Characterization of common marmoset (Callithrix jacchus) bone marrow-derived mesenchymal stem cells

Abstract: Mesenchymal stem cells (MSCs) could be useful for regenerative medicine because they can beharvested easily from the bone marrow of living donors and the cells can be differentiated into adipogenic, osteogenic, and chondrogenic lineages in vitro. To apply MSCs for the medical treatment of human diseases as regenerative medicine, detailed experimental characterization of the cells is required. Recently, a New World primate, the common marmoset (Callithrix jacchus), has been widely used as a new human disease model because of its ease of handling and breeding. Although common marmoset MSCs have been established and will be used in preclinical studies of regenerative medicine, the characteristics of these cells remain unclear. Aiming to characterize common marmoset MSCs further, we harvested common marmoset bone marrow-derived cells (cmBMDCs) from the femurs of newborn males. We revealed that the morphology of the cells was similar to common marmoset fibroblasts, and extracellular matrix components, such as gelatin and fibronectin, were effective for their proliferation and formation of colony-forming unit fibroblasts. Furthermore, we were able to differentiate cmBMDCs into adipocytes, osteocytes, and chondrocytes in vitro, and they expressed the MSCmarkers CD44, CD73, CD90, and CD105, but their expression decreased with increasing passage number. The data demonstrate that cmBMDCs exhibit characteristics of MSCs and thus it would be beneficial to use these cells in preclinical studies

The matrix vesicle cargo miR-125b accumulates in the bone matrix, inhibiting bone resorption in mice

Communication between osteoblasts and osteoclasts plays a key role in bone metabolism. We describe here an unexpected role for matrix vesicles (MVs), which bud from boneforming osteoblasts and have a well-established role in initiation of bone mineralization, in osteoclastogenesis. We show that the MV cargo miR-125b accumulates in the bone matrix, with increased accumulation in transgenic (Tg) mice overexpressing miR-125b in osteoblasts. Bone formation and osteoblasts in Tg mice are normal, but the number of bone-resorbing osteoclasts is reduced, leading to higher trabecular bone mass. miR-125b in the bone matrix targets and degrades Prdm1, a transcriptional repressor of anti-osteoclastogenic factors, in osteoclast precursors. Overexpressing miR-125b in osteoblasts abrogates bone loss in different mouse models. Our results show that the MV cargo miR-125b is a regulatory element of osteoblast-osteoclast communication, and that bone matrix provides extracellular storage of miR-125b that is functionally active in bone resorption.T.M. and Y.T. were supported in part by MEXT KAKENHI (JP16K11443, T.M.; JP26861548, Y.T.). Y.Y. was supported by MEXT KAKENHI (JP18K19647), the Raffinee International Foundation and the Ono Pharmaceutical Foundation.Supplementary information is available for this paper at https://doi.org/10.1038/s42003-020-0754-2

Mel-18 Controls the Enrichment of Tumor-initiating Cells in SP Fraction in Mouse Breast Cancer

Side population (SP) cell analysis has been used to identify and isolate a minor population of cells with stem cell properties in normal tissues and in many cancers including breast cancer cells. However, the molecular mechanisms that operate in tumor-initiating cells (TICs) in SP fraction remain unclear. The Polycomb group genes, including Bmi1 and Mel-18, have been implicated in the maintenance of hematopoietic stem cells (HSCs) and suggested to be oncogenic and tumor suppressive, respectively, in breast cancer. In this study, we determined the critical role of Mel-18 in the enrichment mechanisms of TICs with the SP phenotype in a mouse breast cancer cell line, MMK3, that was established from a breast cancer developed spontaneously in Mel-18+/- mice. The Mel-18 protein expression level significantly correlates to the percentage of SP fraction in the mouse breast cancer cell line MMK3 series. The comparison between MMK3V3 (V3) cells containing one copy of the Mel-18 gene and MMK3S2 (S2) cells having twice the amount of Mel-18 expression clearly demonstrates the above relationship. Similar results obtained with the percentage of ALDH+ cells in V3 and S2 further confirmed the correlation between protein expression level of Mel-18 and the TICs. More importantly, transplantation of SP and non-SP cells of V3 and S2 cells into the NOD/SCID mice clearly showed that the heterozygous level of Mel-18 leads to the disappearance of enrichment of TICs into SP fraction in vivo. Stem cell pathway focused gene expression profiling of V3 and S2 cells revealed that the genes Abcg2, Aldh1a1 and Dhh were highly down-regulated in V3 compared to S2. These results indicate that the precise Mel-18 expression level controls TIC enrichment mechanisms through the regulation of channel molecule of Abcg2 and functional TIC marker of Aldh1a1. In conclusion, our findings revealed the significance of fine-tuning mechanisms for Mel-18 protein expression level in the maintenance of TIC into SP fractions in mouse breast cance