Crosslink between mutations in mitochondrial genes and brain disorders:implications for mitochondrial-targeted therapeutic interventions

At the present,association of mitochondrial dysfunction and progression of neurological disorders has gained significant attention.Defects in mitochondrial network dynamics,point mutations,deletions,and interaction of pathogenomic proteins with mitochondria are some of the possible underlying mechanisms involved in these neurological disorders.Mitochondrial genetics,defects in mitochondrial oxidative phosphorylation machinery,and reactive oxygen species production might share common crosstalk in the progression of these neurological disorders.It is of significant interests to explore and develop therapeutic strategies aimed at correcting mitochondrial abnormalities.This review provided insights on mitochondrial dysfunction/mutations involved in the progression of Alzheimer’s disease,Huntington’s disease,and epilepsy with a special focus on Parkinson’s disease pathology.Along with the deleterious effects of mitochondrial mutations in aforesaid neurological disorders,this paper unraveled the available therapeutic strategy,specifically aiming to improve mitochondrial dysfunction,drugs targeting mitochondrial proteins,gene therapies aimed at correcting mutant mtDNA,peptide-based approaches,and lipophilic cations.

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes correlates with heteroplasmic mutations of mitochondrial DNA 3243 A single-case genealogy analysis

BACKGROUND： Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes （MELAS） is a common syndrome of mitochondrial diseases caused primarily by a mutation from adenine to guanine at mitochondrial DNA 3243. However, the correlation between heteroplasmic mutations and clinical characteristics of hereditary MELAS syndrome is unclear. OBJECTIVE： To survey the clinical behaviors, biochemical outcomes, and imaging data in a patient with suspected MELAS syndrome by maternal inheritance, and to investigate the correlation with heteroplasmic mutations of hemocyte mitochondrial DNA. DESIGN, TIME AND SETTING： A case analysis based on hereditary family surgery was performed in the Enliang Hospital of Anshan, Taian County, and biochemical tests and gene diagnosis were performed at the Department of Laboratory and Institute of Neurology, the First Affiliated Hospital of China Medical University, between March and September 2009. PARTICIPANTS： A 22-year-old female patient with MELAS syndrome was diagnosed in the First Affiliated Hospital of China Medical University in January, 2009. She had five males and seven females in her maternal family. METHODS： We obtained stroke and convulsion history in the patient and her family, as well as performing routine blood tests, plasma lactic acid levels before and after movement, and magnetic resonance of the head. A mutation at m.3243A 〉 G was verified using polymerase chain reaction-restriction fragment length polymorphism and DNA sequencing, and quantitated using real-time polymerase chain reaction. MAIN OUTCOME MEASURES： Correlation of clinical behaviors and biochemical outcomes, as well as imaging data with heteroplasmic mutations in family members with typical and atypical MELAS syndrome. RESULTS： Some family members had typical symptoms of convulsion, stroke, and MELAS syndrome, as well as atypical symptoms of microsomia, movement intolerance, febrile, and migraine. Magnetic resonance of the head was consistent with typical imaging data of MELAS syndrome during attacks, and family members showed cerebellar atrophy. A heteroplasmic mutation of mitochondrial DNA 3243 occurred in all family members, although higher levels caused severe typical symptoms. The age of first-onset convulsion was negatively correlated with level of heteroplasmic mutation （r = -0.852, P 〈 0.05）, but lactic acid was positively correlated with mutation levels （before movement, r = 0.945, P 〈 0.001; after movement, r= 0.945, P 〈 0.001）. CONCLUSION： MELAS syndrome was diagnosed in this family by maternal inheritance, and the etiological factor was a mutation of mitochondrial A3243G. The level of heteroplasmic mutation correlated with anticipated convulsion and lactic acid levels.

