During the perinatal period, unique metabolic adaptations support energetic requirements for rapid growth. To gain insight into perinatal adaptations, quantitative proteomics were performed comparing ...the livers of yorkshire pigs at postnatal day seven and adult. These data revealed differences in the metabolic control of liver function including significant changes in lipid and carbohydrate metabolic pathways. Newborn livers showed an enrichment of proteins in lipid catabolism and gluconeogenesis concomitant with elevated liver carnitine and acylcarnitines levels. Sugar kinases were some of the most dramatically differentially enriched proteins comparing neonatal and adult pigs including galactokinase 1 (Galk1), ketohexokinase (KHK), hexokinase 1 (HK1) and hexokinase 4 (GCK). Interestingly, hexokinase domain containing 1 (HKDC1), a newly identified fifth hexokinase associated with glucose disturbances in pregnant women was highly enriched in the liver during the prenatal and perinatal periods and continuously declined throughout postnatal development in pigs and mice. These changes were confirmed via Western blot and mRNA expression. These data provide new insights into the developmental and metabolic adaptations in the liver during the transition from the perinatal period to adulthood in multiple mammalian species.
The liver is critical for maintaining systemic energy balance during starvation. To understand the role of hepatic fatty acid β-oxidation on this process, we generated mice with a liver-specific ...knockout of carnitine palmitoyltransferase 2 (Cpt2L−/−), an obligate step in mitochondrial long-chain fatty acid β-oxidation. Fasting induced hepatic steatosis and serum dyslipidemia with an absence of circulating ketones, while blood glucose remained normal. Systemic energy homeostasis was largely maintained in fasting Cpt2L−/− mice by adaptations in hepatic and systemic oxidative gene expression mediated in part by Pparα target genes including procatabolic hepatokines Fgf21, Gdf15, and Igfbp1. Feeding a ketogenic diet to Cpt2L−/− mice resulted in severe hepatomegaly, liver damage, and death with a complete absence of adipose triglyceride stores. These data show that hepatic fatty acid oxidation is not required for survival during acute food deprivation but essential for constraining adipocyte lipolysis and regulating systemic catabolism when glucose is limiting.
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•Hepatic fatty acid oxidation (FAO) is critical for liver physiology during starvation•Hepatic FAO suppresses adipose lipolysis and systemic catabolism•Upon fasting, loss of hepatic FAO induces Pparα target genes in the liver•A ketogenic diet induces severe lipolysis and lethality in hepatic FAO-deficient mice
Lee et al. have generated mice that lack mitochondrial long-chain fatty acid β-oxidation specifically in the liver. They report that these mice can survive a 24-hr fast but not a low-carbohydrate ketogenic diet. Surprisingly, whole-body energy expenditure is largely maintained due to increased peripheral catabolism.
Odontocete cetaceans exhibit genomic mutations in key ketogenesis genes. In order to validate an inferred lack of ketogenesis made by observations from genome sequencing, we biochemically analyzed ...tissues from several odontocete cetacean species and demonstrate that they indeed do not exhibit appreciable hepatic β-hydroxybutyrate (βHB) or its carnitine ester. Furthermore, liver tissue exhibited significantly lower long chain acylcarnitines and increased odd chain acylcarnitines indicative of a decreased reliance on hepatic long chain fatty acid oxidation in these carnivorous mammals. Finally, we performed single molecule, real-time next generation sequencing of liver and brain RNA of Tursiops truncatus and demonstrate that the succinyl-CoA transferase required for acetoacetate catabolism is expressed in the nervous system. These data show that odontocete cetaceans have lost the ability to perform ketogenesis and suggest a hepatocentric coenzyme A recycling function rather than a predominantly systemic-bioenergetic role for ketogenesis in other ketogenic competent mammals such as humans.
