Ligand-Mediated Endocytosis Is Regulated in a Sexually Dimorphic Way in Osteocytes in vivo

Endocytosis is a critical cellular process involved in many physiological functions. Most research on endocytosis has been performed in vitro, however, understanding this process in vivo is necessary in tissues like bone that have a unique 3D extra-cellular matrix. Here, we present a live-cell study of endocytosis in osteocytes, mechanosensory cells embedded in mouse bone. We visualized real-time fluorescent nanoparticle uptake and trafficking in osteocytes by using intravital imaging combined with multiphoton microscopy within living animals. We applied pharmacologic inhibitors to distinguish between general and receptor-specific endocytosis pathways in vivo. Our findings reveal rapid nanoparticle uptake in osteocytes, with marked differences in the timescale and pattern of uptake depending on nanoparticle surface functionality. We also discovered differences in dynamin-dependent endocytosis in osteocytes between male and female animals. These results offer the first in vivo derived insights into how osteocytes take up materials and provide new evidence for chemically altering receptor-mediated endocytosis in live bone tissue.