Luminespib counteracts the Kifunensine-induced lung endothelial barrier dysfunction

Endothelial Unfolded Protein Response-Mediated Cytoskeletal Effects

The endothelial semipermeable monolayers ensure tissue homeostasis, are subjected to a plethora of stimuli, and their function depends on cytoskeletal integrity and remodeling. The permeability of those membranes can fluctuate to maintain organ homeostasis. In cases of severe injury, inflammation or disease, barrier hyperpermeability can cause irreparable damage of endothelium-dependent issues, and eventually death. Elucidation of the signaling regulating cytoskeletal structure and barrier integrity promotes the development of targeted pharmacotherapies towards disorders related to the impaired endothelium (e.g., acute respiratory distress syndrome, sepsis). Recent reports investigate the role of unfolded protein response in barrier function. Herein we review the cytoskeletal components, the unfolded protein response function; and their interrelations on health and disorder. Moreover, we emphasize on unfolded protein response modulators, since they ameliorate illness related to endothelial leak.

Growth hormone - releasing hormone in the immune system

GHRH is a neuropeptide associated with a diverse variety of activities in human physiology and immune responses. The present study reviews the latest information on the involvement of GHRH in the immune system and inflammation, suggesting that GHRH antagonists may deliver a new therapeutic possibility in disorders related to immune system dysfunction and inflammation.

Unfolded protein response suppression potentiates LPS-induced barrier dysfunction and inflammation in bovine pulmonary artery endothelial cells

The development of novel strategies to counteract diseases related to barrier dysfunction is a priority, since sepsis and acute respiratory distress syndrome are still associated with high mortality rates. In the present study, we focus on the effects of the unfolded protein response suppressor (UPR) 4-Phenylbutyrate (4-PBA) in Lipopolysaccharides (LPS)-induced endothelial injury, to investigate the effects of that compound in the corresponding damage. 4-PBA suppressed binding immunoglobulin protein (BiP) - a UPR activation marker - and potentiated LPS - induced signal transducer and activator of transcription 3 (STAT3) and extracellular signal‑regulated protein kinase (ERK) 1/2 activation. In addition to those effects, 4-PBA enhanced paracellular hyperpermeability in inflamed bovine pulmonary endothelial cells, and did not affect cell viability in moderate concentrations. Our observations suggest that UPR suppression due to 4-PBA augments LPS-induced endothelial injury, as well as the corresponding barrier disruption.

Ceapin-A7 potentiates lipopolysaccharide-induced endothelial injury

Barrier dysfunction is the hallmark of severe lung injury, including acute respiratory distress syndrome. Efficient medical countermeasures to counteract endothelial hyperpermeability do not exist, hence the mortality rates of disorders related to barrier abnormalities are unacceptable high. The unfolded protein response is a highly conserved mechanism, which aims to support the cells against endoplasmic reticulum stress, and ATF6 is a protein sensor that triggers its activation. In the current study, we investigate the effects of ATF6 suppression in LPS-induced endothelial inflammation. Our observations suggest that Ceapin-A7, which is an ATF6 suppressor, potentiates LPS-induced STAT3 and JAK2 activation. Hence ATF6 activation may serve as a new therapeutic possibility toward diseases related to barrier dysfunction.

The vascular perspective on acute and chronic lung disease

The pulmonary vasculature has been frequently overlooked in acute and chronic lung diseases, such as acute respiratory distress syndrome (ARDS), pulmonary fibrosis (PF), and chronic obstructive pulmonary disease (COPD). The primary emphasis in the management of these parenchymal disorders has largely revolved around the injury and aberrant repair of epithelial cells. However, there is increasing evidence that the vascular endothelium plays an active role in the development of acute and chronic lung diseases. The endothelial cell network in the capillary bed and the arterial and venous vessels provides a metabolically highly active barrier that controls the migration of immune cells, regulates vascular tone and permeability, and participates in the remodeling processes. Phenotypically and functionally altered endothelial cells, and remodeled vessels, can be found in acute and chronic lung diseases, although to different degrees, likely because of disease-specific mechanisms. Since vascular remodeling is associated with pulmonary hypertension, which worsens patient outcomes and survival, it is crucial to understand the underlying vascular alterations. In this Review, we describe the current knowledge regarding the role of the pulmonary vasculature in the development and progression of ARDS, PF, and COPD; we also outline future research directions with the hope of facilitating the development of mechanism-based therapies.

P53 in endothelial function and unfolded protein response regulation

Vascular barrier dysfunction due to endothelial hyperpermeability has been associated with the pathophysiology of sepsis and severe lung injury, which may inflict acute respiratory distress syndrome (ARDS). Our group is focused on the mechanisms operating towards the regulation of endothelial permeability, to contribute in the development of efficient and targeted countermeasures against ARDS. Unfortunately, the number of ARDS-related deaths in the intensive care units has dramatically increased during the COVID-19 era. The findings described herein inform the corresponding scientific and medical community on the relation of P53 and stress responses in barrier function.

