SIRT1 Modulates Aggregation and Toxicity through Deacetylation of the Androgen Receptor in Cell Models of SBMA

Abstract

Posttranslational protein modifications can play a major role in disease pathogenesis; phosphorylation, sumoylation, and acetylation modulate the toxicity of a variety of proteotoxic proteins. The androgen receptor (AR) is substantially modified, in response to hormone binding, by phosphorylation, sumoylation, and acetylation; these modifications might thus contribute to DHT-dependent polyglutamine (polyQ)-expanded AR proteotoxicity in spinal and bulbar muscular atrophy (SBMA). SIRT1, a nuclear protein and deacetylase of the AR, is neuroprotective in many neurodegenerative disease models. Our studies reveal that SIRT1 also offers protection against polyQ-expanded AR by deacetylating the AR at lysines 630/632/633. This finding suggested that nuclear AR acetylation plays a role in the aberrant metabolism and toxicity of polyQ-expanded AR. Subsequent studies revealed that the polyQ-expanded AR is hyperacetylated and that pharmacologic reduction of acetylation reduces mutant AR aggregation. Moreover, genetic mutation to inhibit polyQ-expanded AR acetylation of lysines 630/632/633 substantially decreased its aggregation and completely abrogated its toxicity in cell lines and motor neurons. Our studies also reveal one means by which the AR acetylation state likely modifies polyQ-expanded AR metabolism and toxicity, through its effect on DHT-dependent AR stabilization. Overall, our findings reveal a neuroprotective function of SIRT1 that operates through its deacetylation of polyQ-expanded AR and highlight the potential of both SIRT1 and AR acetylation as powerful therapeutic targets in SBMA.

Proteasome-mediated Proteolysis of the Polyglutamine-expanded Androgen Receptor Is a Late Event in Spinal and Bulbar Muscular Atrophy (SBMA) Pathogenesis

“…Dissociated spinal cord cultures from wild-type mice were differentiated for 3 weeks and then infected with AAV to express full-length human AR (AR24Q or AR111Q) tagged with a C-terminal FLAG epitope. As previously shown for motor neurons expressing untagged polyglutamine-expanded AR (27,29,30), a substantial number of motor neurons died by 8 days of treatment with DHT (Fig. 2D, right panel).…”

“…Generation of Adeno-associated Viruses-Adeno-associated viruses containing C-terminal FLAG-tagged human AR (111-CAG or 25-CAG) were created as described (27). Briefly, adeno-associated virus (AAV) cis plasmids carrying AR with 111 or 25 CAGs and containing N-terminal nuclear localization signal (NLS; ϫ3) to ensure nuclear localization were co-transfected with Trans (H21) and Adenovirus Helper (␦6) into HEK293T cells using calcium/phosphate transfection.…”

Regulation of the androgen receptor by post-translational modifications

“…SIRT1 is a deacetylase enzyme that can repress DHTmediated AR expression by binding to and deacetylating AR. This deacetylation event has been found to be neuroprotective and can protect against proteotoxicity in Kennedy's disease (Montie et al 2011). It can also reduce the AR N/C terminal interaction and inhibit contact-independent cell growth.…”

SIRT1 deacetylase in aging‐induced neuromuscular degeneration and amyotrophic lateral sclerosis

“…In addition to modulating transcription factors and metabolic enzymes, SIRT1 has been shown to directly deacetylate proteins that impact neurodegenerative disorders (Herskovits & Guarente, 2014; Min et al, 2010; Montie, Pestell, & Merry, 2011). Studies using resveratrol, a polyphenolic compound that activates SIRT1 and other targets, have shown mixed effects in the SOD1 G93A mouse model of ALS, with some dosing regimens showing protection and others indicating no effect on disease progression (Han, Choi, Soon Shin, & Kang, 2012; Kim et al, 2007; Mancuso et al, 2014; Markert, Kim, Gifondorwa, Childers, & Milligan, 2010; Song, Chen, & Zhang, 2014).…”