Involvement of endoplasmic reticulum stress in a novel Classic Galactosemia model

Mol Genet Metab. Sep-Oct 2007;92(1-2):78-87. doi: 10.1016/j.ymgme.2007.06.005. Epub 2007 Jul 20.

Abstract

Inherited deficiency of galactose-1-phosphate uridyltransferase (GALT) activity in humans leads to a potentially lethal disorder called Classic Galactosemia. It is well known that patients often accumulate high levels of galactose metabolites such as galactose-1-phosphate (gal-1-p) in their tissues. However, specific targets of gal-1-p and other accumulated metabolites remain uncertain. In this study, we developed a new model system to study this toxicity using primary fibroblasts derived from galactosemic patients. GALT activity was reconstituted in these primary cells through lentivirus-mediated gene transfer. Gene expression profiling showed that GALT-deficient cells, but not normal cells, responded to galactose challenge by activating a set of genes characteristic of endoplasmic reticulum (ER) stress. Western blot analysis showed that the master regulator of ER stress, BiP, was up-regulated at least threefold in these cells upon galactose challenge. We also found that treatment of these cells with galactose, but not glucose or hexose-free media reduced Ca2+ mobilization in response to activation of Gq-coupled receptors. To explore whether the muted Ca2+ mobilization is related to reduced inositol turnover, we discovered that gal-1-p competitively inhibited human inositol monophosphatase (hIMPase1). We hypothesize that galactose intoxication under GALT-deficiency resulted from accumulation of toxic galactose metabolite products, which led to the accumulation of unfolded proteins, altered calcium homeostasis, and subsequently ER stress.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5'-Nucleotidase / antagonists & inhibitors
  • 5'-Nucleotidase / metabolism
  • Blotting, Western
  • Calcium / metabolism
  • Cells, Cultured / drug effects
  • Cells, Cultured / metabolism
  • Endoplasmic Reticulum / drug effects
  • Endoplasmic Reticulum / metabolism*
  • Fibroblasts / metabolism*
  • Fibroblasts / pathology
  • Galactose / pharmacology
  • Galactosemias / enzymology*
  • Galactosemias / pathology
  • Galactosephosphates / metabolism*
  • Gene Transfer Techniques
  • Glucose / pharmacology
  • Heat-Shock Proteins / metabolism
  • Humans
  • Lentivirus / genetics
  • Molecular Chaperones / metabolism
  • UTP-Hexose-1-Phosphate Uridylyltransferase / genetics
  • UTP-Hexose-1-Phosphate Uridylyltransferase / metabolism*

Substances

  • Galactosephosphates
  • Heat-Shock Proteins
  • Molecular Chaperones
  • galactose-1-phosphate
  • UTP-Hexose-1-Phosphate Uridylyltransferase
  • 5'-Nucleotidase
  • Glucose
  • Calcium
  • Galactose
  • molecular chaperone GRP78