Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Several biomaterials have been widely used in bone regeneration in both orthopedic and oral surgeries. However, it is poorly understood how these biomaterials alter osteoblast phenotype. It prompted us to examine the involvement of signaling proteins during preosteoblast adhesion (attachment), proliferation, and differentiation on natural hydroxyapatite (HA) from bovine bone. Our results indicated that natural HA is able to promote osteoblast adhesion, proliferation, and differentiation. The osteoblast/HA interaction requires phosphorylation of tyrosine residues of focal adhesion kinase, Src, and Paxillin upon integrin activation, which culminates in the control of cofilin phosphorylation (at serine 03) via rac-1 activation. In part, these signaling pathways are responsible for actin-rearrangement, responsible to adapt cell-shape on HA particles. In regarding to osteoblast differentiation, we showed that natural HA favored extracellular matrix remodeling by stimulating matrix metalloproteinase activities and alkaline phosphatase activity. Overall, this study demonstrates that osteoblast response toward bovine bone HA is initially mediated by activation of focal adhesion components, culminating on actin-rearrangement executed by cofilin activation via rac-1. Moreover, bovine bone HA provided an excellent microenvironment for osteoblast activity, since adhesion to differentiation. (C) 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 97A: 193-200, 2011.97A2193200Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [08/53003-9]