A functionalized collagen-I scaffold delivers microRNA 21-loaded exosomes for spinal cord injury repair

MicroRNA (miRNA)-based therapies have shown great potential in the repair of spinal cord injury (SCI). MicroRNA 21 (miR21) has been proven to have an essential protective effect on SCI. However, there are some challenges for miRNAs application due to their easy degradation and ineffective cell penetration. As natural vesicles, exosomes were considered ideal carriers for miRNAs delivery for their advantages of low immunogenicity, inherent stability and tissue/cell penetration. However, poor targeting and the low capacity of specific miRNAs impede their practical applications. This study aims to develop a type of genetically engineered miR21-loaded exosomes that can be entrapped in collagen-I (Col-I) scaffold to repair SCI. The collagen-binding domain (CBD)-fused lysosome-associated membrane glycoprotein 2b (Lamp2b) protein (CBD-LP) and miR21 were overexpressed in host HEK293T (293T) cells that were used to produce engineered miR21-loaded exosomes. The CBD peptide fused in Lamp2b on the exosome surface can stably tether exosomes to Col-I scaffold, facilitate the retention of miR21-loaded exosomes in lesion sites, promote the sustained release of miR21 to cells. Finally, a functionalized Col-I scaffold biomaterial enriched with miR21-loaded exosomes was developed and it could benefit the repair of SCI. STATEMENT OF SIGNIFICANCE: MiRNA-based therapeutics have promising potential in spinal cord injury (SCI) repair. However, easy degradation and ineffective cell penetration impede miRNAs application. Exosomes are natural vehicles for miRNAs delivery but face the challenge of diffusion in vivo. Here, the collagen-binding domain (CBD)-fused Lamp2b and miR21 were overexpressed in HEK293T cells to produce miR21-loaded and CBD-modified exosomes (CBD-LP-miR21-EXOs). The CBD modified on the exosome surface can stably tether exosomes to collagen-I scaffold to form functionalized CBD-LP-miR21-EXO-Col scaffold that can facilitate the retention of miR21-loaded exosomes, promote the sustained release of miR21 to cells and finally benefit SCI repair. Furthermore, this type of functionalized collagen-I materials can be widely applied for other tissue injury repairs by enriching the CBD-LP-EXOs loaded with appropriate miRNAs.