What's the News:
It's no secret that having lunch messes with your biochemistry. Once that sandwich hits your stomach, genes related to digestion have been activated and are causing the production of the many molecules that help break food down. But a new study suggests that the connection between your food's biochemistry and your own may be more intimate than we thought. Tiny RNAs usually found in plants have been discovered circulating in blood, and animal studies indicate that they are directly manipulating the expression of genes.
What's the Context:
MicroRNAs, or miRNAs, are molecules involved in regulation of gene expression, the transcription of genes into proteins. miRNAs bind to the messenger RNAs that ferry genetic information from DNA to the ribosomes, which translate messenger RNAs into proteins.
When a miRNA binds a messenger RNA, it keeps it from being translated, thus preventing that gene from being expressed.
How the Heck:
This team of researchers at Nanjing University had been studying the miRNAs that circulate in human blood and were surprised to find that some of the miRNAs weren't homegrown but instead came from plants. One of the most common plant miRNAs was from rice, a staple of their Chinese subjects' diets. Intrigued, they confirmed with a variety of tests in mice that the miRNA, which, in its native environs, usually regulates plant development, was definitely coming from food.
When they put the rice miRNA in cells, they found that levels of a receptor that filters out LDL, aka "bad" cholesterol, in the liver went down. As it turned out, the miRNA was binding to the receptor's messenger RNA and preventing it from being expressed, sending receptor levels down and bad-cholesterol levels up. They saw the same effect when they tried it in mice.
Going further, when they fed rice to mice but also gave them a molecule that would turn off the miRNA, the liver receptor bounced back and bad cholesterol levels went down.
The team concludes that miRNAs may be a new class of functional components in food, like vitamins or minerals — even in an animal that's pretty far removed from their home organism, they can manipulate gene expression and have an effect on nutrition.
The Future Holds:
It's only logical that what we eat has an effect on the expression of our genes, in the general sense that nutrients from food are involved in cellular processes that control and are controlled by gene expression. But this is an unusually direct route, and surprising from an organism that's so different from mammals.
Since miRNAs from plants haven't been on scientists' radar before, this should be a field ripe for further exploration. Do corn miRNAs circulate in the blood of people in societies that eat gigantic quantities of corn, like the US? What receptors might those miRNAs control?
Reference: Zhang, et al. 2011 Exogenous plant MIR168a specifically targets mammalian LDLRAP1: evidence of cross-kingdom regulation by microRNA. Cell Research. doi:10.1038/cr.2011.158