PDK4 Deficiency Induces Intrinsic Apoptosis in Response to Starvation in Fibroblasts from Doberman Pinschers with Dilated Cardiomyopathy

Comprehensive analysis of geographic and breed-purpose influences on genetic diversity and inherited disease risk in the Doberman dog breed

BACKGROUND

Publicly available phenotype data and genotyping array data from two citizen science projects: "Doberman Health Surveys" and "The Doberman Diversity Project" were analyzed to explore relative homozygosity, diversity, and disorder risk according to geographical locale and breeding purpose in the Doberman.

RESULTS

From the phenotypic data cohort, life expectancy of a Doberman at birth is 9.1 years. The leading causes of death were heart disease (accounting for 28% of deaths) and cancers (collectively accounting for 14% of deaths). By genotyping, the world Doberman population exists as four major cohorts (European exhibition-bred, Americas exhibition-bred, European work, Americas pet/informal). Considering the entire Doberman population, four genomic regions longer than 500 Kb are fixed in 90% or more of 3,226 dogs included in this study. The four fixed regions reside on two autosomal chromosomes: CFA3:0.8-2.3 Mb (1.55 Mb); CFA3: 57.9-59.8 Mb (1.8 Mb); CFA31:0-1.2 Mb (1.2 Mb); and CFA31:4.80-6.47 Mb (1.67 Mb). Using public variant call files including variants for eight Doberman pinschers, we observed 30 potentially functional alternate variants that were evolutionarily diverged relative to the wider sequenced dog population within the four strongly homozygous chromosomal regions. Effective population size (Ne) is a statistical measure of breed diversity at the time of sampling that approximates the number of unique individuals. The major identified sub-populations of Dobermans demonstrated Ne in the range 70-236. The mean level of inbreeding in the Doberman breed is 40% as calculated by the number of array variants in runs of homozygosity divided by the assayed genome size (excluding the X chromosome). The lowest observed level of inbreeding in the Dobermans assayed was 15% in animals that were first generation mixes of European and USA bred Dobermans. Array variant analysis shows that inter-crossing between European and USA-bred Dobermans has capacity to re-introduce variation at many loci that are strongly homozygous.

CONCLUSIONS

We conclude that efforts to improve breed diversity first should focus on regions with the highest fixation levels, but managers must ensure that mutation loads are not worsened by increasing the frequencies of rarer haplotypes in the identified regions. The analysis of global data identified regions of strong fixation that might impact known disorder risks in the breed. Plausible gene candidates for future analysis of the genetic basis of cardiac disease and cancer were identified in the analysis.

Evaluation of L-Selenomethionine on Ameliorating Cardiac Injury Induced by Environmental Ammonia

L-Selenomethionine is one of the important organic selenium sources. The supplementation of L-selenomethionine in diets is significant to improve the health of pigs. Ammonia is a major pollutant in the atmosphere and piggery, posing a threat to human and animal health. Although ammonia exposure can damage the heart, the mechanism of cardiac toxicity by ammonia is still unknown. In this study, we investigated the mechanism of cardiac injury induced by ammonia exposure in pigs and the protective effect of L-selenomethionine on its cardiotoxicity. The results showed that the blood ammonia content of pig increased significantly in ammonia group, the expressions of energy metabolism-related genes (LDHA, PDK4, HK2, and CPTIB) and the oxidative stress indexes were significantly changed (P < 0.05), the AMPK/PPAR-γ/NF-κB signaling pathways were activated, the chromatin edge aggregation and nuclear pyknosis were observed in ultrastructure, the apoptotic cells were significantly increased (P < 0.05), and the mRNA and protein expressions of apoptosis-related genes (Bcl-2, Bax, Cyt-c, caspase-3, and caspase-9) were significantly affected (P < 0.05). The above changes were significantly alleviated in ammonia + L-selenomethionine group, but there were still significant differences compared with the C group (P < 0.05). Our results indicated that ammonia exposure could cause energy metabolism disorder and oxidative stress and induce apoptosis of cardiomyocytes through AMPK/PPAR-γ/NF-κB pathways, which could lead to cardiac injury and affect cardiac function. L-Selenomethionine could effectively alleviate the cardiac damage caused by ammonia and antagonize the cardiotoxicity of ammonia.

