The role of AMPKα2 in the HFD-induced nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is associated with hepatic steatosis, inflammation and liver fibrosis and has become one of the leading causes of hepatocellular carcinoma and liver failure. However, the underlying molecular mechanism of hepatic steatosis and the progression to nonalcoholic steatohepatitis (NASH) are not fully understood. Herein, we discovered that AMPKα2 catalytic subunit showed reduced expression in the liver following high fat diet (HFD) feeding to mice. Importantly, knockout of AMPKα2 in mice aggravated NAFLD, hepatic steatosis, inflammation and fibrosis. On the other hand, hepatocyte-targeted overexpression of AMPKα2 prevented or reversed NAFLD indications. In vivo mechanistic studies revealed that increased phosphorylation of IKKα/β and NF-κB in HFD-fed AMPKα2^−/− mice compared to WT mice, and treatment of these mouse cohorts with an inhibitor of NF-κB signaling for 4 weeks, effectively attenuated the progression of steatohepatitis and metabolic disorder features. In summary, AMPKα2 provides a protective role in the process of hepatic steatosis to NASH progression through suppression of liver NF-κB signaling.     

Ketogenic essential amino acids replacement diet ameliorated hepatosteatosis with altering autophagy-associated molecules

Ketogenic amino acid (KAA) replacement diet has been shown to cure hepatic steatosis, a serious liver disease associated with diverse metabolic defects. In this study, we investigated the effects of KAA replacement diet on nutrition sensing signaling pathway and analyzed whether induction of hepatic autophagy was involved. Mice are fed with high fat diet (HFD) or KAA replacement in high-fat diet (30% fat in food; HFD)-fed (HFD^KAAR) and sacrificed at 8, 12, 16 weeks after initiation of experimental food. Hepatic autophagy was analyzed in protein expression of several autophagy-associated molecules and in light chain-3 green fluorescent protein (LC-3 GFP) transgenic mice. HFD^KAAR showed increased AMP-activated protein kinase (AMPK) phosphorylation and enhanced liver kinase B1 (LKB1) expression compared to control HFD-fed mice. The KAA-HFD-induced activation of AMPK was associated with an increased protein expression of sirtuin 1 (Sirt1), decreased forkhead box protein O3a (Foxo3a) level, and suppression of mammalian target of rapamycin (mTOR) phosphorylation compared with the HFD-fed mice. The intervention study revealed that a KAA-replacement diet also ameliorated all the established metabolic and autophagy defects in the HFD-fed mice, suggesting that a KAA-replacement diet can be used therapeutically in established diseases. These results indicate that KAA replacement in food could be a novel strategy to combat hepatic steatosis and metabolic abnormalities likely involvement of an induction of autophagy.     

Involvement of SIRT1–AMPK signaling in the protective action of indole-3-carbinol against hepatic steatosis in mice fed a high-fat diet

This study addressed the effect of indole-3-carbinol (I3C) supplementation on hepatic steatosis in mice fed a high-fat diet (HFD) and clarified the underlying mechanism. Male C57BL/6N mice were divided into three groups: those who received a normal diet, those fed with HFD and those fed with 0.1% I3C-supplemented diet (I3CD). In the present study, an HFD supplemented with 0.1% I3C significantly decreased body and liver weight as well as plasma and hepatic lipid levels. The activation of the silent mating type information regulation 2 homolog 1 (SIRT1)–AMP-activated protein kinase (AMPK) signaling system by I3C correlated with decreased mRNA levels of sterol regulatory element-binding protein-1c-regulated lipogenic enzymes. In addition, I3C significantly reversed HFD-induced up-regulation of ER stress-mediated signaling molecules in the liver, which may have contributed to the protective effects of I3C against hepatic steatosis. Furthermore, HFD-induced up-regulations of inflammatory genes such as tumor necrosis factor α and interleukin 6 were significantly reversed by dietary I3C supplementation. Our study suggests that the protective action of I3C against hepatic steatosis is mediated, at least in part, through the up-regulation of a SIRT1–AMPK signaling system in the livers of HFD-fed mice. Further investigations revealed that alleviation of the ER stress response represented a critical mechanism underlying the beneficial effects of I3C on hepatic steatosis.     

