Projects / Programmes
The role of cyclic adenosine monophosphate in normal beta cell physiology and during development of type 2 diabetes mellitus
| Code |
Science |
Field |
Subfield |
| 3.07.00 |
Medical sciences |
Metabolic and hormonal disorders |
|
| Code |
Science |
Field |
| B470 |
Biomedical sciences |
Physiology |
| Code |
Science |
Field |
| 3.02 |
Medical and Health Sciences |
Clinical medicine |
diabetes mellitus, Epac 2A, western diet, tissue slice, beta cells, electrophysiology, optophysiology, in vivo measurements, complex network theory
Researchers (21)
Organisations (1)
Abstract
In beta cells, glucose stimulates insulin secretion by way of intracellular metabolism, which yields ATP and closes ATP-dependent potassium channels. This, in turn, leads to depolarization, opening of voltage-dependent calcium channels, and calcium influx. The resulting increase in intracellular calcium is the secondary message triggering exocytosis. The therapeutically important sulfonylureas bind directly to ATP-dependent potassium channels and depolarize the cell and trigger insulin secretion in a largely glucose-independent manner. In contrast, the incretin hormones or therapeutic agents that mimic their action act on beta cells by binding to extracellular G-protein coupled receptors that stimulate adenylyl cyclase and thus increase intracellular cAMP. This second messenger acts via two distinct intracellular pathways, either PKA or Epac2A, to influence different steps of the triggering cascade, but seems to be unable to trigger exocytosis in the absence of glucose- or sulfonylurea-initiated triggering signal. Lately, evidence has been presented that sulfonylureas directly modulate Epac2A activity, and that incretins are also able to produce the triggering increase in calcium concentration, suggesting that there are many intersections of signaling pathways activated by glucose, sulfonylureas, and incretins. In addition to its intracellular effects on stimulus-secretion coupling, cAMP might influence intercellular spreading of glucose- or sulfonylurea-induced depolarization and calcium waves. This intercellular functional coupling normally serves to align beta cell glucose responsiveness at the level of all beta cells coupled in an islet of Langerhans, but is also target of diabetogenic insults during development of insulin resistance and type 2 diabetes. However, how exactly cAMP influences intra- and intercellular signal conduction and what is its role for whole body glucose tolerance in normal conditions and during development of type 2 diabetes, remains poorly understood and this might at least partly account for the present lack of long-term therapeutic success of sulfonylureas and our inability to better stratify patients to different treatment groups depending on the duration of disease or knowledge of specific beta cell defects. More specifically, there is gap in our knowledge on the differential roles of PKA and Epac2A in the above processes and a better understanding of how their mode of action could lead to development of novel therapeutic agents. By studying glucose-, sulfonylurea- and incretin-induced stimulus-secretion coupling from most proximal (membrane depolarization) to most distal steps (exocytosis), intercellular coupling, and whole animal glucose tolerance in control and Epac2 knock-out mice, fed either a control diet or a western diet to induce insulin resistance and beta cell adaptation and failure, within the framework of this project we aim to achieve the following four main objectives:
To clarify the role of Epac2A and PKA in mediating the effects of cAMP on various steps of stimulus-secretion coupling.
To clarify the role of Epac2A and PKA in mediating the effects of cAMP on intercellular functional coupling.
To explore the role of Epac2A and PKA in mediating the effects of not only glucose but also various sulfonylureas, especially their influence upon changes in membrane potential and calcium oscillations, the sensitivity of the exocytotic machinery and intercellular functional coupling between beta cells.
To help mechanistically explain the role of Epac2A and PKA in beta-cell adaptation and dysfunction during development of western diet-induced mouse model of type 2 diabetes mellitus at the multicellular level of islets of Langerhans, as well as their effect on whole animal glucose tolerance in both normal and insulin resistant mice.
Significance for science
In the project, we will employ western diet (WD), which shows a greater degree of translational relevance than the high fat diet. Normal chow and western diet will be fed to control mice and Epac2A KO mice. In all four groups of mice, we will perform in vivo measurements, electro- and optophysiological measurements in pancreas tissue slices, and additional studies on the pancreatic as well as some other tissues. Together with statistical methods, complex network theory will be used to interpret the data. A combination of the described methods shall help us contribute to science by the following:
Further validation of the new mouse model of T2DM (i.e., WD) and establishment of the acute tissue slice method.
