Follistatin-344 Research Guide: Myostatin Inhibition, Dosage Protocol & Reconstitution (2026)

# Follistatin-344: The Myostatin Inhibitor Reshaping Muscle Biology and Multi-Tissue Research

Researchers can use our peptide comparison page to evaluate pricing and sourcing options for follistatin and related research compounds.

For dosing, reconstitution, and protocol details, see our Follistatin-344 Dosage Protocol Guide: Myostatin Inhibitor Reconstitution & Administration (2026).

What Is Follistatin-344?

Follistatin-344 (FS-344) is a naturally occurring glycoprotein encoded by the FST gene in humans, belonging to the follistatin family of activin-binding proteins. The "344" designation refers to the amino acid count of the full-length precursor molecule before post-translational processing generates shorter circulating isoforms. Within the broader follistatin protein family, FS-344 is the principal research variant of interest for skeletal muscle biology, having become a central tool for investigators studying myostatin inhibition, muscle wasting disease, and growth factor signaling.

As a member of the TGF-β superfamily antagonist class, follistatin neutralizes several ligands simultaneously — most importantly myostatin and activin A, two proteins that independently suppress skeletal muscle growth through the activin receptor type IIB (ActRIIB) pathway. This dual antagonism makes FS-344 a uniquely potent research compound, capable of producing muscle hypertrophy responses substantially larger than myostatin inhibition alone.

The compound's expression is not confined to skeletal muscle: follistatin is found in the pituitary gland, ovaries, liver, skin, and multiple other tissues, making it a research subject across diverse biological domains including reproductive endocrinology, oncology, bone biology, and wound healing. For researchers studying muscle-focused growth factor analogs, our IGF-1 LR3 research profile covers a complementary research compound operating through distinct anabolic signaling pathways.

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Isoforms: FS-344 vs FS-288 — Why the Distinction Matters

The follistatin gene produces two primary splice variants through alternative splicing at the 3'' end between exon 5 and exon 6: FS-317 and FS-344. After post-translational processing, these give rise to the biologically active protein isoforms FS-288 and FS-315, respectively.

Understanding the isoform distinction is critical for contextualizing research findings:

FS-344 → FS-315 (Circulating Isoform)

FS-344 is processed into FS-315, a soluble, serum-based isoform with lower affinity for heparan sulfate proteoglycans (HSPGs) on cell surfaces. Because FS-315 circulates freely in the bloodstream rather than binding tightly to tissue surfaces, it preferentially distributes to skeletal muscle while avoiding high-affinity binding in gonadal and pituitary tissue. This differential distribution is what makes FS-344 the preferred isoform for skeletal muscle research — its reduced affinity for pituitary activin (approximately 10-fold lower than FS-288) minimizes disruption of reproductive hormone signaling via FSH feedback loops.

FS-317 → FS-288 (Tissue-Bound Isoform)

The shorter FS-288 isoform binds tightly to HSPG sites on cell surfaces throughout the body. It demonstrates particularly high affinity for ovarian follicular tissue and pituitary cell surfaces. While this makes FS-288 important for reproductive biology research, it also raises off-target signaling concerns for muscle-focused investigations — which is why early gene therapy programs selected the FS-344 gene cassette specifically over FS-317.

> Research context: When investigators refer to "follistatin-344" as a recombinant peptide research compound, they are typically working with the full-length FS-344 protein or its processed FS-315 form, characterized by its systemic distribution and preferential myostatin/activin A binding in peripheral muscle tissue.

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Mechanism of Action: TGF-β Superfamily Antagonism

Follistatin-344 operates through high-affinity non-covalent binding to multiple members of the transforming growth factor-beta (TGF-β) superfamily. The principal targets and their relevance to research applications:

Myostatin (GDF-8)

Myostatin is the body's primary negative regulator of skeletal muscle mass. Under normal conditions, circulating myostatin binds to ActRIIB, recruits the type I receptor (ALK4 or ALK5), and activates the Smad2/3 signaling cascade — transcriptionally suppressing muscle protein synthesis and promoting protein degradation. Follistatin neutralizes myostatin in the extracellular space before it can engage ActRIIB, effectively removing the brake on muscle hypertrophy pathways.

