Can you smell touch? Can you touch smells? The questions sound zen-ish. Like “What is the sound of one hand clapping?” The questions could be asked by an existentialist in search of the esoteric. The matter, though, may not be just esoteric. It’s real. Researchers from Southern Methodist University (SMU) in Dallas discovered that a gene linked to a human’s sense of touch may also have a role in the sense of smell.
“This gene has previously been identified as a potential therapeutic target for chronic pain. Now that we know the gene is also involved in olfaction [the act of smelling] it might present an opportunity for treating or understanding olfactory defects, such as the mysterious loss of smell that many COVID-19 patients have reported,” explains SMU’s Adam D. Norris, an assistant professor in the Department of Biological Sciences at SMU. He worked with SMU graduate students Xiaoyu Liang and Canyon Calovich-Benne on the research.
The sense of touch requires the nervous system to process the mechanical input it receives from touch receptors in skin, converting it into electrical signals that are sent to the brain. This is known as mechanosensation. It enables the brain to characterize the touch, such as hot/cold, sharp/dull, firm/soft, and countless other features.
The worm Caenorhabditis elegans is often used for research, for its simple physiology and because many of the genes that create nerve cells in C. elegans have comparable, functional genes in humans. Previous research had established that a gene called ‘mec-2’ was vital to activating touch neurons in C. elegans. In this current study, the researchers discovered that activating touch isn’t mec-2’s only role.
“In addition to turning genes on and off, another way to control a neuron’s function is to generate different (but functionally similar) versions of a single gene called isoforms. We looked for different neurons that contain different isoforms of important genes,” Norris says. “This led us to the fundamental discovery outlined in this paper, which is that different isoforms work to enable both mechanosensation and olfaction.”
The scientists discovered that the mec-2 isoform responsible for mechanosensation requires the activation of a gene called mec-8, Norris explained. “Mec-8 makes sure that mec-2 is made in the mechanosensory isoform,” Norris said. Without mec-8, mec-2 genes instead produce isoforms that are necessary for smell in C. elegans.
Having established mec-2’s role in the sense of smell in C. elegans, Norris intends to investigate whether a human gene called stomatin can do the same thing. The mec-2 gene, however, is found in worms, not humans. The stomatin, produced by humans, is highly similar in function to mec-2 regarding the sense of touch.
If stomatin’s function is found to apply to smell as well, Norris suggests that similar methods being studied to treat chronic pain could also be used to address loss of smell for people who have had COVID-19.
Norris stresses, though, that this theory needs more research. “Thus far experiments have been done in C. elegans and mice that agree with each other. It is natural to hypothesize that similar results will hold in humans,” he said. “But that needs to be proven.”
The study is published in the journal Nucleic Acids Research.