Inflammation driven by NF-ĸB compromises bone formation by inducing the differentiation of osteoblasts into atypical inflammatory osteocyte-like cells.

Inflammation causes bone loss by dysregulating the differentiation and functions of osteoclasts, osteoblasts, and osteocytes. This process can be modeled by the expression of constitutively activated IKK2 (IKK2ca), a strategy that we leveraged to investigate the mechanisms through which inflammation negatively affects cells of the osteoblast/osteocyte lineage. We found that mice expressing IKK2ca in osteoblasts exhibit significant bone loss. Mechanistically, IKK2ca downregulates the expression of osteoblast genes while inducing the differentiation of bone-forming osteoblasts into catabolic osteocytes like cells, expressing high levels of Podoplanin, Fgf23, Dkk1 and Sclerostin. We term these atypical inflammatory osteocyte-like cells (aiOCy-L cells) as they highly express inflammatory and senescence markers and promote osteoclast differentiation as well. Additional data show that inflammation induces abnormal differentiation of OB into aiOCy-L cells through upregulating mTOR and glycolysis. In summary, we uncovered a mechanism by which inflammation alters osteoblast differentiation and fate decision via the IKK2/mTOR/glycolysis axis.