Mitochondrial enzyme deficiencies in Down's syndrome

Down syndrome is an oxidative phosphorylation disorder

Down syndrome is the most common genomic disorder of intellectual disability and is caused by trisomy of chromosome 21. Several genes in this chromosome repress mitochondrial biogenesis. The goal of this study was to evaluate whether early overexpression of these genes may cause a prenatal impairment of oxidative phosphorylation negatively affecting neurogenesis. Reduction in the mitochondrial energy production and a lower mitochondrial function have been reported in diverse tissues or cell types, and also at any age, including early fetuses, suggesting that a defect in oxidative phosphorylation is an early and general event in Down syndrome individuals. Moreover, many of the medical conditions associated with Down syndrome are also frequently found in patients with oxidative phosphorylation disease. Several drugs that enhance mitochondrial biogenesis are nowadays available and some of them have been already tested in mouse models of Down syndrome restoring neurogenesis and cognitive defects. Because neurogenesis relies on a correct mitochondrial function and critical periods of brain development occur mainly in the prenatal and early neonatal stages, therapeutic approaches intended to improve oxidative phosphorylation should be provided in these periods.

Meta-analysis of metabolites involved in bioenergetic pathways reveals a pseudohypoxic state in Down syndrome

Clinical observations and preclinical studies both suggest that Down syndrome (DS) may be associated with significant metabolic and bioenergetic alterations. However, the relevant scientific literature has not yet been systematically reviewed. The aim of the current study was to conduct a meta-analysis of metabolites involved in bioenergetics pathways in DS to conclusively determine the difference between DS and control subjects. We discuss these findings and their potential relevance in the context of pathogenesis and experimental therapy of DS. Articles published before July 1, 2020, were identified by using the search terms “Down syndrome” and “metabolite name” or “trisomy 21” and “metabolite name”. Moreover, DS-related metabolomics studies and bioenergetics literature were also reviewed. 41 published reports and associated databases were identified, from which the descriptive information and the relevant metabolomic parameters were extracted and analyzed. Mixed effect model revealed the following changes in DS: significantly decreased ATP, CoQ10, homocysteine, serine, arginine and tyrosine; slightly decreased ADP; significantly increased uric acid, succinate, lactate and cysteine; slightly increased phosphate, pyruvate and citrate. However, the concentrations of AMP, 2,3-diphosphoglycerate, glucose, and glutamine were comparable in the DS vs. control populations. We conclude that cells of subjects with DS are in a pseudo-hypoxic state: the cellular metabolic and bio-energetic mechanisms exhibit pathophysiological alterations that resemble the cellular responses associated with hypoxia, even though the supply of the cells with oxygen is not disrupted. This fundamental alteration may be, at least in part, responsible for a variety of functional deficits associated with DS, including reduced exercise difference, impaired neurocognitive status and neurodegeneration.

mitoXplorer, a visual data mining platform to systematically analyze and visualize mitochondrial expression dynamics and mutations

Mitochondria participate in metabolism and signaling. They adapt to the requirements of various cell types. Publicly available expression data permit to study expression dynamics of genes with mitochondrial function (mito-genes) in various cell types, conditions and organisms. Yet, we lack an easy way of extracting these data for mito-genes. Here, we introduce the visual data mining platform mitoXplorer, which integrates expression and mutation data of mito-genes with a manually curated mitochondrial interactome containing ∼1200 genes grouped in 38 mitochondrial processes. User-friendly analysis and visualization tools allow to mine mitochondrial expression dynamics and mutations across various datasets from four model species including human. To test the predictive power of mitoXplorer, we quantify mito-gene expression dynamics in trisomy 21 cells, as mitochondrial defects are frequent in trisomy 21. We uncover remarkable differences in the regulation of the mitochondrial transcriptome and proteome in one of the trisomy 21 cell lines, caused by dysregulation of the mitochondrial ribosome and resulting in severe defects in oxidative phosphorylation. With the newly developed Fiji plugin mitoMorph, we identify mild changes in mitochondrial morphology in trisomy 21. Taken together, mitoXplorer (http://mitoxplorer.ibdm.univ-mrs.fr) is a user-friendly, web-based and freely accessible software, aiding experimental scientists to quantify mitochondrial expression dynamics.

Study on amniotic fluid metabolism in the second trimester of Trisomy 21

BACKGROUND

Trisomy 21 is a common aneuploid condition in humans and accounts for approximately one quarter of all aneuploid live births. To date, early diagnosis of Trisomy 21 remains a challenging task. Metabolomics may prove an innovative tool to study the early pathophysiology of Trisomy 21 at a functional level.

METHODS

Ultra-performance liquid chromatography coupled with mass spectrometer (UPLC-MS) was used for untargeted metabolomic analysis of amniotic fluid samples from women having normal and trisomy 21 fetuses.

RESULTS

Many significantly changed metabolites were identified between amniotic fluid samples from Trisomy 21 pregnancies and normal euploid pregnancies, such as generally lower levels of several steroid hormones and their derivatives, higher levels of glutathione catabolites coupled with lower levels of gamma-glutamyl amino acids, and increased levels of phospholipid catabolites, sugars, and dicarboxylic acids. The identification of a human milk oligosaccharide in amniotic fluid may worth further investigation, since confirmation of this observation may have significant implications for regulation of fetal development.

CONCLUSIONS

The metabolisms in amniotic fluid from Trisomy 21 and normal pregnancies are quite different, and some of the significantly changed metabolites may be considered as candidates of early diagnostic biomarkers for Trisomy 21.

