ELP2‐NLRP3‐GSDMD/GSDME‐mediated pyroptosis is induced by TNF‐α in MC3T3‐E1 cells during osteogenic differentiation

Abstract

Tumour necrosis factor‐α (TNF‐α) is a cytokine involved in systemic inflammation. TNF‐α slows down osteogenic differentiation, which may contribute to poor bone development in the inflammatory microenvironment. TNF‐α inhibits osteogenic differentiation by activating the JAK‐STAT3 pathway, of which Signal transducer and activator of transcription 3 (STAT3)‐interacting protein 1 (StIP1, also known as elongator complex protein 2, ELP2) is a key protein in the JAK‐STAT3 pathway. We investigated whether and how ELP2 activation mediates the TNF‐α‐induced pyroptosis during osteoblastic differentiation. Using in vitro cell cultures of preosteoblastic MC3T3‐E1 cells, we found that TNF‐α exposure causes cell pyroptosis in an inflammatory microenvironment during osteoblastic differentiation. Bioinformatics, protein docking model and co‐immunoprecipitation analysis revealed an association between ELP2, STAT3 and NLRP3. Forced ELP2 expression promoted MC3T3‐E1 cells pyroptosis, with an increase in the expression of STAT3, NLRP3 inflammasome, GSDMD/GSDME, osteoblast marker genes, and the activity of alkaline phosphatase. In contrast, ELP2 silencing ameliorated MC3T3‐E1 cells pyroptosis, and osteogenic differentiation, especially after TNF‐α stimulation. The TNF‐α‐induced cells pyroptosis during osteoblastic differentiation was therefore mediated by ELP2. These results suggest that ELP2 is upregulated at the pyroptosis of MC3T3‐E1 cells and inhibits osteogenic differentiation in response to TNF‐α through NLRP3‐GSDMD/GSDME activation.

Pyroptosis mediates osteoporosis via the inflammation immune microenvironment

“…Upon stimulation with TNF-a, osteoblast MC3T3-E1 underwent pyroptosis, which is regulated by ELP2, a key protein in the JAK-STAT3 pathway. Additionally, the ELP2 protein inhibited osteogenic differentiation through activation of the NLRP3-GSDMD/GSDME pathway (62). Estrogen deficiency curtailed osteogenic differentiation of BMSCs by promoting the Capsase-1/GSDMD/IL-18 and IL-1b pyroptosis pathways, culminating in osteoporosis, while NLRP3 knockdown fostered bone formation (26).…”