Microinjury-Induced Tumor Necrosis Factor-α Surge Stimulates Hair Regeneration in Mice

Introduction: Tumor necrosis factor (TNF)-alpha released after follicular injury such as that caused by plucking plays a role in the activation of hair regeneration. Microneedle (MN) treatment is applied to the scalp to increase permeability and facilitate the delivery of any number of compounds. Because the MN treatment causes injury to the epidermis, albeit minor, we reasoned that this treatment would lead to a temporary TNF-alpha surge and thereby promote hair regeneration. Methods: To investigate the effects of MN-treatment-induced microinjury and TNF-alpha on hair growth, we used C57BL/6N mice which were divided into six experimental groups: three groups of 1) negative control (NC), 2) plucking positive control (PK), and 3) MN therapy system (MTS) mice; and three groups identical to above were treated with a TNF-alpha blocker for 3 weeks: 4) NCB, 5) PKB, and 6) MTSB group. Results: After injury, TNF-alpha surge occurred on day 3 in the PK group and on day 6 in the MTS group. Wnt proteins and VEGF expression were markedly increased in the PK group on day 3 and on day 6 in the MTS group compared to the NC group. Following wound healing, only MTS and PK groups displayed thickened epidermis and longer HF length. Within the 2 weeks following treatment, the rate of hair growth was much slower in the injured mice treated with the TNF-alpha blocker. Conclusion: Our findings indicate that microinjury stimulates the wound-healing mechanism via TNF-alpha/Wnt/VEGF surge to induce hair growth, and that blocking TNF-alpha inhibits this growth process. (c) 2023 The Author(s). Published by S. Karger AG, Basel