Introduction

Mature surfactant protein (SP)-A, secreted in alveolar space, is a combination of SP-A1 and SP-A2 oligomers, mainly reported as octadecamers. Heterozygous mutations in the genes encoding SP-A (SFTPA1 and SFTPA2) are associated with interstitial lung disease (ILD) and lung adenocarcinoma. To date, no specific treatment exists.

The present study investigates the effect of mutant SP-A1 or SP-A2 on SP-A oligomerization.

Methods

cDNA expression vector carrying non synonymous mutations in SFTPA1 and SFTPA2 as well as WT sequences were transfected or co-transfected in HEK293T cells. Proteins were extracted from cell lysate and supernatant and analyzed by western blot and co-immunoprecipitation (co-IP).

Results

Mutant forms of SP-A resulted in an abnormal oligomerization in the soluble lysate with an absence of hexamers. Interestingly, co-expression with WT SP-A increased the quantity of mutant SP-A expressed in soluble lysate and restored hexamers. Mirrored, mutant SP-A (not transfected with WT) was more presented in the insoluble lysate than when co-expressed with WT in favor of a rescue of mutant SP-A solubilization by the WT SP-A. 

We previously described that mutant SP-A was not secreted. However, a co-transfection with WT SP-A allowed a partial rescue of the secretion of mutant proteins.

Co-IP confirmed the direct interaction between WT and mutant SP-A in soluble lysate and supernatant.

Conclusions

We herein report for the first time the benefit of WT SP-A on mutant SP-A to restore oligomerization profile and partial secretion of mutant SP-A. These findings pave the way for the development of targeted treatments using SP-A lung supplementation for patients with SFTPA1 or SFTPA2 mutations.