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Lipotoxic disruption of NHE1 interaction with PI(4,5)P2 expedites proximal tubule apoptosis.

ABSTRACT: Chronic kidney disease progression can be predicted based on the degree of tubular atrophy, which is the result of proximal tubule apoptosis. The Na+/H+ exchanger NHE1 regulates proximal tubule cell survival through interaction with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2], but pathophysiologic triggers for NHE1 inactivation are unknown. Because glomerular injury permits proximal tubule luminal exposure and reabsorption of fatty acid/albumin complexes, we hypothesized that accumulation of amphipathic, long-chain acyl-CoA (LC-CoA) metabolites stimulates lipoapoptosis by competing with the structurally similar PI(4,5)P2 for NHE1 binding. Kidneys from mouse models of progressive, albuminuric kidney disease exhibited increased fatty acids, LC-CoAs, and caspase-2-dependent proximal tubule lipoapoptosis. LC-CoAs and the cytosolic domain of NHE1 directly interacted, with an affinity comparable to that of the PI(4,5)P2-NHE1 interaction, and competing LC-CoAs disrupted binding of the NHE1 cytosolic tail to PI(4,5)P2. Inhibition of LC-CoA catabolism reduced NHE1 activity and enhanced apoptosis, whereas inhibition of proximal tubule LC-CoA generation preserved NHE1 activity and protected against apoptosis. Our data indicate that albuminuria/lipiduria enhances lipotoxin delivery to the proximal tubule and accumulation of LC-CoAs contributes to tubular atrophy by severing the NHE1-PI(4,5)P2 interaction, thereby lowering the apoptotic threshold. Furthermore, these data suggest that NHE1 functions as a metabolic sensor for lipotoxicity.

SUBMITTER: Khan S

PROVIDER: S-EPMC3934167 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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Lipotoxic disruption of NHE1 interaction with PI(4,5)P2 expedites proximal tubule apoptosis.

Khan Shenaz S Abu Jawdeh Bassam G BG Goel Monu M Schilling William P WP Parker Mark D MD Puchowicz Michelle A MA Yadav Satya P SP Harris Raymond C RC El-Meanawy Ashraf A Hoshi Malcolm M Shinlapawittayatorn Krekwit K Deschênes Isabelle I Ficker Eckhard E Schelling Jeffrey R JR

The Journal of clinical investigation 20140217 3

Chronic kidney disease progression can be predicted based on the degree of tubular atrophy, which is the result of proximal tubule apoptosis. The Na+/H+ exchanger NHE1 regulates proximal tubule cell survival through interaction with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2], but pathophysiologic triggers for NHE1 inactivation are unknown. Because glomerular injury permits proximal tubule luminal exposure and reabsorption of fatty acid/albumin complexes, we hypothesized that accumulation ...[more]

PMID: 24531551

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Project description:Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) regulates activities of numerous ion channels including inwardly rectifying potassium (K(ir)) channels, KCNQ, TRP, and voltage-gated calcium channels. Several studies suggest that voltage-gated potassium (K(V)) channels might be regulated by PI(4,5)P(2). Wide expression of K(V) channels in different cells suggests that such regulation could have broad physiological consequences. To study regulation of K(V) channels by PI(4,5)P(2), we have coexpressed several of them in tsA-201 cells with a G protein-coupled receptor (M(1)R), a voltage-sensitive lipid 5-phosphatase (Dr-VSP), or an engineered fusion protein carrying both lipid 4-phosphatase and 5-phosphatase activity (pseudojanin). These tools deplete PI(4,5)P(2) with application of muscarinic agonists, depolarization, or rapamycin, respectively. PI(4,5)P(2) at the plasma membrane was monitored by Förster resonance energy transfer (FRET) from PH probes of PLCδ1 simultaneously with whole-cell recordings. Activation of Dr-VSP or recruitment of pseudojanin inhibited K(V)7.1, K(V)7.2/7.3, and K(ir)2.1 channel current by 90-95%. Activation of M(1)R inhibited K(V)7.2/7.3 current similarly. With these tools, we tested for potential PI(4,5)P(2) regulation of activity of K(V)1.1/K(V)β1.1, K(V)1.3, K(V)1.4, and K(V)1.5/K(V)β1.3, K(V)2.1, K(V)3.4, K(V)4.2, K(V)4.3 (with different KChIPs and DPP6-s), and hERG/KCNE2. Interestingly, we found a substantial removal of inactivation for K(V)1.1/K(V)β1.1 and K(V)3.4, resulting in up-regulation of current density upon activation of M(1)R but no changes in activity upon activating only VSP or pseudojanin. The other channels tested except possibly hERG showed no alteration in activity in any of the assays we used. In conclusion, a depletion of PI(4,5)P(2) at the plasma membrane by enzymes does not seem to influence activity of most tested K(V) channels, whereas it does strongly inhibit members of the K(V)7 and K(ir) families.

Project description:β-arrestins regulate many cellular functions including intracellular signaling and desensitization of G protein-coupled receptors (GPCRs). Previous studies show that β-arrestin signaling and receptor endocytosis are modulated by the plasma membrane phosphoinositide lipid phosphatidylinositol-(4, 5)-bisphosphate (PI(4,5)P2). We found that β-arrestin also helped promote synthesis of PI(4,5)P2 and up-regulated GPCR endocytosis. We studied these questions with the Gq-coupled protease-activated receptor 2 (PAR2), which activates phospholipase C, desensitizes quickly, and undergoes extensive endocytosis. Phosphoinositides were monitored and controlled in live cells using lipid-specific fluorescent probes and genetic tools. Applying PAR2 agonist initiated depletion of PI(4,5)P2, which then recovered during rapid receptor desensitization, giving way to endocytosis. This endocytosis could be reduced by various manipulations that depleted phosphoinositides again right after phosphoinositide recovery: PI(4)P, a precusor of PI(4,5)P2, could be depleted at either the Golgi or the plasma membrane (PM) using a recruitable lipid 4-phosphatase enzyme and PI(4,5)P2 could be depleted at the PM using a recruitable 5-phosphatase. Endocytosis required the phosphoinositides. Knock-down of β-arrestin revealed that endogenous β-arrestin normally doubles the rate of PIP5-kinase (PIP5K) after PAR2 desensitization, boosting PI(4,5)P2-dependent formation of clathrin-coated pits (CCPs) at the PM. Desensitized PAR2 receptors were swiftly immobilized when they encountered CCPs, showing a dwell time of ∼90 s, 100 times longer than for unactivated receptors. PAR2/β-arrestin complexes eventually accumulated around the edges or across the surface of CCPs promoting transient binding of PIP5K-Iγ. Taken together, β-arrestins can coordinate potentiation of PIP5K activity at CCPs to induce local PI(4,5)P2 generation that promotes recruitment of PI(4,5)P2-dependent endocytic machinery.

Dataset Information

Lipotoxic disruption of NHE1 interaction with PI(4,5)P2 expedites proximal tubule apoptosis.

Publications

Lipotoxic disruption of NHE1 interaction with PI(4,5)P2 expedites proximal tubule apoptosis.

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