Mitochondrial function in fibroblasts with aging in culture and/or Alzheimer's disease

A Lombard Variety of Sweet Pepper Regulating Senescence and Proliferation: The Voghera Pepper

Aging and its related disorders are important issues nowadays and the first cause of this physio-pathological condition is the overproduction of ROS. Ascorbic acid is an antioxidant mediator and its anti-aging proprieties are well known. Our previous data demonstrated that Voghera sweet pepper (VP), a distinctive type of pepper cultivated in Italy, is particularly rich in ascorbic acid. Based on these data, the anti-aging effect mediated by extracts of the edible part of VP was evaluated on an in vitro model of both young and old Normal Human Diploid Fibroblasts (NHDF). Using phase contrast microscopy, we observed that VP may help cells in the maintenance of physiological morphology during aging. Cytofluorimetric analyses revealed that VP extracts led to an increase in DNA synthesis and percentage of living cells, linked to a consequent increase in mitotic events. This hypothesis is supported by the enhancement of PCNA expression levels observed in old, treated fibroblasts, corroborating the idea that this extract could recover a young phenotype in adult fibroblasts, confirmed by the study of p16 and p53 expression levels and TEM analyses. Based on these results, we may suppose that VP can lead to the partial recovery of "young-like" phenotypes in old fibroblasts.

Posttraumatic stress disorder is characterized by functional dysregulation of dermal fibroblasts

Incidence of mental health disorders are rising in modernity, with psychological stress linked to a propensity for developing various chronic diseases due to a relative inability of the body to counter the allostatic load on cellular level. Despite these high rates of comorbidities associated with posttraumatic stress disorder (PTSD), there is still a lack of understanding in terms of the peripheral effects of PTSD on tissue level. Therefore, the purpose of this study was to profile basal dermal fibroblast functional status in PTSD using a wide range of markers involved in the cell-to-cell communication facilitated by fibroblasts. Primary dermal fibroblasts derived from patients diagnosed with PTSD (n = 11) and matched trauma exposed controls (i.e. who did not develop PTSD, n = 10) were cultured using standard techniques. The patients and controls were matched based on age, sex, body-mass index (BMI) and lifestyle. The growth rate, population doubling time, cell surface marker expression (CD31, FNDC5) (flow cytometry), secretome (TIMP-2, MMP-9) (ELISAs), intracellular signalling capacity (Fluo-4 Ca2+ flux) and gene expression (IL-6, IL-10, PTX-3, iNOS, Arg1) were compared between groups. The data illustrated significant PTSD-associated fibroblast conditioning resulting in a blunted signalling capacity. This observation highlights the importance of including tissue-specific investigations in future studies focused on elucidating the association between PTSD and subsequent risk for somatic disease.

Human Derived Dermal Fibroblasts as in Vitro Research Tool to Study Circadian Rhythmicity in Psychiatric Disorders

A number of psychiatric disorders are defined by persistent or recurrent sleep-wake disturbances alongside disruptions in circadian rhythm and altered clock gene expression. Circadian rhythms are present not only in the hypothalamic suprachiasmatic nucleus but also in peripheral tissues. In this respect, cultures of human derived dermal fibroblasts may serve as a promising new tool to investigate cellular and molecular mechanisms underlying the pathophysiology of mental illness. In this article, we discuss the advantages of fibroblast cultures to study psychiatric disease. More specifically, we provide an update on recent advances in modeling circadian rhythm disorders using human fibroblasts.

