TBK1 regulates autophagic clearance of soluble mutant huntingtin and inhibits aggregation/toxicity in different models of Huntington's disease

Phosphorylation of the N-terminal domain of the Huntingtin (HTT) protein (at T3, S13, and S16) has emerged as a key regulator of HTT stability, clearance, localization, aggregation and toxicity. Herein, we report the discovery and validation of a kinase, TANK-binding kinase 1 (TBK1), that specifically and efficiently phosphorylates both wild-type and mutant full-length or N-terminal fragments of HTT in vitro (S13/S16) and in cell/ neuronal cultures (S13). We show that overexpression of TBK1 in mammalian cells, primary neurons and a Caenorhabditis elegans model of Huntington's Disease (HD) increases mutant HTTex1 phosphorylation, lowers its levels, increases its nuclear localization and significantly reduces its aggregation and cytotoxicity. Our mechanistic studies demonstrate that the TBK1-mediated neuroprotective effects are due to phosphorylation-dependent inhibition of mutant HTTex1 aggregation and an increase in autophagic flux. These findings suggest that upregulation and/or activation of TBK1 represents a viable strategy for the treatment of HD.