Acetylated cyclophilin A is a major mediator in hypoxia-induced autophagy and pulmonary vascular angiogenesis

Endothelial HIFα/PDGF-B to smooth muscle Beclin1 signaling sustains pathological muscularization in pulmonary hypertension

Mechanisms underlying maintenance of pathological vascular hypermuscularization are poorly delineated. Herein, we investigated retention of smooth muscle cells (SMCs) coating normally unmuscularized distal pulmonary arterioles in pulmonary hypertension (PH) mediated by chronic hypoxia with or without Sugen 5416, and reversal of this pathology. With hypoxia in mice or culture, lung endothelial cells (ECs) upregulated hypoxia-inducible factor 1α (HIF1-α) and HIF2-α, which induce platelet-derived growth factor B (PDGF-B), and these factors were reduced to normoxic levels with re-normoxia. Re-normoxia reversed hypoxia-induced pulmonary vascular remodeling, but with EC HIFα overexpression during re-normoxia, pathological changes persisted. Conversely, after establishment of distal muscularization and PH, EC-specific deletion of Hif1a, Hif2a, or Pdgfb induced reversal. In human idiopathic pulmonary artery hypertension, HIF1-α, HIF2-α, PDGF-B, and autophagy-mediating gene products, including Beclin1, were upregulated in pulmonary artery SMCs and/or lung lysates. Furthermore, in mice, hypoxia-induced EC-derived PDGF-B upregulated Beclin1 in distal arteriole SMCs, and after distal muscularization was established, re-normoxia, EC Pdgfb deletion, or treatment with STI571 (which inhibits PDGF receptors) downregulated SMC Beclin1 and other autophagy products. Finally, SMC-specific Becn1 deletion induced apoptosis, reversing distal muscularization and PH mediated by hypoxia with or without Sugen 5416. Thus, chronic hypoxia induction of the HIFα/PDGF-B axis in ECs is required for non-cell-autonomous Beclin1-mediated survival of pathological distal arteriole SMCs.

Circ-calm4 regulates hypoxia-induced pulmonary artery smooth muscle autophagy by binding Purb

Pulmonary hypertension (PH) is a serious and fatal disease characterized by pulmonary vasoconstriction and pulmonary vascular remodeling. The excessive autophagy of pulmonary artery smooth muscle cells (PASMCs) is one of the important factors of pulmonary vascular remodeling. A number of studies have shown that circular RNA (circRNA) can participate in the onset of PH. Our previous studies have shown that circRNA calmodulin 4 (circ-calm4) is involved in the progression of hypoxic PH. However, the role of circ-calm4 on regulation of hypoxic PH autophagy has not been reported. In this study, we demonstrated for the first time that hypoxia-mediated upregulated circ-calm4 expression has a key regulatory effect on autophagy in hypoxia-induced PASMCs and hypoxic PH mouse models. Knockdown of circ-calm4 both in vivo and in vitro can inhibit the autophagy in PASMCs induced by hypoxia. We also performed bioinformatics predictions and conducted experiments to verify that circ-calm4 bound to the purine-rich binding protein (Purb) to promote its expression in the nucleus, thereby initiating the transcription of autophagy-related protein Beclin1. Interestingly, we found that Beclin1 transcription initiated by Purb was accompanied by a modification of Beclin1 super-enhancer to improve transcription activity and efficiency. Overall, our results confirm that the circ-calm4/Purb/Beclin1 signal axis is involved in the occurrence of hypoxia-induced PASMCs autophagy, and the novel regulatory mechanisms and signals transduction pathways in PASMC autophagy induced by hypoxia.

