CPT1A-mediated fatty acid oxidation confers cancer cell resistance to immune-mediated cytolytic killing.

Although tumor-intrinsic fatty acid ß-oxidation (FAO) is implicated in multiple aspects of tumorigenesis and progression, the impact of this metabolic pathway on cancer cell susceptibility to immunotherapy remains unknown. Here, we report that cytotoxicity of killer T cells induces activation of FAO and upregulation of carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme of FAO in cancer cells. The repression of CPT1A activity or expression renders cancer cells more susceptible to destruction by cytotoxic T lymphocytes. Our mechanistic studies reveal that FAO deficiency abrogates the prosurvival signaling in cancer cells under immune cytolytic stress. Furthermore, we identify T cell-derived IFN-γ as a major factor responsible for induction of CPT1A and FAO in an AMPK-dependent manner, indicating a dynamic interplay between immune effector cells and tumor targets. While cancer growth in the absence of CPT1A remains largely unaffected, established tumors upon FAO inhibition become significantly more responsive to cellular immunotherapies including chimeric antigen receptor-engineered human T cells. Together, these findings uncover a mode of cancer resistance and immune editing that can facilitate immune escape and limit the benefits of immunotherapies.

Impaired intestinal FXR signaling is involved in aberrant stem cell function leading to intestinal failure-associated liver disease in pediatric patients with short bowel syndrome.

Intestinal failure-associated liver disease (IFALD) is a serious complication of long-term parenteral nutrition in patients with short bowel syndrome (SBS), and is the main cause of death in SBS patients. Prevention of IFALD is one of the major challenges in the treatment of SBS. Impairment of intestinal barrier function is a key factor in triggering IFALD, therefore promoting intestinal repair is particularly important. Intestinal repair mainly relies on the function of intestinal stem cells (ISC), which require robust mitochondrial fatty acid oxidation (FAO) for self-renewal. Herein, we report that aberrant LGR5+ ISC function in IFALD may be attributed to impaired farnesoid X receptor (FXR) signaling, a transcriptional factor activated by steroids and bile acids. In both surgical biopsies and patient-derived organoids (PDOs), SBS patients with IFALD represented lower population of LGR5+ cells and decreased FXR expression. Moreover, treatment with T-ßMCA in PDOs (an antagonist for FXR) dose-dependently reduced the population of LGR5+ cells and the proliferation rate of enterocytes, concomitant with decreased key genes involved in FAO including CPT1a. Interestingly, however, treatment with Tropifexor in PDOs (an agonist for FXR) only enhanced FAO capacity, without improvement in ISC function and enterocyte proliferation. In conclusion, these findings suggested that impaired FXR may accelerate the depletion of LGR5 + ISC population through disrupted FAO processes, which may serve as a new potential target of preventive interventions against IFALD for SBS patients.

Impaired FXR-CPT1a signaling contributes to parenteral nutrition-induced villus atrophy in short-bowel syndrome.

Parenteral nutrition (PN)-induced villus atrophy is a major cause of intestinal failure (IF) for children suffering from short bowel syndrome (SBS), but the precise mechanism remains unclear. Herein, we report a pivotal role of farnesoid X receptor (FXR) signaling and fatty acid oxidation (FAO) in PN-induced villus atrophy. A total of 14 pediatric SBS patients receiving PN were enrolled in this study. Those patients with IF showed longer PN duration and significant intestinal villus atrophy, characterized by remarkably increased enterocyte apoptosis concomitant with impaired FXR signaling and decreased FAO genes including carnitine palmitoyltransferase 1a (CPT1a). Likewise, similar changes were found in an in vivo model of neonatal Bama piglets receiving 14-day PN, including villus atrophy and particularly disturbed FAO process responding to impaired FXR signaling. Finally, in order to consolidate the role of the FXR-CPT1a axis in modulating enterocyte apoptosis, patient-derived organoids (PDOs) were used as a mini-gut model in vitro. Consequently, pharmacological inhibition of FXR by tauro-ß-muricholic acid (T-ßMCA) evidently suppressed CPT1a expression leading to reduced mitochondrial FAO function and inducible apoptosis. In conclusion, impaired FXR/CPT1a axis and disturbed FAO may play a pivotal role in PN-induced villus atrophy, contributing to intestinal failure in SBS patients.

