Calcium release channel RyR2 regulates insulin release and glucose homeostasis
Gaetano Santulli, Gennaro Pagano, Celestino Sardu, Wenjun Xie, Steven Reiken, Salvatore Luca D’Ascia, Michele Cannone, Nicola Marziliano, Bruno Trimarco, Theresa A. Guise, Alain Lacampagne, Andrew R. Marks
Gaetano Santulli, Gennaro Pagano, Celestino Sardu, Wenjun Xie, Steven Reiken, Salvatore Luca D’Ascia, Michele Cannone, Nicola Marziliano, Bruno Trimarco, Theresa A. Guise, Alain Lacampagne, Andrew R. Marks
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Research Article Cardiology Metabolism

Calcium release channel RyR2 regulates insulin release and glucose homeostasis

Abstract

The type 2 ryanodine receptor (RyR2) is a Ca2+ release channel on the endoplasmic reticulum (ER) of several types of cells, including cardiomyocytes and pancreatic β cells. In cardiomyocytes, RyR2-dependent Ca2+ release is critical for excitation-contraction coupling; however, a functional role for RyR2 in β cell insulin secretion and diabetes mellitus remains controversial. Here, we took advantage of rare RyR2 mutations that were identified in patients with a genetic form of exercise-induced sudden death (catecholaminergic polymorphic ventricular tachycardia [CPVT]). As these mutations result in a “leaky” RyR2 channel, we exploited them to assess RyR2 channel function in β cell dynamics. We discovered that CPVT patients with mutant leaky RyR2 present with glucose intolerance, which was heretofore unappreciated. In mice, transgenic expression of CPVT-associated RyR2 resulted in impaired glucose homeostasis, and an in-depth evaluation of pancreatic islets and β cells from these animals revealed intracellular Ca2+ leak via oxidized and nitrosylated RyR2 channels, activated ER stress response, mitochondrial dysfunction, and decreased fuel-stimulated insulin release. Additionally, we verified the effects of the pharmacological inhibition of intracellular Ca2+ leak in CPVT-associated RyR2-expressing mice, in human islets from diabetic patients, and in an established murine model of type 2 diabetes mellitus. Taken together, our data indicate that RyR2 channels play a crucial role in the regulation of insulin secretion and glucose homeostasis.

Authors

Gaetano Santulli, Gennaro Pagano, Celestino Sardu, Wenjun Xie, Steven Reiken, Salvatore Luca D’Ascia, Michele Cannone, Nicola Marziliano, Bruno Trimarco, Theresa A. Guise, Alain Lacampagne, Andrew R. Marks

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Figure 3

Leaky RyR2 channels lead to abnormal mitochondrial structure and function in pancreatic β cells.

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Leaky RyR2 channels lead to abnormal mitochondrial structure and functio...
(A) Representative transmission electron micrographs of pancreatic β cell mitochondria from 4-month-old WT, RyR2-R2474S, and RyR2-N2386I mice, treated for 4 weeks with S107 or vehicle. Original magnification, ×30,000; insets, ×65000. N, nucleus. Scale bars: 500 nm. (B–D) Morphometric analyses of mitochondria reveal ultrastructural abnormalities in CPVT mice. (B) Mitochondrial area, (C) cristae density, (D) percentage of abnormal mitochondria per cell (mitochondria were defined as abnormal when a loss of electron density was detectable in more than 20% of the area of a mitochondrion). (E) mtDNA/nDNA copy number, (F) ROS production, (G) UCP2 expression, (H) aconitase activity, and (I) mt-ATP6 expression in isolated pancreatic islets. (J and K) ATP production in isolated pancreatic islets challenged with glucose (at indicated concentrations, J) or pyruvate (10 mM, K). Islets were isolated from n = 7–10 mice per group. Data are shown as mean ± SEM (triplicate measurements per sample). Box plots in B indicate upper/lower quartiles, lines in the middle of each box are the medians, and the whiskers represent the range of minimum and maximum values of total mitochondrial area per section. *P < 0.05 vs. WT, ANOVA, Tukey-Kramer post hoc correction.