Local thiamet-G delivery by a thermosensitive hydrogel confers ischemic cardiac repair via myeloid M2-like activation in a STAT6 O-GlcNAcylation-dependent manner.

Infarct healing requires a dynamic and orchestrated inflammatory reaction following myocardial infarction (MI). While an uncontrolled excessive inflammatory response exaggerates ischemic injury post-MI, M2-like reparative macrophages may facilitate inflammation regression and promote myocardial healing. However, how protein post-translational modification regulates post-MI cardiac repair and dynamic myeloid activation remains unknown. Here we show that M2-like reparative, but not M1-like inflammatory activation, is enhanced by pharmacologically-induced hyper-O-GlcNAcylation. Mechanistically, myeloid knockdown of O-GlcNAc hydrolase O-GlcNAcase (Oga), which also results in hyper-O-GlcNAcylation, positively regulates M2-like activation in a STAT6-dependent fashion, which is controlled by O-GlcNAcylation of STAT6. Of note, both systemic and local supplementation of thiamet-G (TMG), an Oga inhibitor, effectively facilitates cardiac recovery in mice by elevating the accumulation of M2-like macrophages in infarcted hearts. Our study provides a novel clue for monocyte/macrophage modulating therapies aimed at reducing post-MI hyperinflammation in ischemic myocardium.

Endothelial Sp1/Sp3 are essential to the effect of captopril on blood pressure in male mice.

Endothelial dysfunction represents a major cardiovascular risk factor for hypertension. Sp1 and Sp3 belong to the specificity protein and Krüppel-like transcription factor families. They are ubiquitously expressed and closely associated with cardiovascular development. We investigate the role of Sp1 and Sp3 in endothelial cells in vivo and evaluate whether captopril, an angiotensin-converting enzyme inhibitor (ACEI), targets Sp1/Sp3 to exert its effects. Inducible endothelial-specific Sp1/Sp3 knockout mice are generated to elucidate their role in endothelial cells. Tamoxifen-induced deletion of endothelial Sp1 and Sp3 in male mice decreases the serum nitrite/nitrate level, impairs endothelium-dependent vasodilation, and causes hypertension and cardiac remodeling. The beneficial actions of captopril are abolished by endothelial-specific deletion of Sp1/Sp3, indicating that they may be targets for ACEIs. Captopril increases Sp1/Sp3 protein levels by recruiting histone deacetylase 1, which elevates deacetylation and suppressed degradation of Sp1/Sp3. Sp1/Sp3 represents innovative therapeutic target for captopril to prevent cardiovascular diseases.

Intestinal Epithelial STAT6 Activation Rescues the Defective Anti-Helminth Responses Caused by Ogt Deletion.

Dynamic regulation of intestinal epithelial cell (IEC) proliferation and differentiation is crucial for maintaining mucosa homeostasis and the response to helminth infection. O-GlcNAc transferase (OGT), an enzyme catalyzing the transfer of GlcNAc from the donor substrate UDP-GlcNAc onto acceptor proteins, has been proposed to promote intestinal epithelial remodeling for helminth expulsion by modifying and activating epithelial STAT6, but whether the IEC intrinsic OGT-STAT6 axis is involved in anti-helminth responses has not been tested in vivo. Here, we show that the inducible deletion of Ogt in IECs of adult mice leads to reduced tuft and goblet cell differentiation, increased crypt cell proliferation, and aberrant Paneth cell localization. By using a mouse model with concurrent Ogt deletion and STAT6 overexpression in IECs, we provide direct in vivo evidence that STAT6 acts downstream of OGT to control tuft and goblet cell differentiation in IECs. However, epithelial OGT regulates crypt cell proliferation and Paneth cell differentiation in a STAT6-independent pathway. Our results verify that protein O-GlcNAcylation in IECs is crucial for maintaining epithelial homeostasis and anti-helminthic type 2 immune responses.

Sirtuin 6 maintains epithelial STAT6 activity to support intestinal tuft cell development and type 2 immunity.

