Dorsal Root Ganglia Mitochondrial Biochemical Changes in Non-diabetic and Streptozotocin-Induced Diabetic Mice Fed with a Standard or High-Fat Diet.

BACKGROUND: Mitochondrial dysfunction is purported as a contributory mechanism underlying diabetic neuropathy, but a defined role for damaged mitochondria in diabetic nerves remains unclear, particularly in standard diabetes models. Experiments here used a high-fat diet in attempt to exacerbate the severity of diabetes and expedite the time-course in which mitochondrial dysfunction may occur. We hypothesized a high-fat diet in addition to diabetes would increase stress on sensory neurons and worsen mitochondrial dysfunction. METHODS: Oxidative phosphorylation proteins and proteins associated with mitochondrial function were quantified in lumbar dorsal root ganglia. Comparisons were made between non-diabetic and streptozotocin-induced (STZ) C57Bl/6 mice fed a standard or high-fat diet for 8 weeks. RESULTS: Complex III subunit Core-2 and voltage dependent anion channel were increased (by 36% and 28% respectively, p<0.05) in diabetic mice compared to nondiabetic mice fed the standard diet. There were no differences among groups in UCP2, PGC-1α, PGC-1ß levels or Akt, mTor, or AMPK activation. These data suggest compensatory mitochondrial biogenesis occurs to offset potential mitochondrial dysfunction after 8 weeks of STZ-induced diabetes, but a high-fat diet does not alter these parameters. CONCLUSION: Our results indicate mitochondrial protein changes early in STZ-induced diabetes. Interestingly, a high-fat diet does not appear to affect mitochondrial proteins in either nondiabetic or STZ- diabetic mice.

Mitochondria, Cybrids, Aging, and Alzheimer's Disease.

Mitochondrial and bioenergetic function change with advancing age and may drive aging phenotypes. Mitochondrial and bioenergetic changes are also documented in various age-related neurodegenerative diseases, including Alzheimer's disease (AD). In some instances AD mitochondrial and bioenergetic changes are reminiscent of those observed with advancing age but are greater in magnitude. Mitochondrial and bioenergetic dysfunction could, therefore, link neurodegeneration to brain aging. Interestingly, mitochondrial defects in AD patients are not brain-limited, and mitochondrial function can be linked to classic AD histologic changes including amyloid precursor protein processing to beta amyloid. Also, transferring mitochondria from AD subjects to cell lines depleted of endogenous mitochondrial DNA (mtDNA) creates cytoplasmic hybrid (cybrid) cell lines that recapitulate specific biochemical, molecular, and histologic AD features. Such findings have led to the formulation of a "mitochondrial cascade hypothesis" that places mitochondrial dysfunction at the apex of the AD pathology pyramid. Data pertinent to this premise are reviewed.

Reduced gray matter volume in normal adults with a maternal family history of Alzheimer disease.

OBJECTIVE: A consistently identified risk factor for Alzheimer disease (AD) is family history of dementia, with maternal transmission significantly more frequent than paternal transmission. A history of maternal AD may be related to AD-like glucose consumption in cognitively healthy subjects. In this cross-sectional study, we tested whether cognitively healthy people with a family history of AD have less gray matter volume (GMV), an endophenotype for late-onset AD, than individuals with no family history, and whether decreases in GMV are different in subjects with a maternal family history. METHODS: As part of the Kansas University Brain Aging Project, 67 cognitively intact individuals with a maternal history of late-onset AD (FHm, n = 16), a paternal history of AD (FHp, n = 8), or no parental history of AD (FH-, n = 43), similar in age, gender, education, and Mini-Mental State Examination score, were scanned at 3 T. We used voxel-based morphometry to examine GMV differences between groups, controlling for age, gender, and apoE4. RESULTS: Cognitively healthy individuals with a family history of late-onset AD had significantly decreased GMV in the precuneus, middle frontal, inferior frontal, and superior frontal gyri compared with FH- individuals. FHm subjects had significantly smaller inferior frontal, middle frontal, precuneus, and lingual gyri compared with FH- and FHp subjects. CONCLUSIONS: Overall, maternal family history of Alzheimer disease (AD) in cognitively normal individuals is associated with lower gray matter volume in AD-vulnerable brain regions. These data complement and extend reports of cerebral metabolic differences in subjects with a maternal family history.

