98 Interleukin-11 supplementation alters the composition of in vitro-produced bovine blastocysts

Inner cell mass (ICM) is an indicator of bovine blastocyst quality. Interleukin-6 is an embryokine that increases ICM cell numbers in in vitro-produced (IVP) bovine blastocysts. Receptors for other IL6-family members, including the interluekin-11 receptor, are expressed in the bovine embryo, but their specific role in early embryonic development and cell differentiation is not well understood. This work determined whether IL11 supplementation influences IVP embryo development and ICM and trophectoderm (TE) cell numbers. Cumulus–oocyte complexes were harvested from bovine ovaries and were then matured and fertilized using pooled Holstein semen. Presumptive zygotes were cultured in 45-μL drops of SOF-BE1 (25–31 embryos/drop; 2 drops/treatment; five replicate studies). Recombinant human IL11 (rhIL11) was supplemented beginning on Day 5 of development at 25, 50, or 100 ng mL⁻¹ or a carrier only (control; SOF with 1% [wt/vol] BSA). Blastocyst development was evaluated on Days 7 and 8. A subset of Day 8 blastocysts (five per treatment; four replicates) were fixed and processed for immunofluorescence staining of caudal homobox type 2 (CDX2; TE marker) and DNA (DAPI). Statistical analyses were completed by least-squares ANOVA using a generalized linear model (PROC GLM) in SAS. None of the IL11 treatments influenced blastocyst development at Day 7, but the 25 ng mL⁻¹ treatment tended to increase both blastocyst development and expansion rates on Day 8 (P < 0.1). Total cell number was not affected by rhIL11 supplementation. Each IL11 treatment level increased ICM cell numbers (P ≤ 0.01; control, 22.8 ± 3.4; treatment avg., 36.9 ± 3.4) and decreased TE numbers (P ≤ 0.05; control, 87.05 ± 5.5; treatment avg., 66 ± 5.5). The ICM:TE ratio was greater across all IL11 treatments (P ≤ 0.05; control, 0.33 ± 0.07; treatment avg., 0.65 ± 0.07). In summary, rhIL11 supplementation had limited effects on blastocyst development but influenced the cellular composition of blastocysts. Further work is needed to explore whether IL11 may shift cell differentiation in favor of ICM development or promote ICM development and diminish TE development as the blastocyst is forming. Additionally, more research is needed to determine how IL11 supplementation affects embryo development past Day 8 and what its role is in maintaining pregnancies after transfer.

Funding for this work was provided by USDA-NIFA (2021-67015-34485).