The re-emerging pathophysiological role of the cystathionine-β-synthase - hydrogen sulfide system in Down syndrome

Down syndrome (DS) is associated with significant perturbances in many morphological and biochemical features. Cystathionine-β-synthase (CBS) is one of the key mammalian enzymes that is responsible for the biological production of the gaseous transmitter hydrogen sulfide (H₂ S). When H₂ S is overproduced, it can exert detrimental cellular effects, in part due to inhibition of mitochondrial Complex IV activity. An increased expression of CBS and the consequent overproduction of H₂ S are well documented in individuals with DS. Two decades ago, it has been proposed that a toxic overproduction of H₂ S importantly contributes to the metabolic and neurological deficits associated with DS. However, until recently, this hypothesis has not yet been tested experimentally. Recent data generated in human dermal fibroblasts show that DS cells overproduce H₂ S, which, in turn, suppresses mitochondrial Complex IV activity and impairs mitochondrial oxygen consumption and ATP generation. Therapeutic CBS inhibition lifts the tonic (and reversible) suppression of Complex IV: This results in the normalization of mitochondrial function in DS cells. H₂ S may also contribute to the cellular dysfunction via several other molecular mechanisms through interactions with various mitochondrial and extramitochondrial molecular targets. The current article provides a historical background of the field, summarizes the recently published data and their potential implications, and outlines potential translational approaches (such as CBS inhibition and H₂ S neutralization) and future experimental studies in this re-emerging field of pathobiochemistry.

Overproduction of H2S, generated by CBS, inhibits mitochondrial Complex IV and suppresses oxidative phosphorylation in Down syndrome

Down syndrome (DS) is associated with significant perturbances in mitochondrial function. Here we tested the hypothesis that the suppression of mitochondrial electron transport in DS cells is due to high expression of cystathionine-β-synthase (CBS) and subsequent overproduction of the gaseous transmitter hydrogen sulfide (H₂S). Fibroblasts from DS individuals showed higher CBS expression than control cells; CBS localization was both cytosolic and mitochondrial. DS cells produced significantly more H₂S and polysulfide and exhibited a profound suppression of mitochondrial electron transport, oxygen consumption, and ATP generation. DS cells also exhibited slower proliferation rates. In DS cells, pharmacological inhibition of CBS activity with aminooxyacetate or siRNA-mediated silencing of CBS normalized cellular H₂S levels, restored Complex IV activity, improved mitochondrial electron transport and ATP synthesis, and restored cell proliferation. Thus, CBS-derived H₂S is responsible for the suppression of mitochondrial function in DS cells. When H₂S overproduction is corrected, the tonic suppression of Complex IV is lifted, and mitochondrial electron transport is restored. CBS inhibition offers a potential approach for the pharmacological correction of DS-associated mitochondrial dysfunction.

Diagnosis of 'possible' mitochondrial disease: an existential crisis

Primary genetic mitochondrial diseases are often difficult to diagnose, and the term 'possible' mitochondrial disease is used frequently by clinicians when such a diagnosis is suspected. There are now many known phenocopies of mitochondrial disease. Advances in genomic testing have shown that some patients with a clinical phenotype and biochemical abnormalities suggesting mitochondrial disease may have other genetic disorders. In instances when a genetic diagnosis cannot be confirmed, a diagnosis of 'possible' mitochondrial disease may result in harm to patients and their families, creating anxiety, delaying appropriate diagnosis and leading to inappropriate management or care. A categorisation of 'diagnosis uncertain', together with a specific description of the metabolic or genetic abnormalities identified, is preferred when a mitochondrial disease cannot be genetically confirmed.

Novel Metabolic Abnormalities in the Tricarboxylic Acid Cycle in Peripheral Cells From Huntington's Disease Patients

Metabolic dysfunction is well-documented in Huntington's disease (HD). However, the link between the mutant huntingtin (mHTT) gene and the pathology is unknown. The tricarboxylic acid (TCA) cycle is the main metabolic pathway for the production of NADH for conversion to ATP via the electron transport chain (ETC). The objective of this study was to test for differences in enzyme activities, mRNAs and protein levels related to the TCA cycle between lymphoblasts from healthy subjects and from patients with HD. The experiments utilize the advantages of lymphoblasts to reveal new insights about HD. The large quantity of homogeneous cell populations permits multiple dynamic measures to be made on exactly comparable tissues. The activities of nine enzymes related to the TCA cycle and the expression of twenty-nine mRNAs encoding for these enzymes and enzyme complexes were measured. Cells were studied under baseline conditions and during metabolic stress. The results support our recent findings that the activities of the pyruvate dehydrogenase complex (PDHC) and succinate dehydrogenase (SDH) are elevated in HD. The data also show a large unexpected depression in MDH activities. Furthermore, message levels for isocitrate dehydrogenase 1 (IDH1) were markedly increased in in HD lymphoblasts and were responsive to treatments. The use of lymphoblasts allowed us to clarify that the reported decrease in aconitase activity in HD autopsy brains is likely due to secondary hypoxic effects. These results demonstrate the mRNA and enzymes of the TCA cycle are critical therapeutic targets that have been understudied in HD.

Evaluation of extracellular adenine nucleotides hydrolysis in platelets and biomarkers of oxidative stress in Down syndrome individuals

PURPOSE

Down syndrome (DS) is caused by the triplication of chromosome 21. Studies have demonstrated platelets abnormalities and oxidative stress in DS subjects. The enzymes NTPDase, 5'-nucleotidase and adenosine deaminase (ADA) represent an important therapeutic target since they interfere in the extracellular nucleotide pool altering platelet functions. In this study, we evaluated the ectonucleotidases activities and oxidative stress parameters in samples of DS and healthy individuals.

