Characterization of Vsx1 expressing cells after spinal cord injury

Details

Supervisors

Clotman, Frédéric ; Donnay, Isabelle

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

When a spinal cord injury (SCI) occurs, the damage disturbs the complex organization between the different neuronal populations composing the spinal cord, causing important changes in its functionality. It is followed by multiple negative outcomes and a potentially positive event, neuroplasticity. Currently, no effective regenerative treatment exists, making the identification of mechanisms to promote functional recovery urgent. Interneurons (INs) were already shown to be involved in neuroplasticity, but which specific subclasses are implicated remains unknown. V2 INs arise from an intermediate population of V2 precursors characterized by the transient expression of the transcription factor Vsx1. Previous data of my host laboratory suggested that Vsx1 was not expressed in the adult spinal cord and that its expression increased after SCI. Thus, the aim of my master thesis was to uncover how SCI affected Vsx1 expression in the spinal cord. For this purpose, we used transgenic mice that underwent a contusion at T11 level and in which cells expressing Vsx1 after the lesion were labelled using the fluorescent reporter tdTomato. The spinal cords were collected 30 days post-injury. The first objective was to verify the reproducibility of the lesion and of its outcomes. The second objective was to test the hypothesis that some INs and possibly additional other cells could start expressing Vsx1 after a SCI, and, if it is the case, to characterize these cells in terms of number, identity, and location. Our results showed that our injury model seemed consistent. The lesion volume was comparable across the mice, even though there were slight variations in the location of the lesion. Consequently, slight variations in the recovery process across the lesioned mice were observed. Additionally, the recovery time was short (2-3 weeks), which raises questions about possible different recovery mechanisms between mice and humans. The characterization of the Vsx1 expressing cells unveiled that Vsx1 is actually expressed in the adult healthy mouse spinal cord. Some of these cells corresponded to neurons and were less numerous in the lesion area. Interestingly, these cells were involved in neuroplasticity rostrally and caudally to the lesion, as attested by the difference in number of tdTomato-labelled structures in lesioned animals. This could indicate that a reorganization of local neuronal circuits involving Vsx1-expressing cells occurs in the grey matter after SCI. The detected amount of Vsx1 expressing cells was lower than the total number of V2 INs suggesting that Vsx1 is possibly only expressed in a specific subclass of V2 INs.