Thrombospondin-2 facilitates assembly of a type-I collagen-rich matrix in marrow stromal cells undergoing osteoblastic differentiation. (12th July 2013)

• Record Type: Journal Article
• Authors: Alford, Andrea I.; Golicz, Andrew Z.; Cathey, Amber Lee; Reddy, Anita B.
• Is Part Of: Connective tissue research. Volume 54:Number 4/5(2013:Aug.)
• Page Start: 275
• Page End: 282
• Publication Date: 2013-07-12
• Subjects: Collagen pro-peptides -- matricellular -- mineralization -- TSP2-null mouse; Connective tissues -- Periodicals; 616.770072
• DOI: 10.3109/03008207.2013.811236
• Languages: English
• ISSNs: 0300-8207

Abstract

Abstract: We examined the effects of Thrombospondin-2 (TSP2) deficiency on assembly of collagenous extracellular matrix (ECM) by primary marrow-derived mesenchymal stromal cells (MSC) undergoing osteoblast differentiation in culture. After 30 d, wild-type cells had accumulated and mineralized a collagen-rich insoluble matrix, whereas the TSP2-null cultures contained markedly lower amounts of matrix collagen and displayed reduced mineral. Differences in matrix collagen were seen as early as day 9, at which time wild-type cultures contained more total collagen per cell than did TSP2-null cells. Collagen was unevenly distributed amongst different extracellular compartments in the two cell-types. Collagen levels in conditioned medium of wild-type cells were higher than those of TSP2-null cells, but were roughly equivalent in the acid-soluble, newly cross-linked matrixes. Conversely, the mature, cross-linked acid-insoluble matrix layer of wild-type cells contained about twice as much collagen as TSP2-null cell-derived matrix. Western blot analysis of type-I collagen in detergent-soluble and insoluble matrix fractions supported the premise that matrix collagen levels were reduced in TSP2-null MSC undergoing osteoblastic differentiation in vitro . Western blot and immunofluorescent analysis suggested that assembly of fibronectin into matrix was not affected by TSP2 deficiency. Instead, western blots of conditioned medium demonstrated a marked reduction in mature, fully processed type-I collagen in the absence of TSP2. Our data suggest that in the context of osteoblast differentiation, TSP2 promotes the assembly of a type-I collagen-rich matrix by facilitating pro-collagen processing.