EFFECTS OF TRANSFORMING GROWTH FACTOR‐β 1 AND FIBRONECTIN ON SPARC EXPRESSION IN CULTURES OF HUMAN PERIODONTAL LIGAMENT CELLS

Transforming growth factor‐β 1 (TGF‐β 1 ) increases synthesis of secreted protein, acidic and rich in cysteine (SPARC), as well as fibronectin (FN) and type I collagen. However, little is known about the regulatory mechanism of SPARC expression. We examined the effect of FN on SPARC expression by TGF‐β 1 in cultures of human periodontal ligament cells (HPL cells). TGF‐β 1 increased the SPARC and SPARC mRNA levels in HPL cells. Extracellular matrix (ECM) produced by HPL cells in the presence of TGF‐β 1 also increased the SPARC levels. Contents of FN and type I collagen in the ECM were increased by TGF‐β 1 . HPL cells cultured on FN‐coated plates secreted more SPARC than those on non‐coated plates. However, type I collagen had little effect on SPARC levels. The addition of anti‐α5 antibody to the cultures abolished the increase in SPARC mRNA expression by TGF‐β 1 . This study demonstrated that FN may be partly involved in the increase in SPARC expression by TGF‐β 1 in HPL cells.