Keratinocyte-Specific Angiotensin II Type 1 Receptor-Associated Protein Deficiency Exacerbates Ultraviolet-Induced Skin Aging

Skin aging is caused by various factors. It is well known that ultraviolet (UV) radiation is the major extrinsic cause of skin aging, which is suggested to involve inflammation and oxidative stress. Previous reports have shown that keratinocytes, which contribute to the formation of epidermis and the skin barrier, can produce and secrete various cytokines, chemokines, and growth factors, affecting the skin microenvironment. These keratinocyte-derived cytokines may be related to cellular senescence of the skin. On the other hand, skin expresses most of the renin-angiotensin system (RAS) components, including angiotensinogen, renin, angiotensin-converting enzyme (ACE), angiotensin II type 1 receptor (AT1R), and AT1R-associated protein (ATRAP). ATRAP is an endogenous suppressor of tissue RAS activity, which can directly bind to AT1R and promote its internalization, resulting in the inhibition of AT1R signaling pathways. We have reported that systemic ATRAP deficiency promotes aging-related renal fibrosis and shortens longevity. However, there have been no reports investigating the relationship between skin aging and skin tissue RAS. In this study, we investigated whether UV exposure exacerbates skin aging in keratinocyte-specific ATRAP knockout mice.

We generated keratinocyte-specific ATRAP knockout (K14-ATRAP-KO)mice on a C57BL/6 background using the Cre-loxP system. We used 10-12 week-old K14-ATRAP-KO（KO） mice and Littemate ATRAP-loxP （Ctrl）mice for subsequent experiments. All experimental mice were housed in a controlled environment with a 12:12 light/dark cycle, ambient temperature (25℃) and humidity (55%), and free access to food and water. They were fed a standard diet with 0.5% NaCl, 3.6 kcal/g, and 13.3% energy as fat.KO mice and littermates (ATRAP-loxP; Ctrl) were divided into UVB-irradiated and non-irradiated groups. The dorsal skin of the mice was exposed to UV radiation for three consecutive days, with the total accumulated dose calculated to be 100mJ/cm2. Transepidermal water loss (TEWL), which reflects function of the skin barrier, was measured before the first irradiation (Day 1), 24 hours after the final irradiation (Day 4), and 4 days after the final irradiation (Day 7). Mice were sacrificed and skin tissues were harvested 5 days after the final irradiation. The collected tissues were subjected to H-E staining to measure skin thickness. Furthermore, beta-galactosidase immunohistochemistry, a senescence marker, was performed to evaluate the staining intensity in each group.

In the non-irradiated groups, no significant difference in TEWL was observed between KO and Ctrl mice. UVB irradiation significantly increased TEWL at both Day 4 and Day 7. In the UVB-irradiated groups, KO mice showed a significantly greater increase in TEWL compared to Ctrl mice. Histological analysis by H-E staining revealed no difference in epidermal and dermal thickness between KO and Ctrl mice in the non-irradiated groups, and both increased following UVB irradiation. In the UVB-irradiated groups, KO mice exhibited a significantly greater increase in epidermal thickness compared to Ctrl mice. Similarly, beta-galactosidase-positive cells in the epidermis were more intensely stained in the UVB-irradiated groups, and this finding was more pronounced in KO mice.

Keratinocyte-specific ATRAP deficiency may exacerbate UV-induced skin aging. Our findings suggest that skin tissue RAS may contribute to the progression of UV-induced skin aging.