Project description:Cold-exposure triggers neogenesis in classic interscapular brown adipose tissue (BAT) that involves activation of b1-adrenergic receptors, proliferation of PDGFRA+ adipose tissue stromal cells (ASCs), and recruitment of immune cells whose phenotypes are presently unknown. Single-cell RNA-sequencing (scRNA-seq) identified three ASC subpopulations that occupied distinct tissue locations. Of these, interstitial ASC1 were found to be direct precursors of new brown adipocytes (BA). Surprisingly, knockout of b1-adrenergic receptors in ASCs did not prevent cold-induced neogenesis, whereas pharmacological activation of the b3-adrenergic receptor on BAs was sufficient, suggesting that signals derived from mature BAs indirectly trigger ASC proliferation and differentiation. In this regard, cold exposure induced the delayed appearance of multiple macrophage and dendritic cell populations whose recruitment strongly correlated with the onset and magnitude of neogenesis across diverse experimental conditions. High resolution immunofluorescence and single molecule fluorescence in situ hybridization demonstrated that cold-induced neogenesis involves dynamic interactions between ASC1 and recruited immune cells that occur on the micrometer scale in distinct tissue regions. Our results indicate that neogenesis is not a reflexive response of progenitors to b-adrenergic signaling, but rather is a complex adaptive response to elevated metabolic demands within brown adipocytes.
Project description:Cold-exposure triggers neogenesis in classic interscapular brown adipose tissue (BAT) that involves activation of b1-adrenergic receptors, proliferation of PDGFRA+ adipose tissue stromal cells (ASCs), and recruitment of immune cells whose phenotypes are presently unknown. Single-cell RNA-sequencing (scRNA-seq) identified three ASC subpopulations that occupied distinct tissue locations. Of these, interstitial ASC1 were found to be direct precursors of new brown adipocytes (BA). Surprisingly, knockout of b1-adrenergic receptors in ASCs did not prevent cold-induced neogenesis, whereas pharmacological activation of the b3-adrenergic receptor on BAs was sufficient, suggesting that signals derived from mature BAs indirectly trigger ASC proliferation and differentiation. In this regard, cold exposure induced the delayed appearance of multiple macrophage and dendritic cell populations whose recruitment strongly correlated with the onset and magnitude of neogenesis across diverse experimental conditions. High resolution immunofluorescence and single molecule fluorescence in situ hybridization demonstrated that cold-induced neogenesis involves dynamic interactions between ASC1 and recruited immune cells that occur on the micrometer scale in distinct tissue regions. Our results indicate that neogenesis is not a reflexive response of progenitors to b-adrenergic signaling, but rather is a complex adaptive response to elevated metabolic demands within brown adipocytes.
Project description:Brown and beige fats generate heat via uncoupled respiration to defend against cold, mechanistically, through the action of a network of transcription factors and cofactors. Here we globally profiled long noncoding RNAs (lncRNAs) gene expression during thermogenic adipocyte formation and identified Brown fat lncRNA 1 (Blnc1) as a novel nuclear lncRNA that promotes brown and beige adipocyte differentiation and function by forming a feedforward regulatory loop with EBF2 to drive adipogenesis toward thermogenic phenotype. LncRNAs expression were measured in BAT and WAT from mice injected saline/CL and during brown adipocyte differentiation with two replicates using Arraystar Mouse LncRNA microarray V2.0
Project description:Brown and beige fats generate heat via uncoupled respiration to defend against cold, mechanistically, through the action of a network of transcription factors and cofactors. Here we globally profiled long noncoding RNAs (lncRNAs) gene expression during thermogenic adipocyte formation and identified Brown fat lncRNA 1 (Blnc1) as a novel nuclear lncRNA that promotes brown and beige adipocyte differentiation and function by forming a feedforward regulatory loop with EBF2 to drive adipogenesis toward thermogenic phenotype.
Project description:Non-shivering thermogenesis in adipocytes is mediated by brown adipose tissue, purportedly through the sole action of uncoupling protein 1 (UCP1). The physiological relevance of UCP1-dependent thermogenesis has primarily been inferred from the attenuation of thermogenic output of mice genetically lacking Ucp1 from birth (germline Ucp1-/-). However, germline Ucp1-/- mice harbor secondary changes within brown adipose tissue beyond UCP1, such as reduced electron transport chain abundance. We show here that these secondary changes also encompass reduced expression of genes regulating fuel liberation, changes that would attenuate the capacity of any thermogenic pathway. Therefore, the quantitative contribution of UCP1-dependent and -independent thermogenesis is not fully understood. To mitigate the potentially confounding ancillary changes to brown adipose tissue of germline Ucp1-/- mice, we constructed mice with inducible adipocyte-selective disruption of Ucp1. We find that, while germline Ucp1-/- mice succumb to cold-induced hypothermia with complete penetrance, most mice with inducible deletion of Ucp1 maintain homeothermy in the cold. However, inducible adipocyte-selective co-deletion of Ucp1 and creatine kinase B (Ckb, an effector of UCP1-independent thermogenesis) exacerbates cold-intolerance, indicative of a negative genetic interaction and thus a parallel thermogenic function. We find no evidence for impairments in insulation or non-shivering thermogenesis in skeletal muscle that would drive this phenotype. Furthermore, following UCP1 deletion or UCP1/CKB co-deletion from mature adipocytes, moderate cold exposure triggers the regeneration of mature adipocytes that coordinately restore UCP1 and CKB to brown adipose tissue, providing further evidence of their parallel thermogenic relationship. Our findings suggest that thermogenic adipocytes utilize non-paralogous protein redundancy – through UCP1 and CKB – to promote cold-induced energy dissipation.
Project description:Vaspin previously was identified as part of the secretome of activated brown adipose tissue in mice. For microarray analysis and to determine the effect of adipocyte-sepcific vaspin overexpression on transcriptional changes during acute cold exposure, brown adipose tissue of female vaspin transgenic mice on C57BL/6N background (published in 10.3389/fendo.2023.1146454; VasTg) and wild type control mice were investigated after acute 6 h cold exposure of 8°C.
Project description:Brown adipose tissue (BAT) generates heat via uncoupled respiration, providing mammals with an evolutionary defense against environmental cold. Although the molecular pathways by which cold activates brown adipocytes are well understood, little is known about how BAT maintains its thermogenic capacity during adaptation to environmental warmth. Here, we identify the transcriptional repressor BCL6 as the switch for maintaining brown adipocyte cellular identity under warm conditions. Mice lacking BCL6 in their brown adipocytes display normal thermogenic responses when housed in a cool environment, but fail to maintain thermogenic fitness when housed under warm conditions. In a temperature-dependent manner, BCL6 suppresses apoptosis, fatty acid storage, and coupled respiration to maintain thermogenic competence in brown adipocytes. Enhancer analysis revealed that BCL6 reinforces brown-specific while opposing white-specific enhancers to maintain cellular identity. Thus, unlike other regulators, BCL6 is dispensable for differentiation and activation of brown adipocytes, but specifically required for their maintenance in warmth.