ROCK1 in AgRP neurons regulates energy expenditure and locomotor activity in male mice

Astrocytic insulin receptor controls circadian behavior via dopamine signaling in a sexually dimorphic manner

Mammalian circadian clocks respond to feeding and light cues, adjusting internal rhythms with day/night cycles. Astrocytes serve as circadian timekeepers, driving daily physiological rhythms; however, it's unknown how they ensure precise cycle-to-cycle rhythmicity. This is critical for understanding why mistimed or erratic feeding, as in shift work, disrupts circadian physiology- a condition linked to type 2 diabetes and obesity. Here, we show that astrocytic insulin signaling sets the free-running period of locomotor activity in female mice and food entrainment in male mice. Additionally, ablating the insulin receptor in hypothalamic astrocytes alters cyclic energy homeostasis differently in male and female mice. Remarkably, the mutants exhibit altered dopamine metabolism, and the pharmacological modulation of dopaminergic signaling partially restores distinct circadian traits in both male and female mutant mice. Our findings highlight the role of astrocytic insulin-dopaminergic signaling in conveying time-of-feeding or lighting cues to the astrocyte clock, thus governing circadian behavior in a sex-specific manner.

Neurochemical Basis of Inter-Organ Crosstalk in Health and Obesity: Focus on the Hypothalamus and the Brainstem

Precise neural regulation is required for maintenance of energy homeostasis. Essential to this are the hypothalamic and brainstem nuclei which are located adjacent and supra-adjacent to the circumventricular organs. They comprise multiple distinct neuronal populations which receive inputs not only from other brain regions, but also from circulating signals such as hormones, nutrients, metabolites and postprandial signals. Hence, they are ideally placed to exert a multi-tier control over metabolism. The neuronal sub-populations present in these key metabolically relevant nuclei regulate various facets of energy balance which includes appetite/satiety control, substrate utilization by peripheral organs and glucose homeostasis. In situations of heightened energy demand or excess, they maintain energy homeostasis by restoring the balance between energy intake and expenditure. While research on the metabolic role of the central nervous system has progressed rapidly, the neural circuitry and molecular mechanisms involved in regulating distinct metabolic functions have only gained traction in the last few decades. The focus of this review is to provide an updated summary of the mechanisms by which the various neuronal subpopulations, mainly located in the hypothalamus and the brainstem, regulate key metabolic functions.

GLP-1 rescued gestational diabetes mellitus-induced suppression of fetal thalamus development

Diabetes can be classified as type 1, type 2, and gestational diabetes mellitus (GDM). It has been reported that children born from mothers with GDM present motor impairment, however, underlying mechanisms of GDM-induce fetal neurological diseases remain unknown. In this study, NOD (nonobese diabetic) mice were used to construct the GDM model; after 2 weeks of gestation, thalamocortical axon development of fetal was evaluated by immunofluorescence. PCR of LRRC4C was used to confirm axon development of the thalamus cortex. RNA array was used to predict possible targets affected by GDM during fetal neurodevelopment. Western blot was used to investigate the underlying mechanism, PI3K inhibitor, and MAPK inhibitor was used to determine key pathway involved in this model, in vitro axonal growth was evaluated using neural stem cells, tactile sensory behavior of offspring was assessed to confirm neurological influence further. The result shown that maternal diabetes significantly suppressed axonal development of fetal thalamus cortex, PCR array of GDM fetal brain indicated that upregulation of GLP-1R compared with normal fetal, ELISA confirmed that GLP-1 level was decreased in GDM maternal serum compared with that of wild type pregnant mice. In vitro study observed enhanced axonal elongation after supplements of GLP-1 analog, GLP-1 analog PI3K-dependently active ROCK1 activity, IP injection of GLP-1 analog could partly reverse GDM-induced suppression of fetal thalamocortical axon development and improve tactile sensory behavior of GDM offspring. Our study provided a novel mechanism of GDM induced-neurological diseases and predicted GLP-1 as possible prevention supplement during gestation.

Hypothalamic Grb10 enhances leptin signalling and promotes weight loss

Leptin acts on hypothalamic neurons expressing agouti-related protein (AgRP) or pro-opiomelanocortin (POMC) to suppress appetite and increase energy expenditure, but the intracellular mechanisms that modulate central leptin signalling are not fully understood. Here we show that growth factor receptor-bound protein 10 (Grb10), an adaptor protein that binds to the insulin receptor and negatively regulates its signalling pathway, can interact with the leptin receptor and enhance leptin signalling. Ablation of Grb10 in AgRP neurons promotes weight gain, while overexpression of Grb10 in AgRP neurons reduces body weight in male and female mice. In parallel, deletion or overexpression of Grb10 in POMC neurons exacerbates or attenuates diet-induced obesity, respectively. Consistent with its role in leptin signalling, Grb10 in AgRP and POMC neurons enhances the anorexic and weight-reducing actions of leptin. Grb10 also exaggerates the inhibitory effects of leptin on AgRP neurons via ATP-sensitive potassium channel-mediated currents while facilitating the excitatory drive of leptin on POMC neurons through transient receptor potential channels. Our study identifies Grb10 as a potent leptin sensitizer that contributes to the maintenance of energy homeostasis by enhancing the response of AgRP and POMC neurons to leptin.

