Partner selection ultimately happens in the woman’s reproductive tract

Partner selection ultimately happens in the woman’s reproductive tract

The female reproductive tract has the final say in human mate choice, according to new research from the University of Eastern Finland.

Achieving pregnancy has been shown to be more likely between partners who carry dissimilar human leucocyte antigen (HLA) immune genes.

Accordingly, humans are expected to choose HLA dissimilar reproductive partners.

Earlier studies have demonstrated that HLA dissimilarity preferences are mediated either by body odours or facial preferences.

However, it has been unclear whether HLA-based mating preferences could occur after sexual intercourse in the female reproductive tract. Researchers at the University of Eastern Finland have now shown that the women’s reproductive tract is capable of mediating post-mating sexual selection (known as the “cryptic female choice”) towards the sperm of HLA dissimilar men.

This indicates that the ultimate mating bias towards genetically compatible partners occurs only after mating, at the gamete level.

The researchers conducted two experiments, where they activated sperm from multiple men with follicular fluid (the oocyte surrounding bioactive liquid) or cervical mucus from several different women.

Then they examined sperm motility and other functionally important physiological changes of sperm in all possible male-female combinations. All the participants were also genotyped for their Human Leucocyte Antigen (HLA) class I and II alleles.

In both studies, the results showed that the fertilisation capability and viability of sperm are strongly dependent on the male-female combination.

In other words, women’s reproductive secretions had a stronger effect on the performance of some males than others. Both datasets also showed that the sperm performance was better in HLA dissimilar male-female combinations than in HLA similar males and females.

Together, the results indicate that the fertilisation capability of sperm is dependent on the immunogenetic compatibility of the reproductive partners and that the fusion of the gametes may be a highly selective process.

“These findings can have important implications for a deeper understanding of sexual selection and the fertilisation process in humans and other mammals,” Associate Professor Jukka Kekäläinen from the University of Eastern Finland says.

“Since the gametes of some partners may be immunologically more compatible than others, our results may also open up novel possibilities for the development of more accurate infertility diagnostics,” Annalaura Jokiniemi, MSc, adds.

Source: https://www.sciencedaily.com/releases/2020/08/200819094748.htm

Read more: https://royalsocietypublishing.org/doi/10.1098/rspb.2020.1682


Sperm alterations caused by obesity are not detected in traditional tests

Sperm alterations caused by obesity are not detected in traditional tests

An analysis of sperm from men who were part of a couple whose partner was undergoing in-vitro fertilization (IVF) identified differences in samples between obese vs nonobese men. Specifically, there were differences in the levels of 27 proteins contained in the sperm.

Importantly, all 10 men in these infertile couples (5 obese men and 5 nonobese men) had clinically normal semen, lead study author Taylor Pini, PhD, a postdoctoral scientist at the Colorado Center for Reproductive Medicine, Lone Tree, Colorado said.

That is, the men all had normal sperm concentration, motility, morphology, and DNA fragmentation, which indicates that “these changes in obese men with no overt andrological diagnosis…suggest that traditional clinical semen assessments fail to detect important biochemical changes in spermatozoa which may compromise fertility,” the authors write.

The researchers identified 2034 sperm proteins, of which 24 were significantly less abundant and 3 were more abundant in the obese men than in the men with a healthy weight (P < .05 for both).

The sperm proteins that were less plentiful in the obese men are involved in oxidative stress, inflammation, protein translation, DNA damage repair, and sperm function, and those that were more plentiful are involved in oxidative stress.

“These results suggest that oxidative stress and inflammation are closely tied to reproductive dysfunction in obese men,” the researchers concluded.

These processes likely impact protein translation and folding during spermatogenesis, leading to poor sperm function and subfertility.

Pini noted that “a lot more emphasis has been placed on female as opposed to male obesity” in couples going for infertility work-up, “but I think it is worth considering on the male side as well.”

“It would be worth counseling patients, especially in the very early stages of trying to conceive, that overall health and particularly things like obesity are really worth considering prior to conception,” she emphasized.

The study was published online in the Journal of Assisted Reproduction and Genetics.

An estimated 38% of men of reproductive age (20 to 59 years) in the United States have obesity (body mass index [BMI] ≥30 kg/m2), Pini and colleagues note.

