SPARC/osteonectin in mineralized tissue

Abstract

Secreted protein acidic and rich in cysteine (SPARC/osteonectin/BM40) is one of the most abundant non-collagenous protein expressed in mineralized tissues. This review will focus on elucidating functional roles of SPARC in bone formation building upon results from non-mineralized cells and tissues, the phenotype of SPARC-null bones, and recent discoveries of human diseases with either dysregulated expression of SPARC or mutations in the gene encoding SPARC that give rise to bone pathologies. The capacity of SPARC to influence pathways involved in extracellular matrix assembly such as procollagen processing and collagen fibril formation as well as the capacity to influence osteoblast differentiation and osteoclast activity will be addressed. In addition, the potential for SPARC to regulate cross-linking of extracellular matrix proteins by members of the transglutaminase family of enzymes is explored. Elucidating defined biological functions of SPARC in terms of bone formation and turnover are critical. Further insight into specific cellular mechanisms involved in the formation and homeostasis of mineralized tissues will lead to a better understanding of disease progression.

Osteogenesis and mineralization of mesenchymal stem cells in collagen type I‐based recombinant peptide scaffolds

“…The greatest increase was observed in DHT crosslinked samples. Osteonectin, which is incorporated into the ECM at a high rate during bone deposition, tended to be up‐regulated with osteogenic media . The expression of osteonectin did not significantly vary between the crosslinkers, nor did measurements of the HA content in the scaffolds, Figure (a).…”

Human adipose stem cells induced to osteogenic differentiation by an innovative collagen/hydroxylapatite hybrid scaffold

“…The genes ALP, ON, CHAD, SP7, and Sox9 had a higher expression with respect to cells t h a tw e r eg r o w no nt h ep l a s t i cv e s s e l( T C P S )a td3 postseeding. Cells that were grown on scaffold displayed higher expression levels of mRNAs of ALP, CHAD, SP7,andSOX9 genes than did those that were grown in the presence of OM at d 3 postseeding (29)(30)(31)(32)(33). Three genes-OCN, CHAD,andSox9-had a higher expression with respect to cells that were grownontheplasticvessel(TCPS),witha2-2.5 log 2 fold increase at d 9 postseeding.…”

“…4A). Of interest, the scaffold induced osteogenic gene markers, such as ALP, CHAD, ON, and transcription factors SP7 and SOX9 with respect to control at d 3 (29)(30)(31)(32)(33). The biomaterial continued to produce its osteogenic effect at d 9.…”

Altered bone‐regulating myokine expression in skeletal muscle Of Duchenne muscular dystrophy mouse models

“…Despite reports on their distinct up‐regulated expression in dystrophic muscle, the pathological roles of POSTN and SPARC in dystrophic muscle along with the effects of muscle‐derived POSTN and SPARC on bone are still largely unknown. As abundant noncollagenous proteins in mineralized tissue, both molecules play critical roles in regulating bone remodeling and maintaining bone mass and quality by a variety of mechanisms . With the exception of reports that high serum POSTN is associated with a higher fracture risk in postmenopausal women by means of unknown mechanisms, there is currently little information on the function of circulating POSTN and SPARC on bone.…”