Mitochondrial impairment and synaptic dysfunction are associated with neurological defects in iPSCs-derived cortical neurons of MERRF patients.

BACKGROUND: Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome is a rare inherited mitochondrial disease mainly caused by the m.8344A > G mutation in mitochondrial tRNALys gene, and usually manifested as complex neurological disorders and muscle weakness. Currently, the pathogenic mechanism of this disease has not yet been resolved, and there is no effective therapy for MERRF syndrome. In this study, MERRF patients-derived iPSCs were used to model patient-specific neurons for investigation of the pathogenic mechanism of neurological disorders in mitochondrial disease. METHODS: MERRF patient-derived iPSCs were differentiated into excitatory glutamatergic neurons to unravel the effects of the m.8344A > G mutation on mitochondrial bioenergetic function, neural-lineage differentiation and neuronal function. By the well-established differentiation protocol and electrophysiological activity assay platform, we examined the pathophysiological behaviors in cortical neurons of MERRF patients. RESULTS: We have successfully established the iPSCs-derived neural progenitor cells and cortical-like neurons of patients with MERRF syndrome that retained the heteroplasmy of the m.8344A > G mutation from the patients' skin fibroblasts and exhibited the phenotype of the mitochondrial disease. MERRF neural cells harboring the m.8344A > G mutation exhibited impaired mitochondrial bioenergetic function, elevated ROS levels and imbalanced expression of antioxidant enzymes. Our findings indicate that neural immaturity and synaptic protein loss led to the impairment of neuronal activity and plasticity in MERRF neurons harboring the m.8344A > G mutation. By electrophysiological recordings, we monitored the in vivo neuronal behaviors of MERRF neurons and found that neurons harboring a high level of the m.8344A > G mutation exhibited impairment of the spontaneous and evoked potential-stimulated neuronal activities. CONCLUSIONS: We demonstrated for the first time the link of mitochondrial impairment and synaptic dysfunction to neurological defects through impeding synaptic plasticity in excitatory neurons derived from iPSCs of MERRF patients harboring the m.8344A > G mutation. This study has provided new insight into the pathogenic mechanism of the tRNALys gene mutation of mtDNA, which is useful for the development of a patient-specific iPSCs platform for disease modeling and screening of new drugs to treat patients with MERRF syndrome.

Effects of Tolerance-Induced Preconditioning on Mitochondrial Biogenesis in Undifferentiated and Differentiated Neuronal Cells.

BACKGROUND: Mitochondrial biogenesis occurs in response to chronic stresses as an adaptation to the increased energy demands and often renders cells more refractive to subsequent injuries which is referred to as preconditioning. This phenomenon is observed in several non-neuronal cell types, but it is not yet fully established in neurons, although it is fundamentally important for neuroprotection and could be exploited for therapeutic purposes. METHODS: This study was designed to examine whether the preconditioning treatment with hypoxia or nitric oxide could trigger biogenesis in undifferentiated and differentiated neuronal cells (rat PC12 and human NT2 cells) as well as in primary mouse cortical neurons. RESULTS: The results showed that both preconditioning paradigms induced mitochondrial biogenesis in undifferentiated cell lines, as indicated by an increase of mitochondrial mass (measured by flow cytometry of NAO fluorescence) and increased expression of genes required for mitochondrial biogenesis (Nrf1, Nrf2, Tfam, Nfκb1) and function (Cox3, Hk1). All these changes translated into an increase in the organelle copy number from an average of 20-40 to 40-60 mitochondria per cell. The preconditioning treatments also rendered the cells significantly less sensitive to the subsequent oxidative stress challenge brought about by oxygen/glucose deprivation, consistent with their improved cellular energy status. Mitochondrial biogenesis was abolished when preconditioning treatments were performed in the presence of antioxidants (vitamin E or CoQ10), indicating clearly that ROS-signaling pathway(s) played a critical role in the induction of this phenomenon in undifferentiated cells. However, mitochondrial biogenesis could not be re-initiated by preconditioning treatments in any of the post-mitotic neuronal cells tested, i.e., neither rat PC12 cells differentiated with NGF, human NT2 cells differentiated with retinoic acid nor mouse primary cortical neurons. Instead, differentiated neurons had a much higher organelle copy number per cell than their undifferentiated counterparts (100-130 mitochondria per neuron vs. 20-40 in proliferating cells), and this feature was not altered by preconditioning. CONCLUSIONS: Our study demonstrates that mitochondrial biogenesis occurred during the differentiation process resulting in more beneficial energy status and improved tolerance to oxidative stress in neurons, putting in doubt whether additional enhancement of this phenomenon could be achieved and successfully exploited as a way for better neuroprotection.

