Dicer inactivation in osteoprogenitor cells compromises fetal survival and bone formation, while excision in differentiated osteoblasts increases bone mass in the adult mouse

Abstract

MicroRNA attenuation of protein translation has emerged as an important regulator of mesenchymal cell differentiation into the osteoblast lineage. A compelling question is the extent to which miR biogenesis is obligatory for bone formation. Here we show conditional deletion of Dicer in osteoprogenitors by Col1a1-Cre compromised fetal survival after E14.5. A mechanism was associated with the post-commitment stage of osteoblastogenesis, demonstrated by impaired ECM mineralization and expression of mature osteoblast markers in ex vivo deleted Dicerc/c during differentiation of mesenchymal cells. In contrast, in vivo excision of Dicer by Osteocalcin-Cre in mature osteoblasts generated a viable mouse with a perinatal phenotype of delayed bone mineralization which was resolved by 1 month. However, a second phenotype of significantly increased bone mass developed by 2 months, which continued up to 8 months in long bones and vertebrae, but not calvariae. Cortical bone width and trabecular thickness in DicerΔoc/Δoc was twice that of Dicerc/c controls. Normal cell and tissue organization was observed. Expression of osteoblast and osteoclast markers demonstrated increased coupled activity of both cell types. We propose that Dicer generated miRs are essential for two periods of bone formation, to promote osteoblast differentiation before birth, and control bone accrual in the adult.

MicroRNAs as regulators of bone homeostasis and bone metastasis

“…When dicer was ablated by Osteocalcin-Cre, eliminating miRNA processing in mature osteoblasts, the mice were viable but exhibited delayed bone development that corresponded with reduced osteoblast numbers. 5 Similarly, Dicer knockout in chondrocytes, using Col2a1-Cre mice, modulated proliferation and differentiation. 6 These transgenic mice presented with significant skeletal defects that were associated with the differentiation of cells into postmitotic hypertrophic chondrocytes featuring decreased proliferation.…”

“…For example, in vivo deletion of Dicer in osteoprogenitors, osteoblasts and chondrocytes, using a Col1a1 promoter-driven Cre recombinase, resulted in severe skeletal deformities in fetal mice. 5 These mice exhibited a misproportioned cartilage skeleton at E14.5 and displayed a reduction in mineralized tissue formation due to defects in osteoblast maturation. When dicer was ablated by Osteocalcin-Cre, eliminating miRNA processing in mature osteoblasts, the mice were viable but exhibited delayed bone development that corresponded with reduced osteoblast numbers.…”

miR-34s inhibit osteoblast proliferation and differentiation in the mouse by targeting SATB2

“…To determine whether miR-34s are involved in osteogenesis, we used a gain-of-function approach and generated transgenic mice overexpressing one representative member of this family, DICER, a protein necessary for processing of miRNAs, affects osteoblast differentiation (Gaur et al, 2010). Accordingly, it has been suggested that miRNAs may be involved in osteoblast proliferation and/or differentiation (Hassan et al, 2010;Zhang et al, 2011).…”

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

“…For example, in vivo ablation of Dicer in osteoprogenitors, osteoblasts and chondrocytes by Col1a1-Cre resulted in severe skeletal deformities in fetal mice as it inhibited their maturation into cells that lay down bone mineral. 11 The mice had a disproportione cartilage skeleton and a reduction in mineralized tissue at E14.5. Excision of Dicer in mature osteoblasts by Osteocalcin-Cre produced a viable mice, which exhibited delayed bone development that corresponded with reduced osteoblast numbers.…”

“…Excision of Dicer in mature osteoblasts by Osteocalcin-Cre produced a viable mice, which exhibited delayed bone development that corresponded with reduced osteoblast numbers. 11 Similarly, Dicer deletion in chondrocytes, using Col2a1-Cre mice, modulated the proliferation and differentiation of cells into postmitotic hypertrophic chondrocytes leading to significant skeletal defects. 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.…”