What they tested
Li, Zhang, Zhang, Zhao, Shang, and Pan at Harbin Medical University asked whether exosomes can be used to deliver miR-21 to human dental pulp stem cells (hDPSCs) and whether that delivery nudges the stem cells toward an endothelial phenotype (Li et al. 2026, OBJECTIVES). The work sits in the pulp and dentin repair program, where revascularization of regenerated pulp tissue is one of the recurring bottlenecks. Rather than genetically modify the pulp stem cells directly, the authors used human umbilical vein endothelial cells (HUVECs) as a vector: they transfected HUVECs to raise or lower miR-21 levels, collected the resulting exosomes, and exposed hDPSCs to the conditioned media.
Exosome engineering and readouts
The study prepared several conditioned-media groups based on how much miR-21 the HUVEC-derived exosomes carried (Li et al. 2026, MATERIALS AND METHODS). The authors then measured hDPSC proliferation, migration, adhesion, and angiogenic capability. A dual-luciferase reporter assay was used to test whether miR-21 directly targets JAG1, and the downstream JAG1/NOTCH1/VEGF signaling pathway was examined.
What changed in the stem cells
Both unmodified HUVEC exosomes and exosomes from miR-21-overexpressing HUVECs enhanced hDPSC adhesion, proliferation, migration, and angiogenic ability compared with the appropriate controls (Li et al. 2026, RESULTS). The overexpression group had a more pronounced effect than the unmodified HUVEC-exosome group, while the miR-21 inhibition group did not show a statistically significant difference from its control. The luciferase assay supported a direct targeting relationship between miR-21 and JAG1, and changes in miR-21 level were associated with changes in JAG1/NOTCH1/VEGF pathway expression (Li et al. 2026, RESULTS).
What it means for pulp-dentin repair
The take-home for the pulp and dentin repair program is that endothelial-cell exosomes can be loaded with a pro-angiogenic microRNA and used as a cell-free intervention to steer DPSCs toward a vascular phenotype. That adds to the growing list of extracellular-vesicle approaches in regenerative endodontics. It also points to a specific mechanistic route, miR-21 -> JAG1 -> NOTCH1/VEGF, that could be tested in more complex pulp-dentin injury models.
What it does not show
The study is entirely in vitro. It does not report survival, integration, or vessel formation inside a tooth, an animal model, or a patient. The authors used HUVECs as the exosome factory, not dental endothelial cells, so it remains to be shown whether the same cargo loading and release profile would come from a dental source. The abstract does not report donor numbers, exosome dose ranges, or the exact fold changes in the functional assays, so quantitative boundaries should not be inferred. Finally, enhancing angiogenic behavior in a dish is not the same as building a perfused, innervated pulp-like tissue in vivo.
Provenance: grounded in the PubMed record for Li P, Zhang S, Zhang W, Zhao S, Shang C, Pan S. Exosomes Loaded With MiR-21 Promote Differentiation of Dental Pulp Stem Cells Into Endothelial Cells. Int Dent J. 2026;76(5):109790. doi:10.1016/j.identj.2026.109790 (PMID 42664586), verified against the structured abstract and metadata. The article is gold open access at ScienceDirect, but the publisher site blocked automated retrieval during this run. Method and sourcing standard at /method/.