Interleukin-38 alleviates hepatic steatosis through AMPK/autophagy-mediated suppression of endoplasmic reticulum stress in obesity models

Interleukin-38 (IL-38), recently recognized as a cytokine with anti-inflammatory properties that mitigate type 2 diabetes, has been associated with indicators of insulin resistance and nonalcoholic fatty liver disease (NAFLD). This study investigated the impact of IL-38 on hepatic lipid metabolism and endoplasmic reticulum (ER) stress. We assessed protein expression levels using Western blot analysis, while monodansylcadaverine staining was employed to detect autophagosomes in hepatocytes. Oil red O staining was utilized to examine lipid deposition. The study revealed elevated serum IL-38 levels in high-fat diet (HFD)-fed mice and IL-38 secretion from mouse keratinocytes. IL-38 treatment attenuated lipogenic lipid accumulation and ER stress markers in hepatocytes exposed to palmitate. Furthermore, IL-38 treatment increased AMP-activated protein kinase (AMPK) phosphorylation and autophagy. The effects of IL-38 on lipogenic lipid deposition and ER stress were nullified in cultured hepatocytes by suppressing AMPK through small interfering (si) RNA or 3-methyladenine (3MA). In animal studies, IL-38 administration mitigated hepatic steatosis by suppressing the expression of lipogenic proteins and ER stress markers while reversing AMPK phosphorylation and autophagy markers in the livers of HFD-fed mice. Additionally, AMPK siRNA, but not 3MA, mitigated IL-38-enhanced fatty acid oxidation in hepatocytes. In summary, IL-38 alleviates hepatic steatosis through AMPK/autophagy signaling-dependent attenuation of ER stress and enhancement of fatty acid oxidation via the AMPK pathway, suggesting a therapeutic strategy for treating NAFLD.     

Blocking Nuclear Factor-Kappa B Protects against Diet-Induced Hepatic Steatosis and Insulin Resistance in Mice

Inflammation critically contributes to the development of various metabolic diseases. However, the effects of inhibiting inflammatory signaling on hepatic steatosis and insulin resistance, as well as the underlying mechanisms remain obscure. In the current study, male C57BL/6J mice were fed a chow diet or high-fat diet (HFD) for 8 weeks. HFD-fed mice were respectively treated with p65 siRNA, non-silence control siRNA or vehicle every 4^th day for the last 4 weeks. Vehicle-treated (HF) and non-silence siRNA-treated (HFNS) mice displayed overt inflammation, hepatic steatosis and insulin resistance compared with chow-diet-fed (NC) mice. Upon treatment with NF-κB p65 siRNA, HFD-fed (HFPS) mice were protected from hepatic steatosis and insulin resistance. Furthermore, Atg7 and Beclin1 expressions and p-AMPK were increased while p-mTOR was decreased in livers of HFPS mice in relative to HF and HFNS mice. These results suggest a crosslink between NF-κB signaling pathway and liver AMPK/mTOR/autophagy axis in the context of hepatic steatosis and insulin resistance.     

Hepatic peroxisomal β-oxidation suppresses lipophagy via RPTOR acetylation and MTOR activation

ABSTRACT

Hepatic lipid homeostasis is controlled by a coordinated regulation of various metabolic pathways involved in de novo synthesis, uptake, storage, and catabolism of lipids. Disruption of this balance could lead to hepatic steatosis. Peroxisomes play an essential role in lipid metabolism, yet their importance is often overlooked. In a recent study, we demonstrated a role for hepatic peroxisomal β-oxidation in autophagic degradation of lipid droplets. ACOX1 (acyl-Coenzyme A oxidase 1, palmitoyl), the rate-limiting enzyme of peroxisomal β-oxidation, increases with fasting or high-fat diet (HFD). Liver-specific acox1 knockout (acox1-LKO) protects mice from hepatic steatosis induced by starvation or HFD via induction of lipophagy. Mechanistically, we showed that hepatic ACOX1 deficiency decreases the total cytosolic acetyl-CoA levels, which leads to reduced acetylation of RPTOR/RAPTOR, a component of MTORC1, which is a key regulator of macroautophagy/autophagy. These results identify peroxisome-derived acetyl-CoA as a critical metabolic regulator of autophagy that controls hepatic lipid homeostasis.     

