Transgenic Lewis rats overexpressing the proteolipid protein gene: myelin degeneration and its effect on T cell-mediated experimental autoimmune encephalomyelitis
M. Bradl et al., Transgenic Lewis rats overexpressing the proteolipid protein gene: myelin degeneration and its effect on T cell-mediated experimental autoimmune encephalomyelitis, ACT NEUROP, 97(6), 1999, pp. 595-606
Transgenic Lewis rats overexpressing proteolipid protein (PLP) genes in per
ipheral and central nervous myelin were produced by microinjecting murine g
enomic PLP sequences into fertilized eggs. The mouse PLP gene shares 98.7%
homology in the nucleotide sequence with its rat counterpart, but both are
fully identical on protein level. Homozygous rats show tremors early in pos
tnatal life, eventually develop seizures, and die before they reach weaning
age, while hemizygous animals are phenotypically normal and have a normal
life expectancy. Transgene expression in the central nervous system (CNS) h
as profound consequences for myelin formation and maintenance: approximatel
y twofold overexpression of PLP/DM-20, as seen in homozygotes, results in a
poptosis of mature, and a developmental arrest of the remaining immature ol
igodendrocytes. Severe dysmyelination ensues, associated with reactive astr
ogliosis and microglia activation/proliferation. Activation of microglia is
also prominent in hemizygous rats with low levels of transgene overexpress
ion. In these animals, myelin sheaths remain intact, but there is low-grade
myelin degeneration throughout life witnessed by myelin uptake and activat
ion of microglia and astrocytes, in the absence of the expression of major
histocompatibility complex class II gene products. There were no spontaneou
s lymphocytic infiltrates in areas of myelin degeneration. However, hemizyg
ous LEW.PLP rats were more sensitive to experimental autoimmune encephalomy
elitis mediated by T cells specific for PLP, but not another encephalitogen
ic myelin protein, MBP.