Follistatin 344

Follistatin 344 (FST-344) is one of two major naturally occurring isoforms produced by alternative splicing of the human FST gene (chromosome 5q11.2, UniProt P19883), the other being the shorter, more heparin-avid FST-315. Both isoforms are built around a heparin-binding N-terminal domain followed by three cysteine-rich follistatin domains (FSD1, FSD2, FSD3) that together form the surface responsible for binding and neutralizing members of the TGF-beta superfamily, most notably myostatin (GDF-8) and activin A.

At Verified Peptides, we want to note upfront that FST-344 is considerably larger than most compounds in this catalog: as a 344-residue protein, its native molecular weight is approximately 38 kDa (38,006.8 Da for the unmodified precursor), and recombinant Fc-tagged research versions can run considerably higher (up to roughly 61.7 kDa) depending on expression system and tagging. This makes FST-344 more accurately described as a full-length signaling protein than a short synthetic peptide, even though it is conventionally sold and discussed within the "research peptide" category. Because of its size, standard small-molecule identifiers like CAS numbers and PubChem CIDs are not typically assigned to it; UniProt accession P19883 is the more appropriate reference identifier for this class of molecule, and we use that here rather than fabricate a small-molecule-style identifier that would not accurately describe a protein of this size.

FST-344 is distinguished from FST-315 by lacking the C-terminal acidic extension present on the longer isoform, which gives FST-315 much lower heparin-binding affinity and allows it to circulate more freely in serum; FST-344, by contrast, binds heparan sulfate proteoglycans on cell surfaces more readily and is understood to act in a more localized, tissue-associated manner.

At Verified Peptides, we think Follistatin 344 has one of the more substantial human evidence bases in this entire catalog, and we want to walk through exactly what that evidence does and does not show. The Phase 1/2a trial (PMID 25322757) enrolled BMD and sIBM patients in a dose-escalation design, delivering an AAV1-FST344 vector by direct intramuscular injection into a single leg muscle, with the untreated contralateral leg serving as an internal control. In the first cohort of two BMD patients, the treated leg showed measurable increases in muscle fiber size, and functional testing showed a robust improvement on the 6-minute walk test — 58 meters for one patient and 125 meters for the other — a clinically meaningful functional outcome measure, not just a biomarker change. The trial reported the therapy was reasonably well tolerated in this small cohort.

We want to be direct about the limits of this evidence: this was a small, early-phase (Phase 1/2a), open-label, dose-escalation safety and proof-of-concept trial, not a large randomized controlled trial, and it tested gene-therapy-delivered FST-344 (sustained local production from transduced muscle cells), not exogenous recombinant protein administration of the kind sold as a research peptide. Researchers should not assume that periodic injection of recombinant FST-344 protein would reproduce the same magnitude or durability of effect seen with continuous local gene-therapy-driven expression — these are pharmacologically distinct delivery approaches even though they act through the same underlying FST-344 protein and mechanism.

Beyond this human trial, FST-344 and follistatin more broadly have a substantial preclinical literature in muscle hypertrophy, sarcopenia, and muscular dystrophy animal models, consistent with myostatin inhibition being one of the most extensively studied strategies for enhancing muscle mass in the broader TGF-beta/muscle-biology research field — a research area with substantial independent, multi-group, non-proprietary literature, distinct from the single-institute-lineage pattern seen in several other compounds in this catalog.

Myostatin inhibition as a broader therapeutic strategy has also been pursued through other molecular approaches beyond follistatin itself, including monoclonal antibodies directly targeting myostatin or the activin receptor (such as bimagrumab, which targets ActRII) and engineered soluble receptor decoys like ACE-031 (also built on this site), giving researchers a genuinely comparative field of myostatin-pathway-targeting research tools with different molecular strategies for achieving a broadly similar downstream effect: removing the myostatin/activin brake on muscle growth.

No exogenous FST-344 protein formulation has received FDA approval for any indication; the gene-therapy vector used in the cited trial is itself an investigational product, not an approved drug. At Verified Peptides, we sell research-grade FST-344 exclusively for laboratory research, and we think this compound's human proof-of-concept data, despite its early-phase and gene-therapy-specific limitations, represents genuinely stronger real-world evidence than most other compounds in this catalog.

Follistatin's myostatin-antagonist mechanism sits within one of the most extensively validated pathways in muscle biology: myostatin-null ("double-muscled") cattle breeds such as Belgian Blue, and naturally occurring myostatin mutations in specific human individuals and dog breeds (notably whippets), provide direct genetic proof-of-concept that removing myostatin signaling produces substantial muscle-mass increases — independent confirmation of the pathway's biological importance that predates and does not depend on any specific follistatin research program.

Follistatin's dual myostatin-and-activin-neutralizing activity is a genuine double-edged consideration for researchers: because activin A has its own substantial, separate biology (including roles in reproductive hormone regulation, wound healing, and fibrotic signaling), a compound that broadly neutralizes activin alongside myostatin cannot be assumed to have effects isolated to muscle tissue alone — a nuance that is sometimes glossed over in commercial descriptions that frame follistatin purely as a "muscle growth peptide."

The AAV1-FST344 gene therapy studied in the cited Becker muscular dystrophy trial represents a genuinely different pharmacological approach from most other compounds in this catalog: rather than periodic exogenous protein or peptide dosing, the gene therapy causes the patient's own transduced muscle cells to continuously produce and locally secrete FST-344 protein, a sustained-expression strategy that is mechanistically closer to a form of localized gene-based hormone replacement than to conventional peptide dosing.

Because FST-344 and FST-315 are both natural splice products of the same FST gene rather than being engineered as separate drugs, commercial "research peptide" material sold as FST-344 specifically should be verified for isoform identity, since the two isoforms have meaningfully different heparin-binding and tissue-distribution properties despite being derived from the same underlying gene.

At Verified Peptides, we require independent third-party analytical verification — including SDS-PAGE and mass spectrometry identity confirmation, appropriate for a protein of this size — for every batch of research-grade Follistatin 344 we offer, with a Certificate of Analysis (COA) available for each lot. As a 344-residue glycoprotein, FST-344 requires more complex recombinant expression and purification (typically in mammalian or insect cell expression systems capable of proper folding and glycosylation) than the short synthetic peptides that make up most of this catalog, and this added complexity makes independent identity and purity verification especially important.

We source exclusively from manufacturers operating under Good Manufacturing Practice (GMP)-aligned quality systems, and every lot is independently verified rather than accepted solely on a supplier's internal documentation. Researchers should confirm which specific isoform (FST-344 versus FST-315) and which expression/tagging system (e.g., Fc-tagged versus untagged) a given lot represents, since these variables affect both molecular weight and functional properties.

Lyophilized Follistatin 344 should be stored at -20°C or colder, protected from light and moisture; as a larger glycoprotein rather than a short synthetic peptide, FST-344 may be more sensitive to freeze-thaw-induced structural disruption than the smaller peptides elsewhere in this catalog, and researchers should follow lot-specific handling guidance closely. At Verified Peptides, we ship lyophilized material with appropriate cold-chain packaging to preserve stability in transit.

Once reconstituted, FST-344 solution should be stored refrigerated at 2–8°C and used within the timeframe indicated on the product's documentation, or aliquoted and stored frozen at -20°C or below for longer-term storage, avoiding repeated freeze-thaw cycles, which are a particular concern for larger, structurally complex proteins prone to aggregation.

Because FST-344 is a glycoprotein, researchers should also be aware that improper handling can affect its glycosylation-dependent properties in ways that would not necessarily be apparent from a simple purity assay, making adherence to supplier-specific handling recommendations particularly important for this compound.