Induction of cyclooxygenase-2 expression in glomeruli by aggregated protein

Protective effect of prostaglandin EP4-receptor agonist on anti-glomerular basement membrane antibody-associated nephritis

Prostaglandin E(2)-receptor subtypes, EP(1), EP(2), EP(3), and EP(4), are present in the kidney. The aim of this study was to elucidate the anti-nephritic effect of an EP(4)-receptor agonist on an experimental nephritic model. Mice were injected i.v. with anti-glomerulus antiserum to induce nephritis. Nephritic glomeruli generated more prostaglandin E(2) (2.6 and 0.7 ng) and less cyclic AMP than normal glomeruli (11 and 26 pmol). The production of cyclic AMP in nephritic glomeruli increased 67% in response to AE1-329, an EP(4) agonist, at 10(-5) M. Nephritic glomeruli expressed a lesser amount of mRNA of prostaglandin E(2)-receptor subtypes as compared with normal glomeruli. AE1-329 was administered s.c. at 100 microg/kg per day for 3 weeks. AE1-329 suppressed the increase in creatinine and cholesterol compared to those in the control nephritic mice. AE1-329-treated nephritic mice had less crescentic glomeruli and less deposition of rabbit IgG (anti-glomerular basement membrane antibody) in glomeruli than the control mice. AE1-329 prevented the development of glomerulonephritis. These findings suggest that EP(4)-receptor agonists are a promising drug to prevent the development of glomerulonephritis.

Insufficient Expression of Cyclooxygenase-2 Protein Is Associated With Retarded Degradation of Aggregated Protein in Diabetic Glomeruli

To elucidate the involvement of cyclooxygenase (COX) in degradation of aggregated protein in diabetic glomeruli, we used streptozotocin (STZ)-induced diabetic mice and aggregated bovine serum albumin (a-BSA) as a model protein. There was a higher deposition of a-BSA in diabetic glomeruli compared to normal glomeruli 18 h after a-BSA injection at 4 and 8 weeks after STZ. Degradation of a-BSA was confirmed using isolated glomeruli. Diabetic glomeruli produced prostaglandin E(2) (PGE(2)) more than normal glomeruli in the basal level at 8 weeks. a-BSA caused further increase of PGE(2) production in normal glomeruli, but not in diabetic glomeruli. Niflimic acid, a selective COX-2 inhibitor, reduced PGE(2) production of normal glomeruli in the a-BSA loading group, but not that in the control group. In diabetic glomeruli, niflimic acid reduced PGE(2) production in both the control group and a-BSA loading group. In normal glomeruli, a-BSA increased expressions of both COX-2 mRNA and protein. However, in diabetic glomeruli, a-BSA increased COX-2 mRNA expression but not COX-2 protein expression. These results suggest that retarded degradation of aggregated protein in diabetic glomeruli is associated with lack of further expression of COX-2 protein and further production of PGE(2) in response to aggregated protein.

Increase in the Deposition of Aggregated Protein in the Glomeruli of Spontaneously Diabetic Mice

The aim of this study was to investigate the disposal of aggregated protein in the glomeruli of spontaneously diabetic mice. Diabetic mice, KK-A(y) and db/db, and age-matched ICR mice were injected intravenously with aggregated bovine serum albumin (a-BSA) at 0.6 mg/g, and the glomeruli and the blood were obtained. Diabetic mice had larger amounts of a-BSA in their glomeruli than the ICR mice, threefold in KK-A(y) and twofold in db/db, at 3 h after the a-BSA injection. Additionally, the disappearance of a-BSA was retarded in the diabetic glomeruli. KK-A(y) displayed a-BSA in the glomeruli 24 h after the a-BSA injection and db/db did after 12 h, while the ICR did by 8 h. In spite of increases of insulin to similar degrees in both strains of diabetic mice after the a-BSA injection, blood glucose levels markedly decreased in KK-A(y) compared with db/db. There were no histopathological alterations in the glomeruli of the diabetic mice. Depositions of a-BSA were confirmed to be higher in the diabetic glomeruli by the immunofluorescence technique, and KK-A(y) displayed higher depositions of a-BSA than did db/db. The present study suggests that hyperglycemia is involved in the increased deposition of aggregated protein in the glomeruli and that the degradation of aggregated protein is retarded in diabetic glomeruli.