Endocrinology
Abstract
BACKGROUND While saturated fat intake leads to insulin resistance and nonalcoholic fatty liver, Mediterranean-like diets enriched in monounsaturated fatty acids (MUFA) may have beneficial effects. This study examined effects of MUFA on tissue-specific insulin sensitivity and energy metabolism.METHODS A randomized placebo-controlled cross-over study enrolled 16 glucose-tolerant volunteers to receive either oil (OIL, ~1.18 g/kg), rich in MUFA, or vehicle (VCL, water) on 2 occasions. Insulin sensitivity was assessed during preclamp and hyperinsulinemic-euglycemic clamp conditions. Ingestion of 2H2O/acetaminophen was combined with [6,6-2H2]glucose infusion and in vivo 13C/31P/1H/ex vivo 2H-magnet resonance spectroscopy to quantify hepatic glucose and energy fluxes.RESULTS OIL increased plasma triglycerides and oleic acid concentrations by 44% and 66% compared with VCL. Upon OIL intervention, preclamp hepatic and whole-body insulin sensitivity markedly decreased by 28% and 27%, respectively, along with 61% higher rates of hepatic gluconeogenesis and 32% lower rates of net glycogenolysis, while hepatic triglyceride and ATP concentrations did not differ from VCL. During insulin stimulation hepatic and whole-body insulin sensitivity were reduced by 21% and 25%, respectively, after OIL ingestion compared with that in controls.CONCLUSION A single MUFA-load suffices to induce insulin resistance but affects neither hepatic triglycerides nor energy-rich phosphates. These data indicate that amount of ingested fat, rather than its composition, primarily determines the development of acute insulin resistance.TRIAL REGISTRATION ClinicalTrials.gov NCT01736202.FUNDING German Diabetes Center, German Federal Ministry of Health, Ministry of Culture and Science of the state of North Rhine-Westphalia, German Federal Ministry of Education and Research, German Diabetes Association, German Center for Diabetes Research, Portugal Foundation for Science and Technology, European Regional Development Fund, and Rede Nacional de Ressonancia Magnética Nuclear.
Authors
Theresia Sarabhai, Sabine Kahl, Julia Szendroedi, Daniel F. Markgraf, Oana-Patricia Zaharia, Cristina Barosa, Christian Herder, Frithjof Wickrath, Pavel Bobrov, Jong-Hee Hwang, John Griffith Jones, Michael Roden
Abstract
EIF2AK4, which encodes the amino acid deficiency–sensing protein GCN2, has been implicated as a susceptibility gene for type 2 diabetes in the Japanese population. However, the mechanism by which GCN2 affects glucose homeostasis is unclear. Here, we show that insulin secretion is reduced in individuals harboring the risk allele of EIF2AK4 and that maintenance of GCN2-deficient mice on a high-fat diet results in a loss of pancreatic β cell mass. Our data suggest that GCN2 senses amino acid deficiency in β cells and limits signaling by mechanistic target of rapamycin complex 1 to prevent β cell failure during the consumption of a high-fat diet.
Authors
Ayumi Kanno, Shun-ichiro Asahara, Ayuko Furubayashi, Katsuhisa Masuda, Risa Yoshitomi, Emi Suzuki, Tomoko Takai, Maki Kimura-Koyanagi, Tomokazu Matsuda, Alberto Bartolome, Yushi Hirota, Norihide Yokoi, Yuka Inaba, Hiroshi Inoue, Michihiro Matsumoto, Kenichi Inoue, Takaya Abe, Fan-Yan Wei, Kazuhito Tomizawa, Wataru Ogawa, Susumu Seino, Masato Kasuga, Yoshiaki Kido
Abstract
Insulin receptor signaling is crucial for white adipose tissue (WAT) function. Consequently, lack of insulin receptor (IR) in WAT results in a diabetes-like phenotype. Yet, causes for IR downregulation in WAT of diabetic patients are not well understood. By using multiple mouse models of obesity and insulin resistance, we identify a common downregulation of the IR with a reduction of mRNA expression of the selenoproteins Txnrd3, Sephs2, and Gpx3. Consistently, GPX3 is also decreased in adipose tissue of insulin resistant and obese patients. Inducing Gpx3 expression via selenite treatment enhances IR expression via activation of the transcription factor Sp1 in 3T3-L1 preadipocytes and improves adipocyte differentiation and function. Feeding mice a selenium-enriched high-fat diet alleviates diet-induced insulin resistance with increased insulin sensitivity, decreased tissue inflammation and elevated IR expression in WAT. Again, IR expression correlates positively with Gpx3 expression, a phenotype which is also conserved in humans. Consequently, decreasing GPx3 using siRNA technique reduces IR expression in 3T3-L1 preadipocytes and insulin sensitivity. Overall our data identify GPx3 as a novel regulator of IR expression and insulin sensitivity in adipose tissue.
