Advanced MicroRNA delivery for lung inflammatory therapy: surfactant protein A controls cellular internalisation and degradation of extracellular vesicles

Introduction Alveolar macrophages (AMs) are the first line of defence against pathogens that initiate an inflammatory response in the lungs and exhibit a strong affinity for surfactant protein A (SP-A). Extracellular vesicles (EVs) have emerged as a promising drug delivery platform due to their minimal cytotoxicity. However, precise targeting of specific cell types and the rapid lysosomal degradation of EVs within recipient cells remain persistent challenges.Method In this study, we explored the biological significance of SP-A-EVs as novel drug delivery systems for combating lung inflammation. We first verified that respiratory EVs express SP-A receptor (SP-R210), facilitating the conjugation of SP-A with EVs. The delivery efficiency, cellular internalisation pathways and therapeutic effects were evaluated using an in vivo mouse model.Results SP-A-EVs were robustly internalised into AMs both in vitro and in vivo. Furthermore, our investigation revealed that the toll-like receptor 4-mediated endocytosis pathway was employed for the uptake of SP-A-EVs, significantly delaying their degradation compared with natural EVs, which primarily followed the conventional lysosomal degradation pathway within AMs. In a functional study, we successfully loaded anti-inflammatory microRNA (let-7b) into SP-A-EVs, leading to the suppression of AM activation and the alleviation of lung inflammation induced by lipopolysaccharide.Conclusion These findings underscore the potential of SP-A-EVs as highly effective drug delivery systems for targeted therapeutics in lung-related disorders, capitalising on the strong affinity between AMs and SP-A and the modulation of cellular internalisation.