Activating transcription factor 6 protects against endothelial barrier dysfunction

BACKGROUND

Endothelial hyperpermeability is associated with sepsis and acute respiratory distress syndrome (ARDS). The identification of molecular pathways involved in barrier dysfunction; may reveal promising therapeutic targets to combat ARDS. Unfolded protein response (UPR) is a highly conserved molecular pathway, which ameliorates endoplasmic reticulum stress. The present work focuses on the effects of ATF6, which is a UPR sensor, in lipopolysaccharides (LPS)-induced endothelial hyperpermeability.

METHODS

The in vitro effects of AA147 and Ceapin-A7 in LPS-induced endothelial barrier dysfunction were investigated in bovine pulmonary artery endothelial cells (BPAEC). Small interfering (si) RNA was utilized to "silence" ATF6, and electric cell-substrate impedance sensing (ECIS) measured transendothelial resistance. Fluorescein isothiocyanate (FITC)-dextran assay was utilized to assess paracellular permeability. Protein expression levels were evaluated with Western blotting, and cell viability with MTT assay.

RESULTS

We demonstrated that AA147 prevents LPS-induced barrier disruption by counteracting Cofilin and myosin light chain 2 (MLC2) activation, as well as VE-Cadherin phosphorylation. Moreover, this ATF6 inducer opposed LPS-triggered decrease in transendothelial resistance (TEER), as well as LPS-induced paracellular hyperpermeability. On the other hand, ATF6 suppression due to Ceapin-A7 or small interfering RNA exerted the opposite effects, and potentiated LPS-induced endothelial barrier disruption. Moderate concentrations of both ATF6 modulators did not affect cell viability.

CONCLUSIONS

ATF6 activation protects against endothelial barrier function, suggesting that this UPR sensor may serve as a therapeutic target for sepsis and ARDS.

Hsp90 inhibition protects brain endothelial cells against LPS-induced injury

Dysfunction of the blood-brain barrier (BBB) endothelium increases infiltration of lymphocytes and innate immune cells in the brain, leading to the development of neurological disorders. Heat shock protein 90 (Hsp90) inhibitors are anti-inflammatory agents and P53 inducers, which reduce the production of reactive oxygen species (ROS) in a diverse variety of human tissues. In this study, we investigate the effects of those compounds in LPS-induced brain endothelial inflammation, by utilizing human cerebral microvascular endothelial cells (hCMEC/D3). Our results suggest that Hsp90 inhibitors suppress inflammation by inhibiting the LPS-induced signal transducer and activator of transcription 3 (STAT3); and P38 activation. Moreover, those compounds reduce the P53 suppressors murine double minute 2 (MDM2) and murine double minute 4 (MDM4). Immunoglobulin heavy chain binding protein/glucose-regulated protein 78 (BiP/Grp78)-a key element of endothelial barrier integrity-was also increased by Hsp90 inhibition. Hence, we conclude that application of Hsp90 inhibitors in diseases related to BBB dysfunction may deliver a novel therapeutic possibility in the affected population.

Unfolded protein response in endothelial injury

Endothelial barrier dysfunction is associated with sepsis and lung injury, both direct and indirect. We discuss the involvement of unfolded protein response in the protective effects of heat shock protein 90 inhibitors and growth hormone releasing hormone antagonists in the vascular barrier, to reveal new possibilities in acute respiratory distress syndrome treatment.

Tunicamycin Protects against LPS-Induced Lung Injury

The pulmonary endothelium is a dynamic semipermeable barrier that orchestrates tissue-fluid homeostasis; regulating physiological and immunological responses. Endothelial abnormalities are caused by inflammatory stimuli interacting with intracellular messengers to remodel cytoskeletal junctions and adhesion proteins. Those phenomena are associated with sepsis, acute lung injury, and acute respiratory distress syndrome. The molecular processes beyond those responses are the main interest of our group. Unfolded protein response (UPR) is a highly conserved molecular pathway resolving protein-folding defects to counteract cellular threats. An emerging body of evidence suggests that UPR is a promising target against lung and cardiovascular disease. In the present study, we reveal that Tunicamycin (TM) (UPR inducer) protects against lipopolysaccharide (LPS)-induced injury. The barrier function of the inflamed endothelium was evaluated in vitro (transendothelial and paracellular permeability); as well as in mice exposed to TM after LPS. Our study demonstrates that TM supports vascular barrier function by modulating actomyosin remodeling. Moreover, it reduces the internalization of vascular endothelial cadherin (VE-cadherin), enhancing endothelial integrity. We suggest that UPR activation may deliver novel therapeutic opportunities in diseases related to endothelial dysregulation.

