Gene expression of enzymes regulating ketogenesis and fatty acid metabolism in regenerating rat liver.
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ABSTRACT: Levels of mRNA for mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase, carnitine palmitoyltransferase I (CPT I) and carnitine palmitoyltransferase II (CPT II), fatty acid synthase (FAS) and actin were analysed during liver regeneration. mRNA levels for mitochondrial HMG-CoA synthase decreased rapidly, reaching a minimum 12 h after partial hepatectomy and returning to normal at 24-36 h. In contrast, CPT I, CPT II and FAS mRNAs increased throughout the period examined. Expression of actin increased significantly during regeneration. Levels of mRNA for mitochondrial HMG-CoA synthase also decreased as a result of surgical stress, although the effect of hepatectomy was much greater. We determined the levels of mitochondrial HMG-CoA synthase using specific antibodies. The amount of protein rapidly decreased, although less markedly than the corresponding mRNA levels. These results show that the decrease described in ketogenesis in partially hepatectomized rats correlated with the decrease in the expression of mitochondrial HMG-CoA synthase, suggesting that this enzyme may also be a control point in ketogenesis in the regenerating liver, as it is in normal and diabetic rats.
Project description:ObjectivesShcKO mice have low body fat and resist weight gain on a high fat diet, indicating that Shc proteins may influence enzymes involved in β-oxidation. To investigate this idea, the activities of β-oxidation and ketone body metabolism enzymes were measured.MethodsThe activities of β-oxidation enzymes (acyl-CoA dehydrogenase, 3-hydroxyacyl-CoA dehydrogenase and ketoacyl-CoA thiolase) in liver and hindlimb skeletal muscle, ketolytic enzymes (acetoacetyl-CoA thiolase, β-hydroxybutyrate dehydrogenase and 3-oxoacid-CoA transferase) in skeletal muscle, and ketogenic enzymes (acetoacetyl-CoA thiolase and β-hydroxybutyrate dehydrogenase) in liver were measured from wild-type and ShcKO mice.ResultsThe activities of β-oxidation enzymes were increased (P<.05) in the ShcKO compared to wild-type mice in the fasted but not the fed state. In contrast, no uniform increases in the ketolytic enzyme activities were observed between ShcKO and wild-type mice. In liver, the activities of ketogenic enzymes were increased (P<.05) in ShcKO compared to wild-type mice in both the fed and fasted states. Levels of phosphorylated hormone sensitive lipase from adipocytes were also increased (P<.05) in fasted ShcKO mice.ConclusionThese studies indicate that the low Shc levels in ShcKO mice result in increased liver and muscle β-oxidation enzyme activities in response to fasting and induce chronic increases in the activity of liver ketogenic enzymes. Decreases in the level of Shc proteins should be considered as possible contributors to the increase in activity of fatty acid oxidation enzymes in response to physiological conditions which increase reliance on fatty acids as a source of energy.
Project description:In regenerating rat liver slices 24 h after partial hepatectomy, the incorporation of [1-14C]glucosamine into 'free sialic acid' (N-acetylneuraminic acid + CMP-N-acetylneuraminic acid) decreased to below 50% of the control values and the incorporation into protein-bound sialic acid decreased to the same extent. The incorporation of [14C]glucosamine into 'free sialic acid' decreased during the period from 6 to 47 h after hepatectomy, showing a minimum at 12 h, and recovered to the control value by 96 h. At 12 h, the activities of UDP-N-acetylglucosamine 2-epimerase (UDP-2-acetoamido-2-deoxy-D-glucose 2-epimerase, EC 5.1.3.14) and N-acyl-D-mannosamine kinase (ATP: 2-acylamino-2-deoxy-D-mannose 6-phosphotransferase, EC 2.7.1.60) in the liver were significantly decreased. The amount of protein-bound sialic acid in the liver was not changed after partial hepatectomy, but the amount in plasma was changed, with a similar pattern to that of the incorporation of [14C]glucosamine into slice 'free sialic acid'. These results indicate that the synthesis of sialic acid in the liver much decreases in the early stage of regeneration and that this may be correlated with the decreased synthesis of plasma sialoglycoproteins.
Project description:Ketogenesis is a dynamic metabolic conduit supporting hepatic fat oxidation particularly when carbohydrates are in short supply. Ketone bodies may be recycled into anabolic substrates, but a physiological role for this process has not been identified. Here, we use mass spectrometry-based 13C-isotope tracing and shotgun lipidomics to establish a link between hepatic ketogenesis and lipid anabolism. Unexpectedly, mouse liver and primary hepatocytes consumed ketone bodies to support fatty acid biosynthesis via both de novo lipogenesis (DNL) and polyunsaturated fatty acid (PUFA) elongation. While an acetoacetate intermediate was not absolutely required for ketone bodies to source DNL, PUFA elongation required activation of acetoacetate by cytosolic acetoacetyl-coenzyme A synthetase (AACS). Moreover, AACS deficiency diminished free and esterified PUFAs in hepatocytes, while ketogenic insufficiency depleted PUFAs and increased liver triacylglycerols. These findings suggest that hepatic ketogenesis influences PUFA metabolism, representing a molecular mechanism through which ketone bodies could influence systemic physiology and chronic diseases.
