THE FREQUENCY OF PDPN+ CD146- HUMAN SKELETAL STEM CELLS AND ITS PROGENY VARIES IN ADULT BONES OF DIFFERENT ANATOMICAL LOCATIONS

Abstract

<h3>Background</h3> Adult human skeletal stem and progenitor cells (hSSPCs), also known as bone marrow mesenchymal stem/stromal cells, are envisioned for bone bioengineering applications. Nevertheless, optimization of the procedures for the manufacture of clinical-grade cellular products are still needed. Recently, new phenotypic markers of the different hSSPCs subsets were described, but the frequency of these populations in bones of different anatomical locations are still unknown. In order to determine the best sourcing bone for improved hSSPCs isolation, in this study we evaluated the frequency of four cellular subpopulations within this system: the multipotent self-renewing skeletal stem cell pool (SSCs, PDPN+ CD146- CD164+ CD73+), the early bone, cartilage, and stroma progenitor (BCSPs, PDPN+ CD146+), the committed osteoprogenitors (OPs, PDPN- CD146+), and the chondroprogenitors (CPs, PDPN+ CD146-) in bone samples from hip and humerus. <h3>Methods</h3> Following ethical approval (CAAE n° 21768719.0.0000.5257), surgical waste bone from humerus or hip (acetabulum) were collected from patients of both sex, older than 18 years-old, undergoing primary arthroplasty. Following bone marrow dissociation and lineage depletion, the frequency of SSCs, BCSPs, OPs, and CPs in each sample was determined by FACS. <h3>Results</h3> In hip samples (n = 8), all four subpopulations were detected. SSCs accounted for 0.076% ± 0.20% of the CD45- CD31- pool, while BCSPs were 2.95% ± 3.95%, CPs were 8.29% ± 11.60%, and OPs were 7.41% ± 11.88%. In humerus (n = 3), however, only BCSPs and OPs were identified. Comparatively, the frequency of BCSPs in humerus was lower than in hip (0,025% ± 0,11%). In compensation, humerus samples had an increased frequency of OPs (25,05% ± 5,30%). <h3>Conclusion</h3> Our preliminary findings indicate that the frequency of the cell populations that compose the bone marrow SSPCs system significantly varies in bones, depending on their anatomical location. Therefore, the distinct bone sources investigated herein could be differentially explored to manufacture cellular products with specific combinations of SSPCs subsets and, consequently, with specific and more predictable biological properties. These tailor-made cellular products could translate in enhanced effectiveness in unique therapeutic contexts, changing the current perspective of trial-and-error in SSPCs application in skeletal regenerative medicine.