Ketohexokinase-C regulates global protein acetylation to decrease carnitine palmitoyltransferase 1a-mediated fatty acid oxidation.

BACKGROUND & AIMS: The consumption of sugar and a high-fat diet (HFD) promotes the development of obesity and metabolic dysfunction. Despite their well-known synergy, the mechanisms by which sugar worsens the outcomes associated with a HFD are largely elusive. METHODS: Six-week-old, male, C57Bl/6 J mice were fed either chow or a HFD and were provided with regular, fructose- or glucose-sweetened water. Moreover, cultured AML12 hepatocytes were engineered to overexpress ketohexokinase-C (KHK-C) using a lentivirus vector, while CRISPR-Cas9 was used to knockdown CPT1α. The cell culture experiments were complemented with in vivo studies using mice with hepatic overexpression of KHK-C and in mice with liver-specific CPT1α knockout. We used comprehensive metabolomics, electron microscopy, mitochondrial substrate phenotyping, proteomics and acetylome analysis to investigate underlying mechanisms. RESULTS: Fructose supplementation in mice fed normal chow and fructose or glucose supplementation in mice fed a HFD increase KHK-C, an enzyme that catalyzes the first step of fructolysis. Elevated KHK-C is associated with an increase in lipogenic proteins, such as ACLY, without affecting their mRNA expression. An increase in KHK-C also correlates with acetylation of CPT1α at K508, and lower CPT1α protein in vivo. In vitro, KHK-C overexpression lowers CPT1α and increases triglyceride accumulation. The effects of KHK-C are, in part, replicated by a knockdown of CPT1α. An increase in KHK-C correlates negatively with CPT1α protein levels in mice fed sugar and a HFD, but also in genetically obese db/db and lipodystrophic FIRKO mice. Mechanistically, overexpression of KHK-C in vitro increases global protein acetylation and decreases levels of the major cytoplasmic deacetylase, SIRT2. CONCLUSIONS: KHK-C-induced acetylation is a novel mechanism by which dietary fructose augments lipogenesis and decreases fatty acid oxidation to promote the development of metabolic complications. IMPACT AND IMPLICATIONS: Fructose is a highly lipogenic nutrient whose negative consequences have been largely attributed to increased de novo lipogenesis. Herein, we show that fructose upregulates ketohexokinase, which in turn modifies global protein acetylation, including acetylation of CPT1a, to decrease fatty acid oxidation. Our findings broaden the impact of dietary sugar beyond its lipogenic role and have implications on drug development aimed at reducing the harmful effects attributed to sugar metabolism.

Implantation of CPT1AM-expressing adipocytes reduces obesity and glucose intolerance in mice.

Obesity and its associated metabolic comorbidities are a rising global health and social issue, with novel therapeutic approaches urgently needed. Adipose tissue plays a key role in the regulation of energy balance and adipose tissue-derived mesenchymal stem cells (AT-MSCs) have gained great interest in cell therapy. Carnitine palmitoyltransferase 1A (CPT1A) is the gatekeeper enzyme for mitochondrial fatty acid oxidation. Here, we aimed to generate adipocytes expressing a constitutively active CPT1A form (CPT1AM) that can improve the obese phenotype in mice after their implantation. AT-MSCs were differentiated into mature adipocytes, subjected to lentivirus-mediated expression of CPT1AM or the GFP control, and subcutaneously implanted into mice fed a high-fat diet (HFD). CPT1AM-implanted mice showed lower body weight, hepatic steatosis and serum insulin and cholesterol levels alongside improved glucose tolerance. HFD-induced increases in adipose tissue hypertrophy, fibrosis, inflammation, endoplasmic reticulum stress and apoptosis were reduced in CPT1AM-implanted mice. In addition, the expression of mitochondrial respiratory chain complexes was enhanced in the adipose tissue of CPT1AM-implanted mice. Our results demonstrate that implantation of CPT1AM-expressing AT-MSC-derived adipocytes into HFD-fed mice improves the obese metabolic phenotype, supporting the future clinical use of this ex vivo gene therapy approach.

