The protein produced by bees retains the pluripotency of stem cells in mice

The active protein component of royal jelly helps the bees to grow new queens. Scientists from Stanford discovered a similar protein in mammals that is able to preserve the pluripotency of embryonic stem cell culture.

According to researchers from the Stanford University School of Medicine, the protein found in mammals functions as a kind of fountain of youth for mouse embryonic stem cells (ESCs). In its structure, it is similar to the active component of royal jelly – a special food with which worker bees grow the queen of the hive. The results of the study were published on December 4, 2018 in Nature Communications.

The unexpected discovery is likely to fan the flames of millennia-old debates about the regenerative power of royal jelly. More importantly, the discovery offers new ways to keep stem cells in a state of pluripotency until they are needed for future treatments.

“In folklore, royal jelly is kind of like a super-medicine, particularly in Asia and Europe”, – said assistant professor of dermatology Kevin Wang, MD, Ph.D., “But the DNA sequence of royalactin, the active component in the jelly, is unique to honeybees. Now, we’ve identified a structurally similar mammalian protein that can maintain stem cell pluripotency.”

Hive hierarchy component

Royal jelly is an essential component in the strict hierarchical structure of the beehive. Under normal conditions, a single queen lays fertilized eggs, from which working female bees emerge. They work by collecting pollen and nectar, build the honeycombs, lay unfertilized eggs and take care of larvae.

The new queen is needed for the hive when the old one dies, or the hive becomes too large and requires its division into two parts. In this case, worker bees choose few female larvae, which are fed throughout the development period exclusively with royal jelly — a viscous, slightly acidic substance consisting of water, proteins and sugars.

All larvae are fed with royal jelly for the first few days after hatching, but the worker larvae are quickly switched to a combination of royal jelly, honey, and a mixture of pollen, known as “bee bread”.

It is still unclear exactly how royal jelly stimulates the formation of a large and fertile queen, and not a simple worker bee. However, people believe that what is good for the development of the bee queen must be good for them.

Although royal jelly has been suggested to have effects on cholesterol levels, blood pressure, nervous system and hormonal activity, it has not been approved by the Food and Drug Administration (FDA) for medical use.

“How does this happen?”

Wang wondered how a diet of royal jelly could lead to such huge differences between queen bees and much smaller workers. After all, both insect castes share an identical genome.

“I’ve always been interested in the control of cell size”, – Wang said, “and the honeybee is a fantastic model to study this. These larvae all start out the same on day zero, but end up with dramatic and lasting differences in size. How does this happen?”

The Wang group focused on royalactin protein, which was previously had been considered to be the active ingredient in royal jelly. They applied royalactin to mouse embryonic stem cells to study the cells’ response.

“For royal jelly to have an effect on queen development, it has to work on early progenitor cells in the bee larvae”, – Wang said. “So we decided to see what effect it had, if any, on embryonic stem cells.”

ESCs have great potential, but they are unstable. When cultured in the laboratory, they often seek to differentiate into specialized cells, losing the properties of stem cells. Researchers have developed methods for maintaining cell lines by adding differentiation inhibiting compounds to the nutrient medium.

To his surprise, Wang and his colleagues found that the addition of royalactin stopped the differentiation of embryonic stem cells even in the absence of inhibitors.

“This was unexpected”, – Wang said. “Normally, these embryonic stem cells are grown in the presence of an inhibitor called leukemia inhibitor factor that stops them from differentiating inappropriately in culture, but we found that royalactin blocked differentiation even in the absence of LIF.”

Researchers found that the cultured LIF-free cells grew successfully for up to 20 generations, without losing their “stemness”.

Additional experiments showed that royalactin-treated stem cells demonstrated gene expression profiles similar to stem cells, grown in the presence of the inhibitors, producing proteins known to be associated with pluripotency, while reducing the production of proteins important for differentiation.

And yet, the cell response was confusing, since mammals do not produce roalactin.

For answers, the researchers turned to a database of the three-dimensional structure of proteins. Like a lock and a key, many proteins interact, precisely connecting with other proteins or biological molecules. Scientists wondered if there could be a similar protein in mammals that mimics the shape, but not the sequence, of royalactin.

Wang discovered a mammalian protein called NHLRC3, that was predicted to form a structure similar to royalactin, and that was produced at an early stage of embryonic development in all animals, from eels to humans.

In addition, they found that NHLRC3, like royalactin, was able to maintain pluripotency in mouse embryonic cells, and that it produced a similar pattern of gene expression in them, as in those cells that were exposed to roalactin. Researchers renamed protein Regina, which in Latin means queen.

Next, researchers plan to find out whether Regina has any therapeutic value in wound healing or cell regeneration in adult animals. They also hope that their discovery will help researchers find more effective ways to preserve the pluripotency of embryonic stem cells when grown in a laboratory.