Chronic Microglia Activation Is Suffcient to Induce Significant Increase in Pulmonary Pressure

Abstract

Introduction: Microglia, the primary resident immune cells of the brain, can be activated very early in disease. Our previous studies have indicated that microglia activation and neuroinflammation in autonomic brain areas were associated with pulmonary hypertension (PH). Furthermore, we also demonstrated that the attenuation of neuroinflammation by either pharmacological inhibition of microglia with minocycline or genetic disruption of neuro-microglia interaction by CX3CR1 depletion led to protection against pulmonary hypertension. Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) plays a crucial role in controlling inflammatory responses via gene expression regulation. NF-κB signaling in microglia triggers a distinct neuroinflammatory response with increased migration, phagocytosis, and release of proinflammatory cytokines such as IL-6, IL-1β and TNF-α. Thus, in this study we investigated if targeted microglia activation was suffcient to initiate the cascade of events that may contribute to the development of pulmonary hypertension. Study Objective: This study was designed to test the hypothesis that chronic microglia activation is suffcient to induce pulmonary hypertension Methods To evaluate the specific contribution of microglia pro-inflammatory activation to modulate pulmonary pressure, we used a mouse line with inducible expression of the Cre-recombinase directed to the Cx3cr1 promoter crossed with IKKcaflox-flox mice. The breeding scheme CX3CR1creER/+: IKKcaflox-flox allows the Cre-recombination events, as induced by tamoxifen administration, to occur in many myeloid cell types. However, when recombination is followed by at least six weeks of time for the repopulation of cells with high turnover rates, this protocol promotes a relatively selective activation of NF-κB signaling on microglia. First, CX3CR1creER/+:IKKcaflox-flox mice (n=14) were injected with tamoxifen or oil (control) (i.p.) daily at 150 mg/kg body weight for six consecutive days. After 8 weeks, invasive RVSP measurement was performed, and tissues were harvested for following analysis. Briefly, a Millar catheter is inserted into the right ventricle. Ventricle pressures and ECG were recorded and analyzed. PH phenotype also included the measurement of the Fulton index (RV:LV+S) and histological and flow cytometry analyses of lung. Data was collected in two separate experiments with similar results. Results: Activation of NF-κB on microglia was suffcient to induce a slight but significant increase in right ventricular systolic pressure (RVSP), surrogate of pulmonary pressure (RVSP: Tamoxifen: 26.23 ± 0.5861 mmHg; Oil: 23.16 ± 0.4339 mmHg (p = 0.001)), and increased right heart contractility (+dP/dt: Tamoxifen: 1586± 90.18 mmHg/s; Oil: 1250 ± 65.39 mmHg/s (p = 0.0092). Interestingly, activation of NF-κB on microglia also induced a significant increase in lung infiltration of monocytic myeloid-derived suppressor cells (Mo-MDSC, CD11b+Ly6ChiLy6G−) and granulocytic-like MDSCs (PMN-MDSC, CD11b+Ly6Clo Ly6G+). Conclusion: Activation of NF-κB on microglia was suffcient to induce a significant increase in pulmonary pressure and increase lung infiltration of myeloid-derived suppressor cells associated with smooth muscle cell proliferation in pulmonary hypertension. K99 HL165026, R01 HL142776. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.