The role of endothelial leak in pulmonary hypertension (2017 Grover Conference Series)

Early detection of pulmonary arterial hypertension through [18F] positron emission tomography imaging with a vascular endothelial receptor small molecule

The objective of this study is to provide a positron emission tomography (PET) imaging modality targeting vascular endothelial growth factor receptors (VEGFR) for the early noninvasive detection and assessment of pulmonary arterial hypertension (PAH) severity. To validate the effectiveness of the [18F]VEGFR PET tracer, we utilized a monocrotaline (MCT)-induced PAH rat model. Molecular optical imaging, using a Cy5.5-conjugated VEGFR targeting agent, was employed to demonstrate the uptake of the agent at pulmonary arterioles, correlating with the onset and progression of PAH. Histological examinations of the MCT-PAH rat lung revealed a significant correlation between VEGFR2 expression and the pathogenesis of PAH. Molecular optical imaging demonstrated heightened uptake of the Cy5.5-conjugated VEGFR targeting agent at pulmonary arterioles, corresponding with the onset and progression of PAH. [18F]VEGFR PET showed increased lung uptake detectable in early-stage PAH before increase in pulmonary artery pressures, and this uptake correlated with increased PAH severity. Moreover, when compared to [18F]FDG PET, [18F]VEGFR PET exhibited markedly lower background cardiac signal, enhancing imaging sensitivity for lung abnormalities. Our study provides a compelling evidence for the potential utility of the innovative [18F]VEGFR PET tracer, in non-invasively detecting early signs of PAH, and monitoring its progression. The observed correlations between VEGFR2 expression, molecular optical imaging results, and [18F]VEGFR PET findings support the use of this tracer for early detection, and assessment of PAH severity. The lower background cardiac signal observed with [18F]VEGFR PET further enhances its imaging sensitivity, emphasizing its potential clinical significance.

The Role of TRIM Proteins in Vascular Disease

There are more than 80 different tripartite motifs (TRIM) proteins within the E3 ubiquitin ligase subfamily, including proteins that regulate intracellular signaling, apoptosis, autophagy, proliferation, inflammation, and immunity through the ubiquitination of target proteins. Studies conducted in recent years have unraveled the importance of TRIM proteins in the pathophysiology of vascular diseases. In this review, we describe the effects of TRIM proteins on vascular endothelial cells, smooth muscle cells, heart, and lungs. In particular, we discuss the potential mechanisms by which TRIMs regulate diseases and shed light on the potential therapeutic applications of TRIMs.

Pentastatin, a matrikine of the collagen IVα5, is a novel endogenous mediator of pulmonary endothelial dysfunction

Deposition of basement membrane components, such as collagen IVα5, is associated with altered endothelial cell function in pulmonary hypertension. Collagen IVα5 harbors a functionally active fragment within its C-terminal noncollageneous (NC1) domain, called pentastatin, whose role in pulmonary endothelial cell behavior remains unknown. Here, we demonstrate that pentastatin serves as a mediator of pulmonary endothelial cell dysfunction, contributing to pulmonary hypertension. In vitro, treatment with pentastatin induced transcription of immediate early genes and proinflammatory cytokines and led to a functional loss of endothelial barrier integrity in pulmonary arterial endothelial cells. Mechanistically, pentastatin leads to β1-integrin subunit clustering and Rho/ROCK activation. Blockage of the β1-integrin subunit or the Rho/ROCK pathway partially attenuated the pentastatin-induced endothelial barrier disruption. Although pentastatin reduced the viability of endothelial cells, smooth muscle cell proliferation was induced. These effects on the pulmonary vascular cells were recapitulated ex vivo in the isolated-perfused lung model, where treatment with pentastatin-induced swelling of the endothelium accompanied by occasional endothelial cell apoptosis. This was reflected by increased vascular permeability and elevated pulmonary arterial pressure induced by pentastatin. This study identifies pentastatin as a mediator of endothelial cell dysfunction, which thus might contribute to the pathogenesis of pulmonary vascular disorders such as pulmonary hypertension.NEW & NOTEWORTHY This study is the first to show that pentastatin, the matrikine of the basement membrane (BM) collagen IVα5 polypeptide, triggers rapid pulmonary arterial endothelial cell barrier disruption, activation, and apoptosis in vitro and ex vivo. Mechanistically, pentastatin partially acts through binding to the β1-integrin subunit and the Rho/ROCK pathway. These findings are the first to link pentastatin to pulmonary endothelial dysfunction and, thus, suggest a major role for BM-matrikines in pulmonary vascular diseases such as pulmonary hypertension.

