Quinolinic Acid Induces Alterations in Neuronal Subcellular Compartments, Blocks Autophagy Flux and Activates Necroptosis and Apoptosis in Rat Striatum

Abstract

Quinolinic acid (QUIN) is an agonist of N-methyl-D-aspartate receptor (NMDAr) used to study the underlying mechanism of excitotoxicity in animal models. There is evidence indicating that impairment in autophagy at early times contributes to cellular damage in excitotoxicity; however, the status of autophagy in QUIN model on day 7 remains unexplored. In this study, the ultrastructural analysis of subcellular compartments and the status of autophagy, necroptosis, and apoptosis in the striatum of rats administered with QUIN (120 nmol and 240 nmol) was performed on day 7. QUIN induced circling behavior, neurodegeneration, and cellular damage; also, it promoted swollen mitochondrial crests, spherical-like morphology, and mitochondrial fragmentation; decreased ribosomal density in the rough endoplasmic reticulum; and altered the continuity of myelin sheaths in axons with separation of the compact lamellae. Furthermore, QUIN induced an increase and a decrease in ULK1 and p-70-S6K phosphorylation, respectively, suggesting autophagy activation; however, the increased microtubule-associated protein 1A/1B-light chain 3-II (LC3-II) and sequestosome-1/p62 (SQSTM1/p62), the coexistence of p62 and LC3 in the same structures, and the decrease in Beclin 1 and mature cathepsin D also indicates a blockage in autophagy flux. Additionally, QUIN administration increased tumor necrosis factor alpha (TNFα) and receptor-interacting protein kinase 3 (RIPK3) levels and its phosphorylation (p-RIPK3), as well as decreased B-cell lymphoma 2 (Bcl-2) and increased Bcl-2-associated X protein (Bax) levels and c-Jun N-terminal kinase (JNK) phosphorylation, suggesting an activation of necroptosis and apoptosis, respectively. These results suggest that QUIN activates the autophagy, but on day 7, it is blocked and organelle and cellular damage, neurodegeneration, and behavior alterations could be caused by necroptosis and apoptosis activation.

Keywords: Apoptosis; Autophagy impairment; Excitotoxicity; Necroptosis; Quinolinic acid.