Tubulointerstitial nephritis causes decreased renal expression and urinary excretion of cauxin, a major urinary protein of the domestic cat.

Cauxin, a member of mammalian carboxylesterases (EC 3.1.1.1), is excreted as a major urinary protein in the domestic cat. Urinary cauxin is derived from the kidney proximal straight tubules. Here, we report changes in the renal expression and urinary excretion of cauxin in cats with tubulointerstitial nephritis (TIN). Immunohistochemistry using anti-cauxin antibody showed fewer cauxin-positive tubules in 15 TIN cases than in normal animals. In areas with tubulointerstitial damage, fibroblasts and inflammatory cells replaced renal tubules, and cauxin-positive tubules consequently disappeared. Urine was analysed in six of the 15 cases. In the two cases with mild tubulointerstitial changes, urinary cauxin was detected using SDS-PAGE with Coomassie staining. In the four cases with severe tubulointerstitial changes, urinary cauxin was below the detection limit using Western blotting. These results indicate that the renal expression and urinary excretion of cauxin decrease with the progression of TIN in cats.

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