Delayed necrostatin-1s infusion attenuates cystic white matter injury in preterm fetal sheep.

Severe, cystic white matter injury (WMI) in preterm infants is associated with neurodevelopmental impairment. Strikingly, it often develops weeks after birth. In the present study we tested the hypothesis that necrotic programmed cell death, necroptosis, may be a key mediator of severe WMI, using the specific inhibitor necrostatin-1s (Nec-1s). Chronically instrumented preterm fetal sheep (0.7 gestation) received 25 ​min of hypoxia-ischaemia induced by complete umbilical cord occlusion (UCO) or sham-UCO (controls, n ​= ​9), followed by intracerebroventricular infusion of Necrostatin-1s at 3, 8 and 13 days after UCO (UCO-Nec-1s, n ​= ​8) or vehicle (UCO-vehicle, n ​= ​9). Histology was obtained at 21 days after UCO. UCO-vehicle was associated with a spectrum of brain injury including diffuse WMI, and in 7/9 fetuses, generalised white matter atrophy, ventriculomegaly and/or temporal lobe cystic lesions. Necrostatin-1s infusion was associated with less severe WMI in the temporal lobe (1/8, p ​= ​0.041), with reduced atrophy, increased density of mature oligodendrocyte cells, myelin area fraction, and reduced microgliosis but increased numbers of apoptotic cells. Interestingly, diffuse white matter injury in the parietal tracts was not affected. This study suggests that delayed, severe white matter injury after acute hypoxia-ischaemia is mediated by slowly evolving necroptosis and neuroinflammation. We speculate that Nec-1s shifts the dominant cell death pathway from necrosis toward apoptosis, allowing reduced inflammation and so preserving oligodendrocyte populations and myelination in the temporal lobe. These results suggest that necroptosis is a promising therapeutic target to mitigate severe white matter injury.