The importance of myostatin inhibition in research is underscored by natural experiments: humans and animals with loss-of-function mutations in the MSTN gene display dramatic muscle hypermass phenotypes, with documented human cases showing more than double normal muscle mass without pathological consequence. Follistatin-344 provides a pharmacological equivalent of this genetic scenario.

Activin A (and Activin B)

Activin A is a second TGF-β superfamily member that independently suppresses muscle growth through the same ActRIIB receptor pathway used by myostatin. Importantly, elevated activin A is observed in cachexia, aging-related sarcopenia, and cancer-associated muscle wasting, making it a parallel target of significant research interest.

A pivotal study published in Skeletal Muscle (Rahimov et al., 2018) demonstrated that blocking both myostatin and activin A simultaneously produced substantially greater muscle mass recovery in the mdx mouse model (a Duchenne muscular dystrophy model) than myostatin blockade alone — providing mechanistic justification for why follistatin''s dual antagonism generates outsized preclinical results.

GDF-11, BMP-2, BMP-7, and Others

Follistatin also binds GDF-11 (a myostatin homolog with roles in cardiac and neural aging research), BMP-2, and BMP-7 with varying affinities. These secondary interactions expand follistatin''s research footprint into bone remodeling, neurogenesis, and cardiac biology, though the binding kinetics and in vivo significance of each interaction remain active areas of investigation.

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Skeletal Muscle Research: The Primary Application

The most extensively studied application of FS-344 in preclinical research is skeletal muscle hypertrophy and the treatment of muscle wasting conditions. The body of evidence is substantial.

Transgenic Animal Models

Transgenic mice overexpressing the follistatin gene consistently demonstrate dramatic increases in skeletal muscle mass. Research published in PNAS (Rodino-Klapac et al., 2007; PMC2393740) reported muscle mass increases of 194–327% in follistatin-overexpressing mice compared to wild-type animals — substantially exceeding the approximately 100% increase observed in myostatin-knockout mice alone. This finding was particularly important because it confirmed that activin antagonism was contributing meaningfully to the follistatin phenotype beyond myostatin inhibition.

In aged mouse models, follistatin-induced hypertrophy was shown to improve not only muscle mass but also neuromuscular junction integrity and functional strength performance, raising research interest in applications targeting sarcopenia — the progressive loss of muscle mass and function associated with aging. For comparative context on regenerative research peptides that target overlapping recovery pathways, see our BPC-157 vs TB-500 research comparison.

AAV1-FS344 Gene Therapy: Muscular Dystrophy Research

The most clinically developed application of FS-344 has been AAV-mediated gene therapy for inherited muscle diseases. Using adeno-associated virus serotype 1 (AAV1) as a vector, researchers delivered FS-344 intramuscularly in multiple clinical research programs.

Becker Muscular Dystrophy (BMD): A Phase 1/2a trial enrolled six ambulatory BMD patients, delivering AAV1-FS344 to the extensor digitorum brevis muscle. The trial demonstrated safety and reported an average 11.5% improvement in six-minute walk test distance at six months (p = 0.02), published in Molecular Therapy (Mendell et al., 2015; PMC5240576). While designed primarily for safety assessment, the functional improvement signal justified continued investigation.

Duchenne Muscular Dystrophy (DMD) and Inclusion Body Myositis: Preclinical work in mdx mice and subsequent protocol development established the rationale for expanded trials in more severe dystrophic conditions, with follistatin''s anti-fibrotic properties (via activin A neutralization) considered particularly relevant for halting connective tissue replacement of muscle.

Satellite Cell Proliferation

Beyond receptor-level antagonism, follistatin influences skeletal muscle regeneration through a parallel mechanism: stimulation of satellite cell (muscle stem cell) proliferation. Research published in the American Journal of Physiology: Endocrinology and Metabolism (Gilson et al., 2009; doi:10.1152/ajpendo.00193.2009) demonstrated that follistatin promotes hypertrophy through two concurrent pathways — myostatin/activin inhibition and direct promotion of satellite cell activation, the cellular machinery responsible for post-exercise muscle repair and adaptation.

