Implication of hyperoxaluria on osteopontin and ER stress mediated apoptosis in renal tissue of rats.

Hyperoxaluria is a stress that leads to calcium oxalate crystal deposition which further causes inflammation and renal cell necroptosis. Many studies have linked osteopontin expression with apoptosis and inflammation but so far its association with apoptosis with regard to hyperoxaluria is undiscovered. Moreover, a recent report has suggested that osteopontin induces endoplasmic reticulum stress and subsequently apoptosis in myocytes. In this study, the impact of hyperoxaluria on the modulation of osteopontin expression and endoplasmic reticulum (ER) stress mediated apoptosis in rats is explored. Hyperoxaluria was induced in rats by three different doses viz. ethylene glycol alone, ethylene glycol and ammonium chloride together and third group were fed with hydroxyl-l-proline. After hyperoxaluria induction rats were sacrificed and renal tissue was analysed for crystal depositions, osteopontin expression, inflammation, ER stress and subsequent unfolded protein response intermediates (UPR). Altered histoarchitecture of renal tissue and elevated levels of reactive oxygen species (ROS) along with the presence of calcium oxalate crystals were observed in the hyperoxaluric groups. As expected, inflammation and apoptosis was significantly high in all hyperoxaluria groups. Osteopontin expression showed significant up-regulation following hyperoxaluria. Further, a similar trend between expression of osteopontin and elevated ER stress level was observed. Moreover, UPR intermediates expression was also concurrent with osteopontin levels. It is observed that the extent of calcium oxalate crystal deposition is directly associated with the expression of osteopontin, inflammation and ER stress. The results advocate possible association of osteopontin with ER stress, thus suggesting that the ER could be a new target for developing therapeutic regimes for kidney stones.