Lipid-induced monokine cyclophilin-A promotes adipose tissue dysfunction implementing insulin resistance and type 2 diabetes in zebrafish and mice models of obesity

Several studies have implicated obesity-induced macrophage-adipocyte cross-talk in adipose tissue dysfunction and insulin resistance. However, the molecular cues involved in the cross-talk of macrophage and adipocyte causing insulin resistance are currently unknown. Here, we found that a lipid-induced monokine cyclophilin-A (CyPA) significantly attenuates adipocyte functions and insulin sensitivity. Targeted inhibition of CyPA in diet-induced obese zebrafish notably reduced adipose tissue inflammation and restored adipocyte function resulting in improvement of insulin sensitivity. Silencing of macrophage CyPA or pharmacological inhibition of CyPA by TMN355 effectively restored adipocytes' functions and insulin sensitivity. Interestingly, CyPA incubation markedly increased adipocyte inflammation along with an impairment of adipogenesis, however, mutation of its cognate receptor CD147 at P309A and G310A significantly waived CyPA's effect on adipocyte inflammation and its differentiation. Mechanistically, CyPA-CD147 interaction activates NF-κB signaling which promotes adipocyte inflammation by upregulating various pro-inflammatory cytokines gene expression and attenuates adipocyte differentiation by inhibiting PPARγ and C/EBPβ expression via LZTS2-mediated downregulation of β-catenin. Moreover, inhibition of CyPA or its receptor CD147 notably restored palmitate or CyPA-induced adipose tissue dysfunctions and insulin sensitivity. All these results indicate that obesity-induced macrophage-adipocyte cross-talk involving CyPA-CD147 could be a novel target for the management of insulin resistance and type 2 diabetes.

Ubiquitinated AIF is a major mediator of hypoxia-induced mitochondrial dysfunction and pulmonary artery smooth muscle cell proliferation

BACKGROUND

Excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) is the main cause of hypoxic pulmonary hypertension (PH), and mitochondrial homeostasis plays a crucial role. However, the specific molecular regulatory mechanism of mitochondrial function in PASMCs remains unclear.

METHODS

In this study, using the CCK8 assay, EdU incorporation, flow cytometry, Western blotting, co-IP, mass spectrometry, electron microscopy, immunofluorescence, Seahorse extracellular flux analysis and echocardiography, we investigated the specific involvement of apoptosis-inducing factor (AIF), a mitochondrial oxidoreductase in regulating mitochondrial energy metabolism and mitophagy in PASMCs.

RESULTS

In vitro, AIF deficiency in hypoxia leads to impaired oxidative phosphorylation and increased glycolysis and ROS release because of the loss of mitochondrial complex I activity. AIF was also downregulated and ubiquitinated under hypoxia leading to the abnormal occurrence of mitophagy and autophagy through its interaction with ubiquitin protein UBA52. In vivo, treatment with the adeno-associated virus vector to overexpress AIF protected pulmonary vascular remodeling from dysfunctional and abnormal proliferation.

CONCLUSIONS

Taken together, our results identify AIF as a potential therapeutic target for PH and reveal a novel posttranscriptional regulatory mechanism in hypoxia-induced mitochondrial dysfunction.

Silencing cyclophilin A improves insulin secretion, reduces cell apoptosis, and alleviates inflammation as well as oxidant stress in high glucose-induced pancreatic β-cells via MAPK/NF-kb signaling pathway

Cyclophilin A is increased in the plasm of diabetic patients, while its effects on high glucose (HG)-stimulated pancreatic β-cells are still pending. The aim of this research is to investigate the effects of cyclophilin A inhibition on HG-challenged pancreatic β-cells. For investigating the effects of cyclophilin A decrease on HG-induced pancreatic β-cells, the cells were separated into normal glucose (NG), Mannitol, HG, HG + shRNA-NC, and HG + shRNA-Cyclophilin A-1 groups. The protein and mRNA expression were detected via Western blot and qRT-PCR. CCK-8 assay and flow cytometry were employed for assessing cell viability and apoptosis. The levels of oxidative stress, inflammation, and insulin secretion were detected by corresponding kits. The cyclophilin A was higher in HG group. Knockdown of cyclophilin A was able to increase insulin secretion, decrease cell apoptosis, and alleviate inflammation as well as oxidant stress in HG-treated pancreatic β-cells via MAPK/NF-kb pathway. Taken together, Cyclophilin A, highly expressed in pancreatic β-cells induced by HG, is a promising therapeutic target for diabetes. Knockdown of cyclophilin A has protective effects against HG-challenged pancreatic β-cells via regulation of MAPK/NF-kb pathway. The findings in this study provided a new strategy for diabetic treatment and paved the way for future researches on diabetes treatment.

