Osteoclast precursor variability from mandible and femur-derived bone marrow cells in older mice: a descriptive study

Abstract

Aim: To determine if there are differences between osteoclasts from the mandible andfemur of 1-year-old mice by evaluating gene expression and differentiation potential. Methods: Monocytes were collected from male and female C57BL/6 mice aged to 1-year- old. Osteoclast differentiation of the monocytes collected was performed by plating the cells in osteoclast media supplemented with 1.5% CMG 14-12 culture supernatant and 5 ng/mL RANKL in preparation for differentiation experiments. TRAP staining was done to evaluate the quantity and size of the osteoclasts at each skeletal site. qRT-PCR analyzed osteoclast precursor gene expression in the mandible and femur. Bulk RNA-Seq allowed for an unbiased look at the overall gene expression signature of the monocytes collected from the two skeletal sites. Results: Osteoclasts from the mandible of 1-year-old mice were larger in size compared to those in the femur, but significantly less in number. The differentially regulated genes with increased expression in the mandible are associated with osteoclast lineage commitment, proliferation, and inflammation; similar to those in the 2-month old mice. The femur only showed increased expression of inflammatory modulators. Bulk RNA sequencing demonstrated that the mandible had more upregulated genes compared to the femur, and the pathways enriched in the mandible were distinct from those in the femur. Conclusions: • The osteoclast precursors from the mandible of 1-year-old mice demonstrate differences in gene expression and differentiation capabilities compared to the femur. • Craniofacial and appendicular regions of the skeleton may be regulated by different mechanisms. • The femoral data collected from the 1-year-old mice exhibits a more inflammatory environment compared to the data collected from 2-month-old mice. • The differences seen the in osteoclasts between young and old mice requires further investigation, with emphasis in understanding how these difference impact orthodontic tooth movement and bone remodeling in older patients.