干擾素-γ與腫瘤壞死因子-α對乳腺構形及功能的影響

乳腺的發育主要是在出生後，其功能在於合成乳汁以哺育新生兒。泌乳能力依靠乳腺正確的發育，這是由許多荷爾蒙和生長因子所調控。近年來發現免疫系統也參與其中，例如細胞激素。第二型輔助型 T 細胞（T helper 2, Th2）的細胞激素—介白素（interleukin, IL）-4 與介白素-13 能促進懷孕時期乳腺的腺泡生成（alveologenesis），而第一型輔助型 T 細胞（Th1）分泌之干擾素-γ（interferon-γ, IFN-γ）則是會抑制青春期乳腺乳管的延伸與分支。由於感染或發炎時體內環境會偏向Th1，即干擾素-γ和腫瘤壞死因子-α（tumor necrosis factor-α, TNF-α）的表現量增加，我們推測這可能會阻礙乳腺的發育，進而影響到之後的泌乳功能。在本篇研究，我們以初代小鼠乳腺上皮細胞進行體外三維細胞培養，發現干擾素-γ和腫瘤壞死因子-α的共同刺激會抑制泌乳激素所誘發 STAT5 酪胺酸磷酸化及乙型酪蛋白（β-casein）的表現。乙型酪蛋白是一種乳蛋白，其表現量常被用來反應乳汁產量及乳腺細胞的分化。這些細胞激素還導致乳腺腺泡結構改變，形成不具內腔或內腔變小、細胞排列紊亂。此外，經干擾素-γ和腫瘤壞死因子-α刺激後，有些細胞的形狀由立方形（cuboidal）變為柱形（columnar）。由於細胞增生與死亡皆可調控乳腺腺泡內腔形成，我們檢測了干擾素-γ和腫瘤壞死因子-α對細胞增生以及死亡的影響。結果顯示，細胞激素刺激後對細胞增生並無明顯改變，細胞死亡則只有些許的增高。干擾素-γ和腫瘤壞死因子-α共同刺激誘導 iNOS(inducible nitric oxide synthase, iNOS)的表現，而抑制 iNOS 則稍微改善了乳腺腺泡的形態及乙型酪蛋白的表現。綜上所述，在干擾素-γ和腫瘤壞死因子-α共同刺激下，會抑制乙型酪蛋白的表現及改變乳腺腺泡構形，而其誘導的iNOS 可能是原因之一。

Mammary gland development occurs primarily after birth, and its main function is to synthesize milk to feed the newborn. Proper lactation depends on the correct development of the mammary gland, which is regulated by many hormones and growth factors. Recent studies reveal that the immune system is also involved, such as cytokines. The T helper (Th)-2 cytokines, interleukin (IL)-4 and IL-13, promote alveologenesis during pregnancy, while interferon (IFN)-γ secreted by Th1 cells inhibits ductal growth and branching during puberty. Since infection or inflammation would lead to a Th1 milieu, that is, levels of interferon- and tumor necrosis factor (TNF)-α is increased, we speculate that this may hinder the development of the mammary gland, which in turn affects subsequent lactation. In this study, We use 3D cultures of primary mouse mammary epithelial cells to explore the effects of IFN-γ and TNF-α on structure and function of mammary glands. Our results showed that combined treatment with IFN-γ and TNF-α inhibited prolactin-induced STAT5 tyrosine phosphorylation and β-casein expression. β-casein is a milk protein whose expression is often used to reflect milk production and cell differentiation. These cytokines also altered structure of mammary acini, resulting in formation of no lumens or smaller lumens, as well as disordered cell arrangement. In addition, the shape of some cells changed from cuboidal to columnar. Since both cell proliferation and cell death regulate lumen formation, we examined the effect of IFN-γ and TNF-α on these events. Cotreatment with these cytokines did not affect cell proliferation, and slightly increased cell death.Following IFN-γ/TNF-α stimulation iNOS (inducible nitric oxide synthase, iNOS) expression was induced, and inhibition of iNOS moderatly improved mammary acinar morphology and β-casein expression. In summary, co-stimulation of IFN-γ/TNF-α inhibits β-casein expression and influences acinar morphology, and its induced iNOS may play a part in it.