Feline Hypertrophic Cardiomyopathy: The Consequence of Cardiomyocyte-Initiated and Macrophage-Driven Remodeling Processes?

Feline hypertrophic cardiomyopathy: Does the microRNA-mRNA regulatory network contribute to heart sarcomeric protein remodelling?

Feline primary hypertrophic cardiomyopathy (HCM) is an intrinsic myocardial disease characterized by concentric hypertrophy of the left ventricle. In the present study, we investigated the microRNA-mRNA regulatory network in feline myocardial tissue affected by primary (HCMI) and secondary HCM (HCMII). MRNA expression levels of sarcomeric genes, including, TNNT2, TNNI3, MYH7, MYBPC3, TPM1 and ACTC1 were assessed in the FFPE myocardial tissues. FFPE tissues from healthy cats were sequenced by the NGS, to explore, in the entire non-deposited miRNome, the expression level of microRNAs targeting the complementary sequences of selected sarcomeric mRNAs. The sarcomeric genes TNNT2, MYH7, MYBPC3 and TPM1 showed a statistically significant upregulation in HCMI compared to HCMII (p < .01), except ACTC1 which was downregulated (p < .01); TNNI3 showed no statistically significant difference. In HCMII miR-122-5p, miR-338-3p, miR-484, miR-370-3p, miR-92b-3p, miR-375 and miR-370-3p showed a significant upregulation (p < .01) compared to control. The exception was miR-30a-5p which showed downregulation. Worthy of note is the 4-fold higher expression of miR-370-3p, a key regulator of MYBPC3, in HMCI compared to HMCII. This research does not solve the aetiological mystery of HCM, but it may help to find a way to help diagnose and define the prognosis of HCM in cats.

The Unseen Side of Feline Hypertrophic Cardiomyopathy: Diagnostic and Prognostic Utility of Electrocardiography and Holter Monitoring

Hypertrophic cardiomyopathy (HCM) is a common heart disease in cats, characterized by regional or diffuse hypertrophy of the left ventricular walls, with an uncertain etiology and heterogenous natural history. Several types of rhythm disturbances are often associated with the disease. This study conducts a comprehensive review of the current literature, in order to evaluate the diagnostic and prognostic effectiveness of electrocardiography and Holter monitoring in the management of feline hypertrophic cardiomyopathy. The main subjects of discussion will include general information about HCM and its connection to arrhythmias. We will explore the rhythm disturbances documented in the current literature on Holter monitoring, as well as the techniques used for Holter monitoring. Additionally, the review will cover classical electrocardiography (ECG) and its diagnostic utility. Prognostic indicators and anti-arrhythmic therapy will also be discussed in detail. The findings highlight the importance of understanding arrhythmias in feline HCM for accurate diagnosis, risk assessment, and therapeutic intervention. ECG and Holter monitoring may offer valuable insights into managing feline HCM.

Advancing Treatments for Feline Hypertrophic Cardiomyopathy: The Role of Animal Models and Targeted Therapeutics

Feline HCM is the most common cardiovascular disease in cats, leading to devastating outcomes, including congestive heart failure (CHF), arterial thromboembolism (ATE), and sudden death. Evidence demonstrating long-term survival benefit with currently available therapies is lacking. Therefore, it is imperative to explore intricate genetic and molecular pathways that drive HCM pathophysiology to inspire the development of novel therapeutics. Several clinical trials exploring new drug therapies are currently underway, including those investigating small molecule inhibitors and rapamycin. This article outlines the key work performed using cellular and animal models that has led to and continues to guide the development of new innovative therapeutic strategies.

The Role of Autoantibodies in Companion Animal Cardiac Disease

Clinical studies exploring the role of autoimmune diseases in cardiac dysfunction have become increasingly common in both human and veterinary literature. Autoantibodies (AABs) specific to cardiac receptors have been found in human and canine dilated cardiomyopathy, and circulating autoantibodies have been suggested as a sensitive biomarker for arrhythmogenic right ventricular cardiomyopathy in people and Boxer dogs. In this article, we will summarize recent literature on AABs and their role in cardiac diseases of small animals. Despite the potential for new discoveries in veterinary cardiology, current data in veterinary medicine are limited and further studies are needed.