Transient Receptor Potential (TRP) Channels in Airway Toxicity and Disease: An Update

Our respiratory system is exposed to toxicants and pathogens from both sides: the airways and the vasculature. While tracheal, bronchial and alveolar epithelial cells form a natural barrier in the airways, endothelial cells protect the lung from perfused toxic compounds, particulate matter and invading microorganism in the vascular system. Damages induce inflammation by our immune response and wound healing by (myo)fibroblast proliferation. Members of the transient receptor potential (TRP) superfamily of ion channel are expressed in many cells of the respiratory tract and serve multiple functions in physiology and pathophysiology. TRP expression patterns in non-neuronal cells with a focus on TRPA1, TRPC6, TRPM2, TRPM5, TRPM7, TRPV2, TRPV4 and TRPV6 channels are presented, and their roles in barrier function, immune regulation and phagocytosis are summarized. Moreover, TRP channels as future pharmacological targets in chronic obstructive pulmonary disease (COPD), asthma, cystic and pulmonary fibrosis as well as lung edema are discussed.

Culture of pulmonary artery endothelial cells from pulmonary artery catheter balloon tips: considerations for use in pulmonary vascular disease

Endothelial dysfunction is a hallmark of pulmonary arterial hypertension (PAH) but there are no established methods to study pulmonary artery endothelial cells (PAECs) from living patients. We sought to culture PAECs from pulmonary artery catheter (PAC) balloons used during right-heart catheterisation (RHC) to characterise successful culture attempts and to describe PAEC behaviour.PAECs were grown in primary culture to confluence and endothelial cell phenotype was confirmed. Standard assays for apoptosis, migration and tube formation were performed between passages three to eight. We collected 49 PAC tips from 45 subjects with successful PAEC culture from 19 balloons (39%).There were no differences in subject demographic details or RHC procedural details in successful versus unsuccessful attempts. However, for subjects who met haemodynamic criteria for PAH, there was a higher but nonsignificant (p=0.10) proportion amongst successful attempts (10 out of 19, 53%) versus unsuccessful attempts (nine out of 30, 30%). A successful culture was more likely in subjects with a lower cardiac index (p=0.03) and higher pulmonary vascular resistance (p=0.04). PAECs from a subject with idiopathic PAH were apoptosis resistant compared to commercial PAECs (p=0.04) and had reduced migration compared to PAECs from a subject with portopulmonary hypertension with high cardiac output (p=0.01). PAECs from a subject with HIV-associated PAH formed fewer (p=0.01) and shorter (p=0.02) vessel networks compared to commercial PAECs.Sustained culture and characterisation of PAECs from RHC balloons is feasible, especially in PAH with high haemodynamic burden. This technique may provide insight into endothelial dysfunction during PAH pathogenesis.

Is there a role for prostanoid-mediated inhibition of IL-6 trans-signalling in the management of pulmonary arterial hypertension?

Inflammation has been highlighted as a key factor in pulmonary arterial hypertension (PAH) development, particularly interleukin-6 (IL-6). IL-6 activates JAK-STAT signalling to induce transcription of pro-inflammatory and pro-angiogenic genes, enabling PAH progression, as well as the transcription of suppressor of cytokine signalling 3 (SOCS3) which limits IL-6 signalling. Current PAH therapies include prostanoid drugs which induce vasodilation via stimulating intracellular 3',5'-cyclic adenosine monophosphate (cAMP) levels. cAMP can also inhibit IL-6-mediated endothelial dysfunction via the induction of SOCS3. Thus, we propose that an important mechanism by which cAMP-mobilising prostanoid drugs limit PAH is by inhibiting IL-6-mediated pulmonary inflammation and remodelling via SOCS3 inhibition of IL-6 signalling. Further clarification may result in effective strategies with which to target the IL-6/JAK-STAT signalling pathway in PAH.