A Translational Model of MASLD-Associated HFpEF Defines Mitochondrial Dysfunction and Cardiac Plasticity During Disease Progression and Regression

This study establishes the Alms1-/- (Foz/Foz) mouse model as a robust translational platform demonstrating that mitochondrial dysfunction and fibroinflammatory remodeling drive MASLD-associated HFpEF, a condition characterized by reversible cardiac and hepatic phenotypes upon dietary intervention.

The Gist

The Big Picture: The "Liver-Heart" Connection

Imagine your body is a bustling city. In this city, the Liver is the main recycling plant and fuel processing center, while the Heart is the central power station that keeps the lights on and the water flowing.

For a long time, doctors knew that if the recycling plant (Liver) got clogged with trash (fatty liver disease, now called MASLD), the power station (Heart) often started to struggle. But nobody knew exactly how the trash in the recycling plant was breaking the power station, or if fixing the plant could fix the power station.

This paper is like a detective story that solves that mystery using a special group of mice.

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The Experiment: The "Fast Food" Mice

The researchers used a special breed of mice called Foz/Foz. Think of these mice as having a genetic "glitch" that makes them incredibly hungry.

• The Control Group: They ate healthy, normal mouse food.
• The "Fast Food" Group: They were fed a "Western Diet" (high in fat, sugar, and cholesterol), which is like giving them a constant diet of burgers, fries, and soda.

What happened?

1. The Liver: The "Fast Food" mice developed a clogged, scarred recycling plant (severe liver fibrosis).
2. The Heart: Their power stations started to fail. They got thick and stiff (hypertrophy), and they couldn't pump as hard as they should, even though they were still beating at a normal speed. This is called HFpEF (Heart Failure with Preserved Ejection Fraction). It's a tricky condition where the heart looks okay on a basic test but is actually failing under pressure.
3. The Result: The mice with the worst liver scarring were the ones whose hearts failed first, and they died much sooner.

The Discovery: The "Engine" is Broken

The researchers zoomed in to see why the hearts were failing. They found two main problems:

1. The Fuel Mix-Up: A healthy heart runs on high-quality fuel (fats). But in these sick mice, the heart stopped burning fat and tried to run on cheap, inefficient fuel (sugar/glucose). It was like trying to run a heavy-duty truck on cheap gasoline; the engine sputtered.
2. The Broken Spark Plugs (Mitochondria): Inside every heart cell are tiny batteries called mitochondria. In the sick mice, these batteries were swollen, broken, and had their internal wiring (cristae) torn apart. The heart cells were essentially running out of power.

The "Smoking Gun": The researchers found that the more scarred the liver was, the more broken the heart's batteries were. The liver wasn't just a victim; it was actively sending signals that broke the heart's engine.

The Twist: The "Reset Button" Works

Here is the most exciting part of the story.

The researchers took the "Fast Food" mice that had already developed liver scarring and heart trouble (at 12 weeks old) and switched them back to healthy food.

The Result?

• The Liver: The scar tissue started to dissolve. The recycling plant got cleaned out.
• The Heart: The broken batteries (mitochondria) started to repair themselves. The heart cells got their wiring back. The heart started pumping strongly again.
• The Survival: The mice that stayed on the bad food died at a high rate. The mice that switched to the healthy food? 100% of them survived.

It was as if they hit a "Reset Button" on the body's systems. Even though the heart had been damaged, it was surprisingly flexible (plastic) and could heal itself once the toxic environment from the liver was removed.

The Takeaway for Humans

This study is a massive breakthrough for three reasons:

1. It Proves the Link: It confirms that a bad liver doesn't just hurt the liver; it directly breaks the heart's engine.
2. It Identifies the Culprit: The main villain is mitochondrial dysfunction (broken batteries). If we can fix the batteries, we might fix the heart failure.
3. It Offers Hope: It shows that lifestyle changes (eating better) aren't just about losing weight. They are a powerful medicine that can reverse heart failure caused by metabolic disease.

