Non-alcoholic fatty liver disease (NAFLD) is a clinicopathological change characterized by the accumulation of triglycerides in hepatocytes and has frequently been associated with obesity, type 2 diabetes mellitus, hyperlipidemia, and insulin resistance. It is an increasingly recognized condition that has become the most common liver disorder in developed countries, affecting over one-third of the population and is associated with increased cardiovascular- and liver-related mortality. NAFLD is a spectrum of disorders, beginning as simple steatosis. In about 15% of all NAFLD cases, simple steatosis can evolve into non-alcoholic steatohepatitis, a medley of inflammation, hepatocellular injury, and fibrosis, often resulting in cirrhosis and even hepatocellular cancer. However, the molecular mechanism underlying NAFLD progression is not completely understood. Its pathogenesis has often been interpreted by the "double-hit" hypothesis. The primary insult or the "first hit" includes lipid accumulation in the liver, followed by a "second hit" in which proinflammatory mediators induce inflammation, hepatocellular injury, and fibrosis. Nowadays, a more complex model suggests that fatty acids (FAs) and their metabolites may be the true lipotoxic agents that contribute to NAFLD progression; a multiple parallel hits hypothesis has also been suggested. In NAFLD patients, insulin resistance leads to hepatic steatosis via multiple mechanisms. Despite the excess hepatic accumulation of FAs in NAFLD, it has been described that not only de novo FA synthesis is increased, but FAs are also taken up from the serum. Furthermore, a decrease in mitochondrial FA oxidation and secretion of very-low-density lipoproteins has been reported. This review discusses the molecular mechanisms that underlie the pathophysiological changes of hepatic lipid metabolism that contribute to NAFLD.

Autophagy genes' expression is upregulated in visceral fat in human obesity, associating with obesity-related cardio-metabolic risk. E2F1 (E2F transcription factor 1) was shown in cancer cells to transcriptionally regulate autophagy. We hypothesize that E2F1 regulates adipocyte autophagy in obesity, associating with endocrine/metabolic dysfunction, thereby, representing non-cell-cycle function of this transcription factor. E2F1 protein (N=69) and mRNA (N=437) were elevated in visceral fat of obese humans, correlating with increased expression of ATG5 (autophagy-related 5), MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3 β), but not with proliferation/cell-cycle markers. Elevated E2F1 mainly characterized the adipocyte fraction, whereas MKI67 (marker of proliferation Ki-67) was elevated in the stromal-vascular fraction of adipose tissue. In human visceral fat explants, chromatin-immunoprecipitation revealed body mass index (BMI)-correlated increase in E2F1 binding to the promoter of MAP1LC3B, but not to the classical cell cycle E2F1 target, CCND1 (cyclin D1). Clinically, omental fat E2F1 expression correlated with insulin resistance, circulating free-fatty-acids (FFA), and with decreased circulating ADIPOQ/adiponectin, associations attenuated by adjustment for autophagy genes. Overexpression of E2F1 in HEK293 cells enhanced promoter activity of several autophagy genes and autophagic flux, and sensitized to further activation of autophagy by TNF. Conversely, mouse embryonic fibroblast (MEF)-derived adipocytes from e2f1 knockout mice (e2f1^−/−) exhibited lower autophagy gene expression and flux, were more insulin sensitive, and secreted more ADIPOQ. Furthermore, e2f1^−/− MEF-derived adipocytes, and autophagy-deficient (by Atg7 siRNA) adipocytes were resistant to cytokines-induced decrease in ADIPOQ secretion. Jointly, upregulated E2F1 sensitizes adipose tissue autophagy to inflammatory stimuli, linking visceral obesity to adipose and systemic metabolic-endocrine dysfunction.

