Osteoclast‐specific Dicer gene deficiency suppresses osteoclastic bone resorption

Abstract

Osteoclasts are unique cells that resorb bone, and are involved in not only bone remodeling but also pathological bone loss such as osteoporosis and rheumatoid arthritis. The regulation of osteoclasts is based on a number of molecules but full details of these molecules have not yet been understood. MicroRNAs are produced by Dicer cleavage an emerging regulatory system for cell and tissue function. Here, we examine the effects of Dicer deficiency in osteoclasts on osteoclastic activity and bone mass in vivo. We specifically knocked out Dicer in osteoclasts by crossing Dicer flox mice with cathepsin K-Cre knock-in mice. Dicer deficiency in osteoclasts decreased the number of osteoclasts (N.Oc/BS) and osteoclast surface (Oc.S/BS) in vivo. Intrinsically, Dicer deficiency in osteoclasts suppressed the levels of TRAP positive multinucleated cell development in culture and also reduced NFATc1 and TRAP gene expression. MicroRNA analysis indicated that expression of miR-155 was suppressed by RANKL treatment in Dicer deficient cells. Dicer deficiency in osteoclasts suppressed osteoblastic activity in vivo including mineral apposition rate (MAR) and bone formation rate (BFR) and also suppressed expression of genes encoding type I collagen, osteocalcin, Runx2, and Efnb2 in vivo. Dicer deficiency in osteoclasts increased the levels of bone mass indicating that the Dicer deficiency-induced osteoclastic suppression was dominant over Dicer deficiency-induced osteoblastic suppression. On the other hand, conditional Dicer deletion in osteoblasts by using 2.3 kb type I collagen-Cre did not affect bone mass. These results indicate that Dicer in osteoclasts controls activity of bone resorption in vivo.

MicroRNAs and post-transcriptional regulation of skeletal development

“…These mice were found to exhibit higher bone mass and a decrease in osteoclast surface and number. Additionally, the expression of not only osteoclast-related genes but also osteoblast-related ones (Col1a1, Bglap, and runt-related transcription factor 2 (Runx2)) was found to be downregulated (Mizoguchi et al 2010). These data indicate that miRNAs are important not only during bone development but also for bone homeostasis throughout life.…”

“…The ablation of Dicer in progenitors prevents their differentiation and compromises fetal survival (Gaur et al 2010). In addition, Mizoguchi et al (2010) have demonstrated that osteoclast Dicer is also crucial for normal osteoclast resorption and osteoblast activity. Osteoclast-specific Dicer knockout mice were generated by crossing Cathepsin K-cre mice with Dicer flox mice.…”

MicroRNAs as regulators of bone homeostasis and bone metastasis

“…7 Cultured bone marrow from these mice was incapable of producing osteoclasts ex vivo, further confirming the defect in osteoclast maturation. 8,9 Importantly, this defect was not confined to Dicer; knockdown of DGCR8 and Ago2 using siRNA similarly resulted in decreased osteoclast differentiation and bone resorption, and osteoclastspecific DGCR8 knockout mice display impaired bone development. 7,10 Taken together, these results reveal the necessity for proper miRNA regulation during the differentiation and maintenance of multiple essential cell types required for bone homeostasis.…”

Bone marrow stroma-derived miRNAs as regulators, biomarkers and therapeutic targets of bone metastasis

“…12 Osteoclast-specific Dicer knockout, using CD11b-Cre or CTSK-Cre transgenic mice, disrupted osteoclastogenesis and reduced the number and activity of multinuclear osteoclasts leading to an increase in bone mass. [13][14][15] Cultured bone marrow from these transgenic mice was also incapable of producing osteoclasts ex vivo, further confirming the defect in osteoclast differentiation. 14,15 Importantly, this defect was not confined to Dicer; ablation of DGCR8 and AGO2 using small interfering RNAs (siRNAs) similarly resulted in decreased osteoclast maturation and bone resorption, and osteoclast-specific DGCR8 knockout mice display impaired bone development (Table 1).…”

“…[13][14][15] Cultured bone marrow from these transgenic mice was also incapable of producing osteoclasts ex vivo, further confirming the defect in osteoclast differentiation. 14,15 Importantly, this defect was not confined to Dicer; ablation of DGCR8 and AGO2 using small interfering RNAs (siRNAs) similarly resulted in decreased osteoclast maturation and bone resorption, and osteoclast-specific DGCR8 knockout mice display impaired bone development (Table 1). 13,16 Taken together, these results reveal the necessity for proper miRNA regulation during the differentiation and maintenance of multiple essential bone marrow cell types required for bone formation and homeostasis.…”