Mitochondrial haplogroups associated with end-stage heart failure and coronary allograft vasculopathy in heart transplant patients

Revisiting Biomarkers of Cardiac Allograft Vasculopathy: Addressing the Achilles Heel of Heart Transplantation

Nearly half of heart transplant recipients will be diagnosed with cardiac allograft vasculopathy (CAV) within five years after transplantation. Advanced CAV can lead to worsening heart failure as well as arrhythmias and sudden cardiac death. The only curative therapy for end-stage CAV is re-transplantation. Current diagnostic methods are invasive and limited by poor sensitivity in early disease. Despite its high prevalence in the post-transplantpopulation, the underlying pathophysiology of this condition has yet to be fully described. It is thought to be primarily related to endothelial dysfunction, immune activation, and cardiometabolic disease. Biomarkers reflecting these underlying processes, particularly endothelial injury and immune activation, have shown early promise in discriminating prevalent CAV. Next-generation sequencing technologies such as proteomic and transcriptomic profiling have also provided further insight into the pathophysiology of CAV through the identification of novel biomarkers. Ultimately, these biomarkers may have a role in not only diagnosing CAV but also highlighting potential targets for disease-specific therapies. In this article, we review the current data for biomarkers in CAV and discuss future directions for biomarker identification..

Inefficient Batteries in Heart Failure: Metabolic Bottlenecks Disrupting the Mitochondrial Ecosystem

Mitochondrial abnormalities have long been described in the setting of cardiomyopathies and heart failure (HF), yet the mechanisms of mitochondrial dysfunction in cardiac pathophysiology remain poorly understood. Many studies have described HF as an energy-deprived state characterized by a decline in adenosine triphosphate production, largely driven by impaired oxidative phosphorylation. However, impairments in oxidative phosphorylation extend beyond a simple decline in adenosine triphosphate production and, in fact, reflect pervasive metabolic aberrations that cannot be fully appreciated from the isolated, often siloed, interrogation of individual aspects of mitochondrial function. With the application of broader and deeper examinations into mitochondrial and metabolic systems, recent data suggest that HF with preserved ejection fraction is likely metabolically disparate from HF with reduced ejection fraction. In our review, we introduce the concept of the mitochondrial ecosystem, comprising intricate systems of metabolic pathways and dynamic changes in mitochondrial networks and subcellular locations. The mitochondrial ecosystem exists in a delicate balance, and perturbations in one component often have a ripple effect, influencing both upstream and downstream cellular pathways with effects enhanced by mitochondrial genetic variation. Expanding and deepening our vantage of the mitochondrial ecosystem in HF is critical to identifying consistent metabolic perturbations to develop therapeutics aimed at preventing and improving outcomes in HF.

Surfing the Big Data Wave: Omics Data Challenges in Transplantation

In both research and care, patients, caregivers, and researchers are facing a leap forward in the quantity of data that are available for analysis and interpretation, marking the daunting "big data era." In the biomedical field, this quantitative shift refers mostly to the -omics that permit measuring and analyzing biological features of the same type as a whole. Omics studies have greatly impacted transplantation research and highlighted their potential to better understand transplant outcomes. Some studies have emphasized the contribution of omics in developing personalized therapies to avoid graft loss. However, integrating omics data remains challenging in terms of analytical processes. These data come from multiple sources. Consequently, they may contain biases and systematic errors that can be mistaken for relevant biological information. Normalization methods and batch effects have been developed to tackle issues related to data quality and homogeneity. In addition, imputation methods handle data missingness. Importantly, the transplantation field represents a unique analytical context as the biological statistical unit is the donor-recipient pair, which brings additional complexity to the omics analyses. Strategies such as combined risk scores between 2 genomes taking into account genetic ancestry are emerging to better understand graft mechanisms and refine biological interpretations. The future omics will be based on integrative biology, considering the analysis of the system as a whole and no longer the study of a single characteristic. In this review, we summarize omics studies advances in transplantation and address the most challenging analytical issues regarding these approaches.

Association between mitochondrial DNA haplogroup variation and coronary artery disease

BACKGROUND AND AIMS

Mitochondrial DNA (mtDNA) haplogroups have been associated with the development of coronary artery disease (CAD) in European populations. However, the specific mtDNA haplogroups associated with CAD have not been investigated in Chinese populations.

