Aim: 

Mitochondrial 3-hydroxy-3-methylglutaryl CoA lyase (HMG-CoA lyase, HL, EC4.1.3.4) plays an essential role in lipid and aminoacid metabolism. It catalyzes the cleavage of HMG-CoA to form acetyl-CoA and acetoacetate, which is the common final step of the ketogenic pathway and leucine catabolism. Here we report the first survey of mRNA levels, protein expression and enzymatic activity of human HMG-CoA lyase from liver, kidney, pancreas, testis and brain.

Methods: 

Quantification of HL mRNA was performed in multiple tissue cDNA (MTC) panels by a real-time quantitative PCR method. We isolated the mitochondrial fraction of human tissues to measure the protein level by immunoblot and the HMG-CoA lyase activity by a spectrophotometric assay.

Results: 

Although HL mRNA was detected in all tissues analyzed, which is consistent with its role of housekeeping gene, its amount was very different in each of them. Liver and kidney, regarded as the main ketogenic organs in mammals, are tissues with an important HL activity. Surprisingly, our data showed that pancreas is, after the liver, the second tissue with more HL activity. These findings reinforce the hypothesis that ketone bodies are related to insulin release induction. In testis, the low HL activity levels detected compared with the high protein expression suggests a regulation of the ketogenic pathway. In contrast, in adult brain there is not any detectable HL activity in the mitochondrial fraction.

Conclusion: 

In our opinion, these findings are a step forward to better understand the physiological role of HMG-CoA lyase in humans.