Effect And Mechanism Of Static Magnetic Field On The Development Of Osteoporosis

Objective: Bone marrow-derived mesenchymal stem cells(BMSC)have the potential to differentiate into a variety of cell types,including osteoblasts,chondrocytes,and adipocytes.Under normal conditions,adipocyte and osteoblast differentiation of BMSC maintains a dynamic balance.Along with aging,hormone alternations,some drug treatment and genetic viarations,this balance may be modulated to adapt the enviroments.For example,BMSCs tend to differentiate into adipocytes,but not into osteoblasts in old people,which easily leads to numerous bone and metabolic diseases,including osteoporosis.Osteoporosis is characterized by increased bone marrow fat accumulation and reduced bone formation.However,the molecular mechanisms on regulation of differentiation of BMSCs into osteoblasts and adipocytes is still unclear,thereby further investigations are desirable for better prevention and treatment of osteoporosis.Biomagnetic materials are widely used in medicine,such as magnetic nanocarriers,medical contrast agents,tracers,artificial bones and dental pulp capsules,which have direct contact with human tissues and may have unexpected physiological effects.These magnetic materials typically produce static magnetic fields(SMF),and flux leakage diffuses into adjacent tissues to exert biological effects.It has been reported that SMF drives the directional migration of nano-iron-modified stem cells,maintains the survival and proliferation of dental pulp stem cells and facilitates them to differentiate into dental bone cells.SMF also can promote BMSCs to differentiate into osteoblasts and skeletal muscle cells.But the role of SMF in the differentiation of BMSCs and development of osteoporosis remains unclear,and the mechanism also need to be further studied.The phenomenon of magnetic reception by cells or organisms is widespread,but controversial.One of debates is the presence of targeting molecules that are magnetically regulated in cells or organisms.There are three types of magnet-sensitive materials or molecules in living organisms: ferrous minerals,iron-binding proteins and iron-sulfur cluster proteins.According to the important role of iron-sulfur cluster proteins in biological activities,scientists speculate that they may be the potential magnetic receptional protein as a target molecule that receives a magnetic field signal.However,the current biological research on magnetic proteins is much limited.This study aims to explore whether SMF affects the differentiation of BMSCs and development of osteoporosis,and to clarify the potential molecular mechanism involved in this process,which could provide new ideas and stratergies for the prevention and treatment of osteoporosis.MethodsAfter harvested and characterized,BMSCs were cultured in adipogenic differentiation medium and osteogenic differentiation medium under normal conditions or SMF environment,respectively.At the end of differentiation,ORO staining or ALP activity assay or alizarin red staining,transcriptome sequencing,RT-PCR and Western blotting were used to detect the effects of SMF on adipogenic differentiation and osteogenic differentiation of BMSC;at the animal level,we established trans-retinoic acid(ATRA)and dexamethasone(Dex)-induced osteoporosis models in mice that exposed to SMF atmosphere or normal conditions,and the effect of SMF on osteoporosis in mice was measured.Further,we explored the molecular mechanisms that SMF affect BMSC differentiation and mouse osteoporosis through gene expression profiling,drug intervention,and genetic deletion.Results1.SMF inhibites the adipogenic differentiation of BMSCs in culture.By Oil red O staining,transcriptome sequencing,RT-PCR and Western Blot,we examined the effect of SMF on adipogenic differentiation from BMSCs.We found that SMF inhibited the expression of adipogenic differentiation-related genes and suppressed BMSC differentiate into adipocytes,at magnetic field intensity-dependent manner to some extent;2.SMF promoted osteogenic differentiation of BMSCs in vitro.Through ALP activity detection,alizarin red staining,transcriptome sequencing,RT-PCR and Western Blot assays,we showed that SMF increased the transcription expression of osteogenic differentiation-related genes to enhance osteogenic differentiation of cultured BMSCs,and higher dose magnetic field displayed stronger impacts;3.SMF prevented the development of osteoporosis in mice.The SMF significantly improved the deterioration of bone mineral density and trabecular bone volume induced by ATRA and Dex in mice.In addition the fat accumulation was reduced,while the activity of osteoblasts was increased in bone tissue after stimulated by SMF.The results imply that SMF amaliorated osteoporosis through inhibiting the fat accumulation and promoting osteogenic differentiation;4.Abce1 played a important role in modulation of BMSC differentiation.SMF inhibited the adipogenic differentiation of BMSC by suppressing the function of RNase L inhibitor of Abce1.The silencing or deletion of Abce1 interrupted the effect of SMF on BMSC differentiation and osteoporosis,indicating that Abce1 mediates the effect of SMF on the differentiation of BMSC.Conclusion:SMF regulates the differentiation of BMSCs toward to adipocytes and osteoblasts,therefore inhibits development of osteoporosis.Through a large number of experiments,we have proved that the SMF effectively inhibits the adipogenic differentiation of BMSC and promote the osteogenic differentiation of BMSC.In addition,SMF reduces the bone loss in mice through two animal models of osteoporosis,and reduces fat accumulation and promotes osteoblast activity in the bone tissue.We also found that Fe-S cluster protein Abce1 plays a critical role in the differentiation process of BMSCs,and silencing or deletion of Abce1 interrupted the effect of SMF on BMSC differentiation and osteoporosis.Thus,SMF may serve as an adjuvant therapy or prevention for osteoporosis through targeting Abce1.