S100A16, a novel lipogenesis promoting factor in livers of mice and hepatocytes in vitro

To investigate the role of S100 calcium-binding protein A16 (S100A16) in hepatic lipid metabolism, S100a16 transgenic, S100a16 knockdown, and wildtype C57BL/6 mice were fed either a high-fat diet (HFD) or normal-fat diet (NFD) for 16 weeks. The results showed that for HFD-fed mice, S100a16 transgenic mice showed significantly more severe fatty liver than other HFD-fed mice, with a significant increase in serum triglyceride (TG) concentration, with more and larger lipid droplets in the liver, whereas S100a16 knockdown mice were completely opposite, with liver fat lesions and TG serological changes being the mildest; for NFD-fed mice, liver fat accumulation and serum TG concentrations were significantly lower than those fed HFD, and no significant lipid droplets were found in the liver. Further, we found that calmodulin (CaM) interacts with S100A16, a member of the AMP-activated protein kinase (AMPK) pathway. Our research found that S100A16 regulates the AMPK pathway-associated protein by interacting with CaM to regulate liver lipid synthesis. S100A16 regulates liver lipid metabolism through the CaM/CAMKK2/AMPK pathway. Overexpression of S100A16 promotes the deterioration of fatty liver induced by HFD, and low expression of S100A16 can attenuate fatty liver.     

Beta-arrestin-1 protein represses diet-induced obesity

Diet-related obesity is a major metabolic disorder. Excessive fat mass is associated with type 2 diabetes, hepatic steatosis, and arteriosclerosis. Dysregulation of lipid metabolism and adipose tissue function contributes to diet-induced obesity. Here, we report that β-arrestin-1 knock-out mice are susceptible to diet-induced obesity. Knock-out of the gene encoding β-arrestin-1 caused increased fat mass accumulation and decreased whole-body insulin sensitivity in mice fed a high-fat diet. In β-arrestin-1 knock-out mice, we observed disrupted food intake and energy expenditure and increased macrophage infiltration in white adipose tissue. At the molecular level, β-arrestin-1 deficiency affected the expression of many lipid metabolic genes and inflammatory genes in adipose tissue. Consistently, transgenic overexpression of β-arrestin-1 repressed diet-induced obesity and improved glucose tolerance and systemic insulin sensitivity. Thus, our findings reveal that β-arrestin-1 plays a role in metabolism regulation.     

Group VIA phospholipase A2 deficiency in mice chronically fed with high-fat-diet attenuates hepatic steatosis by correcting a defect of phospholipid remodeling

A defect of hepatic remodeling of phospholipids (PL) is seen in non-alcoholic fatty liver disease and steatohepatitis (NASH) indicating pivotal role of PL metabolism in this disease. The deletion of group VIA calcium-independent phospholipase A2 (iPla2β) protects ob/ob mice from hepatic steatosis (BBAlip 1861, 2016, 440–461), however its role in high-fat diet (HFD)-induced NASH is still elusive. Here, wild-type and iPla2β-null mice were subjected to chronic feeding with HFD for 6 months. We showed that protection was observed in iPla2β-null mice with an attenuation of diet-induced body and liver-weight gains, liver enzymes, serum free fatty acids as well as hepatic TG and steatosis scores. iPla2β deficiency under HFD attenuated the levels of 1-stearoyl lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), and lysophosphatidylinositol (LPI) as well as elevation of hepatic arachidonate, arachidonate-containing cholesterol esters and prostaglandin E₂. More importantly, this deficiency rescued a defect in PL remodeling and attenuated the ratio of saturated and unsaturated PL. The protection by iPla2β deficiency was not observed during short-term HFD feeding of 3 or 5 weeks which showed no PL remodeling defect. In addition to PC/PE, this deficiency reversed the suppression of PC/PI and PE/PI among monounsaturated PL. However, this deficiency did not modulate hepatic PL contents and PL ratios in ER fractions, ER stress, fibrosis, and inflammation markers. Hence, iPla2β inactivation protected mice against hepatic steatosis and obesity during chronic dietary NASH by correcting PL remodeling defect and PI composition relative to PC and PE.     

microRNA-141 is associated with hepatic steatosis by downregulating the sirtuin1/AMP-activated protein kinase pathway in hepatocytes

