Oncocytic glioblastoma: a glioblastoma showing oncocytic changes and increased mitochondrial DNA copy number

Glioma grade and mortality in relation to sequence variation in the mitochondrial genome

PURPOSE

Glioma arises from glial cells and comprises ∼80 % of malignant adult brain tumors. The polymorphic mitochondrial genome plays a key role in maintaining redox homeostasis and generation of reactive oxygen species (ROS). ROS have a well-established role in glial tumors. We investigated associations between germline mtDNA variants and haplogroups with glioma grade and glioblastoma (GBM) survival.

METHODS

We conducted germline mtDNA sequencing for 388 patients (300 Caucasians, 88 African Americans [AA]) with incident glioma (105 non-GBM, 283 GBM). Across all patients we identified 1431 homoplasmic mtDNA variants, including 692 variants observed only in Caucasians, 474 only in AAs, and 265 in both groups. We estimated Odds Ratios (OR) and 95 % Confidence Intervals (CI) for mtDNA common variants, haplogroups, and gene variant burden in relation to glioma grade and tertiles of survival in GBM patients. Bonferroni and Benjamini-Hochberg correction were applied for multiple comparisons.

RESULTS

No mtDNA haplogroup was associated with glioma grade or patient survival in GBM. Common variants m.3010G>A, m.195T>C, and m.16189T>C were linked to lower-grade glioma risk. For GBM survival, m.1719G>A, m.14766T>C, m.16129G>A, and m.204T>C were associated with a poorer prognosis while variant m.73A>G was associated with an improved prognosis. A higher variant burden in MT-ND1 and MT-ND5 was associated with a better prognosis. No results remained statistically significant after correction.

CONCLUSION

This is the first comprehensive study of germline mtDNA sequence variation in relation to glioma grade at diagnosis and gliobastoma patient survival. Results warrant further study in larger populations and investigation of biologic mechanisms linking mtDNA polymorphism to these endpoints.

Mitochondrial DNA copy number alterations: Key players in the complexity of glioblastoma (Review)

Renowned as a highly invasive and lethal tumor derived from neural stem cells in the central nervous system, glioblastoma (GBM) exhibits substantial histopathological variation and genomic complexity, which drive its rapid progression and therapeutic resistance. Alterations in mitochondrial DNA (mtDNA) copy number (CN) serve a crucial role in GBM development and progression, affecting various aspects of tumor biology, including energy production, oxidative stress regulation and cellular adaptability. Fluctuations in mtDNA levels, whether elevated or diminished, can impair mitochondrial function, potentially disrupting oxidative phosphorylation and amplifying reactive oxygen species generation, thereby fueling tumor growth and influencing treatment responses. Understanding the mechanisms of mtDNA‑CN variations, and their interplay with genetic and environmental elements in the tumor microenvironment, is essential for advancing diagnostic and therapeutic strategies. Targeting mtDNA alterations could strengthen treatment efficacy, mitigate resistance and ultimately enhance the prognosis of patients with this aggressive brain tumor. The present review summarizes the existing literature on mtDNA alterations, specifically emphasizing variations in mtDNA‑CN and their association with GBM by surveying articles published between 1996 and 2024, sourced from databases such as Scopus, PubMed and Google Scholar. In addition, the review provides a brief overview of mitochondrial genome architecture, knowledge regarding the regulation of mtDNA integrity and CN, and how mitochondria significantly impact GBM tumorigenesis. This review further presents information on therapeutic approaches for restoring mtDNA‑CN that contribute to optimized mitochondrial function and improved health outcomes.

Genetic association between mitochondrial DNA copy number and glioma risk: insights from causality

BACKGROUND

The genetic causal association between the mitochondrial DNA copy number (mtDNA-CN) and the development of glioma and glioblastoma (GBM) remains unclear.

