A sensory twist in the story of human evolution

But a few years ago, Jennifer Pluznick, now a professor at Johns Hopkins University, came across olfactory receptors in the kidneys. She was sure a mistake had been made. But in the intervening two decades, work from her lab and others has uncovered smell and taste receptors all over the body. Olfactory receptors are marked in the kidneys, eyes, semen and prostate, and taste receptors in the lungs, spine and sinuses. What are they doing there?

In the kidneys, Pluznick has discovered, one olfactory receptor, Olfr78, picks up messages sent by the microbiome, the array of bacteria and other microorganisms that live in our bodies. She also found that mice lacking this receptor showed remarkable abnormalities in blood pressure. In this new paper, Pluznick and Jiaojiao Xu, a postdoctoral researcher in her lab, looked at the case of Olfr558. They found that male and female mice without the receptor did not show the usual sex-based difference in blood pressure. “It was a big surprise,” says Pluznick.

It turned out that female mice without Olfr558 have higher blood pressure than normal, while males without this receptor have lower blood pressure than normal. The males also showed lower levels of renin, an enzyme made by the kidneys that affects blood pressure, and the females have stiffer blood vessels. Exactly why these differences arise is a topic that the researchers are actively working on. It’s possible that the receptor, or the cells in which it resides, function differently in the presence of sex hormones, Pluznick speculates. “I really want to know the answer,” she says.

As researchers continue to investigate the link between blood pressure and olfactory receptors, their search highlights something most people may not realize about evolution: the place in the body where scientists first identify something may not be the place where it started. Taste receptors, for example, “are just molecules invented by the body,” says Tom Finger, co-director of the Rocky Mountain Taste and Smell Center at the University of Colorado School of Medicine, who studies the evolution of these receptors. “It is entirely possible that what we call taste receptors evolved from receptors that performed very different original functions.” The same goes for odor receptors.

There may be some kind of underlying logic connecting the roles of receptors in different places. Noam Cohen, a professor of otolaryngology at the University of Pennsylvania, was part of a team that discovered bitter taste receptors in the sinuses, where they appear to detect molecules made by bacterial invaders. Whether these receptors are in the mouth or somewhere else in the body that doesn’t have to do with taste, they ultimately play a similar role and sense the outside world: “It’s a way to identify nutrients you need or molecules to avoid those who could do that.” kill you,” he says.

How did odor receptors get to the kidneys? At some point, organisms with cells carrying these receptors may have outpaced their peers. Perhaps the receptors picking up useful signals led to a healthier cardiovascular system. The receptors themselves are, in a sense, the biological equivalent of Tinker Toys. They’re bits and pieces that the body can bring into play or send to deep storage, depending on how well they help an organism survive.

What this also means is that when you take a sip of coffee or smell a hyacinth, your experience is filtered through things that may be much older than the concept of taste or smell. Whether the message they send is interpreted by the body as an odor or as a signal to change blood pressure depends on the tissue they are in, and for the receptors it makes no difference at all.

Veronique Greenwood is a science writer who regularly contributes to Ideas.