Neuro-endocrine basis for altered plasma glucose homeostasis in the Fragile X mouse

Journal of Biomedical Science

Review

William L’Amoreaux¹  Abdeslem El Idrissi²  Xin Yan³  Francoise Sidime³ 

[1] Department of Biology, College of Staten Island, The City University of New York, 2800 Victory Boulevard, 10314, Staten Island, NY, USA;Doctoral Program in Biology – Neuroscience, The Graduate Center, The City University of New York, 365 Fifth Avenue, 10016, New York, NY, USA;Advanced Imaging Facility, College of Staten Island, The City University of New York, 2800 Victory Boulevard, 10314, Staten Island, NY, USA;Department of Biology, College of Staten Island, The City University of New York, 2800 Victory Boulevard, 10314, Staten Island, NY, USA;Doctoral Program in Biology – Neuroscience, The Graduate Center, The City University of New York, 365 Fifth Avenue, 10016, New York, NY, USA;Center for Developmental Neuroscience, College of Staten Island, The City University of New York, 2800 Victory Boulevard, 10314, Staten Island, NY, USA;Doctoral Program in Biology – Neuroscience, The Graduate Center, The City University of New York, 365 Fifth Avenue, 10016, New York, NY, USA;Center for Developmental Neuroscience, College of Staten Island, The City University of New York, 2800 Victory Boulevard, 10314, Staten Island, NY, USA;

关键词: Taurine;    Proliferate Cell Nuclear Antigen;    Plasma Glucose Level;    GABAergic System;    Glucose Injection;   

DOI  :  10.1186/1423-0127-17-S1-S8

来源: Springer

【 摘 要 】

BackgroundThe fragile X mouse model shows an increase in seizure susceptibility, indicating an involvement of the GABAergic system via an alteration in cellular excitability. In the brain, we have previously described a reduction in GABAA receptor expression as a likely basis for this susceptibility. In the brains of fragile X mice, this reduction in receptor expression culminates with a concomitant increase in the expression of glutamic acid decarboxylase (GAD), the enzyme responsible for GABA synthesis. Further, voltage-sensitive calcium channel expression is reduced in the pancreas of the fragile X mouse. Since there are considerable similarities in the GABAergic system in the brain and pancreas, we evaluated the protective role of taurine in pancreatic islet development in both wild type (WT) and fragile X mice (KO).MethodsOne-month-old FVB/NJ males or age-matched fmr1-knockout (KO) mice were supplemented with taurine in drinking water (0.05% w/v) for four weeks. Age-matched controls were fed water only for the same duration. At four weeks, mice were sacrificed and pancreases processed for histology and immunohistochemical studies on changes of insulin, glucagon and somatostatin expression. Additional mice were subjected to a glucose tolerance test.ResultsTaurine treatment resulted in a significant increase in the number and size of islets. WT taurine-fed mice, slightly hypoglycemic prior to glucose injection, showed significantly reduced plasma glucose at 30 min post-injection when compared to control mice. KO mice had normal baseline plasma glucose concentration; however, following glucose injection they had higher plasma glucose levels at 30 min when compared to controls. Supplementation of taurine to KO mice resulted in reduced baseline levels of plasma glucose. After glucose injection, the taurine-fed KO mice had reduced plasma glucose at 30 min compared to KO. Concomitant with the increased islets size and glucose tolerance observed in taurine-fed mice there was an increase in insulin, glucagon and somatostatin immunoreactivity in the islets of WT mice. In the KO mice however, insulin levels were not affected whereas glucagon and somatostatin levels were reduced. Exocytosis of these hormones is calcium-dependent, therefore any exacerbation of calcium homeostasis could affect hormone release. We found the expression of the voltage sensitive calcium channels (VSCC) is drastically reduced in the pancreas of fragile X mice.ConclusionsDuring early development, the VSCC play an important role in calcium-dependent gene expression. Since these channels are also involved in depolarization and calcium-mediated vesicular release of neurotransmitters and pancreatic hormones, alterations in the expression of VSCC not only will affect calcium-mediated gene expression but also hormonal and neurotransmitter release creating therefore a neuroendocrine perturbation in the fragile X that may potentially affect other organ systems. We find that in the fragile X mouse, taurine treatment may partially restore functionality of the neuro-endocrine pancreas.

【 授权许可】

CC BY   
© El Idrissi et al; licensee BioMed Central Ltd. 2010