METHODS

The summary-level datasets for mtDNA-CN were obtained from participants in the UK Biobank and the Cohorts for Heart and Aging Research in Genomic Epidemiology consortium. Additionally, summary statistics datasets related to glioma were collected from a comprehensive meta-analysis genome-wide association study, which included 12,488 cases and 18,169 controls. The main method employed was inverse variance weighting, supplemented by Bonferroni correction to account for multiple tests. Additionally, sensitivity analyses were performed to address potential pleiotropy and strengthen the reliability of the results.

RESULTS

In the primary analysis, no genetic causal association was found between mtDNA-CN and glioma (OR = 1.20, 95%CI = 0.94-1.52, P = 0.1394), nor with low-grade glioma (OR = 1.09, 95%CI = 0.79-1.51, P = 0.5588). However, a suggestive genetic relationship between mtDNA-CN and glioblastoma was observed (OR = 1.42, 95%CI = 1.02-1.96, P = 0.0347). These findings were replicated in the MR analysis. Comprehensive analyses, including heterogeneity and pleiotropy analyses, as well as reverse analysis, confirmed the robustness of these results.

CONCLUSION

Our MR study did not find a genetic causal association between mtDNA-CN and the risk of glioma. A suggestive causal association between GBM and mtDNA-CN was detected.

A case of primary optic pathway demyelination caused by oncocytic oligodendrogliopathy of unknown origin

We report the case of a 22-year-old woman presenting with an acute onset of dizziness, gait dysbalance and blurred vision. Magnetic resonance imaging included 3 Tesla and 7 Tesla imaging and revealed a T2-hyperintense, T1-hypointense, non-contrast-enhancing lesion strictly confined to the white matter affecting the right optic radiation. An extensive ophthalmologic examination yielded mild quadrantanopia but no signs of optic neuropathy. The lesion was biopsied. The neuropathological evaluation revealed a demyelinating lesion with marked tissue vacuolization and granular myelin disintegration accompanied by mild T cell infiltration and a notable absence of myelin uptake by macrophages. Oligodendrocytes were strikingly enlarged, displaying oncocytic characteristics and showed cytoplasmic accumulation of mitochondria, which had mildly abnormal morphology on electron microscopy. The diagnosis of multiple sclerosis was excluded. Harding's disease, a variant of Leber's hereditary optic neuropathy, was then suspected. However, neither PCR for relevant mutations nor whole exome sequencing yielded known pathogenetic mutations in the patient's genome. We present a pattern of demyelinating tissue injury of unknown etiology with an oncocytic change of oligodendrocytes and a lack of adequate phagocytic response by macrophages, which to the best of our knowledge, has not been described before.

Insights regarding mitochondrial DNA copy number alterations in human cancer (Review)

Mitochondria are the critical organelles involved in various cellular functions. Mitochondrial biogenesis is activated by multiple cellular mechanisms which require a synchronous regulation between mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). The mitochondrial DNA copy number (mtDNA-CN) is a proxy indicator for mitochondrial activity, and its alteration reflects mitochondrial biogenesis and function. Despite the precise mechanisms that modulate the amount and composition of mtDNA, which have not been fully elucidated, mtDNA-CN is known to influence numerous cellular pathways that are associated with cancer and as well as multiple other diseases. In addition, the utility of current technology in measuring mtDNA-CN contributes to its extensive assessment of diverse traits and tumorigenesis. The present review provides an overview of mtDNA-CN variations across human cancers and an extensive summary of the existing knowledge on the regulation and machinery of mtDNA-CN. The current information on the advanced methods used for mtDNA-CN assessment is also presented.

Synergistic anti-tumor efficacy of mutant isocitrate dehydrogenase 1 inhibitor SYC-435 with standard therapy in patient-derived xenograft mouse models of glioma

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A novel pair of orthotopic PDX models of glioma bearing IDH1-R132H/R132C mutations.

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New mutant IDH1i (SY-435) with standard therapy led to strong therapeutic efficacy.