ROCK1 regulates insulin secretion from β-cells

OBJECTIVE

The endocrine pancreatic β-cells play a pivotal role in maintaining whole-body glucose homeostasis and its dysregulation is a consistent feature in all forms of diabetes. However, knowledge of intracellular regulators that modulate β-cell function remains incomplete. We investigated the physiological role of ROCK1 in the regulation of insulin secretion and glucose homeostasis.

METHODS

Mice lacking ROCK1 in pancreatic β-cells (RIP-Cre; ROCK1^loxP/loxP, β-ROCK1^-/-) were studied. Glucose and insulin tolerance tests as well as glucose-stimulated insulin secretion (GSIS) were measured. An insulin secretion response to a direct glucose or pyruvate or pyruvate kinase (PK) activator stimulation in isolated islets from β-ROCK1^-/- mice or β-cell lines with knockdown of ROCK1 was also evaluated. A proximity ligation assay was performed to determine the physical interactions between PK and ROCK1.

RESULTS

Mice with a deficiency of ROCK1 in pancreatic β-cells exhibited significantly increased blood glucose levels and reduced serum insulin without changes in body weight. Interestingly, β-ROCK1^-/- mice displayed a progressive impairment of glucose tolerance while maintaining insulin sensitivity mostly due to impaired GSIS. Consistently, GSIS markedly decreased in ROCK1-deficient islets and ROCK1 knockdown INS-1 cells. Concurrently, ROCK1 blockade led to a significant decrease in intracellular calcium and ATP levels and oxygen consumption rates in isolated islets and INS-1 cells. Treatment of ROCK1-deficient islets or ROCK1 knockdown β-cells either with pyruvate or a PK activator rescued the impaired GSIS. Mechanistically, we observed that glucose stimulation in β-cells greatly enhanced ROCK1 binding to PK.

CONCLUSIONS

Our findings demonstrate that β-cell ROCK1 is essential for glucose-stimulated insulin secretion and for glucose homeostasis and that ROCK1 acts as an upstream regulator of glycolytic pyruvate kinase signaling.

Advancements in the Quest to Map, Monitor, and Manipulate Neural Circuitry

Neural circuits and the cells that comprise them represent the functional units of the brain. Circuits relay and process sensory information, maintain homeostasis, drive behaviors, and facilitate cognitive functions such as learning and memory. Creating a functionally-precise map of the mammalian brain requires anatomically tracing neural circuits, monitoring their activity patterns, and manipulating their activity to infer function. Advancements in cell-type-specific genetic tools allow interrogation of neural circuits with increased precision. This review provides a broad overview of recombination-based and activity-driven genetic targeting approaches, contemporary viral tracing strategies, electrophysiological recording methods, newly developed calcium, and voltage indicators, and neurotransmitter/neuropeptide biosensors currently being used to investigate circuit architecture and function. Finally, it discusses methods for acute or chronic manipulation of neural activity, including genetically-targeted cellular ablation, optogenetics, chemogenetics, and over-expression of ion channels. With this ever-evolving genetic toolbox, scientists are continuing to probe neural circuits with increasing resolution, elucidating the structure and function of the incredibly complex mammalian brain.

Hypothalamic control of energy expenditure and thermogenesis

Energy expenditure and energy intake need to be balanced to maintain proper energy homeostasis. Energy homeostasis is tightly regulated by the central nervous system, and the hypothalamus is the primary center for the regulation of energy balance. The hypothalamus exerts its effect through both humoral and neuronal mechanisms, and each hypothalamic area has a distinct role in the regulation of energy expenditure. Recent studies have advanced the understanding of the molecular regulation of energy expenditure and thermogenesis in the hypothalamus with targeted manipulation techniques of the mouse genome and neuronal function. In this review, we elucidate recent progress in understanding the mechanism of how the hypothalamus affects basal metabolism, modulates physical activity, and adapts to environmental temperature and food intake changes.

The hypothalamus is a key regulator of metabolism, controlling resting metabolism, activity levels, and responses to external temperature and food intake. The balance between energy intake and expenditure must be tightly controlled, with imbalances resulting in metabolic disorders such as obesity or diabetes. Obin Kwon at Seoul National University College of Medicine and Ki Woo Kim at Yonsei University College of Dentistry, Seoul, both in South Korea, and coworkers reviewed how metabolism is regulated by the hypothalamus, a small hormone-producing brain region. They report that hormonal and neuronal signals from the hypothalamus influence the ratio of lean to fatty tissue, gender-based differences in metabolism, activity levels, and weight gain in response to food intake. They note that further studies to untangle cause-and-effect relationships and other genetic factors will improve our understanding of metabolic regulation.