Depletion of Sirt3 leads to the impairment of adipogenic differentiation and insulin resistance via interfering mitochondrial function of adipose-derived human mesenchymal stem cells.

Upregulation of mitochondrial function and oxidative metabolism is a hallmark in the differentiation of stem cells. However, the mechanism underlying the metabolic reprogramming and upregulation of mitochondrial function during the differentiation of human mesenchymal stem cells (hMSCs) is largely unclear. Sirt3 has emerged as a sensor in regulating mitochondrial function and antioxidant defence system in cellular response to energy demand or environmental stimuli, but its roles in stem cell differentiation have not been fully understood. In this study, we used adipose-derived hMSCs (ad-hMSCs) to investigate the role of Sirt3 in adipogenic differentiation and in the function of mature adipocytes. We showed that at the early stage of adipogenic differentiation, Sirt3 upregulation is essential for the activation of biogenesis and bioenergetic function of mitochondria. In addition, we found that induction of Forkhead Box O 3a (FoxO3a), an upstream factor that regulates MnSOD gene transcription, is involved in the upregulation of antioxidant enzymes at the early stage of adipogenic differentiation. Silencing of Sirt3 by shRNA decreased the protein level of FoxO3a and subsequently downregulated a number of FoxO3a-mediated antioxidant enzymes and increased oxidative stress in ad-hMSCs after adipogenic induction. Importantly, depletion of Sirt3 compromised the ability of ad-hMSCs to undergo adipogenic differentiation and led to adipocyte dysfunction and insulin resistance. These findings suggest that Sirt3-mediated protein deacetylation plays an important role in regulating oxidative metabolism and antioxidant defence in stem cell differentiation, and that Sirt3 deficiency may be related to insulin resistance.

Promoter analysis and transcriptional regulation of human carbonic anhydrase VIII gene in a MERRF disease cell model.

Myoclonic epilepsy with ragged-red fibers (MERRF) is a maternally inherited mitochondrial neuromuscular disease. We previously reported a significant decrease of mRNA and protein levels of nuclear DNA-encoded carbonic anhydrase VIII (CA8) in MERRF cybrids harboring A8344G mutation in mitochondrial DNA (mtDNA). In this study, we established a reporter construct of luciferase gene-carrying hCA8 promoter containing several putative transcription factor-binding sites, including GC-box, AP-2 and TATA-binding element in the 5'flanking region of the hCA8 gene. Using a series of mutated hCA8 promoter constructs, we demonstrated that a proximal GC-box, recognized by Sp1 and other Sp family members, may be a key cis-element functioning at the promoter. Additionally, a significant increase of the hCA8 promoter activity was observed in the wild-type and mutant cybrids with over-expression of eGFP-Sp1, but no detectable increase in the CA8 protein expression. In contrast, over-expression of Flag-Sp1 and Flag-Sp4 significantly increased the hCA8 promoter activity as well as endogenous CA8 protein expression in neuron-like HEK-293 T cells. However, down-regulation of Sp1, but not Sp4, in 293 T cells revealed a significant reduction of CA8 expression, suggesting that Sp1 is a predominant transcription factor for regulation of CA8 activity. Furthermore, our data indicate that chromatin structure may be involved in the expression of hCA8 gene in MERRF cybrids. Taken together, these results suggest that Sp1 transactivates hCA8 gene through the proximal GC box element in the promoter region. The key modulator-responsive factor to the mtDNA mutation and how it may affect nuclear hCA8 gene transcription need further investigations.

Profiling of cardiolipins and their hydroperoxides in HepG2 cells by LC/MS.