Exploration of Mediators Associated with Myocardial Remodelling in Feline Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) affects both humans and cats and exhibits considerable interspecies similarities that are exemplified by underlying pathological processes and clinical presentation to the extent that developments in the human field may have direct relevance to the feline disease. Characteristic changes on histological examination include cardiomyocyte hypertrophy and interstitial and replacement fibrosis. Clinically, HCM is characterised by significant diastolic dysfunction due to a reduction in ventricular compliance and relaxation associated with extracellular matrix (ECM) remodelling and the development of ventricular hypertrophy. Studies in rodent models and human HCM patients have identified key protein mediators implicated in these pathological changes, including lumican, lysyl oxidase and TGF-β isoforms. We therefore sought to quantify and describe the cellular location of these mediators in the left ventricular myocardium of cats with HCM and investigate their relationship with the quantity and structural composition of the ECM. We identified increased myocardial content of lumican, LOX and TGF-β2 mainly attributed to their increased expression within cardiomyocytes in HCM cats compared to control cats. Furthermore, we found strong correlations between the expressions of these mediators that is compatible with their role as important components of cellular pathways promoting remodelling of the left ventricular myocardium. Fibrosis and hypertrophy are important pathological changes in feline HCM, and a greater understanding of the mechanisms driving this pathology may facilitate the identification of potential therapies.

Metalloproteinases and Hypertrophic Cardiomyopathy: A Systematic Review

Hypertrophic cardiomyopathy (HCM) is a genetic condition determined by an altered collagen turnover of the extracellular matrix. Matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) are abnormally released in patients with HCM. The purpose of this systematic review was to thoroughly summarize and discuss the existing knowledge of MMPs profile in patients with HCM. All studies meeting the inclusion criteria (detailed data regarding MMPs in patients with HCM) were selected, after screening the literature from July 1975 to November 2022. Sixteen trials that enrolled a total of 892 participants were included. MMPs-particularly MMP2-levels were found higher in HCM patients compared to healthy subjects. MMPs were used as biomarkers after surgical and percutaneous treatments. Understanding the molecular processes that control the cardiac ECM's collagen turnover allows for a non-invasive evaluation of HCM patients through the monitoring of MMPs and TIMPs.

Epididymectomy as a novel surgical procedure; application in the domestic cat

Feline overpopulation raises issues concerning health, ecology, economy, and ethics. Procedures to limit overpopulation should carefully address animal welfare, efficiency, costs, and feasibility. Vasectomy in unowned cats is suggested as preferable to standard neutering as it maintains male sexual behaviour which may induce ovulation and pseudopregnancy in intact females and may prevent immigration of other males. Vasectomy is not performed routinely because it is fastidious, time consuming and requires more material than standard neutering. We describe epididymectomy as an alternative. In a first experiment, we analysed semen, testosterone, behaviour and pain in six experimental cats before and after epididymectomy, and after castration two months later. Excised tissues were analysed histologically. Testosterone concentrations did not differ significantly between intact and epididymectomised animals but were significantly different after castration. Sexual behaviour and testicular spermatogenesis persisted after epididymectomy, but with a marked drop in the semen count after 7 days. The Glasgow pain scores did not differ significantly after epididymectomy and castration. In a subsequent experiment, 20 privately owned cats were epididymectomised and castrated immediately afterwards, to analyse the learning curve and perioperative complications. The time required for an epididymectomy was significantly shorter than for castration. The study confirms that epididymectomy is quicker and less invasive than castration, it is associated with minimal risks and post-operative pain while easy to learn and inexpensive. Further field studies are required to test its efficiency for feline feral population control or in other species such as in bears, lions or deer, where infertility is required and castration not wanted.

