Author(s): PEÑAILILLO, L., GUTIÉRREZ, S., FLORES-OPAZO, M., VALLADARES-IDE, D., JANNAS-VELA, S., CABELLO-VERRUGIO, C., PARADA, P., CAMPOS, C., Institution: UNIVERSIDAD ANDRES BELLO, Country: CHILE, Abstract-ID: 1996

INTRODUCTION:
Patients with chronic obstructive pulmonary disease (COPD) present muscle dysfunction (1). The mechanisms for muscle dysfunction include a decrease in muscle oxidative capacity, a shift toward a fast-glycolytic (type II) muscle fiber type and reduced cross-sectional area (CSA) of all muscle fiber types. Skeletal muscle adaptations have shown to be fiber type-specific (i.e., type I or slow-twitch and IIa or fast-twitch) (2). Thus, adaptations of molecular pathways related to oxidative metabolism, protein synthesis and degradation may be in a fiber-specific manner in COPD. Aim: To compare the protein content of the protein synthesis and oxidative metabolism protein pathways in type I and IIa skeletal muscle fibers from COPD and healthy aged individuals.
METHODS:
Ten COPD (age=67.6±5.1 y) and eight healthy (age= 64.2±7,7 y) individuals underwent a muscle biopsy from the vastus lateralis. Muscle specimens were lyophilized, after which muscle fibers were identified and isolated manually. Dot-blot technique was used to identify type I and IIa MHC isoforms, after which the same fiber-type fibers were pooled. Total ubiquitination, Akt-1, p70s6K, S6 ribosomal protein, OXPHOS, COX-IV, MCU, Mitofusin2, DRP1, and AMPK total proteins from whole muscle and fiber-type pooled samples were quantified by Western blot. Indirect immunofluorescence and hematoxylin/eosin staining were used in serial cryosection to evaluate muscle fiber morphology. Two-way ANOVA and independent t-test were used to compare conditions and fiber types, and whole muscle samples, respectively.
RESULTS:
Total levels of Akt-1, S6RP, AMPK, and MCU protein were similar between muscle fiber types and between whole muscle homogenates from both COPD and healthy individuals. COPD patients showed greater levels of p70S6k in whole muscle homogenates and IIa muscle fiber. Both groups showed greater levels of MCU protein in type I muscle fibers. COPD patients showed lesser levels of COX IV and subunits I to IV of OXPHOS compared to healthy individuals. Total protein ubiquitination was greater in COPD than in healthy, which was greater in type IIa fibers, opposite to healthy individuals, which showed greater levels of ubiquitination of type I fibers. Mitofusin2 and DRP1 proteins were greater in COPD patients compared to healthy individuals.
CONCLUSION:
These results suggest that COPD patients have compensatory machinery for protein synthesis in response to greater ubiquitination through a p70s6K-dependent pathway, particularly in type IIa muscle fibers. Greater oxidative metabolism in healthy individuals was expected. However, greater mitofusin1 and DRP1 expression may also reveal a compensatory mechanism for increased mitophagy in COPD.