Insight Into Rho Kinase Isoforms in Obesity and Energy Homeostasis

Obesity and associated complications increasingly jeopardize global health and contribute to the rapidly rising prevalence of type 2 diabetes mellitus and obesity-related diseases. Developing novel methods for the prevention and treatment of excess body adipose tissue expansion can make a significant contribution to public health. Rho kinase is a Rho-associated coiled-coil-containing protein kinase (Rho kinase or ROCK). The ROCK family including ROCK1 and ROCK2 has recently emerged as a potential therapeutic target for the treatment of metabolic disorders. Up-regulated ROCK activity has been involved in the pathogenesis of all aspects of metabolic syndrome including obesity, insulin resistance, dyslipidemia and hypertension. The RhoA/ROCK-mediated actin cytoskeleton dynamics have been implicated in both white and beige adipogenesis. Studies using ROCK pan-inhibitors in animal models of obesity, diabetes, and associated complications have demonstrated beneficial outcomes. Studies via genetically modified animal models further established isoform-specific roles of ROCK in the pathogenesis of metabolic disorders including obesity. However, most reported studies have been focused on ROCK1 activity during the past decade. Due to the progress in developing ROCK2-selective inhibitors in recent years, a growing body of evidence indicates more attention should be devoted towards understanding ROCK2 isoform function in metabolism. Hence, studying individual ROCK isoforms to reveal their specific roles and principal mechanisms in white and beige adipogenesis, insulin sensitivity, energy balancing regulation, and obesity development will facilitate significant breakthroughs for systemic treatment with isoform-selective inhibitors. In this review, we give an overview of ROCK functions in the pathogenesis of obesity and insulin resistance with a particular focus on the current understanding of ROCK isoform signaling in white and beige adipogenesis, obesity and thermogenesis in adipose tissue and other major metabolic organs involved in energy homeostasis regulation.

Rho-Kinase as a Therapeutic Target for Nonalcoholic Fatty Liver Diseases

Nonalcoholic fatty liver disease (NAFLD) is a major public health problem and the most common form of chronic liver disease, affecting 25% of the global population. Although NAFLD is closely linked with obesity, insulin resistance, and type 2 diabetes mellitus, knowledge on its pathogenesis remains incomplete. Emerging data have underscored the importance of Rho-kinase (Rho-associated coiled-coil-containing kinase [ROCK]) action in the maintenance of normal hepatic lipid homeostasis. In particular, pharmacological blockade of ROCK in hepatocytes or hepatic stellate cells prevents the progression of liver diseases such as NAFLD and fibrosis. Moreover, mice lacking hepatic ROCK1 are protected against obesity-induced fatty liver diseases by suppressing hepatic de novo lipogenesis. Here we review the roles of ROCK as an indispensable regulator of obesity-induced fatty liver disease and highlight the key cellular pathway governing hepatic lipid accumulation, with focus on de novo lipogenesis and its impact on therapeutic potential. Consequently, a comprehensive understanding of the metabolic milieu linking to liver dysfunction triggered by ROCK activation may help identify new targets for treating fatty liver diseases such as NAFLD.

ROCK2-Specific Inhibitor KD025 Suppresses Adipocyte Differentiation by Inhibiting Casein Kinase 2

KD025, a ROCK2 isoform-specific inhibitor, has an anti-adipogenic activity which is not mediated by ROCK2 inhibition. To identify the target, we searched binding targets of KD025 by using the KINOMEscanTM screening platform, and we identified casein kinase 2 (CK2) as a novel target. KD025 showed comparable binding affinity to CK2α (Kd = 128 nM). By contrast, CK2 inhibitor CX-4945 and ROCK inhibitor fasudil did not show such cross-reactivity. In addition, KD025 effectively inhibited CK2 at a nanomolar concentration (IC50 = 50 nM). We examined if the inhibitory effect of KD025 on adipocyte differentiation is through the inhibition of CK2. Both CX-4945 and KD025 suppressed the generation of lipid droplets and the expression of proadipogenic genes Pparg and Cebpa in 3T3-L1 cells during adipocyte differentiation. Fasudil exerted no significant effect on the quantity of lipid droplets, but another ROCK inhibitor Y-27632 increased the expression of Pparg and Cebpa. Both CX-4945 and KD025 acted specifically in the middle stage (days 1-3) but were ineffective when treated at days 0-1 or the late stages, indicating that CX-4945 and KD025 may regulate the same target, CK2. The mRNA and protein levels of CK2α and CK2β generally decreased in 3T3-L1 cells at day 2 but recovered thereafter. Other well-known CK2 inhibitors DMAT and quinalizarin inhibited effectively the differentiation of 3T3-L1 cells. Taken together, the results of this study confirmed that KD025 inhibits ROCK2 and CK2, and that the inhibitory effect on adipocyte differentiation is through the inhibition of CK2.

Suprachiasmatic Nucleus-Arcuate Nucleus Axis: Interaction Between Time and Metabolism Essential for Health

In mammals, time and metabolism are tightly coupled variables; this relationship can be illustrated by numerous examples, such as the circadian variation in food intake or the circadian response to a glucose bolus. We review evidence that the interaction between the suprachiasmatic nucleus and the arcuate nucleus plays a key role in the execution of these functions. The nuclei are reciprocally connected via different projections, and this interaction provides an ideal anatomical framework to modify the temporal output of the hypothalamus to metabolic organs as a consequence of the feedback from the periphery. The suprachiasmatic nucleus-arcuate nucleus relationship is essential to integrate metabolic information into the circadian system and thus adapt circadian rhythms in core body temperature, locomotor activity, food intake, and circulating molecules such as glucose and corticosterone. With the rise in obesity-associated diseases in the world population, gaining knowledge about this relationship, and the consequences of disturbing this liaison, is essential to understand the pathogenesis of obesity.

