The receptor in the uterus can detect a sperm molecule, helps sperm survival

Why do you need 200 million sperm to fertilize a single egg? Isolated sperm that reached the finished line managed to survive several checkpoints in the female reproductive tract, dubbed the pre-fertilization event. A new study shows that the uterus contains receptors that facilitate sperm survival.

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A team of researchers from the University of California at San Diego discovered that the uterus contains many innate lectins, similar to sialic acid binding immunoglobulins (Siglecs), that facilitate survival. spermatozoa when they enter the uterus.

The study, published in the journal Journal of biological chemistry, Show that one of the reasons that it takes millions of sperm to fertilize an egg is that when they arrive in the uteres, they are bombarded by the immune system. Researchers believe that it takes millions of sperms for the one who fertilizes the egg to survive.

"I am a lonely zoologist in a medical school, my basic principle is that all life is a big compromise: for an egg, being too easy to fertilize is bad, but also difficult to fertilize is bad," said Pascal Gagneux . lead author of the study, said.

Uterine receptor cells contribute to sperm survival

In the study, however, they found the marks of a connection between the sperm and the cells lining the uterus. Uterine cells release a receptor that can detect a glycan molecule on the surface of the sperm. The researchers believe that the interaction could possibly regulate the woman's immune response, helping sperm survive through pre-fertilization events, such as leukocyte reaction.

Before reaching the egg, sperm must survive thanks to the female immune system. An interaction between glycans (branched structures) on the surface of the sperm and receptors located on endometrial cells can act as a "secret handshake," which helps the sperm survive – or can help the system immune to target defective sperm. Credit: American Society of Biochemistry and Molecular Biology

The leukocyte response is a pre-fertilization event in which sperm can stimulate an immune response. This promotes the movement of leukocytes circulating in the uterus to kill or destroy most sperm.

The attack of the immune system destroys most of the spermatozoa of the sperm, which reduces the number to a few hundred that can penetrate the fallopian tubes. The answer is how the body prevents polyspermia, a condition in which an egg is fertilized by more than one sperm.

Sialic acid binding receptors contribute to sperm survival

However, glycoconjugates cover the surface of the sperm. These include the sialic acids that are predominant on the surface of the sperm, where they cap numerous chains of glycans and control the movements of sperm through cervical mucus, sperm capacitation and the formation of an oviductal reservoir of sperm. In addition, the immune system uses sialic acid to differentiate human cells from foreign invaders.

The researchers initially predicted that glycan might be involved in neutrophil interactions, but after evaluation, they found that neutrophils could not distinguish sperm with or without sialic acid.

Researchers used in vitro interactions between spermatozoa and neutrophils, as well as binding badays between spermatozoa and recombinant Siglec-Fc chimeric proteins to quantify interactions.

In addition, the researchers examined whether sialic acid binding receptors, called siglecs, are expressed on the human uterus or on mouse models, which can trigger leukocyte reaction.

They also found that when badyzing siglecs on endometrial cells, the endometrial receptors can bind to the entire sperm. Binding can help sperm dampen the immune response. The uterus can also perform this operation to separate the defective sperm and, at the same time, the immune system can recognize the sperm as 'self', thereby reducing inflammation. On the other hand, if sperm is perceived as an invader, it can cause inflammation.

"Surprisingly less sialylated, sperm capacitances did not increase neutrophil activation in vitro. However, we have observed the expression of several Siglecs on the endometrium and the fact that these receptors interact with sialylated sperm, "the researchers wrote.

"Our results indicate that spermatozoa sperm acids can interact with endometrial Siglecs and that these interactions facilitate sperm survival in the face of women's immunity," they added.

The researchers encourage further studies on the region. It is important to know more about the direct interaction between the sperm and the uterine cells, in addition to looking at the sperm interacting with certain purified proteins.

They believe that the study can pave the way for further research to work on a poorly understood field, especially with regard to reproduction, a very delicate concept.

"The fact that there is (also) this current immune game is completely fascinating," added Gagneux.