Highlights
Alternative splicing of TPM1 appears to be a previously underrecognized myofilament mechanism contributing to impaired relaxation and increased stiffness in heart failure with preserved ejection fraction (HFpEF).
The study identifies a specific pathogenic isoform shift toward TPM1b, generated by skipping exon 9a, in both human HFpEF samples and mouse models.
SRPK3 is positioned upstream of this splice event and experimentally drives myofiber disarray and diastolic dysfunction, whereas SRPK3 knockdown improves the phenotype in preclinical models.
These findings raise the possibility that splice-modifying strategies could complement current hemodynamic and metabolic approaches to HFpEF.
Background and Clinical Context
HFpEF is now the dominant heart failure phenotype in many clinical settings and remains one of the most difficult syndromes in cardiovascular medicine to treat effectively. Unlike heart failure with reduced ejection fraction, HFpEF is defined by preserved left ventricular ejection fraction despite clear evidence of heart failure symptoms, elevated filling pressures, impaired ventricular relaxation, and increased chamber stiffness. The syndrome is heterogeneous, often arising in older adults with multimorbidity, including obesity, hypertension, diabetes, chronic kidney disease, atrial fibrillation, and systemic inflammation.
Therapeutic progress in HFpEF has historically lagged behind advances in reduced-ejection-fraction heart failure. Sodium-glucose cotransporter-2 inhibitors have improved outcomes, but residual risk remains high, and disease-modifying mechanisms are still incompletely understood. Mechanistic work in HFpEF has largely focused on fibrosis, microvascular inflammation, titin-based stiffness, altered calcium handling, and extracardiac contributors. Less attention has been given to whether disordered RNA processing within the sarcomere directly contributes to the diastolic phenotype.
Tropomyosin 1, encoded by TPM1, is a central component of the thin filament in striated muscle. Its position along actin influences myosin binding and therefore contractile regulation. TPM1 has multiple alternative exons, allowing production of distinct protein isoforms with potentially different biomechanical properties. Although sarcomeric mutations are well established in inherited cardiomyopathies, the role of acquired alternative splicing of sarcomeric genes in HFpEF has been far less clear. The present study by Chen and colleagues directly addresses that gap, linking TPM1 exon selection to myocardial compliance and diastolic performance.
Proposed Section Structure for Interpreting This Study
A clinically appropriate structure for this topic includes: disease burden and unmet need in HFpEF; rationale for examining sarcomeric alternative splicing; study design and experimental platforms; key mechanistic findings; translational relevance and therapeutic implications; limitations and unanswered questions; and a practice-oriented conclusion. That framework is used below.
Study Design and Experimental Approach
Overall design
This was a translational mechanistic study integrating human samples, murine disease models, engineered gene-expression interventions, and human pluripotent stem cell-derived cardiomyocytes. The central question was whether alternative splicing of TPM1 contributes to HFpEF pathobiology and whether the upstream splicing kinase SRPK3 regulates this process.
Biological systems used
The investigators examined myocardial ultrastructure in HFpEF using transmission electron microscopy and assessed myocardial compliance using nanoindentation, a technique that can quantify tissue mechanical properties at small scales. They then used cardiomyocyte-directed adeno-associated virus serotype 9 constructs in mice to overexpress distinct TPM1 isoforms or manipulate SRPK3 expression. Human pluripotent stem cell-derived cardiomyocytes were used as a complementary human cellular system to test isoform-specific effects.
Mechanistic methods
To define upstream regulation, the study incorporated RNA pulldown, mass spectrometry, alternative splicing analyses, and related molecular assays. This multi-platform approach is a strength because it links phenotype to mechanism rather than relying only on descriptive transcriptomic association.
Key endpoints
The principal endpoints were structural myofilament integrity, myocardial compliance, and indices of diastolic dysfunction. Additional endpoints included TPM1 isoform expression, exon 9a inclusion or exclusion, and the consequences of SRPK3 gain- and loss-of-function.
Key Findings
HFpEF hearts showed distinctive myofilament abnormalities
The study reports that HFpEF was associated with unique myofiber or myofilament disorganization on transmission electron microscopy. This is noteworthy because HFpEF is often discussed primarily in terms of fibrosis and passive stiffness, yet these observations suggest that intrinsic sarcomeric architectural disruption may also contribute. The accompanying nanoindentation data indicated reduced myocardial compliance, consistent with a mechanically stiffer myocardium.
