Transcriptional regulation analysis of FAM3A gene and its effect on adipocyte differentiation

Genome-Wide Phylogenetic Analysis, Expression Pattern, and Transcriptional Regulatory Network of the Pig C/EBP Gene Family

The CCAAT/enhancer binding protein (C/EBP) transcription factors (TFs) regulate many important biological processes, such as energy metabolism, inflammation, cell proliferation etc. A genome-wide gene identification revealed the presence of a total of 99 C/EBP genes in pig and 19 eukaryote genomes. Phylogenetic analysis showed that all C/EBP TFs were classified into 6 subgroups named C/EBPα, C/EBPβ, C/EBPδ, C/EBPε, C/EBPγ, and C/EBPζ. Gene expression analysis showed that the C/EBPα, C/EBPβ, C/EBPδ, C/EBPγ, and C/EBPζ genes were expressed ubiquitously with inconsistent expression patterns in various pig tissues. Moreover, a pig C/EBP regulatory network was constructed, including C/EBP genes, TFs and miRNAs. A total of 27 feed-forward loop (FFL) motifs were detected in the pig C/EBP regulatory network. Based on the RNA-seq data, gene expression patterns related to FFL sub-network were analyzed in 27 adult pig tissues. Certain FFL motifs may be tissue specific. Functional enrichment analysis indicated that C/EBP and its target genes are involved in many important biological pathways. These results provide valuable information that clarifies the evolutionary relationships of the C/EBP family and contributes to the understanding of the biological function of C/EBP genes.

Loss of family with sequence similarity 107, member A (FAM107A) induces browning in 3T3-L1 adipocytes

Induction of white fat browning (beiging) and activation of brown fat has been considered a promising strategy to treat obesity and associated metabolic complications. However, the molecular mechanisms regulating brown and beige fat-mediated thermogenesis remains unclear. Our study aimed to identify genes with a hitherto unknown mechanism in the metabolic functions of adipocytes and identified family with sequence similarity 107, member A (FAM107A) as a factor that interferes with fat browning in white adipocytes. We explored physiological roles of FAM107A in cultured 3T3-L1 white adipocytes and HIB1B brown adipocytes by using FAM107A-deficient adipocytes. Significant loss in FAM107A gene functionality induced fat browning was evidenced by evaluating the gene and protein expression level of brown fat-associated markers through real-time qRT-PCR and immunoblot analysis, respectively. Deficiency of FAM107A promoted mitochondrial biogenesis and significantly upregulated core fat-browning marker proteins (PGC-1α, PRDM16, and UCP1) and beige-specific genes (Cd137, Cited1, Tbx1, and Tmem26). Furthermore, FAM107A increased adipogenesis and negatively regulated lipid metabolism in 3T3-L1 adipocytes. In addition, in-silico analysis revealed a strong interaction between FAM107A and β3-AR based on their energy binding score. Next, mechanistic study revealed that specific knockdown of FAM107A induces browning in white adipocytes via activation of β3-AR, AMPK and p38 MAPK-dependent signaling pathways. Our data unveiled a previously unknown mechanism of FAM107A in the regulation of lipid metabolism and identified its significant role in metabolic homeostasis. This highlighted the potential of FAM107A as a pharmacotherapeutic target in treating obesity and related metabolic disorders.

MiR-543 regulates myoblast proliferation and differentiation of C2C12 cells by targeting KLF6

MicroRNA-543 (miR-543) has been found to play a suppressive role in various human cancers in many studies, whereas the specific functions of miR-543 in muscle development remain poorly understood. Here, we found that the expression of miR-543 was high in skeletal muscle and increased during the differentiation of C2C12 cells. Overexpression of miR-543 repressed C2C12 cell proliferation and promoted differentiation, while knockdown of miR-543 expression produced the opposite results. During myogenesis, we predicted and verified that Krüppel-like factor 6 (KLF6), a suppressor of multiple tumor cells, was a target gene of miR-543. Then, miR-543 was found to specifically target KLF6 and repress its expression. Besides this, knockdown of KLF6 promoted the differentiation but inhibited the proliferation of C2C12 cells. Si-KLF6 can rescue the influence of miR-543 inhibitor on C2C12 cell differentiation. Our results indicate a new regulatory mechanism of miR-543 on KLF6 expression and suggest the possibility of using the miR-543/KLF6 pathway as a potential target for studying myogenesis.