Authors
Robert Hauffe, Vanessa Stein, Chantal Chudoba, Tanina Flore, Michaela Rath, Katrin Ritter, Mareike Schell, Kristina Wardelmann, Stefanie Deubel, Johannes F. Kopp, Maria Schwarz, Kai Kappert, Matthias Blüher, Tanja Schwerdtle, Anna P. Kipp, Andre Kleinridders
Abstract
Pancreatic islets secrete insulin from β cells and glucagon from α cells and dysregulated secretion of these hormones is a central component of diabetes. Thus, an improved understanding of the pathways governing coordinated β and α cell hormone secretion will provide insight into islet dysfunction in diabetes. However, the three-dimensional multicellular islet architecture, essential for coordinated islet function, presents experimental challenges for mechanistic studies of intracellular signaling pathways in primary islet cells. Here, we developed an integrated approach to study the function of primary human islet cells using genetically modified pseudoislets that resemble native islets across multiple parameters. Further, we developed a microperifusion system that allowed synchronous acquisition of GCaMP6f biosensor signal and hormone secretory profiles. We demonstrate the utility of this experimental approach by studying the effects of Gi and Gq GPCR pathways on insulin and glucagon secretion by expressing the designer receptors exclusively activated by designer drugs (DREADDs) hM4Di or hM3Dq. Activation of Gi signaling reduced insulin and glucagon secretion, while activation of Gq signaling stimulated glucagon secretion but had both stimulatory and inhibitory effects on insulin secretion which occur through changes in intracellular Ca2+. The experimental approach of combining pseudoislets with a microfluidic system, allowed the co-registration of intracellular signaling dynamics and hormone secretion and demonstrated differences in GPCR signaling pathways between human β and α cells.
Authors
John T. Walker, Rachana Haliyur, Heather A. Nelson, Matthew Ishahak, Gregory Poffenberger, Radhika Aramandla, Conrad Reihsmann, Joseph R. Luchsinger, Diane C. Saunders, Peng Wang, Adolfo Garcia-Ocana, Rita Bottino, Ashutosh Agarwal, Alvin C. Powers, Marcela Brissova
Abstract
In type 1 diabetes (T1D), autoimmune destruction of pancreatic β cells leads to insulin deficiency and loss of glycemic control. However, knowledge about human pancreas pathophysiology in T1D remains incomplete. To address this limitation, we established a pancreas tissue slice platform of donor organs with and without diabetes, facilitating the first live cell studies of human pancreas in T1D pathogenesis to our knowledge. We show that pancreas tissue slices from organ donors allow thorough assessment of processes critical for disease development, including insulin secretion, β cell physiology, endocrine cell morphology, and immune infiltration within the same donor organ. Using this approach, we compared detailed pathophysiological profiles for 4 pancreata from donors with T1D with 19 nondiabetic control donors. We demonstrate that β cell loss, β cell dysfunction, alterations of β cell physiology, and islet infiltration contributed differently to individual cases of T1D, allowing insight into pathophysiology and heterogeneity of T1D pathogenesis. Thus, our study demonstrates that organ donor pancreas tissue slices represent a promising and potentially novel approach in the search for successful prevention and reversal strategies of T1D.
