Kifunensine compromises lung endothelial barrier function

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.

Research progress on the role of p53 in pulmonary arterial hypertension

PURPOSE OF REVIEW

Pulmonary arterial hypertension (PAH) is a devastating disease characterized by increased pulmonary vascular resistance and pulmonary arterial pressure. At present, the definitive pathology of PAH has not been elucidated and its effective treatment remains lacking. Despite PAHs having multiple pathogeneses, the cancer-like characteristics of cells have been considered the main reason for PAH progression.

RECENT FINDINGS

p53 protein, an important tumor suppressor, regulates a multitude of gene expressions to maintain normal cellular functions and suppress the progression of malignant tumors. Recently, p53 has been found to exert multiple biological effects on cardiovascular diseases. Since PAH shares similar metabolic features with cancer cells, the regulatory roles of p53 in PAH are mainly the induction of cell cycle, inhibition of cell proliferation, and promotion of apoptosis.

SUMMARY

This paper summarized the advanced findings on the molecular mechanisms and regulatory functions of p53 in PAH, aiming to reveal the potential therapeutic targets for PAH.

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.

Protective effects of GHRH antagonists against hydrogen peroxide-induced lung endothelial barrier disruption

PURPOSE

Growth hormone-releasing hormone (GHRH) is a hypothalamic hormone, which regulates growth hormone release from the anterior pituitary gland. GHRH antagonists (GHRHAnt) are anticancer agents, which also exert robust anti-inflammatory activities in malignancies. GHRHAnt exhibit anti-oxidative and anti-inflammatory effects in vascular endothelial cells, indicating their potential use against disorders related to barrier dysfunction (e.g. sepsis). Herein, we aim to investigate the effects of GHRHAnt against lung endothelial hyperpermeability.

METHODS

The in vitro effects of GHRHAnt in H₂O₂-induced endothelial barrier dysfunction were investigated in bovine pulmonary artery endothelial cells (BPAEC). Electric cell-substrate impedance sensing (ECIS) was utilized to measure transendothelial resistance, an indicator of barrier function.

RESULTS

Our results demonstrate that GHRHAnt protect against H₂O₂-induced endothelial barrier disruption via P53 and cofilin modulation. Both proteins are crucial modulators of vascular integrity. Moreover, GHRHAnt prevent H₂O₂ - induced decrease in transendothelial resistance.

CONCLUSIONS

GHRHAnt represent a promising therapeutic intervention towards diseases related to lung endothelial hyperpermeability, such as acute respiratory distress syndrome - related or not to COVID-19 - and sepsis. Targeted medicine for those potentially lethal disorders does not exist.

Growth Hormone-Releasing Hormone in Endothelial Inflammation

The discovery of hypothalamic hormones propelled exciting advances in pharmacotherapy and improved life quality worldwide. Growth hormone-releasing hormone (GHRH) is a crucial element in homeostasis maintenance, and regulates the release of growth hormone from the anterior pituitary gland. Accumulating evidence suggests that this neuropeptide can also promote malignancies, as well as inflammation. Our review is focused on the role of that 44 - amino acid peptide (GHRH) and its antagonists in inflammation and vascular function, summarizing recent findings in the corresponding field. Preclinical studies demonstrate the protective role of GHRH antagonists against endothelial barrier dysfunction, suggesting that the development of those peptides may lead to new therapies against pathologies related to vascular remodeling (eg, sepsis, acute respiratory distress syndrome). Targeted therapies for those diseases do not exist.

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.

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).

Elucidation of the Molecular Pathways Involved in the Protective Effects of AUY-922 in LPS-Induced Inflammation in Mouse Lungs

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) cause thousands of deaths every year and are associated with high mortality rates (~40%) due to the lack of efficient therapies. Understanding the molecular mechanisms associated with those diseases will most probably lead to novel therapeutics. In the present study, we investigated the effects of the Hsp90 inhibitor AUY-922 in the major inflammatory pathways of mouse lungs. Mice were treated with LPS (1.6 mg/kg) via intratracheal instillation for 24 h and were then post-treated intraperitoneally with AUY-922 (10 mg/kg). The animals were examined 48 h after AUY-922 injection. LPS activated the TLR4-mediated signaling pathways, which in turn induced the release of different inflammatory cytokines and chemokines. AUY-922 suppressed the LPS-induced inflammation by inhibiting major pro-inflammatory pathways (e.g., JAK2/STAT3, MAPKs), and downregulated the IL-1β, IL-6, MCP-1 and TNFα. The expression levels of the redox regulator APE1/Ref1, as well as the DNA-damage inducible kinases ATM and ATR, were also increased after LPS treatment. Those effects were counteracted by AUY-922. Interestingly, this Hsp90 inhibitor abolished the LPS-induced pIRE1α suppression, a major component of the unfolded protein response. Our study elucidates the molecular pathways involved in the progression of murine inflammation and supports our efforts on the development of new therapeutics against lung inflammatory diseases and sepsis.

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.

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.

Autophagy, Unfolded Protein Response and Lung Disease

Acute Respiratory Distress Syndrome is a severe disorder affecting thousands of individuals worldwide. The available medical countermeasures do not sufficiently suppress the unacceptable high mortality rates associated with those in need. Thus, intense efforts aim to delineate the function of the lung endothelium, so to deliver new therapeutic approaches against this disease. The present manuscript attempts to shed light on the interrelations between the unfolded protein response and autophagy towards lung disease, to deliver a new line of possible therapeutic approaches against the ferocious Acute Respiratory Distress Syndrome.

Luminespib counteracts the Kifunensine-induced lung endothelial barrier dysfunction

Unfolded protein response (UPR) suppression by Kifunensine has been associated with lung hyperpermeability, the hallmark of Acute Respiratory Distress Syndrome. The present study investigates the effects of the heat shock protein 90 inhibitor Luminespib (AUY-922) towards the Kifunensine-triggered lung endothelial dysfunction. Our results indicate that the UPR inducer Luminespib counteracts the effects of Kifunensine in both human and bovine lung endothelial cells. Hence, we suggest that UPR manipulation may serve as a promising therapeutic strategy against potentially lethal respiratory disorders, including the ARDS related to COVID-19.

P53 in the impaired lungs

Our laboratory is focused on investigating the supportive role of P53 towards the maintenance of lung homeostasis. Acute lung injury, acute respiratory distress syndrome, chronic obstructive pulmonary disease, pulmonary fibrosis, bronchial asthma, pulmonary arterial hypertension, pneumonia and tuberculosis are respiratory pathologies, associated with dysfunctions of this endothelium defender (P53). Herein we review the evolving role of P53 towards the aforementioned inflammatory disorders, to potentially reveal new therapeutic possibilities in pulmonary disease.