Abstract

Tubular atrophy predicts chronic kidney disease progression, and is caused by proximal tubular epithelial cellcaused by proximal tubular epithelial cell (PTC) apoptosis. The normally quiescent Na(+)/H(+) exchanger-1 (NHE1) defends against PTC apoptosis, and is regulated by PI(4,5)P(2) binding. Because of the vast array of plasma membrane lipids, we hypothesized that NHE1-mediated cell survival is dynamically regulated by multiple anionic inner leaflet phospholipids. In membrane overlay and surface plasmon resonance assays, the NHE1 C terminus bound phospholipids with low affinity and according to valence (PIP(3) > PIP(2) > PIP = PA > PS). NHE1-phosphoinositide binding was enhanced by acidic pH, and abolished by NHE1 Arg/Lys to Ala mutations within two juxtamembrane domains, consistent with electrostatic interactions. PI(4,5)P(2)-incorporated vesicles were distributed to apical and lateral PTC domains, increased NHE1-regulated Na(+)/H(+) exchange, and blunted apoptosis, whereas NHE1 activity was decreased in cells enriched with PI(3,4,5)P(3), which localized to basolateral membranes. Divergent PI(4,5)P(2) and PI(3,4,5)P(3) effects on NHE1-dependent Na(+)/H(+) exchange and apoptosis were confirmed by selective phosphoinositide sequestration with pleckstrin homology domain-containing phospholipase Cδ and Akt peptides, PI 3-kinase, and Akt inhibition in wild-type and NHE1-null PTCs. The results reveal an on-off switch model, whereby NHE1 toggles between weak interactions with PI(4,5)P(2) and PI(3,4,5)P(3). In response to apoptotic stress, NHE1 is stimulated by PI(4,5)P(2), which leads to PI 3-kinase activation, and PI(4,5)P(2) phosphorylation. The resulting PI(3,4,5)P(3) dually stimulates sustained, downstream Akt survival signaling, and dampens NHE1 activity through competitive inhibition and depletion of PI(4,5)P(2).

Highlights

  • Chronic kidney disease is perpetuated by tubular epithelial cell apoptosis, and the NHE1 Naϩ/Hϩ exchanger defends against apoptosis in response to undefined regulatory mechanisms

  • PI[4,5]P2 and PI[3,4,5]P3 Differentially Regulate Apoptosis—We have previously shown that NHE1 activity inhibits Proximal renal tubular epithelial cell (PTC) apoptosis [22, 45, 58]

  • We previously demonstrated that the NHE1 Naϩ/Hϩ exchanger is instrumental in defending against PTC apoptotic stress, but the regulatory mechanisms had not been elucidated

Read more

Summary

Background

Chronic kidney disease is perpetuated by tubular epithelial cell apoptosis, and the NHE1 Naϩ/Hϩ exchanger defends against apoptosis in response to undefined regulatory mechanisms. Because of the vast array of plasma membrane lipids, we hypothesized that NHE1-mediated cell survival is dynamically regulated by multiple anionic inner leaflet phospholipids. Proximal renal tubular epithelial cell (PTC) apoptosis is a prominent feature in human renal biopsies and mouse models of chronic, progressive kidney diseases, and an important mechanism of tubular atrophy [7,8,9,10,11,12]. The plasma membrane inner leaflet phospholipid PI[4,5]P2 binds to and regulates multiple ion channels and exchangers (24 –28), including NHE1 (29 –31), consistent with studies suggesting that in some cell types NHE1 is compartmentalized to lipid rafts [30, 32, 33], which may be enriched for phosphoi-. We show that NHE1 is regulated by toggling between low affinity interactions with PI[4,5]P2 and PI[3,4,5]P3

EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call