EXPRESSION OF GLUTAMINE-FRUCTOSE-6-PHOSPHATE AMIDOTRANSFERASE IN HUMAN TISSUES - EVIDENCE FOR HIGH VARIABILITY AND DISTINCT REGULATION IN DIABETES

Recent in vitro and in vivo studies suggested that the increased flux of glucose through the hexosamine biosynthetic pathway may contribute to glucose-induced insulin resistance and to the induction of the synt hesis of growth factors. Because glutamine:fructose-6-phosphate amidot ransferase (GFAT) catalyzes the first and rate-limiting step in the fo rmation of hexosamine products, tills enzyme is the key regulator in t his pathway and is therefore possibly also involved in the alterations occurring in preclinical or manifest diabetic patients, To study the expression of GFAT in human tissues, we produced and characterized a p eptic antiserum specifically recognizing GFAT protein and a riboprobe for the detection of GFAT mRNA. Immunohistochemical and nonradioactive in situ hybridization analysis revealed high levels of expression of GFAT protein and mRNA in adipocytes and skeletal muscle. Furthermore, a marked GFAT expression war; found in vascular smooth muscle cells wi th unexpectedly high variability and lower levels in other cells, e.g. , peripheral nerve sheath cells or endocrine-active cells, including t he pancreatic islet cell, GFAT protein expression was below detection level in endothelium, osteocytes, lymphocytes, granulocytes, and in mo st quiescent fibroblasts, In renal tissue, GFAT was expressed ins tubu lar epithelial cells, while glomerular cells remained essentially unst ained, Renal sections obtained from patients with diabetic nephropathy showed significant GFAT expression in some glomerular epithelial and mesangial cells, indicating that GFAT expression may be induced by man ifest diabetes, Our data indicate that GFAT is expressed in most tissu es involved in the development of diabetic late complications. Further more, the results suggest that GFAT gene expression is highly regulate d.