Preferential fat accumulation in visceral vs. subcutaneous depots makes obese individuals more prone to metabolic complications. Body fat distribution (FD) is regulated by genetics. FD patterns vary across ethnic groups independent of obesity. Asians have more and Africans have less visceral fat compared with Europeans. Consequently, Asians tend to be more susceptible to type 2 diabetes even with lower BMIs when compared with Europeans. To date, genome-wide association studies (GWAS) have identified more than 460 loci related to FD traits. However, the majority of these data were generated in European populations. In this review, we aimed to summarize recent advances in FD genetics with a focus on comparisons between European and non-European populations (Asians and Africans). We therefore not only compared FD-related susceptibility loci identified in three ethnicities but also discussed whether known genetic variants might explain the FD pattern heterogeneity across different ancestries. Moreover, we describe several novel candidate genes potentially regulating FD, including NID2, HECTD4 and GNAS, identified in studies with Asian populations. It is of note that in agreement with current knowledge, most of the proposed FD candidate genes found in Asians belong to the group of developmental genes.

Objective: Bone morphogenetic proteins (BMPs) are important regulators of adipogenesis and may play a role in obesity. In this study, the hypothesis that BMP2 is related to adipose tissue (AT) distribution in obesity was tested.Methods: BMP2 serum concentration (n = 439) and BMP2 and Schnurri‐1 and −2 mRNA expression were measured in paired samples of visceral and subcutaneous AT from 547 individuals with a wide range of body mass index. In addition, a single nucleotide polymorphism rs979012 in the BMP2 gene was genotyped for subsequent association studies on quantitative traits related to obesity in 631 individuals.Results: BMP2 and Schnurri‐1 mRNA were significantly higher in visceral compared with subcutaneous AT. Compared with individuals who were healthy and lean, BMP2 expression in both depots was significantly higher in people with obesity. Significantly higher BMP2 serum concentrations were found in patients with type 2 diabetes with moderate but not morbid obesity. Schnurri‐1 and −2 mRNA expression was not related to either BMP2 expression or circulating BMP2. Finally, rs979012 showed nominal association with body mass index and total cholesterol levels.Conclusions: Data suggest that with increasing demand to store excessive energy, AT BMP2 expression increases and may contribute to partitioning of energy storage into visceral and subcutaneous AT depots.

Background/Objectives: Non-alcoholic fatty liver disease (NAFLD) causes a wide spectrum of liver damage, from simple steatosis (SS) to cirrhosis. SS and non-alcoholic steatohepatitis (NASH) cannot be distinguished by clinical or laboratory features. Dysregulation of the gut microbiota is involved in NASH pathogenesis. The aim of this study was to assess the relationship between microbiota-derived metabolites and the degrees of NAFLD; also, to investigate whether these metabolites could be included in a panel of NASH biomarkers. Subjects/Methods: We used liquid chromatography coupled to triple-quadrupole-mass spectrometry (LC-QqQ) analysis to quantify choline and its derivatives, betaine, endogenous ethanol, bile acids, short-chain fatty acids and soluble TLR4 in serum from women with normal weight (n = 29) and women with morbid obesity (MO) (n = 82) with or without NAFLD. We used real-time polymerase chain reaction (RT-PCR) analysis to evaluate the hepatic and intestinal expression level of all genes studied (TLR2, TLR4, TLR9, LXRα, SREBP1C, ACC1, FAS, PPARα, CPT1α, CROT, SREBP2, ABCA1, ABCG1 and FXR in the liver; TLR2, TLR4, TLR5, TLR9, GLP-1R, DPP-4, FXR and PPARɣ in the jejunum) in 82 women with MO with normal liver histology (NL, n = 29), SS (n = 32), and NASH (n = 21). Results: Hepatic FAS, TLR2, and TLR4 expression were overexpressed in NAFLD patients. TLR2 was overexpressed in NASH patients. In women with MO with NAFLD, we found upregulation of intestinal TLR9 expression and downregulation of intestinal FXR expression in women with NASH. Circulating TMAO, glycocholic acid and deoxycholic acid levels were significantly increased in NAFLD patients. Endogenous circulating ethanol levels were increased in NASH patients in comparison to those in SS patients. Conclusions: These findings suggest that the intestine participates in the progression of NAFLD. Moreover, levels of certain circulating microbiota-related metabolites are associated with NAFLD severity and could be used as a “liquid biopsy” in the noninvasive diagnosis of NASH.