Caveolin-1, transforming growth factor-β receptor internalization, and the pathogenesis of systemic sclerosis

Donor caveolin 1 (CAV1) genetic polymorphism influences graft function after renal transplantation

Background

Identification of the culprit genes underlying multifactorial diseases is one of the most important current challenges of molecular genetics. While recent advances in genomics research have accelerated the discovery of susceptibility genes, much remains to be learned about the functions of disease-associated genetic variants. Recently, Moore and co-workers identified, in the donor genome, an association between a common genetic variant (rs4730751) in the gene encoding caveolin-1 (CAV1), a major structural component of caveolae, and long-term allograft survival.

Methods

Four hundred seventy-five renal recipients consecutively transplanted were included in this study. Donor genomic DNA was extracted and used to genotype CAV1 rs4730751 Single Nucleotide Polymorphism.

Results

Patients receiving a graft carrying CAV1 rs4730751 AA genotype displayed a significant decrease in estimated glomerular filtration rate and a significant increase in serum creatinine in both univariate and multivariate analyzes. Moreover, patients receiving a graft with CAV1 AA genotype significantly developed more interstitial fibrosis lesions on systematic biopsies performed 3 months post-transplantation.

Conclusions

Genotyping of CAV1 may be relevant to identify patients at risk of adverse renal transplant outcome.

Gene network and canonical pathway analysis in canine myxomatous mitral valve disease: a microarray study

Myxomatous mitral valve disease (MMVD) is the single most common acquired heart disease of the dog and is particularly common in small pedigree breed dogs such as the Cavalier King Charles spaniel (CKCS). There are limited data on the mitral valve transcriptome and the aim of this study was to use the microarray technology in conjunction with bioinformatics platforms to analyse transcript changes in MMVD in CKCS compared to normal dogs (non-CKCS). Differentially expressed genes (n = 5397) were identified using cut-off settings of fold change, false discovery rate (FDR) and P <0.05. In total, 4002 genes were annotated to a specific transcript in the Affymetrix canine database, and after further filtering, 591 annotated canine genes were identified: 322 (55%) were up-regulated and 269 (45%) were down-regulated. Canine microRNAs (cfa-miR; n = 59) were also identified. Gene ontology and network analysis platforms identified between six and 10 significantly different biological function clusters from which the following were selected as relevant to MMVD: inflammation, cell movement, cardiovascular development, extracellular matrix organisation and epithelial-to-mesenchymal (EMT) transition. Ingenuity Pathway Analysis identified three canonical pathways relevant to MMVD: caveolar-mediated endocytosis, remodelling of epithelial adherens junctions, and endothelin-1 signalling. Considering the biological relevance to MMVD, the gene families of importance with significant difference between groups included collagens, ADAMTS peptidases, proteoglycans, matrix metalloproteinases (MMPs) and their inhibitors, basement membrane components, cathepsin S, integrins, tight junction cell adhesion proteins, cadherins, other matrix-associated proteins, and members of the serotonin (5-HT)/transforming growth factor -β signalling pathway.

The significance of macrophage polarization subtypes for animal models of tissue fibrosis and human fibrotic diseases

The systemic and organ-specific human fibrotic disorders collectively represent one of the most serious health problems world-wide causing a large proportion of the total world population mortality. The molecular pathways involved in their pathogenesis are complex and despite intensive investigations have not been fully elucidated. Whereas chronic inflammatory cell infiltration is universally present in fibrotic lesions, the central role of monocytes and macrophages as regulators of inflammation and fibrosis has only recently become apparent. However, the precise mechanisms involved in the contribution of monocytes/macrophages to the initiation, establishment, or progression of the fibrotic process remain largely unknown. Several monocyte and macrophage subpopulations have been identified, with certain phenotypes promoting inflammation whereas others display profibrotic effects. Given the unmet need for effective treatments for fibroproliferative diseases and the crucial regulatory role of monocyte/macrophage subpopulations in fibrogenesis, the development of therapeutic strategies that target specific monocyte/macrophage subpopulations has become increasingly attractive. We will provide here an overview of the current understanding of the role of monocyte/macrophage phenotype subpopulations in animal models of tissue fibrosis and in various systemic and organ-specific human fibrotic diseases. Furthermore, we will discuss recent approaches to the design of effective anti-fibrotic therapeutic interventions by targeting the phenotypic differences identified between the various monocyte and macrophage subpopulations.

Update on scleroderma-associated interstitial lung disease

PURPOSE OF REVIEW

Systemic sclerosis (SSc), or scleroderma, is a heterogeneous and complex autoimmune disease characterized by varying degrees of skin and organ fibrosis and obliterative vasculopathy. The disease results in significant morbidity and mortality, and to date, available treatments are limited. Lung involvement is the leading cause of death of patients with SSc. Over the past year, significant advances have been made in our understanding of SSc-associated lung disease, and this review attempts to encapsulate these most recent findings and place them in context.

RECENT FINDINGS

We divide our discussion of the most recent literature into the following: first, clinical aspects of SSc lung management, including classification, imaging, biomarkers, and treatment; second, promising new animal models that may improve our ability to accurately study this disease; and third, studies that advance or change our understanding of SSc lung disease pathogenesis, thereby raising the potential for new targets for therapeutic intervention.

SUMMARY

Recent advances have resulted in a better understanding of SSc-associated lung disease, the development of new in-vivo models for exploring disease pathogenesis, and the identification of potential novel targets for the development of therapies.

Systemic Sclerosis is a Complex Disease Associated Mainly with Immune Regulatory and Inflammatory Genes

Systemic sclerosis (SSc) is a fibrotic and autoimmune disease characterized clinically by skin and internal organ fibrosis and vascular damage, and serologically by the presence of circulating autoantibodies. Although etiopathogenesis is not yet well understood, the results of numerous genetic association studies support genetic contributions as an important factor to SSc. In this paper, the major genes of SSc are reviewed. The most recent genome-wide association studies (GWAS) are taken into account along with robust candidate gene studies. The literature search was performed on genetic association studies of SSc in PubMed between January 2000 and March 2014 while eligible studies generally had over 600 total participants with replication. A few genetic association studies with related functional changes in SSc patients were also included. A total of forty seven genes or specific genetic regions were reported to be associated with SSc, although some are controversial. These genes include HLA genes, STAT4, CD247, TBX21, PTPN22, TNFSF4, IL23R, IL2RA, IL-21, SCHIP1/IL12A, CD226, BANK1, C8orf13-BLK, PLD4, TLR-2, NLRP1, ATG5, IRF5, IRF8, TNFAIP3, IRAK1, NFKB1, TNIP1, FAS, MIF, HGF, OPN, IL-6, CXCL8, CCR6, CTGF, ITGAM, CAV1, MECP2, SOX5, JAZF1, DNASEIL3, XRCC1, XRCC4, PXK, CSK, GRB10, NOTCH4, RHOB, KIAA0319, PSD3 and PSOR1C1. These genes encode proteins mainly involved in immune regulation and inflammation, and some of them function in transcription, kinase activity, DNA cleavage and repair. The discovery of various SSc-associated genes is important in understanding the genetics of SSc and potential pathogenesis that contribute to the development of this disease.

Caveolin-1 deficiency may predispose African Americans to systemic sclerosis-related interstitial lung disease

OBJECTIVE

Interstitial lung disease (ILD) is the leading cause of death in patients with systemic sclerosis (SSc; scleroderma). Although SSc-related ILD is more common and severe in African Americans than in Caucasians, little is known about factors underlying this significant health disparity. The aim of this study was to examine the role that low expression of caveolin-1 might play in susceptibility to ILD among African Americans.

METHODS

Assays of monocyte migration toward stromal cell-derived factor 1 (SDF-1) were performed using monocytes from Caucasian and African American healthy donors and patients with SSc. For fibrocyte differentiation studies, total peripheral blood mononuclear cells were incubated on fibronectin-coated plates. Protein expression was evaluated by immunohistochemistry and Western blotting.

RESULTS

Monocytes from healthy African American donors and those from patients with SSc had low caveolin-1 levels, enhanced migration toward the CXCR4 ligand SDF-1, and enhanced differentiation to fibrocytes. Enhanced migration and differentiation of monocytes from African Americans and patients with SSc appeared to be attributable to the lack of caveolin-1, because restoring caveolin-1 function using a caveolin-1 scaffolding domain peptide inhibited these processes. Although they differed from monocytes from Caucasians, monocytes from both African Americans and patients with SSc were not identical, because SSc monocytes showed major increases from baseline in ERK, JNK, p38, and Smad2/3 activation, while monocytes from African Americans showed only limited ERK activation and no activation of JNK, p38, or Smad2/3. In contrast, SDF-1 exposure caused no additional ERK activation in SSc monocytes but did cause significant additional activation in monocytes from African Americans.

