Cold exposure induces lipid dynamics and thermogenesis in brown adipose tissue of goats

Abstract

Background: Adaptive thermogenesis by brown adipose tissue (BAT) is important to the maintenance of temperature in newborn mammals. Cold exposure activates gene expression and lipid metabolism to provide energy for BAT thermogenesis. However, knowledge of BAT metabolism in large animals after cold exposure is still limited.

Results: In this study, we found that cold exposure induced expression of BAT thermogenesis genes and increased the protein levels of UCP1 and PGC1α. Pathway analysis showed that cold exposure activated BAT metabolism, which involved in cGMP-PKG, TCA cycle, fatty acid elongation, and degradation pathways. These were accompanied by decreased triglyceride (TG) content and increased phosphatidylcholine (PC) and phosphatidylethanolamine (PE) content in BAT.

Conclusion: These results demonstrate that cold exposure induces metabolites involved in glycerolipids and glycerophospholipids metabolism in BAT. The present study provides evidence for lipid composition associated with adaptive thermogenesis in goat BAT and metabolism pathways regulated by cold exposure.

Keywords: Brown adipose tissue; Cold exposure; Lipid metabolism; RNA-seq; Thermogenesis.

Fig. 1

Cold exposure promotes BAT thermogenesis of perirenal BAT in newborn goats. (A) Representative images are shown for perirenal fat and histological sections were stained with hematoxylin and eosin of room temperature (RT, 25 °C) or cold exposure (Cold, 6 °C) group, scale bar: 50 μm; (B) Western blotting of UCP1 and PGC1α between RT and Cold group in BAT; (C) Volcano plot showed differential gene expression profiles of RT and Cold group; (D) Unsupervised hierarchical clustering showed that the RT and Cold groups clustered into two classes; (E) Heatmaps of the fragments per kilobase million (FPKM) values of upregulated genes in BAT thermogenesis pathway after cold exposure

Fig. 2

KEGG pathway analysis of upregulated genes of BAT upon cold exposure. (A) Enrichment of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of cold-induced upregulated genes using KEGG database [16]; (B) cGMP-PKG (ko04022) and cAMP signaling pathway (ko04024) analysis was used by gene set enrichment analysis (GSEA) on RNA-seq data from RT and Cold group. The green line represented the enrichment of pathway in the Cold or RT group according to gene expression levels, with genes enriched in the Cold group shown on the left and genes enriched in the RT group shown on the right; (C-D) Heatmaps of the FPKM expression values of differentially expressed genes in cGMP-PKG signaling pathway and Citrate cycle (TCA cycle) after cold exposure. IRS1_x1 represented IRS1 isoform 1, and PRKG1_x2 represented PRKG1 isoform 2

Fig. 3

Cold exposure changes the overall lipid composition of perirenal BAT. (A) The orthogonal partial least squares-discriminant analysis (OPLS-DA) showed that RT and Cold group were separated into two clusters; (B-C) The intensity fold change of sphingolipids and cholesterol esters; (D) Log2 fold changes in lipid species in Cold vs. RT group. Each dot represents a lipid species and the dot size indicates the significance. Only lipids with P < 0.05 are displayed. Error bars represent standard error of mean (SEM), n = 5, * P < 0.05

Fig. 4

Cold exposure changes fatty acyl levels of TG in perirenal BAT. (A) The intensity fold change of glycerolipids; (B-E) The total intensity fold change of TG individual fatty-acyls chains, (B), odd-numbered fatty-acyl chains (ODD), (C), saturated fatty-acyl chains (SFA), (D), monounsaturated fatty-acyl chains (MUFA), (E), polyunsaturated fatty-acyl chains (PUFA); (F-G) Heatmaps of the FPKM values of differentially expressed genes in regulation of lipolysis, and fatty acid degradation and elongation pathway after cold exposure. Error bars represent standard error of mean (SEM), n = 5, * P < 0.05

Fig. 5

The lipolysis and fatty acid metabolism are induced in perirenal BAT after cold exposure. Pathway analysis of TG lipolysis and fatty acid metabolism, with indications of quantified lipid classes (circles), genes, and pathway (rectangles) regulated in perirenal BAT by acute cold exposure. Colors indicate significantly upregulated (red) or downregulated (blue) genes after cold exposure. For lipids, colors indicate the increasing (yellow) and decreasing (green) trend of the lipid classes, and only * represent significant different lipid classes

Fig. 6

Cold exposure changes glycerophospholipid metabolism in perirenal BAT. (A) Glycerophospholipid metabolism (ko00564) pathway analysis using GSEA on RNA-seq data from RT and Cold group. The green line represented the enrichment of pathway in the Cold or RT group according to gene expression levels, with genes enriched in the cold group shown on the left and genes enriched in the RT group shown on the right; (B) The intensity fold change of glycerophospholipid; (C) All phospholipid species were significantly changed as shown in this figure. Log2 fold changes in significantly different glycerophospholipid species in RT vs. Cold group, and top 30 species are listed according to intensity; (D) Heatmaps of the FPKM expression values of upregulated genes in glycerophospholipid metabolism pathway after cold exposure. Error bars represent standard error of mean (SEM), n = 5, * P < 0.05

Fig. 7

The glycerophospholipid metabolism is induced in perirenal BAT after cold exposure. Pathway analysis of glycerophospholipid metabolism, with indications of quantified lipid classes (circles), genes (rectangles) regulated in perirenal BAT by cold exposure. Colors indicate significantly upregulated (red) or downregulated (blue) genes after cold exposure. For lipids, colors indicate the increasing (yellow) and decreasing (green) trend of the lipid classes. LPA: Lysophosphatidic acid; LPC: Lysophosphatidylcholine; PC: Phosphatidylcholine; PE: Phosphatidylethanolamine; LPG: Lysophosphatidylglycerol; PG: Phosphatidylglycerol; CL: cardiolipin; G3P: Glycerol-3-phosphate