In a nutshell: If your liver is clogged with fat and scar tissue, it's poisoning your heart's batteries. But the good news is that if you clean up your diet, your liver can heal, and your heart can reboot, potentially saving your life. The body is more resilient than we thought, as long as we give it the right fuel.

Technical Summary

1. Problem Statement

• Clinical Context: Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) and its progressive form, Metabolic Dysfunction-Associated Steatohepatitis (MASH), are strongly linked to cardiovascular disease, specifically Heart Failure with Preserved Ejection Fraction (HFpEF).
• Knowledge Gap: Despite the high comorbidity, the mechanistic "liver-heart axis" remains poorly understood. There is a lack of robust preclinical models that recapitulate the integrated metabolic, hepatic, and cardiac features of human MASLD-associated HFpEF. Furthermore, the reversibility of cardiac dysfunction through lifestyle modification (dietary reversal) in the context of advanced liver fibrosis is largely unexplored.
• Specific Challenge: Differentiating whether cardiac dysfunction is driven by general metabolic syndrome (MetS) or specifically by advanced liver fibrosis/MASH, and identifying the molecular drivers of this progression.

2. Methodology

The study utilized a translational approach combining a specific genetic mouse model with rigorous physiological, histological, and transcriptomic analyses.

• Animal Model:

  • Genotype: Alms1−/− (Foz/Foz) mice on a C57BL/6J background. These mice are hyperphagic and develop metabolic syndrome spontaneously.
  • Dietary Protocol:
    • Control: Wild-type (WT) and Foz mice on Normal Chow (NC).
    • Disease Induction: Foz mice fed a Western Diet (WD; 40% fat, 15% protein, 44% carbs, 0.2% cholesterol) for up to 34 weeks.
    • Regression Model: A subset of Foz mice fed WD for 12 weeks (establishing MASH and fibrosis) was switched back to Normal Chow for an additional 12 weeks to model dietary intervention and disease regression.
  • Timepoints: Analysis performed at 12 weeks (early MASH/F2 fibrosis), 24 weeks (advanced MASH/F4 fibrosis), and post-regression.

• Phenotyping Techniques:

  • Cardiac Function: Echocardiography (M-mode, Doppler), invasive hemodynamics with dobutamine stress testing (measuring $dP/dt_{max}$ and $dP/dt_{min}$), and isolated cardiomyocyte contractility assays (IonOptix).
  • Histology & Ultrastructure: H&E and Sirius Red staining for liver fibrosis; Wheat Germ Agglutinin (WGA) for cardiomyocyte size; Perilipin 2 IHC for lipid accumulation; Transmission Electron Microscopy (TEM) for mitochondrial and sarcomeric integrity.
  • Omics: Bulk RNA sequencing (RNA-seq) of Left Ventricular (LV) tissue. Differential gene expression (DEG) analysis, Overrepresentation Analysis (ORA), and Gene Set Enrichment Analysis (GSEA).
  • Cross-Species Validation: Comparison of mouse LV transcriptomes with publicly available human HFpEF datasets (ENA accession PRJEB62450).

3. Key Contributions

• Establishment of a Translational Model: Validated the Foz/Foz + WD model as a robust platform for studying MASLD-associated HFpEF, recapitulating the full spectrum from MetS to MASH, advanced fibrosis, and cardiac failure.
• Decoupling MetS from Fibrosis: Demonstrated that while MetS and MASH cause cardiac hypertrophy, advanced liver fibrosis is the critical driver of overt HFpEF, contractile failure, and mortality.
• Demonstration of Plasticity: Provided definitive evidence that the liver-heart axis is plastic; reversing liver fibrosis via dietary intervention restores cardiac function and survival, even after the establishment of advanced disease.
• Mechanistic Insight: Identified mitochondrial dysfunction and altered substrate utilization (shift from fatty acid oxidation to glucose/glycogen) as central mediators of cardiac failure in this context.

