Loss of cardiomyocytes (CM) after myocardial infarction (MI) and their replacement by scar tissue impairs cardiac pump function. MI remains the world’s leading cause of death, therefore, effective therapies addressing CM loss are urgently needed. The post-MI immune response, triggered by ischaemic damage, orchestrates tissue repair and scar formation and thus represents a promising therapeutic target. Activation of the NLRP3 inflammasome is one of the earliest responses during ischaemia and leads to IL-1β-mediated inflammation and Gasdermin D-mediated pyroptosis. Hence, NLRP3 inhibition may reduce cell death and preserve cardiac pump function.
MI was induced by ligation of the left anterior descending coronary artery (LAD) in C57 Bl/6 J mice (10 - 12 weeks old); immediately after ligation 2x105 embryonic CM (eCM) were injected into the ischaemic myocardium. Prior to transplantation, eCM (E 13.5) were loaded with magnetic nanoparticles and a magnetic field was applied during and for 10 min after injection to increase local cell retention. Additionally, mice were treated with the NLRP3 inhibitor MCC950 (20 mg/kg i.p.) peri-operatively and every other day post-MI until d14. Cardiac function was assessed by echocardiography and pressure-volume loop measurements 2 and 8 weeks post-MI. Hearts were collected after 1 and 3 days, as well as after functional assessment for histological analyses.
Significant reduction of NLRP3 and cleaved IL-1β expression in histological sections d3 post-MI proved effective NLRP3 inhibition. Consequently, MCC950 significantly decreased infiltration of CD45+ leukocytes into the infarction area at peak infiltration d3 post-MI compared to untreated LAD mice. TUNEL staining (indicator of dying cells) of hearts d1 post-MI revealed a significant reduction of dying TUNEL+ cells after inhibitor treatment (LAD: 49.21%, LAD+eCM: 46.51%, LAD+MCC950: 14.9%, LAD+eCM+MCC950: 19.44%). Accordingly, eCM engraftment showed a significant 4.8-fold increase d14 post-MI after MCC950 treatment (2,283 vs. 11,109 cells). Functional assessment 2 weeks post-MI showed significantly preserved cardiac function after MCC950 treatment. While eCM transplantation alone did not improve function at this time, combined treatment significantly preserved ejection fraction (EF; LAD: 39.28%, LAD+MCC950: 48.56%, LAD+eCM: 36.78%, LAD+eCM+MCC950: 59.65%). Scar volume did not differ between groups, but MCC950-treated hearts exhibited no transmural scars after 2 weeks. Although engrafted cells numbers declined over time, the ratio between groups (4.3-fold) remained stable until 8 weeks post-MI (LAD+eCM: 638 vs. LAD+eCM+MCC950: 2,772 cells). Importantly, cardiac function remained significantly preserved in both inhibitor-treated groups and even improved in the eCM-transplanted group (EF: LAD: 36.78%, LAD+MCC950: 62.57%, LAD+eCM+MCC950: 65.39%, LAD+eCM: 56.27%). After 8 weeks, scar size remained comparable between groups and all groups showed at least partially transmural scars.
In conclusion, these findings demonstrate that MCC950 treatment effectively reduces early graft cell loss after MI, thereby improving long-term engraftment and survival of transplanted eCM. The observed functional benefits of combining CM transplantation with NLRP3 inflammasome inhibition underscore the therapeutic potential of this dual approach and support its further development as a regenerative strategy for acute MI.