Development and validation of a novel PCR-RFLP based method for the detection of 3 primary mitochondrial mutations in Leber's hereditary optic neuropathy patients

Background:Leber’s Hereditary Optic Neuropathy(LHON;MIM 535000)is one of the most commonly inherited optic neuropathies and it results in significant visual morbidity among young adults with a peak age of onset between the ages of 15–30.The worldwide incidence of LHON is approximately 1 in 31,000.95%of LHON patients will have one of 3 primary mitochondrial mutations,G3460A(A52T of ND1),G11778A(R340H of ND4)and T14484C(M64V of ND6).There is incomplete penetrance and a marked gender bias in the development of visual morbidity with approximately 50%of male carriers and 10%of female carriers developing optic neuropathy.Visual recovery can occur but is dependent on the mutation present with the highest level of visual recovery seen in patients who have the T14484C mutation.The 3 primary mutations are typically identified by individual end-point PCR-restriction fragment length polymorphism(RFLP)or individual targeted bi-directional Sanger sequencing reactions.The purpose of this study was to design a simple multiplex PCR-RFLP that could detect these 3 primary LHON mutations in one assay.Methods:PCR primers were designed to incorporate a MaeIII restriction site in the presence of 3460A and 14484C mutations with the 11778A mutation naturally incorporating a MaeIII site.A multiplex PCR-RFLP assay was developed to detect the 3 common mutations in a single assay.Synthetic LHON controls based on the mitochondrial genome harbouring the 3 common mutations were synthesized and cloned into plasmids to act as reliable assay controls.DNA from previously tested patients and the synthetic LHON controls were subjected to the multiplex PCR-RFLP assay.The RFLP products were detected by agarose gel electrophoresis.Results:The novel PCR-RFLP assay accurately detects the 3 primary mutations both in patient DNA and in synthesized DNA control samples with a simple visual mutation detection procedure.The synthesized DNA was demonstrated to be a robust control for the detection of LHON Mutations.Conclusion:In this paper,we describe a novel,robust and simple PCR-RFLP based method for the detection of mutations causing LHON,and report the generation of a series of LHON DNA controls suitable for all currently published assays.

Implications of mitochondrial DNA mutations and mitochondrial dysfunction in tumorigenesis

Alterations in oxidative phosphorylation resulting from mitochondriai dysfunction have long been hypothesized to be involved in tumorigenesis. Mitochondria have recently been shown to play an important role in regulating both programmed cell death and cell proliferation. Furthermore, mitochondrial DNA （mtDNA） mutations have been found in various cancer cells. However, the role of these mtDNA mutations in tumorigenesis remains largely unknown. This review focuses on basic mitochondrial genetics, mtDNA mutations and consequential mitochondrial dysfunction associated with cancer. The potential molecular mechanisms, mediating the pathogenesis from mtDNA mutations and mitochondrial dysfunction to tumorigenesis are also discussed.

Mitochondrial DNA Mutations Associated with Aminoglycoside Ototoxicity

The mitochondrial 12S rRNA has been shown to be the hot spot for mutations associated with both aminoglycoside-induced and non-syndromic hearing loss. Of all the mutations, the homoplasmic A1555G and C1494T mutations at a highly conserved decoding region in the 12S rRNA have been associated with aminoglycoside-induced and non-syndromic hearing loss in many families worldwide. The A1555G or C1494T mutation is expected to form novel 1494C-G1555 or 1494U-A1555 base-pair at the highly conserved A-site of 12S rRNA. These transitions make the secondary structure of this RNA more closely resemble the corresponding region of bacterial 16S rRNA. Thus, the new U-A or G-C pair in 12S rRNA created by the C1494T or A1555G transition facilitates the binding of aminoglycosides, thereby accounting for the fact that the exposure to aminoglycosides can induce or worsen hearing loss in individuals carrying these mutations. Furthermore, the growth defect and impairment of mitochondrial translation were observed in cell lines carrying the A1555G or C1494T mutation in the presence of high concentration of aminoglycosides. In addition, nuclear modifier genes and mitochondrial haplotypes modulate the phenotypic manifestation of the A1555G and C1494T mutations. These observations provide the direct genetic and biochemical evidences that the A1555G or C1494T mutation is a pathogenic mtDNA mutation associated with aminoglycoside-induced and nonsyndromic hearing loss. Therefore, these data have been providing valuable information and technology to predict which individuals are at risk for ototoxicity, to improve the safety of aminoglycoside antibiotic therapy, and eventually to decrease the incidence of deafness.

