Peroxisome proliferator-activated receptor δ activation promotes cell survival following hypertonic stress

COX2-selective non-steroidal anti-inflammatory drugs (NSAIDs) cause selective apoptosis of renal medullary interstitial cells (RMIC) in vivo and reduce their ability to tolerate hypertonic stress in vitro. To determine the mechanism by which COX2 activity promotes RMIC viability, we examined the capacity of COX2-derived prostanoids to promote RMIC survival. Although RMICs synthesize prostaglandin E2 (PGE2) >> PGI2 > PGF2a > TxA2, only PGI2 enhanced RMIC viability following hypertonic stress. RMICs do not express the prostacyclin receptor, but they do express the prostacyclin responsive nuclear transcription factor peroxisome proliferator-activated receptor delta (PPARdelta). Hypertonic stress increased PGI2 synthesis 330% above base line and also activated a PPARdelta specific reporter (delta response element (DRE)) by 90% above base line. Conversely DRE activity was only inhibited by the COX2-selective inhibitor SC236 but not by a COX1-selective NSAID (SC560). Overexpression of PPARdelta using an adenovirus not only drove DRE activity but also prevented RMIC death due to COX2 inhibition. These studies are consistent with a model whereby hypertonicity activates COX2-derived prostaglandin production, which promotes RMIC viability through PPARdelta. Inhibition of PPARdelta activity may contribute to the renal papillary necrosis associated with analgesic and/or NSAID use.