Comprehensive summary of mitochondrial DNA alterations in the postmortem human brain: A systematic review

Background: Mitochondrial DNA (mtDNA) encodes 37 genes necessary for synthesizing 13 essential subunits of the oxidative phosphorylation system. mtDNA alterations are known to cause mitochondrial disease (MitD), a clinically heterogeneous group of disorders that often present with neuropsychiatric symptoms. Understanding the nature and frequency of mtDNA alterations in health and disease could be a cornerstone in disentangling the relationship between biochemical findings and clinical symptoms of brain disorders. This systematic review aimed to summarize the mtDNA alterations in human brain tissue reported to date that have implications for further research on the pathophysiological significance of mtDNA alterations in brain functioning. Methods: We searched the PubMed and Embase databases using distinct terms related to postmortem human brain and mtDNA up to June 10, 2021. Reports were eligible if they were empirical studies analysing mtDNA in postmortem human brains. Findings: A total of 158 of 637 studies fulfilled the inclusion criteria and were clustered into the following groups: MitD (48 entries), neurological diseases (NeuD, 55 entries), psychiatric diseases (PsyD, 15 entries), a miscellaneous group with controls and other clinical diseases (5 entries), ageing (20 entries), and technical issues (5 entries). Ten entries were ascribed to more than one group. Pathogenic single nucleotide variants (pSNVs), both homo- or heteroplasmic variants, have been widely reported in MitD, with heteroplasmy levels varying among brain regions; however, pSNVs are rarer in NeuD, PsyD and ageing. A lower mtDNA copy number (CN) in disease was described in most, but not all, of the identified studies. mtDNA deletions were identified in individuals in the four clinical categories and ageing. Notably, brain samples showed significantly more mtDNA deletions and at higher heteroplasmy percentages than blood samples, and several of the deletions present in the brain were not detected in the blood. Finally, mtDNA heteroplasmy, mtDNA CN and the deletion levels varied depending on the brain region studied. Interpretation: mtDNA alterations are well known to affect human tissues, including the brain. In general, we found that studies of MitD, NeuD, PsyD, and ageing were highly variable in terms of the type of disease or ageing process investigated, number of screened individuals, studied brain regions and technology used. In NeuD and PsyD, no particular type of mtDNA alteration could be unequivocally assigned to any specific disease or diagnostic group. However, the presence of mtDNA deletions and mtDNA CN variation imply a role for mtDNA in NeuD and PsyD. Heteroplasmy levels and threshold effects, affected brain regions, and mitotic segregation patterns of mtDNA alterations may be involved in the complex inheritance of NeuD and PsyD and in the ageing process. Therefore, more information is needed regarding the type of mtDNA alteration, the affected brain regions, the heteroplasmy levels, and their relationship with clinical phenotypes and the ageing process. Funding: Hospital Universitari Institut Pere Mata; Institut d'Investigació Sanitària Pere Virgili; Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación (PI18/00514)

High number of mitochondrial DNA alterations in postmortem brain tissue of patients with schizophrenia compared to healthy controls

