Identification of osteolineage cell-derived extracellular vesicle cargo implicated in hematopoietic support.

Osteolineage cell-derived extracellular vesicles (EVs) play a regulatory role in hematopoiesis and have been shown to promote the ex vivo expansion of human hematopoietic stem and progenitor cells (HSPCs). Here, we demonstrate that EVs from different human osteolineage sources do not have the same HSPC expansion promoting potential. Comparison of stimulatory and non-stimulatory osteolineage EVs by next-generation sequencing and mass spectrometry analyses revealed distinct microRNA and protein signatures identifying EV-derived candidate regulators of ex vivo HSPC expansion. Accordingly, the treatment of umbilical cord blood-derived CD34+ HSPCs with stimulatory EVs-altered HSPC transcriptome, including genes with known roles in cell proliferation. An integrative bioinformatics approach, which connects the HSPC gene expression data with the candidate cargo in stimulatory EVs, delineated the potentially targeted biological functions and pathways during hematopoietic cell expansion and development. In conclusion, our study gives novel insights into the complex biological role of EVs in osteolineage cell-HSPC crosstalk and promotes the utility of EVs and their cargo as therapeutic agents in regenerative medicine.

Cross-Talk Between Human Tenocytes and Bone Marrow Stromal Cells Potentiates Extracellular Matrix Remodeling In Vitro.

Tendon and ligament (T/L) pathologies account for a significant portion of musculoskeletal injuries and disorders. Tissue engineering has emerged as a promising solution in the regeneration of both tissues. Specifically, the use of multipotent human mesenchymal stromal cells (hMSC) has shown great promise to serve as both a suitable cell source for tenogenic regeneration and a source of trophic factors to induce tenogenesis. Using four donor sets, we investigated the bidirectional paracrine tenogenic response between human hamstring tenocytes (hHT) and bone marrow-derived hMSC. Cell metabolic assays showed that only one hHT donor experienced sustained notable increases in cell metabolic activity during co-culture. Histological staining confirmed that co-culture induced elevated collagen protein levels in both cell types at varying time-points in two of four donor sets assessed. Gene expression analysis using qPCR showed the varied up-regulation of anabolic and catabolic markers involved in extracellular matrix maintenance for hMSC and hHT. Furthermore, analysis of hMSC/hHT co-culture secretome using a reporter cell line for TGF-ß, a potent inducer of tenogenesis, revealed a trend of higher TGF-ß bioactivity in hMSC secretome compared to hHT. Finally, hHT cytoskeletal immunostaining confirmed that both cell types released soluble factors capable of inducing favorable tenogenic morphology, comparable to control levels of soluble TGF-ß1. These results suggest a potential for TGF-ß-mediated signaling mechanism that is involved during the paracrine interplay between the two cell types that is reminiscent of T/L matrix remodeling/turnover. These findings have significant implications in the clinical use of hMSC for common T/L pathologies.

Extracellular Vesicles Derived From Adult and Fetal Bone Marrow Mesenchymal Stromal Cells Differentially Promote ex vivo Expansion of Hematopoietic Stem and Progenitor Cells.

Recently, we and others have illustrated that extracellular vesicles (EVs) have the potential to support hematopoietic stem and progenitor cell (HSPC) expansion; however, the mechanism and processes responsible for the intercellular communication by EVs are still unknown. In the current study, we investigate whether primary human bone marrow derived mesenchymal stromal cells (BMSC) EVs isolated from two different origins, fetal (fEV) and adult (aEV) tissue, can increase the relative low number of HSPCs found in umbilical cord blood (UCB) and which EV-derived components are responsible for ex vivo HSPC expansion. Interestingly, aEVs and to a lesser extent fEVs, showed supportive ex vivo expansion capacity of UCB-HSPCs. Taking advantage of the two BMSC sources with different supportive effects, we analyzed the EV cargo and investigated how gene expression is modulated in HSPCs after incubation with aEVs and fEVs. Proteomics analyses of the protein cargo composition of the supportive aEV vs. the less-supportive fEV identified 90% of the Top100 exosome proteins present in the ExoCarta database. Gene Ontology (GO) analyses illustrated that the proteins overrepresented in aEVs were annotated to oxidation-reduction process, mitochondrial ATP synthesis coupled proton transport, or protein folding. In contrast, the proteins overrepresented in fEVs were annotated to extracellular matrix organization positive regulation of cell migration or transforming growth factor beta receptor (TGFBR) signaling pathway. Small RNA sequencing identified different molecular signatures between aEVs and fEVs. Interestingly, the microRNA cluster miR-99b/let-7e/miR-125a, previously identified to increase the number of HSPCs by targeting multiple pro-apoptotic genes, was highly and significantly enriched in aEVs. Although we identified significant differences in the supportive effects of aEVs and fEVs, RNAseq analyses of the 24 h treated HSPCs indicated that a limited set of genes was differentially regulated when compared to cells that were treated with cytokines only. Together, our study provides novel insights into the complex biological role of EVs and illustrates that aEVs and fEVs differentially support ex vivo expansion capacity of UCB-HSPCs. Together opening new means for the application of EVs in the discovery of therapeutics for more efficient ex vivo HSPC expansion.

