Hypoxic proliferation requires EGFR-mediated ERK activation in human pulmonary microvascular endothelial cells

Human pulmonary microvascular endothelial cell DDAH1-mediated nitric oxide production promotes pulmonary smooth muscle cell apoptosis in co-culture

Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease in preterm infants, and pulmonary hypertension (PH) develops in 25%-40% of patients with BPD, increasing morbidity and mortality. BPD-PH is characterized by vasoconstriction and vascular remodeling. Nitric oxide (NO) is a pulmonary vasodilator and apoptotic mediator made in the pulmonary endothelium by NO synthase (eNOS). Asymmetric dimethylarginine (ADMA) is an endogenous eNOS inhibitor, primarily metabolized by dimethylarginine dimethylaminohydrolase-1 (DDAH1). Our hypothesis is that DDAH1 knockdown in human pulmonary microvascular endothelial cells (hPMVEC) will result in lower NO production, decreased apoptosis, and greater proliferation of human pulmonary arterial smooth muscle cells (hPASMC), whereas DDAH1 overexpression will have the opposite effect. hPMVECs were transfected with small interfering RNA targeting DDAH1 (siDDAH1)/scramble or adenoviral vector containing DDAH1 (AdDDAH1)/AdGFP for 24 h and co-cultured for 24 h with hPASMC. Analyses included Western blot for cleaved and total caspase-3, caspase-8, caspase-9, β-actin; trypan blue exclusion for viable cell numbers; terminal deoxynucleotide transferase dUTP nick end labeling (TUNEL); and BrdU incorporation. Small interfering RNA targeting DDAH1 (siDDAH1) transfected into hPMVEC resulted in lower media nitrites, cleaved caspase-3 and caspase-8 protein expression, and TUNEL staining; and greater viable cell numbers and BrdU incorporation in co-cultured hPASMC. Adenoviral-mediated transfection of the DDAH1 gene (AdDDAH1) into hPMVEC resulted in greater cleaved caspase-3 and caspase-8 protein expression and lower viable cell numbers in co-cultured hPASMC. Partial recovery of hPASMC viable cell numbers after AdDDAH1-hPMVEC transfection was observed when media were treated with hemoglobin to sequester NO. In conclusion, hPMVEC-DDAH1-mediated NO production positively regulates hPASMC apoptosis, which may prevent/attenuate aberrant pulmonary vascular proliferation/remodeling in BPD-PH.NEW & NOTEWORTHY BPD-PH is characterized by vascular remodeling. NO is an apoptotic mediator made in the pulmonary endothelium by eNOS. ADMA is an endogenous eNOS inhibitor metabolized by DDAH1. EC-DDAH1 overexpression resulted in greater cleaved caspase-3 and caspase-8 protein expression and lower viable cell numbers in co-cultured SMC. After NO sequestration, SMC viable cell numbers partially recovered despite EC-DDAH1 overexpression. EC-DDAH1-mediated NO production positively regulates SMC apoptosis, which may prevent/attenuate aberrant pulmonary vascular proliferation/remodeling in BPD-PH.

Hypoxic pulmonary endothelial cells release epidermal growth factor leading to vascular smooth muscle cell arginase-2 expression and proliferation

The hallmark of pulmonary hypertension (PH) is vascular remodeling. We have previously shown that human pulmonary microvascular endothelial cells (hPMVEC) respond to hypoxia with epidermal growth factor (EGF) mediated activation of the receptor tyrosine kinase, EGF receptor (EGFR), resulting in arginase-2 (Arg2)-dependent proliferation. We hypothesized that the release of EGF by hPMVEC could result in the proliferation of human pulmonary arterial smooth muscle cells (hPASMC) via activation of EGFR on the hPASMC leading to Arg2 up-regulation. To test this hypothesis, we used conditioned media (CM) from hPMVEC grown either in normoxia (NCM) or hypoxia (HCM). Human PASMC were incubated in normoxia with either HCM or NCM, and HCM caused significant induction of Arg2 and viable cell numbers. When HCM was generated with either an EGF-neutralizing antibody or an EGFR blocking antibody the resulting HCM did not induce Arg2 or increase viable cell numbers in hPASMC. Adding an EGFR blocking antibody to HCM, prevented the HCM-induced increase in Arg2 and viable cell numbers. HCM induced robust phosphorylation of hPASMC EGFR. When hPASMC were transfected with siRNA against EGFR the HCM-induced increase in viable cell numbers was prevented. When hPASMC were treated with the arginase antagonist nor-NOHA, the HCM-induced increase in viable cell numbers was prevented. These data suggest that hypoxic hPMVEC releases EGF, which activates hPASMC EGFR leading to Arg2 protein expression and an increase in viable cell numbers. We speculate that EGF neutralizing antibodies or EGFR blocking antibodies represent potential therapeutics to prevent and/or attenuate vascular remodeling in PH associated with hypoxia.

