The Impact Of Sema3A On Bone Loss Under Simulated Gravity Changes

Reduced blood flow shear may lead to the occurrence of bone loss,and osteoporosis is one of the obvious manifestations of bone loss as a secondary condition.Spaceflight astronauts are in a weightless state during which weightbearing bone is unloaded,increasing bone resorption and uncoupling of bone metabolism,and the release of calcium from unweighted weight-bearing bone contributes to bone loss.Genomic analysis has shown that the expression of hundreds of genes in osteoblasts is altered upon exposure to microgravity.Previous studies by our group have shown that Sema 3A expression in vascular endothelial cells is elevated in the overweight condition,and the level of Sema 3A is significantly reduced in the weight loss condition,and osteoporosis caused by weight loss is closely associated with the downregulation of Sema 3A,but studies on the specific causes of bone loss caused by weight loss conditions have not been fully elucidated.Therefore,in this study,we used mice and vascular endothelial cells b End3.0 as the subjects to study the role of weightlessness conditions on bone loss production in mouse bones by simulating different gravity conditions,and also to elucidate the mechanism of the occurrence of spatial bone loss by systematically studying and analyzing at the cellular molecular level.The main results of this study are as follows:Firstly,mice were used as research subjects,and a mouse osteoporosis model was constructed using the hind limb unloading(HLU)method to simulate microgravity conditions,and Mirco-CT was used for image acquisition and bone morphological analysis of isolated samples from the mouse model to detect various bone morphological parameters in mice,and then the bone histological study method and Elisa assay were used to verify again and determine the osteoporosis of mice and the changes of Sema 3A expression in their bones and peripheral blood.The results showed that the majority of the animal models of osteoporosis established under simulated microgravity conditions developed osteoporosis,and the expression of Sema3 A was significantly reduced in mice with osteoporosis compared with normal mice.This indicates that Sema 3A has an important role in triggering bone loss in mice under simulated weightlessness.Next,we used vascular endothelial cells b End3.0 as the object of study,simulated hypergravity conditions to construct a rotary cell model,treated the cell model with different signaling pathway inhibitors,and used various molecular experimental techniques to detect the changes of Sema 3A and related signaling pathway protein expression.The results showed that treatment of the cell model with PI3K/AKT/m TOR signaling pathway inhibitor LY294002 resulted in a decrease in Sema 3A expression and an increase in PI3 K protein expression.It indicates that the changes in bone volume triggered by Sema 3A under simulated gravity conditions may be related to the PI3K/AKT/m TOR signaling pathway.Finally,to further illustrate the role of Sema 3A protein structure in triggering bone loss under simulated gravity conditions,analysis of its structural domain using Py MOL software showed that Sema 3A cross-supports components with Nrp1 s,bridging between Sema structural domains between Sema 3A and Plxn A2 subunits from two heterotrimers.It is confirmed that this binding mode stabilizes the canonical but attenuated Sema3-Plxn A interaction and increases co-receptor control of receptor dimerization and oligomerization-triggered signaling mechanisms.In summary,under weightless conditions,the bone associated cytokine Sema 3A triggers osteoporosis in mice through the PI3K/AKT/m TOR signaling pathway,with reduced relative expression and changes in its own structural domain.