Tumour necrosis factor blockade after asphyxia in foetal sheep ameliorates cystic white matter injury.

Cystic white matter injury is highly associated with severe neurodevelopmental disability and cerebral palsy in preterm infants, yet its pathogenesis remains poorly understood and there is no established treatment. In the present study, we tested the hypothesis that slowly evolving cystic white matter injury after hypoxia-ischaemia is mediated by programmed necrosis initiated by tumour necrosis factor. Tumour necrosis factor blockade was begun 3 days after hypoxia-ischaemia to target the tertiary phase of injury, when most secondary cell death is thought to be complete. Chronically instrumented preterm foetal sheep (0.7 gestation) received 25 min of hypoxia-ischaemia induced by complete umbilical cord occlusion or sham-umbilical cord occlusion (controls, n = 10), followed by intracerebroventricular infusion of the soluble TNF inhibitor, Etanercept, at 3, 8 and 13 days after umbilical cord occlusion (n = 9) or vehicle (n = 9). Foetal brains were processed for histology at 21 days after umbilical cord occlusion. Umbilical cord occlusion with vehicle was associated with a spectrum of macroscopic white matter degeneration, including white matter atrophy, ventriculomegaly and overt temporal lobe cystic white matter injury. Oligodendrocyte maturational arrest and impaired labelling of myelin proteins, characteristic of diffuse white matter injury, was observed in the parietal lobe and surrounding the cystic lesions in the temporal lobe. Etanercept markedly attenuated cystic white matter injury on the side of the intracerebroventricular infusion, with partial contralateral protection. Further, Etanercept improved oligodendrocyte maturation and labelling of myelin proteins in the temporal and parietal lobes. The present study shows that cystic white matter injury reflects late-onset tertiary cell death mediated by delayed neuroinflammation through the tumour necrosis factor pathway. Delayed tumour necrosis factor blockade markedly attenuated cystic white matter injury and restored oligodendrocyte maturation and deficits in myelin protein expression. These data suggest that delayed tumour necrosis factor blockade may represent a viable therapeutic strategy to reduce the risk of cystic and diffuse white matter injury and potentially cerebral palsy after preterm birth, with a surprisingly wide therapeutic window.

Tertiary cystic white matter injury as a potential phenomenon after hypoxia-ischaemia in preterm f sheep.

White matter injury, including both diffuse and cystic elements, remains highly associated with neurodevelopmental disability and cerebral palsy in preterm infants, yet its pathogenesis and evolution are still poorly understood and there is no established treatment. We examined the long-term evolution of white matter injury in chronically instrumented preterm fetal sheep (0.7 gestation) after 25 min of complete umbilical cord occlusion or sham occlusion. Fetal brains were processed for histology after 3 days (n = 9, sham n = 9), 7 days (n = 8, sham n = 8), 14 days (n = 9, sham n = 8) and 21 days (n = 9, sham n = 9) of recovery. At 3 and 7 days recovery, umbilical cord occlusion was associated with diffuse white matter injury, with loss of total and mature oligodendrocytes and reduced myelination in both the parietal and temporal lobes. At 14 days after umbilical cord occlusion, extensive microglial and astrocytic activation were observed in the temporal lobe. At 21 days recovery a spectrum of severe white matter degeneration was observed, including white matter atrophy, ventriculomegaly and overt cystic white matter lesions. The most severe injury was observed in the temporal lobe after 21 days recovery, including the majority of cystic lesions, persistent oligodendrocyte maturational arrest and impaired myelination. The spatial distribution of delayed white matter degeneration at 21 days recovery was closely related to the location of dense microglial aggregates at earlier time-points, implicating a role for exuberant inflammation originating from microglial aggregates in the pathogenesis of cystic white matter injury. The delayed appearance of cystic injury is consistent with continuing tertiary evolution of necrotic cell death. This slow evolution raises the tantalizing possibility that there may a relatively long therapeutic window to mitigate the development of cystic white matter injury. Delayed anti-inflammatory treatments may therefore represent a promising strategy to reduce neurodevelopmental disability in the preterm infants.