CONCLUSION

African Americans may be predisposed to SSc-related ILD due to low baseline caveolin-1 levels in their monocytes, potentially affecting signaling, migration, and fibrocyte differentiation. The monocytes of African Americans may lack caveolin-1 due to high levels of transforming growth factor β in their blood.

Caveolin-1 is a negative regulator of NADPH oxidase-derived reactive oxygen species

Changes in the expression and function of caveolin-1 (Cav-1) have been proposed as a pathogenic mechanism underlying many cardiovascular diseases. Cav-1 binds to and regulates the activity of numerous signaling proteins via interactions with its scaffolding domain. In endothelial cells, Cav-1 has been shown to reduce reactive oxygen species (ROS) production, but whether Cav-1 regulates the activity of NADPH oxidases (Noxes), a major source of cellular ROS, has not yet been shown. Herein, we show that Cav-1 is primarily expressed in the endothelium and adventitia of pulmonary arteries (PAs) and that Cav-1 expression is reduced in isolated PAs from multiple models of pulmonary artery hypertension (PH). Reduced Cav-1 expression correlates with increased ROS production in the adventitia of hypertensive PA. In vitro experiments revealed a significant ability of Cav-1 and its scaffolding domain to inhibit Nox1-5 activity and it was also found that Cav-1 binds to Nox5 and Nox2 but not Nox4. In addition to posttranslational actions, in primary cells, Cav-1 represses the mRNA and protein expression of Nox2 and Nox4 through inhibition of the NF-κB pathway. Last, in a mouse hypoxia model, the genetic ablation of Cav-1 increased the expression of Nox2 and Nox4 and exacerbated PH. Together, these results suggest that Cav-1 is a negative regulator of Nox function via two distinct mechanisms, acutely through direct binding and chronically through alteration of expression levels. Accordingly, the loss of Cav-1 expression in cardiovascular diseases such as PH may account for the increased Nox activity and greater production of ROS.

Role of caveolin-1 in asthma and chronic inflammatory respiratory diseases

Caveolin-1 (Cav-1) is the major protein present in invaginations of the plasma membrane of cells known as caveolae. Cav-1 is expressed in numerous resident and inflammatory cells implicated in the pathogenesis of asthma and chronic inflammatory respiratory diseases including chronic obstructive pulmonary disease. A remarkable repertoire of functions has been identified for Cav-1 and these extend to, and have relevance to, asthma and chronic inflammatory respiratory diseases. Important processes influenced by Cav-1 include inflammation, fibrosis, smooth muscle contractility, regulation of apoptosis and cell senescence as well as epithelial barrier function and homeostasis. A better understanding of Cav-1 may be useful in developing new therapies for chronic inflammatory respiratory diseases.

Tumor microenvironment and metabolic synergy in breast cancers: critical importance of mitochondrial fuels and function

Metabolic synergy or metabolic coupling between glycolytic stromal cells (Warburg effect) and oxidative cancer cells occurs in human breast cancers and promotes tumor growth. The Warburg effect or aerobic glycolysis is the catabolism of glucose to lactate to obtain adenosine triphosphate (ATP). This review summarizes the main findings on this stromal metabolic phenotype, and the associated signaling pathways, as well as the critical role of oxidative stress and autophagy, all of which promote carcinoma cell mitochondrial metabolism and tumor growth. Loss of Caveolin 1 (Cav-1) and the upregulation of monocarboxylate transporter 4 (MCT4) in stromal cells are novel markers of the Warburg effect and metabolic synergy between stromal and carcinoma cells. MCT4 and Cav-1 are also breast cancer prognostic biomarkers. Reactive oxygen species (ROS) are key mediators of the stromal Warburg effect. High ROS also favors cancer cell mitochondrial metabolism and tumorigenesis, and anti-oxidants can reverse this altered stromal and carcinoma metabolism. A pseudo-hypoxic state with glycolysis and low mitochondrial metabolism in the absence of hypoxia is a common feature in breast cancer. High ROS induces loss of Cav-1 in stromal cells and is sufficient to generate a pseudo-hypoxic state. Loss of Cav-1 in the stroma drives glycolysis and lactate extrusion via HIF-1α stabilization and the upregulation of MCT4. Stromal cells with loss of Cav-1 and/or high expression of MCT4 also show a catabolic phenotype, with enhanced macroautophagy. This catabolic state in stromal cells is driven by hypoxia-inducible factor (HIF)-1α, nuclear factor κB (NFκB), and JNK activation and high ROS generation. A feed-forward loop in stromal cells regulates pseudo-hypoxia and metabolic synergy, with Cav-1, MCT4, HIF-1α, NFκB, and ROS as its key elements. Metabolic synergy also may occur between cancer cells and cells in distant organs from the tumor. Cancer cachexia, which is due to severe organismal metabolic dysregulation in myocytes and adipocytes, shares similarities with stromal-carcinoma metabolic synergy, as well. In summary, metabolic synergy occurs when breast carcinoma cells induce a nutrient-rich microenvironment to promote tumor growth. The process of tumor metabolic synergy is a multistep process, due to the generation of ROS, and the induction of catabolism with autophagy, mitophagy and glycolysis. Studying epithelial-stromal interactions and metabolic synergy is important to better understand the ecology of cancer and the metabolic role of different cell types in tumor progression.

Improved understanding of the pathophysiology of atrial fibrillation through the lens of discrete pathological pathways

Atrial fibrillation (AF) is a common disorder with a complex and incompletely understood pathophysiology. Genetic approaches to understanding the pathophysiology of AF have led to the identification of several biological pathways important in the pathogenesis of the arrhythmia. These include pathways important for cardiac development, generation and propagation of atrial electrical impulses, and atrial remodeling and fibrosis. While common and rare genetic variants in these pathways are associated with increased susceptibility to AF, they differ substantially among patients with lone versus typical AF. Furthermore, how these pathways converge to a final common clinical phenotype of AF is unclear and might also vary among different patient populations. Here, we review the contemporary knowledge of AF pathogenesis and discuss how derangement in cardiac development, ion channel dysfunction, and promotion of atrial fibrosis may contribute to this common and important clinical disorder.

Catabolic cancer-associated fibroblasts transfer energy and biomass to anabolic cancer cells, fueling tumor growth

Fibroblasts are the most abundant "non-cancerous" cells in tumors. However, it remains largely unknown how these cancer-associated fibroblasts (CAFs) promote tumor growth and metastasis, driving chemotherapy resistance and poor clinical outcome. This review summarizes new findings on CAF signaling pathways and their emerging metabolic phenotypes that promote tumor growth. Although it is well established that altered cancer metabolism enhances tumor growth, little is known about the role of fibroblast metabolism in tumor growth. New studies reveal that metabolic coupling occurs between catabolic fibroblasts and anabolic cancer cells, in many types of human tumors, including breast, prostate, and head & neck cancers, as well as lymphomas. These catabolic phenotypes observed in CAFs are secondary to a ROS-induced metabolic stress response. Mechanistically, this occurs via HIF1-alpha and NFκB signaling, driving oxidative stress, autophagy, glycolysis and senescence in stromal fibroblasts. These catabolic CAFs then create a nutrient-rich microenvironment, to metabolically support tumor growth, via the local stromal generation of mitochondrial fuels (lactate, ketone bodies, fatty acids, glutamine, and other amino acids). New biomarkers of this catabolic CAF phenotype (such as caveolin-1 (Cav-1) and MCT4), which are reversible upon treatment with anti-oxidants, are strong predictors of poor clinical outcome in various types of human cancers. How cancer cells metabolically reprogram fibroblasts can also help us to understand the effects of cancer cells at an organismal level, explaining para-neoplastic phenomena, such as cancer cachexia. In conclusion, cancer should be viewed more as a systemic disease, that engages the host-organism in various forms of energy-transfer and metabolic co-operation, across a whole-body "ecosystem".

