mTORC1 Is Involved in Hypoxia-Induced Pulmonary Hypertension Through the Activation of Notch3

RGS10 inhibits proliferation and migration of pulmonary arterial smooth muscle cell in pulmonary hypertension via AKT/mTORC1 signaling

Objective: Excessive proliferation and migration of pulmonary arterial smooth muscle cell (PASMC) is a core event of pulmonary hypertension (PH). Regulators of G protein signaling 10 (RGS10) can regulate cellular proliferation and cardiopulmonary diseases. We demonstrate whether RGS10 also serves as a regulator of PH.Methods: PASMC was challenged by hypoxia to induce proliferation and migration. Adenovirus carrying Rgs10 gene (Ad-Rgs10) was used for external expression of Rgs10. Hypoxia/SU5416 or MCT was used to induce PH. Right ventricular systolic pressure (RVSP) and right ventricular hypertrophy index (RVHI) were used to validate the establishment of PH model.Results: RGS10 was downregulated in hypoxia-challenged PASMC. Ad-Rgs10 significantly suppressed proliferation and migration of PASMC after hypoxia stimulus, while silencing RGS10 showed contrary effect. Mechanistically, we observed that phosphorylation of S6 and 4E-Binding Protein 1 (4EBP1), the main downstream effectors of mammalian target of rapamycin complex 1 (mTORC1) as well as phosphorylation of AKT, the canonical upstream of mTORC1 in hypoxia-induced PASMC were negatively modulated by RGS10. Both recovering mTORC1 activity and restoring AKT activity abolished these effects of RGS10 on PASMC. More importantly, AKT activation also abolished the inhibitory role of RGS10 in mTORC1 activity in hypoxia-challenged PASMC. Finally, we also observed that overexpression of RGS10 in vivo ameliorated pulmonary vascular wall thickening and reducing RVSP and RVHI in mouse PH model.Conclusion: Our findings reveal the modulatory role of RGS10 in PASMC and PH via AKT/mTORC1 axis. Therefore, targeting RGS10 may serve as a novel potent method for the prevention against PH."

Culin5 aggravates hypoxic pulmonary hypertension by activating TRAF6/NF-κB/HIF-1α/VEGF

Hypoxic pulmonary hypertension (HPH) lacks effective pharmacologic treatments. Microarray-based gene expression indicates the crucial role of Cullin 5 (Cul 5) in HPH. This study showed that Cul 5 was upregulated in HPH patients and a murine model of HPH. In vitro, Cul 5 promoted the angiogenesis and adhesion capacity of human pulmonary artery endothelial cells (PAECs), which could be mitigated by Cul 5 inactivation mediated by pevonedistat or NEDD8 silence. In vivo, silencing of Cul 5 in the endothelium and Cul 5 inactivation by pevonedistat could also alleviate hypoxic vascular remodeling. Mechanistic research showed that Cul 5 participated in HPH pathogenesis via the TRAF6/NF-κB/HIF-1α/VEGF pathway. Inhibition of the TRAF6/NF-κB/HIF-1α/VEGF pathway could reverse Cul 5-induced human PAEC dysfunction. These findings demonstrate that Cul 5 is an important mediator of HPH via the TRAF6/NF-κB/HIF-1α/VEGF pathway firstly, and could be considered as a potential therapeutic target in the clinical treatment of HPH.

The combination of high glucose and LPS induces autophagy in bovine kidney epithelial cells via the Notch3/mTOR signaling pathway

BACKGROUND

Aside respiratory diseases, beef cattle may also suffer from serious kidney diseases after transportation. Hyperglycemia and gram-negative bacterial infection may be the main reasons why bovine is prone to severe kidney disease during transportation stress, however, the precise mechanism is still unclear. The purpose of the current study is to explore whether the combined treatment of high glucose (HG) and lipopolysaccharide (LPS) could induce madin-darby bovine kidney (MDBK) cells injury and autophagy, as well as investigate the potential molecular mechanisms involved.

RESULTS

As we discovered, the combined effect of HG and LPS decreased MDBK cells viability. And, HG and LPS combination also induced autophagy in MDBK cells, which was characterized by increasing the expression of LC3-II/I and Beclin1 and decreasing p62 expression. LC3 fluorescence signal formation was also significantly increased by HG and LPS combination treatment. Furthermore, we measured whether the mammalian target of rapamycin (mTOR) and the Notch3 signaling pathways were involved in HG and LPS-induced autophagy. The results showed that the combination of HG and LPS significantly increased the protein expression of Notch3 and decreased protein expression of p-mTOR, indicating that Notch3 and mTOR signaling pathways were activated. However, co-treatment with the Notch3 inhibitor (DAPT) could reverse the induction of autophagy, and increased the protein expression of p-mTOR.

CONCLUSIONS

This study demonstrated that the combination effect of HG and LPS could induce autophagy in MDBK cells, and the Notch3/mTOR signaling pathway was involved in HG and LPS-induced autophagy.

Notch3-Mediated mTOR Signaling Pathway Is Involved in High Glucose-Induced Autophagy in Bovine Kidney Epithelial Cells

It is reported that Notch3 and mTOR signaling pathways are involved in autophagy, and both can be activated by high glucose (HG). However, the relationship between Notch3 and mTOR and how Notch3 affects mTOR to regulate HG-induced autophagy in bovine kidney epithelial cells is still unclear. The purpose of this study is to explore how Notch3 affects mTOR to modulate HG-induced autophagy in bovine kidney cells. Our results showed that HG treatment significantly decreased the cell viability of MDBK cells in a dose-dependent manner. HG treatment significantly increased the expression of LC3-II/I ratio and Beclin1 protein and significantly decreased the expression of p62 protein. Consistently, LC3 fluorescence signal formation was detected by immunofluorescence in both dose and time-dependent manners. In addition, HG treatment significantly increased the expression of Notch3 protein and decreased the expression of the p-mTOR protein in both dose and time-dependent manners. Inhibition of Notch3 upregulated the expression of p-mTOR and p62 protein, and downregulated the expression of LC3-II/I ratio and Beclin1 protein. Besides, the function of Notch3 was investigated. In this study, inhibition of Notch3 activity significantly increased the viability of HG-stimulated MDBK cells. In summary, our results revealed that the Notch3-mediated mTOR signaling pathway was involved in HG-induced autophagy in MDBK cells.

Interleukin-17 aggravates right ventricular remodeling via activating STAT3 under both normoxia and hypoxia

OBJECTIVE

Proinflammatory cytokine interleukin 17 (IL-17) is involved in ventricular remodeling, mainly of the left ventricle. This study was designed to explore the role of IL-17 played in the pathogenesis of right ventricular hypertrophy (RVH), aiming to provide a novel treatment target or diagnostic biomarker options for improving the care of RVH patients.

METHODS

C57BL/6 mice were maintained in 10% O2 chamber or room air for four weeks. Right ventricular hypertrophy index (RVHI), RV/body weight ratio, pulmonary arteriolar remodeling determined by percent media thickness (%MT), and the cardiomyocyte diameter of RV were evaluated. Mice were treated with exogenous recombinant mouse IL-17 (rmIL-17, 1 μg per dose twice a week) for four weeks. H9c2 cardiomyocytes were cultured and treated with IL-17 (10 ng/mL) and STAT3 inhibitor (10 ng/mL) either under normoxia (21% O2, 5% CO2, 74% N2) or under hypoxia (3% O2, 5% CO2, 92% N2). Cardiomyocyte viability was assessed by Cell counting kit 8 (CCK-8) assay. The mRNA level was detected by RT-PCR, where as the protein expression was measured by Western blot, immunohistochemistry, and immunofluorescent analyses.

