Background: Recovery of neuronal function is a major healthcare challenge for patients with various types of brain injuries, yet therapies to functionally replace degenerated neurons are lacking.

Hypothesis: An interplay between the Cxcr3 and Tlr2 signaling pathways and EV-induced reactivity forms a key molecular checkpoint regulating glial scar formation. Understanding of this interplay would enable interventions that specifically interfere with scar formation to improve tissue regeneration.

Strategy: We plan to pursue integrative spatial and single-cell analysis to reveal the mechanisms of scar formation in animal models.

Summary

Traumatic brain injuries (TBIs) cause primary tissue damage and activate glial cells to build glial border, thereby delineating the injured brain parenchyma from the healthy surrounding tissue. However, this necessary primary reaction of glial cells often persists. This long-lasting glial activation results in prolonged and exacerbated neuroinflammationthat prevents tissue restoration. Therefore, understanding the checkpoints responsible for turning the necessary initial glial activation into long-lasting, detrimental glial reactivity is critical for developing regenerative therapies. Using a combination of single-cell transcriptomics and spatial transcriptomics in zebrafish and mice, we have identified the Cxcr3 and Tlr2 innate immunity pathways as triggers of glial reactivity in subpopulations transitioning toward long-lasting neuroinflammation. The inhibition of these pathways blocks long-lasting neuroinflammation in the mouse cerebral cortex. The second feature of the transition of the glial populations toward neuroinflammation is the upregulation of pathways involved in the production of extracellular vesicles (EVs). Consequently, we hypothesized that specific cargos released from these vesicles might define a checkpoint for the transition of glial border cells with beneficial function to detrimental neuroinflammation. Our preliminary data have suggested that EVs isolated from the injured mouse cerebral cortex and applied at the uninjured brain surface induce the neuroinflammatory response. On the basis of these preliminary data, we propose that a cross-regulatory network between innate immunity pathways and EV cargo defines an important checkpoint that turns protective glial border cells into tissue scaring cells. To address this hypothesis, we will answer the following questions:

  1. How does Cxcr3 and Tlr2 induced glial reactivity hinder neuronal circuit repair?
  2. What change in EV cargo composition is necessary for the switch from beneficial glial reaction to neuroinflammation?
  3. What is the relationship between innate immunity pathways (Cxcr3 and Tlr2) and the switch in EV cargo?