The Role of Transforming Growth Factor-β Signaling in Myxomatous Mitral Valve Degeneration

Mitral valve prolapse (MVP) due to myxomatous degeneration is one of the most important chronic degenerative cardiovascular diseases in people and dogs. It is a common cause of heart failure leading to significant morbidity and mortality in both species. Human MVP is usually classified into primary or non-syndromic, including Barlow’s Disease (BD), fibro-elastic deficiency (FED) and Filamin-A mutation, and secondary or syndromic forms (typically familial), such as Marfan syndrome (MFS), Ehlers-Danlos syndrome, and Loeys–Dietz syndrome. Despite different etiologies the diseased valves share pathological features consistent with myxomatous degeneration. To reflect this common pathology the condition is often called myxomatous mitral valve degeneration (disease) (MMVD) and this term is universally used to describe the analogous condition in the dog. MMVD in both species is characterized by leaflet thickening and deformity, disorganized extracellular matrix, increased transformation of the quiescent valve interstitial cell (qVICs) to an activated state (aVICs), also known as activated myofibroblasts. Significant alterations in these cellular activities contribute to the initiation and progression of MMVD due to the increased expression of transforming growth factor-β (TGF-β) superfamily cytokines and the dysregulation of the TGF-β signaling pathways. Further understanding the molecular mechanisms of MMVD is needed to identify pharmacological manipulation strategies of the signaling pathway that might regulate VIC differentiation and so control the disease onset and development. This review briefly summarizes current understanding of the histopathology, cellular activities, molecular mechanisms and pathogenesis of MMVD in dogs and humans, and in more detail reviews the evidence for the role of TGF-β.

FAK Inhibition Attenuates Corneal Fibroblast Differentiation In Vitro

Corneal fibrosis (or scarring) occurs in response to ocular trauma or infection, and by reducing corneal transparency, it can lead to visual impairment and blindness. Studies highlight important roles for transforming growth factor (TGF)-β1 and -β3 as modulators in corneal wound healing and fibrosis, leading to increased extracellular matrix (ECM) components and expression of α-smooth muscle actin (αSMA), a myofibroblast marker. In this study, human corneal fibroblasts (hCF) were cultured as a monolayer culture (2D) or on poly-transwell membranes to generate corneal stromal constructs (3D) that were treated with TGF-β1, TGF-β3, or TGF-β1 + FAK inhibitor (FAKi). Results show that hCF 3D constructs treated with TGF-β1 or TGF-β3 impart distinct effects on genes involved in wound healing and fibrosis-ITGAV, ITGB1, SRC and ACTA2. Notably, in the 3D construct model, TGF-β1 enhanced αSMA and focal adhesion kinase (FAK) protein expression, whereas TGF-β3 did not. In addition, in both the hCF 2D cell and 3D construct models, we found that TGF-β1 + FAKi attenuated TGF-β1-mediated myofibroblast differentiation, as shown by abrogated αSMA expression. This study concludes that FAK signaling is important for the onset of TGF-β1-mediated myofibroblast differentiation, and FAK inhibition may provide a novel beneficial therapeutic avenue to reduce corneal scarring.

TRPV1 Receptor Identification in Bovine and Canine Mitral Valvular Interstitial Cells

Myxomatous mitral valve degeneration (MMVD) is the most common acquired cardiac disease in canine species, and valvular interstitial cells (VICs) are considered the main responsible for the development of this pathology. The scientific interest is focused on isolating and characterizing these cells. The aims of the present study were to verify a novel VICs mechanical isolation method and to characterize isolated cells using immunocytochemistry and immunofluorescence, with parallel histological and immunohistochemistry assays on bovine and canine healthy and MMVD mitral valves. Antibodies against vimentin (VIM), smooth muscle actin (SMA), von Willebrand (vW) factor, Transforming Growth Factor (TGF) β1, and Transient Receptor Potential Vanilloid 1 (TRPV1) were used. The isolation method was considered reliable and able to isolate only VICs. The different assays demonstrated a different expression of SMA in healthy and MMVD mitral valves, and TRPV1 was isolated for the first time from bovine and canine VICs and the correspondent mitral valve leaflets. The novelties of the present study are the new isolation method, that may allow correlations between laboratory and clinical conditions, and the identification of TRPV1, which will lead to further investigations to understand its function and possible role in the etiology of MMVD and to the design of new therapeutic strategies.