P53 mediates the protective effects of metformin in inflamed lung endothelial cells

The endothelial barrier regulates interstitial fluid homeostasis by transcellular and paracellular means. Dysregulation of this semipermeable barrier may lead to vascular leakage, edema, and accumulation of pro-inflammatory cytokines, inducing microvascular hyperpermeability. Investigating the molecular pathways involved in those events will most probably provide novel therapeutic possibilities in pathologies related to endothelial barrier dysfunction. Metformin (MET) is an anti-diabetic drug, opposes malignancies, inhibits cellular transformation, and promotes cardiovascular protection. In the current study, we assess the protective effects of MET in LPS-induced lung endothelial barrier dysfunction and evaluate the role of P53 in mediating the beneficial effects of MET in the vasculature. We revealed that this biguanide (MET) opposes the LPS-induced dysregulation of the lung microvasculature, since it suppressed the formation of filamentous actin stress fibers, and deactivated cofilin. To investigate whether P53 is involved in those phenomena, we employed the fluorescein isothiocyanate (FITC) - dextran permeability assay, to measure paracellular permeability. Our observations suggest that P53 inhibition increases paracellular permeability, and MET prevents those effects. Our results contribute towards the understanding of the lung endothelium and reveal the significant role of P53 in the MET-induced barrier enhancement.

Suppression of reactive oxygen species in endothelial cells by an antagonist of growth hormone-releasing hormone

Growth hormone-releasing hormone (GHRH) is a hypothalamic hormone, which regulates the secretion of growth hormone (GH) from the anterior pituitary gland. The effects of GHRH extend beyond the GH-insulin-like growth factor I axis, and that neuropeptide has been involved in the potentiation of several malignancies and other inflammatory disorders. The development of GHRH antagonists (GHRHAnt) delivers an exciting possibility to counteract the pathogenesis of the GHRH-related effects in human pathophysiology, especially when considered that GHRHAnt support endothelial barrier integrity. Those GHRHAnt-mediated effects are exerted at least in part due to the suppression of major inflammatory pathways, and the modulation of major cytoskeletal components. In the present study, we measured the production of reactive oxygen species (ROS) in bovine pulmonary artery endothelial cells, human cerebral microvascular endothelial cells, and human lung microvascular endothelial cells exposed to GHRH or a commercially available GHRHAnt. Our findings reveal the antioxidative effects of GHRHAnt in all three cell lines, which express GHRH receptors. The redox status of NIH/3T3 cells, which do not produce GHRH receptors, was not significantly affected by GHRH or GHRHAnt. Hence, the application of GHRHAnt in pathologies related to increased ROS production should be further investigated.

Brefeldin A and kifunensine modulate LPS-induced lung endothelial hyperpermeability in human and bovine cells

Endothelial hyperpermeability is the hallmark of acute respiratory distress syndrome (ARDS). Laborious efforts in the investigation of the molecular pathways involved in the regulation of the vascular barrier shall reveal novel therapeutic targets toward that respiratory disorder. Herein, we investigate in vitro the effects of the α-1,2-mannosidase 1 inhibitor kifunensine (KIF) and brefeldin A (BFA) in the lipopolysaccharides (LPS)-induced endothelial breakdown. Our results suggest that BFA opposes the deteriorating effects of KIF [unfolded protein response (UPR) suppressor] toward the lung microvasculature. Since KIF is a UPR suppressor, and brefeldin A is a UPR inducer, we suggest that a carefully devised UPR manipulation may deliver novel therapeutic avenues in diseases related to endothelial barrier dysfunction (e.g., ARDS and sepsis).

Growth Hormone Releasing Hormone in Endothelial Barrier Function

Growth hormone releasing hormone (GHRH) is the integral regulator of the growth hormone (GH)-insulin-like growth factor 1 (IGF-1) axis. It exerts mitogenic effects in a plethora of progressive cancers. Recent evidence suggests the emerging role of that 44-amino acid (aa) neuropeptide in lung endothelial barrier function (EBF), which will be discussed herein.

Restoring the endothelial barrier function in the elderly

Endothelial barrier dysfunction in the elderly has been associated with severe disorders, including acute respiratory distress syndrome, sepsis and COVID-19. Herein we deliver an opinion regarding the development of alternative therapeutic avenues to counteract the pathogenesis of the corresponding diseases.

Insights on supporting the aging brain microvascular endothelium

Blood brain barrier hyperpermeability has been associated with age-related affective disorders, including depression, mania, anxiety, Alzheimer’s and Parkinson’s disease. Our recent efforts suggest that a promising therapeutic approach may arise due to the activation of the unfolded protein response (UPR) element in the affected tissues. Growth hormone releasing hormone antagonists and heat shock protein 90 inhibitors have been shown to induce UPR. This mechanism (UPR) has been associated with tissue repairing processes.