Short-term intermittent cigarette smoke exposure enhances alveolar type 2 cell stemness via fatty acid oxidation.

BACKGROUND: Cigarette smoke (CS) is associated with chronic obstructive pulmonary disease (COPD) and cancer. However, the underlying pathological mechanisms are not well understood. We recently reported that mice exposed to long-term intermittent CS for 3 months developed more severe emphysema and higher incidence of adenocarcinoma than mice exposed to long-term continuous CS for 3 months and long-term continuous CS exposure activated alveolar stem cell proliferation. However, the influence of variations in the CS exposure pattern in alveolar stem cell in unknown. Here, we exposed mice to 3 weeks of continuous or intermittent CS to identify whether different CS exposure patterns would result in differential effects on stem cells and the mechanisms underlying these potential differences. METHODS: Female mice expressing GFP in alveolar type 2 (AT2) cells, which are stem cells of the alveolar compartment, were exposed to mainstream CS via nasal inhalation. AT2 cells were collected based on their GFP expression by flow cytometry and co-cultured with fibroblasts in stem cell 3D organoid/colony-forming assays. We compared gene expression profiles of continuous and intermittent CS-exposed AT2 cells using microarray analysis and performed a functional assessment of a differentially expressed gene to confirm its involvement in the process using activator and inhibitor studies. RESULTS: AT2 cells sorted from intermittent CS-exposed mice formed significantly more colonies compared to those from continuous CS-exposed mice, and both CS-exposed groups formed significantly more colonies when compared to air-exposed cells. Comparative microarray analysis revealed the upregulation of genes related to fatty acid oxidation (FAO) pathways in AT2 cells from intermittent CS-exposed mice. Treatment of intermittent CS-exposed mice with etomoxir, an inhibitor of the FAO regulator Cpt1a, for 5 weeks resulted in a significant suppression of the efficiency of AT2 cell colony formation. In vitro treatment of naïve AT2 cells with a FAO activator and inhibitor further confirmed the relationship between FAO and AT2 stem cell function. CONCLUSIONS: Alveolar stem cell function was more strongly activated by intermittent CS exposure than by continuous CS exposure. We provide evidence that AT2 stem cells respond to intermittent CS exposure by activating stem cell proliferation via the activation of FAO.

Dual inhibition of CPT1A and G6PD suppresses glioblastoma tumorspheres.

PURPOSE: Limited treatment options are currently available for glioblastoma (GBM), an extremely lethal type of brain cancer. For a variety of tumor types, bioenergetic deprivation through inhibition of cancer-specific metabolic pathways has proven to be an effective therapeutic strategy. Here, we evaluated the therapeutic effects and underlying mechanisms of dual inhibition of carnitine palmitoyltransferase 1A (CPT1A) and glucose-6-phosphate dehydrogenase (G6PD) critical for fatty acid oxidation (FAO) and the pentose phosphate pathway (PPP), respectively, against GBM tumorspheres (TSs). METHODS: Therapeutic efficacy against GBM TSs was determined by assessing cell viability, neurosphere formation, and 3D invasion. Liquid chromatography-mass spectrometry (LC-MS) and RNA sequencing were employed for metabolite and gene expression profiling, respectively. Anticancer efficacy in vivo was examined using an orthotopic xenograft model. RESULTS: CPT1A and G6PD were highly expressed in GBM tumor tissues. Notably, siRNA-mediated knockdown of both genes led to reduced viability, ATP levels, and expression of genes associated with stemness and invasiveness. Similar results were obtained upon combined treatment with etomoxir and dehydroepiandrosterone (DHEA). Transcriptome analyses further confirmed these results. Data from LC-MS analysis showed that this treatment regimen induced a considerable reduction in the levels of metabolites associated with the TCA cycle and PPP. Additionally, the combination of etomoxir and DHEA inhibited tumor growth and extended survival in orthotopic xenograft model mice. CONCLUSION: Our collective findings support the utility of dual suppression of CPT1A and G6PD with selective inhibitors, etomoxir and DHEA, as an efficacious therapeutic approach for GBM.

