Disruption Of Mitochondrial Homeostasis Research Articles

Disruption of mitochondrial homeostasis in chronic kidney disease: a mini-review.

Chronic kidney disease (CKD) is recognized as a worldwide health problem. Progression of CKD may lead to many serious complications, which are associated with increased morbidity and mortality. Presently, there is no satisfactory treatment. Thus, targeted therapies are urgently needed. The kidneys are second to the heart in terms of mitochondrial abundance and oxygen consumption. Thus, it is not surprising that mitochondrial homeostasis is absolutely essential for the normal function of the kidney. In fact, a number of reports indicate that mitochondria are involved in the progression of CKD. In this review, we summarize our current knowledge on mitochondrial homeostasis in CKD. We also provide an update on recent developments in the field of mitochondria-targeting therapeutic approaches against CKD.

Disruption of mitochondrial homeostasis with artemisinin unravels anti-angiogenesis effects via auto-paracrine mechanisms.

Rationale: Tumor angiogenesis promotes tumor development, progression, growth, and metastasis. Metronomic chemotherapy involves the frequent administration of low-dose chemotherapeutic agents to block angiogenic activity and reduce side effects.Methods: MDA-MB-231 cells were treated with various concentrations of artemisinin (ART) and vinorelbine (NVB) and the cytotoxic effects of ART/NVB were determined using the CCK-8 assay. Mitochondrial reactive oxygen species (ROS) levels, mitochondrial membrane potential (∆Ψm) and mass were assessed using MitoSOX, TMRE and MitoTracker green staining. Western blot analysis was used to quantify the expression of autophagy-related proteins. Herein, by using bioinformatics analysis and experimental verification, we identified CREB as a master in MDA-MB-231 cells.Results: We found that artemisinin (ART), which exhibits anti-angiogenic and anti-cancer effects via mitochondrial regulation, synergized with vinorelbine (NVB) to inhibit MDA-MB-231 cell proliferation. ART and NVB cooperated to regulate mitochondrial biogenesis. CREB acted as a crucial regulator of PGC1α and VEGF, which played critical roles in NVB-dependent growth factor depletion. Moreover, CREB suppression significantly reversed mitochondrial dysfunction following ART/NVB co-treatment. In addition, combination treatment with ART and NVB significantly suppressed tumor growth in a nude mouse xenograft model, with downregulated CREB and PGC1α expression levels observed in tumor biopsies, in agreement with our in vitro and ex vivo data.Conclusions: These findings support the hypothesis that ART affects cancer and endothelial cells by targeting the auto-paracrine effects of VEGF to suppress mitochondrial biogenesis, angiogenesis, and migration between cancer cells and endothelial cells.

Defective mitochondrial protein import contributes to complex I-induced mitochondrial dysfunction and neurodegeneration in Parkinson\u2019s disease

Mitochondria are the prime energy source in most eukaryotic cells, but these highly dynamic organelles are also involved in a multitude of cellular events. Disruption of mitochondrial homeostasis and the subsequent mitochondrial dysfunction plays a key role in the pathophysiology of Parkinson’s disease (PD). Therefore, maintenance of mitochondrial integrity through different surveillance mechanisms is critical for neuronal survival. Here, we have studied the mitochondrial protein import system in in vitro and in vivo models of PD. Complex I inhibition, a characteristic pathological hallmark in PD, impaired mitochondrial protein import, which was associated with a downregulation of two key components of the system: translocase of the outer membrane 20 (TOM20) and translocase of the inner membrane 23 (TIM23), both in vitro and in vivo. In vitro, those changes were associated with OXPHOS protein downregulation, accumulation of aggregated proteins inside mitochondria and downregulation of mitochondrial chaperones. Most of these pathogenic changes, including mitochondrial dysfunction and dopaminergic cell death, were abrogated by TOM20 or TIM23 overexpression, in vitro. However, in vivo, while TOM20 overexpression exacerbated neurodegeneration in both substantia nigra (SN) pars compacta (pc) and striatum, overexpression of TIM23 partially protected dopaminergic neurons in the SNpc. These results highlight mitochondrial protein import dysfunction and the distinct role of two of their components in the pathogenesis of PD and suggest the need for future studies to further characterize mitochondrial protein import deficit in the context of PD.

Mitochondrial Quality Control in Neurodegenerative Diseases: Focus on Parkinson's Disease and Huntington's Disease.

