No excess of mitochondrial DNA deletions within muscle in progressive multiple sclerosis.

BACKGROUND: Mitochondrial dysfunction is an established feature of multiple sclerosis (MS). We recently described high levels of mitochondrial DNA (mtDNA) deletions within respiratory enzyme-deficient (lacking mitochondrial respiratory chain complex IV with intact complex II) neurons and choroid plexus epithelial cells in progressive MS. OBJECTIVES: The objective of this paper is to determine whether respiratory enzyme deficiency and mtDNA deletions in MS were in excess of age-related changes within muscle, which, like neurons, are post-mitotic cells that frequently harbour mtDNA deletions with ageing and in disease. METHODS: In progressive MS cases (n=17), known to harbour an excess of mtDNA deletions in the central nervous system (CNS), and controls (n=15), we studied muscle (paraspinal) and explored mitochondria in single fibres. Histochemistry, immunohistochemistry, laser microdissection, real-time polymerase chain reaction (PCR), long-range PCR and sequencing were used to resolve the single muscle fibres. RESULTS: The percentage of respiratory enzyme-deficient muscle fibres, mtDNA deletion level and percentage of muscle fibres harbouring high levels of mtDNA deletions were not significantly different in MS compared with controls. CONCLUSION: Our findings do not provide support to the existence of a diffuse mitochondrial abnormality involving multiple systems in MS. Understanding the cause(s) of the CNS mitochondrial dysfunction in progressive MS remains a research priority.

Insufficient endogenous redox buffer capacity may underlie neuronal vulnerability to cerebral ischemia and reperfusion.

Reactive oxygen species (ROS) are key players in ischemia-induced neurodegeneration. We investigated whether hippocampal neurons may lack sufficient redox-buffering capacity to protect against ROS attacks. Using organotypic hippocampal slice cultures (OHSCs) transiently exposed to oxygen and glucose deprivation (OGD) and gerbils suffering from a two-vessel occlusion (2VO) as complementary ex vivo and in vivo models, we have elucidated whether the intrinsic redox systems interfere with ischemia-induced neurodegeneration. Cell- type-specific immunohistological staining of hippocampal slice cultures revealed that pyramidal neurons, in contrast to astrocytes and microglia, express free thiols only weakly. In addition, free thiol levels were extensively decreased throughout the hippocampal formation immediately after OGD, but recovered within 24 hr after reperfusion. In parallel, progressive glia activation and proliferation were observed. Increased neuronal exposure to ROS was monitored by dihydroethidium oxidation in hippocampal pyramidal cell layers immediately after OGD. Coadministration of reduction equivalents (α-lipoic acid) and thiol-stimulating agents (enalapril, ambroxol) decreased ischemia-induced neuronal damage in OGD-treated OHSCs and in gerbils exposed to 2VO, whereas single drug applications remained ineffective. In summary, limited redox buffering capacities of pyramidal neurons may underlie their exceptional vulnerability to cerebral ischemia. Consistently, multidrug treatments supporting endogenous redox systems may offer a strategy to promote valid neuroprotection.

Mitochondrial DNA deletions and neurodegeneration in multiple sclerosis.

OBJECTIVE: Cerebral atrophy is a correlate of clinical progression in multiple sclerosis (MS). Mitochondria are now established to play a part in the pathogenesis of MS. Uniquely, mitochondria harbor their own mitochondrial DNA (mtDNA), essential for maintaining a healthy central nervous system. We explored mitochondrial respiratory chain activity and mtDNA deletions in single neurons from secondary progressive MS (SPMS) cases. METHODS: Ninety-eight snap-frozen brain blocks from 13 SPMS cases together with complex IV/complex II histochemistry, immunohistochemistry, laser dissection microscopy, long-range and real-time PCR and sequencing were used to identify and analyze respiratory-deficient neurons devoid of complex IV and with complex II activity. RESULTS: The density of respiratory-deficient neurons in SPMS was strikingly in excess of aged controls. The majority of respiratory-deficient neurons were located in layer VI and immediate subcortical white matter (WM) irrespective of lesions. Multiple deletions of mtDNA were apparent throughout the gray matter (GM) in MS. The respiratory-deficient neurons harbored high levels of clonally expanded mtDNA deletions at a single-cell level. Furthermore, there were neurons lacking mtDNA-encoded catalytic subunits of complex IV. mtDNA deletions sufficiently explained the biochemical defect in the majority of respiratory-deficient neurons. INTERPRETATION: These findings provide evidence that neurons in MS are respiratory-deficient due to mtDNA deletions, which are extensive in GM and may be induced by inflammation. We propose induced multiple deletions of mtDNA as an important contributor to neurodegeneration in MS.

