Exosomes of human adipose stem cells mitigate irradiation injury to salivary glands by inhibiting epithelial-mesenchymal transition through miR-199a-3p targeting Twist1 and regulating TGFβ1/Smad3 pathway

<b>Rationale:</b> Currently, irradiation-injured salivary glands (IR-SG) lack effective clinical treatment options. Emerging treatments using exosomes (Exo) have shown promising outcomes for various diseases. However, the efficacy of exosome in treating IR-SG remains unexplored. This study aimed to use exosomes to restore IR-SG function and to explore their underlying mechanisms. <b>Methods:</b> Exosomes isolated from human adipose-derived stem cell (ADSC-Exo) were injected into C57BL/6 mice that had their salivary glands injured with 14Gy. RNA sequencing profiled differentially expressed miRNAs and mRNAs of IR-SG. Epithelial-mesenchymal transition (EMT) mechanisms were further examined using SMG-C6 cells. <b>Results:</b> Exo-treated mice had a 96% increase in saliva secretion, higher cell proliferation, upregulated tissue repair/regeneration genes, and preserved functional cells with fewer collagen fibers compared to saline-treated mice. Exo treatment increased the expression of epithelial cell markers while decreasing mesenchymal cell markers. Notably, miR-199a-3p was significantly upregulated in Exo-treated mice, promoting cell growth and reducing EMT. Twist1, an EMT transcription factor, was identified as a direct target of miR-199a-3p and confirmed by luciferase assays. Twist1 overexpression promoted EMT, but Exo treatment or Twist1 knockdown reduced EMT marker expression and inactivated the TGFβ1/Smad3 pathway. <b>Conclusions:</b> ADSC-Exo is a promising therapy for IR-SG, primarily by mitigating EMT through miR-199a-3p targeting Twist1 and regulating the TGFβ1/Smad3 pathway.