Mitochondrial pathology in human schizophrenic striatum: a postmortem ultrastructural study

Mitochondrial complex I subunits expression is altered in schizophrenia: a postmortem study

BACKGROUND

Several independent lines of evidence indicate mitochondrial dysfunction in schizophrenia in the brain and periphery, including mitochondrial hypoplasia, dysfunction of the oxidative phosphorylation system, and altered mitochondrial-related gene expression.

METHODS

In this study, three subunits of mitochondrial complex I were analyzed at the level of mRNA and protein in postmortem brain specimens from the prefrontal and the ventral parietooccipital cortex of patients with schizophrenia, major depression, bipolar disorder, and normal control subjects.

RESULTS

Both mRNA and protein levels of the 24-kDa and 51-kDa subunits of complex I were significantly decreased in the prefrontal cortex, but increased in the ventral parietooccipital cortices of schizophrenia patients compared with normal control subjects. In the latter region, protein levels of both subunits were increased in bipolar patients as well, being in line with the significant overlap in clinical symptoms between schizophrenia and bipolar patients. No change was observed in the 75-kDa subunit expression in the prefrontal cortex.

CONCLUSIONS

The schizophrenia-specific reduction in complex I subunits in the prefrontal cortex is consistent with one of schizophrenia's most prominent deficits, namely, hypofrontality, thus further supporting the hypothesis of mitochondrial dysfunction in this disorder. The abnormal, bidirectional expression of complex I in various brain regions, rather than in a circumscribed area, supports the idea of impaired cerebral circuitry in schizophrenia.

State-dependent alterations in mitochondrial complex I activity in platelets: a potential peripheral marker for schizophrenia

Schizophrenia, the most severe psychiatric disorder, is characterized by heterogeneity of clinical signs, often categorized into positive and negative symptoms. Among a wide array of competing biological mechanisms, altered cerebral energy metabolism and mitochondrial dysfunction have been suggested to play an important role in the pathophysiology of schizophrenia. In this study we investigated mitochondrial complex I in platelets of 113 schizophrenic patients divided into three groups (acute psychotic episode, chronic active state and residual schizophrenia) and 37 control subjects. Complex I was analysed at the level of enzymatic activity, mRNA and protein levels by enzyme kinetics, RT-PCR and Western blot analyses, respectively. Complex I activity in platelets of schizophrenic patients altered with disease state presenting high specificity and sensitivity. Thus, increased activity was associated with psychotic symptomology, while its decrease was observed in patients with residual schizophrenia. The relationship between the clinical state and complex I activity in schizophrenia was further supported by its positive correlation with the severity of patients' positive symptoms assessed by clinical ratings. In addition, similar alterations were observed at the levels of mRNA and protein of the 24- and 51-kDa iron-sulfur flavoprotein subunits of the complex. Taken together these results point to the potential of platelet complex I to turn into a reliable novel marker for schizophrenia. At present, definitive diagnosis depends only on descriptive behavioral and symptomatic information, therefore a peripheral measurable specific marker will contribute to diagnosis and monitoring of the disease.

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.

Identification of candidate genes for psychosis in rat models, and possible association between schizophrenia and the 14-3-3eta gene

Although the genetic contribution to schizophrenia is substantial, positive findings in whole-genome linkage scans have not been consistently replicated. We analyzed gene expression in various rat conditions to identify novel candidate genes for schizophrenia. Suppression subtraction hybridization (SSH), with polyA mRNA from temporal and frontal cortex of rats, was used to identify differentially expressed genes. Expression of mRNA was compared between adult Lewis and Fischer 344 (F344) rats, adult and postnatal day 6 (d6) F344, and adult F344 treated with haloperidol or control vehicle. These groups were chosen because each highlights a particular aspect of schizophrenia: differences in strain vulnerability to behavioral analogs of psychosis; factors that may relate to disease onset in relation to CNS development; and improvement of symptoms by haloperidol. The 14-3-3 gene family, as represented by 14-3-3gamma and 14-3-3zeta isoforms in the SSH study, and SNAP-25 were among the candidate genes. Genetic association between schizophrenia and the 14-3-3eta gene, positioned close to a genomic locus implicated in schizophrenia, and SNAP-25 genes was analyzed in 168 schizophrenia probands and their families. These findings address three different genes in the 14-3-3 family. We find a significant association with schizophrenia for two polymorphisms in the 14-3-3eta gene: a 7 bp variable number of tandem repeats in the 5' noncoding region (P=0.036, 1 df), and a 3' untranslated region SNP (753G/A) that is an RFLP visualized with Ava II (P=0.028). There was no significant genetic association with SNAP-25. The candidate genes identified may be of functional importance in the etiology, pathophysiology or treatment response of schizophrenia or psychotic symptoms. This is to our knowledge the first report of a significant association between the 14-3-3eta-chain gene and schizophrenia in a family-based sample, strengthening prior association reports in case-control studies and microarray gene expression studies.

