Section 01
What it's used for
Gene Therapy Trial in Becker MD
An early-stage gene therapy trial gave AAV-follistatin to people with Becker muscular dystrophy. They walked 58-125 meters farther in 6 minutes and had better muscle function. A Duchenne group was dosed, but results aren't published yet.
▸Clinical wording
Phase 1/2a gene therapy trials using AAV-follistatin in Becker muscular dystrophy reported improved 6-minute walk test distances (58-125 meters) and muscle function. A Duchenne muscular dystrophy arm of the trial was registered and dosed, but no peer-reviewed results for that Duchenne cohort have been published.
Muscle Wasting Research
Follistatin is being studied for age-related muscle loss, severe illness-related wasting, and muscle loss from inactivity. It blocks myostatin, a protein that limits muscle growth, which may help build muscle even during tissue breakdown.
▸Clinical wording
Research for sarcopenia, cachexia, and disuse atrophy. Follistatin's myostatin-blocking mechanism promotes muscle growth even in catabolic conditions.
Fertility Hormone Research
Researchers are studying how the balance between two related proteins, activin and follistatin, controls release of the hormone FSH and growth of ovarian follicles — work that could matter for fertility treatments.
▸Clinical wording
Activin/follistatin balance regulates FSH secretion and follicular development, with implications for fertility treatment.
Blood Sugar and Insulin
Researchers observed that follistatin-driven increases in muscle mass improve how the body clears blood sugar and responds to insulin, since more muscle tissue gives glucose more places to be absorbed and used.
▸Clinical wording
Follistatin-induced muscle mass increase enhances glucose disposal and insulin sensitivity through increased metabolic sink tissue.
Section 02
Mechanism of Action
Wrapping growth blockers so they cannot signal
- Crystal structures show two follistatin molecules encircling the ligand pair and burying a third of its residues.
- One follistatin end mimics a receptor motif and occupies that site, covering both receptor surfaces.
- With myostatin that end rearranges its shape, which appears to set which ligands are blocked.
- These are structural and cell-free observations rather than results in a living animal.
▸Clinical wording
Structural neutralisation of activin receptor type II ligands
Crystallography of the follistatin:activin complex shows two follistatin molecules encircling the ligand dimer and burying about a third of its residues; the follistatin N-terminal domain adopts a fold that mimics a universal type I receptor motif and occupies that site, so both type I and type II receptor surfaces are covered. The myostatin:follistatin-288 structure adds that this N-terminal domain rearranges conformationally to accommodate myostatin, which appears to set antagonist specificity. In cell-free assays the purified myostatin C-terminal dimer binds ActRIIB and, more weakly, ActRIIA, and follistatin blocks that binding. These are structural and in vitro observations.
Removing a standing brake on muscle
- Three muscle-limiting proteins bind one receptor, which relays a signal through to the cell nucleus.
- In rodent muscle that signal raises two protein-breakdown tags and weakens the growth signalling chain.
- It also lowers a mitochondrial regulator and competes with the parallel growth signal for a shared partner.
- Trapping those proteins removes this standing input rather than adding a growth signal of its own.
▸Clinical wording
Loss of ActRIIB-ALK4/5-Smad2/3 output in muscle
Myostatin, activin A and GDF11 bind ActRIIB, which recruits and transphosphorylates ALK4/ALK5; the type I receptor then phosphorylates Smad2/3, which oligomerise with Smad4 and enter the nucleus. In rodent muscle this output raises the E3 ubiquitin ligases MuRF1 and MAFbx/atrogin-1, attenuates Akt/mTOR/p70S6K signalling, downregulates PGC1-alpha and competes with hypertrophic Smad1/5/8 for shared Smad4, while Smad7 and SMURF1/2 provide feedback shutdown. Sequestering the ligands removes this standing input rather than adding a growth signal of its own.
Building protein through a growth switch
- A virus delivering the follistatin gene into mouse muscle, not the peptide itself, raised mass and force.
- Protein synthesis and the growth switch rose, and blocking that switch cancelled both effects.
- Forcing the opposing signal on prevented growth, placing it upstream of this arm.
- Growth persisted in myostatin-free animals, so it is not simply relief from myostatin.