RESULTS

In vivo experiments showed that IL-17 did not affect the pulmonary artery under normoxia, after treatment with rmIL-17, %MT was not changed, while RVHI and the RV/body weight ratio were increased, indicating that IL-17 directly induced right ventricular hypertrophy. In a time-course study, the mice were exposed to hypoxia for 0, 1, 2, 3, 4 weeks, respectively. We found that the expression of IL-17 was gradually upregulated in RV tissue in a time-dependent manner after one week of hypoxia exposure, especially at the third and fourth week. Cardiomyocyte hypertrophy and apoptosis were observed after the exposure of the mice to hypoxia for four weeks, rmIL-17 further aggravated the hypoxia-induced cardiomyocyte hypertrophy and apoptosis. The expression of p-STAT3 in the IL-17-deficient mice was lower than in the wild-type mice. In vitro, IL-17 inhibited cardiomyocyte viability and induced cardiomyocyte apoptosis via STAT3 under both normoxic and hypoxic conditions.

CONCLUSIONS

These findings support a role for IL-17 as a mediator in the pathogenesis RVH, which might be considered as a potential novel anti-inflammation therapeutic strategy or diagnostic biomarker for RVH.

Hypoxia-induced inhibition of mTORC1 activity in the developing lung: a possible mechanism for the developmental programming of pulmonary hypertension

Perinatal hypoxia induces permanent structural and functional changes in the lung and its pulmonary circulation that are associated with the development of pulmonary hypertension (PH) in later life. The mechanistic target of the rapamycin (mTOR) pathway is vital for fetal lung development and is implicated in hypoxia-associated PH, yet its involvement in the developmental programming of PH remains unclear. Pregnant C57/BL6 dams were placed in hyperbaric (760 mmHg) or hypobaric chambers during gestation (505 mmHg, day 15 through postnatal day 4) or from weaning through adulthood (420 mmHg, postnatal day 21 through 8 wk). Pulmonary hemodynamics and right ventricular systolic pressure (RVSP) were measured at 8 wk. mTOR pathway proteins were assessed in fetal (day 18.5) and adult lung (8 wk). Perinatal hypoxia induced PH during adulthood, even in the absence of a sustained secondary hypoxic exposure, as indicated by reduced pulmonary artery acceleration time (PAAT) and peak flow velocity through the pulmonary valve, as well as greater RVSP, right ventricular (RV) wall thickness, and RV/left ventricular (LV) weight. Such effects were independent of increased blood viscosity. In fetal lung homogenates, hypoxia reduced the expression of critical downstream mTOR targets, most prominently total and phosphorylated translation repressor protein (4EBP1), as well as vascular endothelial growth factor, a central regulator of angiogenesis in the fetal lung. In contrast, adult offspring of hypoxic dams tended to have elevated p4EBP1 compared with controls. Our data suggest that inhibition of mTORC1 activity in the fetal lung as a result of gestational hypoxia may interrupt pulmonary vascular development and thereby contribute to the developmental programming of PH.NEW & NOTEWORTHY We describe the first study to evaluate a role for the mTOR pathway in the developmental programming of pulmonary hypertension. Our findings suggest that gestational hypoxia impairs mTORC1 activation in the fetal lung and may impede pulmonary vascular development, setting the stage for pulmonary vascular disease in later life.

The pathophysiological role of novel pulmonary arterial hypertension gene SOX17

Pulmonary arterial hypertension (PAH) is a progressive disease predominantly targeting pre-capillary blood vessels. Adverse structural remodelling and increased pulmonary vascular resistance result in cardiac hypertrophy and ultimately failure of the right ventricle. Recent whole-genome and whole-exome sequencing studies have identified SOX17 as a novel risk gene in PAH, with a dominant mode of inheritance and incomplete penetrance. Rare deleterious variants in the gene and more common variants in upstream enhancer sites have both been associated with the disease, and a deficiency of SOX17 expression may predispose to PAH. This review aims to consolidate the evidence linking genetic variants in SOX17 to PAH, and explores the numerous targets and effects of the transcription factor, focusing on the pulmonary vasculature and the pathobiology of PAH.

mTOR Signaling in Pulmonary Vascular Disease: Pathogenic Role and Therapeutic Target

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease without a cure. The exact pathogenic mechanisms of PAH are complex and poorly understood, yet a number of abnormally expressed genes and regulatory pathways contribute to sustained vasoconstriction and vascular remodeling of the distal pulmonary arteries. Mammalian target of rapamycin (mTOR) is one of the major signaling pathways implicated in regulating cell proliferation, migration, differentiation, and protein synthesis. Here we will describe the canonical mTOR pathway, structural and functional differences between mTOR complexes 1 and 2, as well as the crosstalk with other important signaling cascades in the development of PAH. The pathogenic role of mTOR in pulmonary vascular remodeling and sustained vasoconstriction due to its contribution to proliferation, migration, phenotypic transition, and gene regulation in pulmonary artery smooth muscle and endothelial cells will be discussed. Despite the progress in our elucidation of the etiology and pathogenesis of PAH over the two last decades, there is a lack of effective therapeutic agents to treat PAH patients representing a significant unmet clinical need. In this review, we will explore the possibility and therapeutic potential to use inhibitors of mTOR signaling cascade to treat PAH.

Astragaloside IV attenuates hypoxia‑induced pulmonary vascular remodeling via the Notch signaling pathway

The Notch signaling pathway participates in pulmonary artery smooth muscle cell (PASMC) proliferation and apoptosis. Astragaloside IV (AS-IV) is an effective antiproliferative treatment for vascular diseases. The present study aimed to investigate the protective effects and mechanisms underlying AS-IV on hypoxia-induced PASMC proliferation and pulmonary vascular remodeling in pulmonary arterial hypertension (PAH) model rats. Rats were divided into the following four groups: i) normoxia; ii) hypoxia (10% O₂); iii) treatment, hypoxia + intragastrical administration of AS-IV (2 mg/kg) daily for 28 days; and iv) DAPT, hypoxia + AS-IV treatment + subcutaneous administration of DAPT (10 mg/kg) three times daily. The effects of AS-IV treatment on the development of hypoxia-induced PAH, right ventricle (RV) hypertrophy and pulmonary vascular remodeling were examined. Furthermore, PASMCs were treated with 20 µmol/l AS-IV under hypoxic conditions for 48 h. To determine the effect of Notch signaling in vascular remodeling and the potential mechanisms underlying AS-IV treatment, 5 mmol/l γ-secretase inhibitor [N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT)] was used. Cell viability and apoptosis were determined by performing the MTT assay and flow cytometry, respectively. Immunohistochemistry was conducted to detect the expression of proliferating cell nuclear antigen (PCNA). Moreover, the mRNA and protein expression levels of Notch-3, Jagged-1, hes family bHLH transcription factor 5 (Hes-5) and PCNA were measured via reverse transcription-quantitative PCR and western blotting, respectively. Compared with the normoxic group, hypoxia-induced PAH model rats displayed characteristics of PAH and RV hypertrophy, whereas AS-IV treatment alleviated PAH and prevented RV hypertrophy. AS-IV also inhibited hypoxia-induced pulmonary vascular remodeling, as indicated by reduced wall thickness and increased lumen diameter of pulmonary arterioles, and decreased muscularization of distal pulmonary vasculature in hypoxia-induced PAH model rats. Compared with normoxia, hypoxia promoted PASMC proliferation in vitro, whereas AS-IV treatment inhibited hypoxia-induced PASMC proliferation by downregulating PCNA expression in vitro and in vivo. In hypoxia-treated PAH model rats and cultured PASMCs, AS-IV treatment reduced the expression levels of Jagged-1, Notch-3 and Hes-5. Furthermore, Notch signaling inhibition via DAPT significantly inhibited the pulmonary vascular remodeling effect of AS-IV in vitro and in vivo. Collectively, the results indicated that AS-IV effectively reversed hypoxia-induced pulmonary vascular remodeling and PASMC proliferation via the Notch signaling pathway. Therefore, the present study provided novel insights into the mechanism underlying the use of AS-IV for treatment of vascular diseases, such as PAH.

