Creation of cybrid cultures containing the mitochondrial genome mutation m.1555A>G (MT-RNR1 gene), which has a protective effect in atherosclerosis

Введение. В настоящее время все больший интерес ученых мира вызывают цибридные клеточные модели, которые являются одним из лучших объектов для изучения патологических процессов в организме человека. Например, сотрудниками нашей лаборатории были впервые созданы подобные модели для изучения протективного эффекта некоторых мутаций митохондриального генома, защищающих организм человека от дисфункции митохондрий и атеросклеротических поражений. Цель: исследования - создание цибридных культур с высоким уровнем гетероплазмии по мутации митохондриального генома m.1555A>G, локализованной в кодирующем регионе митохондриального генома человека в гене MT-RNR1. В наших предварительных исследованиях было установлено, что пороговый уровень гетероплазмии мутации m.1555A>G имеет при атеросклерозе протективный эффект. Методика. Цибридные культуры были созданы путем слияния rho0(безмитохондриальных)-клеток и митохондрий из тромбоцитов с высоким уровнем гетероплазмии исследуемых мутаций. Для получения безмитохондриальных клеток была использована культура моноцитарного происхождения THP-1. Результаты. Получены 4 цибридные клеточные линии, содержащие мутацию m.1555A>G с уровнем гетероплазмии выше порогового значения. Заключение. В данной работе были созданы 4 цибридные культуры с высоким уровнем гетероплазмии по мутации мтДНК m.1555A>G, имеющей при атеросклерозе протективный эффект. Полученные цибридные клеточные линии могут служить моделями для отработки методов генотерапии у пациентов с атеросклерозом. Кроме того, с помощью данных цибридных клеточных моделей можно будет изучать молекулярно-клеточные механизмы, защищающие клетки от митохондриальной дисфункции. Introduction. Cybrid cell models are one of the best objects for studying pathological processes in the human body, and they are of increasing interest to scientists worldwide. Our laboratory was the first to create such models for studying the protective effect of mutations in the mitochondrial genome that protect the human body from mitochondrial dysfunction and atherosclerotic lesions. Aim: To create cybrid cultures with a high heteroplasmy level for the mitochondrial genome mutation m.1555A>G localized within the coding region of the human mitochondrial genome in the MT-RNR1 gene. Preliminary studies showed that the threshold heteroplasmy level for the m.1555A>G mutation has a protective effect in atherosclerosis. Methods. Cybrid cultures were created by fusion of rho0 (mtDNA-depleted) cells and mitochondria from platelets with a high heteroplasmy level for the studied mutations. To obtain mtDNA-free cells, a culture of monocytic origin, THP-1, was used. Results. We obtained four cybrid cell lines containing the m.1555A>G mutation with a heteroplasmy level above the threshold value. Conclusion. Four cybrid cultures with a high heteroplasmy level for the mtDNA mutation m.1555A>G were created. These cybrid cell lines can serve as models for developing methods of gene therapy for patients with atherosclerosis. In addition, using these cybrid cell models, it will be possible to study molecular and cellular mechanisms that protect cells from mitochondrial dysfunction.

A high mutation load of m.14597A>G in MT-ND6 causes Leigh syndrome

Leigh syndrome (LS) is an early-onset progressive neurodegenerative disorder associated with mitochondrial deficiency. m.14597A>G (p.Ile26Thr) in the MT-ND6 gene was reported to cause Leberʼs hereditary optic neuropathy (LHON) or dementia/dysarthria. In previous reports, less than 90% heteroplasmy was shown to result in adult-onset disease. Here, by whole mitochondrial sequencing, we identified m.14597A>G mutation of a patient with LS. PCR–RFLP analysis on fibroblasts from the patient revealed a high mutation load (> 90% heteroplasmy). We performed functional assays using cybrid cell models generated by fusing mtDNA-less rho0 HeLa cells with enucleated cells from patient fibroblasts carrying the m.14597A>G variant. Cybrid cell lines bearing the m.14597A>G variant exhibited severe effects on mitochondrial complex I activity. Additionally, impairment of cell proliferation, decreased ATP production and reduced oxygen consumption rate were observed in the cybrid cell lines bearing the m.14597A>G variant when the cells were metabolically stressed in medium containing galactose, indicating mitochondrial respiratory chain defects. These results suggest that a high mutation load of m.14597A>G leads to LS via a mitochondrial complex I defect, rather than LHON or dementia/dysarthria.

