DJ-1 protein has multiple specific mechanisms to protect dopaminergic neurons against neurodegeneration in Parkinson's disease. Wild type DJ-1 can acts as oxidative stress sensor and as an antioxidant. DJ-1 exhibits the properties of molecular chaperone, protease, glyoxalase, transcriptional regulator that protects mitochondria from oxidative stress. DJ-1 increases the expression of two mitochondrial uncoupling proteins (UCP 4 and UCP5), that decrease mitochondrial membrane potential and leads to the suppression of ROS production, optimizes of a number of mitochondrial functions, and is regarded as protection for the neuronal cell survival. We discuss also the stabilizing interaction of DJ-1 with the mitochondrial Bcl-xL protein, which regulates the activity of (Inositol trisphosphate receptor) IP 3 R, prevents the cytochrome c release from mitochondria and inhibits the apoptosis activation. Upon oxidative stress DJ-1 is able to regulate various transcription factors including nuclear factor Nrf2, PI3K/PKB, and p53 signal pathways. Stress-activated transcription factor Nrf2 regulates the pathways to protect cells against oxidative stress and metabolic pathways initiating the NADPH and ATP production. DJ-1 induces the Nrf2 dissociation from its inhibitor Keap1 (Kelch-like ECH-associated protein 1), promoting Nrf2 nuclear translocation and binding to antioxidant response elements. DJ-1 is shown to be a co-activator of the transcription factor NF-kB. Under nitrosative stress, DJ-1 may regulate PI3K/PKB signaling through PTEN transnitrosylation, which leads to inhibition of phosphatase activity. DJ-1 has a complex modulating effect on the p53 pathway: one side DJ-1 directly binds to p53 to restore its transcriptional activity and on the other hand DJ-1 can stimulate deacylation and suppress p53 transcriptional activity. The ability of the DJ-1 to induce activation of different transcriptional factors and change redox balance protect neurons against aggregation of α-synuclein and oligomer-induced neurodegeneration.

The specific autophagic elimination of mitochondria (mitophagy) plays the role of quality control for this organelle. Deregulation of mitophagy leads to an increased number of damaged mitochondria and triggers cell death. The deterioration of mitophagy has been hypothesized to underlie the pathogenesis of several neurodegenerative diseases, most notably Parkinson disease. Although some of the biochemical and molecular mechanisms of mitochondrial quality control are described in detail, physiological or pathological triggers of mitophagy are still not fully characterized. Here we show that the induction of mitophagy by the mitochondrial uncoupler FCCP is independent of the effect of mitochondrial membrane potential but dependent on acidification of the cytosol by FCCP. The ionophore nigericin also reduces cytosolic pH and induces PINK1/PARKIN-dependent and -independent mitophagy. The increase of intracellular pH with monensin suppresses the effects of FCCP and nigericin on mitochondrial degradation. Thus, a change in intracellular pH is a regulator of mitochondrial quality control.Continuous ATP production is essential for cell survival. Mitochondria are the major ATP producers in the cell; these are distributed throughout different tissues in varying amounts depending on energy demand. The number of mitochondria within cells is regulated by the balance between mitochondrial biogenesis (1) and the removal of damaged mitochondria. Furthermore, mitochondria also regulate cell death, which is triggered by release of intramitochondrial proteins (2). Considering this, the removal of dysfunctional mitochondria is an important process for ensuring cell survival.Damaged mitochondria, as well as other impaired organelles and proteins in cells are degraded by specific autophagy. Mitochondrial autophagy (mitophagy) 2 plays a role in the quality control of this organelle, whereas dysfunction in mitophagy can lead to an increase in the number of damaged mitochondria that can trigger the activation of cell death pathways (3, 4). Over the last several years, a number of studies have provided substantial evidence showing the PINK1-Parkin pathway (familial forms of Parkinson disease caused by mutations in the genes encoding the PTEN (phosphatase and tensin homolog)-induced putative kinase-1 (PINK1) and Parkin E3 ubiquitin ligase) promotes mitophagy. PINK1 accumulates at the outer mitochondrial membrane of depolarized mitochondria, which recruits cytoplasmic Parkin to the damaged organelle. This results in the ubiquitination of mitofusins (Mfns) by Parkin, the engulfment of the dysfunctional mitochondria by autophagosomes, and subsequent mitophagy (5-8). In recent years, abnormal autophagy and mitophagy has been shown for toxininjured dopaminergic neurons as well as in all the major genetic models of Parkinson disease (PD), including ␣-synuclein, leucine-rich repeat kinase 2 (LRRK2), parkin, PTEN-induced kinase 1 (PINK1), and DJ-1 (9, 10). Historically, mitophagy research focuses on the biochemical and molecular mechanisms of PD; ...

