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Control of metabolism and hormone secretion from pancreatic alpha and beta cells

Stamenkovic, Jelena LU (2014) In Lund University, Faculty of Medicine Doctoral Dissertation Series 2014:79.
Abstract (Swedish)
Popular Abstract in Swedish

Diabetes mellitus är en endokrin sjukdom. Hos friska individer producerar beta och alpha cellerna i bukspottkörteln insulin och glukagon, de viktigaste hormonerna för att reglera blodglukos¬koncentrationen. Insulin utsöndras som svar på förhöjda blodglukosnivåer. Hormonet minskar glukosproduktion från levern och ökar glukosupptaget samt dess användning och lagring i fett och muskler. Glukagon har motsatta effekter: det höjer glukos i blodet genom att stimulera dess produktion i lever.



Diabetes mellitus är heterogen sjukdom. Den åtföljs av ett stort antal komplikationer i det sena skedet. Det tydligaste tecknet på sjukdomen är förhöjd blodglukosnivå. När sjukdomen förekommer hos... (More)
Popular Abstract in Swedish

Diabetes mellitus är en endokrin sjukdom. Hos friska individer producerar beta och alpha cellerna i bukspottkörteln insulin och glukagon, de viktigaste hormonerna för att reglera blodglukos¬koncentrationen. Insulin utsöndras som svar på förhöjda blodglukosnivåer. Hormonet minskar glukosproduktion från levern och ökar glukosupptaget samt dess användning och lagring i fett och muskler. Glukagon har motsatta effekter: det höjer glukos i blodet genom att stimulera dess produktion i lever.



Diabetes mellitus är heterogen sjukdom. Den åtföljs av ett stort antal komplikationer i det sena skedet. Det tydligaste tecknet på sjukdomen är förhöjd blodglukosnivå. När sjukdomen förekommer hos barn och ungdomar, som en följd av absolut insulinbrist på grund av autoimmun destruktion av beta celler, talar vi om typ 1-diabetes (T1D). Patienter med T1D kräver livslång behandling med insulin. Om sjukdomen förekommer hos vuxna på grund av otillräcklig insulinfrisättning och insulinresistens benämns den typ 2-diabetes (T2D). Förekomsten av T2D ökar stadigt – vi säger att en diabetespandemi utbreder sig på kontinenterna. Sjukdomsutvecklingen, dvs. patogenes, är komplicerad och inte fullt klarlagd, eftersom många faktorer bidrar till dess utveckling. Livsstil med övervikt och fysisk inaktivitet samt en stark genetisk komponent är välkända faktorer förknippade med T2D.



Vi studerade olika processer som kan vara bakomliggande mekanismer för utveckling av T2D. Ett föremål för våra undersökningar var dygnsrytm. Vi försökte att hitta en möjlig roll för gener som styr cellens ”klocka” vid insulinsekretion och beta cellsfunktion. Vi fann att uttryck av gener som PER2, PER3 och CRY2 minskade i humana Langerhanska öar från T2D donatorer. Deras nivåer korrelerade med metabola parametrar som är viktiga för T2D patogenes, t.ex. långtidsblodglukos (HbA1c). En minskning av Per3-gennivåer i odlade β-celler hämmade insulinsekretion.



Störd glukagonutsöndring är också en del av patogenesen vid T2D. En balanserad frisättning av insulin och glukagon är avgörande för att upprätthålla stabila blodglukosnivåer. Tyvärr saknas fortfarande en etablerad mekanism för glukagonutsöndringen. Därför har vi försökt att lösa åtminstone en del av problemet. Vi tittade på metabola svar från en odlad alpha cellinje. Vi bekräftade tidigare fynd att alpha-celler frisätter glukagon vid förhöjda glukoskoncentrationer – detta liknar svaret från beta-cellerna för frisättning av insulin. Vi fann i egentlig mening att de två cellinjerna betedde sig ganska lika även om en svagare mitokondriell aktivitet sågs i alpha-cellerna.



