Disease Associated Microglia Is Identified As A Major Contributor To Neuroinflammation Associated To Chronic Hypoxia Induced‐Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive disease that leads to right heart failure and death. Increased sympathetic activity in PH patients is associated with a worse prognosis due to a series of well-established downstream sequelae. However, the mechanism behind chronic elevation in sympathetic activity in PH is poorly understood. Our fundamental hypothesis is that neuroinflammation in the hypothalamic paraventricular nucleus (PVN) is essential for elevated sympathetic activity in PH. This hypothesis is supported by our published data demonstrating: 1) increased number of microglia in the PVN is observed in multiple animal models of PH; 2) Microglia inhibition attenuates sympathetic activity and PH cardiopulmonary effects. However, microglia are, a heterogeneous with respect to gene expression and function. Indicating that characterization of the specific microglia subtypes involved in PH pathophysiology would be the key to identify possible targets to improve PH therapy. 3-months-old SD rats were subjected to monocrotaline induced PH model. After 28 days, CD45+CD11b+ cells were isolated from the PVN followed by single-cell RNA Sequencing (scRNA Seq) analysis. The disease associated microglia (DAM), which highly express Trem2, displayed the most significant phenotypic changes in PH. 3-months-old WT mice (n=12/group) were exposed to chronic hypoxia induced-PH (CH-PH) (10%O2) or Normoxia for 4 weeks in a ventilated chamber. CD45+CD11b+ cells were isolated from the PVN to evaluate TREM2 expression by flow cytometry in the same population. Then, TREM2 global knock-out mice (TREM2-KO) and WT (n=10/group) were exposed to CH-PH model and pulmonary hemodynamics were evaluated using a Millar pressure catheter in a terminal procedure. We identified 10 clusters as microglia/macrophage. Following evaluation of several cluster markers used to identify microglia subtypes, we found the cluster with the most significant differences in gene profile and biological processes by comparing control and PH samples. This cluster was identified as the disease-associated microglia (DAM), characterized by high expression of TREM2. Data was also confirmed in chronic hypoxia induced PH (CH-PH) model by flow cytometry. CH induced a two-fold increase of TREM2+microglia (CD11+, CD45+, TMEM119+) expression compared to normoxia controls. Fascinatingly, TREM2 deficient mice demonstrated a significant attenuation in the pulmonary pressure, represented by its surrogate the right ventricular systolic pressure (RVSP), and remarkably, reduction in overall lung inflammation induced by hypoxia. While TREM2 contribution has been extensively studied in neurodegenerative diseases and cancer therapy, these experiments are the first to demonstrate the potential of Trem2 targeted therapy in context of PH. Moreover, we believe that data generated from these studies may lead to translational studies evaluating the potential of TREM2 as a therapeutic target for PH.