▸Clinical wording
Smad3-gated Akt/mTOR/S6K protein synthesis
An AAV6 vector expressing follistatin-288 delivered to mouse skeletal muscle increased muscle mass and force-producing capacity together with higher protein synthesis and mTOR activation; both effects were attenuated by mTOR inhibition and by deletion of S6K1/2. Constitutively active Smad3 prevented the growth and suppressed follistatin-induced Akt/mTOR/S6K signalling, placing Smad3 upstream of this arm. The response persisted with myostatin overexpression and in myostatin-null animals, so it is not simply relief from myostatin. Mouse model, viral gene delivery rather than peptide.
It blocks more than one muscle brake
- Adding a follistatin gene to myostatin-free mice doubled muscle again, reaching roughly four times normal.
- That implies it also neutralises other proteins that bind the same receptor family.
- Myostatin-free gains came from more fibres and thicker fibres, while follistatin gains came mainly from thickening.
- Growth occurred without satellite cell fusion or added nuclei, and deleting the receptor in fibres alone sufficed.
▸Clinical wording
Ligands beyond myostatin and the myofiber as target cell
A follistatin transgene on a myostatin-null background doubled muscle weights again, producing mice with roughly four times normal muscle, which implies follistatin also neutralises other ActRII ligands such as activins and GDF11. In that study myostatin-null gains involved both fiber number (about 48%) and fiber diameter (about 19%), while follistatin transgenics gained mainly by hypertrophy. Blockade of the pathway also produced hypertrophy in mice lacking syndecan-4 or Pax7, without satellite-cell proliferation, fusion or added myonuclei, and myofiber-specific Acvr2b deletion alone was sufficient.
Dragging blockers to the cell for disposal
- One follistatin variant sticks to sugar chains on the cell surface while the other does not.
- In rat pituitary cells that variant pulled activin onto the surface and sped its breakdown inside.
- Blocking the sugar chains or the disposal compartment abolished the effect.
- Structures show bound myostatin creates a strongly positive surface with much higher affinity for those sugars.
▸Clinical wording
Heparan sulfate binding and ligand clearance
The FS288 splice variant binds cell-surface heparan sulfate proteoglycans with high affinity while FS315 does not. In primary rat pituitary cells FS288 drove activin A onto the cell surface and accelerated its internalisation and lysosomal degradation, an effect abolished by heparan sulfate, chloroquine and lysosomal enzyme inhibitors. Crystallography showed that myostatin bound to Fst288 creates a continuous electropositive surface with markedly higher heparin affinity, and that both isoforms enhance myostatin degradation. The same activin-clearing action underlies follistatin's original role in pituitary FSH regulation.
Section 03
Biological Pathways
- Structural neutralisation of ActRII ligandsCrystal structures show two follistatin molecules encircling the ligand dimer, burying about a third of its surface; the N-terminal domain mimics a type I receptor motif, blocking myostatin binding to ActRIIB.
- Loss of ActRIIB-ALK4/5-Smad2/3 signallingMyostatin, activin A and GDF11 normally bind ActRIIB to phosphorylate Smad2/3, raising MuRF1 and MAFbx, attenuating Akt/mTOR/p70S6K and downregulating PGC1-alpha; follistatin removes this standing atrophy signal.
- Smad3-gated Akt/mTOR/S6K protein synthesisIn mouse muscle, viral follistatin-288 raised protein synthesis and mTOR activation, blocked by mTOR inhibition and S6K1/2 deletion; constitutively active Smad3 prevented the growth even in myostatin-null animals.
- Heparan sulfate-driven ligand clearanceThe FS288 splice variant binds cell-surface heparan sulfate proteoglycans and drove activin A into accelerated internalisation and lysosomal degradation in pituitary cells, underlying its role in FSH regulation.
