High glucose induces type 1 hexokinase gene expression in isolated glomeruli of diabetic rats and in mesangial cells.
BACKGROUND
Diabetic nephropathy, which is characterized by renal hypertrophy and accumulation of extracellular matrix, is one of the leading causes for end-stage renal disease. Pathophysiological changes, which finally lead to the development of diabetic nephropathy, act through an increase in the intracellular NADH/NAD ratio and the activation of the polyol and protein kinase C pathways. The first rate-limiting enzymes in intracellular glucose metabolism are the hexokinases, which catalyze the phosphorylation of glucose. Therefore, in order to examine a possible link between increased glucose metabolism and the development of diabetic nephropathy mRNA and protein expression as well as enzyme activity of type 1 hexokinase were examined in kidneys of control and diabetic rats and in mesangial cells.


METHODS
Diabetes in rats was induced by intravenous injection of streptozotocin and animals were treated or not treated with insulin. RNA or protein was extracted from isolated glomeruli at different time intervals. In addition, glomerular mesangial cells were incubated in high glucose medium and hexokinase expression determined along with enzyme activity.


RESULTS
The experiments demonstrate a significant increase in gene and protein expression of type 1 hexokinase in glomeruli of diabetic rats throughout a three week observation period. Insulin therapy reduced glomerular type 1 hexokinase mRNA expression. Gene expression and hexokinase enzyme activity were also increased in mesangial cells grown in high glucose medium.


CONCLUSIONS
The present experiments demonstrate that the expression of type 1 hexokinase is increased in isolated glomeruli of diabetic animals and is regulated by high ambient glucose concentrations. These results add further evidence to the fact that the kidney is one of the tissues most sensitive to high glucose levels in diabetes.
Henningsen
C
C
Department of Internal Medicine, Division of Nephrology and Osteology, University Hospital, Hamburg, Germany.
Zahner
G
G
Thaiss
F
F
D000818:Animals; D001786:Blood Glucose / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000201:enzymology* / Q000235:genetics / Q000503:physiopathology; D004790:Enzyme Induction / Q000187:drug effects / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects* / Q000502:physiology*; D005920:Glomerular Mesangium / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology*; D005947:Glucose / Q000494:pharmacology*; D006593:Hexokinase / Q000096:biosynthesis* / Q000235:genetics*; D007678:Kidney Glomerulus / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D009929:Organ Size / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D013311:Streptozocin
D001786:Blood Glucose; D012333:RNA, Messenger; D013311:Streptozocin; D006593:Hexokinase; D005947:Glucose