NLRP3 Inflammasome Activates Matrix Metalloproteinase-9: Potential Role in Smooth Muscle Cell Dysfunction in Thoracic Aortic Disease
Introduction
Excessive matrix metalloproteinase (MMP) activity during inflammation disrupts aortic wall homeostasis, causing progression of thoracic aortic aneurysms and dissections (TAAD). The NLRP3-ASC-caspase-1 inflammasome complex is critically involved in the activation and secretion of inflammatory factors. However, the role of this complex in regulating MMP activity remains unknown. We hypothesize that the NLRP3 inflammasome complex activates MMP-9, leading to cleavage of contractile proteins, resulting in thoracic aortic smooth muscle cell (SMC) dysfunction.
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Methods
Cultured thoracic SMCs were treated with palmitic acid (PA) and NLRP3 siRNA, ASC siRNA, or caspase-1 siRNA. MMP-9 cleavage and activity was assessed by immunoblotting and zymography, respectively.Protein interactions were examined by co-immunoprecipitation of protein lysate from SMCs. Direct cleavage of contractile proteins was determined by incubation of recombinant caspase-1 and recombinant MMP-9 with co-immunoprecipitated proteins.
Results
In SMCs treated with PA, there were dose-dependent increases in NLRP3, ASC, and caspase-1 levels. Palmitic acid also increased MMP-9 cleavage to a 67 KDa active fragment. NLRP3 siRNA, ASC siRNA, and caspase-1 siRNA decreased PA-induced MMP-9 cleavage. Co-immunoprecipitation of protein lysate from PA-treated SMCs indicates MMP-9 binds to NLRP3, ASC, and caspase-1. In vitro activity assay showed that recombinant caspase-1 directly cleaved recombinant MMP-9. Addition of recombinant tissue
Conclusions
In thoracic aortic SMCs, MMP-9 can be cleaved and activated by the NLRP3-ASC-caspase-1 inflammasome complex. Caspase-1 and MMP-9 are involved in the cleavage of sarcomere proteins. This study provides a novel mechanism for intracellular MMP-9 activation and SMC dysfunction. In addition to MMP-9’s well-established role in mediating extracellular matrix destruction during the development of TAAD, MMP-9-mediated alterations in SMC function may also contribute to the progression of this disease.