Angiotensin-converting enzyme 2 alleviates pulmonary artery hypertension through inhibition of focal adhesion kinase expression

Focal adhesion kinase (FAK) is an important therapeutic target in pulmonary artery hypertension (PAH); however, the mechanism of its activation remains unknown. The present study aimed to investigate whether angiotensin-converting enzyme 2 (ACE2) could regulate FAK and alleviate PAH in a rat model of PAH established with a single administration of monocrotaline followed by continuous hypoxia treatment. In the current study, right ventricular pressure, body weight and the right ventricular hypertrophy index were measured, and hematoxylin-eosin staining was performed on lung tissues to determine whether the modeling was successful. Changes in the serum levels of FAK were measured using an ELISA kit to evaluate the association between ACE2 and FAK. The mRNA expression levels of ACE2, FAK, caspase-3 and survivin were determined using reverse transcription-quantitative PCR (RT-qPCR). The protein expression levels of ACE2, phosphorylated FAK/FAK, cleaved caspase-3/pro-caspase-3 and survivin were determined via western blotting. Immunohistochemistry was applied to detect the expression of FAK around the pulmonary arterioles. Apoptosis of smooth muscle cells around pulmonary arterioles was observed by TUNEL staining. After treatment with the ACE2 activator DIZE or inhibitor DX-600, the results demonstrated that ACE2 reduced PAH-induced changes in arteriole morphology compared with the control. It also inhibited FAK expression in serum. WB and RT-qPCR results suggested that ACE2 inhibited the expression of FAK and pathway-related proteins, and promoted caspase-3 expression. Additionally, ACE2 reduced FAK expression around the pulmonary arterioles and promoted smooth muscle cell apoptosis. The results indicated that ACE2 activation inhibited FAK expression, leading to alleviation of the symptoms of PAH.

Dysregulated autophagy contributes to the pathogenesis of enterovirus A71 infection

Enterovirus A71 (EVA71) infection continues to remain a vital threat to global public health, especially in the Asia–Pacific region. It is one of the most predominant pathogens that cause hand, foot, and mouth disease (HFMD), which occurs mainly in children below 5 years old. Although EVA71 prevalence has decreased sharply in China with the use of vaccines, epidemiological studies still indicate that EVA71 infection involves severe and even fatal HFMD cases. As a result, it remains more fundamental research into the pathogenesis of EVA71 as well as to develop specific anti-viral therapy. Autophagy is a conserved, self-degradation system that is critical for maintaining cellular homeostasis. It involves a variety of biological functions, such as development, cellular differentiation, nutritional starvation, and defense against pathogens. However, accumulating evidence has indicated that EVA71 induces autophagy and hijacks the process of autophagy for their optimal infection during the different stages of life cycle. This review provides a perspective on the emerging evidence that the “positive feedback” between autophagy induction and EVA71 infection, as well as its potential mechanisms. Furthermore, autophagy may be involved in EVA71-induced nervous system impairment through mediating intracranial viral spread and dysregulating host regulator involved self-damage. Autophagy is a promising therapeutic target in EVA71 infection.

BCAT1 binds the RNA-binding protein ZNF423 to activate autophagy via the IRE1-XBP-1-RIDD axis in hypoxic PASMCs

Abnormal functional changes in pulmonary artery smooth muscle cells are the main causes of many lung diseases. Among, autophagy plays a crucial role. However, the specific molecular regulatory mechanism of autophagy in PASMCs remains unclear. Here, we first demonstrate that BCAT1 played a key role in the autophagy of hypoxic PASMCs and hypoxic model rats. BCAT1-induced activation and accumulation of the autophagy signaling proteins BECN1 and Atg5 by the endoplasmic reticulum (ER) stress pathway. Interestingly, we discovered that BCAT1 bound IRE1 on the ER to activate expression of its downstream pathway XBP-1-RIDD axis to activate autophagy. More importantly, we identified an RNA-binding protein, zinc finger protein 423, which promoted autophagy by binding adenylate/uridylate (AU)-rich elements in the BCAT1 mRNA 3′-untranslated region. Overall, our results identify BCAT1 as a potential therapeutic target for the clinical treatment of lung diseases and reveal a novel posttranscriptional regulatory mechanism and signaling pathway in hypoxia-induced PASMC autophagy.

