Functional Characterization of the Human Islet Microvasculature Using Living Pancreas Slices

Abstract

Pancreatic islets are clusters of endocrine cells that secrete different hormones to regulate blood glucose levels. Efficient hormone secretion requires a close interaction of endocrine cells with their vascular system. Islets receive blood through feeding arteriole(s) that branch into capillaries made of endothelial cells covered by pericytes. While a lot is known about rodent islet blood vessels, the structure and function of the human islet microvasculature has been less investigated. In this study, we used living pancreas slices from non-diabetic human donors to examine the function of human islet blood vessels. Living human pancreas slices were incubated with a membrane permeant calcium indicator and pericytes/smooth muscle cells were visualized with a fluorescent antibody against the mural cell marker NG2 proteoglycan. By confocal microscopy, we simultaneously recorded changes in the diameter of lectin-labeled blood vessels and cytosolic calcium levels in mural cells in islets. We tested several stimuli with vasoactive properties, such as norepinephrine, endothelin-1 and adenosine and compared human vascular responses with those previously published for mouse islet blood vessels. Norepinephrine and endothelin-1 significantly constricted human islet feeding arterioles, while adenosine dilated them. Islet capillaries were less responsive and only 15–20% of the mouse and human islet capillary network showed vasomotion. Nevertheless, in these responsive regions, norepinephrine and endothelin-1 decreased both mouse and human islet capillary diameter. Changes in islet blood vessel diameter were coupled to changes in cytosolic calcium levels in adjacent mouse and human islet mural cells. Our study shows that mural cells in islets are the targets of different regulatory mechanisms of islet blood perfusion. Several alterations of the human islet microvasculature occur during diabetes progression. Elucidating their functional consequences in future studies will be critical for our understanding of disease pathogenesis.

The Role of the α Cell in the Pathogenesis of Diabetes: A World beyond the Mirror

“…Currently, there is some consensus regarding hyperglucagonemia origin. This is centred on two possible mechanisms: (1) a progressive loss in the regulatory mechanisms in the secretion patterns due to α cells functional alterations [75,76], or (2) modification in both the islet microarchitecture and cellularity [77][78][79][80].…”

Pericyte control of pancreatic islet blood flow impacts glucose homeostasis

“…2) and were not included in the study. We defined normoglycemia as 3 consecutive readings of non-fasting blood glucose below 200 mg/dl (2,4,5).…”

“…The density of pericytes is much higher in mouse and human islets than in the surrounding exocrine tissue of the pancreas and approximately half of pericytes in islet capillaries in mice and humans express high levels of the contractile protein alpha smooth muscle actin [Supplementary Fig. 1; 3,4 ], suggesting that pericytes work as internal gates (sphincters) that regulate blood flow at the level of the islet capillaries.…”

Dual Mode of Action of Acetylcholine on Cytosolic Calcium Oscillations in Pancreatic Beta and Acinar Cells In Situ

“…Preserved environment of the endocrine and exocrine part of the pancreas is important to understand in vivo physiology and pathophysiology [ 55 ]. Pancreatic tissue slices have recently become a standard technique in a number of laboratories and have been successfully used for a broad spectrum of studies ranging from the characterization of islet microvasculature [ 56 ], analysis of diabetes pathogeneses [ 57 ], studying the function of pancreatic ductal cells [ 58 ], interaction between the different cell types [ 59 ], and Ca 2+ dynamics [ 60 ]. The major aim of this paper has been to use the in situ character of the pancreatic slice preparation to learn about the cholinergic signaling by simultaneous observations of [Ca 2+ ] c dynamics in endocrine and acinar cells, in both physiological and supraphysiological conditions.…”