Matrix produced by diseased cardiac fibroblasts affects early myotube formation and function

The extracellular matrix (ECM) provides both physical and chemical cues that dictate cell function and contribute to muscle maintenance. Muscle cells require efficient mitochondria to satisfy their high energy demand, however, the role the ECM plays in moderating mitochondrial function is not clear. We hypothesized that the ECM produced by stromal cells with mitochondrial dysfunction (Barth syndrome, BTHS) provides cues that contribute to metabolic dysfunction independent of muscle cell health. To test this, we harnessed the ECM production capabilities of human pluripotent stem-cell-derived cardiac fibroblasts (hPSC-CFs) from healthy and BTHS patients to fabricate cell-derived matrices (CDMs) with controlled topography, though we found that matrix composition from healthy versus diseased cells influenced myotube formation independent of alignment cues. To further investigate the effects of matrix composition, we then examined the influence of healthy- and BTHS-derived CDMs on myotube formation and metabolic function. We found that BTHS CDMs induced lower fusion index, lower ATP production, lower mitochondrial membrane potential, and higher ROS generation than the healthy CDMs. These findings imply that BTHS-derived ECM alone contributes to myocyte dysfunction in otherwise healthy cells. Finally, to investigate potential mechanisms, we defined the composition of CDMs produced by hPSC-CFs from healthy and BTHS patients using mass spectrometry and identified 15 ECM and related proteins that were differentially expressed in the BTHS-CDM compared to healthy CDM. Our results highlight that ECM composition affects skeletal muscle formation and metabolic efficiency in otherwise healthy cells, and our methods to generate patient-specific CDMs are a useful tool to investigate the influence of the ECM on disease progression and to investigate variability among diseased patients. STATEMENT OF SIGNIFICANCE: Muscle function requires both efficient metabolism to generate force and structured extracellular matrix (ECM) to transmit force, and we sought to examine the interactions between metabolism and ECM when metabolic disease is present. We fabricated patient-specific cell derived matrices (CDMs) with controlled topographic features to replicate the composition of healthy and mitochondrial-diseased (Barth syndrome) ECM. We found that disease-derived ECM negatively affects metabolic function of otherwise healthy myoblasts, and we identified several proteins in disease-derived ECM that may be mediating this dysfunction. We anticipate that our patient-specific CDM system could be fabricated with other topographies and cell types to study cell functions and diseases of interest beyond mitochondrial dysfunction and, eventually, be applied toward personalized medicine.

Genetic Basis of Dilated Cardiomyopathy in Dogs and Its Potential as a Bidirectional Model

Simple Summary

Heart disease is a leading cause of death for both humans and dogs. Inherited heart diseases, including dilated cardiomyopathy (DCM), account for a proportion of these cases. Human and canine patients with DCM suffer from an enlarged heart that can no longer pump efficiently, resulting in heart failure. This causes symptoms or clinical signs like difficulty breathing, irregular heartbeat, and eventually death. The symptoms or clinical signs of this disease vary in age of onset at the beginning of symptoms, sex predisposition, and overall disease progression. Despite the many similarities in DCM in both species, only a few candidate genes so far have been linked to this disease in dogs versus tens of genes identified in human DCM. Additionally, the use of induced pluripotent stem cells, or engineered stem cells, has been widely used in the study of human genetic heart disease but has not yet been fully adapted to study heart disease in dogs. This review describes the current knowledge on the genetics and subtypes of naturally occurring DCM in dogs, and how advances in research might benefit the dog but also the human patient. Additionally, a novel method using canine engineered stem cells to uncover unknown contributions of mistakes in DNA to the progression of DCM will be introduced along with its applications for human DCM disease modeling and treatment.