Genetics of canine myxomatous mitral valve disease

Myxomatous mitral valve disease (MMVD) is the most common heart disease and cause of cardiac death in domestic dogs. MMVD is characterised by slow progressive myxomatous degeneration from the tips of the mitral valves onwards with subsequent mitral valve regurgitation, and left atrial and ventricular dilatation. Although the disease usually has a long asymptomatic period, in dogs with severe disease, mortality is typically secondary to left-sided congestive heart failure. Although it is not uncommon for dogs to survive long enough in the asymptomatic period to die from unrelated causes; a proportion of dogs rapidly advance into congestive heart failure. Heightened prevalence in certain breeds, such as the Cavalier King Charles Spaniel, has indicated that MMVD is under a genetic influence. The genetic characterisation of the factors that underlie the difference in progression of disease is of strong interest to those concerned with dog longevity and welfare. Advanced genomic technologies have the potential to provide information that may impact treatment, prevalence, or severity of MMVD through the elucidation of pathogenic mechanisms and the detection of predisposing genetic loci of major effect. Here we describe briefly the clinical nature of the disorder and consider the physiological mechanisms that might impact its occurrence in the domestic dog. Using results from comparative genomics we suggest possible genetic approaches for identifying genetic risk factors within breeds. The Cavalier King Charles Spaniel breed represents a robust resource for uncovering the genetic basis of MMVD.

A Genomic Study of Myxomatous Mitral Valve Disease in Cavalier King Charles Spaniels

Cavalier King Charles spaniels (CKCSs) show the earliest onset and the highest incidence of myxomatous mitral valve disease (MMVD). Previous studies have suggested a polygenic inheritance of the disease in this breed and revealed an association with regions on canine chromosomes 13 and 14. Following clinical and echocardiographic examinations, 33 not-directly-related CKCSs were selected and classified as cases (n = 16) if MMVD was present before 5 years of age or as controls (n = 17) if no or very mild MMVD was present after 5 years of age. DNA was extracted from whole blood and genotyped with a Canine 230K SNP BeadChip instrument. Cases and controls were compared with three complementary genomic analyses (Wright's fixation index-F_ST, cross-population extended haplotype homozygosity-XP-EHH, and runs of homozygosity-ROH) to identify differences in terms of heterozygosity and regions of homozygosity. The top 1% single-nucleotide polymorphisms (SNPs) were selected and mapped, and the genes were thoroughly investigated. Ten consensus genes were found localized on chromosomes 3-11-14-19, partially confirming previous studies. The HEPACAM2, CDK6, and FAH genes, related to the transforming growth factor β (TGF-β) pathway and heart development, also emerged in the ROH analysis. In conclusion, this work expands the knowledge of the genetic basis of MMVD by identifying genes involved in the early onset of MMVD in CKCSs.

Comparative pathology of human and canine myxomatous mitral valve degeneration: 5HT and TGF-β mechanisms

Myxomatous mitral valve degeneration (MMVD) is a leading cause of valve repair or replacement secondary to the production of mitral regurgitation, cardiac enlargement, systolic dysfunction, and heart failure. The pathophysiology of myxomatous mitral valve degeneration is complex and incompletely understood, but key features include activation and transformation of mitral valve (MV) valvular interstitial cells (VICs) into an active phenotype leading to remodeling of the extracellular matrix and compromise of the structural components of the mitral valve leaflets. Uncovering the mechanisms behind these events offers the potential for therapies to prevent, delay, or reverse myxomatous mitral valve degeneration. One such mechanism involves the neurotransmitter serotonin (5HT), which has been linked to development of valvulopathy in a variety of settings, including valvulopathy induced by serotonergic drugs, Serotonin-producing carcinoid tumors, and development of valvulopathy in laboratory animals exposed to high levels of serotonin. Similar to humans, the domestic dog also experiences naturally occurring myxomatous mitral valve degeneration, and in some breeds of dogs, the lifetime prevalence of myxomatous mitral valve degeneration reaches 100%. In dogs, myxomatous mitral valve degeneration has been associated with high serum serotonin, increased expression of serotonin-receptors, autocrine production of serotonin within the mitral valve leaflets, and downregulation of serotonin clearance mechanisms. One pathway closely associated with serotonin involves transforming growth factor beta (TGF-β) and the two pathways share a common ability to activate mitral valve valvular interstitial cells in both humans and dogs. Understanding the role of serotonin and transforming growth factor beta in myxomatous mitral valve degeneration gives rise to potential therapies, such as 5HT receptor (5HT-R) antagonists. The main purposes of this review are to highlight the commonalities between myxomatous mitral valve degeneration in humans and dogs, with specific regards to serotonin and transforming growth factor beta, and to champion the dog as a relevant and particularly valuable model of human disease that can accelerate development of novel therapies.

