Cd59 and inflammation regulate Schwann cell development.

Efficient neurotransmission is essential for organism survival and is enhanced by myelination. However, the genes that regulate myelin and myelinating glial cell development have not been fully characterized. Data from our lab and others demonstrates that cd59, which encodes for a small GPI-anchored glycoprotein, is highly expressed in developing zebrafish, rodent, and human oligodendrocytes (OLs) and Schwann cells (SCs), and that patients with CD59 dysfunction develop neurological dysfunction during early childhood. Yet, the function of Cd59 in the developing nervous system is currently undefined. In this study, we demonstrate that cd59 is expressed in a subset of developing SCs. Using cd59 mutant zebrafish, we show that developing SCs proliferate excessively and nerves may have reduced myelin volume, altered myelin ultrastructure, and perturbed node of Ranvier assembly. Finally, we demonstrate that complement activity is elevated in cd59 mutants and that inhibiting inflammation restores SC proliferation, myelin volume, and nodes of Ranvier to wildtype levels. Together, this work identifies Cd59 and developmental inflammation as key players in myelinating glial cell development, highlighting the collaboration between glia and the innate immune system to ensure normal neural development.

The nervous system of vertebrates is made of up of complex networks of nerve cells that send signals to one another. In addition to these cells, there are a number of supporting cells that help nerves carry out their role. Schwann cells, for example, help nerve cells to transmit information faster by wrapping their long extensions in a fatty membrane called myelin. When myelin is not produced properly, this can disturb the signals between nerve cells, leading to neurological defects. Schwann cells mature simultaneously with nerve cells in the embryo. However, it was not fully understood how Schwann cells generate myelin during development. To investigate, Wiltbank et al. studied the embryos of zebrafish, which, unlike other vertebrates, are transparent and develop outside of the womb. These qualities make it easier to observe how cells in the nervous system grow in real-time using a microscope. First, the team analyzed genetic data collected from the embryo of zebrafish and mice to search for genes that are highly abundant in Schwann cells during development. This led to the discovery of a gene called cd59, which codes for a protein that also interacts with the immune system. To find out whether Schwann cells rely on cd59, Wiltbank et al. deleted the cd59 gene in zebrafish embryos. Without cd59, the Schwann cells produced too many copies of themselves and this, in turn, impaired the appropriate production of myelin. Since the protein encoded by cd59 normally balances inflammation levels, it was possible that losing this gene overactivated the immune system in the zebrafish embryos. In support of this hypothesis, when the cd59 mutant embryos were treated with an anti-inflammatory drug, this corrected Schwann cell overproduction and restored myelin formation. Taken together, these findings reveal how inflammation helps determine the number of Schwann cells produced during development, and that cd59 prevents this process from getting carried away. This suggests that the nervous system and immune system may work together to build the nervous system. In the future, it will be interesting to investigate whether cd59 acts in a similar way during the development of the human nervous system.

Diversity and convergence within peripheral glia development.

In a recent study, Tasdemir-Yilmaz and colleagues used single-cell RNA sequencing to reveal how diversity among peripheral glia changes with development and also identified unifying genetic profiles that are shared between mature glia. These data highlight new tools and pathways in which to understand peripheral glial development and function.

Myeloid Cells in the Central Nervous System.

The central nervous system (CNS) and its meningeal coverings accommodate a diverse myeloid compartment that includes parenchymal microglia and perivascular macrophages, as well as choroid plexus and meningeal macrophages, dendritic cells, and granulocytes. These myeloid populations enjoy an intimate relationship with the CNS, where they play an essential role in both health and disease. Although the importance of these cells is clearly recognized, their exact function in the CNS continues to be explored. Here, we review the subsets of myeloid cells that inhabit the parenchyma, meninges, and choroid plexus and discuss their roles in CNS homeostasis. We also discuss the role of these cells in various neurological pathologies, such as autoimmunity, mechanical injury, neurodegeneration, and infection. We highlight the neuroprotective nature of certain myeloid cells by emphasizing their therapeutic potential for the treatment of neurological conditions.

Characterization of meningeal type 2 innate lymphocytes and their response to CNS injury.

The meningeal space is occupied by a diverse repertoire of immune cells. Central nervous system (CNS) injury elicits a rapid immune response that affects neuronal survival and recovery, but the role of meningeal inflammation remains poorly understood. Here, we describe type 2 innate lymphocytes (ILC2s) as a novel cell type resident in the healthy meninges that are activated after CNS injury. ILC2s are present throughout the naive mouse meninges, though are concentrated around the dural sinuses, and have a unique transcriptional profile. After spinal cord injury (SCI), meningeal ILC2s are activated in an IL-33-dependent manner, producing type 2 cytokines. Using RNAseq, we characterized the gene programs that underlie the ILC2 activation state. Finally, addition of wild-type lung-derived ILC2s into the meningeal space of IL-33R-/- animals partially improves recovery after SCI. These data characterize ILC2s as a novel meningeal cell type that responds to SCI and could lead to new therapeutic insights for neuroinflammatory conditions.