Manuela Grazina

Mitochondrial dysfunction in autism spectrum disorders: a population-based study

A minority of cases of autism has been associated with several different organic conditions, including bioenergetic metabolism deficiency. In a population-based study, we screened associated medical conditions in a group of 120 children with autism (current age range 11y 5mo to 14y 4mo, mean age 12y 11mo [SD 9.6mo], male:female ratio 2.9:1). Children were diagnosed using Diagnostic and Statistical Manual of Mental Disorders criteria, the Autism Diagnostic Interview--Revised, and the Childhood Autism Rating Scale; 76% were diagnosed with typical autism and 24% with atypical autism. Cognitive functional level was assessed with the Griffiths scale and the Wechsler Intelligence Scale for Children and was in the normal range in 17%. Epilepsy was present in 19 patients. Plasma lactate levels were measured in 69 patients, and in 14 we found hyperlactacidemia. Five of 11 patients studied were classified with definite mitochondrial respiratory chain disorder, suggesting that this might be one of the most common disorders associated with autism (5 of 69; 7.2%) and warranting further investigation.

Mitochondrial metabolism in Parkinson's disease impairs quality control autophagy by hampering microtubule-dependent traffic

Abnormal presence of autophagic vacuoles is evident in brains of patients with Parkinsons disease (PD), in contrast to the rare detection of autophagosomes in a normal brain. However, the actual cause and pathological significance of these observations remain unknown. Here, we demonstrate a role for mitochondrial metabolism in the regulation of the autophagy-lysosomal pathway in ex vivo and in vitro models of PD. We show that transferring mitochondria from PD patients into cells previously depleted of mitochondrial DNA is sufficient to reproduce the alterations in the autophagic system observed in PD patient brains. Although the initial steps of this pathway are not compromised, there is an increased accumulation of autophagosomes associated with a defective autophagic activity. We prove that this functional decline was originated from a deficient mobilization of autophagosomes from their site of formation toward lysosomes due to disruption in microtubule-dependent trafficking. This contributed directly to a decreased proteolytic flux of α-synuclein and other autophagic substrates. Our results lend strong support for a direct impact of mitochondria in autophagy as defective autophagic clearance ability secondary to impaired microtubule trafficking is driven by dysfunctional mitochondria. We uncover mitochondria and mitochondria-dependent intracellular traffic as main players in the regulation of autophagy in PD.

Mitochondrial-dependent apoptosis in Huntington's disease human cybrids

We investigated the involvement of mitochondrial-dependent apoptosis in Huntingtons disease (HD) vs. control (CTR) cybrids, obtained from the fusion of human platelets with mitochondrial DNA-depleted NT2 cells, and further exposed to 3-nitropropionic acid (3-NP) or staurosporine (STS). Untreated HD cybrids did not exhibit significant modifications in the activity of mitochondrial respiratory chain complexes I-IV or in mtDNA sequence variations suggestive of a primary role in mitochondrial susceptibility in the subpopulation of HD carriers studied. However, a slight decrease in mitochondrial membrane potential and increased formation of intracellular hydroperoxides was observed in HD cybrids under basal conditions. Furthermore, apoptotic nuclei morphology and a moderate increase in caspase-3 activation, as well as increased levels of superoxide ions and hydroperoxides were observed in HD cybrids upon 3-NP or STS treatment. 3-NP-evoked apoptosis in HD cybrids involved cytochrome c and AIF release from mitochondria, which was associated with mitochondrial Bax translocation. CTR cybrids subjected to 3-NP showed increased mitochondrial Bax and Bim levels and the release of AIF, but not cytochrome c, suggesting a different mode of cell death, linked to the loss of membrane integrity. Additionally, increased mitochondrial Bim and Bak levels, and a slight release of cytochrome c in untreated HD cybrids may help to explain their moderate susceptibility to mitochondrial-dependent apoptosis.

Genetic basis of Alzheimer's dementia: role of mtDNA mutations

Alzheimers disease (AD) is the most common neurodegenerative disorder associated to dementia in late adulthood. Amyloid precursor protein, presenilin 1 and presenilin 2 genes have been identified as causative genes for familial AD, whereas apolipoprotein E ɛ4 allele has been associated to the risk for late onset AD. However, mutations on these genes do not explain the majority of cases. Mitochondrial respiratory chain (MRC) impairment has been detected in brain, muscle, fibroblasts and platelets of Alzheimers patients, indicating a possible involvement of mitochondrial DNA (mtDNA) in the aetiology of the disease. Several reports have identified mtDNA mutations in Alzheimers patients, suggesting the existence of related causal factors probably of mtDNA origin, thus pointing to the involvement of mtDNA in the risk contributing to dementia, but there is no consensual opinion in finding the cause for impairment. However, mtDNA mutations might modify age of onset, contributing to the neurodegenerative process, probably due to an impairment of MRC and/or translation mechanisms.

Coenzyme Q10 deficiency in mitochondrial DNA depletion syndromes

We evaluated coenzyme Q₁₀ (CoQ) levels in patients studied under suspicion of mitochondrial DNA depletion syndromes (MDS) (n=39). CoQ levels were quantified by HPLC, and the percentage of mtDNA depletion by quantitative real-time PCR. A high percentage of MDS patients presented with CoQ deficiency as compared to other mitochondrial patients (Mann-Whitney-U test: p=0.001). Our findings suggest that MDS are frequently associated with CoQ deficiency, as a possible secondary consequence of disease pathophysiology. Assessment of muscle CoQ status seems advisable in MDS patients since the possibility of CoQ supplementation may then be considered as a candidate therapy.