Dynamic regulation of intestinal epithelial cell (IEC) differentiation is crucial for both homeostasis and the response to helminth infection. SIRT6 belongs to the NAD+-dependent deacetylases and has established diverse roles in aging, metabolism and disease. Here, we report that IEC Sirt6 deletion leads to impaired tuft cell development and type 2 immunity in response to helminth infection, thereby resulting in compromised worm expulsion. Conversely, after helminth infection, IEC SIRT6 transgenic mice exhibit enhanced epithelial remodeling process and more efficient worm clearance. Mechanistically, Sirt6 ablation causes elevated Socs3 expression, and subsequently attenuated tyrosine 641 phosphorylation of STAT6 in IECs. Notably, intestinal epithelial overexpression of constitutively activated STAT6 (STAT6vt) in mice is sufficient to induce the expansion of tuft and goblet cell linage. Furthermore, epithelial STAT6vt overexpression remarkedly reverses the defects in intestinal epithelial remodeling caused by Sirt6 ablation. Our results reveal a novel function of SIRT6 in regulating intestinal epithelial remodeling and mucosal type 2 immunity in response to helminth infection.

αSMA-Cre-mediated Ogt deletion leads to heart failure and vascular smooth muscle cell dysfunction in mice.

Dilated cardiomyopathy, a type of heart muscle disease defined by the presence of left ventricular dilatation and contractile dysfunction, is an important cause of sudden cardiac death and heart failure. O-GlcNAcylation is an important post-translational modification of proteins by the addition of O-GlcNAc moieties at serine or threonine residues. Several studies have shown that proper control of O-GlcNAcylation is required for maintaining physiological function of heart by using Ogt (O-GlcNAc transferase) cardiomyocyte-specific knockout mouse models. In this study, we generated a new mouse model (αSMA-Ogt KO) in which Ogt was deleted in both cardiomyocytes and smooth muscle cells by crossing Ogt floxed mice with αSMA-Cre mice. αSMA-Cre-mediated Ogt deletion in mice led to severe postnatal lethality; the survived mice were smaller than control mice, had dilated hearts, and showed observable signs of heart failure. Moreover, the αSMA-Ogt KO heart had more apoptotic cells and fibrosis. The arteries of αSMA-Ogt KO mice exhibited significantly reduced expression of contractile genes and a trend towards arterial stiffness. In conclusion, our data emphasize the importance of OGT in maintaining normal heart function and reveal a novel role of OGT in regulating arterial contractility.

Epithelial STAT6 O-GlcNAcylation drives a concerted anti-helminth alarmin response dependent on tuft cell hyperplasia and Gasdermin C.

The epithelium is an integral component of mucosal barrier and host immunity. Following helminth infection, the intestinal epithelial cells secrete "alarmin" cytokines, such as interleukin-25 (IL-25) and IL-33, to initiate the type 2 immune responses for helminth expulsion and tolerance. However, it is unknown how helminth infection and the resulting cytokine milieu drive epithelial remodeling and orchestrate alarmin secretion. Here, we report that epithelial O-linked N-Acetylglucosamine (O-GlcNAc) protein modification was induced upon helminth infections. By modifying and activating the transcription factor STAT6, O-GlcNAc transferase promoted the transcription of lineage-defining Pou2f3 in tuft cell differentiation and IL-25 production. Meanwhile, STAT6 O-GlcNAcylation activated the expression of Gsdmc family genes. The membrane pore formed by GSDMC facilitated the unconventional secretion of IL-33. GSDMC-mediated IL-33 secretion was indispensable for effective anti-helminth immunity and contributed to induced intestinal inflammation. Protein O-GlcNAcylation can be harnessed for future treatment of type 2 inflammation-associated human diseases.

NAMPT-mediated NAD+ biosynthesis suppresses activation of hepatic stellate cells and protects against CCl4-induced liver fibrosis in mice.

