β Cell–specific deletion of Zfp148 improves nutrient-stimulated β cell Ca2+ responses
Christopher H. Emfinger, Eleonora de Klerk, Kathryn L. Schueler, Mary E. Rabaglia, Donnie S. Stapleton, Shane P. Simonett, Kelly A. Mitok, Ziyue Wang, Xinyue Liu, Joao A. Paulo, Qing Yu, Rebecca L. Cardone, Hannah R. Foster, Sophie L. Lewandowski, José C. Perales, Christina M. Kendziorski, Steven P. Gygi, Richard G. Kibbey, Mark P. Keller, Matthias Hebrok, Matthew J. Merrins, Alan D. Attie
Christopher H. Emfinger, Eleonora de Klerk, Kathryn L. Schueler, Mary E. Rabaglia, Donnie S. Stapleton, Shane P. Simonett, Kelly A. Mitok, Ziyue Wang, Xinyue Liu, Joao A. Paulo, Qing Yu, Rebecca L. Cardone, Hannah R. Foster, Sophie L. Lewandowski, José C. Perales, Christina M. Kendziorski, Steven P. Gygi, Richard G. Kibbey, Mark P. Keller, Matthias Hebrok, Matthew J. Merrins, Alan D. Attie
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Research Article Endocrinology Metabolism

β Cell–specific deletion of Zfp148 improves nutrient-stimulated β cell Ca2+ responses

Abstract

Insulin secretion from pancreatic β cells is essential for glucose homeostasis. An insufficient response to the demand for insulin results in diabetes. We previously showed that β cell–specific deletion of Zfp148 (β-Zfp148KO) improves glucose tolerance and insulin secretion in mice. Here, we performed Ca2+ imaging of islets from β‑Zfp148KO and control mice fed both a chow and a Western-style diet. β-Zfp148KO islets demonstrated improved sensitivity and sustained Ca2+ oscillations in response to elevated glucose levels. β-Zfp148KO islets also exhibited elevated sensitivity to amino acid–induced Ca2+ influx under low glucose conditions, suggesting enhanced mitochondrial phosphoenolpyruvate-dependent (PEP-dependent), ATP-sensitive K+ channel closure, independent of glycolysis. RNA-Seq and proteomics of β-Zfp148KO islets revealed altered levels of enzymes involved in amino acid metabolism (specifically, SLC3A2, SLC7A8, GLS, GLS2, PSPH, PHGDH, and PSAT1) and intermediary metabolism (namely, GOT1 and PCK2), consistent with altered PEP cycling. In agreement with this, β-Zfp148KO islets displayed enhanced insulin secretion in response to l-glutamine and activation of glutamate dehydrogenase. Understanding pathways controlled by ZFP148 may provide promising strategies for improving β cell function that are robust to the metabolic challenge imposed by a Western diet.

Authors

Christopher H. Emfinger, Eleonora de Klerk, Kathryn L. Schueler, Mary E. Rabaglia, Donnie S. Stapleton, Shane P. Simonett, Kelly A. Mitok, Ziyue Wang, Xinyue Liu, Joao A. Paulo, Qing Yu, Rebecca L. Cardone, Hannah R. Foster, Sophie L. Lewandowski, José C. Perales, Christina M. Kendziorski, Steven P. Gygi, Richard G. Kibbey, Mark P. Keller, Matthias Hebrok, Matthew J. Merrins, Alan D. Attie

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Figure 4

Possible pathway for enhanced mitochondrial PEP production and cycling in β-Zfp148KO islets.

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Possible pathway for enhanced mitochondrial PEP production and cycling i...
Pyruvate generated from PEP can either be converted to acetyl-coA by pyruvate dehydrogenase (PDH) and enter the TCA cycle or it can be converted to OAA by pyruvate carboxylase (PCX). OAA can be converted into PEP via PCK2. PEP can then be converted back to pyruvate by pyruvate kinase (PKM2), completing a PEP cycle. Conversion of PEP into pyruvate by PKM2 generates the ATP, which closes the KATP channels and triggers membrane depolarization, Ca2+ entry, and insulin release. Proteins increased in β-Zfp148KO islets vs. control islets include enzymes involved in amino acid metabolism and mitochondrial PEP production. In the proposed model, altered amino acid (AA) metabolism intersects mitochondrial PEP production and cycling at key points (highlighted in light blue boxes). Initially, increased production of l-serine results in increased activation of PKM2. Increased GOT1 may mediate regeneration of NAD+ for glycolysis and serine biosynthesis via the malate–aspartate shuttle. Additionally, key genes involved in AA metabolism result in increased substrate flux to the TCA cycle via α-ketoglutarate and acetyl-coA. Increased AA transporters (SLC3A2/SLC7A8, and others) mediate influx of Gln, Leu, Val, and Ile. Ile and Leu produce acetyl-coA, resulting in increased inhibition of PDH and activation of PCX. Valine metabolism may result in increased succinyl-coA. Finally, increased levels of several enzymes may mediate increased production of α-ketoglutarate from Glu and Gln, a process enhanced by Leu activation of GDH. The α-ketoglutarate then provides substrate for producing OAA, which is then converted to PEP by increased PCK2. Collectively, metabolic genes altered by loss of Zfp148 in β cells may thereby contribute to enhanced mitochondrial PEP production and cycling, resulting in enhanced insulin secretion.