Notch3 signalling and vascular remodelling in pulmonary arterial hypertension

Notch signalling is critically involved in vascular morphogenesis and function. Four Notch isoforms (Notch1–4) regulating diverse cellular processes have been identified. Of these, Notch3 is expressed almost exclusively in vascular smooth muscle cells (VSMCs), where it is critically involved in vascular development and differentiation. Under pathological conditions, Notch3 regulates VSMC switching between the contractile and synthetic phenotypes. Abnormal Notch3 signalling plays an important role in vascular remodelling, a hallmark of several cardiovascular diseases, including pulmonary arterial hypertension (PAH). Because of the importance of Notch3 in VSMC (de)differentiation, Notch3 has been implicated in the pathophysiology of pulmonary vascular remodelling in PAH. Here we review the current literature on the role of Notch in VSMC function with a focus on Notch3 signalling in pulmonary artery VSMCs, and discuss potential implications in pulmonary artery remodelling in PAH.

Notch3 in Development, Health and Disease

Notch3 is one of four mammalian Notch proteins, which act as signalling receptors to control cell fate in many developmental and adult tissue contexts. Notch signalling continues to be important in the adult organism for tissue maintenance and renewal and mis-regulation of Notch is involved in many diseases. Genetic studies have shown that Notch3 gene knockouts are viable and have limited developmental defects, focussed mostly on defects in the arterial smooth muscle cell lineage. Additional studies have revealed overlapping roles for Notch3 with other Notch proteins, which widen the range of developmental functions. In the adult, Notch3, in collaboration with other Notch proteins, is involved in stem cell regulation in different tissues in stem cell regulation in different tissues, and it also controls the plasticity of the vascular smooth muscle phenotype involved in arterial vessel remodelling. Overexpression, gene amplification and mis-activation of Notch3 are associated with different cancers, in particular triple negative breast cancer and ovarian cancer. Mutations of Notch3 are associated with a dominantly inherited disease CADASIL (cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy), and there is further evidence linking Notch3 misregulation to hypertensive disease. Here we discuss the distinctive roles of Notch3 in development, health and disease, different views as to the underlying mechanisms of its activation and misregulation in different contexts and potential for therapeutic intervention.

A high-dose rapamycin treatment alleviates hepatopulmonary syndrome in cirrhotic rats

BACKGROUND

Rapamycin is a type of immunosuppressive agent that acts through inhibition of mammalian target of rapamycin (mTOR). Hepatopulmonary syndrome (HPS) is a lethal complication in cirrhotic patients. It is characterized by hypoxia and increased intrapulmonary shunts, in which pulmonary inflammation and angiogenesis play important roles. The current study aimed to evaluate the effect of rapamycin on HPS using the experimental model of common bile duct ligation (CBDL)-induced cirrhosis in rats.

METHODS

The rats received low-dose (0.5 mg/kg), high-dose (2 mg/kg) rapamycin, or vehicle from the 15th to the 28th day post CBDL. Then the mortality rate, hemodynamics, biochemistry parameters, arterial blood gas and plasma levels of vascular endothelial growth factor (VEGF) and tumor necrosis factor (TNF)-α were evaluated on the 28th day post CBDL. Pulmonary histopathological stains were performed, and protein expression was examined. In parallel groups, the intrapulmonary shunts of CBDL rats were measured.

RESULTS

Compared with the control, a high-dose rapamycin treatment decreased portal pressure and improved hypoxia in CBDL rats. It also reduced the plasma level of VEGF and TNF-α and decreased intrapulmonary shunts. Meanwhile, it ameliorated pulmonary inflammation and angiogenesis and downregulated the protein expression of mTOR, P70S6K, nuclear factor kappa B (NFκB), VEGF, and VEGF receptor 2. In contrast, low-dose rapamycin did not attenuate intrapulmonary shunts despite ameliorating portal hypertension.

CONCLUSION

High-dose rapamycin ameliorates HPS in cirrhotic rats as evidenced by the alleviated hypoxia and decreased intrapulmonary shunts. Downregulation of the mTOR/P70S6K, NFκB, and VEGF signaling pathways might play a key role.

Autophagy and its role in pulmonary hypertension

Pulmonary hypertension (PH) is a very common kind of pulmonary vascular disease, which can cause a heavier burden on patient's quality of life, even lead to death. Yet, the mechanism of PH is incomprehensive and not so clear nowadays. In recent years, more and more studies show that autophagy plays a pivotal role in the development of PH. Some modalities target on the formation or maturation of autophagosome that has emerged from our increasing knowledge of autophagy machinery, which may prevent or eliminate the process of PH. The deciphering of molecular selectivity of autophagy has also been a source of novel modulators that act specifically on selective forms of autophagy. Tremendous recent progress has opened a new possibility for modulating autophagy in complex diseases. Thus, autophagy may become a prospective choice for treatment of PH. Herein, we reviewed the literatures and discussed the role of autophagy in the development and treatment of PH.

Notch3 signaling activation in smooth muscle cells promotes extrauterine growth restriction-induced pulmonary hypertension

BACKGROUND AND AIMS

Early postnatal life is a critical developmental period that affects health of the whole life. Extrauterine growth restriction (EUGR) causes cardiovascular development problems and diseases, including pulmonary arterial hypertension (PAH). PAH is characterized by proliferation, migration, and anti-apoptosis of pulmonary artery smooth muscle cells (PASMCs). However, the role of PASMCs in EUGR has not been studied. Thus, we hypothesized that PASMCs dysfunction played a role in EUGR-induced pulmonary hypertension.