Sirtuin1 (SIRT1) is a crucial regulator of metabolism and it is implicated in the metabolic pathophysiology of several disorders inclusive of Type 2 diabetes and fatty liver disease (NAFLD). The aim of this study was to investigate the role of miR-141 in hepatic steatosis via regulation of SIRT1/AMP-activated protein kinase (AMPK) pathway in hepatocytes. Liver hepatocellular cells (HepG2) were treated with high concentration of glucose to be subsequently used for the assessment of miR-141 and SIRT1 levels in a model of hepatic steatosis. On the other hand, cells were transfected with miR-141 to investigate its effect on hepatocyte steatosis and viability as well as SIRT1 expression and activity along with AMPK phosphorylation. Targeting of SIRT1 by miR-141 was evaluated by bioinformatics tools and confirmed by luciferase reporter assay. Following the intracellular accumulation of lipids in HepG2 cells, the level of miR-141 was increased while SIRT1 mRNA and protein levels, as well as AMPK phosphorylation, was decreased. Transfection with miR-141 mimic significantly downregulated SIRT1 expression and activity while miR-141 inhibitor had the opposite effects. Additionally, modulation of miR-141 levels significantly influenced AMPK phosphorylation status. The results of luciferase reporter assay verified SIRT1 to be directly targeted by miR-141. miR-141 could effectively suppress SIRT1 and lead to decreased AMPK phosphorylation in HepG2 cells. Thus, miR-141/SIRT1/AMPK signaling pathway may be considered a potential target for the therapeutic management of NAFLD.     

Distinct Time Course of the Decrease in Hepatic AMP-Activated Protein Kinase and Akt Phosphorylation in Mice Fed a High Fat Diet

AMP-activated protein kinase (AMPK) plays an important role in insulin resistance, which is characterized by the impairment of the insulin-Akt signaling pathway. However, the time course of the decrease in AMPK and Akt phosphorylation in the liver during the development of obesity and insulin resistance caused by feeding a high fat diet (HFD) remains controversial. Moreover, it is unclear whether the impairment of AMPK and Akt signaling pathways is reversible when changing from a HFD to a standard diet (SD). Male ddY mice were fed the SD or HFD for 3 to 28 days, or fed the HFD for 14 days, followed by the SD for 14 days. We examined the time course of the expression and phosphorylation levels of AMPK and Akt in the liver by immunoblotting. After 3 days of feeding on the HFD, mice gained body weight, resulting in an increased oil red O staining, indicative of hepatic lipid accumulation, and significantly decreased AMPK phosphorylation, in comparison with mice fed the SD. After 14 days on the HFD, systemic insulin resistance occurred and Akt phosphorylation significantly decreased. Subsequently, a change from the HFD to SD for 3 days, after 14 days on the HFD, ameliorated the impairment of AMPK and Akt phosphorylation and systemic insulin resistance. Our findings indicate that AMPK phosphorylation decreases early upon feeding a HFD and emphasizes the importance of prompt lifestyle modification for decreasing the risk of developing diabetes.     

β-Arrestin mediates oxytocin receptor signaling, which regulates uterine contractility and cellular migration

Desensitization of the oxytocin receptor (OXTR) in the setting of prolonged oxytocin exposure may lead to dysfunctional labor, which increases the risk for cesarean delivery, and uterine atony, which may result in postpartum hemorrhage. The molecular mechanism for OXTR desensitization is through the agonist-mediated recruitment of the multifunctional protein β-arrestin. In addition to its desensitizing function, β-arrestins have recently been shown to simultaneously activate downstream signaling. We tested whether oxytocin stimulation promotes β-arrestin-mediated OXTR desensitization in vivo and activates β-arrestin-mediated mitogen-activated protein kinase (MAPK) growth signaling. Uterine muscle strips isolated from wild-type mice exhibited diminished uterine contractility following repeated exposure to oxytocin, whereas uterine muscle strips from β-arrestin-1 and β-arrestin-2 knockout mice showed no desensitization. Utilizing siRNA knockdown of β-arrestin-1 and β-arrestin-2 in HEK-293 cells expressing the OXTR, we demonstrated oxytocin-mediated MAPK signaling that was dependent on β-arrestin-1 and β-arrestin-2. Wild-type and β-arrestin-1 and β-arrestin-2 knockout mice receiving intravenous oxytocin also demonstrated oxytocin-mediated MAPK signaling that was dependent on β-arrestin-1 and β-arrestin-2. Finally, to test the significance of β-arrestin-mediated signaling from the OXTR, HEK-293 cells expressing the OXTR showed β-arrestin-dependent proliferation in a cell migration assay following oxytocin treatment. In conclusion, β-arrestin is a multifunctional scaffold protein that mediates both desensitization of the OXTR, leading to decreases in uterine contractility, and MAPK growth signaling following stimulation by oxytocin. The development of unique OXTR ligands that prevent receptor desensitization may be a novel approach in the treatment of adverse clinical events secondary to prolonged oxytocin therapy.     

