ACE 031 is a recombinant fusion protein combining the extracellular, ligand-binding domain of the activin receptor type IIB (ActRIIB) with the Fc portion of human immunoglobulin G. It is studied as a “ligand trap” that binds and neutralises myostatin and activin A before these naturally occurring proteins can engage their membrane-bound receptors on skeletal muscle, a mechanism reported to relieve the normal negative regulation these ligands impose on muscle growth. ACE 031 is of particular research interest because it was previously developed and studied in human clinical trials for Duchenne muscular dystrophy, giving it an unusually well-characterised pharmacological and safety profile for a research-grade protein. This article reviews its structure, mechanism, the published preclinical and clinical literature, research applications and the handling requirements relevant to a laboratory setting.
What is ACE 031?
Unlike the short synthetic peptides covered elsewhere in research-chemical catalogues, ACE 031 is a larger recombinant fusion protein, not a peptide in the conventional sense. It is constructed from the extracellular, ligand-binding domain of ActRIIB, a type II receptor in the TGF-β superfamily, genetically fused to the Fc (crystallisable fragment) domain of human IgG1. The Fc portion is reported to serve two purposes: it promotes dimerisation of the fusion protein, since IgG Fc domains associate through disulfide bonds in the hinge region, and it extends the protein’s circulating half-life relative to the ActRIIB extracellular domain alone, by a mechanism related to Fc receptor recycling used by native antibodies.
ActRIIB is the principal high-affinity receptor for myostatin (also known as growth differentiation factor-8, or GDF-8), the TGF-β superfamily member best known as a negative regulator of skeletal muscle mass, and also binds activin A and several other TGF-β family ligands with lower affinity. ACE 031 was developed by Acceleron Pharma as a soluble decoy version of this receptor, designed to intercept circulating myostatin and activin A and prevent them from reaching native, membrane-bound ActRIIB on muscle tissue. Its development and initial human pharmacology were reported by Attie and colleagues in Muscle & Nerve in 2013 (Attie et al., 2013, PubMed).
Mechanism of action
Myostatin and activin A normally bind membrane-bound ActRIIB receptors on skeletal muscle cells, triggering recruitment of a type I receptor co-receptor and activation of intracellular Smad2/3 signalling. This Smad2/3 pathway is reported to suppress muscle protein synthesis pathways, including Akt/mTOR signalling, and to promote muscle protein degradation, together constraining muscle fibre growth; myostatin in particular is well established in the literature as a potent negative regulator of muscle mass, since animals and humans with loss-of-function myostatin mutations show pronounced muscle hypertrophy.
ACE 031 acts upstream of this receptor-level signalling, as a soluble decoy or “ligand trap.” Because its ActRIIB extracellular domain retains the ligand-binding properties of the native receptor but is not membrane-anchored and has no intracellular signalling domain, circulating ACE 031 is reported to bind myostatin and activin A in the bloodstream, sequestering them before they can engage native membrane ActRIIB and trigger the Smad2/3 suppressive pathway. The result, reported across the preclinical and clinical studies described below, is an increase in muscle mass attributed to relief of this normal inhibitory signalling, rather than to direct stimulation of muscle growth through an independent anabolic pathway.
Because ActRIIB also binds other TGF-β superfamily ligands with lower affinity, including some bone morphogenetic proteins, ACE 031’s ligand-trap mechanism is reported in the literature to be less selective than antibody-based approaches that target myostatin alone, a distinction relevant to interpreting both its efficacy and its reported safety profile in the clinical studies summarised below.
What the research shows
The initial human pharmacology of ACE 031 was reported by Attie and colleagues in Muscle & Nerve in 2013, in a single ascending-dose study conducted in healthy volunteers. The investigators reported dose-dependent increases in markers consistent with the proposed mechanism, alongside observations of epistaxis (nosebleeds) and telangiectasia (dilated small blood vessels, particularly of the skin and gums) at higher doses, adverse findings that became central to the compound’s subsequent clinical development history (Attie et al., 2013, PubMed).
A subsequent randomised, placebo-controlled Phase 2 clinical trial was reported by Campbell and colleagues in Muscle & Nerve in 2017, examining ACE 031 in ambulatory boys with Duchenne muscular dystrophy. The study reported trends toward increased lean body mass and an attenuation of the decline in thigh muscle volume and six-minute walk distance, measures of disease progression, in the treated group relative to placebo, within the specific trial population studied. The same adverse events, nosebleeds and skin telangiectasias, were again observed in this trial population and, alongside the earlier healthy-volunteer findings, led to the clinical hold and subsequent discontinuation of ACE 031’s development programme.
More recently, a preprint study examining ACE-031 in the common marmoset, a non-human primate, was reported in 2025. Marmosets were randomised to receive ACE-031 or a vehicle control for 14 weeks, and the investigators reported significantly greater absolute and specific isometric twitch force in a treated hindlimb muscle (the extensor digitorum longus) relative to control animals, alongside increases in muscle mass, extending the preclinical efficacy evidence for ACE-031’s mechanism into a non-human primate model (marmoset study, 2025, PubMed).