MitochondrialtRNA^(leu(UUR)) Gene Mutation and the DecreasedActivity of Cytochrom e c Oxidase in Preeclam psia

To explore the roles of mitochondria tRNA leu(UUR) gene mutation at nucleotide 3243 and the activity of cytochrome c oxidase in pathogenesis of preeclampsia, 57 patients with preeclampsia and 60 normotension pregnancy women were screened for tRNA leu(UUR) nt3243 A→G mutation with the method of polymers chain reaction (PCR) and restriction fragment length polymorphism. Cytochrome c oxidase activity was determined by measuring the rate of cyanide sensitive oxidation of reduced cytochrome c using luminosity photographer. The results showed that cytochrome c oxidase activity was significantly lower in the preeclampsia group (0.30±0.39/min, n = 32) than that in the controls (0.73±0.54/min, n = 26, P <0.01). The mitochondria DNA mutation at position 3243 was not found in our series. The results suggested that the decreased activity of cytochrome c oxidase might impair the energy production, leading to the mitochondria dysfunction and placenta dysfunction in preeclampsia patients. Mitochondria dysfunction may be involved in the pathogenesis of preeclampsia. The mutation of mitochondria DNA may not be the common contributor of preeclampsia in our series.

Late-onset mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes syndrome with mitochondrial DNA 3243A>G mutation masquerading as autoimmune encephalitis:A case report

BACKGROUND Here,we present a unique case of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes(MELAS)syndrome,which initially appeared to be autoimmune encephalitis and was ultimately confirmed as MELAS with the mitochondrial DNA 3243A>G mutation.CASE SUMMARY A 58-year-old female presented with acute-onset speech impediment and auditory hallucinations,symmetrical bitemporal lobe abnormalities,clinical and laboratory findings,and a lack of relevant prodromal history,which suggested diagnosis of autoimmune encephalitis.Further work-up,in conjunction with the patient’s medical history,family history,and lactate peak on brain lesions on magnetic resonance imaging,suggested a mitochondrial disorder.Mitochondrial genome analysis revealed the m.3243A>G variant in the MT-TL1 gene,which led to a diagnosis of MELAS syndrome.CONCLUSION This case underscores the importance of considering MELAS as a potential cause of autoimmune encephalitis even if patients are over 40 years of age,as the symptoms and signs are atypical for MELAS syndrome.

Somatic alterations in mitochondrial DNA and mitochondrial dysfunction in gastric cancer progression

Energy metabolism reprogramming was recently identified as one of the cancer hallmarks.One of the underlying mechanisms of energy metabolism reprogramming is mitochondrial dysfunction caused by mutations in nuclear genes or mitochondrial DNA(mtDNA).In the past decades,several types of somatic mtDNA alterations have been identified in gastric cancer.However,the role of these mtDNA alterations in gastric cancer progression remains unclear.In this review,we summarize recently identified somatic mtDNA alterations in gastric cancers as well as the relationship between these alterations and the clinicopathological features of gastric cancer.The causative factors and potential roles of the somatic mtDNA alterations in cancer progression are also discussed.We suggest that point mutations and mtDNA copy number decreases are the two most common mtDNA alterations that result in mitochondrial dysfunction in gastric cancers.The two primary mutation types(transition mutations and mononucleotide or dinucleotide repeat instability)imply potential causative factors.Mitochondrial dysfunction-generated reactive oxygen species may be involved in the malignant changes of gastric cancer.The search for strategies to prevent mtDNA alterations and inhibit the mitochondrial retrograde signaling will benefit the development of novel treatments for gastric cancer and other malignancies.

Detection of A3243G point mutation in mitochondrial DNA from 10 cases of MELAS

Objective To search for A3243G point mutations in mitochondrial DNA (mtDNA) from 10 cases of mitochondrial encephalomyopathy, lactic acidosis and strokelike episodes (MELAS) Methods Using PCR restriction analysis, we investigated A3243G point mutations in mtDNA of muscle and/or blood cells from 10 patients and their 8 maternal relatives We also quantitated the A3243G mtDNA in samples harboring the mutation Results A3243G point mutations were identified in all muscle and/or blood samples from 10 MELAS patients The proportion of mutant mtDNA was 10 8%-47 8% in blood (7 cases), and 39 4%-67 7% in muscle (5 cases) This ratio was invariably higher in muscle than in blood from two patients whose blood and muscle samples were both available Younger patients usually carried higher proportions of A3243G mutant mtDNA in blood Eight maternal relatives from 6 families were also examined Maternal transmission of the disease could be identified in one family No A3243G point mutations were found in mothers' blood from 3 families and siblings' blood from 2 families Conclusions All 10 MELAS patients were found to have the mtDNA A3243G mutation in their muscle and/or blood The A3243G mutation seems to be sporadic in 5 of the families examined, suggesting the mechanism of de novo mutation for the pathogenesis of their MELAS syndrome

