Myeloid cell recruitment propels right ventricular dysfunction in HFpEF via sterile inflammation

Background

In contrast to what has already been shown in HFpEF associated left ventricular (LV) diastolic dysfunction, leukocytes’ role in frequently occurring right ventricular dysfunction (RVD) secondary to HFpEF are so far missing, partially due to the lack of suitable small animal models. Here, we follow a translational research approach by establishing a murine HFpEF model developing manifest RVD and analyzed human HFpEF cohorts to study the mechanistic link between leukocytes and RVD in HFpEF.

Methods

8-week-old male and female C57BL/6J or Cx3cr1 ^CreER /+R26 ^tdTomato/+ mice were divided into four experimental groups: i) chow, ii) HFpEF (N[ω]-nitro-l-arginine methyl ester (L-NAME), 60% high-fat diet), iii) chronic hypoxia (10% O ₂ ) and iv) HFpEF and hypoxia (RV-HFpEF) to assess bi-ventricular function and myeloid cell dynamics. To test whether myeloid cells are causally involved in the development of RV remodeling in HFpEF, we additionally treated RV-HFpEF mice with the colony stimulating factor 1 receptor inhibitor PLX-5622 (PLX) to deplete myeloid cells. After 12 weeks, all experimental groups were subjected to transthoracic echocardiography, invasive hemodynamics or flow cytometry.

Results

RV-HFpEF resulted in LV diastolic dysfunction indicated by increased E/E’ ratio, reduced global longitudinal peak strain, smaller end-diastolic diameters and increased isovolumetric relaxation time compared to chow. RV-HFpEF animals developed RV hypertrophy and RVD evident as increased Fulton’s index and collagen content as well as elevated RV systolic pressures (RVSPs) and reduced tricuspid annular plane systolic excursion, respectively. Flow cytometric analyses revealed elevated total leukocyte, monocyte, and macrophage counts in RV tissue of RV-HFpEF compared to chow or LV tissue from RV-HFpEF animals. These data were confirmed by unbiased proteomic analyses of RV tissue from RV-HFpEF mice, demonstrating increased abundance of proteins involved in activation of the innate immune system, macrophage chemotaxis, cell adhesion and extracellular matrix organization when compared to LV tissue or other experimental groups. Fate mapping experiments revealed that recruited monocyte-derived macrophages became the main source of total cardiac macrophages in RV tissue from RV-HFpEF mice. Depletion of myeloid cells was associated with rescued RVSP profiles compared to RV-HFpEF control mice. In HFpEF patients, RV dilation was associated with an increased percentage of circulating monocytes. In RV biopsies from HFpEF patients, we found increased expression of adhesion molecules, fibrotic markers and inflammatory transcripts.

Conclusion

We demonstrate that dysregulated myeloid cell dynamics are associated with, and directly contribute to, the pathogenesis of HFpEF-associated RVD in humans and mice.

Clinical Perspective

What is new:

• We explore myeloid cell dynamics in a novel three-hit experimental HFpEF mouse model with RV hypertrophy, RV end-systolic pressure and RV dysfunction.

• In this model, RV dysfunction was associated with macrophage expansion, monocyte recruitment and extracellular matrix deposition, whilst macrophage depletion partly reversed these changes and rescued RV hemodynamics.

• HFpEF patients with RV dilation or RV dysfunction exhibit unique leukocyte dynamics and inflammatory profiles when compared to HFpEF patients with normal RV function or diameters.

Clinical implications:

• There exists a major clinical discrepancy between high incidence of RV dysfunction associated to HFpEF and a lack of targeted treatment strategies.

• Our novel three-hit mouse model recapitulates many features of the clinical scenario of HFpEF patients with RV dysfunction, therefore representing an important step towards systematic testing and development of targeted treatment options.

• Sterile inflammation and dysregulation of innate immune cells may be suitable targets for therapeutic interventions against RV dysfunction in HFpEF.