Autosomal dominant subcortical gliosis presenting as frontotemporal dementia.

OBJECTIVE: To describe a multigenerational kindred with a frontotemporal dementia clinical syndrome (FTDS), extensive subcortical gliosis pathology, and autosomal dominant genetics. METHODS: Clinical, imaging, and pathologic evaluations of multiple family members. RESULTS: Symptom onset commonly occurred in the fifth or sixth decade, although some kindred members did not develop obvious symptoms until their eighth decade. White matter changes were prominent on both MRI and CT imaging. Results from six brain autopsy evaluations showed consistent but varying degrees of pathology that, while unique, share some histologic similarities with leukodystrophies. These brains were notably devoid of both tau- and ubiquitin-containing inclusions. CONCLUSIONS: Subcortical gliosis in this kindred arises from mutation of a novel gene or else represents a unique frontotemporal dementia clinical syndrome variant caused by mutation of an already known gene. Clinical relevance and research implications are discussed.

Cardiorespiratory fitness and brain atrophy in early Alzheimer disease.

OBJECTIVE: To examine the correlation of cardiorespiratory fitness with brain atrophy and cognition in early-stage Alzheimer disease (AD). BACKGROUND: In normal aging physical fitness appears to mitigate functional and structural age-related brain changes. Whether this is observed in AD is not known. METHODS: Subjects without dementia (n = 64) and subjects with early-stage AD (n = 57) had MRI and standard clinical and psychometric evaluations. Peak oxygen consumption (VO(2)(peak)), the standard measure of cardiorespiratory fitness, was assessed during a graded treadmill test. Normalized whole brain volume, a brain atrophy estimate, was determined by MRI. Pearson correlation and linear regression were used to assess fitness in relation to brain volume and cognitive performance. RESULTS: Cardiorespiratory fitness (VO(2)(peak)) was modestly reduced in subjects with AD (34.7 [5.0] mL/kg/min) vs subjects without dementia (38.1 [6.3] mL/kg/min, p = 0.002). In early AD, VO(2)(peak) was associated with whole brain volume (beta = 0.35, p = 0.02) and white matter volume (beta = 0.35, p = 0.04) after controlling for age. Controlling for additional covariates of sex, dementia severity, physical activity, and physical frailty did not attenuate the relationships. VO(2)(peak) was associated with performance on delayed memory and digit symbol in early AD but not after controlling for age. In participants with no dementia, there was no relationship between fitness and brain atrophy. Fitness in participants with no dementia was associated with better global cognitive performance (r = 0.30, p = 0.02) and performance on Trailmaking A and B, Stroop, and delayed logical memory but not after controlling for age. CONCLUSIONS: Increased cardiorespiratory fitness is associated with reduced brain atrophy in Alzheimer disease (AD). Cardiorespiratory fitness may moderate AD-related brain atrophy or a common underlying AD-related process may impact both brain atrophy and cardiorespiratory fitness.

A novel deafness/dystonia peptide gene mutation that causes dystonia in female carriers of Mohr-Tranebjaerg syndrome.

Sex-linked male deafness and dystonia (Mohr-Tranebjaerg syndrome) arises from mutation of the deafness/dystonia peptide (DDP) gene. We describe a novel guanine deletion at nucleotide 108 of the DDP gene in a family with Mohr-Tranebjaerg syndrome, which terminates this 97-amino acid protein at codon 25. Unlike previously reported kindreds, carrier females in this family also manifest dystonias, including torticollis and writer's cramp. A family history of male deafness should alert clinicians to the possibility of DDP mutation in women with focal dystonias.

Biochemical analysis of cybrids expressing mitochondrial DNA from Contursi kindred Parkinson's subjects.

Complex I activity is reduced in cytoplasmic hybrid (cybrid) cell lines that contain mitochondrial DNA (mtDNA) from sporadic Parkinson's disease (PD) patients. This implies that mtDNA aberration occurs in sporadic PD. To assess the integrity of mtDNA in autosomal dominant PD arising from mutation of the alpha-synuclein gene, we transferred mitochondrial genes from PD-affected members of the Italian-American Contursi kindred to cells previously depleted of their endogenous mtDNA. Unlike cybrid cell lines expressing mtDNA from persons with sporadic or maternally inherited PD, the resultant Contursi cybrid lines did not manifest complex I deficiency, indicating that in Contursi PD mtDNA integrity is relatively preserved. Compared to control cybrids, however, Contursi cybrid lines did show some evidence of oxidative stress. For reasons that are unclear, at least a limited amount of mtDNA damage may nevertheless develop in PD patients with alpha-synuclein mutation.