Feline myocardial transcriptome in health and in hypertrophic cardiomyopathy-A translational animal model for human disease

Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats, characterized by primary left ventricular hypertrophy. Feline HCM closely resembles human HCM and is suggested as translational animal model for the human disease. A genetic cause is established in humans and suspected for cats, but little is known about the gene expression and pathways involved in the pathogenesis of HCM. To investigate the myocardial transcriptome changes in HCM, RNA sequencing was conducted on left ventricle (LV) and left atrium (LA) samples of healthy cats and cats with HCM (each n = 5; 20 samples). Ingenuity Pathway Analysis was used to determine functional pathways, regulators, and networks. Distinct gene expression profiles were identified in the LV and LA of the feline healthy and HCM myocardium. Analysis of differentially expressed mRNAs (>2 fold; FDR < 0.01) found chamber-specific (LV vs. LA) expression in both healthy and HCM groups, with higher transcriptional activity in the LA. Genes that contribute to the distinct structure and function of each chamber in health and HCM were identified in the regional comparison. The gene expression profiles of HCM compared to healthy hearts revealed disease related genes, including THBS4 and KLHL33 (LV), FAM177B and THRSP (LA), the latter 3 have not been reported for the myocardium so far, as the top differently expressed genes in the HCM heart. Differently expressed genes and functional pathways found in the HCM heart are associated with cardiac remodeling and fibrosis, inflammation, microvascular changes, calcium signaling and cardiac metabolism, with some regional differences. RhoGDI-RhoGTPase signaling, integrin and ILK signaling pathways, the LXR/RXR pathway in the LA, and the PPARα/RXRα, HIF1α and CXCR4 pathways in the LV might be of particular importance in the HCM disease process. This study identified region-specific myocardial gene transcription patterns as well as novel genes and pathways associated with HCM.

Identification of the Immune Status of Hypertrophic Cardiomyopathy by Integrated Analysis of Bulk- and Single-Cell RNA Sequencing Data

Objectives

Hypertrophic cardiomyopathy (HCM) is the most common hereditary cardiomyopathy and immune infiltration is considered an indispensable factor involved in its pathogenesis. In this study, we attempted to combine bulk sequencing and single-cell sequencing to map the immune infiltration-related genes in hypertrophic cardiomyopathy.

Methods

The GSE36961, GSE160997, and GSE122930 datasets were obtained from the Gene Expression Omnibus database. The compositional patterns of the 18 types of immune cell fraction and pathway enrichment score in control and HCM patients were estimated based on the GSE36961 cohort using xCell algorithm. The Weighted Gene Coexpression Network Analysis (WGCNA) was performed to identify genes associated with immune infiltration for hypertrophic cardiomyopathy. The area under the curve (AUC) value was obtained and used to evaluate the discriminatory ability of common immune-related DEGs. “NetworkAnalyst” platform was used to identify TF-gene and TF-miRNA interaction with identified common genes. Heat map was used to determine the association between common DEGs and various immune cells.

Results

Immune infiltration analysis by the xCell algorithm showed a higher level of CD8+ naive T cells, CD8+ T cells, as well as a lower level of activated dendritic cells (aDC), dendritic cells (DC), immature dendritic cells (iDC), conventional dendritic cells (cDC), macrophages, M1 macrophages, monocytes, and NKT cell in HCM compared with the control group in GSE36961 dataset. aDC, macrophages, and M1 macrophages were the top three discriminators between HCM and control groups with the area under the curve (AUC) of 0.907, 0.867, and 0.941. WGCNA analysis showed that 1258 immune-related genes were included in four different modules. Of these modules, the turquoise module showed a pivotal correlation with HCM. 13 common immune-related DEGs were found by intersecting common DEGs in GSE36961 and GSE160997 datasets with genes from the genes in turquoise module. 5 hub immune-related genes (S100A9, TYROBP, FCER1G, CD14, and S100A8) were identified by protein interaction network. Through analysis of single-cell sequencing data, S100a9, TYROBP, FCER1G, and S100a8 were mainly expressed by infiltrated M1 proinflammatory cells, especially Ccr2-M1 proinflammatory macrophage cells in the heart immune microenvironment while Cd14 was expressed by infiltrated M1 proinflammatory macrophage cells and M2 macrophages in transverse aortic constriction (TAC) mice at 1 week. Higher M2 macrophage and M1 proinflammatory macrophage infiltration as well as lower Ccr2-M1 proinflammatory macrophage and dendritic cells were shown in TAC 1week mice compared with sham mice.

Conclusions

There was a difference in immune infiltration between HCM patients and normal groups. aDC, macrophages, and M1 macrophages were the top three discriminator immune cell subsets between HCM and control groups. S100A9, TYROBP, FCER1G, CD14, and S100A8 were identified as potential biomarkers to discriminate HCM from the control group. S100a9, TYROBP, FCER1G, and S100a8 were mainly expressed by infiltrated M1 proinflammatory cells, especially Ccr2-M1 proinflammatory cells in the heart immune microenvironment while Cd14 was expressed by M2 macrophages in transverse aortic constriction (TAC) mice at 1 week.

