Gallic acid [3,4,5-trihydroxybenzoic acid (GA)], a natural phytochemical, is known to have a variety of cellular functions including beneficial effects on metabolic syndromes. However, the molecular mechanism by which GA exerts its beneficial effects is not known. Here we report that GA plays its role through the activation of AMP-activated protein kinase (AMPK) and by regulating mitochondrial function via the activation of peroxisome proliferator-activated receptor-γ coactivator1α (PGC1α). Sirtuin 1 (Sirt1) knockdown significantly blunted GA's effect on PGC1α activation and downstream genes, suggesting a critical role of the AMPK/Sirt1/PGC1α pathway in GA's action. Moreover, diet-induced obese mice treated with GA showed significantly improved glucose and insulin homeostasis. In addition, the administration of GA protected diet-induced body weight gain without a change in food intake. Biochemical analyses revealed a marked activation of AMPK in the liver, muscle, and interscapular brown adipose tissue of the GA-treated mice. Moreover, uncoupling protein 1 together with other genes related to energy expenditure was significantly elevated in the interscapular brown adipose tissue. Taken together, these results indicate that GA plays its beneficial metabolic roles by activating the AMPK/Sirt1/PGC1α pathway and by changing the interscapular brown adipose tissue genes related to thermogenesis. Our study points out that targeting the activation of the AMPK/Sirt1/PGC1α pathway by GA or its derivatives might be a potential therapeutic intervention for insulin resistance in metabolic diseases.

Skin is the outermost layer of the human body that is constantly exposed to environmental stressors, such as UV radiation and toxic chemicals, and is susceptible to mechanical wounding and injury. The ability of the skin to repair injuries is paramount for survival and it is disrupted in a spectrum of disorders leading to skin pathologies. Diabetic patients often suffer from chronic, impaired wound healing, which facilitate bacterial infections and necessitate amputation. Here, we studied the effects of gallic acid (GA, 3,4,5-trihydroxybenzoic acid; a plant-derived polyphenolic compound) on would healing in normal and hyperglucidic conditions, to mimic diabetes, in human keratinocytes and fibroblasts. Our study reveals that GA is a potential antioxidant that directly upregulates the expression of antioxidant genes. In addition, GA accelerated cell migration of keratinocytes and fibroblasts in both normal and hyperglucidic conditions. Further, GA treatment activated factors known to be hallmarks of wound healing, such as focal adhesion kinases (FAK), c-Jun N-terminal kinases (JNK), and extracellular signal-regulated kinases (Erk), underpinning the beneficial role of GA in wound repair. Therefore, our results demonstrate that GA might be a viable wound healing agent and a potential intervention to treat wounds resulting from metabolic complications.

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The central actions of leptin and insulin are essential for the regulation of energy and glucose homeostasis. In addition to the crucial effects on the hypothalamus, emerging evidence suggests that the leptin and insulin signaling can act on other brain regions to mediate the reward value of nutrients. Recent studies have indicated the midbrain dopaminergic neurons as a potential site for leptin’ and insulin’s actions on mediating the feeding behaviors and therefore affecting the energy balance. Although molecular details about the integrative roles of leptin and insulin in this subset of neurons remain to be investigated, substantial body of evidence by far imply that the signaling pathways regulated by leptin and insulin may play an essential role in the regulation of energy balance through the control of food-associated reward. This review therefore describes the convergence of energy regulation and reward system, particularly focusing on leptin and insulin signaling in the midbrain dopaminergic neurons.

Dopaminergic (DA) neurons are involved in the integration of neuronal and hormonal signals to regulate food consumption and energy balance. Forkhead transcriptional factor O1 (FoxO1) in the hypothalamus plays a crucial role in mediation of leptin and insulin function. However, the homoeostatic role of FoxO1 in DA system has not been investigated. Here we report that FoxO1 is highly expressed in DA neurons and mice lacking FoxO1 specifically in the DA neurons (FoxO1 KODAT) show markedly increased energy expenditure and interscapular brown adipose tissue (iBAT) thermogenesis accompanied by reduced fat mass and improved glucose/insulin homoeostasis. Moreover, FoxO1 KODAT mice exhibit an increased sucrose preference in concomitance with higher dopamine and norepinephrine levels. Finally, we found that FoxO1 directly targets and negatively regulates tyrosine hydroxylase (TH) expression, the rate-limiting enzyme of the catecholamine synthesis, delineating a mechanism for the KO phenotypes. Collectively, these results suggest that FoxO1 in DA neurons is an important transcriptional factor that directs the coordinated control of energy balance, thermogenesis and glucose homoeostasis.

Activated in energy depletion conditions, AMP-activated protein kinase (AMPK) acts as a cellular energy sensor and regulator in both central nervous system and peripheral organs. Hypothalamic AMPK restores energy balance by promoting feeding behavior to increase energy intake, increasing glucose production, and reducing thermogenesis to decrease energy output. Besides energy state, many hormones have been shown to act in concert with AMPK to mediate their anorexigenic and orexigenic central effects as well as thermogenic influences. Here we explore the factors that affect hypothalamic AMPK activity and give the underlying mechanisms for the role of central AMPK in energy homeostasis together with the physiological effects of hypothalamic AMPK on energy balance restoration.

Although the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic agent, it shows limited efficacy in human pancreatic cancer cells. Protein synthesis inhibition has been reported to sensitize cancer cells to apoptosis-inducing agents, but the detailed mechanism by which protein synthesis inhibition sensitize cells to TRAIL has not been determined. To investigate the mechanism underlying pancreatic cancer cell resistance to TRAIL, we performed a small scale high-throughput compound screening in AsPC-1 pancreatic cancer cells using a bioactive small molecule library. We identified 8 compounds that reproducibly sensitize AsPC-1 cells to TRAIL-induced apoptosis. One of these compounds, emetine hydrochloride, when combined with subtoxic concentrations of TRAIL, induced massive apoptosis in AsPC-1 and BxPC-3 pancreatic cancer cells. Cell death analysis revealed that the sensitizing effects of emetine were specific to TRAIL. Emetine downregulated the expression of the TRAIL-related anti-apoptotic protein Mcl-1 in a dose- and time-dependent manner. Furthermore, specific knockdown of Mcl-1 using small interfering RNA without emetine treatment sensitized pancreatic cancer cells to TRAIL. Emetine sensitization of pancreatic cancer cells to TRAIL via Mcl-1 was confirmed under hypoxic conditions. Taken together, these findings strongly suggest that Mcl-1 is involved in pancreatic cancer cell resistance to TRAIL, and emetine facilitates the apoptosis of TRAIL-tolerant pancreatic cancer cells by specifically inhibiting Mcl-1 function.

The ventromedial nucleus of the hypothalamus (VMH) is important for the regulation of whole body energy homeostasis and lesions in the VMH are reported to result in massive weight gain. The nuclear receptor steroidogenic factor 1 (SF-1) is a known VMH marker as it is exclusively expressed in the VMH region of the brain. SF-1 plays a critical role not only in the development of VMH but also in its physiological functions. In this study, we generated prenatal VMH-specific SF-1 KO mice and investigated age-dependent energy homeostasis regulation by SF-1. Deletion of SF-1 in the VMH resulted in dysregulated insulin and leptin homeostasis and late onset obesity due to increased food intake under normal chow and high fat diet conditions. In addition, SF-1 ablation was accompanied by a marked reduction in energy expenditure and physical activity and this effect was significantly pronounced in the aged mice. Taken together, our data indicates that SF-1 is a key component in the VMH-mediated regulation of energy homeostasis and implies that SF-1 plays a protective role against metabolic stressors including aging and high fat diet.