Levodopa Activates Apoptosis Signaling Kinase 1 (ASK1) and Promotes Apoptosis in a Neuronal Model: Implications for the Treatment of Parkinson's Disease

Abstract

Oxidative stress is implicated in the etiology of Parkinson's disease (PD), the second most common neurodegenerative disease. PD is treated with chronic administration of L-3,4-dihydroxyphenylalanine (Levodopa, L-DOPA), and typically increasing doses are used during progression of the disease. Paradoxically L-DOPA is a pro-oxidant and induces cell death in cellular models of PD through disruption of sulfhydryl homeostasis involving loss of the thiol-disulfide oxidoreductase functions of the glutaredoxin (Grx1) and thioredoxin (Trx1) enzyme systems (Sabens et al. 2010). Considering this loss of both Grx1 and Trx1 activities upon L-DOPA treatment, we sought to elucidate the mechanism(s) of L-DOPA induced apoptosis. In other contexts both the NFκB (nuclear factor κB) pathway and the ASK1 (apoptosis signaling kinase 1) pathway have been shown to be regulated by both Grx1 and Trx1, and both pathways have been implicated in cell death signaling in model systems of PD. Moreover, mixed lineage kinase (MLK) has been considered as a potential therapeutic target for PD. Using SHSY5Y cells as model dopaminergic neurons we found that NFκB activity was not altered by L-DOPA treatment, and the selective MLK inhibitor (CEP-1347) did not protect the cells from L-DOPA. In contrast, ASK1 was activated with L-DOPA treatment as indicated by phosphorylation of its downstream mitogen activated protein kinases (MAPK), p38 and JNK. Chemical inhibition of either p38 or JNK provided protection from L-DOPA induced apoptosis. Moreover, direct knockdown of ASK1 protected from L-DOPA induced neuronal cell death. These results identify ASK1 as the main pro-apoptotic pathway activated in response to L-DOPA treatment, implicating it as a potential target for adjunct therapy in PD.

Liver X receptors activation, through TO901317 binding, reduces neuroinflammation in Parkinson’s disease

“…The cells were tested for contamination before use. These well-differentiated cells displays typical dopaminergic characteristics, including expression of tyrosine hydroxylase, dopamine transporter and monoamine oxidase A & B, making this a typical model for dopaminergic neurons [16]. SH-SY5Y neuroblastoma cells can be differentiated into sustainable neuronal morphology.…”

Antioxidant and bioenergetic coupling between neurons and astrocytes

“…Thus dysfunction of these enzymes causes a dopaminergic neuronal death resembling that seen in Parkinson's disease [70][71][72]. Thus dysfunction of these enzymes causes a dopaminergic neuronal death resembling that seen in Parkinson's disease [70][71][72].…”

The Role of Oxidative Stress in Parkinson's Disease

“…Under conditions of moderate oxidative stress, proteins can be S-glutathionylated, and this process may protect the cell by preventing the irreversible oxidation of cysteine to cysteine sulfinic and sulfonic acid [97]. In fact, knock-down of Grx in SH-SY5Y cells results in increased apoptosis, supporting the notion that disrupting the regulation of protein glutathionylation may sensitize dopaminergic neurons to apoptosis [95, 98]. Additionally, consistent with the hypothesis of altered thiol-disulfide homeostasis in stressed dopaminergic neurons, mouse brains lesioned with MPTP exhibit decreased activity of isocitrate dehydrogenease (IDH) [97].…”