a systems biology approach reveals the physiological origin of increased plasma hdl levels and...
TRANSCRIPT
.
Feb. 10, 2015
Natal van Riel, Maaike Oosterveer, Christian Tiemann,
Brenda Hijmans, Aldo Grefhorst, Yared Paalvast,
Yvonne Rozendaal, Jan Albert Kuivenhoven, Albert
Groen
Eindhoven University of Technology, the Netherlands
Dept. of Biomedical Engineering
Systems Biology and Metabolic Diseases
@nvanriel
Liver X Receptor
• Liver X Receptor (LXR, nuclear receptor),
induces transcription of multiple genes
modulating metabolism of fatty acids,
triglycerides, and lipoproteins
• LXR agonists increase plasma high density
lipoprotein cholesterol (HDLc)
• LXR as target for anti-
atherosclerotic therapy?
/ biomedical engineering PAGE 211-2-2015
Levin et al, (2005) Arterioscler
Thromb Vasc Biol. 25(1):135-42
LDLR-/-
RXR: retinoid X receptor Calkin & Tontonoz 2012
Hypothesis 1: increase in HDLc is the result of
increased peripheral cholesterol efflux to HDL
• C57Bl/6J mice
• control, treated with T0901317 for 1, 2, 4, 7, 14, and 21 days
/ biomedical engineering PAGE 311-2-2015
Grefhorst et al. Atherosclerosis, 2012, 222: 382– 389
0 10 200
100
200Hepatic TG
Time [days]
[um
ol/g]
0 10 200
1
2
3Hepatic CE
Time [days]
[um
ol/g]
0 10 200
2
4
6Hepatic FC
Time [days]
[um
ol/g]
0 10 200
50
100Hepatic TG
Time [days]
[um
ol]
0 10 200
0.5
1
1.5Hepatic CE
Time [days]
[um
ol]
0 10 200
2
4Hepatic FC
Time [days]
[um
ol]
0 10 200
1000
2000
3000Plasma CE
Time [days]
[um
ol/L]
0 10 200
1000
2000
3000HDL-CE
Time [days]
[um
ol/L]
0 10 200
500
1000
1500Plasma TG
Time [days]
[um
ol/L]
0 10 206
8
10
12VLDL clearance
Time [days]
[-]
0 10 20100
200
300
400ratio TG/CE
Time [days]
[-]
0 10 200
5
10
15VLDL diameter
Time [days]
[nm
]
0 10 200
1
2
3VLDL-TG production
Time [days]
[um
ol/h]
0 10 201
2
3Hepatic mass
Time [days]
[gra
m]
0 10 200
0.2
0.4DNL
Time [days]
[-]
Mechanism-based model of lipid and
lipoprotein metabolism
• Differential equations
• Mathematical parameters inferred from data
/ biomedical engineering PAGE 411-2-2015
Data integration
• Estimation of unobserved metabolic parameters
• At unobserved time points
/ biomedical engineering PAGE 511-2-2015
1. Metabolite concentrations
-Hepatic free cholesterol (FC)
-Hepatic cholesteryl ester (CE)
-Hepatic triglyceride (TG)
-Plasma free fatty acids (FFA)
-Plasma TG
-Plasma total cholesterol
-HDL cholesterol
-VLDL (very low density lipoprotein) TG/C ratio
-Nascent VLDL particle diameter
2. Fluxes
-VLDL-TG production
-Hepatic cholesterol synthesis
-VLDL catabolism/clearance from the plasma
ADAPT: Analysis of Dynamic Adaptations in
Parameter Trajectories
ADAPT model connects and describes the data accurately
/ biomedical engineering PAGE 611-2-2015
• Data: black bars and
white dots
• Model: the darker the
more likely
• Variability in
data
differences in
accuracy of
mathematical
parameters
quantification
of uncertainty
in predictions
Analysis: HDL cholesterol
/ biomedical engineering PAGE 711-2-2015
Analysis: increased excretion of cholesterol
Observation: increased HDLc
• SR-B1 (Scavenger Receptor-B1)
• Protein activity:
Reduced presence of SR-B1 in liver
membranes contributes to induction of HDLc
• HDL excretion and uptake flux
are increased
• Transcription:
/ biomedical engineering PAGE 811-2-2015
mRNA of cholesterol efflux transporters
Tiemann et al., PLOS Comput Biol 2013
SR-B1 protein content is decreased in
hepatic membranes
Sr-b1 mRNA
expression not
changed
model: decreased
hepatic capacity to
clear cholesterol
Hepatic steatosis
• Hypothesis 2: LXR-induced hepatic steatosis is caused by an
increase in de novo lipogenesis (DNL)
/ biomedical engineering PAGE 911-2-2015
Liver section of mice
treated 4 days with LXR
agonist T0901317
Oil-Red-O staining for
neutral fat
hepatic steatosis
0 10 200
100
200Hepatic TG
Time [days]
[um
ol/g]
0 10 200
1
2
3Hepatic CE
Time [days]
[um
ol/g]
0 10 200
2
4
6Hepatic FC
Time [days]
[um
ol/g]
0 10 200
50
100Hepatic TG
Time [days]
[um
ol]
0 10 200
0.5
1
1.5Hepatic CE
Time [days]
[um
ol]
0 10 200
2
4Hepatic FC
Time [days]
[um
ol]
0 10 200
1000
2000
3000Plasma CE
Time [days]
[um
ol/L]
0 10 200
1000
2000
3000HDL-CE
Time [days]
[um
ol/L]
0 10 200
500
1000
1500Plasma TG
Time [days]
[um
ol/L]
0 10 206
8
10
12VLDL clearance
Time [days]
[-]
0 10 20100
200
300
400ratio TG/CE
Time [days]
[-]
0 10 200
5
10
15VLDL diameter
Time [days]
[nm
]
0 10 200
1
2
3VLDL-TG production
Time [days]
[um
ol/h]
0 10 201
2
3Hepatic mass
Time [days]
[gra
m]
0 10 200
0.2
0.4DNL
Time [days]
[-]
Increased hepatic FFA influx is the initial
contributor to hepatic TG accumulation
• [13C]16-palmitate infusion
• FA mass isotopomer distributions
in hepatic and plasma FAs by GCMS
/ biomedical engineering PAGE 1011-2-2015
SFA = saturated fatty acid
C16:0 palmitate
C18:0 stearate
MUFA = monounsaturated fatty acid
C16:1 palmitoleate
C18:1 oleate
Hijmans et al. (2014) FASEB J.
Conclusions
• LXR activation in C57Bl/6J mice leads to complex time-dependent
perturbations in cholesterol and triglyceride metabolism
HDL cholesterol metabolism
• Peripheral cholesterol efflux to HDL and hepatic HDLc uptake increase over
time
• Reduced presence of SR-B1 in liver membranes despite an increment in
hepatic HDLc uptake
Hepatic triglyceride metabolism
• Input and output fluxes to liver TG are massively upregulated and a minor
imbalance between input and output fluxes causes steatosis
• Increased hepatic FFA influx is the initial contributor to hepatic TG
accumulation
/ biomedical engineering PAGE 1111-2-2015
Acknowledgements
• Peter Hilbers
• Christian Tiemann
• Joep Vanlier
• Yvonne Rozendaal
• Fianne Sips
• Bert Groen
• Jan Albert Kuivenhoven
• Maaike Oosterveer
• Brenda Hijmans
• Yared Paalvast
/ biomedical engineering PAGE 1211-2-2015
Systems Biology of Disease Progression -
ADAPT modeling
http://www.youtube.com/watch?v=x54ysJDS7i8