Calcium Signaling and Mitochondrial Function in Presenilin 2 Knock-Out Mice: Looking for Any Loss-of-Function Phenotype Related to Alzheimer's Disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder in which learning, memory and cognitive functions decline progressively. Familial forms of AD (FAD) are caused by mutations in amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes. Presenilin 1 (PS1) and its homologue, presenilin 2 (PS2), represent, alternatively, the catalytic core of the γ-secretase complex that, by cleaving APP, produces neurotoxic amyloid beta (Aβ) peptides responsible for one of the histopathological hallmarks in AD brains, the amyloid plaques. Recently, PSEN1 FAD mutations have been associated with a loss-of-function phenotype. To investigate whether this finding can also be extended to PSEN2 FAD mutations, we studied two processes known to be modulated by PS2 and altered by FAD mutations: Ca2+ signaling and mitochondrial function. By exploiting neurons derived from a PSEN2 knock-out (PS2-/-) mouse model, we found that, upon IP3-generating stimulation, cytosolic Ca2+ handling is not altered, compared to wild-type cells, while mitochondrial Ca2+ uptake is strongly compromised. Accordingly, PS2-/- neurons show a marked reduction in endoplasmic reticulum-mitochondria apposition and a slight alteration in mitochondrial respiration, whereas mitochondrial membrane potential, and organelle morphology and number appear unchanged. Thus, although some alterations in mitochondrial function appear to be shared between PS2-/- and FAD-PS2-expressing neurons, the mechanisms leading to these defects are quite distinct between the two models. Taken together, our data appear to be difficult to reconcile with the proposal that FAD-PS2 mutants are loss-of-function, whereas the concept that PS2 plays a key role in sustaining mitochondrial function is here confirmed.

Ursodeoxycholic Acid Improves Mitochondrial Function and Redistributes Drp1 in Fibroblasts from Patients with Either Sporadic or Familial Alzheimer's Disease

Alzheimer's disease (AD) is the leading cause of dementia worldwide. Mitochondrial abnormalities have been identified in many cell types in AD, with deficits preceding the development of the classical pathological aggregations. Ursodeoxycholic acid (UDCA), a treatment for primary biliary cirrhosis, improves mitochondrial function in fibroblasts derived from Parkinson's disease patients as well as several animal models of AD and Parkinson's disease. In this paper, we investigated both mitochondrial function and morphology in fibroblasts from patients with both sporadic and familial AD. We show that both sporadic AD (sAD) and PSEN1 fibroblasts share the same impairment of mitochondrial membrane potential and alterations in mitochondrial morphology. Mitochondrial respiration, however, was decreased in sAD fibroblasts and increased in PSEN1 fibroblasts. Morphological changes seen in AD fibroblasts include reduced mitochondrial number and increased mitochondrial clustering around the cell nucleus as well as an increased number of long mitochondria. We show here for the first time in AD patient tissue that treatment with UDCA increases mitochondrial membrane potential and respiration as well as reducing the amount of long mitochondria in AD fibroblasts. In addition, we show reductions in dynamin-related protein 1 (Drp1) level, particularly the amount localized to mitochondria in both sAD and familial patient fibroblasts. Drp1 protein amount and localization were increased after UDCA treatment. The restorative effects of UDCA are abolished when Drp1 is knocked down. This paper highlights the potential use of UDCA as a treatment for neurodegenerative disease.

Sodium Iodate Disrupted the Mitochondrial-Lysosomal Axis in Cultured Retinal Pigment Epithelial Cells

PURPOSE

Low doses of sodium iodate (NaIO₃) impair visual function in experimental animals with selective damage to retinal pigment epithelium (RPE) and serve as a useful model to study diseases caused by RPE degeneration. Mitochondrial dysfunction and defective autophagy have been suggested to play important roles in normal aging as well as many neurodegenerative diseases. In this study, we examined whether NaIO₃ treatment disrupted the mitochondrial-lysosomal axis in cultured RPE.

METHODS

The human RPE cell line, ARPE-19, was treated with low concentrations (≤500 μM) of NaIO₃. The expression of proteins involved in the autophagic pathway and mitochondrial biogenesis was examined with Western blot. Intracellular acidic compartments and lipofuscinogenesis were evaluated by acridine orange staining and autofluorescence, respectively. Mitochondrial mass, mitochondrial membrane potential (MMP), and mitochondrial function were quantified by MitoTracker Green staining, tetramethylrhodamine methyl ester staining, and the MTT assay, respectively. Phagocytosis and the degradation of photoreceptor outer segments (POS) were assessed by fluorescence-based approaches and Western blot against rhodopsin.