Previous studies have shown mitochondrial dysfunction in schizophrenia (SZ) patients, which may be caused by mitochondrial DNA (mtDNA) alterations. However, there are few studies in SZ that have analyzed mtDNA in brain samples by next-generation sequencing (NGS). To address this gap, we used mtDNA-targeted NGS and qPCR to characterize mtDNA alterations in brain samples from patients with SZ (n = 40) and healthy controls (HC) (n = 40). 35 % of SZ patients showed mtDNA alterations, a significantly higher prevalence compared to 10 % of HC. Specifically, SZ patients had a significantly higher frequency of deletions (35 vs. 5 in HC), with a mean number of deletions of 3.8 in SZ vs. 1.0 in HC. Likely pathogenic missense variants were also significantly more frequent in patients with SZ than in HC (10 vs. three HC), encompassing 14 variants in patients and three in HC. The pathogenic tRNA variant m.3243A>G was identified in one SZ patient with a high heteroplasmy level of 32.2 %. While no significant differences in mtDNA copy number (mtDNA-CN) were observed between SZ and HC, antipsychotic users had significantly higher mtDNA-CN than non-users. These findings suggest a potential role for mtDNA alterations in the pathophysiology of SZ that require further validation and functional studies.This work was supported by the Instituto de Salud Carlos III grant numbers PI18/00514 and PI21/01812, the Basque Government (IT-1512/22 and 2021111018), the Catalan Agency for Research and Universities (AGAUR) 2017SGR-00444 and 2021SGR-01065, the IISPV-Cerca program of the Generalitat de Catalunya, and co-funded by the European Union. Alba Valiente-Pallejà received a Talent-URV-Dipta grant from the Diputació de Tarragona. Bengisu K. Bulduk had a scholarship (FIDGR-2020) and Juan Tortajada had an industrial doctorate (DI21–85), both from the Generalitat de Catalunya

Risk factors for metabolic syndrome in individuals with recent-onset psychosis at disease onset and after 1-year follow-up

Metabolic syndrome (MetS) is a cluster of parameters encompassing the most dangerous heart attack risk factors, associated with increased morbidity and mortality. It is highly prevalent in recent-onset psychosis (ROP) patients. In this pilot study, we evaluated MetS parameters (fasting glucose, high-density lipoprotein (HDL) cholesterol (HDL-c), fasting triglycerides, waist circumference, and systolic and diastolic blood pressure), clinical symptoms, pharmacological treatment, lifestyle, and inflammatory markers in 69 patients with ROP and 61 healthy controls (HCs). At baseline, waist circumference (p = 0.005) and fasting triglycerides (p = 0.007) were higher in patients with ROP than in HCs. At the 1-year follow-up, patients showed clinical improvement, with a reduction in the positive and negative syndrome scale (PANSS) score (p < 0.001), dietary intake (p = 0.001), and antipsychotic medication dose (p < 0.001); however, fasting glucose (p = 0.011), HDL-c (p = 0.013) and waist circumference worsened (p < 0.001). We identified sex, age, BMI, dietary intake, physical activity, daily tobacco use, daily cannabis use, and antipsychotic doses as risk factors contributing to baseline MetS parameters. After 1-year follow-up, those factors plus the PANSS and Calgary Depression Scale for Schizophrenia (CDSS) scores were associated with MetS parameters. Further studies are needed to understand the contributions of the studied risk factors in patients with ROP at onset and during disease progression