Mitochondrial dysfunction in schizophrenia: a possible linkage to dopamine

Mitochondria are not only the principal source of high energy intermediates, but play an important role in intracellular calcium buffering, are main producers of reactive oxygen species, and are the source of pro- and antiapoptotic key factors. Moreover, the mitochondria are of a ubiquitous nature and the respiratory chain has a dual genetic basis, i.e. the mitochondrial and the nuclear DNAs. Thus mitochondrial impairment could provide an explanation for the tremendous heterogeneity of clinical and pathological manifestations in schizophrenia. This article reviews several independent lines of evidence that suggest an involvement of mitochondrial dysfunction in schizophrenia. Among them are altered cerebral energy metabolism, mitochondrial hypoplasia, dysfunction of the oxidative phosphorylation system and altered mitochondrial related gene expression. In addition, the interaction between dopamine, a predominant etiological factor in schizophrenia, and mitochondrial respiration is considered as a possible mechanism underlying the hyper- and hypo-activity cycling in schizophrenia. Understanding the role of mitochondria in schizophrenia may encourage novel treatment approaches, the identification of candidate genes and new insights into the pathophysiology and etiology of the disorder.

The other, forgotten genome: mitochondrial DNA and mental disorders

This paper summarizes recent research on mitochondrial DNA (mtDNA)--which might be described as the "other, forgotten genome". Recent studies suggest the possible pathophysiological significance of mtDNA in schizophrenia and neurodegenerative and mood disorders. Decreased activity of the mitochondrial electron transport chain has been implicated in both Parkinson's and Alzheimer's disease and while age-related accumulation of mtDNA deletions has been suggested as a possible cause, there is no concrete evidence that particular mtDNA polymorphisms are responsible. In schizophrenia, the activity and/or mRNA expression of complex IV are involved, but the direction of the alteration is not the same and there is no evidence linking schizophrenia with mtDNA. In bipolar disorder, there is some evidence of parent-of-origin effects and association with mtDNA polymorphisms but further investigation is needed to elucidate the role of mtDNA in mental disorders.

Schizophrenia, a neurodegenerative disorder with neurodevelopmental antecedents

Schizophrenia is a devastating disorder that has been referred to as youth's greatest disabler. Although a number of hypotheses have been proposed in an attempt to explain the pathophysiology of schizophrenia no single theory seems to account for all facets of the disease. Each hypothesis explains some of the phenomena associated with schizophrenia and it is probable that many variables described in these hypotheses interact to produce a disorder characterized by heterogeneous symptomatology, progression and prognosis. Compelling evidence suggests that the primary disturbance is a neurodevelopmental abnormality, possibly resulting from a genetic defect(s), resulting in a predisposition to schizophrenia. Events later in life may then lead to the presentation of symptoms and a subsequent progression of the disease. Recent evidence suggests that the progressive course of schizophrenia is associated with ongoing neurodegenerative processes. Changes in brain derived neurotrophic factor (BDNF) may explain the various changes observed in schizophrenia.