Background: Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step in the salvage pathway of mammalian nicotinamide adenine dinucleotide (NAD+) biosynthesis. Through its NAD+-biosynthetic activity, NAMPT is able to regulate the development of hepatic steatosis and inflammation induced by diet or alcohol. However, the roles NAMPT plays in the development of liver fibrosis remain obscure. Purpose: To investigate the roles of NAMPT-mediated NAD+ biosynthesis in hepatic stellate cell (HSC) activation and liver fibrosis. Research Design: Realtime RT-PCR and western blot analyses were performed to analyze the expression of profibrogenic genes. Sirius red staining was conducted to examine the fibrosis in liver. Mouse liver fibrosis was induced by intraperitoneal injection of carbon tetrachloride (CCl4) 2 times a week for 6 weeks. Adenovirus-mediated NAMPT overexpression or nicotinamide mononucleotide (NMN) administration was carried out to study the effects of elevation of NAD+ levels on protecting CCl4-induced liver fibrosis in mice. LX2 cells or primary HSCs were used to study the role of NAMPT overexpression or NMN treatment in reducing profibrogenic gene expression in vitro. ResultsCCl4 administration suppresses NAMPT expression in liver and reduces hepatic NAD+ content. Tgfß1 treatment decreases intracellular NAD+ levels and NAMPT expression in LX2 cells. Adenovirus-mediated NAMPT overexpression augments liver NAD+ levels, inhibits HSC activation and alleviates CCl4-induced liver fibrosis in mice. Administration of NMN also suppresses HSC activation and protects against CCl4-induced liver fibrosis in mice. Conclusions: NAMPT-mediated NAD+ biosynthesis inhibits HSC activation and protects against CCl4-induced liver fibrosis.

Inhibitor of Differentiation-2 Protein Ameliorates DSS-Induced Ulcerative Colitis by Inhibiting NF-κB Activation in Neutrophils.

The loss of inhibitor of differentiation-2 (ID2) could lead to the development of colitis in mice, supplementation with exogenous ID2 protein might be a potential strategy to ameliorate colitis. In this study, the effects of ID2 protein supplementation on Dextran sodium sulfate (DSS)-induced colitis were investigated. Firstly, we confirmed that the expression of ID2 was reduced in the colon tissues of DSS-induced colitis mice and patients with ulcerative colitis (UC). Then, we constructed a recombinant plasmid containing the human Id2 gene and expressed it in Escherichia coli (E. coli) successfully. After purification and identification, purified hID2 could ameliorate DSS-induced colitis efficiently in mice by improving disease symptoms, decreasing the levels of proinflammatory cytokines in colon tissues, maintaining the integrity of intestinal barrier and reducing the infiltration of neutrophils and macrophages in the colon. Further study showed that hID2 could be endocytosed efficiently by neutrophils and macrophages, and hID2 lost its protection function against colitis when neutrophils were depleted with an anti-Gr-1 antibody. hID2 decreased the mRNA levels of IL-6, IL-1ß and TNF-α in lipopolysaccharides (LPS)-stimulated neutrophils and efficiently inhibited the activation of NF-κB signalling pathway in neutrophils. Interestingly, hID2 showed a synergistic role in inhibition of NF-κB activation with pyrrolidine dithiocarbamic acid (PDTC), an inhibitor of NF-κB activation. Therefore, this study demonstrated the potential use of hID2 to treat UC, and hID2 protein might be a promising anti-inflammatory agent that targets the NF-κB signalling pathway in neutrophils.

Persistent mTORC1 activation via Depdc5 deletion results in spontaneous hepatocellular carcinoma but does not exacerbate carcinogen- and high-fat diet-induced hepatic carcinogenesis in mice.

