Three-Dimensional Imaging of Intact Isolated Islets of Langerhans With Confocal Microscopy

Brelje, T. Clark; Dw, Scharp; Sorenson, Robert L.

doi:10.2337/diab.38.6.808

Cited by 74 publications

(37 citation statements)

References 16 publications

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“…Human islets have been considered to have a modified core-mantle structure. In this view, ␤ cells are contiguous and arranged either into smaller clusters surrounded by non-␤ cells or along invaginations of the exterior surface of the islet (20,21). Our results, however, indicate that human islets do not show obvious subdivisions.…”

Section: Discussioncontrasting

confidence: 53%

The unique cytoarchitecture of human pancreatic islets has implications for islet cell function

Cabrera

Berman

Kenyon

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

1,121

967

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The cytoarchitecture of human islets has been examined, focusing on cellular associations that provide the anatomical framework for paracrine interactions. By using confocal microscopy and multiple immunofluorescence, we found that, contrary to descriptions of prototypical islets in textbooks and in the literature, human islets did not show anatomical subdivisions. Insulin-immunoreactive ␤ cells, glucagon-immunoreactive ␣ cells, and somatostatin-containing ␦ cells were found scattered throughout the human islet. Human ␤ cells were not clustered, and most (71%) showed associations with other endocrine cells, suggesting unique paracrine interactions in human islets. Human islets contained proportionally fewer ␤ cells and more ␣ cells than did mouse islets. In human islets, most ␤, ␣, and ␦ cells were aligned along blood vessels with no particular order or arrangement, indicating that islet microcirculation likely does not determine the order of paracrine interactions. We further investigated whether the unique human islet cytoarchitecture had functional implications. Applying imaging of cytoplasmic free Ca 2؉ concentration, [Ca 2؉ ]i, we found that ␤ cell oscillatory activity was not coordinated throughout the human islet as it was in mouse islets. Furthermore, human islets responded with an increase in [Ca 2؉ ]i when lowering the glucose concentration to 1 mM, which can be attributed to the large contribution of ␣ cells to the islet composition. We conclude that the unique cellular arrangement of human islets has functional implications for islet cell function.␣ cell ͉ ␤ cell ͉ cytoplasmic free Ca 2ϩ concentration ͉ insulin ͉ glucagon I n the last three decades, hundreds of individuals with type 1 diabetes mellitus have received allogeneic transplants of endocrine pancreas, the islets of Langerhans, to cure their chronic condition. In these patients, diabetes is reversed by transplanting cells capable of physiologically regulating insulin secretion. Determining the quality of islets obtained from cadaveric pancreata should be indispensable in this context. However, it is not known which physiological parameters correlate best with a fully functional islet capable of reversing diabetes after transplantation. There is a wealth of information about the physiology of rodent islets, but the biology of human islets remains poorly understood. As assays for determining islet quality are being developed by many laboratories in the field of islet transplantation, a reassessment of the structure and function of human islets is warranted.The islets of Langerhans are small organs located in the pancreas that are crucial for glucose homeostasis. Islets typically consist of four types of secretory endocrine cells, namely, the insulin-containing ␤ cells, the glucagon-containing ␣ cells, the somatostatin-containing ␦ cells, and the pancreatic polypeptideproducing (PP) cells. In rodent islets, the vastly predominating ␤ cells are clustered in the core of a generally round islet, surrounded by a mantle of ␣, ␦, and PP cells. Thus, ...

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Section: Discussioncontrasting

confidence: 53%

The unique cytoarchitecture of human pancreatic islets has implications for islet cell function

Cabrera

Berman

Kenyon

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

1,121

967

View full text Add to dashboard Cite

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“…It is also noteworthy that there are significant differences between rodent and human islet beta cells at the functional (29)(30)(31) and structural levels (32,33), so it will be important to determine whether such connections also occur in stimulated human islet beta cells.…”

Section: Resultsmentioning

confidence: 99%

Direct continuities between cisternae at different levels of the Golgi complex in glucose-stimulated mouse islet beta cells

