The Long Processes of Short Interfering RNAs – RNA Interference and Its Implications in Neuronal Cells

A novel method for RNA interference in neurons using enhanced green fluorescent protein (EGFP)-transgenic rats

RNA interference (RNAi) is the simplest way of examining gene function by inhibiting expression. However, due to the low rate of introducing short interfering RNA (siRNA) into neurons, it is difficult to discriminate into which neurons that have been successfully introduced. Here, we used neurons from transgenic rats expressing enhanced green fluorescent protein (EGFP), and we simultaneously applied small interfering RNAs (siRNAs) against EGFP and a targeted gene to the EGFP-expressing neurons. EGFP fluorescence and immunoreactivity of the protein were then assessed by immunofluorescence microscopy. Quantitative analysis of the immunofluorescence confirmed that loss of EGFP closely correlates with loss of the target protein. These results indicate that this method can be used in a wider range of the neuroscientific research, especially in genome-wide studies.

[Programmed cell death in the retina. Molecular mechanisms and therapeutic strategies]

The cellular suicide program (apoptosis) is important not only for many physiological processes spanning from embryonal development to aging but also for the pathogenesis and the course of a wide spectrum of diseases. Among these disorders are chronic neurodegenerative diseases including acquired and inherited degeneration of photoreceptors as well as retinal ganglion cells during retinitis pigmentosa, macular degeneration, optic neuritis, or glaucoma. In the following review we will address general pro- and antiapoptotic signal transduction cascades, their relevance for retinal degeneration focussing on retinal ganglion cells, and new therapeutic strategies evolving from these findings.

Transfection of “naked” siRNA results in endosomal uptake and metabolic impairment in cultured neurons

RNA interference is rapidly becoming a powerful tool for gene silencing in mammalian cells. Introduction of siRNA into primary cells, however, remains one of the major difficulties of this novel technique. Using cationic lipid-based transfection reagents satisfactory transfection results are observed in cell lines, but low transfection efficiency and cytotoxicity limit applications in primary cells, especially primary neurons. The application of "naked" siRNA has been previously used successfully in nematodes and mammals in vivo. We therefore evaluated the effects of non-cationic-lipid-based siRNA application to primary hippocampal neuron cultures. "Naked" siRNA was bound to the cell surface and was taken up into endosomes. No significant silencing effect of endogenous or reporter genes was observed, rather application of "naked" siRNA was accompanied by a moderate downregulation of metabolic activity in culture. We postulate that endosomal degradation of "naked" siRNA in neurons prevents the induction of significant RNAi-mediated mRNA-downregulation and is accompanied by a global impairment of the cell metabolism. Transfection methods circumventing the endosomal pathway therefore might prove useful for siRNA transduction of primary neurons.