MicroRNA-874-5p regulates autophagy and proliferation in pulmonary artery smooth muscle cells by targeting Sirtuin 3

Autophagy is a major cause of pathological vascular remodeling under hypoxic pulmonary hypertension (PH). Sirtuin 3 (Sirt 3) has recently been reported to be involved in the regulation of autophagy, however, its role as an autophagy regulator during hypoxic PH, particularly the molecular mechanism, remains poorly understood. In the present study, Western blot, immunohistochemistry, immunofluorescence, bromodeoxyuridine incorporation and cell cycle analyses were performed to elucidate the underlying mechanism of hypoxia-induced autophagy and cell proliferation with respect to Sirt 3. We observed that the Sirt 3 expression was decreased under hypoxia and that Sirt 3 overexpression significantly inhibited the effects of hypoxia on autophagy. Next, we investigated the mechanistic role of microRNAs in Sirt 3-associated autophagy under hypoxic conditions, with luciferase reporter, microscale thermophoresis and RNA immunoprecipitation assays, results confirming that Sirt 3 is a direct target of miR-874-5p. Furthermore, miR-874-5p was upregulated following hypoxia, and miR-874-5p depletion in turn inhibited autophagy and consequently suppressed abnormal smooth muscle cell proliferation. These findings provide insight into the contribution of the miR-874-5p/Sirt 3 cascade with regard to changes in autophagy and proliferation associated with PH.

β-arrestin1 inhibits hypoxic injury-induced autophagy in human pulmonary artery endothelial cells via the Akt/mTOR signaling pathway

Autophagy has been greatly implicated in injured endothelial cells during pulmonary arterial hypertension (PAH). β-arrestin1, a multifunctional cytoplasmic protein, has attracted considerable attention as an essential protective factor in PAH. However, its role in autophagy of injured pulmonary arterial endothelial cells (PAECs) remains to be determined. Here, we investigated the potential effects of β-arrestin1 on autophagy and apoptosis in human PAECs (hPAECs) under hypoxic stress. Hypoxic stimuli increases autophagy and decreases the level of β-arrestin1 in hPAECs. Furthermore, pathologic changes, namely increased proliferation, migration, and apoptosis resistance, are observed after hypoxia exposure. These are reversed after β-arrestin1 overexpression (β-arrestin1-OV) or treatment with 3-MA, an autophagy inhibitor. Finally, β-arrestin1 suppresses the increase in autophagy and apoptosis resistance of hypoxic hPAECs. Mechanistically, β-arrestin1 upregulates the activity of the Akt/mTOR signaling pathway and downregulates the expression of BNIP3 and Nix after hypoxic stress. Collectively, we have demonstrated, for the first time, that β-arrestin1 reduces excessive autophagy and apoptosis resistance by activating the Akt/mTOR axis in hypoxic hPAECs. This knowledge suggests a promising therapeutic target for PAH.

Cyclophilin A Inhibitor Debio-025 Targets Crk, Reduces Metastasis, and Induces Tumor Immunogenicity in Breast Cancer

