Genes involved in tasting sweet and savory flavors on the tongue also play a key role in properly working sperm, new research in animals finds.
These findings could lead to novel contraceptives for men, and suggest ways to help treat male infertility, the researchers said.
In this research, scientists investigated proteins known as taste receptors. These receptors help tongues detect sugars, acids, salt and other chemicals responsible for basic tastes such as sweet, sour, salty, bitter and the savory taste known as umami.
Oddly, in the past decade, research has shown taste receptors are also located in other parts of the body, including the stomach, intestines, pancreas, lungs and even the brain.
But the functions of these receptors found outside the mouth have remained unclear.
To help solve the mystery, researchers focused on receptors that help taste buds detect the sugars and amino acids responsible for sweet and savory tastes.
The scientists discovered that one of these taste receptors, called TAS1R3, and a molecule that helps the taste receptor send signals to the brain, called GNAT3, were both found in the testicles and sperm of mice.
The investigators genetically engineered mice to possess the human form of the TAS1R3 receptor (but were missing the mouse version of TAS1R3 and GNAT3). When these mice were given the drug clofibrate, which inhibits the human receptor, the males became sterile due to malformed and fewer sperm. The mice quickly became fertile again once clofibrate was removed from their diet.
The study shows that "taste proteins are very important in male reproduction. We really didn't expect that," researcher Bedrich Mosinger, a molecular biologist at the Monell Chemical Senses Center in Philadelphia, told LiveScience.
"We didn't find similar effects with female reproduction," Mosinger said. "This looks specific to males."
The drug clofibrate that belongs to a class of chemicals called fibrates, which are frequently prescribed to treat lipid disorders, such as high blood cholesterol or high levels of triglycerides. Mosinger speculated the common use of fibrates in medicine could be contributing to the decline of male fertility, a growing problem worldwide. He added that weedkillers known as phenoxy-herbicides, which are widely used globally, also block the human TAS1R3 receptor,
"If our pharmacological findings are indeed related to the global increase in the incidence of male infertility, we now have knowledge to help us devise treatments to reduce or reverse the effects of fibrates and phenoxy compounds on sperm production and quality," Mosinger said.
This research could also help design a male non-hormonal contraceptive, Mosinger added. Such a contraceptive might not disrupt hormone levels vital to normal life.
"We now need to identify the pathways and mechanisms in testes that utilize these taste genes, so we can understand how their loss leads to infertility," said researcher Robert Margolskee, a molecular neurobiologist at the Monell Chemical Senses Center.
The scientists detailed their findings online today (July 1) in the journal Proceedings of the National Academies of Sciences.
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