Deciphering the role of AIM2 in myelin damage and repair in a murine model of multiple sclerosis

Abstract

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system (CNS) targeting the myelin sheath and oligodendrocytes. The destruction of either or both myelin sheath or oligodendroglia can lead to the loss of underlying neurones and functional decline in patients. Myelin regeneration is possible in early stages of the disease, but this often fails with disease progression. There are currently no treatments that therapeutically enhance myelin regeneration and prevent further neurodegeneration thus new ways to enhance myelin regeneration are urgently sought after.

Immune mechanisms implicating inflammasomes have been reported to promote remyelination in experimental MS models. AIM2, a cytosolic dsDNA receptor, is expressed by microglia, astrocytes, oligodendrocytes, and neurons, amongst other CNS cells. AIM2 can form an inflammasome but also has functions independent of inflammasome mechanism, such as by modulating Treg, determining the reactivity of microglia and causing astrogliosis in late phase of EAE experiments of murine models. The role of AIM2 in glial cell biology is still poorly understood, and the possible functions during de-/ and remyelination is not fully known, thus my project aims to investigate the function of AIM2 in the CNS using murine models of MS.

In this work, I investigated the function of AIM2 under naïve homeostatic CNS, healthy mice were euthanized, and their spinal cords stained using immunohistochemistry techniques to ascertain the impact Aim2 deficiency had on microglia, oligodendroglia, and astrocytes. We observed that Aim2 deficiency caused a prolonged proliferation of Iba-1+ cells, had no impact on proliferating OPCs and mature oligodendrocytes (Olig2+CC1+), but significantly increased the number of Olig2+PDGFR+ cells.

Next, using lysolecithin induced focal demyelination model, we show that AIM2 is expressed in cells within the demyelinated lesion. Comparing populations of oligodendroglia and microglia, in control and Aim2 deficient animals. Results showed that Aim2 deficiency did not affect oligodendroglia population. However, Iba-1+ expression was altered in Aim2-/- mice. We further showed that Aim2-/- expressed significantly higher Astrocytic reactivity at 14 days post lesion (dpl). To investigate the impact on de-/remyelination using a crude readout of NFH+MBP+ colocalization. Our findings showed that there was a decrease in the colocalization of NFH+MBP+ detections from 21 dpl (regeneration phase of our model) and a significant decrease in especially MBP+ detection in Aim2-/- naïve mice.

Next, to understand why although there were similar numbers of mature oligodendrocytes (Olig2+CC1+) in naïve CNS and after injury, we had significant decrease in NFH+MBP+ in naïve CNS and after injury in Aim2-/-. Using in vitro experiments, we showed that in Aim2-/- mixed glial (MG) cultures, there were several activated microglia (Iba-1+CD68+) at day 11, and this was accompanied with amoebic shaped Iba-1+. We further report a significant decrease of Olig2+MBP+ cells, and MBP+ area coverage within the culture that was rescued when cocultured with WT MG supernatant.

We further showed that there were differences in the Aim2-/- versus WT glia secretome, supernatant samples ran from both MG cultures on a protein profiler showed that many of the secreted proteins from Aim2-/- MG cultures were dysregulated, from which we identified the 16 most prominent proteins that had a 1.5- or greater fold change to WT.

My findings show that the absence of AIM2 impacts the development of Iba-1+ cells which negatively influence the secretions from Oligodendroglia and impairs myelination/remyelination. Future work will investigate identified proteins with an objective to identify which, if any, would be beneficial in improving the remyelination process in murine and MS patients.

Thesis is embargoed until 31 July 2029.

Date of Award	Jul 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	The Tertiary Education Trust Fund
Supervisor	Beckie Ingram (Supervisor) & Yvonne Dombrowski (Supervisor)