Retinoic Acid Inhibits Adipogenesis Modulating C/EBPβ Phosphorylation and Down Regulating Srebf1a Expression

Functional roles for AGPAT6 in milk fat synthesis of buffalo mammary epithelial cells

AGPAT6 plays a crucial role in the triglyceride (TG) synthesis pathway in mammals. However, its roles in buffalo lactation remain unknown. Therefore, we investigated the functional roles of AGPAT6 in milk fat synthesis by transfecting overexpression and lentivirus interference vectors in buffalo mammary epithelial cells (BuMECs) in vitro. AGPAT6 overexpression in BuMECs significantly enhanced the mRNA expression of FABP4, SLC27A6, ACSL1, DGAT1, DGAT2, LPIN1, INSIG1, CEBPA and SREBF1 genes, and significantly reduced that of XDH, CPT1A, LIPE, INSIG2 and PPARGC1A, but has no significant influence to the mRNA abundance of FABP3, GPAM, PPARG and SREBF2. However, the interference with AGPAT6, the mRNA expression of FABP4, SLC27A6, ACSL1, DGAT1, DGAT2, INSIG1, CEBPA, SREBF1, XDH, CPT1A, LIPE, INSIG2 and PPARGC1A genes in BuMECs changed contrary to the overexpression experiment, and that of GPAM, PPARG and SREBF2 also did not change significantly, but the expression of FABP3 was significantly decreased. In addition, the overexpression/interference of AGPAT6 gene significantly increased/decreased TG content in BuMECs. The results here indicate that AGPAT6 gene is involved in TG synthesis in BuMECs, and affects the expression of major genes associated with FA transport and activation, TG synthesis and transcription regulation, FA oxidation and TG degradation during the lipogenesis of milk.

FAM129B is a cooperative protein that regulates adipogenesis

FAM129B is one of Niban-like proteins described in neoplastic cells and implicated in melanoma cell invasion, but no reports have been published on FAM129B and cell differentiation. We show that FAM129B is early and transiently expressed and crucial for 3T3-F442A adipogenesis. Fam129b is expressed downstream of the early genes Cebpb, Klf4, Klf5 and Srebf1a, but upstream of Pparg2 since knockdown of Fam129b blocked Pparg2 expression and adipose differentiation. Glycogen synthase kinase 3 beta activity, a crucial kinase for adipogenesis, and the ERK1/2 are involved in FAM129B phosphorylation as part of the adipogenic program. Phosphorylated FAM129B is crucial for Pparg2 expression and the lipogenic gene expression downstream of Pparg2, and hence for adipogenesis. Fam129b knockdown reduced adipocyte cluster formation and size, regulating commitment and clonal amplification. In vivo, BAT, inguinal and epidydimal fat expressed Fam129b, suggesting a role in adipose tissue development. We conclude that FAM129B is a cooperative protein that regulates differentiation during the early stages of adipogenesis.

Vitamin A regulates intramuscular adipose tissue and muscle development: promoting high-quality beef production

During growth in cattle, the development of intramuscular adipose tissue and muscle is dependent upon cell hyperplasia (increased number of adipocytes) and hypertrophy (increased size of adipocytes). Based on the results of previous studies, other adipose tissue depots (e.g., perirenal and subcutaneous) develop from the fetal stage primarily as brown adipose tissue. The hyperplastic stage of intramuscular adipose is considered to develop from late pregnancy, but there is no evidence indicating that intramuscular adipose tissue develops initially as brown adipose tissue. Hyperplastic growth of intramuscular adipose continues well into postweaning and is dependent on the timing of the transition to grain-based diets; thereafter, the late-stage development of intramuscular adipose tissue is dominated by hypertrophy. For muscle development, hyperplasia of myoblasts lasts from early (following development of somites in the embryo) to middle pregnancy, after which growth of muscle is the result of hypertrophy of myofibers. Vitamin A is a fat-soluble compound that is required for the normal immunologic function, vision, cellular proliferation, and differentiation. Here we review the roles of vitamin A in intramuscular adipose tissue and muscle development in cattle. Vitamin A regulates both hyperplasia and hypertrophy in in vitro experiments. Vitamin A supplementation at the early stage and restriction at fattening stage generate opposite effects in the beef cattle. Appropriate vitamin A supplementation and restriction strategy increase intramuscular adipose tissue development (i.e., marbling or intramuscular fat) in some in vivo trials. Besides, hyperplasia and hypertrophy of myoblasts/myotubes were affected by vitamin A treatment in in vitro trials. Additionally, some studies reported an interaction between the alcohol dehydrogenase-1C (ADH1C) genotype and vitamin A feed restriction for the development of marbling and/or intramuscular adipose tissue, which was dependent on the timing and level of vitamin A restriction. Therefore, the feed strategy of vitamin A has the visible impact on the marbling and muscle development in the cattle, which will be helpful to promote the quality of the beef.

