Centronuclear myopathies are a group of rare inherited disorders defined by progressive muscle wasting and weakness, named for the abnormal positioning of nuclei at the centre of muscle fibres rather than at their periphery. The most common autosomal dominant form is caused by mutations in the DNM2 gene, which encodes dynamin 2, a GTPase enzyme involved in membrane fission, intracellular trafficking and organelle morphology. Roughly 40 different heterozygous DNM2 mutations have been linked to the disease, which accounts for approximately 15 percent of all centronuclear myopathy cases. Severity ranges broadly, from mild late-onset weakness to severe neonatal forms, and no curative therapy currently exists.

In a study published in the Journal of Cachexia, Sarcopenia and Muscle, a research team used the KI-Dnm2 R465W/+ mouse model, which carries a disease-causing mutation analogous to those found in patients, to test whether inhibiting myostatin could counteract the muscle deterioration characteristic of the disease. Myostatin, also known as growth differentiation factor 8, is widely regarded as the master negative regulator of skeletal muscle mass throughout development and adult life. It signals through the activin type IIB receptor, activating the SMAD2/3 pathway, which suppresses the proliferation and differentiation of muscle precursor cells, represses the IGF1-Akt-mTOR anabolic pathway, downregulates muscle-specific genes and promotes E3 ubiquitin ligases involved in protein degradation.

The researchers first mapped the natural course of the disease in these mice using longitudinal magnetic resonance imaging, repeated at 1, 2 and 8 months of age with a high-field 7-Tesla system. Although the knockin mice were viable and grew normally in body size, their leg muscle cross-sectional area lagged dramatically behind healthy littermates. Between 1 and 2 months of age, a critical postnatal growth window, healthy mice expanded their leg muscle cross-sectional area by 1.5-fold, while the mutant mice managed only a 1.2-fold increase. Functional testing revealed that the trouble began even earlier: impaired motor coordination and reduced grip strength were already detectable at 1 month, before measurable muscle growth failure appeared, and histological analysis of the tibialis anterior muscle showed more than 20 percent of fibres displaying the hallmark central NADH-TR staining pattern of the disease at 2 months.

Digging into the molecular roots of this growth failure, the team found a coordinated disruption of multiple homeostatic systems. The number of Pax7-positive satellite cells, the stem-like reservoir that fuses with growing fibres to supply new myonuclei, was significantly reduced, along with MyoD expression, indicating defective myonuclear accretion. At the same time, the translational repressor Eif4ebp1 was upregulated, suggesting suppressed protein synthesis, while FOXO3 and its downstream E3 ligase targets MuRF1, Atrogin-1 and Musa1 were elevated, pointing to accelerated protein breakdown. Autophagy-related transcripts such as Bnip3 and Map1lc3b were paradoxically reduced while P62 and LC3B-I protein accumulated, a signature of impaired autophagic flux. Together, these findings paint centronuclear myopathy not as a single broken pathway but as a global collapse of muscle protein and nuclear homeostasis.

To test whether myostatin was a viable therapeutic target, the researchers crossed the mutant mice with a myostatin knockout line, producing double-mutant animals completely lacking functional myostatin. The results were dramatic. The double-mutant mice gained substantially more body weight, and the mass of the tibialis anterior, quadriceps, extensor digitorum longus and soleus muscles far exceeded even healthy wild-type levels. Critically, grip strength and rotarod performance, which were significantly impaired in the myopathy mice, were fully restored to normal. Because myostatin is absent from embryogenesis onward in these animals, lifelong suppression appears to be integrated into developmental muscle growth programs, including enhanced satellite cell activation and myoblast proliferation, producing stable structural and functional benefits.

Genetic deletion, however, is not a practical option for patients, so the team next turned to pharmacology. They administered a soluble activin type IIB receptor fused to a human IgG1 Fc fragment, a decoy receptor that sequesters both myostatin and activin A in the circulation, by intraperitoneal injection twice weekly at a dose of 5 milligrams per kilogram. Four-week-old mutant mice received the treatment for four consecutive weeks. The intervention produced a marked anabolic effect: tibialis anterior mass was partially restored, quadriceps mass was completely normalized, and gastrocnemius mass actually exceeded wild-type values by the end of treatment. Serum myostatin concentrations rose during therapy, consistent with the decoy receptor prolonging the circulating half-life of the bound hormone and with increased production from newly expanded muscle mass.