Evaluation of canine 2D cell cultures as models of myxomatous mitral valve degeneration

The utility of cells cultured from the mitral valve as models of myxomatous diseases needs to be properly validated. In this study valve interstitial cells (VICs) and valve endothelial cells (VECs) were cultured from normal and diseased canine mitral valves in 2% (v/v) or 10% FBS media, in the presence of TGFβ1, 2 and 3, the TGFβ RI kinase inhibitor SB431542 and TGFβ neutralising antibodies, 5HT and the 5HT2RB antagonist LY272015. Cultures were examined by morphology, transcriptomic profiling, protein expression of the cell specific markers αSMA and SM22α (VICs), and CD31 (VECs), deposition of proteoglycans (PG), the PG versican, and the TGFβs themselves. VECs derived from normal valves were CD31+/αSMA-, but those from diseased valves were αSMA+, indicating endothelial-to-mesenchymal (EndoMT) transition had occurred. The TGFβs induced EndoMT in normal VECs, and this was abolished by SB431542, with significant changes in αSMA, CD31 and HAS2 expression (P<0.05). Normal VICs cultured in 10% FBS media were αSMA+ (activated myofibroblast (disease) phenotype), but were αSMA- when grown in 2% FBS. VICs from diseased dogs were αSMA+ in 2% FBS (retention of the activated myofibroblast disease phenotype), with significantly increased TGFβ1 expression (P<0.05) compared to normal cells. Treatment of normal and diseased VICs with the TGFβs significantly increased expression of αSMA, SM22α, versican, the TGFβs themselves, and deposition of PGs (P<0.05), with TGFβ1 being the most potent activator. These effects were either abolished or markedly reduced by SB431542 and a pan-TGFβ neutralizing antibody (P<0.05). SB431542 also markedly reduced αSMA expression in VICs from diseased valves, but 5HT and LY272015 had no effect on VIC phenotype. Transcriptomic profiling identified clear differences in gene expression for the different conditions and treatments that partially matched that seen in native diseased valve tissue, including changes in expression of ACTA2 (αSMA), 5HTR2B, TAGLN (SM22α) and MYH10 (SMemb), gene ontology terms and canonical signalling pathways. Normal and diseased VICs and normal VECs from canine mitral valves can be successfully grown in culture with retention of phenotype, which can be manipulated using TGFβ1 and the TGFβ RI kinase inhibitor SB431542. This optimized cell system can now be used to model MMVD to elucidate disease mechanisms and identify key regulators of disease progression.

Comparative Transcriptomic Profiling and Gene Expression for Myxomatous Mitral Valve Disease in the Dog and Human

Myxomatous mitral valve disease is the single most important mitral valve disease in both dogs and humans. In the case of the dog it is ubiquitous, such that all aged dogs will have some evidence of the disease, and for humans it is known as Barlow's disease and affects up to 3% of the population, with an expected increase in prevalence as the population ages. Disease in the two species show many similarities and while both have the classic myxomatous degeneration only in humans is there extensive fibrosis. This dual pathology of the human disease markedly affects the valve transcriptome and the difference between the dog and human is dominated by changes in genes associated with fibrosis. This review will briefly examine the comparative valve pathology and then, in more detail, the transcriptomic profiling and gene expression reported so far for both species.

Pathophysiology of Aortic Stenosis and Mitral Regurgitation

The global impact of the spectrum of valve diseases is a crucial, fast-growing, and underrecognized health problem. The most prevalent valve diseases, requiring surgical intervention, are represented by calcific and degenerative processes occurring in heart valves, in particular, aortic and mitral valve. Due to the increasing elderly population, these pathologies will gain weight in the global health burden. The two most common valve diseases are aortic valve stenosis (AVS) and mitral valve regurgitation (MR). AVS is the most commonly encountered valve disease nowadays and affects almost 5% of elderly population. In particular, AVS poses a great challenge due to the multiple comorbidities and frailty of this patient subset. MR is also a common valve pathology and has an estimated prevalence of 3% in the general population, affecting more than 176 million people worldwide. This review will focus on pathophysiological changes in both these valve diseases, starting from the description of the anatomical aspects of normal valve, highlighting all the main cellular and molecular features involved in the pathological progression and cardiac consequences. This review also evaluates the main approaches in clinical management of these valve diseases, taking into account of the main published clinical guidelines. © 2017 American Physiological Society. Compr Physiol 7:799-818, 2017.

Myxomatous Degeneration of the Canine Mitral Valve: From Gross Changes to Molecular Events

Myxomatous mitral valve disease (MMVD) is the single most common acquired heart disease of the dog, but is also of emerging importance in human medicine, with some features of the disease shared between both species. There has been increased understanding of this disease in recent years, with most research aiming to elucidate the cellular and molecular events of disease pathogenesis. For gross and histological changes, much of our understanding is based on historical studies and there has been no comprehensive reappraisal of the pathology of MMVD. This paper reviews the gross, histological, ultrastructural, cellular and molecular changes in canine MMVD.

