Liming Cheng

Abstract A number of microRNAs (miRNAs, miRs) have been shown to play a role in skeletal muscle atrophy, but their role is not completely understood. Here we show that miR-29b promotes skeletal muscle atrophy in response to different atrophic stimuli in cells and in mouse models. miR-29b promotes atrophy of myotubes differentiated from C2C12 or primary myoblasts, and conversely, its inhibition attenuates atrophy induced by dexamethasone (Dex), TNF-α and H 2 O 2 treatment. Targeting of IGF-1 and PI3K(p85α) by miR-29b is required for induction of muscle atrophy. In vivo , miR-29b overexpression is sufficient to promote muscle atrophy while inhibition of miR-29b attenuates atrophy induced by denervation and immobilization. These data suggest that miR-29b contributes to multiple types of muscle atrophy via targeting of IGF-1 and PI3K(p85α), and that suppression of miR-29b may represent a therapeutic approach for muscle atrophy induced by different stimuli.

DNA methylation is known to regulate cell differentiation and neuronal function in vivo. Here we examined whether deficiency of a de novo DNA methyltransferase, Dnmt3a, affects in vitro differentiation of mouse embryonic stem cells (mESCs) to neuronal and glial cell lineages. Early-passage neural stem cells (NSCs) derived from Dnmt3a-deficient ESCs exhibited a moderate phenotype in precocious glial differentiation compared with wild-type counterparts. However, successive passaging to passage 6 (P6), when wild-type NSCs become gliogenic, revealed a robust phenotype of precocious astrocyte and oligodendrocyte differentiation in Dnmt3a(-/-) NSCs, consistent with our previous findings in the more severely hypomethylated Dnmt1(-/-) NSCs. Mass spectrometric analysis revealed that total levels of methylcytosine in Dnmt3a(-/-) NSCs at P6 were globally hypomethylated. Moreover, the Dnmt3a(-/-) NSC proliferation rate was significantly increased compared with control from P6 onward. Thus, our work revealed a novel role for Dnmt3a in regulating both the timing of neural cell differentiation and the cell proliferation in the paradigm of mESC-derived-NSCs.

Osteoporosis (OP) is a major systemic bone disease leading to an imbalance in bone homeostasis which remains a challenge in the current treatment of bone defects. Our previous studies on strontium (Sr) doping apparently stimulated osteogenesis of bioceramics, which suggested a promising strategy for the treatment of bone defects. However, the potential effects and the underlying mechanisms of Sr-doping on osteoporotic bone defects still remain unclear. Autophagy is a conventional self-degradation process of cells involved in bone homeostasis and regeneration under physiological and pathological conditions. Therefore, it is essential to design appropriate biomaterials and investigate the associated osteogenic mechanisms via autophagy. Based on this hypothesis, Sr-doped 45S5 bioglass (Sr/45S5) was fabricated, and ovariectomy bone marrow-derived mesenchymal stem cells (OVX-BMSCs) were applied as the in vitro cell culture model. First, the optimal Sr-doping concentration of 10 mol% was screened by cell proliferation, ALP staining, alizarin red S staining and the real-time PCR assay. Then, the results of western blot (WB) analysis showed that Sr-induced osteogenic differentiation of OVX-BMSCs was associated with time-dependent modulation of autophagy and related to the AKT/mTOR signaling pathway. Meanwhile, the autophagy in Sr-induced osteogenic differentiation of OVX-BMSCs was detected by WB, immunofluorescence staining and transmission electron microscopy. Furthermore, the effect of osteogenic differentiation of OVX-BMSCs has been significantly inhibited by the administration of autophagy inhibitors and the AKT/mTOR pathway inhibitors, respectively, in the early and late periods of osteogenic differentiation. Finally, the results of the model of femoral condyle defects in OVX-rats indicated that Sr10/45S5 granules remarkably enhanced bone regeneration which provided the evidences in vivo. Our research indicates that Sr-doping provides a promising strategy to promote osteogenic differentiation of OVX-BMSCs and bone regeneration in osteoporotic bone defects via early improvement of autophagy and late activation of the Akt/mTOR signaling pathway.