Knockdown of apoptosis signal‐regulating kinase 1 affects ischaemia‐induced astrocyte activation and glial scar formation

Abstract

Reactive astrocytes play an essential role in determining the tissue response to ischaemia. Formation of a glial scar can block the neuronal outgrowth that is required for restoration of damaged tissue. Therefore, regulation of astrocyte activation is important; however, the mediator of this process has not been fully elucidated. Apoptosis signal-regulating kinase 1 (ASK1) is an early responder to oxidative stress, and plays a pivotal role in the intracellular signalling pathway of apoptosis, inflammation, and differentiation. To confirm whether ASK1 mediates astrocyte activation and leads to glial scar formation after cerebral ischaemia, we conducted in vivo and in vitro experiments. C57BL/6 mice were subjected to occlusion of the middle cerebral artery, and astrocyte cultures were exposed to oxygen-glucose deprivation. After silencing of ASK1 , astrocyte-associated genes were downregulated, as seen with the use of microarrays. The glial fibrillary acidic protein (GFAP) level was decreased, and correlated with the reduction in the ASK1 level. In astrocytes, reduction in the ASK1 level decreased the activity of the p38 pathway, and the levels of transcription factors for GFAP and GFAP transcripts after hypoxia. In the chronic phase, ASK1 depletion reduced glial scar formation and conserved neuronal structure, which may lead to better functional recovery. These data suggest that ASK1 may be an important mediator of ischaemia-induced astrocyte activation and scar formation, and could provide a potential therapeutic target for treatment after ischaemic stroke.

Transgenic expression of HuR increases vasogenic edema and impedes functional recovery in rodent ischemic stroke

“…The molecular response is facilitated by post-transcriptional gene regulation in conjunction with transcription [4]. A large number of inflammatory mediators increased in ischemic stroke is regulated post-transcriptionally through AREs in the 3′ UTR [4, 7, 11, 28, 32]. We have previously shown that many of these targets are positively regulated by HuR in astrocytes and microglia, including TNF-α, IL-6, IL-1β and MMP-12 [22, 25].…”

“…Genes linked to secondary tissue injury including pro-inflammatory cytokines (e.g., IL-1β and TNF-α) and matrix metalloproteinases (e.g., MMP-9 and 12) increase in the hyperacute phase and are modulated post-transcriptionally [3, 10, 11, 13, 16, 21, 26, 28, 32]. The key elements in post-transcriptional gene regulation are adenine- and uridine-rich elements (AREs) in the 3′ and/or 5′ untranslated regions of mRNA [1, 3, 7].…”

MiR-124 and small molecules synergistically regulate the direct generation of neuronal cells from rat cortical reactive astrocytes

“…P38 MAPK and ERK1/2 activation is also associated with astrogliosis [53]. During reactive gliosis, ASK1 phosphorylation is enhanced, and P38 MAPK relays the signal to astrocytes for activation and glial scar formation both in vitro and vivo [54,55]. Thus, suppressing P38 MAPK signalling was more likely to attenuate RA characteristics and favour neuronal induction.…”

Regulation of Microglia and Macrophage Polarization via Apoptosis Signal-Regulating Kinase 1 Silencing after Ischemic/Hypoxic Injury

“…ASK1-siRNA was purchased from Ambion [Austin, TX, United States; sense, 5′-GCUGGUAAUUUAUACACuGtt-3′; antisense, 5′-CAGUGUAUAAAUUACGAGCtt–3′; conc, 5 μM (178.5–192.3 nM/g)] ( Cheon et al, 2016b ; Cho et al, 2016 ). Based on a previous study, a 100-μl solution mixed with siPORT NeoFX (Ambion) and ASK1-siRNA was administrated into the left ventricle of the mice by an osmotic pump with a brain infusion kit (Alzet, Cupertino, CA, United States) for 3 days before MCAO.…”

“…After I/R injury, the excessive accumulation of reactive oxygen species (ROS) in cells induces oxidative stress and subsequent damage ( Cheon et al, 2013 ). ROS is a key player in the pathophysiology of cerebral ischemia and ASK1 is known as the initial responder of ROS ( Kim et al, 2011 ; Cheon et al, 2016b ). Also, ASK1 is activated by various stimuli, such as oxidative stress, calcium overload, and receptor-mediated inflammatory signals ( Hayakawa et al, 2006 ; Takeda et al, 2008 ).…”