MGF (Mechano Growth Factor): Research Guide

Mechano Growth Factor sounds like something from a superhero origin story. In reality, it's a naturally occurring peptide your muscles produce every time you lift heavy, sprint hard, or push your body beyond its comfort zone. What makes MGF interesting to researchers is its role as a molecular first responder—showing up immediately after muscle damage to kickstart the repair process.

But here's where things get complicated. MGF has an extremely short half-life measured in minutes, making it nearly impossible to study in its natural form. Enter PEG-MGF, a laboratory-modified version that lasts for days instead of minutes. This pegylated variant has attracted attention from athletes, bodybuilders, and anti-doping agencies in equal measure.

This guide examines what MGF actually is, how it works at the cellular level, what research shows about its effects, and why it remains firmly in the category of experimental compounds with more questions than answers.

Table of Contents

• Quick Facts
• What Is Mechano Growth Factor?
• How MGF Works: Mechanisms of Action
• Research Evidence
• PEG-MGF: The Modified Variant
• Safety and Side Effects
• Legal Status and Anti-Doping
• Frequently Asked Questions
• Bottom Line

Quick Facts

Property	Details
Full Name	Mechano Growth Factor (MGF)
Type	IGF-1 splice variant peptide
Gene	IGF-1Ec (humans), IGF-1Eb (rodents)
Molecular Weight	~2.8 kDa (24 amino acids for E-peptide region)
Primary Mechanism	Satellite cell activation, muscle stem cell proliferation
Half-Life	5-7 minutes (native), 48-72 hours (PEG-MGF)
Expression Timing	2-24 hours post-muscle damage
Receptor	Unknown (not IGF-1 receptor)
Clinical Status	Preclinical research only
Regulatory Status	Banned by WADA, not FDA-approved

What Is Mechano Growth Factor?

Mechano Growth Factor (MGF) is a splice variant of the insulin-like growth factor 1 (IGF-1) gene. While most people know IGF-1 as a growth hormone that circulates throughout the body, few realize that the IGF-1 gene can be spliced into multiple different versions, each with distinct functions.

The IGF-1 Gene Splicing Process

The human IGF-1 gene contains six exons that can be spliced together in different combinations to create three main isoforms:

• IGF-1Ea: The systemic, liver-derived form most associated with growth hormone
• IGF-1Eb: A variant expressed in some tissues
• IGF-1Ec (MGF): The mechanically-activated, locally-produced form

MGF gets its name from the fact that mechanical stress—particularly the kind generated during resistance exercise—triggers its production in muscle tissue. Research published in In Vivo found that MGF expression increases significantly earlier than other IGF-1 variants following exercise-induced muscle damage.

The Unique E Domain

What makes MGF structurally different from other IGF-1 variants is its E domain—a 49 base pair insert in humans (52 base pairs in rodents) that causes a reading frame shift during gene splicing. This shift produces a unique C-terminal peptide sequence that doesn't exist in standard IGF-1.

This E domain peptide is biologically active on its own. When scientists studied the isolated E peptide, they found it could activate muscle progenitor cells and increase their fusion potential—even without the rest of the IGF-1 molecule attached.

Local Production vs. Systemic IGF-1

Unlike systemic IGF-1, which is produced primarily in the liver and circulates throughout the bloodstream, MGF is produced locally within muscle tissue in response to mechanical stress. This local production means MGF acts as a site-specific signal, directing repair efforts exactly where damage occurred rather than broadcasting a growth signal to the entire body.

A 2007 study in FEBS Letters demonstrated this principle by showing that MGF increased progenitor cell populations in damaged muscle tissue from patients with ALS, muscular dystrophy, and healthy controls—suggesting its repair function operates independently of systemic growth signals.

How MGF Works: Mechanisms of Action

MGF's biological activity differs from standard IGF-1 in ways that have surprised researchers and complicated attempts to understand its therapeutic potential.

A Mysterious Receptor

One of the most intriguing aspects of MGF is that it doesn't work through the IGF-1 receptor—the main receptor responsible for most of IGF-1's growth-promoting effects.

