Gene Silencing of Complement C3 Shields Nerve-Muscle Junctions in Myasthenia Gravis Rats

Myasthenia gravis is one of the best-characterized autoimmune diseases of the nervous system, yet its destructive final steps remain stubbornly difficult to interrupt in the clinic. In a new study published in the Journal of Translational Medicine, researchers at Maastricht University, working together with scientists at Apellis Pharmaceuticals, report that switching off the production of a single liver-derived protein, complement component C3, can largely protect the neuromuscular junction from antibody-driven damage in a rat model of the disease. The findings, based on a modern RNA interference therapy delivered under the skin, offer a striking demonstration of how central the complement cascade is to the muscle weakness that defines this rare condition, and they point to a potential new adjunctive strategy for patients whose antibodies attack the very receptors their muscles depend on.

The biology at the heart of the study begins at the neuromuscular junction, the microscopic relay where motor neurons hand their signals to muscle fibers. In the most common form of myasthenia gravis, autoantibodies bind the acetylcholine receptor clustered on the muscle side of this synapse. Those antibodies do more than simply block the receptor; many of them recruit the complement system, an ancient arm of immune defense designed to punch holes in the membranes of invading microbes. When complement is triggered at the synapse, it assembles the membrane attack complex, a pore-forming structure that tears into the postsynaptic membrane. The result is destruction of the synaptic folds, loss of acetylcholine receptors, inflammatory infiltration of macrophages into the endplate region, and ultimately a failure of neuromuscular transmission that patients experience as drooping eyelids, double vision, and life-threatening weakness of the muscles that control breathing and swallowing.

Complement activation follows a strictly ordered cascade, and C3 sits at its pivotal center. All major activation pathways converge on this protein, which, once cleaved, seeds opsonization of target tissue, amplifies the response through amplification loops, and drives the terminal assembly of the membrane attack complex. This convergence point has long made C3 an attractive therapeutic target, and drugs that inhibit it are already reshaping the treatment landscape of several complement-mediated disorders. What the new study adds is a direct test, in a rigorous animal model, of whether near-total elimination of circulating C3, achieved not with a blocking antibody but by silencing the gene that produces the protein in the liver, can prevent the structural and functional damage of myasthenia gravis during its acute phase.

The experimental approach relied on small interfering RNA, short synthetic RNA molecules that hijack the cell’s own RNA-induced silencing complex to degrade a specific messenger RNA before it can be translated into protein. To make sure the siRNA reached its destination, the researchers equipped it with a triantennary N-acetylgalactosamine ligand, a chemical handle that binds with high affinity to the asialoglycoprotein receptor abundantly displayed on hepatocytes. This GalNAc-targeting technology, which has already transformed the delivery of other liver-directed RNA therapies, allowed the compound to be administered by simple subcutaneous injection rather than intravenous infusion. Female Lewis rats received the C3-siRNA at different dosages before the researchers induced disease by passive transfer, injecting a monoclonal antibody directed against the acetylcholine receptor, a model known as passive transfer myasthenia gravis that reproduces the acute complement-mediated attack on the synapse without requiring the animals to mount their own autoimmune response.

The degree of target engagement was remarkable. Two administrations of the C3-siRNA at 30 milligrams per kilogram, spaced one week apart, reduced plasma C3 levels by more than 98 percent, pushing them below the detection limit of the assay. Against this near-total depletion of the central complement component, the researchers then challenged the animals with the pathogenic anti-receptor antibody and tracked the consequences with an unusually comprehensive battery of readouts: clinical scoring of weakness, direct measurements of muscle strength, electromyographic assessment of transmission failure at the junction, quantification of total and functional acetylcholine receptor levels in muscle, histological analysis of macrophage infiltration and sectional necrosis in the motor endplate region, and immunostaining for complement activation products deposited at the synapse.

The protective effect was evident across essentially every parameter measured. Treated animals showed significantly reduced deposition of the membrane attack complex at the neuromuscular junction, indicating that the terminal complement attack had been blunted. The characteristic tissue damage of the disease was correspondingly diminished: sectional necrosis within the endplate region was reduced, and the influx of macrophages that normally follows complement-mediated injury was attenuated. Skeletal muscle C3 messenger RNA, which is upregulated locally during the disease process, rose less in the treated animals. Importantly, the therapy partially preserved functional acetylcholine receptor levels, meaning that the receptors remaining at the synapse were better able to do their job of transmitting neuronal signals to the muscle. The structural preservation translated into function: muscle strength assessments and electromyography showed that the development of muscle weakness was effectively attenuated in the treated rats compared with controls.

