Rat Mammary Extracellular Matrix Composition and Response to Ibuprofen Treatment During Postpartum Involution by Differential GeLC–MS/MS Analysis

Breast cancer patients diagnosed within five years following
pregnancy
have increased metastasis and decreased survival. A hallmark of postpartum
biology that may contribute to this poor prognosis is mammary gland
involution, involving massive epithelial cell death and dramatic stromal
remodeling. Previous studies show pro-tumorigenic properties of extracellular
matrix (ECM) isolated from rodent mammary glands undergoing postpartum
involution. More recent work demonstrates systemic ibuprofen treatment
during involution decreases its tumor-promotional nature. Utilizing
a proteomics approach, we identified relative differences in the composition
of mammary ECM isolated from nulliparous rats and those undergoing
postpartum involution, with and without ibuprofen treatment. GeLC–MS/MS
experiments resulted in 20327 peptide identifications that mapped
to 884 proteins with a <0.02% false discovery rate. Label-free
quantification yielded several ECM differences between nulliparous
and involuting glands related to collagen-fiber organization, cell
motility and attachment, and cytokine regulation. Increases in known
pro-tumorigenic ECM proteins osteopontin, tenascin-C, and laminin-α1
and pro-inflammatory proteins STAT3 and CD68 further identify candidate
mediators of breast cancer progression specific to the involution
window. With postpartum ibuprofen treatment, decreases in tenascin-C
and three laminin chains were revealed. Our data suggest novel ECM
mediators of breast cancer progression and demonstrate a protective
influence of ibuprofen on mammary ECM composition.