Fibroblast accumulation during progression of CKD in Col4a3 KO and Col4a3;Tsp1 DKO mice. A: Representative photomicrographs of formalin-fixed, paraffin-embedded kidney sections of wild-type control, Col4a3 KO, and Col4a3;Tsp1 DKO mice at 12, 22, and 32 weeks of age. Sections were immunolabeled with antibodies against αSMA (red) and counterstained with methylene green. B: Fibroblast numbers were determined as αSMA+ cells per visual field. The fibroproliferative response over time was more robust in Col4a3 KO mice than in Col4a3;Tsp1 DKO mice and differences reached statistical significance at 22 weeks of age. Data are expressed as means ± SEM. ∗P < 0.05. Original magnification, ×20. αSMA, α-smooth muscle actin.