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Published on: May 17, 2016
p-TAK1 acts as a switch between myoblast proliferation phase and differentiation phase in mdx mice via regulating
Shusheng Fan1, Xiaofei Huang1, Haowei Tong1
1New Drug Screening Center/Jiangsu Center for Pharmacodynamics Research and Evaluation/State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, 210009, China.
Abstract:
Skeletal muscle transforming growth factor-β-activated kinase 1 (TAK1) continuous excessive phosphorylation was observed in Duchenne muscular dystrophy (DMD) patients and mdx mice. Inhibiting TAK1 phosphorylation ameliorated fibrosis and muscular atrophy, while TAK1 knockout also impaired muscle regeneration. The definite effect and mechanism of p-TAK1 in muscle regeneration disorder is still obscure. In this study, BaCl2-induced acute muscle injury model was used to investigate the role of p-TAK1 in myoblast proliferation and differentiation phase. The results showed that TAK1 phosphorylation was significantly up-regulated in proliferation phase along with Keap1/Nrf2/HO-1 signaling pathway activation, which was down-regulated in differentiation phase yet. In C2C12 cells, inhibiting TAK1 phosphorylation markedly suppressed the expression of heme oxygenase-1 (HO-1), and both myoblast proliferation and differentiation were inhibited. As for activation, p-TAK1 promoted myoblast proliferation via up-regulating HO-1 level. However, excessive TAK1 phosphorylation (induced by 20 ng·mL-1 TGF-β1) notably up-regulated HO-1 expression, inhibiting myogenic differentiation antigen (MyOD) and myogenic differentiation. A mild p-TAK1 level (induced by 5 or 10 ng·mL-1 TGF-β1) was beneficial for myoblast differentiation. In mdx mice, robust myoblast proliferation and differentiation arrest were observed with high p-TAK1 level in skeletal muscle. HO-1 expression was significantly up-regulated. TAK1 phosphorylation inhibitor NG25 (N-[4-[(4-ethylpiperazin-1-yl)methyl]-3-(trifluoromethyl)phenyl]-4-methyl-3-(1H-pyrrolo[2,3-b]pyridin-4-yloxy)benzamide) significantly inhibited HO-1 expression, relieved excessive myoblast proliferation and differentiation arrest, promoted new myofiber formation, and eventually improved muscle function. In conclusion, p-TAK1 acted as "a switch" between proliferation and differentiation phase. Mitigating p-TAK1 level transformed myoblast excessive proliferation phase into differentiation phase in mdx mouse via regulating HO-1 expression.
Insights
Transforming growth factor-β-activated kinase 1 (TAK1) phosphorylation acts as a switch in muscle regeneration. Inhibiting excessive TAK1 phosphorylation in Duchenne muscular dystrophy (DMD) models promotes differentiation and improves muscle function by regulating HO-1.
Area of Science:
- Muscle physiology and regeneration
- Molecular signaling pathways in skeletal muscle
- Duchenne muscular dystrophy (DMD) pathogenesis
Background:
- Skeletal muscle transforming growth factor-β-activated kinase 1 (TAK1) is excessively phosphorylated in Duchenne muscular dystrophy (DMD) and mdx mice.
- While inhibiting TAK1 phosphorylation can ameliorate fibrosis and atrophy, its precise role in muscle regeneration disorders remains unclear.
- TAK1 knockout impairs muscle regeneration, indicating a complex regulatory function.
Purpose of the Study:
- To investigate the role of phosphorylated TAK1 (p-TAK1) in myoblast proliferation and differentiation during acute muscle injury.
- To elucidate the mechanism by which p-TAK1 influences muscle regeneration in the context of the Keap1/Nrf2/HO-1 signaling pathway.
- To evaluate the therapeutic potential of inhibiting p-TAK1 in a mouse model of DMD.
Main Methods:
- Established a BaCl2-induced acute muscle injury model in mice.
- Utilized C2C12 myoblast cell line to study the effects of TGF-β1 and TAK1 inhibition on proliferation and differentiation.
- Administered the TAK1 phosphorylation inhibitor NG25 to mdx mice and assessed muscle regeneration and function.
Main Results:
- TAK1 phosphorylation was upregulated during the proliferation phase and downregulated during the differentiation phase in the injury model.
- Inhibiting TAK1 phosphorylation suppressed HO-1 expression and inhibited myoblast proliferation and differentiation in C2C12 cells.
- A mild p-TAK1 level promoted myoblast proliferation via HO-1, while excessive levels inhibited differentiation; NG25 treatment in mdx mice improved muscle regeneration and function.
Conclusions:
- p-TAK1 functions as a critical 'switch' regulating the balance between myoblast proliferation and differentiation.
- Mitigating excessive p-TAK1 levels in mdx mice promotes differentiation and improves muscle function by modulating HO-1 expression.
- Targeting p-TAK1 represents a potential therapeutic strategy for DMD by restoring muscle regeneration.
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