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Bone Metabolism Research

A secondary but well-documented research domain for follistatin is bone biology. Both activin A and several BMPs regulate osteoblast and osteoclast activity — two key effectors of bone formation and resorption. As an antagonist of these ligands, follistatin has been investigated for its capacity to modulate skeletal remodeling.

Research published on PubMed (Follistatin as a potent regulator of bone metabolism, PMID 20569048) demonstrated that activin antagonism by follistatin supports net osteogenesis. Research published in Frontiers in Bioengineering (PMC6405513) further showed that recombinant follistatin promotes mesenchymal stem cell migration, endothelial tube formation, and osteogenic differentiation in vitro — processes relevant to fracture repair and bone regeneration scaffold research.

These findings have opened investigation of follistatin in the context of bone density loss in aging populations, osteoporosis, and post-surgical bone repair, though this remains a less mature research area compared to muscle applications.

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Wound Healing and Angiogenesis Research

Follistatin''s involvement in wound biology was identified through studies of skin homeostasis. Activin A is upregulated at wound sites and modulates the inflammatory phase of repair; follistatin serves as an endogenous counterbalance. Research has demonstrated that the balance between activin and follistatin expression in dermal fibroblasts influences scar formation, inflammatory resolution, and re-epithelialization kinetics.

Additionally, follistatin was shown to regulate endothelial cell activity through autocrine signaling (Kozian et al., 1997; PMID 9042163), stimulating angiogenesis — the formation of new blood vessels essential for tissue repair and tumor vascularization. This endothelial effect makes follistatin relevant to both wound healing research and tumor microenvironment biology.

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Cancer Research Applications

Follistatin occupies a nuanced position in oncology research. While elevated circulating follistatin has been observed in multiple tumor types (PMC5219916), the protein appears to play different roles depending on tissue context.

In ovarian cancer, research has demonstrated that quiescent tumor cells secrete follistatin as a survival mechanism — neutralizing activin A in the microenvironment to shield dormant cancer cells from chemotherapy-induced apoptosis, representing a potential mechanism of treatment resistance. In prostate and breast cancer models, follistatin expression correlates with more aggressive phenotypes and reduced sensitivity to TGF-β-mediated growth suppression.

Conversely, in some gastrointestinal cancers, follistatin appears to inhibit tumor-promoting activin signaling, suggesting context-dependent tumor suppressor functions.

A 2024 review (PMC10887188) examined the role of follistatin in the tumor microenvironment, concluding that follistatin''s effects on drug resistance represent a therapeutically actionable target worthy of further mechanistic investigation. This dual nature makes follistatin a focus of interest for both understanding cancer biology and identifying new research vectors for drug resistance modulation.

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Reproductive and Endocrine Research

Follistatin was originally identified as a follicle-stimulating hormone (FSH)-suppressing protein — hence its name — before its role as a broad TGF-β superfamily antagonist was fully characterized. In the pituitary, activin stimulates FSH secretion; follistatin binding to activin in the pituitary provides the primary negative feedback mechanism that limits FSH output.

The FS-344 isoform''s lower affinity for pituitary cell-surface heparan sulfate proteoglycans (compared to FS-288) means that systemic administration in research models produces less disruption of the hypothalamic-pituitary-gonadal (HPG) axis — a key design consideration in gene therapy program selection. Nevertheless, researchers studying reproductive endocrinology use follistatin as a tool to dissect FSH regulation, ovarian folliculogenesis, and activin signaling in reproductive contexts.

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Follistatin-344 vs. Other Myostatin Inhibitors in Research

Researchers studying myostatin inhibition have several tool compounds available, each with distinct mechanisms and selectivity profiles:

Follistatin-344''s value as a research tool is its dual myostatin + activin A coverage, which more faithfully recapitulates the pathophysiology of multi-ligand muscle wasting conditions such as cachexia and advanced sarcopenia. However, when researchers need to isolate the specific contribution of myostatin vs. activin A to a phenotype, more selective inhibitors are preferable.

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Stability, Storage, and Research Handling

Follistatin-344 used in laboratory research is typically produced as a recombinant human protein expressed in HEK293 or CHO cell systems, with molecular weight approximately 35–38 kDa (monomeric form, though the protein can dimerize under certain conditions).

