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Differentiated Mouse Adipocytes in Primary Culture: A Model of Insulin Resistance
Published on: February 17, 2023
Skeletal muscle insulin resistance induced by adipocyte-conditioned medium: underlying mechanisms and reversibility
Henrike Sell1, Kristin Eckardt, Annika Taube
1Institute of Clinical Biochemistry and Pathobiochemistry, German Diabetes Center, Düsseldorf, Germany.
Abstract:
Insulin resistance in skeletal muscle is an early event in the development of diabetes, with obesity being one of the major contributing factors. In vitro, conditioned medium (CM) from differentiated human adipocytes impairs insulin signaling in human skeletal muscle cells, but it is not known whether insulin resistance is reversible and which mechanisms may underlie this process. CM induced insulin resistance in human myotubes at the level of insulin-stimulated Akt and GSK-3 phosphorylation. In addition, insulin-resistant skeletal muscle cells exhibit enhanced production of reactive oxygen species and ceramide as well as a downregulation of myogenic transcription factors such as myogenin and MyoD. However, insulin resistance was not paralleled by increased apopotosis. Regeneration of myotubes for 24 or 48 h after induction of insulin resistance restored normal insulin signaling. However, the expression level of myogenin could not be reestablished. In addition to decreasing myogenin expression, CM also decreased the release of IL-6 and IL-8 and increased monocyte chemotactic protein-1 (MCP-1) secretion from skeletal muscle cells. Although regeneration of myotubes reestablished normal secretion of IL-6, the release of IL-8 and MCP-1 remained impaired for 48 h after withdrawal of CM. In conclusion, our data show that insulin resistance in skeletal muscle cells is only partially reversible. Although some characteristic features of insulin-resistant myotubes normalize in parallel to insulin signaling after withdrawal of CM, others such as IL-8 and MCP-1 secretion and myogenin expression remain impaired over a longer period. Thus, we propose that the induction of insulin resistance may cause irreversible changes of protein expression and secretion in skeletal muscle cells.
Insights
Insulin resistance in skeletal muscle cells is only partially reversible. While some effects normalize, others like myogenin expression and specific cytokine secretion remain impaired, suggesting irreversible changes.
Area of Science:
- Cell Biology
- Metabolic Disease Research
Background:
- Skeletal muscle insulin resistance is a key factor in diabetes development, often linked to obesity.
- Human adipocyte conditioned medium (CM) induces insulin resistance in skeletal muscle cells in vitro.
- The reversibility and underlying mechanisms of this induced insulin resistance are not fully understood.
Purpose of the Study:
- To investigate the reversibility of insulin resistance in human skeletal muscle cells induced by adipocyte CM.
- To identify specific molecular mechanisms and markers associated with reversible and irreversible changes in insulin-resistant myotubes.
Main Methods:
- Human skeletal muscle cells (myotubes) were treated with conditioned medium (CM) from differentiated human adipocytes to induce insulin resistance.
- Insulin signaling pathways (Akt, GSK-3 phosphorylation) were assessed.
- Production of reactive oxygen species, ceramide, and expression of myogenic transcription factors (myogenin, MyoD) were measured.
- Cellular regeneration was induced by withdrawing CM, followed by analysis of insulin signaling, gene expression, and cytokine secretion (IL-6, IL-8, MCP-1).
Main Results:
- CM induced insulin resistance, characterized by impaired insulin signaling, increased reactive oxygen species and ceramide, and reduced myogenin/MyoD expression.
- Regeneration restored normal insulin signaling but not fully normalized myogenin expression.
- CM altered cytokine secretion (reduced IL-6/IL-8, increased MCP-1).
- While IL-6 secretion normalized upon regeneration, IL-8 and MCP-1 remained impaired for up to 48 hours.
Conclusions:
- Insulin resistance in skeletal muscle cells is only partially reversible.
- Specific molecular changes, including myogenin expression and IL-8/MCP-1 secretion, persist after insulin signaling normalization, indicating potentially irreversible alterations.
- Adipocyte-derived factors may induce lasting changes in skeletal muscle cell protein expression and secretion patterns.
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