Spatial Proteomics of the Normal Breast Collagen Stroma: Links to Density and Body Mass Index

Collagen breast stroma
can become a breast cancer risk
factor,
yet proteomic regulation of normal breast stroma remains poorly defined.
This study evaluates the spatial regulation of the collagen proteome
from normal breast tissue. Normal breast tissue sections from the
Susan G. Komen tissue bank were used (n = 40), with
data including genetic ancestry (n = 20 African ancestry; n = 20 European ancestry), body-mass-index (BMI), age, and
mammogram density by the Breast Imaging Reporting and Data System
(BI-RADS). 10-plex cell marker staining showed CD44 and COL1A1 markers
modulated with BMI. Collagen fiber widths by second harmonic generation
microscopy contrasted in BMI categories by genetic ancestry. Targeted
extracellular matrix proteomics mass spectrometry imaging showed the
collagen alpha-1(I) chain proteome was spatially heterogeneous across
the normal breast microenvironment with site-specific post-translational
modification of proline hydroxylation. Signatures computationally
extracted from stroma-rich regions reported that 47 collagen peptides
distinguished BI-RADS categories (area under the receiver operating
curve >0.7; p-value >0.05). Multivariate modeling
of collagen peptides, fiber metrics, and clinical features supported
a strong positive association with BMI as a determinant of collagen
alterations in the normal breast. This study provides a foundation
for larger studies investigating the clinical value of spatial collagen
proteome alterations in human breast.