Classical Galactosemia: Insight into Molecular Pathomechanisms by Differential Membrane Proteomics of Fibroblasts under Galactose Stress

Classical galactosemia,
a hereditary metabolic disease caused by
the deficiency of galactose-1-phosphate uridyltransferase (GALT; EC
2.7.712), results in an impaired galactose metabolism and serious
long-term developmental affection of the CNS and ovaries, potentially
related in part to endogenous galactose-induced protein dysglycosylation.
In search for galactose-induced changes in membrane raft proteomes
of GALT-deficient cells, we performed differential analyses of lipid
rafts from patient-derived (Q) and sex- and age-matched control fibroblasts
(H) in the presence or absence of the stressor. Label-based proteomics
revealed of the total 454 (female) or 678 (male) proteins a proportion
of ∼12% in at least one of four relevant ratios as fold-changed.
GALT(−) cell-specific effects in the absence of stressor revealed
cell-model-dependent affection of biological processes related to
protein targeting to the plasma membrane (female) or to cellular migration
(male). However, a series of common galactose-induced effects were
observed, among them the strongly increased ER-stress marker GRP78
and calreticulin involved in N-glycoprotein quality control. The membrane-anchored
N-glycoprotein receptor CD109 was concertedly decreased under galactose-stress
together with cadherin-13, GLIPR1, glypican-1, and semaphorin-7A.
A series of proteins showed opposite fold-changes in the two cell
models, whereas others fluctuated in only one of the two models.