In recent years, several important advances have been made in our understanding of the pathways that lead to cell dysfunction and death in Parkinson's disease (PD) and Huntington's disease (HD). Despite distinct clinical and pathological features, these two neurodegenerative diseases share critical processes, such as the presence of misfolded and/or aggregated proteins, oxidative stress, and mitochondrial anomalies. Even though the mitochondria are commonly regarded as the “powerhouses” of the cell, they are involved in a multitude of cellular events such as heme metabolism, calcium homeostasis, and apoptosis. Disruption of mitochondrial homeostasis and subsequent mitochondrial dysfunction play a key role in the pathophysiology of neurodegenerative diseases, further highlighting the importance of these organelles, especially in neurons. The maintenance of mitochondrial integrity through different surveillance mechanisms is thus critical for neuron survival. Mitochondria display a wide range of quality control mechanisms, from the molecular to the organellar level. Interestingly, many of these lines of defense have been found to be altered in neurodegenerative diseases such as PD and HD. Current knowledge and further elucidation of the novel pathways that protect the cell through mitochondrial quality control may offer unique opportunities for disease therapy in situations where ongoing mitochondrial damage occurs. In this review, we discuss the involvement of mitochondrial dysfunction in neurodegeneration with a special focus on the recent findings regarding mitochondrial quality control pathways, beyond the classical effects of increased production of reactive oxygen species (ROS) and bioenergetic alterations. We also discuss how disturbances in these processes underlie the pathophysiology of neurodegenerative disorders such as PD and HD.

The Phosphatidylcholine Transfer Protein Stard7 is Required for Mitochondrial and Epithelial Cell Homeostasis

Mitochondria synthesize select phospholipids but lack the machinery for synthesis of the most abundant mitochondrial phospholipid, phosphatidylcholine (PC). Although the phospholipid transfer protein Stard7 promotes uptake of PC by mitochondria, the importance of this pathway for mitochondrial and cellular homeostasis represents a significant knowledge gap. Haploinsufficiency for Stard7 is associated with significant exacerbation of allergic airway disease in mice, including an increase in epithelial barrier permeability. To test the hypothesis that Stard7 deficiency leads to altered barrier structure/function downstream of mitochondrial dysfunction, Stard7 expression was knocked down in a bronchiolar epithelial cell line (BEAS-2B) and specifically deleted in lung epithelial cells of mice (Stard7epi∆/∆). Stard7 deficiency was associated with altered mitochondrial size and membrane organization both in vitro and in vivo. Altered mitochondrial structure was accompanied by disruption of mitochondrial homeostasis, including decreased aerobic respiration, increased oxidant stress, and mitochondrial DNA damage that, in turn, was linked to altered barrier integrity and function. Both mitochondrial and barrier defects were largely corrected by targeting Stard7 to mitochondria or treating epithelial cells with a mitochondrial-targeted antioxidant. These studies suggest that Stard7-mediated transfer of PC is crucial for mitochondrial homeostasis and that mitochondrial dysfunction contributes to altered barrier permeability in Stard7-deficient mice.

Cancer-induced cardiac cachexia: Pathogenesis and impact of physical activity

Cachexia is a wasting syndrome observed in many patients suffering from several chronic diseases including cancer. In addition to the progressive loss of skeletal muscle mass, cancer cachexia results in cardiac function impairment. During the severe stage of the disease, patients as well as animals bearing cancer cells display cardiac atrophy. Cardiac energy metabolism is also impeded with disruption of mitochondrial homeostasis and reduced oxidative capacity, although the available data remain equivocal. The release of inflammatory cytokines by tumor is a key mechanism in the initiation of heart failure. Oxidative stress, which results from the combination of chemotherapy, inadequate antioxidant consumption and chronic inflammation, will further foster heart failure. Protein catabolism is due to the concomitant activation of proteolytic systems and inhibition of protein synthesis, both processes being triggered by the deactivation of the Akt/mammalian target of rapamycin pathway. The reduction in oxidative capacity involves AMP-activated protein kinase and peroxisome proliferator-activated receptor gamma coactivator1α dysregulation. The nuclear factor-κB transcription factor plays a prominent role in the coordination of these alterations. Physical exercise appears as an interesting non-pharmaceutical way to counteract cancer cachexia-induced-heart failure. Indeed, aerobic training has anti-inflammatory effects, increases anti-oxidant defenses, prevents atrophy and promotes oxidative metabolism. The present review points out the importance of better understanding the concurrent structural and metabolic changes within the myocardium during cancer and the protective effects of exercise against cardiac cachexia.

