Growth factor regulation of remyelination: behind the growing interest in endogenous cell repair of the CNS

Abstract

Remyelination facilitates recovery of saltatory conduction along demyelinated axons and may help prevent axon damage in patients with demyelinating diseases, such as multiple sclerosis. The extent of remyelination in multiple sclerosis lesions varies dramatically, indicating a capacity for repair that is not fulfilled in lesions with poor remyelination. In experimental models of demyelinating disease, remyelination is limited by chronic disease that depletes the oligodendrocyte progenitor (OP) population, inhibits OP differentiation into remyelinating oligodendrocytes and/or perturbs cell survival in the lesion environment. Manipulating the activity of growth factor signaling pathways significantly improves the ability of endogenous OP cells to accomplish extensive remyelination. Specifically, growth factors have been identified that can regulate OP proliferation, differentiation and survival in demyelinated lesions. Therefore, growth factors may be key signals for strategies to improve conditions with poor remyelination. Keywords cuprizone; demyelinating disease; FGF; multiple sclerosis; myelin; oligodendrocyte; PDGF; progenitors; remyelination Transition to in vivo analysis during remyelinationAnalysis of growth factors to promote repair in demyelinating diseases has undergone an important transition to in vivo studies and in doing so has revealed much more than the expected results. Characterization of the bipotential oligodendrocyte-type 2 astrocyte or oligodendrocyte progenitor (OP) cell, and the regulation of cell fate by serum components [1] opened the door for in vitro analysis of growth factor responses in the oligodendrocyte lineage. Numerous subsequent in vitro studies identified specific growth factors capable of regulating differentiation, proliferation, migration and survival at specific stages within this lineage. In vitro studies continue to offer distinct advantages for isolating molecular and cellular mechanisms of action and for characterizing the potential of defined growth factors to induce a specific cellular response. In this context, several cytokines and chemokines have been identified as having direct effects on oligodendrocyte lineage cells that are similar to growth factor actions and so they will be discussed together under the rubric of growth factors. This review will focus on recent in vivo remyelination studies designed to test potential growth factor responses identified in vitro. These in vivo studies demonstrate important effects of growth factors in the context of demyelinating disease models in rodents. However, not all growth factor analyses have resulted in the predicted responses. Importantly, several studies have demonstrated a remarkable capacity of endogenous cells to repair the adult CNS, even following chronic demyelination, using modulation of growth factor signaling to better support oligodendrocyte replacement and myelin formation.

Interactions between oligodendrocyte precursors control the onset of CNS myelination

“…It may be that a residual pool of A2B5+ OPCs remains in the slice following complement mediated lysis and these cells subsequently proliferate and repopulate the entire lineage. Alternatively, a pre-OPC population (Armstrong, 2007; Baracskay et al, 2007; Nait-Oumesmar et al, 1999) could regenerate the entire lineage. Several sources of pre-OPCs have been described (Nait-Oumesmar et al, 1999; Wu et al, 2009).…”

FGF2 and FGFR1 signaling regulate functional recovery following cuprizone demyelination

“…Failed differentiation of oligodendrocyte lineage cells (OLCs) may contribute to poor remyelination in chronic MS lesions and prolonged neurological deficits [9]. Multiple molecular signaling pathways inhibit differentiation of oligodendrocyte progenitor (OP) cells and limit remyelination in experimental models [1]. Modifying inhibitory signals in lesion areas could potentially enhance functional recovery in MS patients by improving the remyelination capacity of immature OLCs that persist in MS lesions [4, 9].…”

Low Cerebrospinal Fluid Sulfatide Predicts Progression of White Matter Lesions – The LADIS Study

“…However, these mechanisms sometimes cannot fully compensate for the demyelination. This has been related to an age factor [38], but also to the possibility that intensity or chronicity of demyelination eventually outpaces the remyelinating capacity, as may be the case in multiple sclerosis [39].…”