METHODS AND RESULTS

The population consisted of 28 subjects with DS and 28 healthy subjects as a control group. Blood was obtained from each subject and used for platelet and serum preparation. NTPDase activity using ATP as substrate was increased in platelets of DS patients in relation to the control group; however, no alterations were observed in the ADP hydrolysis. A decrease in the 5'-nucleotidase activity and an increase in the ADA activity was observed in platelet of DS subjects when compared to healthy individuals (P<0.05). The lipid peroxidation and total thiol content was decreased in serum of DS individuals. Furthermore, superoxide dismutase and catalase activities were increased in whole blood of this group (P<0.05).

CONCLUSION

Alterations in the ectonucleotidase activities in platelets as well as changes in the oxidative stress parameters may contribute to the clinical features of DS.

A Female Patient with Down Syndrome and Low-Penetrance Leber's Hereditary Optic Neuropathy

We present the case of a 19-year-old female with a history of Down syndrome (DS) who was referred to our neuro-ophthalmology clinic for evaluation of Leber's hereditary optic neuropathy (LHON). The patient's family history was significant for a known G11778A mutation in a maternal relative, consistent with LHON. The patient was also positive for the G11778A mutation; however, the genotype demonstrated low penetrance in the pedigree, with only 1 out of 10 adult male offspring showing signs or symptoms of the disease. Mitochondrial mutations implicated in LHON have been shown to impair complex I of the electron transport chain and thereby reducing the effective generation of adenosine triphosphate and increasing the production of toxic reactive oxygen species. Although the partial or complete triplicate of chromosome 21 constitutes the etiology of DS, some of the pleiotropic phenotypes of the syndrome have been attributed to oxidative stress and mitochondrial dysfunction. Given the low penetrance of the mutation and the patient's sex, this case illustrates the possibility that the mitochondrial mutation demonstrated increased penetrance due to pre-existing mitochondrial dysfunction related to DS.

Redox proteomics analysis of HNE-modified proteins in Down syndrome brain: clues for understanding the development of Alzheimer disease

Down syndrome (DS) is the most common genetic cause of intellectual disability, due to partial or complete triplication of chromosome 21. DS subjects are characterized by a number of abnormalities including premature aging and development of Alzheimer disease (AD) neuropathology after approximately 40 years of age. Several studies show that oxidative stress plays a crucial role in the development of neurodegeneration in the DS population. Increased lipid peroxidation is one of the main events causing redox imbalance within cells through the formation of toxic aldehydes that easily react with DNA, lipids, and proteins. In this study we used a redox proteomics approach to identify specific targets of 4-hydroxynonenal modifications in the frontal cortex from DS cases with and without AD pathology. We suggest that a group of identified proteins followed a specific pattern of oxidation in DS vs young controls, probably indicating characteristic features of the DS phenotype; a second group of identified proteins showed increased oxidation in DS/AD vs DS, thus possibly playing a role in the development of AD. The third group of comparison, DS/AD vs old controls, identified proteins that may be considered specific markers of AD pathology. All the identified proteins are involved in important biological functions including intracellular quality control systems, cytoskeleton network, energy metabolism, and antioxidant response. Our results demonstrate that oxidative damage is an early event in DS, as well as dysfunctions of protein-degradation systems and cellular protective pathways, suggesting that DS subjects are more vulnerable to oxidative damage accumulation that might contribute to AD development. Further, considering that the majority of proteins have been already demonstrated to be oxidized in AD brain, our results strongly support similarities with AD in DS.

Defective mitochondrial function in vivo in skeletal muscle in adults with Down's syndrome: a 31P-MRS study

Down's syndrome (DS) is a developmental disorder associated with intellectual disability (ID). We have previously shown that people with DS engage in very low levels of exercise compared to people with ID not due to DS. Many aspects of the DS phenotype, such as dementia, low activity levels and poor muscle tone, are shared with disorders of mitochondrial origin, and mitochondrial dysfunction has been demonstrated in cultured DS tissue. We undertook a phosphorus magnetic resonance spectroscopy ((31)P-MRS) study in the quadriceps muscle of 14 people with DS and 11 non-DS ID controls to investigate the post-exercise resynthesis kinetics of phosphocreatine (PCr), which relies on mitochondrial respiratory function and yields a measure of muscle mitochondrial function in vivo. We found that the PCr recovery rate constant was significantly decreased in adults with DS compared to non-DS ID controls (1.7 ± 0.1 min(-1) vs 2.1 ± 0.1 min(-1) respectively) who were matched for physical activity levels, indicating that muscle mitochondrial function in vivo is impaired in DS. This is the first study to investigate mitochondrial function in vivo in DS using (31)P-MRS. Our study is consistent with previous in vitro studies, supporting a theory of a global mitochondrial defect in DS.

Platelet mitochondrial function: from regulation of thrombosis to biomarker of disease

Circulating blood platelets contain small numbers of fully functional mitochondria. Accumulating evidence demonstrates that these mitochondria regulate the pro-thrombotic function of platelets through not only energy generation, but also redox signalling and the initiation of apoptosis. Beyond its regulation of haemostasis, platelet mitochondrial function has also traditionally been used to identify and study mitochondrial dysfunction in human disease, owing to the easy accessibility of platelets compared with other metabolically active tissues. In the present article, we provide a brief overview of what is currently known about the function of mitochondria in platelets and review how platelet mitochondria have been used to study mitochondrial function in human disease.

