Localization of tamm-horsfall protein and osteopontin in a rat nephrolithiasis model

The possibility of more than one urinary protein being simultaneously associated with calcium oxalate (CaOx) crystallization in vivo was investigated by examining the localization of Tamm-Horsfall protein (THP) and osteopontin (Opn) in a rat model of nephrolithiasis. CaOx crystal deposits were induced in male Sprague-Dawley rats by feeding 0.75% ethylene glycol in drinking water. THP and Opn were localized on kidney sections by immunoperoxidase technique, using specific polyclonal antibodies. When only occasional crystal deposits were seen in the kidney, THP showed a similar to normal pattern of distribution, with positive staining in the thick ascending limbs of the loop of Henle. Opn was localized in some nephrons in the thin limb of loop of Henle and on the papillary surface in the calyceal fornix. In contrast, in samples with a significantly increased number of deposits in the kidneys, the staining for both THP and Opn was strikingly enhanced and altered, with positive staining around the crystals as well as abnormal localization in the papilla. Interestingly, the occurrence of Opn was, however, more consistent than that of THP. This is a first study showing that in this nephrolithiasis model, normal localization of THP and Opn is altered and they are closely and concurrently associated with crystal deposits in vivo.