143 Estrogen Attenuates Oligodendrocyte Apoptosis Caused by Hyperoxia

Background: In the developing human brain, periventricular leukomalacia (PVL) is the predominant white matter injury underlying the development of cerebral palsy. Our group recently showed that a rise of oxygen tissue tension is a powerful trigger to initiate apoptosis in premature and immature, but not in mature oligodendrocytes (OL). Estrogen plays an important role in the development and function of the cerebral nervous system, and estrogen receptors show a specific distribution with high density arround the third ventricle, the region where OL progenitors are generated. We therefore examined the effects of estrogen on hyperoxia-induced cell death in cultured rat immature oligodendroglia cells.Methods: OLN-93 cells, derived from spontaneously transformed cells of 5- to 10-day-old primary rat brain oligodendrocytes were subjected to 24–72 h of hyperoxia (80% O2) in the presence or absence of estrogen (17beta-estradiol) at various concentrations. These immature oligodendrocytes resemble an intermediate stage between oligodendrocyte precursors and mature oligodendrocytes. Flow cytometry was used to assess apoptosis via annexin-V, anti-activated caspase-3 antibody, and propidium iodide staining. Oligodendrocyte maturation status and caspase-3 activation were confirmed by immunochemistry.Results: In immature rat oligodendrocytes (OLN-93), apoptosis was detected at various stages (early: annexin-V, effector: caspase-3) after 24–72 h of hyperoxia (80% O2). Cell death was reduced up to 30% by preincubation with estrogen at a concentration optimum of 10–7 M estrogen.Conclusion: Estrogen reduces apoptosis in immature oligodendrocytes exposed to hyperoxia. The sudden drop in circulating estrogen of placental origin after mammalian birth may aggravate the susceptibility of immature oligodendrocytes to increased oxygen tension. Supported by grants from the German Federal Department of Education and Research (BMBF, # 01 ZZ 0101), Bonn, and the Ernst Schering Research Foundation, Berlin.