Muscle wasting and myostatin

Question 1

What is the relation of grip strength with forearm diameter?

Answer 1

highly correlated

Question 2

What does muscle growth rely on?

Answer 2

• mechanical stimulus (exercise)
• endocrine factors (testosterone, insulin, IGF-1, myostatin, follistatin)
• essential amino acids

Question 3

Specifically, how would the signalling and activation of satellite cells work like?

Answer 3

1. Cytokines, growth factors, integrin signalling - they bind to surface receptors to produce transcription factors.
2. The transcription factors and external androgens and glucocorticoids affect the nucleus. Affects IGF-1/MGF, myostatin, mRNA, rRNA.
3. Translation initiation of ribosomal, regulatory and myofibrillar proteins take place. Due to factors like the mTOR, activated by the external IGF-1/MGF and insulin, binding to surface receptors
4. Satellite cells are activated by the binding of IGF-1/MGF, myostatin and growth factors binding to surface receptors

Question 4

What can cause muscle atrophy?

Answer 4

1. Myostatin binds to ARIIB receptor on sruface
2. This activates precursor activity involving the I-Smad, co-Smad and R-Smad
3. MyoD/myogenin is inhibited and this reduces differentiation and cause atrophy
4. Myostatin binding inhibits AKT pathway, hence inhibiting FoxO1.. this eventually increases degradation and cause atrophy

Question 5

What can cause muscle hypertrophy?

Answer 5

1. IGF-1 binds to surface receptor
2. Activates AKT which activates mTOR
3. Eventually increasing synthesis
4. Causing muscle hypertrophy

Question 6

What can be said of satellite cells and hypertrophy?

Answer 6

• Muscle fibres are permanently differentiated so they cannot add new nuceli in times of hypertrophy
• myonuclear number increases during hypertrophy to maintain myonuclear domain

Question 7

Can muscle memory last into older age? What type of stimuli could lead to this?

Answer 7

Yes. Anabolic stimuli

Question 8

What 4 factors describe ageing?

Answer 8

1. Universal (all species)
2. Intrinsic (causes are endogenous)
3. Progressive (the changes occurring)
4. Deleterious (phenomenon associated are ‘bad’)

Question 9

What are the 2 theories for reasons we age?

Answer 9

• programmed theory

- damage/error theory

Question 10

What is included in programmed theory?

Answer 10

• programmed longitivity
• endocrine theory
• immunological

Question 11

What is included in the damage/errors theory?

Answer 11

• wear and tear
• rate of living
• cross-linking
• free radicals
• DNA damage

Question 12

TRUE OR FALSE. Ageing is not homogenous.

Answer 12

TRUE

Question 13

What is the endocrine hypothesis investigated in mice?

Answer 13

• impairs hypertrophy and recovery from injury in vitro

- cause an ageing phenotype in younger mice

Question 14

Does resistance exercise increase basal testosterone in older males?

Answer 14

No

Question 15

Can we use complex interactions of endocrine factors to predict function with ageing?

Answer 15

Yes (but one marker may not be enough)