Fungicide Bac8c triggers attenuation of mitochondrial homeostasis and caspase-dependent apoptotic death

Bac8c (RIWVIWRR-NH2), an 8-mer peptide modified from amino acids 4–11 of Bac2a, shows broad-spectrum activity against pathogenic bacteria and yeast, and it has been the focus of attention owing to its low cost of synthesis. Although Bac8c is effective against Candida albicans, its mode of action needs to be investigated further. Bac8c causes yeast cell death in a dose-dependent manner by eliciting the production of reactive oxygen species, thereby attenuating the antioxidant defense system. It is also involved in Ca2+ signaling, and produces apoptotic features, such as phosphatidylserine externalization and DNA fragmentation. Bac8c induces cell death by oxidative stress-dependent apoptotic death via disruption of mitochondrial homeostasis and metacaspase activation. This suggests that the concentration of Bac8c is important for the induction of apoptotic death, which is not necessarily accompanied by cell cycle arrest in C. albicans.

Suppression of mitochondrial biogenesis through toll-like receptor 4-dependent mitogen-activated protein kinase kinase/extracellular signal-regulated kinase signaling in endotoxin-induced acute kidney injury.

Although disruption of mitochondrial homeostasis and biogenesis (MB) is a widely accepted pathophysiologic feature of sepsis-induced acute kidney injury (AKI), the molecular mechanisms responsible for this phenomenon are unknown. In this study, we examined the signaling pathways responsible for the suppression of MB in a mouse model of lipopolysaccharide (LPS)-induced AKI. Downregulation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a master regulator of MB, was noted at the mRNA level at 3 hours and protein level at 18 hours in the renal cortex, and was associated with loss of renal function after LPS treatment. LPS-mediated suppression of PGC-1α led to reduced expression of downstream regulators of MB and electron transport chain proteins along with a reduction in renal cortical mitochondrial DNA content. Mechanistically, Toll-like receptor 4 (TLR4) knockout mice were protected from renal injury and disruption of MB after LPS exposure. Immunoblot analysis revealed activation of tumor progression locus 2/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (TPL-2/MEK/ERK) signaling in the renal cortex by LPS. Pharmacologic inhibition of MEK/ERK signaling attenuated renal dysfunction and loss of PGC-1α, and was associated with a reduction in proinflammatory cytokine (e.g., tumor necrosis factor-α [TNF-α], interleukin-1β) expression at 3 hours after LPS exposure. Neutralization of TNF-α also blocked PGC-1α suppression, but not renal dysfunction, after LPS-induced AKI. Finally, systemic administration of recombinant tumor necrosis factor-α alone was sufficient to produce AKI and disrupt mitochondrial homeostasis. These findings indicate an important role for the TLR4/MEK/ERK pathway in both LPS-induced renal dysfunction and suppression of MB. TLR4/MEK/ERK/TNF-α signaling may represent a novel therapeutic target to prevent mitochondrial dysfunction and AKI produced by sepsis.

Aging leads to elevation of O-GlcNAcylation and disruption of mitochondrial homeostasis in retina.

Retina is particularly susceptible to aging as oxidative damage accumulates within retina, leading to age-related retinal dysfunction or even visual loss. However, the underlying mechanisms still remain obscure and effective therapeutic strategy is urgently in need. Here, we quested for the answer particularly focusing on mitochondrial homeostasis and O-GlcNAcylation in rat retina. By comparing expression of electron transfer chain complexes and key factors in mitochondrial biogenesis and dynamics in retinas of aged and young Sprague-Dawley rats, we found that mitochondrial Complex I, II, IV and V were increased in aged retina with decreased mtTFA and Mfn2. Also, we noticed that p38 and JNK of MAPK signaling were substantially more activated in aged retina, suggesting stress induction. In addition, we found that pan-O-GlcNAcylation was remarkably stronger with lower OGA expression in aged retina. To further elucidate the roles of Mfn2 and O-GlcNAcylation, we employed ARPE-19 cells and found that ATP production, oxygen consumption, and mitochondrial membrane potential were reduced and ROS level was increased by Mfn2 knockdown, while treating with PUGNAc or UDP-GlcNAc heightened oxygen consumption and reduced ROS. Our results suggest disrupted mitochondrial homeostasis may increase oxidative stress; yet enhanced O-GlcNAcylation might defend against oxidative stress and promote mitochondrial respiration in aged retina.