Prevalence and clinical characteristics of mitochondrial tRNA leu^((UUR))mt 3243 A→G and ND-1 gene mt 3316 G→A mutations in Chinese patients with type 2 diabetes

Objective To assess the prevalence of mitochondrial Trna leu(uuR)gene mt 3243 A→G mutation and ND-1 gene mt 3316 G→A mutation in Chinese type 2 diabetes.Methods 716 randomly selected,unrelated patients with type 2 diabetes were screened for the mutation with a PCR-RFLP technique.Results Three individuals with mitochondrial Trna leu(UUR)gene mt 3243 A→G mutation were identified,representing approximately 0.4% of the type 2 patients screened.Further screening of first-degree relatives of these 3 patients identified another 4 affected carriers.In comparison with type 2 diabetic patients without the mutation,these 7 carriers of the mt3243 mutation had:1)an earlier diagnosis age of diabetes(38.0 ±10.1 year vs 53.4± 10.0 year,P＜0.001);2)lower Body Mass Index(BMI)(19.5±2.0 kg/m2vs 24.9± 10.9 kg/m2,P ＜ 0.0001);and 3)lower post-challenge insulin levels(Area under the curve of insulin levels during the Oral Glucose Tolerance Test(OGTT),2946 ± 1647.2 μlU· ml-1 vs 7469 ± 6647.7 μlU·ml-1,P ＜ 0.01).ND-1 gene mt 3316 G→A mutation was found in 16 patients with type 2 diabetes(2.2%)and 5 out 181 controls(2.7%)with normal glucose tolerance.Therefore,the frequency of the mutation was not different in patients and controls.Moreover,clinical characteristics such as age of onset of diabetes,BMI,and insulin levels were not different between diabetic patients with the mt 3316 mutation and those without it.Conclusions In this large cohort of Chinese Type 2 diabetes,the prevalence of mitochondrial Trna leu(UUR)gene mt 3243 A→G mutation was 0.4%,and the ND-1 gene mt 3316 G→A mutation is a polymorphism unrelated to diabetes.

Point mutations of muscle mitochondrial DNA from patients with mitochondrial encephalomyopathies

Objective To study the relation between point mutations at nt3243 and nt8344 of muscle mitochondrial DNA from patients with mitochondrial encephalomyopathies and phenotypes. Methods DNA was extracted from muscle specimens from 5 patients with mitochondrial encephalomyopathies and amplified by PCR method, using corresponding oligonucleotide primers. DNA fragments were digested with restriction enzymes BglⅠ and ApaⅠ, then the digested DNA fragments were analyzed with an electrophoresis method.Results The point mutation at nt3243 of mtDNA was found in 2 patients, one with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) and another with myoclonic epilepsy with ragged red fibers (MERRF). The point mutation at nt8344 was found in 2 patients with MERRF, including the one with point mutation at nt3243.Conclusion The point mutation of DNA at nt3243 correlated with MELAS and nt8344 correlated with MERRF. In addition, the detection of point mutations at both nt3243 and nt8344 in a patient with MERRF shows the association of mutation with diversity in clinical manifestations of mitochondrial encephalomyopathies.

A Mitochondrial DNA A8701G Mutation Associated with Maternally Inherited Hypertension and Dilated Cardiomyopathy in a Chinese Pedigree of a Consanguineous Marriage

