Regenerative Potential of Extracellular Vesicles on Intervertebral Disc Degeneration: What is the EV-idence?

Extracellular vesicles (EVs) represent a promising cell-free regenerative therapy. Deciphering their mode and mechanism of action comes with technical and biological challenges. This scoping review presents a complementary perspective to reviews that synthesized EV therapeutic strategies in intervertebral disc (IVD) degeneration. It intends to create awareness of the minimal experimental requirements defined by the International Society for Extracellular Vesicles (MISEV). These have been established to facilitate robust and reproducible protocols in the rapidly expanding EV field, aiming to allow comparative studies, improve reproducibility, and interpretability.

The MISEV were tailored with IVD-related considerations. Within the timeframe 2016-2025, 129 articles studying EVs in the context of IVD were identified on PubMed. From each article, experimental information on EV isolation and characterization studies, and on functional studies was reviewed for compliance to the IVD-tailored MISEV.

The information reporting rates were 57% for EV characterization studies and 67% for EV functional studies. Information on EV nomenclature, storage, quantification, and methodological controls for functional studies specifically needs better reporting. Most studies explore EV functionality through conditioned media processed to be enriched for EVs. These EV-enriched media represent the secretome, the entire collection of secreted molecules, including EVs and co-isolates. In functional studies, intending to study biological effects driven by the EV-cargo, inclusion of key methodological MISEV controls is essential.

Here, we sketch and discuss the consolidated "EV-idence" of EV-mediated IVD tissue regeneration with studies that have specifically included the minimal MISEV requirements, i.e., (1) EV-depletion of serum when supplemented in culture medium and (2) inclusion of EV-depleted conditioned medium as a negative control. Although in several studies, EVs showed homeostatic effects and halted IVD degeneration, solid conclusions are constrained by the limited number of studies complying with the MISEV guidelines.