In vitro absorption and lipid-lowering activity of baicalin esters synthesized by whole-cell catalyzed esterification.

Baicalin, a phenolic glycoside with good lipid-lowering activity, has poor intestinal absorption due to low lipophilicity. In this study, six ester derivatives of baicalin, named BECn (n = 2, 3, 4, 6, 8, and 10) based on their fatty chain lengths, were synthesized by whole-cell catalyzed esterification to improve lipophilicity, and the intestinal absorption and lipid-lowering activity of the synthesized esters were investigated using cell models in vitro. BEC2, BEC3, and BEC4 exhibited higher Papp values than baicalin in Caco-2 cell monolayers. The lipid-lowering activity of the three esters was stronger than baicalin in the cell models of hepatic steatosis, adipocytes and foam macrophages, and was attributed to their higher intracellular accumulation and stronger direct activation of the carnitine palmitoyltransferase 1A. Moreover, these esters were easily hydrolyzed by carboxylesterase and were unstable at pH 7.4, which significantly weakened their absorption and lipid-lowering activity. This study laid the foundation for industrial production and practical application of BAI esters.

Carnitine palmitoyltransferase 1C reverses cellular senescence of MRC-5 fibroblasts via regulating lipid accumulation and mitochondrial function.

Cellular senescence, a state of growth arrest, is involved in various age-related diseases. We previously found that carnitine palmitoyltransferase 1C (CPT1C) is a key regulator of cancer cell proliferation and senescence, but it is unclear whether CPT1C plays a similar role in normal cells. Therefore, this study aimed to investigate the role of CPT1C in cellular proliferation and senescence of human embryonic lung MRC-5 fibroblasts and the involved mechanisms. The results showed that CPT1C could reverse the cellular senescence of MRC-5 fibroblasts, as evidenced by reduced senescence-associated ß-galactosidase activity, downregulated messenger RNA (mRNA) expression of senescence-associated secretory phenotype factors, and enhanced bromodeoxyuridine incorporation. Lipidomics analysis further revealed that CPT1C gain-of-function reduced lipid accumulation and reversed abnormal metabolic reprogramming of lipids in late MRC-5 cells. Oil Red O staining and Nile red fluorescence also indicated significant reduction of lipid accumulation after CPT1C gain-of-function. Consequently, CPT1C gain-of-function significantly reversed mitochondrial dysfunction, as evaluated by increased adenosine triphosphate synthesis and mitochondrial transmembrane potential, decreased radical oxygen species, upregulated respiratory capacity and mRNA expression of genes related to mitochondrial function. In summary, CPT1C plays a vital role in MRC-5 cellular proliferation and can reverse MRC-5 cellular senescence through the regulation of lipid metabolism and mitochondrial function, which supports the role of CPT1C as a novel target for intervention into cellular proliferation and senescence and suggests CPT1C as a new strategy for antiaging.

Inhibition of CPT1a as a prognostic marker can synergistically enhance the antileukemic activity of ABT199.