The liver has a large capacity for mitochondrial fatty acid β-oxidation, which is critical for systemic metabolic adaptations such as gluconeogenesis and ketogenesis. To understand the role of ...hepatic fatty acid oxidation in response to a chronic high-fat diet (HFD), we generated mice with a liver-specific deficiency of mitochondrial long-chain fatty acid β-oxidation (Cpt2L−/− mice). Paradoxically, Cpt2L−/− mice were resistant to HFD-induced obesity and glucose intolerance with an absence of liver damage, although they exhibited serum dyslipidemia, hepatic oxidative stress, and systemic carnitine deficiency. Feeding an HFD induced hepatokines in mice, with a loss of hepatic fatty acid oxidation that enhanced systemic energy expenditure and suppressed adiposity. Additionally, the suppression in hepatic gluconeogenesis was sufficient to improve HFD-induced glucose intolerance. These data show that inhibiting hepatic fatty acid oxidation results in a systemic hormetic response that protects mice from HFD-induced obesity and glucose intolerance.
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•Loss of hepatic fatty acid oxidation (FAO) confers resistance to obesity•Loss of hepatic FAO results in beneficial hormesis•The suppression of FAO is sufficient to improve diet-induced glucose intolerance•Resistance to obesity results from increased energy expenditure
Lee et al. show that, contrary to expectations, the loss of hepatic fatty acid oxidation (FAO) confers resistance to weight gain and adiposity in response to a high-fat diet. Additionally, they show that loss of hepatic FAO—and, consequently, hepatic gluconeogenesis—protects mice from high-fat-diet-induced glucose intolerance.
Ambient temperature affects energy intake and expenditure to maintain homeostasis in a continuously fluctuating environment. Here, mice with an adipose-specific defect in fatty acid oxidation ...(Cpt2A−/−) were subjected to varying temperatures to determine the role of adipose bioenergetics in environmental adaptation and body weight regulation. Microarray analysis of mice acclimatized to thermoneutrality revealed that Cpt2A−/− interscapular brown adipose tissue (BAT) failed to induce the expression of thermogenic genes such as Ucp1 and Pgc1α in response to adrenergic stimulation, and increasing ambient temperature exacerbated these defects. Furthermore, thermoneutral housing induced mtDNA stress in Cpt2A−/− BAT and ultimately resulted in a loss of interscapular BAT. Although the loss of adipose fatty acid oxidation resulted in clear molecular, cellular, and physiologic deficits in BAT, body weight gain and glucose tolerance were similar in control and Cpt2A−/− mice in response to a high-fat diet, even when mice were housed at thermoneutrality.
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•Fatty acid oxidation (FAO) is required for the induction of Ucp1 and Pgc1α in BAT•Increasing ambient temperature potentiates defects in FAO-deficient BAT•Loss of adipose FAO induces mtDNA stress in BAT•Loss of adipose FAO does not alter body weight or adiposity at thermoneutrality
Lee et al. show that a loss of adipose fatty acid oxidation (FAO) at thermoneutrality results in defective induction of thermogenic genes and mtDNA stress in BAT. Long-term housing of FAO-deficient mice results in a loss of interscapular BAT; however, body weight gain and glucose tolerance were unaffected.
The metabolic state of the brain can greatly impact neurologic function. Evidence of this includes the therapeutic benefit of a ketogenic diet in neurologic diseases, including epilepsy. However, ...brain lipid bioenergetics remain largely uncharacterized. The existence, capacity, and relevance of mitochondrial fatty acid β-oxidation (FAO) in the brain are highly controversial, with few genetic tools available to evaluate the question. We have provided evidence for the capacity of brain FAO using a pan-brain-specific conditional knockout (KO) mouse incapable of FAO due to the loss of carnitine palmitoyltransferase 2, the product of an obligate gene for FAO (CPT2
B−/−
). Loss of central nervous system (CNS) FAO did not result in gross neuroanatomical changes or systemic differences in metabolism. Loss of CPT2 in the brain did not result in robustly impaired behavior. We demonstrate by unbiased and targeted metabolomics that the mammalian brain oxidizes a substantial quantity of long-chain fatty acids in vitro and in vivo. Loss of CNS FAO results in robust accumulation of long-chain acylcarnitines in the brain, suggesting that the mammalian brain mobilizes fatty acids for their oxidation, irrespective of diet or metabolic state. Together, these data demonstrate that the mammalian brain oxidizes fatty acids under normal circumstances with little influence from or on peripheral tissues.
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