Sirt1 attenuates astrocyte activation via modulating Dnajb1 and chaperone-mediated autophagy after closed head injury.

Our previous study indicates that Silent information regulator 1 (Sirt1) is involved in macroautophagy by upregulating light chain 3 (LC3) expression in astrocyte to exert a neuroprotective effect. Chaperon-mediated autophagy (CMA), another form of autophagy, is also upregulated after brain injury. However, little is known about the role of Sirt1 in regulation of the CMA. In the present study, an in vivo model of closed head injury (CHI) and an in vitro model of primary cortical astrocyte stimulated with interleukin-1β were employed to mimic the astrocyte activation induced by traumatic brain injury. Lentivirus carrying target complementary DNA (cDNA) or short hairpin RNA (shRNA) sequence was used to overexpress Sirt1 or knockdown DnaJ heat shock protein family member B1 (Dnajb1) (a molecular chaperone). We found that Sirt1 overexpression ameliorated neurological deficits, reduced tissue loss, and attenuated astrocyte activation after CHI, which was reversed by Dnajb1-shRNA administration. The upregulation of CMA activity induced by CHI in vivo and in vitro was inhibited after Dnajb1 knockdown. Sirt1 potently promoted CMA activity via upregulating Dnajb1 expression. Mechanically, Sirt1 could interact with Dnajb1 and modulate the deacetylation and ubiquitination of Dnajb1. These findings collectively suggest that Sirt1 plays a protective role against astrocyte activation, which may be associated with the regulation of the CMA activity via modulating the deacetylation and ubiquitination of Dnajb1 after CHI.
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