Acetylation of cyclophilin A is required for its secretion and vascular cell activation

The physical and evolutionary energy landscapes of devolved protein sequences corresponding to pseudogenes

Protein evolution is guided by structural, functional, and dynamical constraints ensuring organismal viability. Pseudogenes are genomic sequences identified in many eukaryotes that lack translational activity due to sequence degradation and thus over time have undergone "devolution." Previously pseudogenized genes sometimes regain their protein-coding function, suggesting they may still encode robust folding energy landscapes despite multiple mutations. We study both the physical folding landscapes of protein sequences corresponding to human pseudogenes using the Associative Memory, Water Mediated, Structure and Energy Model, and the evolutionary energy landscapes obtained using direct coupling analysis (DCA) on their parent protein families. We found that generally mutations that have occurred in pseudogene sequences have disrupted their native global network of stabilizing residue interactions, making it harder for them to fold if they were translated. In some cases, however, energetic frustration has apparently decreased when the functional constraints were removed. We analyzed this unexpected situation for Cyclophilin A, Profilin-1, and Small Ubiquitin-like Modifier 2 Protein. Our analysis reveals that when such mutations in the pseudogene ultimately stabilize folding, at the same time, they likely alter the pseudogenes' former biological activity, as estimated by DCA. We localize most of these stabilizing mutations generally to normally frustrated regions required for binding to other partners.

Co-translational Installation of Posttranslational Modifications by Non-canonical Amino Acid Mutagenesis

Protein posttranslational modifications (PTMs) play critical roles in regulating cellular activities. Here we provide a survey of genetic code expansion (GCE) methods that were applied in the co-translational installation and studies of PTMs through noncanonical amino acid (ncAA) mutagenesis. We begin by reviewing types of PTM that have been installed by GCE with a focus on modifications of tyrosine, serine, threonine, lysine, and arginine residues. We also discuss examples of applying these methods in biological studies. Finally, we end the piece with a short discussion on the challenges and the opportunities of the field.

Phosphorylation of the prolyl isomerase Cyclophilin A regulates its localisation and release from the centrosome during mitosis

The centrosome acts as a protein platform from which proteins are deployed to function throughout the cell cycle. Previously, we have shown that the prolyl isomerase Cyclophilin A (CypA) localizes to the centrosome in interphase and re-localizes to the midbody during mitosis where it functions in cytokinesis. In this study, investigation of CypA by SDS-PAGE during the cell cycle reveals that it undergoes a mobility shift during mitosis, indicative of a post-translational modification, which may correlate with its subcellular re-localization. Due to the lack of a phospho-specific antibody, we used site-directed mutagenesis to demonstrate that the previously identified serine 77 phosphorylation site within CypA is important for control of CypA centrosome localization. Furthermore, CypA is shown to interact with the mitotic NIMA-related kinase 2 (Nek2) during interphase and mitosis, while also interacting with the Nek2-antagonist PP1 during interphase but not during mitosis, suggesting a potential role for the Nek2-PP1 complex in CypA phospho-regulation. In support of this, Nek2 is capable of phosphorylating CypA in vitro. Overall, this work reveals that phosphorylation of CypA at serine 77 is important for its release from the centrosome during mitosis and may be regulated by the activity of Nek2 and PP1 during the cell cycle.

Non-Immunosuppressive Cyclophilin Inhibitors

Cyclophilins, enzymes with peptidyl-prolyl cis/trans isomerase activity, are relevant to a large variety of biological processes. The most abundant member of this enzyme family, cyclophilin A, is the cellular receptor of the immunosuppressive drug cyclosporine A (CsA). As a consequence of the pathophysiological role of cyclophilins, particularly in viral infections, there is a broad interest in cyclophilin inhibition devoid of immunosuppressive activity. This Review first gives an introduction into the physiological and pathophysiological roles of cyclophilins. The presentation of non-immunosuppressive cyclophilin inhibitors will commence with drugs based on chemical modifications of CsA. The naturally occurring macrocyclic sanglifehrins have become other lead structures for cyclophilin-inhibiting drugs. Finally, de novo designed compounds, whose structures are not derived from or inspired by natural products, will be presented. Relevant synthetic concepts will be discussed, but the focus will also be on biochemical studies, structure-activity relationships, and clinical studies.

Role of Posttranslational Modifications of Proteins in Cardiovascular Disease

Cardiovascular disease (CVD) has become a leading cause of mortality and morbidity globally, making it an urgent concern. Although some studies have been performed on CVD, its molecular mechanism remains largely unknown for all types of CVD. However, recent in vivo and in vitro studies have successfully identified the important roles of posttranslational modifications (PTMs) in various diseases, including CVD. Protein modification, also known as PTMs, refers to the chemical modification of specific amino acid residues after protein biosynthesis, which is a key process that can influence the activity or expression level of proteins. Studies on PTMs have contributed directly to improving the therapeutic strategies for CVD. In this review, we examined recent progress on PTMs and highlighted their importance in both physiological and pathological conditions of the cardiovascular system. Overall, the findings of this review contribute to the understanding of PTMs and their potential roles in the treatment of CVD.

Exploratory Investigation of the Plasma Proteome Associated with the Endotheliopathy of Trauma

BACKGROUND

The endotheliopathy of trauma (EoT) is associated with increased mortality following injury. Herein, we describe the plasma proteome related to EoT in order to provide insight into the role of the endothelium within the systemic response to trauma.

METHODS

99 subjects requiring the highest level of trauma activation were included in the study. Enzyme-linked immunosorbent assays of endothelial and catecholamine biomarkers were performed on admission plasma samples, as well as untargeted proteome quantification utilizing high-performance liquid chromatography and tandem mass spectrometry.

RESULTS

Plasma endothelial and catecholamine biomarker abundance was elevated in EoT. Patients with EoT (n = 62) had an increased incidence of death within 24 h at 21% compared to 3% for non-EoT (n = 37). Proteomic analysis revealed that 52 out of 290 proteins were differentially expressed between the EoT and non-EoT groups. These proteins are involved in endothelial activation, coagulation, inflammation, and oxidative stress, and include known damage-associated molecular patterns (DAMPs) and intracellular proteins specific to several organs.

CONCLUSIONS

We report a proteomic profile of EoT suggestive of a surge of DAMPs and inflammation driving nonspecific activation of the endothelial, coagulation, and complement systems with subsequent end-organ damage and poor clinical outcome. These findings support the utility of EoT as an index of cellular injury and delineate protein candidates for therapeutic intervention.