FAM3A protects chondrocytes against interleukin-1β-induced apoptosis through regulating PI3K/Akt/mTOR pathway

Chondrocyte death due to apoptosis is central for osteoarthritis (OA) pathogenesis. The family with sequence similarity 3A (FAM3A) is a mitochondrial protein that plays an important role for cellular adaptation to stress and cell survival. Yet, whether FAM3A is associated with chondrocyte apoptosis and OA pathogenesis remains uncharacterized. In this study, we found that FAM3A expression was downregulated in cartilage tissue from an experimental OA mouse model. Besides, FAM3A expression was also reduced in chondrocytes treated with interleukin-1β (IL-1β), an inflammatory cytokine that promotes cartilage degradation. Moreover, we discovered that FAM3A attenuated chondrocyte apoptosis induced by IL-1β treatment in vitro, suggesting a protective effect of FAM3A against chondrocyte apoptosis. Moreover, mechanistically, FAM3A activated PI3K/Akt/mTOR pathway in IL-1β-treated chondrocytes, and blockade of PI3K/Akt/mTOR pathway with specific inhibitors, wortmannin and LY294002, diminished FAM3A effect on IL-1β-induced chondrocyte apoptosis, hence demonstrating that FAM3A attenuates IL-1β-induced chondrocyte apoptosis through activating the pro-survival PI3K/Akt/mTOR pathway. In conclusion, our study may identify FAM3A as a potential regulator of chondrocyte apoptosis involved in OA pathogenesis.

27-Hydroxycholesterol Inhibits Sterol Regulatory Element-Binding Protein 1 Activation and Hepatic Lipid Accumulation in Mice

OBJECTIVE

Although 27-hydroxycholesterol (27-HC) has been reported as a potent regulator of lipid homeostasis, its role in hepatic lipogenesis remains obscure. The present study was designed to investigate the impact of 27-HC on sterol regulatory element-binding protein 1 (SREBP-1) and hepatic steatosis.

METHODS

In this study, the 27-HC level in mice was upregulated by overexpressing CYP27A1 or treating primary hepatocytes with 27-HC, and then the hepatic lipid accumulation was detected.

RESULTS

27-HC inhibited hepatic lipid accumulation and decreased the levels of the mature active form of SREBP-1. The expression of lipogenic genes, including acetyl coenzyme A carboxylase, fatty acid synthase, stearoyl-coenzyme A desaturase-1, and glycerol-3-phosphate acyltransferase, were also suppressed after 27-HC intervention. Furthermore, 27-HC induced expression of insulin-induced gene-2 (Insig-2), an endoplasmic reticulum protein that prevents SREBP activation, both in vivo and in vitro. The inhibitory effect of 27-HC on SREBP-1 activation was absent when Insig-2 was silenced. Finally, coimmunoprecipitation showed that 27-HC promoted the binding of Insig-2 to SREBP-1.

CONCLUSIONS

These studies demonstrated the suppressive effect of 27-HC on hepatic lipid accumulation and revealed a novel mechanism by which 27-HC regulates lipogenesis.

FAM3 gene family: A promising therapeutical target for NAFLD and type 2 diabetes

Non-alcoholic fatty liver disease (NAFLD) and diabetes are severe public health issues worldwide. The Family with sequence similarity 3 (FAM3) gene family consists of four members designated as FAM3A, FAM3B, FAM3C and FAM3D, respectively. Recently, there had been increasing evidence that FAM3A, FAM3B and FAM3C are important regulators of glucose and lipid metabolism. FAM3A expression is reduced in the livers of diabetic rodents and NAFLD patients. Hepatic FAM3A restoration activates ATP-P2 receptor-Akt and AMPK pathways to attenuate steatosis and hyperglycemia in obese diabetic mice. FAM3C expression is also reduced in the liver under diabetic condition. FAM3C is a new hepatokine that activates HSF1-CaM-Akt pathway and represses mTOR-SREBP1-FAS pathway to suppress hepatic gluconeogenesis and lipogenesis. In contrast, hepatic expression of FAM3B, also called PANDER, is increased under obese state. FAM3B promotes hepatic lipogenesis and gluconeogenesis by repressing Akt and AMPK activities, and activating lipogenic pathway. Under obese state, the imbalance among hepatic FAM3A, FAM3B and FAM3C signaling networks plays important roles in the pathogenesis of NAFLD and type 2 diabetes. This review briefly discussed the latest research progress on the roles and mechanisms of FAM3A, FAM3B and FAM3C in the regulation of hepatic glucose and lipid metabolism.