Further validation that complex network theory is suitable for analyzing time series in biology.
Confirmation or refutation of previous contradictory findings (obtained on very heterogeneous models), under in situ conditions in acute pancreas tissue slices and in western diet fed mice with greater phenotypical similarity to humans.
Clarification of normal beta cell stimulus-secretion coupling, particularly of the roles of the triggering pathway (initiated by glucose and sulfonylureas) and of the hormonal amplifying pathway (initiated by incretins), the hierarchy of the two pathways, and possible interactions with synergistic effects.
Through use of Epac2KO mice, the specific contributions of Epac2A and PKA (the only other mediator of incretin effects in beta cells) in mediating the effects of incretins on beta cells and their interaction with sulfonylureas will be clarified.
Contribution to understanding the role of gap junctions in normal conditions, during adaptation, and beta cell failure, the influence of sulfonylureas and incretins upon them, and specifically of the differential role of Epac2A compared with PKA.
Better understanding adaptation and early dysfunction of beta cells during development of T2DM, particularly different steps elicited by glucose, sulfonylureas, and incretins, intercellular communication, and the level of functionality of these steps and coupling during beta cell dysfunction, which has clinical implications (see below).
Better understanding unwanted side effects of therapy and suggesting clinical studies focusing on comparisons between the effectiveness of different treatment options (sulfonylureas compared with incretins or both)
Suggesting novel molecular targets for more specific treatments. Due to a relatively tissue specific expression of Epac2A and Connexin36 in beta cells, both molecules are attractive potential targets.
T2DM is a major public health problem: in the world, there are 425 million people with T2DM and annual treatment costs are estimated at 727 billion USD. In Slovenia, there are 160000 people with T2DM and we spend 2500 USD per patient (Diabetes atlas 2017). Even a relatively small advance in understanding disease mechanisms and therapy can have important long-term effects.
Significance for the country
In the project, we will employ western diet (WD), which shows a greater degree of translational relevance than the high fat diet. Normal chow and western diet will be fed to control mice and Epac2A KO mice. In all four groups of mice, we will perform in vivo measurements, electro- and optophysiological measurements in pancreas tissue slices, and additional studies on the pancreatic as well as some other tissues. Together with statistical methods, complex network theory will be used to interpret the data. A combination of the described methods shall help us contribute to science by the following:
Further validation of the new mouse model of T2DM (i.e., WD) and establishment of the acute tissue slice method.
Further validation that complex network theory is suitable for analyzing time series in biology.
Confirmation or refutation of previous contradictory findings (obtained on very heterogeneous models), under in situ conditions in acute pancreas tissue slices and in western diet fed mice with greater phenotypical similarity to humans.
Clarification of normal beta cell stimulus-secretion coupling, particularly of the roles of the triggering pathway (initiated by glucose and sulfonylureas) and of the hormonal amplifying pathway (initiated by incretins), the hierarchy of the two pathways, and possible interactions with synergistic effects.
Through use of Epac2KO mice, the specific contributions of Epac2A and PKA (the only other mediator of incretin effects in beta cells) in mediating the effects of incretins on beta cells and their interaction with sulfonylureas will be clarified.
Contribution to understanding the role of gap junctions in normal conditions, during adaptation, and beta cell failure, the influence of sulfonylureas and incretins upon them, and specifically of the differential role of Epac2A compared with PKA.
Better understanding adaptation and early dysfunction of beta cells during development of T2DM, particularly different steps elicited by glucose, sulfonylureas, and incretins, intercellular communication, and the level of functionality of these steps and coupling during beta cell dysfunction, which has clinical implications (see below).
Better understanding unwanted side effects of therapy and suggesting clinical studies focusing on comparisons between the effectiveness of different treatment options (sulfonylureas compared with incretins or both)
Suggesting novel molecular targets for more specific treatments. Due to a relatively tissue specific expression of Epac2A and Connexin36 in beta cells, both molecules are attractive potential targets.
T2DM is a major public health problem: in the world, there are 425 million people with T2DM and annual treatment costs are estimated at 727 billion USD. In Slovenia, there are 160000 people with T2DM and we spend 2500 USD per patient (Diabetes atlas 2017). Even a relatively small advance in understanding disease mechanisms and therapy can have important long-term effects.
Most important scientific results
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Most important socioeconomically and culturally relevant results
