A novel factor, Tmem176b, induced by activin-like kinase 2 signal promotes the differentiation of myoblasts into osteoblasts

MicroRNA bta-miR-365-3p inhibits proliferation but promotes differentiation of primary bovine myoblasts by targeting the activin A receptor type I

Background

MicroRNAs act as post-transcriptional regulators that repress translation or degrade mRNA transcripts. Each microRNA has many mRNA targets and each mRNA may be targeted by several microRNAs. Skeletal muscles express a plethora of microRNA genes that regulate muscle development and function by controlling the expression of protein-coding target genes. To expand our understanding of the role of microRNA, specifically bta-miR-365-3p, in muscle biology, we investigated its functions in regulating primary bovine myoblast proliferation and differentiation.

Results

Firstly, we found that bta-miR-365-3p was predominantly expressed in skeletal muscle and heart tissue in Chinese Qinchuan beef cattle. Quantitative PCR and western blotting results showed that overexpression of bta-miR-365-3p significantly reduced the expression levels of cyclin D1 (CCND1), cyclin dependent kinase 2 (CDK2) and proliferating cell nuclear antigen (PCNA) but stimulated the expression levels of muscle differentiation markers, i.e., MYOD1, MYOG at both mRNA and protein level. Moreover, downregulation of bta-miR-365-3p increased the expression of CCND1, CDK2 and PCNA but decreased the expression of MYOD1 and MYOG at both mRNA and protein levels. Furthermore, flow cytometry, EdU proliferation assays and immunostaining results showed that increased levels of bta-miR-365-3p suppressed cell proliferation but promoted myotube formation, whereas decreased levels of bta-miR-365-3p resulted in the opposite consequences. Finally, we identified that activin A receptor type I (ACVR1) could be a direct target of bta-miR-365-3p. It was demonstrated that bta-miR-365-3p can bind to the 3’UTR of ACVR1 gene to regulate its expression based on dual luciferase gene reporter assays. Consistently, knock-down of ACVR1 was associated with decreased expressions of CDK2, CCND1 and PCNA but increased expression of MYOG and MYOD1 both at mRNA and protein level.

Conclusion

Collectively, these data suggested that bta-miR-365-3p represses proliferation but promotes differentiation of bovine myoblasts through several biological mechanisms involving downregulation of ACVR1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-020-00528-0.

Fibrodysplasia ossificans progressiva: Basic understanding and experimental models

Fibrodysplasia ossificans progressive (FOP) is an extremely rare autosomal dominant disorder characterized by congenital malformations of the great toes and progressive heterotopic ossification that can induce a disabling second skeleton. Spontaneously occurring flare-ups can cause inflammatory soft tissue to swell, followed by progressive and disabling heterotopic endochondral ossification. FOP is very rare, with an estimated incidence of one case per two million individuals. There is no definitive treatment for FOP, but the longevity of patients with FOP can be extended by early diagnosis and appropriate prevention of flares-up. Some promising treatment strategies and targets have recently been reported. The current review describes the classical phenotype and genotype of FOP, useful methods of diagnosing the condition, therapeutic approaches and commonly used drugs, and experimental models used to study this disease.

LR8 Expression in fibroblasts of healthy and fibrotic human tissues

LR8 gene was first reported in a subpopulation of cultured human lung fibroblasts expressing the receptor for C1q-globular domain, and it was not detectable in cultured endothelial cells and smooth muscle cells. LR8 mRNA levels were higher in fibrotic lungs. In this study we assessed LR8 production in human tissues and determined if the distribution of fibroblasts producing LR8 is affected in fibrosis. Normal and fibrotic tissue sections from human liver, lung and kidneys were immunostained with antibodies to LR8 and examined for the presence of fibroblasts staining positively and negatively. The cells were also examined for co-expression of α-smooth muscle actin (SMA), a marker for myofibroblasts. The results showed that LR8 was expressed by fibroblasts, smooth muscle cells, endothelial cells, bile duct cells, pulmonary alveolar cells and distal and proximal kidney tubule cells. Connective tissues of normal and fibrotic tissues contained fibroblasts staining positively and negatively with anti- LR8 antibody. The number of LR8-positive cells was higher in fibrotic tissues, but differences were not statistically significant. Fibroblasts producing both LR8 and SMA were present in higher numbers in fibrotic tissues as compared to normal tissues and the differences were statistically significant (p<0.05). Our results show that fibroblast subtypes differing in LR8 expression are present in human tissues, and that in fibrotic tissues cells co-expressing LR8 and SMA are present. Our results indicate that LR8 expressing cells may participate in the early stages of fibrotic diseases and that fibroblasts expressing LR8, not LR8 negative cells, have potential to become myofibroblasts in fibrotic tissues.

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Human tissues contain fibroblast populations expressing and not expressing LR8.

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Fibroblasts expressing both LR8 and smooth muscle actin are present and in higher number in fibrotic liver, lungs and kidneys.

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LR8 positive fibroblasts may represent putative myofibroblasts participating in fibrosis.

