Cellular autophagy in α cells plays a role in the maintenance of islet architecture

Abstract Autophagy is known to play a pivotal role in intracellular quality control through the degradation of subcellular damaged organelles and components. Whereas autophagy is essential for maintaining β-cell function in pancreatic islets, it remains unclear as to how the cellular autophagy affects the homeostasis and function of glucagon-secreting α cells. To investigate the role of autophagy in α cells, we generated a mutant mouse model lacking Atg7, a key molecule for autophagosome formation, specifically in α cells. Histological analysis demonstrated an increased number of glucagon-positive cells, with a multilayered structure, in the islets under Atg7 deficiency, although metabolic profiles, such as body weight, blood glucose and plasma glucagon levels, were comparable between Atg7-deficient mice and control littermates. Consistent with our previous findings that Atg7 deficiency suppressed β-cell proliferation, cellular proliferation was suppressed in Atg7-deficient α cells. These findings suggest that α-cell autophagy plays a role in maintaining α-cell area and normal islet architecture, but appears to be dispensable for metabolic homeostasis.

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Role of the Rho-ROCK (Rho-Associated Kinase) Signaling Pathway in the Regulation of Pancreatic β-Cell Function

Endocrinology ◽

10.1210/en.2008-1135 ◽

2008 ◽

Vol 150 (5) ◽

pp. 2072-2079 ◽

Cited By ~ 31

Author(s):

Eva Hammar ◽

Alejandra Tomas ◽

Domenico Bosco ◽

Philippe A. Halban

Keyword(s):

Extracellular Matrix ◽

Insulin Secretion ◽

Actin Cytoskeleton ◽

Cell Function ◽

Pancreatic Β Cell ◽

Β Cell ◽

Β Cell Function ◽

Glucose Stimulated Insulin Secretion ◽

And Function

Extracellular matrix has a beneficial impact on β-cell spreading and function, but the underlying signaling pathways have yet to be fully elucidated. In other cell types, Rho, a well-characterized member of the family of Rho GTPases, and its effector Rho-associated kinase (ROCK), play an important role as downstream mediators of outside in signaling from extracellular matrix. Therefore, a possible role of the Rho-ROCK pathway in β-cell spreading, actin cytoskeleton dynamics, and function was investigated. Rho was inhibited using a new cell-permeable version of C3 transferase, whereas the activity of ROCK was repressed using the specific ROCK inhibitors H-1152 and Y-27632. Inhibition of Rho and of ROCK increased spreading and improved both short-term and prolonged glucose-stimulated insulin secretion but had no impact on basal secretion. Inhibition of this pathway led to a depolymerization of the actin cytoskeleton. Furthermore, the impact of the inhibition of ROCK on stimulated insulin secretion was acute and reversible, suggesting that rapid signaling such as phosphorylation is involved. Finally, quantification of the activity of RhoA indicated that the extracellular matrix represses RhoA activity. Overall these results show for the first time that the Rho-ROCK signaling pathway contributes to the stabilization of the actin cytoskeleton and inhibits glucose-stimulated insulin secretion in primary pancreatic β-cells. Furthermore, they indicate that inhibition of this pathway might be one of the mechanisms by which the extracellular matrix exerts its beneficial effects on pancreatic β-cell function.

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The role of gut microbiota and amino metabolism in the effects of improvement of islet β-cell function after modified jejunoileal bypass

Scientific Reports ◽

10.1038/s41598-021-84355-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Cai Tan ◽

Zhihua Zheng ◽

Xiaogang Wan ◽

Jiaqing Cao ◽

Ran Wei ◽

...

Keyword(s):

Gut Microbiota ◽

Cell Function ◽

Body Weight Gain ◽

Fasting Blood Glucose ◽

Jejunoileal Bypass ◽

Β Cell ◽

Β Cell Function ◽

Branched Chain

AbstractThe change in gut microbiota is an important mechanism of the amelioration of type 2 diabetes mellitus (T2DM) after bariatric surgery. Here, we observe that the modified jejunoileal bypass effectively decreases body weight gain, fasting blood glucose, and lipids level in serum; additionally, islet β-cell function, glucose tolerance, and insulin resistance were markedly ameliorated. The hypoglycemic effect and the improvement in islet β-cell function depend on the changes in gut microbiota structure. modified jejunoileal bypass increases the abundance of gut Escherichia coli and Ruminococcus gnavus and the levels of serum glycine, histidine, and glutamine in T2DM rats; and decreases the abundance of Prevotella copri and the levels of serum branched chain amino acids, which are significantly related to the improvement of islet β-cell function in T2DM rats. Our results suggest that amino acid metabolism may contribute to the islet β-cell function in T2DM rats after modified jejunoileal bypass and that improving gut microbiota composition is a potential therapeutic strategy for T2DM.

