NG2-proteoglycan-dependent contributions of oligodendrocyte progenitors and myeloid cells to myelin damage and repair.
BACKGROUND
The NG2 proteoglycan is expressed by several cell types in demyelinated lesions and has important effects on the biology of these cells. Here we determine the cell-type-specific roles of NG2 in the oligodendrocyte progenitor cell (OPC) and myeloid cell contributions to demyelination and remyelination.


METHODS
We have used Cre-Lox technology to dissect the cell-type-specific contributions of NG2 to myelin damage and repair. Demyelination is induced by microinjection of 1 % lysolecithin into the spinal cord white matter of control, OPC-specific NG2-null (OPC-NG2ko), and myeloid-specific NG2-null (My-NG2ko) mice. The status of OPCs, myeloid cells, axons, and myelin is assessed by light, immunofluorescence, confocal, and electron microscopy.


RESULTS
In OPC-NG2ko mice 1 week after lysolecithin injection, the OPC mitotic index is reduced by 40 %, resulting in 25 % fewer OPCs at 1 week and a 28 % decrease in mature oligodendrocytes at 6 weeks post-injury. The initial demyelinated lesion size is not affected in OPC-NG2ko mice, but lesion repair is delayed by reduced production of oligodendrocytes. In contrast, both the initial extent of demyelination and the kinetics of lesion repair are decreased in My-NG2ko mice. Surprisingly, the OPC mitotic index at 1 week post-injury is also reduced (by 48 %) in My-NG2ko mice, leading to a 35 % decrease in OPCs at 1 week and a subsequent 34 % reduction in mature oligodendrocytes at 6 weeks post-injury. Clearance of myelin debris is also reduced by 40 % in My-NG2ko mice. Deficits in myelination detected by immunostaining for myelin basic protein are confirmed by toluidine blue staining and by electron microscopy. In addition to reduced myelin repair, fewer axons are found in 6-week lesions in both OPC-NG2ko and My-NG2ko mice, emphasizing the importance of myelination for neuron survival.


CONCLUSIONS
Reduced generation of OPCs and oligodendrocytes in OPC-NG2ko mice correlates with reduced myelin repair. Diminished demyelination in My-NG2ko mice may stem from a reduction (approximately 70 %) in myeloid cell recruitment to lesions. Reduced macrophage/microglia numbers may then result in decreased myelin repair via diminished clearance of myelin debris and reduced stimulatory effects on OPCs.
Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, CA, 92037, USA. kkucharo@sbpdiscovery.org.
Karolina
K
Kucharova
Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, CA, 92037, USA.
William B
WB
Stallcup
D000818:Animals; D000941:Antigens / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D016026:Bone Marrow Transplantation; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D020278:Demyelinating Autoimmune Diseases, CNS / Q000139:chemically induced / Q000473:pathology* / Q000601:surgery; D004195:Disease Models, Animal; D008244:Lysophosphatidylcholines / Q000633:toxicity; D008264:Macrophages / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000378:metabolism; D009186:Myelin Sheath / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D022423:Myeloid Cells / Q000473:pathology* / Q000648:ultrastructure; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D000076104:Oligodendrocyte Transcription Factor 2; D009836:Oligodendroglia / Q000378:metabolism / Q000473:pathology*; D010587:Phagocytosis / Q000502:physiology; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism*; D020127:Recovery of Function / Q000502:physiology*; D013116:Spinal Cord / Q000473:pathology*; D013234:Stem Cells / Q000378:metabolism / Q000648:ultrastructure; D000099216:Chondroitin Sulfate Proteoglycan 4
D000941:Antigens; D051792:Basic Helix-Loop-Helix Proteins; D002135:Calcium-Binding Proteins; D008244:Lysophosphatidylcholines; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D000076104:Oligodendrocyte Transcription Factor 2; D011509:Proteoglycans; D000099216:Chondroitin Sulfate Proteoglycan 4; C491049:Aif1 protein, mouse; C512773:Olig2 protein, mouse