Slutligen, mitokondrier var ett genomgående tema i våra studier. Därför undersökte vi i vår sista studie mitokondriens roll i patogenesen av T2D, och särskilt då betydelsen av TFB1M. Detta protein styr kodning av mitokondriella andningsproteiner. Vi utförda våra studier i en mus som sakande genen för Tfb1m i insulin-producerande celler, en s.k. knock out-mus. Våra experiment in vivo och in vitro visade att förlusten av Tfb1m i β-celler ledde till mitokondriell dysfunktion och därmed nedsatt insulinsekretion; tillsammans med en minskning av beta-cellmassa bidrog detta till T2D utveckling.



Våra studier har belyst komplexiteten av orsakerna till T2D, en av vår tids stora folksjukdomar. (Less)
Abstract
Type 2 Diabetes (T2D) is a multifactorial disease, which has made it difficult to resolve its pathophysiology. We investigated processes that could contribute to the development of T2D. In addition to well-known hallmarks of the disease, such as defective insulin secretion, insulin resistance and perturbed glucagon secretion, we aimed to find a possible role for CLOCK genes in the pathogenesis of T2D.

In paper 1, we showed that there is a link between the expression levels of core CLOCK genes in human islets and functional parameters important for T2D. This link to T2D was particularly strong for the core CLOCK components, PER2, PER3 and CRY2. We further investigated this possibility in paper 2, where we found that silencing of... (More)
Type 2 Diabetes (T2D) is a multifactorial disease, which has made it difficult to resolve its pathophysiology. We investigated processes that could contribute to the development of T2D. In addition to well-known hallmarks of the disease, such as defective insulin secretion, insulin resistance and perturbed glucagon secretion, we aimed to find a possible role for CLOCK genes in the pathogenesis of T2D.

In paper 1, we showed that there is a link between the expression levels of core CLOCK genes in human islets and functional parameters important for T2D. This link to T2D was particularly strong for the core CLOCK components, PER2, PER3 and CRY2. We further investigated this possibility in paper 2, where we found that silencing of Per3 in a beta cell line disrupted insulin secretion in response to glucose and other secretagogues. Our observations suggest that exocytosis may be an underlying cause. In support of this assumption, we found down-regulation of crucial genes involved in the exocytotic machinery upon silencing of Per3. Together, our observations suggest that there is a link between the circadian clock machinery and beta cell function.

In paper, 3 we employed an alpha and a beta cell line, which were challenged with the same stimuli. We compared their responses in hormone release and metabolism in order to understand metabolic control of glucagon secretion. We found that two cell lines responded similarly to glucose: alpha cells increased glucagon secretion upon glucose stimulation while beta cells increased secretion of insulin. Differences, however, were primarily found in the coupling of glycolytic and mitochondrial metabolism. Moreover, inhibiting the malate-aspartate shuttle completely abolished glucagon secretion, while insulin secretion was largely preserved. This was likely due to a compensatory activity in the glycerolphosphate shuttle in beta cells.

So far, most observations seemed to involve mitochondrial metabolism in some way. Therefore we studied how mitochondria become molecularly equipped for metabolic coupling in beta cells. Characterization of a beta cell-specific knockout of Tfb1m (beta Tfb1m-/-), which encodes a protein controlling translation of mitochondrial proteins, showed mitochondrial dysfunction. This confirmed previous findings where TFB1M was identified as T2D risk gene in human islets. Islets from β-Tfb1m-/- mice showed impaired insulin secretion, contained less insulin in secretory granules and exhibited reduced beta cell mass. Mitochondria exhibited disrupted architecture. All measured metabolic parameters in mitochondria were impaired. Reactive oxygen species were increased, and signs of apoptosis and necrosis with accompanying inflammation were observed.