ARCAgRP/NPY Neuron Activity Is Required for Acute Exercise-Induced Food Intake in Un-Trained Mice

While much is known about the role of agouti-regulated peptide/neuropeptide Y (AgRP/NPY) and pro-opiomelanocortin (POMC) neurons to regulate energy homeostasis, little is known about how forced energy expenditure, such as exercise, modulates these neurons and if these neurons are involved in post-exercise feeding behaviors. We utilized multiple mouse models to investigate the effects of acute, moderate-intensity exercise on food intake and neuronal activity in the arcuate nucleus (ARC) of the hypothalamus. NPY-GFP reporter mice were utilized for immunohistochemistry and patch-clamp electrophysiology experiments investigating neuronal activation immediately after acute treadmill exercise. Additionally, ARC^AgRP/NPY neuron inhibition was performed using the Designer Receptors Exclusively Activated by Designer Drugs (DREADD) system in AgRP-Cre transgenic mice to investigate the importance of AgRP/NPY neurons in post-exercise feeding behaviors. Our experiments revealed that acute moderate-intensity exercise significantly increased food intake, ARC^AgRP/NPY neuron activation, and PVN^Sim1 neuron activation, while having no effect on ARC^POMC neurons. Strikingly, this exercise-induced refeeding was completely abolished when ARC^AgRP/NPY neuron activity was inhibited. While acute exercise also increased PVN^Sim1 neuron activity, inhibition of ARC^AgRP/NPY neurons had no effect on PVN^Sim1 neuronal activation. Overall, our results reveal that ARC^AgRP/NPY activation is required for acute exercise induced food intake in mice, thus providing insight into the critical role of ARC^AgRP/NPY neurons in maintaining energy homeostasis in cases of exercise-mediated energy deficit.

Central administration of REV-ERBα agonist promotes opposite responses on energy balance in fasted and fed states

The REV-ERBα receptor has a recognised role in the regulation of the circadian rhythm system. However, recent evidence suggests that it also contributes to energy balance regulation. Both expression and function of REV-ERBα can be influenced by the energy status of the body. Considering the possibility of the involvement of REV-ERBα in the regulation of energy balance, which is critically regulated by the hypothalamus, and based on the impact of intermittent fasting, the present study evaluated the effects of central administration of REV-ERBα agonist on energy balance in rats exposed to 24 hours of fasting or ad lib. feeding conditions. Initially, 24-hour fasted rats received an acute i.c.v. administration of agonist at doses of 1, 5, 10 or 15 μg per rat and feed efficiency was evaluated. Because 10 μg was a sufficient dose to affect feed efficiency, subsequent experiments used this dose to assess effects of agonist on the following parameters: energy expenditure induced by physical activity and locomotor activity, time spent in physical activity over 24 hours, and glucose and insulin tolerance. In fasted rats, the agonist promoted increased food intake and feed efficiency, with a greater body weight gain associated with less time spent in locomotor activity, suggesting a reduction in energy expenditure induced by physical activity. Furthermore, a reduction in glucose tolerance was noted. By contrast, free-fed rats exhibited reduced food intake and feed efficiency with decreased body weight gain along with an increase in locomotor activity and physical activity-dependent energy expenditure. Thus, i.c.v. administration of REV-ERBα agonist regulates energy balance depending on the energy status of the organism; that is, it promotes a positive energy balance in the fasted state and a negative energy balance in the fed state. These results may be useful in understanding the underlying mechanisms of energy balance disorders and intermittent fasting for body weight control.

Tissue-Specific Approaches Reveal Diverse Metabolic Functions of Rho-Kinase 1

Rho-kinase 1 (ROCK1) has been implicated in diverse metabolic functions throughout the body, with promising evidence identifying ROCK1 as a therapeutic target in diabetes and obesity. Considering these metabolic roles, several pharmacological inhibitors have been developed to elucidate the mechanisms underlying ROCK1 function. Y27632 and fasudil are two common ROCK1 inhibitors; however, they have varying non-specific selectivity to inhibit other AGC kinase subfamily members and whole-body pharmacological approaches lack tissue-specific insight. As a result, interpretation of studies with these inhibitors is difficult, and alternative approaches are needed to elucidate ROCK1's tissue specific metabolic functions. Fortunately, recent technological advances utilizing molecular carriers or genetic manipulation have facilitated discovery of ROCK1's tissue-specific mechanisms of action. In this article, we review the tissue-specific roles of ROCK1 in the regulation of energy balance and substrate utilization. We highlight prominent metabolic roles in liver, adipose, and skeletal muscle, in which ROCK1 regulates energy expenditure, glucose uptake, and lipid metabolism via inhibition of AMPK2α and paradoxical modulation of insulin signaling. Compared to ROCK1's roles in peripheral tissues, we also describe contradictory functions of ROCK1 in the hypothalamus to increase energy expenditure and decrease food intake via leptin signaling. Furthermore, dysregulated ROCK1 activity in either of these tissues results in metabolic disease phenotypes. Overall, tissue-specific approaches have made great strides in deciphering the many critical metabolic functions of ROCK1 and, ultimately, may facilitate the development of novel treatments for metabolic disorders.

DNA methylation in AgRP neurons regulates voluntary exercise behavior in mice

DNA methylation regulates cell type-specific gene expression. Here, in a transgenic mouse model, we show that deletion of the gene encoding DNA methyltransferase Dnmt3a in hypothalamic AgRP neurons causes a sedentary phenotype characterized by reduced voluntary exercise and increased adiposity. Whole-genome bisulfite sequencing (WGBS) and transcriptional profiling in neuronal nuclei from the arcuate nucleus of the hypothalamus (ARH) reveal differentially methylated genomic regions and reduced expression of AgRP neuron-associated genes in knockout mice. We use read-level analysis of WGBS data to infer putative ARH neural cell types affected by the knockout, and to localize promoter hypomethylation and increased expression of the growth factor Bmp7 to AgRP neurons, suggesting a role for aberrant TGF-β signaling in the development of this phenotype. Together, these data demonstrate that DNA methylation in AgRP neurons is required for their normal epigenetic development and neuron-specific gene expression profiles, and regulates voluntary exercise behavior.

