Dynamic patterns of ventricular remodeling and apoptosis in hearts unloaded by heterotopic transplantation

doi:10.1016/j.healun.2013.10.006

The Journal of Heart and Lung Transplantation

Volume 33, Issue 2, February 2014, Pages 203-210

https://doi.org/10.1016/j.healun.2013.10.006 Get rights and content

Background

Mechanical unloading of failing hearts can trigger functional recovery but results in progressive atrophy and possibly detrimental adaptation. In an unbiased approach, we examined the dynamic effects of unloading duration on molecular markers indicative of myocardial damage, hypothesizing that potential recovery may be improved by optimized unloading time.

Methods

Heterotopically transplanted normal rat hearts were harvested at 3, 8, 15, 30, and 60 days. Forty-seven genes were analyzed using TaqMan-based microarray, Western blot, and immunohistochemistry.

Results

In parallel with marked atrophy (22% to 64% volume loss at 3 respectively 60 days), expression of myosin heavy-chain isoforms (MHC-α/-β) was characteristically switched in a time-dependent manner. Genes involved in tissue remodeling (FGF-2, CTGF, TGFb, IGF-1) were increasingly upregulated with duration of unloading. A distinct pattern was observed for genes involved in generation of contractile force; an indiscriminate early downregulation was followed by a new steady-state below normal. For pro-apoptotic transcripts bax, bnip-3, and cCasp-6 and -9 mRNA levels demonstrated a slight increase up to 30 days unloading with pronunciation at 60 days. Findings regarding cell death were confirmed on the protein level. Proteasome activity indicated early increase of protein degradation but decreased below baseline in unloaded hearts at 60 days.

Conclusions

We identified incrementally increased apoptosis after myocardial unloading of the normal rat heart, which is exacerbated at late time points (60 days) and inversely related to loss of myocardial mass. Our findings suggest an irreversible detrimental effect of long-term unloading on myocardium that may be precluded by partial reloading and amenable to molecular therapeutic intervention.

Section snippets

Methods

All animals used in this study received care in accordance with Swiss Animal Protection Law.

Myocardial unloading leads to immediate and critical loss of myocardial mass

In our experimental setting, prolonged mechanical unloading by HTX of the heart led to a highly reproducible ventricular weight adaptation curve characterized by 2 phases (Figure 1): An initial active “adaptation period” (Days 0 to 15) starting immediately after unloading, during which a rapid and dramatic loss of myocardial volume could be observed (22.4% ± 5.6% at 3 days, 47.4% ± 4.8% at 8 days, and 57.4% ± 1.4% after 15 days), followed by a “steady-state period” (Days 15 to 60) during which

Discussion

We present a non-biased examination of the dynamic gene regulation that occurs in hemodynamically unloaded normal ventricular myocardium. Serial analysis of indicators of myocardial composition and function during a 60-day period led to the identification of 2 phases of atrophic remodeling and, at a molecular level, to the characterization of the kinetics of myocardial adaptation. The existence and effect of unloading-related apoptosis in normal myocardium has been a matter of debate. We

Disclosure statement

The authors thank Dr Martin Flueck for expert advice.

The work presented in this study was supported in part by the Swiss Heart Foundation (H.B. and M.N.G.), the Swiss National Science Foundation (H.T.), and the National Institutes of Health (P01-HL-075443 [Project 2] to W.J.K.)

None of the authors has a financial relationship with a commercial entity that has an interest in the subject of the presented manuscript or other conflicts of interest to disclose.

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Dynamic patterns of ventricular remodeling and apoptosis in hearts unloaded by heterotopic transplantation

Background

Methods

Results

Conclusions

Section snippets

Methods

Myocardial unloading leads to immediate and critical loss of myocardial mass

Discussion

Disclosure statement

J Card Fail

Prog Biophys Molec Biol

J Thorac Cardiovasc Surg

J Heart Lung Transplant

J Am Coll Cardiol

J Thorac Cardiovasc Surg

J Surg Res

Biochem Biophys Res Commun

J Heart Lung Transplant

J Am Coll Cardiol