Type 2 diabetes (T2D) results from insulin resistance and inadequate insulin secretion. Insulin resistance initially causes compensatory islet hyperplasia that progresses to islet disorganization and altered vascularization, inflammation, and, finally, decreased functional β-cell mass and hyperglycemia. The precise mechanism(s) underlying β-cell failure remain to be elucidated. In this study, we show that in insulin-resistant high-fat diet-fed mice, the enhanced islet vascularization and inflammation was parallel to an increased expression of vascular endothelial growth factor A (VEGF). To elucidate the role of VEGF in these processes, we have genetically engineered β-cells to overexpress VEGF (in transgenic mice or after adeno-associated viral vector-mediated gene transfer). We found that sustained increases in β-cell VEGF levels led to disorganized, hypervascularized, and fibrotic islets, progressive macrophage infiltration, and proinflammatory cytokine production, including tumor necrosis factor-α and interleukin-1β. This resulted in impaired insulin secretion, decreased β-cell mass, and hyperglycemia with age. These results indicate that sustained VEGF upregulation may participate in the initiation of a process leading to β-cell failure and further suggest that compensatory islet hyperplasia and hypervascularization may contribute to progressive inflammation and β-cell mass loss during T2D.

Triglyceride accumulation in nonalcoholic fatty liver (NAFL) results from unbalanced lipid metabolism which, in the liver, is controlled by several transcription factors. The Foxa subfamily of winged helix/forkhead box (Fox) transcription factors comprises three members which play important roles in controlling both metabolism and homeostasis through the regulation of multiple target genes in the liver, pancreas and adipose tissue. In the mouse liver, Foxa2 is repressed by insulin and mediates fasting responses. Unlike Foxa2 however, the role of Foxa1 in the liver has not yet been investigated in detail. In this study, we evaluate the role of Foxa1 in two human liver cell models, primary cultured hepatocytes and HepG2 cells, by adenoviral infection. Moreover, human and rat livers were analyzed to determine Foxa1 regulation in NAFL. Results demonstrate that Foxa1 is a potent inhibitor of hepatic triglyceride synthesis, accumulation and secretion by repressing the expression of multiple target genes of these pathways (e.g., GPAM, DGAT2, MTP, APOB). Moreover, Foxa1 represses the fatty acid transporter protein FATP2 and lowers fatty acid uptake. Foxa1 also increases the breakdown of fatty acids by inducing peroxisomal fatty acid β-oxidation and ketone body synthesis. Finally, Foxa1 is able to largely up-regulate UCP1, thereby dissipating energy and consistently decreasing the mitochondria membrane potential. We also report that human and rat NAFL have a reduced Foxa1 expression, possibly through a protein kinase C-dependent pathway. We conclude that Foxa1 is an antisteatotic factor that coordinately tunes several lipid metabolic pathways to block triglyceride accumulation in hepatocytes. However, Foxa1 is down-regulated in human and rat NAFL and, therefore, increasing Foxa1 levels could protect from steatosis. Altogether, we suggest that Foxa1 could be a novel therapeutic target for NAFL disease and insulin resistance.

Type 1 diabetic patients are diagnosed when ␤-cell destruction is almost complete. Reversal of type 1 diabetes will require ␤-cell regeneration from islet cell precursors and prevention of recurring autoimmunity. IGF-I expression in ␤-cells of streptozotocin (STZ)-treated transgenic mice regenerates the endocrine pancreas by increasing ␤-cell replication and neogenesis. Here, we examined whether IGF-I also protects islets from autoimmune destruction. Expression of interferon (IFN)-␤ in

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Hepatocyte nuclear factor 4-alpha (HNF4alpha, NR2A1) is a nuclear receptor (NR) required for liver development and for controlling the expression of many hepatic-specific genes associated with important metabolic pathways. Many studies have also identified HNF4alpha as a direct transactivator of numerous xenobiotic-metabolizing cytochrome P450 (CYP) genes, suggesting that this factor is a global regulator which supports CYP transcription in the liver. Moreover, HNF4alpha expression displays a significant variability in human liver which may account for a proportion of the inter-individual variability in the expression of drug-metabolism genes and the clearance rate of a wide variety of prescribed drugs. In the last few years, a number of complex interactions and cross-talks between HNF4alpha and other transcription factors and coregulators have also surfaced, and the impact on CYP gene expression has been demonstrated. Thus, it is now clear that HNF4alpha modulates CYP expression in the liver by interacting with the xenosensor receptors (PXR and CAR), the glucocorticoid receptor (GR), the feeding-fasting cycle target PGC-1alpha, the sexual-dimorphism factor Stat5b, and other liver-enriched factors, such as C/EBPs. In addition to regulating drug elimination pathways, HNF4alpha also triggers pleiotropic effects on cholesterol and fatty acid metabolism, glucose homeostasis and inflammation. As a whole, current evidence indicates that HNF4alpha is a central regulator in the network of NRs that integrates drug-metabolism not only with the liver intermediate metabolism, but also with a number of patho-physiological conditions where the CYP expression is altered. The purpose of this review is to summarize and discuss these studies and their conclusions, with particular emphasis on the role of HNF4alpha in the regulation of drug-metabolizing CYP genes in the human liver.

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It is estimated that only a few marketed drugs are able to directly induce liver steatosis. However, many other drugs may exacerbate or precipitate fatty liver in the presence of other risk factors or in patients prone to non-alcoholic fatty liver disease. On the other hand, current in vitro tests for drug-induced steatosis in preclinical research are scarce and not very sensitive or reproducible. In the present study, we have investigated the effect of well-characterized steatotic drugs on the expression profile of 47 transcription factors (TFs) in human hepatoma HepG2 cells and found that these drugs are able to up- and down-regulate a substantial number of these factors. Multivariate data analysis revealed a common TF signature for steatotic drugs, which consistently and significantly repressed FOXA1, HEX and SREBP1C in cultured cells. This signature was also observed in the livers of rats and in cultured human hepatocytes. Therefore, we selected these three TFs as predictive biomarkers for iatrogenic steatosis. With these biomarkers, a logistic regression analysis yielded a predictive model, which was able to correctly classify 92 % of drugs. The developed algorithm also predicted that ibuprofen, nifedipine and irinotecan are potential steatotic drugs, whereas troglitazone is not. In summary, this is a sensitive, specific and simple RT-PCR test that can be easily implemented in preclinical drug development to predict drug-induced steatosis. Our results also indicate that steatotic drugs affect expression of both common and specific subsets of TF and lipid metabolism genes, thus generating complex transcriptomic responses that cause or contribute to steatosis in hepatocytes.