METHODS AND RESULTS

Here we identified that postnatal nutritional restriction-induced EUGR rats exhibited an elevated mean pulmonary arterial pressure and vascular remodeling at 12 weeks old. PASMCs of EUGR rats showed increased cell proliferation and migration features. In EUGR-induced PAH rats, Notch3 signaling was activated. Relative mRNA and protein expression levels of Notch3 intracellular domain (Notch3 ICD), and Notch target gene Hey1 in PASMCs were upregulated. We further demonstrated that pharmacological inhibition of Notch3 activity by using a γ-secretase inhibitor DAPT, which blocked the cleavage of Notch proteins to ICD peptides, could effectively inhibit PASMC proliferation. Specifically knocked down of Notch3 in rat PASMCs by shRNA restored the abnormal PASMC phenotype in vitro. We found that administration of Notch signaling inhibitor DAPT could successfully reduce mean pulmonary arterial pressure in EUGR rats.

CONCLUSIONS

The present study demonstrated that upregulation of Notch3 signaling in PASMCs was crucial for the development of EUGR-induced PAH. Blocking Notch3-Hey1 signaling pathway in PASMCs provides a potential therapeutic target for PAH.

Bone marrow mesenchymal stem cells-derived conditioned medium protects cardiomyocytes from hypoxia/reoxygenation-induced injury through Notch2/mTOR/autophagy signaling

Bone marrow mesenchymal stem cells (BMSC) can ameliorate ischemic injury of various tissues. However, the molecular mechanisms involved remain to be clarified. In this study, we intend to investigate the effects of BMSC-derived conditioned medium (BMSC-CM) on hypoxia/reoxygenation (H/R)-induced injury of H9c2 myocardial cells, and the potential mechanisms. Cell injury was determined through level of cell viability, lactate dehydrogenase (LDH) release, total intracellular reactive oxygen species (ROS), mitochondrial membrane potential (Δψm), and cell apoptosis. Autophagic activity of cells was detected through levels of the autophagy-associated proteins and autophagic flux. Results showed that BMSC-CM alleviated H/R-induced injury in H9c2 cells, as demonstrated by increased cell viability and Δψm, decreased ROS production, LDH release, and cell apoptosis. Furthermore, the H/R treatment induced a decrease in autophagic activity and an increase in Notch2 signaling activation in H9c2 cells. In the presence of BMSC-CM, the autophagic activity impaired by the H/R treatment was upregulated with decreased phosphorylation of mTOR, and the activation of Notch2 signaling was downregulated. These effects of BMSC-CM could be replicated by Notch signaling inhibitor. In contrast, inhibitors of cell autophagy including chloroquine (CQ) and 3-methyladenine, diminished the protective effects of BMSC-CM. Taken together results, our study showed that BMSC-CM could protect H9c2 cells from H/R-induced injury potentially through regulating Notch2/mTOR/autophagy signaling. These findings may provide a novel insight into the mechanisms of BMSC-CM in therapy of myocardial ischemia/reperfusion injury as well as other ischemic diseases.

Modulation of autophagy in human diseases strategies to foster strengths and circumvent weaknesses

Autophagy is central to the maintenance of intracellular homeostasis across species. Accordingly, autophagy disorders are linked to a variety of diseases from the embryonic stage until death, and the role of autophagy as a therapeutic target has been widely recognized. However, autophagy-associated therapy for human diseases is still in its infancy and is supported by limited evidence. In this review, we summarize the landscape of autophagy-associated diseases and current autophagy modulators. Furthermore, we investigate the existing autophagy-associated clinical trials, analyze the obstacles that limit their progress, offer tactics that may allow barriers to be overcome along the way and then discuss the therapeutic potential of autophagy modulators in clinical applications.

Targeting IL-17 attenuates hypoxia-induced pulmonary hypertension through downregulation of β-catenin

BACKGROUND

The role of interleukin 17 (IL-17) in hypoxic pulmonary hypertension (HPH) remains unclear. This study is designed to explore whether IL-17 is a potential target for HPH treatment.

METHODS

Clinic samples from the lung tissue and serum were obtained from qualified patients. Western blotting, immunohistochemistry and/or ELISA were used to measure the expression of relevant proteins. HPH models were established in C57BL/6 wild-type (WT) and IL-17 ^-/- mice and were treated with exogenous recombinant mouse IL-17 (rmIL-17) or an IL-17 neutralising antibody. Assays for cell proliferation, angiogenesis and adhesion were employed to analyse the behaviours of human pulmonary arterial endothelial cells (HPAECs). A non-contact Transwell coculture model was used to evaluate intercellular interactions.

RESULTS

Expression of IL-17 was increased in lung tissue of both patients with bronchiectasis/COPD-associated PH and HPH mouse model. Compared with WT mice, IL-17 ^-/- mice had attenuated HPH, whereas administration of rmIL-17 aggravated HPH. In vitro, recombinant human IL-17 (rhIL-17) promoted proliferation, angiogenesis and adhesion in HPAECs through upregulation of Wnt3a/β-catenin/CyclinD1 pathway, and siRNA-mediated knockdown of β-catenin almost completely reversed this IL-17-mediated phenomena. IL-17 promoted the proliferation but not the migration of human pulmonary arterial smooth muscle cells (HPASMCs) cocultured with HPAECs under both normoxia and hypoxia, but IL-17 had no direct effect on proliferation and migration of HPASMCs. Blockade of IL-17 with a neutralising antibody attenuated HPH in WT mice.

CONCLUSIONS

IL-17 contributes to the pathogenesis of HPH through upregulation of β-catenin expression. Targeting IL-17 might provide potential benefits for alternative therapeutic strategies for HPH.

Autophagy and pulmonary disease

Autophagy is a process of cell self-renewal that is dependent on the degradation of the cytoplasmic proteins or organelles of lysosomes. Many diseases, such as metabolic diseases, cancer, neurodegenerative diseases, and lung diseases, have been confirmed to be associated with elevated or impaired levels of autophagy. At present, studies have found that autophagy participates in the regulation of chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis, pulmonary hypertension, acute lung injury, lung cancer, and other pulmonary diseases. Using recent literature on the signal transduction mechanisms of autophagy and the effects of autophagy signalling on lung diseases, this review intends to clarify the mechanisms of lung disease to guide the treatment of related diseases. The reviews of this paper are available via the supplemental material section.

Pathogenic Role of mTORC1 and mTORC2 in Pulmonary Hypertension

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G protein-coupled receptors and tyrosine kinase receptors signal through the phosphoinositide 3-kinase/Akt/mTOR pathway to induce cell proliferation, survival, and growth. mTOR is a kinase present in 2 functionally distinct complexes, mTORC1 and mTORC2.

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Functional disruption of mTORC1 by knockout of Raptor (regulatory associated protein of mammalian target of rapamycin) in smooth muscle cells ameliorated the development of experimental PH.

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Functional disruption of mTORC2 by knockout of Rictor (rapamycin insensitive companion of mammalian target of rapamycin) caused spontaneous PH by up-regulating platelet-derived growth factor receptors.

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Use of mTOR inhibitors (e.g., rapamycin) to treat PH should be accompanied by inhibitors of platelet-derived growth factor receptors (e.g., imatinib).