Background： Cardiovascular diseases, including dilated cardiomyopathy （DCM） and hypertension, are the leading cause of death worldwide.The role of mitochondrial DNA （mtDNA） in the pathogenesis of these diseases has not been completely clarified.In this study, we evaluate whether A8701G mutation is associated with maternally inherited hypertension and DCM in a Chinese pedigree of a consanguineous marriage.Methods： Fourteen subjects in a three-generation Han Chinese family with hypertension and DCM, in which consanguineous marriage was present in the parental generation, were interviewed.We divided all the family members into case （7 maternal members） and control group （7 nonmaternal members） for comparison.Clinical evaluations and sequence analysis ofmtDNA were obtained from all participants.Frequency differences between maternal and nonmaternal members were tested to locate the disease-associated mutations.Results： The majority of the family members presented with a maternal inheritance of hypertension and DCM.Sequence analysis of mtDNA in this pedigree identified eight mtDNA mutations.Among the mutations identified, there was only one significant mutation： A8701G （P =0.005）, which is a homoplasmic mitochondrial missense mutation in all the matrilineal relatives.There was no clear evidence for any synergistic effects between A8701G and other mutations.Conclusions： A8701G mutation may act as an inherited risk factor for the matrilineal transmission of hypertension and DCM in conj unction with genetic disorders caused by consanguineous marriage.

Clinical and Molecular Characteristics in 100 Chinese Pediatric Patients with m.3243A〉G Mutation in Mitochondrial DNA

Background： Mitochondrial diseases are a group of energy metabolic disorders with multisystem involvements. Variable clinical features present a major challenge in pediatric diagnoses. We summarized the clinical spectrum of m.3243A〉G mutation in Chinese pediatric patients, to define the common clinical manifestations and study the correlation between heteroplasmic degree of the mutation and clinical severity of the disease. Methods： Clinical data of one-hundred pediatric patients with symptomatic mitochondrial disease harboring m.3243A〉G mutation from 2007 to 2013 were retrospectively reviewed. Detection of m.3243A〉G mutation ratio was performed by polymerase chain reaction （PCR）-restriction fragment length polymorphism. Correlation between m.3243A〉G mutation ratio and age was evaluated. The differences in clinical symptom frequency of patients with low, middle, and high levels of mutation ratio were analyzed by Chi-square test. Results： Sixty-six patients （66%） had suffered a delayed diagnosis for an average of 2 years. The most frequent symptoms were seizures （76%）, short stature （73%）, elevated plasma lactate （70%）, abnormal magnetic resonance imaging/computed tomography （MRI/CT） changes （68%）, vomiting （55%）, decreased vision （52%）, headache （50%）, and muscle weakness （48%）. The mutation ratio was correlated negatively with onset age （r = -0.470, P 〈 0.001）. Myopathy was more frequent in patients with a high level of mutation ratio. However, patients with a low or middle level of m.3243A〉G mutation ratio were more likely to suffer hearing loss, decreased vision, and gastrointestinal disturbance than patients with a high level of mutation ratio. Conclusions： Our study showed that half of Chinese pediatric patients with m.3243A〉G mutation presented seizures, short stature, abnormal MRI/CT changes, elevated plasma lactate, vomiting, and headache. Pediatric patients with these recurrent symptoms should be considered for screening m.3243A〉G mutation. Clinical manifestations and laboratory abnormalities should be carefully monitored in patients with this point mutation.

Relationship between mutations of mitochondrial DNA ND1 gene and type 2 diabetes

Background Recent studies have indicated that many mutations in mitochondrial (mt)DNA NDI gene region are related to diabetes mellitus. In this study we explored the relationship between various mtDNA ND1 gene mutations and type 2 diabetes mellitus (DM) among Chinese. Methods Using PCR restriction fragment length polymorphism (PCR-RFLP) analysis and gene sequencing, 4 spots of mtDNA (nt3243, nt3316, nt3394, nt3426) were screened in 478 diabetics and 430 non-diabetic subjects.Results In diabetic group, there were 13 carriers (2.72%)of 3316 G→A mutation,12 (2.51%) of 3394 T→C mutation and 2 (0.42%) of 3426A→G mutation. In controls, only 3394 T→C mutation was observed in 2 subjects (0.47%). There was significant difference in the frequency of 3316 and 3394 mutation between two groups (P<0.05, respectively). More subjects with mitochondrial DNA ND1 gene mutations had DM family history and greater tendency of maternal inheritance when compared to those patients without mutation in diabetic group(P<0.01). A 3426 mutation diabetic pedigree was studied, and we found 12 maternal members in the family had the same mutation. Conclusion mtDNA ND1 gene mutations at nt3316 (G→A), nt3394 (T→C) and 3426 (A→G) might contribute to the pathogenesis of DM with other genetic factors and environment factors.