AgRP neurons in the hypothalamic arcuate nucleus (ARH) are involved in regulating hunger and energy balance. Here the authors show that knockout of the DNA methyltransferase Dnmt3a in AgRP neurons of the ARH leads to a reduction in voluntary exercise along with numerous epigenetic and gene expression changes in ARH neurons.

Metformin Ameliorates Lipotoxic β-Cell Dysfunction through a Concentration-Dependent Dual Mechanism of Action

BACKGROUND

Chronic exposure to elevated levels of free fatty acids contributes to pancreatic β-cell dysfunction. Although it is well known that metformin induces cellular energy depletion and a concomitant activation of AMP-activated protein kinase (AMPK) through inhibition of the respiratory chain, previous studies have shown inconsistent results with regard to the action of metformin on pancreatic β-cells. We therefore examined the effects of metformin on pancreatic β-cells under lipotoxic stress.

METHODS

NIT-1 cells and mouse islets were exposed to palmitate and treated with 0.05 and 0.5 mM metformin. Cell viability, glucose-stimulated insulin secretion, cellular adenosine triphosphate, reactive oxygen species (ROS) levels and Rho kinase (ROCK) activities were measured. The phosphorylation of AMPK was evaluated by Western blot analysis and mRNA levels of endoplasmic reticulum (ER) stress markers and NADPH oxidase (NOX) were measured by real-time quantitative polymerase chain reaction analysis.

RESULTS

We found that metformin has protective effects on palmitate-induced β-cell dysfunction. Metformin at a concentration of 0.05 mM inhibits NOX and suppresses the palmitate-induced elevation of ER stress markers and ROS levels in a AMPK-independent manner, whereas 0.5 mM metformin inhibits ROCK activity and activates AMPK.

CONCLUSION

This study suggests that the action of metformin on β-cell lipotoxicity was implemented by different molecular pathways depending on its concentration. Metformin at a usual therapeutic dose is supposed to alleviate lipotoxic β-cell dysfunction through inhibition of oxidative stress and ER stress.

RhoA in tyrosine hydroxylase neurones regulates food intake and body weight via altered sensitivity to peripheral hormones

Dopamine-producing tyrosine hydroxylase (TH) neurones in the hypothalamic arcuate nucleus (ARC) have recently been shown to be involved in ghrelin signalling and body weight homeostasis. In the present study, we investigate the role of the intracellular regulator RhoA in hypothalamic TH neurones in response to peripheral hormones. Diet-induced obesity was found to be associated with increased phosphorylation of TH in ARC, indicating obesity-associated increased activity of ARC TH neurones. Mice in which RhoA was specifically knocked out in TH neurones (TH-RhoA^-/- mice) were more sensitive to the orexigenic effect of peripherally administered ghrelin and displayed an abolished response to the anorexigenic hormone leptin. When TH-RhoA^-/- mice were challenged with a high-fat high-sucrose (HFHS) diet, they became hyperphagic and gained more body weight and fat mass compared to wild-type control mice. Importantly, lack of RhoA prevented development of ghrelin resistance, which is normally observed in wild-type mice after long-term HFHS diet feeding. Patch-clamp electrophysiological analysis demonstrated increased ghrelin-induced excitability of TH neurones in lean TH-RhoA^-/- mice compared to lean littermate control animals. Additionally, increased expression of the orexigenic hypothalamic neuropeptides agouti-related peptide and neuropeptide Y was observed in TH-RhoA^-/- mice. Overall, our data indicate that TH neurones in ARC are important for the regulation of body weight homeostasis and that RhoA is both a central effector in these neurones and important for the development of obesity-induced ghrelin resistance. The obese phenotype of TH-RhoA^-/- mice may be a result of increased sensitivity to ghrelin and decreased sensitivity to leptin, resulting in increased food intake.

Vertical sleeve gastrectomy improves liver and hypothalamic functions in obese mice

Vertical sleeve gastrectomy (VSG) is an effective surgery to treat obesity and diabetes. However, the direct effect of VSG on metabolic functions is not fully understood. We aimed to investigate if alterations in hypothalamic neurons were linked with perturbations in liver metabolism after VSG in an energy intake-controlled obese mouse model. C57BL/6 and hrNPY-GFP reporter mice received HFD for 12 weeks and were then divided into three groups: Sham (ad lib), sham (pair-fed) with VSG, and VSG. Food intake was measured daily, and blood glucose levels were measured before and after the study. Energy expenditure and body composition were determined. Serum parameters, liver lipid and glycogen contents were measured, and gene/protein expression were analyzed. Hypothalamic POMC, AgRP/NPY, and tyrosine hydroxylase expressing neurons were counted. As results, we found that VSG reduced body weight gain and adiposity induced by HFD, increased energy expenditure independent of energy intake. Fed and fasted blood glucose levels were reduced in the VSG group. While serum active GLP-1 level was increased, the active ghrelin and triglycerides levels were decreased along with improved insulin resistance in VSG group. Liver lipid accumulation, glycogen content, and gluconeogenic gene expression were reduced in the VSG group. In the hypothalamus, TH expressing neuron population was decreased, and the POMC-expressing neuron population was increased in the VSG group. Our data suggests that VSG improves metabolic symptoms by increasing energy expenditure and lowering lipid and glycogen contents in the liver. These physiological alterations are possibly related to changes in hypothalamic neuron populations.

