Impact of peripheral ketolytic deficiency on hepatic ketogenesis and gluconeogenesis during the transition to birth

OXCT1 Enhances Gemcitabine Resistance Through NF-κB Pathway in Pancreatic Ductal Adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) is a type of malignant tumor with a five-year survival rate of less than 10%. Gemcitabine (GEM) is the most commonly used drug for PDAC chemotherapy. However, a vast majority of patients with PDAC develop resistance after GEM treatment.

Methods

We screened for GEM resistance genes through bioinformatics analysis. We used immunohistochemistry to analyze 3-oxoacid CoA-transferase 1 (OXCT1) expression in PDAC tissues. The survival data were analyzed using the Kaplan–Meier curve. The expression levels of the genes related to OXCT1 and the NF-κB signaling pathway were quantified using real−time quantitative PCR and western blot analyses. We performed flow cytometry to detect the apoptosis rate. Colony formation assay was performed to measure the cell proliferation levels. The cytotoxicity assays of cells were conducted using RTCA. The downstream pathway of OXCT1 was identified via the Gene Set Enrichment Analysis. Tumor growth response to GEM in vivo was also determined in mouse models.

Results

Bioinformatics analysis revealed that OXCT1 is the key gene leading to GEM resistance. Patients with high OXCT1 expression exhibited short relapse-free survival under GEM treatment. OXCT1 overexpression in PDAC cell lines exerted inhibitory effect on apoptosis after GEM treatment. However, the down-regulation of OXCT1 showed the opposite effect. Blocking the NF-κB signaling pathway also reduced GEM resistance of PDAC cells. Tumor growth inhibition induced by GEM in vivo reduced after OXCT1 overexpression. Moreover, the effect of OXCT1 on GEM refractoriness in PDAC cell lines was reversed through using an NF-κB inhibitor.

Conclusion

OXCT1 promoted GEM resistance in PDAC via the NF-κB signaling pathway both in vivo and in vitro. Our results suggest that OXCT1 could be used as a potential therapeutic target for patients with PDAC.

Diminished ketone interconversion, hepatic TCA cycle flux, and glucose production in D-β-hydroxybutyrate dehydrogenase hepatocyte-deficient mice

Objective

Throughout the last decade, interest has intensified in intermittent fasting, ketogenic diets, and exogenous ketone therapies as prospective health-promoting, therapeutic, and performance-enhancing agents. However, the regulatory roles of ketogenesis and ketone metabolism on liver homeostasis remain unclear. Therefore, we sought to develop a better understanding of the metabolic consequences of hepatic ketone body metabolism by focusing on the redox-dependent interconversion of acetoacetate (AcAc) and D-β-hydroxybutyrate (D-βOHB).

Methods

Using targeted and isotope tracing high-resolution liquid chromatography-mass spectrometry, dual stable isotope tracer nuclear magnetic resonance spectroscopy-based metabolic flux modeling, and complementary physiological approaches in novel cell type-specific knockout mice, we quantified the roles of hepatocyte D-β-hydroxybutyrate dehydrogenase (BDH1), a mitochondrial enzyme required for NAD⁺/NADH-dependent oxidation/reduction of ketone bodies.

Results

Exogenously administered AcAc is reduced to D-βOHB, which increases hepatic NAD⁺/NADH ratio and reflects hepatic BDH1 activity. Livers of hepatocyte-specific BDH1-deficient mice did not produce D-βOHB, but owing to extrahepatic BDH1, these mice nonetheless remained capable of AcAc/D-βOHB interconversion. Compared to littermate controls, hepatocyte-specific BDH1 deficient mice exhibited diminished liver tricarboxylic acid (TCA) cycle flux and impaired gluconeogenesis, but normal hepatic energy charge overall. Glycemic recovery after acute insulin challenge was impaired in knockout mice, but they were not more susceptible to starvation-induced hypoglycemia.

Conclusions

Ketone bodies influence liver homeostasis. While liver BDH1 is not required for whole body equilibration of AcAc and D-βOHB, loss of the ability to interconvert these ketone bodies in hepatocytes results in impaired TCA cycle flux and glucose production. Therefore, through oxidation/reduction of ketone bodies, BDH1 is a significant contributor to hepatic mitochondrial redox, liver physiology, and organism-wide ketone body homeostasis.

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Exogenously administered acetoacetate is reduced to D-β-hydroxybutyrate, increasing hepatic NAD⁺/NADH ratio.

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Liver BDH1 is not required for whole body equilibration of acetoacetate and D-β-hydroxybutyrate.

