Arsenic inhibits hedgehog signaling during P19 cell differentiation

Abstract

Arsenic is a toxicant found in ground water around the world, and human exposure mainly comes from drinking water or from crops grown in areas containing arsenic in soils or water. Epidemiological studies have shown that arsenic exposure during development decreased intellectual function, reduced birth weight, and altered locomotor activity, while in vitro studies have shown that arsenite decreased muscle and neuronal cell differentiation. The sonic hedgehog (Shh) signaling pathway plays an important role during the differentiation of both neurons and skeletal muscle. The purpose of this study was to investigate whether arsenic can disrupt Shh signaling in P19 mouse embryonic stem cells, leading to changes muscle and neuronal cell differentiation. P19 embryonic stem cells were exposed to 0, 0.25, or 0.5 µM of sodium arsenite for up to 9 days during cell differentiation. We found that arsenite exposure significantly reduced transcript levels of genes in the Shh pathway in both a time and dose-dependent manner. This included the Shh ligand, which was decreased 2- to 3-fold, the Gli2 transcription factor, which was decreased 2- to 3-fold, and its downstream target gene Ascl1, which was decreased 5-fold. GLI2 protein levels and transcriptional activity were also reduced. However, arsenic did not alter GLI2 primary cilium accumulation or nuclear translocation. Moreover, additional extracellular SHH rescued the inhibitory effects of arsenic on cellular differentiation due to an increase in GLI binding activity. Taken together, we conclude that arsenic exposure affected Shh signaling, ultimately decreasing the expression of the Gli2 transcription factor. These results suggest a mechanism by which arsenic disrupts cell differentiation.

Prenatal arsenic exposure alters REST/NRSF and microRNA regulators of embryonic neural stem cell fate in a sex-dependent manner

“…Developmental exposure to heavy metals reduces NSC proliferation and/or differentiation in the adult brain [14,23,42,49,50,53]. We have demonstrated that perinatal exposure of 50 µg/L arsenic (through all three trimesters of development) results in reduced differentiation but not proliferation of NSCs in adult male mice [56,60]; these findings are corroborated by other studies using in vivo and in vitro models of arsenic exposure at different time points [34,35]. Additionally, arsenic-induced deficits in neuronal differentiation are associated with reduced expression of neural-specific transcription factors in the adult [20,56,61,63], yet the effect of arsenic on the regulation and expression of transcription factors during embryonic neurogenesis has not been studied to date.…”

Mechanism of arsenite toxicity in embryonic stem cells

“…Together, these results confirm the teratogenicity of iAs as reported previously based on animal studies (Hood et al, 1977;Leonard & Lauwerys, 1980;Chaineau et al, 1990;Machado et al, 1999). In contrast, recent reports claimed ESC differentiation into cardiomyocytes, skeletal muscles and neurons was impaired or inhibited by iAs exposure (Liu & Bain, 2014;Rebuzzini et al, 2015;Wang et al, 2015). However, we did not investigate the directed differentiation of ESCs into specific cell lineages in the presence of iAs.…”

Melittin induces PTCH1 expression by down-regulating MeCP2 in human hepatocellular carcinoma SMMC-7721 cells

“…Shh signaling plays a fundamental role in cell differentiation, cell proliferation, and tissue polarity (Liu and Bain, 2014;Gomes et al, 2015;Islam et al, 2015). To investigate the effect of MeCP2 on Shh signaling in SMMC-7721 cells, we firstly examine the expression profiles of patched1 (PTCH1), a major component of the Shh pathway, as well as Shh and GLI1.…”