Allogenic mesenchymal stem cell-conditioned medium does not affect sperm parameters and mitigates early endometrial inflammatory responses in mares.

The study investigated the impact of mesenchymal stem-cell conditioned medium (MSC-CM) on horse sperm parameters and early endometrial inflammation. It found that adding MSC-CM to semen does not affect sperm parameters, but it does decrease early inflammation in the endometrium of mares post-insemination.

Research Methodology

• This study carried out two experiments. The first one examined the effect of MSC-CM on sperm kinetics and plasma membrane integrity. This was done by taking two ejaculates from ten stallions, extending it to 50 million sperm/mL using a milk-based extender, and then adding different volumes of MSC-CM. The sperm parameters were then evaluated immediately (T0) and 2 hours post-incubation at 37 °C (T2).
• The second experiment involved mares that either showed resistance (n = 13) or susceptibility (n = 7) to endometritis. These mares were inseminated with fresh semen 24 hours post-induction of ovulation in two (Control and CM-1) and three cycles (Control, CM-1, and CM-2). In the control, there was no pharmacological intervention. For CM-1, the semen insemination dose was supplemented in a ratio of 3:4 (v:v, MSC-CM: semen). For CM-2, 30 mL of MSC-CM was infused into the uterus 24 hours before insemination. Endometrial cytology and uterine fluid were collected to assess the number of PMNs and concentrations of interleukins IL6, IL10, and TNFα. Pregnancy status was diagnosed 14 days after ovulation.

Key Findings

• The addition of MSC-CM to semen did not have an impact on sperm parameters at T0 and T2. It did, however, lead to a reduction in the number of PMNs (neutrophils) at 6 hours post-insemination in mares resistant to endometritis.
• In mares susceptible to endometritis, the number of PMNs at 6 and 24 hours post-insemination, as well as intrauterine fluid accumulation, were reduced in both treated cycles (CM-1 and CM-2).
• Furthermore, MSC-CM downregulated IL6 and upregulated IL10 concentrations in the uterus of susceptible mares after insemination. This is indicative of a decrease in inflammation due to an increase in anti-inflammatory cytokines (IL10) and a decrease in pro-inflammatory cytokines (IL6).
• There were no differences in fertility rates among groups both in resistant (Control, 77%, 10/13; CM-1, 62%, 8/13) and susceptible mares (Control, 42.8%, 3/7; CM-1, 57.1%, 4/7; CM-2, 85.7%. 6/7).

Summary

• In conclusion, the study found that MSC-CM does not interfere with sperm parameters when mixed with diluted semen. It does, however, reduce post-insemination inflammatory responses in mares, which is beneficial given that inflammation is a common problem in horses and can impact fertility. The study provides evidence that supports the use of MSC-CM as a potential anti-inflammatory treatment for mares, without impacting fertility.