Metabolic Pathways for Removing Reactive Aldehydes are Diminished in Atrophic Muscle During Heart Failure

Background : Muscle wasting is a serious complication in heart failure patients, and oxidative stress is involved in the pathogenesis of muscle wasting. Oxidative stress leads to the formation of toxic lipid peroxidation products, such as 4-hydroxy-2-nonenal (HNE) and acrolein, which causemuscle wasting. In tissues, these toxic aldehydes are metabolically removed by enzymes such asaldo keto reductases and endogenous nucleophiles, such as glutathione and carnosine. Whether these metabolic pathways could be affected in skeletal muscle during heart failure has never been studied. Methods : Male wild-type C57BL/6J mice were subjected to a pressure overload model of hypertrophy by transaortic constriction (TAC) surgery, and echocardiography was performed after 14 weeks. Different skeletal muscle beds were weighed and analyzed for atrophic and inflammatory markers, Atrogin1 and TRIM63, TNF-α and IL-6 , respectively, by RT‒PCR. Levels of acrolein and HNE-protein adducts, aldehyde-removing enzymes, aldose reductase (AKR1B1) and aldehyde dehydrogenase 2 (ALDH2) were measured by Western blotting, and histidyl dipeptides and histidyl dipeptide aldehyde conjugates were analyzed by LC/MS-MS in the gastrocnemius and soleus muscles of sham- and TAC-operated mice. Furthermore, histidyl dipeptide synthesizing enzyme carnosine synthase (CARNS) and amino acid transporters (PEPT2 and TAUT)wasmeasured in the gastrocnemius muscles of the sham and TAC-operated mice. Results : TAC-induced heart failure decreases body weight and gastrocnemius and soleus muscle weights. The expression of the atrophic and inflammatory markers Atrogin1 and TNF-α, respectively, wasincreased (~1.5-2-fold), and the formation of HNE and acrolein-protein adducts was increased in the gastrocnemius muscle of TAC-operated mice. The expression of AKR1B1 remained unchanged, whereas ALDH2 was decreased, in the gastrocnemius muscle of TAC mice. Similarly, in the atrophic gastrocnemius muscle, levels of total histidyl dipeptides (carnosine and anserine) and, in particular,carnosine were decreased. Depletion of histidyl dipeptides diminished the aldehyde removal capacity of the atrophic gastrocnemius muscle. Furthermore, the expression of CARNS and TAUT wasdecreased in the atrophic gastrocnemius muscle. Conclusions : Collectively, these results show that metabolic pathways involved in the removal of lipid peroxidation products and synthesis of histidyl dipeptides are diminished in atrophic skeletal muscle during heart failure, which could contribute to muscle atrophy.

Abstract 526: Unraveling the Molecular Signature of Pregnancy Induced Hypertrophy

Cardiovascular disease is the leading cause of death in pregnant and postpartum women. During pregnancy, the maternal heart rapidly adapts to the increasing physiological and metabolic demands of the growing fetus. This adaptation often takes the form of a physiological hypertrophy in which the maternal heart grows to increase cardiac output; however, the molecular processes underlying pregnancy-induced hypertrophy (PIH) are poorly understood. The goal of this study was to examine the transcriptomic and metabolic signatures associated with the structural and functional adaptations of the heart to pregnancy. Therefore, we performed timed pregnancy studies in 12-week-old female FVB/NJ mice, which were distributed into the following groups: non-pregnant control (NP; n = 14), mid-pregnancy (MP, 6d pregnant; n = 11), late-pregnancy (LP, 16d pregnant; n = 13), and 1-wk post birth (PB; n = 8). Heart weight to tibia length were higher in MP (7.77±1.02 mg/mm; p <0.05), LP (7.84±0.87 mg/mm; p <0.05), and PB mice (9.86±1.14 mg/mm; p <0.05) compared with NP mice (6.54±0.74 mg/mm). The sustained increase in PB heart weight was associated with increased myocyte cross sectional area, consistent with cardiomyocyte hypertrophy. Compared with NP hearts, echocardiographic measurements suggest significant increases in both end diastolic (36.0±5.1 vs 61.2±5.9 μl; p <0.05) and systolic LV volume (9.4±3.8 vs 21.0±1.4 μl; p <0.05) in PB hearts. These changes in PB hearts were associated with a significant increase in LV mass and a decline in ejection fraction. In LP and PB hearts, we also found higher expression of markers of hypertrophy ( Nppa, Nppb, Myh7 ). Subsequent RNA-seq analyses revealed enrichment in genes involved in cell proliferation, cytokinesis, and transcription in MP hearts; in metabolism genes in LP hearts; and in fibrotic and extracellular matrix genes in PB hearts. Together, these findings reveal the key molecular signature underlying the structural and functional adaptation of the heart during pregnancy and parturition, and may shed light on the molecular processes underlying PIH.

Abstract 208: Reliable Biomimetic Culture System for Pig and Human Heart Slices

Rationale: Heart failure is the number one killer and drug induced cardiotoxicity is a major cause of market withdrawal. The lack of availability of culture systems for human heart tissue that is functionally and structurally viable for more than 24 hours is a limiting factor in validation of novel heart failure therapies as well as reliable cardiotoxicity testing. Therefore, there is an urgent need to develop a reliable system for culturing human heart tissue for testing drug efficacy and toxicity.