Elevated angiotensin-converting enzyme 2 (ACE2) expression in cats with hypertrophic cardiomyopathy

Angiotensin-converting enzyme 2 (ACE2) is an enzyme within the renin-angiotensin-aldosterone system that plays a role in regulating blood pressure. However, it is also a cellular receptor for infection with SARS coronaviruses. Although most cats develop subclinical or mild disease following infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) acquired from human patients, a previous study has suggested hypertrophic cardiomyopathy (HCM) is a potential risk factor for the development of severe disease in the cat. Herein we investigate the ACE2 protein expression in the lung, heart, and kidney from a small subset of cats with (n = 10) and without HCM (n = 10) by immunohistochemistry. The abundance and intensity of ACE2 expression is slightly elevated in alveoli (p = 0.09; 0.07, respectively) and bronchioles (p = 0.095; 0.37, respectively). However, statistically elevated abundance and intensity of ACE-2 expression was only evident in the heart of cats with HCM (p = 0.032; p = 0.011, respectively). Further investigation did not demonstrate a statistical correlation between the ACE2 expression in the heart in relation to the heart weight to body weight ratio, and the ventricular wall ratio. Current findings suggest an overexpression of ACE2 in HCM cases but follow up study is warranted to understand the pathophysiological process.

Cardiac gene activation varies between young and adult cats and in the presence of hypertrophic cardiomyopathy

Little is known about the difference of myocardial gene transcription in young and adult cats and how transcription is further modified in cats with hypertrophic cardiomyopathy (HCM) and with left atrial (LA) thrombus formation. We hypothesized that selected factors for coagulation, endothelial activation, inflammation, and remodelling are modified with age and are activated in the hearts of cats with HCM. Left atrial and ventricular (LV) samples from 12 cats with HCM (seven without (HCMwoAT] and five with LA thrombi [HCMwAT]), and six young (YC) and six adult (AC) control cats without cardiac disease were investigated for relative expression of the following genes using quantitative polymerase chain reaction: von Willebrand factor, a disintegrin and metalloproteinase with a thrombospondin type 1 motif member 13, platelet activating factor, E- and P-selectin, intercellular and vascular adhesion molecules-1, ß2-integrin, vascular endothelial growth factor, interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), heat shock protein-70, and myocyte-specific enhancer factor 2C. Significant differences in gene activation were found between YC and AC, and YC and cats with HCM. Compared to AC, MCP-1 and IL-6 were significantly higher in cats with HCM. The presence of an LA thrombus was associated with higher IL-6 expression. These results illustrate the relevance of age and/or lifestyle on gene expression in the feline heart. The gene transcription pattern found in AC hearts might predispose cats to their characteristic cardiac remodelling processes and thrombus formation if disease occurs. It further supports the involvement of inflammation, but not coagulation and endothelial activation, in HCM.

Dysfunctional Network and Mutation Genes of Hypertrophic Cardiomyopathy

Background

Hypertrophic cardiomyopathy (HCM) is a group of heterogeneous diseases that affects the myocardium. It is also a common familial disease. The symptoms are not common and easy to find.

Objective

In this paper, we aim to explore and analyze the dysfunctional gene network related to hypertrophic cardiomyopathy, and the key target genes with diagnostic and therapeutic significance for HCM were screened.

Methods

The gene expression profiles of 37 samples (GSE130036) were downloaded from the GEO database. Differential analysis was used to identify the related dysregulated genes in patients with HCM. Enrichment analysis identified the biological function and signaling pathway of these differentially expressed genes. Then, PPI network was built and verified in the GSE36961 dataset. Finally, the gene of single-nucleotide variants (SNVs) in HCM samples was screened by means of maftools.

Results

In this study, 920 differentially expressed genes were obtained, and these genes were mainly related to metabolism-related signaling pathways. 187 interacting genes were identified by PPI network analysis, and the expression trends of C1QB, F13A1, CD163, FCN3, PLA2G2A, and CHRDL2 were verified by another dataset and quantitative real-time polymerase chain reaction. ROC curve analysis showed that they had certain clinical diagnostic ability, and they were the potential key dysfunctional genes of HCM. In addition, we found that PRMT5 mutation was the most frequent in HCM samples, which may affect the pathogenesis of HCM.