ANÀLISI DE LA FUNCIÓ MITOCONDRIAL EN TRASTORNS DEL NEURODESENVOLUPAMENT

Hi ha evidències que impliquen la funció mitocondrial en alguns trastorns del neurodesenvolupament (TN) com el trastorn de l'espectre autista (TEA), la discapacitat intel·lectual (DI) i l'esquizofrènia (ESQ). A més, en aquests trastorns és freqüent la presència de característiques clíniques associades a les malalties mitocondrials (CCAMMs). És per aquests antecedents que aquesta tesi doctoral ha volgut posar el focus en aquest orgànul i en el paper que podria tenir en l'etiologia d'alguns TN. Concretament, s'han avaluat diversos aspectes clínics, genètics i metabòlics en un grup de pacients amb DI (N=115), pacients amb DI i TEA (DI-TEA=122), ESQ (N=57) i en persones control (N=33). Segons els resultats obtinguts, les persones amb DI, DI-TEA i ESQ presenten més freqüència de determinades CCAMMs que les persones control. A més, també presenten un menor número de còpies d'ADN mitocondrial i determinades variants de canvi de nucleòtid, que podrien ser patogèniques. Els pacients amb ESQ van mostrar nivells de lactat més elevats que les persones control durant la realització d'exercici físic. Finalment, també s'han identificat diverses alteracions mitocondrials en una família amb els diagnòstics d'ESQ i síndrome de fatiga crònica. Aquest treball de tesi doctoral suggereix que el mitocondri pot tenir un paper rellevant en l'etiopatogènia d'algunes malalties psiquiàtriques.Hay evidencias que implican la función mitocondrial en algunos trastornos del neurodesarrollo (TN) como el trastorno del espectro autista (TEA), la discapacidad intelectual (DI) y la esquizofrenia (ESQ). Además, en estos trastornos es frecuente la presencia de características clínicas asociadas a las enfermedades mitocondriales (CCAEMs). Es por estos antecedentes que esta tesis doctoral ha querido focalizar en este orgánulo y en el papel que podría tener en la etiología de algunos TN. Concretamente, se han evaluado varios aspectos clínicos, genéticos y metabólicos en un grupo de pacientes con DI (N=115), pacientes con DI y TEA (DI-TEA=122), ESQ (N=57) y personas control (N=33). Según los resultados obtenidos, las personas con DI, DI-TEA y ESQ presentan más frecuencia de determinadas CCAEMs que las persones control. Además, también presentan un menor número de copias de ADN mitocondrial y determinadas variantes de cambio de nucleótido que podrían ser patogénicas. Los pacientes con ESQ mostraron niveles de lactato más elevados que las persones control durante la realización de ejercicio físico. Finalmente, también se han identificado varias alteraciones mitocondriales en una familia con los diagnósticos de ESQ y síndrome de fatiga crónica. Este trabajo de tesis doctoral sugiere que la mitocondria puede tener un papel relevante en la etiopatogenia de algunas enfermedades psiquiátricas.There are evidences that involve the mitochondrial function as a key factor in some neurodevelopmental disorders (ND) such as autism spectrum disorders (ASD), intellectual disability (ID) and schizophrenia (ESQ). Besides, in these disorders, the presence of clinical characteristics associated with mitochondrial diseases (CCAMDs) is frequently observed. These two premises set the basis of this doctoral thesis, which focuses on the study of this organul and the role it plays in the etiology of some ND. Specifically, several clinical, genetic and metabolic aspects were evaluated in a group of patients with ID (N=115), with ID and ASD (ID-ASD=122), ESQ (N=57) and a control group (N=33). The results showed that, people with DI, DI-ASD and ESQ present higher frequency of certain CCAMDs compared with the control group. In addition, smaller number of mitochondrial DNA copies was found in the aforementioned patients. Furthermore, some variants of nucleotic change that could be pathogenic are observed as well. Patients with ESQ also presented higher lactate levels during physical exercise. Finally, several mitochondrial alterations have also been identified in a family with SCZ and chronic fatigue syndrome. This doctoral thesis suggests that mitochondria plays a relevant role in the etiopathogeny of some psychiatric disease

Increased blood lactate levels during exercise and mitochondrial DNA alterations converge on mitochondrial dysfunction in schizophrenia

