Objective: There is strong evidence from recent clinical studies that ascending intrauterine infection is associated with an increased incidence of periventricular leukomalacia in very premature fetuses. Periventricular leukomalacia is characterized by disrupted myelination from a loss of oligodendrocyte progenitors. We investigated the effects of proinflammatory cytokines on the survival and differentiation of this cell type.
Methods: Cultures of more than 90% A2B5-positive progenitors were prepared from neonatal rats and kept for 3 days in medium supplemented with factors that stimulate cell proliferation. After 1 day in proliferation medium, cells were treated with interferon-gamma (100 U/mL) and tumor necrosis factor-alpha (100 ng/mL) for 48 hours triggering an increase in apoptotic A2B5 progenitor cells from 3.2 +/- 2.3% to 11.0 +/- 2.6%. After cytokine treatment cultures were transferred to medium containing factors to promote differentiation of progenitors into the myelinating phenotype.
Results: In cytokine pretreated cultures, only 2.6 +/- 1.1% of total cells survived after a total of 9 days in vitro, whereas in untreated cultures most cells differentiated as shown by expression of myelin basic protein, myelin-associated glycoprotein, 2,3-cyclic nucleotide 3-phosphodiesterase, and myelin oligodendrocyte-specific protein. Using ten-fold reduced concentrations of combined interferon-gamma (10 U/mL) and tumor necrosis factor-alpha (10 ng/mL) pretreatment resulted in a survival to 11.2 +/- 4.9% of total cells with 36.3 +/- 11.6% A2B5-positive cells at day 9. This indicates a major enrichment of undifferentiated cells compared with untreated controls which harbored only 1.0 +/- 0.3% A2B5-positive cells.
Conclusion: Inflammatory cytokines not only induced apoptotic cell death but also prevented the differentiation of immature A2B5 oligodendrocyte progenitors into the myelinating phenotype.