A substantial additional body of preclinical work in mouse models of Duchenne muscular dystrophy, including the mdx mouse, has examined ActRIIB blockade more broadly, reporting improvements in muscle mass and contractile force measures consistent with the mechanism described above. Because this rodent literature spans multiple research groups and related but non-identical ActRIIB-targeting approaches, readers wanting further primary detail on specific mouse studies should consult a review of myostatin and activin receptor blockade in muscular dystrophy models rather than rely on a single summarised study here.
Research applications
In the laboratory, ACE 031 is used mainly as a tool for studying myostatin and activin A signalling and its role in skeletal muscle mass regulation. Cell-based assays using myostatin- or activin-responsive reporter systems are used to characterise ACE 031’s ligand-binding and neutralisation activity, often in comparison with other ActRIIB-targeting approaches or myostatin-selective antibodies to examine differences in ligand specificity.
Rodent and non-human primate models of muscle mass and function, following the designs used in the marmoset and mdx mouse studies referenced above, remain the standard approach for examining ACE 031’s effects on lean body mass, muscle fibre size and isometric contractile force. Because ACE 031 has an unusually complete human clinical pharmacology record for a research-grade protein, including the dose-ranging and adverse-event data from its healthy-volunteer and Duchenne muscular dystrophy trials, it is also used as a reference compound in comparative research examining the trade-off between ligand-trap breadth (binding multiple TGF-β superfamily ligands) and target selectivity in muscle-wasting disease research more broadly.
Because the vascular adverse effects reported in its clinical trials, nosebleeds and telangiectasia, have been attributed in the literature to blockade of other ActRIIB ligands involved in vascular biology rather than to myostatin neutralisation itself, ACE 031 is also referenced in research examining the physiological roles of these non-myostatin ActRIIB ligands, an area of mechanistic interest distinct from its original muscle-mass research application.
Purity, storage and handling
Because degradation accelerates once reconstituted, batch-level verification matters more here than with more stable peptides. UK laboratories sourcing ACE 031 should expect a batch-specific certificate of analysis and lyophilised storage at -20°C, and those comparing suppliers should look for the same documentation from any best peptides supplier UK they consider.
Because ACE 031 is a larger, glycosylated fusion protein rather than a short synthetic peptide, purity verification differs somewhat from the single-peak HPLC assays used for peptides under roughly 50 residues. Size-exclusion chromatography is used to confirm correct dimerisation via the Fc domain and to detect aggregation, while reversed-phase HPLC and SDS-PAGE help confirm identity and purity relative to fragmented or incompletely processed protein. Mass spectrometry confirms the expected mass of the glycosylated fusion protein, which can vary somewhat between production batches depending on glycosylation pattern. A batch-specific certificate of analysis, rather than a generic product datasheet, is what links a physical vial to those results and allows unexpected experimental data to be traced back to a defined lot, which matters in particular for a glycoprotein where batch-to-batch glycosylation variability can affect activity.
Lyophilised ACE 031 should be kept sealed at -20°C for long-term storage, protected from moisture and light, and brought to room temperature before opening so that condensation does not enter the vial. Once reconstituted in sterile water or an appropriate buffer, the protein should be divided into single-use aliquots, held at 2–8°C only for short working periods, and otherwise kept frozen, since repeated freeze–thaw cycles risk aggregation and loss of activity in larger proteins of this kind. Aromatic residues within the structure are susceptible to photo-oxidation, so amber vials or foil-wrapped storage are sensible precautions during handling. Published reconstituted-stability data specific to research-grade ACE 031 are limited in the open literature, so laboratories should validate their own working window empirically, for example by comparing size-exclusion profiles and ligand-binding activity of fresh and aged aliquots.
Frequently asked questions
What is ACE 031 used for in research?
It is used mainly as a tool for studying myostatin and activin A signalling and their role in regulating skeletal muscle mass, in cell-based ligand-binding assays and in rodent and non-human primate models of muscle mass and contractile function. It is not evaluated here as a treatment, and this article makes no claims about use in humans.
Is ACE 031 a peptide?
Not in the conventional sense used elsewhere in research-chemical catalogues. ACE 031 is a larger recombinant fusion protein, combining the ActRIIB receptor’s extracellular ligand-binding domain with a human IgG Fc domain, and its handling, purification and analytical characterisation differ in some respects from those used for short synthetic peptides.
Was ACE 031 developed as a human medicine?
Yes, it was investigated in Phase 1 and Phase 2 human clinical trials, including a trial in boys with Duchenne muscular dystrophy, but its clinical development was discontinued after repeated observations of nosebleeds and skin telangiectasia in treated participants. It was never approved as a medicine, and this article concerns laboratory research material only.
How should ACE 031 be stored once reconstituted?
Reconstituted ACE 031 should be divided into single-use aliquots, kept refrigerated only briefly and otherwise frozen, protected from light, and not subjected to repeated freeze–thaw cycles, which risk aggregation in larger fusion proteins of this kind. Because specific published stability data are limited, laboratories should confirm their own storage window empirically, for example with size-exclusion chromatography comparisons of fresh and aged aliquots.
The ACE 031 discussed in this article is supplied for in-vitro and in-vivo laboratory research only. It is not intended for human or veterinary use, and nothing in this article should be read as guidance on administration to people or animals.
