TRPA1 aggravates osteoclastogenesis and osteoporosis through activating endoplasmic reticulum stress mediated by SRXN1.

Osteoporosis (OP) is a disorder of bone remodeling caused by an imbalance between bone resorption by osteoclasts and bone formation by osteoblasts. Therefore, inhibiting excessive osteoclast activity is one of the promising strategies for treating OP. A major transient receptor potential cation channel, known as transient receptor potential ankyrin 1 (TRPA1), was found to alleviate joint pain and cartilage degeneration in osteoarthritis. However, little research has focused on TRPA1 function in OP. As a result, this study aimed to explore the TRPA1 characteristics and its potential therapeutic function during osteoclastogenesis. The TRPA1 expression gradually increased in the osteoclast differentiation process; however, its suppression with small interfering RNA and an inhibitor (HC030031) significantly controlled the osteoclast count and the expression of osteoclast characteristic genes. Its suppression also inhibited endoplasmic reticulum (ER) stress-related pancreatic ER kinase (PERK) pathways. An ER stress inhibitor (thapsigargin) reversed the down-regulated levels of ER stress and osteoclast differentiation by suppressing TRPA1. Transcriptome sequencing results demonstrated that TRPA1 negatively regulated reactive oxygen species (ROS) and significantly increased the expression of an antioxidant gene, SRXN1. The osteoclast differentiation and the levels of ER stress were enhanced with SRXN1 inhibition. Finally, TRPA1 knockdown targeting macrophages by adeno-associated virus-9 could relieve osteoclast differentiation and osteopenia in ovariectomized mice. In summary, silencing TRPA1 restrained osteoclast differentiation through ROS-mediated down-regulation of ER stress via inhibiting PERK pathways. The study also indicated that TRPA1 might become a prospective treatment target for OP.