Victoria L. M. Herrera, M.D.Associate Professor of Medicine
Section of Molecular GeneticsWhitaker Cardiovascular Institute
Boston University School of Medicine
700 Albany Street – W609, Boston MA [email protected]
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
Modeling vulnerable plaque – an underestimated challenge
Analysis of coronary artery disease at end-stage
plq hge
plq eros’n
plq fissure
plqthombosis occlus’n
Pigeon: Carneau, Show Racer* aortic root
nr + nr nr +
Monkey: a. Cynomolgus b. African green c. Rhesus
++nr
nrnrnr
nrnrnr
nrnrnr
++
Pig: a. thiouracil + xrad’n b. FHC: hyperLDL-emia
++
nrnr
+nr
somesome
++
Rabbit: WatanabeHHL* coronary ostia
nr nr nr nr +
Mouse: ApoE/LDLr knockout nr nr nr nr +
Rat: Tg53 rat model + + + + +
[nr, not reported; +, present]
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
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
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
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
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
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 -actin, Fast red im-stn; 400x
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
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,
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
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
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
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
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
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
• ... 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?”
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