RESULTS

Treatment with low concentrations of NaIO₃ decreased cellular acidity, blocked autophagic flux, and resulted in increased lipofuscinogenesis in ARPE-19 cells. Despite increases in protein levels of Sirtuin 1 and PGC-1α, mitochondrial function was compromised, and this decrease was attributed to disrupted MMP. POS phagocytic activities decreased by 60% in NaIO₃-treated cells, and the degradation of ingested POS was also impaired. Pretreatment and cotreatment with rapamycin partially rescued NaIO₃-induced RPE dysfunction.

CONCLUSIONS

Low concentrations of NaIO₃ disrupted the mitochondrial-lysosomal axis in RPE and led to impaired phagocytic activities and degradation capacities.

Human dermal fibroblasts in psychiatry research

In order to decipher the disease etiology, progression and treatment of multifactorial human brain diseases we utilize a host of different experimental models. Recently, patient-derived human dermal fibroblast (HDF) cultures have re-emerged as promising in vitro functional system for examining various cellular, molecular, metabolic and (patho)physiological states and traits of psychiatric disorders. HDF studies serve as a powerful complement to postmortem and animal studies, and often appear to be informative about the altered homeostasis in neural tissue. Studies of HDFs from patients with schizophrenia (SZ), depression, bipolar disorder (BD), autism, attention deficit and hyperactivity disorder and other psychiatric disorders have significantly advanced our understanding of these devastating diseases. These reports unequivocally prove that signal transduction, redox homeostasis, circadian rhythms and gene*environment (G*E) interactions are all amenable for assessment by the HDF model. Furthermore, the reported findings suggest that this underutilized patient biomaterial, combined with modern molecular biology techniques, may have both diagnostic and prognostic value, including prediction of response to therapeutic agents.

Identification of tetrahydrocarbazoles as novel multifactorial drug candidates for treatment of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative brain disorder and the most frequent cause of dementia. To date, there are only a few approved drugs for AD, which show little or no effect on disease progression. Impaired intracellular calcium homeostasis is believed to occur early in the cascade of events leading to AD. Here, we examined the possibility of normalizing the disrupted calcium homeostasis in the endoplasmic reticulum (ER) store as an innovative approach for AD drug discovery. High-throughput screening of a small-molecule compound library led to the identification of tetrahydrocarbazoles, a novel multifactorial class of compounds that can normalize the impaired ER calcium homeostasis. We found that the tetrahydrocarbazole lead structure, first, dampens the enhanced calcium release from ER in HEK293 cells expressing familial Alzheimer's disease (FAD)-linked presenilin 1 mutations. Second, the lead structure also improves mitochondrial function, measured by increased mitochondrial membrane potential. Third, the same lead structure also attenuates the production of amyloid-beta (Aβ) peptides by decreasing the cleavage of amyloid precursor protein (APP) by β-secretase, without notably affecting α- and γ-secretase cleavage activities. Considering the beneficial effects of tetrahydrocarbazoles addressing three key pathological aspects of AD, these compounds hold promise for the development of potentially effective AD drug candidates.

