SFTPC mutations cause SP‐C degradation and aggregate formation without increasing ER stress

Abstract Background Mutations in the gene encoding surfactant protein C ( SP ‐ C ) cause familial and sporadic interstitial lung disease ( ILD ), which is associated with considerable morbidity and mortality. Unfortunately, effective therapeutic options are still lacking due to a very limited understanding of pathomechanisms. Knowledge of mutant SP ‐ C proprotein (pro SP ‐ C ) trafficking, processing, intracellular degradation and aggregation is a crucial prerequisite for the development of specific therapies to correct aberrant trafficking and processing of pro SP ‐C and to hinder accumulation of cytotoxic aggregates. Materials and methods To identify possible starting points for therapeutic intervention, we stably transfected A 549 alveolar epithelial cells with several pro SP ‐ C mutations previously found in patients suffering from ILD . Effects of mutant pro SP ‐ C were assessed by W estern blotting, immunofluorescence and C ongo red staining. Results A group of mutations (p.I73 T , p.L110 R , p.A116 D and p.L188 Q ) resulted in aberrant pro SP ‐ C products, which were at least partially trafficked to lamellar bodies. Another group of mutations (p.P30 L and p.P115L) was arrested in the endoplasmic reticulum ( ER ). Except for p.I73 T , all mutations led to accumulation of intracellular C ongo red–positive aggregates. Enhanced ER stress was detectable in none of these stably transfected cells. Conclusions Different SP ‐ C mutations have unique consequences for alveolar epithelial cell biology. As these cannot be predicted based upon the localization of the mutation, our data emphasize the importance of studying individual mutations in detail in order to develop mutation‐specific therapies.