Resilience of the bone marrow vascular architecture to aging and hematological stress

The vasculature within the bone marrow plays a pivotal role in shaping the hematopoietic environment, significantly influencing the development and function of blood cells. However, the intricate shifts in vascular architecture, especially as the body ages or under physiological stress, remain largely uncharted territory. In this study, we explored these vascular dynamics using light sheet fluorescence microscopy paired with advanced image analysis, focusing on both large, CD31^hi, and smaller, CD105⁺, vessels within murine femora. We compared young adult (aged 8 weeks) mice with moderately aged (52 weeks) mice, and assessed the impact of hematological stress induced by previous blood sampling. Our findings revealed an intriguing balance of resilience and adaptability: larger vessels show a remarkable structural stability across ages, whereas smaller vessels undergo pronounced age-associated remodeling. In aged mice, vascular branching complexity surges, with higher branch density and narrower vessel diameters in specific femur regions, clear hallmarks of vascular aging. Interestingly, even after previous blood sampling, the bone marrow vasculature maintains its integrity, hinting at a robust resilience to hematological stress. This resilience underscores the potential to streamline research models by reusing animals for both cell isolation and histology, supporting the 3R principles (replacement, reduction, and refinement) to minimize animal use. These insights into the stability, adaptability, and regional-specific remodeling of bone marrow vasculature, highlighting its remarkable resilience, provide a deeper understanding of age-related vascular remodeling, and offer valuable implications for experimental design in hematopoiesis research.