BACKGROUND: Fatty acid oxidation (FAO) provides an important source of energy to promote the growth of leukemia cells. Carnitine palmitoyltransferase 1a(CPT1a), a rate-limiting enzyme of the essential step of FAO, can facilitate cancer metabolic adaptation. Previous reports demonstrated that CPT1a acts as a potential molecular target in solid tumors and hematologic disease. However, no systematic study was conducted to explore the prognostic value of CPT1a expression and possible treatment strategies with CPT1a inhibitor on acute myeloid leukemia (AML). METHODS: The expression of CPT1a in 325 cytogenetically normal AML (CN-AML) patients was evaluated using RT-PCR. The combination effects of ST1326 and ABT199 were studied in AML cells and primary patients. MTS was used to measure the cell proliferation rate. Annexin V/propidium iodide staining and flow cytometry analysis was used to measure the apoptosis rate. Western blot was used to measure the expression of Mcl-1. RNAseq and GC-TOFMS were used for genomic and metabolic analysis. RESULTS: In this study, we found AML patients with high CPT1a expression (n = 245) had a relatively short overall survival (P = 0.01) compared to patients in low expression group (n = 80). In parallel, downregulation of CPT1a inhibits proliferation of AML cells. We also conducted genomic and metabolic interactive analysis in AML patients, and found several essential genes and pathways related to aberrant expression of CPT1a. Moreover, we found downregulation of CPT1a sentitized BCL-2 inhibitor ABT199 and CPT1a-selective inhibitor ST1326 combined with ABT199 had a strong synergistic effect to induce apoptosis in AML cells and primary patient blasts for the first time. The underlying synergistic mechanism might be that ST1326 inhibits pGSK3ß and pERK expression, leading to downregulation of Mcl-1. CONCLUSION: Our study indicates that overexpression of CPT1a predicts poor clinical outcome in AML. CPT1a-selective inhibitor ST1326 combined with Bcl-2 inhibitor ABT199 showed strong synergistic inhibitory effects on AML.

Cpt1a promoted ROS-induced oxidative stress and inflammation in liver injury via the Nrf2/HO-1 and NLRP3 inflammasome signaling pathway.

Various liver diseases caused by liver damage seriously affect people's health. The purpose of this study was to clarify the effects and the mechanisms of carnitine palmitoyltransferase 1 (Cpt1a) on oxidative stress and inflammation in liver injury. It was found that the expression of Cpt1a mRNA was upregulated in a model of liver injury in mice. Thus, overexpression of Cpt1a increased reactive oxygen species (ROS) production and malondialdehyde (MDA) levels and reduced superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GSH-px) levels in an in vitro model of liver injury. It was also shown that overexpression of Cpt1a suppressed the nuclear factor erythroid-2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway. In summary, these data indicate that Cpt1a promotes ROS-induced oxidative stress in liver injury via the Nrf2/HO-1 and nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome signaling pathway.

Association of CPT1A gene polymorphism with the risk of gestational diabetes mellitus: a case-control study.

PURPOSE: Gestational diabetes mellitus (GDM) is a growing public health problem worldwide and its etiology remains unclear. The pathophysiology of GDM is similar to that of type 2 diabetes (T2DM) and insulin resistance (IR) is the main reason for the development of GDM. Carnitine palmitoyltransferase 1A (CPT1A) is a candidate gene for metabolic disorders; however, the association of the CPT1A gene and GDM has not yet been studied. We aimed to explore whether single-nucleotide polymorphisms (SNPs) of the CPT1A gene could influence the risk of GDM. METHODS: We examined 18 single-nucleotide polymorphisms (SNPs) in the CPT1A gene and the risk of GDM in a nested case-control study of 334 GDM patients and 334 controls. The controls who had no GDM were randomly selected through matching to cases by age and residence. RESULTS: After adjusting the family history of diabetes, pre-pregnancy body mass index, and multiple comparison correction, the CPT1A rs2846194 and rs2602814 were associated with reduced GDM risk while rs59506005 was associated with elevated GDM risk. Moreover, the GGAC haplotype in the CPT1A gene (rs17399246 rs1016873 rs11228450 rs10896396) was associated with a reduced risk of GDM. CONCLUSION: Our study provides evidence for an association between genetic polymorphisms in the CPT1A and the risk of GDM.

Effects of Simvastatin on Lipid Metabolism in Wild-Type Mice and Mice with Muscle PGC-1α Overexpression.

