TRIM45 causes neuronal damage by aggravating microglia-mediated neuroinflammation upon cerebral ischemia and reperfusion injury

Abstract

Excessive and unresolved neuroinflammation is a key component of the pathological cascade in brain injuries such as ischemic stroke. Tripartite motif-containing 45 (TRIM45) is a ubiquitin E3 ligase involved in various critical biological processes. However, the role of TRIM45 in cerebral ischemia remains unknown. Here, we found that the TRIM45 protein was highly expressed in the peri-infarct areas of mice subjected to cerebral ischemia and reperfusion injury induced by middle cerebral artery occlusion. This study systemically evaluated the putative role of TRIM45 in the regulation of neuroinflammation during ischemic injury and the potential underlying mechanisms. We found that TRIM45 knockdown significantly decreased proinflammatory cytokine and chemokine production in primary cultured microglia challenged with oxygen-glucose deprivation and reoxygenation (OGD/R) treatment. Mechanistically, we demonstrated that TRIM45 constitutively interacted with TAB2 and consequently facilitated the Lys-63-linked polyubiquitination of TAB2, leading to the formation of the TAB1–TAK1–TAB2 complex and activation of TAK1, which was ultimately followed by activation of the nuclear factor-kappa B (NF-κB) signaling pathway. In an in vitro coculture Transwell system, downregulation of TRIM45 expression also inhibited the OGD/R-induced activation of microglia and alleviated neuronal apoptosis. More importantly, microglia-specific knockdown of TRIM45 in mice significantly reduced the infarct size, mitigated neurological deficit scores, and improved cognitive function after ischemic stroke. Taken together, our study reveals that the TRIM45–TAB2 axis is a crucial checkpoint that controls NF-κB signaling in microglia during cerebral ischemia and reperfusion injury. Therefore, targeting TRIM45 may be an attractive therapeutic strategy.

Stroke: Possible therapeutic target for subsequent brain inflammation

Therapies targeting a protein found at high levels following stroke could help reduce subsequent brain inflammation and damage to neurons. The release of cytokines and chemokines, immune system signaling molecules, in the brain following a stroke exacerbates inflammation and can cause extensive damage, even after restoration of blood flow. Xing Li and co-workers at Huazhong University of Science and Technology, Wuhan, China, examined the role of the TRIM45 protein following stroke in mice. The brain’s immune system cells, microglia, activate inflammatory proteins to protect the brain from injury. The team found that stroke triggers the increase of TRIM45 expression in microglia. TRIM45 interacts with another protein to stimulate signalling cascades that result in inflammation and neuronal damage. Blocking TRIM45 expression significantly decreased cytokine production in the mice, suggesting the protein may be a valuable therapeutic target.