Effects of 32 d of spaceflight on tendon collagen fibril morphology and nanomechanics

INTRODUCTION: Collagen is an essential component of connective tissue and plays a crucial role in elasticity, stability, and force distribution. While the adaptations of tendon to internal stimuli have been extensively researched, the impact of environmental factors (such as microgravity) on its structure and function at the nanoscopic scale (i.e., fibril level) remains largely unexplored. The purpose of this study was to determine the effects of 32 days (d) aboard the International Space Station (ISS) on murine tendon collagen fibril morphology and nanomechanics (Young’s Modulus, YM). We hypothesized there would be a decrease in fibril size and YM after spaceflight. Methods: Quadriceps tendon samples from female C57BL/6J mice from NASA Rodent Research-1 underwent chemical processing and mechanical isolation. Subsequently, collagen fibrils (n=56) were studied via atomic force microscopy (AFM; JPK NanoWizard 4a) to compare the morphology (diameter, height) and nanomechanics (average YM) between spaceflight (SF) and ground control (GC) specimens. The qp-BioAC-CB1 cantilever (spring constant: 0.3 N/m, tip radius: 10μm) was used under quantitative imaging mode (QI) for all force and morphological measurements. The data from 56 micrographs (SF n=30; GC n=26) was processed via the JPK Data Processing Software (Version 6.4.5.), and finally analyzed with Gwyddion (Version 2.62). A 2-way MANOVA compared all measurements. Results: More ‘small fibrils’ (height <50nm) were identified in the SF vs GC samples. SF fibrils averaged 20.3% smaller (width) compared to GC, but this difference was not significant (p>0.05). Additionally, while there was a trend for a lower YM in the SF samples, YM for SF specimens was not statistically different between groups (GC=3.26±1.94 MPa; SF= 2.76±1.44 MPa) (p>0.05). CONCLUSION: To our knowledge, this is the first investigation to use AFM QI-mode on tendon collagen fibrils after spaceflight. While there were no statistically significant changes in mean fibril size and YM between SF and GC, these results suggest that collagen fibrils may require more time to adapt to changes in their environment, and/or more rapid changes may take place at different levels of the collagen hierarchy. Our data provides valuable insight into mammalian tissue adaptations during spaceflight. Future research should continue these investigations with longer-duration missions to build a time-course of tendon adaptations to microgravity. FUNDING: CSUBIOTECH New Investigator Grant (JRB). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.