Increased NG2⁺ glial cell proliferation and oligodendrocyte generation in the hypomyelinating mutant shiverer

Abstract

Glial cells that express the NG2 proteoglycan (NG2(+) cells) are considered to be oligodendrocyte progenitors (OPCs) in the central nervous system (CNS), based on their ability to give rise to mature oligodendrocytes in vitro. To understand how dysmyelinated conditions influence OPC proliferation and differentiation, we studied proliferation and differentiation of NG2(+) OPCs in vivo in the shiverer mutant (shi), which do not form compact myelin due to a deletion in the myelin basic protein gene. Acute bromodeoxyuridine (BrdU) labeling studies revealed a 4- to 6-fold increase in NG2(+) cell proliferation in shi spinal cord between postnatal day18 (P18) and P60, and most BrdU(+) cells were NG2(+) after P18. The increased proliferation was accompanied by a 2-fold increase in the number of OPCs and oligodendrocytes. Survival studies following a single injection of BrdU at P18 revealed a decline in the number of BrdU(+)/NG2(+) cells with a concomitant increase in the number of BrdU(+) oligodendrocytes over time, suggesting that the proliferated NG2(+) cells had differentiated into oligodendrocytes. BrdU(+) oligodendrocytes were generated over a longer period of time in shi spinal cord and persisted longer in shi than in wild type spinal cord. These findings suggest that new oligodendrocytes continue to be generated in the dysmyelinated shi spinal cord by enhanced proliferation and differentiation of NG2(+) oligodendrocyte progenitor cells.

Neurochemistry of Hypomyelination Investigated with MR Spectroscopy

“…OPCs in shiverer mice, unlike those in msd mice, can differentiate into oligodendrocytes, and both OPCs and mature oligodendrocytes are increased in number by as much as 2 times (Table). 26 NAA is one of the most abundant free amino acids in the brain (about 10mM in human) and generally considered an important marker of neurons and axons.…”

“…vere hypomyelination in shiverer mice, 26 which leads to a mild reduction of Cho, and the absence of oligodendrocytes with severe hypomyelination in msd mice, 24 which results in a more severe reduction of Cho.…”

Galactocerebrosidase-deficient oligodendrocytes maintain stable central myelin by exogenous replacement of the missing enzyme in mice

“…Here, we show that replacement of GALC enabled twi OLs to maintain stable and widespread myelin throughout the CNS, when these cells were transplanted into another mutant background. The shi mouse serendipitously provides advantages to twi cells as the increase in OLs and their progenitors in shi mice (14), even in the face of their persistent failure to myelinate axons, provides an extraneous source of GALC that the transplanted twi cells can use.…”

NG2 cells generate both oligodendrocytes and gray matter astrocytes

“…Immunohistochemistry was performed as described previously (Bu et al, 2001;Bu et al, 2004). The source and dilution of the antibodies are listed in Table 1.…”

“…Additional evidence that NG2 glia give rise to oligodendrocytes was obtained by pulse-chase labeling with 5-bromo-2Ј-deoxyuridine (BrdU) combined with immunolabeling for cell type-specific antigens at the age and location where the majority of the proliferating cells are NG2 glia. In these areas, which include the juvenile and adult spinal cord, BrdU-incorporated cells were seen to turn into mature oligodendrocytes over time in normal and demyelinated tissues (Bu et al, 2004;Horner et al, 2000;Watanabe et al, 2002;McTigue et al, 2001). It still remains unclear whether these cells go on to become myelinating oligodendrocytes.…”