IL-33 prevents age-related bone loss and memory impairment by suppression of Th17 response: evidence in a <sc>d</sc>-galactose-induced aging mouse model

Cytokines are the primary mediators of age-related disorders. The IL-17/IL-10 axis plays a crucial role in bone destruction and neuro-inflammation. Additionally, a new Th2 cytokine-IL-33-has gained attention for its potential implications in aging-associated conditions. However, the involvement of IL-33 in aging-mediated bone loss and memory impairment remains unclear and needs further investigation. This study reveals the impact of IL-33 on various aspects of the immune system, bone health, and neural functions. To induce senescence, we used d-galactose for its convenience and fewer side effects. The experimental design involved treating 20-week-old C57BL/6J mice with d-galactose subcutaneously for 10 weeks to induce aging-like effects. Thereafter, IL-33 recombinant protein was administered intraperitoneally for 15 days to evaluate its impact on various immune, skeletal, and neural parameters. The results demonstrated that d-galactose-induced aging led to bone loss and compromised osteogenic parameters, accompanied by increased oxidative stress and neurodegeneration in specific brain regions. Behavioral activities were also affected. However, supplementation with IL-33 mitigated these effects, elevating osteogenic parameters and reducing senescence markers in osteoblast cells in an aging mouse model and exerted neuroprotective potential. Notably d-galactose-induced aging was characterized by high bone turnover, reflected by altered serum levels of CTX, PTH, beta-galactosidase, and P1NP. IL-33 treatment attenuated these effects, suggesting its role in regulating bone metabolism. Furthermore, d-galactose-induced aging was associated with increased differentiation of Th17 cells and upregulation of associated markers, such as STAT-3 and ROR-gamma t, while downregulating Foxp3, which antagonizes Th17 cell differentiation. IL-33 treatment countered these effects by suppressing Th17 cell differentiation and promoting IL-10-producing T-regulatory cells. Overall, these findings provide insights into the potential therapeutic implications of IL-33 in addressing aging-induced bone loss and memory impairment.