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Hepatocyte-specific loss of BDH1 reduces hepatic TCA cycle flux, and TCA-cycle sourced gluconeogenesis.

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Hepatocyte-specific loss of BDH1 impairs glycemic recovery without provoking starvation-induced hypoglycemia.

Murine neonatal ketogenesis preserves mitochondrial energetics by preventing protein hyperacetylation

Ketone bodies are generated in the liver and allow for the maintenance of systemic caloric and energy homeostasis during fasting and caloric restriction. It has previously been demonstrated that neonatal ketogenesis is activated independently of starvation. However, the role of ketogenesis during the perinatal period remains unclear. Here, we show that neonatal ketogenesis plays a protective role in mitochondrial function. We generated a mouse model of insufficient ketogenesis by disrupting the rate-limiting hydroxymethylglutaryl-CoA synthase 2 enzyme gene (Hmgcs2). Hmgcs2 knockout (KO) neonates develop microvesicular steatosis within a few days of birth. Electron microscopic analysis and metabolite profiling indicate a restricted energy production capacity and accumulation of acetyl-CoA in Hmgcs2 KO mice. Furthermore, acetylome analysis of Hmgcs2 KO cells revealed enhanced acetylation of mitochondrial proteins. These findings suggest that neonatal ketogenesis protects the energy-producing capacity of mitochondria by preventing the hyperacetylation of mitochondrial proteins.

Role of OXCT1 in ovine adipose and preadipocyte differentiation

3-oxoacid CoA-transferase 1 (OXCT1) is a key enzyme in ketone body metabolism that is expressed in adipose and other tissues. The present study addressed the function of OXCT1 in adipose tissue from Tan sheep. The 1563 bp ovine OXCT1 coding sequence was cloned from ovine adipose tissue. The OXCT1 protein sequence was highly homologous to OXCT1 from other species. OXCT1 was highly expressed in kidney and at lower levels in small intestine, lung, spleen, heart, stomach, liver, tail adipose, and cartilage, but not in longissimus muscle. OXCT1 was expressed at higher levels in perirenal and tail adipose tissues than in subcutaneous adipose tissue. OXCT1 expression levels increased during the in vitro differentiation of adipocytes, but decreased dramatically at day 8. OXCT1 knockdown in ovine adipocytes promoted lipid accumulation, whereas overexpression did the converse. This study demonstrates that OXCT1 may play a role in adipogenesis and provides new insight on adipose deposition in sheep.

A double-hit pre-eclampsia model results in sex-specific growth restriction patterns

Pre-eclampsia is a multifactorial pregnancy-associated disorder characterized by angiogenic dysbalance and systemic inflammation; however, animal models that combine these two pathophysiological conditions are missing. Here, we introduce a novel double-hit pre-eclampsia mouse model that mimics the complex multifactorial conditions present during pre-eclampsia and allows for the investigation of early consequences for the fetus. Adenoviral overexpression of soluble fms-like tyrosine kinase (sFlt-1) and lipopolysaccharide (LPS) administration at mid-gestation in pregnant mice resulted in hypertension and albuminuria comparable to that of the manifestation in humans. A metabolomics analysis revealed that pre-eclamptic dams have increased plasma concentrations of phosphadytilcholines. The fetuses of both sexes were growth restricted; however, in males a brain-sparing effect was seen as compensation for this growth restriction. According to the plasma metabolomics, male fetuses showed changes in amino acid metabolism, while female fetuses showed pronounced alterations in lipid metabolism. Our results show that combined exposure to sFlt-1 and LPS mimics the clinical symptoms of pre-eclampsia and affects fetal growth in a sex-specific manner, with accompanying metabolome changes.

The role of OXCT1 in the pathogenesis of cancer as a rate-limiting enzyme of ketone body metabolism

Cancer cells are well documented to reprogram their metabolism in order to support the maintenance and reproduction. 3-oxoacid CoA-transferase 1 (OXCT1) is a key enzyme in ketone body metabolism that catalyzes the first and rate-determining step of ketolysis. The product of OXCT1 converts to acetyl-CoA and finally fed into the tricarboxylic acid cycle for oxidation and ATP production. However, little is known of its regulation right now. Recently, some studies suggested that OXCT1 participates in tumorigenesis and signaling in cancer cells. Furthermore, our recent work showed that a marked elevation of OXCT1 expression in different categories of cancer cells. Here we review the metabolic functions of OXCT1 and its surprising roles in supporting the biological hallmarks of malignancy. We also review recent efforts in exploring the mechanism responsible for the tumor promoting effect of OXCT1 and suggest a novel therapeutic target for cancer therapy.