Loss of caveolin-1 and adiponectin induces severe inflammatory lung injury following LPS challenge through excessive oxidative/nitrative stress

Excessive reactive oxygen/nitrogen species have been associated with the onset, progression, and outcome of sepsis, both in preclinical and clinical studies. However, the signaling pathways regulating oxidative/nitrative stress in the pathogenesis of sepsis-induced acute lung injury and acute respiratory distress syndrome are not fully understood. Employing the novel mouse model with genetic deletions of both caveolin-1 (Cav1) and adiponectin (ADPN) [double knockout (DKO) mice], we have demonstrated the critical role of Cav1 and ADPN signaling cross talk in regulating oxidative/nitrative stress and resulting inflammatory lung injury following LPS challenge. In contrast to the inhibited inflammatory lung injury in Cav1(-/-) mice, we observed severe lung inflammation and markedly increased lung vascular permeability in DKO mice in response to LPS challenge. Accordingly, the DKO mice exhibited an 80% mortality rate following a sublethal dose of LPS challenge. At basal state, loss of Cav1 and ADPN resulted in a drastic increase of oxidative stress and resultant nitrative stress in DKO lungs. Scavenging of superoxide by pretreating the DKO mice with MnTMPYP (a superoxide dismutase mimetic) restored the inflammatory responses to LPS challenge including reduced lung myeloperoxidase activity and vascular permeability. Thus oxidative/nitrative stress collectively modulated by Cav1 and ADPN signalings is a critical determinant of inflammatory lung injury in response to LPS challenge.

Genetic architecture of human fibrotic diseases: disease risk and disease progression

Genetic studies of human diseases have identified multiple genetic risk loci for various fibrotic diseases. This has provided insights into the myriad of biological pathways potentially involved in disease pathogenesis. These discoveries suggest that alterations in immune responses, barrier function, metabolism and telomerase activity may be implicated in the genetic risks for fibrotic diseases. In addition to genetic disease-risks, the identification of genetic disease-modifiers associated with disease complications, severity or prognosis provides crucial insights into the biological processes implicated in disease progression. Understanding the biological processes driving disease progression may be critical to delineate more effective strategies for therapeutic interventions. This review provides an overview of current knowledge and gaps regarding genetic disease-risks and genetic disease-modifiers in human fibrotic diseases.

The role of caveolae in the pathophysiology of lung diseases

Caveolae are flask-shaped plasma membrane invaginations formed by constitutive caveolin proteins and regulatory cavin proteins. Caveolae harbor a range of signaling components such as receptors, ion channels and regulatory molecules. There is now increasing evidence that caveolins and cavins play an important role in a variety of diseases. However, the mechanisms by which these caveolar proteins affect lung health and disease are still under investigation, with emerging data suggesting complex roles in disease pathophysiology. This review summarizes the current state of understanding of how caveolar proteins contribute to lung structure and function and how their altered expression and/or function can influence lung diseases.

Pathogenesis of pulmonary hypertension: a case for caveolin-1 and cell membrane integrity

Pulmonary hypertension (PH) is a progressive disease with a high morbidity and mortality rate. Despite important advances in the field, the precise mechanisms leading to PH are not yet understood. Main features of PH are loss of vasodilatory response, the activation of proliferative and antiapoptotic pathways leading to pulmonary vascular remodeling and obstruction, elevated pressure and right ventricular hypertrophy, resulting in right ventricular failure and death. Experimental studies suggest that endothelial dysfunction may be the key underlying feature in PH. Caveolin-1, a major protein constituent of caveolae, interacts with several signaling molecules including the ones implicated in PH and modulates them. Disruption and progressive loss of endothelial caveolin-1 with reciprocal activation of proliferative pathways occur before the onset of PH, and the rescue of caveolin-1 inhibits proliferative pathways and attenuates PH. Extensive endothelial damage/loss occurs during the progression of the disease with subsequent enhanced expression of caveolin-1 in smooth muscle cells. This caveolin-1 in smooth muscle cells switches from being an antiproliferative factor to a proproliferative one and participates in cell proliferation and cell migration, possibly leading to irreversible PH. In contrast, the disruption of endothelial caveolin-1 is not observed in the hypoxia-induced PH, a reversible form of PH. However, proliferative pathways are activated in this model, indicating caveolin-1 dysfunction. Thus disruption or dysfunction of endothelial caveolin-1 leads to PH, and the status of caveolin-1 may determine the reversibility versus irreversibility of PH. This article reviews the role of caveolin-1 and cell membrane integrity in the pathogenesis and progression of PH.

Fibrosis-associated single-nucleotide polymorphisms in TGFB1 and CAV1 are not associated with the development of nephrogenic systemic fibrosis

OBJECTIVE

To test the hypothesis that the subset of patients with impaired renal function who are exposed to gadolinium-containing contrast agents (GCCAs) and develop nephrogenic systemic fibrosis (NSF) have a genetic predisposition for disease.

METHODS

We examined whether an intronic single-nucleotide polymorphism (SNP) in caveolin-1 (CAV1 rs4730751) and 2 coding SNPs in transforming growth factor-beta 1 (TGFB1 rs1800471, codon 25; and rs1800470, codon 10) were associated with the NSF phenotype.

RESULTS

Forty-one patients with a history of chronic kidney disease and GCCA administration were studied, including NSF cases (n = 17) and control subjects (n = 24) without clinical or histological evidence of NSF. No significant differences in the genotype frequencies at these SNPs in TGFB1 and CAV1 were found between patients with NSF and subjects without NSF.

CONCLUSIONS

We conclude that polymorphisms in the genes encoding TGFB1 and CAV1 previously associated with the development and progression of fibrosis in several organ systems are not associated with development of NSF in this cohort of patients with renal impairment after GCCA exposure.

Role of endothelial to mesenchymal transition in the pathogenesis of the vascular alterations in systemic sclerosis

The pathogenesis of Systemic Sclerosis (SSc) is extremely complex, and despite extensive studies, the exact mechanisms involved are not well understood. Numerous recent studies of early events in SSc pathogenesis have suggested that unknown etiologic factors in a genetically receptive host trigger structural and functional microvascular endothelial cell abnormalities. These alterations result in the attraction, transmigration, and accumulation of immune and inflammatory cells in the perivascular tissues, which in turn induce the phenotypic conversion of endothelial cells and quiescent fibroblasts into activated myofibroblasts, a process known as endothelial to mesenchymal transition or EndoMT. The activated myofibroblasts are the effector cells responsible for the severe and frequently progressive fibrotic process and the fibroproliferative vasculopathy that are the hallmarks of SSc. Thus, according to this hypothesis the endothelial and vascular alterations, which include the phenotypic conversion of endothelial cells into activated myofibroblasts, play a crucial role in the development of the progressive fibrotic process affecting skin and multiple internal organs. The role of endothelial cell and vascular alterations, the potential contribution of endothelial to mesenchymal cell transition in the pathogenesis of the tissue fibrosis, and fibroproliferative vasculopathy in SSc will be reviewed here.

Systemic sclerosis: current concepts in pathogenesis and therapeutic aspects of dermatological manifestations

Systemic sclerosis (SSc) is a chronic, multisystem connective tissue disease with protean clinical manifestations. Recent advances in understanding the pathogenic mechanisms have led to development of target-oriented and vasomodulatory drugs which play a pivotal role in treating various dermatological manifestations. An exhaustive literature search was done using Medline, Embase, and Cochrane library to review the recent concepts regarding pathogenesis and evidence-based treatment of salient dermatological manifestations. The concept of shared genetic risk factors for the development of autoimmune diseases is seen in SSc. It is divided into fibroproliferative and inflammatory groups based on genome-wide molecular profiling. Genetic, infectious, and environmental factors play a key role; vascular injury, fibrosis, and immune activation are the chief pathogenic factors. Vitamin D deficiency has been documented in SSc and correlates with the severity of skin involvement. Skin sclerosis, Raynaud's phenomenon (RP) with digital vasculopathies, pigmentation, calcinosis, and leg ulcers affect the patient's quality of life. Immunosuppressives, biologicals, and hematopoietic stem cell transplantation are efficacious in skin sclerosis. Endothelin A receptor antagonists, calcium-channel blockers, angiotensin receptor inhibitors, prostacyclin analogs, and phosphodiesterase type 5 (PDE-5) inhibitors are the mainstay in RP and digital vasculopathies. Pigmentation in SSc has been attributed to melanogenic potential of endothelin-1 (ET-1); the role of ET 1 antagonists and vitamin D analogs needs to be investigated. Sexual dysfunction in both male and female patients has been attributed to vasculopathy and fibrosis, wherein PDE-5 inhibitors are found to be useful. The future concepts of treating SSc may be based on the gene expression signature.

Caveolin-1 single nucleotide polymorphism in antineutrophil cytoplasmic antibody associated vasculitis

Objective

Immunosuppression is cornerstone treatment of antineutrophil cytoplasmic antibody associated vasculitis (AAV) but is later complicated by infection, cancer, cardiovascular and chronic kidney disease. Caveolin-1 is an essential structural protein for small cell membrane invaginations known as caveolae. Its functional role has been associated with these complications. For the first time, caveolin-1 (CAV1) gene variation is studied in AAV.