Associations of rs3918242 and rs2285053 MMP-9 and MMP-2 polymorphisms with the risk, severity, and short- and long-term complications of degenerative mitral valve diseases: a 4.8-year prospective cohort study

BACKGROUND

Degenerative forms of mitral valve diseases (MVDs) are very complex pathologies. Thus, it is difficult to make generalizations about the disease pathways or genetic risk factors contributing to these diseases. However, a key role of metalloproteinases (MMPs) in their pathophysiology is emerging. Thus, we performed for the first time a perspective study to assess eventual associations of some functional single nucleotide polymorphisms (SNPs) in MMP-2 and MMP-9 genes with the MVD risk, symptom severity, and short- and long-term (4.8 years) complications.

MATERIALS AND METHODS

For this purpose, 90 patients and two control groups were genotyped for rs3918242, rs243865, and rs2285053 MMP-2 and MMP-9 gene SNPs, and systemic levels of pro-atrial natriuretic peptide (pro-ANP) and two enzymes were quantified and correlated to genotypes of MMP-2 and MMP-9 SNPs studied. In addition, associations between these SNPs and symptom severity and short- and long-term (4.8 years) complications were evaluated.

RESULTS

Interestingly, rs3918242 MMP-9 and rs2285053 MMP-2 SNPs were significantly represented in cases than two control groups and were associated with a higher MVD risk, as demonstrated using dominant/recessive models. Cases stratified for NYHA symptoms and particularly those NYHA III+IV with rs3918242 CT+TT MMP-9 and rs2285053CT+TT genotypes also showed higher severity related to significant higher systemic levels of MMP enzymes and pro-ANP at enrolment and 4.8 follow-up times. In addition, cases with these genotypes and particularly those NYHA III+IV had a very significant percentage of complications, particularly at the 4.8 follow-up. Surprisingly, 20% of patient controls developed MVD at 4.8-year follow-up and were carriers of these genotypes.

CONCLUSION

Thus, the associations observed seem to suggest that the two SNPs might represent useful biomarkers and targets for preventing and monitoring MVDs and developing personalized treatments, consenting a more appropriate management and outcome.

Cytokine expression in peripheral blood mononuclear cells of dogs with mitral valve disease

Inflammation plays an important role in the pathogenesis of congestive heart failure (CHF). In humans with CHF, increased production and high plasma concentrations of tumour necrosis factor-α (TNF-α), interleukin (IL)-6, IL-1, IL-8 and transforming growth factor-β (TGF-β) have been associated with disease progression and a negative prognosis. The aim of this study was to investigate whether differences in cytokine blood mRNA expression exist between clinically healthy dogs and dogs with myxomatous mitral valve disease (MMVD); to determine if the expression was related to the severity of MMVD, and to detect any correlations with echocardiographic parameters of cardiac remodelling. Twenty-three dogs with MMVD of varying severity and six clinically healthy dogs were included in the study. Whole blood samples were obtained for measurement of mRNA expression of IL-1α, IL-1β, IL-6, IL-8, TGF-β1, TNF-α by reverse transcriptase-PCR (RT-PCR). There were statistically significant differences between clinically healthy dogs and dogs with MMVD for IL-8 and TGF-β1 gene expression. IL-8 expression increased with increasing MMVD severity and TGF-β1 expression was higher in asymptomatic dogs with echocardiographic signs of cardiac remodelling (American College Veterinary Internal Medicine class B2) than in all other groups. These results could suggest the involvement of these cytokines at different stages of the disease.

Mitral valve disease--morphology and mechanisms

Mitral valve disease is a frequent cause of heart failure and death. Emerging evidence indicates that the mitral valve is not a passive structure, but--even in adult life--remains dynamic and accessible for treatment. This concept motivates efforts to reduce the clinical progression of mitral valve disease through early detection and modification of underlying mechanisms. Discoveries of genetic mutations causing mitral valve elongation and prolapse have revealed that growth factor signalling and cell migration pathways are regulated by structural molecules in ways that can be modified to limit progression from developmental defects to valve degeneration with clinical complications. Mitral valve enlargement can determine left ventricular outflow tract obstruction in hypertrophic cardiomyopathy, and might be stimulated by potentially modifiable biological valvular-ventricular interactions. Mitral valve plasticity also allows adaptive growth in response to ventricular remodelling. However, adverse cellular and mechanobiological processes create relative leaflet deficiency in the ischaemic setting, leading to mitral regurgitation with increased heart failure and mortality. Our approach, which bridges clinicians and basic scientists, enables the correlation of observed disease with cellular and molecular mechanisms, leading to the discovery of new opportunities for improving the natural history of mitral valve disease.

