Role of the COP9 signalosome in atherogenic inflammation

Milic, Jelena (2022): Role of the COP9 signalosome in atherogenic inflammation. Dissertation, LMU München: Medizinische Fakultät

Abstract

Cytokines, chemokines, and inflammatory signalling pathways orchestrate the inflammatory process promoting the development of atherosclerosis. Among these, the NF-κB is pivotal in driving vascular inflammation and atherogenesis. NF-κB triggering enhances endothelial adhesion molecule expression and cytokine/chemokine production and amplifies myeloid cell-based inflammatory responses. The COP9 signalosome (CSN) is a multi-functional protein complex that regulates the degradation of critical cell cycle and inflammatory proteins by controlling cullin-RING E3 ligase (CRL) activity via its intrinsic deNEDDylase activity. The endogenous inhibitor of the NF-κB pathway, IκB-α, is a key CRL substrate. Its stability is controlled by the CSN/CRL axis, suggesting that the CSN modulates atherogenic processes. In fact, we have previously shown that CSN subunits are strongly overexpressed in advanced human atherosclerotic lesions. Moreover, we demonstrated that myeloid-specific gene deletion of CSN subunit 5 (CSN5), i.e. the subunit that harbours the deNEDDylase activity of the complex, leads to exacerbated atherosclerotic lesion formation in Apoe−/− mice. At the same time, the NEDDylation inhibitor MLN4924 attenuates early atherogenesis (Asare et al., PNAS 2017). Although the intact CSN holocomplex of all 8 subunits is required for the deNEDDylase activity, the role of the holo-complex and that of other CSN subunits in atherogenesis has remained unknown, as also complex-independent functions have been reported for some subunits. Here, I assessed whether the arterial-/endothelial-specific Csn5 knock-out mice in the atherogenic ApoE-/- background recapitulates the exacerbated atherosclerotic phenotype found in myeloid-specific Csn5 knock-out mice. Atherogenic mice with a tamoxifen-inducible arterial Csn5 deletion (C57BL/6 Bmx-Cre ERT2/Csn5flox/flox/Apoe−/− or Csn5arterialApoe−/−) generated and their atherosclerotic phenotype and vascular inflammatory status studied. Data here indicates a marked exacerbation of atherosclerosis in Csn5arterialApoe−/− mice compared to control animals and, for the first time, implicate Csn5 in early atherogenesis. Interestingly, the atherosclerotic phenotype was only found in male Csn5arterialApoe−/− mice, suggesting sex-specific mechanisms. Applying a cytokine and inflammatory marker screen of proteins potentially involved in atherosclerosis, I showed TIMP-1 as a factor related to plaque vulnerability. Furthermore, I demonstrate for the first time a role for the smallest CSN subunit, CSN8, in atherosclerosis in vivo by studying atherosclerosis-prone Csn8myeloid Apoe−/− mice. At the same time, this suggested a role of the CSN holocomplex in atherosclerosis. Accordingly, gene deletion of either Csn5 or Csn8 was found to regulate levels of Timp-1 and those of matrix-metalloproteinases (Mmp), in line with an impact on plaque vulnerability. Mechanistically, this mediated the AP-1 and MAP kinase pathways. Lastly, in a translational approach, I studied small molecule compounds that mimic CSN5 hyperactivation by blocking CRL NEDDylation in a pan-cullin manner or a specific cullin-3-dependent manner. These NEDDylation inhibitors were administered in early and advanced atherogenesis models, and initial data suggest that short-term application can convey a long-term “therapeutic” atheroprotective effect. My thesis contributes to elucidating mechanisms underlying atheroprotection by the CSN and identifies novel therapeutic targets.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: COP9 signalosome, NEDDylation, AP-1, TIMP-1, Plaque vulnerability
• Themengebiete: 600 Technik, Medizin, angewandte Wissenschaften ; 600 Technik, Medizin, angewandte Wissenschaften > 610 Medizin und Gesundheit
• Fakultäten: Medizinische Fakultät
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 19. Oktober 2022
• 1. Bericht­erstatter:in: Bernhagen, Jürgen