Role of PGC-1α in Mitochondrial Quality Control in Neurodegenerative Diseases

Neurochemical Research - As one of the major cell organelles responsible for ATP production, it is important that neurons maintain mitochondria with structural and functional integrity; this is...     

Dopaminergic Toxin 1-Methyl-4-Phenylpyridinium,Proteins α-Synuclein and Glia Maturation Factor Activate Mast Cells and Release Inflammatory Mediators

Parkinson’s disease (PD) is characterized by the presence of Lewy bodies and degeneration of dopaminergic neurons. 1-methyl-4-phenylpyridinium (MPP+), a metabolite of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and Lewy body component α-synuclein activates glia in PD pathogenesis. Mast cells and glia maturation factor (GMF) are implicated in neuroinflammatory conditions including Multiple Sclerosis. However, the role of mast cells in PD is not yet known. We have analyzed the effect of recombinant GMF, MPP+, α-synuclein and interleukin-33 (IL-33) on mouse bone marrow-derived cultured mast cells (BMMCs), human umbilical cord blood-derived cultured mast cells (hCBMCs) and mouse brain-derived cultured astrocytes by quantifying cytokines/chemokines released using ELISA or by detecting the expression of co-stimulatory molecules CD40 and CD40L by flow cytometry. GMF significantly released chemokine (C-C motif) ligand 2 (CCL2) from BMMCs but its release was reduced in BMMCs from GMF knockout mice. GMF, α-synuclein and MPP+ released IL-1β, β-hexosaminidase from BMMCs, and IL-8 from hCBMCs. GMF released CCL5, and IL-33- induced the expression of GMF from hCBMCs. Novel GMF expression was detected in hCBMCs and BMMCs by immunocytochemistry. GMF released tumor necrosis factor-alpha (TNF-α) from mouse astrocytes, and this release was greater in BMMC- astrocyte coculture than in individual cultures. Flow cytometry results showed increased IL-33 expression by GMF and MPP+, and GMF-induced CD40 expression in astrocytes. Proinflammatory mediator release by GMF, MPP+ and α-synuclein, as well as GMF expression by mast cells indicate a potential therapeutic target for neurodegenerative diseases including PD.     

Protective Role of PGC-1α in Diabetic Nephropathy Is Associated with the Inhibition of ROS through Mitochondrial Dynamic Remodeling

The overproduction of mitochondrial reactive oxygen species (ROS) plays a key role in the pathogenesis of diabetic nephropathy (DN). However, the underlying molecular mechanism remains unclear. Our aim was to investigate the role of PGC-1α in the pathogenesis of DN. Rat glomerular mesangial cells (RMCs) were incubated in normal or high glucose medium with or without the PGC-1α-overexpressing plasmid (pcDNA3-PGC-1α) for 48 h. In the diabetic rats, decreased PGC-1α expression was associated with increased mitochondrial ROS generation in the renal cortex, increased proteinuria, glomerular hypertrophy, and higher glomerular 8-OHdG (a biomarker for oxidative stress). In vitro, hyperglycemia induced the downregulation of PGC-1α, which led to increased DRP1 expression, increased mitochondrial fragmentation and damaged network structure. This was associated with an increase in ROS generation and mesangial cell hypertrophy. These pathological changes were reversed in vitro by the transfection of pcDNA3-PGC-1α. These data suggest that PGC-1α may protect DN via the inhibition of DRP1-mediated mitochondrial dynamic remodeling and ROS production. These findings may assist the development of novel therapeutic strategies for patients with DN.     

α-Melanocyte-Stimulating Hormone Protects Retinal Vascular Endothelial Cells from Oxidative Stress and Apoptosis in a Rat Model of Diabetes

Aims

Oxidative stress and apoptosis are among the earliest lesions of diabetic retinopathy. This study sought to examine the anti-oxidative and anti-apoptotic effects of α-melanocyte-stimulating hormone (α-MSH) in early diabetic retinas and to explore the underlying mechanisms in retinal vascular endothelial cells.