Supra-lacrimal protein-based carriers for cyclosporine A reduce Th17-mediated autoimmunity in murine model of Sjögren's syndrome

Sjögren's syndrome (SS) is a multifactorial autoimmune disease with principal symptoms including inflammation and loss of function of lacrimal glands (LG) and salivary glands. While glandular infiltrates includes both B- and T-cells, CD4+ T cells are strongly implicated. Utilizing the male non-obese diabetic (NOD) mouse model of SS, this work: 1) identifies clinically-relevant elevations in cytokines (IL-17A, IL-2) in LG-derived CD4+ T cells; and 2) explores tissue-specific immunosuppression of SS using a novel protein-based drug carrier to concentrate cyclosporine A (CsA) directly in the LG. As a potent immunosuppressant, topical ophthalmic CsA is approved for dry eye disorders; however, it cannot effectively resolve inflammation due to limited accumulation in the LG. Systemic CsA has dose-limiting side effects that also limit its ability to block LG inflammation. Using elastin-like polypeptides (ELPs) fused genetically to cyclophilin, the intracellular cognate receptor of CsA, this manuscript reports a sustained-release formulation of CsA that maintains therapeutic drug concentrations in the LG and extends intervals between doses. This formulation blocked both in vitro Th17 cell differentiation and IL-17A secretion. In vivo treatment significantly decreased the abundance of Th17.1 cells, a helper cell population sharing phenotypes of both Th17 and Th1, in the LG of diseased NOD mice. Treatment with even a single dose of the sustained-release formulation was effective enough to improve basal levels of tear production. Thus, this sustained-release formulation suppressed local LG inflammation driven through IL-17 dependent pathways, while improving ocular surface function.

Vascular hyperacetylation is associated with vascular smooth muscle dysfunction in a rat model of non-obese type 2 diabetes

Background

Advanced type 2 diabetes mellitus (T2DM) accelerates vascular smooth muscle cell (VSMC) dysfunction which contributes to the development of vasculopathy, associated with the highest degree of morbidity of T2DM. Lysine acetylation, a post-translational modification (PTM), has been associated with metabolic diseases and its complications. Whether levels of global lysine acetylation are altered in vasculature from advanced T2DM remains undetermined. We hypothesized that VSMC undergoes dysregulation in advanced T2DM which is associated with vascular hyperacetylation.

Methods

Aged male Goto Kakizaki (GK) rats, a non-obese murine model of T2DM, and age-matched male Wistar rats (control group) were used in this study. Thoracic aortas were isolated and examined for measurement of global levels of lysine acetylation, and vascular reactivity studies were conducted using a wire myograph. Direct arterial blood pressure was assessed by carotid catheterization. Cultured human VSMCs were used to investigate whether lysine acetylation participates in high glucose-induced reactive oxygen species (ROS), a crucial factor triggering diabetic vascular dysfunction.

Results

The GK rats exhibited marked glucose intolerance as well as insulin resistance. Cardiovascular complications in GK rats were confirmed by elevated arterial blood pressure and reduced VSMC-dependent vasorelaxation. These complications were correlated with high levels of vascular global lysine acetylation. Human VSMC cultures incubated under high glucose conditions displayed elevated ROS levels and increased global lysine acetylation. Inhibition of hyperacetylation by garcinol, a lysine acetyltransferase and p300/CBP association factor (PCAF) inhibitor, reduced high glucose-induced ROS production in VSMC.

Conclusion

This study provides evidence that vascular hyperacetylation is associated with VSMC dysfunction in advanced T2DM. Understanding lysine acetylation regulation in blood vessels from diabetics may provide insight into the mechanisms of diabetic vascular dysfunction, and opportunities for novel therapeutic approaches to treat diabetic vascular complications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00441-4.

Abdominal Aortic Aneurysm Formation with a Focus on Vascular Smooth Muscle Cells

Abdominal aortic aneurysm (AAA) is a lethal degenerative vascular disease that affects, mostly, the elder population, with a high mortality rate (>80%) upon rupture. It features a dilation of the aortic diameter to larger than 30 mm or more than 50%. Diverse pathological processes are involved in the development of AAA, including aortic wall inflammation, elastin breakdown, oxidative stress, smooth muscle cell (SMC) phenotypic switching and dysfunction, and extracellular matrix degradation. With open surgery being the only therapeutic option up to date, the lack of pharmaceutical treatment approach calls for identifying novel and effective targets and further understanding the pathological process of AAA. Both lifestyle and genetic predisposition have an important role in increasing the risk of AAA. Several cell types are closely related to the pathogenesis of AAA. Among them, vascular SMCs (VSMCs) are gaining much attention as a critical contributor for AAA initiation and/or progression. In this review, we summarize what is known about AAA, including the risk factors, the pathophysiology, and the established animal models of AAA. In particular, we focus on the VSMC phenotypic switching and dysfunction in AAA formation. Further understanding the regulation of VSMC phenotypic changes may provide novel therapeutic targets for the treatment or prevention of AAA.

Cyclophilin A Is Not Acetylated at Lysine-82 and Lysine-125 in Resting and Stimulated Platelets

Cyclophilin A (CyPA) is widely expressed by all prokaryotic and eukaryotic cells. Upon activation, CyPA can be released into the extracellular space to engage in a variety of functions, such as interaction with the CD147 receptor, that contribute to the pathogenesis of cardiovascular diseases. CyPA was recently found to undergo acetylation at K82 and K125, two lysine residues conserved in most species, and these modifications are required for secretion of CyPA in response to cell activation in vascular smooth muscle cells. Herein we addressed whether acetylation at these sites is also required for the release of CyPA from platelets based on the potential for local delivery of CyPA that may exacerbate cardiovascular disease events. Western blot analyses confirmed the presence of CyPA in human and mouse platelets. Thrombin stimulation resulted in CyPA release from platelets; however, no acetylation was observed-neither in cell lysates nor in supernatants of both untreated and activated platelets, nor after immunoprecipitation of CyPA from platelets. Shotgun proteomics detected two CyPA peptide precursors in the recombinant protein, acetylated at K28, but again, no acetylation was found in CyPA derived from resting or stimulated platelets. Our findings suggest that acetylation of CyPA is not a major protein modification in platelets and that CyPA acetylation is not required for its secretion from platelets.

Redox-sensitive cyclophilin A elicits chemoresistance through realigning cellular oxidative status in colorectal cancer

Cancer cells utilize rapidly elevated cellular antioxidant programs to accommodate chemotherapy-induced oxidative stress; however, the underlying mechanism remains largely unexplored. Here we screen redox-sensitive effectors as potential therapeutic targets for colorectal cancer (CRC) treatment and find that cyclophilin A (CypA) is a compelling candidate. Our results show that CypA forms an intramolecular disulfide bond between Cys115 and Cys161 upon oxidative stress and the oxidized cysteines in CypA are recycled to a reduced state by peroxiredoxin-2 (PRDX2). Furthermore, CypA reduces cellular reactive oxygen species levels and increases CRC cell survival under insults of H₂O₂ and chemotherapeutics through a CypA-PRDX2-mediated antioxidant apparatus. Notably, CypA is upregulated in chemoresistant CRC samples, which predicts poor prognosis. Moreover, targeting CypA by cyclosporine A exhibits promising efficacy against chemoresistant CRC when combined with chemotherapeutics. Collectively, our findings highlight CypA as a component of cellular noncanonical antioxidant defense and as a potential druggable therapeutic target to ameliorate CRC chemoresistance.