These studies have illustrated the complexity of the mechanisms involved in the pathogenesis of T2D. Thus, investigating different metabolic aspects of its pathogenesis, supported the multifactorial nature of the underlying mechanism of T2D development. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Schuit, Frans, Professor
organization
publishing date
type
Thesis
publication status
published
subject
keywords
CLOCK genes, insulin, glucagon, metabolites, mitochondria, knock out
in
Lund University, Faculty of Medicine Doctoral Dissertation Series
volume
2014:79
publisher
Molecular Metabolism
defense location
"Lilla Aulan" Jan Waldenströms gata 5, Skånes universitetssjukhus i Malmö
defense date
2014-06-13 09:00
ISSN
1652-8220
ISBN
978-91-7619-008-1
language
English
LU publication?
yes
id
d39f6051-cf5b-42d4-8bc2-d94fac04b724 (old id 4446883)
date added to LUP
2014-07-09 11:35:45
date last changed
2016-09-19 08:44:45
@phdthesis{d39f6051-cf5b-42d4-8bc2-d94fac04b724,
  abstract     = {Type 2 Diabetes (T2D) is a multifactorial disease, which has made it difficult to resolve its pathophysiology. We investigated processes that could contribute to the development of T2D. In addition to well-known hallmarks of the disease, such as defective insulin secretion, insulin resistance and perturbed glucagon secretion, we aimed to find a possible role for CLOCK genes in the pathogenesis of T2D. <br/><br>
In paper 1, we showed that there is a link between the expression levels of core CLOCK genes in human islets and functional parameters important for T2D. This link to T2D was particularly strong for the core CLOCK components, PER2, PER3 and CRY2. We further investigated this possibility in paper 2, where we found that silencing of Per3 in a beta cell line disrupted insulin secretion in response to glucose and other secretagogues. Our observations suggest that exocytosis may be an underlying cause. In support of this assumption, we found down-regulation of crucial genes involved in the exocytotic machinery upon silencing of Per3. Together, our observations suggest that there is a link between the circadian clock machinery and beta cell function.<br/><br>
In paper, 3 we employed an alpha and a beta cell line, which were challenged with the same stimuli. We compared their responses in hormone release and metabolism in order to understand metabolic control of glucagon secretion. We found that two cell lines responded similarly to glucose: alpha cells increased glucagon secretion upon glucose stimulation while beta cells increased secretion of insulin. Differences, however, were primarily found in the coupling of glycolytic and mitochondrial metabolism. Moreover, inhibiting the malate-aspartate shuttle completely abolished glucagon secretion, while insulin secretion was largely preserved. This was likely due to a compensatory activity in the glycerolphosphate shuttle in beta cells.<br/><br>
So far, most observations seemed to involve mitochondrial metabolism in some way. Therefore we studied how mitochondria become molecularly equipped for metabolic coupling in beta cells. Characterization of a beta cell-specific knockout of Tfb1m (beta Tfb1m-/-), which encodes a protein controlling translation of mitochondrial proteins, showed mitochondrial dysfunction. This confirmed previous findings where TFB1M was identified as T2D risk gene in human islets. Islets from β-Tfb1m-/- mice showed impaired insulin secretion, contained less insulin in secretory granules and exhibited reduced beta cell mass. Mitochondria exhibited disrupted architecture. All measured metabolic parameters in mitochondria were impaired. Reactive oxygen species were increased, and signs of apoptosis and necrosis with accompanying inflammation were observed. <br/><br>
These studies have illustrated the complexity of the mechanisms involved in the pathogenesis of T2D. Thus, investigating different metabolic aspects of its pathogenesis, supported the multifactorial nature of the underlying mechanism of T2D development.},
  author       = {Stamenkovic, Jelena},
  isbn         = {978-91-7619-008-1},
  issn         = {1652-8220},
  keyword      = {CLOCK genes,insulin,glucagon,metabolites,mitochondria,knock out},
  language     = {eng},
  publisher    = {Molecular Metabolism},
  school       = {Lund University},
  series       = {Lund University, Faculty of Medicine Doctoral Dissertation Series},
  title        = {Control of metabolism and hormone secretion from pancreatic alpha and beta cells},
  volume       = {2014:79},
  year         = {2014},
}