Submembrane liprin-α1 clusters spatially localize insulin granule fusion

Area of Science:

• Cell Biology
• Endocrinology
• Biochemistry

Background:

• Insulin granule fusion in pancreatic beta cells occurs at the extracellular matrix (ECM) of islet capillaries.
• The precise mechanisms governing this localization remain poorly understood.

Purpose of the Study:

• To investigate the role of liprin-α1, a protein found at the beta cell-ECM interface, in the localization of insulin granule fusion.
• To elucidate how glucose regulates this process and identify interacting proteins.

Main Methods:

• Stimulation of beta cells using glucose, high K+, or calcium uncaging.
• Liprin-α1 knockdown and assessment of insulin secretion and exocytosis localization.
• Analysis of liprin-α1 cluster dynamics and spatial coupling with exocytosis.
• Immunoprecipitation and mass spectrometry to identify liprin-α1 interactors.

Main Results:

• Granule fusion consistently localized to the beta cell-ECM interface across different stimulation methods.
• Liprin-α1 knockdown impaired glucose-induced insulin secretion and exocytosis localization, but not high K+-stimulated secretion.
• Glucose regulates the size and number of liprin-α1 clusters at the interface, with exocytosis spatially coupled to these clusters.
• β2-syntrophin was identified as an insulin granule-associated protein interacting with liprin-α1.

Conclusions:

• Liprin-α1 is crucial for targeting insulin granules to the beta cell-ECM interface for regulated exocytosis.
• Glucose modulates liprin-α1 clustering, thereby controlling the spatial localization of insulin secretion.
• Liprin-α1 functions within a complex, including β2-syntrophin, to mediate glucose-responsive insulin granule targeting.