Editor’s note: republished with permission from The Biology Files.
By Emily Willingham
A study from a Chinese group led by Chen-Yu Zhang of Nanking University and published in Cell Research, has uncovered the fascinating result that when people eat rice, they can absorb microRNAs (miRNAs)–tiny sequences of RNA–from the rice into the blood. These rice-originating miRNAs turn up in blood and tissues of people who eat rice and…here’s the kicker…one type of rice miRNA interacts with human proteins that are responsible for removing LDL (“bad” cholesterol) from the blood (!). It’s the first report of plant miRNAs ending up in people by way of diet and the finding that at least one of them alters an important process in the body.
The implications could extend in many a direction, but not as far as writer Ari Levaux would like to take them in this remarkably confusing article published on the Atlantic Website. Before taking on the errors and the overstretch that are that piece, let’s look at something far more interesting: miRNAs themselves.
These little bits of RNA, consisting of 22 building blocks linked in a single strand (a human DNA molecule has billions) get around with surprising facility, and their purpose is to regulate genes. They don’t regulate by latching directly onto a DNA sequence but instead lurk in the cell and interfere with processes that come after the gene’s role is complete. If you consider the gene sequence as the directions for building a protein, one job of RNA is to serve as a copy of those directions. It takes on the risky business of toting that copy out of the safety of the nuclear vault in our cells and into the big, bad scary cytoplasm outside. In the cytoplasm, the fluid-ish environment of the cell, RNA has many, many roles, but all of them center on executing the directions encoded in the gene for building proteins, the molecules that help make up our tissues and perform the tasks required to keep us alive.
In some cases, though, RNA occurs in the form of miRNAs, and their job may well be to bollix up the protein-building works. These little molecules–which researchers have identified in the hundreds in humans–can, for example, latch onto an RNA that is a copy of the protein code and cause it to break down or keep the cell from using it. These tiny RNA sequences help fine-tune the process of protein building well beyond the starting point of directions copied from a gene sequence. Thanks to miRNAs and many other steps that can promote or interfere with protein building, the cell–and the organism–has several chances to modulate how much of a specific protein it makes, allowing agile, real-time responses to changing conditions.
Researchers have discovered myriad ways that miRNA influences human development and disease, and these discoveries open the way to using that information to cure disease. But all of the miRNAs investigated thus far in people have come from people themselves, either present for normal functions or overabundant and linked to disease. The flashy take-home from this latest rice study is, We can pick up these tiny regulators from what we eat…and they can interfere with the functions of proteins we make.
This take-home could have huge implications for how diet influences our health and development if other non-human miRNAs turn up that fit the same profile: absorbable after we eat them and modifying how our bodies function. The effects could be good, bad, ugly, or neutral. This paper is simply an open door. Now, for years and years, investigators will walk through it to find a number of research paths to explore, from seeking more non-human miRNAs and identifying their effects to evaluating how modifying diet might influence disease or human development via miRNAs.
In spite of how much lies ahead and how relatively little lies in the present about this discovery–one rice miRNA, one human effect–the piece that appeared today in the Atlantic argues that the implications are immediate and dire and related to genetically modified organisms. I initially read the piece trying to identify how someone could make that leap but instead found myself distracted by how poorly the article presents the science itself.
First, the headline: The Very Real Danger of Genetically Modified Foods. I read the Cell Research paper. I can’t find mention of GMOs in it. I don’t find mention in the paper the the rice miRNA in question derives from a genetically modified rice strain. So, I don’t see that this headline appropriately represents the science here.
Then there’s the dek: “New research shows that when we eat we’re consuming more than just vitamins and proteins. Our bodies are absorbing information, or DNA.” That’s not what this research shows. It shows that the body takes up a specific rice miRNA when people consume it. Not DNA or “information.”
The lede leaves out a crucial modifier: the word “rice”: “Chinese researchers have found small pieces of ribonucleic acid (RNA) in the blood and organs of humans who eat rice.” Actually, miRNAs are present in the blood and organs of…all humans, whether they eat rice or not. I think the writer here means “small pieces of rice ribonucleic acid.”
