Abstract Body: Background: The innate immune receptor CLEC4E (C-type lectin domain family 4 member E) in cardiac resident cells and circulating leukocytes contributes to ischemic myocardial damage and adverse LV remodeling following ischemia reperfusion injury (I/R). Mice with loss of CLEC4E gene function show reduced cardiac injury and better LV remodeling but the mechanisms of this cardioprotection remain unknown.

Aims: We investigated whether Clec4e gene function in cardiac resident cells vs infiltrating immune cells mediates cardioprotection during myocardial ischemia-reperfusion injury.

Methods:We generated chimeric mice by IV infusion of 5 x 10⁶ bone marrow cells originating from C57Bl6/J CLEC4E^-/- and C57Bl6/J wild-type (WT) donor mice in 8w-old lethally irradiated (9.5 Gy) WT (n=36) and CLEC4E^-/- (n=50) receptor mice, respectively. After 4 w, mice were subjected to ischemia reperfusion injury (I/R) by 60 min LAD occlusion. Troponin levels (TnI) were measured at 90 min post I/R and 7T-magnetic resonance imaging with late gadolinium enhancement (LGE) for infarct size evaluation was performed at 24 h and 28 d post I/R. Mice were euthanized at 28 days for immunohistochemistry and analysis of BM chimerism.

Results:Immunohistochemistry for CLEC4E expression on bone marrow smears confirmed successful BM chimerism. At 24h post I/R, TnI levels and LGE-assessed infarct size on MRI were not significantly different between groups (42.1 vs 48.4 ng/ml, and 25.2% vs 31.5% of LVmass in CLEC4E^-/- & WT BM versus in WT & CLEC4E^-/- BM, respectively) suggesting similar myocardial damage . After 28 d, LV end-diastolic volumes (43µL vs 55µL), and end-systolic volumes (13µL vs 25µL) were significantly smaller in CLEC4E^-/- & WT BM than in WT & CLEC4E^-/- BM mice (P<0.05 for both), resulting in better preserved global LV function (LVEF 62% vs 47%, P<0.05) . Infarct size, semiquantitatively assessed using planimetry on Sirius red stains, was smaller in CLEC4E^-/- & WT BM than in WT & CLEC4E^-/- BM (6.9% vs 19.8%, P<0.01).
Conclusion: CLEC4E gene deletion in cardiac resident cells, but not in infiltrating hematopoietic immune cells is associated with better functional and structural remodelling after myocardial I/R. Inhibition of CLEC4E signaling via blocking antibodies or small molecule inhibitors in cardiac myocytes might be a promising cardioprotective strategy.