Research published in Molecular Medicine demonstrated this by experimentally silencing both the IGF-1 receptor and insulin receptor in cells, then exposing them to the synthetic MGF E-peptide. The peptide continued to stimulate cell growth despite the absence of these receptors, leading researchers to conclude that "MGF E-peptide stimulates cell growth via an IGF-1R-independent and insulin receptor-independent mechanism."

The actual receptor MGF binds to remains unknown. This mystery receptor likely mediates many of MGF's unique biological effects that differ from standard IGF-1.

Satellite Cell Activation

Muscle tissue contains a population of resident stem cells called satellite cells. These cells normally sit dormant between the muscle fiber and its surrounding membrane. When muscle damage occurs, satellite cells activate, proliferate, and eventually fuse with existing muscle fibers to donate new nuclei—enabling those fibers to grow larger and repair damage.

MGF appears to be one of the primary signals that wake up these dormant satellite cells. A study on porcine satellite cells found that MGF treatment potently stimulated proliferation while inhibiting differentiation. This keeps satellite cells in their growth phase longer, building up a larger pool of cells available for eventual fusion and repair.

Importantly, this effect differs from mature IGF-1, which primarily promotes differentiation—the process where satellite cells mature into muscle fibers. MGF says "make more stem cells," while IGF-1 says "turn stem cells into muscle." Both are necessary for complete muscle repair, but they happen at different stages of the process.

Timeline of Expression

MGF isn't constitutively expressed—it appears rapidly after muscle damage, peaks early, then disappears as other growth factors take over.

Research on the timeline shows MGF expression increases within 2-24 hours after muscle injury, coinciding with the influx of inflammatory cells. This early expression is why MGF is considered a "first responder" to muscle damage. By the time mature IGF-1 and other long-term growth signals ramp up, MGF has already done its job of activating the satellite cell pool.

This rapid on-off pattern makes sense from a biological perspective. You don't want satellite cells proliferating indefinitely—you want a controlled burst of expansion followed by differentiation and fusion. MGF provides that initial burst, then gets out of the way.

Signaling Pathways

At the molecular level, MGF activates different signaling pathways than mature IGF-1. Studies show MGF activates ERK1/2 phosphorylation but not AKT phosphorylation in muscle cells—a signaling pattern associated with proliferation rather than differentiation.

This selective pathway activation explains why MGF promotes satellite cell expansion while blocking their terminal differentiation. The cell receives a "grow more stem cells" signal without the accompanying "mature into muscle" signal that would normally follow IGF-1 receptor activation.

Research Evidence

Most MGF research exists in animal models and cell culture studies. Human clinical trials remain notably absent from the literature.

Muscle Regeneration Studies

A 2019 study published in Frontiers in Physiology investigated whether MGF could rescue impaired muscle regeneration caused by macrophage depletion in mice. Macrophages are immune cells that play a critical role in clearing cellular debris and supporting tissue repair.

When researchers depleted macrophages, muscle regeneration was severely impaired. But when they injected MGF, it partially ameliorated this impairment. The mechanism appeared to involve modulation of inflammatory cytokines, oxidative stress factors, chemokines, and matrix metalloproteinases.

A separate study examining MGF overexpression in muscle injury found that increasing MGF levels modulated inflammatory cytokine expression and improved macrophage resolution—suggesting MGF plays immunomodulatory functions distinct from its role in satellite cell activation.

These findings point to MGF having multiple roles in muscle repair beyond just activating stem cells. It appears to coordinate the inflammatory response, regulate immune cell activity, and modulate the tissue environment to support regeneration.

Neuroprotection Research

MGF's potential extends beyond muscle tissue. A 2005 study in The FASEB Journal demonstrated strong neuroprotective effects in brain ischemia models.

In a gerbil model of transient brain ischemia, treatment with synthetic MGF C-terminal peptide provided significant protection to vulnerable neurons. Remarkably, the protective effect was as potent as full-length IGF-1 but lasted significantly longer.

Even more interesting: ischemia triggered increased expression of endogenous MGF in ischemia-resistant hippocampal neurons, suggesting the brain naturally upregulates MGF as a protective response to injury.

