Involvement of endoplasmic reticulum stress in a novel Classic Galactosemia model.

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.

• Authors: Tatiana I Slepak, Manshu Tang, Vladlen Z Slepak, Kent Lai
• Journal: Molecular genetics and metabolism (Mol Genet Metab) 2007 Sep-Oct Vol. 92 Issue 1-2 Pg. 78-87 ISSN: 1096-7192 [Print] United States
• PMID: 17643331 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Endoplasmic Reticulum Chaperone BiP
• Galactosephosphates
• Heat-Shock Proteins
• Molecular Chaperones
• galactose-1-phosphate
• UTP-Hexose-1-Phosphate Uridylyltransferase
• 5'-Nucleotidase
• Glucose
• Calcium
• Galactose

Topics

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