Gene therapy has emerged as an influential tool for treating the genetic and specific acquired disorders. Among all kinds of gene delivery systems, the cationic polymer polyethyleneimine (PEI) is considered as a promising non-viral gene delivery vector, although there are still concerns about its magnitude of cytotoxicity. While any cell insult leads to unfolded/misfolded protein accumulation and its consequent unfold protein response, evaluating the expression profile of ER-stress genes would be a sensitive indicator of cell stress. Beside cytotoxicity assays, real-time RT-PCR was used to investigate the effects of PEI nanoparticles on the endoplasmic reticulum. Treating Neuro2A cells revealed that PEI can induce cell toxicity in a concentration-dependent manner. Also, It increased the transcript levels of Grp78 (Bip), Atf4 and Chop, and splicing of Xbp1. To further optimize the transfection properties in Neuro2A cells, PEI was used to deliver a plasmid DNA containing GFP reporter. While different PEI/plasmid ratios revealed similar transfection efficiency, increasing the PEI/plasmid ratio led to induction of ER-stress markers. These results underscored that beside the effectiveness of PEI, using the lowest possible ratio of PEI/plasmid would minimize the detrimental effects of PEI on cells and confer it a beneficial therapeutic importance in nucleic acid delivery.

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