Highly asymmetrical distribution of muscle wasting correlates to the heteroplasmy in a patient carrying a large-scale mitochondrial DNA deletion: a novel pathophysiological mechanism for explaining asymmetry in mitochondrial myopathies.

Mitochondrial diseases are a heterogeneous group of pathologies, caused by missense mutations, sporadic large-scale deletions of mitochondrial DNA (mtDNA) or mutations of nuclear maintenance genes. We report the case of a patient in whom extended muscle pathology, biochemical and genetic mtDNA analyses have proven to be essential to elucidate a unique asymmetrical myopathic presentation. From the age of 34 years on, the patient has presented with oculomotor disorders, right facial peripheral palsy and predominantly left upper limb muscle weakness and atrophy. By contrast, he displayed no motor weakness on the right hemi-body, and no sensory symptoms, cerebellar syndrome, hypoacusis, or parkinsonism. Cardiac function was normal. CK levels were elevated (671 UI/L). Electroneuromyography (ENMG) and muscle MRI showed diffuse myogenic alterations, more pronounced on the left side muscles. Biopsy of the left deltoid muscle showed multiple mitochondrial defects, whereas in the right deltoid, mitochondrial defects were much less marked. Extended mitochondrial biochemical and molecular workup revealed a unique mtDNA deletion, with a 63.4% heteroplasmy load in the left deltoid, versus 8.1% in the right one. This case demonstrates that, in mitochondrial myopathies, heteroplasmy levels may drastically vary for the same type of muscle, rising the hypothesis of a new pathophysiological mechanism explaining asymmetry in hereditary myopathies.

Mitochondrial DNA content reduction in the most fertile spermatozoa is accompanied by increased mitochondrial DNA rearrangement.

STUDY QUESTION: Is there an association between male fertility and spermatozoa mitochondrial DNA (mtDNA) copy number and genome rearrangements? SUMMARY ANSWER: Normal spermatozoa not only have a lower mtDNA copy number but also more DNA rearrangements than spermatozoa of men with severe oligoasthenospermia (SOA). WHAT IS KNOWN ALREADY: While there is a consensus that mtDNA content is decreased in the most fertile spermatozoa, the role of mtDNA sequence alteration in male infertility is unclear. High-throughput sequencing, which allows an exhaustive analysis of mtDNA rearrangements and mutations, could be helpful in this context, but has yet to be used. STUDY DESIGN, SIZE, DURATION: This is an observational study of semen samples obtained from 44 men undergoing ART at an academic infertility centre in France, from October 2018 to November 2020. The men were classified into two groups: 20 men in the SOA group and 24 men with normal semen parameters in the control group. PARTICIPANTS/MATERIALS, SETTING, METHODS: For each patient and control, mtDNA was isolated from sperm fractions from the 40% and 90% layers of the density gradient. The average mtDNA content of each sample was assessed using digital PCR. Deep sequencing was performed using next-generation sequencing. Signal processing and base calling were performed via the embedded pre-processing pipeline, the variants were analysed using an in-house workflow and a dedicated tool, based on soft-clipping, was used to study large mtDNA rearrangements. The distribution and the type of rearrangements and variants were compared between patients with SOA and controls on one hand, and between the 40% and 90% gradient layers, on the other hand. MAIN RESULTS AND THE ROLE OF CHANCE: The mtDNA content of spermatozoa in the SOA group was significantly higher than in the control group (P < 0.0001). Moreover, mtDNA content was significantly higher in spermatozoa from the 40% layer (the most fertile spermatozoa) compared to the 90% layer, both in the SOA (P = 0.02) and the control group (P < 0.0001). The frequency of large mtDNA deletions and duplications was significantly higher in the control group (P = 0.002). Most of these rearrangements are potentially related to DNA breaks and their number was reduced by the removal of the linear mtDNA from the samples. Heteroplasmic variants were found more frequently in the SOA group (P = 0.05) and in the 40% layer (P = 0.03), but none had any obvious functional consequence. LIMITATIONS, REASONS FOR CAUTION: Our findings are novel and significant but should be verified in larger cohorts and other types of male infertility. WIDER IMPLICATIONS OF THE FINDINGS: Our findings suggest that sperm mtDNA rearrangements are not necessarily associated with mitochondrial dysfunction and male infertility. Instead, they seem to be concomitant with the process of mtDNA content reduction in the most potentially fertile spermatozoa. Furthermore, they refute the hypothesis that, in the case of mtDNA alteration, a compensatory mechanism allows an increase in mtDNA copy number to rectify the energy deficit. The increased frequency of mtDNA rearrangements in the most fertile spermatozoa is a novel result that offers new insight into the relation between sperm quality and mtDNA. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by Angers University Hospital (grant AOI CHU Angers 2018), Angers University and the French national research centres INSERM and CNRS. There are no competing interests. TRIAL REGISTRATION NUMBER: N/A.

