Elevated Mutation Load Research Articles

Male reproductive ageing: a radical road to ruin.

In modern post-transition societies, we are reproducing later and living longer. While the impact of age on female reproductive function has been well studied, much less is known about the intersection of age and male reproduction. Our current understanding is that advancing age brings forth a progressive decline in male fertility accompanied by a reduction in circulating testosterone levels and the appearance of age-dependent reproductive pathologies including benign prostatic hypertrophy and erectile dysfunction. Paternal ageing is also associated with a profound increase in sperm DNA damage, the appearance of multiple epigenetic changes in the germ line and an elevated mutational load in the offspring. The net result of such changes is an increase in the disease burden carried by the progeny of ageing males, including dominant genetic diseases such as Apert syndrome and achondroplasia, as well as neuropsychiatric conditions including autism and spontaneous schizophrenia. The genetic basis of these age-related effects appears to involve two fundamental mechanisms. The first is a positive selection mechanism whereby stem cells containing mutations in a mitogen-activated protein kinase pathway gain a selective advantage over their non-mutant counterparts and exhibit significant clonal expansion with the passage of time. The second is dependent on an age-dependent increase in oxidative stress which impairs the steroidogenic capacity of the Leydig cells, disrupts the ability of Sertoli cells to support the normal differentiation of germ cells, and disrupts the functional and genetic integrity of spermatozoa. Given the central importance of oxidative stress in defining the impact of chronological age on male reproduction, there may be a role for antioxidants in the clinical management of this process. While animal studies are supportive of this strategy, carefully designed clinical trials are now needed if we are to realize the therapeutic potential of this approach in a clinical context.

BNIP3-dependent mitophagy safeguards ESC genomic integrity via preventing oxidative stress-induced DNA damage and protecting homologous recombination

Embryonic stem cells (ESCs) have a significantly lower mutation load compared to somatic cells, but the mechanisms that guard genomic integrity in ESCs remain largely unknown. Here we show that BNIP3-dependent mitophagy protects genomic integrity in mouse ESCs. Deletion of Bnip3 increases cellular reactive oxygen species (ROS) and decreases ATP generation. Increased ROS in Bnip3−/− ESCs compromised self-renewal and were partially rescued by either NAC treatment or p53 depletion. The decreased cellular ATP in Bnip3−/− ESCs induced AMPK activation and deteriorated homologous recombination, leading to elevated mutation load during long-term propagation. Whereas activation of AMPK in X-ray-treated Bnip3+/+ ESCs dramatically ascended mutation rates, inactivation of AMPK in Bnip3−/− ESCs under X-ray stress remarkably decreased the mutation load. In addition, enhancement of BNIP3-dependent mitophagy during reprogramming markedly decreased mutation accumulation in established iPSCs. In conclusion, we demonstrated a novel pathway in which BNIP3-dependent mitophagy safeguards ESC genomic stability, and that could potentially be targeted to improve pluripotent stem cell genomic integrity for regenerative medicine.

Precision Medicine in Head and Neck Cancers: Genomic and Preclinical Approaches

Head and neck cancers (HNCs) represent the sixth most widespread malignancy worldwide. Surgery, radiotherapy, chemotherapeutic and immunotherapeutic drugs represent the main clinical approaches for HNC patients. Moreover, HNCs are characterised by an elevated mutational load; however, specific genetic mutations or biomarkers have not yet been found. In this scenario, personalised medicine is showing its efficacy. To study the reliability and the effects of personalised treatments, preclinical research can take advantage of next-generation sequencing and innovative technologies that have been developed to obtain genomic and multi-omic profiles to drive personalised treatments. The crosstalk between malignant and healthy components, as well as interactions with extracellular matrices, are important features which are responsible for treatment failure. Preclinical research has constantly implemented in vitro and in vivo models to mimic the natural tumour microenvironment. Among them, 3D systems have been developed to reproduce the tumour mass architecture, such as biomimetic scaffolds and organoids. In addition, in vivo models have been changed over the last decades to overcome problems such as animal management complexity and time-consuming experiments. In this review, we will explore the new approaches aimed to improve preclinical tools to study and apply precision medicine as a therapeutic option for patients affected by HNCs.

Methylation Pattern Mediated by m6A Regulator and Tumor Microenvironment Invasion in Lung Adenocarcinoma.