Mitochondrial dynamics in aging and disease

Mitochondria are self-replicating organelles but nevertheless strongly depend on supply coded in nuclear genes. They serve many physiological demands in living cells. Supply of the cytoplasm with ATP and engagement in Ca(2+) regulation belong to the main functions of mitochondria. In large eukaryotic cells, in particular in neurons, with their long dendrites and axons, mitochondria have to move to the sites of their action. This trafficking involves several motor molecules and mechanisms to sense the sites of requirements of mitochondria. With aging and as a consequence of some diseases, mitochondrial components may be rendered dysfunctional, and mtDNA mutations arise during the course of replication and by the action of reactive oxygen species. Mutants in motor molecules engaged in trafficking and in the machinery of fusion and fission are causing severe deficiencies on the cellular level; they support neurodegeneration and, thus, cause many diseases. Frequent fusion and fission events mediate the elimination of impaired parts from mitochondria which finally will be degraded by autophagosomes. Extensive fusion provides a basis for functional complementation. Mobility of proteins and small molecules within the mitochondria is necessary to reach the functional goals of fusion and fission, although cristae and a large fraction of proteins of the respiratory complexes proved to be stable for hours after fusion and perform slow exchange of material.

Comparative effect of Piper betle, Chlorella vulgaris and tocotrienol-rich fraction on antioxidant enzymes activity in cellular ageing of human diploid fibroblasts

Background

Human diploid fibroblasts (HDFs) undergo a limited number of cellular divisions in culture and progressively reach a state of irreversible growth arrest, a process termed cellular ageing. Even though beneficial effects of Piper betle, Chlorella vulgaris and tocotrienol-rich fraction (TRF) have been reported, ongoing studies in relation to ageing is of interest to determine possible protective effects that may reverse the effect of ageing. The aim of this study was to evaluate the effect of P. betle, C. vulgaris and TRF in preventing cellular ageing of HDFs by determining the activity of antioxidant enzymes viz.; catalase, superoxide dismutase (SOD) and glutathione peroxidase.

Methods

Different passages of HDFs were treated with P. betle, C. vulgaris and TRF for 24 h prior to enzymes activity determination. Senescence-associated beta-galactosidase (SA β-gal) expression was assayed to validate cellular ageing.

Results

In cellular ageing of HDFs, catalase and glutathione peroxidase activities were reduced, but SOD activity was heightened during pre-senescence. P. betle exhibited the strongest antioxidant activity by reducing SA β-gal expression, catalase activities in all age groups, and SOD activity. TRF exhibited a strong antioxidant activity by reducing SA β-gal expression, and SOD activity in senescent HDFs. C. vulgaris extract managed to reduce SOD activity in senescent HDFs.

Conclusion

P. betle, C. vulgaris, and TRF have the potential as anti-ageing entities which compensated the role of antioxidant enzymes in cellular ageing of HDFs.

Peripheral mitochondrial dysfunction in Alzheimer's disease: focus on lymphocytes

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease. Today, AD affects millions of people worldwide and the number of AD cases will increase with increased life expectancy. The AD brain is marked by severe neurodegeneration like the loss of synapses and neurons, atrophy and depletion of neurotransmitter systems in the hippocampus and cerebral cortex. Recent findings suggest that these pathological changes are causally induced by mitochondrial dysfunction and increased oxidative stress. These changes are not only observed in the brain of AD patients but also in the periphery. In this review, we discuss the potential role of elevated apoptosis, increased oxidative stress and especially mitochondrial dysfunction as peripheral markers for the detection of AD in blood cells especially in lymphocytes. We discuss recent not otherwise published findings on the level of complex activities of the respiratory chain comprising mitochondrial respiration and the mitochondrial membrane potential (MMP). We obtained decreased basal MMP levels in lymphocytes from AD patients as well as enhanced sensitivity to different complex inhibitors of the respiratory chain. These changes are in line with mitochondrial defects obtained in AD cell and animal models, and in post-mortem AD tissue. Importantly, these mitochondrial alterations where not only found in AD patients but also in patients with mild cognitive impairment (MCI). These new findings point to a relevance of mitochondrial function as an early peripheral marker for the detection of AD and MCI.

