Arsenic Attenuates Heparin-Binding EGF-Like Growth Factor/EGFR Signaling That Promotes Matrix Metalloprotease 9-Dependent Astrocyte Damage in the Developing Rat Brain.

Abstract

We earlier reported that exposure to arsenic at concentrations in ground water of India attenuated glial fibrillary acidic protein (GFAP) during brain development. Here, we validated the effects and explored mechanism in cultured astrocytes and developing rat brain. We hypothesized participation of epidermal growth factor receptor (EGFR), known to regulate GFAP. We found that arsenic inactivated EGFR, marked by reduced phospho-EGFR in astrocytes. Screening EGFR ligands revealed an arsenic-mediated attenuation in cellular and secreted-Heparin-binding EGF-like growth factor (HB-EGF). Furthermore, we observed that recombinant-HB-EGF cotreatment with arsenic blocked reduction in HB-EGF, secreted-HB-EGF and phospho-EGFR, which could be reversed by EGFR-inhibitor, gefitinib, suggesting that arsenic attenuated an HB-EGF/EGFR loop in astrocytes. This reduced HB-EGF/EGFR was essentially responsible for arsenic-induced astrocyte damage, obvious from a recombinant-HB-EGF-mediated recovery in GFAP levels and astrocyte morphology and reduction in astrocyte apoptosis, and the reverse by gefitinib. We found that arsenic also suppressed neuronal HB-EGF levels, which additionally contributed towards astrocyte damage. Exploring the pathways downstream of reduced HB-EGFR/EGFR revealed that an upregulated matrix metalloproteinase 9 (MMP9) within the astrocytes ultimately led to apoptosis and GFAP loss. Astrocytes and MMPs are known to regulate the blood-brain barrier (BBB) integrity, and hence we examined the effects of arsenic on BBB. We detected an arsenic-mediated increased BBB permeability, which could be blocked by recombinant-HB-EGF and MMP9 inhibitor, SB-3CT. Thus, our study indicates that via reduced astrocyte and neuronal HB-EGF signaling, arsenic may induce MMP9 levels and GFAP loss in astrocytes, which might adversely affect BBB integrity of the developing rat brain.