The Crk adaptor protein, a critical modifier of multiple signaling pathways, is overexpressed in many cancers where it contributes to tumor progression and metastasis. Recently, we have shown that Crk interacts with the peptidyl prolyl cis-trans isomerase, Cyclophilin A (CypA; PP1A) via a G²¹⁹P²²⁰Y²²¹ (GPY) motif in the carboxyl-terminal linker region of Crk, thereby delaying pY221 phosphorylation and preventing downregulation of Crk signaling. Here, we investigate the physiologic significance of the CypA/Crk interaction and query whether CypA inhibition affects Crk signaling in vitro and in vivo. We show that CypA, when induced under conditions of hypoxia, regulates Crk pY221 phosphorylation and signaling in cancer cell lines. Using nuclear magnetic resonance spectroscopy, we show that CypA binds to the Crk GPY motif via the catalytic PPII domain of CypA, and small-molecule nonimmunosuppressive inhibitors of CypA (Debio-025) disrupt the CypA-CrkII interaction and restores phosphorylation of Crk Y221. In cultured cell lines, Debio-025 suppresses cell migration, and when administered in vivo in an orthotopic model of triple-negative breast cancer, Debio-025 showed antitumor efficacy either alone or in combination with anti-PD-1 mAb, reducing both tumor volume and metastatic lung dispersion. Furthermore, when analyzed by NanoString immune profiling, treatment of Debio-025 with anti-PD-1 mAb increased both T-cell signaling and innate immune signaling in tumor microenvironment. IMPLICATIONS: These data suggest that pharmacologic inhibition of CypA may provide a promising and unanticipated consequence in cancer biology, in part by targeting the CypA/CrkII axis that regulates cell migration, tumor metastasis, and host antitumor immune evasion.

Autophagy, an important therapeutic target for pulmonary fibrosis diseases

As an evolutionarily conserved intracellular degradation pathway, autophagy is essential to cellular homeostasis. Several studies have demonstrated that autophagy showed an important effect on some pulmonary fibrosis diseases, including idiopathic pulmonary fibrosis (IPF), cystic fibrosis lung disease, silicosis and smoking-induced pulmonary fibrosis. For example, autophagy mitigates the pathological progression of IPF by regulating the apoptosis of fibroblasts and the senescence of alveolar epithelial cells. In addition, autophagy ameliorates cystic fibrosis lung disease via rescuing transmembrane conductance regulators (CFTRs) to the plasma membrane. Furthermore, autophagy alleviates the silica-induced pulmonary fibrosis by decreasing apoptosis of alveolar epithelial cells in silicosis. However, excessive macrophage autophagy aggravates the pathogenesis of silicosis fibrosis by promoting the proliferation and migration of lung fibroblasts in silicosis. Autophagy is also involved in smoking-induced pulmonary fibrosis, coal workers' pneumoconiosis, ionizing radiation-mediated pulmonary fibrosis and heavy metal nanoparticle-mediated pulmonary fibrosis. In this review, the role and signalling mechanisms of autophagy in the progression of pulmonary fibrosis diseases have been systematically analysed. It has provided a new insight into the therapeutic potential associated with autophagy in pulmonary fibrosis diseases. In conclusion, the targeting of autophagy might prove to be a prospective avenue for the therapeutic intervention of pulmonary fibrosis diseases.

Programmed death-ligand 1 triggers PASMCs pyroptosis and pulmonary vascular fibrosis in pulmonary hypertension

Pyroptosis is a pro-inflammatory form of programmed cell death, whose genesis directly depended on caspase-1 activation. Pulmonary hypertension (PH) is a disease characterized, in part, by vascular fibrosis. Up to now, there is no report on the relationship between pyroptosis and vascular fibrosis in PH. Here, we confirmed that pyroptosis had occurred in the media of pulmonary arteries in two PH rat models and hypoxic human pulmonary arterial smooth muscle cells (hPASMCs). Caspase-1 inhibition attenuated the pathogenesis of PH, as assessed by vascular remodeling, right ventricular systolic pressure, right ventricle hypertrophy and hemodynamic parameters of pulmonary vasculature. Moreover, caspase-1 inhibition suppressed pulmonary vascular fibrosis as demonstrated by Masson staining, as well as immunohistochemistry and Western blot analysis of fibrillar collagen. In addition, Programmed death-ligand 1 (PD-L1) was markedly increased in PH, which was regulated by the transcription factor STAT1. Furthermore, PD-L1 knockdown in hPASMCs repressed the onset of hypoxia-induced pyroptosis and fibrosis. Overall, these data identify a critical STAT1-dependent posttranscriptional modification that promotes PD-L1 expression in the pyroptosis of PASMCs to modulate pulmonary vascular fibrosis and accelerate the progression of PH.

