Figure 7. Defective epidermal thickening of VDR^−/− skin in response to chronic UV exposure.

Wildtype (WT, n=4) and VDR^−/− (KO, n=4) mice were exposed to six doses of UV (120mJ/cm²) during a 2-week period. Skin samples were collected and fixed 24 h after the final dose. a) Skin samples were stained for PCNA expression and counterstained with hematoxylin. PCNA positive keratinocytes in WT and KO skin were counted as a percentage of total number of keratinocytes. Wildtype epidermis was significantly more proliferative than VDR^−/− epidermis following 6 exposures of UV, * p < 0.025. Error bars=SEM. Differences were analyzed by the two-tailed Student’s t test. b) Representative sections of wildtype and VDR^−/− skin, stained for PCNA expression. Brackets indicate epidermal thickness. Scale bar = 40 μm.

c) Epidermal thickness was calculated from 20–25 measurements from multiple fields of paraffin-embedded skin sections, viewed at 100× magnification. Error bars=SD. Differences in thickness were analyzed by the two-tailed Student’s t test. Wildtype epidermis was significantly thicker than VDR^−/− epidermis following 6 exposures of UV, * p < 0.015.