## 3 Results and Discussion
### Immunohistochemical Staining of Dorsal Skin Tissue in Nude Mice
MT: Mason’s trichrome; UVB: ultraviolet B; NC: normal control; PC: positive control; LPLD, LPMD, and LPHD: administration of LPTWK10 viable cells at 2 \(\times\) 10\({}^{8}\) CFU/kg bw/day, 2 \(\times\) 10\({}^{9}\) CFU/kg bw/day and 2 \(\times\) 10\({}^{10}\) CFU/kg bw/day, respectively; SPLD, SPMD and SPHD: administration of LPTWK10 spray-dried supernatant powders at 0.30 g/kg bw/day, 0.60 g/kg bw/day, and 1.20 g/kg bw/day, respectively. Black arrow: claudin-1 protein in the epidermis layer. The above results suggest that both LPTWK10 and its spray-dried supernatant powders can mitigate UVB-induced skin photoaging in female immunodeficient mice through different pathways. Studies have shown that gut microbiota dysbiosis can increase intestinal permeability, allowing gut microorganisms or their metabolites to translocate into the circulatory system and accumulate in the skin, leading to systemic inflammation and compromising skin health. Probiotics may modulate the gut-skin axis by improving gut microbiota composition [56] In addition to reducing UVB-induced ROS levels and enhancing antioxidant enzyme activities in skin tissue [22; 57], _Lactobacillus_ can regulate the AP-1 pathway, thereby reducing the increase in MMP activities during photoaging. This regulation helps prevent collagen loss, contributing to overall skin health. Research has demonstrated that lysates from _Lactobacillus_ effectively inhibit MMP-1 expression, further supporting the role of probiotics in protecting against UVB-induced skin damage. Additionally, metabolites of probiotics have shown protective effects against UVB-induced oxidative stress and collagen degradation through modulation of signaling pathways such as p38 MAPK [29; 58]. The primary active substances in LPTWK10 spray-dried supernatant powders are likely derived from the metabolites of lactic acid bacteria. For example, short-chain fatty acids (SCFAs) have been documented to exhibit strong anti-inflammatory activity. SCFAs can regulate the gut-skin axis by improving gut microbiota composition and reducing intestinal permeability, thereby decreasing systemic inflammation that may negatively impact skin  
Figure 8: Effects of the administration of LPTWK10 or LPTWK10 spray-dried supernatant powders on dorsal immunohistochemistry stain (laminin) in UVB-induced nude mice. (**A**) NC, (**B**) UVB, (**C**) PC, (**D**) LPLD, (**E**) LPMD, (**F**) LPHD, (**G**) SPLD, (**H**) SPMD, and (**I**) SPHD. Original magnification, 100\(\times\); scale bar = 200 \(\upmu\)m. Data are presented as mean \(\pm\) SD (\(n\) = 7 or 8). MT: Mason’s trichrome; UVB: ultraviolet B; NC: normal control; PC: positive control; LPLD, LPMD, and LPHD: administration of LPTWK10 viable cells at 2 \(\times\) 10\({}^{8}\) CFU/kg bw/day, 2 \(\times\) 10\({}^{9}\) CFU/kg bw/day and 2 \(\times\) 10\({}^{10}\) CFU/kg bw/day, respectively; SPLD, SPMD and SPHD: administration of LPTWK10 spray-dried supernatant powders at 0.30 g/kg bw/day, 0.60 g/kg bw/day, and 1.20 g/kg bw/day, respectively. Black arrow: laminin protein in the basement membrane. health. Additionally, SCFAs enhance skin barrier function by preventing TEWL, which improves skin hydration and elasticity, thus reducing the effects of photoaging. Furthermore, some probiotics produce antioxidant enzymes, such as superoxide dismutase (SOD) and catalase, during their metabolic processes. These enzymes effectively neutralize the excessive ROS generated by UVB exposure, thereby mitigating skin cell damage [59]. Our experimental results indicate that the effects of LPTWK10 are superior to those of the LPTWK10 spray-dried supernatant powders, with the highest dose of LPTWK10 demonstrating the greatest ability to mitigate UVB-induced photoaging. This difference in efficacy may be attributed to the distinct bioactive components present in each form. LPTWK10 consists of live bacteria, which not only enhance skin health through their own activity but also have the potential to generate beneficial metabolites in the gut when interacting with prebiotics.