Project description:Brown adipose tissue (BAT) is critical for non-shivering thermogenesis making it a promising therapeutical strategy to combat obesity and metabolic disease. However, the regulatory mechanisms underlying brown fat formation remain incompletely understood. Here, we found SOX4 is required for BAT development and thermogenic program. Depletion of SOX4 in BAT progenitors (Sox4-MKO) or brown adipocytes (Sox4-BKO) resulted in whitened BAT and hypothermia upon acute cold exposure. The reduced thermogenic capacity observed in Sox4-MKO mice increases their susceptibility to diet-induced obesity. Overexpression of SOX4 enhances BAT thermogenesis counteracting diet-induced obesity. Mechanistically, SOX4 activates transcription of EBF2 which determines brown fat fate. Moreover, phosphorylation of SOX4 at S235 by PKA facilitates its nuclear translocation and EBF2 transcription. Further, SOX4 cooperates with EBF2 to activate transcriptional programs governing thermogenic gene expression. These results demonstrate that SOX4 serves as an upstream regulator of EBF2 providing valuable insights into BAT development and thermogenic function maintenance.
Project description:Activated brown adipose tissue contributes to control of energy and glucose homeostasis in rodents and humans. Defining cell-autonomous processes underlying BAT differentiation and activation may thus reveal novel therapeutic targets for obesity and type 2 diabetes mellitus intervention. Here we show that ageing- and obesity-associated demises in BAT function coincide with down-regulation of mature microRNAs in BAT in the presence of reduced expression of the critical microRNA processing enzyme Dicer1. To mimic this partial down-regulation of microRNA processing in obesity and ageing, we inactivated one allele of Dicer1 selectively in BAT of mice. BAT- restricted heterozygosity of Dicer1 caused glucose intolerance in lean mice and aggravated diet-induced-obesity (DIO)-evoked deterioration of glucose homeostasis. Using combinatorial analyses of altered microRNA-expression in BAT during in vitro preadipocyte commitment and mouse models of progeria, longevity and DIO, we identified 23 microRNAs dysregulated among these conditions. Of these, we identified miR-328 as a novel regulator of BAT differentiation. miR-328 over-expression promotes BAT-differentiation and impairs muscle progenitor commitment, while reducing miR-328 expression blocks BAT specification. We validated the ß-Secretase Bace1 as a target of miR-328, which is consequently over-expressed in BAT of obese and premature ageing mice. Reducing Bace1 expression enhances brown adipocyte, while impairing myogenic differentiation in vitro. In vivo small-molecule Bace1 inhibition in obese mice delayed DIO-induced weight gain, ameliorated obesity-associated deterioration of glucose metabolism and improved insulin sensitivity. Collectively, these experiments reveal reduced Dicer1-miR-328-Bace1 axis in presence of generalized impairment of microRNA processing in ageing and obesity as a novel determinant of ageing- and obesity-associated decline in BAT function. This may define in vivo Bace1-inhibition as an innovative therapeutic approach to not only target age-related neurodegenerative diseases but at the same time improving age-related impairment of BAT-function and metabolism. C57BL/6 mice ( 4 weeks of age) were treated with a calory-rich, high-sugar high-fat diet (HFD) for a course of 4 weeks. Then groups were stratified and one group continued to receive HFD (BAT13-15) or HFD supplemented with an experimental small-molecule Bace 1 inhibitor (BAT17, 33, 35).