Mitochondrial Factors and VACTERL Association-Related Congenital Malformations

VACTERL/VATER association is a group of congenital malformations characterized by at least 3 of the following findings: vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies, and limb abnormalities. To date, no unifying etiology for VACTERL/VATER association has been established, and there is strong evidence for causal heterogeneity. VACTERL/VATER association has many overlapping characteristics with other congenital disorders that involve multiple malformations. In addition to these other conditions, some of which have known molecular causes, certain aspects of VACTERL/VATER association have similarities with the manifestations of disorders caused by mitochondrial dysfunction. Mitochondrial dysfunction can result from a number of distinct causes and can clinically manifest in diverse presentations; accurate diagnosis can be challenging. Case reports of individuals with VACTERL association and confirmed mitochondrial dysfunction allude to the possibility of mitochondrial involvement in the pathogenesis of VACTERL/VATER association. Further, there is biological plausibility involving mitochondrial dysfunction as a possible etiology related to a diverse group of congenital malformations, including those seen in at least a subset of individuals with VACTERL association.

Lymphocyte respiration in children with Trisomy 21

Background

This study measured lymphocyte mitochondrial O₂ consumption (cellular respiration) in children with trisomy 21.

Methods

Peripheral blood mononuclear cells were isolated from whole blood of trisomy 21 and control children and these cells were immediately used to measure cellular respiration rate. [O₂] was determined as a function of time from the phosphorescence decay rates (1/τ) of Pd (II)-meso-tetra-(4-sulfonatophenyl)-tetrabenzoporphyrin. In sealed vials containing lymphocytes and glucose as a respiratory substrate, [O₂] declined linearly with time, confirming the zero-order kinetics of O₂ conversion to H₂O by cytochrome oxidase. The rate of respiration (k, in μM O₂ min^-1), thus, was the negative of the slope of [O₂] vs. time. Cyanide inhibited O₂ consumption, confirming that oxidation occurred in the mitochondrial respiratory chain.

Results

For control children (age = 8.8 ± 5.6 years, n = 26), the mean (± SD) value of k_c (in μM O₂ per min per 10⁷ cells) was 1.36 ± 0.79 (coefficient of variation, Cv = 58%; median = 1.17; range = 0.60 to 3.12; -2SD = 0.61). For children with trisomy 21 (age = 7.2 ± 4.6 years, n = 26), the values of k_c were 0.82 ± 0.62 (Cv = 76%; median = 0.60; range = 0.20 to 2.80), p<0.001. Similar results (p<0.000) were obtained after excluding the five trisomy 21 children with elevated serum TSH (values >6.1 mU/L). Fourteen of 26 (54%) children with trisomy 21 had k_c values of 0.20 to 0.60 (i.e., <−2SD). The values of k_c positively correlated with body-mass index (BMI, R >0.302), serum creatinine (R >0.507), blood urea nitrogen (BUN, R >0.535) and albumin (R >0.446).

Conclusions

Children with trisomy 21 in this study have reduced lymphocyte bioenergetics. The clinical importance of this finding requires further studies.

Oxidative Stress and Down Syndrome: A Route toward Alzheimer-Like Dementia

Down syndrome (DS) is one of the most frequent genetic abnormalities characterized by multiple pathological phenotypes. Indeed, currently life expectancy and quality of life for DS patients have improved, although with increasing age pathological dysfunctions are exacerbated and intellectual disability may lead to the development of Alzheimer's type dementia (AD). The neuropathology of DS is complex and includes the development of AD by middle age, altered free radical metabolism, and impaired mitochondrial function, both of which contribute to neuronal degeneration. Understanding the molecular basis that drives the development of AD is an intense field of research. Our laboratories are interested in understanding the role of oxidative stress as link between DS and AD. This review examines the current literature that showed oxidative damage in DS by identifying putative molecular pathways that play a central role in the neurodegenerative processes. In addition, considering the role of mitochondrial dysfunction in neurodegenerative phenomena, results demonstrating the involvement of impaired mitochondria in DS pathology could contribute a direct link between normal aging and development of AD-like dementia in DS patients.

Mitochondrial dysfunction and Down's syndrome: is there a role for coenzyme Q(10) ?

Structural changes and abnormal function of mitochondria have been documented in Down's syndrome (DS) cells, patients, and animal models. DS cells in culture exhibit a wide array of functional mitochondrial abnormalities including reduced mitochondrial membrane potential, reduced ATP production, and decreased oxido-reductase activity. New research has also brought to central stage the prominent role of oxidative stress in this condition. This review focuses on recent advances in the field with a particular emphasis on novel translational approaches involving the utilization of coenzyme Q(10) (CoQ(10) ) to treat a variety of clinical phenotypes associated with DS that are linked to increased oxidative stress and energy deficits. CoQ(10) has already provided promising results in several different conditions associated with altered energy metabolism and oxidative stress in the CNS. Two studies conducted in Ancona investigated the effect of CoQ(10) treatment on DNA damage in DS patients. Although the effect of CoQ(10) was evidenced only at single cell level, the treatment affected the distribution of cells according to their content in oxidized bases. In fact, it produced a strong negative correlation linking cellular CoQ(10) content and the amount of oxidized purines. Results suggest that the effect of CoQ(10) treatment in DS not only reflects antioxidant efficacy, but likely modulates DNA repair mechanisms.

