MPTP activates ASK1–p38 MAPK signaling pathway through TNF-dependent Trx1 oxidation in parkinsonism mouse model
Authors: Vijayalakshmi Ravindranath
Smitha Karunakaran
Govindan Rangarajan
Ajit Ray
Neha Sehgal
Journal: Free Radical Biology and Medicine (2015)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Cell death; Graph theory; Neurodegeneration; Oxidative stress; Thiols.
Affiliations: National Brain Research Centre, Nainwal Mode, Manesar-122051, India; Centre for Neuroscience, Indian Institute of Science, Bangalore 560012, India., National Brain Research Centre, Nainwal Mode, Manesar-122051, India., Department of Mathematics, Indian Institute of Science, Bangalore 560012, India., Centre for Neuroscience, Indian Institute of Science, Bangalore 560012, India. Electronic address: .

Abstract:  Activation of apoptosis signal-regulating kinase 1 (ASK1)-p38 MAPK death signaling cascade is implicated in the death of dopaminergic neurons in substantia nigra in Parkinson's disease (PD). We investigated upstream activators of ASK1 using an MPTP mouse model of parkinsonism and assessed the temporal cascade of death signaling in ventral midbrain (VMB) and striatum (ST). MPTP selectively activated ASK1 and downstream p38 MAPK in a time-dependent manner in VMB alone. This occurred through selective protein thiol oxidation of the redox-sensitive thiol disulfide oxidoreductase, thioredoxin (Trx1), resulting in release of its inhibitory association with ASK1, while glutathione-S-transferase µ 1 (GSTM1) remained in reduced form in association with ASK1. Levels of tumor necrosis factor (TNF), a known activator of ASK1, increased early after MPTP in VMB. Protein covariation network analysis (PCNA) using protein states as nodes revealed TNF to be an important node regulating the ASK1 signaling cascade. In confirmation, blocking MPTP-mediated TNF signaling through intrathecal administration of TNF-neutralizing antibody prevented Trx1 oxidation and downstream ASK1-p38 MAPK activation. Averting an early increase in TNF, which leads to protein thiol oxidation resulting in activation of ASK1-p38 signaling, may be critical for neuroprotection in PD. Importantly, network analysis can help in understanding the cause/effect relationship within protein networks in complex disease states. 

Retracted: No

PubPeer comments:
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 We, the authors, have replied to the comments raised in the adjoining set of documents. I hope this assuages any concerns raised here. We are individually posting the responses here due to file size restrictions. , 
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 #10 It was brought to our attention that in Figure 8B full blots, the Tubulin blot has been labeled as Trx1. This is the corrected version as the original submission cannot be removed.![file] , 
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 The authors are unsure whether the commenter grasped the loading pattern numbering fully. From the comment about the image being  ...different loadings of the same sample , the authors infer that the commenter incorrectly concluded that the gel loading is of technical replicates, i.e. repeated loading of the same sample in multiples well. That is not the case. Instead, each well is a biological replicate of either of two groups - C (for 0.5 hr saline treated) or M (for 0.5 hr MPTP treated). So, in the full blot shown in Fig 2C, there are four control samples loaded (lanes 1-4) and five MPTP samples (lanes 5-9). In the representative image, only a pair consisting of one control and one MPTP sample are shown. Lanes 3 and 5 were chosen instead of the adjacent lanes 4 and 5 (both representing one control and one MPTP sample), because the tubulin band intensities (loading controls) were closer to each other, and were a better representation of the overall no change in Trx1 expression that we observed in the compiled graph across all our n s. Other lane combinations could also have been chosen to make the case in Fig 2C. , 
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 #17 The commenter has pointed out that lane 1 C1 has a lower band intensity of AMS-Trx1 than C2. Indeed this variability in the levels are reflected in the SD bar size (~30-35% in Fig 5A of the main paper) of the control group. The authors would like to point out the doublet band that you can clearly observe in C1, where the lower band (i.e. nonAMS-Trx1) is putatively oxidized Trx1 (each AMS molecule can bind to one free cysteine residue). This suggests that part of the Trx1 protein in C1 was already oxidized and did not get derivatized with AMS. Such variability is indeed possible. ,