Troponin i-induced cardiac inflammation and dysfunction in mice: a comparative study with the AT-3 tumor-bearing model.

Background: Myocarditis is a potentially fatal condition, with a mortality rate of up to 50% in severe cases. Studies, including those by Nobel Laureate Honjo, have implicated autoantibodies against cardiac troponin I (cTnI) in driving cardiac inflammation in mice. Research has also identified autoantibodies under baseline conditions in some cancer models. However, data on the effects of recombinant cTnI on autoantibody production, myocardial inflammation, and contractile function remain limited. This study investigated cTnI-associated myocardial inflammation and autoantibody formation in both tumor-free and tumor-bearing mouse models.

Methods: Female BALB/c mice were immunized with recombinant cTnI combined with adjuvants and compared to adjuvant-only controls. Cardiac function was assessed using gated cardiac MRI, including myocardial velocities, acceleration, deceleration, and standard volumetric parameters including ejection fraction (EF). Anti-cTnI autoantibodies were quantified using a custom-designed ELISA, while myocardial inflammation was assessed by analyzing T-cell subsets (CD4 + and CD8 +) in myocardial tissue samples. Baseline autoantibody reactivity was evaluated in tumor-bearing mice and tumor-free controls for comparison.

Results: The left ventricular ejection fraction trended lower in the cTnI + adjuvant group (57.80 ± 1.7%) compared to controls (61.67 ± 4.1%), but the difference was not statistically significant (p = 0.073). Myocardial velocity, reflecting contraction speed, was significantly reduced in cTnI-treated mice (control:-1.2 ± 0.8 cm/s; cTnI:-1.05 ± 0.07 cm/s; p = 0.015). Anti-cTnI autoantibody levels increased significantly in cTnI-treated mice at 8 weeks (control:0.1 ± 0.02; cTnI:0.77 ± 0.28; p = 0.007). Additionally, the density of CD8 + T-cells in myocardial tissue was significantly higher in the cTnI group (control:2.2 ± 1.2 cells/mm²; cTnI:4.4 ± 2 cells/mm²; p = 0.013), indicating an enhanced cytotoxic T-cell response. The CD4/CD8 ratio was significantly lower in cTnI-treated mice (control: 8.2 ± 6.8; cTnI:3.1 ± 0.9; p = 0.029), further suggesting a shift toward a cytotoxic immune profile. Baseline autoantibody reactivity in tumor-bearing mice was not significantly different from controls (tumor-bearing: absorbance 0.049 ± 0.029; control: absorbance 0.068 ± 0.05 at 450 nm), indicating no inherent autoimmune reactivity in the tumor-bearing model.

Conclusions: Recombinant cTnI induces myocardial contractile dysfunction and promotes a cytotoxic immune response, supporting its role as an autoantigen in myocarditis. Advanced cardiac MRI revealed subtle functional impairments that EF alone could not detect. These findings highlight the potential for therapies targeting cTnI-induced autoimmunity, particularly in patients with ICI-associated myocarditis.