Prox1 Inhibits Proliferation and Is Required for Differentiation of the Oligodendrocyte Cell Lineage in the Mouse.

Kentaro Kato,Ann Logan,Alicia Hidalgo,Fumio Matsuzaki,Daijiro Konno,Martin Berry,Fernando De Castro

doi:10.1371/journal.pone.0145334

Abstract

Central nervous system injury induces a regenerative response in ensheathing glial cells comprising cell proliferation, spontaneous axonal remyelination, and limited functional recovery, but the molecular mechanisms are not fully understood. In Drosophila, this involves the genes prospero and Notch controlling the balance between glial proliferation and differentiation, and manipulating their levels in glia can switch the response to injury from prevention to promotion of repair. In the mouse, Notch1 maintains NG2 oligodendrocyte progenitor cells (OPCs) in a progenitor state, but what factor may enable oligodendrocyte (OL) differentiation and functional remyelination is not understood. Here, we asked whether the mammalian homologue of prospero, Prox1, is involved. Our data show that Prox1 is distributed in NG2+ OPCs and in OLs in primary cultured cells, and in the mouse spinal cord in vivo. siRNA prox1 knockdown in primary OPCs increased cell proliferation, increased NG2+ OPC cell number and decreased CC1+ OL number. Prox1 conditional knockout in the OL cell lineage in mice increased NG2+ OPC cell number, and decreased CC1+ OL number. Lysolecithin-induced demyelination injury caused a reduction in CC1+ OLs in homozygous Prox1-/- conditional knockout mice compared to controls. Remarkably, Prox1-/- conditional knockout mice had smaller lesions than controls. Altogether, these data show that Prox1 is required to inhibit OPC proliferation and for OL differentiation, and could be a relevant component of the regenerative glial response. Therapeutic uses of glia and stem cells to promote regeneration and repair after central nervous system injury would benefit from manipulating Prox1.

Highlights

Glial cells proliferate throughout life in response to neuronal activity, conveying homeostatic regulation of structure and function
To test whether in the mouse Prox1 might be expressed in the OL cell lineage, we examined the distribution of Prox1 protein in adult mouse spinal cords using anti-Prox1 antibodies and double immunostaining with anti-NG2 to identify Oligodendrocyte Progenitor Cells (OPCs) and anti-CC1 (CC1) for OLs
We have shown that Prox1 is distributed in NG2+ and PDGFRα+ OPCs, and in CC1+ OLs in wild-type mouse spinal cords, in mouse primary cultured OPCs and in heterozygous Prox1Flox/+;; Olig2-CreER control mice in vivo

Summary

Introduction

Glial cells proliferate throughout life in response to neuronal activity, conveying homeostatic regulation of structure and function. NG2+ Oligodendrocyte Progenitor Cells (OPCs) proliferate and differentiate to produce oligodendrocytes (OLs), which ensheath and myelinate axons, PLOS ONE | DOI:10.1371/journal.pone.0145334. CNS damage and acute OL loss induce a robust regenerative response that promotes OPC proliferation, OL differentiation and spontaneous remyelination [2,6,7]. This, does not culminate in full functional repair as the lesion is invaded by microglia, macrophages and astrocytes that form the glial scar, inhibit axonal growth, cause myelin breakdown and cell death [8,9]. Uncovering the molecular mechanisms that control NG2+ OPC proliferation and their differentiation into OLs is essential to understand CNS structural plasticity, the endogenous glial regenerative response to injury, and how to enhance repair [2]

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Results

Conclusion