Down's syndrome and myocardial reperfusion injury

Down syndrome is known to be an independent risk factor for mortality after surgical repair of congenital heart anomalies. It is also associated with neurodegenerative disease and accelerated aging. The mechanism of the latter features has been attributed to abnormal handling of oxygen-free radicals as well as mitochondrial dysfunction. These properties also place the child with Down syndrome at a risk of an exaggerated myocardial ischemia/reperfusion injury. A 6 month old child with Down syndrome is reported who suffered from obvious clinical ischemia/reperfusion injury following an uncomplicated repair of complete AV canal. Both intraoperative as well as postoperative echocardiography documented a satisfactory technical repair. After resting the heart on ECMO the child's myocardial function returned to normal. The mechanisms by which patients with Down syndrome are at risk of ischemia/reperfusion injury are reviewed. Future studies should focus on specific approaches for myocardial protection in the child with Down syndrome undergoing cardiac surgery.

Impairment of F1F0-ATPase, adenine nucleotide translocator and adenylate kinase causes mitochondrial energy deficit in human skin fibroblasts with chromosome 21 trisomy

A central role for mitochondrial dysfunction has been proposed in the pathogenesis of DS (Down's syndrome), a multifactorial disorder caused by trisomy of human chromosome 21. To explore whether and how abnormalities in mitochondrial energy metabolism are involved in DS pathogenesis, we investigated the catalytic properties, gene expression and protein levels of certain proteins involved in mitochondrial ATP synthesis, such as F1F0-ATPase, ANT (adenine nucleotide translocator) and AK (adenylate kinase), in DS-HSF (human skin fibroblasts with trisomic karyotype), comparing them with euploid fibroblasts. In DS-HSF, we found a strong impairment of mitochondrial ATP synthesis due to a reduction in the catalytic efficiency of each of the investigated proteins. This impairment occurred in spite of unchanged gene expression and an increase in ANT and AK protein content, whereas the amount of ATPase subunits was selectively reduced. Interestingly, exposure of DS-HSF to dibutyryl-cAMP, a permanent derivative of cAMP, stimulated ANT, AK and ATPase activities, whereas H89, a specific PKA (protein kinase A) inhibitor, suppressed this cAMPdependent activation, indicating an involvement of the cAMP/PKA-mediated signalling pathway in the ATPase, ANT and AK deficit. Consistently, DS-HSF showed decreased basal levels of cAMP and reduced PKA activity. Despite the impairment of mitochondrial energy apparatus, no changes in cellular energy status, but increased basal levels of L-lactate, were found in DS-HSF, which partially offset for the mitochondrial energy deficit by increasing glycolysis and mitochondrial mass.These results provide new insight into the molecular basis for mitochondrial dysfunction in DS and might provide a molecular explanation for some clinical features of the syndrome.

Oxygen uptake kinetics during exercise in adults with Down syndrome

Persons with Down syndrome (DS) have diminished submaximal and peak work capacity. This study evaluated the dynamic response of oxygen uptake at onset and recovery (VO(2) kinetics) of constant-load exercise (moderate intensity 45% VO(2peak)) in adults with DS. A total of 27 healthy participants aged 18-50 years performed graded treadmill exercise to assess peak VO(2): 14 with DS (9 males and 5 females) and 13 controls without disabilities (9 males and 4 females). Subjects also performed constant-load exercise tests at 45% VO(2peak) to determine VO(2) on-transient and VO(2) off-transient responses. Peak VO(2) was lower in participants with DS as compared to controls (DS 30.2 ± 7.1; controls 46.1 ± 9.6 mL kg(-1) min(-1), P < 0.05). In contrast, at 45% VO(2peak), the time constants for the VO(2) on-transients (DS 34.6 ± 9.1; controls 37.6 ± 9.0 s) and VO(2) off-transients (DS 36.5 ± 12.3; controls 37.7 ± 7.0 s) were not significantly different between the groups. Additionally, there were no differences between on-transient and off-transient time constants in participants with DS or controls. These data demonstrate that the VO(2) kinetics at onset and recovery of moderate intensity exercise is similar between adults with DS and controls. Therefore, the submaximal exercise performance of these individuals is not affected by slowed VO(2) kinetics.

Mitochondrial dysfunction in some oxidative stress-related genetic diseases: Ataxia-Telangiectasia, Down Syndrome, Fanconi Anaemia and Werner Syndrome

Oxidative stress is a phenotypic hallmark in several genetic disorders characterized by cancer predisposition and/or propensity to premature ageing. Here we review the published evidence for the involvement of oxidative stress in the phenotypes of Ataxia-Telangiectasia (A-T), Down Syndrome (DS), Fanconi Anaemia (FA), and Werner Syndrome (WS), from the viewpoint of mitochondrial dysfunction. Mitochondria are recognized as both the cell compartment where energetic metabolism occurs and as the first and most susceptible target of reactive oxygen species (ROS) formation. Thus, a critical evaluation of the basic mechanisms leading to an in vivo pro-oxidant state relies on elucidating the features of mitochondrial impairment in each disorder. The evidence for different mitochondrial dysfunctions reported in A-T, DS, and FA is reviewed. In the case of WS, clear-cut evidence linking human WS phenotype to mitochondrial abnormalities is lacking so far in the literature. Nevertheless, evidence relating mitochondrial dysfunctions to normal ageing suggests that WS, as a progeroid syndrome, is likely to feature mitochondrial abnormalities. Hence, ad hoc research focused on elucidating the nature of mitochondrial dysfunction in WS pathogenesis is required. Based on the recognized, or reasonably suspected, role of mitochondrial abnormalities in the pathogenesis of these disorders, studies of chemoprevention with mitochondria-targeted supplements are warranted.

Long-term outcome of laparoscopic cystogastrostomy performed using a posterior approach with a stapling device

BACKGROUND

Internal drainage of an acute pancreatic pseudocyst is indicated 6 weeks after its first detection. Laparoscopic treatment of pancreatic pseudocysts enables definitive drainage with faster recovery. Pseudocysts located adjacent to the posterior gastric wall are best drained by pseudocyst gastrostomy. Although the anterior approach for drainage has frequently been reported, reports on the posterior approach are rare.

