Linoleic acid, but not cortisol, stimulates accumulation of casein by mouse mammary epithelial cells in serum-free collagen gel culture.

Abstract

A two-step culture system has been developed to analyze the role of hormones in casein accumulation by mammary epithelial cells obtained from adrenaiectomized and ovariectomized adult virgin mice. In the first step cells are grown inside collagen gel in medium containing insulin, epidermal growth factor (EGF), and linoleic acid for 9 days; these conditions stimulate very little casein accumulation. Following this growth phase the gels are released to float in medium containing insulin, prolactin, and linoleic acid. During this second phase the mammary cells will accumulate large amounts of casein, but only in the simultaneous presence of insulin, prolactin, and linoleic acid; in the absence of linoleic acid casein accumulation is greatly reduced. The casein accumulation is not dependent on the presenceofthe glucocorticoid cortisol and will occur in spite of the presence of the antiglucocorticoid agent RU 38 486. To determine if the response to cortisol observed in organ culture by other investigators might be mediated by stromal cells, epithelial cells were grown in collagen gel under fatty acid-free conditions and then cocultured with explants of mammary fat pads from adult virgin mice with or without mammary parenchyma. The cocultures were performed in fatty acid-free medium containing insulin and prolactin with or without cortisol. In the majority of experiments the mammary epithelial cells in the collagen gel accumulate more casein in the presence of cortisol than in its absence, irrespective of the presence of mammary parenchyma in the explant. Thus, mammary epithelial cells are directly dependent on insulin and prolactin for casein accumulation and indirectly dependent on cortisol by means of its effect on the stromal cells. This cortisol effect may be to cause release into the medium of linoleic acid or a metabolic product of linoleic acid from the stromal cells.Despite its long history, the study of the effects of hormones and growth factors on mammary epithelium in culture has not fully defined the roles of these substances in mammary differentiation (for review, see refs. 1 and 2). Extensive studies (3-10) in fragment organ culture using mammary tissue from either mouse or rat under defined, serum-free conditions demonstrated that insulin (5, 6), prolactin (3)(4)(5)(6)(7)(8)(9)(10), and a glucocorticoid, usually cortisol (7-10), were required for the accumulation of casein protein and mRNA. Whole gland organ culture studies (11-13) have substantiated this requirement for the three hormones.Fewer experiments to examine this requirement for glucocorticoid have been performed in cell culture, even though cell culture has become widely used to study differentiation in mammary epithelial cells. Casein accumulation and secretion in cell culture were demonstrated by Emerman et al. in 1977 (14) using cells obtained from midpregnant mice and cultured on top of collagen gel. Casein secretion in this system has been repeatedly shown to be dependent on the presence of insulin, prolactin, and glucocortic...

Phospholipids containing polyunsaturated fatty acyl groups are mitogenic for normal mouse mammary epithelial cells in serum-free primary cell culture.

“…Similarly, the proliferation of normal mammary epithelial cells in primary culture is not absolutely dependent upon exogenous lipids; nevertheless, these cells are highly responsive to linoleate and specific phospholipids. In addition, the hormonal requirements for the differentiation of mouse mammary epithelial cells in vitro can be modulated by linoleate (24). These findings lead us to suggest that these epithelial cells, which grow and differentiate within an adipose tissue matrix, may utilize exogenous fatty acids supplied by the surrounding adipose cells during mammogenesis (4,24).…”

The proliferation of mouse mammary epithelial cells in response to specific mitogens is modulated by the mammary fat pad in vitro

“…Siliconized lens paper has been widely used in whole mammary gland organ culture (Plaut et al, 1993) to permit the bidirectional diffusion of soluble factors between the culture medium and floated tissue. An alternative system (Levay-Young et al, 1987) incorporated a wire grid to support explants at the gas:medium interface. However, the potential for sedimentation of nonadherent cells from tissue explants onto the monolayer under study would likely confound cell growth assays.…”

Diverse and Active Roles for Adipocytes During Mammary Gland Growth and Function

“…In addition, several groups have reported that exogenous unsaturated fatty acids might influence lactogenesis. Whereas Nandi and colleagues found that β-casein synthesis by primary mammary epithelial cells was increased by linoleic acid in culture [ 103 ], a recent report identified the opposite effect in that both oleic and linoleic acids promoted the degradation of hormone-induced β-casein [ 104 ]. This latter finding may be explained by time-dependent changes in the response of mammary epithelial cells to these fatty acids in culture [ 105 ].…”