Glucocorticoid receptor-PPARα axis in fetal mouse liver prepares neonates for milk lipid catabolism

In mammals, hepatic lipid catabolism is essential for the newborns to efficiently use milk fat as an energy source. However, it is unclear how this critical trait is acquired and regulated. We demonstrate that under the control of PPARα, the genes required for lipid catabolism are transcribed before birth so that the neonatal liver has a prompt capacity to extract energy from milk upon suckling. The mechanism involves a fetal glucocorticoid receptor (GR)-PPARα axis in which GR directly regulates the transcriptional activation of PPARα by binding to its promoter. Certain PPARα target genes such as Fgf21 remain repressed in the fetal liver and become PPARα responsive after birth following an epigenetic switch triggered by β-hydroxybutyrate-mediated inhibition of HDAC3. This study identifies an endocrine developmental axis in which fetal GR primes the activity of PPARα in anticipation of the sudden shifts in postnatal nutrient source and metabolic demands.

DOI:http://dx.doi.org/10.7554/eLife.11853.001

Birth is a highly stressful and critical event. In the womb, babies rely on the supply of oxygen and nutrients provided by the placenta. However, once they are born they need to breathe for themselves and gain all their nutrients from suckling milk. The placenta provides a sugar-rich diet, while milk is richer in fat. Failing to cope with this change in diet leads to serious complications and sometimes death. Therefore, a better understanding of how the body adapts to these changes may shed light on pathways that are important for good health in later life.

The liver plays a central role in processing the nutrients absorbed by the gut. It uses fats to produce molecules called ketone bodies, such as β-hydroxybutyrate, which are then used as fuel by other tissues and organs including the heart, muscle and the brain. A protein called PPARα controls the production of ketone bodies primarily by regulating genes that are involved in the uptake and breakdown of fat in the liver. However, little is known about how this protein affects the development of the liver.

Here, Rando, Tan et al. report that mice start to produce more PPARα in the liver shortly before birth. This ultimately activates several genes that encode enzymes that break down fats. The experiments show that during labor, stress hormones called glucocorticoids directly stimulate the production of PPARα in the liver of the fetus to prepare newborn mice for harnessing energy from fat-rich milk.

In the absence of PPARα, mouse liver cells are less able to break down fats after birth and so start to accumulate fat, resulting in fewer ketone bodies being produced. Rando, Tan et al. show that β-hydroxybutyrate regulates some PPARα target genes, including one called Fgf21. The activity of this gene increases only after milk suckling starts and it encodes a protein that enhances the breakdown of fats in the liver. Without PPARα, the expression levels of its target genes, including Fgf21, do not increase after birth, which promotes the build up of fats in liver cells, a condition known as liver steatosis.

Overall, the results reported by Rando, Tan et al. highlight how stress during labor plays an important role in priming the body to cope with a fat-rich diet after birth. Future studies will need to determine if stress hormones and ketone bodies could be used as therapies for babies born by caesarean section with liver steatosis.

DOI:http://dx.doi.org/10.7554/eLife.11853.002

The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome-mediated inflammatory disease

Ketone bodies , β-hydroxybutyrate (BHB) and acetoacetate support mammalian survival during states of energy deficit by serving as alternative source of ATP¹. BHB levels are elevated during starvation, high-intensity exercise or by the low carbohydrate ketogenic diet². Prolonged caloric restriction or fasting reduces inflammation as immune system adapts to low glucose supply and energy metabolism switches towards mitochondrial fatty acid oxidation, ketogenesis and ketolysis^2-6. However, role of ketones bodies in regulation of innate immune response is unknown. We report that BHB, but neither acetoacetate nor structurally-related short chain fatty acids, butyrate and acetate, suppresses activation of the NLRP3 inflammasome in response to several structurally unrelated NLRP3 activators, without impacting NLRC4, AIM2 or non-canonical caspase-11 inflammasome activation. Mechanistically, BHB inhibits NLRP3 inflammasome by preventing K⁺ efflux and reducing ASC oligomerization and speck formation. The inhibitory effects of BHB on NLRP3 were not dependent on chirality or classical starvation regulated mechanisms like AMPK, reactive oxygen species (ROS), autophagy or glycolytic inhibition. BHB blocked NLRP3 inflammasome without undergoing oxidation in TCA cycle, independently of uncoupling protein-2 (UCP2), Sirt2, receptor Gpr109a and inhibition of NLRP3 did not correlate with magnitude of histone acetylation in macrophages. BHB reduced the NLRP3 inflammasome mediated IL-1β and IL-18 production in human monocytes. In vivo, BHB attenuates caspase-1 activation and IL-1β secretion in mouse models of NLRP3-mediated diseases like Muckle-Wells Syndrome (MWS), Familial Cold Autoinflammatory syndrome (FCAS) and urate crystal induce body cavity inflammation. Taken together, these findings suggest that the anti-inflammatory effects of caloric restriction or ketogenic diets may be mechanistically linked to BHB-mediated inhibition of the NLRP3 inflammasome, and point to the potential use of interventions that elevate circulating BHB against NLRP3-mediated proinflammatory diseases.