The mitochondrial DNA content of cumulus cells may help predict embryo implantation.

PURPOSE: The quantification of mtDNA in cumulus granulosa cells (CGCs) surrounding an oocyte has been positively linked with morphological embryonic quality. In the present study, we evaluated the link between the amount of mtDNA in CGCs surrounding an oocyte and the chances for the corresponding embryo of implanting and leading to an ongoing pregnancy. METHODS: This is an observational study, performed on 84 oocyte-cumulus-complexes (OCCs) having led to the replacement of an embryo in the maternal uterus, retrieved from 71 patients undergoing IVF with intracytoplasmic sperm. The OCCs were classified in two groups, one including 26 OCCs having led to an implanted embryo and the other including 58 OCCs having led to a non-implanted embryo. The average mtDNA content of CGCs was assessed by using a quantitative real-time PCR technique. RESULTS: Significantly higher mtDNA copy numbers in CGCs were associated with implanted embryos than with non-implanted embryos (mean 215 [sd 375] and 59 [sd 72], respectively; p < 104). Multivariate analysis, taking into account the women's age, the embryo quality, and the AMH level, suggests an independent relationship between the mtDNA content of CGCs and the potential of embryo implantation. CONCLUSION: During in vitro fertilization (IVF) procedures, the probability of the implantation of the embryo appears to be closely correlated to the mtDNA copy numbers in the CGCs. Our results highlight the interest of mtDNA quantification in GCGs as a biomarker of the potential of embryo implantation.

Mitochondrial complex I defect resulting from exercise-induced lower limb ischemia in patients with peripheral arterial disease.

This study aims to compare the structural and mitochondrial alterations between muscle segments affected by exercise-induced ischemia and segments of the same muscle without ischemia, in the same subject. In a prospective analysis, 34 patients presenting either peripheral arterial disease or chronic coronary syndrome without any evidence of peripheral arterial disease were eligible for inclusion based on findings indicating a need for either a femoro-popliteal bypass or a saphenous harvesting for coronary bypass. Before surgery, we assessed the level of exercise-induced ischemia in proximal and distal sections of the thigh by the measurement of transcutaneous oxygen pressure during an exercise treadmill test. Distal and proximal biopsies of the sartorius muscle were procured during vascular surgical procedures to assess mitochondrial function and morphometric parameters of the sartorius myofibers. Comparisons were made between the distal and proximal biopsies, with respect to these parameters. Thirteen of the study patients that initially presented with peripheral arterial disease had evidence of an isolated distal thigh exercise-induced ischemia, associated with a 35% decrease in the mitochondrial complex I enzymatic activity in the distal muscle biopsy. This defect was also associated with a decreased expression of the manganese superoxide dismutase enzyme and with alterations of the shapes of the myofibers. No functional or structural alterations were observed in the patients with coronary syndrome. We validated a specific model ischemia in peripheral arterial disease characterized by muscular alterations. This "Distal-Proximal-Sartorius Model" would be promising to explore the physiopathological consequences specific to chronic ischemia. NEW & NOTEWORTHY We compared proximal versus distal biopsies of the sartorius muscle in patients with superficial femoral artery stenosis or occlusion and proof of, distal only, regional blood flow impairment with exercise oximetry. We identified a decrease in the mitochondrial complex I enzymatic activity and antioxidant system impairment at the distal level only. We validate a model to explore the physiopathological consequences of chronic muscle ischemia.

Targeted metabolomics reveals reduced levels of polyunsaturated choline plasmalogens and a smaller dimethylarginine/arginine ratio in the follicular fluid of patients with a diminished ovarian reserve.

