Increased cyclooxygenase-2 expression and prostaglandin E₂production in pressurized renal medullary interstitial cells

Abstract

Renal medullary interstitial cells (RMICs) are subjected to osmotic, inflammatory, and mechanical stress as a result of ureteral obstruction, which may influence the expression and activity of cyclooxygenase type 2 (COX-2). Inflammatory stress strongly induces COX-2 in RMICs. To explore the direct effect of mechanical stress on the expression and activity of COX-2, cultured RMICs were subjected to varying amounts of pressure over time using a novel pressure apparatus. COX-2 mRNA and protein were induced following 60 mmHg pressure for 4 and 6 h, respectively. COX-1 mRNA and protein levels were unchanged. PGE(2) production in the RMICs was increased when cells were subjected to 60 mmHg pressure for 6 h and was prevented by a selective COX-2 inhibitor. Pharmacological inhibition indicating that pressure-induced COX-2 expression is dependent on p38 MAPK and biochemical knockdown experiments showed that NF-kappaB might be involved in the COX-2 induction by pressure. Importantly, terminal deoxyneucleotidyl transferase-mediated dUTP nick-end labeling and methylthiazoletetetrazolium assay studies showed that subjecting RMICs to 60 mmHg pressure for 6 h does not affect cell viability, apoptosis, and proliferation. To further examine the regulation of COX-2 in vivo, rats were subjected to unilateral ureteral obstruction (UUO) for 6 and 12 h. COX-2 mRNA and protein level was increased in inner medulla in response to 6- and 12-h UUO. COX-1 mRNA and protein levels were unchanged. These findings suggest that in vitro application of pressure recapitulates the effects on RMICs found after in vivo UUO. This directly implicates pressure as an important regulator of renal COX-2 expression.

ROS dependence of cyclooxygenase-2 induction in rats subjected to unilateral ureteral obstruction

“…We and others (6,15,24,27) have observed increased COX-2 expression in the renal inner medulla in response to ureteral obstruction. There is increasing evidence supporting a cytoprotective role of COX-2 in the renal medulla and increased COX-2 expression as a prerequisite for RMIC survival from hypertonic stress (13,14,33).…”

“…To explore the possible underlying mechanisms that link ROS and COX-2 in RMICs, the MAPK cascade was examined. MAPK pathways mediate the stimulatory effects of different extracellular stimuli on COX-2 expression in a stimulus-and cell type-specific manner (6,34), and studies have also demonstrated that oxidative and mechanical stress can stimulate MAPK pathways in various cell types (1, 3, 10, 31). Here, we studied different classes of MAPKs, including ERK1/2, p38, and JNK, and our data showed that the antioxidants DPI and ROT partly attenuated oxidative stress-induced phosphorylation of both ERK1/2 and p38 in RMICs.…”

“…Our previous study (6) demonstrated that the MAPK pathway plays a role in the regulation of COX-2 expression in RMICs subjected to mechanical stress; therefore, we investigated whether ROS may act via MAPK. To test this, we determined the effects of the antioxidants DPI and ROT on the activation of ERK1/2, p38, and JNK in RMICs exposed to H 2 O 2 .…”

Effects of biomechanical forces on signaling in the cortical collecting duct (CCD)

“…This difference may be explained by the fact that multiple biomechanical forces, other than CS, come into play in obstructive uropathy, such as hydrostatic pressure, which were not studied in the present investigation. In fact, several investigators have demonstrated that increases in intrarenal pressure stimulate COX-2 expression in interstitial cells, but not in the collecting duct, to induce PGE 2 expression (7,27). Therefore, because of the complexity of cell types and mechanical forces present in the hydronephrotic kidney, it is difficult to directly extrapolate our current findings to the hydronephrosis model.…”

The intrinsic prostaglandin E2–EP4 system of the renal tubular epithelium limits the development of tubulointerstitial fibrosis in mice

“…This result is in good agreement with reported results that state that production of PGE 2 increases significantly in the kidney after UUO. 17,18,24,25 In addition, immunohistochemical analysis showed that main COX-2 immunoreactivities were localized to tubular epithelial cells after UUO, suggesting that PGE 2 produced by COX-2 in tubular epithelial cells exhibits some effects on neighboring cells, including tubular epithelial cells themselves and interstitial cells. In addition, we found that the expression level of EP 4 mRNA increases remarkably in WT kidneys after UUO.…”