Methods

Sprague-Dawley rats were injected intravenously with streptozocin to induce diabetes. The diabetic rats were injected intravitreally with α-MSH or saline. At week 5 after diabetes, the retinas were analyzed for reactive oxygen species (ROS) and gene expression. One week later, the retinas were processed for terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and transmission electron microscopy. Retinal vascular endothelial cells were stimulated by high glucose (HG) with or without α-MSH. The expression of Forkhead box O genes (Foxos) was examined through real-time PCR. The Foxo4 gene was overexpressed in endothelial cells by transient transfection prior to α-MSH or HG treatment, and oxidative stress and apoptosis were analyzed through CM-H2DCFDA and annexin-V assays, respectively.

Results

In diabetic retinas, the levels of H₂O₂ and ROS and the total anti-oxidant capacity were normalized, the apoptotic cell number was reduced, and the ultrastructural injuries were ameliorated by α-MSH. Treatment with α-MSH also corrected the aberrant changes in eNOS, iNOS, ICAM-1, and TNF-α expression levels in diabetic retinas. Furthermore, α-MSH inhibited Foxo4 up-regulation in diabetic retinas and in endothelial cells exposed to HG, whereas Foxo4 overexpression abrogated the anti-oxidative and anti-apoptotic effects of α-MSH in HG-stimulated retinal vascular endothelial cells.

Conclusions

α-MSH normalized oxidative stress, reduced apoptosis and ultrastructural injuries, and corrected gene expression levels in early diabetic retinas. The protective effects of α-MSH in retinal vascular endothelial cells may be mediated through the inhibition of Foxo4 up-regulation induced by HG. This study suggests an α-MSH-mediated potential intervention approach to early diabetic retinopathy and a novel regulatory mechanism involving Foxo4.     

Inhibition of SIN-1–Induced Change in Mitochondrial Membrane Permeability in PC12 Cells by Dopamine

Dopamine (50 or 100 microM) attenuated the nuclear damage and cell death due to 500 microM SIN-1, a donor of superoxide and nitric oxide, in differentiated PC12 cells whereas 200 microM dopamine did not depress cell death. Dopamine at 50-100 microM for a 4-h treatment did not show a significant cytotoxic effect on PC12 cells. Dopamine (100 microM) inhibited the decrease in mitochondrial transmembrane potential, cytochrome c release, activation of caspase-3, formation of reactive oxygen species, and depletion of glutathione (GSH) due to 500 microM SIN-1 in PC12 cells. The reaction of dopamine with peroxynitrite reduced an amount of peroxynitrite. The results suggest that dopamine exhibits a biphasic effect against the cytotoxicity of SIN-1 depending on concentrations. Dopamine at 50-100 microM may attenuate the reactive nitrogen species-induced viability loss in PC12 cells by suppressing the mitochondrial membrane permeability change through inhibition of the formation of reactive species, including peroxynitrite.     

Inverse Regulation of the Cytosolic Ca2+ Buffer Parvalbumin and Mitochondrial Volume in Muscle Cells via SIRT1/PGC-1α Axis

Skeletal muscles show a high plasticity to cope with various physiological demands. Different muscle types can be distinguished by the force, endurance, contraction/relaxation kinetics (fast-twitch vs. slow-twitch muscles), oxidative/glycolytic capacity, and also with respect to Ca²⁺-signaling components. Changes in Ca²⁺ signaling and associated Ca²⁺-dependent processes are thought to underlie the high adaptive capacity of muscle fibers. Here we investigated the consequences and the involved mechanisms caused by the ectopic expression of the Ca²⁺-binding protein parvalbumin (PV) in C2C12 myotubes in vitro, and conversely, the effects caused by its absence in in fast-twitch muscles of parvalbumin null-mutant (PV−/−) mice in vivo. The absence of PV in fast-twitch muscle tibialis anterior (TA) resulted in an increase in the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and of its positive regulator, the deacetylase sirtuin 1 (SIRT1). TA muscles from PV−/− mice also have an increased mitochondrial volume. Mild ionophore treatment of control (PV-devoid) C2C12 myotubes causing a moderate elevation in [Ca²⁺]_c resulted in an increase in mitochondrial volume, together with elevated PGC-1α and SIRT1 expression levels, whilst it increased PV expression levels in myotubes stably transfected with PV. In PV-expressing myotubes the mitochondrial volume, PGC-1α and SIRT1 were significantly lower than in control C2C12 myotubes already at basal conditions and application of ionophore had no effect on either one. SIRT1 activation causes a down-regulation of PV in transfected myotubes, whilst SIRT1 inhibition has the opposite effect. We conclude that PV expression and mitochondrial volume in muscle cells are inversely regulated via a SIRT1/PGC-1α signaling axis.     

