Switching-Off Adora2b in Vascular Smooth Muscle Cells Halts the Development of Pulmonary Hypertension

Abstract

Background: Pulmonary hypertension (PH) is a devastating and progressive disease characterized by excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) and remodeling of the lung vasculature. Adenosine signaling through the ADORA2B receptor has previously been implicated in disease progression and tissue remodeling in chronic lung disease. In experimental models of PH associated with chronic lung injury, pharmacological or genetic inhibition of ADORA2B improved markers of chronic lung injury and hallmarks of PH. However, the contribution of ADORA2B expression in the PASMC was not fully evaluated.Hypothesis: We hypothesized that adenosine signaling through the ADORA2B receptor in PASMC mediates the development of PH.Methods: PASMCs from controls and patients with idiopathic pulmonary arterial hypertension (iPAH) were characterized for expression levels of all adenosine receptors. Next, we evaluated the development of PH in ADORA2Bf/f-Transgelin (Tagln)cre mice. These mice or adequate controls were exposed to a combination of SUGEN (SU5416, 20 mg/kg/b.w. IP) and hypoxia (10% O2) for 28 days (HX-SU) or to chronic low doses of bleomycin (BLM, 0.035U/kg/b.w. IP). Cardiovascular readouts including right ventricle systolic pressures (RVSPs), Fulton indices and vascular remodeling were determined. Using PASMCs we identified ADORA2B-dependent mediators involved in vascular remodeling. These mediators: IL-6, hyaluronan synthase 2 (HAS2) and tissue transglutaminase (Tgm2) were determined by RT-PCR and validated in our HX-SU and BLM models.Results: Increased levels of ADORA2B were observed in PASMC from iPAH patients. ADORA2Bf/f-Taglncre mice were protected from the development of PH following HX-SU or BLM exposure. In the BLM model of PH, ADORA2Bf/f- Taglncre mice were not protected from the development of fibrosis. Increased expression of IL-6, HAS2 and Tgm2 was observed in PASMC in an ADORA2B-dependent manner. These mediators were also reduced in ADORA2Bf/f- Taglncre mice exposed to HX-SU or BLM.Conclusions: Our studies revealed ADORA2B-dependent increased levels of IL-6, hyaluronan and Tgm2 in PASMC, consistent with reduced levels in ADORA2Bf/f- Taglncre mice exposed to HX-SU or BLM. Taken together, our data indicates that ADORA2B on PASMC mediates the development of PH through the induction of IL-6, hyaluronan and Tgm2. These studies point at ADORA2B as a therapeutic target to treat PH.

Mechanisms of Pulmonary Hypertension in Acute Respiratory Distress Syndrome (ARDS)

“…In line with this, we hypothesize that the hypoxic environment in ARDS leads to increased expression or activity of CD73 and ADORA2B such as in PH in the setting of lung fibrosis (Garcia-Morales et al, 2015 ) that leads to accumulation of adenosine and subsequent activation of ADORA2B. Activation of this receptor has been shown to promote hyaluronan production through increased expression of hyaluronan synthases (HAS)-1 and 2 (Karmouty-Quintana et al, 2013a ; Mertens et al, 2018 ). Interestingly, many recent publications have linked increased hyaluronan deposition in COVID-19 (Hellman et al, 2020 ; Kaber et al, 2020 ), a disease that is more and more associated with important cardiopulmonary complications (Karmouty-Quintana et al, 2020 ; Potus et al, 2020 ).…”

Adenosine and hyaluronan promote lung fibrosis and pulmonary hypertension in combined pulmonary fibrosis and emphysema

“…Increased vascular or perivascular expression of HAS3 and subsequent hyaluronan deposition could also contribute directly to vascular remodeling and PH by promoting vascular stiffness and proliferation, as has been previously demonstrated by our group (Collum et al, 2017). Pulmonary artery smooth muscle cell expression of HAS has been shown to be modulated by activation of ADORA2B (Karmouty-Quintana et al, 2012; Mertens et al, 2018). This is in line with our studies showing ADORA2B-mediated macrophage HAS3 expression.…”

Purinergic Signaling in Pulmonary Inflammation

“…The study suggests that activation of the A2BAR on alternatively activated macrophages is essential in the development of pulmonary fibrosis and pulmonary hypertension (138). In addition, A2BAR activation on pulmonary artery smooth muscle cells (PASMCs) results in increased IL-6 and hyaluronan, and deletion of A2BAR in these cells leads to reduced severity of pulmonary hypertension (139). Moreover, hypoxia is present in pulmonary fibrosis and its role in modulating alveolar macrophage phenotype was examined by Philip et al Using the mouse bleomycin-induced model of pulmonary fibrosis and IPF lung samples, they determined that inhibition of HIF1α resulted in a reduction in pulmonary fibrosis, along with the diminished expression of A2BAR in alternatively activated macrophages (AAMs).…”