Background Recent research has established the existence of epigenetic modulation of the immune response. The possible involvement of RNA-n6-methyladenosine (m6A) alteration in tumor microenvironment (TME) cell invasion, on the other hand, is unknown. Methods Based on 23 m6A regulators, we examined the alteration patterns of m6A in 629 LUAD tissues and comprehensively connected these modification patterns with TME cell invasion characteristics. The m6A score was calculated, and the m6A modification pattern of a single tumor was quantified using principal component analysis. Then, we further verified the expression of m6A related enzymes and the role hub gene (NOL10) closely related to survival in lung cancer cell lines. Results Three separate m6A alteration modes have been discovered. TME cell invasion characteristics in the three modes were very similar to the three immunological phenotypes of tumors: immunological rejection, immunological inflammation, and immunological desert. We show that assessing the m6A modification pattern in a single tumor may help predict tumor inflammatory stage, subtype, TME interstitial activity, and prognosis. TME phenotypic inflammation is indicated by a high m6A score, which is characterized by elevated mutation load and immunological activation. The low m6A subtype showed matrix activation and ineffective immune infiltration, indicating that the TME phenotype of noninflammation and immunological rejection had a poor survival probability. Increased neoantigen burden was also linked to a high m6A score. Patients with a higher m6A score saw substantial therapeutic and clinical improvements. And reducing hub gene NOL10 expression substantially inhibited lung cancer cell growth and migration. Conclusions This research shows that m6A alteration is critical in the creation of TME variety and complexity. The analysis of a single tumor's m6A alteration pattern will aid in improving our knowledge of TME invasion features and guiding more effective immunotherapy tactics.

Abstract 2072: DNA repair pathway score is associated with cancer aggressiveness and worse survival in hepatocellular carcinoma (HCC)

Abstract Background: Hepatocellular carcinoma (HCC) is one of the most common malignancies and a leading cause of cancer-related deaths worldwide. A prognostic biomarker based on cancer biology can tailor treatments according to patient prognosis. DNA repair mechanisms activated following DNA damage are essential to suppress carcinogenesis. Hence, deficiencies in DNA damage repair pathways promote carcinogenesis. The role of DNA repair genes in HCC is actively being investigated, but contradictory reports on some DNA repair-related genes have complicated our overall understanding of DNA repair in HCC progression. Though it is important to study the function of each individual DNA repair-related gene, it is more important to understand the role of the entire DNA repair pathway in HCC progression. We hypothesize that the enhancement of the DNA repair pathway is associated with worse survival in HCC patients. Method: A total of 749 HCC patients from 5 cohorts (TCGA, GSE6764, GSE89377, GSE56545, GSE76427) were studied to examine the relationships between enhancement of DNA repair and cancer aggressiveness, tumor immune microenvironment, and patient survival in HCC utilizing a DNA repair pathway score, which was calculated by Gene Set Variation Analysis (GSVA) with Hallmark DNA repair gene set. Results: We found that DNA repair pathway was enhanced by stepwise carcinogenic process of HCC and significantly enhanced in higher grade HCC compared with low grade tumor in two cohorts (both p < 0.001). DNA repair high HCC was associated with worse survival (disease-free survival: p < 0.001, disease-specific survival: p = 0.002, and overall survival: p < 0.001), elevated intratumor heterogeneity (p = 0.036) and mutation load (p < 0.001), but not with fraction of immune cell infiltration nor immune response in the TCGA cohort. HCC tumors with DNA repair high score enriched proliferation-related (E2F targets, G2M checkpoint, mitotic spindle, MYC target v1 and v2) and other cancer aggressiveness-related (unfolded protein response, PI3K/AKT/MTOR signaling, MTORC1, notch signaling, and WNT-β catenin signaling) gene sets. Interestingly, these features were more pronounced in early HCC compared to advanced HCC. DNA repair high HCC was associated with elevated mutation load, enriched proliferation- and other cancer aggressiveness-related gene sets and was associated with worse survival in early (grade 1 and grade 2) but not in advanced (grade 3) HCC. To our knowledge, this is the first study to use DNA repair pathway-related gene set expression data to examine and validate the clinical relevance of DNA repair pathway activity in HCC. Conclusion: The DNA repair score may be used to better understand and predict prognosis in HCC. Citation Format: Masanori Oshi, Tae Hee Kim, Yoshihisa Tokumaru, Li Yan, Ryusei Matsuyama, Itaru Endo, Leonid Cherkassky, Kazuaki Takabe. DNA repair pathway score is associated with cancer aggressiveness and worse survival in hepatocellular carcinoma (HCC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2072.