Methods

CAV1 single nucleotide polymorphism rs4730751 was analysed in genomic DNA from 187 white patients with AAV from Birmingham, United Kingdom. The primary outcome measure was the composite endpoint of time to all-cause mortality or renal replacement therapy. Secondary endpoints included time to all-cause mortality, death from sepsis or vascular disease, cancer and renal replacement therapy. Validation of results was sought from 589 white AAV patients, from two European cohorts.

Results

The primary outcome occurred in 41.7% of Birmingham patients. In a multivariate model, non-CC genotype variation at the studied single nucleotide polymorphism was associated with increased risk from: the primary outcome measure [HR 1.86; 95% CI: 1.14-3.04; p=0.013], all-cause mortality [HR:1.83; 95% CI: 1.02-3.27; p=0.042], death from infection [HR:3.71; 95% CI: 1.28-10.77; p=0.016], death from vascular disease [HR:3.13; 95% CI: 1.07-9.10; p=0.037], and cancer [HR:5.55; 95% CI: 1.59-19.31; p=0.007]. In the validation cohort, the primary outcome rate was far lower (10.4%); no association between genotype and the studied endpoints was evident.

Conclusions

The presence of a CC genotype in Birmingham is associated with protection from adverse outcomes of immunosuppression treated AAV. Lack of replication in the European cohort may have resulted from low clinical event rates. These findings are worthy of further study in larger cohorts.

The less-often-traveled surface of stem cells: caveolin-1 and caveolae in stem cells, tissue repair and regeneration

Stem cells are an important resource for tissue repair and regeneration. While a great deal of attention has focused on derivation and molecular regulation of stem cells, relatively little research has focused on how the subcellular structure and composition of the cell membrane influences stem cell activities such as proliferation, differentiation and homing. Caveolae are specialized membrane lipid rafts coated with caveolin scaffolding proteins, which can regulate cholesterol transport and the activity of cell signaling receptors and their downstream effectors. Caveolin-1 is involved in the regulation of many cellular processes, including growth, control of mitochondrial antioxidant levels, migration and senescence. These activities are of relevance to stem cell biology, and in this review evidence for caveolin-1 involvement in stem cell biology is summarized. Altered stem and progenitor cell populations in caveolin-1 null mice suggest that caveolin-1 can regulate stem cell proliferation, and in vitro studies with isolated stem cells suggest that caveolin-1 regulates stem cell differentiation. The available evidence leads us to hypothesize that caveolin-1 expression may stabilize the differentiated and undifferentiated stem cell phenotype, and transient downregulation of caveolin-1 expression may be required for transition between the two. Such regulation would probably be critical in regenerative applications of adult stem cells and during tissue regeneration. We also review here the temporal changes in caveolin-1 expression reported during tissue repair. Delayed muscle regeneration in transgenic mice overexpressing caveolin-1 as well as compromised cardiac, brain and liver tissue repair and delayed wound healing in caveolin-1 null mice suggest that caveolin-1 plays an important role in tissue repair, but that this role may be negative or positive depending on the tissue type and the nature of the repair process. Finally, we also discuss how caveolin-1 quiescence-inducing activities and effects on mitochondrial antioxidant levels may influence stem cell aging.

Genetic mechanisms of atrial fibrillation: impact on response to treatment

Atrial fibrillation (AF) is the most-common sustained arrhythmia observed in clinical practice, but response to therapy is highly variable between patients. Current drug therapies to suppress AF are incompletely and unpredictably effective and carry substantial risk of proarrhythmia and noncardiac toxicities. The limited success of therapy for AF is partially the result of heterogeneity of the underlying substrate, interindividual differences in disease mechanisms, and our inability to predict response to therapies in individual patients. In this Review, we discuss the evidence that variability in response to drug therapy is also conditioned by the underlying genetic substrate for AF. Increased susceptibility to AF is mediated through diverse genetic mechanisms, including modulation of the atrial action-potential duration, conduction slowing, and impaired cell-to-cell communication, as well as novel mechanisms, such as regulation of signalling proteins important in the pathogenesis of AF. However, the translation of genetic data to the care of the patients with AF has been limited because of poor understanding of the underlying mechanisms associated with common AF-susceptibility loci, a dearth of prospective, adequately powered studies, and the challenges associated with determining efficacy of antiarrhythmic drugs. What is apparent, however, is the need for appropriately designed, genotype-directed clinical trials.

Role of caveolin-1 in fibrotic diseases

Fibrosis underlies the pathogenesis of numerous diseases and leads to severe damage of vital body organs and, frequently, to death. Better understanding of the mechanisms resulting in fibrosis is essential for developing appropriate treatment solutions and is therefore of upmost importance. Recent evidence suggests a significant antifibrotic potential of an integral membrane protein, caveolin-1. While caveolin-1 has been widely studied for its role in the regulation of cell signaling and endocytosis, its possible implication in fibrosis remains largely unclear. In this review we survey involvement of caveolin-1 in various cellular processes and highlight different aspects of its antifibrotic activity. We hypothesize that caveolin-1 conveys a homeostatic function in the process of fibrosis by (a) regulating TGF-β1 and its downstream signaling; (b) regulating critical cellular processes involved in tissue repair, such as migration, adhesion and cellular response to mechanical stress; and (c) antagonizing profibrotic processes, such as proliferation. Finally, we consider this homeostatic function of caveolin-1 as a possible novel approach in treatment of fibroproliferative diseases.

Racial differences between blacks and whites with systemic sclerosis

PURPOSE OF REVIEW

Racial disparities appear to exist in the susceptibility and severity of systemic sclerosis (SSc, scleroderma) and are responsible for a greater health burden in blacks as compared with whites. Disparities in socioeconomic status and access to healthcare do not sufficiently explain the observed differences in prevalence and mortality. It is important to determine whether there might be a biologic basis for the racial disparities observed in SSc.

RECENT FINDINGS

We present data to suggest that the increased susceptibility and severity of SSc in blacks may result in part from an imbalance of profibrotic and antifibrotic factors. Racial differences in the expression of transforming growth factor-β1 (TGF-β1) and caveolin-1, as well as differences in the expression of hepatocyte growth factor and PPAR-γ, have been demonstrated in blacks with SSc, as well as in normal black individuals. A genetic predisposition to fibrosis may account for much of the racial disparities between black and white patients with SSc.

SUMMARY

A better understanding of the biologic basis for the racial disparities observed in SSc may lead to improved therapies, along with the recognition that different therapies may need to be adapted for different groups of patients.

Emerging role of tyrosine phosphatase, TCPTP, in the organelles of the early secretory pathway

T-cell protein tyrosine phosphatase, TCPTP, is a ubiquitously expressed non-receptor type tyrosine phosphatase. There are two splice variants of TCPTP, TC48 and TC45, which differ in their sub-cellular localizations and functions. TC45 is a nuclear protein, which has both nuclear and cytoplasmic substrates, and is involved in many signaling events including endocytic recycling of platelet-derived growth factor β-receptor. TC48 is a predominantly endoplasmic reticulum (ER)-localizing protein, which dephosphorylates some of the substrates of TC45 at the ER. However, recently few specific substrates for TC48 have been identified. These include C3G (RapGEF1), syntaxin 17 and BCR-Abl. TC48 moves from the ER to post-ER compartments, the ER-Golgi intermediate compartment (ERGIC) and Golgi, and it is retrieved back to the ER. The retrieval of ER proteins from post-ER compartments is generally believed as a mechanism of targeting these proteins to the ER. However, it is possible that this shuttling of TC48 serves to regulate signaling in the early secretory pathway. For example, TC48 dephosphorylates phosphorylated C3G at the Golgi and inhibits neurite outgrowth. TC48 interacts with and dephosphorylates syntaxin 17, which is an ER and ERGIC-localizing protein involved in vesicle transport. A yeast two-hybrid screen identified several unique interacting partners of TC48 belonging to two groups - proteins involved in vesicle trafficking and proteins involved in cell adhesion. These interacting proteins could be substrates or regulators of TC48 function and localization. Thus, the role of TC48 seems to be more diverse, which is still to be explored.

