MOLECULAR-CLONING OF RAT MITOCHONDRIAL 3-HYDROXY-3-METHYLGLUTARYL-COALYASE AND DETECTION OF THE CORRESPONDING MESSENGER-RNA AND OF THOSE ENCODING THE REMAINING ENZYMES COMPRISING THE KETOGENIC 3-HYDROXY-3-METHYLGLUTARYL-COA CYCLE IN CENTRAL-NERVOUS-SYSTEM OF SUCKLING RAT

We have investigated, by RNase protection assays in rat brain regions and primary cortical astrocyte cultures, the presence of the mRNA spec ies encoding the three mitochondrially located enzymes acetoacetyl-CoA thiolase, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (mt. HMG-CoA synthase) and HMG-CoA lyase (HMG-CoA lyase) that together cons titute the ketogenic HMG-CoA cycle. As a prerequisite we obtained a fu ll-length cDNA encoding rat HMG-CoA lyase by degenerate oligonucleotid e-primed PCR coupled to a modification of PCR-rapid amplification of c DNA ends (PCR-RACE). We report here: (1) the nucleotide sequence of ra t mt. HMG-CoA lyase, (2) detection of the mRNA species encoding all th ree HMG-CoA cycle enzymes in all regions of rat brain during suckling, (3) approximately twice the abundance of mt. HMG-CoA synthase mRNA in cerebellum than in cortex in 11-day-old suckling rat pups, (4) signif icantly lower abundances of mt. HMG-CoA synthase mRNA in brain regions derived from rats weaned to a high-carbohydrate/low-fat diet compared with the corresponding regions derived from the suckling rat, and (5) the presence of mt. HMG-CoA synthase mRNA in primary cultures of neon atal cortical astrocytes at an abundance similar to that found in live r of weaned animals. These results provide preliminary evidence that c ertain neural cell types possess ketogenic potential and might thus ha ve a direct role in the provision of fatty acid-derived ketone bodies during the suckling period.