STUDY QUESTION: Does the metabolomic profile of the follicular fluid (FF) of patients with a diminished ovarian reserve (DOR) differ from that of patients with a normal ovarian reserve (NOR)? SUMMARY ANSWER: The metabolomic signature of the FF reveals a significant decrease in polyunsaturated choline plasmalogens and methyl arginine transferase activity in DOR patients compared to NOR patients. WHAT IS KNOWN ALREADY: The composition of the FF reflects the exchanges between the oocyte and its microenvironment during its acquisition of gametic competence. Studies of the FF have allowed identification of biomarkers and metabolic pathways involved in various pathologies affecting oocyte quality, but no large metabolomic analysis in the context of ovarian ageing and DOR has been undertaken so far. STUDY DESIGN, SIZE, DURATION: This was an observational study of the FF retrieved from 57 women undergoing in vitro fertilization at the University Hospital of Angers, France, from November 2015 to September 2016. The women were classified in two groups: one including 28 DOR patients, and the other including 29 NOR patients, serving as controls. PARTICIPANTS/MATERIALS, SETTING, METHODS: Patients were enrolled in the morning of oocyte retrieval after ovarian stimulation. Once the oocytes were isolated for fertilization and culture, the FF was pooled and centrifuged for analysis. A targeted quantitative metabolomic analysis was performed using high-performance liquid chromatography coupled with tandem mass spectrometry, and the Biocrates Absolute IDQ p180 kit. The FF levels of 188 metabolites and several sums and ratios of metabolic significance were assessed by multivariate and univariate analyses. MAIN RESULTS AND THE ROLE OF CHANCE: A total of 136 metabolites were accurately quantified and used for calculating 23 sums and ratios. Samples were randomly divided into training and validation sets. The training set, allowed the construction of multivariate statistical models with a projection-supervised method, i.e. orthogonal partial least squares discriminant analysis (OPLS-DA), applied to the full set of metabolites, or the penalized least absolute shrinkage and selection operator with logistic regression (LASSO-LR), applied to the ratios and sums of the metabolites. Both multivariate models showed good predictive performances when applied to the validation set. The final penalized model retained the three most significant variables, i.e. the total dimethylarginine-to-arginine ratio (Total DMA/Arginine), the sum of the polyunsaturated choline plasmalogens (PUFA ae), and the patient's age. The negative coefficients of Total DMA/Arginine and PUFA ae indicated that these FF variables had lower values in DOR patients than in NOR patients. LARGE SCALE DATA: N/A. LIMITATIONS REASONS FOR CAUTION: This study presents two limitations. First, with this targeted metabolomics analysis, we have explored only a limited portion of the FF metabolome. Second, although the signature found was highly significant, the mechanism underlying the dysfunction remains undetermined. WIDER IMPLICATIONS OF THE FINDINGS: The understanding of the mechanisms implied in ovarian ageing is essential for providing an adequate response to affected women desiring pregnancy. Our study proposes an incoming signature that may open new paths towards this goal. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by the University Hospital of Angers, the University of Angers, and the French national research centers, INSERM and the CNRS. There were no competing interests.

Deep sequencing shows that oocytes are not prone to accumulate mtDNA heteroplasmic mutations during ovarian ageing.

STUDY QUESTION: Does ovarian ageing increase the number of heteroplasmic mitochondrial DNA (mtDNA) point mutations in oocytes? SUMMARY ANSWER: Our results suggest that oocytes are not subject to the accumulation of mtDNA point mutations during ovarian ageing. WHAT IS KNOWN ALREADY: Ageing is associated with the alteration of mtDNA integrity in various tissues. Primary oocytes, present in the ovary since embryonic life, may accumulate mtDNA mutations during the process of ovarian ageing. STUDY DESIGN, SIZE, DURATION: This was an observational study of 53 immature oocyte-cumulus complexes retrieved from 35 women undergoing IVF at the University Hospital of Angers, France, from March 2013 to March 2014. The women were classified in two groups, one including 19 women showing signs of ovarian ageing objectified by a diminished ovarian reserve (DOR), and the other, including 16 women with a normal ovarian reserve (NOR), which served as a control group. PARTICIPANTS/MATERIALS, SETTING, METHODS: mtDNA was extracted from isolated oocytes, and from their corresponding cumulus cells (CCs) considered as a somatic cell compartment. The average mtDNA content of each sample was assessed by using a quantitative real-time PCR technique. Deep sequencing was performed using the Ion Torrent Proton for Next-Generation Sequencing. Signal processing and base calling were done by the embedded pre-processing pipeline and the variants were analyzed using an in-house workflow. The distribution of the different variants between DOR and NOR patients, on one hand, and oocyte and CCs, on the other, was analyzed with the generalized mixed linear model to take into account the cluster of cells belonging to a given mother. MAIN RESULTS AND THE ROLE OF CHANCE: There were no significant differences between the numbers of mtDNA variants between the DOR and the NOR patients, either in the oocytes (P = 0.867) or in the surrounding CCs (P = 0.154). There were also no differences in terms of variants with potential functional consequences. De-novo mtDNA variants were found in 28% of the oocytes and in 66% of the CCs with the mean number of variants being significantly different (respectively 0.321, SD = 0.547 and 1.075, SD = 1.158) (P < 0.0001). Variants with a potential functional consequence were also overrepresented in CCs compared with oocytes (P = 0.0019). LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: Limitations may be due to the use of immature oocytes discarded during the assisted reproductive technology procedure, the small size of the sample, and the high-throughput sequencing technology that might not have detected heteroplasmy levels lower than 2%. WIDER IMPLICATIONS OF THE FINDINGS: The alteration of mtDNA integrity in oocytes during ovarian ageing is a recurring question to which our pilot study suggests a reassuring answer. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the University Hospital of Angers, the University of Angers, France, and the French national research centers, INSERM and the CNRS. There are nocompeting interests.

