The Role Of MicroRNA-29 In Regulation Of Skeletal Muscle Development And Atrophy In Mice

MicroRNAs are a class of small noncoding RNAs that are evolutionarily conserved from plants to mammals.MicroRNAs significantly impact muscle growth,regeneration and metabolism.MicroRNA-29 takes part in the progress of skeletal muscle cells differentiation.In the skeletal muscle,most of the studies of microRNA-29 are in the cell level.So we constructed the microRNA-29a,b cluster transgenic mice via Tet-on system.In this study,we found overexpression of miR-29a,b cluster after birth caused mice muscular dystrophy.We observed some mice showed respiratory disorder,exercise capacity decrease and kyphosis as well as scoliosis.Tissue staining and immunofluorescence results showed the diaphragm was thin and the muscle fibers shape changed.The tibialis anterior muscle were also showed uneven fibers diameter,changed fibers shape,centered fiber nuclei,and serious fibrosis between the muscle fibers.These illnesses are the same as human's UCMD.Using Real-Time quantitative PCR(qPCR)and Western Blot,we found the collagen IV was down-regulated in the transgenic mice.Immunofluorescence results showed a lot of muscle stem cells were activated and lots of muscle fibers expressed the regeneration myosin heavy chain(eMYHC).qPCR results showed that the mRNA levels of a variety of myosin heavy chain were up-regulated,but the mRNA level of MYH4 was down-regulated.Using immunofluorescence,we found myosin heavy chain I was abnormal accumulation.MuRF1 is the predicted target gene of miR-29.miR-29 could inhibit the expression of MuRF1 and block the MuRF1-depend degradation of myosin heavy chain I.Loss of MuRF1 can reduce the rate of atrophy upon denervation,glucocorticoid treatment or fasting.Furthermore,we showed that miR-29a,b cluster transgenic mice were resistant to fasting-induced muscle atrophy.And forced expression of miR-29 mimics in myotube resisted the glucocorticoid induced myotube atrophy.Taken together,the present study demonstrated that miR-29a,b cluster transgenic mice are a suitable model for Ullrich congenital muscular dystrophy.miR-29a,b cluster transgenic mice show a series of myopathy phenotypes,including respiratory disorder,exercise capacity decrease and kyphosis as well as scoliosis.The molecular results show that these illnesses are related to the collagen ?.miR-29a,b cluster transgenic mice are resistant to fasting-induced muscle atrophy.And forced expression of miR-29a,b mimics in myotube can resist the glucocorticoid induced myotube atrophy.So miR-29a,b cluster transgenic mice can be used for pathogenesis exploration,accumulation of clinical experience and accelerate drug development.At the same time,miR-29a,b cluster transgenic mice provide new ideas and theoretical basis for the treatment of muscle atrophy.