation was not identified. We now demonstrate, using our experimental IBM model based on genetic overexpression of AβPP into cultured normal human muscle fibers, that: (1) AβPP overexpression increased αBC 3.7-fold (p = 0.025); (2) additional inhibition of proteasome with epoxomicin increased αBC 7-fold (p = 0.002); and (3) αBC physically associated with AβPP and Aβ oligomers. We also show that in biopsied s-IBM muscle fibers, αBC was similarly increased 3-fold (p = 0.025) and physically associated with AβPP and Aβ oligomers. We propose that increased AβPP is a stressor increasing αBC expression in s-IBM muscle fibers. Determining the consequences of αBC association with Aβ oligomers could have clinical therapeutic relevance.