The mitochondrial DNA content of cumulus granulosa cells is linked to embryo quality.

STUDY QUESTION: Could the mitochondrial DNA (mtDNA) content of cumulus granulosa cells (CGCs) be related to oocyte competence? SUMMARY ANSWER: The quality of embryos obtained during IVF procedures appears to be linked to mtDNA copy numbers in the CGCs. WHAT IS KNOWN ALREADY: Oocyte quality is linked to oocyte mtDNA content in the human and other species, and the mtDNA copy number of the oocyte is related to that of the corresponding CGCs. Moreover, the quantification of CGC mtDNA has recently been proposed as a biomarker of embryo viability. STUDY DESIGN SIZE, DURATION: An observational study was performed on 452 oocyte-cumulus complexes retrieved from 62 patients undergoing ICSI at the ART Center of the University Hospital of Angers, France, from January to May 2015. PARTICIPANTS/MATERIALS, SETTING, METHODS: The average mtDNA content of CGCs was assessed by using a quantitative real-time PCR technique. The relationship between CGC mtDNA content and oocyte maturity and fertilizability, on one hand, and embryo quality, on the other, was investigated using univariate and multivariate generalized models with fixed and mixed effects. MAIN RESULTS AND THE ROLE OF CHANCE: No relationship was found between CGC mtDNA content and oocyte maturity or fertilizability. In contrast, there was a significant link between the content of mtDNA in CGCs surrounding an oocyte and the embryo quality, with significantly higher mtDNA copy numbers being associated with good quality embryos compared with fair or poor quality embryos [interquartile range, respectively, 738 (250-1228) and 342 (159-818); P = 0.006]. However, the indication provided by the quantification of CGC mtDNA concerning the eventuality of good embryo quality was seriously subject to patient effect (AUC = 0.806, 95%CI = 0.719-0.869). The quantity of CGC mtDNA was influenced by BMI and smoking. LARGE SCALE DATA: N/A. LIMITATIONS REASONS FOR CAUTION: The quantification of CGC mtDNA may indicate embryo quality. However, since it is affected by patient specificity, it should be used with caution. It remains to be seen whether this marker could directly predict the implantation capacity of the embryo, which is the main objective in IVF practice. WIDER IMPLICATIONS OF THE FINDINGS: Our study suggests that the quantification of CGC mtDNA may be a novel biomarker of embryo viability. However, patient specificity makes it impossible to establish a general threshold value, valid for all patients. Nevertheless, further studies are needed to determine whether the quantification of CGC mtDNA may, in combination with the morpho-kinetic method, offer an additional criterion for selecting the best embryo for transfer from a given cohort. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the University Hospital of Angers, the University of Angers, France, and the French national research centres INSERM and the CNRS. There were no competing interests.

Multiethnic involvement in autosomal-dominant optic atrophy in Singapore.

