Kibrom Gebre-Eqziabher ACF Abstract FY12

"Exposure to hypergravity during pregnancy and early lactation alters abundance of cytoskeletal and extracellular matrix proteins in a rat model"

Conference Name: Annual Biomedical Research Conference for Minority Students

Kibrom Gebre-Egziabher 1, James Resau 2, Karen Plaut 3, Osman Patel 1

1 Department of Cell and Molecular Biology, GVSU, 1 Campus Dr, Allendale, MI 49401-9403, USA

2 Program for Biospecimen Science, Van Andel Institute, 333 Bostwick Ave N.E, Grand Rapids, MI 49503, USA

3 College of Agriculture, Purdue University, West Lafayette, IN 47907, USA

Exponential growth of the mammary gland and differentiation of secretory epithelium are most evident pre-partum. This dynamic epithelial differentiation and secretion is dependent on an integral cytoskeletal and extracellular support structure and modulated by changing hormones. Previous studies have revealed that there is a down-regulation of PRL receptor (PRLR) and reduced lipogenesis in the mammary gland of dams exposed to hypergravity (HG). It is known that intact cytoskeletal architecture is pivotal for PRLR-mediated signaling in the mammary gland. We hypothesize that the decreased PRLR-mediated signaling in HG exposed rats is associated with aberrant abundance levels of cytoskeletal and extracellular support proteins. Therefore, the objective of this study is to determine the effects of HG exposure from mid-pregnancy to early lactation on pre-partum /postpartum abundance of the cytoskeletal and extracellular components in the rat mammary gland. Pregnant rats were exposed to either twice the level of gravity (2g) (HG) or 1g (control) from days 11 to 20 of gestation (G20) through Postnatal days 1 (P1) and 3 (P3). On G20 (n=4/treatment), P1 (n=4/treatment) and P3 (n=4/treatment), mammary tissue was collected and processed for immunohistochemical quantification of alpha-smooth muscle actin, tubulin, cytokeratin and vimentin proteins. Four random low power (10X) micrographs/slide were taken and the antigen amount per lobule (n=3-7 lobules/micrograph) was measured using the Nuance spectral imaging software. The HG and control groups were compared using analysis of variance and a P-value of <0.05 was considered significant. At G20, significant amounts (Mean± SEM) of actin (p<0.001: 1.4 ± 0.09 vs 0.6 ± 0.09), tubulin (p<0.001: 5.0 ± 0.2 vs 3.4 ± 0.2), and vimentin (p<0.05: 2.7 ± 0.5 vs 1.0 ± 0.5) were detected in HG rats compared to control animals. Interestingly, the only observed change at P1 was an increase in vimentin (p<0.001: 4.5 ± 0.6 Vs 2.9 ± 0.5) in rats exposed to HG compared to controls. At P3, more quantities of actin (p<0.001: 2.0 ± 0.09 vs 1.2 ± 0.09), tubulin (p<0.001: 5.8 ± 0.2 vs 2.5 ± 0.2), vimentin (p<0.05: 13.5 ± 0.6 vs 8.1 ± 0.5), and cytokeratin (p<0.001: 0.6 ± 0.04 vs 0.4 ± 0.03) were detected in HG rats compared to controls. These results suggest that changes in quantity of cytoskeletal and extracellular support proteins contribute to the reduced postpartum mammary metabolic activity in rats exposed to chronic HG. (Supported by NASA NNA05CP91A)