Project description:Thoracic perivascular adipose tissue (PVAT) is a unique adipose depot that likely influences vascular function and susceptibility to pathogenesis in obesity and metabolic syndrome. Surprisingly, PVAT has been reported to share characteristics of both brown and white adipose, but a detailed direct comparison to interscapular brown adipose tissue (BAT) has not been performed. Here we show by full genome DNA microarray analysis that global gene expression profiles of PVAT are virtually identical to BAT, with equally high expression of Ucp-1, Cidea and other genes known to be uniquely or very highly expressed in BAT. PVAT and BAT also displayed nearly identical phenotypes upon immunohistochemical analysis, and electron microscopy confirmed that PVAT contained multilocular lipid droplets and abundant mitochondria. Compared to white adipose tissue (WAT), PVAT and BAT from C57BL/6 mice fed a high fat diet for 13 weeks had markedly lower expression of immune cell-enriched mRNAs, suggesting resistance to obesity-induced inflammation. Indeed, staining of BAT and PVAT for macrophage markers (F4/80, CD68) in obese mice showed virtually no macrophage infiltration, and FACS analysis of BAT confirmed the presence of very few CD11b+/CD11c+ macrophages in BAT (1.0%) in comparison to WAT (31%). In summary, murine PVAT from the thoracic aorta is virtually identical to interscapular BAT, is resistant to diet-induced macrophage infiltration, and thus may play an important role in protecting the vascular bed from thermal and inflammatory stress. 8-week-old male C57BL6/J mice were fed a normal (ND) or high fat diet (HFD) (Research Diets 12451, 45 kcal% fat) for 13 weeks. Mice were then euthanized and four different adipose depots were harvested for RNA analysis: perivascular fat from the lesser curvature of the aortic arch (PVAT), interscapular brown adipose (BAT), inguinal adipose tissue (SAT), and epididymal adipose tissue (VAT). 250 ng total RNA pooled from two mice was used for cDNA synthesis; 3 biological replicates per tissue and diet were performed for a total of 24 hybridizations.
Project description:Obesity results from a caloric imbalance between energy intake, absorption and expenditure. In both rodents and humans, diet-induced thermogenesis contributes to energy expenditure and involves the activation of brown adipose tissue (BAT). We hypothesized that environmental toxicants commonly used as food additives or pesticides might reduce BAT thermogenesis through suppression of uncoupling protein 1 (UCP1) and this may contribute to the development of obesity. Using a step-wise screening approach, we discovered that the organophosphate insecticide chlorpyrifos suppresses UCP1 and mitochondrial respiration in BAT at concentrations as low as 1 pM. In mice housed at thermoneutrality and fed a high-fat diet, chlorpyrifos impaired BAT mitochondrial function and diet-induced thermogenesis, promoting greater obesity, non-alcoholic fatty liver disease (NAFLD) and insulin resistance. This was associated with reductions in cAMP; activation of p38MAPK and AMPK; protein kinases critical for maintaining UCP1 and mitophagy, respectively in BAT. These data indicate that the commonly used pesticide chlorpyrifos, suppresses diet-induced thermogenesis and the activation of BAT, suggesting its use may contribute to the obesity epidemic.
Project description:To understand the role of TH target genes in BAT, we developped a murine transgenic model in which TH signaling is selectively lost in BAT (BATKO mice). After establishing TH target genes in BAT, we used BATKO mice to understand which pathways were controlled by TH in BAT during metabolic stressors, i.e., cold and high-fat diet (HFD)
Project description:Brown adipose tissue (BAT) is involved in dissipating energy as heat (non-shivering thermogenesis), not only under cold exposure but also in the dissipation of excess ingested energy. Therefore, harnessing energy utilisation by BAT is a potential avenue to combat weight gain and its comorbidities. Dietary macronutrient composition can directly influence BAT size and has recently been shown to influence BAT size of daughters through non-genetic effects in the patriline of C57BL/6J mice. However, the effects of dietary macronutrient composition and any non-genetic paternal effects on BAT function have yet to be characterised. Using the Geometric Framework for Nutrition, we investigated the effects of dietary protein, carbohydrate, and fat composition on the BAT proteome in male mice (F0) and intergenerational effects in their offspring (F1). In F0 males, >50% of the proteome was affected by dietary macronutrient composition, with distinct clusters of proteins that responded to diet in similar ways. We identified two clusters with inverse expression patterns that correlated with BAT weight. Notably, Ucp1 was reduced on low fat diet compositions that promoted increased BAT mass, while on those same diets there were increased levels of proteins involved in protein turnover. These diets also led to a reduction in proteins involved in purine biosynthesis (often Ucp1 inhibitors) and increased Hsl, which facilitates free fatty acid release, critical for Ucp1 activation. We did not find any effects of paternal diet on the BAT proteome in sons, but paternal protein intake negatively affected Basigin expression in daughters; a protein that regulates Ucp1 transcription. Our study is the first characterisation of BAT protein abundance across a broad range of dietary macronutrient compositions and across two generations, with implications for our understanding of non-shivering thermogenesis and metabolism.