But the pharmacological results came with two sobering caveats. First, the muscle gains proved entirely reversible: five weeks after treatment stopped, muscle mass had fallen back to untreated disease levels, indicating that continuous administration would be required to maintain any benefit. Second, and perhaps more importantly, the drug restored size without restoring power. In situ force measurements of the tibialis anterior showed no improvement in maximal absolute or specific force despite the hypertrophy. Molecular analysis explained why: while Akt Ser473 phosphorylation increased, confirming an anabolic signal, the treatment failed to correct the core pathological features of the disease, including elevated E3 ligase expression, impaired autophagic flux, reduced ribosomal and myosin heavy chain transcripts, and dysregulated expression of excitation-contraction coupling genes such as Chrna1, RyR1 and Casq1. Because dynamin 2 is known to organize transverse tubules, the membrane invaginations that transmit electrical signals deep into the fibre, these contractile defects appear intrinsic to the disease and beyond the reach of simply growing bigger fibres.

The contrast between the two strategies carries a clear message for the field. In mice, permanent myostatin inactivation reshapes developmental programs and delivers lasting improvements in both mass and function, whereas transient pharmacological blockade produces short-lived hypertrophy that leaves the underlying contractile and metabolic defects untouched. The authors note that combined myostatin and activin A inhibition may hold particular promise for human medicine, since activin A circulates at higher levels in people than in mice and signals through the same SMAD2/3 axis. Their conclusion is that future therapies for autosomal dominant centronuclear myopathy should be judged not merely by their ability to bulk up muscle, but by whether they durably restore contractile performance, likely in combination with approaches that directly repair the excitation-contraction machinery. The work was supported by AFM-Téléthon through the strategic MyoNeurALP programme.

Subject of Research: Myostatin inhibition therapy for dynamin 2-related centronuclear myopathy

Article Title: Genetic and Pharmacologic Inhibition of Myostatin Restores Muscle Mass in a Dynamin 2‐Related Centronuclear Myopathy Mouse Model

Article References: Anne‐Cécile, D., David, A., Mathias, V., Valentine, A., Chloé, P., Quentin, D., Esra, K., Sidney, C., Emmanuelle, G., Louise, C., Alexandre, G., Josiane, C., Aja, P., Maximilien, B., Baptiste, M., Christophe, H., Schaeffer, L., Olli, R., Marc, B., … Damien, F. (2026). Genetic and Pharmacologic Inhibition of Myostatin Restores Muscle Mass in a Dynamin 2 ‐Related Centronuclear Myopathy Mouse Model. Journal of Cachexia, Sarcopenia and Muscle, 17(5), Article e70338. https://doi.org/10.1002/jcsm.70338

Image Credits: AI Generated

DOI: 10.1002/jcsm.70338

Keywords: centronuclear myopathy, myostatin, dynamin 2, sActRIIB-Fc, muscle mass, muscle force, satellite cells, autophagy, excitation-contraction coupling, mouse model, neuromuscular disease, Akt signalling

Arrhythmias arise when the heart’s electrical impulses become irregular, leading to potentially life-threatening conditions such as atrial fibrillation and ventricular tachycardia. The ionic imbalances and miscommunications within cardiac cells frequently trigger these disturbances. The recent study asserts that disrupting pathological calcium cycling through the inhibition of the late sodium current (I_Na-L) and ryanodine receptors (RyR2) showcases an innovative avenue for therapeutic intervention.

Calcium ions play a critical role in the excitation-contraction coupling model of the heart. When the balance of calcium influx and release is perturbed, the heart’s ability to contract effectively is jeopardized. The profound impact of I_Na-L blockade stands out in this context, as excessive late sodium current can lead to calcium overload, ultimately causing cellular dysfunction and arrhythmogenic risk. This research provides compelling evidence that mitigating the late sodium current can restore homeostasis within cardiac myocytes, thus stabilizing rhythmical activity.

In addition to I_Na-L blockade, the ryanodine receptor remains a focal point in the authors’ investigation. RyR2 is responsible for calcium-induced calcium release, a fundamental process underpinning cardiac contraction. Abnormal RyR2 activity can lead to excessive calcium release during systole and insufficient calcium uptake during diastole, presenting a critical factor in the development of arrhythmias. The study underscores that targeting RyR2 signifies a double-edged sword; the correct modulation can reduce pathological calcium cycling, fostering healthier cardiac rhythms.

A pivotal aspect of the study emphasizes the normalization of CaMKII (Calcium/Calmodulin-dependent protein kinase II) signaling. CaMKII acts as a pivotal regulator in the calcium cycle and is integral to cellular response to calcium fluctuations. Pathological conditions often lead to CaMKII dysregulation, amplifying arrhythmic events through hyperphosphorylation of various substrates. By partnering the inhibition of I_Na-L with RyR2 blockade, there exists the potential to recalibrate CaMKII activity, steering it towards a balanced state that promotes cardiac health.

The implications of this research extend to clinical application, as the combination of pharmacologically targeting I_Na-L and RyR2 opens new avenues for patient-specific antiarrhythmic therapies. Current antiarrhythmic agents often yield unpredictable results due to their non-specificity or adverse effects. Thus, the refined therapeutic strategies articulated in this study stand to transform patient outcomes, providing tailored interventions that align closely with underlying pathophysiological mechanisms.

