Endothelial-to-mesenchymal transition (EndoMT) is a cellular process often initiated by the transforming growth factor β (TGF-β) family of ligands. Although required for normal heart valve ...development, deregulated EndoMT is linked to a wide range of pathological conditions. Here, we demonstrate that endothelial fatty acid oxidation (FAO) is a critical in vitro and in vivo regulator of EndoMT. We further show that this FAO-dependent metabolic regulation of EndoMT occurs through alterations in intracellular acetyl-CoA levels. Disruption of FAO via conditional deletion of endothelial carnitine palmitoyltransferase II (Cpt2E-KO) augments the magnitude of embryonic EndoMT, resulting in thickening of cardiac valves. Consistent with the known pathological effects of EndoMT, adult Cpt2E-KO mice demonstrate increased permeability in multiple vascular beds. Taken together, these results demonstrate that endothelial FAO is required to maintain endothelial cell fate and that therapeutic manipulation of endothelial metabolism could provide the basis for treating a growing number of EndoMT-linked pathological conditions.
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•Induction of EndoMT triggers a reduction in FAO•FAO is required to maintain endothelial acetyl-CoA levels•FAO modulates in vitro and in vivo EndoMT
Xiong et al. demonstrate that endothelial fatty acid oxidation (FAO) is a critical in vitro and in vivo regulator of endothelial-to-mesenchymal transition (EndoMT) and that therapeutic manipulation of endothelial metabolism could provide the basis for treating a growing number of EndoMT-linked pathological conditions.
Hypothesis: Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease in developed countries yet there are no FDA-approved therapies for the disease. AMPK is a cellular ...energy sensor that coordinates metabolic pathways to balance energy demand with production. Growing evidence suggests loss of AMPK activity contributes to NAFLD. We recently identified an orphan F-box protein, FBXO48, which mediates the ubiquitination and proteasomal degradation of phosphorylated AMPKα (pAMPK). We hypothesized that increasing pAMPK levels via inhibition of FBXO48 would improve glucose homeostasis and slow NAFLD progression.
Methods: Twelve-week old male wildtype (WT) mice were fed low-fat diet (LFD) or “fast food” diet (FFD) for 24 weeks and then given vehicle (VEH) or a small molecule FBXO48 inhibitor (SMI; 5 mg/kg/d) for 8 weeks. We measured changes in body weight/composition, performed glucose tolerance tests (GTT), and collected plasma and liver for analysis.
Results: SMI had no significant effect on body weight or composition, although body weight and fat mass were 2.4 and 2.1 g less in SMI FFD compared with VEH FFD mice, suggesting a modest effect on weight loss. SMI significantly improved glucose homeostasis in FFD mice and restored plasma glucose levels during GTT to those observed in LFD mice. SMI had no effect on liver triglyceride levels in LFD mice and produced a 15% non-significant reduction in FFD mice. Gene expression of inflammation markers Cd68 and Ccl2 were significantly reduced in SMI FFD compared with VEH FFD mice, as were markers of fibrosis Col1a1 and Col3a1.
Conclusions: Our data suggest that increasing pAMPK levels through inhibition of FBXO48 may be a viable treatment option for improving glucose homeostasis and reducing inflammation/fibrosis associated with NAFLD.
Disclosure
A. Murali: None. L. R. Edmunds: None. B. Xie: None. B. Chen: Board Member; Self; Generian, Employee; Self; Generian. Y. Liu: Employee; Self; Generian. M. J. Jurczak: None.
Funding
National Institute of Diabetes and Digestive and Kidney Diseases (DK007052R01, DK119627)
myc−/− rat fibroblasts (KO cells) differ from myc+/+ (WT) cells and KO cells with enforced Myc re-expression (KO-Myc cells) with respect to mitochondrial structure and function, utilization of ...glucose and glutamine as energy-generating substrates, and ATP levels. Specifically, KO cells demonstrate low levels of glycolysis and oxidative phosphorylation, dysfunctional mitochondria and electron transport chain complexes, and depleted ATP stores. We examined here how these cells adapt to their energy-deficient state and how they differ in their uptake and utilization of long- and medium-chain fatty acids such as palmitate and octanoate, respectively. Metabolic tracing of these molecules showed that KO cells preferentially utilize them as β-oxidation substrates and that, rather than directing them into phospholipids, preferentially store them as neutral lipids. KO cell transcriptional profiling and functional assays revealed a generalized up-regulation of pathways involved in fatty acid transport and catabolism as well as evidence that these cells attempt to direct acetyl-CoA into the tricarboxylic acid (TCA) cycle for ATP production rather than utilizing it for anabolic purposes. Additional evidence to support this idea included the finding that AMP-dependent protein kinase was constitutively activated in KO cells. The complex control of pyruvate dehydrogenase, which links glycolysis to the TCA cycle, was also maximized to ensure the conversion of pyruvate to acetyl-CoA. Despite these efforts to maximize acetyl-CoA for energy-generating purposes, its levels remained chronically low in KO cells. This suggests that tumor cells with Myc deregulation might be susceptible to novel therapies that limit acetyl-CoA availability.
