Cyclooxygenase-2, prostaglandin E₂, and prostanoid receptor EP2 in fluid flow shear stress-mediated injury in the solitary kidney

Abstract

Hyperfiltration subjects podocytes to increased tensile stress and fluid flow shear stress (FFSS). We showed a 1.5- to 2.0-fold increase in FFSS in uninephrectomized animals and altered podocyte actin cytoskeleton and increased synthesis of prostaglandin E2 (PGE2) following in vitro application of FFSS. We hypothesized that increased FFSS mediates cellular changes through specific receptors of PGE2. Presently, we studied the effect of FFSS on cultured podocytes and decapsulated isolated glomeruli in vitro, and on solitary kidney in uninephrectomized sv129 mice. In cultured podocytes, FFSS resulted in increased gene and protein expression of cyclooxygenase (COX)-2 but not COX-1, prostanoid receptor EP2 but not EP4, and increased synthesis and secretion of PGE2, which were effectively blocked by indomethacin. Next, we developed a special flow chamber for applying FFSS to isolated glomeruli to determine its effect on an intact glomerular filtration barrier by measuring change in albumin permeability (Palb) in vitro. FFSS caused an increase in Palb that was blocked by indomethacin (P < 0.001). Finally, we show that unilateral nephrectomy in sv129 mice resulted in glomerular hypertrophy (P = 0.006), increased glomerular expression of COX-2 (P < 0.001) and EP2 (P = 0.039), and increased urinary albumin excretion (P = 0.001). Activation of the COX-2-PGE2-EP2 axis appears to be a specific response to FFSS in podocytes and provides a mechanistic basis for alteration in podocyte structure and the glomerular filtration barrier, leading to albuminuria in hyperfiltration-mediated kidney injury. The COX-2-PGE2-EP2 axis is a potential target for developing specific interventions to ameliorate the effects of hyperfiltration-mediated kidney injury in the progression of chronic kidney disease.

Reduced Krüppel-Like Factor 2 Aggravates Glomerular Endothelial Cell Injury and Kidney Disease in Mice with Unilateral Nephrectomy

“…Glomerular hyperfiltration causes shear stress in endothelial cells, 32 which is known to increase KLF2 expression. 26 Recently, we reported that reduced KLF2 expression in endothelial cells leads to more severe glomerular endothelial cell injury and kidney damage in early diabetic nephropathy, which is characterized by glomerular hyperfiltration.…”

Rheological Influence Upon the Glomerular Podocyte and Resultant Mechanotransduction

“…Srivastava et al also showed that FSS caused an increase of E-prostanoid receptor 2 (EP2) protein and mRNA expression in cultured podocytes, and increased EP2 protein expression in glomeruli of Os/+ oligosyndactyl mice (a model of hyperfiltration) [51]. Further work with cultured podocytes exposed to FSS showed increased COX-2 and EP2 gene and protein expression, and increased intracellular and secreted PGE 2 [52]. EP2 has been shown to mediate both G protein-coupled (modulating cAMP, Rap1/2, et al) and G proteinindependent (modulating β-arrestin, Src/EGFR, ERK, F-actin, et al) downstream signaling [53].…”

Hyperfiltration-associated biomechanical forces in glomerular injury and response: Potential role for eicosanoids

“…Commercially available equipment can be used for treating multiple slides simultaneously (Streamer System, Flexcell Corporation). We have developed a special flow chamber for studies using FFSS-treated isolated glomeruli [25]. …”

“…COX-1 is expressed constitutively whereas COX-2 is generally an inducible enzyme [30]. Podocytes express both COX-1 and COX-2 [31,32] and, we found that the COX2-PGE 2 -EP 2 axis plays an important role in hyperfiltration-mediated glomerular injury in mouse models of solitary kidney as well as in cultured podocytes [25, 33]. PGE 2 is the major prostanoid under physiological conditions and interacts with four E-prostanoid (EP) receptors that have been cloned and characterized in both human and mouse [34,35].…”