Simulated Microgravity Increases the Permeability of HUVEC Monolayer through Up-Regulation of Rap1GAP and Decreased Rap2 Activation

Loss of RAP2A Aggravates Cartilage Degradation in TMJOA via YAP Signaling

Abnormal stress loading has been considered a major contributor to the initiation of temporomandibular joint osteoarthritis (TMJOA), but studies to date have not identified a functional molecule that transforms physical stress into biological or biochemical signaling in chondrocytes in response to excessive mechanical stress. Ras-related protein Rap-2a (RAP2A) is reportedly a molecular switch that relays extracellular matrix rigidity signals via the Hippo/Yes-associated protein (YAP) pathway. In the present study, RAP2A diminished with cartilage degradation in unilateral anterior crossbite-induced TMJOA mice, as well as severe cartilage matrix degeneration and TMJOA formation in Cre-loxP-mediated conditional RAP2A knockout mice. RAP2A in chondrocytes regulated the Hippo/YAP pathway directly in response to matrix stiffness, and RAP2A/Hippo/YAP was critical for a chondrocyte phenotype switch and matrix synthesis function. Loss of RAP2A impaired cartilage homeostasis and altered chondrocyte phenotype via Hippo/YAP/SRY-box transcription factor 9 signaling. It may be possible to generate therapeutic strategies using RAP2A or YAP to attenuate the TMJOA pathological process at an early stage. This is the first study to reveal the molecular function of RAP2A in TMJOA progression as a mechanotransduction molecule in condylar chondrocytes.

Testing 3D printed biological platform for advancing simulated microgravity and space mechanobiology research

The advancement of microgravity simulators is helping many researchers better understanding the impact of the mechanically unloaded space environment on cellular function and disfunction. However, performing microgravity experiments on Earth, using simulators such as the Random Positioning Machine, introduces some unique practical challenges, including air bubble formation and leakage of growth medium from tissue culture flask and plates, all of which limit research progress. Here, we developed an easy-to-use hybrid biological platform designed with the precision of 3D printing technologies combined with PDMS microfluidic fabrication processes to facilitate reliable and reproducible microgravity cellular experiments. The system has been characterized for applications in the contest of brain cancer research by exposing glioblastoma and endothelial cells to 24 h of simulated microgravity condition to investigate the triggered mechanosensing pathways involved in cellular adaptation to the new environment. The platform demonstrated compatibility with different biological assays, i.e., proliferation, viability, morphology, protein expression and imaging of molecular structures, showing advantages over the conventional usage of culture flask. Our results indicated that both cell types are susceptible when the gravitational vector is disrupted, confirming the impact that microgravity has on both cancer and healthy cells functionality. In particular, we observed deactivation of Yap-1 molecule in glioblastoma cells and the remodeling of VE-Cadherin junctional protein in endothelial cells. The study provides support for the application of the proposed biological platform for advancing space mechanobiology research, also highlighting perspectives and strategies for developing next generation of brain cancer molecular therapies, including targeted drug delivery strategies.