DEC1 deficiency promotes osteoclastic activity by augmenting NFATc1 signaling via transactivation and the Ca2+/calcineurin pathway.

Abstract

We have previously demonstrated that DEC1 promotes osteoblast differentiation. This study aims to evaluate the impact of DEC1 knockout on osteopenic activities, such as osteoclast differentiation and the expression of bone-degrading genes. To gain mechanistic insights, we employed both in vivo and in vitro experiments, utilizing cellular and molecular approaches, including osteoclast differentiation assays and RNA-seq in combination with ChIP-seq. Our results showed that NFATc1, a master regulator of osteoclast differentiation, and PPP3CB, a member of the calcineurin family, were significantly upregulated in DEC1^-/- mice. In vitro experiments revealed that osteoclast differentiation significantly increased both the number and size of osteoclasts in DEC1^-/- bone marrow macrophages (BMMs) compared to DEC1^+/+ BMMs. Additionally, NFATc1 expression was notably higher in DEC1^-/- BMMs than in DEC1^+/+ BMMs. Overexpression of DEC1 reduced NFATc1 promoter activity, while knockout increased it. Furthermore, intracellular free Ca²⁺ levels and calcineurin activity were elevated (∼150 %) in DEC1^-/- BMMs compared to DEC1^+/+ BMMs. Importantly, the use of calcineurin inhibitors and calcium channel blockers effectively abolished the increased osteoclast differentiation observed in DEC1^-/- BMMs. In summary, DEC1 deficiency promotes osteoclast differentiation by enhancing NFATc1 signaling through transcriptional regulation and the Ca²⁺/calcineurin pathway. Clinically, the mRNA levels of DEC1 were reduced by up to 75 % in patients with osteoporosis. The findings of this study establish that inducing DEC1 expression, alongside attenuators of the Ca²⁺/calcineurin pathway, offers a molecular basis for preventing and treating osteoporosis associated with DEC1 deficiency.