Accumulation of cytoplasmic triacylglycerol (TG) underlies hepatic steatosis, a major cause of cirrhosis. The pathways of cytoplasmic TG metabolism are not well known in hepatocytes, but evidence suggests an important role in lipolysis for adipose triglyceride lipase (ATGL). We created mice with liver-specific inactivation of Pnpla2, the ATGL gene. These ATGLLKO mice had severe progressive periportal macrovesicular and pericentral microvesicular hepatic steatosis (73, 150, and 226 lmol TG/g liver at 4, 8, and 12 months, respectively). However, plasma levels of glucose, TG, and cholesterol were similar to those of controls. Fasting 3-hydroxybutyrate level was normal, but in thin sections of liver, beta oxidation of palmitate was decreased by one-third in ATGLLKO mice compared with controls. Tests of very low-density lipoprotein production, glucose, and insulin tolerance and gluconeogenesis from pyruvate were normal. Plasma alanine aminotransferase levels were elevated in ATGLLKO mice, but histological estimates of inflammation and fibrosis and messenger RNA (mRNA) levels of tumor necrosis factor-a and interleukin-6 were similar to or lower than those in controls. ATGLLKO cholangiocytes also showed cytoplasmic lipid droplets, demonstrating that ATGL is also a major lipase in cholangiocytes. There was a 50-fold reduction of hepatic diacylglycerol acyltransferase 2 mRNA level and a 2.7-fold increase of lipolysosomes in hepatocytes (P < 0.001), suggesting reduced TG synthesis and increased lysosomal degradation of TG as potential compensatory mechanisms. Conclusion: Compared with the hepatic steatosis of obesity and diabetes, steatosis in ATGL deficiency is well tolerated metabolically. ATGLLKO mice will be useful for studying the pathophysiology of hepatic steatosis. (HEPATOLOGY 2011;54:122-132)

MicroRNAs (miRNAs) are small ∼22-nt regulatory RNAs that regulate the stability and translation of cognate mRNAs. MiRNAs participate in the regulation of adipogenesis, and identification of the full repertoire of miRNAs expressed in adipose tissue is likely to significantly increase our understanding of adipose tissue growth and development. Here, we adopted a deep sequencing approach to determine the identity and abundance of miRNAs in developing swine adipose tissue. Via this approach, we identified the sequences and relative expression levels of 227 conserved miRNAs (of which 59 were novel) and 66 potential porcine miRNAs. The expression levels displayed a large range, as reflected by the number of sequence reads, which varied from several counts for rare miRNAs to several million reads for the most abundant miRNAs. The abundant miRNAs principally belonged to 32 miRNA gene families, including miR-143, miR-103, let-7, and miR-148. Of the conserved miRNAs, 93 miRNAs were up-regulated and 33 miRNAs were down-regulated in the adult pig adipose tissue. Moreover, we observed sequence variants and seed edits of the miRNAs. KEGG pathway analysis and GO term enrichment suggested that highly expressed miRNAs are involved in adipose tissue development, signal transduction, cell-cell and cell-extracellular matrix communication, neural development and function, and lipid metabolism including carboxylic acid, oxoacid, fatty acid, steroid, glycerolipid, alcohol and phospholipid metabolism. Our results expand the number of known porcine miRNAs and provide a thorough account of the miRNA transcriptome in porcine adipose tissue.

Sirt1, a NAD + -dependent histone deacetylase, may regulate senescence, metabolism, and apoptosis. In this study, primary pig preadipocytes were cultured in DMEM/F12 medium containing 10% fetal bovine serum (FBS) with or without reagents affecting Sirt1 activity. The adipocyte differentiation process was visualized by light microscopy after Oil red O staining. Proliferation and differentiation of preadipocytes was measured using methylthiazolyldiphenyl-tetrazolium bromide (MTT) and Oil red O extraction. Expression of Sirt1, FoxO1, and adipocyte specific genes was detected with semi-quantitive RT-PCR. The results showed that Sirt1 mRNA was widely expressed in various pig tissues from different developmental stages. Sirt1 mRNA was expressed throughout the entire differentiation process of pig preadipocytes. Resveratrol significantly increased Sirt1 mRNA expression, but decreased the expression of FoxO1 and adipocyte marker gene PPARc2. Resveratrol significantly inhibited pig preadipocyte proliferation and differentiation. Nicotinamide decreased the expression of Sirt1 mRNA, but increased the expression of FoxO1 and adipocyte specific genes. Nicotinamide greatly stimulated the proliferation and differentiation of pig preadipocytes. In conclusion, these results indicate that Sirt1 may modulate the proliferation and differentiation of pig preadipocytes. Sirt1 may down-regulate pig preadipocytes proliferation and differentiation through repression of adipocyte genes or FoxO1.