Mice harboring the obesity-associated SNP rs1421085 exhibit increased body weight and reveal an IRX3 neuronal circuit regulating body weight.

Objective: The single nucleotide polymorphism (SNP) rs1421085 has one of the highest associated risks with obesity of any SNP in the human genome. Through the generation of a novel mouse model harboring rs1421085 (OA-SNP), we examined the impact of this SNP on energy balance. Furthermore, we investigated the role of IRX3, a potential mediator of the metabolic effects of rs1421085, in multiple brain regions.

Diet-dependent modulation of energy balance by CB1 signaling in peripheral sensory neurons.

The endocannabinoid system plays a pivotal role in metabolic regulation, primarily through cannabinoid receptor-1 (CB1) signaling. In this study, we show that rimonabant (Rim), a selective non-restricted CB1 antagonist, induces substantial weight loss across multiple diet groups, although reduced food intake occurred only in the high-fat (HF) diet group. Rim enhanced brown adipose tissue (BAT) thermogenesis across all diets and visceral white adipose tissue (vWAT) thermogenesis in HF and high-carbohydrate (HC) diets.

The brainstem BBSome regulates glucose homeostasis and lean mass in a state-dependent manner.

Objective: Obesity disrupts metabolic homeostasis through changes in brain function. Hypothalamic cilia and associated proteins, such as the BBSome, a protein complex composed of eight Bardet-Biedl syndrome (BBS) proteins, have been implicated in metabolic regulation and disorders. Here, we investigated the significance of brainstem cilia and the BBSome for energy balance and glucose homeostasis.

Β AR Agonists Sustain Thermogenesis and Leanness via .

Unlabelled: Human thermogenesis depends on β2-adrenoceptors (β2AR) expressed in thermogenic adipocytes, which are activated by norepinephrine released from sympathetic neurons. Whether β2AR also modulates thermogenesis via direct presynaptic action within sympathetic neurons has remained unclear. Here, we identify expression in human and rodent cervical sympathetic neurons.

FGF21 reverses MASH through coordinated actions on the CNS and liver.

Metabolic dysfunction-associated steatotic liver disease (MASLD) and its progressive form, metabolic dysfunction-associated steatohepatitis (MASH), represent a growing public health burden with limited therapeutic options. Recent studies have revealed that fibroblast growth factor 21 (FGF21)-based analogs can significantly improve MASH, but the mechanisms for this effect are not well understood. Here, we demonstrate that the beneficial metabolic effects of FGF21 to reverse MASH are mediated through distinct mechanisms to independently lower hepatic triglyceride and cholesterol levels.

Loss of MRAP2 in MC4R neurons protect from obesity-associated autonomic and cardiovascular dysfunctions.

Aims: The melanocortin receptor accessory protein 2 (MRAP2), which is abundantly expressed in the brain including the hypothalamus, has emerged as a key regulator of melanocortin-4 receptor (MC4R) activity. We sought to delineate the physiological significance of MRAP2 in MC4R neurons, with a particular focus on autonomic and cardiovascular functions.

Methods And Results: Selective deletion of MRAP2 in MC4R neurons causes obesity that was associated with hyperphagia and impairment in glucose homeostasis and insulin sensitivity.

Overnutrition causes insulin resistance and metabolic disorder through increased sympathetic nervous system activity.

The mechanisms underlying obesity-induced insulin resistance remain incompletely understood, as impaired cellular insulin signaling, traditionally considered the primary driver of insulin resistance, does not always accompany impaired insulin action. Overnutrition rapidly increases plasma norepinephrine (NE), suggesting overactivation of the sympathetic nervous system (SNS). However, the role of the SNS in obesity is controversial, as both increased and decreased SNS activity (SNA) have been reported.

A kidney-hypothalamus axis promotes compensatory glucose production in response to glycosuria.

