Project description:Activation of brown fat thermogenesis increases energy expenditure and alleviates obesity. Sympathetic nervous system (SNS) is important in brown/beige adipocyte thermogenesis. Here we discover a novel fat-derived “adipokine” neurotrophic factor neurotrophin 3 (NTF3) and its receptor Tropomyosin receptor kinase C (TRKC) as key regulators of SNS growth and innervation in adipose tissue. NTF3 is highly expressed in brown/beige adipocytes, and potently stimulates sympathetic neuron neurite growth. NTF3/TRKC regulates a plethora of pathways in neuronal axonal growth and elongation. Adipose tissue sympathetic innervation is significantly increased in mice with adipocyte-specific NTF3 overexpression, but profoundly reduced in mice with TRKC haploinsufficiency (TRKC+/-). Increasing NTF3 via pharmacological or genetic approach promotes beige adipocyte development, enhances cold-induced thermogenesis and protects against diet-induced obesity (DIO); whereas TRKC+/- mice or SNS TRKC deficient mice are cold intolerant and prone to DIO. Thus, NTF3 is an important fat-derived neurotrophic factor regulating SNS innervation, energy metabolism and obesity.
Project description:Tissue resident macrophages provide a systemic innate immune defense network and critically contribute to establishment and maintenance of tissue homeostasis. Here we used constitutive and inducible mutagenesis to delete the nuclear transcription regulator methyl-CpG binding protein 2 (MeCP2) in defined tissue macrophages. Animals lacking the Rett syndrome-associated gene in macrophages did not show signs of neurodevelopmental disorder, but surprisingly displayed altered body composition and spontaneous obesity. This phenotype involved neither hyper-phagia, primary hyper-insulinemia nor inflammation, but rather could be linked to impaired brown adipose tissue (BAT) function. Specifically, mutagenesis of a BAT-resident CX3CR1+ macrophage subpopulation compromised homeostatic, though not acute cold-induced thermogenesis. Mechanistically, steady state BAT malfunction of pre-obese mice harboring mutant macrophages was associated with decreased sympathetic innervation and lower local norepinephrine titers, resulting in reduced adipocyte expression of the thermogenic factors UCP1 and DIO2. Mutant macrophages were found to over-express PlexinA4, which might contribute to the phenotype by repulsion of Sema6A-expressing sympathetic axons. Collectively, we report a previously unappreciated homeostatic role of macrophages in the control of tissue innervation, disruption of which in BAT results in metabolic imbalance.
Project description:The presence of different types of immune cells in adipose tissue has been demonstrated in numerous studies. Whereas cells of the immune system in white adipose tissue contribute to the low-grade chronic inflammation under obese conditions, their function in brown adipose tissue (BAT) remains largely elusive. Here we report a role of regulatory T (Treg) cells in BAT physiology.Ablation of Treg cells resulted in massive invasion of macrophages into BAT concordant with rearrangement of BAT morphology. Treg ablated animals displayed reduced energy expenditure. Our results for the first time demonstrate a functional role of Treg cells in the regulation of energy homeostasis.
Project description:Regulatory T (Treg) cells are critical determinants of both immune responses and metabolic control. Here we show that systemic ablation of Treg cells compromised the adaptation of whole-body energy expenditure to cold exposure, correlating with impairment in thermogenic marker gene expression and massive invasion of pro-inflammatory macrophages in brown adipose tissue (BAT). Indeed, BAT harbored a unique sub-set of Treg cells characterized by a unique gene signature. As these Treg cells respond to BAT activation upon cold exposure, this study defines a BAT-specific Treg sub-set with direct implications for the regulation of energy homeostasis in response to environmental stress. We isolated regulatory and conventional T cells from brown-adipose tissue of warm-conditioned or cold-conditioned mice. As controls, we harvested spleen-Treg and Tconv cells from warm-treated mice. Cells were isolated pooled organs and target cells purified by FACS. RNA was extracted and gene expression measured.
Project description:Imeglimin is a recently developed anti-diabetic drug that could concurrently promote insulin secretion and insulin sensitivity, while its mechanisms of action are not fully understood. Here we show that imeglimin administration could protect mice from high fat diet-induced weight gain with enhanced energy expenditure and attenuated whitening of brown adipose tissue. Imeglimin administration led to significant alteration of gut microbiota, which included an increase of Akkermansia genus, with attenuation of obesity-associated gut pathologies. Ablation of microbiota by antibiotic treatment partially abrogated the insulin sensitizing effects of imeglimin, while not affecting its actions on body weight gain or brown adipose tissue. Collectively, our results characterize imeglimin as a potential agent promoting energy expenditure and gut integrity, providing new insights into its mechanisms of action.
