CCR2⁺ monocyte-derived macrophages drive cardiac hypertrophy in early HFpEF

Heart failure with preserved ejection fraction (HFpEF) is a chronic syndrome driven by systemic inflammation. Resident and monocyte-derived macrophages play opposing roles in several heart diseases. Though general ablation of macrophages has previously been studied in HFpEF, the individual contribution of these subsets to HFpEF development is unknown. We induced preclinical HFpEF in mice using a model consisting of a high-fat diet, chronic low-dose angiotensin II administration, and salt-supplemented drinking water. Our model was marked by circulating Ly6C^hi monocytosis and elevated proinflammatory C-C motif chemokine receptor 2 (CCR2⁺) macrophage infiltration at the expense of the cardioprotective TIMD4⁺ resident macrophage subset. Beyond an inflammatory signature typical of HFpEF, the mouse model also faithfully recreates cardiac fibrosis, hypertrophy, and functional changes in the heart as measured by echocardiography and pressure-volume loops. The experimental mice also show exercise intolerance. Using a loss-of-function genetic model, we found that CCR2 ablation prevented classical macrophage infiltration and improved the resident TIMD4⁺ macrophage representation early in HFpEF development. CCR2^-/- mice showed a higher accumulation of dysfunctional mitochondria in the heart with diffusely organized cristae without worsened mitochondrial fusion (Mitofusin2) or functioning in general (translocase outer membrane, TOM20). Loss of CCR2 did prevent left ventricle (LV) hypertrophy in our preclinical model but it did not resolve the cardiac fibrosis or diastolic dysfunction. Mitochondrial damage has been suggested to drive hypertrophy, however, we found that preventing classical macrophage recruitment increased the presence of damaged mitochondria, even though hypertrophy is resolved. In the future, our results can contribute to successful therapeutic immunomodulation to tackle HFpEF, if combined with antifibrotic treatment.<b>NEW & NOTEWORTHY</b> Development of a multi-comorbidity model induces early heart failure with preserved ejection fraction (HFpEF) in male mice. Early HFpEF is marked by circulating proinflammatory monocytosis (Ly6C^hi) and a disruption in the balance between monocyte-derived macrophage infiltration (CCR2⁺) and resident macrophages (TIMD4⁺). Ablation of CCR2, which prevents recruitment of classical macrophages, improves left ventricle (LV) hypertrophy in early HFpEF but not cardiac fibrosis or diastolic dysfunction. Anti-inflammatory therapies alone, without antifibrotic treatment, will likely not prevent the development of HFpEF.