Transgenic CETP Dahl Salt-sensitive (Tg53) Rat Model

“Is it promising enough?”

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 02118vherrera@bu.edu

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?”

Acknowledgment

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