Thrombospondin-1 Deficiency Causes a Shift from Fibroproliferative to Inflammatory Kidney Disease and Delays Onset of Renal Failure

Thrombospondin-1 (TSP1) is a multifunctional matricellular protein known to promote progression of chronic kidney disease. To gain insight into the underlying mechanisms through which TSP1 accelerates chronic kidney disease, we compared disease progression in Col4a3 knockout (K0) mice, which develop spontaneous kidney failure, with that of Col4a3;Tsp1 double-knockout (DK0) mice. Decline of excretory renal function was significantly delayed in the absence of TSP1. Although Col4a3;Tsp1 DK0 mice did progress toward end-stage renal failure, their kidneys exhibited distinct histopathological lesions, compared with creatinine level- matched Col4a3 K0 mice. Although kidneys of both Col4a3 K0 and Col4a3;Tsp1 DK0 mice exhibited a widened tubulointerstitium, predominant lesions in Col4a3 K0 kidneys were collagen deposition and fibroblast accumulation, whereas in Col4a3;Tsp1 DK0 kidney inflammation was predominant, with less collagen deposition. Altered disease progression correlated with impaired activation of transforming growth factor-beta 1 (TGF-beta 1) in vivo and in vitro in the absence of TSP1. In summary, our findings suggest that TSP1 contributes to progression of chronic kidney disease by catalyzing activation of latent TGF-beta 1, resulting in promotion of a fibroproliferative response over an inflammatory response. Furthermore, the findings suggest that fibro-proliferative and inflammatory lesions are independent entities, both of which contribute to decline of renal function.