SPP1, Oxidative Stress, and Lead Toxicity

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PROJECT SUMMARY SPP1, Oxidative Stress, and Lead Toxicity Exposure to lead (Pb), a pervasive environmental toxicant, at the early stages of brain development has long-lasting effects on neurocognitive function. However, the molecular mechanisms underlying the unique susceptibility of early brain development to Pb remain poorly understood. As the progenitor cells in the central nervous system, neural stem cells (NSCs) play an essential role in shaping the developing brain. We performed global transcriptional profiling and identified genes whose expression is significantly altered by Pb treatment in neural stem cells. Most of the Pb-upregulated genes are targets of NRF2—the master transcriptional factor for the oxidative stress response, including SPP1 (secreted phosphoprotein 1). SPP1 is known to be neuroprotective, and consistent with this, we demonstrated that addition of recombinant SPP1 protein reduces the inhibitory effect of Pb on NSC growth. Using data from existing genome-wide association studies of an environmental epidemiological cohort, we further showed that a genetic variant in the promoter region of SPP1 significantly associates with improved cognitive development in children. Based on these studies, we hypothesize that NRF2-mediated SPP1 upregulation functions as a self-protective response to reduce Pb exposure-induced injury in neural stem cells. We further hypothesize that failure or compromised ability to upregulate SPP1 in response to Pb exposure contributes to neural stem cell dysfunction and consequently the impairment of early brain development. To test these hypotheses, we propose a highly integrative project that combines molecular mechanistic studies in cultured neural stem cells, in vivo mouse models, and human genetic epidemiology in children exposed to Pb. Aim 1 will investigate the mechanisms thorough which SPP1 upregulation protects against Pb toxicity in neural stem cells. Aim 2 will investigate the role of SPP1 in mediating the effect of Pb on neurodevelopment in mice. Aim 3 will determine the functional association of SPP1 variants with neurodevelopment in children exposed to Pb. Results from this study will establish SPP1 upregulation as a critical mechanism linking Pb exposure with neural stem cell function and neurodevelopment in children, and may identify SPP1 as a novel target for preventative and therapeutic interventions against detrimental neurodevelopment effects of Pb exposure in children.