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An experimental therapy aims to maximize muscle mass by blocking the pathways that restrict muscle growth. Which of the following statements correctly describes how myostatin causes muscle breakdown, and the physiological effect of blocking these pathways?

IGF-1 signalling activates Smad2/3 to degrade muscle; consequently, blocking Myostatin and Activin A in combination yields only an 18% increase in muscle mass.

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Myostatin signalling inhibits ActRIIA/IIB and ALK4 receptors to prevent muscle degradation; consequently, blocking both Activin B and Myostatin leads to severe muscle wasting and a 156% decrease in mass.

❌

Myostatin signalling activates Akt to directly turn on protein synthesis; consequently, blocking Myostatin alone is the most effective therapy, yielding a 117% increase in muscle mass.

❌

Myostatin signalling activates Smad2/3, which inhibits the Akt pathway to allow FOXO3a-induced protein degradation; consequently, blocking both Myostatin and Activin B together yields a synergistic 156% increase in muscle mass.

✅

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