Rho-kinase/AMPK axis regulates hepatic lipogenesis during overnutrition

Obesity is a major risk factor for developing nonalcoholic fatty liver disease (NAFLD). NAFLD is the most common form of chronic liver disease and is closely associated with insulin resistance, ultimately leading to cirrhosis and hepatocellular carcinoma. However, knowledge of the intracellular regulators of obesity-linked fatty liver disease remains incomplete. Here we showed that hepatic Rho-kinase 1 (ROCK1) drives obesity-induced steatosis in mice through stimulation of de novo lipogenesis. Mice lacking ROCK1 in the liver were resistant to diet-induced obesity owing to increased energy expenditure and thermogenic gene expression. Constitutive expression of hepatic ROCK1 was sufficient to promote adiposity, insulin resistance, and hepatic lipid accumulation in mice fed a high-fat diet. Correspondingly, liver-specific ROCK1 deletion prevented the development of severe hepatic steatosis and reduced hyperglycemia in obese diabetic (ob/ob) mice. Of pathophysiological significance, hepatic ROCK1 was markedly upregulated in humans with fatty liver disease and correlated with risk factors clustering around NAFLD and insulin resistance. Mechanistically, we found that hepatic ROCK1 suppresses AMPK activity and a ROCK1/AMPK pathway is necessary to mediate cannabinoid-induced lipogenesis in the liver. Furthermore, treatment with metformin, the most widely used antidiabetes drug, reduced hepatic lipid accumulation by inactivating ROCK1, resulting in activation of AMPK downstream signaling. Taken together, our findings establish a ROCK1/AMPK signaling axis that regulates de novo lipogenesis, providing a unique target for treating obesity-related metabolic disorders such as NAFLD.

Anti-adipogenic effects of KD025 (SLx-2119), a ROCK2-specific inhibitor, in 3T3-L1 cells

Adipose tissue is a specialized organ that synthesizes and stores fat. During adipogenesis, Rho and Rho-associated kinase (ROCK) 2 are inactivated, which enhances the expression of pro-adipogenic genes and induces the loss of actin stress fibers. Furthermore, pan ROCK inhibitors enhance adipogenesis in 3T3-L1 cells. Here, we show that KD025 (formerly known as SLx-2119), a ROCK2-specific inhibitor, suppresses adipogenesis in 3T3-L1 cells partially through a ROCK2-independent mechanism. KD025 downregulated the expression of key adipogenic transcription factors PPARγ and C/EBPα during adipogenesis in addition to lipogenic factors FABP4 and Glut4. Interestingly, adipogenesis was blocked by KD025 during days 1~3 of differentiation; after differentiation terminated, lipid accumulation was unaffected. Clonal expansion occurred normally in KD025-treated cells. These results suggest that KD025 could function during the intermediate stage after clonal expansion. Data from depletion of ROCKs showed that KD025 suppressed cell differentiation partially independent of ROCK’s activity. Furthermore, no further loss of actin stress fibers emerged in KD025-treated cells during and after differentiation compared to control cells. These results indicate that in contrast to the pro-adipogenic effect of pan-inhibitors, KD025 suppresses adipogenesis in 3T3-L1 cells by regulating key pro-adipogenic factors. This outcome further implies that KD025 could be a potential anti-adipogenic/obesity agent.

Neuronal Dnmt1 Deficiency Attenuates Diet-Induced Obesity in Mice

Aberrant neuronal DNA methylation patterns have been implicated in the promotion of obesity development; however, the role of neuronal DNA methyltransferases (Dnmts), enzymes that catalyze DNA methylation, in energy balance remains poorly understood. We investigated whether neuronal Dnmt1 regulates normal energy homeostasis and obesity development using a neuronal Dnmt1 knockout (ND1KO) mouse model, Dnmt1fl/fl Synapsin1Cre, which specifically deletes Dnmt1 in neurons. Neuronal Dnmt1 deficiency reduced adiposity in chow-fed mice and attenuated obesity in high-fat diet (HFD)-fed male mice. ND1KO male mice had reduced food intake and increased energy expenditure with the HFD. Furthermore, these mice had improved insulin sensitivity, as measured using an insulin tolerance test. The HFD-fed ND1KO mice had smaller fat pads and upregulation of thermogenic genes in brown adipose tissue. These data suggest that neuronal Dnmt1 plays an important role in regulating energy homeostasis. Notably, ND1KO male mice had elevated estrogen receptor-α (ERα) gene expression in the medial hypothalamus, which previously has been shown to control body weight. Immunohistochemistry experiments revealed that ERα protein expression was upregulated specifically in the dorsomedial region of the ventromedial hypothalamus, a region that might mediate the central effect of leptin. We conclude that neuronal Dnmt1 regulates energy homeostasis through pathways controlling food intake and energy expenditure. In addition, ERα expression in the dorsomedial region of the ventromedial hypothalamus might mediate these effects.

PGC-1α expression in murine AgRP neurons regulates food intake and energy balance

Objective

Food intake and whole-body energy homeostasis are controlled by agouti-related protein (AgRP) and pro-opiomelanocortin (POMC) neurons located in the arcuate nucleus of the hypothalamus. Key energy sensors, such as the AMP-activated protein kinase (AMPK) or sirtuin 1 (SIRT1), are essential in AgRP and POMC cells to ensure proper energy balance. In peripheral tissues, the transcriptional coactivator PGC-1α closely associates with these sensors to regulate cellular metabolism. The role of PGC-1α in the ARC nucleus, however, remains unknown.

