Lower expression of colony-stimulating factor 2, an embryokine, in the endometrial epithelium of old cows

Context Infertility increases with age in various animals, including cows, owing to unknown mechanisms. The glandular and luminal epithelia of the bovine uterus synthesise and secrete colony-stimulating factor 2 (CSF2), which is a well-studied embryokine. We recently reported the possibility of fibrosis in the uteri of old cows. However, the relationship between CSF2 expression and fibrosis has not yet been clarified. Aims We tested the hypothesis that the endometrial epithelia of old cows have lower CSF2 expression compared to in heifers, and that myofibroblasts [alpha-smooth muscle actin (αSMA)-positive fibroblasts] increase near the epithelium of old cows. Methods We collected caruncle and intercaruncle samples from post-pubertal, growing, nulliparous heifers (n =6; 24.7±1.3months old) and old multiparous cows (n =6; 128.5±15.4months old). We analysed mRNA and protein expression, along with fluorescent immunohistochemistry for CSF2, anti-collagen type IV, anti-Müllerian hormone type 2 receptor, and anti-αSMA. Key results Quantitative reverse transcription polymerase chain reaction and western blot analysis revealed lower CSF2 expression in the caruncle and intercaruncle of old cows than in young heifers. Fluorescence microscopy using the same antibodies and anti-collagen type IV, anti-Müllerian hormone type 2 receptor, and anti-αSMA antibodies showed increased fibroblasts and αSMA signals near the epithelium of old cows compared to young heifers. Conclusion CSF2 expression was lower in endometrial epithelia of old cows compared to those in heifers, and myofibroblasts increased near the epithelia of old cows. Implications Lower CSF2 may play an important role in age-related infertility.