Diversity Supplement: B Cells Directly Alter Adaptive Plasticity to Support Functional Recovery After Stroke

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Our novel data from the past New Investigator R01 award period show post-stroke B cells diapedese into remote regions (e.g. dentate gyrus) that support motor and cognitive recovery after transient middle cerebral artery occlusion (tMCAo). B cells can provide neurotrophic support through secretion of both interleukin (IL)-10 and additional neurotrophin(s) to support post-stroke plasticity. The central hypothesis of this R01 renewal is that a subset of B cells diapedese into brain regions remote from the infarct to provide long-term neurotrophic support for functional recovery. Brain-derived neurotrophic factor (BDNF) mediates synaptic transmission and memory formation during health and protects neurons from glutamate-induced excitotoxicity after stroke. BDNF also mediates B cell egress from bone marrow and can be produced by B cells in response to glutamate stimulation through the NMDAR subunit GluN2A. Based on our pilot data, we will test: if a subset of post-stroke B cells, referred to as B cellsBDNF+, upregulate BDNF after encountering glutamate; if B cellsBDNF+ support motor and cognitive recovery; and if B cell-derived BDNF is impaired in aged females. We will use 4 mos. (“young”) and 16 mos. (“aged”) female and male mice to test if B cellsBDNF+ support neuronal function, plasticity, motor, and multi-domain cognitive recovery post-stroke. Aim 1 will test if (1A) post-tMCAo, glutamate binds to B cell GluN2A to increase BDNF production and drive recovery-linked intracellular Ca2+ signaling that is sex- and age-dependent. We will (1B) use B cellsNtrk2tm1Ddg/J in vitro to test if the BDNF receptor TrkB is required for BDNF production and in vitro neuroprotection. Aim 2 will test if B cellsBDNF+ support remote plasticity, motor and cognitive recovery in a primary motor cortex photothrombosis stroke model. Inducible depletion of (2A) all B cells or (2B) specific B cell-derived BDNF in young and aged female hCD20TamCre/ BDNFfl/fl mice and littermate controls will occur either acute (at D0) or delayed (beginning D7 post-stroke). Primary outcomes will include 1) peri-infarct and contralesional M1 plasticity, 2) improved forelimb precision reaching, and 3) preservation of Pavlovian stimulus-reinforcer learning on an automated touchscreen task. Aim 3 will test if B cell-derived BDNF augments long-term motor and cognitive recovery. Aged C57BL/6J female mice will receive tMCAo or sham surgery and adoptive transfer of B cells that (3A) overexpress BDNF or (3B) lack BDNF, the latter derived from hCD20TamCre/BDNFfl/fl donor mice, beginning D7 post-stroke. Primary outcomes will include 1) improved precision skilled reaching, 2) ameliorated hippocampal-specific cognitive deficits tested via touchscreen pattern separation, and 3) regional ipsi- and contralesional diapedesis of B cells, as determined via whole brain serial two-photon tomography, that correlates to within-animal magnitude of brain circuit-specific cognitive function and motor recovery. These studies will confirm an age-dependent loss of a novel subset of B cells, B cellsBDNF+, in females. They will also confirm that therapeutically targeting B cells can improve motor and cognitive deficits − a potential treatment supporting plasticity-based recovery after any CNS injury or disease.