Methods

Using AgRP and POMC neurons specific knockout (KO) mouse models we studied the consequences of PGC-1α deletion on metabolic parameters during fed and fasted states and on ghrelin and leptin responses. We also took advantage of an immortalized AgRP cell line to assess the impact of PGC-1α modulation on fasting induced AgRP expression.

Results

PGC-1α is dispensable for POMC functions in both fed and fasted states. In stark contrast, mice carrying a specific deletion of PGC-1α in AgRP neurons display increased adiposity concomitant with significantly lower body temperature and RER values during nighttime. In addition, the absence of PGC-1α in AgRP neurons reduces food intake in the fed and fasted states and alters the response to leptin. Finally, both in vivo and in an immortalized AgRP cell line, PGC-1α modulates AgRP expression induction upon fasting.

Conclusions

Collectively, our results highlight a role for PGC-1α in the regulation of AgRP neuronal functions in the control of food intake and peripheral metabolism.

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The AgRP induction upon fasting is modulated by PGC-1α.

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PGC-1α is important for the response of AgRP neurons to fasting and leptin.

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Deletion of PGC-1α in AgRP neurons impairs whole body energy balance.

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PGC-1α deletion in POMC neurons is dispensable for energy homeostasis regulation.

Voluntary exercise improves hypothalamic and metabolic function in obese mice

Exercise plays a critical role in regulating glucose homeostasis and body weight. However, the mechanism of exercise on metabolic functions associated with the CNS has not been fully understood. C57BL6 male mice (n=45) were divided into three groups: normal chow diet, high-fat diet (HFD) treatment, and HFD along with voluntary running wheel exercise training for 12 weeks. Metabolic function was examined by the Comprehensive Lab Animal Monitoring System and magnetic resonance imaging; phenotypic analysis included measurements of body weight, food intake, glucose and insulin tolerance tests, as well as insulin and leptin sensitivity studies. By immunohistochemistry, the amount changes in the phosphorylation of signal transducer and activator of transcription 3, neuronal proliferative maker Ki67, apoptosis positive cells as well as pro-opiomelanocortin (POMC)-expressing neurons in the arcuate area of the hypothalamus was identified. We found that 12 weeks of voluntary exercise training partially reduced body weight gain and adiposity induced by an HFD. Insulin and leptin sensitivity were enhanced in the exercise training group verses the HFD group. Furthermore, the HFD-impaired POMC-expressing neuron is remarkably restored in the exercise training group. The restoration of POMC neuron number may be due to neuroprotective effects of exercise on POMC neurons, as evidenced by altered proliferation and apoptosis. In conclusion, our data suggest that voluntary exercise training improves metabolic symptoms induced by HFD, in part through protected POMC-expressing neuron from HFD and enhanced leptin signaling in the hypothalamus that regulates whole-body energy homeostasis.

Hypothalamic control of brown adipose tissue thermogenesis

It has long been known, in large part from animal studies, that the control of brown adipose tissue (BAT) thermogenesis is insured by the central nervous system (CNS), which integrates several stimuli in order to control BAT activation through the sympathetic nervous system (SNS). SNS-mediated BAT activity is governed by diverse neurons found in brain structures involved in homeostatic regulations and whose activity is modulated by various factors including oscillations of energy fluxes. The characterization of these neurons has always represented a challenging issue. The available literature suggests that the neuronal circuits controlling BAT thermogenesis are largely part of an autonomic circuitry involving the hypothalamus, brainstem and the SNS efferent neurons. In the present review, we recapitulate the latest progresses in regards to the hypothalamic regulation of BAT metabolism. We briefly addressed the role of the thermoregulatory pathway and its interactions with the energy balance systems in the control of thermogenesis. We also reviewed the involvement of the brain melanocortin and endocannabinoid systems as well as the emerging role of steroidogenic factor 1 (SF1) neurons in BAT thermogenesis. Finally, we examined the link existing between these systems and the homeostatic factors that modulate their activities.

Hypothalamic agouti-related peptide neurons and the central melanocortin system are crucial mediators of leptin's antidiabetic actions

Leptin has beneficial effects on glucose metabolism via actions in the hypothalamus, but the roles of specific subgroups of neurons responsible for these antidiabetic effects remain unresolved. We generated diabetic Lep(ob/ob) or Lepr(db/db) mice lacking or re-expressing leptin receptors (LepRb) in subgroups of neurons to explore their contributions to leptin's glucose-lowering actions. We show that agouti-related peptide (AgRP)-expressing neurons are both required and sufficient to correct hyperglycemia by leptin. LepRb in pro-opiomelanocortin (POMC) neurons or steroidogenic factor-1 (SF1) neurons are not required. Furthermore, normalization of blood glucose by leptin is blunted in Lep(ob/ob)/MC4R-null mice, but not in Lep(ob/ob) mice lacking neuropeptide Y (NPY) or gamma-aminobutyric acid (GABA) in AgRP neurons. Leptin's ability to improve glucose balance is accompanied by a reduction in circulating glucagon. We conclude that AgRP neurons play a crucial role in glucose-lowering actions by leptin and that this requires the melanocortin system, but not NPY and GABA.

