ACE-031 Actions on Muscle Cells, Bone Cells, and Fat Cells

ACE-031 is a complex protein structure consisting of a receptor and an antibody. It appears to act as a soluble decoy version of the activin receptor type IIB (ActRIIB), as the receptor is linked to an IgG1 Fc domain. The result is an ActRIIB IgG1 Fc fusion protein that is believed to act as a decoy and may potentially mitigate different ligands from attaching to the endogenous ActRIIB on target cells. Endogenous ActRIIB is a transforming growth factor-beta (TGF beta) family receptor, which interacts with TGF beta ligands such as myostatin (GDF8), GDF11, and activins A/B.

According to researchers such as McPherron et al. the superfamily in question “encompasses a large group of growth and differentiation factors playing important roles in regulating […] development and in maintaining tissue homeostasis.”⁽¹⁾ By binding myostatin (GDF8), GDF11, and activins A/B with high affinity, ACE-031 is thought to mitigate ligand engagement with endogenous ActRIIB on target cells thereby removing their mitigatory potential on growth, differentiation, and remodeling programs in multiple tissues. Currently, the peptide is being researched specifically for removing the mitigatory potential on muscle cells, fat cells, and bone cells.

 

Research

ACE-031 and Muscle Cells

Research by Campbell et al. suggests that ACE-031 binds myostatin and related ligands of the TGF-β superfamily, and thus, it may apparently mitigate potential engagement with endogenous ActRIIB.⁽²⁾ At the cellular level, ActRIIB mitigation may interfere with the activation of Smad2/3 signaling, a pathway normally responsible for suppressing muscle cell growth and satellite cell activity. Contributing to this type of mitigation may, at least in part, release satellite cells from quiescence, thereby allowing their proliferation and self-renewal.

This mechanism may underlie an apparent increase in myofiber size and the preservation of contractile tissue. Also, the researchers reported observations of reduced intramuscular fat in laboratory settings, suggesting a possible diversion of mesenchymal precursors away from adipogenic differentiation. These apparent actions on muscle cells may be mediated, particularly by the blockade of the binding between myostatin (GDF8) and ActRIIB, according to the research by Attie et al.⁽³⁾ Therefore, this may be the main mechanism of ACE-031 stimulating muscle cell hypertrophy.

Further research by Cadena et al. confirms that hypertrophy rather than hyperplasia may be the main mechanism via which ACE-031 may interact with muscle cells. This type of research sometimes suggests that while myostatin (GDF8) may be a key element in the mechanism, blocking the other ligands may also play some role.⁽⁴⁾ Unlike selective myostatin blockade, which appears to act more strongly on type II fibers, ACE-031 seemingly promoted hypertrophy across both slow-twitch (type I) and fast-twitch (type II) fibers.

Cadena et al. apparently observed that the “mean fiber cross-sectional area increased by 22 and 28% in type I and II fibers, respectively.” Therefore, these researchers appear to be suggesting that the compound possibly induces hypertrophy in a non-fiber-type-selective manner. In other words, ACE-031 apparently promotes hypertrophy across both oxidative (type I) and glycolytic (type II) fibers, indicating that its implication is not tied to one fiber type’s baseline metabolism. Moreover, further research by Bechir et al. suggests that the peptide enlarges contractile tissue and augments force.⁽⁵⁾

These scientists comment that hypertrophy was accompanied by higher basal oxygen consumption and energy expenditure, suggesting a metabolic upshift. They concluded that the ACE-031 induced “ActRIIB [mitigation] increased muscle volume (+33%) without changing fiber-type distribution, and increased basal animal oxygen consumption (+22%) and energy expenditure (+23%). Bechir et al. also observed that the “maximum and total absolute contractile forces were larger (+40 and 24%, respectively)” following ACE-031 experimentation.

ACE-031 and Bone Cells

The previously mentioned research by Campbell et al. suggests that bone tissue also appears to be responsive to the peptide.⁽²⁾ As mentioned, ActRIIB and consequently ACE-031 are suggested to interact not only with myostatin but also with activins and growth differentiation factors that play roles in skeletal metabolism. By intercepting these ligands, ACE-031 may indirectly modulate osteoblast and osteoclast activity, leading to alterations in bone mineral deposition.

The apparent increases in mammalian bone density seen in experimental observations may therefore stem from a shift in signaling balance that favors anabolic over catabolic processes within bone tissue. Research by Attie et al. supports the assertion that an increase in markers may be associated with a metabolic shift towards bone formation, such as an increase in the levels of bone-specific alkaline phosphatase (BSAP).

In contrast, the C-terminal telopeptide of type I collagen (CTX) levels decreased.⁽³⁾ Interpreted at the cell level, this pattern is compatible with better-supported osteoblast activity and attenuated osteoclast-mediated resorption. Because activins and certain GDFs participate in osteoblast/osteoclast crosstalk, their sequestration by the decoy receptor ACE-031 may potentially rebalance osteogenic and osteocatabolic signaling. According to research by Puolakkainen et al.⁽⁶⁾ activin A may be a prime candidate mediator of the potential decoy actions of ACE-031 on bone cells, but contributions from other ligands remain possible.

