Extracellular Vesicles Derived from Human Umbilical Cord-Mesenchymal Stem Cells Ameliorate Intervertebral Disc Degeneration

<b>Background:</b> Intervertebral disc degeneration (IVDD) is closely linked to low back pain (LBP), a leading cause of disability worldwide. IVDD is characterized by the loss of proteoglycans (PGs), extracellular matrix (ECM) degradation, and reduced hydration of the nucleus pulposus (NP). Extracellular vesicles (EVs) derived from human umbilical cord mesenchymal stem cells (hUC-MSCs) exhibit tissue repair and immunomodulatory effects and are emerging as promising cell-free therapeutics. <b>Methods:</b> We established a rat IVDD model via fluoroscopy-guided needle puncture of three consecutive coccygeal discs and confirmed degeneration through Alcian Blue and hematoxylin & eosin (H&E) staining. The gene expression of inflammatory and pain markers (<i>ADRβ2</i>, <i>COMP</i>, <i>CXCL1</i>, <i>COX2</i>, <i>PPTA</i>, <i>MMP13</i>, <i>YKL40</i>) was measured by qPCR. Subsequently, we implanted hUC-MSCs or EVs to evaluate their reparative potential. <b>Results:</b> Upregulation of inflammatory and pain genes in IVDD was associated with an immunomodulatory response. Tracking DiI-labelled hUC-MSCs and EVs revealed enhanced survival of hUC-MSCs, retention of EVs, and dispersion within rat tail discs; EVs showed greater retention than hUC-MSCs. Implanted EVs were internalized by NP cells and remained within degenerative IVDs. EVs passively diffused, accumulated at the injury site, interacted with host cells, and enhanced function, as shown by increased expression of human chondrocyte-related markers (SOX9, TGFβ1, TGFβ2, COL2) compared to hUC-MSC treatment. Histological analysis of two weeks post-transplantation showed NP cellular patterns resembling chondromas in treated discs. EVs integrated into and distributed within degenerated NP regions, with greater glycosaminoglycan (GAG) content. <b>Conclusions:</b> Overall, hUC-MSC EVs demonstrated superior regenerative capacity, supporting a safe, cell-free strategy for disc repair.