Developmental differences in HO-induced oligodendrocyte cell death: role of glutathione, mitogen-activated protein kinases and caspase 3.

The molecular mechanisms underlying H(2)O(2)-induced toxicity were characterized in rat oligodendrocyte cultures. While progenitor cells were more sensitive than mature oligodendrocytes to H(2)O(2), the antioxidant, N-acetyl-L-cysteine, blocked toxicity at both stages of development. Differentiated oligodendrocytes contained more glutathione than did progenitors and were less susceptible to decreases in glutathione concentration induced by H(2)O(2) stress. As free radicals have been considered to serve as second messengers, we examined the effect of H(2)O(2) on activation of the mitogen-activated protein kinases (MAPK), extracellular signal-regulated kinases (ERK) 1/2 and p38. H(2)O(2) caused a time- and concentration-dependent increase in MAPK phosphorylation, an effect that was totally blocked by N-acetyl-L-cysteine. Further exploration of potential mechanisms involved in oligodendrocyte cell death showed that H(2)O(2) treatment caused DNA condensation and fragmentation at both stages of development, whereas caspase 3 activation and poly (ADP-ribose) polymerase cleavage were significantly increased only in oligodendrocyte progenitors. The pan-caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone, blocked DNA fragmentation in progenitors and produced a small but significant level of protection from H(2)O(2) toxicity in progenitors and mature oligodendrocytes. In contrast, inhibitors of both p38 and MEK reduced H(2)O(2)-induced death most significantly in oligodendrocytes. The poly (ADP-ribose) polymerase inhibitor, PJ34, reduced H(2)O(2)-induced toxicity on its own but was most effective when combined with benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone or PD169316. The finding that molecular mechanisms conferring resistance to reactive oxygen species toxicity are regulated during oligodendrocyte differentiation may be of importance in designing therapies for certain neurological diseases affecting white matter.

Cytotoxicity of the E(2)-isoprostane 15-E(2t)-IsoP on oligodendrocyte progenitors.

Oxidant stress plays a significant role in the pathogenesis of periventricular leukomalacia (PVL). Isoprostanes (IsoPs) are bioactive products of lipid peroxidation abundantly generated during hypoxic-ischemic injuries. Because loss of oligodendrocytes (OLs) occurs early in PVL, we hypothesized that IsoPs could induce progenitor OL death. 15-E(2t)-IsoP but not 15-F(2t)-IsoP elicited a concentration-dependent death of progenitor OLs by oncosis and not by apoptosis, but exerted minimal effects on mature OLs. 15-E(2t)-IsoP-induced cytotoxicity could not be explained by its conversion into cyclopentenones, because PGA(2) was hardly cytotoxic. On the other hand, thromboxane A(2) (TxA(2)) synthase inhibitor CGS12970 and cyclooxygenase inhibitor ibuprofen attenuated 15-E(2t)-IsoP-induced cytotoxicity. Susceptibility of progenitor OLs was independent of TxA(2) receptor (TP) expression, which was far less in progenitor than in mature OLs. However, TxA(2) synthase was detected in precursor but not in mature OLs, and TxA(2) mimetic U46619 induced hydroperoxides generation and progenitor OL death. The glutathione synthesis enhancer N-acetylcysteine prevented 15-E(2t)-IsoP-induced progenitor cell death. Depletion of glutathione in mature OLs with buthionine sulfoximine rendered them susceptible to cytotoxicity of 15-E(2t)-IsoP. These novel data implicate 15-E(2t)-IsoP as a product of oxidative stress that may contribute in the genesis of PVL.

Selective neuromicrovascular endothelial cell death by 8-Iso-prostaglandin F2alpha: possible role in ischemic brain injury.

BACKGROUND AND PURPOSE: Free radical-induced peroxidation is an important factor in the genesis of hypoxic-ischemic encephalopathy, including that of the preterm infant. Isoprostanes are major peroxidation products. Since microvascular dysfunction seems to contribute to ischemic encephalopathies, we studied the cytotoxicity of 8-iso-prostaglandin F2alpha (PGF2alpha) on cerebral microvascular cells. METHODS: Microvascular endothelial, astroglial, and smooth muscle cells from newborn brain were cultured. The cytotoxicity of 8-iso-PGF2alpha on these cells was determined by MTT assays and lactate dehydrogenase (LDH) release, propidium iodide incorporation, and DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling [TUNEL]). In addition, effects of intraventricular injections of 8-iso-PGF2alpha and possible involvement of thromboxane in 8-iso-PGF2alpha-induced cytotoxicity were determined. RESULTS: 8-Iso-PGF2alpha induced time- and concentration-dependent endothelial cell death (EC50=0.1 nmol/L) but exerted little effect on smooth muscle and astroglial cells; endothelial cell death seemed mostly of oncotic nature (propidium iodide incorporation and LDH release). Cell death was associated with increased endothelial thromboxane A2 (TXA2) formation and was prevented by TXA2 synthase inhibitors (CGS12970 and U63557A); TXA2 mimetics U46619 and I-BOP also caused endothelial cell death. Intraventricular injection of 8-iso-PGF2alpha induced periventricular damage, which was attenuated by CGS12970 pretreatment. CONCLUSIONS: These data disclose a novel action of 8-iso-PGF2alpha involving TXA2 in oxidant stress-induced cerebral microvascular injury and brain damage.