Mammary ECM composition and function are altered by reproductive state

Abstract

To address whether reproductive state alters mammary gland extracellular matrix (ECM) composition and function, ECM was isolated from nulliparous, pregnant, lactating, involuting, and regressed rat mammary glands. The ECM composition of fibronectin, tenascin, laminin, clusterin, and MMPs was found to vary dramatically with reproductive state. In 3-dimensional (3-D) culture, we identified novel effects of these endogenous mammary matrices on mammary epithelial cells. Specifically we found that (1) matrix isolated from nulliparous animals promoted the formation of epithelial ducts with bifurcation, (2) matrix isolated from mid-involuting mammary glands induced cell death, (3) matrix isolated from late-stage involuting glands restored glandular development, while (4) matrix isolated from parous animals restricted glandular morphogenesis. Our data were consistent with mammary gland ECM facilitating epithelial cell proliferation, differentiation, death, and glandular reorganization that occur during the pregnancy and involution cycle. Further, we show that the parous gland has persistent changes in ECM function. Cumulatively, our data demonstrated that the microenvironment of the normal adult mammary gland is highly plastic, which has important implications for mammary tumor cell progression and dormancy. These data also raised the possibility of targeting mammary matrix production with preventive or therapeutic interventions.

Alternatively Activated Macrophages and Collagen Remodeling Characterize the Postpartum Involuting Mammary Gland across Species

“…52 The number of CD68-positive cells was evaluated in the rat at day 6 postweaning (involution day 6), which corresponds to the peak of tissue remodeling during mammary involution. 21,49 Stromal associated CD68 levels were sixfold higher at involution day 6 compared with mammary glands from age-matched nulliparous rats ( Figure 1A). Similarly, the number of CSF-1R-positive cells was increased eightfold on involution day 6 when compared with nulliparous controls ( Figure 1B).…”

“…49 Briefly, 3% polyacrylamide (29:1) gels were prepared using 9.2 mmol/L calcium lactate, pH 6.8; 0.1% TEMED; and 0.07% ammonium persulfate only and pre-run for 1.5 hours at 100 volts with 50 mmol/L Tris, pH 6.6 lactic acid buffer in the cathode region and 0.1 mol/L lactic acid, pH 2.5 in the anode region with reversed electrodes. Mammary ECM samples from involution day 4 to 6 rats were prepared in 0.1 mol/L lactic acid, pH 2.5, and run for 2.5 hours at 70 volts with reversed electrodes.…”

The extracellular matrix in breast cancer predicts prognosis through composition, splicing, and crosslinking

“…Direct contact between stroma and non-malignant epithelia is not observed except during involution [50]. Breast cancers arising during pregnancy and involution tend to be highly aggressive and metastatic [51], suggesting that the collagen-1 rich stromal ECM, along with inflammatory environment observed in lactation and involution, could be pro-tumorigenic [52].…”

“…Furthermore, nonmalignant epithelial cells exposed to increased density of stromallike collagen I and associated increases in ECM biomechanics undergo transition between formation of normal structures and loss of cell structure and increased growth [35]. The microarchitecture of the fibrilar collagen network (typically collagen I) in the stroma is believed to play a major role in specifying both risk of BC and the stiffness of the stromal ECM [37,50,54,55], suggesting that stiff stroma could encourage tumor initiation or progression. Depending on species, age and testing method, breast interstitial ECM has been measured to have a modulus of 167731 Pa [35], 0.4 kPa [37] and 1.13 70.78 kPa [55], and the risk of developing BC has been linked to increases in total breast stiffness both clinically [54].…”

Mammary developmental fate and breast cancer risk

“…In addition, it is important to examine whether the stroma of parous animals supports proliferation of mammary epithelial cells in a quantitatively different manner than the stroma of AMVs. It has been demonstrated that the reproductive state does persistently alter mammary stroma extracellular matrix composition and function (Schedin et al 2004). …”