Modulation of angiotensin II-induced inflammatory cytokines by the Epac1-Rap1A-NHE3 pathway: implications in renal tubular pathobiology

Abstract

Besides the glomerulus, the tubulointerstitium is often concomitantly affected in certain diseases, e.g., diabetic nephropathy, and activation of the renin-angiotensin system, to a certain extent, worsens its outcome because of perturbations in hemodynamics and possibly tubuloglomerular feedback. Certain studies suggest that pathobiology of the tubulointerstitium is influenced by small GTPases, e.g., Rap1. We investigated the effect of ANG II on inflammatory cytokines, while at the same time focusing on upstream effector of Rap1, i.e., Epac1, and some of the downstream tubular transport molecules, i.e., Na/H exchanger 3 (NHE3). ANG II treatment of LLC-PK1 cells decreased Rap1a GTPase activity in a time- and dose-dependent manner. ANG II treatment led to an increased membrane translocation of NHE3, which was reduced with Epac1 and PKA activators. ANG II-induced NHE3 translocation was notably reduced with the transfection of Rap1a dominant positive mutants, i.e., Rap1a-G12V or Rap1a-T35A. Transfection of cells with dominant negative Rap1a mutants, i.e., Rap1a-S17A, or Epac1 mutant, i.e., EPAC-ΔcAMP, normalized ANG II-induced translocation of NHE3. In addition, ANG II treatment led to an increased expression of inflammatory cytokines, i.e., IL-1β, IL-6, IL-8, and TNF-α, which was reduced with Rap1a-G12V or Rap1a-T35A transfection, while it reverted to previous comparable levels following transfection of Rap1a-S17A or EPAC-ΔcAMP. ANG II-induced expression of cytokines was reduced with the treatment with NHE3 inhibitor S3226 or with Epac1 and PKA activators. These data suggest that this novel Epac1-Rap1a-NHE3 pathway conceivably modulates ANG II-induced expression of inflammatory cytokines, and this information may yield the impetus for developing strategies to reduce tubulointertstitial inflammation in various renal diseases.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

“…Remarkably, ANG II-mediated expression of proinflammatory cytokines could be blocked by a NHE3 inhibitor S3226 or with EPAC1 and PKA activators. These data reveal a novel EPAC1-Rap1A-NHE3 pathway that mediates ANG II-induced cytokine production in kidney epithelial cells and may have important implications in tubulointerstitial pathobiology relevant to various renal diseases (1137).…”

RETRACTED ARTICLE: TN-2 modulates LPS-induced inflammatory response in human renal tubular epithelial cells by blocking TLR4-mediated NF-κB activation via MyD88- and TRIF-dependent mechanism

“…Recent studies have shown that the activation of various inflammatory molecules, such as cytokines (IL-6, IL-8, IL-1b, and TNF-a) [24], adhesion molecules (ICAM-1) [25], chemokines (MCP-1) [26], synthetase (iNOS and COX-2), and growth factors (VEGF, TGF-b) [27] contribute to the progression of DN. In our study, LPS up-regulated the production of a spectrum of inflammatory molecules in hRPTECs, including IL-6, IL-8, IL-1b, TNF-a, iNOS, COX-2, MCP-1 and ICAM-1.…”

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

“…Key players in this cascade include TGF-␤1 and various mediators of inflammation, involving several cell types in the kidney, as well as leukocytes and other immune cells. It is also interesting to note that an NHE3 inhibitor, S3236, reduces ANG II-stimulated induction of several cytokines in cultured proximal tubular cells (1172), suggesting a close relationship between renal inflammation and enhanced sodium reabsorption.…”