All-Trans Retinoic Acid Inhibits Bone Marrow Mesenchymal Stem Cell Commitment to Adipocytes via Upregulating FRA1 Signaling

Obesity, caused by an increased number and volume of adipocytes, is a global epidemic that seriously threatens human health. Bone marrow mesenchymal stem cells (BMSCs) can differentiate into adipocytes. All-trans retinoic acid (atRA, the active form of vitamin A) inhibits the adipogenic differentiation of BMSCs through its receptor RARG. The expression level of FRA1 (FOS like 1, AP-1 transcription factor subunit) in atRA-treated BMSCs increased, suggesting that atRA-mediated inhibition of BMSCs adipogenesis involves FRA1. BMSCs were transfected with adenovirus overexpressing Fra1 (ad-fra1) or silenced for Fra1 (si-fra1) and then treated with atRA. BMSCs treated with atRA and treated with ad-fra1 showed decreased mRNA and protein levels of key adipogenic genes (Pparg2, Cebpa) and adipogenesis-associated genes (Cd36, Fabp, Lpl, and Plin); atRA had a stronger inhibitory effect on adipogenesis compared with that in the ad-fra1 group. Adipogenic gene expression in Fra1-silenced BMSCs was significantly upregulated. Compared with that in the atRA group, the si-fra1 + atRA also upregulated adipogenic gene expression. However, compared with si-fra1, si-fra1 + atRA significantly inhibited adipogenic differentiation. Chromatin immunoprecipitation showed that RARG directly regulates Fra1 and FRA1 directly regulates Pparg2 and Cebpa. The results supported the conclusion that atRA inhibits BMSC adipogenesis partially through the RARG-FRA1-PPARG2 or the CEBPA axis or both. Thus, vitamin A might be used to treat obesity and its related diseases.

Retinoids Regulate Adipogenesis Involving the TGFβ/SMAD and Wnt/β-Catenin Pathways in Human Bone Marrow Mesenchymal Stem Cells

Retinoids may regulate cell differentiation as ligands of retinoic acid receptors (RARs) and/or retinoid X receptors (RXRs). We showed that RAR agonists promoted adipogenesis by upregulating the expression of CCAAT/enhancer-binding protein β (C/EBPβ) in the early stages, but blocked adipogenesis at a later stage in human bone marrow mesenchymal stem cells (hBMSCs). RXR agonists promoted adipogenesis at all time points in hBMSCs. The effect of RAR agonists was mediated mainly by the RARβ subtype. RAR agonists, in contrast to RXR agonists, significantly promoted the expression of RARβ. Knockdown of the RARβ gene via small hairpin RNA (shRNA) attenuated the inhibition of RAR agonists toward adipogenesis. Furthermore, we found that RAR agonists upregulated the transforming growth factor β (TGFβ)/SMAD pathway and Wnt/β-catenin pathway on adipogenesis in hBMSCs, and the stimulating effects were noticeably decreased with the RARβ gene knockdown. Both RAR agonists and RXR agonists inhibited adipogenesis and blocked the promoter activity of C/EBPβ and peroxisome proliferator-activated receptor γ (PPARγ) in SW872 cell. These results indicated the RAR agonists perform dual roles in adipogenesis in hBMSCs, and the TGFβ/SMAD pathway and Wnt/β-catenin pathway may involve the inhibitory effect of RAR agonists. RARβ is the main receptor subtype mediating the effect. The roles of RXR agonists in adipogenesis exhibited cell type-specific differences, and may be based on the integration of signals from different RXR dimers.