Hyperosmotic Stress Induces Tau Proteolysis by Caspase-3 Activation in SH-SY5Y Cells

Tau is a microtubule-associated protein implicated in the pathogenesis of Alzheimer's disease and other related tauopathies. In this subset of neurodegenerative disorders, Tau auto-assembles into insoluble fibrils that accumulate in neurons as paired helical filaments (PHFs), promoting cellular dysfunction and cytotoxic effects. Growing evidence suggests that abnormal post-translational regulation, mainly hyperphosphorylation and aberrant cleavage, drives Tau to this pathological state. In this work we show that sorbitol-induced hyperosmotic stress promotes Tau proteolysis in SH-SY5Y neuroblastoma cells. The appearance of cleaved Tau was preceded by the activation of μ-calpain, the proteasome system and caspase-3. Tau proteolysis was completely prevented by caspase-3 inhibition but unaffected by neither the proteasome system nor μ-calpain activity blockade. Concomitantly, hyperosmotic stress induced apoptosis in SH-SY5Y cells, which was efficiently avoided by the inhibition of caspase-3 activity. Altogether, our results provide the first evidence that Tau protein is susceptible to caspase-3 proteolysis under hyperosmotic stress and suggest a positive relationship between Tau proteolysis and apoptosis in SH-SY5Y cells. J. Cell. Biochem. 117: 2781-2790, 2016. © 2016 Wiley Periodicals, Inc.