Objective: To develop a reliable method to culture pig and human heart slices under full physiological conditions for a period of time sufficient to test therapeutic efficacy and acute drug toxicity.

Methods and Results: Here we describe a novel biomimetic culture system that maintains full viability and functionality of human and pig heart slices (300 μm thickness) for 6 days in culture through optimization of the medium and culture conditions with continuous electrical stimulation at 1.2 Hz and oxygenation of the medium. Functional viability of these slices over 6 days was confirmed by assessing their calcium homeostasis, twitch force generation, and response to β-adrenergic stimulation. Temporal transcriptome analysis using RNAseq at day 2, 6, and 10 in culture confirmed overall maintenance of normal gene expression for up to 6 days, while over 500 transcripts were differentially regulated after 10 days. Electron microscopy demonstrated intact mitochondria and Z-disc ultra-structures after 6 days in culture under our optimized conditions. This biomimetic culture system was successful in keeping human heart slices completely viable and functionally and structurally intact for 6 days in culture. We also used this system to demonstrate the effects of a novel gene therapy approach in human heart slices.

Conclusions: We have developed and optimized a reliable and easily reproducible culture system for pig and human heart slices as a platform for testing the efficacy of novel heart failure therapeutics as well as reliable testing of cardiotoxicity in a 3D heart model.

Physiological Biomimetic Culture System for Pig and Human Heart Slices

RATIONALE

Preclinical testing of cardiotoxicity and efficacy of novel heart failure therapies faces a major limitation: the lack of an in situ culture system that emulates the complexity of human heart tissue and maintains viability and functionality for a prolonged time.

OBJECTIVE

To develop a reliable, easily reproducible, medium-throughput method to culture pig and human heart slices under physiological conditions for a prolonged period of time.

METHODS AND RESULTS

Here, we describe a novel, medium-throughput biomimetic culture system that maintains viability and functionality of human and pig heart slices (300 µm thickness) for 6 days in culture. We optimized the medium and culture conditions with continuous electrical stimulation at 1.2 Hz and oxygenation of the medium. Functional viability of these slices over 6 days was confirmed by assessing their calcium homeostasis, twitch force generation, and response to β-adrenergic stimulation. Temporal transcriptome analysis using RNAseq at day 2, 6, and 10 in culture confirmed overall maintenance of normal gene expression for up to 6 days, while over 500 transcripts were differentially regulated after 10 days. Electron microscopy demonstrated intact mitochondria and Z-disc ultra-structures after 6 days in culture under our optimized conditions. This biomimetic culture system was successful in keeping human heart slices completely viable and functionally and structurally intact for 6 days in culture. We also used this system to demonstrate the effects of a novel gene therapy approach in human heart slices. Furthermore, this culture system enabled the assessment of contraction and relaxation kinetics on isolated single myofibrils from heart slices after culture.

CONCLUSIONS

We have developed and optimized a reliable medium-throughput culture system for pig and human heart slices as a platform for testing the efficacy of novel heart failure therapeutics and reliable testing of cardiotoxicity in a 3-dimensional heart model.

Abstract 132: Cardiomyocyte Specific Conditional Overexpression Of Stromal Cell Derived Factor 1 Facilitates Cardiac Regeneration After Permanent Coronary Artery Ligation In Mice

Background: Interruption of cardiac stromal cell derived factor 1 (SDF1)-CXCR4 axis by chronic AMD3100 administration increased myocardial injury after permanent coronary artery ligation demonstrating the important role of this chemokine in cardiac regeneration.

Hypothesis: Cardiomyocyte specific conditional overexpression of SDF1 prevents heart failure after permanent coronary ligation and facilitates cardiac regeneration.

Methods and Results: Tetracycline-controlled, αMyHC promoter directed overexpression of cardiac SDF1, resulted in a significant increase of SDF1 expression (SDF1: 8.1 ng/mg protein) compared to littermate WT mice (0.02 ng/mg protein) four weeks after doxycycline withdraw. SDF1 overexpression increased AKT and casein kinase 1 levels in the heart. Although there was no difference in cardiac function and scar size 1 week after infarction, SDF1 overexpression improved left ventricular (LV) ejection fraction (SDF1 [n=13]: 47±5% [mean±SEM] vs. WT [n=15]: 29±4%, p<0.05) decreased end-diastolic volume (78±10 vs. 158±30, p<0.05) and reduced infarct size measured by trichrome staining (13±3% vs. 23±3% of LV wall, p<0.05) 4 weeks after permanent ligation. Bromodeoxyuridine (BrdU) staining revealed increased regeneration indicated by a 5-fold increase in BrdU + cardiomyocyte (CM) nuclei in the borderzone of the infarct (22±3% vs. 5±1% CM nuclei, p<0.01). Increased proliferation in SDF1 mice was confirmed by a higher number of KI67 + cells compared to WT mice. Cardiomyocyte cross sectional area in the border zone was significantly reduced in SDF1 mice (365±13 μm 2 vs. 434±10 μm 2 , p<0.001) while capillary density was unchanged (2348±151/ mm 2 vs. 2498±153/ mm 2 ) compared to WT mice.

Conclusion: This study demonstrates for the first time that cardiac specific overexpression of SDF1 increases myocardial regeneration and improves LV function 4 weeks after permanent coronary ligation.