Marsh

Volkmann

McIntosh

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

169

137

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Direct continuity between the membranes of cisternae in the Golgi complex in mammalian cells rarely has been observed; when seen, its documentation has been equivocal. Here we have used dualaxis electron microscope tomography to examine the architecture of the Golgi in three dimensions at Ϸ6-nm resolution in rapidly frozen, freeze-substituted murine cells that make and secrete insulin in response to glucose challenge. Our data show three types of direct connections between Golgi cisternae that are normally distinct from one another. These connections all ''bypass'' interceding cisternae. We propose that when pancreatic beta cells are stimulated to synthesize and secrete insulin rapidly in vivo, such connections provide a continuous lumen that facilitates the rapid transit of large amounts of newly made protein for secretion. The heterotypic fusion of cisternae, even transiently, raises important questions about the molecular mechanisms that (i) facilitate the fusion͞fission of cisternal membranes and control the directionality and specificity of such events, and (ii) retain Golgi processing enzymes at specific places within individual cisternae when two cisternae at different levels in the Golgi have fused, maintaining the sequential processing hierarchy that is a hallmark of Golgi organization.T he mechanisms by which proteins and lipids move through the Golgi complex remain controversial. There are three prevailing theories for how membrane and luminal cargo are transported: (i) by carrier vesicles that move cargo between physically distinct Golgi cisternae in both the anterograde and retrograde directions (1, 2), (ii) by the forward movement or ''progression'' of the cisternae themselves, accompanied by vesicle movement in the retrograde direction (3-5), or (iii) by both mechanisms acting in concert (6-8). Direct membrane connections between cisternae at different levels of the Golgi also have been proposed (8-11). Lippincott-Schwartz and colleagues (11) have suggested that such connections might constitute a major mechanism for transport through the Golgi stack, based on data that show first order kinetics for the rate of transport of exogenous viral glycoprotein of vesicular stomatitis virus through the Golgi following its overexpression in cultured cells. Convincing evidence for direct continuity between nonequivalent cisternae has been limited or lacking, although connectivity between cisternae at equivalent levels of the Golgi ribbon is well documented (12)(13)(14).In this study, rapid freezing followed by freeze-substitution fixation of endocrine tissue isolated from mouse pancreas, together with techniques for analyzing electron microscope (EM) data in 3D at Ϸ6-nm resolution (15), have allowed us to capture and visualize such events in ''professional'' secretory cells stimulated to make and secrete large amounts of protein.Our observations of membrane trafficking in primary cells maintained in organ culture and stimulated to secrete at high levels suggest that the overexpression of proteins from transg...

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“…13,58,[65][66][67][68][69] These other signals are not omitted but are unified in the MCN based on the assumption that the primary physiological relationships that are explicit in the model are influenced by these factors.…”

Section: Discussionmentioning

confidence: 99%

Models of Glucagon Secretion, Their Application to the Analysis of the Defects in Glucagon Counterregulation and Potential Extension to Approximate Glucagon Action

Farhy

McCall

2010

J Diabetes Sci Technol

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Abbreviations: (BG) blood glucose, (GABA) γ-aminobutyric acid, (GCR) glucagon counterregulation, (GLP-1) glucagon-like peptide-1, (HGO) hepatic glucose output, (ID 50 AbstractThis review analyzes an interdisciplinary approach to the pancreatic endocrine network-like relationships that control glucagon secretion and glucagon counterregulation (GCR). Using in silico studies, we show that a pancreatic feedback network that brings together several explicit interactions between islet peptides and blood glucose reproduces the normal GCR axis and explains its impairment in diabetes. An α-cell auto-feedback loop drives glucagon pulsatility and mediates triggering of GCR by hypoglycemia by a rapid switch-off of β-cell signals. The auto-feedback explains the enhancement of defective GCR in β-cell deficiency by a switch-off of signals in the pancreas that suppress α cells. Our models also predict that reduced β-cell activity decreases and delays the GCR. A key application of our models is the in silico simulation and testing of possible scenarios to repair defective GCR in β-cell deficiency. In particular, we predict that partial suppression of hyperglucagonemia may repair the impaired GCR. We also outline how the models can be extended and tested using human data to become a part of a larger construct including the regulation of the hepatic glucose output by the pancreas, circulating glucose, and incretins. In conclusion, a model of the normal GCR control mechanisms and their dysregulation in insulin-deficient diabetes is proposed and partially validated. The model components are clinically measurable, which permits its application to the study of the abnormalities of the human endocrine pancreas and their role in the progression of many diseases, including diabetes, metabolic syndrome, polycystic ovary syndrome, and others. It may also be used to examine therapeutic responses.

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Three-Dimensional Imaging of Intact Isolated Islets of Langerhans With Confocal Microscopy

Cited by 74 publications

References 16 publications

The unique cytoarchitecture of human pancreatic islets has implications for islet cell function

The unique cytoarchitecture of human pancreatic islets has implications for islet cell function

Direct continuities between cisternae at different levels of the Golgi complex in glucose-stimulated mouse islet beta cells

Models of Glucagon Secretion, Their Application to the Analysis of the Defects in Glucagon Counterregulation and Potential Extension to Approximate Glucagon Action

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