Strategies for anti-fibrotic therapies

The fibrotic diseases encompass a wide spectrum of entities including such multisystemic diseases as systemic sclerosis, nephrogenic systemic fibrosis and sclerodermatous graft versus host disease, as well as organ-specific disorders such as pulmonary, liver, and kidney fibrosis. Collectively, given the wide variety of affected organs, the chronic nature of the fibrotic processes, and the large number of individuals suffering their devastating effects, these diseases pose one of the most serious health problems in current medicine and a serious economic burden to society. Despite these considerations there is currently no accepted effective treatment. However, remarkable progress has been achieved in the elucidation of their pathogenesis including the identification of the critical role of myofibroblasts and the determination of molecular mechanisms that result in the transcriptional activation of the genes responsible for the fibrotic process. Here we review the origin of the myofibroblast and discuss the crucial regulatory pathways involving multiple growth factors and cytokines that participate in the pathogenesis of the fibrotic process. Potentially effective therapeutic strategies based upon this new information are considered in detail and the major challenges that remain and their possible solutions are presented. It is expected that translational efforts devoted to convert this new knowledge into novel and effective anti-fibrotic drugs will be forthcoming in the near future. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Caveolin-1 deficiency induces spontaneous endothelial-to-mesenchymal transition in murine pulmonary endothelial cells in vitro

It was previously demonstrated that transforming growth factor β (TGF-β) induces endothelial-to-mesenchymal transition (EndoMT) in murine lung endothelial cells (ECs) in vitro. Owing to the important role of caveolin-1 (CAV1) in TGF-β receptor internalization and TGF-β signaling, the participation of CAV1 in the induction of EndoMT in murine lung ECs was investigated. Pulmonary ECs were isolated from wild-type and Cav1 knockout mice using immunomagnetic methods with sequential anti-CD31 and anti-CD102 antibody selection followed by in vitro culture and treatment with TGF-β1. EndoMT was assessed by semiquantitative RT-PCR for Acta2, Col1a1, Snai1, and Snai2; by immunofluorescence for α-smooth muscle actin; and by Western blot analysis for α-smooth muscle actin, SNAIL1, SNAIL2, and the α2 chain of type I collagen. The same studies were performed in Cav1(-/-) pulmonary ECs after restoration of functional CAV1 domains using a cell-permeable CAV1 scaffolding domain peptide. Pulmonary ECs from Cav1 knockout mice displayed high levels of spontaneous Acta2, Col1A, Snai1, and Snai2 expression, which increased after TGF-β treatment. Spontaneous and TGF-β1-stimulated EndoMT were abrogated by the restoration of functional CAV1 domains using a cell-permeable peptide. The findings suggest that CAV1 regulation of EndoMT may play a role in the development of fibroproliferative vasculopathies.

Metabolic reprogramming of cancer-associated fibroblasts by TGF-β drives tumor growth: connecting TGF-β signaling with "Warburg-like" cancer metabolism and L-lactate production

We have previously shown that a loss of stromal Cav-1 is a biomarker of poor prognosis in breast cancers. Mechanistically, a loss of Cav-1 induces the metabolic reprogramming of stromal cells, with increased autophagy/mitophagy, mitochondrial dysfunction and aerobic glycolysis. As a consequence, Cav-1-low CAFs generate nutrients (such as L-lactate) and chemical building blocks that fuel mitochondrial metabolism and the anabolic growth of adjacent breast cancer cells. It is also known that a loss of Cav-1 is associated with hyperactive TGF-β signaling. However, it remains unknown whether hyperactivation of the TGF-β signaling pathway contributes to the metabolic reprogramming of Cav-1-low CAFs. To address these issues, we overexpressed TGF-β ligands and the TGF-β receptor I (TGFβ-RI) in stromal fibroblasts and breast cancer cells. Here, we show that the role of TGF-β in tumorigenesis is compartment-specific, and that TGF-β promotes tumorigenesis by shifting cancer-associated fibroblasts toward catabolic metabolism. Importantly, the tumor-promoting effects of TGF-β are independent of the cell type generating TGF-β. Thus, stromal-derived TGF-β activates signaling in stromal cells in an autocrine fashion, leading to fibroblast activation, as judged by increased expression of myofibroblast markers, and metabolic reprogramming, with a shift toward catabolic metabolism and oxidative stress. We also show that TGF-β-activated fibroblasts promote the mitochondrial activity of adjacent cancer cells, and in a xenograft model, enhancing the growth of breast cancer cells, independently of angiogenesis. Conversely, activation of the TGF-β pathway in cancer cells does not influence tumor growth, but cancer cell-derived-TGF-β ligands affect stromal cells in a paracrine fashion, leading to fibroblast activation and enhanced tumor growth. In conclusion, ligand-dependent or cell-autonomous activation of the TGF-β pathway in stromal cells induces their metabolic reprogramming, with increased oxidative stress, autophagy/mitophagy and glycolysis, and downregulation of Cav-1. These metabolic alterations can spread among neighboring fibroblasts and greatly sustain the growth of breast cancer cells. Our data provide novel insights into the role of the TGF-β pathway in breast tumorigenesis, and establish a clear causative link between the tumor-promoting effects of TGF-β signaling and the metabolic reprogramming of the tumor microenvironment.

CTGF drives autophagy, glycolysis and senescence in cancer-associated fibroblasts via HIF1 activation, metabolically promoting tumor growth

Previous studies have demonstrated that loss of caveolin-1 (Cav-1) in stromal cells drives the activation of the TGF-β signaling, with increased transcription of TGF-β target genes, such as connective tissue growth factor (CTGF). In addition, loss of stromal Cav-1 results in the metabolic reprogramming of cancer-associated fibroblasts, with the induction of autophagy and glycolysis. However, it remains unknown if activation of the TGF-β / CTGF pathway regulates the metabolism of cancer-associated fibroblasts. Therefore, we investigated whether CTGF modulates metabolism in the tumor microenvironment. For this purpose, CTGF was overexpressed in normal human fibroblasts or MDA-MB-231 breast cancer cells. Overexpression of CTGF induces HIF-1α-dependent metabolic alterations, with the induction of autophagy/mitophagy, senescence, and glycolysis. Here, we show that CTGF exerts compartment-specific effects on tumorigenesis, depending on the cell-type. In a xenograft model, CTGF overexpressing fibroblasts promote the growth of co-injected MDA-MB-231 cells, without any increases in angiogenesis. Conversely, CTGF overexpression in MDA-MB-231 cells dramatically inhibits tumor growth in mice. Intriguingly, increased extracellular matrix deposition was seen in tumors with either fibroblast or MDA-MB-231 overexpression of CTGF. Thus, the effects of CTGF expression on tumor formation are independent of its extracellular matrix function, but rather depend on its ability to activate catabolic metabolism. As such, CTGF-mediated induction of autophagy in fibroblasts supports tumor growth via the generation of recycled nutrients, whereas CTGF-mediated autophagy in breast cancer cells suppresses tumor growth, via tumor cell self-digestion. Our studies shed new light on the compartment-specific role of CTGF in mammary tumorigenesis, and provide novel insights into the mechanism(s) generating a lethal tumor microenvironment in patients lacking stromal Cav-1. As loss of Cav-1 is a stromal marker of poor clinical outcome in women with primary breast cancer, dissecting the downstream signaling effects of Cav-1 are important for understanding disease pathogenesis, and identifying novel therapeutic targets.

Caveolin-1 signaling in lung fibrosis

Caveolin-1 is a master regulator of several signaling cascades because it is able to bind to and thereby inhibit members of a variety of kinase families. While associated with caveolae and involved in their generation, caveolin-1 is also present at other sites. A variety of studies have suggested that caveolin-1 may be a useful therapeutic target in fibrotic diseases of the lung and other tissues because in these diseases a low level of caveolin-1 expression is associated with a high level of collagen expression and fibrosis. Reduced caveolin-1 expression is observed not only in the fibroblasts that secrete collagen, but also in epithelial cells and monocytes. This is intriguing because both epithelial cells and monocytes have been suggested to be precursors of fibroblasts. Likely downstream effects of loss of caveolin-1 in fibrosis include activation of TGF-β signaling and upregulation of CXCR4 in monocytes resulting in their enhanced migration into damaged tissue where its ligand CXCL12 is produced. Finally, it may be possible to target caveolin-1 in fibrotic diseases without the use of gene therapy. A caveolin-1 peptide (caveolin-1 scaffolding domain) has been identified that retains the function of the full-length molecule to inhibit kinases and that can be modified by addition of the Antennapedia internalization sequence to allow it to enter cells both in vitro and in vivo.

Caveolins and lung function

The primary function of the mammalian lung is to facilitate diffusion of oxygen to venous blood and to ventilate carbon dioxide produced by catabolic reactions within cells. However, it is also responsible for a variety of other important functions, including host defense and production of vasoactive agents to regulate not only systemic blood pressure, but also water, electrolyte and acid-base balance. Caveolin-1 is highly expressed in the majority of cell types in the lung, including epithelial, endothelial, smooth muscle, connective tissue cells, and alveolar macrophages. Deletion of caveolin-1 in these cells results in major functional aberrations, suggesting that caveolin-1 may be crucial to lung homeostasis and development. Furthermore, generation of mutant mice that under-express caveolin-1 results in severe functional distortion with phenotypes covering practically the entire spectrum of known lung diseases, including pulmonary hypertension, fibrosis, increased endothelial permeability, and immune defects. In this Chapter, we outline the current state of knowledge regarding caveolin-1-dependent regulation of pulmonary cell functions and discuss recent research findings on the role of caveolin-1 in various pulmonary disease states, including obstructive and fibrotic pulmonary vascular and inflammatory diseases.