Background: Mitochondrial dysfunction and an elevation of lactate are observed in patients with schizophrenia (SZ). However, it is unknown whether mitochondrial dysfunction is associated with the presence of mitochondrial DNA (mtDNA) alterations and comorbid clinical conditions. We aimed to identify systemic mitochondrial abnormalities in blood samples of patients with SZ that may have a high impact on the brain due to its high bioenergetic requirements. Methods: Case/control study between 57 patients with SZ and 33 healthy controls (HCs). We measured lactate levels at baseline, during 15 min of exercise (at 5, 10 and 15 min) and at rest. We also evaluated the presence of clinical conditions associated with mitochondrial disorders (CAMDs), measured the neutrophil to lymphocyte ratio (NLR, a subclinical inflammatory marker), and analyzed mtDNA variation and copy number. Results: Linear models adjusting for covariates showed that patients with SZ exhibited higher elevation of lactate than HCs during exercise but not at baseline or at rest. In accordance, patients showed higher number of CAMDs and lower mtDNA copy number. Interestingly, CAMDs correlated with both lactate levels and mtDNA copy number, which in turn correlated with the NLR. Finally, we identified 13 putative pathogenic variants in the mtDNA of 11 participants with SZ not present in HCs, together with a lactate elevation during exercise that was significantly higher in these 11 carriers than in the noncarriers. Conclusions: These results are consistent with systemic mitochondrial malfunctioning in SZ and pinpoint lactate metabolism and mtDNA as targets for potential therapeutic treatments.This work was supported by the Instituto de Salud Carlos III of the Spanish Ministry of Science and Innovation in Spain (grant numbers PS09/01052, PI12/01885, PI18/00514 and FEDER to L.M.). HT was the recipient of an FI-DGR, and GM was the recipient of a BP-DGR scholarship; both are from the Generalitat de Catalunya

Comprehensive summary of mitochondrial DNA alterations in the postmortem human brain: A systematic review

[Background] Mitochondrial DNA (mtDNA) encodes 37 genes necessary for synthesizing 13 essential subunits of the oxidative phosphorylation system. mtDNA alterations are known to cause mitochondrial disease (MitD), a clinically heterogeneous group of disorders that often present with neuropsychiatric symptoms. Understanding the nature and frequency of mtDNA alterations in health and disease could be a cornerstone in disentangling the relationship between biochemical findings and clinical symptoms of brain disorders. This systematic review aimed to summarize the mtDNA alterations in human brain tissue reported to date that have implications for further research on the pathophysiological significance of mtDNA alterations in brain functioning.[Methods] We searched the PubMed and Embase databases using distinct terms related to postmortem human brain and mtDNA up to June 10, 2021. Reports were eligible if they were empirical studies analysing mtDNA in postmortem human brains.[Findings] A total of 158 of 637 studies fulfilled the inclusion criteria and were clustered into the following groups: MitD (48 entries), neurological diseases (NeuD, 55 entries), psychiatric diseases (PsyD, 15 entries), a miscellaneous group with controls and other clinical diseases (5 entries), ageing (20 entries), and technical issues (5 entries). Ten entries were ascribed to more than one group. Pathogenic single nucleotide variants (pSNVs), both homo- or heteroplasmic variants, have been widely reported in MitD, with heteroplasmy levels varying among brain regions; however, pSNVs are rarer in NeuD, PsyD and ageing. A lower mtDNA copy number (CN) in disease was described in most, but not all, of the identified studies. mtDNA deletions were identified in individuals in the four clinical categories and ageing. Notably, brain samples showed significantly more mtDNA deletions and at higher heteroplasmy percentages than blood samples, and several of the deletions present in the brain were not detected in the blood. Finally, mtDNA heteroplasmy, mtDNA CN and the deletion levels varied depending on the brain region studied.[Interpretation] mtDNA alterations are well known to affect human tissues, including the brain. In general, we found that studies of MitD, NeuD, PsyD, and ageing were highly variable in terms of the type of disease or ageing process investigated, number of screened individuals, studied brain regions and technology used. In NeuD and PsyD, no particular type of mtDNA alteration could be unequivocally assigned to any specific disease or diagnostic group. However, the presence of mtDNA deletions and mtDNA CN variation imply a role for mtDNA in NeuD and PsyD. Heteroplasmy levels and threshold effects, affected brain regions, and mitotic segregation patterns of mtDNA alterations may be involved in the complex inheritance of NeuD and PsyD and in the ageing process. Therefore, more information is needed regarding the type of mtDNA alteration, the affected brain regions, the heteroplasmy levels, and their relationship with clinical phenotypes and the ageing process.Hospital Universitari Institut Pere Mata; Institut d'Investigació Sanitària Pere Virgili; Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación (PI18/00514).Peer reviewe