There is then a series of claims about what the research implies, including, mysteriously, that it will help us learn how some “herbal medicines function.” The original paper makes no mention of herbal medicines, although some research indicates that “natural agents” can alter expression of human miRNA. Also among the potential implications described in the piece is, “And it reveals a pathway by which genetically modified (GM) foods might influence human health.” That’s an enormous leap to make from “one rice miRNA in blood and tissues influences activity of one human protein.” A number of steps would be required for a GM food to exert a similar effect, none of which have been investigated yet. These steps include identifying that the modified sequence in the target food either also encodes a miRNA sequence or interacts with its expression or, later in the gene-to-protein process, somehow evades normal miRNA regulation thanks to this change.
Then suddenly, there’s Monsanto and a strange effort to explain the central dogma of molecular biology (DNA–>RNA–>protein) using a pizza/pizza restaurant analogy that involves the “DNA” knowing what kind of pizza “it wants,” although in truth, the cell is the entity in charge of which parts of the DNA it uses. The central dogma, a linear representation of how a cell copies DNA into RNA and then uses the RNA copy instructions to build proteins, is too simple for what we know today about how cells regulate protein expression. But the core dogma remains intact, including that DNA serves as the template for making RNA.
The article makes a number of other scientific errors, including in a bold pull quote claiming, “The Chinese RNA study threatens to blast a major hole in Monsanto’s claim. It means that DNA can code for microRNA (italics mine), which can, in fact, be hazardous.” No. That’s not what the Chinese study “means.” It’s not news that DNA encodes RNA of all kinds. It encodes the messenger form that carries the copy of the code. It encodes the ribosomal form that is a component of ribosomes, the cell factory workers that take the code copy and use it as an instruction book for building proteins. It encodes the RNAs that bring those factory workers the molecular blocks the cell uses for building proteins. And it encodes miRNAs. This latest paper does not carry the meaning that DNA encodes miRNAs–that’s a longstanding part of the Central Dogma, ironically, and not news. Nor does it threaten in any discernible way to “blast a hole” in much of anything. As I noted, the study opens a door.
In closing, Levaux writes,
The news that we’re ingesting information as well as physical material should force the biotech industry to confront the possibility that new DNA can have dangerous implications far beyond the products it codes for. Can we count on the biotech industry to accept the notion that more testing is necessary? Not if such action is perceived as a threat to the bottom line.
“Ingesting information”? The miRNAs are not “information” (they are noncoding molecules), and like all other things of this world that we’ve identified, they’re not somehow distinctive from “physical material.” There is naught in this study that implies that “new DNA” can have “dangerous implications” far beyond the products it “codes for.” The miRNAs in this paper are not “new.” They are from rice, the most-prevalent grain crop in Asia, and presumably something humans have been taking in for hundreds of years. It’s unclear from this study even what the implications of the findings are for consumers of regular rice, much less what they’d be for modified organisms. Furthermore, we are not the only entities that modify organisms. Nature does so, often by way of viruses. I wonder why the fact that miRNAs are also present in viruses and could “potentially regulate host genes” didn’t set off the anti-GMO alarms, too.
The article goes on for several grafs about Monsanto and substantial equivalence–indeed, the writer devotes a mere 180 words or so of 908 to the study itself–and observes that the lead author on the Cell Research paper (wisely) declined to comment on any implications about these findings for GM foods. If only the Atlantic and Ari Levaux had done the same, the real implications of this remarkable work could simply stand on their own.
For an article that focuses more on the research findings from the study, including design and other dietary miRNAs identified, see this piece by Anne-Marie C. Hodge at Scientific American.
ETA: As for the study itself, the effects the authors found weren’t earthshattering, and it seems that there was an issue with images provided that required a rapid erratum after the paper was published.
Follow-up: The author of the piece, Ari Levaux, has responded here, and I have replied just below that.
Follow-up follow-up: Ari Levaux has tweeted that he is going to rewrite the piece, taking the scientific critiques into account. I’m looking forward to seeing the update.
Emily Willingham has a bachelor’s degree in English and a PhD in biological sciences, both from The University of Texas at Austin, with a completed postdoctoral fellowship at the University of California, San Francisco. She blogs at The Biology Files about how science and writing about science take shape around the audience known as You. She is the author of The Complete Idiot’s Guide to College Biology and currently working on a book about lice. Yep, “lice.” She bets you’re about to scratch your head right now.