Exposure to a high fat (HF) diet promotes increased fatty acid uptake, fatty acid oxidation and lipid accumulation in the heart. These maladaptive changes impact cellular energy metabolism and may ...promote the development of cardiac dysfunction. Attempts to increase cardiac glucose utilization have been proposed as a way to reverse cardiomyopathy in obese and diabetic individuals. Adropin is a nutrient-regulated metabolic hormone shown to promote glucose oxidation over fatty acid oxidation in skeletal muscle homogenates in vitro. The focus of the current study was to investigate whether adropin can regulate substrate metabolism in the heart following prolonged exposure to a HF diet in vivo. Mice on a long-term HF diet received serial intraperitoneal injections of vehicle or adropin over three days. Cardiac glucose oxidation was significantly reduced in HF animals, which was rescued by acute adropin treatment. Significant decreases in cardiac pyruvate dehydrogenase activity were observed in HF animals, which were also reversed by adropin treatment. In contrast to previous studies, this change was unrelated to Pdk4 expression, which remained elevated in both vehicle- and adropin-treated HF mice. Instead, we show that adropin modulated the expression of the mitochondrial acetyltransferase enzyme GCN5L1, which altered the acetylation status and activity of fuel metabolism enzymes to favor glucose utilization. Our findings indicate that adropin exposure leads to increased cardiac glucose oxidation under HF conditions, and may provide a future therapeutic avenue in the treatment of diabetic cardiomyopathy.
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•Long-term exposure to a high fat diet can promote metabolic dysfunction in the heart.•Adropin is a nutrient-responsive hormone shown to restore glucose oxidation in the skeletal muscle of diabetic mice.•We show that acute treatment of high fat diet-induced obese mice with adropin restores cardiac glucose oxidation in vivo.•Adropin improves pyruvate dehydrogenase activity in obese mice, which is linked to reduced inhibitory lysine acetylation.
PARKIN, an ubiquitin E3 ligase, regulates mitochondrial homeostasis through a process called mitophagy, where damaged mitochondria are selectively targeted and removed via autophagy. Diminished ...hepatic mitophagy may play a role in mitochondrial dysfunction that occurs alongside insulin resistance and hepatic steatosis in association with obesity. Reduced hepatic mitophagy was observed in obese mice with fatty liver, raising the question as to whether loss of mitophagy contributes to the pathogenesis of fatty liver or is merely associated with the disease. To understand how loss of hepatic mitophagy affects obesity-associated liver disease, we developed a liver-specific PARKIN knockout mouse (LKO). There was no difference in body weight in LKO compared with WT mice fed regular chow (RC) or high-fat diet (HFD; 60% kcal, 12 weeks). There was also no difference in liver steatosis between RC groups, however, liver steatosis was 45% greater in HFD-LKO compared with WT mice (p<0.05). Liver histology demonstrated presence of microvesicular steatosis in zones 2-3 in both HFD groups, but only LKO mice presented with micro and macrosteatosis in zones 1-3. HFD-LKO samples showed presence of an inflammatory cell infiltrate that was less apparent in WT samples. Unbiased transcriptomic analysis by RNA-Seq demonstrated 113 significant differentially expressed genes (82 up, 31 down) in HFD-LKO mice. Unsupervised gene ontology and pathway analysis revealed significant changes in extracellular matrix accumulation, lipid metabolism, metabolic and ROS processes in HFD-LKO mice.
In summary, the increased steatosis and presence of macrovesicular steatosis and inflammation in HFD-LKO mice, alongside changes in gene expression suggesting collagen deposition and extracellular matrix remodeling, suggest that loss of PARKIN-mediated mitophagy increases susceptibility to HFD and may predispose mice to NAFLD.
Disclosure
L.R. Edmunds: None. A. Mills: None. M.J. Jurczak: None.
Funding
American Diabetes Association (1-19-PDF-102 to L.R.E.)