Key research handling considerations:

• •Temperature: Lyophilized follistatin is stable at -20°C long-term; reconstituted solutions should be stored at 4°C and used within 7–14 days to preserve biological activity
• •Reconstitution buffer: PBS with 0.1% BSA is commonly used for stability in cell culture applications
• •Glycosylation sensitivity: As a glycoprotein, follistatin activity can be affected by deglycosylation; researchers should account for this when selecting between recombinant forms
• •Dose-response characterization: Given its multiple binding targets with differing affinities, concentration-response curves for follistatin are non-linear across biological endpoints

For comprehensive guidance on reconstitution and handling of research peptides, see our peptide reconstitution guide.

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Current Research Frontiers

Follistatin and Aging / Longevity

The intersection of follistatin biology with aging research has accelerated significantly. Both myostatin and activin A increase in circulation with advancing age, correlating with sarcopenic muscle loss, while endogenous follistatin levels decline. Preclinical data showing follistatin supplementation can restore neuromuscular junction structure and improve functional strength in aged animals has made this a compelling area for translational investigation. For an overview of other research peptides active in the aging space, see our mitochondrial peptides comparison.

Several longevity-focused research programs are examining follistatin gene therapy not only for rare neuromuscular disease but as a potential intervention for age-associated muscle decline — a far larger indication with enormous epidemiological relevance.

Follistatin and Adipose Tissue

Emerging research has documented follistatin expression in adipose tissue, where it appears to modulate adipogenesis and fat metabolism through BMP pathway antagonism. Some preclinical data suggest that follistatin signaling in white adipose tissue may influence metabolic homeostasis, though this remains an early-stage research area with much mechanistic work remaining.

Follistatin as a Biomarker

Circulating FS-315 is measurable in serum via ELISA, and researchers have begun exploring follistatin as a biomarker for muscle disease progression, frailty, and cancer cachexia staging. Standardization of measurement protocols across research cohorts remains an ongoing challenge in this emerging diagnostic application.

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Research Use Only — Important Disclaimer

All research applications of follistatin-344 discussed in this article refer to in vitro laboratory investigations and preclinical animal model studies conducted under appropriate institutional oversight. Follistatin-344 recombinant protein is supplied exclusively for research use only (RUO). It is not approved for diagnostic or therapeutic use in humans or animals. Researchers should consult current regulatory guidelines and institutional biosafety frameworks before initiating follistatin research programs.

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Research Dosage Protocols in Preclinical Models

Follistatin-344 recombinant protein is not FDA-approved and is used exclusively in laboratory and preclinical animal research. The dosage ranges cited below are derived from published animal model studies and represent investigational parameters only.

> ⚠️ Research Use Only (RUO): Follistatin-344 is not approved for human use by the FDA, EMA, or any regulatory body. The protocols below describe parameters used in preclinical animal research. This information is provided for educational and scientific purposes only.

Typical Preclinical Dosage Parameters

Key Dosage Considerations in Animal Research

Weight-based scaling: Follistatin-344 dosing in animal models is typically weight-normalized (mcg/kg bodyweight) to account for metabolic differences across species. Direct translation of animal doses to human equivalents is not valid without allometric scaling and appropriate safety studies.

Frequency and half-life: Recombinant follistatin-344 has a relatively short serum half-life in rodent models (approximately 1–4 hours), which drives the need for frequent dosing schedules in studies requiring sustained myostatin suppression. Some research programs use longer schedules (every 3–7 days) when studying cumulative hypertrophy endpoints rather than acute receptor occupancy.

Gene therapy vs. recombinant protein: Much of the landmark follistatin research used AAV-delivered FS-344 gene therapy rather than recombinant protein administration. Gene therapy models achieve sustained, high-level expression from a single injection — a fundamentally different pharmacology from repeated recombinant protein dosing. Researchers should not extrapolate gene therapy dose findings to recombinant protein protocols.

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Reconstitution Protocol for Research Use

Follistatin-344 for laboratory research is supplied in lyophilized (freeze-dried) form and requires reconstitution before use. The following protocol reflects standard laboratory practice for recombinant glycoprotein handling.