Abstract

Cardiac disease is a leading cause of death for both humans and dogs. Genetic cardiomyopathies, including dilated cardiomyopathy (DCM), account for a proportion of these cases in both species. Patients may suffer from ventricular enlargement and systolic dysfunction resulting in congestive heart failure and ventricular arrhythmias with high risk for sudden cardiac death. Although canine DCM has similar disease progression and subtypes as in humans, only a few candidate genes have been found to be associated with DCM while the genetic background of human DCM has been more thoroughly studied. Additionally, experimental disease models using induced pluripotent stem cells have been widely adopted in the study of human genetic cardiomyopathy but have not yet been fully adapted for the in-depth study of canine genetic cardiomyopathies. The clinical presentation of DCM is extremely heterogeneous for both species with differences occurring based on sex predisposition, age of onset, and the rate of disease progression. Both genetic predisposition and environmental factors play a role in disease development which are identical in dogs and humans in contrast to other experimental animals. Interestingly, different dog breeds have been shown to develop distinct DCM phenotypes, and this presents a unique opportunity for modeling as there are multiple breed-specific models for DCM with less genetic variance than human DCM. A better understanding of DCM in dogs has the potential for improved selection for breeding and could lead to better overall care and treatment for human and canine DCM patients. At the same time, progress in research made for human DCM can have a positive impact on the care given to dogs affected by DCM. Therefore, this review will analyze the feasibility of canines as a naturally occurring bidirectional disease model for DCM in both species. The histopathology of the myocardium in canine DCM will be evaluated in three different breeds compared to control tissue, and the known genetics that contributes to both canine and human DCM will be summarized. Lastly, the prospect of canine iPSCs as a novel method to uncover the contributions of genetic variants to the pathogenesis of canine DCM will be introduced along with the applications for disease modeling and treatment.

A review of the underlying genetics and emerging therapies for canine cardiomyopathies

Cardiomyopathies such as dilated cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy are common in large breed dogs and carry an overall poor prognosis. Research shows that these diseases have strong breed predilections, and selective breeding has historically been recommended to reduce the disease prevalence in affected breeds. Treatment of these diseases is typically palliative and aimed at slowing disease progression and managing clinical signs of heart failure as they develop. The discovery of specific genetic mutations underlying cardiomyopathies, such as the striatin mutation in Boxer arrhythmogenic right ventricular cardiomyopathy and the pyruvate dehydrogenase kinase 4 and titin mutations in Doberman Pinschers, has strengthened our ability to screen and selectively breed individuals in an attempt to produce unaffected offspring. The discovery of these disease-linked mutations has also opened avenues for the development of gene therapies, including gene transfer and genome-editing approaches. This review article discusses the known genetics of cardiomyopathies in dogs, reviews existing gene therapy strategies and the status of their development in canines, and discusses ongoing challenges in the clinical translation of these technologies for treating heart disease. While challenges remain in using these emerging technologies, the exponential growth of the gene therapy field holds great promise for future clinical applications.

Dexmedetomidine Reverses Postoperative Spatial Memory Deficit by Targeting Surf1 and Cytochrome c

Anesthesia and surgery are associated with perioperative neurocognitive disorders (PND). Dexmedetomidine is known to improve PND in rats; however, little is known about the mechanisms. Male Sprague-Dawley rats were subjected to resection of the hepatic apex under propofol anesthesia to clinically mimic human abdominal surgery. The rats were divided into four groups: control group (C), anesthesia group (A), model group (M), and model + dex group (D). Cognitive function was evaluated with the Morris water maze (MWM). Neuronal morphology was observed with H&E staining, Nissl's staining and immunohistochemistry. Transcriptome analysis and quantitative real-time PCR were performed to investigate functional mitochondrial mRNA changes in the hippocampus. Protein levels were measured by Western blotting at 1, 3, and 7 days after surgery. Surgery-induced cognitive decline lasted for three days, but not seven days after surgery in the M group; however, rats in the D group were significantly improved by dexmedetomidine. No significant differences in the number of neurons were observed between the groups after surgery. Rats from the M group showed significantly greater expression levels of Iba-1 and GFAP compared with the C group and the D group. Rats in the M group demonstrated increased Surf1 and Cytochrome c expression on days 1 and 3, but not day 7; similar changes were not induced in rats in the D group. Dexmedetomidine appears to reverse surgery-induced behavior, mitigate the higher density of Iba-1 and GFAP, and downregulate the expression of Surf1 and Cytochrome c protein in the hippocampus of rats in a PND model.

