Epigenetic regulation of collagen in the mare's placenta: putative relationship with maternal age

Placental plasticity influences fetal development, pregnancy success, and foal growth. Older fertile mares deliver heavier foals and placentas, with increased collagen deposition. In humans, epigenetics regulates placental development and function. Epigenetics, through DNA methylation, also modulates endometrial fibrosis. As such, we hypothesized that as mares get older, collagen deposition in the placenta might be epigenetically modulated. This study assessed if transcription of collagen genes in the equine placenta was epigenetically modulated through DNA methyltransferases (DNMTs), and affected by aging. Immediately after foaling, samples from different chorioallantoic areas (gravid horn, non-gravid horn, and body) were collected from young (n=10; 4-6 years) and older mares (n=10; 12-18 years). Gene transcription of collagen type 1 (COL1A1), collagen type 3 (COL3A1), and DNA methyltransferases (DNMT1, DNMT3A and DNMT3B) was determined (qRT-PCR). Unpaired T-test and Mann-Whitney test were used with statistical significance set a p <0.05. In older mares, COL1A1 mRNA levels were higher in the gravid than in the non-gravid horn (p<0.05), and also upregulated in comparison to young mares’ placentas (p<0.05). In young mares, these transcripts were increased in the placenta body in comparison to the gravid (p<0.05) and non-gravid horns (p<0.01). In older mares, COL3A1 transcriptionwas higher in gravid and non-gravid horns, with respect to the same placenta regions in young mares (p<0.05). In older mares, DNMT1 mRNA expression in the body was lower than in younger mares (p<0.05). For all placentas, DNMT1 transcripts in the non-gravid horn were lowest, compared to the gravid horn (p<0.01) and body (p<0.001). In young mares, DNMT1 mRNA expression in the body was also higher than in the gravid horn (p<0.05). With mares aging, there was a downregulation of DNMT3A transcripts in gravid and non-gravid placenta horns, compared to young mares’ placentas (p< 0.05). In older mares, its levels were lowest in the gravid horn, compared to the non-gravid horn (p<0.05) and body (p<0.01). Similarly, in older mares’ placentas, DNMT3B transcripts were downregulated in the gravid horn (p<0.05) and placenta body (p<0.001), compared to young mares. DNMT3B mRNA levels were lowest in the non-gravid horn, both in young mares, in comparison to placenta body (p<0.01) and in older mares, with respect to the gravid horn and body (p<0.01). Considering mares aging, hypomethylation indicated by decreased DNMTs transcripts, in parallel with upregulation of collagen gene expression in gravid and non-gravid horns, may suggest epigenetic involvement on placental plasticity. However, further research is needed to unravel the intricacies of epigenetic modulation of collagen in equine placentas.