The kidneys facilitate energy conservation through reabsorption of nutrients including glucose. Almost all the filtered blood glucose is reabsorbed by the kidneys. Loss of glucose in urine (glycosuria) is offset by an increase in endogenous glucose production to maintain normal energy supply in the body.

Adipocyte-specific disruption of the BBSome causes metabolic and autonomic dysfunction.

Obesity is a major public health issue due to its association with type 2 diabetes, hypertension, and other cardiovascular risks. The BBSome, a complex of eight conserved Bardet-Biedl syndrome (BBS) proteins, has emerged as a key regulator of energy and glucose homeostasis as well as cardiovascular function. However, the importance of adipocyte BBSome in controlling these physiological processes is not clear.

Reciprocal activity of AgRP and POMC neurons governs coordinated control of feeding and metabolism.

Agouti-related peptide (AgRP)-expressing and proopiomelanocortin (POMC)-expressing neurons reciprocally regulate food intake. Here, we combine non-interacting recombinases to simultaneously express functionally opposing chemogenetic receptors in AgRP and POMC neurons for comparing metabolic responses in male and female mice with simultaneous activation of AgRP and inhibition of POMC neurons with isolated activation of AgRP neurons or isolated inhibition of POMC neurons. We show that food intake is regulated by the additive effect of AgRP neuron activation and POMC neuron inhibition, while systemic insulin sensitivity and gluconeogenesis are differentially modulated by isolated-versus-simultaneous regulation of AgRP and POMC neurons.

A kidney-hypothalamus axis promotes compensatory glucose production in response to glycosuria.

The kidneys facilitate energy conservation through reabsorption of nutrients including glucose. Almost all the filtered blood glucose is reabsorbed by the kidneys. Loss of glucose in urine (glycosuria) is offset by an increase in endogenous glucose production to maintain normal energy supply in the body.

Pharmacological FGF21 signals to glutamatergic neurons to enhance leptin action and lower body weight during obesity.

Objective: Fibroblast growth factor 21 (FGF21) is a peripherally-derived endocrine hormone that acts on the central nervous system (CNS) to regulate whole body energy homeostasis. Pharmacological administration of FGF21 promotes weight loss in obese animal models and human subjects with obesity. However, the central targets mediating these effects are incompletely defined.

Melanocortin MCR receptor is required for energy expenditure but not blood pressure effects of angiotensin II within the mouse brain.

The brain renin-angiotensin system (RAS) is implicated in control of blood pressure (BP), fluid intake, and energy expenditure (EE). Angiotensin II (ANG II) within the arcuate nucleus of the hypothalamus contributes to control of resting metabolic rate (RMR) and thereby EE through its actions on Agouti-related peptide (AgRP) neurons, which also contribute to EE control by leptin. First, we determined that although leptin stimulates EE in control littermates, mice with transgenic activation of the brain RAS (sRA) exhibit increased EE and leptin has no additive effect to exaggerate EE in these mice.

Orexin receptors 1 and 2 in serotonergic neurons differentially regulate peripheral glucose metabolism in obesity.

The wake-active orexin system plays a central role in the dynamic regulation of glucose homeostasis. Here we show orexin receptor type 1 and 2 are predominantly expressed in dorsal raphe nucleus-dorsal and -ventral, respectively. Serotonergic neurons in ventral median raphe nucleus and raphe pallidus selectively express orexin receptor type 1.

Endothelial BBSome is essential for vascular, metabolic, and retinal functions.

Objectives: Endothelial cells that line the entire vascular system play a pivotal role in the control of various physiological processes, including metabolism. Additionally, endothelial dysfunction is associated with many pathological conditions, including obesity. Here, we assessed the role of the BBSome, a protein complex composed of eight Bardet-Biedl syndrome (BBS) proteins in endothelial cells.

Gastric Bypass Sensitizes Sympathetic and Thermogenic Activity of Brown Adipose Tissue to Cold Exposure.

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OPA1 deletion in brown adipose tissue improves thermoregulation and systemic metabolism via FGF21.

