Dairy heifers with gastrointestinal nematodes have reduced growth rates, and delayed age at puberty and milk production onset related to late mammary gland development. IGF1 and Notch signaling systems are important in this process, and an altered profile of serum IGF1 has been associated with the detrimental effect of the nematodes on parenchymal development. In this context, we aimed to study the molecular mechanisms involved in bovine mammary gland development around pre and postpuberty, focusing on proliferative and angiogenic processes that involve the Notch and IGF1 pathways. We used mammary tissue samples from pre and pubertal heifers, treated or untreated with anthelmintics, and MAC-T bovine mammary epithelial cells in vitro. Anthelminthic treatment effectively lowered EPG in feces. Mammary glands from treated heifers had increased proliferation rate (measured by PCNA) and angiogenic marker expression (VEGF and CD34), as well as increased αSMA area compared to age-matched control parasitized heifers. These changes were preceded by increased expression of Notch targets at 20 wk of age (HES1, HEY2, and HEY1), indicating a possible interaction. Similarly, IGF1R expression was increased at 30 weeks of age. To study the crosstalk between systems, bovine MAC-T cells were treated with DAPT (50 μM) to inhibit Notch signaling. DAPT decreased the proliferation of cells as evidenced by a decrease in PCNA, pERK, CYCYLIN D1; and the wound healing capacity of HMEC cells was impaired in the presence of the supernatants of DAPT-treated cells. Furthermore, DAPT decreased IGF1 and increased IGF1R mRNA levels in MAC-T cells. On the other hand, cells treated with 10 ng/mL IGF1 Increased their proliferation (MTS assay), and induced a strong tendency to increase Notch target genes (HEY1, and HES1). Furthermore, IGF1 treatment tampered the decrease in the proliferation rate induced by DAPT. Finally, a positive correlation between the IGF1R and Notch target genes (HEY1, and HES1) further suggested a relation between these two signaling systems in the bovine mammary gland. In conclusion, pubertal delay related to parasitosis is counteracted by anthelminthic treatments, which increase serum IGF1, mammary cell proliferation, and angiogenesis. We postulate the Notch pathway, mainly through the HEY1 target gene, which is modulated by the IGF1 system, may regulate both proliferative and angiogenic processes favoring normal development of the bovine mammary gland during puberty. In addition, we demonstrate that the interaction between the Notch and the IGF1 pathways may affect cell proliferation.