Section 04
Dosage Information
315 or 344 amino acids (FS315 and FS344 isoforms)| Route / system | Context | Range studied | Limitation |
|---|---|---|---|
| Intramuscular — ACE-083 follistatin-Fc | Randomised phase 2 in two muscle-wasting diseases | 150–240 mg per muscle every 3 weeks, up to 5 doses; the controlled part used 240 mg per muscle on both sides, in biceps or shin | Built to stay inside the injected muscle and dosed in milligrams per muscle. Volume rose over 15% with no gain in function, and the programme closed in 2019. |
| Intramuscular — gene transfer | Trials in muscular dystrophy and myositis | A virus carrying the follistatin gene: 3 × 10¹¹ or 6 × 10¹¹ copies/kg per leg in six patients, 6 × 10¹¹ into both thighs in six others | A dose in gene copies: the muscle itself then makes follistatin for years. It converts into no amount of injected protein; twelve patients, none blinded. |
| Intravenous — tracer study in rats | Tracking a labelled dose in rats | 1 µg of labelled follistatin per rat: blood level halved in 4.0 minutes, then every 130.8 minutes; 9% was in the liver within 2 hours | A tracer amount, not a treatment — and a ceiling for the whole class: injected follistatin is swept into the liver within minutes, so micrograms hold no level. |
| Subcutaneous — self-administration | Circulating practice, vials sold as follistatin 344 | 100 µg a day in 10–30 day cycles — about 1.1–1.4 µg/kg for a 70–90 kg adult; 50–200 µg a day and 2–3 injections a week also circulate | Practice in circulation, not a finding: injected follistatin has no human dose at all, and these micrograms sit thousands of times below the trial doses. |
Results
Syringe Fill Level (100u syringe)
Set positive values for: Recommended dose per kg.
Research Use Only. This information is for educational and research purposes only. Not intended for medical advice or self-medication.
Section 05
Protocols
No protocols featuring this peptide yet. Browse All Protocols
Section 06
Stability & Storage
Lyophilised powder
Follistatin is a large glycoprotein that needs careful handling; the lyophilised form is kept at -20 °C or below, with no room-temperature storage described for the powder. It is reconstituted in a sterile buffer containing a carrier protein (0.1% BSA).
After reconstitution
Use the reconstituted solution within 7 days when kept at 2-8 °C. It is sensitive to freeze-thaw cycles, agitation, and temperature extremes, so repeated freezing, shaking, or heat exposure are avoided.
Section 07
Side Effects & Precautions
Follistatin has limited human safety data.
Theoretical concerns from its biology
These include potential effects on reproductive hormones (activin/FSH regulation), liver function, and uncontrolled tissue growth.
Safety data from gene therapy trials
Gene therapy trials show acceptable safety profiles in patients with muscular dystrophy.
Why the data stays incomplete
As a research compound, follistatin lacks comprehensive data on its side effects.
Section 08
Regulatory Status
FDA / United States
Not approved as a protein therapeutic
No recombinant or purified follistatin product holds FDA approval; material sold outside clinical research carries no drug-manufacturing oversight.
Gene therapy vector
Reached early-phase trials only
AAV1-FS344, a viral vector expressing follistatin, held orphan drug status for Duchenne/Becker muscular dystrophy and inclusion body myositis and completed phase 1/2a dosing trials by 2017 (NCT02354781); no later-phase trial has been registered since.
WADA
Prohibited under category S4.3
Follistatin was added to the Prohibited List in 2019 as an agent preventing activin receptor IIB activation — the mechanism by which it blocks myostatin — banned at all times for competing athletes.
A gene-therapy programme reaching early trials is not the same as an approved treatment, and none of this changes the sport ban. Regulatory status differs between jurisdictions and changes over time — check the current documents of your own regulator and sport authority before relying on any of this.