Conclusion

Therefore, the key genes and enrichment results identified by our analysis may provide a reference for the occurrence and development mechanism of HCM. In addition, mutations in PRMT5 may be a useful therapeutic and diagnostic target for HCM. Our results also provide an independent quantitative assessment of functional limitations in patients with unknown history.

Feline hypertrophic cardiomyopathy: reduced microvascular density and involvement of CD34+ interstitial cells

The sequence of pathological events in feline hypertrophic cardiomyopathy (fHCM) is still largely unknown, although we know that fHCM is characterized by interstitial remodeling in a macrophage-driven pro-inflammatory environment and that myocardial ischemia might contribute to its progression. This study aimed to gain further insights into the structural changes associated with interstitial remodeling in fHCM with special focus on the myocardial microvasculature and the phenotype of the interstitial cells. Twenty-eight hearts (16 hearts with fHCM and 12 without cardiac disease) were evaluated in the current study, with immunohistochemistry, RNA-in situ hybridization, and transmission electron microscopy. Morphometrical evaluations revealed a statistically significant lower microvascular density in fHCM. This was associated with structural alterations in capillaries that go along with a widening of the interstitium due to the accumulation of edema fluid, collagen fibers, and mononuclear cells that also proliferated locally. The interstitial cells were mainly of fibroblastic or vascular phenotype, with a substantial contribution of predominantly resident macrophages. A large proportion expressed CD34 mRNA, which suggests a progenitor cell potential. Our results indicate that microvascular alterations are key events in the pathogenesis of fHCM and that myocardial interstitial cell populations with CD34+ phenotype play a role in the pathogenesis of the disease.

The Feline Cardiomyopathies: 2. Hypertrophic cardiomyopathy

Practical relevance:

Hypertrophic cardiomyopathy (HCM) is the most common form of feline cardiomyopathy observed clinically and may affect up to approximately 15% of the domestic cat population, primarily as a subclinical disease. Fortunately, severe HCM, leading to heart failure or arterial thromboembolism (ATE), only occurs in a small proportion of these cats.

Patient group:

Domestic cats of any age from 3 months upward, of either sex and of any breed, can be affected. A higher prevalence in male and domestic shorthair cats has been reported.

Diagnostics:

Subclinical feline HCM may or may not produce a heart murmur or gallop sound. Substantial left atrial enlargement can often be identified radiographically in cats with severe HCM. Biomarkers should not be relied on solely to diagnose the disease. While severe feline HCM can usually be diagnosed via echocardiography alone, feline HCM with mild to moderate left ventricular (LV) wall thickening is a diagnosis of exclusion, which means there is no definitive test for HCM in these cats and so other disorders that can cause mild to moderate LV wall thickening (eg, hyperthyroidism, systemic hypertension, acromegaly, dehydration) need to be ruled out.

Key findings:

While a genetic cause of HCM has been identified in two breeds and is suspected in another, for most cats the cause is unknown. Systolic anterior motion of the mitral valve (SAM) is the most common cause of dynamic left ventricular outflow tract obstruction (DLVOTO) and, in turn, the most common cause of a heart murmur with feline HCM. While severe DLVOTO is probably clinically significant and so should be treated, lesser degrees probably are not. Furthermore, since SAM can likely be induced in most cats with HCM, the distinction between HCM without obstruction and HCM with obstruction (HOCM) is of limited importance in cats. Diastolic dysfunction, and its consequences of abnormally increased atrial pressure leading to signs of heart failure, and sluggish atrial blood flow leading to ATE, is the primary abnormality that causes clinical signs and death in affected cats. Treatment (eg, loop diuretics) is aimed at controlling heart failure. Preventive treatment (eg, antithrombotic drugs) is aimed at reducing the risk of complications (eg, ATE).

Conclusions:

Most cats with HCM show no overt clinical signs and live a normal or near-normal life despite this disease. However, a substantial minority of cats develop overt clinical signs referable to heart failure or ATE that require treatment. For most cats with clinical signs caused by HCM, the long-term prognosis is poor to grave despite therapy.

