Project description:Background: The beneficial effect of thermogenic adipocytes in maintaining body weight and protecting against metabolic disorders has raised interest in understanding the regulatory mechanisms defining white and beige adipocyte identity. Although alternative splicing has been shown to propagate adipose browning signals in mice, this has yet to be thoroughly investigated in human adipocytes. Methods: We performed parallel white and beige adipogenic differentiation using primary adipose stem cells from 6 unrelated healthy subjects, and assessed differential gene and isoform expression in mature adipocytes by RNA sequencing. Results: We find 693 exon junctions with robust differential usage between white and beige adipocytes in all 6 subjects, mapping to 507 genes. Importantly, only 8% of these differentially spliced genes are also differentially expressed, indicating that alternative splicing constitutes an additional layer of gene expression regulation during beige adipocyte adipogenic differentiation. Functional classification of alternative isoforms point to a gain of function for key thermogenic regulators such as PPARG, CITED1 and PEMT. We find that a large majority of the splice variants arise from differential usage of transcription start sites (TSSs), with beige-specific TSSs being enriched for PPARγ and MED1 binding compared to white-specific TSSs. Finally, we validate beige specific isoform expression at the protein level for two thermogenic regulators, PPARγ and PEMT. Discussion: These results indicate that differential isoform expression through alternative TSS usage is an important regulatory mechanism for human adipocyte thermogenic specification.
Project description:Background: The beneficial effect of thermogenic adipocytes in maintaining body weight and protecting against metabolic disorders has raised interest in understanding the regulatory mechanisms defining white and beige adipocyte identity. Although alternative splicing has been shown to propagate adipose browning signals in mice, this has yet to be thoroughly investigated in human adipocytes. Methods: We performed parallel white and beige adipogenic differentiation using primary adipose stem cells from 6 unrelated healthy subjects, and assessed differential gene and isoform expression in mature adipocytes by RNA sequencing. Results: We find 693 exon junctions with robust differential usage between white and beige adipocytes in all 6 subjects, mapping to 507 genes. Importantly, only 8% of these differentially spliced genes are also differentially expressed, indicating that alternative splicing constitutes an additional layer of gene expression regulation during beige adipocyte adipogenic differentiation. Functional classification of alternative isoforms point to a gain of function for key thermogenic regulators such as PPARG, CITED1 and PEMT. We find that a large majority of the splice variants arise from differential usage of transcription start sites (TSSs), with beige-specific TSSs being enriched for PPARγ and MED1 binding compared to white-specific TSSs. Finally, we validate beige specific isoform expression at the protein level for two thermogenic regulators, PPARγ and PEMT. Discussion: These results indicate that differential isoform expression through alternative TSS usage is an important regulatory mechanism for human adipocyte thermogenic specification. Code for data processing and analysis are available at https://github.com/sarahhp/splicing_thermogenesis.
Project description:Prolonged cold exposure stimulates the recruitment of beige adipocytes within white adipose tissue. Beige adipocytes depend on mitochondrial oxidative phosphorylation to drive thermogenesis. The transcriptional mechanisms that promote remodeling in adipose tissue during the cold are not well understood. Here we demonstrate that the transcriptional coregulator transducin-like enhancer of split 3 (TLE3) inhibits mitochondrial gene expression in beige adipocytes. Conditional deletion of TLE3 in adipocytes promotes mitochondrial oxidative metabolism and increases energy expenditure, thereby improving glucose control. Using chromatin immunoprecipitation and deep sequencing, we found that TLE3 occupies distal enhancers in proximity to nuclear-encoded mitochondrial genes and that many of these binding sites are also enriched for early B-cell factor (EBF) transcription factors. TLE3 interacts with EBF2 and blocks its ability to promote the thermogenic transcriptional program. Collectively, these studies demonstrate that TLE3 regulates thermogenic gene expression in beige adipocytes through inhibition of EBF2 transcriptional activity. Inhibition of TLE3 may provide a novel therapeutic approach for obesity and diabetes.
Project description:Beige adipocytes are a distinct type of thermogenic fat cells in human. Since beige adipocytes are distributed sporadically within white adipose, characterization of human beige adipocytes has long been a problem. In this study, we reported a rapid and roboust method in generating human beige adipocyte with chemically defined medium and RNA-Seq was perfomed to reveal the molecular characterization of derived human beige adipocytes.
