Spinobulbar muscular atrophy (SBMA) is an inherited neuromuscular disorder caused by the expansion of a CAG repeat encoding a polyglutamine tract in exon 1 of the androgen receptor (AR) gene. SBMA demonstrates androgen-dependent toxicity due to unfolding and aggregation of the mutant protein. There are currently no disease-modifying therapies, but of increasing interest for therapeutic targeting is autophagy, a highly conserved cellular process mediating protein quality control. We have previously shown that genetic manipulations inhibiting autophagy diminish skeletal muscle atrophy and extend the lifespan of AR113Q knock-in mice. In contrast, manipulations inducing autophagy worsen muscle atrophy, suggesting that chronic, aberrant upregulation of autophagy contributes to pathogenesis. Since the degree to which autophagy is altered in SBMA and the mechanisms responsible for such alterations are incompletely defined, we sought to delineate autophagic status in SBMA using both cellular and mouse models. Here, we confirm that autophagy is induced in cellular and knock-in mouse models of SBMA and show that the transcription factors transcription factor EB (TFEB) and ZKSCAN3 operate in opposing roles to underlie these changes. We demonstrate upregulation of TFEB target genes in skeletal muscle from AR113Q male mice and SBMA patients. Furthermore, we observe a greater response in AR113Q mice to physiological stimulation of autophagy by both nutrient starvation and exercise. Taken together, our results indicate that transcriptional signaling contributes to autophagic dysregulation and provides a mechanistic framework for the pathologic increase of autophagic responsiveness in SBMA.

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The transcriptional regulation of the apoCIII gene by hormonal and metabolic signals plays a significant role in determining plasma triglyceride levels. In the current work we demonstrate that the apoCIII gene is regulated by the mitogen-activated protein (MAP) kinase signaling pathway. In HepG2 cells, repression of MAP kinase activity by treatment with the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibitor PD98059 caused a 5-8-fold increase in apoCIII transcriptional activity. Activation of MAP kinase by phorbol ester treatment caused a 3-5-fold reduction in apoCIII transcription. The region of the apoCIII promoter responsible for this regulation was mapped in transiently transfected HepG2 cells to a 6-base pair element located at ؊740. The major protein binding to this site was identified as the nuclear hormone receptor HNF4. An increase in HNF4 mRNA and protein levels was observed in HepG2 cells after treatment with PD98059, indicating that the MAP kinase pathway regulates the expression of the HNF4 gene. These findings demonstrate that the apoCIII gene can be regulated by signals acting through the MAP kinase pathway and that this regulation is mediated, at least in part, by changes in the amount of HNF4.ApoCIII is a component of very low density lipoprotein and functions as a key regulator of serum triglyceride levels (1). In transgenic animals, overexpression of the apoCIII gene caused hypertriglyceridemia (2), with as little as 30 -40% excess apo-CIII causing a 2-fold increase in triglyceride levels (3). Likewise, mice that did not express apoCIII because of a gene knockout had abnormally low circulating triglyceride levels (4). Genetic studies have demonstrated a key role for apoCIII in determining plasma triglyceride levels in humans. A sequence polymorphism in the 3Ј-untranslated region of the apoCIII gene has been associated with elevated triglyceride levels in several populations (5-9). In addition, clinical studies have reported that some hypertriglyceridemic patients have elevated apoCIII levels and increased apoCIII production rates (10 -12). ApoCIII modulates serum triglyceride metabolism by reducing both lipolysis and uptake of triglyceride-rich lipoproteins (3, 13-16).The apoCIII gene is transcriptionally regulated by a variety of metabolic and hormonal signals. In a previous study, we demonstrated that in a hypoinsulinemic animal model of diabetes, hepatic apoCIII transcriptional activity is regulated by insulin and that these changes correlated with changes in plasma triglyceride levels (17). Further evidence that apoCIII transcriptional activity plays a significant role in determining plasma triglyceride levels comes from the analysis of a genetic polymorphism in the human apoCIII promoter region. Two major sequence variants of the apoCIII promoter can be found in the human population. The most common (wild-type) allele differs from the less common (variant) allele by five single base pair DNA sequence differences. A haplotype of the apoCIII locus contain...

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