Examining the Impact of Growth Hormone on the Collagen Content of Adipose Tissue in Transgenic Mice A thesis presented to the faculty of the College of Health Sciences and Professions of Ohio University In partial fulfillment of the requirements for the degree Master of Science Lara A. Householder December 2013 © 2013 Lara A. Householder. All Rights Reserved. 2 This thesis titled Examining the Impact of Growth Hormone on the Collagen Content of Adipose Tissue in Transgenic Mice by LARA A. HOUSEHOLDER has been approved for the School of Applied Health Sciences and Wellness and the College of Health Sciences and Professions by Darlene E. Berryman Professor of Applied Health Sciences and Wellness Randy Leite Dean, College of Health Sciences and Professions 3 Abstract HOUSEHOLDER, LARA A., M.S., December 2013, Food and Nutrition Sciences Examining the Impact of Growth Hormone on the Collagen Content of Adipose Tissue of Bovine Growth Hormone Transgenic Mice Director of Thesis: Darlene E. Berryman Obesity is characterized by insulin resistance, inflammation, and pathologically accelerated white adipose tissue (WAT) remodeling. Although it has not yet been extensively studied, the extracellular matrix (ECM) of WAT may be linked with these key features of obesity. The ECM is the structural framework of WAT and is made primarily of collagen fibers. An excess of these collagen fibers, called fibrosis, has been observed in obese adipose tissue (AT). AT fibrosis is thought to contribute to the metabolic abnormalities and inflammation present in obese individuals. Growth hormone (GH) has been shown to increase collagen in other tissues and has been reported to impact AT in a depot specific manner. To date, no study has assessed the role of GH in AT ECM deposition. The use of mouse models with differing GH action may help characterize the role of ECM in adipose function/dysfunction. Bovine GH transgenic mice (bGH) are giant and lean with high serum levels of bGH, insulin-like growth factor 1 (IGF-1), and insulin, and have relatively short lifespans. This contradictory phenotype– unhealthy leanness–allows us to examine WAT fibrosis independent of normal adiposity and question whether the amount of ECM in the WAT is more influential to the health of an individual than the overall amount of WAT. Therefore, the purpose of this study was to evaluate measures of ECM deposition in bGH mouse AT. Six-month-old bGH and 4 littermate control mice were dissected and the adipose tissue samples from inguinal, epididymal, retroperitoneal, and mesenteric depots was processed for both histological and expression analysis. To determine the collagen content of WAT, samples were fixed and embedded in paraffin blocks and stained with picosirius red. When assessing overall collagen content, the bGH mice showed dramatic increases in ECM deposition when compared to controls, especially in the inguinal depot. A significant decrease in adipocyte size and number was also observed in bGH mice. However, when the expression of collagen genes Col1α1, Col3α1, Col4α1, Col5α1, and Col6α1 was examined through quantitative PCR analysis, no significant differences due to genotype were found. Therefore, we have established that GH increases the collagen content of WAT, but the mechanism is still undetermined. 5 Dedication For my grandparents, Jack and Ruth, for being who I want to be when I grow up, And for Jake, for loving and feeding me while I get there. 6 Acknowledgments Financially, this project was supported by a Student Enhancement Award, a CHSP Student Research and Scholarly Activity Presentation Award, a Graduate Student Senate Travel Award, and a Growth Hormone Research Society and the IGF Society Travel Award. This thesis would not exist without the contributions and support of so many. To everyone in the Kopchick Lab: thank you for your patience and generosity as I worked through my very first research project. I truly feel as though I’ve stumbled into the best gig around and I’m thankful for everyone who has been and is a part of it. Specifically, thank you to Katie Troike and Abigail Thaxton for their contributions to the collagen story; Adam Jara for PCR, ImageJ, and statistics guidance; Dr. Ed List and Kevin Funk for their essential role in providing me with samples to study; Ellen Lubbers for her immeasurable research assistance throughout; and to our peerless leader, Dr. John Kopchick, for setting the tone with his enthusiasm for research and for serving on my committee. Thank you to my darling husband for his support and patience while I struggled to find my way. I am so fortunate to have you as my partner. Last, but far from least, thank you to the best mentor I’ve ever had the pleasure of working with, Dr. Darlene Berryman. Without you, I would not have even thought to get a masters degree and I cannot express what your guidance and support has meant to me. Thank you for more than I could ever repay. 7 Table of Contents Page Abstract ............................................................................................................................... 3 Dedication ........................................................................................................................... 5 Acknowledgments ............................................................................................................... 6 List of Tables .................................................................................................................... 11 List of Figures ................................................................................................................... 12 Chapter 1: Introduction ..................................................................................................... 14 Obesity ...................................................................................................................... 14 Adipose Tissue. ......................................................................................................... 14 Adipose Tissue Fibrosis ............................................................................................ 16 Growth Hormone. ..................................................................................................... 17 Purpose and Significance of the Study ..................................................................... 18 Research Aims. ......................................................................................................... 19 Limitations and Delimitations ................................................................................... 20 Definitions. ................................................................................................................ 20 Chapter 2: Literature Review ............................................................................................ 23 Overview of Adipose Tissue ..................................................................................... 23 White Adipose Tissue and Brown Adipose Tissue. .................................................. 24 8 Adipose Tissue Depots ............................................................................................. 24 White Adipocytes. ..................................................................................................... 27 Other Cell Types in Adipose Tissue ......................................................................... 28 Obesity. ..................................................................................................................... 29 Introduction to Collagen ........................................................................................... 29 Collagen Structure . .................................................................................................. 31 Collagen Synthesis .................................................................................................... 33 Introduction to Collagen in White Adipose Tissue. .................................................. 40 Adipose Tissue Fibrosis. ........................................................................................... 41 Introduction to Growth Hormone. ............................................................................ 44 Growth Hormone Secretion and Signaling. .............................................................. 44 Growth Hormone Function . ..................................................................................... 48 Insights into Physiological Effect of Growth Hormone Action through Examination of Bovine Growth Hormone Transgenic Mice …………………………………….50 Depot Specific Response to Growth Hormone . ....................................................... 52 Conclusion . .............................................................................................................. 52 Chapter 3: Methodology ................................................................................................... 54 Animals. .................................................................................................................... 54 Body Composition . .................................................................................................. 54 9 Adipose Tissue Samples . ......................................................................................... 54 Immunohistochemistry . ........................................................................................... 55 RNA Isolation and cDNA Synthesis . ......................................................................