Ketogenesis prevents diet-induced fatty liver injury and hyperglycemia

Nonalcoholic fatty liver disease (NAFLD) spectrum disorders affect approximately 1 billion individuals worldwide. However, the drivers of progressive steatohepatitis remain incompletely defined. Ketogenesis can dispose of much of the fat that enters the liver, and dysfunction in this pathway could promote the development of NAFLD. Here, we evaluated mice lacking mitochondrial 3-hydroxymethylglutaryl CoA synthase (HMGCS2) to determine the role of ketogenesis in preventing diet-induced steatohepatitis. Antisense oligonucleotide-induced loss of HMGCS2 in chow-fed adult mice caused mild hyperglycemia, increased hepatic gluconeogenesis from pyruvate, and augmented production of hundreds of hepatic metabolites, a suite of which indicated activation of the de novo lipogenesis pathway. High-fat diet feeding of mice with insufficient ketogenesis resulted in extensive hepatocyte injury and inflammation, decreased glycemia, deranged hepatic TCA cycle intermediate concentrations, and impaired hepatic gluconeogenesis due to sequestration of free coenzyme A (CoASH). Supplementation of the CoASH precursors pantothenic acid and cysteine normalized TCA intermediates and gluconeogenesis in the livers of ketogenesis-insufficient animals. Together, these findings indicate that ketogenesis is a critical regulator of hepatic acyl-CoA metabolism, glucose metabolism, and TCA cycle function in the absorptive state and suggest that ketogenesis may modulate fatty liver disease.

Muscle transcriptomic investigation of late fetal development identifies candidate genes for piglet maturity

Background

In pigs, the perinatal period is the most critical time for survival. Piglet maturation, which occurs at the end of gestation, leads to a state of full development after birth. Therefore, maturity is an important determinant of early survival. Skeletal muscle plays a key role in adaptation to extra-uterine life, e.g. glycogen storage and thermoregulation. In this study, we performed microarray analysis to identify the genes and biological processes involved in piglet muscle maturity. Progeny from two breeds with extreme muscle maturity phenotypes were analyzed at two time points during gestation (gestational days 90 and 110). The Large White (LW) breed is a selected breed with an increased rate of mortality at birth, whereas the Meishan (MS) breed produces piglets with extremely low mortality at birth. The impact of the parental genome was analyzed with reciprocal crossed fetuses.

Results

Microarray analysis identified 12,326 differentially expressed probes for gestational age and genotype. Such a high number reflects an important transcriptomic change that occurs between 90 and 110 days of gestation. 2,000 probes, corresponding to 1,120 unique annotated genes, involved more particularly in the maturation process were further studied. Functional enrichment and graph inference studies underlined genes involved in muscular development around 90 days of gestation, and genes involved in metabolic functions, such as gluconeogenesis, around 110 days of gestation. Moreover, a difference in the expression of key genes, e.g. PCK2, LDHA or PGK1, was detected between MS and LW just before birth. Reciprocal crossing analysis resulted in the identification of 472 genes with an expression preferentially regulated by one parental genome. Most of these genes (366) were regulated by the paternal genome. Among these paternally regulated genes, some known imprinted genes, such as MAGEL2 or IGF2, were identified and could have a key role in the maturation process.

Conclusion

These results reveal the biological mechanisms that regulate muscle maturity in piglets. Maturity is also under the conflicting regulation of the parental genomes. Crucial genes, which could explain the biological differences in maturity observed between LW and MS breeds, were identified. These genes could be excellent candidates for a key role in the maturity.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-797) contains supplementary material, which is available to authorized users.

Cardiomyocyte-specific deficiency of ketone body metabolism promotes accelerated pathological remodeling

OBJECTIVE

Exploitation of protective metabolic pathways within injured myocardium still remains an unclarified therapeutic target in heart disease. Moreover, while the roles of altered fatty acid and glucose metabolism in the failing heart have been explored, the influence of highly dynamic and nutritionally modifiable ketone body metabolism in the regulation of myocardial substrate utilization, mitochondrial bioenergetics, reactive oxygen species (ROS) generation, and hemodynamic response to injury remains undefined.

