Thromboxane A(2) causes retarded clearance of aggregated protein in glomeruli of nephritic mice

Recently, it has been demonstrated that the production of prostaglandins and thromboxane is increased in patients with chronic glomerulonephritis and lupus nephritis. We recently demonstrated that thromboxane A(2) delayed the clearance of heat-aggregated bovine serum albumin deposited in glomeruli. In the present study, we investigated the effect of thromboxane A(2) on the clearance of macromolecules in nephritic glomeruli. First, we attempted to clarify the conditions for the clearance of heat-aggregated bovine serum albumin in nephritic glomeruli, using glomeruli isolated from control and anti-glomerular basement membrane nephritic mice. Heat-aggregated bovine serum albumin was injected twice into each mouse. The glomeruli were then isolated and incubated in culture medium. The heat-aggregated bovine serum albumin content of control glomeruli gradually diminished with incubation time up to 24 h. The heat-aggregated bovine serum albumin content of nephritic glomeruli was 69% higher than that of control glomeruli at 24 h incubation. The production of thromboxane B(2) (the stable metabolite of thromboxane A(2)) in nephritic glomeruli showed about a sevenfold increase compared with control. DP-1904 [6-(1-imidazolylmethyl)-5,6,7,8-tetrahydro-naphthalene-2-carboxylic acid hydrochloride], a thromboxane A(2) synthase inhibitor, and KT2-962 [sodium 3-(4-(4-chlorophenyl-butylsulfonamido) butyl)-6-isopropylazulene-1-sulfonate], a selective thromboxane A(2) receptor antagonist, significantly reduced the heat-aggregated bovine serum albumin content in nephritic glomeruli. Normal glomeruli treated with U-46619 [15S-hydroxy-11a,9a-(epoxymethano)prosta-5Z,13E-dienoic acid], a stable analogue of thromboxane A(2), had significantly more heat-aggregated bovine serum albumin than control glomeruli. We next investigated whether thromboxane A(2) could affect the uptake/disposal of heat-aggregated bovine serum albumin by cultured rat mesangial cells. U-46619 significantly enhanced the uptake and inhibited the disposal of heat-aggregated bovine serum albumin by mesangial cells. Finally, we performed experiments to elucidate the role of the thromboxane A(2) receptor (TP receptor) in the clearance of heat-aggregated bovine serum albumin using TP-deficient mice. The glomerular heat-aggregated bovine serum albumin content of TP-receptor knockout [TP(-/-)] mice was lower than that of wild-type [WT(+/+)] mice. U-46619 dose dependently increased the uptake of heat-aggregated bovine serum albumin by mesangial cells in WT(+/+) mice, but not in the TP(-/-) mice. These findings suggest that thromboxane A(2) retards the clearance of aggregated protein in nephritic glomeruli and may contribute to the pathophysiology of glomerulonephritis.