After experimental diffuse brain injury, we recently uncovered a morphological variant of brain microglia - the rod microglia - originally described 100+ years ago, but largely ignored since then. Current understanding places rod microglia amongst activated microglia, which would typically progress towards phagocytotic, amoeboid microglia/macrophages. However, few primary articles have reported on rod microglia, with an absence of molecular investigations. For the first time, we reproducibly observe microglia with an elongated rod morphology that align in trains across cortical layers adjacent to neuronal processes in foci of neuropathology after diffuse brain-injury. Moreover, trains of rod microglia form in a time course consistent with circuit dismantling (neuropathology) and then recede as neural circuits recover (plasticity), albeit reorganized. Now we have the opportunity to explore the functional implication of these neuronal:glial interactions that may underlie brain reorganization and neurological symptoms after TBI. To begin investigating the significance and impact of rod microglia in acute neurological injury, the current proposal obtains critical preliminary data to distinguish activated rod microglia from activated microglia by gene expression profile. We will induce diffuse brain injury by midline fluid percussion injury in adult male rats and identify rod microglia based on immunohistochemistry and morphology. Laser-capture microdissection will isolate rod microglia and activated microglia, with surrounding neuronal elements, from cortical regions of the same animal to provide an internal control. Next-generation sequencing (RNA-Seq) and subsequent enrichment analysis (gene ontology, pathway data sets, and transcription factor analysis) will identify neuronal:glial expression unique to rod microglia. We expect that expression data will reveal differentiation, migration and proliferation origins of this morphology and inflammatory, cytoskeletal and degenerative functional roles of rod microglia. Results will define rod microglia, enabling the development of molecular tools to detect, isolate and target rod microglia. With refined molecular tools, rod microglia can be investigated across neurological conditions (e.g. seizure, Alzheimer's disease, Autism) and activated or inhibited to drive treatment of neurological symptoms.
Neurological insults, including traumatic brain injury, trigger classical inflammatory pathways in the brain that are mediated by activated microglial cells. In this proposal, we investigate a little-known microglia subtype, the rod microglia, to determine the gene expression unique to their origin and function after diffuse traumatic brain injury. Markers unique to rod microglia could serve as biomarkers in the diagnosis and prognosis of neurological conditions.
| Morrison, Helena; Young, Kimberly; Qureshi, Mahir et al. (2017) Quantitative microglia analyses reveal diverse morphologic responses in the rat cortex after diffuse brain injury. Sci Rep 7:13211 |
