Core Research Projects
Characterizing the spatiotemporal dynamics of microglia-driven synapse remodeling in vivo
Jessica Kahng and Austin Ferro examine a live microglia imaged by two-photon microscopy.
The phagocytic engulfment of synapses is the predominant method through which microglia are thought to regulate synaptic connectivity in the brain. However, defining the detailed structural events through which microglia phagocytose synapses has been challenging due in large part to limitations in the spatial and temporal resolution of two-photon microscopy. Moreover, emerging evidence from our lab suggests that microglia can also shape synapses through non-phagocytic mechanisms that are not well-understood, particularly during developmental phases of experience-dependent synaptic refinement.
To systematically define the structural and functional responses of microglia to sensory stimulation in vivo, we visualize and quantify interactions between microglia and synapses in live, awake mice as the animals are acutely exposed to diverse visual stimuli. To overcome the technical challenges that have thus far hampered attempts to fully define the spatiotemporal dynamics of microglia-synapse interactions, we have built a two-photon microscope capable of rapidly imaging three fluorescent channels at one time and are designing molecular tools (e.g. FRET-based probes and pH-sensitive synaptic reporters) for detecting interactions between microglia and synapses at nanometer resolution. Moreover, we are performing calcium imaging in microglia in order to probe their ability to participate in sensory processing. Through these approaches, we are uncovering fascinating new insights into the roles of these brain-resident immune cells in the experience-dependent remodeling of functional synaptic connections.
Identifying the genetic regulatory machinery that controls experience-dependent transcription in microglia
Experimental plan to identify molecular mechanisms of transcriptional regulation in microglia.
One of the most fascinating findings to emerge from our laboratory is the observation that microglia mount robust transcriptional responses to visual stimulation. We hypothesize that these experience-dependent changes in chromatin accessibility and transcription are coordinated by dedicated genetic regulatory factors in the microglial nucleus. To identify these factors and understand how they coordinate inducible transcription in microglia, we acutely isolate microglia from the cortices of sensory-deprived or -stimulated mice and interrogate (1) transcription using single-cell and bulk RNA-sequencing; (2) chromatin accessibility using ATAC-sequencing; and (3) histone modifications and transcription factor binding using CUT&RUN. It is our ultimate goal to identify the transcriptional regulatory factors that drive sensory-dependent gene expression in microglia, and to harness these genome-wide datasets to develop new mouse lines in which stimulated microglia can be visualized and manipulated experimentally.
In addition to applying these cutting-edge approaches to mice, we also analyze inducible transcription in all cell types of human cortex following electrical stimulation in vivo. This complementary approach allows us to explore the extent to which genetic mechanisms identified in mice are evolutionarily conserved in the human, and has the potential to identify human-specific mechanisms relevant to neurological disease.
Understanding how interactions between different classes of glia shape neural circuits: focus on microglia and OPCs
OPC (magenta) and associated microglia (green) in visual cortex of an awake mouse taken on a two-photon microscope. Points of contact between the cell types shown in cyan.
While the expanding field of glial biology has predominantly focused on direct signaling interactions between glia and neurons, much less is known about how different types of glia work together to coordinate brain form and function. We recently discovered that microglia send signals to a unique but understudied class of glia, oligodendrocyte precursor cells (OPCs), to promote the engulfment of synapses by OPCs in response to sensory experience. In follow-up studies, we are performing in vivo two-photon imaging of OPCs, microglia, and synapses simultaneously to better understand how interactions between these three cell types mediate circuit connectivity. We are also profiling transcriptomic and proteomic dynamics in OPCs and microglia to define the specific signaling pathways through which these cell classes interact. Ultimately, we hope to shed light on the importance of glial:glial interactions in the brain through a unique focus on communication between microglia and OPCs.
Determining how impairments in neuro-immune communication contribute to disorders of the brain
Work in mice and humans is geared toward defining the contributions of inflammation to disorders of the developing brain.
Localized and systemic inflammation have emerged as major risk factors in neurodevelopmental disorders such as autism and schizophrenia. We utilize the maternal immune activation (MIA) mouse model of neurodevelopmental dysfunction to define the specific signals that drive circuit wiring deficits in the context of inflammation. While most studies of the MIA model have focused exclusively on its impact on the brain, we take a broader approach to understand how systemic inflammation coordinates developmental deficits across multiple organs and systems. This project places us at the forefront of understanding how complex biological systems interact at the organismal level. In parallel, we derive additional translational insights by analyzing the transcriptional and synaptic changes that occur in human brain cells in epilepsy, a debilitating disorder that is prevalent in individuals with conditions like autism and schizophrenia and is strongly associated with inflammation.
The Big Picture
By applying a multidisciplinary strategy to the brains of mice and humans, we are making major discoveries about how neurons and immune cells communicate to shape the brain. In addition to becoming leaders in the fields of neuroimmunology and developmental neuroscience over the coming years, we strive to establish a uniquely dynamic and collaborative research program by interfacing with other investigators both within our discipline and beyond. Ultimately, we aim to transform our growing understanding of experience-dependent refinement and plasticity in the healthy brain into new therapeutic strategies for treating neurodevelopmental, psychiatric, and neurodegenerative disorders.