The stimulation of ketogenesis by cannabinoids in cultured astrocytes defines carnitine palmitoyltransferase I as a new ceramide-activated enzyme.
The effects of cannabinoids on ketogenesis in primary cultures of rat astrocytes were studied. Delta9-Tetrahydrocannabinol (THC), the major active component of marijuana, produced a malonyl-CoA-independent stimulation of carnitine palmitoyltransferase I (CPT-I) and ketogenesis from [14C]palmitate. The THC-induced stimulation of ketogenesis was mimicked by the synthetic cannabinoid HU-210 and was prevented by pertussis toxin and the CB1 cannabinoid receptor antagonist SR141716. Experiments performed with different cellular modulators indicated that the THC-induced stimulation of ketogenesis was independent of cyclic AMP, Ca2+, protein kinase C, and mitogen-activated protein kinase (MAPK). The possible involvement of ceramide in the activation of ketogenesis by cannabinoids was subsequently studied. THC produced a CB1 receptor-dependent stimulation of sphingomyelin breakdown that was concomitant to an elevation of intracellular ceramide levels. Addition of exogenous sphingomyelinase to the astrocyte culture medium led to a MAPK-independent activation of ketogenesis that was quantitatively similar and not additive to that exerted by THC. Furthermore, ceramide activated CPT-I in astrocyte mitochondria. Results thus indicate that cannabinoids stimulate ketogenesis in astrocytes by a mechanism that may rely on CB1 receptor activation, sphingomyelin hydrolysis, and ceramide-mediated activation of CPT-I.
Blázquez
C
C
Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, Madrid, Spain.
Sánchez
C
C
Daza
A
A
Galve-Roperh
I
I
Guzmán
M
M
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D013759:Dronabinol / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007657:Ketone Bodies / Q000378:metabolism*; D008316:Malonyl Coenzyme A / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D010880:Piperidines / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D011619:Psychotropic Drugs / Q000494:pharmacology*; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000378:metabolism; D000077285:Rimonabant; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology; D013109:Sphingomyelins / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007657:Ketone Bodies; C064769:N-acetylsphingosine; D010880:Piperidines; D011619:Psychotropic Drugs; D011720:Pyrazoles; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D013109:Sphingomyelins; D008316:Malonyl Coenzyme A; D013759:Dronabinol; D000242:Cyclic AMP; D002334:Carnitine O-Palmitoyltransferase; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D013108:Sphingomyelin Phosphodiesterase; D013110:Sphingosine; D000077285:Rimonabant; D002118:Calcium