Staphylococcus aureusInduces Expression of Receptor Activator of NF-κB Ligand and Prostaglandin E₂in Infected Murine Osteoblasts

Abstract

Osteomyelitis is an inflammatory disease of the bone that is characterized by the presence of necrotic bone tissue and increased osteoclast activity. Staphylococcus aureus is responsible for approximately 80% of all cases of human osteomyelitis. While the disease is especially difficult to treat, the pathogenesis of S. aureus-induced osteomyelitis is poorly understood. Elucidating the molecular mechanisms by which S. aureus induces osteomyelitis could lead to a better understanding of the disease and its progression and development of new treatments. Osteoblasts can produce several soluble factors that serve to modulate the activity or formation of osteoclasts. Receptor activator of NF-B ligand (RANK-L) and prostaglandin E 2 (PGE 2 ) are two such molecules which can promote osteoclastogenesis and stimulate bone resorption. In addition, previous studies in our laboratory have shown that osteoblasts produce inflammatory cytokines, such as interleukin 6, following infection with S. aureus, which could induce COX-2 and in turn PGE 2 , further modulating osteoclast recruitment and differentiation. Therefore, we hypothesized that following infection with S. aureus, osteoblasts will express increased levels of RANK-L and PGE 2 . The results presented in this study provide evidence for the first time that RANK-L mRNA and protein and PGE 2 expression are upregulated in S. aureus-infected primary osteoblasts. In addition, through the use of the specific COX-2 inhibitor NS 398, we show that when PGE 2 production is inhibited, RANK-L production is decreased. These data suggest a mechanism whereby osteoblasts regulate the production of RANK-L during infection.Osteomyelitis is a severe infection of bone tissue that results in progressive inflammatory destruction of bone (41). The gram-positive organism Staphylococcus aureus is the most common causative agent of osteomyelitis, accounting for approximately 80% of all human cases (27). It is often necessary that infected bone be debrided, tissues reconstructed, and longterm antibiotic therapy utilized (18). The current treatment for osteomyelitis is often traumatic and expensive and often leads to further selection of antibiotic-resistant strains of S. aureus. The growing incidence of antibiotic-resistant S. aureus strains can explain the recurrent attacks of osteomyelitis in patients undergoing therapy. In addition, the pathogenesis of S. aureusinduced osteomyelitis is poorly understood. Elucidating the mechanisms by which S. aureus induces osteomyelitis could therefore lead to a better understanding of the disease, its progression, and development of new treatments.Bone remodeling involves a continuous, coordinated equilibrium between bone synthesis and bone resorption, and two cell populations are responsible for the continual process (23). Osteoclasts drive the resorption of bone by acidification and release of lysosomal enzymes, while osteoblasts produce components of the bone matrix, principally type I collagen. Osteoblasts also produce factors which serve to modulate the ...

Perspectives on the prevention and treatment of infection for orthopedic tissue engineering applications

“…If neutrophils are deficient or inadequate to clear bacteria, the presence of bacterial toxins such as lipopolysaccharide (LPS) can induce prolonged and elevated levels of pro-inflammatory cytokines such as IL-1 and TNF-α [11]. Recent studies have shown that the principal causative organism for osteomyelitis, Staphylococcus aureus, is capable of upregulating production of several pro-inflammatory cytokines and inducing resorption of bone through RANK-L-mediated osteoclastogenesis, resulting in delayed or non-union of the fracture [8,12]. Similarly, formation of bacterial biofilms in a cutaneous wound has been shown to result in non-healing in a murine model [10].…”

“…Infection is known to inhibit healing in several tissue types, including bone, gastrointestinal epithelium, and cutaneous epithelium [8][9][10]. Physiologic wound healing in response to injury occurs in four sequential and timed phases: hemostasis, inflammation, proliferation and repair, and remodeling.…”

Effects of Local Antibiotic Delivery from Porous Space Maintainers on Infection Clearance and Induction of an Osteogenic Membrane in an Infected Bone Defect

“…35,36 However, it is also possible that analysis of the membrane does not fully represent the profile of RANKL expression. Previous in vitro work in human and murine osteoblasts has shown that RANKL is upregulated in response to S. aureus infection, 18,19,37 and other studies have indicated that osteocytes, as opposed to osteoblasts or bone marrow stromal cells, are the dominant source of RANKL. 38 Because the objective of this study was to analyze mRNA expression profiles of cells in the induced membrane, the study primarily measures RANKL and OPG production by lymphocytes and stromal cells present in the induced membrane.…”

“…[16][17][18] In vitro studies have shown the effects of S. aureus on local cells to be far reaching, such as decreasing osteoblast viability and differentiation, inhibiting the multilineage potential of mesenchymal stem cells (MSCs), increasing the production of resorptive factors and increasing the production of proinflammatory cytokines. [17][18][19] These effects are not conducive to the regeneration of bone, and thus, local antibiotic delivery is intended to eradicate bacteria to restore the regenerative capacity of local cell types. A study of the characteristics of an induced membrane generated in the presence of antibioticreleasing solid PMMA has demonstrated that antibiotics may also affect the thickness and vascularization of induced membranes in the absence of infection.…”

d-amino Acid Inhibits Biofilm but not New Bone Formation in an Ovine Model

“…For orthopaedic infections, Staphylococcus aureus is the most commonly isolated agent, accounting for more than 1 . 2 of all infections [28]. In addition to increasing trends of antimicrobial resistance, the ability of bacteria to develop and persist in biofilms on implanted biomedical devices is recognized as a major factor contributing to chronic relapsing infections and nonosseous union [4,35,42,44,48,49].…”