Overexpression of nuclear receptor SHP in adipose tissues affects diet-induced obesity and adaptive thermogenesis

Abstract

The orphan nuclear receptor small heterodimer partner (SHP) regulates metabolic pathways involved in hepatic bile acid production and both lipid and glucose homeostasis via the transcriptional repression of other nuclear receptors. In the present study, we generated fat-specific SHP-overexpressed transgenic (TG) mice and determined the potential role of SHP activation, specifically in adipocytes, in the regulation of adipose tissue function in response to stressors. We determined in 2 mo-old SHP TG mice body weight, fat mass index, adipose tissues morphology, thermogenic and metabolic gene expression, metabolic rates at baseline and in response to ␤ adrenergic receptor agonists, and brown fat ultrastructural changes in response to cold exposure (6 -48 h). Mice were fed a 10-wk high-fat diet (HFD; 42% fat). Weight gain, fat mass index, adipose tissues morphology, glucose tolerance, and metabolic rates were determined at the end of the feeding. Young TG mice had increased body weight and adiposity; however, their energy metabolism was increased and brown fat function was enhanced in response to cold exposure through the activation of thermogenic genes and mitochondrial biogenesis. SHP overexpression exacerbated the diet-induced obesity phenotype as evidence by marked weight gain over time, increased adiposity, and severe glucose intolerance compared with wild-type mice fed a HFD. In addition, SHP-TG mice fed HFD had decreased diet-induced adaptive thermogenesis, increased food intake, and decreased physical activity. In conclusion, SHP activation in adipocytes strongly affects weight gain and diet-induced obesity. Developing a synthetic compound to antagonize the effect of SHP may prove to be useful in treating obesity. small heterodimer partner; metabolism; obesity; energy expenditure; nuclear receptor OBESITY IS THE RESULT of an imbalance between energy intake and expenditure (17). Whereas energy intake is solely dependent on food ingestion, energy expenditure depends on several factors, such as exercise and heat production, or so-called adaptive thermogenesis. Despite extensive research focused on the understanding of obesity, the molecular mechanisms underlying increased adiposity are not fully understood.Brown adipose tissue (BAT) is the major site for adrenergic mediated adaptive thermogenesis involving the uncoupling protein-1 (UCP1), whereas white adipose tissue (WAT) is mostly implicated in the regulation of lipid storage and catabolism (8,13,15,26). Adaptive thermogenesis allows rodents to slow the development of obesity when overfed and maintain body temperature when exposed to a cold environment. Excessive caloric intake can be sensed by the sympathetic nervous system through ␤-adrenergic receptors (␤ARs), i.e., ␤1AR, ␤2AR, and ␤3AR, and the increased cyclic AMP (cAMP) leads to an activation of UCP1 and the induction of the uncoupling process in mitochondria that results in heat production (2, 6). cAMP can also activate deiodinase 2 (Dio2) which generates the active form of the thyroid hormone triiodot...

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“…15 Dysregulation of these processes leads to adiposity, dyslipidemia, and metabolic perturbations. 16 …”

Nuclear receptors and liver disease: Summary of the 2017 basic research symposium

“…SHP has been shown to be involved in BA synthesis, lipid and cholesterol metabolism, glucose homeostasis, apoptosis, and cell invasion 36, 37, 38, 39, 40, 41, 42, 43. SHP has also been identified as a mediating factor in the metabolic circadian clock 44, 45, 46, 47, 48.…”

Nuclear Receptors as Therapeutic Targets in Liver Disease: Are We There Yet?

“…However, SHP-null were resistant to HFD-induced fatty liver and obesity (15, 20, 38), which is mediated by the liver Clock and Npas2 genes (39, 40). Interestingly, alcohol-induced macrovesicular lipid vacuoles were diminished in SHP-null mice that were associated with the decreased hyperhomocysteinemia (41).…”