Tissue Kallikrein Mediates Pro-Inflammatory Pathways and Activation of Protease-Activated Receptor-4 in Proximal Tubular Epithelial Cells

Abstract

Tissue kallikrein (KLK1) expression is up-regulated in human diabetic kidney tissue and induced by high glucose (HG) in human proximal tubular epithelial cells (PTEC). Since the kallikrein-kinin system (KKS) has been linked to cellular inflammatory process in many diseases, it is likely that KLK1 expression may mediate the inflammatory process during the development of diabetic nephropathy. In this study, we explored the role of KLK1 in tubular pro-inflammatory responses under the diabetic milieu. Recombinant KLK1 stimulated the production of inflammatory cytokines in PTEC via the activation of p42/44 and p38 MAPK signaling pathways. Molecular knockdown of endogenous KLK1 expression by siRNA transfection in PTEC attenuated advanced glycation end-products (AGE)-induced IL-8 and ICAM-1 productions in vitro. Interestingly, exposure of PTEC to KLK1 induced the expression of protease-activated receptors (PARs). There was a 2.9-fold increase in PAR-4, 1.4-fold increase in PAR-1 and 1.2-fold increase in PAR-2 mRNA levels. Activation of PAR-4 by a selective agonist was found to elicit the pro-inflammatory and pro-fibrotic phenotypes in PTEC while blockade of the receptor by specific antagonist attenuated high glucose-induced IL-6, CCL-2, CTGF and collagen IV expression. Calcium mobilization by the PAR-4 agonist in PTEC was desensitized by pretreatment with KLK1. Consistent with these in vitro findings, there was a markedly up-regulation of tubular PAR-4 expression in human diabetic renal cortical tissues. Together, these results suggest that up-regulation of KLK1 in tubular epithelial cells may mediate pro-inflammatory pathway and PAR activation during diabetic nephropathy and provide a new therapeutic target for further investigation.

Coagulation Factor Xa and Protease-Activated Receptor 2 as Novel Therapeutic Targets for Diabetic Nephropathy

“…29 Interestingly, immunoreactive PAR2, but not PAR1, was higher in biopsy specimens from patients with DN than in specimens from patients without DN. 30 These results support the importance of PAR2 in the pathogenesis of DN. Fondaparinux, a FXa inhibitor, is suggested to reduce DN in db/db mice.…”

The Kallikrein-Kinin System: A Novel Mediator of IL-17-Driven Anti-Candida Immunity in the Kidney

“…albicans- infected IL-17RA -/- mice and in WT mice (Fig 2D). A previous study suggested that Klk1 may induce inflammatory cytokines in human RTECs, at least in vitro [37]. However, we found that overexpression of Klk1 had very little impact on renal inflammatory gene expression or fungal load (Fig 2E and S2D Fig).…”

“…Additionally, Klk1 activates protease-activated receptors (PAR) such as PAR4 to trigger the release of inflammatory mediators from RTEC [37]. To define the role of Bdkrb activation in renal immunity, IL-17RA -/- mice were treated with bradykinin (300 nmol/kg) and survival evaluated following infection.…”

“…In addition, Klk1-mediated activation of PAR4 induces cytokine production and prevents apoptosis in RTEC, known as the bradykinin-independent pathway [37]. Mice deficient in specific PARs or treated with PAR antagonists exhibited compromised renal inflammatory changes [51,52].…”

Kallikreins – The melting pot of activity and function

“…Recent studies indicate contradictory effects of elevated levels of KLK1 expression on diabetic nephropathy. KLK1 exhibits renoprotective effects [139], but can also mediate a pro-inflammatory pathway via Proteinase Activated Receptor (PAR) activation [140]. Despite extensive research aimed at better understanding the molecular basics of renal and cardiovascular diseases, the overall view of interplay between kallikreins and other functional proteins still is unclear.…”