Role of carnitine palmitoyltransferase I in the control of ketogenesis in primary cultures of rat astrocytes.
The role of carnitine palmitoyltransferase I (CPT-I) in the control of ketogenesis was studied in primary cultures of rat astrocytes. Ketone bodies were the major product of [14C]palmitate oxidation by cultured astrocytes, whereas CO2 made a minor contribution to the total oxidation products. Using tetradecylglycidate as a specific, cell-permeable inhibitor of CPT-I, a flux control coefficient of 0.77 +/- 0.07 was calculated for CPT-I over the flux of [14C]palmitate to ketone bodies. CPT-I from astrocytes was sensitive to malonyl-CoA (IC50 = 3.4 +/- 0.8 microM) and cross-reacted on western blots with an antibody raised against liver CPT-I. On the other hand, astrocytes expressed significant acetyl-CoA carboxylase (ACC) activity, and consequently they contained considerable amounts of malonyl-CoA. Western blot analysis of ACC isoforms showed that ACC in astrocytes--like in neurons, liver, and white adipose tissue--mostly comprised the 265-kDa isoform, whereas the 280-kDa isoform--which was highly expressed in skeletal muscle--showed much lower abundance. Forskolin was used as a tool to study the modulation of the ketogenic pathway in astrocytes. Thus, forskolin decreased in parallel ACC activity and intracellular malonyl-CoA levels, whereas it stimulated CPT-I activity and [14C]palmitate oxidation to both ketone bodies and CO2. Results show that in cultured astrocytes (a) CPT-I exerts a very high degree of control over ketogenesis from palmitate, (b) the ACC/malonyl-CoA/CPT-I system is similar to that of liver, and (c) the ACC/malonyl-CoA/CPT-I system is subject to regulation by cyclic AMP.
Blázquez
C
C
Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, Madrid, Spain.
Sánchez
C
C
Velasco
G
G
Guzmán
M
M
D000103:Acetyl-CoA Carboxylase / Q000737:chemistry / Q000187:drug effects; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D002250:Carbon Radioisotopes; D002334:Carnitine O-Palmitoyltransferase / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000201:enzymology; D005576:Colforsin / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D007657:Ketone Bodies / Q000096:biosynthesis* / Q000378:metabolism; D008316:Malonyl Coenzyme A / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000166:cytology; D010084:Oxidation-Reduction; D019308:Palmitic Acid / Q000378:metabolism; D051381:Rats
D002250:Carbon Radioisotopes; D007657:Ketone Bodies; D005576:Colforsin; D019308:Palmitic Acid; D008316:Malonyl Coenzyme A; D002334:Carnitine O-Palmitoyltransferase; D000103:Acetyl-CoA Carboxylase