Reactive Macrophages Increase Oxidative Stress and Alpha-Synuclein Nitration During Death of Dopaminergic Neuronal Cells in Co-Culture: Relevance to Parkinson’s Disease

Parkinson’s disease (PD) is characterized by progressive degeneration of dopaminergic neurons and a substantial decrease in the neurotransmitter dopamine in the nigro-striatal region of the brain. Increased markers of oxidative stress, activated microglias and elevated levels of pro-inflammatory cytokines have been identified in the brains of patients with PD. Although the precise mechanism of loss of neurons in PD remains unclear, these findings suggest that microglial activation may contribute directly to loss of dopaminergic neurons in PD patients. In the present study, we tested the hypothesis that activated microglia induces nitric oxide-dependent oxidative stress which subsequently causes death of dopaminergic neuronal cells in culture. We employed lipopolysaccharide (LPS) stimulated mouse macrophage cells (RAW 264.7) as a reactive microglial model and SH-SY5Y cells as a model for human dopaminergic neurons. LPS stimulation of macrophages led to increased production of nitric oxide in a time and dose dependent manner as well as subsequent generation of other reactive nitrogen species such as peroxynitrite anions. In co-culture conditions, reactive macrophages stimulated SH-SY5Y cell death characterized by increased peroxynitrite concentrations and nitration of alpha-synuclein within SH-SY5Y cells. Importantly 1400W, an inhibitor of the inducible nitric oxide synthase provided protection from cell death via decreasing the levels of nitrated alpha-synuclein. These results suggest that reactive microglias could induce oxidative stress in dopaminergic neurons and such oxidative stress may finally lead to nitration of alpha-synuclein and death of dopaminergic neurons in PD.     

Tumor Associated Macrophages Protect Colon Cancer Cells from TRAIL-Induced Apoptosis through IL-1β- Dependent Stabilization of Snail in Tumor Cells

Background

We recently reported that colon tumor cells stimulate macrophages to release IL-1β, which in turn inactivates GSK3β and enhances Wnt signaling in colon cancer cells, generating a self-amplifying loop that promotes the growth of tumor cells.

Principal Findings

Here we describe that macrophages protect HCT116 and Hke-3 colon cancer cells from TRAIL-induced apoptosis. Inactivation of IL-1β by neutralizing IL-1β antibody, or silencing of IL-1β in macrophages inhibited their ability to counter TRAIL-induced apoptosis. Accordingly, IL-1β was sufficient to inhibit TRAIL-induced apoptosis. TRAIL-induced collapse of the mitochondrial membrane potential (Δψ) and activation of caspases were prevented by macrophages or by recombinant IL-1β. Pharmacological inhibition of IL-1β release from macrophages by vitamin D₃, a potent chemopreventive agent for colorectal cancer, restored the ability of TRAIL to induce apoptosis of tumor cells cultured with macrophages. Macrophages and IL-1β failed to inhibit TRAIL-induced apoptosis in HCT116 cells expressing dnIκB, dnAKT or dnTCF4, confirming that they oppose TRAIL-induced cell death through induction of Wnt signaling in tumor cells. We showed that macrophages and IL-1β stabilized Snail in tumor cells in an NF-κB/Wnt dependent manner and that Snail deficient tumor cells were not protected from TRAIL-induced apoptosis by macrophages or by IL-1β, demonstrating a crucial role of Snail in the resistance of tumor cells to TRAIL.

