Involvement of Growth Factors in the Regulation of Pubertal Mammary Growth in Cattle

Abstract

Pubertal mammary growth in heifers is dependent on interactions of many hormones and growth factors of which some are stimulatory while others are inhibitory. Although estrogen and growth hormone (GH) are of primary importance, more recent studies have suggested a role for both systemic and mammary tissue-specific growth factors. Growth factors may act as mediators of estrogen and GH or through specific effects of their own. These growth factors include insulin (INS), IGFs (IGF-I and IGF-II), epidermal growth factor (EGF), FGFs (FGF-1 and FGF-2), TGFs (TGF-alpha and TGF-beta's, amphiregulin (AR), platelets derived growth factor (PDGF), and mammary derived growth factor-1 (MDGF-1). Using mammary epithelial cells derived from prepubertal heifers and cultured in three-dimensional collagen gels as an in vitro model, we have investigated the mitogenic effects of a number of different growth factors (IGF-I, des(1-3) IGF-I, IGF-II, INS, EGF, TGF-alpha, AR, FGF-1, FGF-2, and TGF-beta 1). As expected, IGF-I, des(1-3)IGF-I, IGF-II and INS all stimulated proliferation of mammary cells with des(1-3)IGF-I being the most potent and INS the least potent. The mitogenic effect of IGF-I could be inhibited by both IGFBP-2 and IGFBP-3 showing that these binding proteins modulate the bioactivity of IGF-I in the mammary gland at the cellular level. Regulation of IGF availability by IGFBPs in the extracellular environment therefore is critical for IGF action in the mammary gland. Proliferation of mammary epithelial cells was also stimulated by growth factors of the EGF family, i.e. EGF, TGF-alpha and AR, however, not as much as growth factors from the IGF family. Members of the fibroblast growth factor family showed various mitogenic activities. FGF-1 stimulated DNA synthesis while FGF-2 in concentrations above 10 ng/ml inhibited DNA synthesis. TGF-beta 1 at very low concentrations stimulated proliferation slightly whereas higher concentrations strongly inhibited proliferation of mammary epithelial cells and inhibited mitogenesis induced by growth factors of both the EGF- and IGF family. This shows that TGF-beta 1 is a very potent regulator of pubertal mammary growth.

Regulation of mammary parenchymal growth by the fat pad in prepubertal dairy heifers: role of inflammation-related proteins

“…TGFb1 has been shown to inhibit bovine mammary epithelial cell proliferation (Woodward et al 1995, Purup et al 2000a.…”

“…4). We also measured TGFb1 expression because it is increased in the serum of rapidly growing heifers and has been shown to inhibit MAC-T and pMEC proliferation (Woodward et al 1995, Purup et al 2000a. TGFb1 expression was not affected by development or nutrition (Fig.…”

“…TGFb1 reduces serum-stimulated proliferation of bovine mammary epithelial cells (Woodward et al 1995, Purup et al 2000a. MCP-1 is a chemoattractant molecule that recruits monocytes to adipose tissue (Chen et al 2005, Kanda et al 2006.…”

Cell-based models to test the effects of milk-derived bioactives

“…This study shows the importance of developing models with polarised mammary epithelial cells and that BME-UV1 may be a good model for studying, for example, developmental processes of the bovine mammary gland in vitro. Primary cells of the bovine mammary gland have also been used as models including both organoids, explants and epithelial cells for studies of effects of growth factors, steroids, lactoferrin, retinoids, cytokines, biogenic amines, mammary extracts, and endpoint parameters such as mitogenic activity and gene expression have been measured Bauman, 1999 andWeber et al, 1999;Akers et al, 2000;Ellis et al, 2000;Purup et al, 2000 andWeng et al, 2005;Thorn et al, 2006 andErnens et al, 2007;Fusi et al, 2008;Swanson et al, 2009;Wang and Baumrucker, 2010). Both primary mammary cells and cell lines of human and rodent origin have been used to study effects of milk-derived bioactives such as CLA and phytoestrogens.…”

“…Several studies have shown that this this model is a very sensitive screening model for milk-derived bioactives (Norup et al, 1997;Weber et al, 1997 and2000;Purup et al, 1999Purup et al, , 2000Purup et al, and 2002Ellis et al, 2000;Lametsch et al, 2000;Sejrsen et al, 2000;Hansen et al, 2003;Thorn et al, 2006;Fusi et al, 2008). Groups of mammary epithelial cells are isolated from parenchymal tissue by enzymatic treatment and precipitation and these isolated organoids are then cultured in collagen gels, allowing the cells to proliferate in three dimensions.…”