Defects in galactose metabolism and glycoconjugate biosynthesis in UDP‐glucose pyrophosphorylase‐deficient fibroblasts are reversed by supplementing the cell growth medium with galactose

Abstract

UDP‐glucose (UDP‐Glc) is required for galactose metabolism and glycoconjugate biosynthesis and is synthesised from glucose‐1‐ phosphate by UDP‐Glc pyrophosphorylase (UGPP). UGPP‐deficient fibroblasts displaying reduced UDP‐Glc, impaired mitochondrial function and increased glucose regulated protein expression have been described. We have now characterised glycoconjugate biosynthesis and galactose metabolism in these cells and show that they display: 1) reduced [6‐3H]galactose incorporation into UDP‐[6‐3H]‐galactose; 2) an inability to glucosylate the dolichol‐linked oligosaccharide required for protein N‐glycosylation; 3) hypo‐N‐glycosylated PrPC; 4) truncated O‐glycans, and 5) reduced glucosylceramide and NeuAcα2,3Galβ1,4Glcβ‐ceramide levels. Transfection of the cells with wild type UGPP restores all the above defects except mitochondrial function. Surprisingly, it was discovered that the effects of transfecting the mutant cells with wild type UGPP were reproduced by prolonged cultivation of the cells with galactose. Accordingly, we describe a novel reversable model with which to study defects in galactose metabolism and glycoconjugate biosynthesis.