These researchers also confirm that by blocking activin signaling through ActRIIB-Fc, bone tissue appears to undergo structural and molecular changes. This type of research points toward both reduced breakdown and better-supported formation. When observing the potential of the peptide on trabecular structures, the authors suggested that bone volume fraction increased by roughly 80%, and the number of trabeculae rose by about 70%. These trabeculae were not only more numerous but also positioned closer together, creating a denser network. In parallel, volumetric mineral density also appeared to be higher, and separation between trabeculae appeared to be reduced, consistent with a more compact microarchitecture.

Based on the observations of the researchers, cortical regions may have also thickened, with thickness increasing by about 14%, and total cross-sectional area expanded by around 10%. Mechanistically, the researchers also reported that osteoblast-associated genes such as type I collagen, osteopontin, and dentin matrix protein 1 were upregulated, consistent with stimulated bone formation.

Evaluations of bone structures conducted in laboratory settings may demonstrate higher maximum force tolerance and increased stiffness, pointing to stronger and more resilient tissue. Taken together, the data indicates that blocking activin A-related signaling may tip the balance of bone remodeling toward formation and consolidation, producing cellular structures that are denser, thicker, and mechanically stronger.

ACE-031 and Fat Cells

Researchers such as Zhang et al. suggest that myostatin mitigation by agents like ACE-031 may not only stimulate muscle cell hypertrophy, but also support the metabolism of adipose cells in mammalian models into a shift toward a “brown-like” (beige) state.⁽⁷⁾ The researchers posit this as they observed an apparent upregulation of thermogenic and mitochondrial genes (Ucp1, Ucp2, Ucp3, Cidea, Dio2, Cpt1b) together with transcriptional drivers of oxidative metabolism and adipocyte remodeling (Pparα/β/γ and Pgc-1α/β).

Morphologically, adipocytes appeared to become smaller and multilocular, which is consistent with better-supported mitochondrial content and uncoupled respiration. A COX-2–prostaglandin axis (elevated Ptgs2/Cox-2, Ptges/Ptges2, and increased release of PGE₂ and 6-keto-PGF₁α from adipose explants) is posited as one upstream driver of this beige conversion, mirroring β-adrenergic-like cues that promote Ucp1 expression and thermogenic competence.

This net result may be greater heat dissipation and energy expenditure within white fat depots observed in mammalian models. This may contribute to reduced adipose mass under lipid surplus conditions. The aforementioned research by Attie et al. also observed an apparent shift is adipose–tissue–related signals.⁽³⁾ Notably, the researchers commented that there may be an increase in adiponectin levels and a decrease in leptin levels following ACE-031 experimentation.

From a cellular perspective, findings like these may indicate altered adipocyte metabolism and adipokine secretion. This may potentially reflect changes in adipocyte differentiation or lipid turnover when ActRIIB-ligand signaling is curtailed. The researchers also observed a reduction in fat cell mass under ACE-031 exposure, which may align with a tissue-level environment favoring reduced adipogenesis or better-supported lipolysis.

NOTE: These products are intended for laboratory research use only. This peptide is not intended for personal use. Please review and adhere to our Terms and Conditions before ordering.

 

References:

1. McPherron AC, Lawler AM, Lee SJ. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member. Nature. 1997 May 1;387(6628):83-90.
2. Campbell C, McMillan HJ, Mah JK, Tarnopolsky M, Selby K, McClure T, Wilson DM, Sherman ML, Escolar D, Attie KM. Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: Results of a randomized, placebo-controlled clinical trial. Muscle Nerve. 2017 Apr;55(4):458-464.
3. Attie KM, Borgstein NG, Yang Y, Condon CH, Wilson DM, Pearsall AE, Kumar R, Willins DA, Seehra JS, Sherman ML. A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers. Muscle Nerve. 2013 Mar;47(3):416-23.
4. Cadena, S. M., Tomkinson, K. N., Monnell, T. E., Spaits, M. S., Kumar, R., Underwood, K. W., Pearsall, R. S., & Lachey, J. L. (2010). Administration of a soluble activin type IIB receptor promotes skeletal muscle growth independent of fiber type. Journal of applied physiology (Bethesda, Md. : 1985), 109(3), 635–642. https://doi.org/10.1152/japplphysiol.00866.2009
5. Béchir N, Pecchi E, Vilmen C, Le Fur Y, Amthor H, Bernard M, Bendahan D, Giannesini B. ActRIIB blockade increases force-generating capacity and preserves energy supply in exercising mdx mouse muscle in vivo. FASEB J. 2016 Oct;30(10):3551-3562.
6. Puolakkainen, Tero et al. “Treatment with soluble activin type IIB-receptor improves bone mass and strength in a mouse model of Duchenne muscular dystrophy.” BMC musculoskeletal disorders vol. 18,1 20. 19 Jan. 2017.
7. Zhang C, McFarlane C, Lokireddy S, Masuda S, Ge X, Gluckman PD, Sharma M, Kambadur R. Inhibition of myostatin protects against diet-induced obesity by enhancing fatty acid oxidation and promoting a brown adipose phenotype in mice. Diabetologia. 2012 Jan;55(1):183-93. doi: 10.1007/s00125-011-2304-4. Epub 2011 Sep 17. Erratum in: Diabetologia. 2015 Mar;58(3):643. PMID: 21927895.