PurposeAutosomal-dominant optic atrophy (ADOA), often associated with mutations in the OPA1 gene (chromosome 3q28-q29) is rarely reported in Asia. Our aim was to identify and describe this condition in an Asian population in Singapore.Patients and methodsPreliminary cross-sectional study at the Singapore National Eye Centre, including patients with clinical suspicion of ADOA, who subsequently underwent genetic testing by direct sequencing of the OPA1 gene.ResultsAmong 12 patients (10 families) with clinically suspected ADOA, 7 patients (5 families) from 3 different ethnic origins (Chinese, Indian, and Malay) carried a heterozygous pathogenic variant in the OPA1 gene. The OPA1 mutations were located on exons 8, 9, 11, and 17: c.869G>A (p.Arg290Glu), c.892A>G (p.Ser298Gly), c.1140G>A (splicing mutation), and c.1669C>T (p.Arg557*), respectively. One splicing mutation (c.871-1G>A) was identified in intron 8. We also identified a novel mutation causing optic atrophy and deafness (c.892A>G (p.Ser298Gly)). Among the phenotypic features, colour pupillometry disclosed a dissociation between low vision and preserved pupillary light reflex in ADOA.ConclusionWe report the first cases of genetically confirmed OPA1-related ADOA from Singapore, including a novel mutation causing 'ADOA plus' syndrome. Further epidemiological studies are needed in order to determine the prevalence of ADOA in South-East Asia.

Estrogens are needed for the improvement in endothelium-mediated dilation induced by a chronic increase in blood flow in rat mesenteric arteries.

Resistance arteries play a key role in the control of local blood flow. They undergo outward remodeling in response to a chronic increase in blood flow as seen in collateral artery growth in ischemic disorders. We have previously shown that mesenteric artery outward remodeling depends on the endothelial estrogen receptor alpha. As outward arterial remodeling is associated with improved endothelium-dependent dilation, we hypothesized that estrogens might also play a role in flow-mediated improvement of endothelium-dependent dilation. Local increase in blood flow in first order mesenteric arteries was obtained after ligation of adjacent arteries in three-month old ovariectomized female rats treated with 17-beta-estradiol (OVX+E2) or vehicle (OVX). After 2 weeks, diameter was equivalent in high flow (HF) than in normal flow (NF) arteries with a greater wall to lumen ratio in HF vessels in OVX rats. Acetylcholine-mediated relaxation was lower in HF than in NF vessels. eNOS and caveolin-1 expression level was equivalent in HF and NF arteries. By contrast, arterial diameter was 30% greater in HF than in NF arteries and the wall to lumen ratio was not changed in OVX+E2 rats. Acetylcholine-mediated relaxation was higher in HF than in NF arteries. The expression level of eNOS was higher and that of caveolin-1 was lower in HF than in NF arteries. Acetylcholine (NO-dependent)-mediated relaxation was partly inhibited by the NO-synthesis blocker L-NAME in OVX rats whereas L-NAME blocked totally the relaxation in OVX+E2 rats. Endothelium-independent relaxation (sodium nitroprusside) was equivalent in OXV and OVX+E2 rats. Similarly, serotonin- and phenylephrine-mediated contractions were higher in HF than in NF arteries in both OVX and OVX+E2 rats in association with high ratio of phosphorylated ERK1/2 to ERK1/2. Thus, we demonstrated the essential role of endogenous E2 in flow-mediated improvement of endothelium (NO)-mediated dilatation in rat mesenteric arteries.

Relationship between diminished ovarian reserve and mitochondrial biogenesis in cumulus cells.

