The prothrombin gene is expressed in the rat kidney - Implications for urolithiasis research

There is considerable interest in determining the role of prothrombin fragm ents, especially urinary prothrombin fragment 1 (UPTF1), in the pathogenesi s of calcium oxalate (CaOx) urinary calculi. This fragment is present in ab undance in the matrix of CaOx crystals generated in human urine in vitro an d has also been detected in human urinary stones containing calcium. More r ecently, prothrombin gene expression has been reported in the human kidney. However, studies examining the renal biosynthesis of prothrombin or perhap s only its fragments during experimental lithogenesis, and in consequence, the role of UPTF1 in stone formation, cannot be carried out in humans. The aim of this investigation therefore was to determine whether prothrombin ge ne expression is present in the rat kidney. Total RNA was isolated from the kidneys and livers of 12 rats. Using revers e transcriptase PCR, mRNAs corresponding to the thrombin and fragment 1 + 2 (F1+2) regions of prothrombin were analysed by agarose gel electrophoresis . The expression of glyceraldehyde 3-phosphate dehydrogenase was also exami ned to determine whether the quality of the tissue mRNAs was adequate for a nalyses. The amplified products were identified by sequence analysis. All kidneys displayed evidence of expression of the thrombin and F1+2 domai ns of the prothrombin gene. Furthermore, the sequences of these PCR-derived products from kidney were identical to those from liver. This suggests tha t the prothrombins secreted by these two organs are identical. The fact tha t prothrombin biosynthesis occurs in both the human and rat kidney presents an opportunity for using established rat models of stone disease to evalua te the influence of lithogenic conditions on prothrombin gene expression, a nd the potential role of UPTF1 in vivo.