Enhanced contextual fear memory in peroxiredoxin 6 knockout mice is associated with hyperactivation of MAPK signaling pathway
Authors: Chien-Chang Chen
Shun-Ping Huang
Pavithra Suresh
Sutisa Nudmamud-Thanoi
Sarayut Phasuk
Narawut Pakaprot
Tanita Pairojana
Sittiruk Roytrakul
Chee-Hing Yang
Supin Chompoopong
Ingrid Y Liu
Journal: Molecular Brain (2021)
Discipline: NEUROSCIENCE & BEHAVIOR
Keywords: Fear memory; MAPK signaling; Peroxiredoxin 6; Posttraumatic stress disorder; Trace fear conditioning.
Affiliations: Institute of Medical Sciences, Tzu Chi University, Hualien, Taiwan., Department of Physiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand., Department of Laboratory Medicine and Biotechnology, Tzu Chi University, Hualien, Taiwan., National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Pathum Thani, Thailand., Department of Molecular Biology and Human Genetics, Tzu Chi University, Hualien, Taiwan., Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan., Department of Anatomy, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand., Department of Anatomy, Faculty of Medical Science, Naresuan University, Phitsanulok, Thailand., Centre of Excellence in Medical Biotechnology, Faculty of Medical Science, Naresuan University, Phitsanulok, Thailand., Institute of Medical Sciences, Tzu Chi University, Hualien, Taiwan. .

Abstract:  Fear dysregulation is one of the symptoms found in post-traumatic stress disorder (PTSD) patients. The functional abnormality of the hippocampus is known to be implicated in the development of such pathology. Peroxiredoxin 6 (PRDX6) belongs to the peroxiredoxin family. This antioxidant enzyme is expressed throughout the brain, including the hippocampus. Recent evidence reveals that PRDX6 plays an important role in redox regulation and the modulation of several signaling molecules involved in fear regulation. Thus, we hypothesized that PRDX6 plays a role in the regulation of fear memory. We subjected a systemic Prdx6 knockout (Prdx6-/-) mice to trace fear conditioning and observed enhanced fear response after training. Intraventricular injection of lentivirus-carried mouse Prdx6 into the 3rd ventricle reduced the enhanced fear response in these knockout mice. Proteomic analysis followed by validation of western blot analysis revealed that several proteins in the MAPK pathway, such as NTRK2, AKT, and phospho-ERK1/2, cPLA2 were significantly upregulated in the hippocampus of Prdx6-/- mice during the retrieval stage of contextual fear memory. The distribution of PRDX6 found in the astrocytes was also observed throughout the hippocampus. This study identifies PRDX6 as a participant in the regulation of fear response. It suggests that PRDX6 and related molecules may have important implications for understanding fear-dysregulation associated disorders like PTSD. 

Retracted: No

PubPeer comments:
 The origin of the Prdx6 knockout mice of this article should be clarified. In the Material and methods, the authors wrote Twelve- to 14-week-old wild-type (C57BL 6J) and Prdx6u2212 u2212 mice were originally generated by Wang X. and colleagues and provided by Dr. Shun-Ping Huang at Tzu Chi University, Taiwan [23] , but we can not find any paper associated with Prdx6 knockout mice research from Dr. Huang s publications. The authors should provide the accurate source where the Prdx6 knockout mice comes from. , 
 First, in the introduction, the authors wrote u201cPRDX6 can modulate both ERK1 2 and AKT [22] expression, supporting our hypothesis that PRDX6 may participate in the neurobiological process of fear memoryu201d, however, this observation is based on the results from esophageal squamous cell carcinoma but not from the neuron cells. Second, supplementary Figure S4C and D showed the quantification data of DHE staining in the hippocampal CA1 and CA3 region, but the authors did not mention how to quantify the DHE staining in the Materials and Methods. Furthermore, each immunofluorescence staining image should be clearly described by which equipment it was taken. Third, in Fig4, Fig5, and Fig6, the results of the comparisons between WT and Prdx6 KO mice were collected during the retrieval of contextual fear memory but the authors did not provide any data of the comparisons between Nau00efve WT and Nau00efve Prdx6 KO. How did the author interpret the data without baseline one? Are those signaling up or down-regulated because of behavior test or because of the effects of gene knockout? The authors should provide baseline data from the Nau00efve WT and Nau00efve Prdx6 KO mice side by side to prove their hypothesis. Four, in Fig7, similar situation, these images were also obtained during the retrieval of contextual fear memory and the authors wrote in the figure legend u201cPRDX6 protein is highly expressed in the astrocytes throughout the hippocampusu201d but without any quantification analysis and without the image taking from nau00efve WT. , 
 ![file] The supplementary Figure S1C:  Immunoblots showing an absence of PRDX6 in knockout mice , 
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