SORCS1 is necessary for normal insulin secretory granule biogenesis in metabolically stressed β cells
Melkam A. Kebede, … , Anjon Audhya, Alan D. Attie
Melkam A. Kebede, … , Anjon Audhya, Alan D. Attie
Published August 26, 2014
Citation Information: J Clin Invest. 2014;124(10):4240-4256. https://doi.org/10.1172/JCI74072.
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Research Article Endocrinology

SORCS1 is necessary for normal insulin secretory granule biogenesis in metabolically stressed β cells

Abstract

We previously positionally cloned Sorcs1 as a diabetes quantitative trait locus. Sorcs1 belongs to the Vacuolar protein sorting-10 (Vps10) gene family. In yeast, Vps10 transports enzymes from the trans-Golgi network (TGN) to the vacuole. Whole-body Sorcs1 KO mice, when made obese with the leptinob mutation (ob/ob), developed diabetes. β Cells from these mice had a severe deficiency of secretory granules (SGs) and insulin. Interestingly, a single secretagogue challenge failed to consistently elicit an insulin secretory dysfunction. However, multiple challenges of the Sorcs1 KO ob/ob islets consistently revealed an insulin secretion defect. The luminal domain of SORCS1 (Lum-Sorcs1), when expressed in a β cell line, acted as a dominant-negative, leading to SG and insulin deficiency. Using syncollin-dsRed5TIMER adenovirus, we found that the loss of Sorcs1 function greatly impairs the rapid replenishment of SGs following secretagogue challenge. Chronic exposure of islets from lean Sorcs1 KO mice to high glucose and palmitate depleted insulin content and evoked an insulin secretion defect. Thus, in metabolically stressed mice, Sorcs1 is important for SG replenishment, and under chronic challenge by insulin secretagogues, loss of Sorcs1 leads to diabetes. Overexpression of full-length SORCS1 led to a 2-fold increase in SG content, suggesting that SORCS1 is sufficient to promote SG biogenesis.

Authors

Melkam A. Kebede, Angie T. Oler, Trillian Gregg, Allison J. Balloon, Adam Johnson, Kelly Mitok, Mary Rabaglia, Kathryn Schueler, Donald Stapleton, Candice Thorstenson, Lindsay Wrighton, Brendan J. Floyd, Oliver Richards, Summer Raines, Kevin Eliceiri, Nabil G. Seidah, Christopher Rhodes, Mark P. Keller, Joshua L. Coon, Anjon Audhya, Alan D. Attie

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Figure 7

Sorcs1 deletion impairs insulin secretion under metabolic stress.

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Sorcs1 deletion impairs insulin secretion under metabolic stress. (A and...
(A and B) Insulin secretion (A) and insulin content (B) in response to a single challenge of 1.7 mM glucose combined with 40 mM KCl or 16.7 mM glucose in B6 ob/ob (n = 5) or Sorcs1 KO ob/ob (n = 5) islets. (C) Representative immunoblotting of freshly isolated B6 ob/ob and Sorcs1 KO ob/ob islet lysates before (left) and 1 hour after (right) exposure to 16.7 mM glucose. Antibody against total insulin, which recognized both the pro- and the mature form of insulin, was used. (D and E) Insulin secretion (D) and insulin content (E) in B6 ob/ob (n = 5) and Sorcs1 KO ob/ob (n = 4) islets after 3 repeated secretagogue challenges. (F and G) Secreted insulin (F) and insulin content (G) from isolated islets of (n = 4) B6 and Sorcs1 KO lean mice cultured for 24 hours with 16.7 mM glucose. (H) Dithizone staining of B6 and Sorcs1 KO lean islets cultured for 18 hours with 16.7 mM glucose and 0.5 mM palmitate. (I and J) Secreted insulin (I) and insulin content (J) from isolated islets of (n = 4) B6 and Sorcs1 KO lean mice cultured for 24 hours with 16.7 mM glucose and 0.5 mM palmitate. Data are represented as mean ± SEM.