Endosomes and Autophagy: Regulators of Pulmonary Endothelial Cell Homeostasis in Health and Disease

Significance: Alterations in oxidant/antioxidant balance injure pulmonary endothelial cells and are important in the pathogenesis of lung diseases, such as Acute Respiratory Distress Syndrome (ARDS), ischemia/reperfusion injury, pulmonary arterial hypertension (PAH), and emphysema. Recent Advances: The endosomal and autophagic pathways regulate cell homeostasis. Both pathways support recycling or degradation of macromolecules or organelles, targeted to endosomes or lysosomes, respectively. Thus, both processes promote cell survival. However, with environmental stress or injury, imbalance in endosomal and autophagic pathways may enhance macromolecular or organelle degradation, diminish biosynthetic processes, and cause cell death. Critical Issues: While the role of autophagy in cellular homeostasis in pulmonary disease has been investigated, the role of the endosome in the lung vasculature is less known. Furthermore, autophagy can either decrease or exacerbate endothelial injury, depending upon inciting insult and disease process. Future Directions: Diseases affecting the pulmonary endothelium, such as emphysema, ARDS, and PAH, are linked to altered endosomal or autophagic processing, leading to enhanced degradation of macromolecules and potential cell death. Efforts to target this imbalance have yielded limited success as treatments for lung injuries, which may be due to the complexity of both processes. It is possible that endosomal trafficking proteins, such as Rab GTPases and late endosomal/lysosomal adaptor, MAPK and MTOR activator 1, may be novel therapeutic targets. While endocytosis or autophagy have been linked to improved function of the pulmonary endothelium in vitro and in vivo, further studies are needed to identify targets for modulating cellular homeostasis in the lung.

Puerarin prevents progression of experimental hypoxia-induced pulmonary hypertension via inhibition of autophagy

Pulmonary arterial hypertension (PAH) is defined as elevation of mean pulmonary arterial pressure to ≥25 mmHg within the low pressure pulmonary circulatory system. PAH is characterized by obstructive vascular remodeling, partially due to excessive pulmonary arterial smooth muscle cell (PASMC) proliferation. Puerarin is a natural flavonoid isolated from the herb Radix puerariae, which has been widely used for the treatment of cardiovascular and cerebrovascular disorders and diabetes. However, how puerarin mediates autophagy in the progression of pulmonary vascular remodeling is unclear. In this study, we explored the effects of puerarin in a hypoxic pulmonary hypertension (PH) rat model using immunohistochemistry, and morphometric analyses of right ventricle. In addition, cell counting kit 8 assay, western blotting and flow cytometry were employed to test cell proliferation in PASMCs, and then autophagy was tested with mRFP-GFP-LC3 fluorescence microscopy and Western blot. We found that puerarin could alleviate hypoxia-induced PH in rats and improved pulmonary histopathology, and also reduced the expression of autophagy markers in vivo and in vitro. Moreover, puerarin also ameliorated hypoxia-induced PASMC proliferation in an autophagy-dependent manner. Overall, these findings demonstrated that puerarin could prevent hypoxia-induced PH in rats, possibly via reducing autophagy and suppressing cell proliferation.

Down-regulation of miR-204 attenuates endothelial-mesenchymal transition by enhancing autophagy in hypoxia-induced pulmonary hypertension

Pulmonary arterial remodeling is a crucial cause of increased pulmonary artery pressure during pulmonary hypertension (PH). Recently, growing evidence has upheld the contribution of endothelial-mesenchymal transition (EndMT) to pulmonary arterial remodeling, but the underlying mechanisms remain largely unaddressed. miR-204 has been implicated in PH, being anti-proliferative and pro-apoptotic in pulmonary artery smooth muscles cells (PASMCs), but its role in EndMT is still unknown. Here we found that miR-204 was down-regulated by hypoxia in rat pulmonary arterial intima and human pulmonary artery endothelial cells (HPAECs), and its further down-regulation by using miR-204 inhibitor suppressed hypoxia-induced EndMT. Moreover, autophagy, evoked by hypoxia in rat pulmonary arterial intima and HPAECs, suppressed hypoxia-induced EndMT via p62-dependent degradation of Snail and Twist. Additionally, autophagy was regulated by miR-204 targeting ATG7. While down-regulation of miR-204 in PASMCs reportedly promoted monocrotaline-induced pulmonary arterial hypertension via increased cell proliferation, our data suggested an important, albeit dichotomous, role of miR-204 down-regulation in endothelial cells in the process of EndMT that it attenuated EndMT by enhancing autophagy, thereby ameliorating hypoxia-induced PH to some extent.