However, it is unclear how obesity may affect male fertility on a molecular level.

Previous studies of sperm proteins in obese men either used a less sensitive method (two-dimensional difference gel electrophoresis), or the more sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) but with a very small sample (3 men) including men with diabetes or smokers.

Pini and colleagues identified 5 obese men (BMI ≥ 30 kg/m2) and 5 non-obese men (BMI ≤ 25 kg/m2) seen at their reproductive medicine center who had clinically normal semen and did not smoke or have diabetes.

They collected semen samples from the men on the day of the oocyte retrieval in the men’s partners, and they used LC-MS/MS to determine the protein content of the sperm.

The control patients had a mean BMI of 24, and the obese patients had a mean BMI of 33. On average, the men in each group were 39 years old (range 33 to 46).

Obese and nonobese men had similar rates of average sperm concentration (88 x 106), total motility (62%), normal morphology (2.9%), and DNA fragmentation (3.3%).

Among the 27 proteins with altered abundance in obese vs normal-weight men, some were involved in oxidative stress (5), inflammation (2), protein translation (3), DNA damage repair (1), and sperm function (3).

The LC-MS/MS findings were confirmed for several proteins by qualitative immunofluorescence and a quantitative protein immunoassay.

“We have shown that obesity significantly impacts the human sperm proteome, potentially to the detriment of important spermatogenic processes and the function of mature spermatozoa,” the researchers report.

“These changes may be both symptoms of, and contributors to, the inflammation and oxidative stress associated with obesity, and may help to explain why obese men may have altered semen parameters, potentially leading to altered fertility.”

“While some of the problems created by paternal obesity may be overcome by assisted reproduction techniques, the swath of implications following fertilization remains to be rigorously investigated,” they note.

The authors conclude the study by writing that efforts should be directed toward the implementation of treatments to correct or limit the observed changes “when weight loss prior to conception is neither practical nor realistic.”

Read more: https://link.springer.com/article/10.1007/s10815-020-01707-8

Male fertility got no boost from zinc, folic acid in study

Male fertility got no boost from zinc, folic acid in study

A rigorous U.S. government-led study found that zinc and folic acid supplements don’t boost men’s fertility, despite claims that they do.

The mineral and the vitamin are important for sperm production and are found in many common foods. Previous studies on whether over-the-counter supplements might boost sperm health have had conflicting results.

There were a few small trials that showed a benefit, but we needed some definitive evidence that this would work,” said lead author Enrique Schisterman, a researcher at the National Institute of Child Health and Human Development. The study published in the Journal of the American Medical Association showed it didn’t.

Schisterman called the results disappointing. Supplements cost about $60 a month compared with tens of thousands of dollars many couples spend on invasive medical treatment for infertility.

People who go through fertility treatment are really, really desperate to find something that works,” he said.

The institute paid for the study, which involved almost 2,400 men planning fertility treatments with their partners at four U.S. clinics.

The researchers avoided using over-the-counter supplements, which aren’t strictly regulated and may contain ingredients other than those listed on the label. Instead they created tablets that combined 5 milligrams of folic acid, similar to previous studies, and 30 mgs of zinc, a lower dose than in some studies to avoid potential side effects.

Half the men studied swallowed one tablet daily for six months; the other men took dummy pills. Several semen tests were performed during the study.

Over 18 months of follow-up, 820 babies were born, about equal numbers in each group. Sperm quality also was similar in both groups.

Sperm DNA changes linked with infertility were slightly more common in the supplement users and those men had more digestive side effects, which have been linked previously with zinc pills.

Infertility affects at least 50 million couples worldwide. It’s usually defined as not being able to conceive after a year of trying. Male infertility including low sperm counts or poor-quality sperm contributes to about 1 in 3 cases. Research suggests sperm counts in western countries have been declining for decades, for unknown reasons.

Read more: https://jamanetwork.com/journals/jama/fullarticle/2758450?guestAccessKey=47179784-451b-4342-aadd-5f74ea3f79b1&utm_source=For_The_Media&utm_medium=referral&utm_campaign=ftm_links&utm_content=tfl&utm_term=010720

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