METHODS

Seven patients underwent laparoscopic cystogastrostomy for pancreatic pseudocysts. The posterior approach that enables the direct visualization of the posterior gastric wall and pseudocyst was used, and the cyst was drained with a needle. After creating a sufficient drainage orifice, the cyst was thoroughly debrided. Cystogastrostomy was performed using the posterior approach with a stapling device. The insertion site of the stapling device closed using a hernia stapler.

RESULTS

Cystogastrostomy was performed using the posterior approach with a stapling device in all patients, without requiring conversion to the anterior approach or open surgery. There were neither operative complications nor late recurrences during the follow-up period (median 65 months).

CONCLUSION

Laparoscopic cystogastrostomy using the posterior approach, which facilitates adequate internal drainage, is a safe and feasible procedure for pancreatic pseudocyst, and it is not accompanied with a risk of recurrence in the long term.

Impact of ER gene polymorphisms on overweight and obesity in Down Syndrome

The impact of ER XbaI and PvuII α gene polymorphisms on overweight and obesity were studied in 77 subjects with Down Syndrome (DS), of which 32 were children (18 boys, 14 girls), mean age 8.7 ± 2.3 years, and 45 adolescents (28 boys, 17 girls) mean age 14 ± 2.5 years. Their lifestyle was compared to 40 healthy age-matched controls. DS subjects had significant lesser physical activity than controls (p<0.05) and a lower caloric intake than the recommended requirements, which was significantly lesser than controls (p<0.05). Body Mass Index (BMI), Arm Circumference (AC) and Triceps Skinfold Thickness (TST) were significantly higher in DS subjects than controls (p<0.05), while metabolic and cardiovascular parameters were not significantly different between the groups (p>0.05). The frequency of ER genotypes in DS subjects was compared with the healthy controls, finding that there was a high prevalence of XXER genotype in DS subjects. Children and adolescents with DS, lacking ER XbaI site, showed significantly higher BMI and body fat distribution than other XbaI genotypes. The lack of ER XbaI site can indicate added risk of obesity in DS. No differences in metabolic and cardiovascular parameters were observed among ER genotypes. However, childhood obesity is associated with increased cardiovascular risk.

Altered expression of mitochondrial and extracellular matrix genes in the heart of human fetuses with chromosome 21 trisomy

BACKGROUND

The Down syndrome phenotype has been attributed to overexpression of chromosome 21 (Hsa21) genes. However, the expression profile of Hsa21 genes in trisomic human subjects as well as their effects on genes located on different chromosomes are largely unknown. Using oligonucleotide microarrays we compared the gene expression profiles of hearts of human fetuses with and without Hsa21 trisomy.

RESULTS

Approximately half of the 15,000 genes examined (87 of the 168 genes on Hsa21) were expressed in the heart at 18-22 weeks of gestation. Hsa21 gene expression was globally upregulated 1.5 fold in trisomic samples. However, not all genes were equally dysregulated and 25 genes were not upregulated at all. Genes located on other chromosomes were also significantly dysregulated. Functional class scoring and gene set enrichment analyses of 473 genes, differentially expressed between trisomic and non-trisomic hearts, revealed downregulation of genes encoding mitochondrial enzymes and upregulation of genes encoding extracellular matrix proteins. There were no significant differences between trisomic fetuses with and without heart defects.

CONCLUSION

We conclude that dosage-dependent upregulation of Hsa21 genes causes dysregulation of the genes responsible for mitochondrial function and for the extracellular matrix organization in the fetal heart of trisomic subjects. These alterations might be harbingers of the heart defects associated with Hsa21 trisomy, which could be based on elusive mechanisms involving genetic variability, environmental factors and/or stochastic events.

Drosophila melanogaster homolog of Down syndrome critical region 1 is critical for mitochondrial function

Mitochondrial dysfunction has emerged as a common theme that underlies numerous neurological disorders, including Down syndrome. Down syndrome cultures and tissues show mitochondrial damage such as impaired mitochondrial enzyme activities, defective mitochondrial DNA repairs and accumulation of toxic free radicals, but the cause of mitochondrial dysfunction remains elusive. Here we demonstrate that the Drosophila melanogaster homolog of human Down syndrome critical region gene 1 (DSCR1), nebula (also known as sarah, sra), has a crucial role in the maintenance of mitochondrial function and integrity. We report that nebula protein is located in the mitochondria. An alteration in the abundance of nebula affects mitochondrial enzyme activities, mitochondrial DNA content, and the number and size of mitochondria. Furthermore, nebula interacts with the ADP/ATP translocator and influences its activity. These results identify nebula/DSCR1 as a regulator of mitochondrial function and integrity and further suggest that an increased level of DSCR1 may contribute to the mitochondrial dysfunction seen in Down syndrome.