Unfolded Protein Response: A Regulator of the Endothelial Barrier

Recent evidence suggest that the endothelial barrier function is enhanced by the mild activation of the unfolded protein response (UPR), which aims to suppress abnormal increases of endoplasmic reticulum stress. Heat shock protein 90 inhibitors and growth hormone releasing hormone antagonists exert the capacity to activate this multifaceted cellular mechanism (UPR). Thus, investigations on the signalling network involved in those events, may deliver exciting opportunities in diseases related to endothelial barrier dysfunction. The diverse spectrum of those pathologies include sepsis and Acute Respiratory Distress Syndrome (ARDS).

Hsp90 inhibition protects the brain microvascular endothelium against oxidative stress

The brain endothelium is an integral element of the blood-brain barrier (BBB). Dysfunction of this formation due to increased generation of reactive oxygen species (ROS) progresses the establishment of neurological disorders including stroke and traumatic brain injury. Heat shock protein 90 inhibitors are anti-inflammatory agents, and their activities are mediated, at least in part, by P53. This is a tumor suppressor protein which regulates the opposing activities of Rac1 and RhoA in the cellular cytoskeleton. In the present study we investigated the role of Hsp90 inhibitors in the H₂O₂-induced brain endothelium breakdown, by employing human cerebral microvascular endothelial cells (hCMEC/D3). Our findings suggest that H₂O₂ downregulates P53 by enhancing the P53 suppressor mouse double minute 2 homolog (MDM2), as well as by increasing the apyrimidinic endonuclease 1/redox factor 1 (APE1/Ref1). The H₂O₂ – triggered violation of the brain endothelium barrier was reflected in measurements of transendothelial resistance, and the increased expression of the key cytoskeletal modulators cofilin and myosin light chain 2 (MLC2). Treatment of the hCMEC/D3 cells with Hsp90 inhibitors counteracted those events, and reduced the generation of the hydrogen peroxide – induced reactive oxygen species. Hence, our study suggests that Hsp90 inhibition supports the BBB integrity, and may represent a promising therapeutic approach for disorders associated with brain endothelium breakdown; including COVID-19.

Metformin in acute respiratory distress syndrome: An opinion

Senior individuals are more susceptible to the irreversible outcomes of endothelial barrier dysfunction, the hallmark of Acute Respiratory Distress Syndrome (ARDS). The Severe Acute Respiratory Syndrome Coronovirus 2 (SARS-CoV-2) - inflicted ARDS delivers the devastating outcomes of the COVID-19 worldwide. Endothelial hyperpermeability has been associated with both the progression and establishment of the COVID-19 - related respiratory failure. In the present study we investigated the in vitro effects of Metformin in the permeability of bovine pulmonary artery endothelial cells. Our preliminary results suggest that moderate doses (0.1, 0.5, 1.0 mM) of this anti-diabetic agent enhance the vascular barrier integrity, since it produces an increase in the transendothelial resistance of endothelial monolayers. Thus, we speculate that Metformin may deliver a new therapeutic possibility in ARDS, alone or in combination with other barrier enhancers.

Involvement of the unfolded protein response in the protective effects of growth hormone releasing hormone antagonists in the lungs

Growth hormone releasing hormone (GHRH) antagonists enhance endothelial barrier function and counteract the LPS-induced lung endothelial hyperpermeability, the cardinal feature of the acute respiratory distress syndrome (ARDS). The unfolded protein response (UPR) is a multifaceted molecular mechanism, strongly involved in tissue defense against injury. The current study introduces the induction of UPR by GHRH antagonists, since those peptides induced several UPR activation markers, including the inositol-requiring enzyme-1α (IRE1α), the protein kinase RNA-like ER kinase (PERK), and the activating transcription factor 6 (ATF6). On the other hand, the GHRH agonist MR-409 exerted the opposite effects. Furthermore, GHRH antagonists counteracted the kifunensine (UPR suppressor)-induced lung endothelial barrier dysfunction. Our observations suggest that UPR mediates, at least in part, the protective effects of GHRH antagonists in the lung microvasculature. To the best of our knowledge; this is the first study to provide experimental evidence in support of the hypothesis that UPR induction is a novel mechanism by which GHRH antagonists oppose severe human disease, including ARDS.

Unfolded protein response in the COVID-19 context

The unfolded protein response (UPR) maintains cellular homeostasis by regulating key elements of cellular growth and defense. Recent evidence suggests that this mechanism affects the vascular barrier function, by modulating lung endothelial permeability. Dysregulation of this barrier contributes in the irreversible outcomes of the SARS-CoV-2 - inflicted acute respiratory distress syndrome (ARDS). Thus, it is highly probable that the targeted activation of those UPR components in charge of repairing the destructed lung endothelium of the COVID-19 patients, may deliver a promising therapeutic possibility for those subjected to the devastating outcomes of the ongoing pandemic.