METHODS

Here we use mice that lack the enzyme required for terminal oxidation of ketone bodies, succinyl-CoA:3-oxoacid CoA transferase (SCOT) to determine the role of ketone body oxidation in the myocardial injury response. Tracer delivery in ex vivo perfused hearts coupled to NMR spectroscopy, in vivo high-resolution echocardiographic quantification of cardiac hemodynamics in nutritionally and surgically modified mice, and cellular and molecular measurements of energetic and oxidative stress responses are performed.

RESULTS

While germline SCOT-knockout (KO) mice die in the early postnatal period, adult mice with cardiomyocyte-specific loss of SCOT (SCOT-Heart-KO) remarkably exhibit no overt metabolic abnormalities, and no differences in left ventricular mass or impairments of systolic function during periods of ketosis, including fasting and adherence to a ketogenic diet. Myocardial fatty acid oxidation is increased when ketones are delivered but cannot be oxidized. To determine the role of ketone body oxidation in the remodeling ventricle, we induced pressure overload injury by performing transverse aortic constriction (TAC) surgery in SCOT-Heart-KO and αMHC-Cre control mice. While TAC increased left ventricular mass equally in both groups, at four weeks post-TAC, myocardial ROS abundance was increased in myocardium of SCOT-Heart-KO mice, and mitochondria and myofilaments were ultrastructurally disordered. Eight weeks post-TAC, left ventricular volume was markedly increased and ejection fraction was decreased in SCOT-Heart-KO mice, while these parameters remained normal in hearts of control animals.

CONCLUSIONS

These studies demonstrate the ability of myocardial ketone metabolism to coordinate the myocardial response to pressure overload, and suggest that the oxidation of ketone bodies may be an important contributor to free radical homeostasis and hemodynamic preservation in the injured heart.

Impairments of hepatic gluconeogenesis and ketogenesis in PPARα-deficient neonatal mice

Peroxisome proliferator activated receptor-α (PPARα) is a master transcriptional regulator of hepatic metabolism and mediates the adaptive response to fasting. Here, we demonstrate the roles for PPARα in hepatic metabolic adaptations to birth. Like fasting, nutrient supply is abruptly altered at birth when a transplacental source of carbohydrates is replaced by a high-fat, low-carbohydrate milk diet. PPARα-knockout (KO) neonatal mice exhibit relative hypoglycemia due to impaired conversion of glycerol to glucose. Although hepatic expression of fatty acyl-CoA dehydrogenases is imparied in PPARα neonates, these animals exhibit normal blood acylcarnitine profiles. Furthermore, quantitative metabolic fate mapping of the medium-chain fatty acid [(13)C]octanoate in neonatal mouse livers revealed normal contribution of this fatty acid to the hepatic TCA cycle. Interestingly, octanoate-derived carbon labeled glucose uniquely in livers of PPARα-KO neonates. Relative hypoketonemia in newborn PPARα-KO animals could be mechanistically linked to a 50% decrease in de novo hepatic ketogenesis from labeled octanoate. Decreased ketogenesis was associated with diminished mRNA and protein abundance of the fate-committing ketogenic enzyme mitochondrial 3-hydroxymethylglutaryl-CoA synthase (HMGCS2) and decreased protein abundance of the ketogenic enzyme β-hydroxybutyrate dehydrogenase 1 (BDH1). Finally, hepatic triglyceride and free fatty acid concentrations were increased 6.9- and 2.7-fold, respectively, in suckling PPARα-KO neonates. Together, these findings indicate a primary defect of gluconeogenesis from glycerol and an important role for PPARα-dependent ketogenesis in the disposal of hepatic fatty acids during the neonatal period.

Metabolic tinkering by the gut microbiome: Implications for brain development and function

Brain development is an energy demanding process that relies heavily upon diet derived nutrients. Gut microbiota enhance the host's ability to extract otherwise inaccessible energy from the diet via fermentation of complex oligosaccharides in the colon. This nutrient yield is estimated to contribute up to 10% of the host's daily caloric requirement in humans and fluctuates in response to environmental variations. Research over the past decade has demonstrated a surprising role for the gut microbiome in normal brain development and function. In this review we postulate that perturbations in the gut microbial-derived nutrient supply, driven by environmental variation, profoundly impacts upon normal brain development and function.