Dynamics of transcriptome and chromatin accessibility revealed sequential regulation of potential transcription factors during the brown adipose tissue whitening in rabbits.

Brown adipose tissue (BAT) represents a valuable target for treating obesity in humans. BAT losses of thermogenic capacity and gains a "white adipose tissue-like (WAT-like)" phenotype (BAT whitening) under thermoneutral environments, which could lead to potential low therapy responsiveness in BAT-based obesity treatments. However, the epigenetic mechanisms of BAT whitening remain largely unknown. In this study, BATs were collected from rabbits at day0 (D0), D15, D85, and 2 years (Y2). RNA-sequencing (RNA-seq) and the assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) were performed to investigate transcriptome and chromatin accessibility of BATs at the four whitening stages, respectively. Our data showed that many genes and chromatin accessible regions (refer to as "peaks") were identified as significantly changed during BAT whitening in rabbits. The BAT-selective genes downregulated while WAT-selective genes upregulated from D0 to Y2, and the de novo lipogenesis-related genes reached the highest expression levels at D85. Both the highly expressed genes and accessible regions in Y2 were significantly enriched in immune response-related signal pathways. Analysis of different relationships between peaks and their nearby genes found an increased proportion of the synchronous changes between chromatin accessibility and gene expression during BAT whitening. The synergistic changes between the chromatin accessibility of promoter and the gene expression were found in the key adipose genes. The upregulated genes which contained increased peaks were significantly enriched in the PI3K-Akt signaling pathway, steroid biosynthesis, TGF-beta signaling pathway, osteoclast differentiation, and dilated cardiomyopathy. Moreover, the footprinting analysis suggested that sequential regulation of potential transcription factors (TFs) mediated the loss of thermogenic phenotype and the gain of a WAT-like phenotype of BAT. In conclusion, our study provided the transcriptional and epigenetic frameworks for understanding BAT whitening in rabbits for the first time and might facilitate potential insights into BAT-based obesity treatments.

Genome-wide identification and characterization of long non-coding RNAs during differentiation of visceral preadipocytes in rabbit.

Emerging evidence suggests that long non-coding RNAs (lncRNAs) are critical regulators of diverse biological processes, including adipogenesis. Despite being considered an ideal animal model for studying adipogenesis, little is known about the roles of lncRNAs in the regulation of rabbit preadipocyte differentiation. In the present study, visceral preadipocytes isolated from newborn rabbits were cultured in vitro and induced for differentiation, and global lncRNA expression profiles of adipocytes collected at days 0, 3, and 9 of differentiation were analyzed by RNA-seq. A total of 2066 lncRNAs were identified from nine RNA-seq libraries. Compared to protein-coding transcripts, lncRNA transcripts exhibited characteristics of a longer length and lower expression level. Furthermore, 486 and 357 differentially expressed (DE) lncRNAs were identified when comparing day 3 vs. day 0 and day 9 vs. day 3, respectively. Target genes of DE lncRNAs were predicted by the cis-regulating approach. Prediction of functions revealed that DE lncRNAs when comparing day 3 vs. day 0 were involved in gene ontology (GO) terms of developmental growth, growth, developmental cell growth, and stem cell proliferation, and involved in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of PI3K-Akt signaling pathway, fatty acid biosynthesis, and the insulin signaling pathway. The DE lncRNAs when comparing day 9 vs. day 3 were involved in GO terms that associated with epigenetic modification and were involved in the KEGG pathway of cAMP signaling pathway. This study provides further insight into the regulatory function of lncRNAs in rabbit visceral adipose and facilitates a better understanding of different stages of preadipocyte differentiation.

Genome-wide identification and characterization of long non-coding RNAs during postnatal development of rabbit adipose tissue.

BACKGROUND: The rabbit is widely used as an important experimental model for biomedical research, and shows low adipose tissue deposition during growth. Long non-coding RNAs (lncRNAs) are associated with adipose growth, but little is known about the function of lncRNAs in the rabbit adipose tissue. METHODS: Deep RNA-sequencing and comprehensive bioinformatics analyses were used to characterize the lncRNAs of rabbit visceral adipose tissue (VAT) at 35, 85 and 120 days after birth. Differentially expressed (DE) lncRNAs were identified at the three growth stages by DESeq. The cis and trans prediction ways predicted the target genes of the DE lncRNAs. To explore the function of lncRNAs, Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed on the candidate genes. RESULTS: A total of 991,157,544 clean reads were generated after RNA-Seq of the three growth stages, of which, 30,353 and 107 differentially expressed (DE) lncRNAs were identified. Compared to the protein-coding transcripts, the rabbit lncRNAs shared some characteristics such as shorter length and fewer exons. Cis and trans target gene prediction revealed, 43 and 64 DE lncRNAs respectively, corresponding to 72 and 20 protein-coding genes. GO enrichment and KEGG pathway analyses revealed that the candidate DE lncRNA target genes were involved in oxidative phosphorylation, glyoxylate and dicarboxylate metabolism, and other adipose growth-related pathways. Six DE lncRNAs were randomly selected and validated by q-PCR. CONCLUSIONS: This study is the first to profile the potentially functional lncRNAs in the adipose tissue growth in rabbits, and contributes to our understanding of mammalian adipogenesis.