Biomarker Validation for Aging: Lessons from mtDNA Heteroplasmy Analyses in Early Cancer Detection

Mitochondrial DNA, nuclear context, and the risk for carcinogenesis

The inheritance of mitochondrial DNA (mtDNA) from mother to child is complicated by differences in the stability of the mitochondrial genome. Although the germ line mtDNA is protected through the minimization of replication between generations, sequence variation can occur either through mutation or due to changes in the ratio between distinct genomes that are present in the mother (known as heteroplasmy). Thus, the unpredictability in transgenerational inheritance of mtDNA may cause the emergence of pathogenic mitochondrial and cellular phenotypes in offspring. Studies of the role of mitochondrial metabolism in cancer have a long and rich history, but recent evidence strongly suggests that changes in mitochondrial genotype and phenotype play a significant role in the initiation, progression and treatment of cancer. At the intersection of these two fields lies the potential for emerging mtDNA mutations to drive carcinogenesis in the offspring. In this review, we suggest that this facet of transgenerational carcinogenesis remains underexplored and is a potentially important contributor to cancer. Environ. Mol. Mutagen. 60:455-462, 2019. © 2018 Wiley Periodicals, Inc.

Ageing gender-specific "Biomarkers of Homeostasis", to protect ourselves against the diseases of the old age

Low-grade inflammatory state causes the development of the principal chronic-degenerative pathologies related with ageing. Consequently, it is required a better comprehension of the physiologic origins and the consequences of the low-grade inflammatory state for the identification of 1) the basic mechanisms that lead to the chronic inflammatory state and, after that, to the progression toward the pathologies and 2) the parallel identification of the prognostic biomarkers typical of these passages. These biomarkers could bring to several improvements in the health quality, allowing an early diagnosis and more effective treatments for: a) the prevention strategies on the healthy population, to assure a healthy longevity and b) the identification of personalized treatment in patients, to assure the benefit of the therapy. For the identification of these biomarkers it is necessary to consider that the ageing processes produce alterations of the physiologic systems and that these modifications compromise the communications between these networks: this state constitutes an obstacle for an appropriate physiologic homeostasis, that plays a fundamental role for the safeguard of the health. It is also to be considered that immune senescence affects both men and women, but it does it in different ways: a sexual dimorphism of immune pathways in the setting of immune response homeostasis is normally present, as we previously underlined. Therefore we hypothesize that, in order to prevent the development of the chronic-degenerative pathologies related with ageing, it is important to identify "Biomarkers of Homeostasis " specific for each gender: these are biologic molecules that should be measurable in a practical and no-invasive way and whose variations can quantify the male and female risk of losing the physiologic system homeostatic capacity. This competence is not only critical in the control of inflammation, but it is also prognostic for the passages from low-grade inflammatory state to the chronic inflammation and to the progression toward the degenerative pathologies. Beginning from the actual results, our intent is 1) to discuss and underline the importance of these new research perspectives in the definition of ageing gender-specific clinical "Biomarkers of Homeostasis" and 2) to propose homeostasis biomarkers, already present in the research results.

Primer effect in the detection of mtDNA heteroplasmy: insights from horse Cytochrome b gene

Heteroplasmy, the presence of bi-allelic mtDNA types within an individual, has been previously detected in the D-loop region and Cytochrome b gene (Cytb) of mitochondrial DNA using PCR-RFLP. However, heteroplasmy was absent in thousands of equine mtDNA sequences deposited in GenBank. To address whether heteroplasmy widely exists in mitochondria of Chinese indigenous horses, we generated the data set of the target sites in Cytb region with Sanger sequencing and PCR-RFLP method as well. In this study, 23 heteroplasmic individuals were detected in 430 Chinese local horses. Both site and length heteroplasmy were identified in horse Cytb, especially in Xinihe and Ujumqin breeds. Our data provide evidence that the forward and reverse primers seem to produce a similar approximation to the proportion of mutation base call. However, locations of primers affected the proper detection of mtDNA heteroplasmy. The data obtained in this study highlight the importance of the primers in the accurate detection of heteroplasmy.