Project description:For placental mammals, the transition from the in utero maternal environment to postnatal life requires the activation of thermogenesis to maintain their core temperature. This is primarily accomplished by induction of uncoupling protein 1 (UCP1) in brown and beige adipocytes, the principal sites for uncoupled respiration. Despite its importance, how placental mammals license their thermogenic adipocytes to participate in postnatal uncoupled respiration is not known. Here, we provide evidence that the 'alarmin' IL-33, a nuclear cytokine that activates type 2 immune responses, licenses brown and beige adipocytes for uncoupled respiration. We find that, in absence of IL-33 or ST2, beige and brown adipocytes develop normally but fail to express an appropriately spliced form of Ucp1 mRNA, resulting in absence of UCP1 protein, and impairment in uncoupled respiration and thermoregulation. Together, these data suggest that IL-33 and ST2 function as a developmental switch to license thermogenesis during the perinatal period.
Project description:Adipose tissue provides a defense against starvation and environmental cold. These dichotomous functions are performed by three distinct cell types: energy-storing white adipocytes, and thermogenic beige and brown adipocytes. Previous studies have demonstrated that exposure to environmental cold stimulates the recruitment of beige adipocytes in the white adipose tissue (WAT) of mice and humans, a process that has been extensively investigated. However, beige adipose tissue also develops during the peri-weaning period in mice, a developmental program that remains poorly understood. Here, we address this gap in our knowledge using genetic, imaging, physiologic, and genomic approaches. We find that, unlike cold-induced recruitment in adult animals, peri-weaning development of beige adipocytes occurs in a temperature- and sympathetic nerve-independent manner. Instead, the transcription factor B cell leukemia/lymphoma 6 (BCL6) acts in a cell autonomous manner to regulate the commitment but not the maintenance phase of beige adipogenesis. Genome-wide RNA-seq studies reveal that BCL6 regulates a core set of genes involved in fatty acid oxidation and mitochondrial uncoupling, which are necessary for development of functional beige adipocytes. Together, our findings demonstrate that distinct transcriptional and signaling mechanisms control peri-weaning development and cold-induced recruitment of beige adipocytes in mammals.
Project description:Prolonged cold exposure stimulates the recruitment of beige adipocytes within white adipose tissue. Beige adipocytes depend on mitochondrial oxidative phosphorylation to drive thermogenesis. The transcriptional coregulator TLE3 inhibits mitochondrial and metabolic gene expression in beige adipocytes.
Project description:Here we show that synthesis of the mitochondrial phospholipid cardiolipin is an indispensable driver of thermogenic fat function. Cardiolipin biosynthesis is robustly induced in brown and beige adipose upon cold exposure. Mimicking this response by overexpressing cardiolipin synthase (Crls1) enhances energy consumption in mouse and human adipocytes. Crls1 deficiency diminishes mitochondrial uncoupling in brown and beige adipocytes and elicits a nuclear transcriptional response through ER stress-mediated retrograde communication. Cardiolipin depletion in brown and beige fat abolishes adipose thermogenesis and glucose uptake and renders animals strikingly insulin resistant. We further identify a rare human CRLS1 variant associated with insulin resistance and show that adipose CRLS1 levels positively correlate with insulin sensitivity. Thus, adipose cardiolipin is a powerful regulator of organismal energy homeostasis through thermogenic fat bioenergetics.
Project description:Two types of UCP1 positive cells-brown and beige adipocytes exist in mammals. Beige adipocytes are very plastic, and can be dynamically regulated by environment.Beige adipocytes formed postnatally in subcutaneous inguinal white adipose tissue (iWAT) lost thermogenic gene expression and multilocular morphology at adult stage, but cold could restore their “beigeing” characteristics, a phenomenon termed as beige adipocyte renaissance. Our results showed that beige cell maintenance and renaissance in adult mice were regulated by cAMP and HDAC4 signaling in white adipocytes non-cell autonomously. Genetic modulations of various components of this cAMP-HDAC4 cascade (e.g. LKB1) led to persistent browning and reduced adiposity independent of thermogenesis. To further study the mechanisms of beige adipocytes maintenance, we performed RNA-seq with samples from inguinal white adipose tissues of WT, AdipoqCre LKB1 F/F, and AdipoqCre LKB1 F/F; HDAC4 F/F mice.Our studies will move the beige adipocyte field forward and attract clinical applications to target beige adipocyte renaissance.