The number of the people affected by neurodegenerative disorders is growing dramatically due to the ageing of population. The major neurodegenerative diseases share some common pathological features including the involvement of mitochondria in the mechanism of pathology and misfolding and the accumulation of abnormally aggregated proteins. Neurotoxicity of aggregated β-amyloid, tau, α-synuclein and huntingtin is linked to the effects of these proteins on mitochondria. All these misfolded aggregates affect mitochondrial energy metabolism by inhibiting diverse mitochondrial complexes and limit ATP availability in neurones. β-Amyloid, tau, α-synuclein and huntingtin are shown to be involved in increased production of reactive oxygen species, which can be generated in mitochondria or can target this organelle. Most of these aggregated proteins are capable of deregulating mitochondrial calcium handling that, in combination with oxidative stress, lead to opening of the mitochondrial permeability transition pore. Despite some of the common features, aggregated β-amyloid, tau, α-synuclein and huntingtin have diverse targets in mitochondria that can partially explain neurotoxic effect of these proteins in different brain regions.

PurposeThis study investigated possible mechanisms of autoregulation of Ca2+ signalling pathways in adipocytes responsible for Ca2+ and NO oscillations and switching phenomena promoted by acetylcholine (ACh), norepinephrine (NE) and atrial natriuretic peptide (ANP).MethodsFluorescent microscopy was used to detect changes in Ca2+ and NO in cultures of rodent white adipocytes. Agonists and inhibitors were applied to characterize the involvement of various enzymes and Ca2+-channels in Ca2+ signalling pathways.ResultsACh activating M3-muscarinic receptors and Gβγ protein dependent phosphatidylinositol 3 kinase induces Ca2+ and NO oscillations in adipocytes. At low concentrations of ACh which are insufficient to induce oscillations, NE or α1, α2-adrenergic agonists act by amplifying the effect of ACh to promote Ca2+ oscillations or switching phenomena. SNAP, 8-Br-cAMP, NAD and ANP may also produce similar set of dynamic regimes. These regimes arise from activation of the ryanodine receptor (RyR) with the implication of a long positive feedback loop (PFL): Ca2+→ NO→cGMP→cADPR→Ca2+, which determines periodic or steady operation of a short PFL based on Ca2+-induced Ca2+ release via RyR by generating cADPR, a coagonist of Ca2+ at the RyR. Interplay between these two loops may be responsible for the observed effects. Several other PFLs, based on activation of endothelial nitric oxide synthase or of protein kinase B by Ca2+-dependent kinases, may reinforce functioning of main PFL and enhance reliability. All observed regimes are independent of operation of the phospholipase C/Ca2+-signalling axis, which may be switched off due to negative feedback arising from phosphorylation of the inositol-3-phosphate receptor by protein kinase G.ConclusionsThis study presents a kinetic model of Ca2+-signalling system operating in adipocytes and integrating signals from various agonists, which describes it as multivariable multi feedback network with a family of nested positive feedback.

No abstract

No abstract

Norepinephrine is one of the key neurotransmitters in the hippocampus, but its role in the functioning of the neuroglial networks remains unclear. Here we show that norepinephrine suppresses NH4Cl‐induced oscillations of the intracellular Ca2+ concentration ([Ca2+]i) in hippocampal neurons. We found that the inhibitory effect of norepinephrine against ammonium‐induced [Ca2+]i oscillations is mediated by activation of alpha‐2 adrenergic receptors. Furthermore, UK 14,304, an agonist of alpha‐2 adrenergic receptors, evokes a biphasic [Ca2+]i elevation in a minor population of astrocytes. This elevation consists of an initial fast, peak‐shaped [Ca2+]i rise, mediated by Giβγ subunit and subsequent PLC‐induced mobilization of Ca2+ from internal stores, and a plateau phase, mediated by a Ca2+ influx from the extracellular medium through store‐operated and TRPC3 channels. We show the correlation between the Ca2+ response in astrocytes and suppression of [Ca2+]i oscillations in neurons. The inhibitory effect of UK 14,304 is abolished in the presence of gallein, an inhibitor of Gβγ‐signaling. In turn, application of the agonist in the presence of the PLC inhibitor decreases the frequency and amplitude of [Ca2+]i oscillations in neurons but does not suppress them. The same effect is observed in the presence of bicuculline, a GABA(A) receptor antagonist. We demonstrate that UK 14,304 application increases the frequency and amplitude of slow outward chloride currents in neurons, indicating the release of GABA by astrocytes. Thus, our findings indicate that the activation of astrocytic alpha‐2 adrenergic receptors stimulates GABA release from astrocytes via Giβγ subunit‐associated signaling pathway, contributing to the suppression of neuronal activity.

No abstract