Upregulated TGF-β1 contributes to hyperglycaemia in type 2 diabetes by potentiating glucagon signalling
Aims/hypothesis Glucagon-stimulated hepatic gluconeogenesis contributes to endogenous glucose production during fasting. Recent studies suggest that TGF-β is able to promote hepatic gluconeogenesis in mice. However, the physiological relevance of serum TGF-β levels to human glucose metabolism and the mechanism by which TGF-β enhances gluconeogenesis remain largely unknown. As enhanced gluconeogenesis is a signature feature of type 2 diabetes, elucidating the molecular mechanisms underlying TGF-β-promoted hepatic gluconeogenesis would allow us to better understand the process of normal glucose production and the pathophysiology of this process in type 2 diabetes. This study aimed to investigate the contribution of upregulated TGF-β1 in human type 2 diabetes and the molecular mechanism underlying the action of TGF-β1 in glucose metabolism. Methods Serum levels of TGF-β1 were measured by ELISA in 74 control participants with normal glucose tolerance and 75 participants with type 2 diabetes. Human liver tissue was collected from participants without obesity and with or without type 2 diabetes for the measurement of TGF-β1 and glucagon signalling. To investigate the role of Smad3, a key signalling molecule downstream of the TGF-β1 receptor, in mediating the effect of TGF-β1 on glucagon signalling, we generated Smad3 knockout mice. Glucose levels in Smad3 knockout mice were measured during prolonged fasting and a glucagon tolerance test. Mouse primary hepatocytes were isolated from Smad3 knockout and wild-type (WT) mice to investigate the underlying molecular mechanisms. Smad3 phosphorylation was detected by western blotting, levels of cAMP were detected by ELISA and levels of protein kinase A (PKA)/cAMP response element-binding protein (CREB) phosphorylation were detected by western blotting. The dissociation of PKA subunits was measured by immunoprecipitation. Results We observed higher levels of serum TGF-β1 in participants without obesity and with type 2 diabetes than in healthy control participants, which was positively correlated with $ HbA_{1c} $ and fasting blood glucose levels. In addition, hyperactivation of the CREB and Smad3 signalling pathways was observed in the liver of participants with type 2 diabetes. Treating WT mouse primary hepatocytes with TGF-β1 greatly potentiated glucagon-stimulated PKA/CREB phosphorylation and hepatic gluconeogenesis. Mechanistically, TGF-β1 treatment induced the binding of Smad3 to the regulatory subunit of PKA (PKA-R), which prevented the association of PKA-R with the catalytic subunit of PKA (PKA-C) and led to the potentiation of glucagon-stimulated PKA signalling and gluconeogenesis. Conclusions/interpretation The hepatic TGF-β1/Smad3 pathway sensitises the effect of glucagon/PKA signalling on gluconeogenesis and synergistically promotes hepatic glucose production. Reducing serum levels of TGF-β1 and/or preventing hyperactivation of TGF-β1 signalling could be a novel approach for alleviating hyperglycaemia in type 2 diabetes. Graphical abstract.
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Artikel |
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| Erscheinungsjahr: |
2023 |
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| Erschienen: |
2023 |
| Enthalten in: |
Zur Gesamtaufnahme - volume:66 |
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| Enthalten in: |
Diabetologia - 66(2023), 6 vom: 14. März, Seite 1142-1155 |
| Sprache: |
Englisch |
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| Beteiligte Personen: |
Xiao, Yang [VerfasserIn] |
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| Links: |
Volltext [lizenzpflichtig] |
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| Anmerkungen: |
© This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2023 |
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| doi: |
10.1007/s00125-023-05889-5 |
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| 520 | |a Aims/hypothesis Glucagon-stimulated hepatic gluconeogenesis contributes to endogenous glucose production during fasting. Recent studies suggest that TGF-β is able to promote hepatic gluconeogenesis in mice. However, the physiological relevance of serum TGF-β levels to human glucose metabolism and the mechanism by which TGF-β enhances gluconeogenesis remain largely unknown. As enhanced gluconeogenesis is a signature feature of type 2 diabetes, elucidating the molecular mechanisms underlying TGF-β-promoted hepatic gluconeogenesis would allow us to better understand the process of normal glucose production and the pathophysiology of this process in type 2 diabetes. This study aimed to investigate the contribution of upregulated TGF-β1 in human type 2 diabetes and the molecular mechanism underlying the action of TGF-β1 in glucose metabolism. Methods Serum levels of TGF-β1 were measured by ELISA in 74 control participants with normal glucose tolerance and 75 participants with type 2 diabetes. Human liver tissue was collected from participants without obesity and with or without type 2 diabetes for the measurement of TGF-β1 and glucagon signalling. To investigate the role of Smad3, a key signalling molecule downstream of the TGF-β1 receptor, in mediating the effect of TGF-β1 on glucagon signalling, we generated Smad3 knockout mice. Glucose levels in Smad3 knockout mice were measured during prolonged fasting and a glucagon tolerance test. Mouse primary hepatocytes were isolated from Smad3 knockout and wild-type (WT) mice to investigate the underlying molecular mechanisms. Smad3 phosphorylation was detected by western blotting, levels of cAMP were detected by ELISA and levels of protein kinase A (PKA)/cAMP response element-binding protein (CREB) phosphorylation were detected by western blotting. The dissociation of PKA subunits was measured by immunoprecipitation. Results We observed higher levels of serum TGF-β1 in participants without obesity and with type 2 diabetes than in healthy control participants, which was positively correlated with $ HbA_{1c} $ and fasting blood glucose levels. In addition, hyperactivation of the CREB and Smad3 signalling pathways was observed in the liver of participants with type 2 diabetes. Treating WT mouse primary hepatocytes with TGF-β1 greatly potentiated glucagon-stimulated PKA/CREB phosphorylation and hepatic gluconeogenesis. Mechanistically, TGF-β1 treatment induced the binding of Smad3 to the regulatory subunit of PKA (PKA-R), which prevented the association of PKA-R with the catalytic subunit of PKA (PKA-C) and led to the potentiation of glucagon-stimulated PKA signalling and gluconeogenesis. Conclusions/interpretation The hepatic TGF-β1/Smad3 pathway sensitises the effect of glucagon/PKA signalling on gluconeogenesis and synergistically promotes hepatic glucose production. Reducing serum levels of TGF-β1 and/or preventing hyperactivation of TGF-β1 signalling could be a novel approach for alleviating hyperglycaemia in type 2 diabetes. Graphical abstract | ||
| 650 | 4 | |a Glucagon | |
| 650 | 4 | |a Hepatocytes | |
| 650 | 4 | |a Hyperglycaemia | |
| 650 | 4 | |a TGF-β | |
| 650 | 4 | |a Type 2 diabetes | |
| 700 | 1 | |a Wang, Yanfei |4 aut | |
| 700 | 1 | |a Ryu, Jiyoon |4 aut | |
| 700 | 1 | |a Liu, Wei |4 aut | |
| 700 | 1 | |a Zou, Hailan |4 aut | |
| 700 | 1 | |a Zhang, Rong |4 aut | |
| 700 | 1 | |a Yan, Yin |4 aut | |
| 700 | 1 | |a Dai, Zhe |4 aut | |
| 700 | 1 | |a Zhang, Deling |4 aut | |
| 700 | 1 | |a Sun, Lu-Zhe |4 aut | |
| 700 | 1 | |a Liu, Feng |4 aut | |
| 700 | 1 | |a Zhou, Zhiguang |4 aut | |
| 700 | 1 | |a Dong, Lily Q. |4 aut | |
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