METHODS AND RESULTS

Here, we carried out a case-control study including 1036 and 481 CAD patients and 973 and 511 geographically matched asymptomatic control subjects in southern and northern China, respectively. After adjusting for age and gender, our results indicated that mtDNA haplogroups are not associated with the occurrence of CAD and its subcategories, acute coronary syndromes and stable coronary heart disease, in both southern and northern Chinese populations. By focusing on the southern Chinese population, we further revealed that mtDNA haplogroups are not associated with CAD severity. Type 2 diabetes (T2D) and hypertension are two key driving factors for the development of CAD, nonetheless, we found that the frequencies of the 12 studied mtDNA haplogroups did not differ between patients with and without T2D or hypertension.

CONCLUSION

mtDNA haplogroups are not associated with the occurrence of CAD or its subcategories in Chinese populations. Other factors such as environment and nuclear genetic background may contribute to the occurrence of CAD.

Mitochondrial DNA Haplogroups and Frailty in Adults Living with HIV

Mitochondrial DNA (mtDNA) haplogroup has been associated with disease risk and longevity. Among persons with HIV (PWH), mtDNA haplogroup has been associated with AIDS progression, neuropathy, cognitive impairment, and gait speed decline. We sought to determine whether haplogroup is associated with frailty and its components among older PWH. A cross-sectional analysis was performed of AIDS Clinical Trials Group A5322 (HAILO) participants with available genome-wide genotype and frailty assessments. Multivariable logistic regression models adjusted for age, gender, education, smoking, hepatitis C, and prior use of didanosine/stavudine. Among 634 participants, 81% were male, 49% non-Hispanic white, 31% non-Hispanic black, and 20% Hispanic. Mean age was 51.0 (standard deviation 7.5) years and median nadir CD4 count was 212 (interquartile range 72, 324) cells/μL; 6% were frail, 7% had slow gait, and 21% weak grip. H haplogroup participants were more likely to be frail/prefrail (p = .064), have slow gait (p = .09), or weak grip (p = .017) compared with non-H haplogroup participants (not all comparisons reached statistical significance). In adjusted analyses, PWH with haplogroup H had a greater odds of being frail versus nonfrail [odds ratio (OR) 4.0 (95% confidence interval 1.0-15.4)] and having weak grip [OR 2.1 (1.1, 4.1)], but not slow gait [OR 1.6 (0.5, 5.0)] compared with non-H haplogroup. Among black and Hispanic participants, haplogroup was not significantly associated with frailty, grip, or gait. Among antiretroviral therapy (ART)-treated PWH, mtDNA haplogroup H was independently associated with weak grip and frailty. This association could represent a mechanism of weakness and frailty in the setting of HIV and ART.

Environmental factors modulated ancient mitochondrial DNA variability and the prevalence of rheumatic diseases in the Basque Country

Among the factors that would explain the distribution of mitochondrial lineages in Europe, climate and diseases may have played an important role. A possible explanation lies in the nature of the mitochondrion, in which the energy generation process produces reactive oxygen species that may influence the development of different diseases. The present study is focused on the medieval necropolis of San Miguel de Ereñozar (13^th-16^th centuries, Basque Country), whose inhabitants presented a high prevalence of rheumatic diseases and lived during the Little Ice Age (LIA). Our results indicate a close relationship between rheumatic diseases and mitochondrial haplogroup H, and specifically between spondyloarthropathies and sub-haplogroup H2. One possible explanation may be the climate change that took place in the LIA that favoured those haplogroups that were more energy-efficient, such as haplogroup H, to endure lower temperatures and food shortage. However, it had a biological trade-off: the increased risk of developing rheumatic diseases.

Mitochondrial DNA variation in sudden cardiac death: a population-based study

Cardiomyopathy and cardiac conduction defects are common manifestations of mitochondrial disease. Previous studies suggest that clinically asymptomatic individuals harbouring pathogenic mitochondrial DNA (mtDNA) mutations in the cardiac muscle may have sudden cardiac death (SCD) as the first manifestation of mitochondrial disease. We investigated the contribution of pathogenic mtDNA point mutations and mtDNA haplogroups in cardiac muscle in a cohort of 280 Finnish subjects that had died from non-ischaemic SCD with the median age of death at 59 years and in 537 population controls. We did not find any common or novel pathogenic mutations, but the frequency of haplogroup H1 was higher in the SCD subjects than that in 537 population controls (odds ratio: 1.76, confidence interval 95%: 1.02-3.04). We conclude that, at the population level, pathogenic point mutations in mtDNA do not contribute to non-ischaemic SCD, but natural variation may modify the risk.