Primary skin fibroblasts as a model of Parkinson's disease

Parkinson's disease is the second most frequent neurodegenerative disorder. While most cases occur sporadic mutations in a growing number of genes including Parkin (PARK2) and PINK1 (PARK6) have been associated with the disease. Different animal models and cell models like patient skin fibroblasts and recombinant cell lines can be used as model systems for Parkinson's disease. Skin fibroblasts present a system with defined mutations and the cumulative cellular damage of the patients. PINK1 and Parkin genes show relevant expression levels in human fibroblasts and since both genes participate in stress response pathways, we believe fibroblasts advantageous in order to assess, e.g. the effect of stressors. Furthermore, since a bioenergetic deficit underlies early stage Parkinson's disease, while atrophy underlies later stages, the use of primary cells seems preferable over the use of tumor cell lines. The new option to use fibroblast-derived induced pluripotent stem cells redifferentiated into dopaminergic neurons is an additional benefit. However, the use of fibroblast has also some drawbacks. We have investigated PARK6 fibroblasts and they mirror closely the respiratory alterations, the expression profiles, the mitochondrial dynamics pathology and the vulnerability to proteasomal stress that has been documented in other model systems. Fibroblasts from patients with PARK2, PARK6, idiopathic Parkinson's disease, Alzheimer's disease, and spinocerebellar ataxia type 2 demonstrated a distinct and unique mRNA expression pattern of key genes in neurodegeneration. Thus, primary skin fibroblasts are a useful Parkinson's disease model, able to serve as a complement to animal mutants, transformed cell lines and patient tissues.

Biogenesis and regulation of microRNA: implication in Alzheimer’s disease

MicroRNAs (miRNAs) represent an intriguing class of small, endogenous noncoding RNAs. miRNAs post-transcriptionally inhibit the expression of their specific target mRNAs, primarily by imperfect base pairing with the 3´ untranslated region. In the nervous system, interest in the functions of miRNAs has recently expanded to include their roles in neurodegeneration. Recent investigations have revealed the influence of miRNAs on neuronal death and in the β-amyloid cascade associated with Alzheimer’s disease.

Evidence of mitochondrial dysfunction in obese adolescents

AIM

Although obesity and weight gain generally are anticipated to be caused by an imbalance between energy intake and energy expenditure, the significance of thyroid hormones (TH) remains unclear. Examination of mitochondrial function may reflect intracellular thyroid hormone effect and elucidate whether a lower metabolic rate is present.

METHODS

In a group of 34 obese adolescents (age <16 years and body mass index above the age-related 95th percentile), and an age- and gender-matched group of 32 lean adolescent, thyroid stimulating hormone (TSH) and basal oxygen consumption were measured and mitochondrial function in peripheral blood monocytes was determined by flow cytometry.

RESULTS

Significant increase in TSH (3.06 +/- 1.56 mU/L vs. 2.33 +/- 0.91 mU/L, p < 0.05) and a decrease in VO2 (129 +/- 16 mL O2/m(2)*min vs. 146 +/- 15 mL O2/m(2)*min, p < 0.05) were observed in obese adolescents compared with lean adolescents. Flow cytometry analysis demonstrated a lower mitochondrial mass (6385 +/- 1962 a.u. vs. 7608 +/- 2328 a.u., p < 0.05) and mitochondrial membrane potential (11426 +/- 3861 a.u. vs. 14017 +/- 5536 a.u., p < 0.05) in obese adolescents compared with lean adolescents. These results are even more pronounced in adolescents with obese mothers.

CONCLUSION

In obese adolescents, the increased TSH and lowered VO2 propose a lowered basal metabolic rate and the impaired mitochondrial function suggests a decreased thyroid hormone stimulation of mitochondrial energy production. The maternal in-heritage is suggestive of a basal metabolic defect or mitochondrial resistance for TH.

