❤️ physiology

Molecular and Structural Basis of Cardiac Remodelling in Niemann-Pick Type C

This study reveals that Niemann-Pick disease type C is associated with significant cardiac structural and functional abnormalities, including ventricular fibrosis, conduction defects, and arrhythmias driven by glycosphingolipid accumulation and inflammation, thereby supporting the need for routine cardiac screening in affected patients.

Original authors: Song, Q., Prachee, I., Stepien, K. M., Herring, N., Bueno-Orovio, A., Capel, R. A., Priestman, D., Ayagama, T., Bell, L., Rashbrook, V. S., Bush, R., Sparrow, D. B., Smith, C., Smith, D., Akerman, E.

Published 2026-07-09

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Song, Q., Prachee, I., Stepien, K. M., Herring, N., Bueno-Orovio, A., Capel, R. A., Priestman, D., Ayagama, T., Bell, L., Rashbrook, V. S., Bush, R., Sparrow, D. B., Smith, C., Smith, D., Akerman, E., Hu, J., Sigalas, C., Sharma, R., Woolfson, P., Lei, M., Platt, F. M., Burton, R. A. B.

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine your body as a bustling city where tiny delivery trucks (lysosomes) zip around, dropping off packages and picking up trash. In a healthy city, these trucks are efficient, keeping the streets clean. But in a rare condition called Niemann-Pick disease type C (NPC), the trucks break down. They get clogged with a sticky, waxy goo called glycosphingolipids, and the trash piles up inside the cells.

For years, doctors knew this traffic jam caused major problems in the brain (leading to seizures and memory loss) and the liver. But a new study by researchers at the University of Oxford and Liverpool suggests something surprising: the heart is also getting clogged up.

Here is the story of what they found, how they found it, and what it might mean for the future.

The Heart's Hidden Traffic Jam

The researchers started by looking at 14 adult patients with NPC. They ran standard heart checks, like an electrocardiogram (ECG), which is like listening to the city's electrical grid to see if the power is flowing smoothly.

The Findings: More than half of these patients (8 out of 14) had weird electrical signals. Some had "fascicular blocks" (like a traffic light stuck on red in one lane), and others had signs of a thickened heart wall.
The Echo: When they looked at the heart's structure using ultrasound (echocardiograms), they saw that some hearts were slightly weaker at pumping, and some had walls that were thicker than they should be for a person in their 30s.

The paper explicitly argues against the idea that these heart issues are just random or caused by high blood pressure. The patients had normal blood pressure, and the heart changes were unusual for their young age. This suggests the heart trouble is likely part of the NPC disease itself, not just a side effect of getting older or living with a chronic illness.

The Mouse Model: A Time-Lapse of the Problem

To understand how this happens, the team studied mice with a broken NPC gene (called Npc1-/-). These mice are like a fast-forwarded version of the human disease.

The Sticky Goo: They found that as the mice got older (from 3 to 9 weeks), their hearts filled up with that same waxy glycosphingolipid goo. It wasn't just a little bit; it was a massive accumulation.
The Scar City: The most shocking discovery was fibrosis. Imagine the heart muscle as a flexible rubber band. In these mice, the rubber band was getting stiff and scarred over with collagen (like a rubber band covered in hardened glue).
- They measured this using special stains (Masson's Trichrome and Picrosirius Red). The results showed a huge increase in scar tissue.
- They even built 3D models of the hearts and found the left atrium (a heart chamber) was significantly larger in the sick mice compared to healthy ones.

The Electrical Short Circuit

A heart full of sticky goo and scars is a recipe for electrical chaos. The researchers took the mouse hearts out and hooked them up to a machine to test their electricity.

The Stress Test: When they gave the hearts a "stress shot" (isoprenaline, which mimics the "fight or flight" rush), the sick hearts started to misbehave.
The Glitch: The sick hearts showed a prolonged QT interval. Think of this as the heart taking too long to reset its electrical system after a beat. This is dangerous because it can lead to dangerous rhythm problems.
The Block: They also saw more "AV blocks," where the signal from the top of the heart gets stuck and doesn't reach the bottom properly. This happened much more often in the sick hearts under stress.