Project description:Thermogenesis is a promising approach to limit weight gain in response to excess nutrition. In contrast to cold-induced thermogenesis, the molecular and cellular mechanisms of diet-induced thermogenesis (DIT) have not been fully characterized. Here, we explored the response of brown adipose tissue (BAT) and beige adipose tissue to high fat diet (HFD) using proteome and phosphoproteome analysis. We observed that after HFD, DIT was only activated in BAT. Furthermore, fatty acid oxidation, tricarboxylic acid cycle, and oxidative phosphorylation were also activated in BAT. Nevertheless, most metabolic pathways downregulated in beige adipose tissue. Strikingly, we found that these metabolic changes accompanied with different variation of mitochondria between BAT and beige adipose tissue as well. HFD treatment impaired mitochondrial functions and mitochondrial protein synthesis in beige adipose tissue while it stimulated mitochondrial autophagy in BAT. Together, in BAT, HFD caused increased mitochondrial activity,
Project description:Brown adipose tissue (BAT) is critical for non-shivering thermogenesis making it a promising therapeutical strategy to combat obesity and metabolic disease. However, the regulatory mechanisms underlying brown fat formation remain incompletely understood. Here, we found SOX4 is required for BAT development and thermogenic program. Depletion of SOX4 in BAT progenitors (Sox4-MKO) or brown adipocytes (Sox4-BKO) resulted in whitened BAT and hypothermia upon acute cold exposure. The reduced thermogenic capacity observed in Sox4-MKO mice increases their susceptibility to diet-induced obesity. Overexpression of SOX4 enhances BAT thermogenesis counteracting diet-induced obesity. Mechanistically, SOX4 activates transcription of EBF2 which determines brown fat fate. Moreover, phosphorylation of SOX4 at S235 by PKA facilitates its nuclear translocation and EBF2 transcription. Further, SOX4 cooperates with EBF2 to activate transcriptional programs governing thermogenic gene expression. These results demonstrate that SOX4 serves as an upstream regulator of EBF2 providing valuable insights into BAT development and thermogenic function maintenance.
Project description:Adaptive thermogenesis of brown adipose tissue (BAT) is critical for thermoregulation and contributes to total energy expenditure. However, whether BAT has non-thermogenic functions is largely unknown. Here, we describe that mice with a BAT-specific Liver kinase b1 deletion (Lkb1BKO mice) exhibited impaired mitochondrial respiration and thermogenesis in BAT, but reduced adiposity and liver triglyceride accumulation under high-fat-diet feeding at room temperature. Importantly, these metabolic benefits were also present in Lkb1BKO mice at thermoneutrality, where BAT thermogenesis was not required. Mechanistically, decreased mRNA levels of mtDNA-encoded electron transport chain (ETC) subunits and ETC proteome imbalance led to impaired mitochondrial respiration in BAT of Lkb1BKO mice. Furthermore, reducing mtDNA gene expression directly in BAT by removing mitochondrial transcription factor A (Tfam) in BAT also showed ETC proteome imbalance and the tradeoff between BAT thermogenesis and systemic metabolism at both room temperature and thermoneutrality. Collectively, our data demonstrates that ETC proteome imbalance in BAT regulates systemic metabolism independently of BAT thermogenic capacity.