Previous studies suggest that statins may disturb skeletal muscle lipid metabolism potentially causing lipotoxicity with insulin resistance. We investigated this possibility in wild-type mice (WT) and mice with skeletal muscle PGC-1α overexpression (PGC-1α OE mice). In WT mice, simvastatin had only minor effects on skeletal muscle lipid metabolism but reduced glucose uptake, indicating impaired insulin sensitivity. Muscle PGC-1α overexpression caused lipid droplet accumulation in skeletal muscle with increased expression of the fatty acid transporter CD36, fatty acid binding protein 4, perilipin 5 and CPT1b but without significant impairment of muscle glucose uptake. Simvastatin further increased the lipid droplet accumulation in PGC-1α OE mice and stimulated muscle glucose uptake. In conclusion, the impaired muscle glucose uptake in WT mice treated with simvastatin cannot be explained by lipotoxicity. PGC-1α OE mice are protected from lipotoxicity of fatty acids and triglycerides by increased the expression of FABP4, formation of lipid droplets and increased expression of CPT1b.

Neonatal hypoglycemia and the CPT1A P479L variant in term newborns: A retrospective cohort study of Inuit newborns from Kivalliq Nunavut.

INTRODUCTION: Neonatal hypoglycemia (NH) in the first days of life can largely be prevented by recognizing those at risk and managing accordingly. The CPT1A P479L variant is prevalent in northern Indigenous populations and is a possible risk factor for hypoglycemia. We report on NH incidence in the Kivalliq region of Nunavut, where all Inuit newborns are screened for NH. METHODS: We reviewed clinical charts of 728 Inuit newborns from Kivalliq (January 1, 2010 to December 31, 2013) for blood glucose (BG) levels and infant/maternal characteristics, linking to CPT1A genotype; 616 newborns had BG data from 2 to 48 hours of life. NH was defined using Canadian Paediatric Society guidelines (≤2.0 mmol/L at 2 hours, <2.6 mmol/L at 2 to 48 hours). RESULTS: NH was documented in 21.4% overall, 24.4% of at-risk newborns and 19.5% of term newborns with no risk factors (≥37 weeks gestation, term-NRF). NH was documented in 22.0% of CPT1A P479L homozygous, 19.8% of P479L heterozygous and 4.8% of noncarrier term-NRF newborns. With multivariable logistic regression, the adjusted ORs for developing NH in term-NRF newborns was 4.97 for CPT1A P479L homozygotes (95% confidence interval [CI]:0.65-38.35, P=0.19) and 4.71 for P479L heterozygotes (95% CI:0.57-37.89, P=0.15). CONCLUSION: Term-NRF newborns had a higher NH incidence than previously reported, similar to that for at-risk newborns, possibly due to the CPT1A P479L variant. Since only Inuit newborns from Kivalliq are screened for NH, further study of long-term outcomes of NH in this population and the role of the P479L variant are warranted to determine if neonatal BG screening is indicated in all Inuit newborns.

Glucometabolic consequences of acute and prolonged inhibition of fatty acid oxidation.

Excessive circulating FAs have been proposed to promote insulin resistance (IR) of glucose metabolism by increasing the oxidation of FAs over glucose. Therefore, inhibition of FA oxidation (FAOX) has been suggested to ameliorate IR. However, prolonged inhibition of FAOX would presumably cause lipid accumulation and thereby promote lipotoxicity. To understand the glycemic consequences of acute and prolonged FAOX inhibition, we treated mice with the carnitine palmitoyltransferase 1 (CPT-1) inhibitor, etomoxir (eto), in combination with short-term 45% high fat diet feeding to increase FA availability. Eto acutely increased glucose oxidation and peripheral glucose disposal, and lowered circulating glucose, but this was associated with increased circulating FAs and triacylglycerol accumulation in the liver and heart within hours. Several days of FAOX inhibition by daily eto administration induced hepatic steatosis and glucose intolerance, specific to CPT-1 inhibition by eto. Lower whole-body insulin sensitivity was accompanied by reduction in brown adipose tissue (BAT) uncoupling protein 1 (UCP1) protein content, diminished BAT glucose clearance, and increased hepatic glucose production. Collectively, these data suggest that pharmacological inhibition of FAOX is not a viable strategy to treat IR, and that sufficient rates of FAOX are required for maintaining liver and BAT metabolic function.

