Thirty 12-week-old male C57BL/6 mice were randomly divided into control group， weightlessness group and weightlessness + PM （200 mg·kg^－1·d^－1） group， and there were 10 mice in each group. After 4 weeks， the ratio of bone volume/tissue volume， the trabecular number， trabecular thickness，and trabecular space of the mice in various groups was detected by micro CT；the BMSCs of the weightlessness mice were obtained by flow sorting.The BMSCs were divided into control group（0 μmol·L^－1 PM） and 10，20，and 40 μmol·L^－1 PM groups.The expression levels of Runx family transcription factor 2 （Runx-2）， alkaline phosphatase （ALP） and Osterix， peroxisome proliferator activated receptor γ （PPARγ）mRNA in BMSCs of the mice in various groups were detected by Real-time fluorescence quantitative PCR（RT-qPCR）method，and the expression levels of Runx-2， ALP， Osterix， PPARγ，mitogen activated protein kinase （MEK）， phosphorylated MEK 1/2（p-MEK1/2）， extracellular regulated protein kinase （ERK） and phosphorylated ERK 1/2（p-ERK1/2） proteins in BMSCs of the mice in various groups were detected by Western blotting method.

Compared with control group， the ratio of bone volume / tissue volume of the mice in weightlessness group was decreased （P<0.01）， the trabecular number was decreased （P<0.01）， the trabecular thickness was decreased （P<0.05）， and the trabecular space was increased （P<0.01）. Compared with weightlessness group， the ratio of bone volume/tissue volume of the mice in weightlessness+PM group was increased （P<0.05），the trabecular number was increased （P<0.01）， the trabecular thickness was increased （P<0.05）， and the trabecular space was decreased （P<0.01）. Compared with weightlessness group， the number of BMSCs of the mice in weightlessness+PM group was increased （P<0.01）， the number of osteoblasts was increased （P<0.01）， the number of adipocytes was decreased （P<0.05）， and the number of osteoclasts was decreased （P<0.05）. Compared with control group， the expression levels of Runx-2， ALP， and Osterix mRNA in BMSCs of the mice in 10， 20， and 40 μmol·L^－1 PM groups were increased （P<0.05）， and the expression level of PPARγ mRNA was decreased （P<0.05）， the expression levels of Runx-2， ALP， and Osterix proteins were increased （P<0.05）， and the expression level of PPARγ protein was decreased （P<0.05）. Compared with control group， the expression levels of p-MEK1/2 and p-ERK1/2 proteins in BMSCs of the mice in 10 μmol·L^－1 PM group were increased （P<0.05）； compared with 10 μmol·L^－1PM group，the expression levels of p-MEK1 / 2 and p-ERK1 / 2 proteins in BMSCs of the mice in 20 μmol·L^－1 PM group were increased （P<0.05）； compared with 20 μmol·L^－1　PM group， the expression levels of p-MEK1/2 and p-ERK1 / 2 proteins in BMSCs of the mice in 40 μmol·L^－1 PM group were increased （P<0.05）.

The extract of PM can promote the differentiation of BMSCs into osteoblasts in the weightlessness mice by activating the MEK/ERK signaling pathway，and improve the bone mass and the micro-structure of trabeculae，relieve the OP caused by weightlessness.