Whole-body sorcin invalidation does not cause hypothalamic ER stress nor worsens obesity in C57BL/6 male mice fed a westernized diet

Abstract

ABSTRACTBackgroundSoluble Resistance Related Calcium Binding Protein (sorcin) is a calcium (Ca2+) binding protein which has been shown to play a role in maintaining intracellular endoplasmic reticulum (ER) Ca2+ stores and lowering ER stress. Recently, our lab has demonstrated that sorcin expression was downregulated in the islets of Langerhans of mice fed a high-fat diet or in human islets incubated with the saturated fatty acid palmitate. We also showed that overexpression of sorcin under control of the rat insulin promoter (RIP7) in C57BL/6J mice, or whole body sorcin deletion in 129S1/SvImJ mice, improves or impairs insulin secretion and pancreatic β-cell function respectively. The mechanisms behind this beneficial role of sorcin in the pancreatic β-cell might depend on protection against lipotoxic endoplasmic reticulum (ER) stress through improved ER Ca2+ dynamics and activation of the Activating Transcription Factor 6 (ATF6) branch of the unfolded protein response (UPR). Whether sorcin is also implicated in hypothalamic ER stress during the progression of obesity is unknown. This could potentially contribute to the diminished satiety typically observed in overweight individuals.AimTo investigate a potential role of sorcin in hypothalamic ER stress, leptin resistance, hyperphagia and obesity.MethodsWhole-body sorcin null mice, backcrossed onto the C57BL/6J genetic background, were used. Body weight, food intake and EchoMRI body composition were measured in vivo whereas qRT-PCR analysis of sorcin and ER stress markers expression were performed on the arcuate nucleus of the hypothalamus. Leptin signalling through STAT3 phosphorylation was measured by Western blots on sorcin-null HEK293 cells, engineered by CRISPR/Cas9, and transfected with leptin receptor (LepRb).ResultsSorcin expression was not influenced in the arcuate nucleus (ARC) of the hypothalamus by diet-induced obesity. Whole-body sorcin ablation did not cause ARC ER stress nor changes in body weight, body composition or food intake in C57BL/6 male mice exposed to a high-fat, high-sugar diet. STAT3 phosphorylation (Y705) in response to leptin was not impaired in sorcin-null HEK293 cells.ConclusionIn our model, whole body sorcin ablation did not increase hypothalamic ER stress nor influenced food intake or body weight.