Thesis (PhD)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: A high fat diet (HFD) reduces beta-cell mass, impairs glucose signalling and is
involved in the development of Type 2 diabetes. Malnutrition during gestation is
hypothesized to irreversibly damage beta-cell development. The transcription
factors Pdx-1 and Pax 4 are involved in islet cell development. Pdx-1 is reported
to regulate expression of GLUT-2, glucokinase (GK) and the insulin gene.
Aims
The aim of this study is to investigate, in the neonatal and weanling rat, the effect
of exposure to a HFD in utero and/or lactation on weight, glucose and insulin
concentrations, islet cell development, pancreatic transcription factors and
glucose sensing genes.
Methods
Neonatal and weanling rats were exposed to a maternal HFD for defined periods
of gestation and/or lactation. After termination, pups were weighed and glucose
and insulin concentrations determined. mRNA expression of Pdx-1, Pax 4,
GLUT-2 and GK was quantified by LightCycler PCR. Pancreatic sections were
immunostained for insulin and glucagon (islet cell development), and for Pdx-1,
GLUT-2 and GK (beta-cell function) followed by image analysis.
Results:
Exposure to an in utero HFD throughout gestation resulted in hyperglycaemic
pups with reduced beta-cell volume and number, Pdx-1 and GK
immunoreactivity. In contrast the alpha-cell volume, number and size were
augmented in neonates exposed to a HFD throughout gestation.
Most weanlings were hyperglycaemic and hypoinsulinaemic. In some weanlings,
reduced beta-cell number and beta- and alpha-cell size was observed. Pdx-1
mRNA was overexpressed in weanlings exposed to a maternal HFD for the final
week of gestation or throughout both gestation and lactation, but reduced in
those only exposed throughout lactation. Pax 4 mRNA was reduced in weanlings
exposed to a maternal HFD for the first or final week of gestation, throughout
gestation or throughout lactation. In most of the weanlings, GLUT-2 mRNA
expression was reduced whereas immunoreactivity for GLUT-2 was increased.
Both GK mRNA expression and immunoreactivity were reduced in most of the
weanlings.
Conclusions
• Exposure to an in utero HFD throughout gestation induced
hyperglycaemia in neonates. The reduced Pdx-1 expression appears to
play a role in the compromised beta-cell development, and concomitant
with the reduced GK levels, contributes to the hyperglycaemia in these
neonates and may make them susceptible to beta-cell failure.
• In most weanlings exposed to a HFD in utero and/or during lactation the
hyperglycaemia and hypoinsulinaemia suggest compromised beta-cell
function. The GK mRNA expression and immunoreactivity were reduced
thereby impairing glycolysis which would result in reduced insulin
secretion contributing to the hyperglycaemia. Furthermore, beta-cell
development is adversely affected by the HFD in some weanlings. This
would contribute to reduced beta-cell function and may eventually result in
beta-cell failure. GLUT-2 immunoreactivity was increased in some,
suggesting a compensatory adaptative mechanism to restore glucose
homeostasis.
• A maternal HFD has adverse effects both in neonates and weanlings on
beta-cell development, transcription factor and glucose sensing gene
expression and induced hyperglycaemia and hypoinsulinaemia in some of
the offspring. Ways to ameliorate the HFD-induced attenuation of key
beta-cell genes to ensure normal beta-cell function are important for future
research in Type 2 diabetes. / AFRIKAANSE OPSOMMING:
‘n Hoe vet diet (HVD) verminder beta-sel masse, glukose signale en speel ‘n rol
in Tipe 2 diabetes. Die hipothese is dat wanvoeding gedurende swangerskap lei
tot onomkeerbare betasel beskadiging. Die transkripsiefaktore Pdx-1 en Pax 4
speel rolle in eilandselontwikkeling. Daar is bewyse dat Pdx-1 die uitdrukking van
die GLUT-2, glucokinase (GK) en insulin gene reguleer.
Doelstelling:
Die doel van hierdie studie is om, in die pasgebore en gespeende rot, die effek
van ’n HVD in utero en/of laktasie op gewig, glukose en insulin konsentrasies,
eilandselontwikkeling, pankreatiese transksripsiefaktore en op glukosewaarnemingsgene
te ondersoek.
