Restoration of alveolar type II cell function contributes to simvastatin-induced attenuation of lung ischemia-reperfusion injury

Abstract

Alveolar type (AT) II cells transdifferentiate into ATI cells and as such represent a promising source for regenerating lung epithelium following lung injury. ATII cells are characterized by the presence of lamellar bodies (LBs), which store and secrete the surfactant protein-C (SP-C). Lung ischemia-reperfusion injury (LIRI) causes a distinct impairment of the ATII cell function, subsequently hindering lung repair by loss of ATI transdifferentiation. In this study, we provide new evidence that the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor simvastatin may restore the function of impaired ATII cells in vitro and in vivo. ATII cell lines, A549 (human) and MLE-12 (mouse), were subjected to hypoxia-reoxygenation (H/R) injury. Simvastatin pretreatment at low (5-20 µM), but not high (50-100 µM) doses markedly reduced apoptosis and increased proliferation and SP-C expression. In a rat lung ischemia-reperfusion (I/R) model, simvastatin treatment also increased ATII cell proliferation in vivo, as demonstrated by proliferating cell nuclear antigen/SP-C double staining. Transmission electron microscopy revealed that the number and volume density of LBs were significantly increased in the simvastatin-treated rat lungs. The protective effects of simvastatin were reversed in vitro by PI3-kinase (PI3K) inhibitors wortmannin and L-mevalonate, indicating that the PI3K/Akt and mevalonate pathways may be involved in simvastatin-induced ATII cell function restoration. These data demonstrate that an appropriate dose of simvastatin has a protective effect on LIRI in vitro and in vivo, due at least partially to restored ATII cell function via the HMG-CoA reductase pathway-dependent activation of PI3K/Akt signaling in a mevalonate pathway-dependent manner.