Influencing chondrogenic differentiation of human mesenchymal stromal cells in scaffolds displaying a structural gradient in pore size.

UNLABELLED: Articular cartilage lesions have a limited ability to heal by themselves. Yet, golden standard treatments for cartilage repair such as drilling, microfracture and mosaicplasty provide further damage and an unstable solution that degenerates into fibrocartilage in time. Articular cartilage presents a number of gradients in cell number and size along with structural gradients in extra cellular matrix (ECM) composition. Therefore, creating scaffolds that display a structural gradient can be an appealing strategy for cartilage tissue regeneration treatments. In the present study, a scaffold with an in-built discrete gradient in pore size was produced by additive manufacturing. Human mesenchymal stromal cells (hMSCs) were seeded within the gradient scaffolds and their proliferation, differentiation and ECM deposition was evaluated with respect to 2 non-gradient scaffolds. Glycosaminoglycan (GAG) deposition was significantly higher in gradient scaffolds and non-gradient scaffolds with the smallest pore size compared to non-gradient scaffolds with the largest pore size. A gradual increase of chondrogenic markers was observed within the gradient structures with decreasing pore size, which was also accompanied by an increasingly compact ECM formation. Therefore, scaffolds displaying a structural gradient in pore size seem to be a promising strategy to aid in the process of hMSC chondrogenic differentiation and could be considered for improved cartilage tissue regeneration applications. STATEMENT OF SIGNIFICANCE: We present the development of a novel hierarchical scaffold obtained by additive manufacturing. Structural hierarchy is obtained by changing pore size within the pore network characterizing the fabricated scaffolds and proves to be a functional element in the scaffold to influence adult stem cell differentiation in the chondrogenic lineage. Specifically, in regions of the scaffolds presenting smaller pores an increasing differentiation of stem cells toward the chondrogenic differentiation is displayed. Taking inspiration from the zonal organization of articular cartilage tissue, pore size gradients could, therefore, be considered as a new and important element in designing 3D scaffolds for regenerative medicine applications, in particular for all those tissues where gradient physical properties are present.

Mesenchymal stromal cell-derived extracellular matrix influences gene expression of chondrocytes.

Decellularized extracellular matrix (ECM) has recently gained a lot of interest as an instructive biomaterial for regenerative medicine applications. In this study, the ability of adult human mesenchymal stem cell (hMSC)-derived ECM to rescue the phenotype of osteoarthritic (OA) chondrocytes and to further stimulate the differentiation of healthy (HL) chondrocytes was evaluated. ECMs were prepared by decellularizing hMSCs cultured in basic medium (BM) and chondrogenic medium (CM). The obtained ECM was then combined with a polymeric solution of Poly (ε-caprolactone) (PCL) dissolved in 1, 1, 1, 3, 3, 3-hexafluoro-2-propanol (HFIP) and electrospun meshes were fabricated. Electrospun ECM scaffolds were characterized using scanning electron microscopy (SEM) and picrosirius red staining was used to confirm the presence of collagen. OA and HL chondrocytes were cultured on scaffolds containing hMSC ECM in BM or CM and compared to PCL electrospun scaffolds without ECM. Metabolic activity and chondrogenic gene expression were assessed by Alamar blue assay and quantitative PCR (qPCR) analysis, respectively. The ECM presence resulted in a significant difference in chondrocyte metabolic activity compared to PCL scaffolds alone. HL chondrocytes cultured for 21 days in chondrogenic medium on electrospun scaffolds containing hMSC ECM from BM showed a significant increase in collagen II and aggrecan expression compared to hMSC ECM from CM and PCL scaffolds without ECM incorporation. No significant influence of hMSC ECM presence on the chondrogenic signature of OA chondrocytes was found. The influence of decellularized hMSC ECM on HL chondrocytes suggests that hMSC-derived ECM scaffolds are promising candidates for cartilage tissue engineering applications.