Highlights d Ablated intestinal stem cells (ISC) restore largely by crypt cell dedifferentiation d ISC-restricted transcription factor ASCL2 is required for this adaptive regeneration d Both absorptive and secretory lineages contribute to ISC restoration d ASCL2-dependent IL11RA1 activity enhances ISC recovery from dedifferentiating cells

Objective Although MRI is the optimal imaging modality to define cerebral white-matter injury (WMI) in preterm survivors, the histopathological features of MRI-defined chronic lesions are poorly defined. We hypothesized that chronic WMI is related to a combination of delayed oligodendrocyte (OL) lineage cell death and arrested maturation of pre-oligodendrocytes (preOLs). We determined whether ex vivo MRI can distinguish distinct microglial and astroglial responses related to WMI progression and arrested preOL differentiation. Methods We employed a preterm fetal sheep model of global cerebral ischemia where acute WMI results in selective preOL degeneration. We developed novel algorithms to register histopathologically defined lesions with contrast- and diffusion-weighted high-field ex vivo MRI data. Results Despite mild delayed preOL degeneration, preOL density recovered to control levels by 7 days after ischemia and was ~2 fold greater at 14 days. However, pre-myelinating OLs were significantly diminished at 7 and 14 days. WMI evolved to mostly gliotic lesions where arrested preOL differentiation was directly proportional to the magnitude of astrogliosis. A reduction in cerebral WM volume was accompanied by four classes of MRI-defined lesions. Each lesion type displayed unique astroglial and microglial responses that corresponded to distinct forms of necrotic or non-necrotic injury. High-field MRI defined two novel hypo-intense signal abnormalities on T2-weighted images that coincided with microscopic necrosis or identified astrogliosis with high sensitivity and specificity. Interpretation These studies support the potential of high-field MRI for early identification of microscopic necrosis and gliosis with preOL maturation arrest, a common form of WMI in preterm survivors.

Children who survive preterm birth exhibit persistent unexplained disturbances in cerebral cortical growth with associated cognitive and learning disabilities. The mechanisms underlying these deficits remain elusive. We used ex vivo diffusion magnetic resonance imaging to demonstrate in a preterm large-animal model that cerebral ischemia impairs cortical growth and the normal maturational decline in cortical fractional anisotropy (FA). Analysis of pyramidal neurons revealed that cortical deficits were associated with impaired expansion of the dendritic arbor and reduced synaptic density. Together, these findings suggest a link between abnormal cortical FA and disturbances of neuronal morphological development. To experimentally investigate this possibility, we measured the orientation distribution of dendritic branches and observed that it corresponds with the theoretically predicted pattern of increased anisotropy within cases that exhibited elevated cortical FA after ischemia. We conclude that cortical growth impairments are associated with diffuse disturbances in the dendritic arbor and synapse formation of cortical neurons, which may underlie the cognitive and learning disabilities in survivors of preterm birth. Further, measurement of cortical FA may be useful for noninvasively detecting neurological disorders affecting cortical development.

Neurological deficits in children, including cerebral palsy, are associated with prior infection during the perinatal period. Experimentally, we have shown that pre-exposure to the Gram-negative component LPS potentiates hypoxic-ischemic (HI) brain injury in newborn animals. LPS effects are mediated by binding to TLR4, which requires recruitment of the MyD88 adaptor protein or Toll/IL-1R domain-containing adapter inducing IFN-β for signal transduction. In this study, we investigated the role of MyD88 in neonatal brain injury. MyD88 knockout (MyD88 KO) and wild-type mice were subjected to left carotid artery ligation and 10% O2 for 50 min on postnatal day 9. LPS or saline were administered i.p. at 14 h before HI. At 5 days after HI in wild-type mice, LPS in combination with HI caused a significant increase in gray and white matter tissue loss compared with the saline-HI group. By contrast, in the MyD88 KO mice there was no potentiation of brain injury with LPS-HI. MyD88 KO mice exhibited reduced NFκB activation and proinflammatory cytokine-chemokine expression in response to LPS. The number of microglia and caspase-3 activation was increased in the brain of MyD88 KO mice after LPS exposure. Collectively, these findings indicate that MyD88 plays an essential role in LPS-sensitized HI neonatal brain injury, which involves both inflammatory and caspase-dependent pathways.