Cardiolipin (CL) exists as crucial functional phospholipid in mitochondria. The oxidation of CL is concerned with mitochondrial dysfunction and various diseases. As main oxidation products, CL hydroperoxide (CL-OOH) plays a key role in intermediating oxidative reaction. Thus, direct analysis of CL-OOH is of great interest. In the present study, CL and CL-OOH profiles were analyzed in oxidized HepG2 cell lipid via HPLC-Orbitrap MS/MS. Furthermore, the contents of individual molecular species were compared between intact and AAPH-oxidized HepG2 cells. In total, 46 CL and 18 CL-OOH were identified from oxidized cell lipids, while 21 CL and 9 CL-OOH were detected in AAPH-treated cells. Most CL depleted significantly after AAPH inducement, with percentages varying from 8.3% (CL70:7) to 73.7% (CL72:4), depending on fatty acyl composition. While almost all the CL-OOH remarkably increased, among them 68:6-, 72:6-, and 72:7-OOHs were only detected in AAPH-treated cells. CL68:5- and CL68:4-OOH were the most abundant species, while CL70:5-OOH among all the species expressed the highest oxidation percentage of the corresponding CL. Our results showed practical separation, identification, and semi-quantitation of CL-OOH species, which could contribute to approaches to lipidomic analysis of CL and CL-OOH, as well as tracing biomarkers in mitochondrial oxidative stress diagnosis. Graphical abstract Illustration represents cardiolipin hydroperoxide structure and its content increasing in AAPH-treated HepG2 cells by LC/MS analysis.

Effects of carbonic anhydrase-related protein VIII on human cells harbouring an A8344G mitochondrial DNA mutation.

MERRF (myoclonus epilepsy associated with ragged-red fibres) is a maternally inherited mitochondrial encephalomyopathy with various syndromes involving both muscular and nervous systems. The most common mutation in MERRF syndrome, the A8344G mutation in mtDNA, has been associated with severe defects in the respiratory function of mitochondria. In the present study, we show that there is a significant decrease in CA8 (carbonic anhydrase-related protein VIII) in cybrids harbouring the MERRF A8344G mutation. CA8 deficiency and mutations were found to be associated with a distinctive lifelong gait disorder in wdl (Waddles) mice and novel syndromes characterized by cerebellar ataxia and mental retardation in humans. The results of the present study showed that overexpression of CA8 in MERRF cybrids significantly decreased cell death induced by STS (staurosporine) treatment, suggesting a protective function of CA8 in cells harbouring the A8344G mutation of mtDNA. Interestingly, an increase in the formation of LC3-II (microtubule-associated protein 1 light chain 3-II) was found in the cybrids with down-regulated CA8 expression, suggesting that reduced expression of CA8 leads to autophagy activation. Furthermore, cybrids exhibiting down-regulated CA8 showed increased cytosolic Ca2+ signals and reduced levels of phospho-Akt compared with those in the cybrids with overexpressed CA8, indicating that phospho-Akt is involved in the protection of cells by CA8. Our findings suggest that CA8 is involved in the autophagic pathway and may have a protective role in cultured cells from patients with MERRF. Targeting CA8 and the downstream autophagic pathway might help develop therapeutic agents for treatment of MERRF syndrome in the future.

High glucose modulates antiproliferative effect and cytotoxicity of 5-fluorouracil in human colon cancer cells.

5-Fluorouracil (5-FU)-based chemotherapy is widely used for the treatment of colorectal cancer (CRC). While optimal doses of 5-FU are generally established based on a patient's estimated body surface area, the plasma concentrations of 5-FU vary among patients. In addition, hyperglycemia in patients with CRC has been reported as a risk factor in poor prognosis. The aim of the present study was to investigate whether hyperglycemia affects antiproliferative effect of 5-FU on the human colon cancer cells (SW480, SW620, LoVo, and HCT116). Growth inhibition of 5-FU was accessed by WST-8 assay. The effect of high glucose (HG, 15 mM) and 5-FU on the cellular proliferation was evaluated by flow cytometry analysis using 5-ethynyl-2'-deoxy-uridine (EdU) incorporation plus 7-AAD. Cell death was determined by flow cytometry using Annexin V-FITC and PI. The results showed that HG, compared to physiological normal glucose (NG) concentration (5 mM), leads to increased cell proliferation and increased GI50 of 5-FU in the four colon cancer cell lines. When the cells were pretreated with a low-dose 5-FU in NG condition, subsequent HG treatment eliminated inhibitory effect of 5-FU in cancer cell growth. In the presence of 5-FU (0.5 µg/mL for LoVo and HCT116; 1 µg/mL for SW480 and SW620), culture with HG for 72 h does not significantly altered cell cycle profile in the four cell lines but significantly increased DNA replication in SW620 (21%) and LoVo (17%). Flow cytometric analysis showed that HG protects cells against 5-FU-induced cell death in SW480. Finally, HG did not alter intracellular level of reactive oxygen species (ROS), although 5-FU indeed induced higher intracellular level of ROS. In conclusion, HG attenuates growth inhibition of 5-FU and our results indicate that decreased cell death and increased DNA replication may account for the attenuating effect of a HG environment on 5-FU-induced tumor growth inhibition.

