Age-related and white adipose tissue depot-specific changes of Ehd2 and Glut4 protein expression in growth hormone receptor-null mice

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 649-677-Adipocyte Biology
Basic
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-675
Han Zhang*1, Lucila Sackmann-Sala1, Darlene E Berryman1, Ellen Richardson Lubbers1, Elahu Sustarsic Gosney2, Edward Owen List1 and John Joseph Kopchick1
1Ohio University, Athens, OH, 2Ohio Univ, Athens, OH
While adipose was once considered a simple triglyceride storage organ, it is now recognized as an active, dynamic endocrine organ, which contributes to whole body homeostasis.  Growth hormone receptor-null (GHR-/-) mice, which lack functional GHRs, are dwarf, insulin sensitive and long-lived in spite of marked obesity. Interestingly, their adiposity is not uniform, with preferential enlargement of the subcutaneous white adipose tissue (WAT) depot. Previous studies in our laboratory have examined age, depot and genotype differences in the proteome from WAT in GHR-/- mice and their littermate controls at 12- and 24-months of age. These proteomic studies identified differences in the levels of several proteins as a function of age and genotype.  One of the proteins identified in this study with unique genotype and depot-specific changes was C-terminal Eps15 homology domain protein 2 (Ehd2).   Specifically, Ehd2 was shown to be increased in GHR-/- mice. Additionally, Ehd2 showed a significant interaction of age x depot, with inguinal, retroperitoneal and epididymal WAT experiencing subtle increases with age. Ehd2 is associated with cytoskeletal rearrangements during endocytosis. Since Ehd2 has been shown to regulate GLUT4 internalization from the cell membrane to endosomes in cultured adipocytes, the alterations of these two proteins could be important in establishing higher insulin sensitivity in GHR-/- than WT mice. In the current study, we attempted to confirm proteomic data by western blotting for Ehd2 as well as determine the levels of Glut4 in epididymal and subcutaneous WAT of 6-, 12-, and 24-month-old GHR-/- mice relative to littermate controls. Western blot data were not consistent with proteomic analyses, particularly in the subcutaneous depot.  These results suggest that specific isoforms, which would not be detected via western blotting, may be important for the previously observed proteomic results and ‘hints’ that identification of proteins by mass spectrometry is  more rigorous than western blotting for the identification of protein isoforms. Collectively, these data may help clarify the contribution of these two proteins in the modification of pathways relevant to insulin sensitivity in WAT. This study also provides insight into factors that could contribute to the well-established preferential enlargement of the subcutaneous depot in GHR-/- mice as well as factors that could potentially impact aging.

Nothing to Disclose: HZ, LS, DEB, ERL, ESG, EOL, JJK

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: This work was supported in part by the State of Ohio’s Eminent Scholar Program that includes a gift from Milton and Lawrence Goll (JK); NIH Grants DK075436 (JK), AG019899 (JK), and 1P01AG031736 (JK, DB, EL); the Diabetes Institute at Ohio Universtiy (LS, DB, EL); and the BioMolecular Innovation and Technology Partnership (LS) at Ohio University; and AMVETS (JK,RM, CV, EL). The authors have no conflict of interest to declare.