Biomarkers for Diagnosis, Prognosis and Response to Immunotherapy in Melanoma.

Simple SummaryCutaneous Melanoma is a form of skin cancer characterized by an elevated mutational load that favors high spread to distant organs and resistance to therapies. The identification of biomarkers, able to dissect normal and pathogenic biological processes and response to therapeutic intervention, is necessary to describe melanoma as accurately as possible, having a positive impact on early diagnosis, in turn selecting the best therapeutic option. Recently, a great number of new biomarkers were evaluated, in order to identify those patients who may have clinical benefit from a therapeutic choice, particularly for immunotherapy. At present, these new biomarkers wait to be validated before clinical use. Hence, the requirement to look at and periodically update the advances in this field.Cutaneous Melanoma classification is constantly looking for specific and sensitive biomarkers capable of having a positive effect on diagnosis, prognosis and risk assessment, eventually affecting clinical outcome. Classical morphological, immunohistochemical and the well-known BRAF and NRAS genetic biomarkers do not allow the correct categorization of patients, being melanoma conditioned by high genetic heterogeneity. At the same time, classic prognostic methods are unsatisfactory. Therefore, new advances in omics and high-throughput analytical techniques have enabled the identification of numerous possible biomarkers, but their potentiality needs to be validated and standardized in prospective studies. Melanoma is considered an immunogenic tumor, being the first form of cancer to take advantage of the clinical use of the immune-checkpoint blockers. However, as immunotherapy is effective only in a limited number of patients, biomarkers associated with different responses are essential to select the more promising therapeutic approach and maximize clinical benefits. In this review, we summarize the most utilized biomarkers for Cutaneous Melanoma diagnosis, focusing on new prognostic and predictive biomarkers mainly associated with immunotherapy.

Precision medicine in head and neck cancer

Head and Neck cancer is among the most common cancers worldwide, with a high prevalence in south East Asia, Brazil and central Europe. Head and Neck Squamous cell carcinoma (HNSCC) is associated with elevated mutational load but lacks specific genetic mutations. Exposure to carcinogens including tobacco and alcohol are the most dominant etiologic factors of HNSCC, while Epstein-Barr (HBV) and Human Papilloma Viruses (HPV) are associated with nasopharyngeal and oropharyngeal carcinoma, respectively. Surgery including open and minimally invasive procedures is considered the standard of care for the majority of oral cavity and early larynx cancers, while radiation therapy or concurrent chemoradiation are used for the other head and neck cancers. The treatment of patients with head and neck cancer is complex and has undergone considerable transformation in the last decade. These modalities include immunotherapy, targeted therapy (small molecule inhibitors or antibodies), or combined modality treatments. Emerging evidence supports a vital role of the immune system in eradicating HNSCC. Cancer cells express programmed death ligand 1 or 2 (PD-L1/2) which binds to the PD receptor on the T-cell, leading to an inactivation of the cytotoxic response of the T-cell. Cytotoxic T lymphocytes antigen-4 (CTLA-4) is another key player, expressed by cancer-activated T-cells, which binds to B7 ligand on the cancer cells, leading to inhibition of T-cells activation. Checkpoint inhibitors such as anti-PD-1 and anti-PD-L1 antibodies, were shown to significantly improve disease free survival and overall survival after failure of platinum-based chemotherapy. In addition, expression of HPV is associated with better response to single modality treatment (e.g. radiotherapy or surgery) and improved survival. In future years we expect to see the establishment of precision medicine modalities in an attempt to extend survival and improve quality of life of advanced stage HNSCC patients. Several phase III clinical trials are in progress to evaluate the utility of checkpoint inhibitors at different treatment settings, including combinations with adjuvant surgery, radiation therapy and chemotherapy.

A dormant TIL phenotype defines non-small cell lung carcinomas sensitive to immune checkpoint blockers

The biological determinants of sensitivity and resistance to immune checkpoint blockers are not completely understood. To elucidate the role of intratumoral T-cells and their association with the tumor genomic landscape, we perform paired whole exome DNA sequencing and multiplexed quantitative immunofluorescence (QIF) in pre-treatment samples from non-small cell lung carcinoma (NSCLC) patients treated with PD-1 axis blockers. QIF is used to simultaneously measure the level of CD3+ tumor infiltrating lymphocytes (TILs), in situ T-cell proliferation (Ki-67 in CD3) and effector capacity (Granzyme-B in CD3). Elevated mutational load, candidate class-I neoantigens or intratumoral CD3 signal are significantly associated with favorable response to therapy. Additionally, a “dormant” TIL signature is associated with survival benefit in patients treated with immune checkpoint blockers characterized by elevated TILs with low activation and proliferation. We further demonstrate that dormant TILs can be reinvigorated upon PD-1 blockade in a patient-derived xenograft model.