Like its muscle effects, MGF's neuroprotective action was independent of the IGF-1 receptor, indicating a distinct mechanism. This has led researchers to propose MGF as a potential therapeutic for stroke and traumatic brain injury, though clinical development remains entirely preclinical.

Cartilage and Osteoarthritis

MGF is highly expressed in chondrocytes (cartilage cells), particularly in damaged cartilage from trauma or osteoarthritis. Research examining MGF's role in cartilage found it plays important roles in chondrocyte proliferation, migration, differentiation, inflammatory responses, and apoptosis.

In a rabbit knee joint osteoarthritis model, researchers found that MGF treatment at concentrations of 0.1-10 μg/ml inhibited cartilage degeneration after two weeks. The mechanism appeared to involve inhibiting pathological apoptosis of chondrocytes while promoting proliferation, migration, and matrix synthesis.

However, the story is complicated. High MGF expression correlates with osteoarthritis severity, raising questions about whether MGF is protective or potentially pathogenic in chronic joint disease. The same factor that helps acute repair might contribute to problems when chronically elevated—a pattern seen with many inflammatory mediators.

Growth Plate Development

Research on growth plate chondrocytes found that MGF protects against mechanical overload-induced damage and promotes chondrocyte migration through the RhoA/YAP signaling pathway. This suggests MGF plays a role in skeletal development and bone growth, not just muscle repair.

The finding that MGF responds to mechanical signals in bone and cartilage, just as it does in muscle, points to a broader biological principle: MGF may be part of a general mechanotransduction system that allows tissues to sense and respond to physical stress.

The Aging Question

A study on human muscle progenitor cells examined whether MGF's effects differ with age. Researchers isolated satellite cells from neonatal, young adult, and old adult muscle tissue, then treated them with MGF-E peptide.

MGF significantly increased the proliferative lifespan and delayed senescence of satellite cells from neonatal and young adult muscle. However, it had no apparent effect on satellite cells from old adult muscle.

This age-dependent response suggests that aging may impair the ability of muscle stem cells to respond to MGF signaling. If confirmed, this would have important implications for potential therapeutic use in older populations—the very demographic most likely to benefit from muscle repair therapies.

The Negative Study

Not all MGF research has been positive. A 2013 study published in the American Journal of Physiology specifically tested MGF's effects on myoblasts and primary muscle stem cells and concluded: "Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cells."

The researchers tested various concentrations of synthetic MGF peptide and found no effects on cell proliferation, differentiation, or survival. They questioned whether previous positive results might have been due to experimental artifacts rather than genuine biological activity.

This negative finding highlights an important point: MGF research contains contradictions. Positive effects seen in some studies don't always replicate in others. This inconsistency might reflect differences in peptide synthesis, cell culture conditions, species differences, or genuine variability in MGF responsiveness across experimental systems.

PEG-MGF: The Modified Variant

Native MGF has a half-life of approximately 5-7 minutes. The moment it enters circulation, enzymatic degradation begins breaking it down. This extremely short half-life makes native MGF nearly impossible to use as a therapeutic agent.

What Is PEGylation?

PEGylation is the chemical attachment of polyethylene glycol (PEG) molecules to a peptide or protein. The attached PEG chains act like a molecular shield, protecting the peptide from enzymatic breakdown and extending its circulation time.

For MGF, PEGylation extends the half-life from minutes to approximately 48-72 hours—a roughly 1,000-fold increase that transforms an impractical research compound into something that might theoretically be dosed a few times per week.

Does PEG-MGF Work the Same Way?

A critical question: does adding a large PEG molecule change how MGF interacts with its (still unknown) receptor? The PEG chains are bulky and could potentially interfere with receptor binding or alter which cells the peptide can reach.

Research directly comparing PEG-MGF to native MGF in controlled studies is limited. Most PEG-MGF data comes from anecdotal reports from bodybuilding communities rather than peer-reviewed research. This makes it difficult to determine whether PEG-MGF retains the same biological activity as the natural peptide.

