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Roles of unconventional ion channels and insulin granule structure in the pathogenesis of type-2 diabetes

Barghouth, Mohammad LU (2023) In Lund University, Faculty of Medicine Doctoral Dissertation Series
Abstract

T2D is the most widespread endocrine disease.
In conventional stimulus secretion coupling increased blood glucose is
metabolized causing an increased intracellular level of ATP and closure of the
KATP channels, and this, in turn, depolarizes the cell membrane
leading to the opening of voltage-gated Ca2+ channels, the influx of
Ca2+ and exocytosis of insulin granules. This model has become
almost an axiom in the diabetes research area. However, there are clear weak
points that so far remain unclarified. More ion channels than potassium
channels are needed to depolarize the membrane. Voltage-gated Ca2+
... (More)

T2D is the most widespread endocrine disease.
In conventional stimulus secretion coupling increased blood glucose is
metabolized causing an increased intracellular level of ATP and closure of the
KATP channels, and this, in turn, depolarizes the cell membrane
leading to the opening of voltage-gated Ca2+ channels, the influx of
Ca2+ and exocytosis of insulin granules. This model has become
almost an axiom in the diabetes research area. However, there are clear weak
points that so far remain unclarified. More ion channels than potassium
channels are needed to depolarize the membrane. Voltage-gated Ca2+
(Cav) channels have an essential role in beta cell function. The
role of high voltage-activated Cav channels is well studied while
the role of low voltage-activated T-type channels remain elusive. Moreover,
glucose-stimulated insulin secretion (GSIS) causes beta cell swelling, which
promotes us to explore mechanotransduction signalling pathways in beta cells
represented by recently discovered Piezo1 mechanosensitive channel and
aquaporins channels. Moreover, we also employed a dSTORM microscope combined
with a single domain (SD) antibody to study the insulin granule cores (IGCs) at
nano levels.



Results: We find that the T-type Cav3.2
channel is abundantly expressed in human islets, and the gene expression is
negatively correlated with HbA1c and strongly positively correlated with the
expression of islet-predominantly expressed L-type subunits. CaV3.2
plays a fundamental role in maintaining normal insulin secretion by controlling
Ca2+ signalling. Meanwhile, we also show that Piezo1 is expressed in
pancreatic alpha and beta cells with heterogeneous distribution and is
upregulated in T2D donors. Chronic hyperglycemia induces translocation of
Piezo1 into the nucleus. In addition, silencing or inhibiting Piezo1 reduces Ca2+
signalling, membrane depolarization, and GSIS. Interestingly, beta-
cell-specific Piezo1-knockout mice show impaired glucose tolerance in vivo and
reduced electrical activity in islets. Subsequently, we identify that AQP1 gene
expression is downregulated in islets from T2D individuals and silencing AQP1
decreased insulin secretion and insulin content. Whereas AQP1 overexpression
significantly increased GSIS, AQP1 silencing elevated Ca2+
signalling due to elevated expression of CaV1.2 and CaV1.3
channels. Moreover, we demonstrate that AqB011, a selective AQP1 inhibitor
blocking ion transport, substantially increases insulin secretion. Finally,
nanoscale imaging for insulin granule cores exhibit that larger size located in
exocytotic granules, the size and shape can be regulated by granule proteins
cargo and the size is decreased after glucose stimulation, due to release of
the readily releasable pool (RRP) part of insulin cores through incomplete
granule fusion. Intriguingly, IGCs size was significantly decreased in
pancreatic beta cells from human T2D donors and indicating that the lack of the
RRP of the insulin core in the diabetic beta cells may be a primary cause for
the impaired exocytosis.



Conclusion: In this thesis, we have challenged
the a consensus model and explored the importance of insulin granule structure
in order to gain knowledge in the field around T2D pathophysiological
progression and to facilitate finding new drug targets for the disease.

(Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Associate professor Stozer, Andraz, Head of the Institute of Physiology, University of Maribor
organization
publishing date
type
Thesis
publication status
published
subject
keywords
T2D, pancreatic islets, mechanosensitive channels, Piezo1, beta-cell specific Piezo1 knockout mouse, KATP channel, dSTORM, Piezo1, Cav3.2, AQP1, SD, RRP, Insulin secretion and action
in
Lund University, Faculty of Medicine Doctoral Dissertation Series
issue
2023:23
pages
76 pages
publisher
Lund University, Faculty of Medicine
defense location
Agardh föreläsningssal, CRC, Jan Waldenströms gata 35, Skånes Universitetssjukhus i Malmö. Join by Zoom: https://lu-se.zoom.us/j/68446120979
defense date
2023-02-15 09:00:00
ISSN
1652-8220
ISBN
978-91-8021-362-2
language
English
LU publication?
yes
id
8b72f806-34f6-4261-afa2-a9e0f4bff80b
date added to LUP
2023-01-18 11:22:56
date last changed
2023-01-24 11:35:08
@phdthesis{8b72f806-34f6-4261-afa2-a9e0f4bff80b,
  abstract     = {{<p class="MsoNormal" style="text-align:justify">T2D is the most widespread endocrine disease.<br>
In conventional stimulus secretion coupling increased blood glucose is<br>
metabolized causing an increased intracellular level of ATP and closure of the<br>
K<sub>ATP</sub> channels, and this, in turn, depolarizes the cell membrane<br>
leading to the opening of voltage-gated Ca<sup>2+</sup> channels, the influx of<br>
Ca<sup>2+</sup> and exocytosis of insulin granules. This model has become<br>
almost an axiom in the diabetes research area. However, there are clear weak<br>
points that so far remain unclarified. More ion channels than potassium<br>
channels are needed to depolarize the membrane. Voltage-gated Ca<sup>2+</sup><br>
(Ca<sub>v</sub>) channels have an essential role in beta cell function. The<br>
role of high voltage-activated Ca<sub>v</sub> channels is well studied while<br>
the role of low voltage-activated T-type channels remain elusive. Moreover,<br>
glucose-stimulated insulin secretion (GSIS) causes beta cell swelling, which<br>
promotes us to explore mechanotransduction signalling pathways in beta cells<br>
represented by recently discovered Piezo1 mechanosensitive channel and<br>
aquaporins channels. Moreover, we also employed a dSTORM microscope combined<br>
with a single domain (SD) antibody to study the insulin granule cores (IGCs) at<br>
nano levels. </p><br>
<br>
<p class="MsoNormal" style="text-align:justify">Results: We find that the T-type Ca<sub>v</sub>3.2<br>
channel is abundantly expressed in human islets, and the gene expression is<br>
negatively correlated with HbA1c and strongly positively correlated with the<br>
expression of islet-predominantly expressed L-type subunits. Ca<sub>V</sub>3.2<br>
plays a fundamental role in maintaining normal insulin secretion by controlling<br>
Ca<sup>2+</sup> signalling. Meanwhile, we also show that Piezo1 is expressed in<br>
pancreatic alpha and beta cells with heterogeneous distribution and is<br>
upregulated in T2D donors. Chronic hyperglycemia induces translocation of<br>
Piezo1 into the nucleus. In addition, silencing or inhibiting Piezo1 reduces Ca<sup>2+</sup><br>
signalling, membrane depolarization, and GSIS. Interestingly, beta-<br>
cell-specific Piezo1-knockout mice show impaired glucose tolerance in vivo and<br>
reduced electrical activity in islets. Subsequently, we identify that AQP1 gene<br>
expression is downregulated in islets from T2D individuals and silencing AQP1<br>
decreased insulin secretion and insulin content. Whereas AQP1 overexpression<br>
significantly increased GSIS, AQP1 silencing elevated Ca<sup>2+</sup><br>
signalling due to elevated expression of Ca<sub>V</sub>1.2 and Ca<sub>V</sub>1.3<br>
channels. Moreover, we demonstrate that AqB011, a selective AQP1 inhibitor<br>
blocking ion transport, substantially increases insulin secretion. Finally,<br>
nanoscale imaging for insulin granule cores exhibit that larger size located in<br>
exocytotic granules, the size and shape can be regulated by granule proteins<br>
cargo and the size is decreased after glucose stimulation, due to release of<br>
the readily releasable pool (RRP) part of insulin cores through incomplete<br>
granule fusion. Intriguingly, IGCs size was significantly decreased in<br>
pancreatic beta cells from human T2D donors and indicating that the lack of the<br>
RRP of the insulin core in the diabetic beta cells may be a primary cause for<br>
the impaired exocytosis. </p><br>
<br>
<p class="MsoNormal" style="text-align:justify">Conclusion: In this thesis, we have challenged<br>
the a consensus model and explored the importance of insulin granule structure<br>
in order to gain knowledge in the field around T2D pathophysiological<br>
progression and to facilitate finding new drug targets for the disease.</p>}},
  author       = {{Barghouth, Mohammad}},
  isbn         = {{978-91-8021-362-2}},
  issn         = {{1652-8220}},
  keywords     = {{T2D, pancreatic islets, mechanosensitive channels, Piezo1, beta-cell specific Piezo1 knockout mouse; KATP channel, dSTORM, Piezo1, Cav3.2, AQP1, SD, RRP; Insulin secretion and action}},
  language     = {{eng}},
  number       = {{2023:23}},
  publisher    = {{Lund University, Faculty of Medicine}},
  school       = {{Lund University}},
  series       = {{Lund University, Faculty of Medicine Doctoral Dissertation Series}},
  title        = {{Roles of unconventional ion channels and insulin granule structure in the pathogenesis of type-2 diabetes}},
  year         = {{2023}},
}