GPCR-ErbB transactivation pathways and clinical implications

Cell surface receptors including the epidermal growth factor receptor (EGFR) family and G-protein coupled receptors (GPCRs) play quintessential roles in physiology, and in diseases, including cardiovascular diseases. While downstream signaling from these individual receptor families has been well studied, the cross-talk between EGF and GPCR receptor families is still incompletely understood. Including members of both receptor families, the number of receptor and ligand combinations for unique interactions is vast, offering a frontier of pharmacologic targets to explore for preventing and treating disease. This molecular cross-talk, called receptor transactivation, is reviewed here with a focus on the cardiovascular system featuring the well-studied GPCR receptors, but also discussing less-studied receptors from both families for a broad understanding of context of expansile interactions, repertoire of cellular signaling, and disease consequences. Attention is given to cell type, level of chronicity, and disease context given that transactivation and comorbidities, including diabetes, hypertension, coronavirus infection, impact cardiovascular disease and health outcomes.

EGFR in enterocytes & endothelium and HIF1α in enterocytes are dispensable for massive small bowel resection induced angiogenesis

Background

Short bowel syndrome (SBS) results from significant loss of small intestinal length. In response to this loss, adaptation occurs, with Epidermal Growth Factor Receptor (EGFR) being a key driver. Besides enhanced enterocyte proliferation, we have revealed that adaptation is associated with angiogenesis. Further, we have found that small bowel resection (SBR) is associated with diminished oxygen delivery and elevated levels of hypoxia-inducible factor 1-alpha (HIF1α).

Methods

We ablated EGFR in the epithelium and endothelium as well as HIF1α in the epithelium, ostensibly the most hypoxic element. Using these mice, we determined the effects of these genetic manipulations on intestinal blood flow after SBR using photoacoustic microscopy (PAM), intestinal adaptation and angiogenic responses. Then, given that endothelial cells require a stromal support cell for efficient vascularization, we ablated EGFR expression in intestinal subepithelial myofibroblasts (ISEMFs) to determine its effects on angiogenesis in a microfluidic model of human small intestine.

Results

Despite immediate increased demand in oxygen extraction fraction measured by PAM in all mouse lines, were no differences in enterocyte and endothelial cell EGFR knockouts or enterocyte HIF1α knockouts by POD3. Submucosal capillary density was also unchanged by POD7 in all mouse lines. Additionally, EGFR silencing in ISEMFs did not impact vascular network development in a microfluidic device of human small intestine.

Conclusions

Overall, despite the importance of EGFR in facilitating intestinal adaptation after SBR, it had no impact on angiogenesis in three cell types–enterocytes, endothelial cells, and ISEMFs. Epithelial ablation of HIF1α also had no impact on angiogenesis in the setting of SBS.

DDAH1 regulates apoptosis and angiogenesis in human fetal pulmonary microvascular endothelial cells