Mitochondrial membrane potential in axons increases with local nerve growth factor or semaphorin signaling

Neurons concentrate mitochondria at sites in the cell that have a high demand for ATP and/or calcium buffering. To accomplish this, mitochondrial transport and docking are thought to respond to intracellular signaling pathways. However, the cell might also concentrate mitochondrial function by locally modulating mitochondrial activity. We tested this hypothesis by measuring the membrane potential of individual mitochondria throughout the axons of chick sensory neurons using the dye tetramethylrhodamine methylester (TMRM). We found no difference in the TMRM mitochondrial-to-cytoplasmic fluorescence ratio (F(m)/F(c)) among three functionally distinct regions: axonal branch points, distal axons, and the remaining axon shaft. In addition, we found no difference in F(m)/F(c) among stationary, retrogradely moving, or anterogradely moving mitochondria. However, F(m)/F(c) was significantly higher in the lamellipodia of growth cones, and among a small fraction of mitochondria throughout the axon. To identify possible signals controlling membrane potential, we used beads covalently coupled to survival and guidance cues to provide a local stimulus along the axon shaft. NGF- or semaphorin 3A-coupled beads caused a significant increase in F(m)/F(c) in the immediately adjacent region of axon, and this was diminished in the presence of the PI3 (phosphatidylinositol-3) kinase inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one] or the MAP (mitogen-activated protein) kinase inhibitor U0126 (1,4-diamino-2,3-dicyano-1,4-bis[2-amino-phenylthio]butadiene), demonstrating that signaling pathways downstream of both ligands affect the DeltaPsi(m) of mitochondria. In addition, general inhibition of receptor tyrosine kinase activity produced a profound global decrease in F(m)/F(c). Thus, two guidance molecules that exert different effects on growth cone motility both elicit local, receptor-mediated increases in membrane potential.

Dynamin-like protein 1 reduction underlies mitochondrial morphology and distribution abnormalities in fibroblasts from sporadic Alzheimer's disease patients

Mitochondrial function relies heavily on its morphology and distribution, alterations of which have been increasingly implicated in neurodegenerative diseases, such as Alzheimer's disease (AD). In this study, we found abnormal mitochondrial distribution characterized by elongated mitochondria that accumulated in perinuclear areas in 19.3% of sporadic AD (sAD) fibroblasts, which was in marked contrast to their normally even cytoplasmic distribution in the majority of human fibroblasts from normal subjects (>95%). Interestingly, levels of dynamin-like protein 1 (DLP1), a regulator of mitochondrial fission and distribution, were decreased significantly in sAD fibroblasts. To explore the potential role of DLP1 in mediating mitochondrial abnormalities in sAD fibroblasts, both the overexpression of a dominant negative DLP1 mutant and the reduced expression of DLP1 by miR RNAi in human fibroblasts from normal subjects significantly increased mitochondrial abnormalities. Moreover, overexpression of wild-type DLP1 in sAD fibroblasts rescued these mitochondrial abnormalities. Based on these data, we conclude that DLP1 reduction causes mitochondrial abnormalities in sAD fibroblasts. We further demonstrate that elevated oxidative stress and increased amyloid beta production are likely the potential pathogenic factors that cause DLP1 reduction and abnormal mitochondrial distribution in AD cells.

Benefits from dietary polyphenols for brain aging and Alzheimer's disease

Brain aging and the most diffused neurodegenerative diseases of the elderly are characterized by oxidative damage, redox metals homeostasis impairment and inflammation. Food polyphenols can counteract these alterations in vitro and are therefore suggested to have potential anti-aging and brain-protective activities, as also indicated by the results of some epidemiological studies. Despite the huge and increasing amount of the in vitro studies trying to unravel the mechanisms of action of dietary polyphenols, the research in this field is still incomplete, and questions about bioavailability, biotransformation, synergism with other dietary factors, mechanisms of the antioxidant activity, risks inherent to their possible pro-oxidant activities are still unanswered. Most of all, the capacity of the majority of these compounds to cross the blood-brain barrier and reach brain is still unknown. This commentary discusses recent data on these aspects, particularly focusing on effects of curcumin, resveratrol and catechins on Alzheimer's disease.