Concentric lung vascular wall thickening due to enhanced proliferation of pulmonary arterial smooth muscle cells is an important pathological cause for the elevated pulmonary vascular resistance reported in patients with pulmonary arterial hypertension. We identified a differential role of mammalian target of rapamycin (mTOR) complex 1 and complex 2, two functionally distinct mTOR complexes, in the development of pulmonary hypertension (PH). Inhibition of mTOR complex 1 attenuated the development of PH; however, inhibition of mTOR complex 2 caused spontaneous PH, potentially due to up-regulation of platelet-derived growth factor receptors in pulmonary arterial smooth muscle cells, and compromised the therapeutic effect of the mTOR inhibitors on PH. In addition, we describe a promising therapeutic strategy using combination treatment with the mTOR inhibitors and the platelet-derived growth factor receptor inhibitors on PH and right ventricular hypertrophy. The data from this study provide an important mechanism-based perspective for developing novel therapies for patients with pulmonary arterial hypertension and right heart failure.

Characteristics of circular RNA expression in lung tissues from mice with hypoxia‑induced pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening lung disease, characterized by an increase in pulmonary arterial pressure caused by vasoconstriction and vascular remodeling. The pathogenesis of PH is not fully understood, and there is a lack of potential biomarkers for the diagnosis and treatment of patients with PH. Non-coding RNAs with a characteristic covalently closed loop structure, termed circular RNAs (circRNAs), are present in a number of pulmonary diseases. To the best of our knowledge, the present study is the first to use microarray analysis to determine the expression profile of circRNAs in lung tissues from mice with hypoxia-induced PH. In total, 23 significantly upregulated and 41 significantly down-regulated circRNAs were identified. Of these, 12 differentially expressed circRNAs were selected for further validation using reverse transcription-quantitative polymerase chain reaction. Putative microRNAs (miRNAs) that bind to the dysregulated circRNAs were predicted. Subsequently, bioinformatics tools were used to construct circRNA-miRNA-mRNA networks for the two most promising circRNAs, namely mmu_circRNA_004592 and mmu_circRNA_018351. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses of target genes of the dysregulated circRNAs revealed that these dysregulated circRNAs may serve an important role in the pathogenesis of hypoxia-induced PH. Therefore, these dysregulated circRNAs are candidate diagnostic biomarkers and potential therapeutic targets for PH.

IL-33 Initiates Vascular Remodelling in Hypoxic Pulmonary Hypertension by up-Regulating HIF-1α and VEGF Expression in Vascular Endothelial Cells

IL-33 may play a role in the vascular remodelling of hypoxic pulmonary hypertension (PH) but the precise mechanisms are still unclear. We hypothesized that hypoxia promotes expression of IL-33 and its receptor ST2 on vascular endothelial cells, which in turn leads to dysfunction of vascular endothelial cells and smooth muscle cells contributing to PH. Immunohistochemistry showed that immunoreactivity for IL-33 and ST2 was significantly increased in lung tissue of murine model of hypoxia-induced PH (HPH) and of subjects with bronchiectasis-PH. trans-Thoracic echocardiography showed that haemodynamic changes and right ventricular hypertrophy associated with HPH were significantly abrogated in St2^−/− compared with WT mice. Administration of IL-33 further exacerbated these changes in the hypoxia-exposed WT mice. In vitro, hypoxia significantly increased IL-33/ST2 expression by human pulmonary arterial endothelial cells (HPAECs), while exogenous IL-33 enhanced proliferation, adhesiveness and spontaneous angiogenesis of HPAECs. Knockdown of endogenous Il33 or St2 using siRNA transfection significantly suppressed these effects in both normoxic and hypoxic culture-conditions. Deletion of the St2 gene attenuated hypoxia-induced, elevated lung expression of HIF-1α/VEGFA/VEGFR-2/ICAM-1, while administration of exogenous VEGFA partially reversed the attenuation of the haemodynamic indices of PH. Correspondingly, knockdown of the St2 or Hif1α genes almost completely abrogated IL-33-induced expression of HIF-1α/VEGFA/VEGFR-2 by HPAECs in vitro. Further, IL-33-induced angiogenesis by HPAECs was extensively abrogated by knockdown of the Hif1α/Vegfa or Vegfr2 genes. These data suggest that hypoxia induces elevated expression of IL-33/ST2 by HPAECs which, at least partly by increasing downstream expression of HIF-1α and VEGF initiates vascular remodelling resulting in HPH.

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Evidence before this study

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We have been focusing on the role of cytokines in the pathogenesis of chronic pulmonary diseases for a long time, including asthma, COPD, fibrosis and bronchiectasis. We and others found that IL-33 might contribute to the occurrence and prognosis of many other diseases through binding its receptor ST2. Based on these findings, we were very eager to know whether IL-33/ST2 axis also exerts a role in hypoxia-induced pulmonary hypertension (HPH), a complication of many chronic respiratory diseases. Although it is well known that HIF-1α and VEGF play critical role in this complication, it is still unclear what the upstream of HIF-1α and VEGF is. Therefore, we first tested immunoreactivity for IL-33 and its receptor ST2 in the lung tissue sections derived from surgical specimens and from our established murine models of HPH. Surprisingly, we noted the increased immunoreactivity for both targets in these tissue sections. These findings inspired us to further explore the details of IL-33/ST2 in the pathogenesis of HPH.

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Added value of this study

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HPH is a life-threatening complication because there is lack of effective treatment. Although pulmonary arteries and ventricular remodelling might be mainly involved in the pathogenesis of the disease, the precise mechanisms are largely unknown. In the present study, we showed that hypoxia is a critical driver which induced expression of IL-33 and ST2 by endothelial cells. These factors, in turn triggered expression of HIF-1α and VEGF by endothelial cells and led to proliferation, adhesion and tube formation of these cells. We also showed that in the presence of IL-33, endothelial cells were able to affect proliferation and migration of artery smooth muscle cells, although IL-33 alone did not have such effects. These findings suggest that hypoxia and IL-33/ST2 might be initiators for HPH, through regulating downstream factors HIF-1α and VEGF.

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Implications of all the available evidence

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Our data suggest that IL-33/ST2 axis plays critical role in the pathogenesis of hypoxia-induced pulmonary hypertension because depletion of these molecules much remitted the phenomenon of complication. These observations might provide alternative therapeutic strategy for clinical treatment of HPH.

Clinical characteristics in lymphangioleiomyomatosis-related pulmonary hypertension: an observation on 50 patients

Lymphangioleiomyomatosis (LAM) is a rare diffuse cystic lung disease. Knowledge on LAM-related pulmonary hypertension (PH) is limited. This study aimed to analyze the clinical characteristics of LAM with elevated pulmonary artery pressure (PAP) and evaluate the potential efficacy of sirolimus. The study involved 50 LAM patients who underwent echocardiography. According to the tricuspid regurgitation velocity (TRV), these patients were divided into the TRV ⩽ 2.8 m/s group and TRV > 2.8 m/s group. Both groups comprised 25 females with an average age of 38.6 ± 8.1 and 41.5 ± 8.9 years. In the TRV > 2.8 m/s group, the estimated systolic PAP (SPAP) was significantly elevated (52.08 ± 12.45 mmHg vs. 30.24 ± 5.25 mmHg, P < 0.01). Linear analysis showed that SPAP was correlated with forced expiratory volume in 1 s (FEV₁), diffusing capacity of the lungs for carbon monoxide, alveolar arterial oxygen gradient (P_A-aO₂), and 6 min walking distance (r =-0.392, -0.351, 0.450, and -0.591, respectively; P < 0.05), in which P_A-aO₂ was a risk factor for SPAP elevation (β = 0.064, OR = 1.066, P < 0.05). Moreover, in 10 patients who received sirolimus therapy, SPAP decreased from 57.0 12.6 mmHg to 35.2 ± 11.1 mmHg. The study showed that LAM patients with PH exhibit poor pulmonary function and hypoxemia and may benefit from sirolimus treatment.

