Mutation of threonine for isoleucine at codon 73 (I73T) in the human surfactant protein C (hSP-C) gene ( SFTPC) accounts for a significant portion of SFTPC mutations associated with interstitial lung disease (ILD). Cell lines stably expressing tagged primary translation product of SP-C isoforms were generated to test the hypothesis that deposition of hSP-C^I73Twithin the endosomal system promotes disruption of a key cellular quality control pathway, macroautophagy. By fluorescence microscopy, wild-type hSP-C (hSP-C^WT) colocalized with exogenously expressed human ATP binding cassette class A3 (hABCA3), an indicator of normal trafficking to lysosomal-related organelles. In contrast, hSP-C^I73Twas dissociated from hABCA3 but colocalized to the plasma membrane as well as the endosomal network. Cells expressing hSP-C^I73Texhibited increases in size and number of cytosolic green fluorescent protein/microtubule-associated protein 1 light-chain 3 (LC3) vesicles, some of which colabeled with red fluorescent protein from the gene dsRed/hSP-C^I73T. By transmission electron microscopy, hSP-C^I73Tcells contained abnormally large autophagic vacuoles containing organellar and proteinaceous debris, which phenocopied ultrastructural changes in alveolar type 2 cells in a lung biopsy from a SFTPC I73T patient. Biochemically, hSP-C^I73Tcells exhibited increased expression of Atg8/LC3, SQSTM1/p62, and Rab7, consistent with a distal block in autophagic vacuole maturation, confirmed by flux studies using bafilomycin A1 and rapamycin. Functionally, hSP-C^I73Tcells showed an impaired degradative capacity for an aggregation-prone huntingtin-1 reporter substrate. The disruption of autophagy-dependent proteostasis was accompanied by increases in mitochondria biomass and parkin expression coupled with a decrease in mitochondrial membrane potential. We conclude that hSP-C^I73Tinduces an acquired block in macroautophagy-dependent proteostasis and mitophagy, which could contribute to the increased vulnerability of the lung epithelia to second-hit injury as seen in ILD.

Inhaled hypertonic saline (HS) is an effective therapy for muco-obstructive lung diseases. However, the mechanism of action and principles pertinent to HS administration remain unclear.Anin vitrosystem aerosolised HS to epithelial cells at rates comparable toin vivoconditions. Airway surface liquid (ASL) volume and cell height responses were measured by confocal microscopy under normal and hyperconcentrated mucus states.Aerosolised HS produced a rapid increase in ASL height and decrease in cell height. Added ASL volume was quickly reabsorbed following termination of nebulisation, although cell height did not recover within the same time frame. ASL volume responses to repeated HS administrations were blunted, but could be restored by a hypotonic saline bolus interposed between HS administrations. HS-induced ASL hydration was prolonged with hyperconcentrated mucus on the airway surface, with more modest reductions in cell volume.Aerosolised HS produced osmotically induced increases in ASL height that were limited by active sodium absorption and cell volume-induced reductions in cell water permeability. Mucus on airway surfaces prolonged the effect of HSviamucus-dependent osmotic forces, suggesting that the duration of action of HS is increased in patients with hyperconcentrated mucus.

Elexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA) was shown to be safe and efficacious in people with cystic fibrosis (CF) heterozygous for F508del and a minimal function mutation (F/MF) or homozygous for F508del (F/F) in two pivotal Phase 3 trials, significantly improving percentage predicted forced expiratory volume in 1 second, Cystic Fibrosis Questionnaire-Revised, Respiratory Domain (CFQ-R RD) scores, and sweat chloride concentration. Here, we analyzed the 11 non-respiratory domains (non-RDs) of the CFQ-R, which assess general health-related quality of life (i.e., Physical Functioning, Role Functioning, Vitality, Health Perceptions, Emotional Functioning, and Social Functioning) and quality of life impacted by CF (i.e., Body Image, Eating Problems, Treatment Burden, Weight, and Digestive Symptoms), for participants in these two Phase 3 trials. ELX/TEZ/IVA treatment led to higher scores in all CFQ-R non-RDs, with improvements in most domains compared with control treatments. These findings demonstrate that ELX/TEZ/IVA improves a range of CF-specific symptoms and general functioning and well-being.