Acute TBK1/IKK-ε Inhibition Enhances the Generation of Disease-Associated Microglia-Like Phenotype Upon Cortical Stab-Wound Injury

Abstract

Traumatic brain injury has a poorer prognosis in elderly patients, possibly because of the enhanced inflammatory response characteristic of advanced age, known as “inflammaging.” Recently, reduced activation of the TANK-Binding-Kinase 1 (Tbk1) pathway has been linked to age-associated neurodegeneration and neuroinflammation. Here we investigated how the blockade of Tbk1 and of the closely related IKK-ε by the small molecule Amlexanox could modify the microglial and immune response to cortical stab-wound injury in mice. We demonstrated that Tbk1/IKK-ε inhibition resulted in a massive expansion of microglial cells characterized by the TMEM119+/CD11c+ phenotype, expressing high levels of CD68 and CD317, and with the upregulation of Cst7a, Prgn and Ccl4 and the decrease in the expression levels of Tmem119 itself and P2yr12, thus a profile close to Disease-Associated Microglia (DAM, a subset of reactive microglia abundant in Alzheimer’s Disease and other neurodegenerative conditions). Furthermore, Tbk1/IKK-ε inhibition increased the infiltration of CD3+ lymphocytes, CD169+ macrophages and CD11c+/CD169+ cells. The enhanced immune response was associated with increased expression of Il-33, Ifn-g, Il-17, and Il-19. This upsurge in the response to the stab wound was associated with the expanded astroglial scars and increased deposition of chondroitin-sulfate proteoglycans at 7 days post injury. Thus, Tbk1/IKK-ε blockade results in a massive expansion of microglial cells with a phenotype resembling DAM and with the substantial enhancement of neuroinflammatory responses. In this context, the induction of DAM is associated with a detrimental outcome such as larger injury-related glial scars. Thus, the Tbk1/IKK-ε pathway is critical to repress neuroinflammation upon stab-wound injury and Tbk1/IKK-ε inhibitors may provide an innovative approach to investigate the consequences of DAM induction.

Direct modulation of microglial function by electrical field

“…In association with it, we also observed prominently upregulated TBK1, a potent anti-inflammatory mediator of microglia, in ES-treated cultures compared to those treated with LPS alone. It is reported that TBK1 inhibition resulted in increased production of IL-17 and IFNγ ( Keren-Shaul et al, 2017 ) and microglial infiltration, which was accompanied by an increase in astrocytic scar formation in the traumatic brain injury model through activation of the canonical pro-inflammatory NFkB pathway ( Rehman et al, 2021 ). Together, these results provided strong evidence supporting a direct modulatory effect of ES on anti-inflammatory gene expression in microglia.…”

The role of TBK1 in cancer pathogenesis and anticancer immunity

“…The biological activity of TBK1 was first recognized in innate defenses against pathogens for its role in regulating the production of Type I interferons (IFN), including IFN-α and IFN-β. Recent studies have demonstrated that TBK1 links the pathogen-stimulated processes of inflammation/immunity, metabolism, and proliferation involved in many human diseases, including inflammatory diseases, type II diabetes (T2D), obesity, neurodegenerative diseases, and some cancers [ 19 – 29 ]. Mutation-associated haploinsufficiency of the TBK1 gene has been implicated as a causal event in several types of inflammatory/neurodegenerative diseases, including amyotrophic lateral sclerosis, frontotemporal dementia, Alzheimer’s disease/tauopathies, childhood herpes simplex virus-1 encephalitis (HSE), progressive supranuclear palsy-like syndrome, and a singular case of Parkinsonian-pyramidal syndrome [ 20 , 22 , 27 , 30 – 35 ].…”

“…In addition, germline Tbk1 −/− mice with a 129S5 background are able to survive due to the lack of the Tnfrsf1b gene [ 187 ]. As cells that die from necroptosis are highly immunogenic/inflammatory, mice with Tbk1 loss-of-function mutations display pathological, whole-body inflammation compared to wild-type mice [ 188 ]. Thus, TBK1 has been shown to play a critical role in the prevention of inflammation by suppressing TNFα-RIPK1-mediated cell death.…”

Neuronal nuclear calcium signaling suppression of microglial reactivity is mediated by osteoprotegerin after traumatic brain injury

“…We characterized the IBA1+ population expanded in PT by immunostaining with the microglia marker TMEM119 and the disease-associated microglia (DAM)-like markers CD11c and CST7 (Rehman et al, 2021; Keren-Shaul et al 2017). We also determined the expression of CD169, a marker of pathogenic phagocytes (Bogie et al, 2018; Rajan et al, 2020).…”

“…In the present study, we set out to investigate whether blunting NC prior to TBI would affect neuronal vulnerability. To our surprise, we found that suppressing neuronal NC triggers a massive build-up of reactive microglia with disease-associated-like phenotypes and local loss of synapses (Rehman et al, 2021; Keren-Shaul et al, 2017. Notably, the comparison of transcriptomes revealed a distinct loss of osteoprotegerin (OPG) upon NC blunting, whereas microglial accumulation and synaptic loss are reversed by the neuronal re-expression of OPG.…”