Clonally expanded mitochondrial DNA deletions within the choroid plexus in multiple sclerosis.

Mitochondrial DNA deletions (∆-mtDNA) have been implicated in the pathogenesis of Alzheimer's disease (AD), multiple sclerosis (MS) and Parkinson's disease (PD), as well as ageing. Clonal expansion of ∆-mtDNA is the process by which a mutant mtDNA molecule increases to high levels within a single cell containing both wild-type and mutant mtDNA. Unlike in AD and PD, the diffuse inflammatory process in MS involves the choroid plexus, and mitochondria are exposed to reactive oxygen and nitrogen species over a prolonged period. We determined the extent of respiratory enzyme deficiency and ∆-mtDNA at a single cell level within choroid plexus epithelial cells in MS as well as in AD, PD and controls. The respiratory enzyme-deficient (lacking complex IV and with intact complex II activity) cells were more prevalent within the choroid plexus in AD, MS and PD compared with controls. The main catalytic subunit of complex IV (subunit-I of cytochrome c oxidase) was lacking in significantly more respiratory enzyme-deficient cells in MS compared with AD, PD and controls. The single cell analysis showed a fourfold increase in the percentage of respiratory enzyme-deficient choroid plexus epithelial cells harbouring clonally expanded ∆-mtDNA in MS. Our findings establish clonal expansion of ∆-mtDNA as a feature relatively more prominent within the choroid plexus epithelium in MS than AD, PD or controls. We propose clonal expansion of ∆-mtDNA as a molecular link between inflammation and part of a delayed cellular energy failure in MS.

Increased mitochondrial content in remyelinated axons: implications for multiple sclerosis.

Mitochondrial content within axons increases following demyelination in the central nervous system, presumably as a response to the changes in energy needs of axons imposed by redistribution of sodium channels. Myelin sheaths can be restored in demyelinated axons and remyelination in some multiple sclerosis lesions is extensive, while in others it is incomplete or absent. The effects of remyelination on axonal mitochondrial content in multiple sclerosis, particularly whether remyelination completely reverses the mitochondrial changes that follow demyelination, are currently unknown. In this study, we analysed axonal mitochondria within demyelinated, remyelinated and myelinated axons in post-mortem tissue from patients with multiple sclerosis and controls, as well as in experimental models of demyelination and remyelination, in vivo and in vitro. Immunofluorescent labelling of mitochondria (porin, a voltage-dependent anion channel expressed on all mitochondria) and axons (neurofilament), and ultrastructural imaging showed that in both multiple sclerosis and experimental demyelination, mitochondrial content within remyelinated axons was significantly less than in acutely and chronically demyelinated axons but more numerous than in myelinated axons. The greater mitochondrial content within remyelinated, compared with myelinated, axons was due to an increase in density of porin elements whereas increase in size accounted for the change observed in demyelinated axons. The increase in mitochondrial content in remyelinated axons was associated with an increase in mitochondrial respiratory chain complex IV activity. In vitro studies showed a significant increase in the number of stationary mitochondria in remyelinated compared with myelinated and demyelinated axons. The number of mobile mitochondria in remyelinated axons did not significantly differ from myelinated axons, although significantly greater than in demyelinated axons. Our neuropathological data and findings in experimental demyelination and remyelination in vivo and in vitro are consistent with a partial amelioration of the supposed increase in energy demand of demyelinated axons by remyelination.

