Altered differentiation and augmented function in Type 1 Diabetic-derived osteoclasts

Periodontal disease, a complication of type 1 diabetes (T1D), is an inflammatory response to oral pathogens that leads to soft and hard tissue destruction (alveolar bone). Even though osteoclasts are the only cell type capable of resorbing bone, the bone resorptive capability of osteoclasts derived from T1D sources have not been elucidated.  Objective: To evaluate the differentiation, functional capabilities, and activational status of osteoclasts derived from T1D and non-diabetic bone marrow under homeostatic and inflammatory conditions.  Methods: Tartrate-resistant acid phosphatase staining was used to evaluate the differentiation of bone marrow-derived osteoclasts (BM-OCs) from a T1D mouse model (NOD) and controls (NOR and C57BL/6).  Bone resorption was evaluated by scanning electron microscopy and collagen I ELISA.  Cathepsin K ELISA, MMP-9 ELISA, and cyto/chemokine analysis by Luminex were evaluated to investigate mechanisms of enhanced bone resorption. All experiments were performed in the presence or absence of E. coli LPS.  Additional experiments were performed in the presence of a pro-inflammatory cytokine cocktail consisting of IL-1β, TNF-α, and IL-6. Results: Although NOD BM-OCs differentiation resulted in smaller osteoclasts, NOD BM-OC cultures resorbed more bone than control BM-OCs as measured by SEM and collagen release.  Potential mechanisms of action included increased cathepsin K and MMP-9 secretion and pro-osteoclastogenic mediator expression [TNF-α, IL-1β, GM-CSF, and RANTES].  These parameters were further enhanced in the presence of LPS and/or pro-inflammatory cytokine cocktail.  Conclusions:   Taken together, these data suggest that NOD-derived osteoclasts are capable of resorbing more bone when compared to controls.  Mechanisms for this augmented bone resorption include increased cathepsin K and MMP-9 secretion which degrades more collagen I leading to increased pit formation.  NOD BM-OCs respond aberrantly to inflammatory stimuli by increased secretion of pro-osteoclastic mediators which may perpetuate the already enhanced resorptive cycle in T1D.