The mechanistic target of rapamycin complex 1 (mTORC1) acts as a central regulator of metabolic pathways that drive cellular growth. Abnormal activation of mTORC1 occurs at high frequency in human and mouse hepatocellular carcinoma (HCC). DEP domain-containing protein 5 (DEPDC5), a component of GATOR1 complex, is a repressor of amino acid-sensing branch of the mTORC1 pathway. In the current study, we found that persistent activation of hepatic mTORC1 signaling caused by Depdc5 ablation was sufficient to induce a pathological program of liver damage, inflammation and fibrosis that triggers spontaneous HCC development. Take advantage of the combinatory treatment with a single dose of diethylnitrosamine (DEN) and chronic feeding with high-fat diet (HFD), we demonstrated that hepatic depdc5 deletion did not aggravate DEN&HFD induced liver tumorigenesis, probably due to its protective effects on diet-induced liver steatosis. In addition, we further showed that chronic rapamycin treatment did not have any apparent tumor-suppressing effects on DEN&HFD treated control mice, whereas it dramatically reduced the tumor burden in mice with hepatic Depdc5 ablation. This study provides the novel in vivo evidence for Depdc5 deletion mediated mTORC1 hyperactivation in liver tumorigenesis caused by aging or DEN&HFD treatment. Moreover, our findings also propose that pharmacological inhibition of mTORC1 signaling maybe a promising strategy to treat HCC patients with mutations in DEPDC5 gene.

Mitochondrial protein IF1 is a potential regulator of glucagon-like peptide (GLP-1) secretion function of the mouse intestine.

IF1 (ATPIF1) is a nuclear DNA-encoded mitochondrial protein whose activity is inhibition of the F1Fo-ATP synthase to control ATP production. IF1 activity remains unknown in the regulation of GLP-1 activity. In this study, IF1 was examined in the diet-induced obese mice using the gene knockout (If1-KO) mice. The mice gained more body weight on a high fat diet without a change in food intake. Insulin tolerance was impaired, but the oral glucose tolerance was improved through an increase in GLP-1 secretion. The KO mice exhibited an improved intestine structure, mitochondrial superstructure, enhanced mitophagy, reduced apoptosis and decreased adenine nucleotide translocase 2 (ANT2) protein in the intestinal epithelial cells together with preserved gut microbiota. The data suggest that GLP-1 secretion was enhanced in the obese If1-KO mice to preserve glucose tolerance through a signaling pathway of ANT2/mitochondria/L-cells/GLP-1/insulin. IF1 is a potential mitochondrial target for induction of GLP-1 secretion in L-cells.

Depdc5 deficiency exacerbates alcohol-induced hepatic steatosis via suppression of PPARα pathway.

Alcohol-related liver disease (ALD), a condition caused by alcohol overconsumption, occurs in three stages of liver injury including steatosis, hepatitis, and cirrhosis. DEP domain-containing protein 5 (DEPDC5), a component of GAP activities towards Rags 1 (GATOR1) complex, is a repressor of amino acid-sensing branch of the mammalian target of rapamycin complex 1 (mTORC1) pathway. In the current study, we found that aberrant activation of mTORC1 was likely attributed to the reduction of DEPDC5 in the livers of ethanol-fed mice or ALD patients. To further define the in vivo role of DEPDC5 in ALD development, we generated Depdc5 hepatocyte-specific knockout mouse model (Depdc5-LKO) in which mTORC1 pathway was constitutively activated through loss of the inhibitory effect of GATOR1. Hepatic Depdc5 ablation leads to mild hepatomegaly and liver injury and protects against diet-induced liver steatosis. In contrast, ethanol-fed Depdc5-LKO mice developed severe hepatic steatosis and inflammation. Pharmacological intervention with Torin 1 suppressed mTORC1 activity and remarkably ameliorated ethanol-induced hepatic steatosis and inflammation in both control and Depdc5-LKO mice. The pathological effect of sustained mTORC1 activity in ALD may be attributed to the suppression of peroxisome proliferator activated receptor α (PPARα), the master regulator of fatty acid oxidation in hepatocytes, because fenofibrate (PPARα agonist) treatment reverses ethanol-induced liver steatosis and inflammation in Depdc5-LKO mice. These findings provide novel insights into the in vivo role of hepatic DEPDC5 in the development of ALD.