Significance

We have identified a positive feedback loop between tumor cells and macrophages that propagates the growth and promotes the survival of colon cancer cells: tumor cells stimulate macrophages to secrete IL-1β, which in turn, promotes Wnt signaling and stabilizes Snail in tumor cells, conferring resistance to TRAIL. Vitamin D₃ halts this amplifying loop by interfering with the release of IL-1β from macrophages. Accordingly, vitamin D₃ sensitizes tumor cells to TRAIL-induced apoptosis, suggesting that the therapeutic efficacy of TRAIL could be augmented by this readily available chemopreventive agent.     

Baicalein-Induced Apoptosis via Endoplasmic Reticulum Stress Through Elevations of Reactive Oxygen Species and Mitochondria Dependent Pathway in Mouse–Rat Hybrid Retina Ganglion Cells (N18)

Studies were designed to investigate the effects of baicalein on mouse–rat hybrid retina ganglion cells (N18) to better understand its effect on apoptosis and apoptosis-related genes in vitro. Cell viability, reactive oxygen species (ROS), cytoplasmic Ca²⁺, mitochondrial membrane potential (MMP), apoptosis induction, and caspases-3 activity were examined by flow cytometric assay. Apoptosis-associated proteins such as p53, Bax, Bcl-2, cytochrome c, and caspase-3 were examined by Western blot. We demonstrated the increase in the levels of p53, Bax, and cytochrome c and decrease in the level of Bcl-2, which are associated with the induction of apoptotic cell death after 24 h treatment with baicalein in N18 cells. Baicalein induced an increase in the cytoplasmic levels of ROS and Ca²⁺ in 1 h and reached their peak at 3 h, and thereafter a loss of MMP by flow cytometry. We also demonstrated a release of the cytochrome c from mitochondria into cytosol and an activation of caspase-3, which led to the occurrence of apoptosis in N18 cells treated with baicalein by Western blot. Pretreatment was conducted with BAPTA (intracellular calcium chelator) in baicalein-treated cells, the decline of MMP was recovered, and the increase in the level of cytoplasmic Ca²⁺ was suppressed, and the proportion of apoptosis was also markedly diminished. In conclusion, our data suggests that oxidative stress and cellular Ca²⁺ modulates the baicalein-induced cell death via a Ca²⁺-dependent mitochondrial death pathway in N18 cells.     

PGC-1α Is a Key Regulator of Glucose-Induced Proliferation and Migration in Vascular Smooth Muscle Cells

Background

Atherosclerosis is a complex pathological condition caused by a number of mechanisms including the accelerated proliferation of vascular smooth muscle cells (VSMCs). Diabetes is likely to be an important risk factor for atherosclerosis, as hyperglycemia induces vascular smooth muscle cell (VSMC) proliferation and migration and may thus contribute to the formation of atherosclerotic lesions. This study was performed to investigate whether PGC-1α, a PPARγ coactivator and metabolic master regulator, plays a role in regulating VSMC proliferation and migration induced by high glucose.

Methodology/Principal Findings

PGC-1α mRNA levels are decreased in blood vessel media of STZ-treated diabetic rats. In cultured rat VSMCs, high glucose dose-dependently inhibits PGC-1α mRNA expression. Overexpression of PGC-1α either by infection with adenovirus, or by stimulation with palmitic acid, significantly reduces high glucose-induced VSMC proliferation and migration. In contrast, suppression of PGC-1α by siRNA mimics the effects of glucose on VSMCs. Finally, mechanistic studies suggest that PGC-1α-mediated inhibition of VSMC proliferation and migration is regulated through preventing ERK1/2 phosphorylation.

Conclusions/Significance

These results indicate that PGC-1α is a key regulator of high glucose-induced proliferation and migration in VSMCs, and suggest that elevation of PGC-1α in VSMC could be a useful strategy in preventing the development of diabetic atherosclerosis.     