Role of osteoclasts in heterotopic ossification enhanced by fibrodysplasia ossificans progressiva-related activin-like kinase 2 mutation in mice

Fibrodysplasia ossificans progressiva (FOP) is a disorder of skeletal malformations and progressive heterotopic ossification. The constitutively activating mutation (R206H) of the bone morphogenetic protein type 1 receptor, activin-like kinase 2 (ALK2), is responsible for the pathogenesis of FOP. Although transfection of the causal mutation of FOP into myoblasts enhances osteoclast formation by transforming growth factor-β (TGF-β), the role of osteoclasts in heterotopic ossification is unknown. We therefore examined the effects of alendronate, SB431542 and SB203580 on heterotopic ossification induced by the causal mutation of FOP. Total bone mineral content as well as numbers of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated and alkaline phosphatase (ALP)-positive cells in heterotopic bone were significantly higher in muscle tissues implanted with ALK2 (R206H)-transfected mouse myoblastic C2C12 cells than in the tissues implanted with empty vector-transfected cells in nude mice. Alendronate, an aminobisphosphonate, did not affect total mineral content or numbers of TRAP-positive multinucleated and ALP-positive cells in heterotopic bone, which were enhanced by the implantation of ALK2 (R206H)-transfected C2C12 cells, although it significantly decreased serum levels of cross-linked C-telopeptide of type I collagen, a bone resorption index. Moreover, neither SB431542, an inhibitor of TGF-β receptor type I kinase, nor SB203580, an inhibitor of p38 mitogen-activated protein kinase, affected the increase in heterotopic ossification due to the implantation of ALK2 (R206H)-transfected C2C12 cells. In conclusion, the present study indicates that osteoclast inhibition does not affect heterotopic ossification enhanced by FOP-related mutation.

The biological function of type I receptors of bone morphogenetic protein in bone

Bone morphogenetic proteins (BMPs) have multiple roles in skeletal development, homeostasis and regeneration. BMPs signal via type I and type II serine/threonine kinase receptors (BMPRI and BMPRII). In recent decades, genetic studies in humans and mice have demonstrated that perturbations in BMP signaling via BMPRI resulted in various diseases in bone, cartilage, and muscles. In this review, we focus on all three types of BMPRI, which consist of activin-like kinase 2 (ALK2, also called type IA activin receptor), activin-like kinase 3 (ALK3, also called BMPRIA), and activin-like kinase 6 (ALK6, also called BMPRIB). The research areas covered include the current progress regarding the roles of these receptors during myogenesis, chondrogenesis, and osteogenesis. Understanding the physiological and pathological functions of these receptors at the cellular and molecular levels will advance drug development and tissue regeneration for treating musculoskeletal diseases and bone defects in the future.

RORγt+ cells selectively express redundant cation channels linked to the Golgi apparatus

Retinoid-related orphan receptor gamma t (RORγt) is a master transcription factor central to type 17 immunity involving cells such as T helper 17, group 3 innate lymphoid cells or IL-17-producing γδ T cells. Here we show that the intracellular ion channel TMEM176B and its homologue TMEM176A are strongly expressed in these RORγt⁺ cells. We demonstrate that TMEM176A and B exhibit a similar cation channel activity and mainly colocalise in close proximity to the trans-Golgi network. Strikingly, in the mouse, the loss of Tmem176b is systematically associated with a strong upregulation of Tmem176a. While Tmem176b single-deficiency has no effect on the course of experimental autoimmune encephalomyelitis, T cell or DSS-induced colitis, it significantly reduces imiquimod-induced psoriasis-like skin inflammation. These findings shed light on a potentially novel specific process linked to post-Golgi trafficking for modulating the function of RORγt⁺ cells and indicate that both homologues should be simultaneously targeted to clearly elucidate the role of this intracellular ion flow.

Interaction between Muscle and Bone

The clinical significance of sarcopenia and osteoporosis has increased with the increase in the population of older people. Sarcopenia is defined by decreased muscle mass and impaired muscle function, which is related to osteoporosis independently and dependently. Numerous lines of clinical evidence suggest that lean body mass is positively related to bone mass, which leads to reduced fracture risk. Genetic, endocrine and mechanical factors affect both muscle and bone simultaneously. Vitamin D, the growth hormone/insulin-like growth factor I axis and testosterone are physiologically and pathologically important as endocrine factors. These findings suggest the presence of interactions between muscle and bone, which might be very important for understanding the physiology and pathophysiology of sarcopenia and osteoporosis. Muscle/bone relationships include two factors: local control of muscle to bone and systemic humoral interactions between muscle and bone. As a putative local inducer of muscle ossification, we found Tmem119, a parathyroid hormone-responsive osteoblast differentiation factor. Moreover, osteoglycin might be one of the muscle-derived humoral bone anabolic factors. This issue may be important for the development of novel drugs and biomarkers for osteoporosis and sarcopenia. Further research will be necessary to clarify the details of the linkage of muscle and bone.