Secreted Extracellular Cyclophilin A Is a Novel Mediator of Ventilator-induced Lung Injury

Rationale: Mechanical ventilation is a mainstay of intensive care but contributes to the mortality of patients through ventilator-induced lung injury. eCypA (extracellular CypA [cyclophilin A]) is an emerging inflammatory mediator and metalloproteinase inducer, and the gene responsible for its expression has recently been linked to coronavirus disease (COVID-19). Objectives: To explore the involvement of eCypA in the pathophysiology of ventilator-induced lung injury. Methods: Mice were ventilated with a low or high Vt for up to 3 hours, with or without blockade of eCypA signaling, and lung injury and inflammation were evaluated. Human primary alveolar epithelial cells were exposed to in vitro stretching to explore the cellular source of eCypA, and CypA concentrations were measured in BAL fluid from patients with acute respiratory distress syndrome to evaluate the clinical relevance. Measurements and Main Results: High-Vt ventilation in mice provoked a rapid increase in soluble CypA concentration in the alveolar space but not in plasma. In vivo ventilation and in vitro stretching experiments indicated the alveolar epithelium as the likely major source. In vivo blockade of eCypA signaling substantially attenuated physiological dysfunction, macrophage activation, and MMPs (matrix metalloproteinases). Finally, we found that patients with acute respiratory distress syndrome showed markedly elevated concentrations of eCypA within BAL fluid. Conclusions: CypA is upregulated within the lungs of injuriously ventilated mice (and critically ill patients), where it plays a significant role in lung injury. eCypA represents an exciting novel target for pharmacological intervention.

Drug discovery focused on novel pathogenic proteins for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a fatal disease in which the wall thickening and narrowing of pulmonary microvessels progress due to complicated interactions among processes such as endothelial dysfunction, the proliferation of pulmonary artery smooth muscle cells (PASMCs) and adventitial fibrocytes, and inflammatory cell infiltration. Early diagnosis of patients with PAH is difficult and lung transplantation is the only last choice to save severely ill patients. However, the number of donors is limited. Many patients with PAH show rapid progression and a high degree of pulmonary arterial remodeling characterized by the abnormal proliferation of PASMCs, which makes treatment difficult even with multidrug therapy comprising pulmonary vasodilators. Thus, it is important to develop novel therapy targeting factors other than vasodilation, such as PASMC proliferation. In the development of PAH, inflammation and oxidative stress are deeply involved in its pathogenesis. Excessive proliferation and apoptosis resistance in PASMCs are key mechanisms underlying PAH. Based on those characteristics, we recently screened novel pathogenic proteins and have performed drug discovery targeting those proteins. To confirm the clinical significance of this, we used patient-derived blood samples to evaluate biomarker potential for diagnosis and prognosis. Moreover, we conducted high throughput screening and found several inhibitors of the pathogenic proteins. In this review, we introduce the recent progress on basic and clinical PAH research, focusing on the screening of pathogenic proteins and drug discovery.

Cyclophilin 19 secreted in the host cell cytosol by Trypanosoma cruzi promotes ROS production required for parasite growth

Infection by Trypanosoma cruzi, the protozoan parasite that causes Chagas disease, depends on reactive oxygen species (ROS), which has been described to induce parasite proliferation in mammalian host cells. It is unknown how the parasite manages to increase host ROS levels. Here, we found that intracellular T. cruzi forms release in the host cytosol its major cyclophilin of 19 kDa (TcCyp19). Parasites depleted of TcCyp19 by using CRISPR/Cas9 gene replacement proliferate inefficiently and fail to increase ROS, compared to wild type parasites or parasites with restored TcCyp19 gene expression. Expression of TcCyp19 in L6 rat myoblast increased ROS levels and restored the proliferation of TcCyp19 depleted parasites. These events could also be inhibited by cyclosporin A, (a cyclophilin inhibitor), and by polyethylene glycol-linked to antioxidant enzymes. TcCyp19 was found more concentrated in the membrane leading edges of the host cells in regions that also accumulate phosphorylated p47^phox , as observed to the endogenous cyclophilin A, suggesting some mechanisms involved with the translocation process of the regulatory subunit p47^phox in the activation of the NADPH oxidase enzymatic complex. We concluded that cyclophilin released in the host cell cytosol by T. cruzi mediates the increase of ROS, required to boost parasite proliferation in mammalian hosts.

Mycoplasma genitalium Protein of Adhesion Induces Inflammatory Cytokines via Cyclophilin A-CD147 Activating the ERK-NF-κB Pathway in Human Urothelial Cells

Mycoplasma genitalium protein of adhesion (MgPa) plays an important role in the process of adhesion and invasion of host cells by M. genitalium, and is thus significant for its pathogenic mechanisms in host cells. Our previous study has demonstrated that cyclophilin A (CypA) is the receptor for MgPa in human urothelial cells (SV-HUC-1) and can, therefore, mediate the adherence and invasion of M. genitalium into host cells by interacting with MgPa. However, the specific pathogenesis of M. genitalium to host cells and the possible pathogenic mechanism involved in the interaction of MgPa and CypA have never been clarified. The study aimed to elucidate the mechanism involved in the pathogenicity of MgPa. Recombinant MgPa (rMgPa) induced extracellular CypA (eCypA) was detected in SV-HUC-1 cells by ELISA, and the interaction between CypA and CD147 was validated using co-localization and co-immunoprecipitation assay. In addition, both extracellular signal-regulated kinases (ERK) phosphorylation and NF-κB activation evoked by rMgPa-induced eCypA were also demonstrated. The findings of this study verified that rMgPa could induce the secretion of eCypA in SV-HUC-1 cells and thus promote the protein and mRNA expression of IL-1β, IL-6, TNF-α and MMP-9 via CypA-CD147 interaction and thus activating ERK-NF-κB pathway, which is beneficial to elucidate the pathogenesis and possible pathogenic mechanism of M. genitalium to host cells.

Genetic and Epigenetic Mechanisms Underlying Vascular Smooth Muscle Cell Phenotypic Modulation in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) refers to the localized dilatation of the infra-renal aorta, in which the diameter exceeds 3.0 cm. Loss of vascular smooth muscle cells, degradation of the extracellular matrix (ECM), vascular inflammation, and oxidative stress are hallmarks of AAA pathogenesis and contribute to the progressive thinning of the media and adventitia of the aortic wall. With increasing AAA diameter, and left untreated, aortic rupture ensues with high mortality. Collective evidence of recent genetic and epigenetic studies has shown that phenotypic modulation of smooth muscle cells (SMCs) towards dedifferentiation and proliferative state, which associate with the ECM remodeling of the vascular wall and accompanied with increased cell senescence and inflammation, is seen in in vitro and in vivo models of the disease. This review critically analyses existing publications on the genetic and epigenetic mechanisms implicated in the complex role of SMCs within the aortic wall in AAA formation and reflects the importance of SMCs plasticity in AAA formation. Although evidence from the wide variety of mouse models is convincing, how this knowledge is applied to human biology needs to be addressed urgently leveraging modern in vitro and in vivo experimental technology.