Neurodegenerative disorders associated with diabetes mellitus

More than 20 syndromes among the significant and increasing number of degenerative diseases of neuronal tissues are known to be associated with diabetes mellitus, increased insulin resistance and obesity, disturbed insulin sensitivity, and excessive or impaired insulin secretion. This review briefly presents such syndromes, including Alzheimer disease, ataxia-telangiectasia, Down syndrome/trisomy 21, Friedreich ataxia, Huntington disease, several disorders of mitochondria, myotonic dystrophy, Parkinson disease, Prader-Willi syndrome, Werner syndrome, Wolfram syndrome, mitochondrial disorders affecting oxidative phosphorylation, and vitamin B(1) deficiency/inherited thiamine-responsive megaloblastic anemia syndrome as well as their respective relationship to malignancies, cancer, and aging and the nature of their inheritance (including triplet repeat expansions), genetic loci, and corresponding functional biochemistry. Discussed in further detail are disturbances of glucose metabolism including impaired glucose tolerance and both insulin-dependent and non-insulin-dependent diabetes caused by neurodegeneration in humans and mice, sometimes accompanied by degeneration of pancreatic beta-cells. Concordant mouse models obtained by targeted disruption (knock-out), knock-in, or transgenic overexpression of the respective transgene are also described. Preliminary conclusions suggest that many of the diabetogenic neurodegenerative disorders are related to alterations in oxidative phosphorylation (OXPHOS) and mitochondrial nutrient metabolism, which coincide with aberrant protein precipitation in the majority of affected individuals.

Glucose/mitochondria in neurological conditions

Impairments of glucose and mitochondrial function are important causes of brain dysfunction and therefore of brain disease. Abnormalities have been found in association with disease of the nervous system in most of the components of glucose/mitochondrial metabolism. In many, molecular genetic abnormalities have been defined. Brain glucose oxidation is abnormal in common diseases of the nervous system, including Alzheimer disease and other dementias, Parkinson disease, delirium, probably schizophrenia and other psychoses, and of course cerebrovascular disease. Defects in a single component and even a single mutation can be associated with different clinical phenotypes. The same clinical phenotype can result from different genotypes. The complex relationship between biological abnormality in brain glucose utilization and clinical disorder is similar to that in other disorders that have been intensively studied at the genetic level. Genes for components of the pathways of brain glucose oxidation are good candidate genes for disease of the brain. Preliminary data support the proposal that treatments to normalize abnormalities in brain glucose oxidation may benefit many patients with common brain diseases.

Risk factors for the neurohumoral alterations underlying personality disturbances

Numerous studies have shown that MAO-B activity in platelets correlates with specific personality characteristics such as sensation seeking and impulsiveness. Low levels of platelet MAO as well as the personality traits associated with these low levels have been associated with type 2 alcoholism, recurrent criminality and antisocial violent behavior. Platelet MAO has a high degree of heritability and regulation of MAOB gene expression seems to explain most of the inter-individual differences in activity. The transcription factor family AP-2 is an important regulatory factor for neural gene expression and neural development, especially in midbrain structures, including the monoaminergic nuclei. In man, the gene encoding AP-2beta contains a polymorphic region in the second intron, consisting of a variable number of tandem repeats [CAAA](4-5). The long AP-2beta allele has previously been associated with specific personality traits as well as with binge-eating disorder characterized by an impulsive temperament. We have shown that males and females homozygous for the long AP-2beta allele display significantly lower platelet MAO activity compared to subjects with one or two short alleles. Thus, we find it likely that the personality disturbances previously linked to low platelet MAO activity could be associated with the presence of two long alleles of the AP-2beta gene. We suggest that the molecular mechanisms underlying the association between platelet MAO and vulnerability, e.g. substance abuse, may involve specific transcription factors that regulate the expression of midbrain monoamine structures as well as that of platelet MAO.

Decreased protein levels of complex I 30-kDa subunit in fetal Down syndrome brains

Defects of mitochondrial electron transport enzymes have been implicated in the pathogenesis of several neurodegenerative diseases. In previous work, we reported decreased protein levels of mitochondrial electron transport enzyme subunits in adult brain with Down syndrome (DS). However it is not clear whether cellular damage due to mitochondrial defects in brain of DS fetus begins in utero. Here we investigated the protein levels of mitochondrial electron transport enzymes in fetal DS brain using the proteomic technologies. Two-dimensional (2-D) gel electrophoresis, matrix-assisted laser desorption ionization mass spectroscopy (MALDI-MS) and specific software for quantification were used. The protein levels of complex I 30-kDa subunit were significantly decreased in cerebral cortex of fetal DS brain. We conclude that decreased mitochondrial electron transport enzyme subunits in fetal DS brains could contribute to the impaired energy and free radical metabolism affecting brain development in DS fetus. Furthermore, the defects of mitochondrial electron enzymes shown in adult DS brains could begin in utero and continue during the life span of the individual with DS.

Genetic mechanisms of behavior--don't forget about the transcription factors

Major changes in psychiatric phenotypes due to genetic factors are seldom the result of single gene polymorphisms, but more often the result of several genetic mechanisms. In this millennium article we discuss the notion that the expression of numerous candidate genes could be regulated by the same transcription factors, and that polymorphisms in transcription factor genes might explain some phenotypes. We describe recent results of studies on the biological marker thrombocyte monoamine oxidase (trbc MAO) and the transcription factor AP-2beta. Low levels of trbc MAO is associated with temperamental characteristics such as sensation seeking and impulsiveness, and the enzyme is genetically regulated by specific transcriptional mechanisms. Transcription factor AP-2beta is important for the development of midbrain structures and AP-2beta has several binding sites in the regulatory regions of genes encoding key proteins in the monoamine transmitter systems. We have recently shown AP-2beta to be linked to personality, binge-eating disorder, treatment with antidepressant drugs, and also to trbc MAO. Regardless of whether transcriptions factors, such as AP-2beta, regulate the expression of eg, the number of monoamine neurons or a variety of candidate genes within the monoamine systems, or both, we would like to emphasize the role of transcription factors, besides polymorphisms in monoaminergic candidate genes, when explaining inter-individual differences in temperament and psychiatric vulnerability.