From a clinical standpoint, this observation aligns with the idea that HFpEF is not solely a disease of interstitial remodeling. Instead, cardiomyocyte-level mechanical dysfunction may be a major determinant of elevated filling pressures and impaired relaxation.
TPM1 alternative splicing shifted toward the TPM1b isoform in HFpEF
In both patients with HFpEF and mouse models, the authors observed increased expression of the TPM1b isoform, which lacks exon 9a because of alternative splicing. This isoform shift is the biological center of the paper. Rather than implicating total TPM1 abundance alone, the data point to qualitative remodeling of sarcomeric protein composition through altered exon usage.
This distinction matters. Alternative splicing can change protein function without large changes in total gene expression, meaning conventional expression profiling may miss clinically important biology. If replicated, TPM1 isoform balance could become a more informative marker than overall TPM1 levels.
Isoform-specific experiments supported a causal role for exon 9a skipping
Cardiomyocyte-specific overexpression studies demonstrated that distinct TPM1 isoforms are not functionally equivalent. The TPM1b isoform lacking exon 9a worsened HFpEF-related phenotypes in mice and in human pluripotent stem cell-derived cardiomyocytes. This is an important causal step: it suggests the splice shift is not merely a bystander effect of myocardial stress but can actively worsen diastolic dysfunction.
The implication is that exon 9a inclusion may preserve a more compliant or better-organized thin-filament state, whereas exon 9a exclusion promotes structural disorder and adverse mechanics. The abstract does not provide effect sizes, confidence intervals, or the precise magnitude of echocardiographic or hemodynamic changes, which limits quantitative interpretation, but the directional consistency across models strengthens the conclusion.
SRPK3 was identified as the upstream regulator of TPM1 exon 9a splicing
The authors then traced the splice alteration upstream to SRPK3, a serine/arginine-rich protein kinase involved in splicing regulation. They report that SRPK3 mediates alternative splicing of TPM1 exon 9a. Cardiomyocyte-specific SRPK3 overexpression induced myofiber disarray and diastolic dysfunction, while SRPK3 knockdown ameliorated these abnormalities.
This part of the study substantially increases translational interest. Instead of targeting a structural protein directly, one might intervene at the level of a regulatory kinase controlling pathologic exon selection. Such an approach could potentially rebalance isoforms rather than simply suppress total protein production.
Rescue experiments supported a TPM1-dependent mechanism
Supplementing TPM1 containing exon 9a partially rescued the diastolic dysfunction caused by SRPK3 overexpression. Partial rescue is biologically plausible and important. It suggests TPM1 exon 9a splicing is a major downstream effector of SRPK3, but probably not the only one. Splicing kinases typically regulate multiple transcripts, so some of the SRPK3 phenotype may reflect broader RNA-processing effects beyond TPM1.
Even so, the rescue experiment helps move the study from correlation toward mechanistic hierarchy: SRPK3 sits upstream, TPM1 exon 9a is a critical target, and disturbed thin-filament composition contributes to the observed dysfunction.
Preventive SRPK3 inactivation improved diastolic dysfunction in a mouse model
Preventive intervention experiments showed that inactivating SRPK3 alleviated diastolic dysfunction in the HFpEF mouse model. This is among the most clinically provocative findings in the paper because it introduces the possibility that maladaptive splicing is therapeutically modifiable.
Still, the wording matters. These were preventive preclinical experiments, not late-stage reversal studies in established human HFpEF. Whether SRPK3 inhibition can reverse advanced disease, improve exercise capacity, reduce congestion, or alter hard outcomes remains unknown.
Mechanistic and Translational Interpretation
This study advances an appealing mechanistic model. In HFpEF, increased SRPK3 activity promotes skipping of TPM1 exon 9a, increasing the TPM1b isoform. The resulting thin-filament remodeling contributes to myofibrillar disarray, reduced myocardial compliance, and impaired diastolic performance. In that framework, altered splicing is not simply a molecular signature of stress; it is a proximal contributor to the mechanical phenotype.
The work is especially interesting because it bridges molecular cardiology and clinical HFpEF pathophysiology. Diastolic dysfunction is often conceptualized at the organ level through elevated filling pressures, ventricular-arterial coupling, and exercise hemodynamics. Chen and colleagues connect those clinical manifestations to an RNA-processing event in the contractile apparatus itself.