Tumor immunotherapy: drug-induced neoantigens (xenogenization) and immune checkpoint inhibitors.

More than 40 years ago, we discovered that novel transplantation antigens can be induced in vivo or in vitro by treating murine leukemia with dacarbazine. Years later, this phenomenon that we called “Chemical Xenogenization” (CX) and more recently, “Drug-Induced Xenogenization” (DIX), was reproduced by Thierry Boon with a mutagenic/carcinogenic compound (i.e. N-methyl-N’-nitro-N-nitrosoguanidine). In both cases, the molecular bases of DIX rely on mutagenesis induced by methyl adducts to oxygen-6 of DNA guanine. In the present review we illustrate the main DIX-related immune-pharmacodynamic properties of triazene compounds of clinical use (i.e. dacarbazine and temozolomide).In recent years, tumor immunotherapy has come back to the stage with the discovery of immune checkpoint inhibitors (ICpI) that show an extraordinary immune-enhancing activity. Here we illustrate the salient biochemical features of some of the most interesting ICpI and the up-to-day status of their clinical use. Moreover, we illustrate the literature showing the direct relationship between somatic mutation burden and susceptibility of cancer cells to host’s immune responses.When DIX was discovered, we were not able to satisfactorily exploit the possible presence of triazene-induced neoantigens in malignant cells since no device was available to adequately enhance host’s immune responses in clinical settings. Today, ICpI show unprecedented efficacy in terms of survival times, especially when elevated mutation load is associated with cancer cells. Therefore, in the future, mutation-dependent neoantigens obtained by appropriate pharmacological intervention appear to disclose a novel approach for enhancing the therapeutic efficacy of ICpI in cancer patients.

Weakened purifying selection leads to elevated mutation load under environmental sex determination

In many gonochoristic taxa, sex is influenced by developmental environment, a system that can lead to temporal fluctuations in offspring sex ratio. Demographic models suggest that only short-lived species with environmental sex determination (ESD) are negatively impacted by sex-ratio fluctuations, yet these models fail to account for the potential mutation load associated with reductions in genetically effective population sizes. In this study, we developed a series of individual-based simulation models that explore the fixation rates of mildly deleterious alleles under different sex-determining systems and examine the impacts of variation in lifespan and offspring sex ratio. Populations with ESD exhibited increases in fixation rates in both short- and long-lived populations, but substantial increases were limited to populations characterized by a combination of high sex-ratio variation and short lifespan. Fixation rates were negatively associated with effective population size, indicating that purifying selection operates less efficiently under ESD relative to genotypic sex determination. Reductions in effective population size could be attributed to both intragenerational forces (unequal sex ratio) and intergenerational forces (variable census population sizes). Levels of temporal sex-ratio variation calculated from wild populations of ESD species were capable of yielding large increases in fixation rates, although this relationship was strongly mediated by lifespan. Our results may help to explain the limited phylogenetic distribution of ESD in short-lived taxa.

Population genomics of the endangered giant Galápagos tortoise.

BackgroundThe giant Galápagos tortoise, Chelonoidis nigra, is a large-sized terrestrial chelonian of high patrimonial interest. The species recently colonized a small continental archipelago, the Galápagos Islands, where it has been facing novel environmental conditions and limited resource availability. To explore the genomic consequences of this ecological shift, we analyze the transcriptomic variability of five individuals of C. nigra, and compare it to similar data obtained from several continental species of turtles.ResultsHaving clarified the timing of divergence in the Chelonoidis genus, we report in C. nigra a very low level of genetic polymorphism, signatures of a weakened efficacy of purifying selection, and an elevated mutation load in coding and regulatory sequences. These results are consistent with the hypothesis of an extremely low long-term effective population size in this insular species. Functional evolutionary analyses reveal a reduced diversity of immunity genes in C. nigra, in line with the hypothesis of attenuated pathogen diversity in islands, and an increased selective pressure on genes involved in response to stress, potentially related to the climatic instability of its environment and its elongated lifespan. Finally, we detect no population structure or homozygosity excess in our five-individual sample.ConclusionsThese results enlighten the molecular evolution of an endangered taxon in a stressful environment and point to island endemic species as a promising model for the study of the deleterious effects on genome evolution of a reduced long-term population size.