Some researchers have raised concerns that PEGylation might fundamentally alter MGF's function. The E domain that gives MGF its unique properties is small—adding a PEG chain might block its interaction with its native receptor or redirect it to different cellular compartments.

Theoretical Advantages

If PEG-MGF retains MGF's biological activity, the extended half-life would offer several theoretical advantages:

• Sustained satellite cell activation: Rather than a brief pulse, cells would be exposed to MGF signaling over days
• Practical dosing: Two to three injections per week instead of continuous infusion
• Systemic distribution: Longer circulation time might allow MGF to reach tissues beyond the injection site

Theoretical Disadvantages

The natural brief pulse of MGF expression might be biologically important. Chronic exposure to MGF signaling could potentially:

• Prevent proper satellite cell differentiation: Keeping cells in proliferation mode indefinitely
• Disrupt normal repair timing: The sequential expression of MGF, then IGF-1Ea, then other factors might be necessary for proper repair
• Increase tumor risk: Chronic stimulation of stem cell proliferation raises theoretical cancer concerns

Until controlled studies directly compare PEG-MGF to native MGF in relevant models, these remain speculative concerns.

Safety and Side Effects

No published human clinical trials have systematically evaluated MGF or PEG-MGF safety. All available safety information comes from preclinical studies and anecdotal reports.

Animal Study Findings

Animal studies using MGF have generally not reported significant adverse effects at the doses tested. Studies in rodents and other models have administered MGF without obvious toxicity.

However, animal studies typically use short treatment durations measured in weeks, not the months or years a human might use a compound. They also don't capture subtle effects on metabolism, hormones, or long-term tissue health that might appear only with chronic use.

Reported Side Effects

Anecdotal reports from research chemical users describe:

• Injection site reactions: Localized swelling, redness, or discomfort
• Fluid retention: Bloating or edema, particularly in hands and feet
• Joint discomfort: Stiffness or pain, possibly related to fluid retention
• Fatigue: Temporary tiredness following injection
• Numbness: Tingling sensations in extremities

The mechanism behind these effects is unclear. Some might reflect off-target effects, immune responses to synthetic peptides, or contaminants in non-pharmaceutical-grade products.

Hypoglycemia Risk

PEG-MGF may lower blood glucose levels, presenting a risk for individuals with diabetes or those prone to hypoglycemia. The mechanism likely involves MGF's structural similarity to IGF-1, which has insulin-like effects on glucose metabolism.

Anyone using diabetes medications or with blood sugar regulation issues would theoretically face increased risk of dangerous hypoglycemia if exposed to MGF or PEG-MGF.

Cancer Concerns

Any agent that stimulates stem cell proliferation raises theoretical cancer concerns. Cancer is fundamentally a disease of uncontrolled cell proliferation—so factors that tell stem cells to multiply could potentially promote tumor growth.

MGF has been banned by the World Anti-Doping Agency in part due to concerns about potential tumor-promoting activity. However, no published studies have directly demonstrated that MGF causes or promotes cancer. This remains a theoretical risk based on mechanism rather than demonstrated harm.

The natural brief expression of MGF after exercise has occurred throughout human evolution without causing cancer epidemics. But chronic pharmacological exposure to supraphysiological levels is a different question entirely.

Liver and Kidney Considerations

PEG-MGF metabolism relies on liver and kidney function. Individuals with hepatic or renal impairment could experience altered clearance, leading to unpredictable drug levels and potentially increased side effects.

No studies have examined MGF pharmacokinetics in hepatic or renal disease, so appropriate dose adjustments (if any) remain unknown.

Lack of Long-Term Data

The most honest answer to "Is MGF safe?" is "We don't know." No long-term follow-up studies exist. No systematic collection of adverse events has occurred. No dose-response safety studies have been published.

Users of research peptides are essentially conducting uncontrolled self-experiments without safety monitoring, follow-up, or systematic data collection. This creates a data vacuum where anecdotes fill the space that should be occupied by controlled research.

Legal Status and Anti-Doping

MGF and PEG-MGF occupy a complex regulatory space that varies by jurisdiction and context.

WADA Prohibition

The World Anti-Doping Agency (WADA) prohibits MGF under its banned substances list. It falls under the category of growth factors and related peptides that are banned both in and out of competition.