Injury and differentiation following inhibition of mitochondrial respiratory chain complex IV in rat oligodendrocytes.

Oligodendrocyte lineage cells are susceptible to a variety of insults including hypoxia, excitotoxicity, and reactive oxygen species. Demyelination is a well-recognized feature of several CNS disorders including multiple sclerosis, white matter strokes, progressive multifocal leukoencephalopathy, and disorders due to mitochondrial DNA mutations. Although mitochondria have been implicated in the demise of oligodendrocyte lineage cells, the consequences of mitochondrial respiratory chain defects have not been examined. We determine the in vitro impact of established inhibitors of mitochondrial respiratory chain complex IV or cytochrome c oxidase on oligodendrocyte progenitor cells (OPCs) and mature oligodendrocytes as well as on differentiation capacity of OPCs from P0 rat. Injury to mature oligodendrocytes following complex IV inhibition was significantly greater than to OPCs, judged by cell detachment and mitochondrial membrane potential (MMP) changes, although viability of cells that remained attached was not compromised. Active mitochondria were abundant in processes of differentiated oligodendrocytes and MMP was significantly greater in differentiated oligodendrocytes than OPCs. MMP dissipated following complex IV inhibition in oligodendrocytes. Furthermore, complex IV inhibition impaired process formation within oligodendrocyte lineage cells. Injury to and impaired process formation of oligodendrocytes following complex IV inhibition has potentially important implications for the pathogenesis and repair of CNS myelin disorders.

Mitochondrial changes within axons in multiple sclerosis.

Multiple sclerosis is the most common cause of non-traumatic neurological impairment in young adults. An energy deficient state has been implicated in the degeneration of axons, the pathological correlate of disease progression, in multiple sclerosis. Mitochondria are the most efficient producers of energy and play an important role in calcium homeostasis. We analysed the density and function of mitochondria using immunohistochemistry and histochemistry, respectively, in chronic active and inactive lesions in progressive multiple sclerosis. As shown before in acute pattern III and Balo's lesions, the mitochondrial respiratory chain complex IV activity is reduced despite the presence of mitochondria in demyelinated axons with amyloid precursor protein accumulation, which are predominantly located at the active edge of chronic active lesions. Furthermore, the strong non-phosphorylated neurofilament (SMI32) reactivity was associated with a significant reduction in complex IV activity and mitochondria within demyelinated axons. The complex IV defect associated with axonal injury may be mediated by soluble products of innate immunity, as suggested by an inverse correlation between complex IV activity and macrophage/microglial density in chronic lesions. However, in inactive areas of chronic multiple sclerosis lesions the mitochondrial respiratory chain complex IV activity and mitochondrial mass, judged by porin immunoreactivity, are increased within approximately half of large (>2.5 microm diameter) chronically demyelinated axons compared with large myelinated axons in the brain and spinal cord. The axon-specific mitochondrial docking protein (syntaphilin) and phosphorylated neurofilament-H were increased in chronic lesions. The lack of complex IV activity in a proportion of Na(+)/K(+) ATPase alpha-1 positive demyelinated axons supports axonal dysfunction as a contributor to neurological impairment and disease progression. Furthermore, in vitro studies show that inhibition of complex IV augments glutamate-mediated axonal injury (amyloid precursor protein and SMI32 reactivity). Our findings have important implications for both axonal degeneration and dysfunction during the progressive stage of multiple sclerosis.

Parkinson disease with dementia: comparing patients with and without Alzheimer pathology.