mTOR-Notch3 signaling mediates pulmonary hypertension in hypoxia-exposed neonatal rats independent of changes in autophagy

BACKGROUND/AIM

Mammalian target of rapamycin (mTOR) is a pivotal regulator of cell proliferation, survival, and autophagy. Autophagy is increased in adult experimental chronic pulmonary hypertension (PHT), but its contributory role to pulmonary vascular disease remains uncertain and has yet to be explored in the neonatal animal. Notch is a major pro-proliferative pathway activated by mTOR. A direct relationship between autophagy and Notch signaling has not been previously explored. Our aim was to examine changes in mTOR-, Notch-, and autophagy-related pathways and the therapeutic effects of autophagy modulators in experimental chronic neonatal PHT secondary to chronic hypoxia.

METHODS

Rat pups were exposed to normoxia or hypoxia (13% O₂ ) from postnatal days 1-21, while receiving treatment with temsirolimus (mTOR inhibitor), DAPT (Notch inhibitor), or chloroquine (inhibitor of autophagic flux).

RESULTS

Exposure to hypoxia up-regulated autophagy and Notch3 signaling markers in lung, pulmonary artery (PA), and PA-derived smooth muscle cells (SMCs). Temsirolimus prevented chronic PHT and attenuated PA and SMC signaling secondary to hypoxia. These effects were replicated by DAPT. mTOR or Notch inhibition also down-regulated smooth muscle content of platelet-derived growth factor β-receptor, a known contributor to vascular remodeling. In contrast, chloroquine had no modifying effects on markers of chronic PHT. Knockdown of Beclin-1 in SMCs had no effect on hypoxia-stimulated Notch3 signaling.

CONCLUSIONS

mTOR-Notch3 signaling plays a critical role in experimental chronic neonatal PHT. Inhibition of autophagy did not suppress Notch signaling and had no effect on markers of chronic PHT.

Pharmacological modulation of autophagy: therapeutic potential and persisting obstacles

Autophagy is central to the maintenance of organismal homeostasis in both physiological and pathological situations. Accordingly, alterations in autophagy have been linked to clinically relevant conditions as diverse as cancer, neurodegeneration and cardiac disorders. Throughout the past decade, autophagy has attracted considerable attention as a target for the development of novel therapeutics. However, such efforts have not yet generated clinically viable interventions. In this Review, we discuss the therapeutic potential of autophagy modulators, analyse the obstacles that have limited their development and propose strategies that may unlock the full therapeutic potential of autophagy modulation in the clinic.

A Time- and Compartment-Specific Activation of Lung Macrophages in Hypoxic Pulmonary Hypertension

Studies in various animal models suggest an important role for pulmonary macrophages in the pathogenesis of pulmonary hypertension (PH). Yet, the molecular mechanisms characterizing the functional macrophage phenotype relative to time and pulmonary localization and compartmentalization remain largely unknown. In this study, we used a hypoxic murine model of PH in combination with FACS to quantify and isolate lung macrophages from two compartments over time and characterize their programing via RNA sequencing approaches. In response to hypoxia, we found an early increase in macrophage number that was restricted to the interstitial/perivascular compartment, without recruitment of macrophages to the alveolar compartment or changes in the number of resident alveolar macrophages. Principal component analysis demonstrated significant differences in overall gene expression between alveolar and interstitial macrophages (IMs) at baseline and after 4 and 14 d hypoxic exposure. Alveolar macrophages at both day 4 and 14 and IMs at day 4 shared a conserved hypoxia program characterized by mitochondrial dysfunction, proinflammatory gene activation, and mTORC1 signaling, whereas IMs at day 14 demonstrated a unique anti-inflammatory/proreparative programming state. We conclude that the pathogenesis of vascular remodeling in hypoxic PH involves an early compartment-independent activation of lung macrophages toward a conserved hypoxia program, with the development of compartment-specific programs later in the course of the disease. Thus, harnessing time- and compartment-specific differences in lung macrophage polarization needs to be considered in the therapeutic targeting of macrophages in hypoxic PH and potentially other inflammatory lung diseases.

Follistatin-like 1 protects against hypoxia-induced pulmonary hypertension in mice

Pulmonary hypertension (PH) remains a life-limiting disease characterized by pulmonary vascular remodelling due to aberrant proliferation and migration of pulmonary artery smooth muscle cells (PASMCs), thus leading to raised pulmonary arterial pressure and right ventricular hypertrophy. Secreted glycoprotein follistatin-like 1 (FSTL1) has been reported to ameliorate tissue remodelling in cardiovascular injuries. However, the role of FSTL1 in deranged pulmonary arteries remains elusive. We found that there were higher serum levels of FSTL1 in patients with PH related to chronic obstructive pulmonary diseases (COPD) and in mice model of hypoxia-induced PH (HPH). Haploinsufficiency of Fstl1 in mice contributed to an exacerbated HPH, as demonstrated by increased right ventricular systolic pressure, pulmonary arterial muscularization and right ventricular hypertrophy index. Conversely, FSTL1 administration attenuated HPH. In cultured human PASMCs, hypoxia-promoted cellular viability, DNA synthesis and migration were suppressed by exogenous FSTL1 but enhanced by small interfering RNA targeting FSTL1. Additionally, FSTL1 inhibited the proliferation and migration of PASMCs via extracellular regulated kinase (ERK) signal pathway. All these findings indicate that FSTL1 imposed a protective modulation on pulmonary vascular remodelling, thereby suggesting its role in the regulation of HPH.

Suppression of NADPH oxidase attenuates hypoxia-induced dysfunctions of endothelial progenitor cells

NADPH oxidases (NOX) - derived reactive oxygen species (ROS) contribute to oxidative injury in hypoxia-induced pulmonary arterial hypertension. This study aims to evaluate the status of NOX in endothelial progenitor cells (EPCs) under hypoxic condition and to determine whether NOX inhibitors could attenuate hypoxia-induced dysfunctions of EPCs. EPCs were isolated from peripheral blood of SD rats and subjected to hypoxia (O₂/N₂/CO₂, 1/94/5) for 24 h. The cells were collected for β-galactosidase or Hoechst staining, or for functional analysis (migration, adhesion and tube formation). The NOX expression, activity and H₂O₂ content in EPCs were measured. The results showed that hypoxia treatment promoted EPC senescence and apoptosis, accompanied by the deteriorated functions of EPCs (the reduced abilities in adhesion, migration and tube formation), as well as an increase in NOX2 and NOX4 expression, NOX activity and H₂O₂ production, these phenomena were attenuated by NOX inhibitors. Furthermore, administration of catalase could also improve the functions of hypoxia-treated EPCs. Based on these observations, we conclude that NOX-derived ROS contributes to the dysfunctions of EPCs under hypoxic condition. Thus, suppression of NOX may provide a novel strategy to improve endothelial functions in hypoxia-relevant diseases.