STUDY QUESTION: What part do mitochondria play in cases of diminished ovarian reserve (DOR)? SUMMARY ANSWER: Mitochondrial biogenesis in cumulus cells may be linked with impaired oocyte competence in patients with DOR. WHAT IS KNOWN ALREADY: DOR, one of the causes of infertility even in young women, is characterized by the depletion of the ovarian pool associated with a decline in oocyte competence. Mitochondria, which play a role in oocyte quality, could be involved in the pathogenesis of DOR. The study of cumulus cells offers an interesting non-invasive approach for evaluating oocyte quality and the metabolic processes on which it depends. If mitochondrial dysfunction is involved in DOR, it is likely to have an impact on the functioning of cumulus cells. STUDY DESIGN, SIZE, DURATION: This is an observational study of 74 immature oocyte-cumulus complexes retrieved from 47 women undergoing in vitro fertilization with intracytoplasmic sperm injection at the University Hospital of Angers, France, from March 2013 to March 2014. The women were divided into two groups: one group included 26 women with DOR, and the other, which included 21 women with a normal ovarian reserve (NOR), served as a control group. PARTICIPANTS/MATERIALS, SETTINGS, METHODS: The oocyte mitochondrial content and the average mitochondrial content of the cumulus cells were assessed by mitochondrial (mt)DNA quantification using a quantitative real-time PCR technique. Microfluidic-based quantitative RT-PCR assays were used to quantify the expression of 13 genes involved in mitochondrial functions such as apoptosis and antioxidant activity or in mitochondrial biogenesis. We used orthogonal partial least-squares discriminant analysis (OPLS-DA) to distinguish between the DOR group and the NOR group of patients, and an OPLS model to predict the value of the oocyte mtDNA content that could be used as a critical marker of oocyte quality. MAIN RESULTS AND THE ROLE OF CHANCE: The OPLS-DA model showed a good predictive capability (Q2 = 0.543). Using the variable importance in projection (VIP) metric we found three mitochondrial variables distinguishing the DOR group from the NOR group of patients, i.e. the oocyte mtDNA content (VIP = 0.92), the cumulus cell mtDNA content (VIP = 0.95) and the expression in cumulus cells of peroxisome proliferator-activated receptor γ coactivator 1 alpha (PPARGC-1A) (VIP = 1.10), all of which were lower in the DOR group than in the NOR group of patients. The OPLS model was able to satisfactorily predict the oocyte mtDNA content in only the NOR group of patients (Q2 = 0.506). We found four new variables positively linked to the oocyte mitochondrial mass, i.e. the cumulus cell mtDNA content (VIP = 1.19), and the expression in cumulus cells of three factors of mitochondrial biogenesis: polymerase gamma (POLG) (VIP = 2.13), optic atrophy 1 (OPA1) (VIP = 1.89) and the transcription factor associated with mitochondria (TFAM) (VIP = 1.32). LIMITATIONS, REASONS OF CAUTION: This is a descriptive study. Because of ethical concerns in human clinical practice, this study has been performed only on immature oocytes and corresponding cumulus cells, which are usually discarded during in vitro fertilization procedures. WIDER IMPLICATIONS OF THE FINDINGS: Cumulus cells may govern mitochondrial biogenesis, creating an adequate oocyte mitochondrial pool to promote embryonic development. The alteration of this process in patients with DOR may account for the impairment of oocyte quality. This suggests that some mitochondrial characteristics of cumulus cells may serve as indicators of oocyte competence and that oocyte quality may be improved by products enhancing mitochondrial biogenesis. STUDY FUNDING/COMPETING INTERESTS: This work was supported by a grant from the University Hospital of Angers, France: 'Appel d'offre interne à la recherche 2014'. TRIAL REGISTRATION NUMBER: N/A.

Mitochondrial macro-haplogroup JT may play a protective role in ovarian ageing.

This study of 200 Caucasian women shows that the distribution of the mtDNA macro-haplogroups in patients with diminished ovarian reserve (DOR) differed significantly from that of patients with normal ovarian reserve (NOR) (p=0.02). The JT macro-haplogroup was significantly under-represented in DOR patients compared with NOR patients (p=0.006) and compared with the estimated frequency of 18.8% in the general French population (p=0.0012). Our findings suggest that the risk of a prematurely depleted ovarian reserve would be three times lower for patients carrying the JT macro-haplogroup than for patients with any of the other mtDNA haplogroups (odds ratio: 0.3; 95% CI: 0.13-0.74). If these preliminary results are confirmed in larger independent studies, they should lead to the better management of infertility.

Perspectives of drug-based neuroprotection targeting mitochondria.

Mitochondrial dysfunction has been reported in most neurodegenerative diseases. These anomalies include bioenergetic defect, respiratory chain-induced oxidative stress, defects of mitochondrial dynamics, increase sensitivity to apoptosis, and accumulation of damaged mitochondria with instable mitochondrial DNA. Significant progress has been made in our understanding of the pathophysiology of inherited mitochondrial disorders but most have no effective therapies. The development of new metabolic treatments will be useful not only for rare mitochondrial disorders but also for the wide spectrum of common age-related neurodegenerative diseases shown to be associated with mitochondrial dysfunction. A better understanding of the mitochondrial regulating pathways raised several promising perspectives of neuroprotection. This review focuses on the pharmacological approaches to modulate mitochondrial biogenesis, the removal of damaged mitochondria through mitophagy, scavenging free radicals and also dietary measures such as ketogenic diet.

