The Role Of Tissue Transglutaminase In The Experimental Diabetic Nephropathy

Objective: To observe the expression of tissue transglutaminase (tTG) in renaltissue of diabetic nephropathy rats, and to investigate its contribution toprogression of diabetic nephropathy. Methods: 1) Wistar rats with diabetes induced by streptozotocin (STZ) weresacrificed at d30, d60, d90, and d120 after injection of STZ. 2) 24-hour microalbuminuria excretion was measured by enzyme-linked immuno sorbent assay (ELISA). 3) Hematoxylin and eosin (HE) staining and periodic acid-silver-methenamine (PASM) staining were used to observe the renal pathologicalchanges. 4) Soluble tTG protein in kidney was examined by immuno-histochemistry, insoluble tTG protein by immunofluorescence. 5) Expression of tTG mRNA in kidney was detected by reversetranscription- polymerase chain reaction (RT-PCR). Results: 1) Microalbuminuria of diabetic rats was progressive during the periodof the experiment. 2) HE and PASM stainings showed progressive increases in bothglomeruli volume and mesangium matrix of diabetic rats throughout theexperiment period. 3) Expression of soluble tTG was predominantly localized to tubulecells of both diabetic kidneys and controls. However, there was a gradualincrease of soluble tTG levels of kidneys from hyperglycemic rats withtime. 4) In diabetic kidneys, insoluble tTG immunostaining was detectablewithin the tubulointerstitial space and glomeruli, and the intensity increasedgradually in the experimental time course, whereas it was difficult toobserve any staining in controls. 5) Soluble tTG expression and insoluble tTG expression relative to24-hour microalbuminuria excretion were positively correlated, r=0.937(P=0.006) and 0.809(P=0.007) respectively. 6) tTG mRNA levels rose in diabetic kidneys at 30d after STZinjection over the controls, continuously increasing to reach a peak at d90,and reduced slightly at d120. Conclusions: The increased intracellular expression and increased externalization oftTG protein and the change of tTG mRNA levels within the diabetic kidneydemonstrated that tTG may play an role in the progression of diabeticnephropathy.