Alda-1 mediates cell senescence and counteracts bone loss in weightlessness through regulating mitophagy

Aims: Astronauts experience weightlessness-induced bone loss (WIBL) due to an imbalanced bone remodeling process involving bone mesenchymal stem cells (BMSCs), osteoblasts, and osteoclasts. Senescence is an important factor contributes to WIBL. In the current study, the effects of Alda-1 on senescence and WIBL were evaluated. Materials and methods: We used the 2D-Rotating Wall Vessel bioreactor and hindlimb suspension rats, the classic cellular and animal models simulating microgravity (SMG). Aging, osteogenic differentiation, osteoclastic differentiation, and lipogenic differentiation were evaluated in the cell and animal models. Differentially expressed proteins in the femurs of rats were further analyzed using bioinformatics analysis. In addition, mitochondrial membrane potential, reactive oxygen species (ROS) production, and mitophagy markers were identified to estimate mitochondrial activity. Key findings: It was revealed that SMG accelerated senescence including osteoblasts, BMSCs, and inhibited senescence of RAW264.7 cells. SMG suppressed osteogenesis while promoting osteoclastogenesis and adipogenesis during cell senescence and bone loss. Aldehyde dehydrogenase-2 (ALDH2) was negatively related to WIBL. It was mainly enriched in mitochondria and involved in oxidative stress pathways. Finally, it was proved that Alda-1 significantly promoted ALDH2 levels. Alda-1 exhibited a robust protective response against senescence and WIBL by eliminating ROS accumulation, restoring mitophagy, and protecting cells and bone from apoptosis. Significance: Our study indicate that Alda-1 exerts a protective effect against SMG-induced skeletal aging and bone loss through mitophagy. It provides a theoretical basis for advancing therapeutic options against WIBL in space.