When controls go wrong in the right way
Yet another article from Nature today on RNA therapeutics, this time on using RNAi to stop angiogenesis in the eye to prevent blindness. Some people have seen that the VEGFR receptor can be targeting for knockdown by RNA interference using short 21-nucleotide siRNAs. Apparently, no one bothered to do the control here.
The authors of this paper did the control, in which one uses a “scrambled” or off-target siRNA to show that the effect of the silencing is sequence-specific. Except, in this case, the effect wasn’t sequence-specific. In fact, any old RNA would work, as long as it was longer than 21 nucleotides.
This might ring some bells about innate immunity. One of the early problems with RNAi in humans was that long double-stranded RNAs, which can be chopped up in cells to form the siRNAs, cause human cells to become inflamed. Specifically, the RNAs activated some Toll-like receptors, leading to a mounting of the innate immune response. This immune response was originally evolved to combat RNA viruses, which often have double-stranded RNA genomes or go through a double-stranded RNA intermediate during infection. This problem was later solved by using pre-made short RNAs, which don’t really induce the immune system response.
In this paper, it seems the authors have found this effect at play again. Many of the RNAs they tried activate the immune response, which in turn causes the cell to suppress angiogenesis!
