Figure 4. Cellular differentiation of SNDC and BMSC in damaged nerve niche at 4 weeks after injection.

(A–C) Typical differentiation of transplanted damaged sciatic nerve-derived freshly isolated cells (SNDC-D). SNDC-D showed differentiation into perineurial/endoneurial cells that encircled the axon and myelin (A), myelin-forming Schwann cells showed double-positive staining for MBP and GFP (B), and endothelial cells (CD31⁺/GFP⁺) were incorporated into blood vessels (C). These differentiation potentials correspond to Sk-MSC-7d (see Fig. 3), whereas the relative engraftment capacity was significantly lower in SMDC-D (see Fig. 2M). (D–H) Typical behavior of transplanted BMSC-7d. Definitive perineurium/endoneurium formation closely encircling axons and myelin, which were observed in both Sk-MSCs and SNDCs, was not seen in the BMSC-7d group; instead, axons with very small diameter and weak reactions for MBP were prominent (D, E). In addition, hollow cavity-like structures around engrafted GFP⁺ tissues (cells) were frequently observed (arrows in D, E). This trend was consistently observed throughout BMSC-7d transplantation. Similarly, GFP⁺ cells (tissues) were not incorporated into CD31⁺ blood vessels (arrows in F). Interestingly, some osteogenesis was observed with BMSC transplantation (G, H), but only in one case (1/13). A large dark area that superficially resembled a large hollow cavity under fluorescence immunohistochemistry (arrows in G) was positive for von Kossa staining (H), representing calcified bone formation in the damaged peripheral nerve niche. Scale bars represent 50 µm (A–F), 200 µm (G).