Endothelial-to-Mesenchymal Transition and Inflammation Play Key Roles in Cyclophilin A-Induced Pulmonary Arterial Hypertension

Oxidative stress and inflammation play key roles in development of pulmonary arterial hypertension (PAH). We previously reported that an endothelial cell (EC)-specific cyclophilin A overexpression mouse developed many characteristics of PAH. In other models of cardiovascular disease, cyclophilin A stimulates smooth muscle proliferation and vascular inflammation, but mechanisms responsible for PAH have not been defined. In particular, the contribution of endothelial-to-mesenchymal transition in cyclophilin A-mediated PAH has not been studied. We identified increased levels of cyclophilin A in endothelial and neointimal cells of pulmonary arteries in patients with PAH and animal pulmonary hypertension models. In the EC-specific cyclophilin A overexpression mouse that exhibited features characteristic of PAH, lineage tracing showed high level expression of mesenchymal markers in pulmonary ECs. A significant number of mesenchymal cells in media and perivascular regions of pulmonary arterioles and alveoli were derived from ECs. Pulmonary ECs isolated from these mice showed phenotypic changes characteristic of endothelial-to-mesenchymal transition in culture. Cultured pulmonary ECs stimulated with extracellular cyclophilin A and acetylated cyclophilin A demonstrated functional changes associated with endothelial-to-mesenchymal transition such as increased cytokine release, migration, proliferation, and mitochondrial dysfunction. Acetylated cyclophilin A stimulated greater increases for most features of endothelial-to-mesenchymal transition. In conclusion, extracellular cyclophilin A (especially acetylated form) contributes to PAH by mechanisms involving increased endothelial-to-mesenchymal transition, cytokine release, EC migration, proliferation, and mitochondrial dysfunction; strengthening the basis for studying cyclophilin A inhibition as a therapy for PAH.

The Release of Cyclophilin A from Rapamycin-Stimulated Vascular Smooth Muscle Cells Mediated by Myosin II Activation: Involvement of Apoptosis but Not Autophagy

INTRODUCTION

The exocytosis of cyclophilin A (CyPA) by a vesicular pathway in response to reactive oxygen species has been determined. However, other sources of extracellular CyPA remain obscure.

OBJECTIVE

The aim of this study was to determine the role of autophagy in the secretion of CyPA.

METHODS AND RESULTS

Rapamycin induced the activation of autophagy and release of CyPA from primary cultured rat aortic smooth muscle cells (RASMCs). However, inhibition of autophagy by knockdown of Atg7 or chloroquine did not affect the rapamycin-induced release of CyPA. With the exception of myosin II activity, rho-associated coiled-coil kinase (ROCK), actin remodelling, and synaptic vesicles were not implicated in the release of rapamycin-induced CyPA. Finally, we confirmed that rapamycin-induced extracellular CyPA originated from apoptotic RASMCs. Furthermore, the decreased activation of myosin II by blebbistatin blocked the release of CyPA from apoptotic RASMCs induced by rapamycin.

CONCLUSIONS

Rapamycin induced the release of CyPA from apoptotic RASMCs but did not affect exocytosis through autophagosomes. ROCK, actin remodelling, and synaptic vesicles were not involved in the apoptosis-related release of CyPA. Myosin II activation modulated the apoptosis of vascular smooth muscle cells and the release of CyPA from rapamycin-induced apoptotic cell death.

Acetylation in cardiovascular diseases: Molecular mechanisms and clinical implications

Acetylation belongs to a class of post-translational modification (PTM) processes that epigenetically regulate gene expression and gene transcriptional activity. Reversible histone acetylation on lysine residues governs the interactions between DNA and histones to mediate chromatin remodeling and gene transcription. Non-histone protein acetylation complicates cellular function whereas acetylation of key mitochondrial enzymes regulates bioenergetic metabolism. Acetylation and deacetylation of functional proteins are essential to the delicated homeostatic regulation of embryonic development, postnatal maturation, cardiomyocyte differentiation, cardiac remodeling and onset of various cardiovascular diseases including obesity, diabetes mellitus, cardiometabolic diseases, ischemia-reperfusion injury, cardiac remodeling, hypertension, and arrhythmias. Histone acetyltransferase (HATs) and histone deacetylases (HDACs) are essential enzymes mainly responsible for the regulation of lysine acetylation levels, thus providing possible drugable targets for therapeutic interventions in the management of cardiovascular diseases.

Dual peptide-dendrimer conjugate inhibits acetylation of transforming growth factor β-induced protein and improves survival in sepsis

Sepsis is a potentially fatal complication of infections and there are currently no effective therapeutic options for severe sepsis. In this study, we revealed the secretion mechanism of transforming growth factor β-induced protein (TGFBIp) that was recently identified as a therapeutic target for sepsis, and designed TGFBIp acetylation inhibitory peptide (TAIP) that suppresses acetylation of lysine 676 in TGFBIp. To improve bioavailability and biodegradation of the peptide, TAIP was conjugated to polyamidoamine (PAMAM) dendrimers. Additionally, the cell-penetrating peptide (CPP) was conjugated to the TAIP-modified PAMAM dendrimers for the intracellular delivery of TGFBIp. The resulting nanostructures, decorated with TAIP and CPP via poly(ethylene glycol) linkage, improved the mortality and organ damage in the septic mouse model and suppressed lipopolysaccharide-activated severe vascular inflammatory responses in endothelial cells. Thus, the dendrimer-based nanostructures for delivery of TAIP using CPP show great promise in practical applications in sepsis therapy.

Cyclophilin a signaling induces pericyte-associated blood-brain barrier disruption after subarachnoid hemorrhage

Objective

The potential roles and mechanisms of pericytes in maintaining blood–brain barrier (BBB) integrity, which would be helpful for the development of therapeutic strategies for subarachnoid hemorrhage (SAH), remain unclear. We sought to provide evidence on the potential role of pericytes in BBB disruption and possible involvement and mechanism of CypA signaling in both cultured pericytes and SAH models.

Methods

Three hundred fifty-three adult male C57B6J mice weighing 22 to 30 g, 29 CypA^−/− mice, 30 CypA^+/+ (flox/flox) mice, and 30 male neonatal C57B6J mice were used to investigate the time course of CypA expression in pericytes after SAH, the intrinsic function and mechanism of CypA in pericytes, and whether the known receptor CD147 mediates these effects.