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.

Autophagy in pulmonary hypertension: Emerging roles and therapeutic implications

Autophagy is an important mechanism for cellular self-digestion and basal homeostasis. This gene- and modulator-regulated pathway is conserved in cells. Recently, several studies have shown that autophagic dysfunction is associated with pulmonary hypertension (PH). However, the relationship between autophagy and PH remains controversial. In this review, we mainly introduce the effects of autophagy-related genes and some regulatory molecules on PH and the relationship between autophagy and PH under the conditions of hypoxia, monocrotaline injection, thromboembolic stress, oxidative stress, and other drugs and toxins. The effects of other autophagy-related drugs, such as chloroquine, 3-methyladenine, rapamycin, and other potential therapeutic drugs and targets, in PH are also described.

Dacomitinib, a new pan-EGFR inhibitor, is effective in attenuating pulmonary vascular remodeling and pulmonary hypertension

Accumulating evidence suggests that epidermal growth factor receptor (EGFR) plays a role in the progression of pulmonary arterial hypertension (PAH). Clinically-approved epidermal growth factor inhibitors such as gefitinib, erlotinib, and lapatinib have been explored for PAH. However, None of them were able to attenuate PAH. So, we explored the role of dacomitinib, a new pan-EGFR inhibitor, in PAH. Adult male Sprague-Dawley rats were used to study hypoxia- or monocrotaline-induced right ventricular remodeling as well as systolic function and hemodynamics using echocardiography and a pressure-volume admittance catheter. Morphometric analyses of lung vasculature and pressure-volume vessels were performed. Immunohistochemical staining, flow cytometry, and viability, as well as scratch-wound, and Boyden chamber migration assays were used to identify the roles of dacomitinib in pulmonary artery smooth muscle cells (PASMCs). The results revealed that dacomitinib has a significant inhibitory effect on the thickening of the media, adventitial collagen increased. Dacomitinib also has a significant role in attenuating pulmonary artery pressure and right ventricular hypertrophy. Additionally, dacomitinib inhibits hypoxia-induced proliferation, migration, autophagy and cell cycle progression through PI3K-AKT-mTOR signaling in PASMCs. Our study indicates that dacomitinib inhibited hypoxia-induced cell cycle progression, proliferation, migration, and autophagy of PASMCs, thereby attenuating pulmonary vascular remodeling and development of PAH via the PI3K-AKT-mTOR signaling pathway. Overall, dacomitinib may serve as new potential therapeutic for the treatment of PAH.

The effect of honokiol on pulmonary artery endothelium cell autophagy mediated by cyclophilin A in hypoxic pulmonary arterial hypertension

Abnormal autophagy plays critical roles in the structure and function of the pulmonary vasculature. Cyclophilin A (CyPA) can be secreted from cells in response to hypoxia and oxidative stress, which are involved in inducing autophagy and regulating the function of endothelial cells in pulmonary arterial hypertension. Honokiol is a small molecule natural compound; it has many bioactivities, such as antitumor, anti-inflammatory, antioxidant and antiangiogenic properties, but how honokiol mediates autophagy in pulmonary arterial hypertension is unclear. Rat' lungs gavaged with honokiol were examined for autophagy via western blot and fluorescence microscopy. In addition, western blot, quantitative RT-PCR and immunofluorescence were employed to test the expression of CyPA and autophagy markers in pulmonary artery endothelial cells (PAECs). Small interfering RNA targeting CyPA (si-CyPA) was used to knockdown the expression of CyPA, and then autophagy was tested with mRFP-GFP-LC3 fluorescence microscopy and western blot. We found that honokiol could reduce the expression of CyPA and autophagy markers in vivo and in vitro. Furthermore, autophagy was also down-regulated by si-CyPA. Taken together, we revealed a novel mechanism by which honokiol regulates autophagy. The results revealed that honokiol can alleviate autophagy and pulmonary arterial hypertension regulated by CyPA in PAECs.