Nitric Oxide (NO) is an endogenous pulmonary vasodilator produced by endothelial NO synthase (eNOS). Asymmetric dimethyl L‐arginine (ADMA) is an endogenous inhibitor of eNOS activity. In endothelial cells, ADMA is hydrolyzed to L‐citrulline primarily by dimethylarginine dimethyl‐aminohydrolase‐1 (DDAH1). We tested the hypothesis that DDAH1 expression is essential for maintaining NO production in human fetal pulmonary microvascular endothelial cells (hfPMVEC), such that knockdown of DDAH1 expression will lead to decreased NO production resulting in less caspase‐3 activation and less tube formation. We found that hfPMVEC transfected with DDAH1 siRNA had lower NO production than control, with no difference in eNOS protein levels between groups. hfPMVEC transfected with DDAH1 siRNA had lower protein levels of cleaved caspase‐3 and ‐8 than control. Both DDAH1 siRNA‐ and ADMA‐treated hfPMVEC had greater numbers of viable cells than controls. Angiogenesis was assessed using tube formation assays in matrigel, and tube formation was lower after either DDAH1 siRNA transfection or ADMA treatment than controls. Addition of an NO donor restored cleaved caspase‐3 and ‐8 protein levels after DDAH1 siRNA transfection in hfPMVEC to essentially the levels seen in scramble control. Addition of a putative caspase‐3 inhibitor to DDAH1 siRNA transfected and NO‐donor treated cells led to greater numbers of viable cells and far less angiogenesis than in any other group studied. We conclude that in hfPMVEC, DDAH1 is central to the regulation of NO‐mediated caspase‐3 activation and the resultant apoptosis and angiogenesis. Our findings suggest that DDAH1 may be a potential therapeutic target in pulmonary hypertensive disorders.

The P2-receptor-mediated Ca2+ signalosome of the human pulmonary endothelium - implications for pulmonary arterial hypertension

Dysfunction of the pulmonary endothelium is associated with most lung diseases. Extracellular nucleotides modulate a plethora of endothelial functions in the lung such as vessel integrity, vasodilatation, inflammatory, and thrombotic responses as well as survival and DNA repair, mostly via Ca²⁺ signaling pathways. However, a comprehensive analysis of the molecular components of the underlying P2 receptor-mediated Ca²⁺ signaling pathways in the lung has not been conducted so far. Therefore, our aim was to identify the principal P2 receptor Ca²⁺ signalosome in the human pulmonary endothelium and investigate potential dysregulation in pulmonary vascular disease. Comparative transcriptomics and quantitative immunohistochemistry were performed on publicly available RNA sequencing and protein datasets to identify the specific expression profile of the P2-receptor Ca²⁺ signalosome in the healthy human pulmonary endothelium and endothelial cells (EC) dysfunctional due to loss of or defective bone morphogenetic protein receptor (BMPR2). Functional expression of signalosome components was tested by single cell Ca²⁺ imaging. Comparative transcriptome analysis of 11 endothelial cell subtypes revealed a specific P2 receptor Ca²⁺ signalosome signature for the pulmonary endothelium. Pulmonary endothelial expression of the most abundantly expressed Ca²⁺ toolkit genes CALM1, CALM2, VDAC1, and GNAS was confirmed by immunohistochemistry (IHC). P2RX1, P2RX4, P2RY6, and P2YR11 showed strong lung endothelial staining by IHC, P2X5, and P2Y1 were found to a much lesser extent. Very weak or no signals were detected for all other P2 receptors. Stimulation of human pulmonary artery (HPA) EC by purine nucleotides ATP, ADP, and AMP led to robust intracellular Ca²⁺ signals mediated through both P2X and P2Y receptors. Pyrimidine UTP and UDP-mediated Ca²⁺ signals were generated almost exclusively by activation of P2Y receptors. HPAEC made dysfunctional by siRNA-mediated BMPR2 depletion showed downregulation of 18 and upregulation of 19 P2 receptor Ca²⁺ signalosome genes including PLCD4, which was found to be upregulated in iPSC-EC from BMPR2-mutant patients with pulmonary arterial hypertension. In conclusion, the human pulmonary endothelium expresses a distinct functional subset of the P2 receptor Ca²⁺ signalosome. Composition of the P2 receptor Ca²⁺ toolkit in the pulmonary endothelium is susceptible to genetic disturbances likely contributing to an unfavorable pulmonary disease phenotype found in pulmonary arterial hypertension.

The Arginase Pathway in Neonatal Brain Hypoxia-Ischemia

Brain damage after hypoxia-ischemia (HI) occurs in an age-dependent manner. Neuroprotective strategies assumed to be effective in adults might have deleterious effects in the immature brain. In order to create effective therapies, the complex pathophysiology of HI in the developing brain requires exploring new mechanisms. Critical determinants of neuronal survival after HI are the extent of vascular dysfunction, inflammation, and oxidative stress, followed later by tissue repair. The key enzyme of these processes in the human body is arginase (ARG) that acts via the bioavailability of nitric oxide, and the synthesis of polyamines and proline. ARG is expressed throughout the brain in different cells. However, little is known about the effect of ARG in pathophysiological states of the brain, especially hypoxia-ischemia. Here, we summarize the role of ARG during neurodevelopment as well as in various brain pathologies.