Neonatal liver failure due to deoxyguanosine kinase deficiency

Deoxyguanosine kinase (dGK) deficiency, a rare severe cause of mitochondrial DNA (mtDNA) depletion, has two forms of presentation: hepatocerebral syndrome and isolated hepatic disease. The authors report three cases with neonatal liver failure due to dGK deficiency. Consanguinity was present in all patients. One patient had a brother who died with a probable diagnosis of neonatal haemochromatosis. All patients had progressive cholestatic liver failure, hypoglycaemia, hyperlactacidaemia, elevated ferritin levels and nystagmus, since first day of life. Liver tissue study revealed: cholestasis, iron deposits, microvesicular steatosis and fibrosis/cirrhosis. Only one patient was submitted to liver transplantation. The other two died, at 2 and 5 months of age. mtDNA quantification and DGUOK gene study should be considered in infants/neonates with acute liver failure and systematically performed in patients with hepatocerebral presentation. Differential diagnosis with neonatal haemochromatosis is needed. Liver transplantation might be a therapeutic option. Early diagnosis is important for genetic counselling.

Mitochondrial respiratory chain: biochemical analysis and criterion for deficiency in diagnosis.

Spectrophotometric evaluation of mitochondrial respiratory chain (MRC) enzymatic complexes is the main approach to the biochemical investigation and diagnosis in oxidative phosphorylation disorders (also known as mitochondrial cytopathies). Regular dual beam spectrophotometers may be used, but we describe the protocols for double wavelength devices, allowing the analysis of complex activities from a small amount of tissue, with high sensitivity. An important concern is which tissue should be selected for analysis. Accordingly, we present the results obtained with different tissues and control values to be used. There are no standards available for the determinations and no interlaboratory quality control schemes are implemented. Additionally, different laboratories may use different protocols and comparison of results may be difficult. Currently, there is no consensus in literature for defining a criterion of an MRC deficiency to be used in biochemical diagnosis. There is statistical evidence that the most adequate criterion to define an MRC deficiency is below 40% of the mean control value normalized to citrate synthase activity.

Secondary coenzyme Q10 deficiencies in oxidative phosphorylation (OXPHOS) and non-OXPHOS disorders.

We evaluated the coenzyme Q₁₀ (CoQ) levels in patients who were diagnosed with mitochondrial oxidative phosphorylation (OXPHOS) and non-OXPHOS disorders (n=72). Data from the 72 cases in this study revealed that 44.4% of patients showed low CoQ concentrations in either their skeletal muscle or skin fibroblasts. Our findings suggest that secondary CoQ deficiency is a common finding in OXPHOS and non-OXPHOS disorders. We hypothesize that cases of CoQ deficiency associated with OXPHOS defects could be an adaptive mechanism to maintain a balanced OXPHOS, although the mechanisms explaining these deficiencies and the pathophysiological role of secondary CoQ deficiency deserves further investigation.

High frequency and founder effect of the CYP3A4*20 loss-of-function allele in the Spanish population classifies CYP3A4 as a polymorphic enzyme

Cytochrome P450 3A4 (CYP3A4) is a key drug-metabolizing enzyme. Loss-of-function variants have been reported as rare events, and the first demonstration of a CYP3A4 protein lacking functional activity is caused by CYP3A4*20 allele. Here we characterized the world distribution and origin of CYP3A4*20 mutation. CYP3A4*20 was determined in more than 4000 individuals representing different populations, and haplotype analysis was performed using CYP3A polymorphisms and microsatellite markers. CYP3A4*20 allele was present in 1.2% of the Spanish population (up to 3.8% in specific regions), and all CYP3A4*20 carriers had a common haplotype. This is compatible with a Spanish founder effect and classifies CYP3A4 as a polymorphic enzyme. This constitutes the first description of a CYP3A4 loss-of-function variant with high frequency in a population. CYP3A4*20 results together with the key role of CYP3A4 in drug metabolism support screening for rare CYP3A4 functional alleles among subjects with adverse drug events in certain populations.

Long term cortical plasticity in visual retinotopic areas in humans with silent retinal ganglion cell loss.

Visual cortical plasticity induced by overt retinal lesions (scotomas) has remained a controversial phenomenon. Here we studied cortical plasticity in a silent model of retinal ganglion cell loss, documented by in vivo optical biopsy using coherence tomography. The cortical impact of non-scotomatous subtle retinal ganglion cell functional and structural loss was investigated in carriers of the mitochondrial DNA 11778G>A mutation causing Lebers hereditary optic neuropathy. We used magnetic resonance imaging (MRI) to measure cortical thickness and fMRI to define retinotopic cortical visual areas V1, V2 and V3 in silent carriers and matched control groups. Repeated Measures analysis of variance revealed a surprising increase in cortical thickness in the younger carrier group (below 21 years of age). This effect dominated in extrastriate cortex, and notably V2. This form of structural plasticity suggests enhanced plastic developmental mechanisms in extrastriate retinotopic regions close to V1 and not receiving direct retinocortical input.