Creation of cybrid cell cultures containing a single-nucleotide substitution associated with atherosclerosis in the MT-TL2 gene

Введение. Цибридные клеточные модели наиболее перспективны для изучения патогенеза различных заболеваний. Авторами статьи впервые были созданы такие модели для изучения митохондриальной дисфункции и патологических процессов, развивающихся при атеросклерозе. Цель работы - создание цибридных культур с высоким уровнем гетероплазмии по мутации митохондриального генома m.12315G>A. В предварительных исследованиях авторами статьи было установлено, что пороговый уровень гетероплазмии мутации m.12315G>A ассоциирован с атеросклерозом. Методика. Цибридные культуры создавали путем слияния безмитохондриальных клеток (rho0) и митохондрий из тромбоцитов участников исследования с высоким уровнем гетероплазмии исследуемых мутаций. Для создания rho0-клеток была взята культура моноцитарного происхождения THP-1. Безмитохондриальные клетки были получены с помощью метода M. Kинга и Г. Аттарди. Тромбоциты выделяли из цельной крови участников исследования. Для этого был применен метод центрифугирования в градиенте плотности фиколла-урографина. Для получения цибридных культур клеток была использована методика «ПЭГ-слияния». В созданных безмитохондриальных и цибридных клеточных культурах был проведен количественный анализ копий митохондриального генома. Согласно результатам данного анализа было подтверждено либо отсутствие митохондрий (rho0-клетки), либо их наличие (цибриды). Количество копий мтДНК детектировалось с помощью реал-тайм ПЦР в присутствии красителя SYBR Green I. Результаты. Получены 4 цибридные клеточные линии, содержащие мутацию m.12315G>A с уровнем гетероплазмии выше порогового значения. Заключение. Созданы 4 цибридные культуры с высоким уровнем гетероплазмии по мутации митохондриального генома m.12315G>A. Полученные цибридные клеточные линии могут служить моделями для изучения молекулярно-клеточных механизмов митохондриальной дисфункции при атеросклерозе и других сердечно-сосудистых заболеваниях. Цибридные культуры можно использовать для моделирования атерогенеза, а также для подбора патогенетически обоснованной лекарственной терапии при атеросклерозе. Introduction. Cybrid cell models are most promising for studying pathological mechanisms in different diseases. The authors for the first time created such models for studying mitochondrial dysfunction and pathological processes underlying atherosclerosis. Aim. Creation of cybrid cultures with a high heteroplasmy level for mitochondrial genome mutation m.12315G>A. A preliminary study by the authors showed that the heteroplasmy level of mutation m.12315G>A was associated with atherosclerosis. Methods. Cybrid cultures were created by fusing non-mitochondrial cells (rho0) and mitochondria from platelets of study participants with a high heteroplasmy level of the mutations under study. A THP-1 culture of monocytic origin was used to create rho0 cells. Non-mitochondrial cells were obtained using the M. King and G. Attardi method. Platelets were extracted from whole blood of study participants with Ficoll-Urografin density gradient centrifugation. Cybrid cell cultures were obtained by the PEG-mediated fusion method. In the created non-mitochondrial and cybrid cell cultures, quantitative analysis of mitochondrial genome copies was performed. This analysis confirmed either the absence of mitochondria (rho0-cells) or their presence (cybrids). The mtDNA copies were quantified using real-time PCR in the presence of the SYBR Green I stain. Results. Four cybrid cell lines were obtained, which contained the m.12315G>A mutation with heteroplasmy levels higher than the threshold level. Conclusion. Four cybrid cultures were created with a high heteroplasmy level for the mitochondrial genome mutation m.12315G>A. The obtained cell lines can be used as models for studying molecular cellular mechanisms of mitochondrial dysfunction in atherosclerosis and cardiovascular diseases. In addition, they may be useful for modeling atherogenesis in cells and for selecting therapy for patients with atherosclerosis.

