Myeloid cell dynamics in right ventricular dysfunction in HFpEF

The current classification of heart failure based on left ventricular ejection fraction (EF) identifies a large group of patients with preserved ejection fraction (HFpEF) with significant morbidity and mortality but without prognostic benefit from current HF therapy. Notably, HFpEF patients frequently present with secondary pulmonary hypertension (PH-HFpEF) and subsequent right ventricular (RV) failure. Lately, HFpEF has been associated with sterile inflammation, evident as active recruitment of myeloid immune cells into the left ventricle where they fuel diastolic dysfunction. Similar data defining the role of monocytes and macrophages in RV remodeling and dysfunction in the context of PH-HFpEF is so far missing, at least in part due to the lack of appropriate small animal models. Here, we designed a novel model of preclinical PH-HFpEF and characterized the abundance of monocytes and macrophages in HFpEF-associated RV dysfunction. 

 

Eight week-old male and female C57BL/6J mice were divided into 4 experimental groups: i) naïve mice serving as controls, ii) mice receiving high-fat diet (HFD) and N[ω]-nitro-l-arginine methyl ester (L-NAME) for 12 weeks to induce HFpEF, iii) mice receiving HFD, L-NAME and two weeks of hypoxia (10% O2) to induce PH-HFpEF, and iv) mice receiving hypoxia (Hx) without HFpEF. After 12 weeks, all experimental groups were subjected to transthoracic echocardiography, invasive hemodynamics and flow cytometry to assess LV diastolic dysfunction, RV dysfunction and innate immune cell dynamics, respectively.

 

The combination of HFD, L-NAME and hypoxia treatment resulted in more pronounced LV diastolic dysfunction with preserved EF, as indicated by slightly decreased end-diastolic volumes (EDV), decreased global longitudinal strain (GLS), as well as increased isovolumetric relaxation time (IVRT) compared to HFpEF mice. Similarly, the velocity across the mitral valve (E/A ratio) was significantly decreased in HFpEF+Hx compared to HFpEF mice. RV hemodynamics changed in line with the development of PH in HFpEF+Hx relative to HFpEF mice, evident as increased right ventricular systolic pressure (RVSP) and decreased tricuspid annular plane systolic excursion (TAPSE). In parallel, HFpEF+Hx increased RV weight to tibia length and RV to LV weight including septum (Fulton’s index) relative to HFpEF alone suggestive of RV hypertrophy. Flow cytometric analyses in HFpEF+Hx mice demonstrated increased innate immune cell counts in the RV compared to HFpEF mice, reflected in significantly elevated levels of leukocytes. Amongst them, Ly6Chi monocyte levels were significantly upregulated in HFpEF+Hx as compared to HFpEF. Additionally, tendencies for increased resident macrophage and monocyte-derived CCR2+ macrophage numbers were observed in HFpEF+Hx relative to HFpEF mice which however did not reach the level of significance. A similar pattern was observed in the LV, with the notable difference that monocyte and macrophage numbers in HFpEF+Hx mice were not significantly elevated compared to HFpEF.

 

Exposing mice with pre-existing HFpEF to hypoxia resulted in secondary PH, RV remodeling and dysfunction. RV remodeling was associated with dysregulated immune cell dynamics in the myeloid cell compartment. Interestingly, this effect was more pronounced in the RV as compared to LV samples. 

 

Funding: This study is supported by the Deutsche Forschungsgemeinschaft  (DFG,  German  Research  Foundation)  –  SFB-1470  –  subproject A04.