Adrenergic stimulation of brown adipocytes alters mitochondrial dynamics, including the mitochondrial fusion protein optic atrophy 1 (OPA1). However, direct mechanisms linking OPA1 to brown adipose tissue (BAT) physiology are incompletely understood. We utilized a mouse model of selective OPA1 deletion in BAT (OPA1 BAT KO) to investigate the role of OPA1 in thermogenesis.

BBSome ablation in SF1 neurons causes obesity without comorbidities.

Objectives: The hypothalamic ventromedial nucleus (VMH) plays a major role in metabolic control, but the molecular mechanisms involved remain poorly defined. We analyzed the relevance of the BBSome, a protein complex composed of 8 Bardet-Biedl syndrome (BBS) proteins including BBS1, in VMH steroidogenic factor 1 (SF1) neurons for the control of energy homeostasis and related physiological processes.

Methods: We generated mice bearing selective BBSome disruption, through Bbs1 gene deletion, in SF1 neurons (SF1/Bbs1).

mTORC1 (Mechanistic Target of Rapamycin Complex 1) Signaling in Endothelial and Smooth Muscle Cells Is Required for Vascular Function.

mTORC1 (Mechanistic target of rapamycin complex 1) serves as a molecular hub and intracellular energy sensor that regulate various cellular processes. Emerging evidence points to mTORC1 signaling as a critical regulator of cardiovascular function with implications for cardiovascular disease. Here, we show that selective disruption of mTORC1, through conditional gene deletion, in endothelial or smooth muscle cells alter vascular function.

Endocannabinoid Receptor-1 and Sympathetic Nervous System Mediate the Beneficial Metabolic Effects of Gastric Bypass.

The exact mechanisms underlying the metabolic effects of bariatric surgery remain unclear. Here, we demonstrate, using a combination of direct and indirect calorimetry, an increase in total resting metabolic rate (RMR) and specifically anaerobic RMR after Roux-en-Y gastric bypass (RYGB), but not sleeve gastrectomy (SG). We also show an RYGB-specific increase in splanchnic sympathetic nerve activity and "browning" of visceral mesenteric fat.

Hypothalamic MC4R regulates glucose homeostasis through adrenaline-mediated control of glucose reabsorption via renal GLUT2 in mice.

Aims/hypothesis: Melanocortin 4 receptor (MC4R) mutation is the most common cause of known monogenic obesity in humans. Unexpectedly, humans and rodents with MC4R deficiency do not develop hyperglycaemia despite chronic obesity and insulin resistance. To explain the underlying mechanisms for this phenotype, we determined the role of MC4R in glucose homeostasis in the presence and absence of obesity in mice.

Activation of hypothalamic AgRP and POMC neurons evokes disparate sympathetic and cardiovascular responses.

The arcuate nucleus of the hypothalamus (ARC) plays a key role in linking peripheral metabolic status to the brain melanocortin system, which influences a wide range of physiological processes including the sympathetic nervous system and blood pressure. The importance of the activity of agouti-related peptide (AgRP)- and proopiomelanocortin (POMC)-expressing neurons, two molecularly distinct populations of ARC neurons, for metabolic regulation is well established, but their relevance for sympathetic and cardiovascular control remains unclear. We used designer receptors exclusively activated by designer drug (DREADD) technology to study how activation of AgRP and POMC neurons affect renal sympathetic nerve traffic and blood pressure.

A leptin-BDNF pathway regulating sympathetic innervation of adipose tissue.

Mutations in the leptin gene (ob) result in a metabolic disorder that includes severe obesity, and defects in thermogenesis and lipolysis, both of which are adipose tissue functions regulated by the sympathetic nervous system. However, the basis of these sympathetic-associated abnormalities remains unclear. Furthermore, chronic leptin administration reverses these abnormalities in adipose tissue, but the underlying mechanism remains to be discovered.