The Rab-GTPase-activating protein TBC1D1 has emerged as a novel candidate involved in metabolic regulation. Our aim was to determine whether TBC1D1 is involved in insulin as well as energy-sensing signals controlling skeletal muscle metabolism. TBC1D1-deficient congenic B6.SJL-Nob1.10 (Nob1.10(SJL)) and wild-type littermates were studied. Glucose and insulin tolerance, glucose utilization, hepatic glucose production, and tissue-specific insulin-mediated glucose uptake were determined. The effect of insulin, AICAR, or contraction on glucose transport was studied in isolated skeletal muscle. Glucose and insulin tolerance tests were normal in TBC1D1-deficient Nob1.10(SJL) mice, yet the 4-h-fasted insulin concentration was increased. Insulin-stimulated peripheral glucose utilization during a euglycemic hyperinsulinemic clamp was similar between genotypes, whereas the suppression of hepatic glucose production was increased in TBC1D1-deficient mice. In isolated extensor digitorum longus (EDL) but not soleus muscle, glucose transport in response to insulin, AICAR, or contraction was impaired by TBC1D1 deficiency. The reduction in glucose transport in EDL muscle from TBC1D1-deficient Nob1.10(SJL) mice may be explained partly by a 50% reduction in GLUT4 protein, since proximal signaling at the level of Akt, AMPK, and acetyl-CoA carboxylase (ACC) was unaltered. Paradoxically, in vivo insulin-stimulated 2-deoxyglucose uptake was increased in EDL and tibialis anterior muscle from TBC1D1-deficient mice. In conclusion, TBC1D1 plays a role in regulation of glucose metabolism in skeletal muscle. Moreover, functional TBC1D1 is required for AICAR- or contraction-induced metabolic responses, implicating a role in energy-sensing signals.

Consumption of a hypercaloric diet upregulates microglial innate immune reactivity along with a higher expression of lipoprotein lipase (Lpl) within the reactive microglia in the mouse brain. Here, we show that knockdown of the Lpl gene specifically in microglia resulted in deficient microglial uptake of lipid, mitochondrial fuel utilization shifting to glutamine, and significantly decreased immune reactivity. Mice with knockdown of the Lpl gene in microglia gained more body weight than control mice on a high-carbohydrate high-fat (HCHF) diet. In these mice, microglial reactivity was significantly decreased in the mediobasal hypothalamus, accompanied by downregulation of phagocytic capacity and increased mitochondrial dysmorphologies. Furthermore, HCHF-diet-induced POMC neuronal loss was accelerated. These results show that LPL-governed microglial immunometabolism is essential to maintain microglial function upon exposure to an HCHF diet. In a hypercaloric environment, lack of such an adaptive immunometabolic response has detrimental effects on CNS regulation of energy metabolism.

