Meningeal Foam Cells and Ependymal Cells in Axolotl Spinal Cord Regeneration

Frontiers in Immunology, 2019 · DOI: 10.3389/ﬁmmu.2019.02558 · Published: November 1, 2019

Regenerative Medicine Immunology Genetics

Simple Explanation

This research investigates the role of foamy macrophages, a type of immune cell, in the regeneration of spinal cords in Axolotls (salamanders). These cells accumulate in the fibrotic meninges during gap regeneration. The study found that these foamy macrophages interact with ependymal cells, which are crucial for spinal cord remodeling after injury. This interaction influences the behavior of ependymal cells during mesenchymal outgrowth. Foamy macrophages take up lipids and myelin, while also degrading the extracellular matrix (ECM) at the injury site. This helps to create a more favorable environment for ependymal cells to rebuild the spinal cord.

Study Duration

Not specified

Participants

Sets of four to six adult Axolotls

Evidence Level

Not specified

Key Findings

1
Foam cells (foamy macrophages) accumulate in the invasive fibrotic meninges during gap regeneration of transected adult Axolotl spinal cord and may act beneficially.
2
Both foam cells and ependymoglia expressed the lipid scavenger receptor CD36 and the co-transporter toll-like receptor-4 (TLR4).
3
Ependymal cells produce glycosaminoglycan and proteoglycan-containing ECM, while both cell types remove ECM.

Research Summary

This study identifies foamy macrophages in the reactive Axolotl spinal cord meninges, revealing their participation in spinal cord regeneration. These cells accumulate in fibrotic meninges during amphibian spinal cord regeneration. Foamy macrophages take up lesion site lipids and myelin while degrading ECM, interacting closely with ependymal cell outgrowth, which remodels the cord after injury. The interaction of foamy macrophage with ependymal cells in vitro modified ependymal cell behavior related to mesenchymal outgrowth. The study characterizes the distribution and functionality of foamy macrophages and some multinucleated giant cells (MNGCs) in the injury-reactive Axolotl spinal cord meninges. It shows that these cells take up lipid via the scavenger receptor CD36, co-expressed with toll-like receptor 4 (TLR4), and produce cathepsin K.

Practical Implications

Understanding Spinal Cord Regeneration

The discovery of foamy macrophages' role in Axolotl spinal cord regeneration offers insights into potential regenerative therapies for spinal cord injuries.

Targeting Lipid Metabolism

The involvement of lipid scavenger receptors like CD36 suggests that targeting lipid metabolism within the injury site could promote a regenerative environment.

ECM Remodeling

The interplay between foamy macrophages and ependymal cells in ECM degradation and synthesis highlights the importance of ECM remodeling in successful spinal cord regeneration.

Study Limitations

1
The study focuses on Axolotls, and the findings may not be directly applicable to mammals due to differences in regenerative capabilities.
2
The exact mechanisms of interaction between foamy macrophages and ependymal cells are not fully elucidated.
3
The source of foamy macrophages and MNGCs in the lesion site is not yet known.

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