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H3K4/K9 methylation/mtDNA-encoded molecules mediate anti-tumor activity of SYC-435.

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Discovered MYO1F, CTC1 and BCL9 as novel genes that mediated SYC-435 resistance.

Clinical outcomes in patients with WHO grade II/III astrocytoma, oligodendroglioma or secondary glioblastoma remain poor. Isocitrate dehydrogenase 1 (IDH1) is mutated in > 70% of these tumors, making it an attractive therapeutic target. To determine the efficacy of our newly developed mutant IDH1 inhibitor, SYC-435 (1-hydroxypyridin-2-one), we treated orthotopic glioma xenograft model (IC-BT142AOA) carrying R132H mutation and our newly established orthotopic patient-derived xenograft (PDX) model of recurrent anaplastic oligoastrocytoma (IC-V0914AOA) bearing R132C mutation. In addition to suppressing IDH1 mutant cell proliferation in vitro, SYC-435 (15 mg/kg, daily x 28 days) synergistically prolonged animal survival times with standard therapies (Temozolomide + fractionated radiation) mediated by reduction of H3K4/H3K9 methylation and expression of mitochondrial DNA (mtDNA)-encoded molecules. Furthermore, RNA-seq of the remnant tumors identified genes (MYO1F, CTC1 and BCL9) and pathways (base excision repair, TCA cycle II, sirtuin signaling, protein kinase A, eukaryotic initiation factor 2 and α-adrenergic signaling) as mediators of therapy resistance. Our data demonstrated the efficacy SYC-435 in targeting IDH1 mutant gliomas when combined with standard therapy and identified a novel set of genes that should be prioritized for future studies to overcome SYC-435 resistance.

Mitochondrial determinants of cancer health disparities

Mitochondria, which are multi-functional, have been implicated in cancer initiation, progression, and metastasis due to metabolic alterations in transformed cells. Mitochondria are involved in the generation of energy, cell growth and differentiation, cellular signaling, cell cycle control, and cell death. To date, the mitochondrial basis of cancer disparities is unknown. The goal of this review is to provide an understanding and a framework of mitochondrial determinants that may contribute to cancer disparities in racially different populations. Due to maternal inheritance and ethnic-based diversity, the mitochondrial genome (mtDNA) contributes to inherited racial disparities. In people of African ancestry, several germline, population-specific haplotype variants in mtDNA as well as depletion of mtDNA have been linked to cancer predisposition and cancer disparities. Indeed, depletion of mtDNA and mutations in mtDNA or nuclear genome (nDNA)-encoded mitochondrial proteins lead to mitochondrial dysfunction and promote resistance to apoptosis, the epithelial-to-mesenchymal transition, and metastatic disease, all of which can contribute to cancer disparity and tumor aggressiveness related to racial disparities. Ethnic differences at the level of expression or genetic variations in nDNA encoding the mitochondrial proteome, including mitochondria-localized mtDNA replication and repair proteins, miRNA, transcription factors, kinases and phosphatases, and tumor suppressors and oncogenes may underlie susceptibility to high-risk and aggressive cancers found in African population and other ethnicities. The mitochondrial retrograde signaling that alters the expression profile of nuclear genes in response to dysfunctional mitochondria is a mechanism for tumorigenesis. In ethnic populations, differences in mitochondrial function may alter the cross talk between mitochondria and the nucleus at epigenetic and genetic levels, which can also contribute to cancer health disparities. Targeting mitochondrial determinants and mitochondrial retrograde signaling could provide a promising strategy for the development of selective anticancer therapy for dealing with cancer disparities. Further, agents that restore mitochondrial function to optimal levels should permit sensitivity to anticancer agents for the treatment of aggressive tumors that occur in racially diverse populations and hence help in reducing racial disparities.

