Glucose Metabolism and AMPK Signaling Regulate Dopaminergic Cell Death Induced by Gene (α-Synuclein)-Environment (Paraquat) Interactions

Abstract

While environmental exposures are not the single cause of Parkinson’s disease (PD), their interaction with genetic alterations is thought to contribute to neuronal dopaminergic degeneration. However, the mechanisms involved in dopaminergic cell death induced by gene-environment interactions remain unclear. In this work, we have revealed for the first time the role of central carbon metabolism and metabolic dysfunction in dopaminergic cell death induced by paraquat (PQ)-α-synuclein interaction. The toxicity of PQ in dopaminergic N27 cells was significantly reduced by glucose deprivation, inhibition of hexokinase with 2-deoxy-D-glucose (2-DG), or equimolar substitution of glucose with galactose, which evidenced the contribution of glucose metabolism to PQ-induced cell death. PQ also stimulated an increase in glucose uptake, and the translocation of glucose transporter type 4 (GLUT4) and Na+-glucose transporters isoform 1 (SGLT1) proteins to the plasma membrane, but only inhibition of GLUT-like transport with STF-31 or ascorbic acid reduced PQ-induced cell death. Importantly, while autophagy protein 5 (ATG5)/unc-51 like autophagy activating kinase 1 (ULK1)-dependent autophagy protected against PQ toxicity, the inhibitory effect of glucose deprivation on cell death progression was largely independent of autophagy or mammalian target of rapamycin (mTOR) signaling. PQ selectively induced metabolomic alterations and adenosine monophosphate-activated protein kinase (AMPK) activation in the midbrain and striatum of mice chronically treated with PQ. Inhibition of AMPK signaling led to metabolic dysfunction and an enhanced sensitivity of dopaminergic cells to PQ. In addition, activation of AMPK by PQ was prevented by inhibition of the inducible nitric oxide syntase (iNOS) with 1400W, but PQ had no effect on iNOS levels. Overexpression of wild type or A53T mutant α-synuclein stimulated glucose uptake and PQ toxicity, and this toxic synergism was reduced by inhibition of glucose metabolism/transport and the pentose phosphate pathway (6-aminonicotinamide). These results demonstrate that glucose metabolism and AMPK regulate dopaminergic cell death induced by gene (α-synuclein)-environment (PQ) interactions.

Metabolic Dysfunction in Parkinson’s Disease: Bioenergetics, Redox Homeostasis and Central Carbon Metabolism

“…Impairment in the PPP leads to the depletion of NADPH and dysfunction in the GSH/Grx, Prx/Trx/TrxR and catalase systems, as well as the decrease in purine synthesis via ribose 5-phoshate [349]. We have recently demonstrated that the PD-related pesticide paraquat hijacks the NADPH from the PPP for its redox cycling, promoting oxidative stress and a toxic synergism when combined with α-synuclein overexpression [14, 186]. NOX and NO-mediated formation of ROS and reactive nitrogen species is also expected to be directly associated with NADPH levels.…”

“…In contrast, lactate has been reported to exert an opposite effect on α-synuclein [151]. We and others have demonstrated that glycolysis is upregulated in response to mitochondrial dysfunction, and that ATP generation via glycolysis exerts a protective role against Complex I inhibition [14, 22, 52–54, 220, 337, 351], As mentioned before, failure of neuronal cells to upregulate this pathway seems to make them rather sensitive to mitochondrial dysfunction [132]. Interestingly, dietary restriction and administration of 2-deoxy-d-glucose exerted protective effects against MPTP toxicity [87].…”

“…Alterations in cellular energy are tightly monitored by the master regulator of metabolism AMPK [48]. We have recently demonstrated that AMPK signaling protects against paraquat-induced dopaminergic cell death and that this effect is independent from glucose metabolism and likely linked to the regulation of mitochondrial bioenergetics (Figure 4.7) [14]. Accordingly, a protective role for AMPK against mitochondrial dysfunction and toxicity induced by Parkin- LRRK2 -mutations, α-synuclein and MPTP/MPP + has also been previously reported [64, 88, 244].…”

Targeting AMPK Signaling as a Neuroprotective Strategy in Parkinson’s Disease

“…However, this idea remains controversial, as other studies have not observed an inhibitory effect of glycogen on AMPK function [29,40]. Nitric-oxide (NO) can activate AMPK via inositol-requiring enzyme 1 (IRE1) [41], providing synchronization between NO production and AMPK activity [42,43]. There is also some evidence that AMPK is regulated by ROS [44].…”

“…Aging, which is the most common risk factor for PD, is associated with decreased mitochondrial function, reduced energy metabolism, and lower AMPK function [66-68]. Decreased ATP generating capacity makes neurons more vulnerable to bioenergetic failure when faced with additional stressors that impair cellular energy metabolism, such as αSyn or environmental toxins [43,69,70]. The neuronal populations that degenerate in PD share some common characteristics that make them particularly vulnerable to bioenergetic failure [71,72].…”