Results

Our data demonstrated both intracellular CypA and CypA secretion increased after SAH and could activate CD147 receptor and downstream NF-κB pathway to induce MMP9 expression and proteolytic functions for degradation of endothelium tight junction proteins and basal membranes. CypA served as autocrine or paracrine ligand for its receptor, CD147. Although CypA could be endocytosed by pericytes, specific endocytosis inhibitor chlorpromazine did not have any effect on MMP9 activation. However, specific knockdown of CD147 could reverse the harmful effects of CypA expression in pericytes on the BBB integrity after SAH.

Conclusions

This study demonstrated for the first time that CypA mediated the harmful effects of pericytes on BBB disruption after SAH, which potentially mediated by CD147/NF-κB/MMP9 signal, and junction protein degradation in the brain. By targeting CypA and pericytes, this study may provide new insights on the management of SAH patients.

Role of CyPA in cardiac hypertrophy and remodeling

Pathological cardiac hypertrophy is a complex process and eventually develops into heart failure, in which the heart responds to various intrinsic or external stress, involving increased interstitial fibrosis, cell death and cardiac dysfunction. Studies have shown that oxidative stress is an important mechanism for this maladaptation. Cyclophilin A (CyPA) is a member of the cyclophilin (CyPs) family. Many cells secrete CyPA to the outside of the cells in response to oxidative stress. CyPA from blood vessels and the heart itself participate in a variety of signaling pathways to regulate the production of reactive oxygen species (ROS) and mediate inflammation, promote cardiomyocyte hypertrophy and proliferation of cardiac fibroblasts, stimulate endothelial injury and vascular smooth muscle hyperplasia, and promote the dissolution of extracellular matrix (ECM) by activating matrix metalloproteinases (MMPs). The events triggered by CyPA cause a decline of diastolic and systolic function and finally lead to the occurrence of heart failure. This article aims to introduce the role and mechanism of CyPA in cardiac hypertrophy and remodeling, and highlights its potential role as a disease biomarker and therapeutic target.

Inhibition of Cyclophilin A on the replication of red spotted grouper nervous necrosis virus associates with multiple pro-inflammatory factors

Cyclophilin A (CypA) is a ubiquitously expressed cellular protein and involves in diverse pathological conditions, including infection and inflammation. CypA acts as a key factor in the replication of several viruses. However, little is known about the role of CypA in the replication of the red-spotted grouper nervous necrosis virus (RGNNV). In the present report, grouper CypA (GF-CypA) was cloned from the grouper fin cell line (GF-1) derived from orange-spotted grouper (Epinephelus coioides). Sequence analysis found that GF-CypA open reading frame (ORF) of 495 bp encodes a polypeptide of 164 amino acids residues with a molecular weight of 17.4 kDa. The deduced amino acid sequence shared highly conserved regions with CypA of other animal species, showing that GF-CypA is a new member of Cyclophilin A family. We observed that GF-CypA was up-regulated in the GF-1 cells infected with RGNNV. Additionally, overexpression of CypA could significantly inhibit the replication of RGNNV in GF-1 cells. By contrast, when the GF-CypA was knock-downed by siRNA in GF-1 cells, the replication of RGNNV was enhanced. Furthermore, the expressions of pro-inflammatory factors, such as TNF-2, TNF-α, IL-1b, and ISG-15, were increased in GF-CypA transfected GF-1 cells challenged with RGNNV, indicating that GF-CypA might be involved in the regulation of the host pro-inflammatory factors. Altogether, we conclude that GF-CypA plays a vital role in the inhibitory effect of RGNNV replication that might be modulating the cytokines secretion in GF-1 cells during RGNNV infection. These results will shed new light on the function of CypA in the replication of RGNNV and will pave a new way for the prevention of the infection of RGNNV in fish.

ATP Binding Cassette Transporter A1 is Involved in Extracellular Secretion of Acetylated APE1/Ref-1

Acetylation of nuclear apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE1/Ref-1) is associated with its extracellular secretion, despite the lack of an N-terminal protein secretion signal. In this study, we investigated plasma membrane targeting and translocation of APE1/Ref-1 in HEK293T cells with enhanced acetylation. While APE1/Ref-1 targeting was not affected by inhibition of the endoplasmic reticulum/Golgi-dependent secretion, its secretion was reduced by inhibitors of ATP-binding cassette (ABC) transporters, and siRNA-mediated down-regulation of ABC transporter A1. The association between APE1/Ref-1 and ABCA1 transporter was confirmed by proximal ligation assay and immunoprecipitation experiments. An APE1/Ref-1 construct with mutated acetylation sites (K6/K7R) showed reduced co-localization with ABC transporter A1. Exposure of trichostatin A (TSA) induced the acetylation of APE1/Ref-1, which translocated into membrane fraction. Taken together, acetylation of APE1/Ref-1 is considered to be necessary for its extracellular targeting via non-classical secretory pathway using the ABCA1 transporter.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Metformin attenuates effects of cyclophilin A on macrophages, reduces lipid uptake and secretion of cytokines by repressing decreased AMPK activity

Growing evidence implicates cyclophilin A secreted by vascular wall cells and monocytes as a key mediator in atherosclerosis. Cyclophilin A in addition to its proliferative effects, during hyperglycemic conditions, increases lipid uptake in macrophages by increasing scavenger receptors on the cell's surface. It also promotes macrophage migration across endothelial cells and conversion of macrophages into foam cells. Given the known effects of metformin in reducing vascular complications of diabetes, we investigated the effect of metformin on cyclophilin A action in macrophages. Using an ex vivo model of cultured macrophages isolated from patients with type 2 diabetes with and without coronary artery disease (CAD), we measured the effect of metformin on cyclophilin A expression, lipid accumulation, expression of scavenger receptors, plasma cytokine levels and AMP-activated protein kinase (AMPK) activity in macrophages. In addition, the effects of metformin on migration of monocytes, reactive oxygen species (ROS) formation, lipid uptake in the presence of cyclophilin A inhibitors and comparison with pioglitazone were studied using THP-1 monocytes. Metformin reduced cyclophilin A expression in human monocyte-derived macrophages. Metformin also decreased the effects of cyclophilin A on macrophages such as oxidized low-density lipoprotein (oxLDL) uptake, scavenger receptor expression, ROS formation and secretion of inflammatory cytokines in high-glucose conditions. Metformin reversed cyclophilin A-induced decrease in AMPK-1α activity in macrophages. These effects of metformin were similar to those of cyclophilin A inhibitors. Metformin can thus function as a suppressor of pro-inflammatory effects of cyclophilin A in high-glucose conditions by attenuating its expression and repressing cyclophilin A-induced decrease in AMPK-1α activity in macrophages.