Perhaps the most scientifically provocative observation came from what the treatment did not achieve. Despite the near-total elimination of C3 from the plasma, low levels of C3 activation products and membrane attack complex were still detectable specifically at the neuromuscular junction. This residual deposition is more than a technical footnote. It demonstrates that even a vanishingly small amount of circulating C3 is sufficient to sustain some degree of complement activation at the inflamed synapse, where local amplification mechanisms and the intense concentration of activating antibodies can make the most of scarce substrate. The authors interpret this as evidence of the powerful pathogenic potency of C3 in acetylcholine receptor-positive myasthenia gravis: the protein is so effective a driver of tissue injury that even trace quantities can leave a molecular fingerprint of damage at the junction.

That observation carries practical implications for how complement-targeted therapies might be deployed in patients. If near-complete suppression of plasma C3 leaves residual terminal pathway activity at the neuromuscular junction, then the therapeutic goal in myasthenia gravis may need to be either maximally deep C3 suppression, combination approaches that pair hepatic silencing with additional inhibition at the tissue level, or careful biomarker monitoring of complement deposition at the synapse itself rather than relying solely on systemic measures. At the same time, the study shows that the degree of protection achieved with hepatic silencing alone was already substantial, preserving receptor function and blunting weakness in the acute disease phase, which supports the idea that C3 silencing could serve as an adjunctive therapy layered onto existing immunosuppressive regimens rather than replacing them outright.

The work also illustrates how the tools of molecular medicine are being repurposed for organ-specific immunology. Rather than designing a protein drug to neutralize C3 in the bloodstream, the team used a GalNAc-conjugated siRNA to instruct the liver itself to stop making the protein, achieving durable, deep, and convenient subcutaneously delivered target reduction. This strategy builds on the broader success of RNA interference therapeutics in hepatic targets and suggests that complement proteins synthesized primarily by the liver are well suited to this modality. For a disease like myasthenia gravis, where chronic immunosuppression carries significant long-term burdens and where existing complement inhibitors require frequent intravenous administration, a long-acting subcutaneous gene-silencing approach could meaningfully change the treatment calculus, although the authors are careful to frame the current results as preclinical support for a potential adjunctive strategy rather than a validated therapy.

As with any animal study, the path from Lewis rats to patients runs through the usual gauntlet of safety, dosing, and clinical trial design, and the passive transfer model captures the acute effector phase of the disease rather than the full chronic autoimmune process that unfolds in patients. Nevertheless, the study delivers a clear and technically rigorous message: C3 is a dominant and remarkably potent driver of the complement-mediated destruction of the neuromuscular junction in antibody-positive myasthenia gravis, silencing its hepatic production protects receptor levels, synaptic architecture, and muscle function, and even the faint residual complement activity that survives near-total depletion underscores how aggressively this pathway must be restrained. For a disease in which the immune system’s own microbial-killing machinery turns against the synapse, teaching the liver to hold that machinery back may prove to be one of the more consequential therapeutic ideas to emerge from complement research in recent years.

Subject of Research: Complement C3 gene silencing as a therapy for complement-mediated neuromuscular junction damage in myasthenia gravis

Article Title: C3 complement silencing prevents acetylcholine receptor loss and reduces complement activation in the rat passive transfer myasthenia gravis model

Article References: Schöttler, A. K., Mané-Damas, M., Arets, B., Peng, S., Molenaar, P. C., De Baets, M. H., Claessen, S. M. H., Barbour, T., Richardson, E., Eyerman, D. J., Scheibler, L., Losen, M., & Martinez-Martinez, P. (2026). C3 complement silencing prevents acetylcholine receptor loss and reduces complement activation in the rat passive transfer myasthenia gravis model. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08832-5

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08832-5

Keywords: myasthenia gravis, complement C3, neuromuscular junction, small interfering RNA, GalNAc delivery, membrane attack complex, acetylcholine receptor, passive transfer model, complement inhibition, gene silencing, autoimmune disease, Lewis rats