Granzyme B deficiency promotes osteoblastic differentiation and calcification of vascular smooth muscle cells in hypoxic pulmonary hypertension

Calcification is a major risk factor for vascular integrity. This pathological symptom and the underlying mechanisms in hypoxic pulmonary artery hypertension remain elusive. Here we report that pulmonary vascular medial calcification is elevated in pulmonary artery hypertension models as a result of an osteoblastic phenotype change of pulmonary arterial smooth muscle cells induced by hypoxia. Notably, inhibiting store-operated calcium channels significantly decreased osteoblastic differentiation and calcification of pulmonary arterial smooth muscle cells under hypoxia. We identified granzyme B, a major constituent of cytotoxic T lymphocytes/natural killer cell granules involved in apoptosis, as the main regulator of pulmonary arterial calcification. Overexpression of granzyme B blocked the mineralization through its effect on store-operated calcium channels in cultured pulmonary arterial smooth muscle cells under hypoxic conditions. Mice with overexpression of granzyme B exposed to hypoxia for 3 weeks showed attenuated vascular calcification and pathological progression of hypoxic pulmonary arterial hypertension. Our findings emphasize the central function of granzyme B in coordinating vascular calcification in hypoxic pulmonary arterial hypertension.

Extracellular Matrix Metalloproteinase Inducer EMMPRIN (CD147) in Cardiovascular Disease

The receptor EMMPRIN is involved in the development and progression of cardiovascular diseases and in the pathogenesis of myocardial infarction. There are several binding partners of EMMPRIN mediating the effects of EMMPRIN in cardiovascular diseases. EMMPRIN interaction with most binding partners leads to disease progression by mediating cytokine or chemokine release, the activation of platelets and monocytes, as well as the formation of monocyte-platelet aggregates (MPAs). EMMPRIN is also involved in atherosclerosis by mediating the infiltration of pro-inflammatory cells. There is also evidence that EMMPRIN controls energy metabolism of cells and that EMMPRIN binding partners modulate intracellular glycosylation and trafficking of EMMPRIN towards the cell membrane. In this review, we systematically discuss these multifaceted roles of EMMPRIN and its interaction partners, such as Cyclophilins, in cardiovascular disease.

Autophagy attenuates endothelial-to-mesenchymal transition by promoting Snail degradation in human cardiac microvascular endothelial cells

Endothelial-to-mesenchymal transition (EndMT) mainly exists in cardiovascular development and disease progression, and is well known to contribute to cardiac fibrosis. Recent studies indicated that autophagy also participates in the regulation of cardiac fibrosis. However, the precise role of autophagy in cardiac fibrosis and the underlying molecular mechanism remain unclear. The present study aimed to explore the role of autophagy in EndMT, reveal the underlying molecular mechanism, and seek new therapy for cardiac fibrosis. In the present study, we found that EndMT and autophagy were induced simultaneously by hypoxia in human cardiac microvascular endothelial cells (HCMECs). Rapamycin, an autophagy enhancer, attenuated EndMT with promoting angiogenesis, while 3-methyladenine (3-MA) and chloroquine (CQ), agents that inhibit autophagy, accelerated the progression accompanied by the decrease in counts of tube formation under hypoxia conditions. Interestingly, intervening autophagy by rapamycin, 3-MA, or CQ did not affect hypoxia-induced autocrine TGFβ signaling, but changed the expression of Snail protein without alterations in the expression of Snail mRNA. Furthermore, the colocalization of LC3 and Snail indicated that autophagy might mediate Snail degradation under hypoxia conditions in HCMECs. Interaction of p62, the substrate of autophagy, with Snail by co-immunoprecipitation especially in hypoxia-incubated cells confirmed the hypothesis. In conclusion, autophagy serves as a cytoprotective mechanism against EndMT to promote angiogenesis by degrading Snail under hypoxia conditions, suggesting that autophagy targetted therapeutic strategies may be applicable for cardiac fibrosis by EndMT.