Cell Specific RIPK3 signaling after traumatic brain injury in mice

点击翻译按钮获取中文摘要

Receptor interacting protein kinases (RIPK)-1 and -3 are serine-threonine kinases that regulate apoptosis, necrosis, and inflammation. RIPKs mediate programmed necrosis via RIPK1-RIPK3-MLKL necrosome assembly, and apoptosis via the ripoptosome involving FLIP, caspase-8, TRADD, and RIPK3, among others. RIPK1 inhibitors are currently in human clinical trials for several systemic diseases. In contrast, RIPK3 has been less studied in part because clinically acceptable RIPK3 inhibitors are not yet available. Building on our prior studies showing improved neurological outcome in mice deficient in TNF and Fas receptor (upstream activators of RIPK3), we used genetic tools to interrogate a possible role for RIPK3 in a mouse controlled cortical impact (CCI) model. Mice lacking RIPK3 had improved motor and cognitive function after CCI, and greater protection in cognitive function tests than RIPK1 kinase dead or MLKL knockout mice, suggesting a unique role for RIPK3- independent of necroptosis because acute neuronal cell death or lesion volume was not reduced by RIPK3 knockout. Using immunopanning to isolate specific brain cell populations, we found the highest levels of RIPK3 expression in endothelium and immune cells. RIPK3 KO mice had reduced HMGB1 release after CCI, reduced interleukin-1 beta processing in brain tissue and endothelial cells, and maintained K48 ubiquitination of neuronal proteins and brain TBK1 levels- mechanisms that have previously been shown to modulate outcome after CCI and contribute to neurodegeneration in aging-related neurodegenerative diseases. We hypothesize that RIPK3 signaling in endothelial and immune cells induces neurological dysfunction after cerebral contusion by activating multiple acute inflammation pathways and is a potential therapeutic target to improve outcome. To test this hypothesis we propose three specific aims: Aim 1, to identify upstream mechanisms regulating RIPK3 activation in specific brain cell types after CCI in mice, using immunopanning and FACS to isolate specific brain cell types; Aim 2, to define cell-specific functional roles for RIPK3 in brain vs. peripheral immune cells using bone marrow chimeras and inducible/conditional RIPK3 knockout mice; and Aim 3, to identify mechanisms downstream of RIPK3 that might contribute to neurodegeneration in the chronic period after TBI.