Upregulation of pancreatic derived factor (FAM3B) expression in pancreatic β-cells by MCP-1 (CCL2)

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.

Fam3c modulates osteogenic differentiation by down-regulating Runx2

Fam3c, a cytokine-like protein, is a member of the Fam3 family (family with sequence similarity 3) and has been implicated to play a crucial role in Epithelial-to- mesenchymal transition (EMT) and subsequent metastasis during cancer progression. A few independent genome-wide association studies on different population cohorts predicted the gene locus of Fam3c to be associated with bone mineral density and fractures. In this study, we examined the role of Fam3c during osteoblast differentiation. Fam3c was found to be expressed during osteogenic differentiation of both primary bone marrow stromal cells and MC3T3-E1 pre-osteoblasts. In differentiating osteoblasts, knockdown of Fam3c increased alkaline phosphatase expression and activity whereas overexpression of Fam3c reduced it. Furthermore, overexpression of Fam3c caused reduction of Runx2 expression at both mRNA and protein levels. Fam3c was localized in the cytoplasm and it was not secreted outside the cell during osteoblast differentiation and therefore, may function intracellularly. Furthermore, Fam3c and TGF-β1 were found to regulate each other reciprocally. Our findings therefore suggest a functional role of Fam3c in the regulation of osteoblast differentiation.

Quantitative proteomic profiling reveals hepatic lipogenesis and liver X receptor activation in the PANDER transgenic model

PANcreatic-DERived factor (PANDER) is a member of a superfamily of FAM3 proteins modulating glycemic levels by metabolic regulation of the liver and pancreas. The precise PANDER-induced hepatic signaling mechanism is still being elucidated and has been very complex due to the pleiotropic nature of this novel hormone. Our PANDER transgenic (PANTG) mouse displays a selective hepatic insulin resistant (SHIR) phenotype whereby insulin signaling is blunted yet lipogenesis is increased, a phenomena observed in type 2 diabetes. To examine the complex PANDER-induced mechanism of SHIR, we utilized quantitative mass spectrometry-based proteomic analysis using Stable Isotope Labeling by Amino Acids in Cell Culture (SILAC) to reveal the global hepatic proteome differences within the PANTG under the metabolic states of fasting, fed and insulin-stimulated conditions. Proteomic analysis identified lipid metabolism as one of the top cellular functions differentially altered in all metabolic states. Differentially expressed proteins within the PANTG having a lipid metabolic role included ACC, ACLY, CD36, CYP7A1, FASN and SCD1. Central to the differentially expressed proteins involved in lipid metabolism was the predicted activation of the liver X receptor (LXR) pathway. Western analysis validated the increased hepatic expression of LXRα along with LXR-directed targets such as FASN and CYP7A1 within the PANTG liver. Furthermore, recombinant PANDER was capable of inducing LXR promoter activity in-vitro as determined by luciferase reporter assays. Taken together, PANDER strongly impacts hepatic lipid metabolism across metabolic states and may induce a SHIR phenotype via the LXR pathway.

Endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

Insulin-secreting pancreatic β-cells are extremely dependent on their endoplasmic reticulum (ER) to cope with the oscillatory requirement of secreted insulin to maintain normoglycemia. Insulin translation and folding rely greatly on the unfolded protein response (UPR), an array of three main signaling pathways designed to maintain ER homeostasis and limit ER stress. However, prolonged or excessive UPR activation triggers alternative molecular pathways that can lead to β-cell dysfunction and apoptosis. An increasing number of studies suggest a role of these pro-apoptotic UPR pathways in the downfall of β-cells observed in diabetic patients. Particularly, the past few years highlighted a cross talk between the UPR and inflammation in the context of both type 1 (T1D) and type 2 diabetes (T2D). In this article, we describe the recent advances in research regarding the interplay between ER stress, the UPR, and inflammation in the context of β-cell apoptosis leading to diabetes.

Intermuscular adipose tissue is associated with monocyte chemoattractant protein-1, independent of visceral adipose tissue

OBJECTIVES

Emerging evidence suggests that intermuscular adipose tissue is a risk factor for insulin resistance, but the underlying mechanism still remains unclear. We investigated whether the levels of leptin, adiponectin, and monocyte chemoattractant protein-1 are associated with intermuscular adipose tissue in obese subjects.