Adipocyte-specific deletion of Depdc5 exacerbates insulin resistance and adipose tissue inflammation in mice.

The mammalian target of rapamycin complex 1 (mTORC1) is a crucial regulator of adipogenesis and systemic energy metabolism. Its dysregulation leads to a diversity of metabolic diseases, including obesity and type 2 diabetes. DEP-domain containing 5 (DEPDC5) is a critical component of GATOR1 complex that functions as a key inhibitor of mTORC1. So far, its function in adipose tissue remains largely unknown. Herein we evaluated how persistent mTORC1 activation in adipocyte via Depdc5 knockout modulates adiposity in vivo. Our data indicated that adipocyte-specific knockout of Depdc5 in aged mice led to reduced visceral fat, aggravated insulin resistance and enhanced adipose tissue inflammation. Moreover, we found that Depdc5 ablation resulted in upregulation of adipose triglyceride lipase (ATGL) in adipocytes and elevated levels of serum free fatty acids (FFAs). Intriguingly, rapamycin treatment did not reverse insulin resistance but alleviated adipose tissue inflammation caused by Depdc5 deletion. Taken together, our findings revealed that mTORC1 activation caused by Depdc5 deletion promotes lipolysis process and further exacerbates insulin resistance and adipose tissue inflammation in mice.

Sirtuin 6 ameliorates alcohol-induced liver injury by reducing endoplasmic reticulum stress in mice.

Alcoholic liver disease (ALD) occurs as a result of chronic and excessive alcohol consumption. It encompasses a wide spectrum of chronic liver abnormalities that range from steatosis to alcoholic hepatitis, progressive fibrosis and cirrhosis. Endoplasmic reticulum (ER) stress induced by ethanol metabolism in hepatocytes has been established as an important contributor to the pathogenesis of ALD. However, whether SIRT6 exerts regulatory effects on ethanol-induced ER stress and contributes to the pathogenesis of ALD is unclear. In this study, we developed and characterized Sirt6 hepatocyte-specific knockout and transgenic mouse models that were treated with chronic-plus-binge ethanol feeding. We observed that hepatic Sirt6 deficiency led to exacerbated ethanol-induced liver injury and aggravated hepatic ER stress. Tauroursodeoxycholic acid (TUDCA) treatment remarkably attenuated ethanol-induced ER stress and ameliorated ALD pathologies caused by Sirt6 ablation. Reciprocally, SIRT6 hepatocyte-specific transgenic mice exhibited reduced ER stress and ameliorated liver injury caused by ethanol exposure. Consistently, knockdown of Sirt6 elevated the expression of ER stress related genes in primary hepatocytes treated with ethanol, whereas overexpression of SIRT6 reduced their expression, indicating SIRT6 regulates ethanol-induced hepatic ER stress in a cell autonomous manner. Collectively, our results suggest that SIRT6 is a positive regulator of ethanol-induced ER stress in the liver and protects against ALD by relieving ER stress.

Protein O-GlcNAc Modification Links Dietary and Gut Microbial Cues to the Differentiation of Enteroendocrine L Cells.

Intestinal L cells regulate a wide range of metabolic processes, and L-cell dysfunction has been implicated in the pathogenesis of obesity and diabetes. However, it is incompletely understood how luminal signals are integrated to control the development of L cells. Here we show that food availability and gut microbiota-produced short-chain fatty acids control the posttranslational modification on intracellular proteins by O-linked ß-N-acetylglucosamine (O-GlcNAc) in intestinal epithelial cells. Via FOXO1 O-GlcNAcylation, O-GlcNAc transferase (OGT) suppresses expression of the lineage-specifying transcription factor Neurogenin 3 and, thus, L cell differentiation from enteroendocrine progenitors. Intestinal epithelial ablation of OGT in mice not only causes L cell hyperplasia and increased secretion of glucagon-like peptide 1 (GLP-1) but also disrupts gut microbial compositions, which notably contributes to decreased weight gain and improved glycemic control. Our results identify intestinal epithelial O-GlcNAc signaling as a brake on L cell development and function in response to nutritional and microbial cues.