Functional Consequences of PDK4 Deficiency in Doberman Pinscher Fibroblasts

A splice site mutation in the canine pyruvate dehydrogenase kinase 4 (PDK4) gene has been shown to be associated with the development of dilated cardiomyopathy (DCM) in Doberman Pinchers (DPs). Subsequent studies have successfully demonstrated the use of dermal fibroblasts isolated from DPs as models for PDK4 deficiency and have shown activation of the intrinsic (mitochondrial mediated) apoptosis pathway in these cells under starvation conditions. For this study, we sought to further explore the functional consequences of PDK4 deficiency in DP fibroblasts representing PDK4^wt/wt, PDK4^wt/del, and PDK4^del/del genotypes. Our results show that starvation conditions cause increased perinuclear localization of mitochondria and decreased cell proliferation, altered expression levels of pyruvate dehydrogenase phosphatase (PDP) and pyruvate dehydrogenase (PDH), dramatically increased PDH activity, and an impaired response to mitochondrial stress in affected cells. In sum, these results show the broad impact of PDK4 deficiency and reveal mechanistic pathways used by these cells in an attempt to compensate for the condition. Our data help to elucidate the mechanisms at play in this extremely prevalent DP disorder and provide further support demonstrating the general importance of metabolic flexibility in cell health.

Increased mtDNA Abundance and Improved Function in Human Barth Syndrome Patient Fibroblasts Following AAV-TAZ Gene Delivery

Barth syndrome (BTHS) is a rare, X-linked, mitochondrial disorder caused by mutations in the gene encoding tafazzin. BTHS results in cardiomyopathy, muscle fatigue, and neutropenia in patients. Tafazzin is responsible for remodeling cardiolipin, a key structural lipid of the inner mitochondrial membrane. As symptoms can vary in severity amongst BTHS patients, we sought to compare mtDNA copy numbers, mitochondrial fragmentation, and functional parameters between primary dermal BTHS fibroblasts isolated from patients with two different mutations in the TAZ locus. To confirm cause‒effect relationships and further support the development of gene therapy for BTHS, we also characterized the BTHS cells following adeno-associated virus (AAV)-TAZ transduction. Our data show that, in response to AAV-TAZ transduction, these remarkably dynamic organelles show recovery of mtDNA copy numbers, mitochondrial structure, and mitochondrial function, providing additional evidence to support the therapeutic potential of AAV-mediated gene delivery for BTHS. This study also demonstrates the direct relationship between healthy mitochondrial membrane structure and maintenance of proper levels of mtDNA copy numbers.

Inherited cardiomyopathies in veterinary medicine

Comparative and translation medicine is of particular value within the field of inherited cardiomyopathies. Despite massive advances in understanding the functional role of mutations in human cardiomyopathies, these advances have frequently failed to translate into medical discoveries that alter patient care. One potential explanation for this failure lies in the lack of suitable translational models that adequately recapitulate human cardiovascular physiology and disease expression. The vast genetic heterogeneity that complicates human cardiomyopathy research is potentially alleviated through the study of naturally occurring large animal models of disease, where incredibly homogenous populations, like those seen in a single breed of dog or cat, may exist (Kol et al., Sci Transl Med 7:308-321, 2015; Ueda and Stern, Yale J Biol Med 90:433-448, 2017). Veterinary medicine is in a unique position to provide research resources and information that may be readily applied to human disease (Kol et al., Sci Transl Med 7:308-321, 2015). Many inherited cardiomyopathies of humans are phenotypically and genotypically similar in veterinary species and ongoing research holds promise for aiding veterinary and human patients alike (Basso et al., Circulation 109:1180-1185, 2004; Fox et al., Cardiovasc Pathol 23:28-34, 2014; Fox et al., Circulation 102:1863-1870, 2000; Kittleson et al., J Vet Cardiol 17 Suppl 1:S53-73, 2015; Ueda and Stern, Yale J Biol Med 90:433-448, 2017). This article presents the current knowledge of inherited cardiomyopathies in dogs, cats, and non-human primates, with a goal of identifying areas of translational research and future directions.