AMPK activation prevents excess nutrient-induced hepatic lipid accumulation by inhibiting mTORC1 signaling and endoplasmic reticulum stress response

Lipid accumulation is a central event in the development of chronic metabolic diseases, including obesity and type 2 diabetes, but the mechanisms responsible for lipid accumulation are incompletely understood. This study was designed to investigate the mechanisms for excess nutrient-induced lipid accumulation and whether activation of AMP-activated protein kinase (AMPK) prevents the hepatic lipid accumulation in excess nutrient-treated HepG2 cells and high fat diet (HFD)-fed mice. Exposure of HepG2 cells to high levels of glucose or palmitate induced the endoplasmic reticulum (ER) stress response, activated sterol regulatory element-binding protein-1 (SREBP-1), and enhanced lipid accumulation, all of which were sensitive to ER stress inhibitor and gene silencing of eukaryotic initiation factor 2α. The increases in ER stress response and lipid accumulation were associated with activation of mammalian target of rapamycin complex 1 (mTORC1) signaling. Inhibition of mTORC1 signaling attenuated the ER stress response and lipid accumulation induced by high glucose or by deletion of tuberous sclerosis 2. In addition, AMPK activation prevented the mTORC1 activation, ER stress response, and lipid accumulation. This effect was mimicked or abrogated, respectively, by overexpression of constitutively active and dominant-negative AMPK mutants. Finally, treatment of HFD-fed mice with 5-aminoimidazole-4-carboxamide-1-β-4-ribofuranoside inhibited the mTORC1 pathway, suppressed the ER stress response, and prevented insulin resistance and hepatic lipid accumulation. We conclude that activation of AMPK prevents excess nutrient-induced hepatic lipid accumulation by inhibiting mTORC1 and ER stress response.     

Hepatocyte-specific deletion of Janus kinase 2 (JAK2) protects against diet-induced steatohepatitis and glucose intolerance

Non-alcoholic fatty liver disease (NAFLD) is becoming the leading cause of chronic liver disease and is now considered to be the hepatic manifestation of the metabolic syndrome. However, the role of steatosis per se and the precise factors required in the progression to steatohepatitis or insulin resistance remain elusive. The JAK-STAT pathway is critical in mediating signaling of a wide variety of cytokines and growth factors. Mice with hepatocyte-specific deletion of Janus kinase 2 (L-JAK2 KO mice) develop spontaneous steatosis as early as 2 weeks of age. In this study, we investigated the metabolic consequences of jak2 deletion in response to diet-induced metabolic stress. To our surprise, despite the profound hepatosteatosis, deletion of hepatic jak2 did not sensitize the liver to accelerated inflammatory injury on a prolonged high fat diet (HFD). This was accompanied by complete protection against HFD-induced whole-body insulin resistance and glucose intolerance. Improved glucose-stimulated insulin secretion and an increase in β-cell mass were also present in these mice. Moreover, L-JAK2 KO mice had progressively reduced adiposity in association with blunted hepatic growth hormone signaling. These mice also exhibited increased resting energy expenditure on both chow and high fat diet. In conclusion, our findings indicate a key role of hepatic JAK2 in metabolism such that its absence completely arrests steatohepatitis development and confers protection against diet-induced systemic insulin resistance and glucose intolerance.     

Mitochondrial ALDH2 protects against lipopolysaccharide-induced myocardial contractile dysfunction by suppression of ER stress and autophagy

Lipopolysaccharide (LPS), an essential component of outer membrane of the Gram-negative bacteria, plays a pivotal role in myocardial anomalies in sepsis. Recent evidence depicted an essential role for mitochondrial aldehyde dehydrogenase (ALDH2) in cardiac homeostasis. This study examined the effect of ALDH2 on endotoxemia-induced cardiac anomalies. Echocardiographic, cardiac contractile and intracellular Ca²⁺ properties were examined. Our results indicated that LPS impaired cardiac contractile function (reduced fractional shortening, LV end systolic diameter, peak shortening, maximal velocity of shortening/relengthening, prolonged relengthening duration, oxidation of SERCA, and intracellular Ca²⁺ mishandling), associated with ER stress, inflammation, O₂⁻ production, increased autophagy, CAMKKβ, phosphorylated AMPK and suppressed phosphorylation of mTOR, the effects of which were significantly attenuated or negated by ALDH2. LPS promoted early endosomal formation (as evidenced by RAB4 and RAB5a), apoptosis and necrosis (MTT and LDH) while decreasing late endosomal formation (RAB7 and RAB 9), the effects were reversed by ALDH2. In vitro study revealed that LPS-induced SERCA oxidation, autophagy and cardiac dysfunction were abrogated by ALDH2 activator Alda-1, the ER chaperone TUDCA, the autophagy inhibitor 3-MA, or the AMPK inhibitor Compound C. The beneficial effect of Alda-1 against LPS was nullified by AMPK activator AICAR or rapamycin. CAMKKβ inhibition failed to rescue LPS-induced ER stress. Tunicamycin–induced cardiomyocyte dysfunction was ameliorated by Alda-1 and autophagy inhibition, the effect of which was abolished by rapamycin. These data suggested that ALDH2 protected against LPS-induced cardiac anomalies via suppression of ER stress, autophagy in a CAMKKβ/AMPK/mTOR-dependent manner.     

