AFM-based nanoscale characterization of physical interaction within hematopoietic stem cells niche at single-cell level

Hematopoietic stem cells (HSCs) produce all blood cells throughout the lifespan of the organism. HSC requires a specialized bone marrow microenvironment, known as the niche, for proper differentiation and self-renewal. While several molecular and cellular elements of the niche are described, the precise understanding of the mechanobiology underlying HSC adhesion to the niche remains poorly understood. Here, we aim to characterize physical interactions and adhesion within the hematopoietic niche by combining cell sorting, surface functionalization, and atomic force microscopy. Using this approach, we quantified and compared the adhesion of bone marrow (BM) mesenchymal stromal cells (MSCs) to different extracellular proteins, as well as the adhesion of HSCs to MSCs. We observed that MSCs adhere with the greatest force to fibronectin in an Arg-Gly-As (RGD) motif mediated and actin cytoskeleton-dependent manner. Additionally, we showed that HSCs strongly adhere to MSC within 30 seconds and that the binding is RGD-independent. In conclusion, we demonstrated how to implement atomic force microscopy to measure the physiological interactions within the HSCs niche in a direct, specific, and quantitative way. This approach provides a more comprehensive and precise characterization of the biology of the HSC niche compared to previously used methods. Furthermore, it highlights the complexity of studying extremely small structures and rare cell populations in biophysical experiments.