Subjects with Parkinson disease (PD) frequently develop dementia with greater than one-third meeting neuropathologic diagnostic criteria for Alzheimer disease (AD). The objective is to identify clinical and neuropathologic differences between Parkinson disease with dementia (PDD) subjects, with and without coexistent AD pathology. Neuropathologic examination was available on subjects diagnosed by clinicopathologic criteria with PDD-AD (N=23) and PDD+AD (N=28). A small subset of subjects with PDD-AD and PDD+AD had received at least 1 standardized neuropsychologic assessment. PDD+AD subjects were significantly older at age of PD onset and death, progressed to onset of dementia in less time, and had a shorter duration of PD symptoms before the onset of dementia. Education, responsiveness of L-dopa and dopaminergic medications, presence of cognitive fluctuations and hallucinations, and mean Mini-Mental State Examination, Global Deterioration Scale, Functional Assessment Staging, and Unified Parkinson Disease Rating Scale scores did not differ significantly between the 2 groups. The PDD+AD group had significantly greater total plaques, neuritic plaques, total tangles, and Braak stages compared with PDD-AD. This study suggests that it is difficult to distinguish PDD+AD and PDD-AD on the basis of movement, clinical, and neuropsychologic assessment. PDD-AD and PDD+AD have similar degrees of dementia and approximately half of PDD subjects have enough AD pathology to attain a neuropathologic diagnosis of AD. PDD can develop in the absence of significant Alzheimer pathology.

Mitochondrial defects in acute multiple sclerosis lesions.

Multiple sclerosis is a chronic inflammatory disease, which leads to focal plaques of demyelination and tissue injury in the CNS. The structural and immunopathological patterns of demyelination suggest that different immune mechanisms may be involved in tissue damage. In a subtype of lesions, which are mainly found in patients with acute fulminant multiple sclerosis with Balo's type concentric sclerosis and in a subset of early relapsing remitting multiple sclerosis, the initial myelin changes closely resemble those seen in white matter stroke (WMS), suggesting a hypoxia-like tissue injury. Since mitochondrial injury may be involved in the pathogenesis of such lesions, we analysed a number of mitochondrial respiratory chain proteins in active lesions from acute multiple sclerosis and from WMS using immunohistochemistry. Functionally important defects of mitochondrial respiratory chain complex IV [cytochrome c oxidase (COX)] including its catalytic component (COX-I) are present in Pattern III but not in Pattern II multiple sclerosis lesions. The lack of immunohistochemically detected COX-I is apparent in oligodendrocytes, hypertrophied astrocytes and axons, but not in microglia. The profile of immunohistochemically detected mitochondrial respiratory chain complex subunits differs between multiple sclerosis and WMS. The findings suggest that hypoxia-like tissue injury in Pattern III multiple sclerosis lesions may be due to mitochondrial impairment.

Cortical serotonin 1A receptor levels are associated with depression in patients with dementia with Lewy bodies and Parkinson's disease dementia.

BACKGROUND: Serotonin 1A receptors (5-HT(1A)) have not been studied in dementia with Lewy bodies (DLB) or Parkinson's disease dementia (PDD) patients with depression. AIM: To examine 5-HT(1A) in DLB and PDD postmortem in relation to depression. METHODS: [(3)H]8-hydroxy-2-dipropylaminotetralin binding to 5-HT(1A) was determined in temporal cortex (Brodmann areas, BA20 and BA36) from 10 DLB patients, 17 PDD patients and 9 controls. RESULTS: 5-HT(1A) density was significantly higher in BA36 in combined DLB/PDD patients with depression, but was unaltered in BA20. CONCLUSION: Higher BA36 5-HT(1A) density in PDD and DLB patients than in control is dependent on whether the patient had experienced depression during life, not DLB/PDD diagnosis. A 5-HT(1A) antagonist adjuvant may improve treatment of depression in dementia.

Cholinergic neuronal deficits in CADASIL.