Areas of uncertainty:

Genetic mutations (variants) that cause HCM have been identified in a few breeds, but, despite valiant efforts, the cause of HCM in the vast majority of cats remains unknown. No treatment currently exists that reverses or even slows the cardiomyopathic process in HCM, again despite valiant efforts. The search goes on.

Electrophysiological and Structural Remodeling of the Atria in a Mouse Model of Troponin-I Mutation Linked Hypertrophic Cardiomyopathy: Implications for Atrial Fibrillation

Hypertrophic cardiomyopathy (HCM) is an inherited cardiac disorder affecting one in 500 of the general population. Atrial fibrillation (AF) is the most common arrhythmia in patients with HCM. We sought to characterize the atrial electrophysiological and structural substrate in young and aging Gly203Ser cardiac troponin-I transgenic (HCM) mice. At 30 weeks and 50 weeks of age (n = 6 per strain each group), the left atrium was excised and placed on a multi-electrode array (MEA) for electrophysiological study; subsequent histological analyses and plasma samples were analyzed for biomarkers of extracellular matrix remodeling and cell adhesion and inflammation. Wild-type mice of matched ages were included as controls. Young HCM mice demonstrated significantly shortened atrial action potential duration (APD), increased conduction heterogeneity index (CHI), increased myocyte size, and increased interstitial fibrosis without changes in effective refractory periods (ERP), conduction velocity (CV), inflammatory infiltrates, or circulating markers of extracellular matrix remodeling and inflammation. Aging HCM mice demonstrated aggravated changes in atria electrophysiology and structural remodeling as well as increased circulating matrix metalloproteinases (MMP)-2, MMP-3, and VCAM-1 levels. This model of HCM demonstrates an underlying atrial substrate that progresses with age and may in part be responsible for the greater propensity for AF in HCM.

Myocardial transcription of inflammatory and remodeling markers in cats with hypertrophic cardiomyopathy and systemic diseases associated with an inflammatory phenotype

Feline hypertrophic cardiomyopathy (HCM) is characterized by macrophage-driven myocardial remodeling processes in a pro-inflammatory environment. To further investigate the mechanisms behind these processes, the myocardial transcription of cytokines and remodeling enzymes was comparatively assessed in cats with HCM and cats without cardiac diseases. Sixty-seven cats were included, 17 cats with HCM (including 5 with atrial thrombus; AT), and 50 cats without cardiac diseases. The latter comprised 10 control cats (no cardiac or relevant systemic disease), 34 cats with diseases suspected to be associated with a systemic inflammatory state of which 18 suffered from feline infectious peritonitis (FIP), and 6 cats with multicentric lymphoma. Samples from atria, ventricular free walls and interventricular septum were examined using quantitative reverse transcriptase PCR. The overall highest myocardial marker transcriptions were observed in cats with multicentric lymphoma, FIP and HCM, followed by diseases likely associated with a systemic inflammatory state, and control cats. Inflammatory marker transcription predominated in the myocardium of cats with systemic inflammatory diseases, whereas in HCM the transcription of remodeling enzymes prevailed. Sex significantly influenced the myocardial transcription of several remodeling enzymes. These results suggest a versatile myocardial response depending on the disease and illustrates the relevance of sex for the cardiac response to cardiac and systemic disease in cats. A systemic inflammatory state appears to elicit an inflammatory phenotype in the myocardium, whereas in HCM, the myocardium mediates its own remodeling. In HCM, the identified markers might be involved in the ongoing remodeling processes causing structural and functional changes.

SPARC production by bone marrow-derived cells contributes to myocardial fibrosis in pressure overload

