Histologic and immunohistochemical changes in amputated and scarring lizard limb of Scincella tsinlingensis

Lizard tail regeneration and limb amputation provide contrasting amniote models for regenerative failure. A limb wound healing model was established in 48 Scincella tsinlingensis through standardized surgical amputation protocols, followed by comprehensive anatomical observation, histological evaluation, and immunohistochemical characterization of regenerative processes. Four fibrotic stages-hemostasis, inflammation, proliferation, and remodeling-were delineated through histopathological analysis and further categorized into five histologically distinct stages. Stages I-II (0-9 days post-amputation, dpa) showed PCNA dominance over Caspase-3, reflecting proliferative priority. Collagen degradation correlated with expression of MMP-9 by fibroblasts and epithelial cells, whereas collagen deposition correlated with α-SMA⁺ myofibroblasts in stages IV-V. VEGF/TSP-1 immunostaining peaked during stages II-III (3-18 dpa) in accordance with angiogenesis and transitioned to restricted expression suggestive of vascular pruning by stage V. Epidermal maturation was associated with Cytokeratin 6 expression during re-epithelialization in stages II-IV (3-40 dpa). Persistent macrophage activity and inflammatory signaling correlated with sustained fibrosis. Key regulators (PCNA, Caspase-3, Cytokeratin 6, MMP-9, α-SMA, VEGF, TSP-1) displayed spatiotemporally restricted roles in scar formation. Despite robust proliferation and remodeling, limb regeneration failed, with myofibroblast-driven ECM accumulation and chronic inflammation overriding regenerative programs, yielding nonfunctional scar tissue devoid of muscle regeneration. These results represent the lizard exhibits no limb regeneration post-amputation, advancing investigation into mechanisms of regenerative failure.