Your nose is not the only organ in your body that can sense cigarette smoke wafting through the air. Scientists at Washington University in St. Louis and the University of Iowa have showed that your lungs have odor receptors as well.

Unlike the receptors in your nose, which are located in the membranes of nerve cells, the ones in your lungs are in the membranes of neuroendocrine cells. Instead of sending nerve impulses to your brain that allow it to “perceive” the acrid smell of a burning cigarette somewhere in the vicinity, they trigger the flask-shaped neuroendocrine cells to dump hormones that make your airways constrict.


“We forget,” said Ben-Shahar, “that our body plan is a tube within a tube, so our lungs and our gut are open to the external environment. Although they’re inside us, they’re actually part of our external layer. So they constantly suffer environmental insults,” he said, “and it makes sense that we evolved mechanisms to protect ourselves.”


The cells might be responsible for the chemical hypersensitivity that characterizes respiratory diseases, such chronic obstructive pulmonary disease (COPD), and asthma. Patients with these diseases are told to avoid traffic fumes, pungent odors, perfumes and similar irritants, which can trigger airway constriction and breathing difficulties.

The odor receptors on the cells, might be a therapeutic target, Ben-Shahar suggests. By blocking them, it might be possible to prevent some attacks, allowing people to cut down on the use of steroids or bronchodilators.

Every breath you take


Aware that airway diseases are characterized by hypersensitivity to volatile stimuli, Ben-Shahar and his colleagues realized that the lungs, like the nose, must have some means of detecting inhaled chemicals.

Earlier a team at the University of Iowa, where Ben-Shahar was a postdoctoral research associate, had searched for genes expressed by patches of tissue from lung transplant donors. They found a group of ciliated cells that express bitter taste receptors. When offending substances were detected, the cilia beat more strongly to sweep them out of the airway. This result was featured on the cover of the August 28, 2009 issue of Science.


This made sense. “When people with airway disease have pathological responses to odors, they’re usually pretty fast and violent,” said Ben-Shahar. “Patients suddenly shut down and can’t breath and these cells may explain why.”


The cells in the airways are secretory not neuronal cells and they may carry more than one receptor, so they are broadly tuned. Instead of sending nerve impulses to the brain, they flood local nerves and muscles with serotonin and neuropeptides. “They are possibly designed,” he said, “to elicit a rapid, physiological response if you inhale something that is bad for you.”




Of mice and men

But there is a problem. “For example, a liver from a mouse and a liver from a human are pretty similar, they express the same types of cells. But the lungs from different mammalian species are often very different; you can see it at a glance,” Ben-Shahar said.

“Clearly. “Ben-Shahar said, “primates have evolved distinct cell lineages and signaling systems for respiratory-specific functions. “

This makes it challenging to unravel the biomolecular mechanisms of respiratory diseases.

Still, he is hopeful that the PNEC pathways will provide targets for drugs that would better control asthma, COPD and other respiratory diseases. They would be welcome. There has been a steep rise in these diseases in the past few decades, treatment options have been limited, and there are no cures.

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