J Neurovirol. 2003 Sep;9(5):539-50
Kong H, Baerbig Q, Duncan L, Shepel N, Mayne M.
Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg, Manitoba, Canada and Division of Neurovirology and Neurodegenerative Disorders, St. Boniface Hospital Research Centre, Winnipeg, Manitoba, Canada.
Accumulating evidence suggests that human herpesvirus type 6 (HHV-6) plays a pathogenic role in diseases of the central nervous system including multiple sclerosis (MS).
Recent studies have indicated that HHV-6 DNA is detected with high frequency in MS lesions compared to normal-appearing white matter, implicating a role for HHV-6 in MS pathogenesis.
It appears that T cells, which infiltrate into the brain in MS patients, and resident oligodendrocytes harbor HHV-6 virus in MS lesions.
Because T cells infected with HHV-6 have elevated proinflammatory gene expression, we hypothesized that HHV-6 could be indirectly cytotoxic to glial cells, including oligodendrocytes.
Supernatants from SupT1 cells infected with HHV-6 variant A (GS or U1102) or variant B (Z29) significantly reduced MO3.1 cell proliferation by 75% +/- 10%, 78% +/- 8% or 51% +/- 9%, respectively.
HHV-6 viral supernatants (GS or U1102 or Z29) significantly increased MO3.1 or primary human oligodendrocyte precursor cells (OPCs) cell death, whereas primary human fetal astrocytes were not affected.
Removal of HHV-6 virions or proteins by trypsin treatment from culture supernatants did not reverse the loss in oligodendrocyte proliferation or viability.
Supernatants from HHV-6 GS or U1102 cultures were significantly more cytotoxic to MO3.1 cells or OPCs compared to supernatants from T cells infected with Z29.
Dying oligodendrocytes did not have an apoptotic-like phenotype and toxicity was not inhibited by general inhibitor of apoptosis, ZVAD.
Further, oligodendrocytes had minimal caspase-3 activation even in the presence of staurosporine, suggesting that cell death followed caspase-independent pathways.
These results indicate that HHV-6 is indirectly cytotoxic to oligodendrocytes and that cell death is driven primarily by caspase-independent pathways.