4. Key Results

A. Disease Progression and Phenotype

• Liver-Heart Correlation: Male Foz mice on WD developed MASH with advanced (Stage 4) liver fibrosis by 24 weeks, accompanied by high mortality (~80% by 34 weeks). Female mice developed MASH but were resistant to fibrosis and cardiac failure, highlighting fibrosis as the key predictor of cardiac outcomes.
• HFpEF Phenotype: Foz+WD 24w mice exhibited:
  • Structural: Left Ventricular (LV) hypertrophy, concentric remodeling, and increased cardiomyocyte size.
  • Functional: Preserved Ejection Fraction (>50%) but impaired Fractional Shortening. Crucially, they showed a complete loss of $\beta$-adrenergic reserve (blunted response to dobutamine) and elevated plasma BNP, hallmarks of HFpEF.
  • Mortality: Mortality closely paralleled the progression of liver fibrosis, not just metabolic syndrome.

B. Transcriptomic and Molecular Mechanisms

• Transcriptomic Clustering: LV transcriptomes clustered into three distinct groups: Healthy, MetS/MASH (without fibrosis), and MASH+Advanced Fibrosis (HFpEF).
• Pathway Dysregulation in HFpEF:
  • Downregulated: Fatty acid $\beta$-oxidation (FAO), amino acid catabolism, oxidative phosphorylation, and mitochondrial electron transport chain genes.
  • Upregulated: Inflammatory pathways (Toll-like receptors, IL-2, NOD1/2), TGF-$\beta$ signaling, extracellular matrix (ECM) remodeling, and fibrosis markers.
  • Metabolic Shift: A shift from lipid to glucose/glycogen metabolism, consistent with human HFpEF signatures.
• Ultrastructural Damage: TEM revealed swollen mitochondria with disrupted cristae and sarcomeric disorganization in Foz+WD 24w hearts.
• Human Concordance: The mouse model showed strong transcriptional overlap with human HFpEF patients, particularly in immune activation, mitochondrial dysfunction, and fibrotic signaling.

C. Disease Regression (Dietary Intervention)

• Reversibility: Switching Foz mice from WD to NC at 12 weeks (when fibrosis was established) resulted in:
  • Liver: Complete resolution of steatosis and fibrosis.
  • Heart: While cardiac hypertrophy persisted (structural remodeling was not fully reversed), functional recovery was profound.
    • Restoration of $\beta$-adrenergic responsiveness.
    • Normalization of contractile velocities and sarcomere shortening in isolated cardiomyocytes.
    • Reduction in plasma BNP to baseline levels.
    • 100% Survival compared to 20% in the progressive group.
• Molecular Recovery: Transcriptomic analysis of regression mice showed:
  • Reactivation of mitochondrial respiration, ATP synthesis, and sarcomere organization genes.
  • Suppression of pro-fibrotic and inflammatory pathways.
  • Re-emergence of a "fetal gene network" indicative of reparative adaptation.
  • TEM confirmed the restoration of mitochondrial cristae and ultrastructural integrity.

5. Significance

• Clinical Implications: The study underscores that liver fibrosis is a primary driver of cardiac dysfunction in metabolic disease, suggesting that treating the liver (e.g., via lifestyle modification or antifibrotics) may directly prevent or reverse HFpEF.
• Therapeutic Window: It establishes a critical window for intervention; even after advanced fibrosis and subclinical cardiac dysfunction are established, dietary reversal can halt progression and restore function, preventing mortality.
• Mechanistic Target: The identification of mitochondrial dysfunction as a central mediator provides a specific therapeutic target (e.g., mitochondrial protectants, metabolic modulators) for MASLD-associated HFpEF.
• Model Utility: The Foz/Foz model is validated as a superior tool for dissecting liver-heart crosstalk and testing mechanism-based therapies, addressing a major gap in preclinical HFpEF research.

In conclusion, this paper defines a reversible, fibrosis-driven pathway linking MASLD to HFpEF, driven by mitochondrial failure and inflammatory remodeling, and proves that lifestyle intervention can restore the liver-heart axis to prevent fatal cardiac outcomes.