The "Why": A Molecular Mystery

So, why is the heart turning into a scarred, waxy mess? The researchers looked at the heart's instruction manual (the RNA) to see which genes were being read.

The Inflammation Alarm: The manual showed that the heart was screaming "Fire!" The genes for inflammation were turned up to maximum volume. It's as if the immune system was constantly sending firefighters (immune cells) to the heart, thinking there was a crisis.
The Scar Builders: Along with the fire alarms, the instructions for building scar tissue (fibrosis) were also turned on. The study suggests a cycle: the waxy buildup triggers inflammation, the inflammation calls in scar-builders, and the scars make the heart stiff and prone to electrical glitches.
The Calcium Connection: The paper notes that NPC is known to mess with calcium levels inside the cell's trash bins. Since calcium is the spark that makes the heart beat, this mix-up might be why the electrical signals are getting delayed (the long QT interval).

What This Means (and What It Doesn't)

The authors are careful to say they haven't "solved" the heart problem yet. They haven't proven that the heart issues cause sudden death in humans, though they suspect it might be a hidden risk. They also admit their mouse study used "bulk" reading of genes, which is like reading a city's average mood rather than checking every single person's diary.

However, the evidence is strong enough to suggest a new rule for doctors: Don't ignore the heart in NPC patients.

The paper suggests that because patients are living longer thanks to new treatments, these slow-building heart problems might become more common.
They recommend that doctors start giving NPC patients regular heart checks (ECGs) and maybe even heart ultrasounds, just to catch these "sticky" and "scarred" hearts early.

In short, the heart in Niemann-Pick disease isn't just a bystander; it's a victim of the same traffic jam that plagues the brain. The city is getting clogged, the streets are getting scarred, and the power grid is flickering. It's a new piece of the puzzle that could help keep these patients safe for longer.

Technical Summary: Molecular and Structural Basis of Cardiac Remodelling in Niemann-Pick Type C

Problem Statement
Niemann-Pick disease type C (NPC) is a rare autosomal recessive lysosomal storage disorder caused by pathogenic variants in NPC1 or NPC2, leading to the accumulation of cholesterol and sphingolipids. While neurological decline and hepatic fibrosis are well-characterized, cardiac involvement in NPC has remained poorly defined. Given that other lysosomal storage disorders (e.g., Fabry, Gaucher, ASMD) frequently present with severe cardiac manifestations such as hypertrophy, fibrosis, and arrhythmias, and considering the known disruption of lysosomal calcium signaling in NPC, this study investigates whether cardiac remodeling and dysfunction occur in NPC patients and Npc1 knockout (Npc1-/-) mice.

Methodology
The study employed a multimodal approach combining clinical data from human patients and experimental analysis in a murine model:

Human Cohort: 14 adult NPC patients (8 male, 6 female; median age 37) underwent 12-lead electrocardiograms (ECG) and transthoracic echocardiography.
Animal Model: Npc1-/- mice (BALB/c background) were compared to wild-type (WT) controls at 3, 7, and 9 weeks of age.
Biochemical Analysis: Glycosphingolipid (GSL) accumulation in cardiac tissue was quantified using Normal-Phase High-Performance Liquid Chromatography (NP-HPLC).
Histology and Morphology:
- Ventricular fibrosis and collagen deposition were assessed via Masson's Trichrome (M&T) and Picrosirius Red (PR) staining.
- Automated image segmentation (Matlab) quantified connective tissue area.
- High-Resolution Episcopic Microscopy (HREM) with 3D reconstruction (Amira software) was used to assess chamber volumes and wall thickness.
Electrophysiology: Ex vivo Langendorff-perfused hearts were subjected to bipolar ECG recordings to measure heart rate, PR, and QT intervals, both at baseline and under $\beta$ -adrenergic stress (isoprenaline).
Transcriptomics: Bulk RNA sequencing was performed on whole hearts at 3, 7, and 9 weeks. Differentially expressed genes (DEGs) were analyzed using Gene Ontology (GO) and KEGG pathway enrichment. RT-qPCR validated specific targets (Lgals3).