Differential display reveals deteriorated mRNA levels of NADH3 (complex I) in cerebellum of patients with Down syndrome

Although gene hunting has been carried out in Down Syndrome (DS) cells, information on expressional differences in DS brain is limited. We have recently described expressional differences in fetal DS brain but cannot assign these findings to "DS per" se or simply to "neurodegeneration". We therefore performed gene hunting in cerebellum of adult patients with DS and Alzheimer's disease (AD) neuropathology, AD and controls. The gene hunting method used was differential display and pools of the individual groups were examined to rule out allelic differences. Differential display revealed the absence of a band, identified by sequencing and gene bank work as matching the NADH3 gene (99.1% identity) in cerebellum of DS patients. Dot blots showed the presence of NADH3 signals in only two out of 7 DS patients. We show at the transcriptional level that a mitochondrial enzyme, the complex I, NADH3, is significantly downregulated in DS cerebellum. This extends previous work on deficiencies of the electron transport chain in platelets of patients with DS.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Transcription factor binding to the core promoter of the human monoamine oxidase B gene in the cerebral cortex and in blood cells

Many studies show that monoamine oxidase B in blood cells is a biological marker for personality characteristics such as sensation seeking. The mechanism underlying this association is so far not explored. In the present study we have performed electrophoretic mobility-shift assays to investigate the pattern of protein binding to a 150 bp fragment of the proximal 5'-flanking region of the human monoamine oxidase B gene. We compared the pattern using nuclear extracts from human brain and lymphocytes. Interestingly, a correlation was observed between monoamine oxidase B enzyme activity in blood cells (platelets) and the binding pattern of two uncharacterized transcription factors. These data are well in line with the long-standing notion that interindividual differences in platelet monoamine oxidase may represent differences in expression of the enzyme rather than genotypic variation.

Recent developments in the molecular genetics of mitochondrial disorders

Rapid progress has been made in the identification of mitochondrial DNA mutations which are typically associated with diseases of the nervous system and muscle. The well established mitochondrial disorders are maternally inherited and males and females are equally affected. An exception is Leber's hereditary optic atrophy (LHON) which is observed much more frequently in males than in females. There are three common point mutations in LHON which can be homoplasmic or heteroplasmic. In mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) most mutations are single base changes and lie within the tRNA-Leu gene. Point mutations in myoclonic epilepsy with ragged red fibres (MERRF) usually occur within the tRNA-Lys gene but mutations of the tRNA-Leu gene are also observed. MELAS and MERRF mutations are heteroplasmic and there is considerable clinical overlap between these diseases. Point mutations within the ATPase6 gene result in either neuropathy, ataxia and retinitis pigmentosa (NARP) or in Leigh's syndrome. The latter occurs if the mutation is present in the majority of mitochondria (extreme heteroplasmy). Finally, mitochondrial DNA deletions are the cause underlying Kearns-Sayre syndrome (KSS). Apart from the well-established mitochondrial diseases, there is increasing evidence that mitochondrial mutations may also play a role in the neurodegenerative disorders Parkinson, Alzheimer and Huntington disease. The complex I defect found in Parkinson disease is especially interesting in this respect. However, no causative mitochondrial mutation has as yet been established in any of these three common disorders.

Molecular cloning and characterization of the human mitochondrial NADH:oxidoreductase 10-kDa gene (NDUFV3)

The human gene for the 10-kDa flavoprotein subunit of the mitochondrial NADH:ubiquinone oxidoreductase (Complex I) was completely cloned and sequenced. The so-called NDUFV3 gene contains three exons, spanning 20 kb. The open reading frame contains a 34-codon import sequence and a 74-codon mature protein sequence. A database search revealed close homology to bovine and rat protein sequence but not to any other known protein. Northern blot analysis showed that the NDUFV3 gene is ubiquitously expressed. The NDUFV3 gene was assigned by FISH to a single location on chromosome 21q22.3 and might contribute to the Down syndrome phenotype.

Calcium homeostasis and reactive oxygen species production in cells transformed by mitochondria from individuals with sporadic Alzheimer's disease

Alzheimer's disease (AD) is associated with defects in mitochondrial function. Mitochondrial-based disturbances in calcium homeostasis, reactive oxygen species (ROS) generation, and amyloid metabolism have been implicated in the pathophysiology of sporadic AD. The cellular consequences of mitochondrial dysfunction, however, are not known. To examine these consequences, mitochondrially transformed cells (cybrids) were created from AD patients or disease-free controls. Mitochondria from platelets were fused to rho0 cells created by depleting the human neuroblastoma line SH-SY5Y of its mitochondrial DNA (mtDNA). AD cybrids demonstrated a 52% decrease in electron transport chain (ETC) complex IV activity but no difference in complex I activity compared with control cybrids or SH-SY5Y cells. This mitochondrial dysfunction suggests a transferable mtDNA defect associated with AD. ROS generation was elevated in the AD cybrids. AD cybrids also displayed an increased basal cytosolic calcium concentration and enhanced sensitivity to inositol-1,4, 5-triphosphate (InsP3)-mediated release. Furthermore, they recovered more slowly from an elevation in cytosolic calcium induced by the InsP3 agonist carbachol. Mitochondrial calcium buffering plays a major role after this type of perturbation. beta-amyloid (25-35) peptide delayed the initiation of calcium recovery to a carbachol challenge and slowed the recovery rate. Nerve growth factor reduced the carbachol-induced maximum and moderated the recovery kinetics. Succinate increased ETC activity and partially restored the AD cybrid recovery rate. These subtle alterations in calcium homeostasis and ROS generation might lead to increased susceptibility to cell death under circumstances not ordinarily toxic.