Introduction Oxidative stress (OS) stimulates autophagy in different cellular systems, but it remains controversial if this rule can be generalized. OS plays a critical role in the pathogenesis of Parkinson's disease (PD), where autophagy is known to be defective, both in neuronal and in glial compartments. To address the relationship between OS and autophagy in PD, we focused on astrocytes, which represent the first cellular targets of xenobiotc dopaminergic toxins crossing the blood brain-barrier and thereby play a neuroprotective function. Methods and Results We have analyzed the effect of chronic OS induced by parkinsonian toxins on autophagy in in astrocytoma cells and primary astrocytes. Paraquat (PQ), rotenone and 6-OH dopamine (6OHDA) decreased the basal levels of LC3-II and LC3-positive vesicles, both in the absence and presence of chloroquine, at lethal and nonlethal concentrations. This was paralleled by increased number and size of SQSTM1/p62 aggregates. Downregulation of autophagy and mitophagy was also observed in cells chronically exposed to hydrogen peroxide or very low dose PQ, and it was associated with a reduced astrocyte capability to protect dopaminergic neurons from OS in co-cultures. Surprisingly, PQ treatment led to inhibition of MTOR and upregulation of BECN1/Beclin1 and other signaling pathways, typically correlating with induction of autophagy. Reduction of OS by NMDPEF, a specific NQO2 inhibitor, but not by N-acetylcysteine, abrogated the inhibitory effect of PQ and 6OHDA and restored autophagic flux. This was accompanied by enhanced NFE2L2/NRF2 activity mediated by NMDPEF in SQSTM1-independent fashion. Activation of NQO2 by PQ or menadione and genetic manipulation of its expression confirmed the role of this enzyme in the inhibitory action of PQ on autophagy. Conclusions Thus, a prolonged OS in astrocytes inhibits LC3 lipidation and impairs autophagosome formation and autophagic flux, in spite of concomitant activation of several pro-autophagic signals. These findings outline an unanticipated neuroprotective role of astrocyte autophagy and identify in NQO2 a novel pharmacological target for its positive modulation.
Defective autophagy in Parkinson's disease: role of dopaminergic toxins and /Quinone Oxidoreductase 2 (NQO2).
JANDA E
2017-01-01
Abstract
Introduction Oxidative stress (OS) stimulates autophagy in different cellular systems, but it remains controversial if this rule can be generalized. OS plays a critical role in the pathogenesis of Parkinson's disease (PD), where autophagy is known to be defective, both in neuronal and in glial compartments. To address the relationship between OS and autophagy in PD, we focused on astrocytes, which represent the first cellular targets of xenobiotc dopaminergic toxins crossing the blood brain-barrier and thereby play a neuroprotective function. Methods and Results We have analyzed the effect of chronic OS induced by parkinsonian toxins on autophagy in in astrocytoma cells and primary astrocytes. Paraquat (PQ), rotenone and 6-OH dopamine (6OHDA) decreased the basal levels of LC3-II and LC3-positive vesicles, both in the absence and presence of chloroquine, at lethal and nonlethal concentrations. This was paralleled by increased number and size of SQSTM1/p62 aggregates. Downregulation of autophagy and mitophagy was also observed in cells chronically exposed to hydrogen peroxide or very low dose PQ, and it was associated with a reduced astrocyte capability to protect dopaminergic neurons from OS in co-cultures. Surprisingly, PQ treatment led to inhibition of MTOR and upregulation of BECN1/Beclin1 and other signaling pathways, typically correlating with induction of autophagy. Reduction of OS by NMDPEF, a specific NQO2 inhibitor, but not by N-acetylcysteine, abrogated the inhibitory effect of PQ and 6OHDA and restored autophagic flux. This was accompanied by enhanced NFE2L2/NRF2 activity mediated by NMDPEF in SQSTM1-independent fashion. Activation of NQO2 by PQ or menadione and genetic manipulation of its expression confirmed the role of this enzyme in the inhibitory action of PQ on autophagy. Conclusions Thus, a prolonged OS in astrocytes inhibits LC3 lipidation and impairs autophagosome formation and autophagic flux, in spite of concomitant activation of several pro-autophagic signals. These findings outline an unanticipated neuroprotective role of astrocyte autophagy and identify in NQO2 a novel pharmacological target for its positive modulation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