The protective roles of phosphorylated heat shock protein 27 in human cells harboring myoclonus epilepsy with ragged-red fibers A8344G mtDNA mutation.

Mitochondrial DNA (mtDNA) mutations are associated with a large number of neuromuscular diseases. Myoclonus epilepsy with ragged-red fibers (MERRF) syndrome is a mitochondrial disease inherited through the maternal lineage. The most common mutation in MERRF syndrome, the A8344G mutation of mtDNA, is associated with severe defects in mitochondrial protein synthesis, which impair the assembly and function of the respiratory chain. We have previously shown that there is a decreased level of heat shock protein 27 (HSP27) in lymphoblastoid cells derived from a MERRF patient and in cytoplasmic hybrids (cybrids) harboring the A8344G mutation of mtDNA. In the present study, we found a dramatic decrease in the level of phosphorylated HSP27 (p-HSP27) in the mutant cybrids. Even though the steady-state level of p-HSP27 was reduced in the mutant cybrids, normal phosphorylation and dephosphorylation were observed upon exposure to stress, indicating normal kinase and phosphatase activities. To explore the roles that p-HSP27 may play, transfection experiments with HSP27 mutants, in which three specific serines were replaced with alanine or aspartic acid, showed that the phosphomimicking HSP27 desensitized mutant cybrids to apoptotic stress induced by staurosporine (STS). After heat shock stress, p-HSP27 was found to enter the nucleus immediately, and with a prolonged interval of recovery, p-HSP27 returned to the cytoplasm in wild-type cybrids but not in mutant cybrids. The translocation of p-HSP27 was correlated with cell viability, as shown by the increased number of apoptotic cells after p-HSP27 returned to the cytoplasm. In summary, our results demonstrate that p-HSP27 provides significant protection when cells are exposed to different stresses in the cell model of MERRF syndrome. Therapeutic agents targeting anomalous HSP27 phosphorylation might represent a potential treatment for mitochondrial diseases.

Decreased heat shock protein 27 expression and altered autophagy in human cells harboring A8344G mitochondrial DNA mutation.

Mitochondrial DNA (mtDNA) mutations are responsible for human neuromuscular diseases caused by mitochondrial dysfunction. Myoclonus epilepsy associated with ragged-red fibers (MERRF) is a maternally inherited mitochondrial encephalomyopathy with various syndromes involving both muscular and nervous systems. The most common mutation in MERRF syndrome, A8344G mutation in mtDNA, has been associated with severe defects in protein synthesis. This defect impairs assembly of complexes in electron transport chain and results in decreased respiratory function of mitochondria. In this study, we showed a significant decrease of the heat shock protein 27 (Hsp27) in lymphoblastoid cells derived from a MERRF patient and in cybrid cells harboring MERRF A8344G mutation. However, normal cytoplasmic distributions of Hsp27 and normal heat shock responses were observed in both wild type and mutant cybrids. Furthermore, overexpression of wild type Hsp27 in mutant MERRF cybrids significantly decreased cell death under staurosporine (STS) treatment, suggesting a protective function of Hsp27 in cells harboring the A8344G mutation of mtDNA. Meanwhile, reverse transcriptase PCR showed no difference in the mRNA level between normal and mutant cybrids, indicating that alterations may occur at the protein level. Evidenced by the decreased levels of Hsp27 upon treatment with proteasome inhibitor, starvation and rapamycin and the accumulation of Hsp27 upon lysosomal inhibitor treatment; Hsp27 may be degraded by the autophagic pathway. In addition, the increased formation of LC3-II and autophagosomes was found in MERRF cybrids under the basal condition, indicating a constitutively-activated autophagic pathway. It may explain, at least partially, the faster turnover of Hsp27 in MERRF cybrids. This study provides information for us to understand that Hsp27 is degraded through the autophagic pathway and that Hsp27 may have a protective role in MERRF cells. Regulating Hsp27 and the autophagic pathway might help develop therapeutic solutions for treatment of MERRF syndrome in the future.