Liver-specific deletion of IGF2 mRNA binding protein-2/IMP2 reduces hepatic fatty acid oxidation and increases hepatic triglyceride accumulation.

Insulin-like growth factor 2 mRNA-binding proteins 1-3 (IGF2BP1-3, also known as IMP1-3) contribute to the regulation of RNAs in a transcriptome-specific context. Global deletion of the mRNA-binding protein insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2 or IMP2) in mice causes resistance to obesity and fatty liver induced by a high-fat diet (HFD), whereas liver-specific IMP2 overexpression results in steatosis. To better understand the role of IMP2 in hepatic triglyceride metabolism, here we crossed mice expressing albumin-Cre with mice bearing a floxed Imp2 gene to generate hepatocyte-specific IMP2 knockout (LIMP2 KO) mice. Unexpectedly, the livers of LIMP2 KO mice fed an HFD accumulated more triglyceride. Although hepatocyte-specific IMP2 deletion did not alter lipogenic gene expression, it substantially decreased the levels of the IMP2 client mRNAs encoding carnitine palmitoyltransferase 1A (CPT1A) and peroxisome proliferator-activated receptor α (PPARα). This decrease was associated with their more rapid turnover and accompanied by significantly diminished rates of palmitate oxidation by isolated hepatocytes and liver mitochondria. HFD-fed control and LIMP2 KO mice maintained a similar glucose tolerance and insulin sensitivity up to 6 months; however, by 6 months, blood glucose and serum triglycerides in LIMP2 KO mice were modestly elevated but without evidence of liver damage. In conclusion, hepatocyte-specific IMP2 deficiency promotes modest diet-induced fatty liver by impairing fatty acid oxidation through increased degradation of the IMP2 client mRNAs PPARα and CPT1A This finding indicates that the previously observed marked protection against fatty liver conferred by global IMP2 deficiency in mice is entirely due to their reduced adiposity.

CPT1 regulates the proliferation of pulmonary artery smooth muscle cells through the AMPK-p53-p21 pathway in pulmonary arterial hypertension.

Abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs) plays a dominant role in the development of pulmonary arterial hypertension (PAH). Some studies and our previous work found that disturbance of fatty acid metabolism existed in PAH. However, the mechanistic link between fatty acid catabolism and cell proliferation remains elusive. Here, we identified an essential role and signal pathway for the key rate-limiting enzyme of mitochondrial fatty acid ß-oxidation, carnitine palmitoyltransferase (CPT) 1, in regulating PASMC proliferation in PAH. We found that CPT1 was highly expressed in rat lungs and pulmonary arteries in monocrotaline-induced PAH, accompanied by decreased adenosine triphosphate (ATP) production and downregulation of the AMPK-p53-p21 pathway. Platelet-derived growth factor (PDGF)-BB upregulated the expression of CPT1 in a dose- and time-dependent manner. PASMC proliferation and ATP production induced by PDGF-BB were partly reversed by the CPT1 inhibitor etomoxir (ETO). The overexpression of CPT1 in PASMCs also promoted proliferation and ATP production and subsequently inhibited the phosphorylation of AMPK, p53, as well as p21 in PASMCs. Furthermore, AMPK was activated by ETO, which increased the expression of p53 and p21, and the proportion of cells in the cell cycle G2/M phase in response to PDGF-BB stimulation in PASMCs. Our work reveals a novel mechanism of CPT1 regulating PASMC proliferation in PAH, and regulation of CPT1 may be a potential target for therapeutic intervention in PAH.

Ceramides and mitochondrial fatty acid oxidation in obesity.

