George Kobrossy
Pronouns: he/him
Research Mentor(s): Andrea Alford
Research Mentor School/College/Department: Orthopaedic Surgery / Medicine
Program:
Authors: Andrea Alford, George Kobrossy
Session: Session 1: 9:00 am – 9:50 am
Poster: 6
Abstract
Integrins are transmembrane protein heterodimers that link the extracellular matrix (ECM) to the cytoskeleton and mediate cell-ECM communication. These interactions are crucial for skeletal health. Thrombospondin-1 (TSP1) and Thrombospondin-2 (TSP2) are ECM proteins expressed in bone and impact mesenchymal progenitor cell fate, osteoblast ECM maturation, and angiogenesis. The two proteins share substantial sequence identity and the same 3-dimensional structure, but they have both overlapping and unique functions, such as affecting ECM strength, and the activity of osteoclasts and osteoblasts. Osteocytes are involved in mechanosensation and transduction, cell-ECM signaling, and are terminally differentiated osteoblasts. Proteomic analysis of osteocyte-rich cortical bone from mice harboring global deficiencies in TSP2 (TSP2KO) revealed significant reductions in several integrin subunits. Integrin protein levels in TSP1/TSP2 double knockout mice (DKO) were often reduced further compared to the single TSP2KO, but were not affected in TSP1KO mice. The purpose of this study was to build on the proteomics data by examining beta-3 integrin (ITGB3) gene expression in osteocyte-rich cortical bone from global TSP2KO and osteoblast-specific TSP2KO (osteocalcin (ocn)-cre; TSP2fl/fl) mice. We selected ITGB3 because it is one of two integrin types enriched on osteocyte dendritic processes. We conducted reverse transcription and polymerase chain reaction (rtPCR) on RNA isolated from bone tissue of wild-type, TSP1KO, TSP2KO, DKO, and ocn-cre; TSP2fl/fl mice. TSP2 and ITGB3 were normalized to the housekeeping gene ATP5b. The double delta CT method was used to determine gene expression relative to WT controls. We hypothesize that ITGB3 gene expression will be lower in TSP2KO and ocn-cre+; TSP2fl/fl when compared to wild-type mice. Preliminary results confirm that TSP2 mRNA is reduced in bone for osteocalcin-cre+; TSP2fl/fl mice compared to the wild-type equivalents. In TSP2KO mice, preliminary results show a reduction in ITGB3 mRNA. Since these integrins link the ECM to the cytoskeleton, TSP2 reductions could have implications in osteocyte mechanosensation or transduction, which diminishes with advancing age and could be associated with bone fragility.
