Wiesner, U. B. | Search bioRxiv

bioRxiv2024

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.

bioengineering↗

bioRxiv2023

Intravital imaging of osteocyte αvβ3 integrin dynamics with locally injectable fluorescent nanoparticles

Osteocytes are the resident mechanosensory cells in bone. They are responsible for skeletal homeostasis and adaptation to mechanical cues. Integrin proteins play an prominent role in osteocyte mechanotransduction, however the details are not well stratified in vivo. Intravital imaging with multiphoton microscopy presents an opportunity to study molecular level mechanobiological events in vivo, and could be used to study integrin dynamics in osteocytes. However, fluorescent imaging limitations with respect to excessive optical scattering and low signal to noise ratio caused by mineralized bone matrix make such investigations non-trivial. Here we demonstrate that ultra-small and bright fluorescent core-shell silica nanoparticles (<7nm diameter), known as Cornell Prime Dots (CDots), are well-suited for the in vivo bone microenvironment and can improve intravital imaging capabilities. We report validation studies for CDots as a novel, locally injected in vivo osteocyte imaging tool for both non-specific cellular uptake and for targeting integrins. The pharmacokinetics of CDots reveal distinct sex differences in nanoparticle cycling and clearance in osteocytes, which represents a novel topic of study in bone biology. Integrin-targeted CDots were used to study osteocyte integrin dynamics. To the best of our knowledge, we report here the first evidence of osteocyte integrin endocytosis and recycling in vivo. Our results provide novel insights in osteocyte biology and will open up new lines of investigation that were previously unavailable in vivo.

bioengineering↗