BACKGROUND AND PURPOSE: Previous evidence from MRI and acetylcholinesterase histochemistry suggests cholinergic fibers are affected in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). METHODS: As a measure of cholinergic function, we assessed choline acetyltransferase (ChAT) activities in the frontal and temporal neocortices and the immunocytochemical distribution of ChAT and p75 neurotrophin receptor (P75(NTR)) by in vitro imaging in the nucleus basalis of Meynert of CADASIL subjects. RESULTS: ChAT activities were significantly reduced by 60% to 70% in frontal and temporal cortices of CADASIL cases, as were ChAT and P75(NTR) immunoreactivities in the nucleus basalis. CONCLUSIONS: Our findings suggest cholinergic neuronal impairment in CADASIL and implicate cholinomimetic therapy for subcortical vascular dementias.

Lewy body disease: thalamic cholinergic activity related to dementia and parkinsonism.

Within the spectrum of Lewy body disease cognitive impairment occurs in PD with dementia (PDD) and dementia with Lewy bodies (DLB). Although neocortical cholinergic deficits are associated with cognitive impairments in PDD and DLB, no neurochemical study has been published describing the thalamic cholinergic activity whereas the thalamus plays a major role in modulating cortical activity. Choline acetyltransferase (ChAT) activity was analyzed in reticular (Re), mediodorsal (MD) and centromedian (CM) thalamic nuclei in series of nine controls, five DLB with parkinsonism (DLB + P), five DLB without parkinsonism (DLB - P), six PD without dementia and 14 PDD cases. Significant reductions in ChAT were apparent in PDD as follows: in Re and MD nuclei compared with controls; in MD and CM nuclei compared with DLB + P; and in MD compared with PD. Increased ChAT activity was found in CM nuclei in DLB + P compared with DLB - P. These findings show that significant thalamic presynaptic cholinergic deficits occur only in cases of combined cortical and subcortical neurodegeneration in which dementia developed after prolonged parkinsonism.

Altered neurogenesis in Alzheimer's disease.

BACKGROUND: Exciting preliminary work indicates an increase in progenitor activity in the subgranular zone of the dentate gyrus of people with Alzheimer's disease (AD) compared to that of controls. We examine progenitor activity in the other main progenitor niche, the subventricular zone (SVZ), as well as potential associations with key pathological and neurochemical substrates. METHOD: Immunocytochemistry techniques utilizing nestin and Musashi1 antibodies were used to examine progenitor activity in the SVZ and to enable comparisons between seven patients with AD and seven controls, based upon the quantification of the percentage area covered, using the Image Pro Plus v.4.1 image analysis system. AD pathology was staged using the Consortium to Establish a Registry for Alzheimer's Disease and Braak criteria. Choline acetyl transferase (ChAT) was measured in the temporal cortex as an indication of the severity of cortical cholinergic deficits. Glial fibrillary acidic protein (GFAP) was used to label astrocytes. RESULTS: There was a significant ninefold decrease (Z = 2.2, P = .046) of Musashi1 immunoreactivity in the SVZ of patients with AD in comparison with that of controls, but there was a significant increase in nestin immunoreactivity in the same region (Z = 2.2, P = .028) without any significant change in GFAP immunoreactivity. Reduced ChAT enzymatic activity was the main association of Musashi immunoreactivity (R = -.90, P = .03). DISCUSSION: The current results indicate a significant reduction of progenitor cells (as labeled by Musashi1) in the SVZ of patients with AD, but an increase in GFAP-negative astrocyte-like cells with progenitor characteristics. Cortical cholinergic loss was strongly associated with the reduction of progenitors, with potential implications of important treatment targets.

Single-cell resolution mapping of neuronal damage in acute focal cerebral ischemia using thallium autometallography.

