Effects of Chronic Intermittent Hypoxia (CIH) on mTORC Signaling in the Lung

Abstract

RationaleThe mechanistic target of rapamycin complex 1 (mTORC1) is a serine/threonine protein kinase that promotes anabolic processes (protein translation, lipogenesis and nucleotide syntheses) and limits catabolic processes, such as autophagy; thus, modulates senesce in various tissues. S6K1 and its downstream targets SKAR and S6 substrate are involved in mTORC1 signaling, whereas 4EB‐P1 is an inhibitory regulator of mTORC1‐induced protein translation. Chronic intermittent hypoxia (CIH)—the hallmark feature of sleep apnea, leads to heterogeneous remodeling in the lung, similar to “senile remodeling” (senile emphysema and fibrosis). However, whether CIH modulates the mTORC1 pathway to underlie these processes remains unknown. We hypothesized that CIH leads to downregulation of mTORC1 signaling, contributing to accelerated aging in the lung.MethodsWild type C57BL/6j, female mice (n=3–4/group), aged 4 months (young) and 23 months (old) were exposed to either CIH, defined as 60 events per hour (40 seconds 20% O2 and 20 seconds 5% O2), for 6 hours per day, or normoxia (Nx), for 8 weeks. Mouse lungs were excised, frozen at −80 C, and analyzed for phosphorylated (P) S6K, S6 and 4EB‐P1 protein levels by Western blot. Total protein was resolved by SDS‐PAGE. Images were quantified by densitometry using ImageJ software. Data were expressed as ratio of phosphorylated component/total protein.ResultsP‐S6K levels (Figure 1A): 1) in the 4/CIH group was significantly lower than in the 4/Nx and comparable to 23/Nx group; 2) in the 23/CIH group trended to be lower than in the 23/Nx. There were no group differences in PS6 levels (p=0.92). Meanwhile, phosphorylated 4E‐BP1 levels (Figure 1B): 1) in the 4/CIH group were higher than in 4/Nx and comparable to 23/Nx group; 2) whereas, in the 23/CIH tended to be higher than the 23/Nx group.ConclusionsLungs exposed to CIH demonstrate reduced downstream mTORC1 P‐S6K signaling, concurrent with increased levels of the inhibitory regulator of mTORC1‐induced protein translation, 4E‐BP1; aging may amplify these effects. These results suggest that CIH could lead to reduced mTOR‐induced protein synthesis and accelerated aging in the lung.Support or Funding InformationSchool of Medicine Pilot funds