SHAPE Society

1. Transgenic CETP Dahl Salt-sensitive
(Tg53) Rat Model
“Is it promising enough?”

2. Victoria L. M. Herrera, M.D.
Associate Professor of Medicine
Section of Molecular Genetics
Whitaker Cardiovascular Institute
Boston University School of Medicine
700 Albany Street – W609, Boston MA 02118
vherrera@bu.edu

3. Tg53 rat model – “is it promising enough?”
Question analyzed –
• a provocative but necessary question posed by
Symposium organizers
• modeling the “vulnerable plaque” has been an
underestimated challenge
• a review of multi-species animal models of
atherosclerosis from the 1960s underscores this
challenge

4. Modeling vulnerable plaque – an underestimated challenge
Analysis of coronary artery
disease at end-stage
plq
hge
plq
eros’n
plq
fissure
plq
thombosis occlus’n
Pigeon: Carneau, Show Racer
* aortic root
nr + nr nr +
Monkey: a. Cynomolgus
b. African green
c. Rhesus
+
+
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
+
+
Pig: a. thiouracil + xrad’n
b. FHC: hyperLDL-emia
+
+
nr
nr
+
nr
some
some
+
+
Rabbit: WatanabeHHL
* coronary ostia
nr nr nr nr +
Mouse: ApoE/LDLr knockout nr nr nr nr +
Rat: Tg53 rat model + + + + +
[nr, not reported; +, present]

5. Elements of a “promising model”
Simulation of coronary artery disease
– plaque site
– disease course
– plaque progression
Model advantages as experimental system
– reproducibility
– duration to valid endpoints
– defined genetic background
– accessible phenotype manipulation
Model value and potential
– as investigative instrument
– as pre-clinical platform

6. Elements of a “promising model”
Tg53 rat model simulates human coronary heart
disease (CHD)
plaque site
 plaque predilection site = coronary arteries
 in contrast to: aortic root plaque predilection site in
mouse models described to date
Tg53 end-stage
plaques in proximal
right coronary artery
[PTAH stain, 40x
original mag]
RV
Ao

7. Elements of a “promising model”
Tg53 rat model simulates human coronary heart
disease (CHD)
disease course
 risk factors consistent with human CHD
• hypertension exacerbates phenotype
• atherogenic lipid profile: increased total
cholesterol and triglyceride levels, low HDL,
increased VLDLc and VLDLtg, increased small
LDLc
• hyperlipidemia increases with age

8. Elements of a “promising model”
Tg53 rat model simulates human coronary heart
disease (CHD)
disease course
 decreased survival compared with non-transgenic –
non-hyperlipidemic, hypertensive, Dahl S rat
controls on regular rat chow [Nat Med 5: 383, 1999; Mol
Med 7:831, 2001].
 “end-stage” simulates cardiac endpoints of CHD
• (+) cardio-respiratory distress
• (+) signs of heart failure

9. Elements of a “promising model”
Tg53 rat model simulates human coronary heart
disease (CHD)
plaque progression
 “culprit” plaque features: foam-cell rich, paucity of smcs, leukocyte
adhesion, intraplaque thrombi, erosion, plaque shoulder
susceptibility
Masson – trichrome stain 400x orig mag PTAH; 1000x orig
mag

10. Elements of a “promising model”
Masson – trichrome; 1000x orig
mag
Tg53 rat model simulates human coronary heart
disease (CHD)
plaque progression
 “culprit plaque features: foam-cell rich, intraplaque hemorrhage,
paucity of smcs, lipid core > 1/3 of plaque volume
smc α-actin, Fast red im-stn; 400x

11. Elements of a “promising model”
Tg53 rat model simulates human coronary heart
disease (CHD)
plaque progression
 “culprit” plaque features: fibrin-positive thrombosis in
proximal coronary lesions; none detected in more distal
stable lesions
PTAH: fibrin(+) thrombus; prox lesion PTAH: distal stable lesion

12. Elements of a “promising model”
Tg53 rat model simulates human coronary heart
disease (CHD)
plaque progression
 recapitulates lesion heterogeneity of “culprit” plaques
associated with human acute coronary syndromes
PTAH: thick cap, smc-rich, but with
intraplq hge & thrombosis, IEL disrup’n
PTAH: reduced cap & smc; foam-cell
rich; + intraplq hge & thrombosis,

13. Elements of a “promising model”
Tg53 rat model: advantages as experimental system
 reproducibility and robustness of phenotype
• lipid profile: increased total cholesterol and
triglycerides predominantly in VLDL, low HDL
• “culprit” plaque phenotype in proximal right coronary
artery
• “stable” occlusive plaque in smaller coronary arteries
 reasonable duration to valid endpoints
• 6-9+ month range of proximal coronary plaque
development on regular rat chow: eccentric
macrophage-foam cell rich plaque which progresses to
“culprit” plaque at endstage

14. Elements of a “promising model”
Tg53 rat model: advantages as experimental system
 defined genetic background – eliminates
differential genetic susceptibility as confounder
• inbred Dahl salt-sensitive hypertensive rat strain
 accessible phenotype manipulation – onset and
course of hyperlipidemia and coronary artery
disease can be experimentally manipulated
• Western Type Diet (0.15% cholesterol) accelerates
onset and levels of hyperlipidemia
• low salt diet (0.0038% NaCl), which reduces level of
hypertension, attenuates coronary artery disease hence
increasing survival

15. Elements of a “promising model”
 Tg53 rat model: value and potential
 identical genetic background and ability to
regulate environmental factors allows well-
controlled in vivo studies for cross-talk
pathogenesis:
a. investigation of mechanisms of coronary
plaque development not possible in humans
b. methodical in vivo investigation of novel
intervention targets
c. maximization of genomic-based technologies
aimed at the investigation of mechanisms and
targets

16. Elements of a “promising model”
 Tg53 rat model: value and potential
 coronary-specific experimental design for
coronary artery-disease studies: with cumulative
evidence of vessel-specific genetic factors, the
Tg53 coronary-specific phenotype is key
 combinatorial modeling: well characterized
inbred rat strains allow cross-breeding for
interaction studies relevant to human disease
 hypertension
• diabetes
• obesity

17. Elements of a “promising model”
 Tg53 rat model: value and potential
 as investigative tool: invaluable new insight
distinct from that observed in current other models
– as a beginning,
1. prelude to culprit plaque: the eccentric macrophage
foam-cell rich lesion becomes the “culprit” plaque, thus
experimentally “capturing” the beginning of the
vulnerable plaque
2. differential pathway hypothesis: proximal vulnerable-
culprit coronary lesions develop distinct from more
distal stable coronary plaques
3. lesion heterogeneity paradigm: given identical genetic
background and environmental factors, lesion
heterogeneity at end-stage reflect stochastic endpoints
of a common pathogenic framework

18. Elements of a “promising model”
 Tg53 rat model: value and potential
 as pre-clinical platform
• identical genetic background
• regulated environmental factors
• robust coronary phenotype
• instrumentation accessibility
• rat physiological and pharmacological information
database
– allow continuity of comparative analysis for
successful new intervention and prevention
strategies

19. • ... can’t promise the world – but along with
other animal models, can together make a
better promise,
• but then again, which model can be
“promising enough” since even humans –
although they are the ultimate benchmarks –
make terrible models, if not the worst, for
human coronary artery disease ...

Tg53 rat model – “is it promising enough?”

20. Acknowledgment
• This work is supported by grants from the
National Institutes of Health and American
Heart Association.