Autophagy is Activated In Vivo during Trimethyltin-Induced Apoptotic Neurodegeneration: A Study in the Rat Hippocampus

Abstract

Trimethyltin (TMT) is an organotin compound known to produce significant and selective neuronal degeneration and reactive astrogliosis in the rodent central nervous system. Autophagy is the main cellular mechanism for degrading and recycling protein aggregates and damaged organelles, which in different stress conditions, such as starvation, generally improves cell survival. Autophagy is documented in several pathologic conditions, including neurodegenerative diseases. This study aimed to investigate the autophagy and apoptosis signaling pathways in hippocampal neurons of TMT-treated (Wistar) rats to explore molecular mechanisms involved in toxicant-induced neuronal injury. The microtubule-associated protein light chain (LC3, autophagosome marker) and sequestosome1 (SQSTM1/p62) (substrate of autophagy-mediated degradation) expressions were examined by Western blotting at different time points after intoxication. The results demonstrate that the LC3 II/I ratio significantly increased at 3 and 5 days, and that p62 levels significantly decreased at 7 and 14 days. Immunofluorescence images of LC3/neuronal nuclear antigen (NeuN) showed numerous strongly positive LC3 neurons throughout the hippocampus at 3 and 5 days. The terminal deoxynucleotidyltransferase dUTP nick end labeling (TUNEL) assay indicated an increase in apoptotic cells starting from 5 days after treatment. In order to clarify apoptotic pathway, immunofluorescence images of apoptosis-inducing factor (AIF)/NeuN did not show nuclear translocation of AIF in neurons. Increased expression of cleaved Caspase-3 was revealed at 5–14 days in all hippocampal regions by Western blotting and immunohistochemistry analyses. These data clearly demonstrate that TMT intoxication induces a marked increase in both autophagy and caspase-dependent apoptosis, and that autophagy occurring just before apoptosis could have a potential role in neuronal loss in this experimental model of neurodegeneration.

Blood Neurofilament Light Chain as a Potential Biomarker for Central and Peripheral Nervous Toxicity in Rats

“…In this study, we employed the Simoa assay to measure serum and CSF NfL levels, evaluated the potential of NfL as a peripheral biomarker of CNS toxicity, and compared the sensitivities of typical neurotoxicity endpoints such as nervous symptoms and histopathology in rat neurotoxicity models induced by trimethyltin (TMT), kainic acid (KA), and MK-801. TMT induces injury in CNS neurons and several nervous symptoms ( Balaban et al , 1988 ; Bushnell and Evans, 1985 ; Ceccariglia et al , 2020 ; Crofton et al , 1990 ; Ogata et al , 2015 ). KA, an agonist of kainate glutamate receptor subtypes, causes glutamate excitotoxicity in rodents ( Zheng et al , 2011 ), and KA treatment is one of the most reliable models for temporal lobe epilepsy ( Bertoglio et al , 2017 ; Levesque and Avoli, 2013 ; Zheng et al , 2011 ).…”

Expression of Ectonucleoside Triphosphate Diphosphohydrolase 2 (NTPDase2) Is Negatively Regulated Under Neuroinflammatory ConditionsIn VivoandIn Vitro

“…Within DG, the expression of NTPDase2 decreased in presynaptic boutons innervating neurons in PoDG ( Amaral et al, 2007 ), whereas the recovery occurred in the PoDG, SGL, and at astrocytic sheats traversing the GrDG . As described in several recent papers, exposure to TMT induces selective neuronal death ( Ceccariglia et al, 2019 ) and consequent massive increase in extracellular ATP, which attracts microglia and initiates inflammatory responses of astrocytes ( Davalos et al, 2005 ), mainly via P2X7 receptors ( Buffo et al, 2010 ). From 2-dpi onwards, PoDG became populated with highly reactive astrocytes, which express iNOS, C3, NFkB, and P2X7R, and secrete pro-inflammatory cytokines IL-1β, IL-6, IFN-γ, and TNF-α in the parenchyma ( Dragic et al, 2021b ; Latini et al, 2010 ; Little et al, 2012 ).…”

Autophagy in trimethyltin-induced neurodegeneration

“…Additionally, Lattanzi et al (2007) reported an increase in autophagyassociated genes using microarray analysis in TMT-treated PC12 cells with respect to untreated controls. Very recently Ceccariglia et al (2019) investigated the autophagy status through the analysis of LC3, p62, and Beclin 1 as main regulatory markers in the rat hippocampus at different time points after TMT administration. Authors concomitantly evaluated the main apoptosis pathways to check for a potential correlation between the autophagy status and apoptosis machinery.…”