In human heart failure and in murine hearts with left-ventricular pressure overload (LVPO), increases in fibrosis are associated with increases in myocardial stiffness. Secreted protein acidic and rich in cysteine (SPARC) is shown to be necessary for both cardiac fibrosis and increases in myocardial stiffness in response to LVPO; however, cellular sources of cardiac SPARC are incompletely defined. Irradiation and bone marrow transfer were undertaken to test the hypothesis that SPARC expression by bone marrow-derived cells is an important mediator of fibrosis in LVPO. In recipient SPARC-null mice transplanted with donor wild-type (WT) bone marrow and subjected to LVPO, levels of fibrosis similar to that of WT mice were found despite the lack of SPARC expression by resident cells. In recipient WT mice with donor SPARC-null bone marrow, significantly less fibrosis versus that of WT mice was found despite the expression of SPARC by resident cells. Increases in myocardial stiffness followed a similar pattern to that of collagen deposition. Myocardial macrophages were significantly reduced in SPARC-null mice with LVPO versus that of WT mice. Recipient SPARC-null mice transplanted with donor WT bone marrow exhibited an increase in cardiac macrophages versus that of SPARC-null LVPO and donor WT mice with recipient SPARC-null bone marrow. Expression of vascular cellular adhesion molecule (VCAM), a previously identified binding partner of SPARC, was assessed in all groups and with the exception of WT mice, increases in VCAM immunoreactivity with LVPO were observed. However, no differences in VCAM expression between bone marrow transplant groups were noted. In conclusion, SPARC expression by bone marrow-derived cells was critical for fibrotic deposition of collagen and influenced the expansion of myocardial macrophages in response to LVPO.NEW & NOTEWORTHY Myocardial fibrosis and the resultant increases in LV and myocardial stiffness represent pivotal consequences of chronic pressure overload (PO). In this study, a murine model of cardiac fibrosis induced by PO was used to demonstrate a critical function of SPARC in bone marrow-derived cells that drives cardiac fibrosis and increases in cardiac macrophages.

Intrahistiocytic Storage of Clofazimine Crystals in a Cat

A 13-year-old castrated male Maine coon cat with a 5-year history of atypical mycobacteriosis was euthanized and submitted for necropsy. The cat had been kept in clinical remission since diagnosis using a combination of the antimycobacterial drug clofazimine and additional multimodal antimicrobial therapy. Grossly, tissues were diffusely discolored red-brown to yellow. Histologically, the myocardial interstitum was expanded by numerous, often multinucleated cells, which were distended by uniformly shaped acicular cytoplasmic spaces. These cells were immunopositive for CD18 and immunonegative for desmin, suggesting a histiocytic rather than muscular origin. Macrophages in other tissues contained similar acicular spaces. Ultrastructurally, the spaces were surrounded by 2 lipid membranes, resembling an autophagosome. Based on the clinical history and histologic, immunohistochemical, and ultrastructural data, we diagnosed clofazimine crystal storage. To our knowledge, this is the first report of clofazimine storage in a cat or within myocardial interstitial macrophages.

Mycobacterium microti: Not Just a Coincidental Pathogen for Cats

Public interest in animal tuberculosis is mainly focused on prevention and eradication of bovine tuberculosis in cattle and wildlife. In cattle, immunodiagnostic tests such as the tuberculin skin test or the interferon gamma (IFN-γ) assay have been established and are commercially available. Feline tuberculosis is rather unknown, and the available diagnostic tools are limited. However, infections with Mycobacterium tuberculosis complex members need to be considered an aetiological differential diagnosis in cats with granulomatous lymphadenopathy or skin nodules and, due to the zoonotic potential, a time-efficient and accurate diagnostic approach is required. The present study describes 11 independent cases of Mycobacterium microti infection in domestic cats in Switzerland. For three cases, clinical presentation, diagnostic imaging, bacteriological results, immunodiagnostic testing, and pathological features are reported. An adapted feline IFN-γ release assay was successfully applied in two cases and appears to be a promising tool for the ante mortem diagnosis of tuberculosis in cats. Direct contact with M. microti reservoir hosts was suspected to be the origin of infection in all three cases. However, there was no evidence of M. microti infection in 346 trapped wild mice from a presumptive endemic region. Therefore, the source and modalities of infection in cats in Switzerland remain to be further elucidated.

Digoxin-specific antibody fragments for the treatment of suspected Nerium oleander toxicosis in a cat

Case summary

A 6-year-old castrated male domestic shorthair cat presented for lethargy and gastrointestinal signs after possible exposure to Nerium oleander leaves. The cat developed a ventricular arrhythmia that responded positively to the administration of digoxin-specific antibody fragments. Underlying hypertrophic cardiomyopathy was also diagnosed after the development of congestive heart failure. Humane euthanasia was elected owing to a lack of significant response to continued therapy.

