Brown, W. A. | Search bioRxiv

bioRxiv2022

ACSS2 Regulates HIF-2α Degradation through the E3-Ubiquitin Ligase MUL1 in Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is an aggressive kidney cancer driven by VHL loss and aberrant HIF-2 signaling. Acetate metabolism may contribute to this axis by ACSS2-dependent acetylation of HIF-2 and may provide opportunities to intervention. Here we tested the effects of pharmacological and genetic manipulation of ACSS2 on HIF-2, ccRCC cells, and tumors. ACSS2 inhibition led to HIF-2 degradation and suppressed ccRCC growth in vitro, in vivo, and in primary cell cultures of ccRCC patient tumors. This treatment resulted in reduced glucose and cholesterol metabolism, mitochondrial biogenesis and altered cristae deformation, that are consistent with loss of HIF-2. Mechanistically, HIF-2 protein levels are regulated through proteolytic degradation and we found, in parallel to VHL, HIF-2 stability was dependent on ACSS2 activity to prevent direct interaction with the E3 ligase MUL1. These findings highlight ACSS2 as a critical upstream regulator of HIF-2 that may be exploited to overcome resistance to HIF-2 inhibitor therapies. STATEMENT OF SIGNIFICANCEWe have unveiled ACSS2 as a critical upstream regulator of HIF-2 in ccRCC. Targeting ACSS2 potently promotes HIF-2 degradation via MUL1 to effectively deplete mitochondrial activity and block ccRCC primary tumor models and growth models resistant to HIF-2 inhibitor therapy.

cancer biology↗

bioRxiv2022

Mechanisms underlying the efficacy of a rodent model of vertical sleeve gastrectomy - a focus on energy expenditure

Background and aimsBariatric surgery remains the only effective and durable treatment option for morbid obesity. Vertical Sleeve Gastrectomy (VSG) is currently the most widely performed of these surgeries primarily because of its proven efficacy in generating rapid onset weight loss, improved glucose regulation and reduced mortality compared with other invasive procedures. VSG is associated with reduced appetite, however, the relative importance of energy expenditure to VSG-induced weight loss and changes in glucose regulation, particularly that in brown adipose tissue (BAT), remains unclear. The aim of this study is to investigate the role of BAT thermogenesis in the efficacy of VSG in a rodent model. MethodsDiet-induced obese male Sprague-Dawley rats were either sham-operated, underwent VSG surgery or were pairfed to the food consumed by the VSG group. Rats were also implanted with biotelemetry devices between the interscapular lobes of BAT to assess local changes in BAT temperature as a surrogate measure of thermogenic activity. Metabolic parameters including food intake, body weight and changes in body composition were assessed. To further elucidate the contribution of energy expenditure via BAT thermogenesis to VSG-induced weight loss, a separate cohort of lean rats underwent complete excision of the interscapular BAT (iBAT lipectomy) or chemical denervation using 6-hydroxydopamine (6-OHDA). To localize glucose uptake in specific tissues, an oral glucose tolerance test was combined with an intraperitoneal injection of 2 deoxy-D-glucose (2DG)-14C, administered intraperitoneally. Transneuronal viral tracing was used to identify 1) sensory neurons directed to the stomach or small intestine (H129-RFP) or 2) chains of polysynaptically linked neurons directed to BAT (PRV-GFP) in the same animals. ResultsFollowing VSG, there was a rapid reduction in body weight that was associated with reduced food intake, elevated BAT temperature and improved glucose regulation. Rats that underwent VSG had elevated glucose uptake into BAT compared to sham operated animals as well as elevated gene markers related to increased BAT activity (Ucp1, Dio2, Cpt1b, Cox8b, Ppargc) and markers of increased browning of white fat (Ucp1, Dio2, Cited1, Tbx1, Tnfrs9). Both iBAT lipectomy and 6-OHDA treatment significantly attenuated the impact of VSG on changes in body weight and adiposity in lean animals. In addition, surgical excision of iBAT following VSG significantly reversed VSG-mediated improvements in glucose tolerance, an effect that was independent of circulating insulin levels. Viral tracing studies highlight a patent neural link between the gut and BAT that include groups of premotor BAT-directed neurons in the dorsal raphe and raphe pallidus. ConclusionCollectively, these data support a role for BAT in mediating the metabolic sequelae, particularly the improvement in glucose regulation following VSG surgery and highlight the need to better understand the contribution from this tissue in human patients.

physiology↗