Authors
Julia K. Panzer, Helmut Hiller, Christian M. Cohrs, Joana Almaça, Stephen J. Enos, Maria Beery, Sirlene Cechin, Denise M. Drotar, John R. Weitz, Jorge Santini, Mollie K. Huber, Mirza Muhammad Fahd Qadir, Ricardo L. Pastori, Juan Domínguez-Bendala, Edward A. Phelps, Mark A. Atkinson, Alberto Pugliese, Alejandro Caicedo, Irina Kusmartseva, Stephan Speier
Abstract
Glucokinase (GK) is highly expressed in the hypothalamic paraventricular nucleus (PVN); however its role is currently unknown. We found that glucokinase in the PVN acts as part of a glucose sensing mechanism within the PVN that regulates glucose homeostasis by controlling glucagon like peptide 1 (GLP-1) release. GLP-1 is released from enteroendocrine L-cells in response to oral glucose. Here we identify a brain mechanism critical to the release of GLP-1 in response to oral glucose. We show that increasing expression of GK or injection of glucose into the PVN increases GLP-1 release in response to oral glucose. On the contrary decreasing expression of GK or injection of non-metabolisable glucose into the PVN prevents GLP-1 release. Our results demonstrate that glucosensitive GK neurones in the PVN, are critical to the response to oral glucose and subsequent release of GLP-1.
Authors
Yue Ma, Risheka Ratnasabapathy, Ivan De Backer, Chioma Izzi-Engbeaya, Marie-Sophie Nguyen-Tu, Joyceline Cuenco, Ben Jones, Christopher D. John, Brian Y. H. Lam, Guy A. Rutter, Giles Yeo, Waljit Dhillo, James Gardiner
Abstract
Familial Hypocalciuric Hypercalcemia (FHH) is a genetic condition associated with hypocalciuria, hypercalcemia and in some cases inappropriately high levels of circulating parathyroid hormone (PTH). FHH is associated with inactivating mutations in CaSR encoding the Ca2+ sensing receptor (CaSR), a G protein coupled receptor (GPCR) and GNA11 encoding G protein subunit alpha 11 (Gα11), implicating defective GPCR signaling as the root pathophysiology for FHH. However, the downstream mechanism by which CaSR activation inhibits PTH production/secretion is incompletely understood. Here, we show that mice lacking the transient receptor potential canonical channel 1 (TRPC1) develop chronic hypercalcemia, hypocalciuria, and elevated PTH levels mimicking human FHH. Ex vivo and in vitro studies reveal that TRPC1 serves a necessary and sufficient mediator to suppress PTH secretion from parathyroid glands (PTG) downstream of CaSR in response to high extracellular Ca2+ concentration. Gα11 physically interacts with both the N- and C-termini of TRPC1 and enhances CaSR-induced TRPC1 activity in transfected cells. These data identify TRPC1-mediated Ca2+ signaling as an essential component of the cellular apparatus controlling PTH secretion in the PTG downstream of CaSR.
Authors
Marta Onopiuk, Bonnie Eby, Vasyl Nesin, Peter Ngo, Megan Lerner, Caroline M. Gorvin, Victoria J. Stokes, Rajesh V. Thakker, Maria Luisa Brandi, Wenhan Chang, Mary Beth Humphrey, Leonidas Tsiokas, Kai Lau
Abstract
A GLP-2 analogue is used in individuals with intestinal failure at risk for liver disease, yet the hepatic actions of GLP-2 are not understood. Treatment of high fat diet (HFD)-fed mice with GLP-2 did not modify development of hepatosteatosis or hepatic inflammation. In contrast, Glp2r-/- mice exhibited increased hepatic lipid accumulation, deterioration in glucose tolerance, and upregulation of biomarkers of hepatic inflammation. Both mouse and human liver expressed the canonical GLP-2R, and hepatic Glp2r expression was upregulated in mice with hepatosteatosis. Cell fractionation localized the Glp2r to hepatic stellate cells (HSC), and markers of HSC activation and fibrosis were increased in livers from Glp2r-/- mice. Moreover, GLP-2 directly modulated gene expression in isolated HSCs ex vivo. Taken together, these findings define an essential role for the GLP-2R in hepatic adaptation to nutrient excess and unveil a gut hormone-HSC axis, linking GLP-2R signaling to control of hepatic stellate cell activation.
