Nail proximal fold stem cells participate in nail growth, orchestrating enhanced digit regeneration via bone morphogenetic protein signaling activation.

Rodent and primate digit tips exhibit a remarkable regenerative capacity following amputation, driven by highly proliferative nail stem cells with active canonical Wnt signaling. Recently, a distinct, slow-cycling population of bi-functional nail proximal fold stem cells (NPFSCs) has been identified, contributing to both peri-nail epidermis and nail plate (NP). Here, we demonstrate that NPFSCs actively participate in nail growth, orchestrating digit regeneration, with bone morphogenetic protein (BMP) signaling serving as a key regulator. Inhibition of BMP resulted in an epidermalized NP-like structure with limited regeneration due to impaired Wnt pathway activation in the nail matrix cells. Conversely, BMP activation enhanced NPFSCs' involvement in the nail matrix and significantly promoted digit regeneration. We further revealed that enhanced BMP activity not only accelerated nail and bone regrowth but also extended the regenerative boundary proximally, enabling full regeneration after up to ∼60% removal of the distal phalanx (P3). Moreover, in BMP gain-of-function models, extreme proximal amputation, removing the majority of the P3, still permitted partial NP regeneration despite the absence of bone reconstruction. Finally, we isolated and cultured lineage-traced NPFSCs and transplanted them into immunocompromised mice, where they integrated into the nail proximal fold and contributed to nail matrix progenitors during regeneration. Transplanted NPFSCs retained their regenerative capacity in vivo, highlighting their therapeutic potential. Collectively, our findings identify a pivotal role of BMP signaling in mediating NPFSC-driven digit regeneration, reveal BMP-Wnt cross-talk as essential to this process, and provide a framework for enhancing regenerative outcomes in previously non-regenerative contexts following traumatic amputation.