  Basement membranes (BMs) are thin layers of condensed extracellular matrix
proteins serving as permeability filters, cellular anchoring sites, and
barriers against cancer cell invasion. It is believed that their biomechanical
properties play a crucial role in determining cellular behavior and response,
especially in mechanically active tissues like breast glands. In spite of this,
so far relatively little attention has been dedicated to their analysis due to
the difficulty of isolating and handling such thin layers of material. Here, we
isolated basement membranes derived from MCF10A spheroids - 3D breast glands
model systems mimicking in-vitro the most relevant phenotypic characteristics
of human breast lobules - and characterized them by atomic force microscopy
(AFM), enhanced resolution confocal microscopy (LSM), and scanning electron
microscopy (SEM). By performing AFM height-clamp experiments, we obtained force
relaxation curves that offered the first biomechanical data on isolated breast
gland BMs. Based on LSM and SEM imaging data, we modeled the system as a
polymer network immersed in liquid and described it as a poroelastic material.
Finite Element (FE) simulations matching the experimental force relaxation
curves allowed for the first quantification of the bulk and shear moduli of the
membrane, as well as its water permeability. These results represent a first
step towards a deeper understanding of the mechanism of tensional homeostasis
regulating mammary gland activity, as well as its disruption during processes
of membrane breaching and metastatic invasion.