Caveolin-1 deficiency protects from pulmonary fibrosis by modulating epithelial cell senescence in mice

Idiopathic pulmonary fibrosis is associated with a decreased expression of caveolin-1 (cav-1), yet its role remains unclear. To investigate the role of cav-1, we induced pulmonary fibrosis in wild-type (WT) and cav-1-deficient (cav-1(-/-)) mice using intratracheal instillation of bleomycin. Contrary to expectations, significantly less collagen deposition was measured in tissue from cav-1(-/-) mice than in their WT counterparts, consistent with reduced mRNA expression of procollagen1a2 and procollagen3a1. Moreover, cav-1(-/-) mice demonstrated 77% less α-smooth muscle actin staining, suggesting reduced mesenchymal cell activation. Levels of pulmonary injury, assessed by tenascin-C mRNA expression and CD44v10 detection, were significantly increased at Day 21 after injury in WT mice, an effect significantly attenuated in cav-1(-/-) mice. The apparent protective effect against bleomycin-induced fibrosis in cav-1(-/-) mice was attributed to reduce cellular senescence and apoptosis in cav-1(-/-) epithelial cells during the early phase of lung injury. Reduced matrix metalloproteinase (MMP)-2 and MMP-9 expressions indicated a low profile of senescence-associated secretory phenotype (SASP) in the bleomycin-injured cav-1(-/-) mice. However, IL-6 and macrophage inflammatory protein 2 were increased in WT and cav-1(-/-) mice after bleomycin challenge, suggesting that bleomycin-induced inflammatory response substantiated the SASP pool. Thus, loss of cav-1 attenuates early injury response to bleomycin by limiting stress-induced cellular senescence/apoptosis in epithelial cells. In contrast, decreased cav-1 expression promotes fibroblast activation and collagen deposition, effects that may be relevant in later stages of reparative response. Hence, therapeutic strategies to modulate the expression of cav-1 should take into account cell-specific effects in the regenerative responses of the lung epithelium to injury.

Caveolins and lung function

The primary function of the mammalian lung is to facilitate diffusion of oxygen to venous blood and to ventilate carbon dioxide produced by catabolic reactions within cells. However, it is also responsible for a variety of other important functions, including host defense and production of vasoactive agents to regulate not only systemic blood pressure, but also water, electrolyte and acid-base balance. Caveolin-1 is highly expressed in the majority of cell types in the lung, including epithelial, endothelial, smooth muscle, connective tissue cells, and alveolar macrophages. Deletion of caveolin-1 in these cells results in major functional aberrations, suggesting that caveolin-1 may be crucial to lung homeostasis and development. Furthermore, generation of mutant mice that under-express caveolin-1 results in severe functional distortion with phenotypes covering practically the entire spectrum of known lung diseases, including pulmonary hypertension, fibrosis, increased endothelial permeability, and immune defects. In this Chapter, we outline the current state of knowledge regarding caveolin-1-dependent regulation of pulmonary cell functions and discuss recent research findings on the role of caveolin-1 in various pulmonary disease states, including obstructive and fibrotic pulmonary vascular and inflammatory diseases.

A genetic polymorphism in the CAV1 gene associates with the development of bronchiolitis obliterans syndrome after lung transplantation

Background

Caveolin 1 (Cav-1) is the primary structural component of cell membrane invaginations called 'caveolae'. Expression of Cav-1 is implicated in the pathogenesis of pulmonary fibrosis. Genetic polymorphisms in the CAV1 gene influence the function of Cav-1 in malignancies and associate with renal allograft fibrosis. Chronic allograft rejection after lung transplantation, called 'bronchiolitis obliterans syndrome' (BOS), is also characterised by the development of fibrosis.

In this study, we investigated whether CAV1 genotypes associate with BOS and whether Cav-1 serum levels are influenced by the CAV1 genotype and can be used as a biomarker to predict the development of BOS.

Methods

Twenty lung transplant recipients with BOS (BOS^pos), ninety without BOS (BOS^neg) and four hundred twenty-two healthy individuals donated DNA samples. Four SNPs in CAV1 were genotyped. Serial Cav-1 serum levels were measured in a matched cohort of 10 BOS^pos patients and 10 BOS^neg patients. Furthermore, single-time point Cav-1 serum levels were measured in 33 unmatched BOS^neg patients and 60 healthy controls.

Results

Homozygosity of the minor allele of rs3807989 was associated with an increased risk for BOS (odds ratio: 6.13; P = 0.0013). The median Cav-1 serum level was significantly higher in the BOS^pos patients than in the matched BOS^neg patients (P = 0.026). Longitudinal analysis did not show changes in Cav-1 serum levels over time in both groups. The median Cav-1 serum level in the group of 43 BOS^neg patients was lower than that in the healthy control group (P = 0.046).

In lung transplant recipients, homozygosity of the minor allele of rs3807989 and rs3807994 was associated with increased Cav-1 serum levels.

Conclusion

In lung transplant recipients, the CAV1 SNP rs3807989 was associated with the development of BOS and Cav-1 serum levels were influenced by the CAV1 genotype.

The relationship between fibrogenic TGFβ1 signaling in the joint and cartilage degradation in post-injury osteoarthritis

OBJECTIVE

To review the literature on modulation of chondrocyte activities in the osteoarthritic joint, and to discuss these changes in relation to established hard and soft tissue repair paradigms, with an emphasis on transforming growth factor beta (TGFβ1)-mediated signaling which can promote either a chondrogenic or fibrogenic phenotype.

METHODS

Papers addressing the close relationship between repair in general, and the specific post-injury response of joint tissues are summarized. Different interpretations of the role of TGFβ1 in the emergence of an "osteoarthritic" chondrocyte are compared and the phenotypic plasticity of "reparative" progenitor cells is examined. Lastly, emerging data on a central role for A-Disintegrin-And-Metalloproteinase-with-Thrombospondin-like-Sequences-5 (ADAMTS5) activity in modulating TGFβ1 signaling through activin receptor-like kinase 1 (ALK1) and activin receptor-like kinase 5 (ALK5) pathways is discussed.

RESULTS

The review illustrates how a transition from ALK5-mediated fibrogenic signaling to ALK1-mediated chondrogenic signaling in joint cells represents the critical transition from a non-reparative to a reparative cell phenotype. Data from cell and in vivo studies illustrates the mechanism by which ablation of ADAMTS5 activity allows the transition to reparative chondrogenesis. Multiple large gene expression studies of normal and osteoarthritis (OA) human cartilages (CAs) also support an important role for TGFβ1-mediated pro-fibrogenic activities during disease progression.

CONCLUSIONS

We conclude that progressive articular CA damage in post-injury OA results primarily from biomechanical, cell biologic and mediator changes that promote a fibroblastic phenotype in joint cells. Since ADAMTS5 and TGFβ1 appear to control this process, agents which interfere with their activities may not only enhance endogenous CA repair in vivo, but also improve the properties of tissue-engineered CA for implantation.

A role for caveolin-1 in desmoglein binding and desmosome dynamics

Desmoglein-2 (Dsg2) is a desmosomal cadherin that is aberrantly expressed in human skin carcinomas. In addition to its well-known role in mediating intercellular desmosomal adhesion, Dsg2 regulates mitogenic signaling that may promote cancer development and progression. However, the mechanisms by which Dsg2 activates these signaling pathways and the relative contribution of its signaling and adhesion functions in tumor progression are poorly understood. In this study we show that Dsg2 associates with caveolin-1 (Cav-1), the major protein of specialized membrane microdomains called caveolae, which functions in both membrane protein turnover and intracellular signaling. Sequence analysis revealed that Dsg2 contains a putative Cav-1-binding motif. A permeable competing peptide resembling the Cav-1 scaffolding domain bound to Dsg2, disrupted normal Dsg2 staining and interfered with the integrity of epithelial sheets in vitro. Additionally, we observed that Dsg2 is proteolytically processed; resulting in a 95-kDa ectodomain shed product and a 65-kDa membrane-spanning fragment, the latter of which localizes to lipid rafts along with full-length Dsg2. Disruption of lipid rafts shifted Dsg2 to the non-raft fractions, leading to the accumulation of these proteins. Interestingly, Dsg2 proteolytic products are elevated in vivo in skin tumors from transgenic mice overexpressing Dsg2. Collectively, these data are consistent with the possibility that accumulation of truncated Dsg2 protein interferes with desmosome assembly and/or maintenance to disrupt cell-cell adhesion. Furthermore, the association of Dsg2 with Cav-1 may provide a mechanism for regulating mitogenic signaling and modulating the cell-surface presentation of an important adhesion molecule, both of which could contribute to malignant transformation and tumor progression.