Concomitant Transitory Up-Regulation of X-Linked Inhibitor of Apoptosis Protein (XIAP) and the Heterogeneous Nuclear Ribonucleoprotein C1–C2 in Surviving Cells During Neuronal Apoptosis

Although cap-dependent translation initiation is the prevalent mode of ribosome binding to mRNAs in eukaryotes, some mRNAs exhibit the ability to bypass the requirement for the cap structure. The translation of X-chromosome-linked inhibitor of apoptosis protein (XIAP) mRNA is controlled by an internal ribosome entry site (IRES) element, which requires the interaction of the heterogeneous nuclear ribonucleoprotein C1–C2 (hnRNP-C1/C2). We analyze, at the protein level, the time course and distribution of XIAP and hnRNP-C1/C2 upon ischemia in mice or staurosporine (STP)-induced apoptosis in HT22 cells. Both ischemia and STP induced a parallel upregulation of XIAP and hnRNP-C1/C2 protein levels in the penumbra and in HT22 cells. These results suggest that the increased levels of hnRNP C1/C2 may modulate XIAP translation, probably by interacting with the XIAP-IRES. The up-regulation of hnRNP-C1/C2 may foster the synthesis of XIAP as a protective pathway by which neurons try to counteract the initial deleterious effects of apoptosis.     

The Role of Ca2+ on the DADS-induced Apoptosis in Mouse–Rat Hybrid Retina Ganglion Cells (N18)

Diallyl disulfide (DADS), a component of garlic, has been shown to induce growth inhibition and apoptosis in human cancer cell types. The present studies were designed to investigate the effects of DADS on mouse–rat hybrid retina ganglion cells (N18) to better understand its effect on apoptosis and apoptosis-related genes in vitro. Cell viability, cell cycle analysis, reactive oxygen species (ROS), Ca²⁺ production, mitochondria membrane potential, apoptosis induction, associated gene expression and caspases-3 activity were examined by flow cytometric assay and/or Western blot. After 24-h treatment with DADS, a dose- and time-dependent decrease in the viability of N18 cells was observed and the approximate IC₅₀ was 27.6 μM. The decreased percentage of viable cells are associated with the production of ROS then followed by the production of Ca²⁺ which is induced by DADS. DADS induced apoptosis in N18 cells via the activation of caspase-3. DADS increased the protein levels of p53, cytochrome c and phosphated JNK within 24 h of treatment and it decreased the levels of Bcl-2 and those factors may have led to the mitochondria depolarization of N18 cells. DADS induced apoptosis were accompanied by increased levels of Ca²⁺ and decreased mitochondrial membrane potential which then led to release the cytochrome c, cleavage of pro-caspase-3. Deleted levels of Ca²⁺ by BAPTA-AM 10 μM (intracellular calcium chelator) then led to decrease DADS-induced apoptosis. Inhibition of caspase-3 activation by inhibitor (z-VAD-fmk) completely blocked DADS-induced apoptosis on N18 cells. The results indicated that oxidative stress modulates cell proliferation and Ca²⁺ modulates the cell death induced by DADS.     

Adipose Tissue-specific Inhibition of Hypoxia-inducible Factor 1α Induces Obesity and Glucose Intolerance by Impeding Energy Expenditure in Mice

Hypoxia in adipose tissue has been postulated as a possible contributor to obesity-related chronic inflammation, insulin resistance, and metabolic dysfunction. HIF1α (hypoxia-inducible factor 1α), a master signal mediator of hypoxia response, is elevated in obese adipose tissue. However, the role of HIF1α in obesity-related pathologies remains to be determined. Here we show that transgenic mice with adipose tissue-selective expression of a dominant negative version of HIF1α developed more severe obesity and were more susceptible to high fat diet-induced glucose intolerance and insulin resistance compared with their wild type littermates. Obesity in the transgenic mice was attributed to impaired energy expenditure and reduced thermogenesis. Histological examination of interscapular brown adipose tissue (BAT) in the transgenic mice demonstrated a markedly increased size of lipid droplets and decreased mitochondrial density in adipocytes, a phenotype similar to that in white adipose tissue. These changes in BAT of the transgenic mice were accompanied by decreased mitochondrial biogenesis and reduced expression of key thermogenic genes. In the transgenic mice, angiogenesis in BAT was decreased but was little affected in white adipose tissue. These findings support an indispensable role of HIF1α in maintaining the thermogenic functions of BAT, possibly through promoting angiogenesis and mitochondrial biogenesis in this tissue.