Relevance and novel information

To our knowledge, this is the first report to describe the use of digoxin-specific antibody fragments in a cat. Nerium oleander toxicosis is associated with significant morbidity and mortality, and digoxin-specific antibody fragments have been used effectively in humans and animals. The development of cardiac necrosis may have contributed to worsening arrhythmias and highlights the importance of early intervention. The use of digoxin-specific antibody fragments for suspected N oleander toxicosis in a cat resulted in a rapid response and appeared to be well tolerated.

Novel biomarkers in cats with congestive heart failure due to primary cardiomyopathy

The pathogenesis of feline cardiomyopathy and congestive heart failure (CHF) requires further understanding. In this study, we assessed serum proteome change in feline CHF, aiming to identify novel biomarker for both research and clinical use. The study comprised 15 cats in CHF, 5 cats in preclinical cardiomyopathy and 15 cats as healthy controls. Serum proteome profiles were obtained by tandem mass tag labelling followed by mass spectrometry. Protein concentrations in CHF cats were compared with healthy controls. Western blot was performed for proteomic validation. Correlations were assessed between the altered proteins in CHF and clinical variables in cats with cardiomyopathy to evaluate protein-cardiac association. Bioinformatic analysis was employed to identify pathophysiological pathways involved in feline CHF. Sixteen serum proteins were significantly different between CHF and healthy control cats (P < .05). These included serine protease inhibitors, apolipoproteins and other proteins associated with inflammation and coagulation. Clinical parameters from cats with cardiomyopathy significantly correlated with the altered proteins (P < .05). Bioinformatic analysis identified 13 most relevant functional profiles in feline CHF, which mostly associated with extracellular matrix organization and metabolism. Data are available via ProteomeXchange with identifier PXD017761. SIGNIFICANCE: Cardiomyopathies affect both cats and humans, and they can cause serious consequence such as congestive heart failure (CHF). To date, the pathophysiological mechanism of CHF is not fully understood. In this study, for the first time, we used a proteomic approach combined with bioinformatic analysis to evaluate serum protein change in cats with CHF. Results indicate systemic inflammation, coagulation protein changes, innate immunity and extracellular matrix remodeling are involved in feline CHF, which are largely comparable with findings in previous human studies. Our study provides new insights into CHF and cardiomyopathy in cats, and the identified novel biomarkers and pathophysiological pathways provide valuable information for future studies.

Canine Dilated Cardiomyopathy: Diffuse Remodeling, Focal Lesions, and the Involvement of Macrophages and New Vessel Formation

Dilated cardiomyopathy (DCM) is among the most common cardiac diseases in dogs. Its pathogenesis is not fully understood, but myocardial remodeling and inflammation are suspected to be involved. The present study aimed to characterize the pathological processes in canine DCM, investigating morphological changes in association with the expression of relevant cytokines and remodeling markers. The myocardium of 17 dogs with DCM and 6 dogs without cardiac diseases was histologically evaluated, and selected cases were further examined by immunohistochemistry, morphometry, and reverse transcription quantitative PCR. In DCM, the myocardium exhibited subtle but statistically significant diffuse quantitative changes. These comprised increased interstitial collagen deposition and macrophage numbers, as well as an overall reduced proportion of contractile tissue. This was accompanied by a significant increase in myocardial transcription of intracellular adhesion molecule (ICAM) 1, inflammatory cytokines, and remodeling enzymes. Laser microdissection showed that cardiomyocytes transcribed most relevant markers including ICAM-1, tumor necrosis factor α, transforming growth factor β (TGF-β), matrix metalloproteinase 2 (MMP-2), tissue inhibitor of MMP (TIMP) 1 and TIMP-2. In addition, there were multifocal cell-rich lesions characterized by fibrosis, neovascularization, macrophage infiltration, and cardiomyocyte degeneration. In these, macrophages were often found to express ICAM-1, TGF-β, and vascular endothelial growth factor; the former two were also expressed by cardiomyocytes. These results characterize the diffuse myocardial remodeling processes that occur in DCM. The observed multifocal cell-rich lesions might result from reduced tissue perfusion. Macrophages and cardiomyocytes seem to actively contribute to the remodeling processes, which ultimately lead to cardiac dilation and dysfunction. The precise role of the involved cells and the factors initiating the remodeling process still needs to be identified.