> ⚠️ RUO Disclaimer: The following protocol is intended for qualified researchers conducting preclinical laboratory investigations under appropriate institutional oversight. Not for human administration.

Reconstitution Reference Table

Step-by-Step Reconstitution

1. Pre-warm solvent: Allow bacteriostatic water to reach room temperature

2. Clean septum: Wipe the rubber stopper with a 70% isopropanol swab; allow to dry

3. Draw solvent: Aspirate the calculated volume into an insulin syringe

4. Inject slowly: Direct solvent stream gently down the inside wall of the vial

5. Wait and swirl: Allow 5 minutes; gently swirl (do not vortex) until fully dissolved

6. Inspect visually: Solution should be clear and colorless; discard if cloudy or particulate

7. Aliquot immediately: Transfer to clean labeled vials (date, lot, concentration) if making single-use aliquots

8. Store correctly: Aliquots at -20°C; working solution at 4°C

Concentration Calculation Example

For a 1 mg vial targeting a 100 mcg/mL stock solution:

• •Add 10 mL bacteriostatic water → 100 mcg/mL (0.1 mg/mL)
• •For 500 mcg/mL stock: Add 2 mL bacteriostatic water

Use our peptide reconstitution calculator for automated volume calculations.

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Administration Routes in Animal Research Models

Research programs using follistatin-344 in preclinical animal models employ several administration routes depending on study design and target tissue:

Subcutaneous (SC) Injection

Most common route for systemic research studies. SC injection delivers follistatin into the subcutaneous space for gradual absorption into systemic circulation. This route is technically simple, minimizes procedural stress in repeated-dosing models, and produces reliable pharmacokinetic profiles.

• •Best for: Whole-body hypertrophy studies, cachexia models, sarcopenia research
• •Injection sites: Scruff of neck (rodents), alternating flanks for repeated dosing
• •Absorption timeline: Peak plasma levels typically within 1–3 hours in rodents

Intramuscular (IM) Injection

Preferred for localized muscle-specific effect studies. IM injection delivers follistatin directly into target muscle tissue, allowing researchers to study local versus systemic effects. The landmark AAV1-FS344 gene therapy trials (Mendell et al., 2015) used intramuscular delivery to the extensor digitorum brevis for this reason.

• •Best for: Localized hypertrophy studies, gene therapy protocols, direct muscle delivery
• •Technical consideration: Injection volume should not exceed 50 µL for small rodent muscles to avoid pressure injury
• •Research context: IM delivery increases local tissue concentration but may not produce equivalent systemic effects to SC

Intravenous (IV) Administration

Used primarily in pharmacokinetic and receptor occupancy studies where rapid, complete bioavailability is required. IV administration delivers 100% bioavailability but requires greater technical skill and causes more procedural stress in small animal models. Typically reserved for PK/PD characterization rather than long-term efficacy studies.

Route Comparison Table

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Research Safety Considerations

Follistatin-344 research programs should account for the following safety parameters based on published preclinical literature:

Known Physiological Effects in Animal Models

Reproductive axis modulation: As an FSH-suppressing protein in the pituitary, FS-344 at supratherapeutic doses can suppress FSH secretion. The FS-315 circulating form has markedly lower pituitary affinity than FS-288, making HPG axis disruption less likely at standard research doses — but researchers running multi-week studies should monitor reproductive biomarkers in relevant models.

Cardiovascular considerations: High-dose follistatin may influence cardiac muscle similarly to skeletal muscle. Research in larger animal models (primates, canines) has flagged potential for cardiac hypertrophy at sustained supratherapeutic exposures, though this has not been a significant finding in standard rodent research dosing ranges.

Tumor microenvironment effects: Given follistatin's documented role in cancer cell survival via activin A suppression, researchers using follistatin in oncology models should design appropriate controls to account for potential confounding effects on tumor cell viability and drug sensitivity.

Immunogenicity: Recombinant human follistatin-344 may elicit immune responses in non-human animal models depending on production system and glycosylation profile. Researchers planning longitudinal studies should consider immunogenicity monitoring as part of their experimental design.

