Plant microRNAs in Your Blood?

 

Last month the science magazines and websites were all talking about a paper by Zhang et al. (2012) published in Cell Research. These workers discovered plant micoRNAs in the serum of mice and humans. The microRNAs seem to come from ingested rice. Presumably the micoRNAs are taken up in the intestine and secreted into the blood in small vesicles. The concentration of the major rice miRNAs in serum is about 10 fM or 10×10^-15 moles per liter.¹

The authors have shown that microRNA MI168a binds to the mRNA of low-density lipoprotein receptor adapter protein 1, inhibiting translation. This leads to the idea that ingested plant microRNAs can regulate the expression of human genes. That's the story that generated the most press [What You Eat Affects Your Genes: RNA from Rice Can Survive Digestion and Alter Gene Expression, Food We Eat Might Control Our Genes].

This is one of those findings where the explanation doesn't make a lot of sense but the data seem sound. It seems very unlikely that small plant RNAs could survive the processing and digestion of rice or any other food and even less likely that they would find their way into the bloodstream where they could play a role in regulating mammalian gene expression. I think I'll wait for confirmation.

It's a shame that none of the articles in the popular press expressed any sort of skepticism. That's one of the problems with science journalism. How do you convey the idea that all scientific results are preliminary until they have been confirmed by others?

---

1. That concentration is far below the concentration where effective binding can occur but the idea seems to be that the micoRNAs are contained in small vesicles that subsequently fuse with liver cells and deliver the rice microRNA to the cytoplasm where it can inhibit translation of specific mammalian RNAs. It's difficult to see how one could get an effective concentration of plant microRNA in one of these mammalian cells.

Zhang, L., Hou, D., Chen, X., Li, D., Zhu, L., Zhang, Y., Li, J., Bian, Z., Liang, X., Cai, X., Yin, Y., Wang, C., Zhang, T., Zhu, D., Zhang, D., Xu, J., Chen, Q., Ba, Y., Liu, J., Wang, Q., Chen, J., Wang, J., Wang, M., Zhang, Q., Zhang, J., Zen, K., and Zhang, CY. (2012) Exogenous plant MIR168a specifically targets mammalian LDLRAP1: evidence of cross-kingdom regulation by microRNA. Cell Research 22:107–126 [PubMed] [doi:10.1038/cr.2011.158]

An important correction to several of the figures in this paper has also been published.

Zhang et al. (2012) Corrigendum [doi:10.1038/cr.2011.174]