ROCK1 isoform-specific deletion reveals a role for diet-induced insulin resistance

Rho kinase (ROCK) isoforms regulate insulin signaling and glucose metabolism negatively or positively in cultured cell lines and skeletal muscle. However, the in vivo function of the ROCK1 isoform in adipose tissue has not been addressed. To determine the specific role of the adipose ROCK1 isoform in the development of insulin resistance and obesity, mice lacking ROCK1 in adipose tissue globally or selectively were studied. Here, we show that insulin's ability to activate IRS-1/PI3K/Akt signaling was greatly enhanced in adipose tissue of ROCK1(-/-) mice compared with wild-type mice. These effects resulted from the inhibitory effect of ROCK1 on insulin receptor action, as evidenced by the fact that IR tyrosine phosphorylation was abolished in ROCK1(-/-) MEF cells when ROCK1 was reexpressed. Consistently, adipose-specific disruption of ROCK1 increased IR tyrosine phosphorylation in adipose tissue and modestly improved sensitivity to insulin in obese mice induced by high-fat feeding. This effect is independent of any changes in adiposity, number or size of adipocytes, and metabolic parameters, including glucose, insulin, leptin, and triglyceride levels, demonstrating a minimal effect of adipose ROCK1 on whole body metabolism. Enzymatic activity of ROCK1 in adipose tissue remained ∼50%, which likely originated from the fraction of stromal vascular cells, suggesting involvement of these cells for adipose metabolic regulation. Moreover, ROCK isoform activities were increased in adipose tissue of diet-induced or genetically obese mice. These data suggest that adipose ROCK1 isoform plays an inhibtory role for the regulation of insulin sensitivity in diet-induced obesity in vivo.

Leptin signaling is required for leucine deprivation-enhanced energy expenditure

Leptin signaling in the hypothalamus is crucial in energy homeostasis. We have previously shown that dietary deprivation of the essential amino acid leucine in mice stimulates fat loss by increasing energy expenditure. The involvement of leptin signaling in this regulation, however, has not been reported. Here, we show that leucine deprivation promotes leptin signaling in mice maintained on an otherwise normal diet and restores leptin responses in mice maintained on a high fat diet, a regimen known to induce leptin resistance. In addition, we found that leucine deprivation stimulated energy expenditure, and fat loss was largely blocked in db/db mice homozygous for a mutation in leptin receptor and a knock-in mouse line Y3F with abrogation of leptin receptor Tyr(1138)-mediated signal transducer and activator transcript 3 signaling. Overall, our studies describe a novel link between hypothalamic leptin signaling and stimulation of energy expenditure under leucine deprivation.

Somato-dendritic localization and signaling by leptin receptors in hypothalamic POMC and AgRP neurons

Leptin acts via neuronal leptin receptors to control energy balance. Hypothalamic pro-opiomelanocortin (POMC) and agouti-related peptide (AgRP)/Neuropeptide Y (NPY)/GABA neurons produce anorexigenic and orexigenic neuropeptides and neurotransmitters, and express the long signaling form of the leptin receptor (LepRb). Despite progress in the understanding of LepRb signaling and function, the sub-cellular localization of LepRb in target neurons has not been determined, primarily due to lack of sensitive anti-LepRb antibodies. Here we applied light microscopy (LM), confocal-laser scanning microscopy (CLSM), and electron microscopy (EM) to investigate LepRb localization and signaling in mice expressing a HA-tagged LepRb selectively in POMC or AgRP/NPY/GABA neurons. We report that LepRb receptors exhibit a somato-dendritic expression pattern. We further show that LepRb activates STAT3 phosphorylation in neuronal fibers within several hypothalamic and hindbrain nuclei of wild-type mice and rats, and specifically in dendrites of arcuate POMC and AgRP/NPY/GABA neurons of Leprb^+/+ mice and in Leprb^db/db mice expressing HA-LepRb in a neuron specific manner. We did not find evidence of LepRb localization or STAT3-signaling in axon-fibers or nerve-terminals of POMC and AgRP/NPY/GABA neurons. Three-dimensional serial EM-reconstruction of dendritic segments from POMC and AgRP/NPY/GABA neurons indicates a high density of shaft synapses. In addition, we found that the leptin activates STAT3 signaling in proximity to synapses on POMC and AgRP/NPY/GABA dendritic shafts. Taken together, these data suggest that the signaling-form of the leptin receptor exhibits a somato-dendritic expression pattern in POMC and AgRP/NPY/GABA neurons. Dendritic LepRb signaling may therefore play an important role in leptin’s central effects on energy balance, possibly through modulation of synaptic activity via post-synaptic mechanisms.

Metabolic actions of Rho-kinase in periphery and brain

Obesity has increased at an alarming rate in recent years and is now a worldwide public health problem. Elucidating the mechanisms behind the metabolic dysfunctions associated with obesity is of high priority. The metabolic function of Rho-kinase (Rho-associated coiled-coil-containing kinase; ROCK) has been the subject of a great deal of investigation in metabolic-related diseases. It appears that inhibition of ROCK activity is beneficial for the treatment of a wide range of cardiovascular-related diseases. However, recent studies with genetic models of ROCK demonstrate that ROCK plays a positive role in insulin and leptin signaling. Here we discuss the newly identified functions of ROCK in regulating glucose and energy metabolism, with particular emphasis on metabolic actions of insulin and leptin.