Extracellular and Intracellular Cyclophilin A, Native and Post-Translationally Modified, Show Diverse and Specific Pathological Roles in Diseases

CypA (cyclophilin A) is a ubiquitous and highly conserved protein with peptidyl prolyl isomerase activity. Because of its highly abundant level in the cytoplasm, most studies have focused on the roles of CypA as an intracellular protein. However, emerging evidence suggests an important role for extracellular CypA in the pathogenesis of several diseases through receptor (CD147 or other)-mediated autocrine and paracrine signaling pathways. In this review, we will discuss the shared and unique pathological roles of extracellular and intracellular CypA in human cardiovascular diseases. In addition, the evolving role of post-translational modifications of CypA in the pathogenesis of disease is discussed. Finally, recent studies with drugs specific for extracellular CypA show its importance in disease pathogenesis in several animal models and make extracellular CypA a new therapeutic target.

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.

The clinical implication of serum cyclophilin A in patients with chronic obstructive pulmonary disease

Background

Cyclophilin A (CyPA) is a secreted molecule that is regulated by inflammatory stimuli. Although inflammation has an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD), little is known regarding the relationship between serum CyPA and COPD.

Methods

Ninety-three COPD patients with acute exacerbation were enrolled in the study and were reassessed during the convalescence phase. Eighty-eight controls were matched for age, gender, body mass index, smoking index and comorbidity. The basic clinical information and pulmonary function of all participants were collected. Serum levels of CyPA and other inflammation indexes were further measured.

Results

Serum CyPA was significantly increased in convalescent COPD patients compared to healthy controls, and further elevated in COPD patients with acute exacerbation. Serum CyPA positively correlated with serum interleukin-6, matrix metalloproteinase-9 and high-sensitivity C-reactive protein in both the exacerbation and convalescence phases of COPD. Furthermore, it negatively correlated with percent value of forced expiratory volume in 1 second (FEV₁%) predicted and FEV₁/forced vital capacity in convalescent COPD patients.

Conclusion

These results suggest that serum CyPA can be used as a potential inflammatory biomarker for COPD and assessment of serum CyPA may reflect the severity of inflammation in COPD.

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

BACKGROUND

Autophagy is a major intracellular degradation and recycling process that maintains cellular homeostasis, which is involved in structural and functional abnormalities of pulmonary vasculature in hypoxic pulmonary arterial hypertension (HPAH). Cyclophilin A (CyPA) is a secreted, oxidative stress-induced factor. Its role in inducing autophagy and augmenting endothelial cell dysfunction has never been explored.

METHODS

Lungs from rats exposed to chronic hypoxia were examined for autophagy with electron microscopy, western blotting, and fluorescence microscopy.

RESULTS

Activated autophagy was seen in the endothelium of the pulmonary artery from experimental rat models of HPAH and cultured bovine pulmonary arterial endothelial cells under hypoxia. Inhibiting autophagy attenuated the pathological progression of HPAH and repressed endothelial cell migration and angiogenesis. We also showed that CyPA was upregulated and acetylated under hypoxia and led to the abnormal occurrence of autophagy through its interaction with autophagy protein 5 and autophagy protein 7. Moreover, acetylated CyPA was essential for the excessive proliferation, migration, and tube formation networks of pulmonary arterial endothelial cells.

CONCLUSION

Our results indicate the crucial role of acetylated CyPA in the abnormal occurrence of autophagy and subsequent pulmonary vascular angiogenesis.

Extracellular Cyclophilin A, Especially Acetylated, Causes Pulmonary Hypertension by Stimulating Endothelial Apoptosis, Redox Stress, and Inflammation

OBJECTIVE

Oxidative stress and inflammation play key roles in the development of pulmonary arterial hypertension (PAH). Cyclophilin A (CypA) is secreted in response to oxidative stress and promotes inflammation and cardiovascular disease. Endothelial cell (EC) dysfunction is an early event in the pathogenesis of PAH. We evaluated the role of extracellular CypA in PAH and compared the effects of acetylated CypA (AcK-CypA, increased by oxidative stress) and CypA on EC dysfunction.

APPROACH AND RESULTS

In transgenic mice that express high levels of CypA in EC specifically, a PAH phenotype was observed at 3 months including increased right ventricular systolic pressure, α-smooth muscle actin expression in small arterioles, and CD45-positive cells in the lungs. Mechanistic analysis using cultured mouse pulmonary microvascular EC and human pulmonary microvascular EC showed that extracellular CypA and AcK-CypA stimulated EC inflammatory signals: increased VCAM1 (vascular cell adhesion molecule 1) and ICAM1 (intercellular adhesion molecule 1), phosphorylation of p65, and degradation of IkB. Extracellular CypA and AcK-CypA increased EC apoptosis measured by TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) staining, Apo-ONE assay, and caspase 3 cleavage. Oxidative stress stimulated CypA and AcK-CypA secretion, which further promoted EC oxidative stress. AcK-CypA, compared with CypA, stimulated greater increases in apoptosis, inflammation, and oxidative stress. MM284, a specific inhibitor of extracellular CypA, attenuated EC apoptosis induced by CypA and AcK-CypA.

CONCLUSIONS

EC-derived CypA (especially AcK-CypA) causes PAH by a presumptive mechanism involving increased EC apoptosis, inflammation, and oxidative stress. Our results suggest that inhibiting secreted extracellular CypA is a novel therapeutic approach for PAH.

Secreted miR-27a Induced by Cyclic Stretch Modulates the Proliferation of Endothelial Cells in Hypertension via GRK6

Abnormal proliferation of endothelial cells (ECs) is important in vascular remodeling during hypertension, but the mechanisms are still unclear. In hypertensive rats caused by abdominal aortic coarctation, the expression of G-protein-coupled receptor kinase 6 (GRK6) in ECs at common carotid artery was repressed in vivo, and EC proliferation was increased. 15% cyclic stretch in vitro, which mimics the pathologically increased stretch in hypertension, repressed EC GRK6 expression via paracrine control by vascular smooth muscle cells (VSMCs). Furthermore, VSMC-derived microparticles (VSMC-MPs) were detected in the conditioned medium from VSMCs and in artery. VSMC-MPs from cells exposed to 15% cyclic stretch decreased GRK6 expression and increased EC proliferation. miR-27a was detected in VSMC-MPs and was upregulated by 15% cyclic stretch. miR-27a was transferred from VSMCs to ECs via VSMC-MPs and directly targeted on GRK6. Finally, a multi-point injection of antagomiR-27a around carotid artery decreased miR-27a expression in vivo, induced GRK6 expression, and reversed the abnormal EC proliferation. Pathologically elevated cyclic stretch increased the secretion of miR-27a, which was transferred from VSMCs to ECs via the VSMC-MPs, subsequently targeted GRK6, and induced EC proliferation. Locally decreasing miR-27a could be a novel therapeutic approach to attenuate the abnormal EC proliferation in hypertension.

