Isocitrate-to-SENP1 signaling amplifies insulin secretion and rescues dysfunctional β cells
Mourad Ferdaoussi, Xiaoqing Dai, Mette V. Jensen, Runsheng Wang, Brett S. Peterson, Chao Huang, Olga Ilkayeva, Nancy Smith, Nathanael Miller, Catherine Hajmrle, Aliya F. Spigelman, Robert C. Wright, Gregory Plummer, Kunimasa Suzuki, James P. Mackay, Martijn van de Bunt, Anna L. Gloyn, Terence E. Ryan, Lisa D. Norquay, M. Julia Brosnan, Jeff K. Trimmer, Timothy P. Rolph, Richard G. Kibbey, Jocelyn E. Manning Fox, William F. Colmers, Orian S. Shirihai, P. Darrell Neufer, Edward T.H. Yeh, Christopher B. Newgard, Patrick E. MacDonald
Mourad Ferdaoussi, Xiaoqing Dai, Mette V. Jensen, Runsheng Wang, Brett S. Peterson, Chao Huang, Olga Ilkayeva, Nancy Smith, Nathanael Miller, Catherine Hajmrle, Aliya F. Spigelman, Robert C. Wright, Gregory Plummer, Kunimasa Suzuki, James P. Mackay, Martijn van de Bunt, Anna L. Gloyn, Terence E. Ryan, Lisa D. Norquay, M. Julia Brosnan, Jeff K. Trimmer, Timothy P. Rolph, Richard G. Kibbey, Jocelyn E. Manning Fox, William F. Colmers, Orian S. Shirihai, P. Darrell Neufer, Edward T.H. Yeh, Christopher B. Newgard, Patrick E. MacDonald
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Research Article Endocrinology

Isocitrate-to-SENP1 signaling amplifies insulin secretion and rescues dysfunctional β cells

Abstract

Insulin secretion from β cells of the pancreatic islets of Langerhans controls metabolic homeostasis and is impaired in individuals with type 2 diabetes (T2D). Increases in blood glucose trigger insulin release by closing ATP-sensitive K+ channels, depolarizing β cells, and opening voltage-dependent Ca2+ channels to elicit insulin exocytosis. However, one or more additional pathway(s) amplify the secretory response, likely at the distal exocytotic site. The mitochondrial export of isocitrate and engagement with cytosolic isocitrate dehydrogenase (ICDc) may be one key pathway, but the mechanism linking this to insulin secretion and its role in T2D have not been defined. Here, we show that the ICDc-dependent generation of NADPH and subsequent glutathione (GSH) reduction contribute to the amplification of insulin exocytosis via sentrin/SUMO-specific protease-1 (SENP1). In human T2D and an in vitro model of human islet dysfunction, the glucose-dependent amplification of exocytosis was impaired and could be rescued by introduction of signaling intermediates from this pathway. Moreover, islet-specific Senp1 deletion in mice caused impaired glucose tolerance by reducing the amplification of insulin exocytosis. Together, our results identify a pathway that links glucose metabolism to the amplification of insulin secretion and demonstrate that restoration of this axis rescues β cell function in T2D.

Authors

Mourad Ferdaoussi, Xiaoqing Dai, Mette V. Jensen, Runsheng Wang, Brett S. Peterson, Chao Huang, Olga Ilkayeva, Nancy Smith, Nathanael Miller, Catherine Hajmrle, Aliya F. Spigelman, Robert C. Wright, Gregory Plummer, Kunimasa Suzuki, James P. Mackay, Martijn van de Bunt, Anna L. Gloyn, Terence E. Ryan, Lisa D. Norquay, M. Julia Brosnan, Jeff K. Trimmer, Timothy P. Rolph, Richard G. Kibbey, Jocelyn E. Manning Fox, William F. Colmers, Orian S. Shirihai, P. Darrell Neufer, Edward T.H. Yeh, Christopher B. Newgard, Patrick E. MacDonald

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Figure 3

ICDc is required for glucose-dependent glutathione reduction and the amplification of β cell exocytosis.

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ICDc is required for glucose-dependent glutathione reduction and the amp...
Knockdown of ICDc (siICDc) in human β cells blunts amplification of exocytosis by (A) glucose (10 mM; n = 24, 41, 18, 49 cells; 7 donors) or (B) isocitrate (100 μM; n = 16, 14, 10, 27 cells; 4 donors), (C) which was rescued by NADPH (10:1 with NADP+; n = 16, 33, 29, 26, 31 cells; 5 donors). (D) Oxidation state of Grx1-roGFP expressed in reaggregated human islets (n = 7 donors). (E and H) Normalized to baseline GSSG, GSH is increased by glucose in INS 832/13 cells. (F and I) As GSSG is unchanged, (G and J) the ratio of reduced-to-oxidized glutathione (GSH:GSSG) is increased by glucose. Compared with siScrambled or BSA-treated controls, these responses are lost in INS 832/13 cells following (E–G) knockdown of ICDc (siICDc; n = 9 replicates in 3 experiments) or (H–J) 48-hour culture with 400 μM oleate/palmitate (O/P; n = 6 replicates in 2 experiments). (K) Measurement of amino acids in INS 832/13 cells reveals glucose-dependent increases in alanine (Ala) and glutamic acid/glutamine (Glx) and a drop in asparagine/aspartic acid (Asx), which are blocked by aminooxyacetic acid (AOA; n = 3 separate experiments). Intracellular dialysis of GSH amplified exocytosis in (L) INS 832/13 cells (n = 18, 12, 13, 12 cells) and (M) human β cells (n = 33, 24, 14, 49, 15 cells; 5 donors). Data are mean ± SEM and were compared with (A–C, E–K, and M) ANOVA followed by Bonferroni post-test, (D) Wilcoxon matched pairs test, or (L) with the nonparametric Kruskal-Wallis 1-way ANOVA followed by Dunn’s post-test. n values correspond to graph bars from left to right, respectively. *P < 0.05, **P < 0.01, ***P < 0.001 compared with the control 1 mM glucose condition, unless indicated otherwise.