Signaling Heterogeneity is Defined by Pathway Architecture and Intercellular Variability in Protein Expression

Area of Science:

• Cellular biology
• Molecular signaling
• Systems biology

Background:

• Insulin activates PI3K/Akt signaling, promoting glucose uptake via GLUT4 transporter delivery to the cell surface.
• Intercellular heterogeneity in insulin signaling responses is observed, but its origins are not fully understood.

Purpose of the Study:

• To investigate the sources of intercellular heterogeneity in insulin signaling pathways.
• To determine the contribution of intrinsic versus extrinsic factors to variations in Akt activation and GLUT4 levels.

Main Methods:

• Quantitative analysis of Akt activation and GLUT4 levels in single cells.
• Development and application of generalized mechanistic models.
• Experimental validation of model predictions.

Main Results:

• Akt activation explained approximately 25% of the variance in GLUT4 levels, indicating other factors contribute significantly.
• Observed reproducibility within single cells suggests variance is primarily extrinsic (between cells).
• Intercellular variation in protein expression levels was sufficient to explain the observed heterogeneity in Akt and GLUT4 responses.

Conclusions:

• Single-cell heterogeneity is a major driver of population-level responses to insulin signaling.
• Extrinsic factors, particularly variations in gene and protein expression between cells, are the primary source of this heterogeneity.
• Understanding single-cell variability is crucial for comprehending insulin action and metabolic regulation.