Mitochondrial DNA copy number in whole blood and glioma risk: A case control study

Alterations in mitochondrial DNA (mtDNA) copy number are observed in human gliomas. However, whether variations in mtDNA copy number in whole blood play any role in glioma carcinogenesis is still largely unknown. In current study with 395 glioma patients and 425 healthy controls, we intended to investigate the association between mtDNA copy number in whole blood and glioma risk. Overall, we found that levels of mtDNA copy number were significantly higher in glioma cases than healthy controls (mean: 1.48 vs. 1.32, P < 0.01). In both cases and controls, levels of mtDNA copy number were inversely correlated with age (P < 0.01, respectively). And in cases, newly diagnosed, glioblastoma (GBM), and high grade glioma patients had significantly lower mtDNA copy number than their counterparts (P = 0.02, P < 0.01, and P = 0.04, respectively). In the multivariate analysis, elevated mtDNA copy number levels were associated with a 1.63-fold increased risk of glioma (adjusted odds ratio (OR) = 1.63, 95% confidence interval (CI) = 1.23-2.14). In further quartile analysis, study subjects who had highest levels of mtNDA copy number had 1.75-fold increased risk of gliomas (adjOR = 1.75, 95%CI = 1.18-2.61). In brief, our findings support the role of mtDNA copy number in the glioma carcinogenesis. © 2016 Wiley Periodicals, Inc.

A comprehensive characterization of mitochondrial DNA mutations in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most malignant brain cancer in adults, with a poor prognosis, whose molecular stratification still represents a challenge in pathology and clinics. On the other hand, mitochondrial DNA (mtDNA) mutations have been found in most tumors as modifiers of the bioenergetics state, albeit in GBM a characterization of the mtDNA status is lacking to date. Here, a characterization of the burden of mtDNA mutations in GBM samples was performed. First, investigation of tumor-specific vs. non tumor-specific mutations was carried out with the MToolBox bioinformatics pipeline by analyzing 45 matched tumor/blood samples, from whole genome or whole exome sequencing datasets obtained from The Cancer Genome Atlas (TCGA) consortium. Additionally, the entire mtDNA sequence was obtained in a dataset of 104 fresh-frozen GBM samples. Mitochondrial mutations with potential pathogenic interest were prioritized based on heteroplasmic fraction, nucleotide variability, and in silico prediction of pathogenicity. A preliminary biochemical analysis of the activity of mitochondrial respiratory complexes was also performed on fresh-frozen GBM samples. Although a high number of mutations was detected, we report that the large majority of them does not pass the prioritization filters. Therefore, a relatively limited burden of pathogenic mutations is indeed carried by GBM, which did not appear to determine a general impairment of the respiratory chain. This article is part of a Directed Issue entitled: Energy Metabolism Disorders and Therapies.

Oncocytic meningioma: a case report and review of the literature

Oncocytic meningioma is an uncommon variant of meningioma, with only 20 reported cases to date, that is histologically characterized by the presence of neoplastic cells with granular eosinophilic cytoplasm rich in mitochondria. We present the clinicopathological features of a case of oncocytic meningioma in a 49-year-old Chinese female, along with a literature review. Brain computed tomography and magnetic resonance imaging demonstrated a slightly hyperintense mass located in the right frontal region and attached to the dura. In addition, it was homogeneously enhanced following contrast administration. She underwent gross total surgical resection of the tumor and adjacent dura. Grossly, the well-demarcated, nonencapsulated mass had a solid and tan-white appearance with soft and rubbery consistency. The lesions were composed primarily of sheets, nests, and cords of large polygonal bland cells with finely granular eosinophilic cytoplasm rich in mitochondria. Mitotic figures were rare, and necrosis was absent. There was no infiltration of the dura or brain cortex. Immunohistochemical staining revealed that the neoplastic cells were positive for vimentin, epithelial membrane antigen, antimitochondrial antibody, and progesterone receptor, whereas MIB-1 stained only approximately 1% of the tumor cells. This is the first known report of an oncocytic meningioma arising in a Chinese patient. The patient was followed for 19 months without any evidence of metastasis or recurrence.