Mitochondrial DNA mutation-elicited oxidative stress, oxidative damage, and altered gene expression in cultured cells of patients with MERRF syndrome.

Myoclonic epilepsy and ragged-red fibers (MERRF) syndrome is a rare disorder characterized by myoclonus, muscle weakness, cerebellar ataxia, heart conduction block, and dementia. It has been documented that 80-90% of the patients with MERRF syndrome are caused by the A8344G mutation in the tRNA(Lys) gene of mitochondrial DNA (mtDNA). We and other investigators have reported that the mtDNA mutation results in not only inefficient generation of adenosine triphosphate but also increased production of reactive oxygen species (ROS) in cultured cells harboring A8344G mutation of mtDNA. In addition, we found an imbalance in the gene expression of antioxidant enzymes in the skin fibroblasts of MERRF patients. The mRNA, protein, and enzyme activity levels of manganese-superoxide dismutase were increased, but those of Cu,Zn-SOD, catalase, and glutathione peroxidase did not show significant changes. Recently, we showed that the excess ROS could damage voltage-dependent anion channel, prohibitin, Lon protease, and aconitase in the MERRF cells. Moreover, there was a dramatic increase in the gene expression and activity of matrix metalloproteinase 1, which may contribute to the cytoskeleton remodeling involved in the weakness and atrophy of muscle commonly seen in MERRF patients. Taken together, we suggest that mtDNA mutation-elicited oxidative stress, oxidative damage, and altered gene expression are involved in the pathogenesis and progression of MERRF syndrome.

Respiratory function decline and DNA mutation in mitochondria, oxidative stress and altered gene expression during aging.

Aging is a biological process that is characterized by the gradual loss of physiological function and increases in the susceptibility to disease of an individual. During the aging process, a wide spectrum of alterations in mitochondria and mitochondrial DNA (mtDNA) has been observed in somatic tissues of humans and animals. This is associated with the decline in mitochondrial respiratory function; excess production of the reactive oxygen species (ROS); increase in the oxidative damage to mtDNA, lipids and proteins in mitochondria; accumulation of point mutations and large-scale deletions of mtDNA; and altered expression of genes involved in intermediary metabolism. It has been demonstrated that the ROS may cause oxidative damage and mutations of mtDNA and alterations of the expression of several clusters of genes in aging tissues and senescent cells. We found that intracellular levels of hydrogen peroxide (H2O2) and oxidative damage to DNA in the tissue cells and skin fibroblasts of old donors were higher than those of young donors. In H2O2-induced senescent skin fibroblasts, we observed an increase in the protein expression and activity levels of manganese-dependent superoxide dismutase and a concurrent decrease in the activity of cytochrome c oxidase and the rate of oxygen consumption. Moreover, the mRNA and protein expression levels of pyruvate dehydrogenase (PDH) were decreased but those of PDH kinase and lactate dehydrogenase were increased in senescent skin fibroblasts. The changes in the expression of these enzymes suggest a metabolic shift from mitochondrial respiration to glycolysis as a major supply of ATP in aging human cells. On the other hand, recent studies on mitochondrial mutant mice, which carry a proofreading deficient subunit of DNA polymerase gamma, revealed that mtDNA mutations accumulated in somatic tissues in the mice that displayed prominent features of aging. Taken together, we suggest that the respiratory function decline and increase in the production of the ROS in mitochondria, accumulation of mtDNA mutation and oxidative damage, and altered expression of a few clusters of genes that culminated in the metabolic shift from mitochondrial respiration to glycolysis for major supply of ATP were key contributory factors in the aging process in the human and animals.

Response to the increase of oxidative stress and mutation of mitochondrial DNA in aging.