Methotrexate (MTX) is a widely used anticancer and antirheumatic drug that has been postulated to protect against metabolic risk factors associated with type 2 diabetes, although the mechanism remains unknown. MTX inhibits 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/inosine monophosphate cyclohydrolase (ATIC) and thereby slows the metabolism of 5-aminoimidazole-4-carboxamide-1-b-D-ribofuranosyl-59-monophosphate (ZMP) and its precursor AICAR, which is a pharmacological AMPK activator. We explored whether MTX promotes AMPK activation in cultured myotubes and isolated skeletal muscle. We found MTX markedly reduced the threshold for AICAR-induced AMPK activation and potentiated glucose uptake and lipid oxidation. Gene silencing of the MTX target ATIC activated AMPK and stimulated lipid oxidation in cultured myotubes. Furthermore, MTX activated AMPK in wildtype HEK-293 cells. These effects were abolished in skeletal muscle lacking the muscle-specific, ZMP-sensitive AMPK-g3 subunit and in HEK-293 cells expressing a ZMP-insensitive mutant AMPK-g2 subunit. Collectively, our findings underscore a role for AMPK as a direct molecular link between MTX and energy metabolism in skeletal muscle. Cotherapy with AICAR and MTX could represent a novel strategy to treat metabolic disorders and overcome current limitations of AICAR monotherapy.Chronic therapy with methotrexate (MTX), a broadly used anticancer and antirheumatic drug, may protect rheumatic patients against metabolic risk factors associated with cardiovascular disease, obesity (1), and type 2 diabetes (2). This notion is supported by recent observations that MTX alleviates hyperglycemia and insulin resistance in diabetic (db/db) mice (3) and obese mice fed a high-fat diet (4). MTX is a folate antagonist and inhibits DNA replication (5), which explains its anticancer action but the not improvements in glucose homeostasis in type 2 diabetes or obesity. Suppression of chronic inflammation, thought to arise from MTX-stimulated adenosine release (6), may improve glucose homeostasis indirectly (7). Because antirheumatic drugs are not invariably associated with metabolic protection (1,8), other mechanisms are likely. Although MTX-induced adenosine release may have direct metabolic effects (4), its exact role is ambiguous, because adenosine receptor activation (9) and blockage (10) both improve insulin sensitivity. Clearly, the molecular underpinnings of MTX action in relation to metabolic disease remain undefined.MTX has several pharmacological targets, including 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/inosine monophosphate cyclohydrolase (ATIC) (11). ATIC is essential for the conversion of 5-aminoimidazole-4-carboxamide-1-b-D-ribofuranosyl-59-monophosphate (ZMP) to inosine monophosphate in the final two steps of the de novo purine synthesis pathway. Thus, congenital ATIC deficiency or MTX therapy elevates intracellular ZMP content and excretion of its metabolites (6,12,13). The purine precursor ZMP is also an AMP mimetic and activa...

We assessed the efficacy of simultaneous agonism at the glucagon-like peptide-1 receptor (GLP-1R) and the melanocortin-4 receptor (MC4R) for the treatment of obesity and diabetes in rodents. Diet-induced obese (DIO) mice were chronically treated with either the long-acting GLP-1R agonist liraglutide, the MC4R agonist RM-493 or a combination of RM-493 and liraglutide. Co-treatment of DIO mice with RM-493 and liraglutide improves body weight loss and enhances glycemic control and cholesterol metabolism beyond what can be achieved with either mono-therapy. The superior metabolic efficacy of this combination therapy is attributed to the anorectic and glycemic actions of both drugs, along with the ability of RM-493 to increase energy expenditure. Interestingly, compared to mice treated with liraglutide alone, hypothalamic Glp-1r expression was higher in mice treated with the combination therapy after both acute and chronic treatment. Further, RM-493 enhanced hypothalamic Mc4r expression. Hence, co-dosing with MC4R and GLP-1R agonists increases expression of each receptor, indicative of minimized receptor desensitization. Together, these findings suggest potential opportunities for employing combination treatments that comprise parallel MC4R and GLP-1R agonism for the treatment of obesity and diabetes.

ObjectiveLeptin is a cytokine produced by adipose tissue that acts mainly on the hypothalamus to regulate appetite and energy homeostasis. Previous studies revealed that the leptin receptor is expressed not only in neurons, but also in glial cells. Microglia are resident immune cells in the brain that play an essential role in immune defense and neural network development. Previously we reported that microglial morphology and cytokine production are changed in the leptin receptor deficient db/db mouse, suggesting that leptin's central effects on metabolic control might involve signaling through microglia. In the current study, we aimed to uncover the role of leptin signaling in microglia in systemic metabolic control.MethodsWe generated a mouse model with leptin receptor deficiency, specifically in the myeloid cells, to determine the role of microglial leptin signaling in the development of metabolic disease and to investigate microglial functions.ResultsWe discovered that these mice have increased body weight with hyperphagia. In the hypothalamus, pro-opiomelanocortin neuron numbers in the arcuate nucleus (ARC) and α-MSH projections from the ARC to the paraventricular nucleus (PVN) decreased, which was accompanied by the presence of less ramified microglia with impaired phagocytic capacity in the PVN.ConclusionsMyeloid cell leptin receptor deficient mice partially replicate the db/db phenotype. Leptin signaling in hypothalamic microglia is important for microglial function and a correct formation of the hypothalamic neuronal circuit regulating metabolism.