Athletes subject to WADA rules—which includes Olympic athletes and competitors in most professional sports—cannot use MGF or PEG-MGF under any circumstances without risking sanctions, including competition bans.

The 2013 Australian Crime Commission investigation into organized doping identified MGF as one of several performance-enhancing substances being used across multiple professional sports, highlighting its appeal among athletes seeking recovery and muscle growth advantages.

FDA Status

MGF and PEG-MGF are not approved by the U.S. Food and Drug Administration for any medical use. They are not prescribed medications. No pharmaceutical company has submitted a New Drug Application for MGF in any formulation.

This means:

• No quality control: Products sold online have no guaranteed purity, potency, or sterility
• No prescribing information: Appropriate doses, indications, and contraindications are unknown
• No adverse event monitoring: Problems that occur aren't systematically tracked
• Legal gray area: Possession and use may not be explicitly illegal, but sale for human consumption is not permitted

Research Chemical Market

MGF and PEG-MGF are available from research chemical suppliers, typically labeled "for research purposes only" or "not for human consumption." This labeling is a legal strategy to avoid FDA regulation of drugs intended for human use.

Despite these disclaimers, these products are widely understood to be purchased for self-administration. The research chemical market operates in regulatory gray zones, selling compounds that haven't been approved as drugs but aren't explicitly controlled substances.

Quality varies enormously. Some suppliers may provide relatively pure peptides accurately dosed, while others sell mislabeled, contaminated, or completely inert products. Without independent testing, buyers have no way to verify what they're actually receiving.

International Variations

Some countries regulate peptides more strictly than others. In Australia, for example, MGF is illegal to possess without a prescription. European countries vary in their approaches. Some classify research peptides as medicines requiring prescriptions; others allow them to be sold legally as research chemicals.

Anyone considering obtaining MGF or PEG-MGF should research their local laws carefully. Possession might be legal in some jurisdictions but illegal in others, with potentially serious consequences for violations.

Frequently Asked Questions

What is MGF peptide used for?

MGF is not used for any approved medical purpose. It remains in preclinical research investigating potential applications in muscle repair, nerve regeneration, cartilage healing, and other tissue regeneration contexts. Athletes and bodybuilders have used research chemical versions, typically seeking accelerated muscle recovery after training, but this use lacks clinical validation or safety monitoring.

How does MGF differ from regular IGF-1?

MGF is a splice variant of the IGF-1 gene with a unique E domain that gives it different properties. Unlike systemic IGF-1 produced by the liver, MGF is made locally in muscle tissue in response to mechanical stress. It doesn't bind to the IGF-1 receptor but works through an unknown alternative receptor. MGF promotes satellite cell proliferation while blocking differentiation, whereas mature IGF-1 primarily promotes differentiation. The two work sequentially—MGF early after damage, IGF-1 later—to coordinate muscle repair.

What is PEG-MGF and how is it different from MGF?

PEG-MGF is MGF with polyethylene glycol chains chemically attached. This modification extends the half-life from 5-7 minutes to 48-72 hours, making it practical to dose intermittently rather than requiring continuous administration. However, PEGylation may alter how MGF interacts with its receptor or which tissues it reaches. Direct comparisons of PEG-MGF to native MGF in controlled studies are limited, so whether they produce identical biological effects remains unclear.

Does MGF build muscle?

MGF activates satellite cells, which are necessary for muscle growth and repair. In animal models, MGF increases satellite cell numbers and supports muscle regeneration after damage. However, no human clinical trials have tested whether MGF actually increases muscle mass or strength in people. The natural pulse of MGF after exercise is part of normal muscle adaptation, but whether pharmacological MGF produces additional muscle growth beyond what training alone provides has not been demonstrated in controlled research.

Is MGF safe?

The safety profile of MGF and PEG-MGF in humans is unknown. No systematic clinical trials have evaluated safety, and all available information comes from animal studies and anecdotal reports. Reported side effects include injection site reactions, fluid retention, joint discomfort, and fatigue. Theoretical concerns include hypoglycemia risk, potential cancer promotion through chronic stem cell stimulation, and unknown long-term effects. Anyone considering MGF would be participating in an uncontrolled self-experiment without safety monitoring.