In the aging process, mitochondrial function gradually declines with an increase of mutations in mitochondrial DNA (mtDNA) in tissue cells. Some of the aging-associated mtDNA mutations have been shown to result in not only inefficient generation of ATP but also increased production of reactive oxygen species (ROS) such as superoxide anions (O2-) and hydrogen peroxide (H2O2) in the mitochondria of aging tissues. Extensive studies have revealed that such an increase of oxidative stress is a contributory factor for alterations in the expression and activities of antioxidant enzymes and increased oxidative damage to DNA, RNA, proteins, and lipids in tissues and cultured cells from elderly subjects. Recently, we observed that gene expression of several proteins and enzymes related to iron metabolism is altered and that aconitase is extremely susceptible to oxidative damage in senescent skin fibroblasts and in cybrids harboring aging-associated A8344G mutation of mtDNA. Of great importance is the perturbation at the protein and activity levels of several enzymes containing iron-sulfur clusters in skin fibroblasts of elderly subjects. Taken together, these findings suggest that cellular response to oxidative stress and oxidative damage elicited by mitochondrial dysfunction and/or mtDNA mutations plays an important role in human aging.

MtDNA mutations, functional decline and turnover of mitochondria in aging.

Aging is a complex biological process that involves gradual function deterioration in various tissues and organs of an individual. Mitochondrial function decline can lead to cellular overproduction of reactive oxygen species (ROS) and increase in oxidative damage to biological molecules in the aging process. We have hypothesized that increased production of ROS by the mitochondria in affected tissues in patients with mitochondrial diseases and elderly subject results in increased oxidative stress and oxidative damage. Due to the similarity of human aging process to diseases related to bioenergetic function decline and mitochondrial DNA (mtDNA) alterations, aging is sometimes viewed as a "chronic" version of such diseases. Recent studies have also established that the expression profiles of several clusters of genes are altered, oxidative modification of proteins are increased and their turnover are decreased in tissues of old human subjects and animals. Accumulating evidence has suggested that mtDNA mutations, oxidative stress, defective disposal of dysfunctional proteins and a slower turnover of mitochondria are associated with aging.

Oculopharyngeal somatic myopathy in a patient with a novel large-scale 3,399 bp deletion and a homoplasmic T5814C transition of the mitochondrial DNA.

We report a 65-year-old woman with a sporadic form of progressive oculopharyngeal somatic myopathy due to a novel large-scale 3,399 base pair (bp) deletion of the mitochondrial DNA (mtDNA) and co-occurrence of a homoplasmic T5814C transition. The onset of myopathy began from chronic progressive external ophthalmoplegia (CPEO) at age of 20 years. Bulbar weakness, neck and proximal limb paralysis, slowly progressed to eventual respiratory failure. The plasma levels of pyruvate (1.5 mg/dL) and lactate (20.2 mg/dL) were elevated. Muscle biopsy showed decreased enzymatic activity of cytochrome c oxidase, but no ragged-red fibers. Electron microscopy showed "parking-lot" paracrystalline inclusions in the enlarged mitochondria suggestive for mitochondrial myopathy. Sequencing of the whole mitochondrial genome of the patient's muscle and leukocytes showed 3,399 bp deletion of the mtDNA from nucleotide position 8,024 to 11,423 and a homoplasmic thymidine to cytosine transition at nucleotide position 5,814 of the tRNA(Cys) gene of mtDNA (T5814C). T5814C was absent in the white blood cells of the patient's daughter and in 205 normal controls. We conclude that a large-scale deletion may coexist with T5814C transition in patients with sporadic form of mitochondrial cytopathy manifested by slowly progressive oculopharyngeal somatic myopathy.

Upregulation of matrix metalloproteinase 1 and disruption of mitochondrial network in skin fibroblasts of patients with MERRF syndrome.

By using cDNA microarray and RT-PCR techniques, we investigated the genome-wide alteration of gene expression in skin fibroblasts from patients with myoclonic epilepsy and ragged-red fibers (MERRF) syndrome. By screening for the genes with altered levels of expression, we first discovered that matrix metalloproteinase 1 (MMP1) was highly induced in the primary culture of skin fibroblasts of a female patient in a four-generation family with MERRF syndrome. This phenomenon was confirmed in skin fibroblasts from three other MERRF patients harboring about 85% of mtDNA with A8344G mutation. A further study revealed that the expression of MMP1 could be further induced by treatment of the skin fibroblasts with 200 microM hydrogen peroxide (H2O2) and inhibited by 1 mM N-acetylcysteine. Moreover, the intracellular level of H2O2 in skin fibroblasts of the female MERRF patient was higher than those of the asymptomatic family members and age-matched healthy controls. These findings imply that the increase in the expression of MMP1 may represent one of the responses to the increased oxidative stress in the skin fibroblasts of MERRF patients. We suggest that in affected tissues the oxidative stress-elicited overexpression of MMP1, and probably other matrix metalloproteinases involved in cytoskeleton remodeling, may play an important role in the pathogenesis and progression of mitochondrial encephalomyopathies such as MERRF syndrome.

