ErbB Family Members in Human Pulmonary Microvascular Endothelial Cells Respond Differently when Exposed to Hypoxia

Pulmonary hypertension (PH) is seen in diseases associated with hypoxia (WHO classification Group 3), and one of those diseases is bronchopulmonary dysplasia (BPD). BPD is the most common co‐morbidity following preterm birth, and the incidence is as high as 100% in babies born at 22 weeks' gestation. There are currently no available preventative or curative therapies for PH associated with BPD. Vascular remodeling is a hallmark of PH diseases including that seen with BPD. The proliferation of pulmonary endothelial cells, as well as release of pro‐proliferative substances from endothelial cells that can induce vascular smooth muscle cells to proliferate, are central to the pathogenesis of vascular remodeling in PH. We have previously shown that human pulmonary microvascular endothelial cells (hPMVEC) respond to hypoxia by proliferating. We have also shown that hypoxia‐induced proliferation depends on epidermal growth factor (EGF) release resulting in epidermal growth factor receptor (EGFR) activation. EGFR is a member of the ErbB family of receptor proteins, of which there are 4 described and EGFR is also known as ErbB1. We have recently shown that hPMVEC express ErbB2 and ErbB4, but that ErbB3 mRNA and protein are absent in hPMVEC. We hypothesized that hypoxia would also regulate ErbB2 and ErbB4 expression levels in hPMVEC. We used standard western blotting techniques to identify ErbB2 and ErbB4 protein levels in fetal hPMVEC incubated in normoxia (21% O2, 5% CO2) or hypoxia (1% O2, 5% CO2, balance N2) at 37° C for 24 hours. We found that ErbB4 protein levels were similar between normoxic and hypoxic hPMVEC's, while ErbB2 protein levels were lower in hypoxic hPMVEC than in normoxic hPMVEC. The absence of change in ErbB4 protein expression levels in hypoxia does not exclude the possibility for alteration in ErbB4 signaling in hypoxia. To begin to explore the role of ErbB4 signaling in hypoxia we determined if the ErbB4 ligand neuregulin‐4 would increase protein levels of ErbB4 in hPMVEC and we found that in normoxic hPMVEC addition of neuregulin‐4 increased protein levels of ErbB4. To determine if ErbB4 siRNA would knockdown ErbB4 specifically, i.e. without affecting ErbB1 or ErbB2 protein levels, we used an siRNA approach. Results show notable decreased protein expression level of ErbB4 exposed to siRNA as compared to cells exposed to scramble controls, but no notable changes in the expression levels of ErbB2 protein. We speculate that ErbB4 is involved in the hypoxic response of hPMVEC to hypoxia and may represent a potential novel therapeutic target for pulmonary hypertensive disorders associated with hypoxia. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .