Baicalin alleviates uterine inflammaging and improves eggshell quality in aged laying hens
Aging is a major contributor to the decline in egg quality, with uterine inflammaging playing a key role in this process. Implementing anti-aging strategies to prevent uterine inflammaging and sustain optimal eggshell quality is imperative. This study aimed to characterize age-related changes in the eggshells and uteri of hens at different laying stages and the regulatory effect of baicalin (BAI). Uterine inflammaging became progressively more evident with advancing hen age, as indicated by fibrosis of the lamina propria connective tissue, decreased height and width of primary uterine folds ( P < 0.05), an increased immunohistochemically positive area for the age-related protein p53, a component of the p53/p21 pathway involved in cellular senescence, elevated expression levels of the proinflammatory cytokines tumor necrosis factor alpha (TNF- α ) and interleukin-6 (IL-6), and decreased messenger RNA (mRNA) expression of the longevity gene sirtuin 1 (SIRT1) ( P < 0.05). Additionally, uterine inflammaging was associated with decreased eggshell thickness and breaking strength and with ultrastructural deterioration ( P < 0.05). Conversely, in vivo , BAI treatment alleviated uterine inflammaging, mainly reflected in reduced secretion of the proinflammatory cytokines interleukin-1 beta (IL-1 β) , IL-6, and interleukin-8 (IL-8) and reduced expression of TNF- α , IL-1 β , p53, and p21 ( P < 0.05). SIRT1 mRNA expression was significantly increased after BAI treatment ( P < 0.05). Furthermore, BAI ameliorated eggshell ultrastructure, with fewer type B mammillary knobs and increased effective-layer thickness; it also increased eggshell thickness and breaking strength ( P < 0.05). In vitro , compared to uterine epithelial cells cultured with β -galactosidase, BAI pretreatment increased cell viability, decreased the positive staining rate of senescent cells, downregulated the relative expression of IL-6, IL-1 β , TNF- α , p53, and p21, and increased SIRT1 mRNA levels ( P < 0.05). Overall, uterine inflammaging was closely associated with age-related deterioration in eggshell quality, and BAI administration was associated with improved eggshell quality and reduced uterine inflammaging.