Beta cell-specific Znt8 deletion in mice causes marked defects in insulin processing, crystallisation and secretion

Area of Science:

• Endocrinology
• Molecular Biology
• Diabetes Research

Background:

• Zinc transporter 8 (ZnT8) is highly expressed in pancreatic beta cells and plays a role in insulin storage.
• Genetic variations in the ZnT8 gene (SLC30A8) are linked to an increased risk of type 2 diabetes.
• Previous studies using global ZnT8 knockout mice had confounding effects due to ZnT8 expression in extra-pancreatic tissues.

Purpose of the Study:

• To investigate the specific roles of ZnT8 in pancreatic beta and alpha cells.
• To elucidate the functional and anatomical impact of ZnT8 deletion in these distinct cell types.
• To understand ZnT8's contribution to insulin secretion and glucose homeostasis without extra-pancreatic influences.

Main Methods:

• Generation of beta cell-specific (Znt8BKO) and alpha cell-specific (Znt8AKO) knockout mouse models.
• In vivo and in vitro characterization of phenotypes, including zinc accumulation, insulin granule morphology, and insulin secretion.
• Assessment of glucose homeostasis and glucagon levels.

Main Results:

• Znt8BKO mice exhibited glucose intolerance, reduced beta cell zinc, atypical insulin granules, and impaired first-phase glucose-stimulated insulin secretion.
• Reduced insulin processing enzyme transcripts and elevated proinsulin levels were observed in Znt8BKO mice.
• Znt8AKO mice showed no significant abnormalities in plasma glucagon or glucose homeostasis.

Conclusions:

• ZnT8 is essential for proper beta cell function, including insulin synthesis, processing, and secretion.
• ZnT8 appears largely dispensable for alpha cell function and glucagon regulation under the studied conditions.
• This study provides critical insights into the cell-specific roles of ZnT8 in pancreatic islet function and diabetes risk.