Strain Differences in Behavioral and Cellular Responses to Perinatal Hypoxia and Relationships to Neural Stem Cell Survival and Self-Renewal

Abstract

Premature infants have chronic hypoxia, resulting in cognitive and motor neurodevelopmental handicaps caused by suboptimal neural stem cell (NSC) repair/ recovery in neurogenic zones (including the subventricular and the subgranular zones). Understanding the variable central nervous system repair response is crucial to identifying "at risk" infants and to increasing survival and clinical improvement of affected infants. Using mouse strains found to span the range of responsiveness to chronic hypoxia, we correlated differential NSC survival and self-renewal with differences in behavior. We found that C57BL/6 (C57) pups displayed increased hyperactivity after hypoxic insult; CD-1 NSCs exhibited increased hypoxia-induced factor 1␣ (HIF-1␣) mRNA and protein, increased HIF-1␣, and decreased prolyl hydroxylase domain 2 in nuclear fractions, which denotes increased transcription/translation and decreased degradation of HIF-1␣. C57 NSCs exhibited blunted stromal-derived factor 1-induced migratory responsiveness, decreased matrix metalloproteinase-9 activity, and increased neuronal differentiation. Adult C57 mice exposed to hypoxia from P3 to P11 exhibited learning impairment and increased anxiety. These findings support the concept that behavioral differences between C57 and CD-1 mice are a consequence of differential responsiveness to hypoxic insult, leading to differences in HIF-1␣ signaling and resulting in lower NSC proliferative/migratory and higher apoptosis rates in C57 mice. Information gained from these studies will aid in design and effective use of preventive therapies in the very low birth weight infant population. Preterm birth is known to result in cognitive and motor disabilities and recent evidence suggests that there can be significant recovery over time in some patients.

GSK-3β: a signaling pathway node modulating neural stem cell and endothelial cell interactions

“…Specifically, we demonstrate differences in GSK-3b activity and localization, and changes in downstream signaling cascades involving b-catenin, HIF-1a & 2a, BDNF, VEGF and SDF-1. Neural stem cell (NSC) and brain microvascular endothelial cell (BEC) proliferation, survival, migration and differentiation are all dramatically modulated in a manner consistent with differences in behaviors noted previously in these two strains following recovery from hypoxic insult [5]. Further, we demonstrate that inhibition of GSK-3b elicits changes in C57 cellular behavior that approximate those observed in CD1 NSC and BEC.…”

“…These differences mimic the range of neurodevelopmental handicaps observed in the very low birth weight premature infant population [5,9]. Exploiting these strain-specific differences, in which the C57 pups are susceptible to hypoxic insult and display poor recovery in vivo and in vitro while the CD1 pups exhibit a robust recovery in vivo and in vitro [2,5,9], we now demonstrate that differences in GSK-3b activity and the resulting effects on downstream signaling cascades are critical factors in the response to hypoxia in the neurovascular niche. Specifically, we demonstrate differences in GSK-3b activity and localization, and changes in downstream signaling cascades involving b-catenin, HIF-1a & 2a, BDNF, VEGF and SDF-1.…”

“…CD1 and C57BL/6 (C57) male and female breeders were obtained from Charles River Laboratories (Wilmington, MA) or laboratory stock derived from Charles River Laboratories breeders. At post-natal day 3 (P3) cohorts of mothers and pups were subjected to hypoxic (10% O 2 ) treatment while control mice remained under normoxic conditions as described [5]. Pups were sacrificed at P11 and for analyses of SVZ tissue, at P1 for NSC isolation, or at P60 for BEC isolation, as described [5,9,10].…”

“…Previously, we have demonstrated differences in susceptibility to and recovery from hypoxic injury in the perinatal period in two mouse strains (CD1-which we determined to respond to and recover from a hypoxic insult from P3 to P11 well both in vivo and intro vs. C57BL/6 [C57]-which we have found to respond to and recover from a hypoxic insult from P3 to P11 poorly both in vivo and in vitro [2,5,9]). These differences mimic the range of neurodevelopmental handicaps observed in the very low birth weight premature infant population [5,9].…”

“…The wide range of recoveries observed following CNS injury may be explained by the variable (individual) responsiveness within neurogenic zones (the subventricular and subgranular zones-SVZ and SGZ, respectively) which have been found to be important in the recovery phases following CNS injury [3][4][5].…”