Transforming growth factor beta 1 activation, storage, and signaling pathways in idiopathic pulmonary fibrosis in dogs

BACKGROUND

The pathogenesis of idiopathic pulmonary fibrosis (IPF) in dogs is poorly understood. In human, transforming growth factor β1 (TGF-β1) is considered central in the pathogenesis.

OBJECTIVES

To investigate TGF-β1 pathway in IPF.

ANIMALS

Lung tissues from 12 affected and 11 control dogs. Serum from 16 affected West Highland white Terriers (WHWTs) and healthy dogs from predisposed (13 WHWTs, 12 Scottish Terriers and 13 Bichons Frise) and nonpredisposed breeds (10 Whippets, 10 Belgian shepherds, 8 Labradors).

METHODS

In this prospective study, immunohistochemistry was used to evaluate expression and localization of TGF-β1 protein and proteins involved in TGF-β1 signaling (TGF-β receptor type I and phospho-Smad2/3). Pulmonary expression of TGF-β1 and molecules involved in its storage (latent TGF-β binding proteins [LTBP] 1, 2, and 4), activation (ανβ6 and ανβ8 integrins, thrombospondin-1) and signal inhibition (Smad 7) was analyzed by quantitative reverse transcriptase PCR. Circulating TGF-β1 concentration was measured by ELISA.

RESULTS

In IPF, high level of TGF-β1 protein was found in areas of fibrosis, epithelial cells had strong expression of TGF-β receptor type 1 and phospho-Smad2/3, gene expression was decreased for LTBP 4 (P = .009) and β8 integrin (P < .001) and increased for thrombospondin-1 (P = .016); no difference was seen for Smad7, LTBP1 and 2. Serum TGF-β1 concentration was higher in predisposed compared with nonpredisposed breeds (P < .0001).

CONCLUSIONS AND CLINICAL IMPORTANCE

This study identified an enhanced TGF-β1 signaling activity in IPF. TGF-β1 storage and activation proteins with altered expression represent potential therapeutic targets. Higher circulating TGF-β1 concentration in predisposed breeds might partly explain their susceptibility for IPF.

Matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs) and transforming growth factor-β (TGF-β) in advanced canine myxomatous mitral valve disease

This study investigated mitral valve and myocardial protein and gene expression of matrix metalloproteinases (MMPs), their tissue inhibitors (TIMPs) and transforming growth factor-β (TGF-β) and plasma MMP and TGF-β concentrations in age-matched dog groups euthanized due to either advanced myxomatous mitral valve disease (MMVD) or other reasons. Furthermore, echocardiographic data and lumen/area ratio were correlated with tissue and plasma levels of MMPs, TIMPs and TGF-βs. Mitral valve and myocardial gene expression of MMP2, MMP14, TGF-β1 and TGF-β2 were increased and plasma MMP9 was decreased in advanced MMVD dogs. Myocardial gene expression of TIMP2 and TIMP3 were increased in advanced MMVD. All affected markers correlated to echocardiographic parameters. Significantly narrowed lumen/area ratio was associated with increased myocardial expression of MMP2, MMP14, TIMP2 and TIMP3. No differences in tissue protein expression were recorded. MMP2, MMP14, TIMP2, TIMP3, TGF-β1 and TGF-β2 appear to play a local role in the development of advanced MMVD.

The transcriptomic profile of peripheral blood nuclear cells in dogs with heart failure

Background

In recent years advances have been made in the investigative methods of molecular background of canine heart disease. Studies have been conducted to identify specific genes which, when pathologically expressed, could lead to the dysfunction of the canine heart or are correlated with heart failure. For this purpose genome wide microarray experiments on tissues from failing hearts have been performed. In the presented study a whole genome microarray analysis was used for the first time to describe the transcription profile of peripheral blood nuclear cells in dogs with heart failure. Dogs with recognized heart disease were classified according the ISACHC (International Small Animal Cardiac Health Council) classification scheme as class 1 (asymptomatic) - 13 dogs, class 2 (mild to moderate heart failure) - 13 dogs and class 3 (severe heart failure) - 12 dogs. The control group consisted of 14 healthy dogs. The clinical picture of the animals included: animal history, clinical examination, echocardiographic examination and where applicable electrocardiographic and radiographic examinations.

Results

In the present study we identified four sets of differentially expressed genes, namely heart-failure-specific genes and ISACHC1-specific genes, ISACHC2-sepcific genes and ISACHC-3 specific genes. The most important set consisted of genes differentially expressed in all dogs with heart failure, despite the ISACHC stage. We identified 71 heart-failure-specific genes which were involved in two statistically significant receptor signalling pathways, namely angiotensinR - > CREB/ELK-SRF/TP53 signalling and ephrinR - > actin signalling. The number of ISACHC1-specific genes was 83; ISACHC2-specific genes - 1247 and ISACHC3-specific - 200.