Mitochondrial Homeostasis in Acute Organ Failure

The kidneys compose approximately 0.5% of the body mass but consume about 10% of the oxygen in cellular respiration. This discordance is due to the high energy demands on the kidney for reabsorption of filtered blood components and makes the kidney sensitive to mitochondrial stress, the primary source of cellular ATP. Regardless of the etiology, acute kidney injury (AKI) almost always involves aspects of mitochondrial dysfunction. Recent evidence from experimental models suggests that preserving mitochondrial function or promoting mitochondrial repair rescues renal function during AKI. In this review we discuss the effect of AKI on disruption of mitochondrial homeostasis, and how the dynamic processes of mitochondrial biogenesis, fission/fusion, and mitophagy influence renal injury and recovery.

Interplay of reactive oxygen species, intracellular Ca2+ and mitochondrial homeostasis in the apoptosis of prostate cancer cells by deoxypodophyllotoxin

The limited treatment option for recurrent prostate cancer and the eventual resistance to conventional chemotherapy drugs has fueled continued interest in finding new anti-neoplastic agents of natural product origin. We previously reported anti-proliferative activity of deoxypodophyllotoxin (DPT) on human prostate cancer cells. Using the PC-3 cell model of human prostate cancer, the present study reveals that DPT induced apoptosis via a caspase-3-dependent pathway that is activated due to dysregulated mitochondrial function. DPT-treated cells showed accumulation of the reactive oxygen species (ROS), intracellular Ca (i)(2+) surge, increased mitochondrial membrane potential (MMP, ΔΨ(m)), Bax protein translocation to mitochondria and cytochrome c release to the cytoplasm. This resulted in caspase-3 activation, which in turn induced apoptosis. The antioxidant N-acetylcysteine (NAC) reduced ROS accumulation, MMP and Ca (i)(2+) surge, on the other hand the Ca(2+) chelator BAPTA inhibited the Ca( i)(2+) overload and MMP without affecting the increase of ROS, indicating that the generation of ROS occurred prior to Ca(2+) flux. This suggested that both ROS and Ca( i)(2+) signaling play roles in the increased MMP via Ca (i)(2+)-dependent and/or -independent mechanisms, since ΔΨ(m) elevation was reversed by NAC and BAPTA. This study provides the first evidence for the involvement of both ROS- and Ca( i)(2+)-activated signals in the disruption of mitochondrial homeostasis and the precedence of ROS production over the failure of Ca(2+) flux homeostasis.

Disruption of Mitochondrial Homeostasis by Phytanic Acid in Cerebellum of Young Rats

Phytanic acid (Phyt) brain concentrations are highly increased in Refsum disease, a peroxisomal disorder clinically characterized by neurological features, cardiac abnormalities, and retinitis pigmentosa. Considering that the pathogenesis of cerebellar ataxia, a common finding in this disease, is still unknown, in the present work we investigated the in vitro effects of Phyt at concentrations similar to those found in affected patients on important parameters of mitochondrial homeostasis in cerebellum from young rats. The respiratory parameters states 3 and 4 and respiratory control ratio (RCR) determined by oxygen consumption, membrane potential (∆Ψm), NAD(P)H pool content, and swelling were evaluated in mitochondrial preparations from this cerebral structure. Phyt markedly increased state 4 respiration, whereas state 3 respiration, the RCR, the mitochondrial matrix NAD(P)H content, and ∆Ψm were decreased by this fatty acid, being the latter effect partially prevented by N-acetylcysteine. These data indicate that Phyt behaves as an uncoupler of oxidative phosphorylation and as a metabolic inhibitor disrupting mitochondrial homeostasis in cerebellum. It is proposed that these pathomechanisms may contribute at least in part to the cerebellar alterations found in Refsum disease.

Disruption of mitochondrial homeostasis in organic acidurias: insights from human and animal studies

Organic acidurias or organic acidemias constitute a group of inherited disorders caused by deficient activity of specific enzymes of amino acids, carbohydrates or lipids catabolism, leading to large accumulation and excretion of one or more carboxylic (organic) acids. Affected patients usually present neurologic symptoms and abnormalities, sometimes accompanied by cardiac and skeletal muscle alterations, whose pathogenesis is poorly known. However, in recent years growing evidence has emerged indicating that mitochondrial dysfunction is directly or indirectly involved in the pathology of various organic acidemias. Mitochondrial impairment in some of these diseases are generally due to mutations in nuclear genes of the tricarboxylic acid cycle or oxidative phosphorylation, while in others it seems to result from toxic influences of the endogenous organic acids to the mitochondrion. In this minireview, we will briefly summarize the present knowledge obtained from human and animal studies showing that disruption of mitochondrial homeostasis may represent a relevant pathomechanism of tissue damage in selective organic acidemias. The discussion will focus on mitochondrial alterations found in patients affected by organic acidemias and by the deleterious effects of the accumulating organic acids on mitochondrial pathways that are crucial for ATP formation and transfer. The elucidation of the mechanisms of toxicity of these acidic compounds offers new perspectives for potential novel adjuvant therapeutic strategies in selected disorders of this group.

