Sulfonylurea receptor 1 in the germinal matrix of premature infants

Abstract

Germinal matrix (GM) hemorrhage (GMH) is a major cause of mortality and of life-long morbidity from cerebral palsy. GMH is typically preceded by hypoxic/ischemic events and is believed to arise from rupture of weakened veins in the GM. In the CNS, hypoxia/ischemia up-regulate sulfonylurea receptor 1 (SUR1)-regulated NCCa-ATP channels in microvascular endothelium, with channel activation by depletion of ATP being responsible for progressive secondary hemorrhage. We hypothesized that this channel might be up-regulated in the GM of preterm infants at risk for GMH. Here, we studied expression of the regulatory subunit of the channel, SUR1, and its transcriptional antecedent, hypoxia inducible factor 1 (HIF1), in postmortem tissues of premature infants who either were at risk for or who sustained GMH. We found regionally specific up-regulation of HIF1 and of SUR1 protein and mRNA in GM tissues, compared with remote cortical tissues. Up-regulation was prominent in most progenitor cells, whereas in veins, SUR1 was found predominantly in infants who had sustained GMH compared with those without hemorrhage. Our data suggest that the SUR1-regulated NCCa-ATP channel may be associated with GMH, and that pharmacological block of these channels could potentially reduce the incidence of this devastating complication of prematurity.

Figure 1. SUR1 and HIF1 are upregulated in the germinal matrix of premature infants

A–C: Low power micrographs (A,B) or montage of micrographs (C) of periventricular tissue stained with H&E (A), showing densely packed neural progenitor cells of the GM, with an arrow pointing to a small intraparenchymal hematoma, or labeled for mRNA for Abcc8, which encodes SUR1, using in situ hybridization (B), or immunolabeled for SUR1 (C); the latter two demonstrate regionally-specific labeling for SUR1 mRNA and protein in the GM; the montage in (C) shows positive immunolabeling in black pseudocolor; case #9 in Table 1: premature infant of 22 wk gestation who lived ~12 hr and was hypoxic prior to death, necessitating intubation and mechanical ventilation; post-mortem interval, 3 hr. D–F: Micrographs of cortical tissues (D) or GM tissues (E,F) processed for in situ hybridization for mRNA for Abcc8, using antisense probe (D,E) or sense probe (F). G–J: Micrographs of GM tissues immunolabeled for SUR1 (red, CY3 for SUR1, and blue, DAPI for nuclei), and double-labeled for von Willebrand factor (green; panels I and J only); co-labeling is indicated by yellow color; SUR1 was identified in neural progenitor cells (G), and in thin-walled veins from infants with GMH (panel H, red and panel I, yellow) but not in an infant without GMH (panel J, green); panels H, I, J are from cases #11, 10, 1 in Table 1, respectively. K–M: Low (K) and high (L,M) power micrographs of sections immunolabeled for HIF1α (green, FITC for HIF1α, and blue, DAPI for nuclei), showing HIF1α in a microvessel (L) and in neural progenitor cells (M). In panels D–M, the bars represent 50 µm.

Figure 2. Events in the germinal matrix of premature infants

Scheme depicting the reciprocal relationship between O₂ tension on the one hand, and HIF1 activation and SUR1 expression on the other hand. Mild hypoxia, which may be the norm due to the ventriculopetal blood supply, promotes neurogenesis, whereas moderate hypoxia may promote apoptosis resulting in involution of the GM. More severe hypoxia may promote expression of SUR1-regulated NC_Ca-ATP channels, which remain inactive until critical ATP depletion is reached (~30 µM), at which point the channels open, leading to oncotic death of cells, including endothelial cells, thereby compromising the structural integrity of veins and predisposing to GMH during episodes of venous hypertension.