Generation of mega brown adipose tissue in adults by controlling brown adipocyte differentiation in vivo.

Brown adipose tissue (BAT) is a highly specialized adipose tissue in its immobile location and size during the entire adulthood. In response to cold exposure and other ß3-adrenoreceptor stimuli, BAT commits energy consumption by nonshivering thermogenesis (NST). However, the molecular machinery in controlling the BAT mass in adults is unknown. Here, we show our surprising findings that the BAT mass and functions can be manipulated in adult animals by controlling BAT adipocyte differentiation in vivo. Platelet-derived growth factor receptor α (PDGFα) expressed in BAT progenitor cells served a signaling function to avert adipose progenitor differentiation. Genetic and pharmacological loss-of-function of PDGFRα eliminated the differentiation barrier and permitted progenitor cell differentiation to mature and functional BAT adipocytes. Consequently, an enlarged BAT mass (megaBAT) was created by PDGFRα inhibition owing to increases of brown adipocyte numbers. Under cold exposure, a microRNA-485 (miR-485) was identified as a master suppressor of the PDGFRα signaling, and delivery of miR-485 also produced megaBAT in adult animals. Noticeably, megaBAT markedly improved global metabolism, insulin sensitivity, high-fat-diet (HFD)-induced obesity, and diabetes by enhancing NST. Together, our findings demonstrate that the adult BAT mass can be increased by blocking the previously unprecedented inhibitory signaling for BAT progenitor cell differentiation. Thus, blocking the PDGFRα for the generation of megaBAT provides an attractive strategy for treating obesity and type 2 diabetes mellitus (T2DM).

The multifaceted role of ATF4 in regulating glucose-stimulated insulin secretion.

Stress-inducible transcription factor ATF4 is essential for survival and identity of ß-cell during stress conditions. However, the physiological role of ATF4 in ß-cell function is not yet completely understood. To understand the role of ATF4 in glucose-stimulated insulin secretion (GSIS), ß-cell-specific Atf4 knockout (ßAtf4KO) mice were phenotypically characterized. Insulin secretion and mechanistic analyses were performed using islets from control Atf4f/f and ßAtf4KO mice to assess key regulators for triggering and amplifying signals for GSIS. ßAtf4KO mice displayed glucose intolerance due to reduced insulin secretion. Moreover, ßAtf4KO islets exhibited a decrease in both the insulin content and first-phase insulin secretion. The analysis of ßAtf4KO islets showed that ATF4 is required for insulin production and glucose-stimulated ATP and cAMP production. The results demonstrate that ATF4 contributes to the multifaceted regulatory process in GSIS even under stress-free conditions.

Identification of an endoplasmic reticulum proteostasis modulator that enhances insulin production in pancreatic ß cells.

Perturbation of endoplasmic reticulum (ER) proteostasis is associated with impairment of cellular function in diverse diseases, especially the function of pancreatic ß cells in type 2 diabetes. Restoration of ER proteostasis by small molecules shows therapeutic promise for type 2 diabetes. Here, using cell-based screening, we report identification of a chemical chaperone-like small molecule, KM04794, that alleviates ER stress. KM04794 prevented protein aggregation and cell death caused by ER stressors and a mutant insulin protein. We also found that this compound increased intracellular and secreted insulin levels in pancreatic ß cells. Chemical biology and biochemical approaches revealed that the compound accumulated in the ER and interacted directly with the ER molecular chaperone BiP. Our data show that this corrector of ER proteostasis can enhance insulin storage and pancreatic ß cell function.

Endoplasmic reticulum stress enhances γ-secretase activity.

The endoplasmic reticulum (ER) copes with unfolded proteins in the lumen (ER stress) by activating three distinct intracellular signaling pathways of unfolded protein response (UPR). ER stress contributes to the pathogenesis of obesity and diabetes, which are risk factors for Alzheimer's disease (AD) that accelerate the pathogenesis of AD. However, whether ER stress is involved in the development of AD remains unclear. In this study, we demonstrate that ER stress induces presenilin-1 expression through activating transcription factor 4 (ATF4), resulting in increased amyloid-ß (Aß) secretion by γ-secretase activity, which is suppressed by quercetin by modifying UPR signaling. This result suggests that ER stress may be stimulated in obesity and type 2 diabetes, thereby enhancing γ-secretase activity that is the underlying molecular mechanism affecting the pathogenesis of AD.