Caveolin-2 is a negative regulator of anti-proliferative function and signaling of transforming growth factor-β in endothelial cells

Using a combination of wild-type (WT) and caveolin-2 (Cav-2) knockout along with retroviral reexpression approaches, we provide the evidence for the negative role of Cav-2 in regulating anti-proliferative function and signaling of transforming growth factor β (TGF-β) in endothelial cells (ECs). Although, TGF-β had a modest inhibitory effect on WT ECs, it profoundly inhibited proliferation of Cav-2 knockout ECs. To confirm the specificity of the observed difference in response to TGF-β, we have stably reexpressed Cav-2 in Cav-2 knockout ECs using a retroviral approach. Similar to WT ECs, the anti-proliferative effect of TGF-β was dramatically reduced in the Cav-2 reexpressing ECs. The reduced anti-proliferative effect of TGF-β in Cav-2-positive cells was evidenced by three independent proliferation assays: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), cell count, and bromodeoxyuridine incorporation and correlated with a loss of TGF-β-mediated upregulation of cell cycle inhibitor p27 and subsequent reduction of the levels of hyperphosphorylated (inactive) form of the retinoblastoma protein in Cav-2 reexpressing ECs. Mechanistically, Cav-2 inhibits anti-proliferative action of TGF-β by suppressing Alk5-Smad2/3 pathway manifested by reduced magnitude and length of TGF-β-induced Smad2/3 phosphorylation as well as activation of activin receptor-like kinase-5 (Alk5)-Smad2/3 target genes plasminogen activator inhibitor-1 and collagen type I in Cav-2-positive ECs. Expression of Cav-2 does not appear to significantly change targeting of TGF-β receptors I and Smad2/3 to caveolar and lipid raft microdomains as determined by sucrose fractionation gradient. Overall, the negative regulation of TGF-β signaling and function by Cav-2 is independent of Cav-1 expression levels and is not because of changing targeting of Cav-1 protein to plasma membrane lipid raft/caveolar domains.

Scleroderma-like properties of skin from caveolin-1-deficient mice: implications for new treatment strategies in patients with fibrosis and systemic sclerosis

Caveolin-1 (Cav-1), the principal structural component of caveolae, participates in the pathogenesis of several fibrotic diseases, including systemic sclerosis (SSc). Interestingly, affected skin and lung samples from patients with SSc show reduced levels of Cav-1, as compared to normal skin. In addition, restoration of Cav-1 function in skin fibroblasts from SSc patients reversed their pro-fibrotic phenotype. Here, we further investigated whether Cav-1 mice are a useful pre-clinical model for studying the pathogenesis of SSc. For this purpose, we performed quantitative transmission electron microscopy, as well as biochemical and immuno-histochemical analysis, of the skin from Cav-1 (-/-) null mice. Using these complementary approaches, we now show that skin from Cav-1 null mice exhibits many of the same characteristics as SSc skin from patients, including a decrease in collagen fiber diameter, increased tensile strength, and stiffness, as well as mononuclear cell infiltration. Furthermore, an increase in autophagy/mitophagy was observed in the stromal cells of the dermis from Cav-1 (-/-) mice. These findings suggest that changes in cellular energy metabolism (e.g., a shift towards aerobic glycolysis) in these stromal cells may be a survival mechanism in this "hostile" or pro-inflammatory microenvironment. Taken together, our results demonstrate that Cav-1 (-/-) null mice are a valuable new pre-clinical model for studying scleroderma. Most importantly, our results suggest that inhibition of autophagy and/or aerobic glycolysis may represent a new promising therapeutic strategy for halting fibrosis in SSc patients. Finally, Cav-1 (-/-) null mice are also a pre-clinical model for a "lethal" tumor micro-environment, possibly explaining the link between fibrosis, tumor progression, and cancer metastasis.

Molecular profiling of a lethal tumor microenvironment, as defined by stromal caveolin-1 status in breast cancers

Breast cancer progression and metastasis are driven by complex and reciprocal interactions, between epithelial cancer cells and their surrounding stromal microenvironment. We have previously shown that a loss of stromal Cav-1 expression is associated with an increased risk of early tumor recurrence, metastasis and decreased overall survival. To identify and characterize the signaling pathways that are activated in Cav-1 negative tumor stroma, we performed gene expression profiling using laser microdissected breast cancer-associated stroma. Tumor stroma was laser capture microdissected from 4 cases showing high stromal Cav-1 expression and 7 cases with loss of stromal Cav-1. Briefly, we identified 238 gene transcripts that were upregulated and 232 gene transcripts that were downregulated in the stroma of tumors showing a loss of Cav-1 expression (p ≤ 0.01 and fold-change ≥ 1.5). Gene set enrichment analysis (GSEA) revealed "stemness," inflammation, DNA damage, aging, oxidative stress, hypoxia, autophagy and mitochondrial dysfunction in the tumor stroma of patients lacking stromal Cav-1. Our findings are consistent with the recently proposed "Reverse Warburg Effect" and the "Autophagic Tumor Stroma Model of Cancer Metabolism." In these two complementary models, cancer cells induce oxidative stress in adjacent stromal cells, which then forces these stromal fibroblasts to undergo autophagy/mitophagy and aerobic glycolysis. This, in turn, produces recycled nutrients (lactate, ketones and glutamine) to feed anabolic cancer cells, which are undergoing oxidative mitochondrial metabolism. Our results are also consistent with previous biomarker studies showing that the increased expression of known autophagy markers (such as ATG16L and the cathepsins) in the tumor stroma is specifically associated with metastatic tumor progression and/or poor clinical outcome.

Caveolin-1 modulates TGF-β1 signaling in cardiac remodeling

The cardiac response to myocardial injury includes fibrotic and hypertrophic processes and a key mediator in this response is transforming growth factor-β1 (TGF-β1). Caveolin-1 (cav1), the main structural protein of caveolae, is an inhibitor of the TGF-β1 signaling pathway. To examine the role of cav1 in cardiac repair, cav1 deficient (Cav1(-/-)) and wild type (WT) mice were subjected to cryoinjury of the left ventricle (LV). At baseline the two groups exhibited no inflammation, similar collagen content, and similar cardiac function. After injury, Cav1(-/-) animals displayed enhanced TGF-β1 signaling, as reflected by a 3-fold increase in the activation of the Smad2-dependent pathway and more widespread collagen deposition in the heart. Qualitative and quantitative analyses indicated that collagen deposition peaked in the WT LV 14days after injury, accompanied by increased mRNA abundance for procol1a2 (2-fold) and procol3a1 (3-fold). Collagen deposition was further enhanced in Cav1(-/-) mice, which was accompanied by reduced expression of matrix metalloproteinases MMP-8 (3-fold) and -13 mRNA (2-fold). The levels of expression of inflammatory markers of acute phase were similar between the strains However, macrophage clearance in the damaged region was delayed in Cav1(-/-) mice. We observed a 4-fold decrease in collagen deposition in Cav1(-/-) mice injected with a cav1 scaffolding domain peptide (CSD) and a 2-fold decrease in WT mice treated with the CSD. We conclude that cav1 has a direct role in reducing TGF-β1 signaling and as such might be an appropriate target for therapies to influence cardiac remodeling.

