Th1 Cytokines Inhibit Acinar Morphogenesis and Milk Protein Expression in 3D Mammary Cultures

Background: The principal function of mammary glands is to produce milk to nourish the newborn. Optimal lactation is controlled by various hormones, growth factors, and cytokines. Objectives: Using 3D cultures of primary mouse mammary epithelial cells, we explored the effects of T helper (Th)1 cytokines, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α on the structure and function of mammary cells as well as the underlying mechanism. Methods: Three-dimensional cultures of mammary cells were treated with IFN-γ/TNF-α, and milk protein expression and acinar structures were analyzed by immunoblotting and immunofluorescence microscopy. Results: Our results revealed that combined treatment with IFN-γ and TNF-α inhibits prolactin-induced STAT5 tyrosine phosphorylation and β-casein expression. These cytokines also disrupted the structure of mammary acini, resulting in smaller or no lumens, disordered cell arrangements, and multilayered cells in certain regions. Additionally, some cells became elongated rather than maintaining their usual cube-like shape. Since cell proliferation and death can modulate the structural organization of acini, we examined the influences of IFN-γ and TNF-α on these events. Combined cytokine treatment moderately increased cell proliferation and cell death. Notably, stimulation with IFN-γ and TNF-α induced the expression of inducible nitric oxide synthase (iNOS), and the inhibition of iNOS partially restored acinar morphology and β-casein expression, revealing a novel mechanism for cytokine-induced acinar disruption. Conclusions: When a Th1 cytokine milieu is dominant, such as during inflammation and infection, IFN-γ and TNF-α might cause mammary gland ductal occlusion and lactation insufficiency.