Presenting Author:

Colleen Zaccard, Ph.D.

Principal Investigator:

Peter Penzes, Ph.D.

Department:

Physiology

Keywords:

microglia, neurons, intercellular communication, membrane nanotubes, inflammation, TGF-β

Location:

Third Floor, Feinberg Pavilion, Northwestern Memorial Hospital

B167 - Basic Science

Cytokine regulation and function of microglia-derived membrane nanotubes at the neuro-immune interface

Microglia are brain-resident innate immune cells that continually survey their surroundings with dynamic membrane processes and shape neural circuits by complement-dependent elimination of extranumerary synapses. Microglia morphology and function are highly related and dependent on complex environmental signals, including pro- and anti-inflammatory cytokines. Acutely activated microglia mediate innate responses to immunologic stimuli and injury, but chronic activation can contribute to numerous neurodevelopmental and neurodegenerative disorders. While direct microglia-neuron interactions are critical in health and disease, the underlying mechanisms are not fully understood. Membrane nanotubes (MNTs) are long, ultrafine conduits that can support rapid intercellular communication and can be induced by pro-inflammatory cytokines in other innate immune cell types. Here we investigate for the first time the role of MNTs in microglia-neuron cross-talk using a novel mouse co-culture system comprised of microglia and primary cortical neurons. We first used live-cell confocal microscopy to demonstrate that isolated microglia can develop extensive MNT networks, which were typically not attached to the substratum. MNTs formed by filopodia extension or withdrawal of primary processes from target cell contact and supported cell surface molecule exchange. Migrating microglia additionally left behind long trails of substratum-attached retraction fibers, which were also recently shown to facilitate intercellular communication. MNTs were notably CD11b+ and originated from the tips of CD11b-enriched primary processes. Super-resolution structured illumination and lattice light sheet microscopy were used to resolve synaptic nano-domains and closely opposed MNTs and to improve spatio-temporal resolution of dynamic MNT-neuron interactions, respectively. Co-cultures were treated with a pleiotropic cytokine essential for maintenance of steady-state microglia, TGF-β, which substantially increased CD11b+ MNT and retraction fiber formation in intermediate and ramified microglia. These processes contacted other microglia or synaptic elements, including dendritic spines and axon terminals, and often formed along the length of axons. Pro-inflammatory cytokine (IFN-g + TNF-α) treatment of co-cultures enhanced MNT formation in amoeboid microglia. These data show that ultrafine membrane processes can be induced by TGF-β in ramified microglia or pro-inflammatory cytokines in amoeboid microglia. The conduits can interact directly with neuronal elements or interconnect microglia and likely function in CD11b-dependent processes such as adhesion and/or complement-dependent synapse elimination. An improved understanding of MNT-mediated microglia-neuron communication may identify novel therapeutic targets for neurological disorders in which aberrant cytokine production contributes to pathology.