Tissue inhibitors of metalloproteinases (TIMPS) in mammary gland morphogenesis, differentiation, and apoptosis.

摘要

During the maturation of the mammary gland, mammary epithelial cells (mecs) exhibit many characteristics most often reserved for embryonic cells. Although not pluripotent, mecs have the capacity to repeatedly undergo branching morphogenesis, differentiation and/or apoptosis during the life of the female. These characteristics are not cell autonomous, but instead often involve reciprocal information exchanged between mecs and the extracellular matrix (ECM) on which they reside. We hypothesized that factors that can maintain ECM integrity, such as the four member family of tissue inhibitors of metalloproteinases (TIMPs), will influence mec morphogenesis, differentiation and/or apoptosis.; Our initial efforts focused on the generation and characterization of transgenic mice with mammary gland downregulation of TIMP-1. Transgenics displayed augmentation of both mammary ductal elongation/branching concomitant with amplified epithelial proliferation and excessive laminin degradation. Conversely, through biochemical manipulation, upregulation of mammary gland TIMP-1 inhibited ductal elongation and mec proliferation. These results indicate that TIMP-1 modulated mec proliferation and ECM integrity, which ultimately affected branching morphogenesis.; Determining the extent of in vivo mec differentiation in response to hormones is generally performed via manipulations of the endocrine system. However, we undertook a unique approach entailing examination of the mec response to physiological levels of hormones. We showed that morphological differentiation, mec proliferation and apoptosis were positively correlated with circulating progesterone levels, but not 17-β-estradiol. Furthermore, TIMP-3, -4, matrix metalloproteinase (MMPs) -9, -13 mRNAs, and ECM remodeling in the mammary gland exhibited regulation that was estrous stage-dependent. Therefore, the mammary gland response to systemic hormones is precisely controlled at the level of differentiation, cellular turnover, TIMP/MMP gene expression and ECM remodeling.; Extensive mec apoptosis occurs during postlactational involution. TIMP-3 deficient mice were induced to undergo mammary gland involution to assess the function of this gene during physiological apoptosis. TIMP-3 deficient females exhibited rapid mammary gland involution, extensive unscheduled epithelial apoptosis, early loss of β-casein expression, and inappropriate MMP-2 activation and fibronectin fragmentation. Importantly, restoration of lactation, after 2 days of involution, was inefficient in TIMP-3 deficient mice. These findings indicate that TIMP-3 is necessary for determining the kinetics of a process that is inherent to all mammalian species.