OGA Inhibition Alters Energetics and Nutrient Sensing in Alzheimer’s Disease Cytoplasmic Hybrids

Background: Alzheimer’s disease (AD) features reductions in key bioenergetic fluxes and perturbed mitochondrial function. Cytoplasmic hybrids (cybrids) generated through the transfer of AD subject mitochondria to mtDNA-depleted SH-SY5Y neuroblastoma cells recapitulate some of these features in an in vitro setting. Objective: For this study, we used the AD cybrid model to assess the impact of a nutrient-excess like-state via increasing O-GlcNAcylation on whole cell and mitochondrial homeostasis. Methods: We induced increased O-GlcNAc by treating AD and control cybrid cell lines with Thiamet G (TMG), an inhibitor of the O-GlcNAcase enzyme that mediates removal of the nutrient-dependent O-GlcNAc modification. Results: Relative to control cybrid cell lines, AD cybrid lines showed a blunted response to TMG-induced O-GlcNAcylation. At baseline, AD cybrid cell line mitochondria showed partial activation of several proteins that help maintain bioenergetic homeostasis such as AMP-Regulated Kinase suggesting that AD mitochondria initiate a state of nutrient stress promoting energetic compensation; however, this compensation reduces the capacity of cells to respond to additional nutrient-related stresses such as TMG treatment. Also, TMG caused disruptions in acetylation and Sirtuin 3 expression, while lowing total energetic output of the cell. Conclusion: Together, these findings suggest that modulation of O-GlcNAc is essential for proper energetic function of the mitochondria, and AD mitochondrial capacity to handle nutrient-excess is limited.

Mitochondrial DNA Manipulations Affect Tau Oligomerization

Background: Mitochondrial dysfunction and tau aggregation occur in Alzheimer’s disease (AD), and exposing cells or rodents to mitochondrial toxins alters their tau. Objective: To further explore how mitochondria influence tau, we measured tau oligomer levels in human neuronal SH-SY5Y cells with different mitochondrial DNA (mtDNA) manipulations. Methods: Specifically, we analyzed cells undergoing ethidium bromide-induced acute mtDNA depletion, ρ0 cells with chronic mtDNA depletion, and cytoplasmic hybrid (cybrid) cell lines containing mtDNA from AD subjects. Results: We found cytochrome oxidase activity was particularly sensitive to acute mtDNA depletion, evidence of metabolic re-programming in the ρ0 cells, and a relatively reduced mtDNA content in cybrids generated through AD subject mitochondrial transfer. In each case tau oligomer levels increased, and acutely depleted and AD cybrid cells also showed a monomer to oligomer shift. Conclusion: We conclude a cell’s mtDNA affects tau oligomerization. Overlapping tau changes across three mtDNA-manipulated models establishes the reproducibility of the phenomenon, and its presence in AD cybrids supports its AD-relevance.

Leigh Syndrome in a Pedigree Harboring the m.1555A>G Mutation in the Mitochondrial 12S rRNA

Background: Leigh syndrome (LS) is a serious genetic disease that can be caused by mutations in dozens of different genes. Methods: Clinical study of a deafness pedigree in which some members developed LS. Cellular, biochemical and molecular genetic analyses of patients’ tissues and cybrid cell lines were performed. Results: mitochondrial DNA (mtDNA) m.1555A>G/MT-RNR1 and m.9541T>C/MT-CO3 mutations were found. The first one is a well-known pathologic mutation. However, the second one does not appear to contribute to the high hearing loss penetrance and LS phenotype observed in this family. Conclusion: The m.1555A>G pathological mutation, accompanied with an unknown nuclear DNA (nDNA) factor, could be the cause of the phenotypic manifestations in this pedigree.