Gender ratio differences between Parkinson's disease patients and their affected relatives.

Mitochondrial dysfunction in Parkinson's disease (PD) is suspected to arise from either acquired or inherited mutation of mitochondrial DNA (mtDNA). If inherited, epidemiologic analysis may reveal maternal transmission. We looked for maternal inheritance bias in our PD clinical database. About 13% of 600 PD probands reported an affected parent. Although 60% of the PD probands were male, only 42% of the affected parents were. The gender ratios for the proband and affected parent generations were dissimilar (p<0.005), indicating an underrepresentation of affected fathers or an overrepresentation of affected mothers. To address these possibilities we analyzed a non-PD control cohort. Four percent of the controls had a PD affected parent, and 75% of these affected parents were male. Apparent maternal inheritance bias in our PD cohort is therefore more likely due to overrepresentation of affected mothers, and is consistent with mitochondrial inheritance in some of our ascertained cases.

Further evidence for mitochondrial dysfunction in progressive supranuclear palsy.

Recent data from our laboratory have identified a role for mitochondrial dysfunction in the pathogenesis of progressive supranuclear palsy (PSP). To extend this finding, we measured key parameters of mitochondrial function in platelet-derived cytoplasmic hybrid (cybrid) cell lines expressing mitochondrial genes from patients with PSP. We observed significant decreases in aconitase activity, cellular ATP levels, and oxygen consumption in PSP cybrids as compared to control cybrids, further suggesting a contributory role of impaired mitochondrial energy metabolism in PSP, possibly due to genetic abnormalities of mitochondrial DNA.

Mitochondrial dysfunction in cybrid lines expressing mitochondrial genes from patients with progressive supranuclear palsy.

Progressive supranuclear palsy (PSP) is a neurodegenerative movement disorder of unknown etiology. We hypothesized that mitochondrial DNA (mtDNA) aberration could occur in this disease and contribute to its pathogenesis. To address this we created transmitochondrial cytoplasmic hybrid (cybrid) cell lines expressing mitochondrial genes from persons with PSP. The presence of cybrid mtDNA aberration was screened for by biochemical assay of mitochondrial gene products. Relative to a control cybrid set, complex I activity was reduced in PSP cybrid lines (p<0.005). Antioxidant enzyme activities were elevated in PSP cybrid lines. These data suggest that mtDNA aberration occurs in PSP, causes electron transport chain pathology, and can produce oxidative stress. Further study of mitochondrial dysfunction in PSP may yield insights into why neurodegeneration occurs in this disease.

Disrupted mitochondrial electron transport function increases expression of anti-apoptotic bcl-2 and bcl-X(L) proteins in SH-SY5Y neuroblastoma and in Parkinson disease cybrid cells through oxidative stress.

Death of dopamine neurons in Parkinson disease (PD) may arise from consequences of the complex I (C-I) defect in the mitochondrial electron transport chain (ETC). Whether cells activate programmed death (apoptosis) pathways derives, in part, from relative activities of proteins such as bcl-2 and bcl-X(L), that have anti-apoptotic actions. We studied the responses of bcl-2 and bcl-X(L) genes in pharmacologic (acute incubation with methylpyridinium (MPP+)) and mitochondrial transgenic ("cybrid") models of Parkinson disease C-I defects. MPP+ incubation increased levels of bcl-2 and bcl-X(L) proteins in native SH-SY5Y cells but not in rho(0) cells devoid of ETC activity. MPP+ increased bcl-2 mRNA levels by 40% at 8 hr. Confocal microscopic imaging showed that the intracellular distribution of immunoreactive bcl-2 was not significantly associated with mitochondrial membranes at baseline but was associated with mitochondria after 12 hr of MPP+. Immunoreactive bcl-X(L) protein was significantly and equally associated with mitochondrial membranes both at baseline and after MPP+. PD cybrids showed increased basal levels of bcl-2 and bcl-X(L) proteins, similar to the maximum levels found after MPP+ treatment of control SY5Y cells. After MPP+ exposure, bcl-2 protein levels increased in control cybrids but did not increase further in PD cybrids. Both pharmacologically generated and transgenically induced C-I inhibition increases levels of anti-apoptotic bcl proteins, possibly from increased gene transcription. Augmentation of bcl-2 and bcl-X(L) expression may delay neurodegeneration in PD.

