Regulation of ENaC-mediated alveolar fluid clearance by insulin via PI3K/Akt pathway in LPS-induced acute lung injury

Abstract

BackgroundStimulation of epithelial sodium channel (ENaC) increases Na+ transport, a driving force of alveolar fluid clearance (AFC) to keep alveolar spaces free of edema fluid that is beneficial for acute lung injury (ALI). It is well recognized that regulation of ENaC by insulin via PI3K pathway, but the mechanism of this signaling pathway to regulate AFC and ENaC in ALI remains unclear. The aim of this study was to investigate the effect of insulin on AFC in ALI and clarify the pathway in which insulin regulates the expression of ENaC in vitro and in vivo.MethodsA model of ALI (LPS at a dose of 5.0 mg/kg) with non-hyperglycemia was established in Sprague-Dawley rats receiving continuous exogenous insulin by micro-osmotic pumps and wortmannin. The lungs were isolated for measurement of bronchoalveolar lavage fluid(BALF), total lung water content(TLW), and AFC after ALI for 8 hours. Alveolar epithelial type II cells were pre-incubated with LY294002, Akt inhibitor and SGK1 inhibitor 30 minutes before insulin treatment for 2 hours. The expressions of α-,β-, and γ-ENaC were detected by immunocytochemistry, reverse transcriptase polymerase chain reaction (RT-PCR) and western blotting.ResultsIn vivo, insulin decreased TLW, enchanced AFC, increased the expressions of α-,β-, and γ-ENaC and the level of phosphorylated Akt, attenuated lung injury and improved the survival rate in LPS-induced ALI, the effects of which were blocked by wortmannin. Amiloride, a sodium channel inhibitor, significantly reduced insulin-induced increase in AFC. In vitro, insulin increased the expressions of α-,β-, and γ-ENaC as well as the level of phosphorylated Akt but LY294002 and Akt inhibitor significantly prevented insulin-induced increase in the expression of ENaC and the level of phosphorylated Akt respectively. Immunoprecipitation studies showed that levels of Nedd4-2 binding to ENaC were decreased by insulin via PI3K/Akt pathway.ConclusionsOur study demonstrated that insulin alleviated pulmonary edema and enhanced AFC by increasing the expression of ENaC that dependent upon PI3K/Akt pathway by inhibition of Nedd4-2.

Anti-inflammatory effects of Panax notoginseng saponins ameliorate acute lung injury induced by oleic acid and lipopolysaccharide in rats

“…This study has demonstrated that OA injection followed by LPS administration is capable of inducing severe pulmonary parenchymal damage in rats, consistent with various adverse effects on lung water homeostasis that are associated with ALI in animal models (8,23). OA has been reported to inhibit alveolar fluid reabsorption (24) and the endotoxin, LPS, has been indicated to adversely affect ENaC-mediated Na + transport (25,26).…”

“…In a lipopolysaccharide (LPS)-induced model of ALI in rats, all three ENaC subunits were observed to be downregulated in lung epithelial tissue at the protein and mRNA levels. This was concomitant with LPS-induced ALI (8).…”

“…The present study showed that in a model of ALI, PNS treatment demonstrated anti-inflammatory properties with a similar cytokine profile to that reported previously, and prevented the reduction in αENaC mRNA and protein levels in the lung tissue. As this was an exploratory investigation, only the α subunit of ENaC was investigated; however, of note, it has been reported that the β and γ subunits may be involved in rat models of ALI (8). Further in-depth investigations are required to elucidate the complex interrelation between cytokines, ENaCs and PNS in the damage associated with ALI.…”

Resolvin D1 Stimulates Alveolar Fluid Clearance through Alveolar Epithelial Sodium Channel, Na,K-ATPase via ALX/cAMP/PI3K Pathway in Lipopolysaccharide-Induced Acute Lung Injury

“…The PI3K has been identified as integral for regulation of ENaC-mediated AFC by insulin (32). Previous studies showed that RvD1 treatment in Par-Cro cells prevents TNF-a-mediated disruption of salivary epithelia formation and enhances cell migration and cell polarity via PI3K signaling (60).…”

“…Extracellular signals interact with GPCRs to activate adenylate cyclase (AC)/guanylyl cyclase and stimulate formation of the second messenger cAMP/ cGMP, which activates protein kinase A (PKA)/protein kinase C. Indeed, b 2 AR agonists have been shown to enhance AFC transport via a cAMP-dependent mechanism under physiological conditions (30) and in experimental models of lung injury (31), as well as in one prospective study of extravascular lung water in patients with ALI (19). In contrast, PI3K has been identified as integral for regulation of ENaC-mediated AFC by insulin (32).…”