Substrate Modulation of Osteoblast Adhesion Strength, Focal Adhesion Kinase Activation, and Responsiveness to Mechanical Stimuli

Osteoblast interactions with extracellular matrix (ECM) proteins are known to influence many cell functions, which may ultimately affect osseointegration of implants with the host bone tissue. Some adhesion- mediated events include activation of focal adhesion ki- nase, and subsequent changes in the cytoskeleton and cell morphology, which may lead to changes in adhe- sion strengthand cell responsivenessto mechanical stim- uli. In this study we examined focal adhesion kinase ac- tivation (FAK), F-actin cytoskeleton reorganization, ad- hesion strength, and osteoblast responsiveness to fluid shear when adhered to typeI collagen (ColI), glass,poly- L-lysine (PLL), fibronectin (FN), vitronectin (VN), and serum (FBS). In general, surfaces that bind cells through integrins (FN, VN, FBS) elicited the highest adhesion strength, FAK activation, and F-actin stress fiber forma- tion after both 15 and 60 minutes of adhesion. In con- trast,cells attached throughnon-integrinmediated means (PLL, glass) showedthe lowestFAK activation, adhesion strength, and little F-actin stress fiber formation. When subjected to steady fluid shear using a parallel plate flow chamber, osteoblasts plated on FN released significantly more prostaglandin E2 (PGE2) compared to those on glass. In contrast, PGE2 release of osteoblasts attached to FN or glass was not different in the absence of fluid shear, suggestingthat differences in bindingalone are in- sufficient to alter PGE2 secretion. The increased adhe- sion strengthas well as PGE2 secretion of osteoblastsad- hered via integrins may be due to increased F-actin fiber formation, which leads to increased cell stiffness.