Activation of ROS/MAPKs/NF-κB/NLRP3 and inhibition of efferocytosis in osteoclast-mediated diabetic osteoporosis

Diabetes mellitus (DM) affects bone metabolism and leads to osteoporosis; however, its pathogenetic mechanisms remain unknown. We found that high glucose (HG) conditions induced the production of reactive oxygen species (ROS) and the expression of proteins related to MAPKs [phosphorylated (p)-ERK, p-JNK, and p-p38], NF-kappa B (NF-kappa B, p-I kappa B, and IKK), and NACHT-LRR-PYD domains-containing protein 3 (NALP3) (NLRP3) [apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), caspase-1, IL-18, IL-1 beta, and NLRP3] in osteoclasts (OCs) in vitro. Further analysis showed that in HG-induced OCs, ROS is an upstream signal for MAPKs, NF-kappa B, and the NLRP3 inflammasome. Moreover, MAPKs mediated the activation of NF-kappa B and NLRP3, whereas NF-kappa B up-regulated the NLRP3 inflammasome response. Interestingly, HG inducement enhanced the bone resorption of OCs but inhibited their efferocytosis, whereas insulin and lipoxin A4 (4) treatment reversed this phenomenon. In streptozotocin-induced diabetic rats in vivo, the numbers and the bone-resorption capacity of OCs as well as the serum levels of TRACP-5b were significantly increased, and the expression of MAPK-, NF-kappa B-, and NLRP3 inflammasome- related proteins in the proximal tibia were also significantly elevated; however, treatment with insulin and LXA4 reversed this elevation. Together, these results demonstrated that the activation of ROS/MAPKs/NF-kappa B/NLRP3 and the inhibition of efferocytosis in OCs are the main causes of osteoporosis in DM.