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Introduction
Cellular proteins are continually renewed by synthesis and degradation. Macroautophagy, a process by which cells autodigest parts of their cytoplasm, is a fundamental cellular mechanism of protein degradation (1). Autophagy is an evolutionarily conserved pathway that leads to stress-induced degradation of intracellular proteins and organelles (2). This type of degradation has been reported to be mediated by interactions with microtubule-associated protein 1 light chain 3 (LC3), a mammalian homologue of autophagy-related gene 8, which was demonstrated to proceed via recruitment to the phagophore/isolation membrane, where it remained associated with the completed autophagosome (3).
The present study investigated the involvement of autophagy in the degradation of gap junction proteins following traumatic brain injury (TBI). Gap junctions are components of the plasma membrane that contain clusters of oligomeric assemblies of proteins called connexins (Cxs), which form channels to allow the passage of ions and small molecules between adjacent cells. Previous studies have shown that several Cxs are expressed by numerous types of cells in the central nervous system (4). Cx43 was shown to be expressed exclusively in astrocytes (5), demonstrated using immunogold labeling for Cx43 (6). Phosphorylated Cx43 (p-Cx43), via the extracellular regulated protein kinase signaling pathway, reduces intercellular permeability via gap junctions, correlating with tissue homeostasis (7). Using HeLa and normal rat kidney epithelial cell models, Lichtenstein et al (8) reported that autophagy-regulated connexin degradation may be induced by starvation. However, the mechanism of neuronic autophagy, which contributed to astrocytic p-Cx43 degradation in the hippocampus following TBI in vivo, remains to be elucidated. In the present study, the involvement of autophagy in the degradation of p-Cx43 was examined in the rat hippocampus following experimental TBI.
Materials and methods
Animals and TBI model
The study was approved by the ethics committee of the Hebei United University (Tangshan, China). All experimental procedures were performed in accordance with the guidelines of the Chinese Council on Animal Protection and were approved by Hebei United University Committee for the Use of Animals in Research (Tangshan, China). A total of 60 male Sprague-Dawley rats (age, 12–16 weeks; weight, 350–375 g; Vital River Laboratory Animal Technology Co., Ltd., Beijing, China) were used in the present study. All animals were housed using the standard 12-h light/dark cycle and access to water and...