The discovery of how gender influences age immunological mechanisms in health and disease, and the identification of ageing gender-specific biomarkers, could lead to specifically tailored treatment and ultimately improve therapeutic success rates

The control of human health and diseases in the elderly population is becoming a challenge, since mean age and life expectation are progressively increasing as well as chronic degenerative diseases. These disorders are of complex diagnosis and they are difficult to be treated, but it is hoped that the predictive medicine will lead to more specific and effective treatment by using specific markers to identify persons with high risk of developing disease, before the clinical manifestation. Peripheral blood targets and biomarkers are currently the most practical, non-invasive means of disease diagnosing, predicting prognosis and therapeutic response. Human longevity is directly correlated with the optimal functioning of the immune system. Recent findings indicate that the sexual dimorphism of T helper (Th) cytokine pathways and the regulation of Th cell network homeostasis are normally present in the immune response and undergoes to adverse changes with ageing. Furthermore, immune senescence affects both men and women, but it does not affect them equally. Therefore, we hypothesize that the comprehension of the interferences between these gender specific pathways, the ageing immunological mechanism in pathological or healthy state and the current therapies, could lead to specifically tailored treatment and eventually improve the therapeutic success rates. Reaching this aim requires the identification of ageing gender-specific biomarkers that could easily reveal the above mentioned correlations.

Nail DNA and possible biomarkers: a pilot study

OBJECTIVES

Nail has been a substitute DNA source for genotyping. To investigate the integrity and consistency of nail DNA amplification for biomarker study, nail clippings from 12 subjects were collected at monthly intervals. The possibility of longer amplification and existence of GAPDH RNA/protein, were also investigated with three nail samples.

METHODS

Three primer sets were designed for quantitative amplification of nuclear and mitochondrial genes and analysis of their consistency. The mean threshold cycles in amplification of the target genes were compared to test the consistency of polymerase chain reaction (PCR) performance among individual factors including age groups, sex, family, the nail source, and by the size of the amplification segments.

RESULTS

The amplification of the target genes from nail DNA showed similar integrity and consistency between the nail sources, and among the serial collections. However, nail DNA from those in their forties showed earlier threshold cycles in amplification than those in their teens or seventies. Mitochondrial DNA (mtDNA) showed better DNA integrity and consistency in amplification of all three targets than did nuclear DNA (nucDNA). Over 9 kb of mtDNA was successfully amplified, and nested quantitative PCR showed reliable copy numbers (%) between the two loci. Reverse transcription PCR for mRNA and immunoblotting for GAPDH protein successfully reflected their corresponding amounts. Regarding the existence of RNA and protein in nails, more effective extraction and detection methods need to be set up to validate the feasibility in biomarker study.

CONCLUSIONS

Nail DNA might be a feasible intra-individual monitoring biomarker. Considering integrity and consistency in target amplification, mtDNA would be a better target for biomarker research than nucDNA.

Potential pitfalls in MitoChip detected tumor-specific somatic mutations: a call for caution when interpreting patient data

BACKGROUND

Several investigators have employed high throughput mitochondrial sequencing array (MitoChip) in clinical studies to search mtDNA for markers linked to cancers. In consequence, a host of somatic mtDNA mutations have been identified as linked to different types of cancers. However, closer examination of these data show that there are a number of potential pitfalls in the detection tumor-specific somatic mutations in clinical case studies, thus urging caution in the interpretation of mtDNA data to the patients. This study examined mitochondrial sequence variants demonstrated in cancer patients, and assessed the reliability of using detected patterns of polymorphisms in the early diagnosis of cancer.

METHODS

Published entire mitochondrial genomes from head and neck, adenoid cystic carcinoma, sessile serrated adenoma, and lung primary tumor from clinical patients were examined in a phylogenetic context and compared with known, naturally occurring mutations which characterize different populations.

RESULTS

The phylogenetic linkage analysis of whole arrays of mtDNA mutations from patient cancerous and non-cancerous tissue confirmed that artificial recombination events occurred in studies of head and neck, adenoid cystic carcinoma, sessile serrated adenoma, and lung primary tumor. Our phylogenetic analysis of these tumor and control leukocyte mtDNA haplotype sequences shows clear cut evidence of mixed ancestries found in single individuals.

CONCLUSIONS

Our study makes two prescriptions: both in the clinical situation and in research 1. more care should be taken in maintaining sample identity and 2. analysis should always be undertaken with respect to all the data available and within an evolutionary framework to eliminate artifacts and mix-ups.