Mitochondrial genetic haplogroups and cardiovascular diseases: Data from the Osteoarthritis Initiative

Background

Some case-control studies reported that mitochondrial haplogroups could be associated with the onset of cardiovascular diseases (CVD), but the literature regarding this topic is limited. We aimed to investigate whether any mitochondrial haplogroup carried a higher or lower risk of CVD in a large cohort of North American people affected by knee osteoarthritis or at high risk for this condition.

Materials and methods

A longitudinal cohort study including individuals from the Osteoarthritis Initiative was done. Haplogroups were assigned through a combination of sequencing and PCR-RFLP techniques. All the mitochondrial haplogroups have been named following this nomenclature: HV, JT, UK, IWX, and superHV/others. The strength of the association between mitochondrial haplogroups and incident CVD was evaluated through a Cox’s regression analysis, adjusted for potential confounders, and reported as hazard ratios (HRs) with their 95% confidence intervals (CIs).

Results

Overall, 3,288 Caucasian participants (56.8% women) with a mean age of 61.3±9.2 years without CVD at baseline were included. During a median follow-up of 8 years, 322 individuals (= 9.8% of baseline population) developed a CVD. After adjusting for 11 potential confounders at baseline and taking those with the HV haplotype as reference (the most frequent), those with JT carried a significant lower risk of CVD (HR = 0.75; 95%CI: 0.54–0.96; p = 0.03). Participants with the J haplogroup had the lowest risk of CVD (HR = 0.71; 95%CI: 0.46–0.95; p = 0.02).

Conclusions

The presence of JT haplogroups (particularly J) may be associated with a reduced risk of CVD. However, this result was not based on a high level of statistical significance. Thus, future research with larger sample size is needed to assess whether our results can be corroborated.

Mitochondrial DNA haplogroups influence the risk of aortic stenosis

AIM

The underlying pathophysiologic mechanisms of aortic stenosis are not clear. Mitochondrial dysfunction plays a role in many pathological conditions including cardiac diseases. We aimed to analyze the mitochondrial DNA haplogroups in a group of patients undergoing valve replacement surgery due to severe aortic stenosis.

METHODS

Mitochondrial DNA haplogroups were assessed in 176 patients with severe aortic stenosis and 308 control subjects. Cardiovascular risk factors and demographics were similar in both groups.

RESULTS

Patients carrying haplogroup Uk had a lower risk of developing aortic stenosis, especially compared to patients carrying haplogroup H (odds ratio = 0.507; 95% confidence interval: 0.270-0.952, p = 0.035).

CONCLUSIONS

Mitochondrial DNA haplogroups could be involved in the development of severe aortic stenosis. Specifically, haplogroup H could be a risk factor and Uk a protective factor for severe aortic stenosis in a population from Spain.

Applying genomics in heart transplantation

While advances in patient care and immunosuppressive pharmacotherapies have increased the lifespan of heart allograft recipients, there are still significant comorbidities post-transplantation and 5-year survival rates are still significant, at approximately 70%. The last decade has seen massive strides in genomics and other omics fields, including transcriptomics, with many of these advances now starting to impact heart transplant clinical care. This review summarizes a number of the key advances in genomics which are relevant for heart transplant outcomes, and we highlight the translational potential that such knowledge may bring to patient care within the next decade.

Generating Rho-0 Cells Using Mesenchymal Stem Cell Lines

Introduction

The generation of Rho-0 cells requires the use of an immortalization process, or tumor cell selection, followed by culture in the presence of ethidium bromide (EtBr), incurring the drawbacks its use entails. The purpose of this work was to generate Rho-0 cells using human mesenchymal stem cells (hMSCs) with reagents having the ability to remove mitochondrial DNA (mtDNA) more safely than by using EtBr.

Methodology

Two immortalized hMSC lines (3a6 and KP) were used; 143B.TK-Rho-0 cells were used as reference control. For generation of Rho-0 hMSCs, cells were cultured in medium supplemented with each tested reagent. Total DNA was isolated and mtDNA content was measured by real-time polymerase chain reaction (PCR). Phenotypic characterization and gene expression assays were performed to determine whether 3a6 Rho-0 hMSCs maintain the same stem properties as untreated 3a6 hMSCs. To evaluate whether 3a6 Rho-0 hMSCs had a phenotype similar to that of 143B.TK-Rho-0 cells, in terms of reactive oxygen species (ROS) production, apoptotic levels and mitochondrial membrane potential (Δψm) were measured by flow cytometry and mitochondrial respiration was evaluated using a SeaHorse XFp Extracellular Flux Analyzer. The differentiation capacity of 3a6 and 3a6 Rho-0 hMSCs was evaluated using real-time PCR, comparing the relative expression of genes involved in osteogenesis, adipogenesis and chondrogenesis.

