Follistatin-344 (FS344) is an alternatively spliced form of follistatin, a protein that binds and neutralizes myostatin and activins. Most of the published work is in mice, non-human primates and one small gene-transfer trial. It does not describe an injected vial of peptide. This guide sets out what the studies tested, where the evidence stops, how researchers verify a vial before it enters a study, and what Australian rules apply.
TL;DR
- FS344 is studied as a myostatin antagonist. Follistatin competitively blocks myostatin and activin binding to ActRIIB receptors (Mendell et al., 2015).
- The key animal and human studies used AAV gene delivery of FS344, not recombinant protein. Their results do not transfer to a research vial.
- Rigorous human safety data for unapproved peptides are scarce (Mendias & Awan, 2026).
- Before use in a study, check identity (mass spectrometry), purity (HPLC) and the batch Certificate of Analysis.
- In Australia, research-use-only status does not make a peptide a therapeutic good. Check TGA peptide rules before ordering.
Table of Contents
- What Follistatin-344 is
- How it is proposed to work
- What the published studies show
- Thymosin alpha-1 research in brief
- How researchers verify a peptide before use
- Storage and handling for laboratory use
- Australian rules researchers need to know
- Ordering for research
- FAQ
- Sources
What Follistatin-344 is
Follistatin is a secreted glycoprotein and a potent myostatin antagonist. It has been investigated for increasing muscle mass and strength. FS344 is one alternatively spliced form. A 2009 review reports that cleavage of its 29-amino-acid signal peptide produces FS315, the follistatin form found in circulation (Haidet and colleagues' review of myostatin inhibition).
This is why the name causes confusion. "FS344" can refer to:
- the gene sequence (cDNA) delivered by a viral vector
- the precursor protein, which is processed to FS315
- a synthetic or recombinant product sold for laboratory use
The literature is mostly about the first. Any claim built on it needs to say which one is meant.
How it is proposed to work
Myostatin and activins belong to the TGF-beta family and limit muscle growth through ActRIIB receptors. Follistatin neutralizes myostatin and components of the activin-inhibin complex by competitively inhibiting their binding to those receptors (Mendell et al., 2015).
Why FS344 rather than other isoforms
The same paper explains why FS344/FS315 is preferred over FS317 and FS288 for muscle-directed work. FS315 is serum-based and has roughly tenfold lower affinity for activin than FS288. That reduces concern about interference with FSH-related reproductive signalling. This is a design rationale in the literature, not a demonstration of safety in people using a peptide product.
| Feature | What the literature reports |
|---|---|
| Target | Myostatin, activins |
| Receptor pathway | ActRIIB (competitive inhibition) |
| Circulating form | FS315, after signal-peptide cleavage |
| Activin affinity | About tenfold lower than FS288 |
| Main delivery in published studies | AAV vector, intramuscular |
What the published studies show
Non-human primate study
The 2010 Science Translational Medicine study tested AAV1-FS344. The vector was injected into quadriceps muscle, where it expressed follistatin. The authors reported durable increases in muscle size and strength, with no abnormal morphology or function of key organs during the study (Kota et al.). The intervention was gene delivery. No vial of follistatin protein was injected.
Becker muscular dystrophy trial
The phase 1/2a trial (Mendell et al., 2015) delivered AAV1.CMV.FS344 by direct bilateral intramuscular quadriceps injections to six patients (trial report). Muscle cells were given DNA to produce the follistatin product. Patients did not receive recombinant FS344 protein as the active intervention.
Key limits of this study:
- six participants, open-label, no placebo arm
- the six-minute-walk test improved in two of three participants in each dose cohort
- follow-up reached up to 12 months for the low-dose cohort and six months for the high-dose cohort (Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy)
These results come from patients with a muscle disease, under clinical supervision. They say little about healthy gym populations or a research peptide.
Reading the evidence correctly
A 2026 review notes that many unapproved peptides show favorable tissue-repair and metabolic outcomes in animal models. It also states that rigorous human safety data are scarce and that potential for serious harm exists (Mendias & Awan, 2026). For FS344 this means a study design should treat animal and gene-transfer findings as the basis for mechanistic questions only.
Useful questions for a protocol:
- Is the research question about myostatin or activin signalling in a defined model?
- Is the test article recombinant protein, and does the cited prior work use the same form?
- What endpoints and controls are set before the vial is opened?
- Is the work covered by the institution's ethics and compliance approvals?
Thymosin alpha-1 research in brief
Readers who look into FS344 often look at thymosin alpha-1 (Tα1) next. The two are unrelated in mechanism. Tα1 is a 28-amino-acid peptide originally isolated from the thymus. It has been investigated for immune modulation, infections, malignancies and immune dysfunction. A comprehensive literature review describes toll-like receptor (TLR) activity, T-cell maturation and cytokine effects (Thymosin alpha 1: A comprehensive review).
The same discipline applies. Check which preparation a paper used, which model, and what the endpoints were before borrowing its conclusions. Immunology work also needs tighter documentation of identity and contaminants, since impurities can confound immune readouts.
How researchers verify a peptide before use
A vial label is a claim. The documents behind it are the evidence. A sound check covers four items.