Metodes:
Pasgebore en gespeende rotte is vir bepaalde periodes van gestasie en/of
laktasie blootgestel aan ’n HVD van die moeder. Na terminase, is kleinjies
geweeg en die glukose- en insulienkinsentrasies bepaal. mRNA uitdrukking van
Pdx-1, Pax 4, GLUT-2 en GK is geoes met LightCycler PCR. Snitte van die
pankreas is gekleur met insulien en glukagon (eilandsontwikkeling) en vir Pdx-1,
GLUT-2 en GK (betaselfunksie) gevolg deur beeldanalise.
Resultate:
Bloodstelling aan ’n in utero HVD regdeur gestasie het hiperglisemie versoorsaak
in pasgebore rotte met verlaagde betasel volume en aantal, Pdx-1 en GK
immunoreaktiwiteit. In teenstelling daarmee was die alfasel se volume, aantal en
grootte verhoog in pasgebore rotte wat regdeur gestasie aan 'n HVD blootgestel
was.
Meeste van die gespeende rotte was hiperglisemies en hipoinsulinemies. In
sommige gespeende rotte, was daar ’n verlaging van betasel hoeveelheid en
grootte en in alfasel groote. Oormatige uitdrukking van Pdx-1 mRNA het
plaasgevind in speenlinge wat aan ’n HVD van die moeder vir die laaste week
van gestasie of regdeur gestasie en laktasie blootgestel was, maar dit was
verlaag in die speenlinge wat net tydens laktasie blootgestel was. Pax 4 mRNA
was verlaag in speenlinge wat aan ’n HVD van die moeder blootgestel was vir
die eerste of laaste week van gestasie, regdeur gestasie of regdeur laktasie. In
meeste van die speenlinge is onder-uitdrukking van GLUT-2 mRNA, maar ’n
verhoging van GLUT-2 immunoreaktiwiteit gevind. Beide GK mRNA uitdrukking
en immunoreaktiwiteit was laer in meeste van die speenlinge.
Gevolgtrekkings:
• Blootstelling aan ’n in utero HVD regdeur gestasie lei tot hiperglisemie in
pasgebore rotte. Die verlaagde Pdx-1 immunoreaktiwiteit speel
klaarblyklik ’n rol by die geaffekteerde betaselontwikkeling. Dit, saam met die verlaagde immunoreaktiwiteit vir GK, kan bydra tot die hiperglisemie in
hierdie pasgebore rotte.
In die meeste van die speenlinge wat aan ’n HVD blootgestel was, dui die
hiperglisemie en hipoinsulinemie op geaffekteerde betaselfunksie. Die GK
mRNA uitdrukking en immunoreaktiwiteit is verlaag, wat weer glikolise
benadeel, en dit sal lei tot verminderde insulienafskeiding wat bydra tot die
hiperglisemie. Betaselontwikkeling word voorts negatief beinvloed deur
die HVD, wat blyk uit die verlaagde aantal en grootte van betaselle. Dit sal
bydra tot verminderde betaselfunksie. Dit kan uiteindelik tot
betaselversaking lei. GLUT-2 immunoreaktiwiteit was verhoog in hierdie
speenlinge, wat dui op ’n kompenserende aanpassingsmeganisme om
glukose homeostase te herstel.
’n HVD van die moeder het ’n negatiewe uitwerking op
betaselontwikkeling, transkripsiefaktor en glukosewaarneming
geenuitdrukking in beide die pasgebore en gespeende rotte, en
geinduseerde hiperglisemie en hipoinsulinemie in sommige kleintjies. Dis
belangrik vir toekomstige Tipe 2 diabetes navorsing dat daar na gekyk
moet word om die HVD-geinduseerde verlaging van sleutel betaselgene
te verbeter vir optimale betaselfunksie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50484 |
| Date | 12 1900 |
| Creators | Cerf, Marlon Eugene |
| Contributors | Du Toit, D. F., Louw, J., Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Anatomy and Histology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 215 p. : ill. |
| Rights | Stellenbosch University |
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