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Increased fluid‐flow shear stress (FFSS) contributes to hyperfiltration‐induced podocyte and glomerular injury resulting in progression of chronic kidney disease (CKD). We reported that increased FFSS in vitro and in vivo upregulates PGE2 receptor EP2 (but not EP4 expression), COX2‐PGE2‐EP2 axis, and EP2‐linked Akt‐GSK3β‐β‐catenin signaling pathway in podocytes. To understand and use the disparities between PGE2 receptors, specific agonists, and antagonists of EP2 and EP4 were used to assess phosphorylation of Akt, GSK3β and β‐catenin in podocytes using Western blotting, glomerular filtration barrier function using in vitro albumin permeability (Palb) assay, and mitigation of hyperfiltration‐induced injury in unilaterally nephrectomized (UNX) mice at 1 and 6 months. Results show an increase in Palb by PGE2, EP2 agonist (EP2AGO) and EP4 antagonist (EP4ANT), but not by EP2 antagonist (EP2ANT) or EP4 agonist (EP4AGO). Pretreatment with EP2ANT blocked the effect of PGE2 or EP2AGO on Palb. Modulation of EP2 and EP4 also induced opposite effects on phosphorylation of Akt and β‐Catenin. Individual agonists or antagonists of EP2 or EP4 did not induce significant improvement in albuminuria in UNX mice. However, treatment with a combination EP2ANT + EP4AGO for 1 or 6 months caused a robust decrease in albuminuria. EP2ANT + EP4AGO combination did not impact adaptive hypertrophy or increased serum creatinine. Observed differences between expression of EP2 and EP4 on the glomerular barrier highlight these receptors as potential targets for intervention. Safe and effective mitigating effect of EP2ANT + EP4AGO presents a novel opportunity to delay the progression of hyperfiltration‐associated CKD as seen in transplant donors. [ABSTRACT FROM AUTHOR]

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 Palbumin permeability (PPalb) in vitro. FFSS caused an increase in PPalb 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 Palbumin 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 Palbuminuria 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. [ABSTRACT FROM AUTHOR]

Increased fluid flow shear stress (FFSS) in solitary kidney alters podocyte function in vivo. FFSS-treated cultured podocytes show upregulated AKT-GSK3β-β-catenin signaling. The present study was undertaken to confirm (i) the activation of β-catenin signaling in podocytes in vivo using unilaterally nephrectomized (UNX) TOPGAL mice with the β-galactosidase reporter gene for β-catenin activation, (ii) β-catenin translocation in FFSS-treated mouse podocytes, and (iii) β-catenin signaling using publicly available data from UNX mice. The UNX of TOPGAL mice resulted in glomerular hypertrophy and increased the mesangial matrix consistent with hemodynamic adaptation. Uninephrectomized TOPGAL mice showed an increased β-galactosidase expression at 4 weeks but not at 12 weeks, as assessed using immunofluorescence microscopy (p < 0.001 at 4 weeks; p = 0.16 at 12 weeks) and X-gal staining (p = 0.008 at 4 weeks; p = 0.65 at 12 weeks). Immunofluorescence microscopy showed a significant increase in phospho-β-catenin (Ser552, p = 0.005) at 4 weeks but not at 12 weeks (p = 0.935) following UNX, and the levels of phospho-β-catenin (Ser675) did not change. In vitro FFSS caused a sustained increase in the nuclear translocation of phospho-β-catenin (Ser552) but not phospho-β-catenin (Ser675) in podocytes. The bioinformatic analysis of the GEO dataset, #GSE53996, also identified β-catenin as a key upstream regulator. We conclude that transcription factor β-catenin mediates FFSS-induced podocyte (glomerular) injury in solitary kidney. [ABSTRACT FROM AUTHOR]