Identity
Mass spectrometry confirms molecular mass and, with sequencing, amino acid sequence. Clinical-grade peptide protocols typically specify both: identity by mass spectrometry, purity by HPLC, and in some cases amino acid analysis to further confirm identity (example protocol).
Purity
HPLC separates the main peak from related impurities. Ask for the chromatogram, not only a percentage. A stated purity such as ≥99% means little without the method, the wavelength and the integration shown.
Batch traceability
The Certificate of Analysis (CoA) should carry a batch or lot number that matches the vial. Check the testing date, the laboratory and whether testing was in-house or third-party.
Labelling
The TGA says poorly labelled or unmarked peptide vials make ingredients and manufacturing safety impossible to verify. It lists contamination, uncertain dosing and exposure to unknown or harmful substances as risks (TGA media release, 19 June 2026). A vial with only a code and no ingredient or concentration information fails this check.
| Check | Document | Red flag |
|---|---|---|
| Identity | Mass spec report | No mass or sequence data |
| Purity | HPLC chromatogram | Percentage only, no trace |
| Traceability | CoA with batch number | Batch does not match vial |
| Labelling | Name, quantity, batch on vial | Code-only label |
Storage and handling for laboratory use
Lyophilized peptides are generally handled under controlled conditions and reconstituted only as the protocol requires. Follow the storage guidance on the supplier's documentation and your institution's SOPs. Record the reconstitution date, diluent and storage temperature for each vial. Keep aliquot records so that a result can be traced to a batch.
Australian rules researchers need to know
Research-use-only labelling does not remove a product from regulatory scrutiny. The TGA reports serious adverse effects associated with unapproved peptide products, including liver damage, severe allergic reactions requiring hospitalisation, and inflammation (TGA, 19 June 2026).
Points that matter at the border and in the lab:
- Personal Importation Scheme. Individuals may import up to a three-month supply of unapproved medicines for personal or immediate family use, with a valid Australian prescription if the medicine is prescription-only (TGA, Personal Importation Scheme). This is a pathway for treatment, not for laboratory research stock.
- Labelling at the border. The TGA says poorly labelled peptide imports, including products marked only with codes or missing ingredient or concentration information, may be seized and destroyed when intercepted (TGA warning, 7 May 2026).
- Human use. Research peptides are not approved for human use. Anyone considering a therapy for muscle loss or any medical condition should speak with a doctor.
Our guides cover the detail: research peptide compliance in Australia, the documents labs attach to imports, preventing customs holds and prescription requirements.
Our perspective
Most confusion around FS344 starts with sourcing and documentation, not biology. A researcher cannot interpret a result if the vial's identity and purity are unknown.
At Peptastic Labs, each batch is designed to go through independent HPLC and mass spectrometry testing, with traceable batch documentation. Certificates of Analysis are available on request. Our catalog lists compounds verified to ≥99% purity by HPLC.
We supply for research use only. We ask researchers to match the form they buy to the form their cited literature used, and to keep the CoA with the protocol record. Documentation does not make a study sound, but a study without it cannot be reproduced.
Tintastic
Ordering for research
Peptastic Labs supplies independently tested research-grade peptides with batch documentation and Certificates of Analysis on request. Bulk and wholesale options are available. Lines include Metabolic, Cognitive & Neuro, Tissue & Repair, Longevity, Cosmetic Science, Blends, Hormone & Reproductive, and Ancillaries & Reagents.
Browse the full research peptide catalogue and request the CoA for the batch you plan to use. Prices are listed on the site. Costs are also covered in our peptide cost guide.
FAQ
Is Follistatin-344 approved for human use in Australia?
No approval is reported in the sources reviewed here. The TGA treats unapproved peptide products as a public health concern and has warned about their risks. Research peptides are for laboratory use only. See our TGA peptide rules guide for what applies.
Do the Becker muscular dystrophy results apply to FS344 peptide?
No. The trial delivered the FS344 gene by AAV1 injection into muscle to six patients. It did not test recombinant protein. The sample was small and open-label, so it cannot be read as evidence for a vial of peptide.
What should a Certificate of Analysis include?
Look for the compound name, batch number, HPLC purity with the chromatogram, mass spectrometry identity data, the testing laboratory and the date. The batch number must match the vial. If any element is missing, ask the supplier before use.
Can a peptide be imported into Australia as a research product?
Imports are assessed on what the product is and how it is labelled, not only on the label's wording. The TGA says poorly labelled products may be seized and destroyed. Check importation guidance for labs and confirm requirements with the relevant authorities before ordering.
Sources
- Inhibition of myostatin with emphasis on follistatin (2009 review)
- Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy
- Phase 1/2a Follistatin Gene Therapy Trial for Becker Muscular Dystrophy
- Follistatin Gene Delivery Enhances Muscle Growth and Strength in Nonhuman Primates
- Safety and Efficacy of Approved and Unapproved Peptide Therapies
- Thymosin alpha 1: A comprehensive review of the literature
- TGA: Concerns regarding the public health risks associated with unapproved peptide products
- TGA: Warning on the risks of importing unapproved peptide products
- TGA: Personal Importation Scheme
- Clinical peptide protocol: identity and purity testing by mass spectrometry and HPLC