Mitochondrial dysfunction affecting visual pathways.

Mitochondrial dysfunction leads to cellular energetic impairment, which may affect the visual pathways, from the retina to retrochiasmal structures. The most common mitochondrial optic neuropathies include Leber's hereditary optic neuropathy and autosomal dominant optic atrophy, but the optic nerve can be affected in other syndromic conditions, such as Wolfram syndrome and Friedreich's ataxia. These disorders may result from mutations in either the mitochondrial DNA or in the nuclear genes encoding mitochondrial proteins. Despite the inconstant genotype-phenotype correlations, a clinical classification of mitochondrial disorders may be made on the basis of distinct neuro-ophthalmic presentations such as optic neuropathy, pigmentary retinopathy and retrochiasmal visual loss. Although no curative treatments are available at present, recent advances throw new light on the pathophysiology of mitochondrial disorders. Current research raises hopes for novel treatment of hereditary optic neuropathies, particularly through the use of new drugs and mitochondrial gene therapy.

Key role of estrogens and endothelial estrogen receptor α in blood flow-mediated remodeling of resistance arteries.

OBJECTIVE: Flow- (shear stress-)mediated outward remodeling of resistance arteries is involved in collateral growth during postischemic revascularization. As this remodeling is especially important during pregnancy, we hypothesized that estrogens may be involved. A surgical model eliciting a local increase in blood flow in 1 mesenteric resistance artery was used in 3-month-old ovariectomized female rats either treated with 17-ß-estradiol (E2) or left untreated. METHODS AND RESULTS: After 14 days, arterial diameter was greater in high-flow arteries than in normal-flow vessels. An ovariectomy suppressed high-flow remodeling, while E2 restored it. High-flow remodeling was absent in mice lacking the estrogen receptor α but not estrogen receptor ß. The kinetics of inflammatory marker expression, macrophage infiltration, oxidative stress, and metaloproteinases expression were not altered by the absence of E2 after 2 and 4 days, that is, during remodeling. Nevertheless, E2 was required for the increase in endothelial nitric oxide synthase expression and activation at day 4 when diameter expansion occurs. Finally, the impact of E2 on the endothelium appeared crucial for high-flow remodeling, as this E2 action was abrogated in mice lacking endothelial NOS, as well as in Tie2-Cre(+) ERα(f/f) mice. CONCLUSIONS: We demonstrate the essential role of E2 and endothelial estrogen receptor α in flow-mediated remodeling of resistance arteries in vivo.

Natural disease course and genotype-phenotype correlations in Complex I deficiency caused by nuclear gene defects: what we learned from 130 cases.

Mitochondrial complex I is the largest multi-protein enzyme complex of the oxidative phosphorylation system. Seven subunits of this complex are encoded by the mitochondrial and the remainder by the nuclear genome. We review the natural disease course and signs and symptoms of 130 patients (four new cases and 126 from literature) with mutations in nuclear genes encoding structural complex I proteins or those involved in its assembly. Complex I deficiency caused by a nuclear gene defect is usually a non-dysmorphic syndrome, characterized by severe multi-system organ involvement and a poor prognosis. Age at presentation may vary, but is generally within the first year of life. The most prevalent symptoms include hypotonia, nystagmus, respiratory abnormalities, pyramidal signs, dystonia, psychomotor retardation or regression, failure to thrive, and feeding problems. Characteristic symptoms include brainstem involvement, optic atrophy and Leigh syndrome on MRI, either or not in combination with internal organ involvement and lactic acidemia. Virtually all children ultimately develop Leigh syndrome or leukoencephalopathy. Twenty-five percent of the patients died before the age of six months, more than half before the age of two and 75 % before the age of ten years. Some patients showed recovery of certain skills or are still alive in their thirties . No clinical, biochemical, or genetic parameters indicating longer survival were found. No clear genotype-phenotype correlations were observed, however defects in some genes seem to be associated with a better or poorer prognosis, cardiomyopathy, Leigh syndrome or brainstem lesions.

Correlation between genetic polymorphisms and stroke recovery: analysis of the GAIN Americas and GAIN International Studies.

