Abstract
Delayed neuronal death is associated with neurological deficits and mortality after traumatic brain injury (TBI), where post-synaptic density (PSD) proteins are thought to play key roles. The immediate-early gene (IEG) coded protein Arc is a brain-specific PSD protein that controls synaptic plasticity and learning behaviors. In this study, we investigated the expression and biological function of Arc in neuronal death after TBI in an in vitro model mimicked by traumatic neuronal injury (TNI) in cortical neurons. TNI caused a temporal increase of Arc expression at 3 and 6 h. Knockdown of Arc expression using small interfering RNA (Si-Arc-3) promoted TNI-induced cytotoxicity and apoptosis. The results of western blot showed that Si-Arc-3 transfection further enhanced the activation of endoplasmic reticulum (ER) stress-associated factors, including glucose-regulated protein 78 (GRP78), C/EBP homologous protein (CHOP) and caspase-12 after TNI. In addition, knockdown of Arc significantly increased expression of (receptor-interacting protein kinase 1) RIP1 and the number of necroptotic cells, which were apparently prevented by necrostatin-1 (Nec-1). The results of immunostaining and western blot showed that knockdown of Arc activated the metabotropic glutamate receptor 1 (mGluR1) and intracellular Ca2+ release in neurons. Mechanistically, the Si-Arc-3-induced activation of ER stress-associated factors, RIP1 expression, apoptosis, and necroptosis were partially reversed by the mGluR1 antagonist AIDA. In summary, our data suggest that silence of Arc expression aggravates neuronal death after TNI by promoting apoptosis and necroptosis. These data support for the first time that Arc may represent a novel candidate for therapies against TBI.
Highlights
Traumatic brain injury (TBI) is still a major public health problem worldwide, especially in China, where >10 million people suffered from TBI each year, mostly caused by road traffic incidents[1]
The results of western blot showed that traumatic neuronal injury (TNI) caused a temporal increase of activity-regulated cytoskeletal (Arc) expression at 3 and 6 h (Fig. 1b)
Downregulation of Arc expression by small interfering RNAs (siRNAs) transfection To investigate the biological function of Arc in TNI, we designed three specific targeted siRNAs (Si-Arc-1, Si-Arc-2, and Si-Arc-3), which were transfected to neurons with the control siRNA (Si-Control)
Summary
Traumatic brain injury (TBI) is still a major public health problem worldwide, especially in China, where >10 million people suffered from TBI each year, mostly caused by road traffic incidents[1]. The mechanisms underlying neuronal injury after TBI are not well understood, and there is no effective treatment to date. The major cause of neurological deficits and mortality after TBI is neuronal cell death, which occurs in two distinct ways, known as the primary and secondary death. The primary neuronal death represents a passive process with morphological features of disrupted membrane and organelle swelling and the secondary one refers to a delayed, programmed, and energy-dependent fashion characterized by nuclear condensation and fragmentation[3,4]. The TBI-induced neuronal death has been commonly delineated into two different categories: necrosis in the primary phase and apoptosis in the secondary phase. Necroptosis, a recently discovered form of necrosis, is demonstrated to be a programmed cell death
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