DESIGN AND METHODS

A cross-sectional study was performed on 77 obese Korean women. Areas of visceral adipose tissue, subcutaneous adipose tissue, and intermuscular adipose tissue were measured by computed tomography scan, and serum concentrations of adipokines were measured by enzyme-linked immunosorbent assays. Correlation between the levels of adipokines and the fat areas was assessed using Pearson correlation and covariate-adjusted multivariable regression.

RESULTS

Leptin was positively correlated with subcutaneous adipose tissue (r=0.452, P<0.001), fasting insulin (r=0.403, P<0.001), and homeostasis model assessment of insulin resistance (r=0.360, P=0.001), whereas monocyte chemoattractant protein-1 was positively correlated with intermuscular adipose tissue (r=0.483, P<0.001). After adjustment for age, height, and other body composition metrics, leptin was still related to subcutaneous adipose tissue (β=0.390, P=0.001). Monocyte chemoattractant protein-1 was associated with intermuscular adipose tissue (β=0.433, P=0.001) after adjustment for visceral adipose tissue.

CONCLUSIONS

Intermuscular adipose tissue was correlated with monocyte chemoattractant protein-1, suggesting its role in the development of insulin resistance.

Family with sequence similarity 3 gene family and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) comprises a disease spectrum ranging from simple steatosis (fatty liver) and nonalcoholic steatohepatitis to fibrosis and cirrhosis. NAFLD has become the leading cause of chronic liver diseases as well as liver-related morbidity and mortality worldwide. NAFLD is also associated with increased risk of cardiovascular diseases, hyperlipidemia, and type 2 diabetes. Insulin resistance in adipose tissues and the liver plays crucial roles in the progression of NAFLD. The family with sequence similarity 3 (FAM3) gene family is a cytokine-like gene family with four members designated FAM3A, FAM3B, FAM3C, and FAM3D, respectively. Increasing evidence suggests that the FAM3 gene family members are involved in the pathogenesis of NAFLD. In particular, FAM3B, also called pancreatic-derived factor, is an important regulator of glucose and lipid metabolism. In obesity status, increased expression and secretion of FAM3B in pancreatic islets and liver may induce lipid accumulation in the liver via the induction of hepatic insulin resistance and lipogenesis. FAM3A and FAM3D may also participate in the regulation of lipid and energy metabolism. In this brief review, we discussed the latest findings regarding the role of FAM3 gene family members, in particular FAM3B, in the pathogenesis of NAFLD.

Effect of PANDER in βTC6-cell lipoapoptosis and the protective role of exendin-4

Chronic exposure to high concentrations of saturated fatty acids, such as palmitic acid (PA), leads to apoptosis of pancreatic β-cells through the activation of the c-Jun N-terminal kinase (JNK) signaling pathway. This study of β-cell lipoapoptosis was designed to investigate the roles of pancreatic-derived factor (PANDER), a pro-apoptosis cytokine-like peptide, and exendin-4, a long-acting agonist of the hormone glucagon-like peptide-1 (GLP-1) receptor and anti-apoptosis factor. The glucose-sensitive mouse β-pancreatic cell line, βTC6, was used to investigate the mechanisms of PA-induced apoptosis. Twenty-four hours of PA exposure led to increased PANDER expression in a dose- and time-dependent manner, and significantly increased phosphorylation of JNK. Treatment with the JNK-specific inhibitor SP600125 reduced the PA-induced PANDER expression. After the 24h of PA exposure, cells also underwent marked apoptosis and showed increased activation of the apoptosis protease, caspase-3. The small interfering (si)RNA-mediated silencing of PANDER gene expression significantly reduced both of these effects. When PA-treated βTC6 cells were exposed to exogenous exendin-4, JNK activation was inhibited, PANDER expression was decreased, and the numbers of apoptotic cells were reduced. Collectively, these results demonstrated that the JNK-mediated signaling mechanism of PA-induced β-cell apoptosis involves up-regulated expression of PANDER and activation of caspase-3. Exendin-4 may protect against lipoapoptosis by interfering with the JNK-PANDER pathway.