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Metabolic Transcription Factors Mediate Conserved Functions Largely via Species-Specific Binding Regions

ABSTRACT: The winged helix protein FOXA2 and the nuclear receptor PPARg are highly conserved, regionally-expressed transcription factors that regulate networks of genes controlling complex metabolic functions. Cistrome analysis for FOXA2 in mouse liver and PPARg in mouse adipocytes has previously produced consensus binding sites that are nearly identical to those used by the factors in human cells. Despite this conservation of the canonical binding motif, we report here that the great majority of specific binding regions for FOXA2 in human liver and for PPARg in human adipocytes are not in the orthologous locations to the mouse genome. Nevertheless, gene-centric analysis reveals strong shared transcription factor occupancy near genes in tissue-specific metabolic pathways that are functionally conserved across species. Genes with only species-specific binding sites fail to show enrichment for these pathways. Thus, the biological functions of transcription factors that control specific metabolic functions are highly shared across species.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE25836 | GEO | 2011/04/06

SECONDARY ACCESSION(S): PRJNA135749

REPOSITORIES: GEO

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Project description:The winged helix protein FOXA2 and the nuclear receptor PPARg are highly conserved, regionally-expressed transcription factors that regulate networks of genes controlling complex metabolic functions. Cistrome analysis for FOXA2 in mouse liver and PPARg in mouse adipocytes has previously produced consensus binding sites that are nearly identical to those used by the factors in human cells. Despite this conservation of the canonical binding motif, we report here that the great majority of specific binding regions for FOXA2 in human liver and for PPARg in human adipocytes are not in the orthologous locations to the mouse genome. Nevertheless, gene-centric analysis reveals strong shared transcription factor occupancy near genes in tissue-specific metabolic pathways that are functionally conserved across species. Genes with only species-specific binding sites fail to show enrichment for these pathways. Thus, the biological functions of transcription factors that control specific metabolic functions are highly shared across species. Two TFs, FOXA2 and PPARg, were studied for genome-wide conservation of binding between mouse and human in specific tissues/cell-types (liver for FOXA2, adipocytes for PPARg). The number of replicates for each TF was chosen to obtain a comparable number of reads between the TFs and species. Human FOXA2 ChIP-seq was performed on two biological replicates of human liver samples, in three technical replicates each. Input DNA was also collected and sequenced from both biological samples. Mouse FOXA2 ChIP-seq was performed on four biological replicates of mouse liver samples. The ChIP and sequencing were repeated on two of these biological replicates to create technical replicates for additional sequence reads. Input DNA was sequenced from three additional mouse livers. Human PPARg ChIP-seq was performed on a human adipocyte cell-line (SGBS) differentiated in two replicate cultures. Input DNA was also collected and sequenced from one culture. Mouse PPARg ChIP-seq was performed on 3T3-L1 cells differentiated into adipocytes in culture in a single replicate, and this sequence data was pooled with existing data previously generated by the same lab, already available in GEO (GSE21314). A standard pool of input DNA sample sequence from multiple mouse tissue was used for analyzing the Mouse PPARg ChIP-seq data.

Project description:Obesity due to overnutrition causes adipose tissue dysfunction, serving as a critical pathological step on the road to Type 2 diabetes (T2D) and other metabolic disorders. Here, we performed an unbiased investigation into the fundamental molecular mechanisms by which adipocytes transition to an unhealthy state during obesity. We fed NuTRAP (Nuclear tagging and Translating Ribosome Affinity Purification) mice crossed with Adipoq-Cre with chow or high fat diet (HFD) for 10 weeks and determined adipocyte-specific transcriptomic profiles by RNA-seq, active promoter and enhancer activities by H3K27ac ChIP-seq, and the PPARg cistrome by ChIP-seq. We also assessed the impact of the PPARg agonist rosiglitazone (Rosi) on gene expression and cellular state of adipocytes from HFD-fed mice. We used bioinformatic approaches to find transcriptional pathways and performed functional studies using shRNA-mediated loss-of-function approaches in 3T3-L1 adipocytes. Adipocytes from HFD-fed mice exhibited reduced expression of adipocyte markers and metabolic genes while showing enhanced expression of myofibroblast marker genes involved in cytoskeletal organization, accompanied by the formation of actin filament structures within the cell. PPARg binding was globally reduced in adipocytes after HFD feeding, and Rosi restored the molecular and cellular phenotypes of adipocytes associated with HFD feeding. SMAD binding motifs were over-represented in HFD-induced promoters and enhancers, while TGFb1 expression was elevated in adipose tissues after HFD feeding. TGFb1 treatment of mature 3T3-L1 adipocytes induced gene expression and cellular changes similar to those seen after HFD in vivo, and knockdown of Smad3 blunted the effects of TGFb1. Our data demonstrate that adipocytes fail to maintain cellular identity after HFD, acquiring characteristics of a myofibroblast-like cell type through reduced PPARg activity and elevated TGFb-SMAD signaling. This cellular identity crisis may serve as a fundamental mechanism that drives functional decline of adipose tissues during obesity.

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Metabolic Transcription Factors Mediate Conserved Functions Largely via Species-Specific Binding Regions

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