Alzheimer's disease cybrids replicate beta-amyloid abnormalities through cell death pathways.

Alzheimer's disease (AD) is characterized by the deposition in brain of beta-amyloid (Abeta) peptides, elevated brain caspase-3, and systemic deficiency of cytochrome c oxidase. Although increased Abeta deposition can result from mutations in amyloid precursor protein or presenilin genes, the cause of increased Abeta deposition in sporadic AD is unknown. Cytoplasmic hybrid ("cybrid") cells made from mitochondrial DNA of nonfamilial AD subjects show antioxidant-reversible lowering of mitochondrial membrane potential (delta(gYm), secrete twice as much Abeta(1-40) and Abeta(1-42), have increased intracellular Abeta(1-40) (1.7-fold), and develop Congo red-positive Abeta deposits. Also elevated are cytoplasmic cytochrome c (threefold) and caspase-3 activity (twofold). Increased AD cybrid Abeta(1-40) secretion was normalized by inhibition of caspase-3 or secretase and reduced by treatment with the antioxidant S(-)pramipexole. Expression of AD mitochondrial genes in cybrid cells depresses cytochrome c oxidase activity and increases oxidative stress, which, in turn, lowers delta(psi)m. Under stress, cells with AD mitochondrial genes are more likely to activate cell death pathways, which drive caspase 3-mediated Abeta peptide secretion and may account for increased Abeta deposition in the AD brain. Therapeutic strategies for reducing neurodegeneration in sporadic AD can address restoration of delta(psi)m and reduction of elevated Abeta secretion.

Interaction among mitochondria, mitogen-activated protein kinases, and nuclear factor-kappaB in cellular models of Parkinson's disease.

Oxidative stress induced by acute complex I inhibition with 1-methyl-4-phenylpyridinium ion activated biphasically the stress-activated c-Jun N-terminal kinase (JNK) and the early transcription factor nuclear factor-kappaB (NF-kappaB) in SH-SY5Y neuroblastoma cells. Early JNK activation was dependent on mitochondrial adenine nucleotide translocator (ANT) activity, whereas late-phase JNK activation and the cleavage of signaling proteins Raf-1 and mitogen-activated protein kinase (MAPK) kinase (MEK) kinase (MEKK)-1 appeared to be ANT-independent. Early NF-kappaB activation depended on MEK, later activation required an intact electron transport chain (ETC), and Parkinson's disease (PD) cybrid (mitochondrial transgenic cytoplasmic hybrid) cells had increased basal NF-kappaB activation. Mitochondria appear capable of signaling ETC impairment through MAPK modules and inducing protective NF-kappaB responses, which are increased by PD mitochondrial genes amplified in cybrid cells. Irreversible commitment to apoptosis in this cell model may derive from loss of Raf-1 and cleavage/activation of MEKK-1, processes reported in other models to be caspase-mediated. Therapeutic strategies that reduce mitochondrial activation of proapoptotic MAPK modules, i.e., JNK, and enhance survival pathways, i.e., NF-kappaB, may offer neuroprotection in this debilitating disease.

Abnormal mitochondrial morphology in sporadic Parkinson's and Alzheimer's disease cybrid cell lines.

