Heart-Specific Immune Responses in an Animal Model of Autoimmune-Related Myocarditis Mitigated by an Immunoproteasome Inhibitor and Genetic Ablation

Abstract

Background: Immune checkpoint inhibitor (ICI) therapy is often accompanied by immune-related pathology, with an increasing occurrence of high-risk ICI-related myocarditis. Understanding the mechanisms involved in this side effect could enable the development of management strategies. In mouse models, immune checkpoints, such as PD-1 (programmed cell death protein 1), control the threshold of self-antigen responses directed against cardiac TnI (troponin I). We aimed to identify how the immunoproteasome, the main proteolytic machinery in immune cells harboring 3 distinct protease activities in the LMP2 (low-molecular-weight protein 2), LMP7 (low-molecular-weight protein 7), and MECL1 (multicatalytic endopeptidase complex subunit 1) subunit, affects TnI-directed autoimmune pathology of the heart. Methods: TnI-directed autoimmune myocarditis (TnI-AM), a CD4 + T-cell–mediated disease, was induced in mice lacking all 3 immunoproteasome subunits (triple-ip −/− ) or lacking either the gene encoding LMP2 and LMP7 by immunization with a cardiac TnI peptide. Alternatively, before induction of TnI-AM or after establishment of autoimmune myocarditis, mice were treated with the immunoproteasome inhibitor ONX 0914. Immune parameters defining heart-specific autoimmunity were investigated in experimental TnI-AM and in 2 cases of ICI-related myocarditis. Results: All immunoproteasome-deficient strains showed mitigated autoimmune-related cardiac pathology with less inflammation, lower proinflammatory and chemotactic cytokines, less interleukin-17 production, and reduced fibrosis formation. Protection from TnI-directed autoimmune heart pathology with improved cardiac function in LMP7 −/− mice involved a changed balance between effector and regulatory CD4 + T cells in the spleen, with CD4 + T cells from LMP7 − /− mice showing a higher expression of inhibitory PD-1 molecules. Blocked immunoproteasome proteolysis, by treatment of TLR2 (Toll-like receptor 2)–engaged and TLR7 (Toll-like receptor 7)/TLR8 (Toll-like receptor 8)–engaged CD14 + monocytes with ONX 0914, diminished proinflammatory cytokine responses, thereby reducing the boost for the expansion of self-reactive CD4 + T cells. Correspondingly, in mice, ONX 0914 treatment reversed cardiac autoimmune pathology, preventing the induction and progression of TnI-AM when self-reactive CD4 + T cells were primed. The autoimmune signature during experimental TnI-AM, with high immunoproteasome expression, immunoglobulin G deposition, interleukin-17 production in heart tissue, and TnI-directed humoral autoimmune responses, was also present in 2 cases of ICI-related myocarditis, demonstrating the activation of heart-specific autoimmune reactions by ICI therapy. Conclusions: By reversing heart-specific autoimmune responses, immunoproteasome inhibitors applied to a mouse model demonstrate their potential to aid in the management of autoimmune myocarditis in humans, possibly including patients with ICI-related heart-specific autoimmunity.

ONX 0914 Lacks Selectivity for the Cardiac Immunoproteasome in CoxsackievirusB3 Myocarditis of NMRI Mice and Promotes Virus-Mediated Tissue Damage

“…Progression towards chronic heart tissue injury in this strain is a consequence of acute myocarditis, which in A/J mice, showing a severe systemic inflammatory response after infection with cardiotropic CVB3 [44], is principally reversible by ONX 0914 [38]. Nevertheless, our data clearly demonstrate that the profound anti-inflammatory effects induced by ONX 0914, illustrated in the context of both viral infection [38,47] and autoimmunity [20,28,29,48], do not primarily affect the pathogenesis induced by viral infection in NMRI mice. In fact, we found that intact proteasome activity enables mice to cope better with the invading pathogen.…”

“…These involve control of DAMP-or PAMP-triggered signaling responses, resulting in elevated production of cytokines, e.g., by innate myeloid cells, altered T cell activation and differentiation, B cell function, or immune cell survival [23][24][25]. Based on these multidimensional immune cellular functions, it was expected that i-proteasome inhibitors would be capable of hindering inflammation-driven carcinogenesis [26,27], autoimmune-related inflammation [20,28,29], or transplant rejection [22,30].…”

Immunoproteasome in IgA Nephropathy: State-of-Art and Future Perspectives

“…However, before the immunoproteasome becomes a therapeutic target in IgAN, further research is necessary to clarify whether and how the immunoproteasome participate in pathogenesis and/or progression of the disease. The advantages and disadvantages of immunoproteasome as a therapeutic target are summarized in Table 1 [60][61][62][63][64][65][66][67]. More basic studies on immunoproteasome structure and functions are needed to guide immunoproteasome-specific therapy [66,67] Influence on some physiological processes Apart from immune response, immunoproteasome is involved in some physiological processes such as protein degradation, cell proliferation and survival…”

Tofacitinib for treatment in immune-mediated myocarditis: The first reported cases

“…7 In addition, there are also theories about heart-specific immunity, preclinical data show that PD-1-deficient mice develop myocarditis through the generation of cardiac autoantibodies (cTnI) provide further supportive evidence for the autoimmune etiology of ICI-related myocarditis. 8…”