Conclusions

The transcriptomic profile of peripheral blood nuclear cells in dogs with heart failure seems to reflect the presence of clinical signs of the disease in patients based on the observation that the largest number of differentially expressed genes was identified in ISACHC 2 group of patients. This group consists of dogs just starting to show clinical signs of heart failure. A set of genes was also found to have changed expression in all dogs with heart failure, despite the stage of the disease.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-509) contains supplementary material, which is available to authorized users.

Pathogenesis of mitral valve disease in mucopolysaccharidosis VII dogs

Mucopolysaccharidosis VII (MPS VII) is due to the deficient activity of β-glucuronidase (GUSB) and results in the accumulation of glycosaminoglycans (GAGs) in lysosomes and multisystemic disease with cardiovascular manifestations. The goal here was to determine the pathogenesis of mitral valve (MV) disease in MPS VII dogs. Untreated MPS VII dogs had a marked reduction in the histochemical signal for structurally-intact collagen in the MV at 6 months of age, when mitral regurgitation had developed. Electron microscopy demonstrated that collagen fibrils were of normal diameter, but failed to align into large parallel arrays. mRNA analysis demonstrated a modest reduction in the expression of genes that encode collagen or collagen-associated proteins such as the proteoglycan decorin which helps collagen fibrils assemble, and a marked increase for genes that encode proteases such as cathepsins. Indeed, enzyme activity for cathepsin B (CtsB) was 19-fold normal. MPS VII dogs that received neonatal intravenous injection of a gamma retroviral vector had an improved signal for structurally-intact collagen, and reduced CtsB activity relative to that seen in untreated MPS VII dogs. We conclude that MR in untreated MPS VII dogs was likely due to abnormalities in MV collagen structure. This could be due to upregulation of enzymes that degrade collagen or collagen-associated proteins, to the accumulation of GAGs that compete with proteoglycans such as decorin for binding to collagen, or to other causes. Further delineation of the etiology of abnormal collagen structure may lead to treatments that improve biomechanical properties of the MV and other tissues.

Expression of matrix metalloproteinases, their inhibitors, and lysyl oxidase in myocardial samples from dogs with end-stage systemic and cardiac diseases

OBJECTIVE

To compare the degree of mRNA expression for matrix metalloproteinases (MMPs), tissue inhibitors (TIMPs), and lysyl oxidase in myocardial samples from dogs with cardiac and systemic diseases and from healthy control dogs.

SAMPLE

Myocardial samples from the atria, ventricles, and septum of 8 control dogs, 6 dogs with systemic diseases, 4 dogs with dilated cardiomyopathy (DCM), and 5 dogs with other cardiac diseases.

PROCEDURES

Degrees of mRNA expression for MMP-1, -2, -3, -9, and -13; TIMP-1, -2, -3, and -4; and lysyl oxidase were measured via quantitative real-time PCR assay. Histologic examination of the hearts was performed to identify pathological changes.

RESULTS

In myocardial samples from control dogs, only TIMP-3 and TIMP-4 mRNA expression was detected, with a significantly higher degree in male versus female dogs. In dogs with systemic and cardiac diseases, all investigated markers were expressed, with a significantly higher degree of mRNA expression than in control dogs. Furthermore, the degree of expression for MMP-2, TIMP-1, and TIMP-2 was significantly higher in dogs with DCM than in dogs with systemic diseases and cardiac diseases other than DCM. Expression was generally greater in atrial than in ventricular tissue for MMP-2, MMP-13, and lysyl oxidase in samples from dogs with atrial fibrillation.

CONCLUSIONS AND CLINICAL RELEVANCE

Degrees of myocardial MMP, TIMP, and lysyl oxidase mRNA expression were higher in dogs with cardiac and systemic diseases than in healthy dogs, suggesting that expression of these markers is a nonspecific consequence of end-stage diseases. Selective differences in the expression of some markers may reflect specific pathogenic mechanisms and may play a role in disease progression, morbidity and mortality rates, and treatment response.

Plasma proANP and SDMA and microRNAs are associated with chronic mitral regurgitation in a pig model

OBJECTIVE

NON-ISCHEMIC MITRAL REGURGITATION (MR) IS PRIMARILY CAUSED BY MYXOMATOUS MITRAL VALVE (MV) DISEASE LEADING TO ADAPTIVE REMODELING, ENLARGEMENT, AND DYSFUNCTION OF THE LEFT VENTRICLE. THE AIM OF THIS STUDY WAS TO EXAMINE THE REGULATION OF PLASMA MARKERS AND SEVERAL CARDIAC KEY GENES IN A NOVEL PORCINE MODEL OF NON-ISCHEMIC MR.

