Pulmonary hypertension due to left-heart disease (PH-LHD) is the most common form of PH globally and a frequent consequence of heart failure (HF). As PH rapidly facilitates right ventricular remodeling and ultimately right ventricular failure, PH development contributes critically to morbidity and mortality in HF. HF-associated passive congestion into the pulmonary vasculature fuels active lung vascular remodeling, further raising pulmonary arterial pressure. Leukocytes are well-known to drive vascular inflammation and remodeling, yet their role in the pathophysiology of PH-LHD remains unclear. Here, we investigated spatial and temporal leukocyte dynamics in the pulmonary vasculature in PH-LHD, hypothesizing that myocardial infarction (MI)-associated HF causes chronic leukocyte accumulation in the pulmonary vasculature resulting in lung vascular remodeling.
MI was induced via a permanent ligation of the left anterior descending artery in female 9- to 20-week-old C57Bl/6J mice. All mice undergoing MI were assessed at 1d, 3d, 1w, 3w and 6w post-MI. Naïve mice were used as controls. First, we assessed cardiopulmonary physiology by high-resolution echocardiography, biventricular hemodynamics using a Millar catheter and H&E staining of lung tissue. Second, blood, heart and lung tissue was collected to determine leukocyte counts using multi-color flow cytometry. Third, we conducted multiphoton intravital microscopy (IVM) of the lung in female 20-week-old CX3CR1-GFP reporter mice (for visualization of monocytes) and using anti-Ly6G-BV421 to label neutrophils and Evans Blue for visualization of the pulmonary vasculature.
Acute MI led to increased troponin-I levels 24 hours post-MI and induced HF, evident as reduced LV ejection fraction, decreased cardiac output and increased LV volumes compared to controls. While the HF phenotype remained stable over the subsequent six weeks, right ventricular end-systolic pressures progressively increased and were significantly elevated at three- and six-weeks post-MI. This rise in RV pressure was associated with lung vascular remodeling, evident as wall thickening of pulmonary arteries. In the heart, monocyte and neutrophil counts increased rapidly and peaked 3d post-MI, then returned to baseline after one week. In contrast, in the lung, monocytes and neutrophils increased progressively over time, both peaking 6w post-MI. To visualize neutrophils and monocyte behavior in the lung vasculature in real-time, we performed high-resolution IVM imaging of the lung post-MI. Interestingly, we found altered morphodynamics of neutrophils and monocytes 6w post-MI when compared to naïve mice, evident as increased frequency of activated and migratory cell shapes. Monocytes from MI-mice also showed greater directionality, suggesting transition from patrolling to directed migratory behavior.
In sum, we found lung-specific innate immune cell profiles, morphology and behavior in a mouse model of MI-associated HF. Our findings suggest that pulmonary leukocyte dynamics in PH-LHD represent a sustained, spatially distinct immune response that may contribute to the progression of PH-LHD.
