Skin photoaging, driven primarily by ultraviolet radiation, remains a critical dermatological concern. Carotenoids, a class of natural pigments with potent antioxidant properties, have emerged as promising agents for preventing and mitigating photoaging. This review comprehensively integrates current understanding regarding the triggers of skin photoaging, oxidative stress and their associated signal pathways, the photoprotective roles and mechanisms of carotenoids, as well as their bioavailability. Common C₄₀ carotenoids, such as β-carotene, lycopene, astaxanthin, lutein, and zeaxanthin demonstrate remarkable antioxidant activity, primarily attributed to their conjugated double bond structures. Many studies have demonstrated that both oral and topical administration of these C₄₀ carotenoids can effectively alleviate skin photoaging. Specifically, they play a crucial role in promoting the formation of a new skin barrier and enhancing the production of collagen and elastin, key structural proteins essential for maintaining skin integrity and elasticity. Mechanistically, these carotenoids combat photoaging by effectively scavenging reactive oxygen species and modulating oxidative stress responsive signal pathways, including MAPK, Nrf2, and NF-κB. Notably, we also anticipate the anti-photoaging potential of novel carotenoids, with a particular emphasis on bacterioruberin, a C₅₀ carotenoid derived from halophilic archaea. Bacterioruberin exhibits a superior radical scavenging capacity, outperforming the conventional C₄₀ carotenoids. Furthermore, when considering the application of carotenoids, aspects such as safe dosage, bioavailability, and possible long term usage issues, including allergies and pigmentation disorders, must be taken into account. This review underscores the anti-photoaging mechanism of carotenoids, providing strategies and theoretical basis for the prevention and treatment of photoaging.

The juvenile hormone (JH) signaling pathway is crucial for reproductive development, molting, and metamorphosis in model insects. However, the molecular mechanisms of key components in the JH signaling pathway remain poorly understood in crustaceans. This study elucidates the function of RXR gene and JH analogs (JHAs) in the reproductive development of the brine shrimp Artemia parthenogenetica (A. parthenogenetica). Using an ELISA kit, we detected JH-like immunoreactivity in A. parthenogenetica that peaks during stage IV of ovarian development, coinciding with maximal expression of CYP15. The RXR homolog in A. parthenogenetica (Ar-RXR) features conserved DNA- and ligand-binding domains and shares close phylogenetic affinity with Daphnia magna (D. magna). Its expression profile aligns with JHA fluctuations, suggesting coordinated regulation of oogenesis. RNAi-mediated knockdown of Ar-RXR significantly suppressed RXR expression (P < 0.01) and downregulated JH pathway genes (Ar-Met, Ar-Kr-h1, Ar-Vg), accompanied by abnormal cytological characteristics: concentric membranes and lipid droplet accumulation in fat body cells, reduced yolk granules in embryos, and decreased offspring formation. Conversely, JH Ⅲ injection upregulated ovarian Ar-RXR and other JH pathway genes (except Ar-Kr-h1), yielding plump, well-arranged eggs. Co-injection of JH Ⅲ and dsRXR partially rescued JH pathway gene expression and reduced the number of egg abnormalities. Our findings demonstrate that a JH-like signal and Ar-RXR functionally interact to regulate reproductive development in A. parthenogenetica, providing mechanistic insights into JH signaling and advancing understanding of arthropod reproductive evolution.