Spiny mice (Acomys cahirinus) demonstrate impaired epimorphic regeneration after digit tip amputation

BACKGROUND: The regeneration of the terminal phalanx of the finger represents a rare example of complete regeneration without the development of fibrosis in adult mammals. Spiny mice of the genus Acomys are capable of regenerating many tissues, including epidermis, muscle, etc., without scar formation. The ability of A. cahirinus to fully regenerate the terminal phalanx of the finger is not known. AIM: Evaluation of the dynamics of restoration of the terminal phalanx of the finger after amputation in spiny mice. METHODS: The dynamics of regeneration of the terminal phalanges of the fingers in rodents M. musculus and A. cahirinus was assessed for 28 days after amputation. To model epimorphic regeneration by blastema formation, amputation of the terminal phalanx was performed distal to the nail bed. To model damage ending in the formation of a fibrous scar, amputation was performed proximal to the nail bed. Recovery was assessed using visual analysis, microcomputed tomography, and histological examination. RESULTS: In contrast to M.musculus, which demonstrates complete restoration of the entire tissue complex of the distal phalanx of the finger, amputation does not result in complete restoration in A.cahirinus. In these animals, amputation of the terminal phalanx of the finger distal to the nail bed resulted in shortening of the fingers and their deformation according to the "drumstick" type. Histological analysis showed hypertrophy of the bones of the damaged phalanx in spiny mice. Using microcomputer tomography, it was established that the bone of the phalanx damaged as a result of amputation undergoes lysis up to complete degradation, and hypertrophy occurs in the bone of the finger of the next phalanx, located proximal to the plane of amputation. CONCLUSION: Complete restoration of the tissues of the terminal phalanx, including bone, does not occur in A. сahirinus after amputation. This may be due to excessive lysis of the damaged bone stump, as well as insufficient formation of the blastema at the site of injury.