Legit Growth Hormone Peptides , Human Growth Steroid GDF-8 / Myostatin

Myostatin
Myostatin (also known as growth differentiation factor 8, abbreviated GDF-8) is a myokine, a protein produced and released by myocytes that acts on muscle cells autocrine function to inhibit myogenesis: muscle cell growth and differentiation. In humans it is encoded by the MSTN gene. Myostatin is a secreted growth differentiation factor that is a member of the TGF beta protein family.
Animals either lacking myostatin or treated with substances that block the activity of myostatin have significantly more muscle mass. Furthermore, individuals who have mutations in both copies of the myostatin gene have significantly more muscle mass and are stronger than normal. Blocking the activity of myostatin may have therapeutic application in treating muscle wasting diseases such as muscular dystrophy.

Discovery and sequencing
The gene encoding myostatin was discovered in 1997 by geneticists Se-Jin Lee and Alexandra McPherron who produced a strain of mutant mice that lack the gene. These myostatin "knockout" mice have approximately twice as much muscle as normal mice. These mice were subsequently named "mighty mice".
Naturally occurring deficiencies of myostatin have been identified in cattle by Ravi Kambadur, whippets, and humans; in each e the result is a dramatic increase in muscle mass. A mutation in the 3 UTR of the myostatin gene in Texel sheep creates target sites for the microRNAs miR-1 and miR-206. This is likely to cause the muscular phenotype of this breed of sheep.

Structure and mechanism of action
Human myostatin consists of two identical subunits, each consisting of 109 (NCBI database claims human myostatin is 375 residues long) amino acid residues. Its total molecular weight is 25.0 kDa. The protein is inactive until a protease cleaves the NH2-terminal, or "pro-domain" portion of the molecule, resulting in the active COOH-terminal dimer. Myostatin binds to the activin type II receptor, resulting in a recruitment of either coreceptor Alk-3 or Alk-4. This coreceptor then initiates a cell signaling cade in the muscle, which includes the activation of transcription factors in the SMAD family - SMAD2 and SMAD3. {{|}}These factors then induce myostatin-specific gene regulation. When applied to myoblasts, myostatin inhibits their differentiation into mature muscle fibers.
Myostatin also inhibits Akt, a kinase that is sufficient to cause muscle hypertrophy, in part through the activation of protein synthesis. However, Akt is not responsible for all of the observed muscle hyperthrophic effects which are mediated by myostatin inhibition[8] Thus myostatin acts in two ways: by inhibiting muscle differentiation, and by inhibiting Akt-induced protein synthesis.

Clinical significance
Mutations
A technique for detecting mutations in myostatin variants has been developed. Mutations that reduce the production of functional myostatin lead to an overgrowth of muscle tissue. Myostatin-related muscle hypertrophy has an incomplete autosomal dominance pattern of inheritance. People with a mutation in both copies of the MSTN gene in each cell (homozygotes) have significantly increased muscle mass and strength. People with a mutation in one copy of the MSTN gene in each cell (heterozygotes) have increased muscle bulk, but to a lesser degree.
In 2004, a German boy was diagnosed with a mutation in both copies of the myostatin-producing gene, making him considerably stronger than his peers. His mother has a mutation in one copy of the gene. An American boy born in 2005 was diagnosed with a clinically similar condition but with a somewhat different cause: his body produces a normal level of functional myostatin; but, because he is stronger and more muscular than most others his age, it is believed that a defect in his myostatin receptors prevents his muscle cells from responding normally to myostatin. He appeared on the television show, Worlds Strongest Toddler.

Therapeutic potential
Further research into myostatin and the myostatin gene may lead to therapies for muscular dystrophy. The idea is to introduce substances that block myostatin. A monoclonal antibody specific to myostatin increases muscle mass in mice and monkeys.

A two-week treatment of normal mice with soluble activin type IIB receptor, a molecule that is normally attached to cells and binds to myostatin, leads to a significantly increased muscle mass (up to 60%).[33] It is thought that binding of myostatin to the soluble activin receptor prevents it from interacting with the cell-bound receptors.

It remains unclear as to whether long-term treatment of muscular dystrophy with myostatin inhibitors is beneficial, as the depletion of muscle stem cells could worsen the disease later on. As of 2012, no myostatin-inhibiting drugs for humans are on the market. An antibody genetically engineered to neutralize myostatin, stamulumab, which was under development by pharmaceutical company Wyeth., is no longer under development. Some athletes, eager to get their hands on such drugs, turn to the internet where fake "myostatin blockers" are being sold.

Myostatin levels are effectively decreased by creatine supplementation.

Gene doping
See Gene doping
Inhibition of myostatin leads to muscle hyperplasia and hypertrophy. Myostatin inhibitors can improve athletic performance and therefore there is a concern these inhibitors might be abused in the field of sports. However, studies in mice suggest that myostatin inhibition does not directly increase the strength of individual muscle fibers.

Polypeptide: