Brd4 modulates diet-induced obesity via PPARγ-dependent Gdf3 expression in adipose tissue macrophages
Xiangming Hu, Xingchen Dong, Guo Li, Yanheng Chen, Jinjing Chen, Xiaoxin He, Hao Sun, Dong-Hyun Kim, Jongsook Kim Kemper, Lin-Feng Chen
Xiangming Hu, Xingchen Dong, Guo Li, Yanheng Chen, Jinjing Chen, Xiaoxin He, Hao Sun, Dong-Hyun Kim, Jongsook Kim Kemper, Lin-Feng Chen
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Research Article Metabolism

Brd4 modulates diet-induced obesity via PPARγ-dependent Gdf3 expression in adipose tissue macrophages

Abstract

Macrophage-mediated inflammatory response has been implicated in the pathogenesis of obesity and insulin resistance. Brd4 has emerged as a key regulator in the innate immune response. However, the role of Brd4 in obesity-associated inflammation and insulin resistance remains uncharacterized. Here, we demonstrated that myeloid lineage-specific Brd4 knockout (Brd4-CKO) mice were protected from high-fat diet–induced (HFD-induced) obesity with less fat accumulation, higher energy expenditure, and increased lipolysis in adipose tissue. Brd4-CKO mice fed a HFD also displayed reduced local and systemic inflammation with improved insulin sensitivity. RNA-Seq of adipose tissue macrophages (ATMs) from HFD-fed WT and Brd4-CKO mice revealed that expression of antilipolytic factor Gdf3 was significantly decreased in ATMs of Brd4-CKO mice. We also found that Brd4 bound to the promoter and enhancers of Gdf3 to facilitate PPARγ-dependent Gdf3 expression in macrophages. Furthermore, Brd4-mediated expression of Gdf3 acted as a paracrine signal targeting adipocytes to suppress the expression of lipases and the associated lipolysis in cultured cells and mice. Controlling the expression of Gdf3 in ATMs could be one of the mechanisms by which Brd4 modulates lipid metabolism and diet-induced obesity. This study suggests that Brd4 could be a potential therapeutic target for obesity and insulin resistance.

Authors

Xiangming Hu, Xingchen Dong, Guo Li, Yanheng Chen, Jinjing Chen, Xiaoxin He, Hao Sun, Dong-Hyun Kim, Jongsook Kim Kemper, Lin-Feng Chen

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Figure 5

Brd4 increased adiposity through modulating Gdf3-dependent impairment of lipolysis.

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Brd4 increased adiposity through modulating Gdf3-dependent impairment of...
(A) mRNA levels of indicated genes were measured by real-time PCR in eWAT of WT or Brd4-CKO mice fed a ND or a HFD for 20 weeks. (B) Protein levels of ATGL, Gdf3, and Actin in eWAT of WT or Brd4-CKO mice fed a ND or a HFD for 20 weeks were determined by immunoblotting. Each lane represents 1 mouse. ELISA assay of TG (C) or glycerol (D) levels in eWAT of WT or Brd4-CKO mice fed a ND or a HFD for 20 weeks. (E) Differentiated 3T3-L1 cells were cocultured without or with WT or Brd4-CKO BMDMs as indicated for 12 hours, followed by stimulation with Iso for 3 hours. The mRNA levels of indicated genes in 3T3-L1cells were analyzed by real-time PCR. (F) Differentiated 3T3-L1 cells were cocultured without or with WT or Brd4-deficient BMDMs with 1 nM insulin and 50 μM Rsg for 12 hours, followed by stimulation with Iso for 3 hours. (G) Media collected from WT or Brd4-deficient BMDMs treated with insulin and Rsg for 16 hours were incubated with differentiated 3T3-L1 cells for 12 hours, followed by the treatment of Iso for 3 hours. 3T3-L1 cells cultured with media from Brd4-CKO BMDMs with the addition of rGdf3 (100 pg/mL) were also shown. (H) Analysis of mRNA expression levels of Brd4 in peripheral blood cells from normal weight or overweight individuals from the GEO dataset (GSE109597). (I) Correlation of mRNA levels of Brd4 and Gdf3 in circulating monocytes in obese individuals from the GEO dataset (GSE32575). Spearman r values and P values are indicated. Data are mean and SD and are determined by an unpaired 2-tailed Student’s t test (H), 1-way (A, C, D, and E), or 2-way ANOVA (F and G). n = 2–5 mice as indicated (A–D). n = 3-4 culture dishes from 3–4 independent experiments (E–G). *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ns, statistically not significant. Brd4-CKO, myeloid lineage-specific Brd4 knockout; HFD, high-fat diet–induced; ND, normal diet; Iso, isoproterenol; Rsg, rosiglitazone; TG, triglyceride; BMDMs, BM-derived macrophages.