Genetic and Epigenetic Regulation of Aortic Aneurysms

Aneurysms are characterized by structural deterioration of the vascular wall leading to progressive dilatation and, potentially, rupture of the aorta. While aortic aneurysms often remain clinically silent, the morbidity and mortality associated with aneurysm expansion and rupture are considerable. Over 13,000 deaths annually in the United States are attributable to aortic aneurysm rupture with less than 1 in 3 persons with aortic aneurysm rupture surviving to surgical intervention. Environmental and epidemiologic risk factors including smoking, male gender, hypertension, older age, dyslipidemia, atherosclerosis, and family history are highly associated with abdominal aortic aneurysms, while heritable genetic mutations are commonly associated with aneurysms of the thoracic aorta. Similar to other forms of cardiovascular disease, family history, genetic variation, and heritable mutations modify the risk of aortic aneurysm formation and provide mechanistic insight into the pathogenesis of human aortic aneurysms. This review will examine the relationship between heritable genetic and epigenetic influences on thoracic and abdominal aortic aneurysm formation and rupture.

Targeting Extracellular Cyclophilin A Reduces Neuroinflammation and Extends Survival in a Mouse Model of Amyotrophic Lateral Sclerosis

Neuroinflammation is a major hallmark of amyotrophic lateral sclerosis (ALS), which is currently untreatable. Several anti-inflammatory compounds have been evaluated in patients and in animal models of ALS, but have been proven disappointing in part because effective targets have not yet been identified. Cyclophilin A, also known as peptidylprolyl cis-/trans-isomerase A (PPIA), as a foldase is beneficial intracellularly, but extracellularly has detrimental functions. We found that extracellular PPIA is a mediator of neuroinflammation in ALS. It is a major inducer of matrix metalloproteinase 9 and is selectively toxic for motor neurons. High levels of PPIA were found in the CSF of SOD1^G93A mice and rats and sporadic ALS patients, suggesting that our findings may be relevant for familial and sporadic cases. A specific inhibitor of extracellular PPIA, MM218, given at symptom onset, rescued motor neurons and extended survival in the SOD1^G93A mouse model of familial ALS by 11 d. The treatment resulted in the polarization of glia toward a prohealing phenotype associated with reduced NF-κB activation, proinflammatory markers, endoplasmic reticulum stress, and insoluble phosphorylated TDP-43. Our results indicates that extracellular PPIA is a promising druggable target for ALS and support further studies to develop a therapy to arrest or slow the progression of the disease in patients.SIGNIFICANCE STATEMENT We provide evidence that extracellular cyclophilin A, also known as peptidylprolyl cis-/trans-isomerase A (PPIA), is a mediator of the neuroinflammatory reaction in amyotrophic lateral sclerosis (ALS) and is toxic for motor neurons. Supporting this, a specific extracellular PPIA inhibitor reduced neuroinflammation, rescued motor neurons, and extended survival in the SOD1^G93A mouse model of familial ALS. Our findings suggest selective pharmacological inhibition of extracellular PPIA as a novel therapeutic strategy, not only for SOD1-linked ALS, but possibly also for sporadic ALS. This approach aims to address the neuroinflammatory reaction that is a major hallmark of ALS. However, given the complexity of the disease, a combination of therapeutic approaches may be necessary.

Cyclophilin A enhances macrophage differentiation and lipid uptake in high glucose conditions: a cellular mechanism for accelerated macro vascular disease in diabetes mellitus

Background

Vascular disease in diabetes is initiated by monocyte adhesion to vascular endothelium, transmigration and formation of foam cells. Increasing clinical evidence supports a role for the secretory protein, cyclophilin A in diabetic vascular disease. The means by which cyclophilin A contributes to vascular lesion development in diabetes is however largely unknown.

Methods

In this study we investigated using THP1 cells and human monocytes whether cyclophilin A under hyperglycemic conditions, functions in the inflammatory cascade as a chemoattractant and increases lipid uptake by formation of foam cells invitro. We developed an invitro model of monocytes cultured in 20 mm glucose (high glucose) equivalent to 360 mg/dL of plasma glucose levels. These monocytes were then differentiated into macrophages using PMA and subsequently transformed to lipid laden foam cells using oxidized low density lipoproteins in the presence and absence of cyclophilin A. This cellular model was used to study monocyte to macrophage differentiation, transmigration and foam cell formation. A similar cellular model using siRNA mediated transient elimination of the cyclophilin A gene as well as chemical inhibitors were used to further confirm the role of cyclophilin A in the differentiation and foam cell formation process.

Results

Cyclophilin A effectively increased migration of high glucose treated monocytes to the endothelial cell monolayer (p < 0.0001). In the presence of cyclophilin A, differentiated macrophages, when treated with oxLDL had a 36 percent increase in intracellular lipid accumulation (p = 0.01) when compared to cells treated with oxLDL alone. An increased flux of reactive oxygen species was also observed (p = 0.01). Inflammatory cytokines such as TNF-α, MCP-1 and cyclophilin A were significantly increased. Silencing cyclophilin A in THP-1 cells and human monocytes using siRNA or chemical inhibitor, TMN355 resulted in decrease in lipid uptake by 65–75% even after exposure to oxidized LDL. The expression of scavenger receptors expressed during differentiation process, CD36 and LOX-1 were decreased (p < 0.0001). Levels of extracellular cyclophilin A and other inflammatory cytokines such as TNF-α and MCP-1also significantly reduced.

Conclusions

Taken together, we describe here a possible cellular basis by which cyclophilin A may accelerate atherogenesis in diabetes mellitus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0467-5) contains supplementary material, which is available to authorized users.

Identification of low abundance cyclophilins in human plasma

Cylophilins (Cyps) belong to the ubiquitously distributed enzyme class of peptidyl prolyl cis/trans isomerases (EC5.2.1.8), which are foldases capable of accelerating slow steps in the refolding of denatured proteins. At least 20 different Cyp isoenzymes are broadly distributed among all organs and cellular compartments in humans. Extracellularly localized Cyps came into the scientific focus recently because of their involvement in the control of inflammatory diseases, as well as viral and bacterial infections. However, detailed insights into Cyp functions are often hampered by the lack of sensitive detection methods. We present an improved method for affinity purification and detection of Cyp in biotic samples in this manuscript. The procedure takes advantage of two novel cyclosporine A derivatives. Derivative 1 was used to capture Cyps from the sample while derivative 2 was applied for selective release from the affinity matrix. Using this approach, eight different Cyp (CypA, CypB, CypC, Cyp40 (PPID), CypE, CypD (PPIF), CypH, and CypL1) were unambiguously detected in healthy human blood plasma. Moreover, extracellular CypA was found to be partially modified by N^ε acetylation on residues Lys44, Lys133, Lys155, as well as N^α  acetylation at the N-terminal Val residue. N^α  acetylation of Ser2 residue was also found for Cyp40.

