Untitled

Abstract

An increase in the interaction between advanced glycation end-products (AGEs) and their receptor RAGE is believed to contribute to the pathogenesis of chronic complications of Diabetes mellitus, which can include bone alterations such as osteopenia. We have recently found that extracellular AGEs can directly regulate the growth and development of rat osteosarcoma UMR106 cells, and of mouse calvaria-derived MC3T3E1 osteoblasts throughout their successive developmental stages (proliferation, differentiation and mineralisation), possibly by the recognition of AGEs moieties by specific osteoblastic receptors which are present in both cell lines. In the present study we examined the possible expression of RAGE by UMR106 and MC3T3E1 osteoblastic cells, by immunoblot analysis. We also investigated whether short-, medium- or long-term exposure of osteoblasts to extracellular AGEs, could modify their affinity constant and maximal binding for AGEs (by 125I-AGE-BSA binding experiments), their expression of RAGE (by immunoblot analysis) and the activation status of the osteoblastic ERK 1/2 signal transduction mechanism (by immunoblot analysis for ERK and P-ERK). Our results show that both osteoblastic cell lines express readily detectable levels of RAGE. Short-term exposure of phenotypically mature osteoblastic UMR106 cells to AGEs decrease the cellular density of AGE-binding sites while increasing the affinity of these sites for AGEs. This culture condition also dose-dependently increased the expression of RAGE and the activation of ERK. In proliferating MC3T3E1 pre-osteoblasts, 24-72 h exposure to AGEs did not modify expression of RAGE, ERK activation or the cellular density of AGE-binding sites. However, it did change the affinity of these binding sites forAGEs, with both higher- and lower-affinity sites now being apparent. Medium-term ( 1 week) incubation of differentiated MC3T3E1 osteoblasts with AGEs, induced a simultaneous increase in RAGE expression and in the relative amount of P-ERK. Mineralising MC3T3E1 cultures grown for 3 weeks in the presence of extracellular AGEs showed a decrease both in RAGE and P-ERK expression. These results indicate that, in phenotypically mature osteoblastic cells, changes in ERK activation closely follow the AGEs-induced regulation of RAGE expression. Thus, the AGEs-induced biological effects that we have observed previously in osteoblasts, could be mediated by RAGE in the later stages of development, and mediated by other AGE receptors in the earlier pre-osteoblastic stage.

Non-enzymatic Glycation of Bone Collagen Modifies Osteoclastic Activity and Differentiation

“…7). It has been shown that AGEs themselves have the ability to stimulate RAGE expression in osteoblastic cells (27), as well as AGE-R3 (Galectin-3) expression (61). However, we could not see any change in the level of expression of AGE-R3 in RAW264.7 cells, probably due to cell-type specificity.…”

“…AGE-modified collagen also interferes with integrinmediated osteoblastic attachment (26). RAGE has been shown to be expressed in osteoblasts (21,27) and may modulate AGEdependent signaling in osteoblasts (27). This observation could explain in part the decreased expression of transcription factors responsible for osteoblastic differentiation in type I diabetic mice model (28).…”

“…The contribution of non-enzymatic glycations to bone remodeling has been poorly investigated in vivo, mainly due to a lack of suitable animal models; for instance, insulin deficiency or resistance in diabetic animal models might interfere with cell differentiation or function processes. Although the role of AGEs in osteoblasts differentiation and function has been well characterized in vitro (23,26,27,29), their contribution to osteoclast activity and differentiation is unknown. In the present study we first investigated the effects of matrix AGEs on bone resorption by osteoclasts, using an in vitro resorption assay on AGE-modified mineralized matrices.…”

AGEs induce caspase-mediated apoptosis of rat BMSCs via TNFα production and oxidative stress

“…AGEs accumulate in bone tissue during DM (Katayama et al 1996, Saito et al 2006 and may participate in the pathogenesis of DM-related osteoporosis. In support of this possibility, AGEs are capable of affecting bone cells directly since cultured osteoblastic cells (Cortizo et al 2003, Santana et al 2003 as well as bone tissue in vivo (Santana et al 2003) express receptor for AGEs (RAGE).…”

Advanced Glycation: Implications in Tissue Damage and Disease

“…AGE receptors have been identified on various cell types including macrophages, endothelial cells [45], various renal cell types such as proximal tubular cells, mesangial cells and podocytes [46,47] nerve cells, muscle cells [48] and cells in the vasculature [12]. The AGE receptor system can be broadly divided into two arms: one is associated with increases in oxidative stress, growth, and inflammation probably best represented by RAGE [49,50], the other is involved in AGE detoxification and includes scavenger receptors such as CD36 (liver) as well as the AGE receptors AGE-R1 and AGE-R3 (via renal clearance).…”