Hypoxic-induction of arginase II requires EGF-mediated EGFR activation in human pulmonary microvascular endothelial cells

We have previously shown that hypoxia-induced proliferation of human pulmonary microvascular endothelial cells (hPMVEC) depends on arginase II, and that epidermal growth factor receptor (EGFR) is necessary for hypoxic-induction of arginase II. However, it remains unclear how hypoxia activates EGFR-mediated signaling in hPMVEC. We hypothesized that hypoxia results in epidermal growth factor (EGF) production and that EGF binds to EGFR to activate the signaling cascade leading to arginase II induction and proliferation in hPMVEC. We found that hypoxia significantly increased the mRNA levels of EGF, EGFR, and arginase in hPMVEC. Hypoxia significantly increased pEGFR(Tyr845) protein levels and an EGF neutralizing antibody prevented the hypoxic induction of pEGFR. Inhibiting EGFR activation prevented hypoxia-induced arginase II mRNA and protein induction. Treatment of hPMVEC with exogenous EGF resulted in greater levels of arginase II protein both in normoxia and hypoxia. An EGF neutralizing antibody diminished hypoxic induction of arginase II and resulted in fewer viable cells in hPMVEC. Similarly, siRNA against EGF prevented hypoxic induction of arginase II and resulted in fewer viable cells. Finally, conditioned media from hypoxic hPMVEC induced proliferation in human pulmonary artery smooth muscle cells (hPASMC), however, conditioned media from a group of hypoxic hPMVEC in which EGF were knocked down did not promote hPASMC proliferation. These findings demonstrate that hypoxia-induced arginase II expression and cellular proliferation depend on autocrine EGF production leading to EGFR activation in hPMVEC. We speculate that EGF-EGFR signaling may be a novel therapeutic target for pulmonary hypertensive disorders associated with hypoxia.

ATP-sensitive potassium (KATP) channel openers diazoxide and nicorandil lower intraocular pressure by activating the Erk1/2 signaling pathway

Elevated intraocular pressure is the most prevalent and only treatable risk factor for glaucoma, a degenerative disease of the optic nerve. While treatment options to slow disease progression are available, all current therapeutic and surgical treatments have unwanted side effects or limited efficacy, resulting in the need to identify new options. Previous reports from our laboratory have established a novel ocular hypotensive effect of ATP-sensitive potassium channel (KATP) openers including diazoxide (DZ) and nicorandil (NCD). In the current study, we evaluated the role of Erk1/2 signaling pathway in KATP channel opener mediated reduction of intraocular pressure (IOP). Western blot analysis of DZ and NCD treated primary normal trabecular meshwork (NTM) cells, human TM (isolated from perfusion cultures of human anterior segments) and mouse eyes showed increased phosphorylation of Erk1/2 when compared to vehicle treated controls. DZ and NCD mediated pressure reduction (p<0.02) in human anterior segments (n = 7 for DZ, n = 4 for NCD) was abrogated by U0126 (DZ + U0126: -9.7 ± 11.5%, p = 0.11; NCD + U0126: -0.1 ± 11.5%, p = 1.0). In contrast, U0126 had no effect on latanoprostfree acid-induced pressure reduction (-52.5 ± 6.8%, n = 4, p = 0.001). In mice, DZ and NCD reduced IOP (DZ, 14.9 ± 3.8%, NCD, 16.9 ± 2.5%, n = 10, p<0.001), but the pressure reduction was inhibited by U0126 (DZ + U0126, 0.7 ± 3.0%; NCD + U0126, 0.9 ± 2.2%, n = 10, p>0.1). Histologic evaluation of transmission electron micrographs from DZ + U0126 and NCD + U0126 treated eyes revealed no observable morphological changes in the ultrastructure of the conventional outflow pathway. Taken together, the results indicate that the Erk1/2 pathway is necessary for IOP reduction by KATP channel openers DZ and NCD.