Misfolded proinsulin accumulates in expanded pre‐Golgi intermediates and endoplasmic reticulum subdomains in pancreatic beta cells of Akita mice

C Zuber, JY Fan, B Guhl, J Roth - The FASEB journal, 2004 - Wiley Online Library
C Zuber, JY Fan, B Guhl, J Roth
The FASEB journal, 2004Wiley Online Library
ABSTRACT A missense mutation of the insulin 2 gene (Cys96Tyr) in Akita mice disrupting
one of the two interchain disulfide bonds results in intracellular accumulation of misfolded
proinsulin. We analyzed the secretory pathway of pancreatic β cells by electron microscopy
and morphometry and identified sites of proinsulin accumulation by quantitative immunogold
electron microscopy in this protein‐folding disease. In Akita mice β cells, the volume density
of dilated endoplasmic reticulum subdomains was increased by 2.9‐fold, resulting in a 1.7 …
Abstract
A missense mutation of the insulin 2 gene (Cys96Tyr) in Akita mice disrupting one of the two interchain disulfide bonds results in intracellular accumulation of misfolded proinsulin. We analyzed the secretory pathway of pancreatic β cells by electron microscopy and morphometry and identified sites of proinsulin accumulation by quantitative immunogold electron microscopy in this protein‐folding disease. In Akita mice β cells, the volume density of dilated endoplasmic reticulum subdomains was increased by 2.9‐fold, resulting in a 1.7‐fold increased volume density of the entire rough endoplasmic reticulum. The volume density of pre‐Golgi intermediates was increased by 4.9‐fold, and that of the Golgi apparatus was increase by 3.4‐fold. The relative labeling intensity for proinsulin was 2.1‐fold higher in dilated endoplasmic reticulum subdomains and 2.9‐fold higher in pre‐Golgi intermediates as compared with narrow endoplasmic reticulum, resulting in a significantly different distribution pattern between Akita and control mice β cells (X2= 29.97, P<0.001). The numerical density of insulin secretory granules was equal in Akita and control mice β cells. However, their volume density and average volume were reduced to 20% and their average diameter to 58% in Akita mice. Together, these data demonstrate that misfolded proinsulin accumulates mainly in pre‐Golgi intermediates and to a lesser extent in dilated endoplasmic reticulum subdomains, providing evidence for the importance of pre‐Golgi intermediates in a protein folding disease.
Wiley Online Library