Genome damage in induced pluripotent stem cells: Assessing the mechanisms and their consequences

In 2006, Shinya Yamanaka and colleagues discovered how to reprogram terminally differentiated somatic cells to a pluripotent stem cell state. The resulting induced pluripotent stem cells (iPSCs) made a paradigm shift in the field, further nailing down the disproval of the long-held dogma that differentiation is unidirectional. The prospect of using iPSCs for patient-specific cell-based therapies has been enticing. This promise, however, has been questioned in the last two years as several studies demonstrated intrinsic epigenetic and genomic anomalies in these cells. Here, we not only review the recent critical studies addressing the genome integrity during the reprogramming process, but speculate about the underlying mechanisms that could create de novo genome damage in iPSCs. Finally, we discuss how much an elevated mutation load really matters considering the safety of future therapies with cells heavily cultured in vitro.

Neuromelanin, neurotransmitter status and brainstem location determine the differential vulnerability of catecholaminergic neurons to mitochondrial DNA deletions

BackgroundDeletions of the mitochondrial DNA (mtDNA) accumulate to high levels in dopaminergic neurons of the substantia nigra pars compacta (SNc) in normal aging and in patients with Parkinson's disease (PD). Human nigral neurons characteristically contain the pigment neuromelanin (NM), which is believed to alter the cellular redox-status. The impact of neuronal pigmentation, neurotransmitter status and brainstem location on the susceptibility to mtDNA damage remains unclear. We quantified mtDNA deletions (ΔmtDNA) in single pigmented and non-pigmented catecholaminergic, as well as non-catecholaminergic neurons of the human SNc, the ventral tegmental area (VTA) and the locus coeruleus (LC), using laser capture microdissection and single-cell real-time PCR.ResultsIn healthy aged individuals, ΔmtDNA levels were highest in pigmented catecholaminergic neurons (25.2 ± 14.9%), followed by non-pigmented catecholamergic (18.0 ± 11.2%) and non-catecholaminergic neurons (12.3 ± 12.3%; p < 0.001). Within the catecholaminergic population, ΔmtDNA levels were highest in dopaminergic neurons of the SNc (33.9 ± 21.6%) followed by dopaminergic neurons of the VTA (21.9 ± 12.3%) and noradrenergic neurons of the LC (11.1 ± 11.4%; p < 0.001). In PD patients, there was a trend to an elevated mutation load in surviving non-pigmented nigral neurons (27.13 ± 16.73) compared to age-matched controls (19.15 ± 11.06; p = 0.052), but levels where similar in pigmented nigral neurons of PD patients (41.62 ± 19.61) and controls (41.80 ± 22.62).ConclusionsCatecholaminergic brainstem neurons are differentially susceptible to mtDNA damage. Pigmented dopaminergic neurons of the SNc show the highest ΔmtDNA levels, possibly explaining the exceptional vulnerability of the nigro-striatal system in PD and aging. Although loss of pigmented noradrenergic LC neurons also is an early feature of PD pathology, mtDNA levels are not elevated in this nucleus in healthy controls. Thus, ΔmtDNA are neither an inevitable consequence of catecholamine metabolism nor a universal explanation for the regional vulnerability seen in PD.

Populations with elevated mutation load do not benefit from the operation of sexual selection

Theory predicts that if most mutations are deleterious to both overall fitness and condition-dependent traits affecting mating success, sexual selection will purge mutation load and increase nonsexual fitness. We explored this possibility with populations of mutagenized Drosophila melanogaster exhibiting elevated levels of deleterious variation and evolving in the presence or absence of male-male competition and female choice. After 60 generations of experimental evolution, monogamous populations exhibited higher total reproductive output than polygamous populations. Parental environment also affected fitness measures - flies that evolved in the presence of sexual conflict showed reduced nonsexual fitness when their parents experienced a polygamous environment, indicating trans-generational effects of male harassment and highlighting the importance of a common garden design. This cost of parental promiscuity was nearly absent in monogamous lines, providing evidence for the evolution of reduced sexual antagonism. There was no overall difference in egg-to-adult viability between selection regimes. If mutation load was reduced by the action of sexual selection in this experiment, the resultant gain in fitness was not sufficient to overcome the costs of sexual antagonism.