PARKIN is an E3 ubiquitin ligase that regulates mitochondrial quality control through a process called mitophagy. Recent human and rodent studies suggest that loss of hepatic mitophagy may occur ...during the pathogenesis of obesity-associated fatty liver and contribute to changes in mitochondrial metabolism associated with this disease. Whole-body Prkn knockout mice are paradoxically protected against diet-induced hepatic steatosis; however, liver-specific effects of Prkn deficiency cannot be discerned in this model due to pleotropic effects of germline Prkn deletion on energy balance and subsequent protection against diet-induced obesity. We therefore generated the first liver-specific Prkn knockout mouse strain (LKO) to directly address the role of hepatic Prkn.
Littermate control (WT) and LKO mice were fed regular chow (RC) or high-fat diet (HFD) and changes in body weight and composition were measured over time. Liver mitochondrial content was assessed using multiple, complementary techniques, and mitochondrial respiratory capacity was assessed using Oroboros O2K platform. Liver fat was measured biochemically and assessed histologically, while global changes in hepatic gene expression were measured by RNA-seq. Whole-body and tissue-specific insulin resistance were assessed by hyperinsulinemic-euglycemic clamp with isotopic tracers.
Liver-specific deletion of Prkn had no effect on body weight or adiposity during RC or HFD feeding; however, hepatic steatosis was increased by 45% in HFD-fed LKO compared with WT mice (P < 0.05). While there were no differences in mitochondrial content between genotypes on either diet, mitochondrial respiratory capacity and efficiency in the liver were significantly reduced in LKO mice. Gene enrichment analyses from liver RNA-seq results suggested significant changes in pathways related to lipid metabolism and fibrosis in HFD-fed Prkn knockout mice. Finally, whole-body insulin sensitivity was reduced by 35% in HFD-fed LKO mice (P < 0.05), which was primarily due to increased hepatic insulin resistance (60% of whole-body effect; P = 0.11).
These data demonstrate that PARKIN contributes to mitochondrial homeostasis in the liver and plays a protective role against the pathogenesis of hepatic steatosis and insulin resistance.
•Mitochondrial respiratory capacity is reduced in liver-specific Prkn knockout mice.•Liver-specific Prkn knockout mice develop more severe steatosis during high-fat diet feeding.•Pathogenesis of NAFLD, including insulin resistance and markers of fibrosis, is enhanced in liver-specific Prkn knockout mice.
The c-Myc (Myc) oncoprotein and AMP-activated protein kinase (AMPK) regulate glycolysis and oxidative phosphorylation (Oxphos) although often for different purposes. Because Myc over-expression ...depletes ATP with the resultant activation of AMPK, we explored the potential co-dependency of and cross-talk between these proteins by comparing the consequences of acute Myc induction in ampk+/+ (WT) and ampk-/- (KO) murine embryo fibroblasts (MEFs). KO MEFs showed a higher basal rate of glycolysis than WT MEFs and an appropriate increase in response to activation of a Myc-estrogen receptor (MycER) fusion protein. However, KO MEFs had a diminished ability to increase Oxphos, mitochondrial mass and reactive oxygen species in response to MycER activation. Other differences between WT and KO MEFs, either in the basal state or following MycER induction, included abnormalities in electron transport chain function, levels of TCA cycle-related oxidoreductases and cytoplasmic and mitochondrial redox states. Transcriptional profiling of pathways pertinent to glycolysis, Oxphos and mitochondrial structure and function also uncovered significant differences between WT and KO MEFs and their response to MycER activation. Finally, an unbiased mass-spectrometry (MS)-based survey capable of quantifying ~40% of all mitochondrial proteins, showed about 15% of them to be AMPK- and/or Myc-dependent in their steady state. Significant differences in the activities of the rate-limiting enzymes pyruvate kinase and pyruvate dehydrogenase, which dictate pyruvate and acetyl coenzyme A abundance, were also differentially responsive to Myc and AMPK and could account for some of the differences in basal metabolite levels that were also detected by MS. Thus, Myc and AMPK are highly co-dependent and appear to engage in significant cross-talk across numerous pathways which support metabolic and ATP-generating functions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Adropin is a liver‐ and brain‐secreted peptide hormone with striking effects on fuel metabolism regulation in a number of tissues. Previous studies demonstrated that adropin secretion is decreased in ...obese mice subjected to a long‐term high‐fat diet (HFD), and that whole‐body loss of adropin expression resulted in systemic insulin resistance. Treatment of obese mice with adropin improves glucose tolerance, which has been linked to increased glucose oxidation and inhibition of fatty acid utilization in isolated skeletal muscle homogenates. In this study, we used in vivo physiological measurements to determine how treatment of obese mice with adropin affects whole‐body glucose metabolism. Treatment with adropin reduced fasting blood glucose and, as shown previously, increased glucose tolerance in HFD mice during standard glucose tolerance tests. Under hyperinsulinemic‐euglycemic clamp conditions, adropin treatment led to a nonsignificant increase in whole‐body insulin sensitivity, and a significant reduction in whole‐body glucose uptake. Finally, we show that adropin treatment suppressed hepatic glucose production and improved hepatic insulin sensitivity. This correlated with reduced expression of fatty acid import proteins and gluconeogenic regulatory enzymes in the liver, suggesting that adropin treatment may impact the pathways that drive vital aspects of hepatic glucose metabolism.
