Arsenite toxicity is regulated by queuine availability and oxidation-induced reprogramming of the human tRNA epitranscriptome.

Cells respond to environmental stress by regulating gene expression at the level of both transcription and translation. The ∼50 modified ribonucleotides of the human epitranscriptome contribute to the latter, with mounting evidence that dynamic regulation of transfer RNA (tRNA) wobble modifications leads to selective translation of stress response proteins from codon-biased genes. Here we show that the response of human hepatocellular carcinoma cells to arsenite exposure is regulated by the availability of queuine, a micronutrient and essential precursor to the wobble modification queuosine (Q) on tRNAs reading GUN codons. Among oxidizing and alkylating agents at equitoxic concentrations, arsenite exposure caused an oxidant-specific increase in Q that correlated with up-regulation of proteins from codon-biased genes involved in energy metabolism. Limiting queuine increased arsenite-induced cell death, altered translation, increased reactive oxygen species levels, and caused mitochondrial dysfunction. In addition to demonstrating an epitranscriptomic facet of arsenite toxicity and response, our results highlight the links between environmental exposures, stress tolerance, RNA modifications, and micronutrients.

Silk fibroin aerogels: potential scaffolds for tissue engineering applications.

Silk fibroin (SF) is a natural protein, which is derived from the Bombyx mori silkworm. SF based porous materials are extensively investigated for biomedical applications, due to their biocompatibility and biodegradability. In this work, CO2 assisted acidification is used to synthesize SF hydrogels that are subsequently converted to SF aerogels. The aqueous silk fibroin concentration is used to tune the morphology and textural properties of the SF aerogels. As the aqueous fibroin concentration increases from 2 to 6 wt%, the surface area of the resultant SF aerogels increases from 260 to 308 m(2) g(-1) and the compressive modulus of the SF aerogels increases from 19.5 to 174 kPa. To elucidate the effect of the freezing rate on the morphological and textural properties, SF cryogels are synthesized in this study. The surface area of the SF aerogels obtained from supercritical CO2 drying is approximately five times larger than the surface area of SF cryogels. SF aerogels exhibit distinct pore morphology compared to the SF cryogels. In vitro cell culture studies with human foreskin fibroblast cells demonstrate the cytocompatibility of the silk fibroin aerogel scaffolds and presence of cells within the aerogel scaffolds. The SF aerogels scaffolds created in this study with tailorable properties have potential for applications in tissue engineering.

Analysis of embryoid bodies derived from human induced pluripotent stem cells as a means to assess pluripotency.

Human induced pluripotent stem cells (hiPSCs) have core properties of unlimited self-renewal and differentiation potential and have emerged as exciting cell sources for applications in regenerative medicine, drug discovery, understanding of development, and disease etiology. Key among numerous criteria to assess pluripotency includes the in vivo teratoma assay that has been widely proposed as a standard functional assay to demonstrate the pluripotency of hiPSCs. Yet, the lack of reliability across methodologies, lack of definitive clinical significance, and associated expenses bring into question use of the teratoma assay as the "gold standard" for determining pluripotency. We propose use of the in vitro embryoid body (EB) assay as an important alternative to the teratoma assay. This paper summarizes the methodologies for creating EBs from hiPSCs and the subsequent analyses to assess pluripotency and proposes its use as a cost-effective, controlled, and reproducible approach that can easily be adopted to determine pluripotency of generated hiPSCs.