Antenatal inflammation reduces expression of caveolin-1 and influences multiple signaling pathways in preterm fetal lungs

Bronchopulmonary dysplasia (BPD), associated with chorioamnionitis, results from the simultaneous effects of disrupted lung development, lung injury, and repair superimposed on the developing lung. Caveolins (Cavs) are implicated as major modulators of lung injury and remodeling by multiple signaling pathways, although Cavs have been minimally studied in the injured developing lung. We hypothesized that chorioamnionitis-associated antenatal lung inflammation would decrease the expression of Cav-1 in preterm fetal lungs. We tested whether changes occurred in the transcription factors Smad2/3, Smad1/5, Stat3, and Stat1, and we also studied the activation of acid-sphingomyelinase (a-SMase) with the generation of ceramide, along with changes in the expression of heme oxygenase-1 (HO-1) as indicators of possible Cav-1-mediated effects. Fetal sheep were exposed to 10 mg of intra-amniotic endotoxin or saline for 2, 7, or 2 + 7 days before preterm delivery at 124 days of gestation. The expression of Cav-1 and HO-1 and the phosphorylation of Smad and Stat were evaluated by real-time PCR, Western blotting, and/or immunohistochemistry. The activity of a-SMase and the concentrations of ceramide were measured. Intra-amniotic endotoxin decreased Cav-1 mRNA and protein expression in the lungs, with a maximum reduction of Cav-1 mRNA to 50% ± 7% of the control value (P < 0.05), and of Cav-1 protein expression to 20% ± 5% of the control value (P < 0.05). Decreased concentrations of Cav-1 were associated with the elevated phosphorylation of Smad2/3, Stat3, and Stat1, but not of Smad1/5. The expression of HO-1, a-SMase activity, and ceramide increased. Antenatal inflammation decreased the expression of Cav-1 in the preterm fetal lung. The decreased expression of Cav-1 was associated with the activation of the Smad2/3, Stat, and a-SMase/ceramide pathways, and with the increased expression of HO-1. The decreased concentrations of Cav-1 and changes in other signaling pathways may contribute to BPD.

Is spleen circulation impaired in systemic sclerosis and what is the role of liver fibrosis?

AIM: To investigate the spleen vascular involvement and the presence of liver fibrosis in a population of subjects with established systemic sclerosis (SSc).

METHODS: In a cross-sectional fashion, 17 patients with SSc were compared with 18 patients suffering from hepatitis C virus (HCV)-related liver cirrhosis, grade A and B Child-Pugh classification. Eighteen non elderly subjects, apparently healthy, were used as the control group. Splenic artery resistivity index (SARI) at doppler ultraSound, transient elastography of liver and nailfold capillaroscopy were the main outcomes.

RESULTS: Transient elastography values of SSc patients were similar to those of controls; 5.2 ± 1.1 vs 4.5 ± 1, (P = 0.07). Median Alanine amino transferase (ALT) concentrations of cirrhotic patients were greater than those of controls and SSc patients, i.e. 66.5 (36-89) U/L vs 29 (22-34) U/L and 31 (22-41) U/L, respectively, (P = 0.005). SARI determinations in cirrhotic patients, although significantly higher than those found in controls and SSc patients, showed some degree of overlap with SSc patients, i.e. 0.59 vs 0.52 and 0.57, respectively, (P = 0.04). Mean systolic blood pressure was significantly higher in SSc patients than in cirrhotics and controls, i.e. 142 mmHg vs 128.2 mmHg and 127 mmHg, respectively, (P = 0.005). Mean diastolic blood pressure behaved in a similar fashion, i.e. 84 mmHg vs 72.2 mmHg and 76.9 mmHg (P = 0.005). Nailfold Capillaroscopy grades and diastolic blood pressure values correlated well with SARI results.

CONCLUSION: An enhanced resistivity of the splenic artery was found in patients suffering from SSc; they did not have evidence of splenomegaly as well as no liver fibrosis or any other form of liver damage.

Molecular characterization of caveolin-1 in pigs infected with Haemophilus parasuis

Caveolin-1 (Cav1) plays a critical role in the invasion of pathogenic microbes into host cells, yet little is known about porcine Cav1. In this study, we provide the molecular characterization of Cav1 in pigs following stimulation with LPS/polyinosinic-polycytidylic acid as well as during infection with Haemophilus parasuis. The porcine Cav1 gene is 35 kb long and is located at SSC18q21; two isoforms (Cav1-α and Cav1-β) are produced by alternative splicing. Three point mutations were identified in the coding region of the gene, two of which were significantly associated with nine immunological parameters in Landrace pigs, including the Ab response against porcine reproductive and respiratory syndrome virus and lymphocyte counts. Promoter analysis indicated that NF-κB activates both Cav1 transcripts, but the forkhead gene family specifically regulates Cav1-β in the pig. Porcine Cav1 is expressed ubiquitously, with Cav1-α more abundantly expressed than Cav1-β in all tissues investigated. Basal expression levels of Cav1 in PBMCs are relatively similar across different pig breeds. LPS and polyinosinic-polycytidylic acid markedly induced the expression of Cav1 in porcine kidney-15 cells in vitro, likely through NF-κB activation. Pigs infected with H. parasuis exhibited decreased expression of Cav1, particularly in seriously impaired organs such as the brain. This study provides new evidence that supports the use of Cav1 as a potential diagnostic and genetic marker for disease resistance in animal breeding. In addition, our results suggest that Cav1 may be implicated in the pathogenesis of Glasser's disease, which is caused by H. parasuis.

Caveolin-1: a critical regulator of lung injury

Caveolin-1 (cav-1), a 22-kDa transmembrane scaffolding protein, is the principal structural component of caveolae. Cav-1 regulates critical cell functions including proliferation, apoptosis, cell differentiation, and transcytosis via diverse signaling pathways. Abundant in almost every cell type in the lung, including type I epithelial cells, endothelial cells, smooth muscle cells, fibroblasts, macrophages, and neutrophils, cav-1 plays a crucial role in the pathogenesis of acute lung injury (ALI). ALI and its severe form, acute respiratory distress syndrome (ARDS), are responsible for significant morbidity and mortality in intensive care units, despite improvement in ventilation strategies. The pathogenesis of ARDS is still poorly understood, and therapeutic options remain limited. In this article, we summarize recent data regarding the regulation and function of cav-1 in lung biology and pathology, in particular as it relates to ALI. We further discuss the potential molecular and cellular mechanisms by which cav-1 expression contributes to ALI. Investigating the cellular functions of cav-1 may provide new insights for understanding the pathogenesis of ALI and provide novel targets for therapeutic interventions in the future.

Telmisartan regresses left ventricular hypertrophy in caveolin-1-deficient mice

The role of angiotensin II (Ang II) in promoting cardiac hypertrophy is well known; however, its role in a spontaneous model of hypertrophy in mice lacking the protein caveolin-1 (Cav-1 KO) has not been explored. In this study, WT and Cav-1 KO mice were treated with angiotensin receptor blocker (ARB), telmisartan (Telm), and cardiac function was assessed by echocardiography. Treatment of Cav-1 KO mice with Telm significantly improved cardiac function compared with age-matched vehicle-treated Cav-1 KO mice, whereas Telm did not affect cardiac function in WT mice. Both left ventricular (LV) weight to body weight ratios and LV to tibial length ratios were also reverted by Telm in Cav-1 KO but not in WT mice. LV hypertrophy was associated with increased expression of natriuretic peptides A and B, β-myosin heavy chain and TGF-β, and Telm treatment normalized the expression of these genes. Telm reduced the expression of collagen genes (Col1A and Col3A) and associated perivascular fibrosis in intramyocardial vessels in Cav-1 KO mice. In conclusion, Telm treatment reduces indexes of cardiac hypertrophy in this unique genetic model of spontaneous LV hypertrophy.

Integrin {alpha}1{beta}1 promotes caveolin-1 dephosphorylation by activating T cell protein-tyrosine phosphatase

Integrin α1β1 is a collagen receptor that down-regulates collagen and reactive oxygen species (ROS) production, and mice lacking this receptor show increased ROS levels and exacerbated glomerular sclerosis following injury. Caveolin-1 (Cav-1) is a multifunctional protein that is tyrosine-phosphorylated in response to injury and has been implicated in ROS-mediated injury. Cav-1 interacts with integrins, and integrin α1β1 binds/activates T cell protein-tyrosine phosphatase (TCPTP), which is homologous to the tyrosine phosphatase PTP1B known to dephosphorylate Cav-1. In this study, we analyzed whether phosphorylated Cav-1 (pCav-1) is a substrate of TCPTP and if integrin α1β1 is essential for promoting TCPTP-mediated Cav-1 dephosphorylation. We found that Cav-1 phosphorylation is significantly higher in cells lacking integrin α1β1 at base line and following oxidative stress. Overexpression of TCPTP leads to reduced pCav-1 levels only in cells expressing integrin α1β1. Using solid phase binding assays, we demonstrated that 1) purified Cav-1 directly interacts with TCPTP and the integrin α1 subunit, 2) pCav-1 is a substrate of TCPTP, and 3) TCPTP-mediated Cav-1 dephosphorylation is highly increased by the addition of purified integrin α1β1 or an integrin α1 cytoplasmic peptide to which TCPTP has been shown to bind. Thus, our results demonstrate that pCav-1 is a new substrate of TCPTP and that integrin α1β1 acts as a negative regulator of Cav-1 phosphorylation by activating TCPTP. This could explain the protective function of integrin α1β1 in oxidative stress-mediated damage and why integrin α1-null mice are more susceptible to fibrosis following injury.