We recently reported that arsenic caused insulin resistance in differentiated human neuroblastoma SH-SY5Y cells. Herein, we further investigated the effects of sodium arsenite on IGF-1 signaling, which shares downstream signaling with insulin. A time-course experiment revealed that sodium arsenite began to decrease IGF-1-stimulated Akt phosphorylation on Day 3 after treatment, indicating that prolonged sodium arsenite treatment disrupted the neuronal IGF-1 response. Additionally, sodium arsenite decreased IGF-1-stimulated tyrosine phosphorylation of the IGF-1 receptor β (IGF-1Rβ) and its downstream target, insulin receptor substrate 1 (IRS1). These results suggested that sodium arsenite impaired the intrinsic tyrosine kinase activity of IGF-1Rβ, ultimately resulting in a reduction in tyrosine-phosphorylated IRS1. Sodium arsenite also reduced IGF-1 stimulated tyrosine phosphorylation of insulin receptor β (IRβ), indicating the potential inhibition of IGF-1R/IR crosstalk by sodium arsenite. Interestingly, sodium arsenite also induced neurite shortening at the same concentrations that caused IGF-1 signaling impairment. A 24-h IGF-1 treatment partially rescued neurite shortening caused by sodium arsenite. Moreover, the reduction in Akt phosphorylation by sodium arsenite was attenuated by IGF-1. Inhibition of PI3K/Akt by LY294002 diminished the protective effects of IGF-1 against sodium arsenite-induced neurite retraction. Together, our findings suggested that sodium arsenite-impaired IGF-1 signaling, leading to neurite shortening through IGF-1/PI3K/Akt.
Keywords: IGF-1; PI3K/Akt; arsenic; neurite shortening; neurons.
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