Pilot proteomics study of three different human femur sites and autologous serum samples

Tissue proteomics will help discover the molecular pathophysiology of bone diseases. So far, most human studies have been performed on serum/plasma samples. We present an initial pilot proteomics analysis comparing three clinically important anatomical femur sites (caput, collum, and trochanter). The specimens were obtained from osteoarthritic patients undergoing hip replacement surgery and represented predominantly cortical bone from collum and mostly trabecular bone from caput, together with a mixture from trochanter. The bone and the corresponding serum samples were analyzed by high-throughput data-independent acquisition (DIA) liquid chromatography-mass spectrometry (LC-MS/MS). The results showed that the protein composition of bone/bone marrow was substantially more complex than serum, presenting a total of 3085 and 597 detected proteins, respectively. A major part of the detected osteoblast/osteocyte, adipocyte, mesenchymal stem cell (MSC), and hematological/immunological characteristic proteins were similar between the corresponding femur sites in all donors and different from serum. Although the majority of the bone proteome was conserved across anatomical sites, exploratory analyses of the global proteomic landscape revealed site-specific protein signatures and associated functional pathways that were highly consistent across individuals. These findings suggest that anatomically adjacent femoral sites share a conserved core bone proteome while maintaining distinct molecular characteristics of potential functional relevance. With validation in larger cohorts, the results will contribute to the development of a human bone tissue proteomics atlas providing novel insight in the molecular microarchitecture and functionality relevant for bone health.