Obesity is an epidemic, complex disease that is characterized by increased glucose, lipids, and low-grade inflammation in the circulation, among other factors. It creates the perfect scenario for the production of ceramide, the building block of the sphingolipid family of lipids, which is involved in metabolic disorders such as obesity, diabetes, and cardiovascular disease. In addition, obesity causes a decrease in fatty acid oxidation (FAO), which contributes to lipid accumulation within the cells, conferring more susceptibility to cell dysfunction. C16:0 ceramide, a specific ceramide species, has been identified recently as the principal mediator of obesity-derived insulin resistance, impaired fatty acid oxidation, and hepatic steatosis. In this review, we have sought to cover the importance of the ceramide species and their metabolism, the main ceramide signaling pathways in obesity, and the link between C16:0 ceramide, FAO, and obesity.-Fucho, R., Casals, N., Serra, D., Herrero, L. Ceramides and mitochondrial fatty acid oxidation in obesity.

The protein-sparing effect of α-lipoic acid in juvenile grass carp, Ctenopharyngodon idellus: effects on lipolysis, fatty acid ß-oxidation and protein synthesis.

To investigate the protein-sparing effect of α-lipoic acid (LA), experimental fish (initial body weight: 18·99 (sd 1·82) g) were fed on a 0, 600 or 1200 mg/kg α-LA diet for 56 d, and hepatocytes were treated with 20 µm compound C, the inhibitor of AMP kinase α (AMPKα), treated for 30 min before α-LA treatment for 24 h. LA significantly decreased lipid content of the whole body and other tissues (P0·05). Consistent with results from the experiment in vitro, LA activated phosphorylation of AMPKα and notably increased the protein content of adipose TAG lipase in intraperitoneal fat, hepatopancreas and muscle in vivo (P<0·05). Meanwhile, LA significantly up-regulated the mRNA expression of genes involved in fatty acid ß-oxidation in the same three areas, and LA also obviously down-regulated the mRNA expression of genes involved in amino acid catabolism in muscle (P<0·05). Besides, it was observed that LA significantly activated the mammalian target of rapamycin (mTOR) pathway in muscle of experimental fish (P<0·05). LA could promote lipolysis and fatty acid ß-oxidation via increasing energy supply from lipid catabolism, and then, it could economise on the protein from energy production to increase protein deposition in grass carp. Besides, LA might directly promote protein synthesis through activating the mTOR pathway.

Dietary soya protein improves intra-myocardial lipid deposition and altered glucose metabolism in a hypertensive, dyslipidaemic, insulin-resistant rat model.

This study investigates the effects of replacing dietary casein by soya protein on the underlying mechanisms involved in the impaired metabolic fate of glucose and lipid metabolisms in the heart of dyslipidaemic rats chronically fed (8 months) a sucrose-rich (62·5 %) diet (SRD). To test this hypothesis, Wistar rats were fed an SRD for 4 months. From months 4 to 8, half the animals continued with the SRD and the other half were fed an SRD in which casein was substituted by soya. The control group received a diet with maize starch as the carbohydrate source. Compared with the SRD-fed group, the following results were obtained. First, soya protein significantly (P<0·001) reduced the plasma NEFA levels and normalised dyslipidaemia and glucose homoeostasis, improving insulin resistance. The protein levels of fatty acid translocase at basal state and under insulin stimulation and the protein levels and activity of muscle-type carnitine palmitoyltransferase 1 were normalised. Second, a significant (P<0·001) reduction of TAG, long-chain acyl CoA and diacylglycerol levels was observed in the heart muscle. Third, soya protein significantly increased (P<0·01) GLUT4 protein level under insulin stimulation and normalised glucose phosphorylation and oxidation. A reduction of phosphorylated AMP protein kinase protein level was recorded without changes in uncoupling protein 2 and PPARα. Fourth, hydroxyproline concentration decreased in the left ventricle and hypertension was normalised. The new information provided shows the beneficial effects of soya protein upon the altered pathways of glucose and lipid metabolism in the heart muscle of this rat model.