In CD-1 mice, siRNA conjugates targeting MSTN increase leg muscle area by 14.8%, while siRNA conjugates targeting ActRIIB increase it by 8.6%.
See the scientific wording
In CD-1 mice, MSTN-targeting siRNA conjugates produce greater muscle mass augmentation than ActRIIB-targeting siRNA conjugates, with a 14.8% increase in leg muscle area compared to an 8.6% increase for ActRIIB-targeting conjugates.
Correlational — new studies may shift this
ObservationalOne low-scoring study links this claim to the outcome, but causation is not established.
What the research says
1 study reviewedSupporting (1)
2185-LB: Antibody-siRNA Conjugate Targeting Myostatin Preserves Muscle Mass during GLP-1R Agonism
Case-Control StudyAnimal
In mice, a new muscle-growing treatment that targets myostatin made legs 14.8% bigger, while a similar treatment targeting ActRIIB only made them 8.6% bigger — so the myostatin one worked better, just like the claim says.
Contradicting (0)
No contradicting studies found yet
That doesn't mean it's settled — it just means no study has tested the opposite.
Quality-weighted scoring: we follow the GRADE framework — each study is rated High, Moderate, Low, or Very Low based on study design, methodology rigor, and risk of bias. A single high-quality RCT can outweigh several weaker observational studies.
Scores reflect study quality, not just count.
A special molecule delivers a genetic signal into muscle cells that turns off the myostatin gene. When myostatin is turned off, it stops blocking the signals that tell muscle cells to grow and make more protein. This causes muscle fibers to get bigger, leading to more muscle mass in the legs.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 1 supporting study
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In CD-1 mice, siRNA conjugates targeting MSTN increase leg muscle area by 14.8%, while siRNA conjugates targeting ActRIIB increase it by 8.6%.
Mechanism
1 studyTurning off the myostatin gene with a targeted genetic tool makes muscle cells grow bigger because it removes a natural brake on muscle growth. Targeting myostatin directly works better than blocking its receptor because it stops the brake signal at the source, not just at the door.
A special molecule delivers a genetic signal into muscle cells that turns off the myostatin gene. When myostatin is turned off, it stops blocking the signals that tell muscle cells to grow and make more protein. This causes muscle fibers to get bigger, leading to more muscle mass in the legs.
A conjugate binds to transferrin receptor 1 on the surface of skeletal muscle cells
The conjugate is internalized into muscle cells via receptor-mediated endocytosis
The siRNA component is processed by the RNA-induced silencing complex and degrades myostatin mRNA
Myostatin protein levels decrease, removing inhibition of the SMAD2/3 signaling pathway
De-repression of SMAD2/3 signaling increases muscle protein synthesis and myofiber hypertrophy
Evidence from Studies
Supporting (1)
Community contributions welcome
In mice, a new muscle-growing treatment that targets myostatin made legs 14.8% bigger, while a similar treatment targeting ActRIIB only made them 8.6% bigger — so the myostatin one worked better, just like the claim says.
Contradicting (0)
Community contributions welcome
Score Breakdown
No multi-axis breakdown available yet. The overall Pro / Against score above is the best signal.
- No clinical evidence is available; the score reflects mechanistic plausibility only.
What Would Prove This
Per GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this claim, ordered from strongest to weakest.
Systematic Review of MSTN vs. ActRIIB siRNA Conjugates for Muscle Mass Augmentation in Murine Models
Systematic review and meta-analysis of all peer-reviewed studies comparing MSTN-targeting and ActRIIB-targeting siRNA conjugates in CD-1 mice, with standardized measurement of leg muscle area, controlled for delivery method, dose, and duration
Randomized Double-Blind Trial of MSTN vs. ActRIIB siRNA Conjugates for Leg Muscle Area Increase in CD-1 Mice
Randomized, double-blind, placebo-controlled trial in CD-1 mice comparing MSTN-targeting siRNA conjugates to ActRIIB-targeting siRNA conjugates, with leg muscle area measured by imaging after a standardized treatment period
Cohort Study Comparing Long-Term Muscle Area Changes in CD-1 Mice Treated with MSTN vs. ActRIIB siRNA Conjugates
Prospective cohort study following CD-1 mice treated with either MSTN-targeting or ActRIIB-targeting siRNA conjugates over time, measuring leg muscle area at multiple time points without randomization
Comparative Study of MSTN and ActRIIB siRNA Conjugates on Leg Muscle Area in CD-1 Mice
Single-center study in CD-1 mice comparing two groups: one treated with MSTN-targeting siRNA conjugates, one with ActRIIB-targeting siRNA conjugates, measuring leg muscle area via imaging at endpoint
In Vitro Comparison of MSTN and ActRIIB siRNA Conjugate Effects on Myoblast Proliferation and Differentiation
In vitro experiment comparing the effects of MSTN-targeting and ActRIIB-targeting siRNA conjugates on proliferation and differentiation of murine myoblasts, measuring markers of muscle growth