Mechanisms of hypercholesterolaemia in glycogen storage disease type I: defective metabolism of low density lipoprotein in cultured skin fibroblasts

Abstract

Hyperlipidaemia is a feature of glycogen storage disease type I (GSD-I) (Levy et al. [1]). High levels of LDL cholesterol (200 .+-. 25 mg dl-1) and apo B (387 .+-. 44 mg dl-1) were found in association with hypercholesterolaemia in GSD-I. Related causative factors might be attributed to overproduction and/or delayed removal of LDL. In this study, a possible alteration in the clearance of LDL was examined. Using cultured fibroblasts for LDL receptor activity, the following observations were made: 1 GSD-I fibroblasts revealed only a slight decrease in LDL binding (65 .+-. 7) when compared with controls (74 .+-. 4 ng mg-1 protein), however, LDL internalization (382 .+-. 24 vs. 570 .+-. 52 ng mg-1 protein) and proteolytic degradation (2082 .+-. 280 vs. 2916 .+-. 12.5 ng mg-1 protein) were significantly affected (P < 0.01). 2 Binding, internalization and proteolytic degradation of LDL from GSD-I were compared with that of controls, and were found to be significantly lower (P < 0.01). 3 Substitution of control lipoprotein-deficient serum (LPDS) by GSD-I LPDS further diminished the above processes (P < 0.05). Our results demonstrate that increased plasma cholesterol in GSD-I is due to a decreased catabolism of LDL. The data suggest that the problem may well be multifactorial, due to diminished receptor expression, abnormal LDL composition and impaired LDL receptor interaction due to a circulating inhibitory factor.