Neuronal damage shortly after onset or after brief episodes of cerebral ischemia has remained difficult to assess with clinical and preclinical imaging techniques as well as with microscopical methods. We here show, in rodent models of middle cerebral artery occlusion (MCAO), that neuronal damage in acute focal cerebral ischemia can be mapped with single-cell resolution using thallium autometallography (TlAMG), a histochemical technique for the detection of the K(+)-probe thallium (Tl(+)) in the brain. We intravenously injected rats and mice with thallium diethyldithiocarbamate (TlDDC), a lipophilic chelate complex that releases Tl(+) after crossing the blood-brain barrier. We found, within the territories of the affected arteries, areas of markedly reduced neuronal Tl(+) uptake in all animals at all time points studied ranging from 15 minutes to 24 hours after MCAO. In large lesions at early time points, areas with neuronal and astrocytic Tl(+) uptake below thresholds of detection were surrounded by putative penumbral zones with preserved but diminished Tl(+) uptake. At 24 hours, the areas of reduced Tl(+)uptake matched with areas delineated by established markers of neuronal damage. The results suggest the use of (201)TlDDC for preclinical and clinical single-photon emission computed tomography (SPECT) imaging of hyperacute alterations in brain K(+) metabolism and prediction of tissue viability in cerebral ischemia.

The distribution pattern of pathology and cholinergic deficits in amygdaloid complex in Alzheimer's disease and dementia with Lewy bodies.

We studied the distribution pattern of pathology and cholinergic deficits in the subnuclei of the amygdaloid complex (AC) in five patients with Alzheimer's disease (AD), eight with dementia with Lewy bodies (DLB) and five normal controls. In controls, the basal nucleus contained the highest choline acetyltransferase activity; the activity in the lateral and central nuclei and those in the cortical, medial and accessory basal nuclei were comparable. In AD, there was a significant decrease in choline acetyltransferase activity in the accessory basal and lateral nuclei, in DLB a significant decrease was observed in the accessory basal, lateral and cortical nuclei. Compared to controls the hyperphosphorylated tau-pathology burden was significantly higher in the basal, central and medial nuclei in AD and in the central, cortical, lateral and medial nuclei in DLB. The amyloid plaque burden was significantly higher in the accessory basal, basal, lateral and cortical nuclei in AD and in all nuclei in DLB. The alpha-synuclein burden was significantly higher in all nuclei in both AD and DLB. Compared to AD alpha-synuclein burden was higher in all nuclei in DLB. There were no correlations between the distribution pattern of hyperphosphorylated tau-pathology, amyloid plaques and alpha-synuclein-positive structures, and choline acetyltransferase activity, except the lateral nucleus in DLB. In conclusion we found no relationship between the pattern of cholinergic deficits and the distribution pattern of lesions in the AC of patients with AD or DLB. Cholinergic deficits were more prominent in the nuclei of basolateral (BL) group in AD, whereas the nuclei of both BL and corticomedial groups were involved in DLB, which may be due to the involvement of both basal forebrain and brainstem cholinergic nuclei in the latter.

Selective nicotinic acetylcholine receptor subunit deficits identified in Alzheimer's disease, Parkinson's disease and dementia with Lewy bodies by immunoprecipitation.

Antibodies raised against human alpha2-6 and beta2-4 nicotinic receptor subunits were utilized to fractionate (3)H-epibatidine binding in human temporal cortex and striatum. The predominant receptor subtypes in both regions contained alpha4 and beta2 subunits. In normal cortex, 10% of binding was also associated with alpha2 subunits, whereas in the striatum, contributions by alpha6 (17%) and beta3 (23%) were observed. Minimal binding (< or =5%) was associated with alpha3. In Alzheimer's disease and dementia with Lewy bodies, cortical loss of binding was associated with reductions in alpha4 (50%, P < 0.01) and beta2 (30-38%, P < 0.05). In Parkinson's disease and dementia with Lewy bodies, striatal deficits in alpha6 (91 and 59% respectively, P < 0.01) and beta3 (72 and 75%, P < 0.05) tended to be greater than for alpha4 and beta2 (50-58%, P < 0.05). This study demonstrates distinct combinations of subunits contributing to heteromeric nicotinic receptor binding in the human brain that are area/pathway specific and differentially affected by neurodegeneration.