The ɛ-Amino Group of Protein Lysine Residues Is Highly Susceptible to Nonenzymatic Acylation by Several Physiological Acyl-CoA Thioesters

Mitochondrial enzymes implicated in the pathophysiology of diabetes, cancer, and metabolic syndrome are highly regulated by acetylation. However, mitochondrial acetyltransferases have not been identified. Here, we show that acetylation and also other acylations are spontaneous processes that depend on pH value, acyl-CoA concentration and the chemical nature of the acyl residue. In the case of a peptide derived from carbamoyl phosphate synthetase 1, the rates of succinylation and glutarylation were up to 150 times than for acetylation. These results were confirmed by using the protein substrate cyclophilin A (CypA). Deacylation experiments revealed that SIRT3 exhibits deacetylase activity but is not able to remove any of the succinyl groups from CypA, whereas SIRT5 is an effective protein desuccinylase. Thus, the acylation landscape on lysine residues might largely depend on the enzymatic activity of specific sirtuins, and the availability and reactivity of acyl-CoA compounds.

Molecular cloning and functional characterization of cyclophilin A in yellow catfish (Pelteobagrus fulvidraco)

Cyclophilin A (CypA) is a ubiquitously expressed protein which involves in diverse pathological conditions including infection and inflammation. In this report, a CypA gene (designated as YC-CypA) was cloned from yellow catfish (Pelteobagrus fulvidraco) which is an important cultured fish species in Asian countries. The open reading frame (ORF) of YC-CypA encoded a polypeptide of 164 amino acids with calculated molecular weight of 17.70 kDa. The deduced amino acid sequences of the YC-CypA shared highly conserved structures with CypAs from the other species, indicating that YC-CypA should be a new member of the CypA family. Full-length YC-CypA protein was expressed in Escherichia coli and specific polyclonal antibody against YC-CypA was generated. The YC-CypA protein showed chemotactic activity by transwell migration assay. The mRNA and protein of YC-CypA could be detected in all examined tissues with relatively higher mRNA level in spleen and higher protein level in head kidney, respectively. The temporal expression patterns of YC-CypA, IL-1β and TNF-α mRNAs were analyzed in the liver, spleen and head kidney post of Edwardsiella ictaluri infection. By immunohistochemistry assay, slight enhancement of YC-CypA protein was observed in the liver, spleen, body kidney and head kidney of yellow catfish infected with E. ictaluri. In conclusion, YC-CypA of yellow catfish showed chemotactic activity in vitro and might have been involved in cytokines secretion in yellow catfish during the infection of E. ictaluri.

Helicobacter pylori cytotoxin-associated gene A activates tumor necrosis factor-α and interleukin-6 in gastric epithelial cells through P300/CBP-associated factor-mediated nuclear factor-κB p65 acetylation

Helicobacter pylori‑initiated chronic gastritis is characterized by the cytotoxin‑associated gene (Cag) pathogenicity island‑dependent upregulation of pro‑inflammatory cytokines in gastric epithelial cells, which is largely mediated by the activation of nuclear factor (NF)‑κB as a transcription factor. However, the precise regulation of NF‑κB activation, particularly post‑translational modifications in the CagA‑induced inflammatory response, has remained elusive. The present study showed that Helicobacter pylori CagA, an important virulence factor, induced the expression of P300/CBP‑associated factor (PCAF) in gastric epithelial cells. Further study revealed that PCAF was able to physically associate with the NF‑κB p65 sub‑unit and enhance its acetylation. More importantly, PCAF‑induced p65 acetylation was shown to contribute to p65 phosphorylation and further upregulation of tumor necrosis factor (TNF)‑α and interleukin (IL)‑6 in gastric adenocarcinoma cells. In conclusion, the results of the present study indicated that Helicobacter pylori CagA enhanced TNF‑α and IL‑6 in gastric adenocarcinoma cells through PCAF‑mediated NF‑κB p65 sub‑unit acetylation.

Ionizing radiation induces immediate protein acetylation changes in human cardiac microvascular endothelial cells

Reversible lysine acetylation is a highly regulated post-translational protein modification that is known to regulate several signaling pathways. However, little is known about the radiation-induced changes in the acetylome. In this study, we analyzed the acute post-translational acetylation changes in primary human cardiac microvascular endothelial cells 4 h after a gamma radiation dose of 2 Gy. The acetylated peptides were enriched using anti-acetyl conjugated agarose beads. A total of 54 proteins were found to be altered in their acetylation status, 23 of which were deacetylated and 31 acetylated. Pathway analyses showed three protein categories particularly affected by radiation-induced changes in the acetylation status: the proteins involved in the translation process, the proteins of stress response, and mitochondrial proteins. The activation of the canonical and non-canonical Wnt signaling pathways affecting actin cytoskeleton signaling and cell cycle progression was predicted. The protein expression levels of two nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases, sirtuin 1 and sirtuin 3, were significantly but transiently upregulated 4 but not 24 h after irradiation. The status of the p53 protein, a target of sirtuin 1, was found to be rapidly stabilized by acetylation after radiation exposure. These findings indicate that post-translational modification of proteins by acetylation and deacetylation is essentially affecting the radiation response of the endothelium.

The roles of CD147 and/or cyclophilin A in kidney diseases

CD147 is a widely expressed integral plasma membrane glycoprotein and has been involved in a variety of physiological and pathological activities in combination with different partners, including cyclophilins, caveolin-1, monocarboxylate transporters, and integrins. Recent data demonstrate that both CyPA and CD147 significantly contribute to renal inflammation, acute kidney injury, renal fibrosis, and renal cell carcinoma. Here we review the current understanding of cyclophilin A and CD147 expression and functions in kidney diseases and potential implications for treatment of kidney diseases.

Extracellular cyclophilins in health and disease

BACKGROUND

Extracellular cyclophilins (eCyPs) are pro-inflammatory factors implicated in pathogenesis of a number of inflammatory diseases. Most pathogenic activities of eCyPs are related to their chemotactic action towards leukocytes, which is mediated by eCyP receptor on target cells, CD147, and involves peptidyl-prolyl cis-trans isomerase activity of cyclophilins. This activity is inhibited by cyclosporine A (CsA) and non-immunosuppressive derivatives of this drug. Accumulating evidence for the role of eCyPs in disease pathogenesis stimulated research on the mechanisms of eCyP-initiated events, resulting in identification of multiple signaling pathways, characterization of a variety of effector molecules released from eCyP-treated cells, and synthesis of CsA derivatives specifically blocking eCyPs. However, a number of important questions related to the mode of action of eCyPs remain unanswered.

SCOPE OF REVIEW

In this article, we integrate available information on release and function of extracellular cyclophilins into a unified model, focusing on outstanding issues that need to be clarified.

MAJOR CONCLUSIONS

Extracellular cyclophilins are critical players in pathogenesis of a number of inflammatory diseases. Their mechanism of action involves interaction with the receptor, CD147, and initiation of a poorly characterized signal transduction process culminating in chemotaxis and production of pro-inflammatory factors.

GENERAL SIGNIFICANCE

Extracellular cyclophilins present an attractive target for therapeutic interventions that can be used to alleviate symptoms and consequences of acute and chronic inflammation. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.