Moreover, the embrace of advanced investigative techniques, including electrophysiological assessments and molecular biology methods, underscores the robustness of this research. The authors leverage cutting-edge tools to delve deeply into the mechanistic interactions between calcium cycling, signaling pathways, and their arrhythmic consequences. This meticulous approach not only enhances the reliability of their findings but also sets a precedent for future investigations to build upon.

Understanding the multifaceted nature of cardiac arrhythmias necessitates the integration of genetic, molecular, and environmental factors. The research advocates for a holistic view, encouraging an exploration of patient-derived models that may reflect individual variability in calcium handling and signaling. This perspective is essential as it aligns therapeutic interventions with distinct patient profiles, potentially enhancing efficacy and minimizing adverse effects.

This fusion of basic science with clinical application resonates powerfully in the cardiovascular research community, fostering dialogues around innovative therapeutic avenues that tackle the complexities of arrhythmias. As researchers seek to uncover the underlying mechanisms of heart rhythm disorders, the findings presented by Ju et al. will likely catalyze further studies that interrogate the longevity and durability of these inhibition strategies.

Furthermore, the exploration of concomitant therapies may optimize results. The potential to combine I_Na-L and RyR2 blockade with lifestyle modifications or other medical therapies warrants significant exploration. Integrative approaches, where lifestyle factors bolster the effects of pharmacological interventions, could yield substantial holistic benefits for those battling arrhythmogenesis.

The significance of this research cannot be overstated. As healthcare systems are increasingly tasked with managing chronic diseases, innovations that address arrhythmias represent a substantial step towards enhanced cardiovascular health. This study posits that the strategic targeting of I_Na-L and RyR2 may not only mitigate present ailments but also serve preventative purposes for future patients, thereby reshaping the landscape of cardiac healthcare delivery.

In conclusion, the study by Ju, Qiu, Wang et al. not only elucidates the nuanced interplay between calcium signaling, sodium currents, and arrhythmias, but it also champions a transformative approach to treatment. By advocating for localized and nuanced therapeutic strategies, this research lays essential groundwork for the development of more sophisticated, patient-centered interventions that ultimately promise to enhance the quality of life for patients suffering from cardiac arrhythmias.

Subject of Research: Arrhythmias, Calcium Cycling, Sodium Channel Blockade, and Ryanodine Receptor Modulation

Article Title: Synergistic antiarrhythmic mechanism of I_Na-L and RyR2 blockade: normalization of pathological calcium cycling and CaMKII signaling.

Article References:

Ju, M., Qiu, S., Wang, Y. et al. Synergistic antiarrhythmic mechanism of I_Na-L and RyR2 blockade: normalization of pathological calcium cycling and CaMKII signaling.
J Transl Med (2025). https://doi.org/10.1186/s12967-025-07652-3

Image Credits: AI Generated

DOI: 10.1186/s12967-025-07652-3

Keywords: arrhythmias, antiarrhythmic therapy, calcium signaling, sodium channel blockers, calcium cycling, CaMKII, cardiovascular health

The cardiac ryanodine receptor, a massive homotetrameric calcium release channel embedded in the sarcoplasmic reticulum membrane, plays a pivotal role in regulating intracellular calcium levels that govern heartbeat rhythm and contractility. Despite its crucial physiological function, visualizing RyR at nanometer resolution within the cellular context has remained an ambitious challenge. Traditional super-resolution fluorescence techniques have either lacked the necessary spatial precision or failed to accurately reconstruct three-dimensional orientations due to optical and physical constraints. Here, the integration of MINFLUX microscopy delivers a transformative leap.

MINFLUX (MINimal emission FLUXes) microscopy represents a state-of-the-art localization technique combining the photon efficiency of stimulated emission depletion (STED) microscopy with single-molecule tracking fidelity. Its approach centers on positioning a doughnut-shaped excitation laser pattern over fluorescent labels, enabling precise triangulation of emitter positions with localization precision down to a few nanometers. The reduced photon budget required for localization, along with the minimized photobleaching, renders MINFLUX especially suited for detailed structural mapping of proteins in native cellular milieus over extended durations.

By applying MINFLUX microscopy specifically to fluorescently tagged cardiac RyRs in live cardiomyocytes, the researchers achieved unprecedented resolution in discerning individual subunits’ spatial arrangements within the complex tetrameric assembly. The analysis revealed distinct subunit clustering and conformational heterogeneity correlating with functional states. This subunit-level resolution was not only spatially defined but also contextualized within the cell’s three-dimensional environment, a feat unattainable with prior two-dimensional imaging modalities.