Results

The results showed the capacity of the 3a6 cell line to deplete its mtDNA and to survive in culture with uridine. Of all tested drugs, Stavudine (dt4) was the most effective in producing 3a6-Rho cells. The data indicate that hMSC Rho-0 cells continue to express the characteristic MSC cell surface receptor pattern. Phenotypic characterization showed that 3a6 Rho-0 cells resembled 143B.TK-Rho-0 cells, indicating that hMSC Rho-0 cells are Rho-0 cells. While the adipogenic capability was higher in 3a6 Rho-0 cells than in 3a6 cells, the osteogenic and chondrogenic capacities were lower.

Conclusion

Among the drugs and conditions tested, the use of d4t was the best option for producing Rho-0 cells from hMSCs. Rho-0 cells are useful for studying the role of mitochondria in hMSC differentiation.

Functional Characterization of Three Concomitant MtDNA LHON Mutations Shows No Synergistic Effect on Mitochondrial Activity

The presence of more than one non-severe pathogenic mutation in the same mitochondrial DNA (mtDNA) molecule is very rare. Moreover, it is unclear whether their co-occurrence results in an additive impact on mitochondrial function relative to single mutation effects. Here we describe the first example of a mtDNA molecule harboring three Leber's hereditary optic neuropathy (LHON)-associated mutations (m.11778G>A, m.14484T>C, m.11253T>C) and the analysis of its genetic, biochemical and molecular characterization in transmitochondrial cells (cybrids). Extensive characterization of cybrid cell lines harboring either the 3 mutations or the single classic m.11778G>A and m.14484T>C mutations revealed no differences in mitochondrial function, demonstrating the absence of a synergistic effect in this model system. These molecular results are in agreement with the ophthalmological characteristics found in the triple mutant patient, which were similar to those carrying single mtDNA LHON mutations.

Genetics in dilated cardiomyopathy

Discoveries made during the last 20 years have revealed a genetic origin in many cases of dilated cardiomyopathy (DCM). Currently, over 40 genes have been associated with the disease. Mutations in DCM-causing genes induce the condition through a variety of different pathological pathways with complex and not completely understood mechanisms. Genes that encode for sarcomeric, cytoskeletal, nuclear membrane, dystrophin-associated glycoprotein complex and desmosomal proteins are the principal genes involved. In this review we discuss the most frequent DCM-causing genes. We propose a classification in which DCM genes are considered as being major or minor genes according to their mutation frequency and the available supporting evidence. The main phenotypic characteristics associated with each gene are discussed.

Mitochondrial haplogroups H and J: risk and protective factors for ischemic cardiomyopathy

Background

Since mitochondria are the principal source of reactive oxygen species (ROS), these organelles may play an important role in ischemic cardiomyopathy (IC) development. The mitochondrial genome may influence this disease. The aim of the present study was to test the relationship between IC development and the impact of single nucleotide polymorphisms (SNPs) in mitochondrial DNA (mtDNA) defining the mitochondrial haplogroups in a population study.

Methodology and principal findings

Ten major European haplogroups were identified by using the single base extension technique and by polymerase chain reaction-restriction fragment length polymorphism. Frequencies and Odds Ratios for the association between IC patients (n = 358) and healthy controls (n = 423) were calculated. No convincing associations between classical risk factors for ischemic cardiomyopathy development and haplogroups were found. However, compared to healthy controls, the prevalence of haplogroup H was significantly higher in IC patients (40.0% vs 50.0%, p-value  = 0.039) while the frequency of haplogroup J was significantly lower (11.1% vs 5.6%, p-value  = 0.048). The analysis of the SNPs characterizing the European mtDNA haplogroups showed that the m.7028C allele (40.0% vs 50.0%, p-value  = 0.005) and m.14766C allele (43.0% vs 54.2%, p-value  = 0.002) were overrepresented in IC patients, meanwhile the m.10398G allele (19.8% vs 13.1%, p-value  = 0.015) and m.4216C allele (22.2% vs 16.5%, p-value  = 0.044) were found as protective factors against IC.

Conclusions and significance

Our results showed that the haplogroups H and J were found as a risk and protective factors for ischemic cardiomyopathy development, respectively.