Up-regulation of the mammalian target of rapamycin complex 1 subunit Raptor by aldosterone induces abnormal pulmonary artery smooth muscle cell survival patterns to promote pulmonary arterial hypertension

Activation of the mammalian target of rapamycin complex 1 (mTORC1) subunit Raptor induces cell growth and is a downstream target of Akt. Elevated levels of aldosterone activate Akt, and, in pulmonary arterial hypertension (PAH), correlate with pulmonary arteriole thickening, which suggests that mTORC1 regulation by aldosterone may mediate adverse pulmonary vascular remodeling. We hypothesized that aldosterone-Raptor signaling induces abnormal pulmonary artery smooth muscle cell (PASMC) survival patterns to promote PAH. Remodeled pulmonary arterioles from SU-5416/hypoxia-PAH rats and monocrotaline-PAH rats with hyperaldosteronism expressed increased levels of the Raptor target, p70S6K, which provided a basis for investigating aldosterone-Raptor signaling in human PASMCs. Aldosterone (10(-9) to 10(-7) M) increased Akt/mTOR/Raptor to activate p70S6K and increase proliferation, viability, and apoptosis resistance in PASMCs. In PASMCs transfected with Raptor-small interfering RNA or treated with spironolactone/eplerenone, aldosterone or pulmonary arterial plasma from patients with PAH failed to increase p70S6K activation or to induce cell survival in vitro Optimal inhibition of pulmonary arteriole Raptor was achieved by treatment with Staramine-monomethoxy polyethylene glycol that was formulated with Raptor-small interfering RNA plus spironolactone in vivo, which decreased arteriole muscularization and pulmonary hypertension in 2 experimental animal models of PAH in vivo Up-regulation of mTORC1 by aldosterone is a critical pathobiologic mechanism that controls PASMC survival to promote hypertrophic vascular remodeling and PAH.-Aghamohammadzadeh, R., Zhang, Y.-Y., Stephens, T. E., Arons, E., Zaman, P., Polach, K. J., Matar, M., Yung, L.-M., Yu, P. B., Bowman, F. P., Opotowsky, A. R., Waxman, A. B., Loscalzo, J., Leopold, J. A., Maron, B. A. Up-regulation of the mammalian target of rapamycin complex 1 subunit Raptor by aldosterone induces abnormal pulmonary artery smooth muscle cell survival patterns to promote pulmonary arterial hypertension.

Salusin-β contributes to vascular inflammation associated with pulmonary arterial hypertension in rats

OBJECTIVE

Inflammation is closely linked to pulmonary arterial hypertension (PAH). Salusin-β, a bioactive peptide, has been reported to participate in vascular inflammation. We therefore hypothesized that salusin-β contributes to monocrotaline (MCT)-induced PAH in rats.

METHODS

Male Sprague-Dawley rats were treated with MCT (60 mg kg(-1), single intraperitoneal injection). Salusin-β expression in the lungs of the MCT-treated rats was evaluated using immunofluorescence staining, western blot, and real-time PCR. For salusin-β blockade assay, rats injected with MCT were given a chronic infusion of anti-salusin-β immunoglobulin G (IgG) (salusin-β blocker, 1.0 μg kg(-1) h(-1)) or isotype-matched control IgG. Four weeks after MCT+anti-salusin-β treatment, the effects of salusin-β blockade were determined using hemodynamics, western blot, real-time PCR, and immunohistochemical detection. The effect of salusin-β on human pulmonary arterial endothelial cell (HPAEC) function was detected by adhesion and tube formation experiments in vitro.

RESULTS

Salusin-β expression was significantly increased in the lungs of the MCT-treated rats, and immunofluorescence results showed that salusin-β was predominantly expressed in pulmonary macrophages and vascular endothelial cells. Salusin-β blockade significantly ameliorated PAH by acting against pulmonary vascular remodeling, decreasing macrophage infiltration, and reducing pro-inflammatory cytokine expression and nuclear factor-kappa B (NF-κB) activity in the lungs of the MCT-treated rats. In addition, salusin-β could induce cell adhesion and accelerate angiogenesis by activating the NF-κB pathway and promoting pro-inflammatory cytokine expression in the cultured HPAECs. This effect was suppressed by addition of the NF-κB inhibitor, N-acetyl-L-cysteine.

CONCLUSIONS

Salusin-β plays a crucial role in the development of MCT-induced PAH models.

Leptin knockout attenuates hypoxia-induced pulmonary arterial hypertension by inhibiting proliferation of pulmonary arterial smooth muscle cells

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by excessive vascular smooth muscle cells proliferation in small pulmonary arteries, leading to elevation of pulmonary vascular resistance with consequent right ventricular (RV) failure and death. Recently, emerging evidence has shown that leptin signaling is involved in different cardiac pathologies; however, the role of leptin remains limited in the setting of PAH. Thus, in this study, we tested the hypothesis of direct involvement of leptin in the development of PAH. Our data show that leptin activity in plasma and protein level in the lung were higher in hypoxia- and monocrotaline-induced PAH models compared with control animals. Wild-type (WT) and C57BL/6J-Lep(ob) (ob/ob) male mice were exposed to normobaric hypoxia (10% O(2)) or normoxia (21% O(2)). After 2 and 4 weeks of chronic hypoxia exposure, WT mice developed PAH as reflected by the increased values of RV systolic pressure, RV hypertrophy index, the medial wall thickness of pulmonary arterioles, and muscularization of pulmonary arterioles. And, all these alterations were attenuated in ob/ob mice treated with hypoxia. Leptin could stimulate the proliferation of pulmonary arterial smooth muscle cells (PASMCs) by activating extracellular signal-regulated kinase (ERK), signal transducer and activator of transcription 3 (STAT3), and Akt pathways. These data suggest that the leptin signaling pathway is crucial for the development of PAH. Leptin activates ERK, STAT, and Akt pathways and subsequently PASMCs proliferation, providing new mechanistic information about hypoxia-induced PAH.

mTORC1 Prevents Preosteoblast Differentiation through the Notch Signaling Pathway

The mechanistic target of rapamycin (mTOR) integrates both intracellular and extracellular signals to regulate cell growth and metabolism. However, the role of mTOR signaling in osteoblast differentiation and bone formation is undefined, and the underlying mechanisms have not been elucidated. Here, we report that activation of mTOR complex 1 (mTORC1) is required for preosteoblast proliferation; however, inactivation of mTORC1 is essential for their differentiation and maturation. Inhibition of mTORC1 prevented preosteoblast proliferation, but enhanced their differentiation in vitro and in mice. Activation of mTORC1 by deletion of tuberous sclerosis 1 (Tsc1) in preosteoblasts produced immature woven bone in mice due to excess proliferation but impaired differentiation and maturation of the cells. The mTORC1-specific inhibitor, rapamycin, restored these in vitro and in vivo phenotypic changes. Mechanistically, mTORC1 prevented osteoblast maturation through activation of the STAT3/p63/Jagged/Notch pathway and downregulation of Runx2. Preosteoblasts with hyperactive mTORC1 reacquired the capacity to fully differentiate and maturate when subjected to inhibition of the Notch pathway. Together, these findings identified the role of mTORC1 in osteoblast formation and established that mTORC1 prevents preosteoblast differentiation and maturation through activation of the Notch pathway.