BACKGROUND AND PURPOSE: Recovery after stroke occurs on the basis of specific molecular events. Genetic polymorphisms associated with impaired neural repair or plasticity might reduce recovery from stroke and might also account for some of the intersubject variability in stroke recovery. This study hypothesized that the ApoE ε4 polymorphism and the val(66) met polymorphism for brain-derived neurotrophic factor (BDNF) are each associated with poorer outcome after stroke. Associations with mitochondrial genotype were also explored. METHODS: Genotypes were determined in 255 stroke patients who also received behavioral evaluations in the Glycine Antagonist In Neuroprotection (GAIN) clinical trials. The primary outcome measure was recovery during the first month post-stroke, as this is the time when neural repair is at a maximum and so when genetic influences might have their largest impact. Two secondary outcome measures at 3 months post-stroke were also examined. RESULTS: Genotype groups were similar acutely post-stroke. Presence of the ApoE ε4 polymorphism was associated with significantly poorer recovery over the first month post-stroke (P = 0.023) and with a lower proportion of subjects with minimal or no disability (modified Rankin score 0-1, P = 0.01) at 3 months post-stroke. Indeed, those with this polymorphism were approximately half as likely to achieve minimal or no disability (18.2%) versus those with polymorphism absent (35.5%). Findings were confirmed in multivariate models. Results suggested possible effects from the val(66) met BDNF polymorphism and from the R0 mitochondrial DNA haplotype. CONCLUSIONS: Genetic factors, particularly the ApoE ε4 polymorphism, might contribute to variability in outcomes after stroke.

[Hereditary optic atrophies]. / Les atrophies optiques héréditaires.

INTRODUCTION: Hereditary optic neuropathies, resulting from retinal ganglion cell degeneration, are a heterogeneous group of diseases ranging from asymptomatic forms to legal blindness. STATE OF KNOWLEDGE: Two most frequent phenotypes are Kjer's disease, an autosomal dominant optic atrophy caused by OPA1 gene mutations, and Leber's disease due to maternally inherited mitochondrial DNA mutations. PROSPECTS AND CONCLUSION: Both optic neuropathies usually isolated are sometimes associated with extraocular symptoms, especially neurological symptoms, thus justifying a systematic neurological evaluation and brain imaging.

Mitochondrial DNA A3243G mutation involved in familial diabetes, chronic intestinal pseudo-obstruction and recurrent pancreatitis.

AIMS: To report on a family with five members who carry the A3243G mutation in mitochondrial tRNA for leucine 1 (MTTL1) and present with diabetes, chronic intestinal pseudo-obstruction (CIPO) and recurrent pancreatitis, and to screen for this mutation in a cohort of 36 unrelated patients with recurrent pancreatitis. METHODS: The mutation was quantified in several tissue samples from patients. Respiratory chain activity was studied in muscle biopsies and fibroblast cultures. In addition, the thymidine phosphorylase gene (TP) involved in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and three genes involved in chronic pancreatitis - PRSS1, SPINK1 and CFTR - were sequenced in affected patients. Finally, the MTTL1 gene was examined in 36 unrelated patients who had recurrent pancreatitis, but no mutations in the PRSS1 and SPINK1 genes. RESULTS: Heteroplasmy for the mtDNA A3243G mutation was found in all tissue samples from these patients, but no mutations were found in the genes coding for thymidine phosphorylase, PRSS1, SPINK1 and CFTR. Also, none of the 36 unrelated patients with recurrent pancreatitis were carrying any MTTL1 mutations. CONCLUSION: The mtDNA A3243G mutation associated with the gastrointestinal manifestations observed in the affected family should be regarded as a possible cause of CIPO and unexplained recurrent pancreatitis. However, the mutation is probably only weakly involved in cases of isolated recurrent pancreatitis.

Rapid identification of mitochondrial DNA (mtDNA) mutations in neuromuscular disorders by using surveyor strategy.

Mutations of mitochondrial genome are responsible for respiratory chain defects in numerous patients. We have used a strategy, based on the use of a mismatch-specific DNA endonuclease named " Surveyor Nuclease", for screening the entire mtDNA in a group of 50 patients with neuromuscular features, suggesting a respiratory chain dysfunction. We identified mtDNA mutations in 20% of patients (10/50). Among the identified mutations, four are not found in any mitochondrial database and have not been reported previously. We also confirm that mtDNA polymorphisms are frequently found in a heteroplasmic state (15 different polymorphisms were identified among which five were novel).