Induction of parkinsonism‐related proteins in the spinal motor neurons of transgenic mouse carrying a mutant SOD1 gene

Amyotrophic lateral sclerosis is a progressive and fatal disease caused by selective death of motor neurons, and a number of these patients carry mutations in the superoxide dismutase 1 (SOD1) gene involved in ameliorating oxidative stress. Recent studies indicate that oxidative stress and disruption of mitochondrial homeostasis is a common mechanism for motor neuron degeneration in amyotrophic lateral sclerosis and the loss of midbrain dopamine neurons in Parkinson's disease. Therefore, the present study investigated the presence and alterations of familial Parkinson's disease-related proteins, PINK1 and DJ-1, in spinal motor neurons of G93ASOD1 transgenic mouse model of amyotrophic lateral sclerosis. Following onset of disease, PINK1 and DJ-1 protein expression increased in the spinal motor neurons. The activated form of p53 also increased and translocated to the nuclei of spinal motor neurons, followed by increased expression of p53-activated gene 608 (PAG608). This is the first report demonstrating that increased expression of PAG608 correlates with activation of phosphorylated p53 in spinal motor neurons of an amyotrophic lateral sclerosis model. These results provide further evidence of the profound correlations between spinal motor neurons of amyotrophic lateral sclerosis and parkinsonism-related proteins.

Lethal toxin from Clostridium sordellii induces apoptotic cell death by disruption of mitochondrial homeostasis in HL-60 cells.

Lethal toxin (LT) from Clostridium sordellii (strain IP82) inactivates in glucosylating the small GTPases Ras, Rap, Ral and Rac. In the present study we show that LT-IP82 induces cell death via an intrinsic apoptotic pathway in the myeloid cell-line HL-60. LT-IP82 was found to disrupt mitochondrial homeostasis as characterized by a decrease in mitochondrial transmembrane potential and cardiolipin alterations, associated with the release of cytochrome c in the cytosol. Time-course studies of caspase activation revealed that caspase-9 and caspase-3 were activated before caspase-8. Moreover, although LT-IP82-induced cell death was abrogated by caspase-inhibitors, these inhibitors did not suppress mitochondrial alterations, indicating that caspase activation occurs downstream of mitochondria. Protection of mitochondria by Bcl-2 overexpression prevented mitochondrial changes as well as apoptosis induction. Furthermore, evidence is provided that LT-IP82-induced apoptosis is not a consequence of cortical actin disorganization, suggesting that Rac inactivation does not initiate the apoptotic process. Cell exposure to LT-IP82 leads to a co-localization of the toxin with a mitochondrial marker within 2 h. Therefore, we suggest that LT-IP82 could act at the mitochondrion level independently of its enzymatic effect on small GTPases.

Epidermal Growth Factor Up-regulates the Transcription of Mouse Lon Homology ATP-Dependent Protease Through Extracellular Signal-Regulated Protein Kinase- and Phosphatidylinositol-3-Kinase-dependent Pathways

Epidermal growth factor (EGF) induces tumorigenic transformation of mouse epidermal cells (JB6 P +). We cloned a full-length EGF-responsive cDNA in JB6P + cells; EGF up-regulated mRNA expression of this gene 5- to 6-fold. The deduced amino acid sequence of this cDNA exhibited 84 and 96% homology with human and rat Lon homology ATP-dependent protease, respectively, and all conserved domains of Lon, such as ATPase/protease domains, are present in the mouse gene, indicating that this gene is mouse Lon. EGF increased the transcriptional rate without affecting the mRNA stability of m-Lon. The level of m-Lon in irreversibly transformed mouse epidermal cells (JB7) was 3.4-fold higher than that in parental JB6 P + cells. Similarly, human mammary epithelial cells overexpressing the proto-oncogene ErbB2 expressed significantly higher levels of Lon than normal mammary epithelial cells. EGF failed to regulate Lon expression in ERK-deficient JB6 P − cells or cells that expressed the dominant-negative p85 P13-K regulatory unit. Furthermore, selective chemical blockers for MEK1 and P13-K (PD98059 and LY294002) inhibited EGF-mediated induction. Mitochondria-localized Lon protease plays a critical role in the regulation of mitochondrial gene expression and genome integrity. Disruption of mitochondrial homeostasis is a general characteristic of tumorigenic transformation. Thus, the role of Lon in tumor promotion warrants further study.