The epigenetic regulator SIRT6 protects the liver from alcohol-induced tissue injury by reducing oxidative stress in mice.

BACKGROUND & AIMS: As a nicotinamide adenine dinucleotide-dependent deacetylase and a key epigenetic regulator, sirtuin 6 (SIRT6) has been implicated in the regulation of metabolism, DNA repair, and inflammation. However, the role of SIRT6 in alcohol-related liver disease (ALD) remains unclear. The aim of this study was to investigate the function and mechanism of SIRT6 in ALD pathogenesis. METHODS: We developed and characterized Sirt6 knockout (KO) and transgenic mouse models that were treated with either control or ethanol diet. Hepatic steatosis, inflammation, and oxidative stress were analyzed using biochemical and histological methods. Gene regulation was analyzed by luciferase reporter and chromatin immunoprecipitation assays. RESULTS: The Sirt6 KO mice developed severe liver injury characterized by a remarkable increase of oxidative stress and inflammation, whereas the Sirt6 transgenic mice were protected from ALD via normalization of hepatic lipids, inflammatory response, and oxidative stress. Our molecular analysis has identified a number of novel Sirt6-regulated genes that are involved in antioxidative stress, including metallothionein 1 and 2 (Mt1 and Mt2). Mt1/2 genes were downregulated in the livers of Sirt6 KO mice and patients with alcoholic hepatitis. Overexpression of Mt1 in the liver of Sirt6 KO mice improved ALD by reducing hepatic oxidative stress and inflammation. We also identified a critical link between SIRT6 and metal regulatory transcription factor 1 (Mtf1) via a physical interaction and functional coactivation. Mt1/2 promoter reporter assays showed a strong synergistic effect of SIRT6 on the transcriptional activity of Mtf1. CONCLUSIONS: Our data suggest that SIRT6 plays a critical protective role against ALD and it may serve as a potential therapeutic target for ALD. LAY SUMMARY: The liver, the primary organ for ethanol metabolism, can be damaged by the byproducts of ethanol metabolism, including reactive oxygen species. In this study, we have identified a key epigenetic regulator SIRT6 that plays a critical role in protecting the liver from oxidative stress-induced liver injury. Thus, our data suggest that SIRT6 may be a potential therapeutic target for alcohol-related liver disease.

NAMPT overexpression alleviates alcohol-induced hepatic steatosis in mice.

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in mammalian nicotinamide adenine dinucleotide (NAD)+ biosynthesis. Through its NAD+-biosynthetic activity, NAMPT influences the activity of NAD+-dependent enzymes, such as sirtuins. NAMPT is able to modulate processes involved in the pathogenesis of non-alcohol induced fatty liver disease (NAFLD), but the roles NAMPT plays in development of alcoholic liver disease (ALD) still remain unknown. Here, we show that ethanol treatment suppresses the expression of Nampt in hepatocytes. Consistently, chronic ethanol administration also reduces Nampt expression in the mouse liver. We next demonstrate that hepatocytes infected with Ad-NAMPT adenovirus exhibit significantly elevated intracellular NAD+ levels and decreased ethanol-induced triglyceride (TG) accumulation. Similarly, adenovirus-mediated overexpression of NAMPT in mice ameliorates ethanol induced hepatic steatosis. Moreover, we demonstrate that SIRT1 is required to mediate the effects of NAMPT on reduction of hepatic TG accumulation and serum ALT, AST levels in ethanol-fed mice. Our results provide important insights in targeting NAMPT for treating alcoholic fatty liver disease.

Deficiency in intestinal epithelial O-GlcNAcylation predisposes to gut inflammation.