The team’s experimental methodology involved the genetic incorporation of fluorescent probes strategically positioned on RyR subunits, enabling selective and precise labeling without compromising receptor function. Sequential localization events were acquired under cryogenic conditions to further stabilize molecular structures for imaging, minimizing thermal drift and enhancing spatial accuracy. Such meticulous sample preparation harmonized with MINFLUX’s photon-efficient detection, culminating in clarity and positional exactitude that illuminates RyR’s nano-architecture.

One of the most revealing outcomes of this study was the observation of RyR subunits’ angular orientation regarding the sarcoplasmic reticulum membrane. Prior assumptions centered on a planar, symmetrical distribution; however, the three-dimensional reconstructions disclosed subtle yet significant tilts and rotations of subunits, suggesting a dynamic conformational plasticity potentially linked to gating mechanisms. These findings resonate profoundly with electrophysiological data hinting at allosteric modulation within the receptor complex.

Moreover, the capacity to differentiate individual RyR subunits in situ lays the groundwork for dissecting complex interactions with accessory proteins and regulatory factors that modulate receptor activity. This approach, bridging structural biology with cell physiology at unmatched resolution, could unravel how molecular perturbations contribute to arrhythmogenic pathologies such as catecholaminergic polymorphic ventricular tachycardia (CPVT) and heart failure.

The implications extend beyond cardiology, as RyRs share structural and functional homology with other intracellular calcium channels implicated in neurological and skeletal muscle disorders. The methodology introduces a versatile platform for probing such macromolecular assemblies’ architecture and orientation, potentially catalyzing targeted drug design tailored to specific conformational states.

From a technical standpoint, this study underscores MINFLUX microscopy’s versatility and robustness in real biological systems, confronting challenges such as fluorophore density heterogeneity, background noise, and cellular autofluorescence. The researchers capitalized on advanced computational algorithms to filter and correct localization events, ensuring that data interpretation faithfully represented molecular positioning and orientation.

Importantly, the use of MINFLUX revealed functional heterogeneity even within a nominally uniform population of RyR clusters, suggesting that cardiac calcium release units operate with subtle structural variations that could fine-tune excitation-contraction coupling in response to physiological demands. This insight aligns with recent paradigms emphasizing spatial microdomain specificity in intracellular signaling.

The study also opens exciting prospects for longitudinal imaging, enabling visualization of dynamic conformational changes in RyRs during various physiological and pathological states. Coupled with optogenetic or pharmacological manipulation, it becomes possible to experimentally interrogate real-time correlations between molecular structure, calcium flux, and contractile behavior in intact cardiac tissue.

Although the current work focused on isolated cardiomyocytes, future extensions to in vivo models and human cardiac tissue biopsies could validate these structural signatures and their clinical relevance. The researchers envisage integrating MINFLUX data with complementary modalities such as cryo-electron tomography for a comprehensive multi-scale mapping of cardiomyocyte architecture.

In conclusion, this pioneering application of MINFLUX microscopy represents a landmark achievement in nanoscale cardiac biology, illuminating the RyR’s subunit layout and orientation with unprecedented clarity. By merging cutting-edge optical imaging with molecular labeling strategy and sophisticated image analysis, the study heralds a new era of precision cardiac proteomics aimed at decoding the spatial logic of cellular calcium signaling. The findings promise to catalyze innovative therapeutic avenues for arrhythmia and heart failure by targeting ryanodine receptor microstructure.

This investigation stands as a testament to the power of technological innovation in unraveling fundamental biological questions, prophetizing the transformative impact of next-generation microscopy in life sciences. As MINFLUX continues to evolve and integrate with functional assays, the molecular choreography underlying cellular physiology will become increasingly accessible, enabling scientific discoveries once relegated to theoretical speculation.

The ongoing refinement and adoption of MINFLUX microscopy techniques will likely spur a wave of new insights across diverse fields, from neuroscience and immunology to cancer biology and developmental studies. This study exemplifies how pushing the boundaries of spatial resolution directly translates into enhanced understanding of biological function, driving progress in biomedical research and precision medicine.

Ultimately, the detailed visualization of cardiac ryanodine receptor subunits and their 3D orientation in cells fuels hope for deciphering the molecular basis of cardiac excitability and contractility at an unprecedented scale. With such clarity, even the most intricate physiological processes become tangible, paving the way for interventions crafted at the nanoscopic interface of structure and function.

Subject of Research: Cardiac ryanodine receptor structural organization and 3D orientation in cells

Article Title: MINFLUX microscopy resolves subunits of the cardiac ryanodine receptor and its 3D orientation in cells

Article References:
Clowsley, A.H., Meletiou, A., Janicek, R. et al. MINFLUX microscopy resolves subunits of the cardiac ryanodine receptor and its 3D orientation in cells. Nat Commun (2025). https://doi.org/10.1038/s41467-025-67801-6

Image Credits: AI Generated