EFFECTS OF TRANSFORMING GROWTH FACTOR-β1 AND FIBRONECTIN ON SPARC EXPRESSION IN CULTURES OF HUMAN PERIODONTAL LIGAMENT CELLS

Abstract

Transforming growth factor‐β₁ (TGF‐β₁) 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‐β₁ in cultures of human periodontal ligament cells (HPL cells). TGF‐β₁ increased the SPARC and SPARC mRNA levels in HPL cells. Extracellular matrix (ECM) produced by HPL cells in the presence of TGF‐β₁ also increased the SPARC levels. Contents of FN and type I collagen in the ECM were increased by TGF‐β₁. 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‐β₁. This study demonstrated that FN may be partly involved in the increase in SPARC expression by TGF‐β₁ in HPL cells.