(237d) Quantifying the Effects of Elevated Hydrostatic Pressure on the Barrier Function of Mammary Epithelial Cells

The onset of pregnancy in mammals begets dramatic changes in the mammary gland to prepare for breastmilk production. Tight junctions, intercellular junctional structures that regulate paracellular transport, are crucial for regulating pregnancy-induced morphogenesis in the mammary gland. Strong tight junctions with a high “barrier function” prevent milk from leaking out of the lactating gland into the surrounding interstitium, and weak tight junctions with a reduced barrier function coincide with involution (shrinkage) of the mammary gland during weaning. Although it is known that hydrostatic pressure exerted by accumulated milk helps to weaken tight junctions during involution, the exact mechanism is unclear. To identify how pressure regulates tight junctions, we custom-built a novel cell culture system to expose mammary epithelial cells to different pressures, up to 1.5 kPa, on their apical (luminal) sides. After exposure to pressure for 6 and 24 h, we observed significant decreases in transepithelial electrical resistance (TEER), a measure of barrier function, for pressures greater than 1 kPa (Figure). Additionally, we found that exposure to pressure decreases the expression of E-Cadherin at intercellular boundaries. Lastly, we found that exposure to pressure has no apparent effect on either cell proliferation or death. Ultimately, these findings may have implications for better understanding mechanisms underlying complications related to breastfeeding, such as mastitis.