Abstract: 【Abstract】 Objective To investigate the role of the calcium-sensing receptor （CaSR） in ultraviolet B （UVB）-induced epidermal damage in mice, and to explore its potential mechanisms in regulating ferroptosis and the expression of keratinization-related proteins. Methods Twenty-four BALB/c mice were randomly divided into 3 groups: a normal control group, a UVB group, and a UVB + CaSR inhibitor （NPS?2143） group, with 8 mice in each group. Mice in the UVB group and UVB + NPS?2143 group were exposed to daily UVB irradiation at 600 mJ/cm2 for 10 minutes on the shaved back, and the treatment lasted 7 days. Thirty minutes after each session of UVB irradiation, mice in the UVB + NPS?2143 group received a local intradermal injection of 100 μl of 1 μmol/L NPS?2143 on the back, while those in the UVB group were injected with an equal volume of dimethyl sulfoxide, and those in the normal control group were injected with 100 μl of phosphate-buffered saline. Macroscopic evaluation of photodamage to the mouse back skin was performed daily before UVB irradiation. After the experiment, dorsal skin samples were collected for hematoxylin-eosin （HE） staining to assess histopathological changes, an immunohistochemical assay was performed to observe the expression of glutathione peroxidase 4 （GPX4）, acyl-CoA synthetase long-chain family member 4 （ACSL4）, CaSR, and keratinization-related proteins （loricrin and keratin 10 ［K10］）, Western blot analysis was conducted to determine the protein expression of GPX4, ACSL4, and CaSR, real-time quantitative PCR （qPCR） was employed to determine ACSL4 mRNA expression, malondialdehyde （MDA） levels in skin tissues were measured using the thiobarbituric acid method, and iron content was determined by colorimetry. One-way analysis of variance was used for comparisons among groups, and the least significant difference-t test for multiple comparisons. Results Macroscopic observation and HE staining showed significantly increased epidermal thickness and hyperkeratosis in the UVB group; compared with the UVB group, the UVB + NPS?2143 group showed markedly decreased epidermal thickness, with significantly alleviated pathological changes. Before irradiation on day 7, the photodamage score of the mouse back skin was significantly higher in the UVB group （2.830 ± 1.169 points） than in the normal control group （0.166 ± 0.044 points, P < 0.001） and the UVB + NPS?2143 group （1.670 ± 0.890 points, P < 0.001）. As Western blot analysis showed, the UVB group exhibited significantly decreased GPX4 protein expression, but significantly increased CaSR protein expression compared with the normal control group （both P < 0.001）; compared with the UVB group, the UVB + NPS?2143 group showed a significant increase in GPX4 protein expression, but a significant decrease in CaSR protein expression （both P = 0.002）; there was no significant difference in ACSL4 protein expression among the 3 groups （F = 0.40, P = 0.686）. qPCR revealed that ACSL4 mRNA expression was significantly higher in the UVB group than in the normal control group （P < 0.001） and the UVB + NPS?2143 group （P < 0.001）. Both MDA and iron content in the mouse skin tissues were significantly higher in the UVB group than in the normal control group （both P < 0.001） and the UVB + NPS?2143 group （P < 0.001, = 0.030, respectively）. The immunohistochemical assay demonstrated downregulated expression of GPX4, loricrin, and K10, but upregulated expression of CaSR and ACSL4 in the mouse back skin after UVB exposure, while NPS?2143 intervention lessened the expression changes of these proteins. Conclusion The CaSR inhibitor NPS?2143 may improve UVB-induced epidermal keratinization abnormality in mice, possibly through the regulation of ferroptosis-related protein expression.

Key words: Dermatitis, phototoxic, Receptors, calcium-sensing, Ultraviolet B, Animal experimentation, Ferroptosis, Glutathione peroxidase 4, Acyl-CoA synthetase long-chain family member 4, Loricrin, Keratin-10, Malondialdehyde