Enhanced apoptosis, oxidative stress and mitochondrial dysfunction in lymphocytes as potential biomarkers for Alzheimer's disease

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease. Today, AD affects millions of people worldwide and the number of AD cases will increase with increased life expectancy. The AD brain is marked by severe neurodegeneration like the loss of synapses and neurons, atrophy and depletion of neurotransmitter systems in the hippocampus and cerebral cortex. Recent findings suggest that these pathological changes are causally induced by mitochondrial dysfunction, increased oxidative stress and elevated apoptosis. Until now, AD cannot be diagnosed by a valid clinical method or a biomarker before the disease has progressed so far that dementia is present. Furthermore, no valid method is available to determine which patient with mild cognitive impairment (MCI) will progress to AD. Therefore, a correct diagnosis in the early stage of AD is not only of importance considering that early drug treatment is more effective but also that the psychological burden of the patients and relatives could be decreased. In this review, we discuss the potential role of elevated apoptosis, increased oxidative stress and mitochondrial dysfunction as biomarker for AD in a peripheral cell model, the lymphocytes.

Effects of beta-amyloid peptide and estrogen on platelet mitochondrial function of Sprague-Dawley rats

Beta-amyloid peptide (Abeta) peptides play a central role in the development of Alzheimer's disease. They are known to induce mitochondrial dysfunction and caspase activation, resulting in apoptosis of neuronal cells. In the present experiment, an Abeta-induced damage model of platelets was established to observe the effects of Abeta, estradiol benzoate (EB) and genistein on platelets and platelet mitochondria. It was found that after the addition of Abeta, platelet number, platelet mitochondrial membrane potential (DeltaPsim) and adenosine triphosphate (ATP) content were lowered while no protective effects of EB and genistein had been observed. The platelets could serve as a biomarker for detection of mitochondrial function and age related disease.

Intersection between mitochondrial permeability pores and mitochondrial fusion/fission

The goal of this review is to highlight recent developments in the field of mitochondrial membrane processes, which provide new insights into the relation between mitochondrial fission/fusion events and the mitochondrial permeability transition (MPT). First, we distinguish between pore opening events at the inner and outer mitochondrial membranes. Inner membrane pore opening, or iMPT, leads to membrane depolarization, release of low molecular weight compounds, cristae reorganization and matrix swelling. Outer membrane pore opening, or oMPT, allows partial release of apoptotic proteins, while complete release requires additional remodeling of inner membrane cristae. Second, we summarize recent data that supports a similar temporal and physical separation between inner and outer mitochondrial membrane fusion events. Finally, we focus on cristae remodeling, which may be the intersection between oMPT and iMPT events. Interestingly, components of fusion machinery, such as mitofusin 2 and OPA1, appear to play a role in cristae remodeling as well.

Simultaneous age-related depolarization of mitochondrial membrane potential and increased mitochondrial reactive oxygen species production correlate with age-related glutamate excitotoxicity in rat hippocampal neurons

Mitochondria are implicated in glutamate excitotoxicity by causing bioenergetic collapse, loss of Ca(2+) homeostasis, and generation of reactive oxygen species (ROS), all of which become increasingly important clinically with age. Little is known about how aging affects the relative importance of mitochondrial membrane potential (DeltaPsi(m)) and ROS production. To determine aging affects on DeltaPsi(m) and ROS production in individual somal and axonal/dendritic mitochondria, we compared ROS production while simultaneously monitoring DeltaPsi(m) before and after glutamate treatment of live neurons from embryonic (day 18), middle-aged (9-12 months), and old (24 months) rats. At rest, old neuronal mitochondria 1) showed a higher rate of ROS production that was particularly strong in axonal/dendritic mitochondria relative to that in middle-age neurons, 2) were more depolarized in comparison with neurons of other ages, and 3) showed no differences in ROS or DeltaPsi(m) as a function of distance from the nucleus. All DeltaPsi(m) grouped into three classes of high (less than -120 mV), medium (-85 to -120 mV), and low (greater than -85 mV) polarization that shifted toward the lower classes with age at rest. Glutamate exposure dramatically depolarized the DeltaPsi(m) in parallel with greatly increased ROS production, with a surprising absence of an effect of age or distance from the nucleus on these mitochondrial parameters. These data suggest that old neurons are more susceptible to glutamate excitotoxicity because of an insidious depolarization of DeltaPsi(m) and rate of ROS generation at rest that lead to catastrophic failure of phosphorylative and reductive energy supplies under stress.