High prevalence of the COII/tRNA(Lys) intergenic 9-bp deletion in mitochondrial DNA of Taiwanese patients with MELAS or MERRF syndrome.

The COII/tRNA(Lys) intergenic 9-bp deletion (MIC9D) of mitochondrial DNA (mtDNA) has been established as a genetic polymorphism for Asian-Pacific populations. We investigated whether this small mtDNA deletion is co-transmitted with human diseases such as mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) and myoclonic epilepsy with ragged-red fibers (MERRF) syndromes. Forty unrelated Taiwanese families, including 12 families with MERRF and A8344G mtDNA mutation and 28 families with MELAS and A3243G mutation of mtDNA, respectively, were recruited in this study. In addition, 199 healthy subjects were recruited as control. We found that the frequency of occurrence of mtDNA with the MIC9D polymorphism in healthy subjects was 21% (41/199). However, the incidence of the MIC9D polymorphism was 67% (8/12) among the probands of all the families with MERRF syndrome (P = 0.001; OR = 8) and 39% (11/28) among the probands of the families with MELAS syndrome (P = 0.038; OR = 2). This finding indicates that the frequency of occurrence of mtDNA with the MIC9D polymorphism in patients with MERRF or MELAS syndrome is higher than that of healthy subjects. The prevalence of mitochondrial encephalomyopathies in relation to the MIC9D polymorphism of mtDNA in Taiwanese population is discussed.

Oxidative stress-related alteration of the copy number of mitochondrial DNA in human leukocytes.

The role of oxidative stress in the regulation of the copy number of mitochondrial DNA (mtDNA) in human leukocytes is unclear. In this study, we investigated the redox factors in plasma that may contribute to the alteration of mtDNA copy number in human leukocytes. A total of 156 healthy subjects of 25-80 years of age who exhibited no significant difference in the distribution of subpopulations of leukocytes in blood were recruited. Small-molecular-weight antioxidants and thiobarbituric acid reactive substances (TBARS) in plasma and 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4,977bp deletion of mtDNA in leukocytes were determined. The mtDNA copy number in leukocytes was determined by real-time PCR. The results showed that the copy number of mtDNA in leukocytes was changed with age in a biphasic manner that fits in a positively quadratic regression model (P = 0.001). Retinol (P = 0.005), non-protein thiols (P = 0.001) and ferritin (P = 0.004) in plasma and total glutathione in erythrocytes (P = 0.046) were the significant redox factors that correlated with the mtDNA copy number in leukocytes in a positive manner. By contrast, alpha-tocopherol levels in plasma (P = 0.001) and erythrocytes (P = 0.033) were negatively correlated with the mtDNA copy number in leukocytes. Three oxidative indices including the incidence of 4,977 bp deletion of mtDNA (P = 0.016) and 8-OHdG content in leukocytes (P = 0.003) and TBARS in plasma (P = 0.001) were all positively correlated with the copy number of mtDNA in leukocytes. Taken these findings together, we suggest that the copy number of mtDNA in leukocytes is affected by oxidative stress in blood circulation elicited by the alteration of plasma antioxidants/prooxidants and oxidative damage to DNA.

Clinical phenotype, prognosis and mitochondrial DNA mutation load in mitochondrial encephalomyopathies.