Institutional Requirements

All preclinical follistatin research should be conducted under:

• •IACUC (Institutional Animal Care and Use Committee) approval for animal studies
• •Biosafety committee review for recombinant protein work
• •Adherence to ARRIVE guidelines for animal research reporting

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Frequently Asked Questions

What is Follistatin-344 used for in research?

Follistatin-344 is used primarily in preclinical skeletal muscle biology research to study myostatin inhibition, muscle hypertrophy mechanisms, and potential therapeutic strategies for muscular dystrophies, cachexia, and sarcopenia. Secondary applications include bone biology, wound healing, reproductive endocrinology, and cancer biology research.

What is the difference between Follistatin-344 and Follistatin-315?

FS-344 is the full-length precursor molecule (344 amino acids) encoded by the FST gene. When processed, it generates FS-315, the circulating active isoform. The "344" designation on commercial recombinant products typically refers to the gene cassette construct — in research contexts, these terms are often used interchangeably to mean the systemic-distributing form of follistatin.

How is Follistatin-344 different from BPC-157 or TB-500?

Follistatin-344 is an endogenous glycoprotein that binds and neutralizes TGF-β family ligands (myostatin, activin A). BPC-157 and TB-500 are synthetic peptides with angiogenic and tissue regeneration mechanisms. The three compounds operate through distinct molecular pathways and are studied for fundamentally different research applications.

Can Follistatin-344 be used in humans?

No. Follistatin-344 is not FDA-approved for human administration. It is a research-use-only compound for in vitro and preclinical in vivo studies only. Any human use outside of properly authorized clinical trials would be unauthorized and is outside the scope of this research profile.

How should Follistatin-344 be stored?

Lyophilized follistatin-344 is stable at -20°C for 24+ months when properly sealed. After reconstitution with bacteriostatic water, store at 4°C and use within 7–14 days. Minimize freeze-thaw cycles for aliquoted material.

Where can I source Follistatin-344 for research?

Follistatin-344 is available from multiple research peptide suppliers. Use our supplier comparison tool to evaluate quality grades, certificates of analysis, and pricing from verified vendors.

What does the research say about Follistatin-344's muscle effects?

Transgenic animal studies (Rodino-Klapac et al., 2007) demonstrated muscle mass increases of 194–327% in follistatin-overexpressing mice. Clinical gene therapy trials (Mendell et al., 2015) showed an 11.5% improvement in six-minute walk test distance in Becker Muscular Dystrophy patients following AAV1-FS344 delivery — establishing a robust preclinical evidence base for myostatin/activin dual inhibition in muscle research.

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Key Scientific References

1. Rodino-Klapac LR et al. "Long-term enhancement of skeletal muscle mass and strength by single gene administration of myostatin inhibitors." PNAS (2007). PMC2393740

2. Mendell JR et al. "Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy." Molecular Therapy (2015). PMC5240576

3. Gilson H et al. "Follistatin induces muscle hypertrophy through satellite cell proliferation and inhibition of both myostatin and activin." Am J Physiol Endocrinol Metab (2009). doi:10.1152/ajpendo.00193.2009

4. Keutmann HT et al. "Inhibition of myostatin with emphasis on follistatin as a therapy for muscle disease." PMC (2009). PMC2717722

5. "Follistatin as a potent regulator of bone metabolism." PubMed (2010). PMID 20569048

6. Kozian DH et al. "The activin-binding protein follistatin regulates autocrine endothelial cell activity and induces angiogenesis." Blood (1997). PMID 9042163

7. Rogers PAW et al. "Clinical and Therapeutic Implications of Follistatin in Solid Tumours." Int J Mol Sci (2016). PMC5219916

8. Trouillas M et al. "The Reign of Follistatin in Tumors and Their Microenvironment." PMC (2024). PMC10887188

9. Fong MY et al. "Follistatin Effects in Migration, Vascularization, and Osteogenesis in vitro and Bone Repair in vivo." Front Bioeng Biotechnol (2019). PMC6405513

10. Rahimov F et al. "Myostatin and activin blockade by engineered follistatin results in hypertrophy and improves dystrophic pathology in mdx mouse." Skeletal Muscle (2018). doi:10.1186/s13395-018-0180-z

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