Why is MGF banned by WADA?

WADA bans MGF because it could theoretically provide performance advantages by accelerating muscle repair and recovery. Its classification as a growth factor, its role in satellite cell activation, and its potential to support muscle regeneration make it a performance-enhancing substance. The ban also reflects concerns about safety, particularly potential tumor-promoting activity. Athletes are prohibited from using MGF both in competition and during training.

Can MGF help with injuries?

MGF shows promise in preclinical models of muscle injury, nerve damage, and cartilage degeneration. Animal studies demonstrate that MGF can support tissue repair in various contexts. However, whether these preclinical findings translate to meaningful benefits for human injuries remains completely untested. The gap between animal model results and human clinical efficacy is substantial—many compounds that work in animals fail in human trials.

What's the difference between MGF-24 and the E peptide?

The MGF E peptide refers to the unique C-terminal region created by the alternative splicing that produces MGF. This E domain is approximately 24 amino acids long in its biologically active form. When people refer to MGF-24, they're typically talking about a synthetic version of this E peptide region. Research has shown this E peptide fragment retains biological activity even when separated from the rest of the IGF-1 molecule, suggesting it contains the key functional domain responsible for MGF's unique effects.

Does MGF work for older adults?

Research on satellite cells from different age groups found that MGF effectively activated satellite cells from neonatal and young adult muscle but had no apparent effect on satellite cells from old adult muscle. This suggests aging may impair the ability of muscle stem cells to respond to MGF signaling. If this age-dependent response holds true in humans, MGF might be less effective—or ineffective—in older populations who would theoretically benefit most from muscle repair therapies.

Bottom Line

Mechano Growth Factor represents a fascinating piece of the muscle repair puzzle. Its rapid expression after mechanical stress, unique E domain structure, and ability to activate satellite cells without promoting their differentiation point to a specialized role as an injury response initiator. The breadth of effects seen in preclinical research—spanning muscle, nerve, bone, and cartilage—suggests MGF might be part of a general mechanotransduction system that helps tissues respond to physical stress.

But interesting science doesn't equal proven therapy. MGF research remains almost entirely preclinical. No human clinical trials have tested whether it actually improves muscle growth, accelerates recovery, heals injuries, or provides any of the benefits its mechanism suggests it might.

The development of PEG-MGF addressed one practical barrier—the extremely short half-life—but introduced new questions about whether the modified version retains the biological activity of the natural peptide. The research chemical market has embraced PEG-MGF despite this uncertainty, creating a situation where human use is happening outside any controlled research framework.

For anyone considering MGF or PEG-MGF, the honest assessment is this: you would be using a compound with no established human safety data, no proven efficacy, no quality control, questionable legality depending on jurisdiction, and explicit prohibition if you're a competitive athlete. The gap between "interesting preclinical data" and "safe and effective therapy" is vast—and MGF hasn't bridged it.

The more productive approach is to recognize that your body already produces MGF naturally in response to exercise. Every hard training session triggers the same biological cascade that MGF research is trying to understand. Sleep, nutrition, recovery practices, and appropriate training stimulus already optimize the MGF response without the risks of injecting poorly characterized peptides from unregulated suppliers.

If you have a specific medical condition where tissue repair is impaired—muscle dystrophy, chronic injury, degenerative joint disease—working with a physician to address the underlying problem makes more sense than self-experimenting with research peptides. When MGF or related compounds eventually progress through proper clinical development (if they do), they'll be available with known dosing, established safety monitoring, and demonstrated efficacy rather than speculation and anecdote.

Disclaimer

This article is for educational purposes only and does not constitute medical advice. MGF and PEG-MGF are not FDA-approved medications and should not be used outside of approved clinical trials. The information presented here is based on preclinical research and does not establish safety or efficacy in humans. Anyone considering peptide therapy should consult with a qualified healthcare provider. Competitive athletes should note that MGF is prohibited by the World Anti-Doping Agency.

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