Rod-shaped microglia interact with neuronal dendrites to attenuate cortical excitability during TDP-43-related neurodegeneration

Microglia, the principal immune cells of the central nervous system, have emerged as important players in sensing and regulating neuronal activity. While microglial activation is a hallmark in neurodegeneration, the specific role of microglia in disease-related cortical excitability remains unknown. Utilizing multichannel probe recordings and longitudinal in vivo calcium imaging, we observed neuronal hyperactivity at the initial stage of disease progression in a mouse model of TAR DNA-binding protein 43 (TDP-43) neurodegeneration (rNLS8, regulated nuclear localization sequence-deleted human TDP-43 transgenic mouse model). Spatial and single-cell RNA sequencing revealed a specific subpopulation of microglia, rod-shaped microglia, with a distinct morphology and direct response to cortical hyperactivity. Rod-shaped microglia predominantly interacted with neuronal dendrites and remodeled excitatory synaptic inputs to attenuate motor cortical hyperactivity. Triggering receptor expressed on myeloid cells 2 (TREM2) deficiency led to a marked reduction of rod-shaped microglia accompanied by increased neuronal activity in rNLS8 mice. Together, our results suggest that rod-shaped microglia play a neuroprotective role by attenuating cortical hyperexcitability in TDP-43-related neurodegeneration.