Lecture 3 | (Inflammation &) Muscle Mechanisms II, III & IV

Question 1

Serotonin and food intake

Answer 1

Inhibits NPY/AgRP nuclei that normally stimulate food intake.
Stimulates POMC/CART nuclei that inhibit food intake.
Serotonin is upregulated in inflammation (cachexia)

Question 2

Methods to measure protein synthesis

Answer 2

• Radioactive isotopes
• Stable isotopes -> usually used in humans
• SUnSET
• Biomarkers (24hr. urinary creatine)

Question 3

SUnSET

Answer 3

Puromycin (= antibiotic) resembles tyrosine-tRNA
Incorporated by ribosomes > stops translation > uncomplete proteins > measure with puromycin specific antibodies.
ONLY for cells and animal studies!

Question 4

Goal mTOR pathway

Answer 4

Regulated pathway for muscle protein synthesis

AKT inhibits FOXO and therefore the proteosome pathway

Question 5

Steps mTOR pathway

Answer 5

1. Activation by IGF-1 and/or sufficient energy (ATP, glucose, AA)
2. Phosphorylation of AKT
3. Phosphorylation of mTOR
4. mTOR phosphorylates 4EBP1 and 70S6K (= elongation factor binding proteins)
5. Free elF4E and elF3 (= elongation factors) form initation complex to start translation.

Question 6

Goal autophagy

Answer 6

Degradation of damaged or dysfunctional proteins (cell parts or organelles)
Important to maintain functionality of cells.

Question 7

Steps autophagy

Answer 7

Nucleation - Formation of phagophore membrane
Elongation - Elongation of phagophore (Atg5-Atg12 & LC3) to form autophagosome
Fusion - Fusion of autophagosome with lysosome to form autophagolysosome
Degradation - degradation of proteins.

Question 8

mTOR & autophagy

Answer 8

mTOR inhibits autophagy by inhibiting ULK1

Question 9

Microautophagy

Answer 9

No formation of autophagosome but direct fusion of proteins with lysosome

Question 10

Goal regeneration

Answer 10

Formation of new muscle cells

Question 11

Steps regeneration

Answer 11

1. Quiescent satellite cells (PAX7+MYF5-)
2. Committed satellite cell (PAX7+MYF5+)
3. Proliferation (PAX7+MYF5+MYOD+)
4. Differentiation (PAX7-MYF5+MYOD+myogenin+)
5. Fusion with existing muscle fibers

Question 12

Regeneration in cachexia

Answer 12

Inflammation prevents downregulation of PAX7. Therefore, the cell proliferate but do not differentiate into myocytes (no fusion).