NLRP3‐Dependent Crosstalk between Pyroptotic Macrophage and Senescent Cell Orchestrates Trauma‐Induced Heterotopic Ossification During Aberrant Wound Healing

Abstract

Heterotopic ossification (HO) represents an unwanted ossific wound healing response to the soft tissue injury which caused catastrophic limb dysfunction. Recent studies established the involvement of inflammation and cellular senescence in the tissue healing process, though their role in HO still remained to be clarified. Here, a novel crosstalk where the pyroptotic macrophages aroused tendon‐derived stem cells (TDSCs) senescence is revealed to encourage osteogenic healing during trauma‐induced HO formation. Macrophage pyroptosis blockade reduces the senescent cell burden and HO formation in NLRP3 knockout mice. Pyroptosis‐driven IL‐1β and extracellular vesicles (EVs) secretion from macrophages are determined to motivate TDSCs senescence and resultant osteogenesis. Mechanistically, pyroptosis in macrophages enhances the exosomal release of high mobility group protein 1 (HMGB1), which directly bounds TLR9 in TDSCs to trigger morbid signaling. NF‐κB signaling is confirmed to be the converging downstream pathway of TDSCs in response to HMGB1‐containing EVs and IL‐1β. This study adds insights into aberrant regeneration‐based theory for HO formation and boosts therapeutic strategy development.

Role of the NF-kB signalling pathway in heterotopic ossification: biological and therapeutic significance

“…Generally, NF-κB mediates the expression of many proinflammatory genes in the innate immune system [ 9 , 22 ]. In general, during the inflammatory stage of HO, sirtuin1 (SIRT1), AMPK and the NLRP3 inflammasome are involved in the NF-κB signalling pathway in macrophages [ 8 , 23 – 25 ]. Specifically, the expression of SIRT1 and AMPK, which can inhibit NF-κB signalling, was decreased in macrophages [ 23 – 25 ].…”

“…In general, during the inflammatory stage of HO, sirtuin1 (SIRT1), AMPK and the NLRP3 inflammasome are involved in the NF-κB signalling pathway in macrophages [ 8 , 23 – 25 ]. Specifically, the expression of SIRT1 and AMPK, which can inhibit NF-κB signalling, was decreased in macrophages [ 23 – 25 ]. Therefore, this decrease in expression could disinhibit the secretion of proinflammatory cytokines [ 23 – 25 ].…”

“…Specifically, the expression of SIRT1 and AMPK, which can inhibit NF-κB signalling, was decreased in macrophages [ 23 – 25 ]. Therefore, this decrease in expression could disinhibit the secretion of proinflammatory cytokines [ 23 – 25 ]. Additionally, macrophage-derived inflammatory cytokines can act in a Toll-like receptor 4 (TLR4)-dependent manner to trigger the activation of NF-κB signalling, thereby promoting NLRP3 inflammasome induction and further proinflammatory cytokine activation and secretion [ 25 ] (Fig.…”

“…Among the various inflammasomes, the NLRP3 inflammasome is the most widely studied and is composed of ASC, NLRP3, NIMA-related kinase 7 (NEK7) and pro-caspase-1 [ 9 ]. Recently, a study examined the effect of the NLRP3 inflammasome on macrophage-mediated inflammation in the context of HO [ 25 ]. In this study, Li et al reported that macrophage pyroptosis occurred during HO through an inflammation-driven process, as indicated by significantly increased levels of pyroptosis‐associated molecules, including NOD‐like receptor protein 3 (NLRP3), caspase‐1, gasdermin D (GSDMD) and F4/80 (macrophage marker), 3 and 7 days after tenotomy in mice with HO [ 25 ].…”

“…Recently, a study examined the effect of the NLRP3 inflammasome on macrophage-mediated inflammation in the context of HO [ 25 ]. In this study, Li et al reported that macrophage pyroptosis occurred during HO through an inflammation-driven process, as indicated by significantly increased levels of pyroptosis‐associated molecules, including NOD‐like receptor protein 3 (NLRP3), caspase‐1, gasdermin D (GSDMD) and F4/80 (macrophage marker), 3 and 7 days after tenotomy in mice with HO [ 25 ]. Since NF-κB is the central regulator of NLRP3 inflammasome activation, this inflammatory mechanism in macrophages might involve activating the transcription of pro-IL-1β and the NLRP3 gene, which contains NF-κB binding sites within their promoter regions [ 9 , 39 ].…”