Bradykinin Regulates Cyclooxygenase-2 in Rat Renal Thick Ascending Limb Cells

Abstract

Abstract-Cyclooxygenase-2 (COX-2) is constitutively expressed in a subset of thick ascending limb cells in the cortex and medulla and increases when the renin-angiotensin and kallikrein-kinin systems are activated. Although the contribution of angiotensin II to the regulation of COX-2 is known, the effects of bradykinin on COX-2 expression have not been determined in this nephron segment. We evaluated expression of B2 bradykinin receptors in thick ascending limb cells containing COX-2 and the effect of bradykinin on COX-2 expression in primary cultured medullary thick ascending cells. The presence of B2 receptors was studied in renal sections by immunohistochemistry with antibodies against B2, COX-2, and Tamm-Horsfall glycoprotein. B2 receptors were detected on the apical and basolateral portion of the thick ascending cells. These cells also contained COX-2, suggesting that COX-2 expression may be regulated via B2 receptor. Incubation of cultured medullary thick ascending cells with bradykinin (10 Ϫ7 to 10 Ϫ5 mol/L) induced a significant increase on COX-2 protein expression. Maximal expression of COX-2 was observed 4 hours after exposure to bradykinin (10 Ϫ7 mol/L), effect abolished by a B2 receptor antagonist (HOE-140; 10 Ϫ6 mol/L). Prostaglandin E 2 production increased when these cells were challenged with bradykinin for 4 hours, indicating that COX-2 was enzymatically active. We have demonstrated (1) the presence of B2 receptors in thick ascending limb cells expressing COX-2 and (2) the stimulatory effect of bradykinin on COX-2 protein expression, via B2 receptors, in cultured medullary thick ascending cells. We suggest that bradykinin can affect ion transport in the thick ascending limb via a COX-2-mediated mechanism. Key Words: cyclooxygenase Ⅲ bradykinin Ⅲ immunohistochemistry Ⅲ rats Ⅲ kidney Ⅲ receptors, bradykinin Ⅲ prostaglandins P rostaglandins participate in the regulation of the renal circulation 1 and tubular ion transport as well as renin secretion, the latter via a cyclooxygenase-2 (COX-2)-dependent mechanism. 2,3 The constitutive enzyme cyclooxygenase-1 (COX-1) has been identified in the collecting tubules and the renal vasculature. 4,5 Immunohistochemical localization studies have detected COX-2 in the perimacula densa region and a subset of thick ascending limb (TAL) epithelial cells located in the cortex (cTAL) 6,7 and outer medulla (mTAL) 7 as well as in interstitial medullary cells. 8 COX-2 expression in the kidney under basal conditions suggests that COX-2 may have a physiological role. Expression of the COX-2 isoform is increased in the kidney during development, 9,10 adrenalectomy, 11,12 and low-salt diet 13 ; it is decreased by glucocorticoids. 11,12 The kallikrein-kinin system (KKS) 14 contributes to the regulation of renal blood flow and salt and water excretion. The renal effects of bradykinin under physiological conditions are mediated by the B2 receptor, whereas the B1 receptor is expressed in pathological states such as inflammation. 15 Activation of the renin-angiotensin and KKS ...

Bradykinin stimulates glutamate uptake via both B1R and B2R activation in a human retinal pigment epithelial cells

“…BK has been reported to act as an important mediator in various cell types through the activation of COX-2 (Rodriguez et al, 2004;Hsieh et al, 2007). Alterations in the regulation of COX-2 have been implicated in the function of RPE cells (Fang et al, 2007).…”

Both B1R and B2R act as intermediate signaling molecules in high glucose‐induced stimulation of glutamate uptake in ARPE cells

“…BK has been reported to act as an important mediator via COX-2 activation in different cell types (Rodriguez et al, 2004;Hsieh et al, 2007), and the alteration of COX-2 regulation is implicated in RPE cell function (Fang et al, 2007). Moreover, NF-kB is a transcriptional regulator of COX-2 gene expression (Lim et al, 2001) and has been demonstrated to be a key signaling molecule in hyperglycemia-induced dysfunction of retinal Muller cells (Shelton et al, 2007).…”

Characterization of a long-term rat mTAL cell line

“…Secondary antibodies included corresponding AlexaFluor 488-, 586-, and 594-tagged antibodies (Molecular Probes, Eugene, OR). The specificity of the antibodies was demonstrated by comparison with preimmune sera, competition after preadsorption with the appropriate peptide, or omission of primary antibodies, as reported previously (32,40). The Biomol green reagent used in the ATPase assay was obtained from Biomol.…”