Post-translational modifications in intestinal epithelial cells (IECs) allow for precise control in intestinal homeostasis, the breakdown of which may precipitate the pathological damage and inflammation in inflammatory bowel disease. The O-linked ß-N-acetylglucosamine (O-GlcNAc) modification on intracellular proteins controls diverse biological processes; however, its roles in intestinal homeostasis are still largely unexplored. Here, we found that levels of protein O-GlcNAcylation and the expression of O-GlcNAc transferase (OGT), the enzyme adding the O-GlcNAc moiety, were reduced in IECs in human IBD patients. Deletion of OGT specifically in IECs resulted in disrupted epithelial barrier, microbial dysbiosis, Paneth cell dysfunction, and intestinal inflammation in mice. Using fecal microbiota transplantation in mice, we demonstrated that microbial dysbiosis although was insufficient to induce spontaneous inflammation but exacerbated chemical-induced colitis. Paneth cell-specific deletion of OGT led to Paneth cell dysfunction, which might predispose mice to chemical-induced colitis. On the other hand, the augmentation of O-GlcNAc signaling by inhibiting O-GlcNAcase, the enzyme removing O-GlcNAcylation, alleviated chemical-induced colitis. Our data reveal that protein O-GlcNAcylation in IECs controls key regulatory mechanisms to maintain mucosal homeostasis.

Overexpression of NRK1 ameliorates diet- and age-induced hepatic steatosis and insulin resistance.

NAD+ is a co-enzyme in redox reactions and a substrate required for activity of various enzyme families, including sirtuins and poly(ADP-ribose) polymerases. Dietary supplementation of NAD+ precursors nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR) protects against metabolic disease, neurodegenerative disorders and age-related physiological decline in mammals. Here we sought to identify the roles of nicotinamide riboside kinase 1 (NRK1) plays in regulating hepatic NAD+ biosynthesis and lipid metabolism. Using adenovirus mediated gene transduction to overexpress or knockdown NRK1 in mouse liver, we have demonstrated that NRK1 is critical for maintaining hepatic NAD+ levels and triglyceride content. We have further shown that the hepatic expression of Nmrk1 mRNA is significantly decreased either in mice treated with high-fat diet or in aged mice. However, adenoviral delivery of NRK1 in these diet- and age-induced mice elevates hepatic NAD+ levels, reduces hepatic steatosis, and improves glucose tolerance and insulin sensitivity. Our results provide important insights in targeting NRK1 for treating hepatic steatosis.

Fabp4-Cre-mediated Sirt6 deletion impairs adipose tissue function and metabolic homeostasis in mice.

SIRT6 is a member of sirtuin family of deacetylases involved in diverse processes including genome stability, metabolic homeostasis and anti-inflammation. However, its function in the adipose tissue is not well understood. To examine the metabolic function of SIRT6 in the adipose tissue, we generated two mouse models that are deficient in Sirt6 using the Cre-lox approach. Two commonly used Cre lines that are driven by either the mouse Fabp4 or Adipoq gene promoter were chosen for this study. The Sirt6-knockout mice generated by the Fabp4-Cre line (Sirt6f/f:Fabp4-Cre) had a significant increase in both body weight and fat mass and exhibited glucose intolerance and insulin resistance as compared with the control wild-type mice. At the molecular levels, the Sirt6f/f :Fabp4-Cre-knockout mice had increased expression of inflammatory genes including F4/80, TNFα, IL-6 and MCP-1 in both white and brown adipose tissues. Moreover, the knockout mice showed decreased expression of the adiponectin gene in the white adipose tissue and UCP1 in the brown adipose tissue, respectively. In contrast, the Sirt6 knockout mice generated by the Adipoq-Cre line (Sirt6f/f :Adipoq-Cre) only had modest insulin resistance. In conclusion, our data suggest that the function of SIRT6 in the Fabp4-Cre-expressing cells in addition to mature adipocytes plays a critical role in body weight maintenance and metabolic homeostasis.