We studied 42 individuals, including 8 patients with either complete or partial syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), 8 patients with either complete or partial syndrome of myoclonic epilepsy with ragged-red fibers (MERRF) and 26 maternal family members who carried either the A3243G or A8344G mutation of mitochondrial DNA (mtDNA). Clinical manifestations and prognosis were followed up in the patients harboring the A3243G or A8344G mutation. The relationship between clinical features and proportions of mutant mtDNAs in muscle biopsies, blood cells and/or hair follicles was studied. In the 8 regularly followed patients with the A3243G mutation, 4 died within 1 month to 7 years due to status epilepticus and/or recurrent stroke-like episodes. Two patients developed marked mental deterioration and 2 remained stationary. All of the patients harboring the A8344G mutation were stable or deteriorated slightly, except for 1 patient who died due to brain herniation after putaminal hemorrhage. The A3243G and A8344G mtDNA mutations were heteroplasmic in the muscle biopsies, blood cells and hair follicles of both the probands and their maternal family members. The mean proportion of A3243G mutant mtDNA in the muscle biopsies of the patients with MELAS syndrome (68.5 +/- 21.3%, range 33-92%) was significantly higher than that of the asymptomatic family members (37.1 +/- 12.6%, range 0-51%). The average proportions of A8344G mutant mtDNA in the muscle biopsies (90.1 +/- 3.9%, range 89-95%) and hair follicles (93.9 +/- 6.4%, range 84-99%) of the patients with MERRF syndrome were also significantly higher than those of the asymptomatic family members (muscle: 40.3 +/- 39.5%, range 1-80%; hair follicles: 51.0 +/- 44.5%, range 0.1-82%). We concluded that measurement of the proportion of mutant mtDNA in muscle biopsies may provide useful information in the identification of symptomatic patients with mitochondrial encephalomyopathies. For patients with the A3243G mutation, the prognosis was related to status epilepticus and the number of recurrent stroke-like episodes and was much worse than for patients with the A8344G mutation of mtDNA, who had stable or slowly deteriorating clinical courses.

Mitochondrial DNA mutations and oxidative damage in skeletal muscle of patients with chronic uremia.

Abundant evidence has been gathered to suggest that mitochondrial DNA (mtDNA) sustains many more mutations and greater oxidative damage than does nuclear DNA in human tissues. Uremic patients are subject to a state of enhanced oxidative stress due to excess production of oxidants and a defective antioxidant defense system. This study was conducted to investigate mtDNA mutations and oxidative damage in skeletal muscle of patients with chronic uremia. Results showed that large-scale deletions between nucleotide position (np) 7,900 and 16,300 of mtDNA occurred at a high frequency in muscle of uremic patients. Among them, the 4,977-bp deletion (mtDNA(4977)) was the most frequent and most abundant large-scale mtDNA deletion in uremic skeletal muscle. The proportion of mtDNA(4977) was found to correlate positively with the level of 8-hydroxy 2'-deoxyguanosine (8-OHdG) in the total DNA of skeletal muscle (r = 0.62, p < 0.05). Using long-range PCR and DNA sequencing, we identified and characterized multiple deletions of mtDNA in skeletal muscle of 16 of 19 uremic patients examined. The 8,041-bp deletion, which occurred between np 8035 and 16,075, was flanked by a 5-bp direct repeat of 5'-CCCAT-3'. Some of the deletions were found in more than 1 patient. On the other hand, we found that the mean 8-OHdG/10(5 )dG ratio in the total cellular DNA of muscle of uremic patients was significantly higher than that of the controls (182.7 +/- 63.6 vs. 50.9 +/- 21.5, p = 0.05). In addition, the mean 8-OHdG/10(5 )dG ratio in muscle mtDNA of uremic patients was significantly higher than that in nuclear DNA (344.0 +/- 56.9 vs. 146.3 +/- 95.8, p = 0.001). Moreover, we found that the average content of lipid peroxides in mitochondrial membranes of skeletal muscle of uremic patients was significantly higher than that of age-matched healthy subjects (23.76 +/- 6.06 vs. 7.67 +/- 0.95 nmol/mg protein; p < 0.05). The average content of protein carbonyls in the mitochondrial membranes prepared from uremic skeletal muscles was significantly higher than that in normal controls (24.90 +/- 4.00 vs. 14.48 +/- 1.13 nmol/mg protein; p < 0.05). Taken together, these findings suggest that chronic uremia leads to mtDNA mutations together with enhanced oxidative damage to DNA, lipids, and proteins of mitochondria in skeletal muscle, which may contribute to the impairment of mitochondrial bioenergetic function and to skeletal myopathy commonly seen in uremic patients.