Diseases linked to defective mitochondrial function are characterized by morphologically abnormal, swollen mitochondria with distorted cristae. Several lines of evidence now suggest that sporadic forms of Parkinson's disease (PD) and Alzheimer's disease (AD) are linked to mitochondrial dysfunction arising from defects in mitochondrial DNA (mtDNA). Human neuroblastoma (SH-SY5Y) cells that are deficient in mtDNA (Rho(0)) were repopulated with mitochondria from AD or PD patients or age-matched controls. These cytoplasmic hybrid (cybrid) cell lines differ only in the source of their mtDNA. Differences between cybrid cell lines therefore arise from differences in mtDNA and provide a model for the study of how impaired mitochondrial function alters the mitochondria themselves and how these changes adversely affect the neuronal cells they occupy. Cybrid cell mitochondria were labeled with the mitochondrial membrane potential-sensitive dye, JC-1. Analysis of these JC-1 labeled mitochondria by confocal microscopy revealed that mitochondrial membrane potential was significantly reduced in both PD and AD cybrid cells when compared with controls. Ultrastructural examination showed that control cybrid cells contained small, morphologically normal, round or oval mitochondria with a dark matrix and regular distribution of cristae. PD cybrid cells contained a significant and increased percentage of mitochondria that were enlarged or swollen and had a pale matrix with few remaining cristae (0.26-0.65 microm(2)). AD cybrid cells also contained a significantly increased percentage of enlarged or swollen mitochondria (0.25-5.0 microm(2)) that had a pale matrix and few remaining cristae. Other pathological features such as crystal-like intramitochondrial inclusions and cytoplasmic inclusion bodies were also found in PD and AD cybrids. These observations suggest that transfer of PD or AD mtDNA into Rho(0) cells was sufficient to produce pathological changes in mitochondrial ultrastructure that are similar to those seen in other mitochondrial disorders. These data were reported in abstract form (Trimmer et al., 1998, Soc. Neurosci. Abstr. 24: 476).

Role of mitochondria in amyotrophic lateral sclerosis.

Neurodegeneration in amyotrophic lateral sclerosis (ALS) is characterized by the specific loss of central and peripheral motor neurons. While this pattern of neuronal demise gives rise to a distinct clinical syndrome, at the cellular and molecular level ALS pathology is similar to that seen in other neurodegenerative diseases. In particular, mitochondrial dysfunction in ALS is reminiscent of that observed in Alzheimer's and Parkinson's diseases. Mitochondria in persons with ALS demonstrate impaired electron transport, increased free radical generation, and an inability to adequately buffer cytosolic calcium shifts. These abnormalities are probably systemic and potentially due to mutation of mitochondrial DNA.

Mitochondrial abnormalities in non-alcoholic steatohepatitis.

BACKGROUND/AIMS: We assessed mitochondrial morphology by electron microscopy and the prevalence of a mitochondrial gene deletion in patients with non-alcoholic steatohepatitis (NASH), alcohol-related liver disease and non-fatty liver diseases. Respiratory chain function using a cytoplasmic hybrid (cybrid) assay was further studied in NASH patients and healthy controls. METHODS: Electron microscopy was performed in 26 specimens. Fifteen patients were studied by polymerase chain reaction to detect a 520-bp deletion product of the mitochondrial genome (dmtDNA). Cybrids were created by fusion of platelets with anaerobic neuroblastoma cells in six NASH patients and 12 controls. RESULTS: Eight of ten NASH, one of seven alcoholics and two of nine other patients had linear crystalline inclusions in megamitochondria (p<0.05). Three of five patients with alcohol-related liver disease had dmtDNA compared to one of five NASH patients and one of five non-steatohepatitis controls. Cybrid respiratory chain function in platelets was not different from that of controls. CONCLUSIONS: Respiratory chain dysfunction, if present in NASH, is not expressed in platelet-derived mitochondria. In contrast to alcohol-related liver disease with active drinking, NASH patients do not commonly express the 5-kb mitochondrial DNA gene deletion in liver tissue. As previously described in early alcohol-related liver disease, crystalline inclusions of unknown composition are seen in hepatic mitochondria in NASH. Their presence suggests either an adaptive process or mitochondrial injury.

Characterization of cybrid cell lines containing mtDNA from Huntington's disease patients.

Electron transport chain (ETC) dysfunction may arise from mitochondrial genetic, nuclear genetic, or toxic etiologies. Cytoplasmic hybrid (cybrid) systems can help distinguish between these possibilities by facilitating expression of suspect mitochondrial DNA (mtDNA) within a nuclear and environmentally controlled context. Perpetuation of ETC dysfunction in cybrids is consistent with an mtDNA pathogenesis while defect correction is not. We previously used cybrids to screen sporadic Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis patients for mtDNA mutation with positive results. To further address the fidelity of these experiments, we created and characterized cybrids expressing mtDNA from persons with Huntington's disease (HD), an autosomal dominant, nuclear DNA-determined disorder in which mitochondrial ETC functioning is abnormal. On ETC, oxidative stress, and calcium homeostasis assays HD cybrid lines were indistinguishable from control cybrid lines. These data support the use of the cybrid technique for mtDNA mutation screening in candidate diseases.