The human oral cavity harbors more than 500 species of bacteria. Periodontitis, a bacterially induced inflammatory disease that leads to tooth loss, is believed to result from infection by a select group of gram-negative periodontopathogens that includes Porphyromonas gingivalis, Treponema denticola, and "Tannerella forsythia" (opinion on name change from Tannerella forsythensis pending; formerly Bacteroides forsythus). Epithelial cell invasion by periodontopathogens is considered to be an important virulence mechanism for evasion of the host defense responses. Further, the epithelial cells with invading bacteria also serve as reservoirs important in recurrent infections. The present study was therefore undertaken to address the epithelial cell adherence and invasion properties of T. forsythia and the role of the cell surface-associated protein BspA in these processes. Further, we were interested in determining if P. gingivalis, one of the pathogens frequently found associated in disease, or its outer membrane vesicles (OMVs) could modulate the epithelial cell adherence and invasion abilities of T. forsythia. Here we show that epithelial cell attachment and invasion by T. forsythia are dependent on the BspA protein. In addition, P. gingivalis or its OMVs enhance the attachment and invasion of T. forsythia to epithelial cells. Thus, interactions between these two bacteria may play important roles in virulence by promoting host cell attachment and invasion.

Tannerella forsythia is a gram-negative anaerobe strongly associated with chronic human periodontitis. This bacterium expresses a cell surface-associated and secreted protein, designated BspA, which has been recognized as an important virulence factor. The BspA protein belongs to the leucine-rich repeat (LRR) and bacterial immunoglobulin-like protein families. BspA is, moreover, a multifunctional protein which interacts with a variety of host cells, including monocytes which appear to respond to BspA through Toll-like receptor (TLR) signaling. Since gingival epithelium forms a barrier against periodontal pathogens, this study was undertaken to determine if gingival epithelial cells respond to BspA challenge and if TLRs play any role in BspA recognition. This study was also directed towards identifying the BspA domains responsible for cellular activation. We provide direct evidence for BspA binding to TLR2 and demonstrate that the release of the chemokine interleukin-8 from human gingival epithelial cells by BspA is TLR2 dependent. Furthermore, the LRR domain of BspA is involved in activation of TLR2, while TLR1 serves as a signaling partner. Thus, our findings suggest that BspA is an important modulator of host innate immune responses through activation of TLR2 in cooperation with TLR1.

Dentin matrix phosphoprotein 1 (DMP1) is a non-collagenous, acidic extracellular matrix protein expressed chiefly in bone and dentin. We examined the DMP1 ability to engage cellsurface receptors and subsequently activate intracellular signaling pathways. Our data indeed show that the presence of extracellular DMP1 triggers focal adhesion point formation in human mesenchymal stem cells and osteoblast-like cells. We determine that DMP1 acts via interaction with ␣v␤3 integrin and stimulates phosphorylation of focal adhesion kinase. The extracellular matrix (ECM)2 is a complex and dynamic network of proteins known to be involved in tissue compartmentalization, controlling differentiation events and mediation of communication from one cell to another (2). Cell-ECM interactions are known to be critical to many biological processes, including embryonic development and morphogenesis, cell growth and differentiation, tissue regeneration and cellular homeostasis (3). In mineralizing tissues such as bone and dentin, the organic ECM comprises both a structural, collagenous component, and a second component of non-collagenous proteins. These non-collagenous proteins are thought to be essential regulators of the mineralization process, and recent evidence suggests that they are also likely involved in regulating cellular morphogenesis and differentiation (4). One such noncollagenous protein, known as DMP1, is a member of the family known as small integrin binding ligand N-linked glycoproteins (SIBLINGs). DMP1 is an acidic, highly phosphorylated protein normally present as two separate proteolytic fragments, a 37-kDa N-terminal species and a 57-kDa C-terminal species.Expressed chiefly in the ECM of bone and dentin, DMP1 is unique in its content of a large number of acidic domains (5) These properties have been shown to be important in DMP1 affinity for Ca 2ϩ and the ability to induce in vitro mineralization (6). Because of these physicochemical properties, DMP1 has been extensively studied, initially for its role in biomineralization, but more recently several roles have emerged underscoring its importance in bone biology. 1) Overexpression of DMP1 is sufficient to induce the differentiation of mesenchyme-derived cells to functional odontoblast-like cells and enhance mineralization (7-9). 2) DMP1 can be endocytosed via the GRP-78 receptor and transported into the nucleus to act as a transcriptional regulator for the phosphophoryn gene (10, 11). 3) the DMP1 role in the regulation of phosphate homeostasis and mineral metabolism has been underscored by the characterization of null mice displaying a recessive hypophosphatemic rickets and hypomineralized bone phenotype as well as morphological changes in osteocytes including irregular, buckled cell membranes and an absence of dendritic extensions (1, 12). These DMP1 null mice also showed a loss of osteocyte dendritic processes, which is normally a hallmark feature of these cells, and an irregular, buckled osteocyte cell membrane. Furthermore, the osteocyte lacunae were larger, ran...