Key Results

Clinical Findings in Patients:
- ECG Abnormalities: 8 out of 14 patients exhibited ECG abnormalities, including abnormal QRS transitions (N=8), increased QRS amplitude (N=4), fascicular blocks (N=2), and T-wave inversion (N=1).
- Echocardiography: 13 patients underwent echocardiography, revealing mildly impaired left ventricular (LV) systolic function in two patients and increased septal wall thickness/LV mass in four patients. No significant valvular disease was observed.
Lipid Accumulation in Mouse Hearts:
- Npc1-/- hearts showed age-dependent accumulation of glycosphingolipids starting at 7 weeks.
- Specific elevations were noted in Gb3, Gb4, GA1, GM3-Gc, and GM1a compared to WT controls.
Structural Remodeling and Fibrosis:
- Histology: Npc1-/- ventricles displayed significant fibrotic remodeling. There was a marked increase in the percentage area of connective tissue and the connective-to-cardiac tissue ratio in both M&T and PR staining (p<0.0001).
- Morphology: 3D reconstruction revealed a significantly larger left atrium-to-ventricle ratio in Npc1-/- mice (p=0.0286), though ventricular volume itself did not differ significantly from WT.
Electrophysiological Defects:
- While baseline heart rates were similar between groups, Npc1-/- hearts exhibited significant QT prolongation at baseline and under isoprenaline stress.
- Under $\beta$ -adrenergic stress, the incidence of first- and second-degree atrioventricular (AV) blocks increased significantly in Npc1-/- hearts (from 2/9 to 5/9 hearts).
Transcriptomic Profiling:
- Over 5,300 DEGs were identified by week 9, with distinct separation from WT in PCA plots.
- Pathways: Enrichment analysis highlighted activation of inflammatory and immune-related pathways (GO:BP) as early as week 3.
- Key Genes: Upregulation of Lgals3, Mmp12, Mgl2, Cx3cr1, Ccl3, and Ccl4 suggested activation of NF- $\kappa$ B signaling and macrophage/neutrophil recruitment.
- Cardiac Pathways: KEGG analysis at week 9 revealed pathways related to dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), and extracellular matrix (ECM) organization.
- Calcium Signaling: Upregulation of Atp6v0d2 (lysosomal proton transporter) was observed, supporting the hypothesis of lysosomal calcium dysregulation independent of pH changes.

Significance and Claims
The authors claim to provide the first evidence of significant cardiovascular phenotypes in NPC, characterized by fibrosis, inflammation, and electrophysiological instability. The study posits that cardiac remodeling in NPC is driven by a mechanism linking lysosomal lipid accumulation to inflammation (via NF- $\kappa$ B) and subsequent fibrosis (via TGF- $\beta$ and myofibroblast activation).

The paper concludes that these findings support the implementation of routine cardiac screening (annual ECG and follow-up echocardiography/MRI) for NPC patients. The authors suggest that previously unexplained sudden death events in NPC, often attributed to seizures, may instead be triggered by malignant ventricular arrhythmias or bradyarrhythmias arising from this underlying cardiac substrate. The study emphasizes that as neurological symptoms are managed and patient lifespans extend, cardiac complications may become a more prominent long-term risk.

Limitations Acknowledged
The authors note that bulk RNA sequencing limits cell-type-specific attribution of gene expression changes. Additionally, the lack of in vivo mouse echocardiography and telemetry (due to ethical and infrastructure constraints) means the mouse data relies on ex vivo functional assessment and histological correlation rather than longitudinal physiological monitoring.

The Heart's Hidden Traffic Jam

The Mouse Model: A Time-Lapse of the Problem

The Electrical Short Circuit

The "Why": A Molecular Mystery

What This Means (and What It Doesn't)

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