The findings may also complement established HFpEF biology rather than compete with it. Fibrosis, titin phosphorylation, inflammation, and endothelial dysfunction may all coexist with sarcomeric splice remodeling. In practice, HFpEF likely reflects interacting modules of disease. Alternative splicing of TPM1 could define one biologically coherent subgroup, perhaps particularly relevant in patients with prominent cardiomyocyte stiffness or cytoskeletal disorder.
Clinical Relevance
At present, the findings are not ready for direct clinical implementation, but they have several implications for clinicians and translational investigators.
First, they reinforce that HFpEF is a myocardial disease at the level of contractile protein regulation, not merely a syndrome of comorbidity and extracellular matrix expansion.
Second, they suggest that isoform-resolved molecular profiling may eventually improve patient stratification. Future biopsy, circulating RNA, or imaging-correlated biomarker studies could determine whether TPM1 splicing signatures identify a treatment-responsive HFpEF endotype.
Third, the study nominates SRPK3 as a therapeutic target. Conceptually, candidate strategies could include splice-switching oligonucleotides, small-molecule kinase modulators, or targeted RNA therapeutics. These approaches are technically challenging in the heart, but success in other genetic and RNA-mediated disorders makes the concept credible.
Fourth, the findings may influence how clinicians think about “diastolic dysfunction” as a phenotype. Beyond abnormalities in relaxation kinetics and passive stiffness, there may be a specific sarcomere-splicing component that is measurable and modifiable.
Strengths of the Study
The study has several notable strengths. It spans human HFpEF tissue, mouse models, and human-derived cardiomyocytes, improving biological plausibility across systems. It combines structural imaging, mechanical testing, molecular splicing analysis, and functional intervention experiments. It uses both gain-of-function and knockdown approaches for SRPK3, which is much more convincing than a single-direction perturbation. Finally, the partial rescue with exon 9a-containing TPM1 provides mechanistic specificity.
Limitations and Cautions
Several limitations should temper interpretation.
First, the report as summarized does not provide quantitative clinical data such as sample size, patient phenotype details, absolute effect sizes, variability measures, or statistical estimates. Without those details, it is difficult to judge robustness, reproducibility, and the magnitude of benefit.
Second, HFpEF is highly heterogeneous, and no single model fully captures the human syndrome. Mouse HFpEF models generally approximate selected features such as hypertensive remodeling, metabolic stress, or concentric hypertrophy, but may not reproduce the complexity of older multimorbid patients.
Third, human pluripotent stem cell-derived cardiomyocytes are useful but relatively immature compared with adult ventricular cardiomyocytes. Their sarcomeric organization and electrophysiologic properties may not fully mimic the adult HFpEF myocardium.
Fourth, SRPK3 likely regulates multiple splicing events. Therefore, targeting SRPK3 therapeutically could have broader consequences beyond TPM1. These could be beneficial, neutral, or harmful. On-target but off-pathway effects will need careful definition.
Fifth, preventive benefit in a mouse model does not establish therapeutic efficacy in patients with established symptomatic HFpEF. The translational path will require demonstration of safety, cardiac selectivity, and durable functional benefit.
How This Fits With the Current HFpEF Therapeutic Landscape
Current guideline-directed treatment for HFpEF emphasizes symptom relief, management of congestion, treatment of hypertension and atrial fibrillation, aggressive control of comorbidities, and use of sodium-glucose cotransporter-2 inhibitors to reduce hospitalization risk. None of these therapies directly target sarcomeric splice regulation.
That is why this study is important. It points to a potentially novel disease-modifying axis distinct from hemodynamic unloading or neurohormonal modulation. Whether such an approach will benefit all HFpEF patients is doubtful, but that may not be necessary. A precision-medicine strategy aimed at a molecularly defined subgroup could still be highly impactful.
Conclusion
Chen and colleagues provide compelling preclinical and translational evidence that alternative splicing of TPM1 exon 9a, regulated by SRPK3, contributes to myofilament disarray, reduced myocardial compliance, and diastolic dysfunction in HFpEF. The work expands the mechanistic map of HFpEF from fibrosis and titin biology into splice-dependent thin-filament remodeling. Although the findings require validation, quantitative clinical correlation, and therapeutic development, they identify SRPK3 and TPM1 exon 9a splicing as an intriguing new pathway for biomarker discovery and targeted intervention in a syndrome with major unmet need.
Funding and ClinicalTrials.gov
Funding information was not provided in the supplied abstract summary. No ClinicalTrials.gov registration number is applicable to the mechanistic preclinical work described in the abstract.
References
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