Differential role of Presenilin-1 and -2 on mitochondrial membrane potential and oxygen consumption in mouse embryonic fibroblasts

Increasing evidence indicates that mitochondrial alterations contribute to the neuronal death in Alzheimer's disease (AD). Presenilin 1 (PS1) and Presenilin 2 (PS2) mutations have been shown to sensitize cells to apoptosis by mechanisms suggested to involve impaired mitochondrial function. We have previously detected active gamma-secretase complexes in mitochondria. We investigated the impact of PS/gamma-secretase on mitochondrial function using mouse embryonal fibroblasts derived from wild-type, PS1-/-, PS2-/- and PS double knock-out (PSKO) embryos. Measurements of mitochondrial membrane potential (DeltaPsim) showed a higher percentage of fully functional mitochondria in PS1-/- and PSwt as compared to PS2-/- and PSKO cells. This result was evident both in whole cell preparations and in isolated mitochondria. Interestingly, pre-treatment of isolated mitochondria with the gamma-secretase inhibitor L-685,458 resulted in a decreased population of mitochondria with high DeltaPsim in PSwt and PS1-/- cells, indicating that PS2/gamma-secretase activity can modify DeltaPsim. PS2-/- cells showed a significantly lower basal respiratory rate as compared to other cell lines. However, all cell lines demonstrated competent bioenergetic function. These data point toward a specific role of PS2/gamma-secretase activity for proper mitochondrial function and indicate interplay between PS1 and PS2 in mitochondrial functionality.

Aging sensitizes toward ROS formation and lipid peroxidation in PS1M146L transgenic mice

Mutations in the presenilins (PS) account for the majority of familial Alzheimer disease (FAD) cases. To test the hypothesis that oxidative stress can underlie the deleterious effects of presenilin mutations, we analyzed lipid peroxidation products (4-hydroxynonenal (HNE) and malondialdehyde) and antioxidant defenses in brain tissue and levels of reactive oxygen species (ROS) in splenic lymphocytes from transgenic mice bearing human PS1 with the M146L mutation (PS1M146L) compared to those from mice transgenic for wild-type human PS1 (PS1wt) and nontransgenic littermate control mice. In brain tissue, HNE levels were increased only in aged (19-22 months) PS1M146L transgenic animals compared to PS1wt mice and not in young (3-4 months) or middle-aged mice (13-15 months). Similarly, in splenic lymphocytes expressing the transgenic PS1 proteins, mitochondrial and cytosolic ROS levels were elevated to 142.1 and 120.5% relative to controls only in cells from aged PS1M146L animals. Additionally, brain tissue HNE levels were positively correlated with mitochondrial ROS levels in splenic lymphocytes, indicating that oxidative stress can be detected in different tissues of PS1 transgenic mice. Antioxidant defenses (activities of antioxidant enzymes Cu/Zn-SOD, GPx, or GR) or susceptibility to in vitro oxidative stimulation was unaltered. In summary, these results demonstrate that the PS1M146L mutation increases mitochondrial ROS formation and oxidative damage in aged mice. Hence, oxidative stress caused by the combined effects of aging and PS1 mutations may be causative for triggering neurodegenerative events in FAD patients.