Mu-opioid receptors are present in functionally identified sympathoexcitatory neurons in the rat rostral ventrolateral medulla

Agonists of the mu-opioid receptor (MOR) produce profound hypotension and sympathoinhibition when microinjected into the rostral ventrolateral medulla (RVL). These effects are likely to be mediated by the inhibition of adrenergic and other presympathetic vasomotor neurons located in the RVL. The present ultrastructural studies were designed to determine whether these vasomotor neurons, or their afferents, contain MORs. RVL bulbospinal barosensitive neurons were recorded in anesthetized rats and filled individually with biotinamide by using a juxtacellular labeling method. Biotinamide was visualized by using a peroxidase method and MOR was identified by using immunogold localization of an antipeptide antibody that recognizes the cloned MOR, MOR1. The subcellular relationship of MOR1 to RVL neurons with fast- or slow-conducting spinal axons was examined by electron microscopy. Fast- and slow-conducting cells were not morphologically distinguishable. Immunogold-labeling for MOR1 was found in all RVL bulbospinal barosensitive neurons examined (9 of 9). MOR1 was present in 52% of the dendrites from both types of cells and in approximately half of these dendrites the MOR1 was at nonsynaptic plasmalemmal sites. A smaller portion of biotinamide-labeled dendrites (16%) from both types of cells were contacted by MOR1-containing axons or axon terminals. Together, these results suggest that MOR agonists can directly influence the activity of all types of RVL sympathoexcitatory neurons and that MOR agonists may also influence the activity of afferent inputs to these cells. The heterogenous distribution of MORs within individual RVL neurons indicates that the receptor is selectively targeted to specific pre- and postsynaptic sites.

N-methyl-D-aspartate-type glutamate receptors are found in post-synaptic targets of adrenergic terminals in the thoracic spinal cord

Adrenergic (C1) neurons in the rostral ventrolateral medulla (RVL) are sympathoexcitatory and project directly to sympathetic preganglionic neurons (SPNs) in the thoracic spinal cord. C1 neurons also contain glutamate which may mediate the excitatory effects of RVL stimulation on SPNs through the N-methyl-D-aspartate (NMDA)-type receptor. Dual-labeling immunocytochemistry, combined with electron microscopy, was used to determine if NMDA receptors are located post-synaptic to adrenergic terminals in the spinal cord. Adrenergic terminals were labeled using an antibody directed against phenylethanolamine-N-methyl transferase (PNMT) and the NMDA receptor was identified using an antibody directed against the R1 subunit of the receptor (NMDAR1). NMDAR1 was found primarily in large and small dendrites and a few perikarya. The presence of NMDAR1 in the dendritic targets of PNMT-containing terminals was quantified in spinal cords sectioned either horizontally or coronally. PNMT-labeled terminals formed asymmetric synapses on dendrites containing immunogold labeling for NMDAR1, but NMDAR1 was more often detected in the targets of PNMT terminals when spinal cords were sectioned horizontally (59%) rather than coronally (28%). This difference in prevalence of NMDAR1 in targets of PNMT terminals is likely due to the preferential orientation of SPN dendrites in the horizontal plane, since longer dendritic shafts were visible in horizontal sections. When NMDAR1 was present in the dendritic targets of many adrenergic terminals, it was usually located at sites distal to the adrenergic input. We conclude that NMDA receptor ligands are likely to modulate the activity of dendritic targets of adrenergic terminals in the spinal cord, but are not closely associated with adrenergic synaptic input.

The neuropathological effects of antipsychotic drugs

In addition to their neurochemical effects, antipsychotic (neuroleptic) drugs produce structural brain changes. This property is relevant not only for understanding the drugs' mode of action, but because it complicates morphological studies of schizophrenia. Here the histological neuropathological effects of antipsychotics are reviewed, together with brief mention of those produced by other treatments sometimes used in schizophrenia (electroconvulsive shock, lithium and antidepressants). Most data come from drug-treated rats, though there are also some human post-mortem studies with broadly congruent findings. The main alteration associated with antipsychotic medication concerns the ultrastructure and proportion of synaptic subpopulations in the caudate nucleus. In rats, synapses and dendrites in lamina VI of the prefrontal cortex are also affected. The changes are indicative of a drug-induced synaptic plasticity, although the underlying mechanisms are poorly understood. Similarly, it is unclear whether the neuropathological features relate primarily to the therapeutic action of antipsychotics or, more likely, to their predisposition to cause tardive dyskinesia and other motor side-effects. Clozapine seems to cause lesser and somewhat different alterations than do typical antipsychotics, albeit based on few data. There is no good evidence that antipsychotics cause neuronal loss or gliosis, nor that they promote neurofibrillary tangle formation or other features of Alzheimer's disease.