Development and validation of a new method to isolate, expand, and differentiate circulating osteogenic precursor (COP) cells

Analysis of circulating osteoclast and osteogenic precursors in patients with Gorham-Stout disease

PURPOSE

Gorham-Stout disease is a very rare disorder characterized by progressive bone erosion and angiomatous proliferation; its etiopathogenesis is still unknown, and diagnosis is still performed by exclusion criteria. The alteration of bone remodeling activity has been reported in patients; in this study, we characterized circulating osteoclast and osteogenic precursors that could be important to better understand the osteolysis observed in patients.

METHODS

Flow cytometry analysis of PBMC (Peripheral Blood Mononuclear Cells) was performed to characterize circulating osteoclast and osteogenic precursors in GSD patients (n = 9) compared to healthy donors (n = 55). Moreover, ELISA assays were assessed to evaluate serum levels of bone markers including RANK-L (Receptor activator of NF-κB ligand), OPG (Osteoprotegerin), BALP (Bone Alkaline Phosphatase) and OCN (Osteocalcin).

RESULTS

We found an increase of CD16-/CD14+CD11b+ and CD115+/CD14+CD11b+ osteoclast precursors in GSD patients, with high levels of serum RANK-L that could reflect the increase of bone resorption activity observed in patients. Moreover, no significant alterations were found regarding osteogenic precursors and serum levels of BALP and OCN.

CONCLUSION

The analysis of circulating bone cell precursors, as well as of RANK-L, could be relevant as an additional diagnostic tool for these patients and could be exploited for therapeutic purposes.

Differential responses to aging amongst the transcriptome and proteome of mesenchymal progenitor populations

The biological aging of mesenchymal stem cells is proposed to contribute to the development of a range of musculoskeletal and systemic diseases associated with older adults, such as osteoporosis, sarcopenia, and frailty. Despite this, little is understood about the specific mechanisms which drive this stem cell exhaustion, with most studies evaluating indirect effects of other aging changes, such as DNA damage, senescence, and inflammaging. In this study, we assess the transcriptomic and proteomic changes in three different populations of mesenchymal progenitor cells from older (50-70 years) and younger (20-40 years) individuals to uncover potential mechanisms driving stem cell exhaustion in mesenchymal tissues. To do this, we harvested primary bone marrow mesenchymal stem and progenitor cells (MPCs), circulating osteoprogenitors (COP), and adipose-derived stem cells (ADSCs) from younger and older donors, with an equal number of samples from males and females. These samples underwent RNA sequencing and label-free proteomic analysis, comparing the younger samples to the older ones. There was a distinct transcriptomic phenotype associated with the pooled older stem cells, indicative of suppressed proliferation and differentiation; however, there was no consistent change in the proteome of the cells. Older MPCs had a distinct phenotype in both the transcriptome and proteome, again consistent with altered differentiation and proliferation, but also a pro-inflammatory immune shift in older adults. COP cells showed a strong transcriptomic shift to pro-inflammatory signaling but no consistent proteomic phenotype. Similarly, ADSCs displayed transcriptomic shift in physiologies associated with cell migration, adherence, and immune activation, but no consistent proteomic change with age. These results show that there are underlying transcriptomic changes with stem cell aging that likely contribute to a decline in tissue regeneration; however, contextual factors such as the microenvironment and general health status also have a strong role in this.

Circulating Osteoprogenitor Cells Have a Mixed Immune and Mesenchymal Progenitor Function in Humans

BACKGROUND

Circulating osteoprogenitors (COP) are a population of cells in the peripheral circulation that possess functional and phenotypical characteristics of multipotent stromal cells (MSCs). This population has a solid potential to become an abundant, accessible, and replenishable source of MSCs with multiple potential clinical applications. However, a comprehensive functional characterization of COP cells is still required to test and fully develop their use in clinical settings.

METHODS

This study characterized COP cells by comparing them to bone marrow-derived MSCs (BM-MSCs) and adipose-derived MSCs (ASCs) through detailed transcriptomic and proteomic analyses.

RESULTS

We demonstrate that COP cells have a distinct gene and protein expression pattern with a significantly stronger immune footprint, likely owing to their hematopoietic lineage. In addition, regarding progenitor cell differentiation and proliferation pathways, COP cells have a similar expression pattern to BM-MSCs and ASCs.

CONCLUSION

COP cells are a unique but functionally similar population to BM-MSCs and ASCs, sharing their proliferation and differentiation capacity, thus presenting an accessible source of MSCs with strong potential for translational regenerative medicine strategies.

Higher Levels of Circulating Osteoprogenitor Cells Are Associated With Higher Bone Mineral Density and Lean Mass in Older Adults: A Cross-Sectional Study

Circulating osteo progenitor (COP) cells are a heterogeneous population of cells that circulate within the peripheral blood with characteristics of the bone marrow mesenchymal stem and progenitor pool. Little is known about the behavior of this cell population in humans. The aim of this study was to identify whether a relationship exists between COP cells (as a percentage of the peripheral blood monocytic cells) and musculoskeletal morphometry and to identify if COP have potential clinical utility as a biomarker for osteoporosis. We recruited 57 older adults (median age: 69 years; IQR: 65, 75 years) living independently in the community and performed cross‐sectional analysis to identify associations between the percentage of COP cells and body composition parameters, and through receiver operating characteristic analysis, we evaluated their ability to act as a biomarker of osteoporosis. COP cells were moderately associated with whole‐body bone mineral density (BMD) (r = 0.323, p = 0.014) and bone mineral content (BMC) (r = 0.387, p = 0.003), neck of femur BMD (r = 0.473, p < 0.001), and BMC (r = 0.461, p < 0.001) as well as appendicular lean mass (ALM) (p = 0.038) and male sex (p = 0.044) in univariable analysis. In multivariable analysis controlling for age, gender, height, and weight, COP cells remained strongly associated with neck of femur BMD (p = 0.001) and content (p = 0.003). COP cells were also a good predictor of osteoporosis (dual‐energy X‐ray absorptiometry [DXA] T‐score < −2.5) at the neck of femur (cutoff: 0.4%; sensitivity: 100%; specificity 79%) and total body (cutoff: 0.35%; sensitivity: 80%; specificity: 81%). This study shows strong relationships between bone parameters and COP cell number and male sex. They also have potential as a biomarker of osteoporosis, which may provide a new tool for advanced detection and screening in clinical settings. Future larger evaluation studies should verify the cutoffs for biomarker use, and further explore the relationship between COP cells and muscle. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.