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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 exploredmechanism 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 froma recombinant-HB-EGF-mediated recovery in GFAP levels and astrocytemorphology 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 downstreamof reduced HB-EGFR/EGFR revealed that an upregulated matrixmetalloproteinase 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, arsenicmay induceMMP9 levels and GFAP loss in astrocytes, whichmight adversely affect BBB integrity of the developing rat brain. [ABSTRACT FROM AUTHOR]

Arsenic promotes hippocampal neuronal damage inducing cognitive impairments. However, mechanism arbitrating arsenic-mediated cognitive deficits remains less-known. Here, we identified that chronic exposure to environmentally relevant doses of arsenic increased apoptosis, characterized by caspase-3 activation, poly(ADP-ribose) polymerase cleavage and Terminal deoxynucleotidyl transferase dUTP nick-end labeling of rat hippocampal neurons, marked by NeuN. Investigating apoptotic mechanism through in vivo and in vitro studies revealed that arsenic promoted bone morphogenetic protein-2 (BMP2) expression, supported by increased BMP-receptor2 (BMPR2) and p-Smad1/5 in hippocampal neurons. BMP2-silencing and treatment with BMP antagonist, noggin, attenuated the arsenic-induced apoptosis and loss in hippocampal neurons. We then investigated whether BMP2/Smad signaling stimulated neuronal apoptosis independently or required other intermediate pathways. We hypothesized participation of brain-derived neurotrophic factor (BDNF) that promotes neuronal survival. We identified an arsenic-mediated attenuation of BDNF-dependent TrkB signaling, and observed that co-treatment with recombinant-BDNF reinstated BDNF/TrkB and reduced neuronal apoptosis. To probe whether BMP2/Smad and BDNF/TrkB pathways could be linked, we co-treated arsenic with noggin or recombinant BDNF. We detected a noggin-mediated restored BDNF/TrkB, while recombinant-BDNF failed to affect BMP2/Smad signaling. In addition, we found that TrkB-inhibitor, K252a, nullified noggin-induced protection, proving the necessity of a downstream reduced BDNF/TrKB signaling for BMP2/Smad-mediated apoptosis in arsenic-treated neurons. We further related our observations with cognitive performances, and detected noggin-mediated restoration of transfer latency time and learningmemory ability for passive avoidance and Y-Maze tests respectively in arsenic-treated rats. Overall, our study proves that arsenic promotes hippocampal neuronal apoptosis through an up-regulated BMP2/Smad-dependent attenuation of BDNF/ TrkB pathway, inducing cognitive deficits. [ABSTRACT FROM AUTHOR]