SOME RESEARCH ON MECHANISM AND COUNTERMEASURE OF MICROGRAVITY-INDUCED OSTEOPOROSIS

© Lian-wenSun, XiaoYang, ChaoWang, Yu-boFan
© Государственный музей истории космонавтики им. К.Э. Циолковского, г. Калуга
Секция "К.Э. Циолковский и проблемы космической медицины и биологии"
2010 г.

Exercise has been used to counter bone loss during spaceflight. However, the existing exercise methods couldn’t fully prevent bone loss in astronauts. There are two possible causes: 1) the existing exercises are not proper for using in space. 2) The ability of bone to sense loading has changed in space. Based on these, studies as followed are mainly carrying out in our group.

1. Comparing the efficacy of active and passive exercise on countering microgravity-induced osteoporosis for finding out efficient countermeasure.

The hypothesis was provided by our groups that the absence of gravity might change the active exercise to passive motion in space in some degree. Rat tail-suspended model was used to simulate microgravity. A device has been developed by our group for training tail-suspended rat to do active or passive exercise. SD rats were randomly divided into four groups: tail-suspended (TS), TS+passive motion (TSP), TS+ active exercise (TSA) and control (CON) and were raised for 21d. Bone mineral density (BMD) was measured by DXA, trabecular microstructure by microCT and mechanical properties of femurs were measured by three-point bending test. The results showed BMD decreased significantly in TS and TSP compared with CON while there was no significant difference between TSA and CON. And the bone microstructure and mechanical properties in TSA were most similar to CON. These indicate the effect of active exercise on preventing bone loss induced by hindlimb unloading is better than that of passive motion.

2. Investigating the mechanosensibility of osteocytes under simulated microgravity for understanding mechanism of microgravity-induced osteoporosis.

Most researches previously showed that osteocytes as mechanosensors would response to the mechanical stimulation and regulate the function of other effector cells. However, whether the mechanical sensitivity of osteocytes changes in microgravity is not well understood. Cell rotary culture was used to simulated microgravity. An osteocyte-like cell line, MLO-Y4, was cultured in rotation and then was sheared by fluid in flow chamber. At 5, 10, 15, 20, 30 and 40min, nitric oxide (NO) and prostaglandin E2 (PGE2) were measured by Griess Reagent and ELISA respectively. In addition, alkaline phosphatase (ALP) and osteocalcin (BGP) were measured after 6h shear stress by PNPP and ELISA respectively. The results showed that: (1) Exposing to shear stress, the peak of NO was retarded both in control and rotary cells while the increase extend was smaller in rotary cells than that in control. Meanwhile, the peak of PGE2 appeared in rotary cells later than that in control. (2) Exposing to shear stress, ALP increased both in rotary and control group while the increase extend was smaller in rotary cells than that in control. BGP decreased both in rotary and control group while the decrease extend was smaller in rotary cells than in control. All these indicated the mechanosensibility of osteocytes changed under simulated microgravity.