Differential HMG-CoA lyase expression in human tissues provides clues about 3-hydroxy-3-methylglutaric aciduria

Abstract

3-Hydroxy-3-methylglutaric aciduria is a rare human autosomal recessive disorder caused by deficiency of 3-hydroxy-3-methylglutaryl CoA lyase (HL). This mitochondrial enzyme catalyzes the common final step of leucine degradation and ketogenesis. Acute symptoms include vomiting, seizures and lethargy, accompanied by metabolic acidosis and hypoketotic hypoglycaemia. Such organs as the liver, brain, pancreas, and heart can also be involved. However, the pathophysiology of this disease is only partially understood. We measured mRNA levels, protein expression and enzyme activity of human HMG-CoA lyase from liver, kidney, pancreas, testis, heart, skeletal muscle, and brain. Surprisingly, the pancreas is, after the liver, the tissue with most HL activity. However, in heart and adult brain, HL activity was not detected in the mitochondrial fraction. These findings contribute to our understanding of the enzyme function and the consequences of its deficiency and suggest the need for assessment of pancreatic damage in these patients.

Fig 1

Comparative analysis of mRNA levels, protein expression and enzymatic activity of HMG-CoA lyase in different human tissues. a Relative levels of mRNA HL expression in human tissues were measured by the ∆∆CT method with GAPDH as control. The expression levels of mRNA HL in skeletal muscle were arbitrarily taken as the calibrator for all calculations, and all other tissues were normalized accordingly. The values given are the average of four meausures, two from each subject. b HL protein expression was measured in mitochondrial fraction from human tissues. Four tissue samples were measured, two from each subject. The image shows a representative immunoblot from HL in different tissues. c HL activity was measured in the mitochondrial fraction of human tissues spectrophotometrically. Data are presented as mean±SEM (n = 4). Four tissue samples were measured, two from each subject