Impact of ΔF508 CFTR mutation on diaphragm function during acute inflammation.

Abstract

Cystic fibrosis is caused by cystic fibrosis transmembrane conductance regulator (CFTR) mutations and is associated with skeletal muscle dysfunction. Prior work showed exaggerated inflammatory activation of proteolysis pathways in the diaphragms of CFTR-null mice. However, the effects of the more clinically relevant ΔF508 (DF-CFTR) mutation on diaphragm function are unknown. Homozygous DF-CFTR mice (Cftr^tm1EUR) and wild-type littermates received intraperitoneal phosphate-buffered saline or lipopolysaccharide (LPS) (5 mg/kg). After 24 h, we evaluated diaphragm mass and fiber types; expression (mRNA) of cytokines (IL1β, IL6), the unfolded protein response (UPR), and proteolysis (ubiquitin-proteasome, autophagy-lysosome); calpain activity; oxidative stress markers (malondialdehyde, 3-nitrotyrosine); and ex vivo muscle contractility. Oxidative stress markers were higher in DF-CFTR diaphragms at baseline and in response to LPS. Atrogin1 and autophagy markers (LC3B, Gabarapl1) were more strongly induced by LPS in DF-CFTR. Expression of cytokines, UPR, and other proteolysis pathways (MuRF1, calpain) was equivalent. Diaphragm mass, fiber diameter, and fiber type proportions did not differ between groups. Contractile function did not differ at baseline, but only DF-CFTR diaphragms showed reduced force production after LPS. During an acute inflammatory challenge, DF-CFTR diaphragms exhibit exaggerated oxidative stress and proteolysis signaling together with greater force loss. These findings support an increased vulnerability to diaphragm dysfunction linked to the DF-CFTR mutation.NEW & NOTEWORTHY The most common CFTR mutation in cystic fibrosis (CF), ΔF508 (DF-CFTR), was associated with increased oxidative stress in the diaphragm without weakness or atrophy under basal conditions. Acute systemic inflammation triggered further induction of oxidative stress and proteolytic pathways along with greater force loss in the diaphragm, compared with wild-type controls. This previously unrecognized vulnerability of the DF-CFTR diaphragm to systemic inflammation may predispose to respiratory muscle dysfunction in CF, particularly during acute infectious exacerbations.