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Role of Sex Steroids in β Cell Function, Growth, and Survival

Trends in Endocrinology and Metabolism ◽

10.1016/j.tem.2016.08.008 ◽

2016 ◽

Vol 27 (12) ◽

pp. 844-855 ◽

Cited By ~ 39

Author(s):

Franck Mauvais-Jarvis

Keyword(s):

Sex Steroids ◽

Cell Function ◽

Β Cell ◽

Growth And Survival ◽

Β Cell Function

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Functional Role of Serotonin in Insulin Secretion in a Diet-Induced Insulin-Resistant State

Endocrinology ◽

10.1210/en.2014-1687 ◽

2014 ◽

Vol 156 (2) ◽

pp. 444-452 ◽

Cited By ~ 55

Author(s):

Kyuho Kim ◽

Chang-Myung Oh ◽

Mica Ohara-Imaizumi ◽

Sangkyu Park ◽

Jun Namkung ◽

...

Keyword(s):

Insulin Secretion ◽

Pancreatic Islets ◽

Cell Function ◽

Β Cell ◽

Pancreas Perfusion ◽

Insulin Resistant ◽

Β Cell Function ◽

Resistant State ◽

Insulin Resistant State

The physiological role of serotonin, or 5-hydroxytryptamine (5-HT), in pancreatic β-cell function was previously elucidated using a pregnant mouse model. During pregnancy, 5-HT increases β-cell proliferation and glucose-stimulated insulin secretion (GSIS) through the Gαq-coupled 5-HT2b receptor (Htr2b) and the 5-HT3 receptor (Htr3), a ligand-gated cation channel, respectively. However, the role of 5-HT in β-cell function in an insulin-resistant state has yet to be elucidated. Here, we characterized the metabolic phenotypes of β-cell-specific Htr2b−/− (Htr2b βKO), Htr3a−/− (Htr3a knock-out [KO]), and β-cell-specific tryptophan hydroxylase 1 (Tph1)−/− (Tph1 βKO) mice on a high-fat diet (HFD). Htr2b βKO, Htr3a KO, and Tph1 βKO mice exhibited normal glucose tolerance on a standard chow diet. After 6 weeks on an HFD, beginning at 4 weeks of age, both Htr3a KO and Tph1 βKO mice developed glucose intolerance, but Htr2b βKO mice remained normoglycemic. Pancreas perfusion assays revealed defective first-phase insulin secretion in Htr3a KO mice. GSIS was impaired in islets isolated from HFD-fed Htr3a KO and Tph1 βKO mice, and 5-HT treatment improved insulin secretion from Tph1 βKO islets but not from Htr3a KO islets. Tph1 and Htr3a gene expression in pancreatic islets was not affected by an HFD, and immunostaining could not detect 5-HT in pancreatic islets from mice fed an HFD. Taken together, these results demonstrate that basal 5-HT levels in β-cells play a role in GSIS through Htr3, which becomes more evident in a diet-induced insulin-resistant state.

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Non-Coding RNA in Pancreas and β-Cell Development

Non-Coding RNA ◽

10.3390/ncrna4040041 ◽

2018 ◽

Vol 4 (4) ◽

pp. 41 ◽

Cited By ~ 7

Author(s):

Wilson K. M. Wong ◽

Anja E. Sørensen ◽

Mugdha V. Joglekar ◽

Anand A. Hardikar ◽

Louise T. Dalgaard

Keyword(s):

Cell Function ◽

Islet Cells ◽

Current Knowledge ◽

Cell Development ◽

Pancreas Development ◽

Β Cell ◽

Neighboring Gene ◽

Non Coding Rnas ◽

And Function

In this review, we provide an overview of the current knowledge on the role of different classes of non-coding RNAs for islet and β-cell development, maturation and function. MicroRNAs (miRNAs), a prominent class of small RNAs, have been investigated for more than two decades and patterns of the roles of different miRNAs in pancreatic fetal development, islet and β-cell maturation and function are now emerging. Specific miRNAs are dynamically regulated throughout the period of pancreas development, during islet and β-cell differentiation as well as in the perinatal period, where a burst of β-cell replication takes place. The role of long non-coding RNAs (lncRNA) in islet and β-cells is less investigated than for miRNAs, but knowledge is increasing rapidly. The advent of ultra-deep RNA sequencing has enabled the identification of highly islet- or β-cell-selective lncRNA transcripts expressed at low levels. Their roles in islet cells are currently only characterized for a few of these lncRNAs, and these are often associated with β-cell super-enhancers and regulate neighboring gene activity. Moreover, ncRNAs present in imprinted regions are involved in pancreas development and β-cell function. Altogether, these observations support significant and important actions of ncRNAs in β-cell development and function.

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