Section 09
Research Studies
- [1]The structure of the follistatin:activin complex reveals antagonism of both type I and type II receptor bindingThompson TB, Lerch TF, Cook RW, Woodruff TK, Jardetzky TS. · Developmental Cell · 2005
- [2]The structure of myostatin:follistatin 288: insights into receptor utilization and heparin bindingCash JN, Rejon CA, McPherron AC, Bernard DJ, Thompson TB. · The EMBO Journal · 2009
- [3]Regulation of myostatin activity and muscle growthLee SJ, McPherron AC. · Proceedings of the National Academy of Sciences · 2001
- [4]Myostatin/Activin Receptor Ligands in Muscle and the Development Status of Attenuating DrugsRodgers BD, Ward CW. · Endocrine Reviews · 2022
- [5]Follistatin-mediated skeletal muscle hypertrophy is regulated by Smad3 and mTOR independently of myostatinWinbanks CE, Weeks KL, Thomson RE, et al. · Journal of Cell Biology · 2012
- [6]Quadrupling muscle mass in mice by targeting TGF-beta signaling pathwaysLee SJ. · PLoS ONE · 2007
- [7]Role of satellite cells versus myofibers in muscle hypertrophy induced by inhibition of the myostatin/activin signaling pathwayLee SJ, Huynh TV, Lee YS, et al. · Proceedings of the National Academy of Sciences · 2012
- [8]A novel role of follistatin, an activin-binding protein, in the inhibition of activin action in rat pituitary cells: endocytotic degradation of activin and its acceleration by follistatin associated with cell-surface heparan sulfateHashimoto O, Nakamura T, Shoji H, Shimasaki S, Hayashi Y, Sugino H. · Journal of Biological Chemistry · 1997
- [9]Cell-type specific modulation of pituitary cells by activin, inhibin and follistatinBilezikjian LM, Justice NJ, Blackler AN, Wiater E, Vale WW. · Molecular and Cellular Endocrinology · 2012
- [10]A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophyMendell JR, Sahenk Z, Malik V, et al. · Molecular Therapy · 2015
Section 10
Frequently Asked Questions
In mice, follistatin gene therapy has produced 100 to 200% increases in muscle mass by neutralizing myostatin (the 'mighty mice' experiments), and in human gene-therapy trials for Becker muscular dystrophy it improved six-minute walk distances by 58 to 125 meters. But that is delivered by a virus that makes the muscle produce its own follistatin for years — it is not the same as injecting the protein. A rat tracer study found injected follistatin's blood level falls by half within about 4 minutes and is swept mostly into the liver within 2 hours, which is why injectable follistatin products have no human dosing trial behind them at all.
Circulating self-administration practice for injectable 'follistatin 344' is around 100 µg a day for 10 to 30 days, though 50 to 200 µg a day and two to three injections a week also circulate — none of this is based on a human trial. The actual clinical trials used entirely different units: a follistatin-Fc fusion protein was injected at 150 to 240 mg directly into a single target muscle every 3 weeks, and gene therapy delivered a virus at 3 to 6 ×10¹¹ copies per kilogram per leg. Neither converts into a microgram dose of injected native follistatin protein, because no such dose-finding study has ever been run.
No timeline exists for the injectable peptide products sold as follistatin — there is no human trial of injected native follistatin protein to reference for onset. The closest data point is a related follistatin-Fc fusion protein, dosed every 3 weeks for up to 5 doses in a controlled trial: muscle volume increased over 15% during that period, but with no corresponding gain in strength or function, and the program was discontinued in 2019.
There is no published evidence that follistatin causes cancer, but there is also very little human safety data of any kind to rule it out. Because follistatin blocks activin and other growth-regulating signals system-wide, not just myostatin in muscle, theoretical concerns raised include effects on reproductive hormone regulation, liver function, and unchecked tissue growth. The muscular dystrophy gene-therapy trials reported acceptable safety, but that involved localized muscle expression, not systemic protein injection, and no long-term cancer-surveillance study has been done for either approach.
Follistatin as an injectable protein is not FDA-approved for any use and is sold only as a research compound; gene-therapy versions are still investigational, tested under FDA IND status for muscular dystrophy. It is prohibited by WADA under category S4.2, myostatin inhibitors, for athletes in and out of competition.
No published research addresses hair loss with follistatin specifically. Its documented effects are on the TGF-β superfamily — myostatin and activin signaling in muscle, and activin/FSH regulation in the pituitary and reproductive tissue — a different pathway than the androgen-driven mechanism usually discussed for hair loss, but no study has actually tested it.
As a lyophilised powder it is kept at -20 °C or colder — no room-temperature storage window is described, reflecting how fragile this large glycoprotein is. It is reconstituted in a buffer containing a carrier protein to help stabilize it, and once mixed the solution should be used within 7 days at 2-8 °C; repeated freeze-thaw cycles, shaking, and temperature swings degrade it.