Adropin is a liver‐ and brain‐secreted peptide hormone with striking effects on fuel metabolism regulation in a number of tissues. In this study, we used in vivo physiological measurements to determine how treatment of obese mice with adropin affects whole‐body glucose metabolism. We show that adropin treatment suppressed hepatic glucose production, which correlated with reduced expression of fatty acid import proteins in the liver, suggesting that adropin treatment may impact the bioenergetic pathways needed to drive hepatic metabolism.
Hepatoblastoma (HB) is associated with aberrant activation of the β-catenin and Hippo/YAP signaling pathways. Overexpression of mutant β-catenin and YAP in mice induces HBs that express high levels ...of c-Myc (Myc). In light of recent observations that Myc is unnecessary for long-term hepatocyte proliferation, we have now examined its role in HB pathogenesis using the above model. Although Myc was found to be dispensable for in vivo HB initiation, it was necessary to sustain rapid tumor growth. Gene expression profiling identified key molecular differences between myc+/+ (WT) and myc−/− (KO) hepatocytes and HBs that explain these behaviors. In HBs, these included both Myc-dependent and Myc-independent increases in families of transcripts encoding ribosomal proteins, non-structural factors affecting ribosome assembly and function, and enzymes catalyzing glycolysis and lipid bio-synthesis. In contrast, transcripts encoding enzymes involved in fatty acid β-oxidation were mostly down-regulated. Myc-independent metabolic changes associated with HBs included dramatic reductions in mitochondrial mass and oxidative function, increases in ATP content and pyruvate dehydrogenase activity, and marked inhibition of fatty acid β-oxidation (FAO). Myc-dependent metabolic changes included higher levels of neutral lipid and acetyl-CoA in WT tumors. The latter correlated with higher histone H3 acetylation. Collectively, our results indicate that the role of Myc in HB pathogenesis is to impose mutually dependent changes in gene expression and metabolic reprogramming that are unattainable in non-transformed cells and that cooperate to maximize tumor growth.
Kidney proximal tubule (PT) cells have high‐metabolic demands to drive the extraordinary ion and solute transport, water reabsorption, and endocytic uptake that occur in this nephron segment. ...Increases in renal blood flow alter glomerular filtration rate and lead to rapid mechanosensitive adaptations in PT transport, impacting metabolic demand. Although the PT reabsorbs essentially all of the filtered glucose, PT cells rely primarily on oxidative metabolism rather than glycolysis to meet their energy demands. We lack an understanding of how PT functions are impacted by changes in O2 availability via cortical capillaries and mechanosensitive signaling in response to alterations in luminal flow. Previously, we found that opossum kidney (OK) cells recapitulate key features of PT cells in vivo, including enhanced endocytic uptake and ion transport, when exposed to mechanical stimulation by culture on an orbital shaker. We hypothesized that increased oxygenation resulting from orbital shaking also contributes to this more physiologic phenotype. RNA seq of OK cells maintained under static conditions or exposed to orbital shaking for up to 96 hours showed significant time‐ and culture‐dependent changes in gene expression. Transcriptional and metabolomics data were consistent with a decrease in glycolytic flux and with an increased utilization of aerobic metabolic pathways in cells exposed to orbital shaking. Moreover, we found spatial differences in the pattern of mitogenesis vs development of ion transport and endocytic capacities in our culture system that highlight the complexity of O2‐dependent and mechanosensitive crosstalk to regulate PT cell function.
The proximal tubule (PT) relies primarily on oxidative metabolism rather than glycolysis to meet the high‐energy demands needed to drive ion transport and endocytic reclamation of filtered proteins. Many of the available model cell lines fail to replicate the key features of this nephron segment. We found that culturing PT cells under continuous shear stress enhances cell differentiation and drives a metabolic shift toward oxidative metabolism. Moreover, oxygen availability and shear stress differentially regulate PT responses in this culture model.
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