Authors
Shai Fuchs, Bernardo Yusta, Laurie L. Baggio, Elodie M. Varin, Dianne Matthews, Daniel J. Drucker
Abstract
Background: Metabolic disorders such as type 2 diabetes have been associated with a decrease in insulin pulse frequency and amplitude. We hypothesized that the T-allele at rs7903146 in TCF7L2, previously associated with β–cell dysfunction, would be associated with changes in these insulin pulse characteristics. Methods: 29 nondiabetic subjects (age = 46 ± 2, BMI = 28 ± 1 Kg/M2) participated in this study. Of these, 16 were homozygous for the C allele at rs7903146 and 13 were homozygous for the T allele. Deconvolution of peripheral C-peptide concentrations allowed the reconstruction of portal insulin secretion over time. This data was used for subsequent analyses. Pulse orderliness was assessed by Approximate Entropy (ApEn) and the dispersion of insulin pulses was measured by a Frequency Dispersion Index (FDI) applied to a Fourier Transform of individual insulin secretion rates. Results: During fasting conditions, the CC genotype group exhibited decreased pulse disorderliness compared to the TT genotype group (1.10 ± 0.03 vs. 1.19 ± 0.04, p = 0.03). FDI decreased in response to hyperglycemia in the CC genotype group, perhaps reflecting less entrainment of insulin secretion during fasting.Conclusion: Diabetes-associated variation in TCF7L2 is associated with decreased orderliness and pulse dispersion unchanged by hyperglycemia. Quantification of ApEn and FDI could represent novel markers of β-cell health.
Authors
Marcello C. Laurenti, Chiara Dalla Man, Ron T. Varghese, James C. Andrews, Robert A. Rizza, Aleksey Matveyenko, Giuseppe De Nicolao, Claudio Cobelli, Adrian Vella
Abstract
Leptin receptor (LepRb)-expressing neurons of the nucleus tractus solitarius (NTS; LepRbNTS neurons) receive gut signals that synergize with leptin action to suppress food intake. NTS neurons that express preproglucagon (Ppg) (and which produce the food intake-suppressing PPG cleavage product, glucagon-like peptide-1 (GLP1)) represent a subpopulation of mouse LepRbNTS cells. Using Leprcre, Ppgcre, and Ppgflox mouse lines, along with designer receptors exclusively activated by designer drugs (DREADDs), we examined roles for Ppg in GLP1NTS and LepRbNTS cells for the control of food intake and energy balance. We found that the cre-dependent ablation of NTS Ppgflox early in development or in adult mice failed to alter energy balance, suggesting the importance of pathways independent of NTS GLP1 for the long-term control of food intake. Consistently, while activating GLP1NTS cells decreased food intake, LepRbNTS cells elicited larger and more durable effects. Furthermore, while the ablation of NTS Ppgflox blunted the ability of GLP1NTS neurons to suppress food intake during activation, it did not impact the suppression of food intake by LepRbNTS cells. While Ppg/GLP1-mediated neurotransmission plays a central role in the modest appetite-suppressing effects of GLP1NTS cells, additional pathways engaged by LepRbNTS cells dominate for the suppression of food intake.
Authors
Wenwen Cheng, Ermelinda Ndoka, Chelsea R. Hutch, Karen Roelofs, Andrew Mackinnon, Basma Khoury, Irwin J. Magrisso, Ki-Suk Kim, Christopher J. Rhodes, David P. Olson, Randy J. Seeley, Darleen A. Sandoval, Martin G. Myers Jr.
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