The coordinated activities of osteoblasts and osteoclasts in bone deposition and resorption form the internal structure of bone. Disruption of the balance between bone formation and resorption results in loss of bone mass and causes bone diseases such as osteoporosis. Current therapies for osteoporosis are limited to anti-resorptive agents, while bone diseases due to reduced osteoblast activity, such as senile osteoporosis, urgently require targeted treatment and novel strategies to promote bone formation. mTORC1 has emerged as a critical regulator of bone formation and is therefore a potential target in the development of novel bone-promoting therapeutics. Identifying the detailed function of mTORC1 in bone formation and clarifying the underlying mechanisms may uncover useful therapeutic targets. In this study, we reveal the role of mTORC1 in osteoblast formation. mTORC1 stimulated preosteoblast proliferation but prevented their differentiation and attenuated bone formation via activation of the Notch pathway. Pharmaceutical coordination of the pathways and agents in preosteoblasts may be beneficial in bone formation.

A Critical Role of the mTOR/eIF2α Pathway in Hypoxia-Induced Pulmonary Hypertension

Enhanced proliferation of pulmonary arterial vascular smooth muscle cells (PASMCs) is a key pathological component of vascular remodeling in hypoxia-induced pulmonary hypertension (HPH). Mammalian targeting of rapamycin (mTOR) signaling has been shown to play a role in protein translation and participate in the progression of pulmonary hypertension. Eukaryotic translation initiation factor-2α (eIF2α) is a key factor in regulation of cell growth and cell cycle, but its role in mTOR signaling and PASMCs proliferation remains unknown. Pulmonary hypertension (PH) rat model was established by hypoxia. Rapamycin was used to treat rats as an mTOR inhibitor. Proliferation of primarily cultured rat PASMCs was induced by hypoxia, rapamycin and siRNA of mTOR and eIF2α were used in loss-of-function studies. The expression and activation of eIF2α, mTOR and c-myc were analyzed. Results showed that mTOR/eIF2α signaling was significantly activated in pulmonary arteries from hypoxia exposed rats and PASMCs cultured under hypoxia condition. Treatment with mTOR inhibitor for 21 days attenuated vascular remodeling, suppressed mTOR and eIF2α activation, inhibited c-myc expression in HPH rats. In hypoxia-induced PASMCs, rapamycin and knockdown of mTOR and eIF2α by siRNA significantly abolished proliferation and increased c-myc expression. These results suggest a critical role of the mTOR/eIF2αpathway in hypoxic vascular remodeling and PASMCs proliferation of HPH.

Wnt5a attenuates hypoxia-induced pulmonary arteriolar remodeling and right ventricular hypertrophy in mice

Hypoxic pulmonary hypertension (HPH), which is characterized by pulmonary arteriolar remodeling and right ventricular hypertrophy, is still a life-threatening disease with the current treatment strategies. The underlying molecular mechanisms of HPH remain unclear. Our previously published study showed that Wnt5a, one of the ligands in the Wnt family, was critically involved in the inhibition of hypoxia-induced pulmonary arterial smooth muscle cell proliferation by downregulation of β-catenin/cyclin D1 in vitro. In this study, we investigated the possible functions and mechanisms of Wnt5a in HPH in vivo. Recombinant mouse Wnt5a (rmWnt5a) or phosphate buffered saline (PBS) was administered to male C57/BL6 mice weekly from the first day to the end of the two or four weeks after exposed to hypoxia (10% O2). Hypoxia-induced pulmonary hypertension was associated with a marked increase in β-catenin/cyclin D1 expression in lungs. Right ventricular systolic pressure and right ventricular hypertrophy index were reduced in animals treated with rmWnt5a compared with PBS. Histology showed less pulmonary vascular remodeling and right ventricular hypertrophy in the group treated with rmWnt5a than with PBS. Treatment with rmWnt5a resulted in a concomitant reduction in β-catenin/cyclin D1 levels in lungs. These data demonstrate that Wnt5a exerts its beneficial effects on HPH by regulating pulmonary vascular remodeling and right ventricular hypertrophy in a manner that is associated with reduction in β-catenin/cyclin D1 signaling. A therapy targeting the β-catenin/cyclin D1 signaling pathway might be a potential strategy for HPH treatment.

Autophagy in lung disease pathogenesis and therapeutics

Autophagy, a cellular pathway for the degradation of damaged organelles and proteins, has gained increasing importance in human pulmonary diseases, both as a modulator of pathogenesis and as a potential therapeutic target. In this pathway, cytosolic cargos are sequestered into autophagosomes, which are delivered to the lysosomes where they are enzymatically degraded and then recycled as metabolic precursors. Autophagy exerts an important effector function in the regulation of inflammation, and immune system functions. Selective pathways for autophagic degradation of cargoes may have variable significance in disease pathogenesis. Among these, the autophagic clearance of bacteria (xenophagy) may represent a crucial host defense mechanism in the pathogenesis of sepsis and inflammatory diseases. Our recent studies indicate that the autophagic clearance of mitochondria, a potentially protective program, may aggravate the pathogenesis of chronic obstructive pulmonary disease by activating cell death programs. We report similar findings with respect to the autophagic clearance of cilia components, which can contribute to airways dysfunction in chronic lung disease. In certain diseases such as pulmonary hypertension, autophagy may confer protection by modulating proliferation and cell death. In other disorders, such as idiopathic pulmonary fibrosis and cystic fibrosis, impaired autophagy may contribute to pathogenesis. In lung cancer, autophagy has multiple consequences by limiting carcinogenesis, modulating therapeutic effectiveness, and promoting tumor cell survival. In this review we highlight the multiple functions of autophagy and its selective autophagy subtypes that may be of significance to the pathogenesis of human disease, with an emphasis on lung disease and therapeutics.

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Autophagy may impact the pathogenesis of pulmonary diseases.

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Mitophagy may exert deleterious effects in the pathogenesis of COPD.

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Autophagy can exert pleiotropic effects in lung cancer.

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Targeting autophagy may represent a promising therapeutic strategy in human diseases.

Emerging role of selective autophagy in human diseases

Autophagy was originally described as a highly conserved system for the degradation of cytosol through a lysosome-dependent pathway. In response to starvation, autophagy degrades organelles and proteins to provide metabolites and energy for its pro-survival effects. Autophagy is recognized as playing a role in the pathogenesis of disease either directly or indirectly, through the regulation of vital processes such as programmed cell death, inflammation, and adaptive immune mechanisms. Recent studies have demonstrated that autophagy is not only a simple metabolite recycling system, but also has the ability to degrade specific cellular targets, such as mitochondria, cilia, and invading bacteria. In addition, selective autophagy has also been implicated in vesicle trafficking pathways, with potential roles in secretion and other intracellular transport processes. Selective autophagy has drawn the attention of researchers because of its potential importance in clinical diseases. Therapeutic strategies to target selective autophagy rather than general autophagy may maximize clinical benefit by enhancing selectivity. In this review, we outline the principle components of selective autophagy processes and their emerging importance in human disease, with an emphasis on pulmonary diseases.