Group 2 innate lymphoid cells promote inhibitory synapse development and social behavior

In early brain development, the formation and remodeling of neuronal synaptic connections is critical to forming functional neural circuits. The innate immune system plays essential roles in neurodevelopment, including in synapse remodeling, but the immune cells and signals that contribute are not well defined. Innate lymphocytes are the most recently discovered member of the innate immune arsenal, whose developmental expansion and activation make them potential mediators of brain-immune communication during synapse formation. Here we show that a subset of innate lymphocytes (group 2 innate lymphoid cells, ILC2s) populates the developing brain meninges and is required for cortical inhibitory synapse maturation and adult social behavior. ILC2s produced a surge of their canonical cytokine Interleukin 13 (IL-13) between postnatal days 5-15. Loss of ILC2s decreased cortical inhibitory synapse numbers in the postnatal period and led to impaired social recognition memory in adulthood. Postnatal administration of IL-13 or ILC2s into the brain ventricles was sufficient to drive an increase in inhibitory synapses. Deletion of the IL-4/IL-13 receptor (Il4ra) specifically from inhibitory neurons, but not myeloid cells, also reduced inhibitory synapses and impaired adult social behavior. These data define novel type 2 immune signaling that mediates lymphocyte-neuron communication in early life and shapes adult brain function

A novel environment-evoked transcriptional signature predicts reactivity in single dentate granule neurons.

Activity-induced remodeling of neuronal circuits is critical for memory formation. This process relies in part on transcription, but neither the rate of activity nor baseline transcription is equal across neuronal cell types. In this study, we isolated mouse hippocampal populations with different activity levels and used single nucleus RNA-seq to compare their transcriptional responses to activation. One hour after novel environment exposure, sparsely active dentate granule (DG) neurons had a much stronger transcriptional response compared to more highly active CA1 pyramidal cells and vasoactive intestinal polypeptide (VIP) interneurons. Activity continued to impact transcription in DG neurons up to 5 h, with increased heterogeneity. By re-exposing the mice to the same environment, we identified a unique transcriptional signature that selects DG neurons for reactivation upon re-exposure to the same environment. These results link transcriptional heterogeneity to functional heterogeneity and identify a transcriptional correlate of memory encoding in individual DG neurons

Differentiation of inflammation-responsive astrocytes from glial progenitors generated from human induced pluripotent stem cells

WOS: 000402964700027PubMed ID: 28591655Astrocyte dysfunction and neuroinflammation are detrimental features in multiple pathologies of the CNS. Therefore, the development of methods that produce functional human astrocytes represents an advance in the study of neurological diseases. Here we report an efficient method for inflammation-responsive astrocyte generation from induced pluripotent stem cells (iPSCs) and embryonic stem cells. This protocol uses an intermediate glial progenitor stage and generates functional astrocytes that show levels of glutamate uptake and calcium activation comparable with those observed in human primary astrocytes. Stimulation of stem cell-derived astrocytes with interleukin-1 beta or tumor necrosis factor a elicits a strong and rapid pro-inflammatory response. RNA-sequencing transcriptome profiling confirmed that similar gene expression changes occurred in iPSC-derived and primary astrocytes upon stimulation with interleukin-1 beta. This protocol represents an important tool for modeling in-a-dish neurological diseases with an inflammatory component, allowing for the investigation of the role of diseased astrocytes in neuronal degeneration.Paul G. Allen Family Foundation; JPB Foundation; Leona M. and Harry B. Helmsley Charitable Trust [2012-PG-MED002]; Annette C. Merle-Smith [R01 MH095741, U19MH106434]; G. Harold & Leila Y. Mathers Foundation; Flow Cytometry Core Facility of the Salk Institute; NIH-NCI CCSG [P30 014195]; Next Generation Sequencing Core Facility of the Salk Institute; Chapman Foundation; Helmsley Charitable Trust; Razavi Newman Integrative Genomics and Bioinformatics Core Facility of the Salk Institute; Swiss-NSF outgoing PD fellowship; Lynn and Edward Streim fellowship; EMBO long-term fellowship; Bettencourt Schueller Foundation; Philippe Foundation; Bob and Mary Jane EngmanFor the production of the iPSCs, the authors would like to acknowledge financial support from Janssen Pharmaceuticals. This work was supported by the Paul G. Allen Family Foundation, Bob and Mary Jane Engman, The JPB Foundation, The Leona M. and Harry B. Helmsley Charitable Trust grant # 2012-PG-MED002, Annette C. Merle-Smith, R01 MH095741 (F.H.G.), U19MH106434 (F.H.G.), and The G. Harold & Leila Y. Mathers Foundation. This work was supported by the Flow Cytometry Core Facility of the Salk Institute with funding from NIH-NCI CCSG: P30 014195; the Next Generation Sequencing Core Facility of the Salk Institute with funding from NIH-NCI CCSG: P30 014195; the Chapman Foundation and the Helmsley Charitable Trust and by The Razavi Newman Integrative Genomics and Bioinformatics Core Facility of the Salk Institute with funding from NIH-NCI CCSG: P30 014195. This research was also supported by the Swiss-NSF outgoing PD fellowship (K.C.V.), Lynn and Edward Streim fellowship (K.C.V.), EMBO long-term fellowship (B.N.J.), the Bettencourt Schueller Foundation (B.N.J.), and the Philippe Foundation (B. N. J.). The authors would like to thank M. L. Gage for editorial comments

Microglial pattern recognition via IL-33 promotes synaptic refinement in developing corticothalamic circuits in mice

Microglia are critical regulators of brain development that engulf synaptic proteins during postnatal synapse remodeling. However, the mechanisms through which microglia sense the brain environment are not well defined. Here, we characterized the regulatory program downstream of interleukin-33 (IL-33), a cytokine that promotes microglial synapse remodeling. Exposing the developing brain to a supraphysiological dose of IL-33 altered the microglial enhancer landscape and increased binding of stimulus-dependent transcription factors including AP-1/FOS. This induced a gene expression program enriched for the expression of pattern recognition receptors, including the scavenger receptor MARCO. CNS-specific deletion of IL-33 led to increased excitatory/inhibitory synaptic balance, spontaneous absence-like epileptiform activity in juvenile mice, and increased seizure susceptibility in response to chemoconvulsants. We found that MARCO promoted synapse engulfment, and Marco-deficient animals had excess thalamic excitatory synapses and increased seizure susceptibility. Taken together, these data define coordinated epigenetic and functional changes in microglia and uncover pattern recognition receptors as potential regulators of postnatal synaptic refinement

Microglial Remodeling of the Extracellular Matrix Promotes Synapse Plasticity

Synapse remodeling is essential to encode experiences into neuronal circuits. Here, we define a molecular interaction between neurons and microglia that drives experience-dependent synapse remodeling in the hippocampus. We find that the cytokine interleukin-33 (IL-33) is expressed by adult hippocampal neurons in an experience-dependent manner and defines a neuronal subset primed for synaptic plasticity. Loss of neuronal IL-33 or the microglial IL-33 receptor leads to impaired spine plasticity, reduced newborn neuron integration, and diminished precision of remote fear memories. Memory precision and neuronal IL-33 are decreased in aged mice, and IL-33 gain of function mitigates age-related decreases in spine plasticity. We find that neuronal IL-33 instructs microglial engulfment of the extracellular matrix (ECM) and that its loss leads to impaired ECM engulfment and a concomitant accumulation of ECM proteins in contact with synapses. These data define a cellular mechanism through which microglia regulate experience-dependent synapse remodeling and promote memory consolidation