Project description:Regulatory T (Treg) cells are critical determinants of both immune responses and metabolic control. Here we show that systemic ablation of Treg cells compromised the adaptation of whole-body energy expenditure to cold exposure, correlating with impairment in thermogenic marker gene expression and massive invasion of pro-inflammatory macrophages in brown adipose tissue (BAT). Indeed, BAT harbored a unique sub-set of Treg cells characterized by a unique gene signature. As these Treg cells respond to BAT activation upon cold exposure, this study defines a BAT-specific Treg sub-set with direct implications for the regulation of energy homeostasis in response to environmental stress.
Project description:Mice carrying a mutation which deletes Bmal1 in Gfap-expressing astrocytes, and control animals were fed either a standard diet or a high fat diet for 16 weeks. Conditional deletion of Bmal1 in Gfap cells decreased weight gain and increased energy expenditure under high fat diet, hence the transcriptome of Brown Adipose Tissue (BAT) and Ventromedial Hypothalamus (VMH) were obtained.
Project description:Brown and beige adipose tissue are emerging as distinct endocrine organs. These tissues are functionally associated with skeletal muscle, adipose tissue metabolism and systemic energy expenditure, suggesting an interorgan signaling network. Using metabolomics, we identify 3-methyl-2-oxovaleric acid, 5-oxoproline, and β-hydroxyisobutyric acid as small molecule metabokines synthesized in browning adipocytes and secreted via monocarboxylate transporters. 3-methyl-2-oxovaleric acid, 5-oxoproline and β-hydroxyisobutyric acid induce a brown adipocyte-specific phenotype in white adipocytes and mitochondrial oxidative energy metabolism in skeletal myocytes both in vitro and in vivo. 3-methyl-2-oxovaleric acid and 5-oxoproline signal through cAMP-PKA-p38 MAPK and β-hydroxyisobutyric acid via mTOR. In humans, plasma and adipose tissue 3-methyl-2-oxovaleric acid, 5-oxoproline and β-hydroxyisobutyric acid concentrations correlate with markers of adipose browning and inversely associate with body mass index. These metabolites reduce adiposity, increase energy expenditure and improve glucose and insulin homeostasis in mouse models of obesity and diabetes. Our findings identify beige adipose-brown adipose-muscle physiological metabokine crosstalk.
Project description:Adipose tissue is central to regulation of systemic energy homeostasis. Adaptive thermogenesis in brown and beige adipocytes, which relies on mitochondrial oxidative phosphorylation, dissipates energy to counteract obesity. On the other hand, chronic inflammation in adipose tissue is linked to insulin resistance, type 2 diabetes and obesity. Here we show that nuclear factor I-A (NFIA), a transcriptional regulator of brown and beige adipocytes, improves systemic glucose homeostasis via up-regulation of oxidative phosphorylation and reciprocal down-regulation of inflammation. Mice with transgenic expression of NFIA in adipocytes exhibited improved glucose tolerance, increased energy expenditure and limited weight gain on high fat diet. NFIA coordinately up-regulate genes involved in oxidative phosphorylation as well as a battery of brown-fat-specific genes through enhancer activation that involves facilitated genomic binding of PPARγ. In contrast, NFIA in adipocytes, but not in macrophages, down-regulate pro-inflammatory cytokine genes to ameliorate adipose tissue inflammation in vivo. NFIA binds to enhancer/promoter region of Ccl2 gene that encodes pro-inflammatory cytokine MCP-1, to down-regulate its transcription. NFIA expression and CCL2 expression was negatively correlated in human adipose tissue. These results indicate that NFIA in adipocytes reciprocally regulate mitochondrial and inflammatory gene program to improve systemic glucose homeostasis.
Project description:Adipose tissue is central to regulation of systemic energy homeostasis. Adaptive thermogenesis in brown and beige adipocytes, which relies on mitochondrial oxidative phosphorylation, dissipates energy to counteract obesity. On the other hand, chronic inflammation in adipose tissue is linked to insulin resistance, type 2 diabetes and obesity. Here we show that nuclear factor I-A (NFIA), a transcriptional regulator of brown and beige adipocytes, improves systemic glucose homeostasis via up-regulation of oxidative phosphorylation and reciprocal down-regulation of inflammation. Mice with transgenic expression of NFIA in adipocytes exhibited improved glucose tolerance, increased energy expenditure and limited weight gain on high fat diet. NFIA coordinately up-regulate genes involved in oxidative phosphorylation as well as a battery of brown-fat-specific genes through enhancer activation that involves facilitated genomic binding of PPARγ. In contrast, NFIA in adipocytes, but not in macrophages, down-regulate pro-inflammatory cytokine genes to ameliorate adipose tissue inflammation in vivo. NFIA binds to enhancer/promoter region of Ccl2 gene that encodes pro-inflammatory cytokine MCP-1, to down-regulate its transcription. NFIA expression and CCL2 expression was negatively correlated in human adipose tissue. These results indicate that NFIA in adipocytes reciprocally regulate mitochondrial and inflammatory gene program to improve systemic glucose homeostasis.