Project description:1. Synthesis de novo of fatty acids in the rat liver, measured per g wet wt. of tissue, was increased by a factor of about two, between 1 and 4 days after partial hepatectomy, compared with rates in sham-operated control rat livers. 2. There were no associated changes in the rates of liver cholesterol synthesis or of adipose-tissue fatty acid synthesis in rats after partial hepatectomy, compared with rates in sham-operated rats. 3. In regenerating livers, perfused under three different conditions, there was no alteration in the capacity for fatty acid synthesis compared with that of control rats. 4. The increased synthesis of fatty acids in regenerating liver was associated with insignificant increases in plasma concentrations of tricylglycerols and free fatty acids, with a decrease in content of liver glycogen, and with no change in hepatic activity of acetyl-CoA carboxylase. 5. The accelerated rate of synthesis of fatty adids in regenerating liver appears not to be due to any intrinsic alteration in hepatic capacity for fatty acid synthesis, but it may be caused by the continuous action on liver of unidentified circulating factors.
Project description:1. The incorporation of thymidine into DNA of regenerating rat liver was measured at various times after partial hepatectomy. A single intravenous injection of 30mumol of beryllium/kg given immediately after the operation inhibited DNA synthesis 12, 16, 20, 24 and 28h later. 2. The activity of several enzymes critical to DNA synthesis (thymidine kinase, thymidylate kinase, thymidylate synthetase, deoxycytidylate deaminase and DNA polymerase) increased in control rats 20-24h after partial hepatectomy severalfold over the activity found in resting livers. After beryllium treatment this rise in activity was much less and it seemed as if beryllium would partially block the induction of DNA-synthesizing enzymes after partial hepatectomy. 3. Enzymes whose activities do not rise during liver regeneration were not affected by beryllium (aspartate transcarbamoylase, carbamoyl phosphate synthetase, uridine kinase and glucose 6-phosphatase). 4. No evidence was found in vitro that beryllium would specifically inhibit thymidine kinase or DNA polymerase. 5. The time-effect relationship between beryllium administration and thymidine kinase activity in vivo was examined. Measured 24h after partial hepatectomy, thymidine kinase activity was only affected if beryllium was given within the first 9-12h after partial hepatectomy. Beryllium given later, even in greatly increased doses, failed to have any effect on thymidine kinase. The possibility is discussed that beryllium inhibits enzyme induction at the transcriptional level.
Project description: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.
Project description:1. Glycoprotein synthesis was investigated with [1-14C]glucosamine in vivo. [14C]Glucosamine was administered intravenously 24h after hepatectomy to rats. 2. Incorporation into the acid-soluble fraction was maximum at 15 min after injection both in sham-operated and hepatectomized rats. 3. Enhancement of incorporation into UDP-N-acetylhexosamine in regenerating liver was observed. However, its specific activity was lower, because of a greater enhancement of synthesis de novo of the amino sugar. 4. In the liver acid-insoluble fraction, maximum incorporation of [14C]glucosamine was at 30 min in sham-operated rats and 2 h in hepatectomized rats respectively. 5. In sham-operated rats, incorporation into the plasma acid-insoluble fraction followed that of the liver acid-insoluble fraction, but hepatectomy resulted in a rapid enchancement of incorporation into plasma. 6. It is concluded that synthesis of liver glycoproteins is stimulated after partial hepatectomy and that glycoproteins synthesized are released rapidly into the plasma.
Project description:1. Rats trained on a controlled lighting and feeding schedule were subjected to partial hepatectomy or sham operation. 2. After a large period of about 6h the activity of UDP-galactose 4-epimerase increased threefold, reaching a maximum 4 days after partial hepatectomy, and returned to normal values within a fortnight. 3. The enzyme pattern of the UDP-galactose-glycoprotein galactosyltransferase was biphasic, one peak appearing at 20 h, the second at 72 h after partial hepatectomy. 4. The rise in enzyme activities could be blocked by the injection of actinomycin D, and the Km values for UDP-glucose and UDP-galactose were nearly identical in regenerating and adult liver. It is therefore concluded that the increase in enzyme activity is due to synthesis de novo of enzyme protein.
Project description:The concentrations of malonyl-CoA, citrate, ketone bodies and long-chain acylcarnitine were measured in freeze-clamped liver samples from fed or starved normal, partially hepatectomized or sham-operated rats. These parameters were used in conjunction with measurements of the concentration of plasma non-esterified fatty acids and the rates of hepatic lipogenesis to obtain correlations between rates of fatty acid delivery to the liver, lipogenesis and fatty acid oxidation to ketone bodies and CO2. These correlations indicated that the development of fatty liver after partial hepatectomy is due to an increased partitioning of long-chain acyl-CoA towards acylglycerol synthesis and away from acylcarnitine formation. However, this did not appear to be due to an altered relationship between hepatic malonyl-CoA concentration and acylcarnitine formation. For any concentration of long-chain acylcarnitine, the concentrations of both hepatic and blood ketone bodies were significantly lower in partially hepatectomized rats than in normal or sham-operated animals. This indicated that a lower proportion of the product of beta-oxidation was used for ketone-body formation and more for citrate synthesis in the regenerating liver, especially during the first 24 h after resection. This inference was supported by the changes in hepatic citrate concentrations observed. The high rates of lipogenesis that occurred in the liver remnant were accompanied by an altered relationship between lipogenic rate and hepatic malonyl-CoA concentration, such that much lower concentrations of malonyl-CoA were associated with any given rate of lipogenesis. These adaptations are discussed in relation to the requirements by the remnant for high rates of energy formation through the tricarboxylic acid cycle during the first 24 h after resection, and the possibility that cycling between fatty acid oxidation and synthesis may occur to a greater degree in regenerating liver.