Prothrombin gene expression in rat kidneys provides an opportunity to examine its role in urinary stone pathogenesis

Urinary form of prothrombin (PT) fragment 1 is the most abundant protein in calcium oxalate crystals generated in human urine. The protein has also been detected in human calcium-containing stones. In its purified form, the protein inhibits calcium oxalate crystal growth and, more importantly, aggregation in aqueous inorganic solutions and undiluted human urine. Recently, PT gene expression has been reported in human kidneys. However, access to human renal tissue for studies is limited, and it is not possible to easily manipulate PT biosynthesis in human subjects. The aim of this investigation, therefore, was to determine whether PT gene expression is present in rat kidneys. Samples of total RNA were isolated from the kidneys and livers (positive controls) of 12 male hooded Wistar rats. Using reverse transcription-PCR, mRNA corresponding to the thrombin and F1+2 regions of PT was analyzed by agarose gel electrophoresis. The expression of the "housekeeping" gene glyceraldehyde-3-phosphate dehydrogenase was also examined, to determine the availability of amplifiable substrate in each specimen. The amplified products were also sequenced, to determine their identities. All rat kidneys displayed evidence of expression of the thrombin and F1+2 domains of the PT gene. This similarity between human and rat kidneys allows the possibility of using established rat models of stone disease to evaluate therapeutic strategies to reduce stone formation.