Expanding the molecular and phenotypic spectrum of truncating MT-ATP6 mutations

ObjectiveTo describe the clinical and functional consequences of 1 novel and 1 previously reported truncating MT-ATP6 mutation.MethodsThree unrelated probands with mitochondrial encephalomyopathy harboring truncating MT-ATP6 mutations are reported. Transmitochondrial cybrid cell studies were used to confirm pathogenicity of 1 novel variant, and the effects of all 3 mutations on ATPase 6 and complex V structure and function were investigated.ResultsPatient 1 presented with adult-onset cerebellar ataxia, chronic kidney disease, and diabetes, whereas patient 2 had myoclonic epilepsy and cerebellar ataxia; both harbored the novel m.8782G>A; p.(Gly86*) mutation. Patient 3 exhibited cognitive decline, with posterior white matter abnormalities on brain MRI, and severely impaired renal function requiring transplantation. The m.8618dup; p.(Thr33Hisfs*32) mutation, previously associated with neurogenic muscle weakness, ataxia, and retinitis pigmentosa, was identified. All 3 probands demonstrated a broad range of heteroplasmy across different tissue types. Blue-native gel electrophoresis of cultured fibroblasts and skeletal muscle tissue confirmed multiple bands, suggestive of impaired complex V assembly. Microscale oxygraphy showed reduced basal respiration and adenosine triphosphate synthesis, while reactive oxygen species generation was increased. Transmitochondrial cybrid cell lines studies confirmed the deleterious effects of the novel m.8782 G>A; p.(Gly86*) mutation.ConclusionsWe expand the clinical and molecular spectrum of MT-ATP6-related mitochondrial disorders to include leukodystrophy, renal disease, and myoclonic epilepsy with cerebellar ataxia. Truncating MT-ATP6 mutations may exhibit highly variable mutant levels across different tissue types, an important consideration during genetic counseling.

Creation of Cybrid Cultures Containing mtDNA Mutations m.12315G>A and m.1555G>A, Associated with Atherosclerosis

In the present work, a pilot creation of four cybrid cultures with high heteroplasmy level was performed using mitochondrial genome mutations m.12315G>A and m.1555G>A. According to data of our preliminary studies, the threshold heteroplasmy level of mutation m.12315G>A is associated with atherosclerosis. At the same time, for a mutation m.1555G>A, such a heteroplasmy level is associated with the absence of atherosclerosis. Cybrid cultures were created by fusion of rho0-cells and mitochondria from platelets with a high heteroplasmy level of the investigated mutations. To create rho0-cells, THP-1 culture of monocytic origin was taken. According to the results of the study, two cybrid cell lines containing mutation m.12315G>A with the heteroplasmy level above the threshold value (25% and 44%, respectively) were obtained. In addition, two cybrid cell lines containing mutation m.1555G>A with a high heteroplasmy level (24%) were obtained. Cybrid cultures with mtDNA mutation m.12315G>A can be used to model both the occurrence and development of atherosclerosis in cells and the titration of drug therapy for patients with atherosclerosis. With the help of cybrid cultures containing single nucleotide replacement of mitochondrial genome m.1555G>A, it is possible to develop approaches to the gene therapy of atherosclerosis.

Cybrid Models of Pathological Cell Processes in Different Diseases

Modelling of pathological processes in cells is one of the most sought-after technologies of the 21st century. Using models of such processes may help to study the pathogenetic mechanisms of various diseases. The aim of the present study was to analyse the literature, dedicated to obtaining and investigating cybrid models. Besides, the possibility of modeling pathological processes in cells and treatment of different diseases using the models was evaluated. Methods of obtaining Rho0 cell cultures showed that, during their creation, mainly a standard technique, based on the use of mtDNA replication inhibitors (ethidium bromide), was applied. Cybrid lines were usually obtained by PEG fusion. Most frequently, platelets acted as donors of mitochondria. According to the analysis of the literature data, cybrid cell cultures can be modeled to study the dysfunction of the mitochondrial genome and molecular cellular pathological processes. Such models can be very promising for the development of therapeutic approaches to the treatment of various human diseases.