Control of hepatic mitochondrial 3‐hydroxy‐3‐methylglutaryl‐CoA synthase during the foetal/neonatal transition, suckling and weaning in the rat

Abstract

(1) We assayed active and total (i.e. active plus succinylated) 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase in mitochondria isolated from foetal, neonatal, suckling or weaned rats.(2) HMG-CoA synthase was substantially succinylated and inactivated in mitochondria isolated from termfoetal, (1-h-old, 6-h-old, 1 -day-old) neonatal, suckling and high carbohydrate/low-fat (hc)-weaned rats. Succinylation of HMG-CoA synthase was very low in mitochondria isolated from the livers of foetal, 30-min-old neonatal and high-fat/carbohydrate-free (hf)-weaned rats.(3) There was a negative correlation between active HMG-CoA synthase and succinyl-CoA content in mitochondria isolated from term-foetal, suckling and hc-weaned rats.(4) Differences in active enzyme could not be entirely accounted for by differences in succinylation and inactivation of the synthase. Immunoassay confirmed that the absolute amounts of mitochondrial HMG-CoA synthase increased during the foetal/neonatal transition and decreased with hc weaning. The levels remained elevated with hf weaning.(5) From these data we propose that mitochondrial HMG-CoA synthase is controlled by two different mechanisms in young rats. Regulation by succinylation provides a mechanism for rapid modification of existing enzyme in response to changing metabolic states. Changes in the absolute amounts of HMG-CoA synthase provide a more long-term control in response to nutritional changes.Hepatic ketogenesis increases rapidly in young rats during the perinatal period [l -31 and decreases during weaning [4-81. The control mechanisms involved in the changing capacity of isolated liver mitochondria to synthesize ketone bodies during these periods of hormonal and nutritional transition have been only partially identified.In adult rats the regulation of carnitine palmitoyltransferase I activity by malonyl-CoA contributes to intrahepatic control of ketogenesis [9, 101. However, carnitine palmitoyltransferase I, which is involved in the transfer of long-chain fatty acids into mitochondria, is not thought to be a major control site in young rats [3, 71. The milk diet of suckling rats contains 40% (of total triacylglycerols) mediumchain triacylglycerols [l 11. These are metabolised independently of carnitine palmitoyltransferase I, as they are activated directly inside the mitochondria, suggesting a further control site may regulate ketogenic flux in mitochondria of neonatal and suckling rats.Decaux et al. [7] have shown decreased fatty-acid oxidation and ketogenesis in mitochondria isolated from the livers of weaned rats, compared to mitochondria of suckling rats. Interestingly, this results not only from decreased carnitine palmitoyltransferase I activity, but also from a limited capacity for the utilization of acetyl-CoA in the 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) pathway of ketogenesis. No control mechanism for the latter effect was proposed, although mitochondrial 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) synthase, the second enzyme of the HMG-CoA pathway, is reputed to be ra...

Hepatic ketogenesis in newborn pigs is limited by low mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase activity

“…The low HMG-CoA synthase activity did not result from a high succinylation state. Indeed, the succinylation state of pig mitochondria (5 %) was 4-fold lower than that of suckling rat liver mitochondria (Quant et al, 1991) that possess an active mitochondrial ketogenesis (Escriva et al, 1986). In fact, the low ketogenic capacity of newborn-pig liver mitochondria resulted from the extremely low amount of HMG-CoA synthase protein in newborn-or adult-pig liver mitochondria, as shown by Western-blot analysis ( Figure 2).…”

“…Immune complexes were revealed as described previously (Quant et al, 1991). The polyclonal antibody was raised in the rabbit against the purified ox liver mitochondrial HMG-CoA synthase and shown to cross-react with the rat enzyme (Quant et al, 1991).…”

Proteomics analysis reveals diabetic kidney as a ketogenic organ in type 2 diabetes

“…We found that the expression of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase 2 (HMGCS2), the rate-limiting enzyme in ketogenesis in the liver (10,23,29), was significantly increased in the kidneys of db/db mice. We also measured the renal production of its major metabolite, ␤-hydroxybutyrate (␤-HB), in db/db mice and examined the effect of ␤-HB on TGF-␤ expression and collagen I production, as well as the epithelial-to-mesenchymal transition (EMT) in cultured rat proximal tubule cells.…”

Molecular cloning of rat mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase and detection of the corresponding mRNA and of those encoding the remaining enzymes comprising the ketogenic 3-hydroxy-3-methylglutaryl-CoA cycle in central nervous system of suckling rat

“…HMG-CoA synthase gene because rats weaned to a high-fat diet display elevated hepatic abundances of mt. HMG-CoA synthase mRNA [4,6], protein [4], and enzyme activity [5]. The brain, which requires a large input of fuel energy, is regarded as non-ketogenic [3] ; this is supported by the inability to detect, so far, mt.…”

“…HMG-CoA synthase mRNA [4] and mt. HMG-CoA synthase protein [4], which is proposed to be a major regulatory step in fatty acid-driven ketogenesis [5]. Changes in circulating fatty acid concentrations seem to regulate the expression of the mt.…”