METHODS AND RESULTS

Twenty-eight production pigs (Sus scrofa) were randomized to experimental MR or sham surgery controls. MR was induced by external suture(s) through the posterior MV leaflet and quantified using echocardiography. The experimental group was subdivided into mild MR (mMR, MR=20-50%, n=10) and moderate/severe MR (sMR, MR >50%, n=6) and compared with controls (CON, MR ≤10%, n=12). Eight weeks postoperatively, follow-up examinations were performed followed by killing. Circulating concentrations of pro-atrial natriuretic peptide (proANP), l-arginine, asymmetric dimethylarginine, and symmetric dimethylarginine (SDMA) were measured. MV, anterior papillary muscle, and left ventricular free wall tissues were collected to quantify mRNA expression of eNOS (NOS3), iNOS (NOS2), MMP9, MMP14, ANP (NPPA), BNP (NPPB), and TGFB1, 2, and 3 and five microRNAs by quantitative real-time PCR. Pigs with sMR displayed markedly increased plasma proANP and SDMA concentrations compared with both controls and mMR (P<0.05). The expression of all genes examined differed significantly between the three localizations in the heart. miR-21 and miR-133a were differently expressed among the experimental groups (P<0.05).

CONCLUSIONS

Plasma proANP and SDMA levels and tissue expression of miR-21 and miR-133a are associated with severity of chronic MR in an experimental porcine model.

Chondrogenic differentiation of immortalized human mesenchymal stem cells on zirconia microwell substrata

Human mesenchymal stem cells (hMSCs) that can differentiate into chondrocytes are a potential autologous cell source for repair of damaged tissue. Current methods usually induce the formation of all three chondrocyte phenotypes, hyaline, fibrous, and elastic, without the ability to selectively induce only one of them. By controlling the size of hMSC cell clusters, it may be possible to direct differentiation more uniformly toward hyaline chondrocytes. We designed new cell culture platforms containing microwells of different diameters. The platforms and wells were composed of a zirconia ceramics substratum. hMSCs briefly adhered to the substratum before releasing and entering the microwells. The physical restraints imposed by the microwells enabled hMSC clusters to homogenously differentiate into hyaline chondrocyte-like cells. Chondrogenic aggregates in microwells expressed the hyaline chondrocyte-specific genes Col II, aggrecan (ACAN), and cartilage oligomeric protein (COMP). The cultures also produced hyaline chondrocyte-specific matrix proteins Col II and ACAN homogenously throughout the aggregates. In contrast, chondrogenesis in pellet cultures was heterogeneous with the expression of nonhyaline chondrocyte genes CD105, Col X, and Col I. In these pellet cultures, hyaline and nonhyaline chondrocyte-specific matrix proteins were distributed heterogeneously. Thus, this novel ceramic microwell substratum technology efficiently directed the differentiation of hyaline chondrocyte-like cells from hMSCs. These results indicate that there is a close relationship between hMSC cluster size regulation in the microwells and differentiation tendency. This microwell culture differentiation method will provide a valuable experimental system for both experimental and potential clinical studies.

Animal models of organic heart valve disease

Heart valve disease is a frequently encountered pathology, related to high morbidity and mortality rates in industrialized and developing countries. Animal models are interesting to investigate the causality, but also underlying mechanisms and potential treatments of human valvular diseases. Recently, animal models of heart valve disease have been developed, which allow to investigate the pathophysiology, and to follow the progression and the potential regression of disease with therapeutics over time. The present review provides an overview of animal models of primary, organic heart valve disease: myxoid age-related, infectious, drug-induced, degenerative calcified, and mechanically induced valvular heart disease.

Genomic and genetic aspects of heart failure in dogs - a review

The most common causes of heart failure in dogs are valvular disease, predominantly endocardiosis, and myocardial disease, predominantly dilated cardiomyopathy. They are related to changes in the expression of several genes in the heart muscle and in peripheral blood nuclear cells which could be considered as prognostic or diagnostic markers of heart disease in dogs. Since many human genetic markers of heart failure have turned out to be useless in dogs, the screening for genomic markers of canine heart failure could give more insight into the molecular pathology of these diseases and aid the development of new treatment strategies.