A complete map of the Calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) signaling pathway

Calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) is a serine/threonine-protein kinase belonging to the Ca²⁺/calmodulin-dependent protein kinase subfamily. CAMKK2 has an autocatalytic site, which gets exposed when Ca²⁺/calmodulin (CAM) binds to it. This results in autophosphorylation and complete activation of CAMKK2. The three major known downstream targets of CAMKK2 are 5′-adenosine monophosphate (AMP)-activated protein kinase (AMPKα), calcium/calmodulin-dependent protein kinase 1 (CAMK1) and calcium/calmodulin-dependent protein kinase 4 (CAMK4). Activation of these targets by CAMKK2 is important for the maintenance of different cellular and physiological processes within the cell. CAMKK2 is found to be important in neuronal development, bone remodeling, adipogenesis, and systemic glucose homeostasis, osteoclastgensis and postnatal myogensis. CAMKK2 is reported to be involved in pathologies like Duchenne muscular dystrophy, inflammation, osteoporosis and bone remodeling and is also reported to be overexpressed in prostate cancer, hepatic cancer, ovarian and gastric cancer. CAMKK2 is involved in increased cell proliferation and migration through CAMKK2/AMPK pathway in prostate cancer and activation of AKT in ovarian cancer. Although CAMKK2 is a molecule of great importance, a public resource of the CAMKK2 signaling pathway is currently lacking. Therefore, we carried out detailed data mining and documentation of the signaling events associated with CAMKK2 from published literature and developed an integrated reaction map of CAMKK2 signaling. This resulted in the cataloging of 285 reactions belonging to the CAMKK2 signaling pathway, which includes 33 protein–protein interactions, 74 post-translational modifications, 7 protein translocation events, and 22 activation/inhibition events. Besides, 124 gene regulation events and 25 activator/inhibitors involved in CAMKK2 activation were also cataloged. The CAMKK2 signaling pathway map data is made freely accessible through WikiPathway database (https://www.wikipathways.org/index.php/Pathway:WP4874). We expect that data on a signaling map of CAMKK2 will provide the scientific community with an improved platform to facilitate further molecular as well as biomedical investigations on CAMKK2 and its utility in the development of biomarkers and therapeutic targets.Electronic supplementary materialThe online version of this article (10.1007/s12079-020-00592-1) contains supplementary material, which is available to authorized users.     

Hypoxia inducible factor-1 promotes liver fibrosis in nonalcoholic fatty liver disease by activating PTEN/p65 signaling pathway

Obesity is a major contributor to the development of steatohepatitis and fibrosis from nonalcoholic fatty liver disease (NAFLD). Hypoxia aggravates progression of NAFLD. In mice on high-fat diet (HFD), hepatic steatosis leads to liver tissue hypoxia, evidenced by accumulation of hypoxia inducible factor-1-alpha (HIF-1α), which is a central regulator of the global response to hypoxia. Hepatocyte cell signaling is an important factor in hepatic fibrogenesis. We here hypothesize that HIF-1α knockout in hepatocyte may protect against liver fibrosis. We first found that HFD led to 80% more hepatic collagen deposition than Hif1a^−/−hep mice, which was confirmed by a-SMA staining of liver tissue. Body weight and liver weight were similar between groups. We then found the increasing HIF1a expression and decreasing PTEN expression in the mice on HFD and in PA-treated HepG2 cells. Finally, we found that HIF1 mediated PTEN/nfkb-p65 pathway plays an important role in the development of NAFLD to liver fibrosis. Collectively, these results identify a novel HIF1a/PTEN/NF-κ Bp65 signaling pathway in NAFLD, which could be targeted for the therapy.