Inhibition of the NLRP3 Inflammasome enhances engraftment of transplanted cells and augments cardiac function in a murine infarction model

The loss of cardiomyocytes (CM) following myocardial infarction (MI) is the most important determinant of infarct size and subsequent deterioration of cardiac function. Since the regenerative potential of CM in adults is negligible, modulation of scar formation and cellular tissue replacement after MI represent an interesting therapeutic approach. However, long-term engraftment of intramyocardially transplanted cells is limited for several reasons. Firstly, the initial immune response after MI plays a central role in the healing process but does not support the engraftment of freshly transplanted cells. The NLRP3 inflammasome is an important part of the innate immune response and activates within hours after lesion onset. It is responsible for the cleavage of interleukin (IL)-1β, which is highly pro-inflammatory. Secondly, technical and mechanical issues interfere with cell engraftment. Loading of embryonic cardiomyocytes (eCM) with magnetic nanoparticles (MNP) and transplanting these cells under the influence of a magnetic field has been established previously and significantly increased short- and long-term engraftment of transplanted cells. Therefore, we hypothesized that systemic treatment with the NLRP3 inflammasome inhibitor MCC950 in combination with MNP/magnetic field-guided intramyocardial transplantation of eCM could significantly improve cell engraftment and influence scar formation.
To test this, MI was induced via ligation of the left anterior descending (LAD) coronary artery or sham surgery was performed in C57Bl/6 J mice (10 – 12 weeks). GFP expressing eCM (E 13.5) were freshly isolated the day before surgery from α actin-GFP embryos and loaded with SoMag5-MNP (200 pg Fe/cell) in vitro overnight. Immediately following LAD ligation, 2 x 10⁵ eCM were transplanted intramyocardially under influence of a magnetic field during and 10 minutes following injection. MCC950 (20 mg/kg, i.p.) or vehicle (PBS, i.p.) was administered intraoperatively and every other day until day 12. Functional analysis was performed by left heart catheter measurements on day 14 post-surgery. Mice were euthanised while still under anaesthesia and hearts were excised for further histological investigation.
Treatment with MCC950 was able to reduce infarct volume after LAD ligation (n=6 each; LAD: 16,0% vs. MCC950: 9.2% of LV Vol.), resulting in improved stroke volume (SV: 22.7 µl, n=9) compared to LAD (12.9 µl, n=10) and thus preserved cardiac output (CO, LAD: 5,850 µl/min vs MCC950: 10,500 µl/min). Transplantation of eCM into the lesion alone had no effect on infarct volume and only slightly improved SV compared to LAD-ligated mice. The combination of eCM transplantation and MCC950 treatment improved engraftment of eCM by 3.7-fold compared to untreated eCM-transplanted mice (eCM: 39,726 vs eCM+MCC950: 146,295 engrafted cells, n=3 and 4, respectively). Infarct size after combined eCM+MCC950 therapy was similarly reduced as in LAD+MCC950 treated mice, SV (23.7 µl, n=8), CO (12,053 µl/min), and ejection fraction (EF, 55.7%) were also significantly improved compared to LAD mice.
In conclusion, MCC950 treatment after LAD ligation reduced myocardial scar size and thus significantly increased cardiac pump function 14 days postoperatively. Furthermore, the engraftment of transplanted eCM after MCC950 treatment increased almost four-fold, which did result in a further, but not significant improvement in cardiac pump function compared to MCC950 application alone.