Pathology, protein expression and signaling in myxomatous mitral valve degeneration: comparison of dogs and humans

Myxomatous degenerative mitral valve disease (MMVD) is a common heart disease in dogs. Although several morphological similarities occur between human and canine MMVD differences exist. However, in advanced stages the accumulation of proteoglycans is the main finding in both species. The extracellular matrix (ECM) in normal canine and human mitral valves is similar. In MMVD of both species proteoglycans is the major alteration, although specific changes in collagen distribution exists. The valvular expression pattern of matrix metalloproteinases (MMPs) and of their inhibitors (TIMPs) differs, in part, between dogs and humans. The MMPs and TIMPs expression patterns are similar in normal canine and human mitral valves, but they are quite different during degenerative progression. Valve endothelial cells (VEC) and interstitial cells (VIC) are phenotypically transformed in canine and human MMVD. Inflammation is an unlikely cause of valve degeneration in humans and dogs. There are several lines of evidence suggesting that transforming growth factor β1 (TGF β1) and serotonin signaling may mediate valve degeneration in humans and dogs. Although human and canine MMVD share structural similarities, there are some differences in ECM changes, enzyme expression and cell transformation, which may reflect a varied pathogenesis of these diseases.

Differentiating the aging of the mitral valve from human and canine myxomatous degeneration

During the course of both canine and human aging, the mitral valve remodels in generally predictable ways. The connection between these aging changes and the morbidity and mortality that accompany pathologic conditions has not been made clear. By exploring work that has investigated the specific valvular changes in both age and disease, with respect to the cells and the extracellular matrix found within the mitral valve, heretofore unexplored connections between age and myxomatous valve disease can be found. This review addresses several studies that have been conducted to explore such age and disease related changes in extracellular matrix, valvular endothelial and interstitial cells, and valve innervation, and also reviews attempts to correlate aging and myxomatous disease. Such connections can highlight avenues for future research and help provide insight as to when an individual diverts from an aging pattern into a diseased pathway. Recognizing these patterns and opportunities could result in earlier intervention and the hope of reduced morbidity and mortality for patients.

Signaling pathways in mitral valve degeneration

Heart valves exhibit a highly-conserved stratified structure exquisitely designed to counter biomechanical forces delivered over a lifetime. Heart valve structure and competence is maintained by heart valve cells through a process of continuous turnover extracellular matrix (ECM). Degenerative (myxomatous) mitral valve disease (DMVD) is an important disease associated with aging in both dogs and humans. DMVD is increasingly regarded as a disease with identifiable signaling mechanisms that control key genes associated with regulation and dysregulation of ECM homeostasis. Initiating stimuli for these signaling pathways have not been fully elucidated but likely include both mechanical and chemical stimuli. Signaling pathways implicated in DMVD include serotonin, transforming growth factor β (TGFβ), and heart valve developmental pathways. High circulating serotonin (carcinoid syndrome) and serotoninergic drugs are known to cause valvulopathy that shares pathologic features with DMVD. Recent evidence supports a local serotonin signaling mechanism, possibly triggered by high tensile loading on heart valves. Serotonin initiates TGFβ signaling, which in turn has been strongly implicated in canine DMVD. Recent evidence suggests that degenerative aortic and mitral valve disease may involve pathologic processes that mimic osteogenesis and chondrogenesis, respectively. These processes may be mediated by developmental pathways shared by heart valves, bone, and cartilage. These pathways include bone morphogenic protein (BMP) and Wnt signaling. Other signaling pathways implicated in heart valve disease include Notch, nitric oxide, and angiotensin II. Ultimately, increased understanding of signaling mechanisms could point to therapeutic strategies aimed at slowing or halting disease progression.

Increased blood mRNA expression of inflammatory and anti-fibrotic markers in dogs with congestive heart failure

Inflammation and extracellular matrix (ECM) remodeling contribute to the development of congestive heart failure (CHF), but the pathogenesis is still incompletely understood. Therefore, whole blood samples from eight dogs without cardiac disease and eight dogs with CHF were investigated for mRNA expression of IL1β, IL2, IL4, IL6, IL8, IL10, TNFα, IFNγ, TGFβ1-3, MMP1, -2, -3, -9 and TIMP1-4 using quantitative PCR. Dogs with CHF had significantly higher IL1β (P=0.015), IL2 (P=0.043), MMP1 (P=0.031), TIMP3 (P=0.012) and lower TNFα (P<0.001), TGFβ3 (P=0.006), TIMP1 (P=0.015) and TIMP2 (P=0.011) mRNA levels. Increased pro-inflammatory IL1β and anti-fibrotic MMP1 and reduced pro-fibrotic TGFβ and TIMP1 and TIMP2 in dogs with CHF suggest progressive left ventricular remodeling. The reduction of TNFα and increase of immunomodulatory IL2 and TIMP3 might suggest control of the inflammatory response. A better understanding of inflammation and ECM remodeling in cardiac diseases may lead to novel treatment approaches.