Lecture 12.2: Paper 4 – Prioritization of Skeletal Muscle Growth for Emergence from Hibernation

Question 1

What is summer euthermy?

Answer 1

temperature is kept constant

• anabolism and body fat reserve

Question 2

What is winter heterothermy?

Answer 2

temperature goes up and down

• catabolism – used up fuel that has been reserved

Question 3

What did the authors of this paper want to know?

Answer 3

want to know what occurs to muscle overall during the winter time, and whether or not there is a time difference (is everything consistent throughout the hibernation season)

• checked muscle volume
• checked muscle mass
• looked at some individual cross-section and density of muscle cells to see what occurs at the cellular level

Question 4

What were the overall results of this study?

Answer 4

• during the first half of winter there is a decrease in muscle volume and mass
• during the second half of winter, it goes back
• some muscles were steady throughout the whole hibernation season
• compared what happens in muscle to liver and kidney to see if those organs are also going through the same process (increasing or decreasing volume)
• overall results suggest that there is a difference between early part of hibernation season compared to the late part of hibernation season for muscle modeling
• concluded that this is in preparation for getting back to the active season

Question 5

What is an annual cycle?

Answer 5

• active period: growth, reproduction, and accumulating metabolic fuel
• hibernation: inactive, fasting, reduced metabolic rate and Tb

Question 6

What do tissues need to cope with?

Answer 6

tissues need to cope with extended period of inactivity

• the study of the coping mechanisms have potential for translation to medicine in areas such as disuse atrophy in bone, muscle, and gut, body weight regulation, and ischemia-reperfusion injury

Question 7

What are the two research questions?

Answer 7

1. Are protein synthesis rates a function of time within the winter fast?

• know that muscle volume and mass was changing differently in early vs. late season – possibly explained by differences in protein synthesis based on previous research

2. Are there potentially differing muscle maintenance strategies in early versus late winter, and immediately in advance of spring emergence?

Question 8

Figure 1: Annual Cycle in Tissue Size

Answer 8

whole mass decreases during hibernation season, and goes back during active season

Question 9

Figure 2: Skeletal Muscle Mass

Answer 9

• whole body mass decreases during hibernation
• upper hindlimb muscles (rectus femoris, biceps brachii, gastrocnemius, soleus) showed increase in first half of hibernation, then decrease in second half of hibernation
• soleus muscle stayed constant

Question 10

Figure 3: Stability in Myocyte Size and Density Across Hibernation

Answer 10

• no evidence of over-winter atrophy of individual myocytes in any muscle examined

Question 11

Figure 4: Protein Synthesis is Differentially Regulated Across Hibernation

Answer 11

• found that protein synthesis will significantly decrease during early hibernation season, and would significantly increase during the second half of hibernation – could explain what they saw in muscle volume and mass
• compared this to other tissues in the body (heart, liver, intestine) – stayed relatively similar across hibernation season

Question 12

Figure 5: Body Composition is Stable Until Late Winter

Answer 12

• lean mass is more constant than fat mass
• towards the end of hibernation (late winter), increased contribution of lean or protein tissue to overall body composition, while fat content declined – fat tissue is being consumed by the body as a fuel, whereas protein and lean tissue are being kept