Adipogenesis

Question 1

Brown adipose tissue and white adipose tissue are originated from __________ ____________.

Answer 1

Distinct progenitors

Question 2

Where is brown adipose tissue derived from?

Answer 2

Derived from paraxial mesoderm and Myf5+ progenitors (same as skeletal muscle)

Question 3

Where is white adipose tissue derived from?

Answer 3

Derived from lateral mesoderm and Myf- progenitors

Question 4

What does Myf5 stand for? What does it regulate?

Answer 4

• Myf5 = Myogenic factor 5
• Regulates muscle differentiation or myogenesis

Question 5

What is adipogenesis?

Answer 5

Adipogenesis = the formation of adipocytes (fat cells) from stem cells.

Question 6

Describe the FIRST step of adipogenesis.

Answer 6

1) Mesenchymal stem cells go through determination, which is where stem cells become specialized (also known as precursor cells). After determination, the mesenchymal stem cells turn into adipoblast.

Question 7

Describe the SECOND step of adipogenesis.

Answer 7

2) The adipoblast goes through commitment, which is a process during which stem or precursory cells set their fate and become a preadipocyte.

Question 8

Describe the THIRD step of adipogenesis.

Answer 8

3) The preadipocyte goes through proliferation, which expands the cell population and increases the number of preadipocytes.

Question 9

Describe the FOURTH step of adipogenesis.

Answer 9

4) The preadipocytes go through differentiation and become “developing adipocytes,” which are a few small lipid droplets that express some lipogenic enzymes.

Question 10

Describe the FIFTH step of adipogenesis.

Answer 10

5) The developing adipocytes then go through maturation and become mature adipocytes. Mature adipocytes are large lipid droplets, express abundant lipogenic enzymes, and have an enlarged cell size.

Question 11

What are mesenchymal stem cells (MSCs)?

Answer 11

• are multipotent stem cells
• can differentiate into adipocytes, osteoblasts, chondrocytes, and myoblasts.

Question 12

What are adipoblasts?

Answer 12

• precursor of preadipocytes
• does not contain lipogenic enzymes or lipid droplets

Question 13

What are preadipocytes?

Answer 13

• fat cell progenitors with only the potential to differentiate into adipocytes.
• low lipogenic gene expression
• no lipid droplets

Question 14

Adipocytes collect together to form ______ that eventually develop into larger ________.

Answer 14

Lobules, lobes

Question 15

Lobules of fat are separated and supported by _________ connective tissue called __________.

Answer 15

loose, septa

Question 16

True or False: Septa carries blood vessels and neurons to adipose tissue.

Answer 16

FALSE - Septa carries blood vessels and NERVES to adipose tissue.

Question 17

For the molecular regulation of adipogenesis, there are “master” ____________ factors for adipocyte differentiation.

Answer 17

Transcription

Question 18

What are the “master” transcription factors for adipocyte differentiation?

Answer 18

• CCAAT/Enhancer Binding Proteins (C/EBPs)
• Peroximose Proliferator-Activated Receptors y (PPARy)

Question 19

What is lipogenesis?

Answer 19

Lipogenesis = synthesis or absorption of fatty acids (FA) from blood and subsequent esterification to form triacylglycerol (TAG).

Question 20

What is lipogenesis efficient at?

Answer 20

Very efficient at storing fat

Question 21

What is lipolysis?

Answer 21

Lipolysis = release of fatty acids from the adipocytes, which involves the breakdown of triacylglycerols (TAG) within adipocytes and results in diffusion of fatty acids across cell membranes.

Question 22

What is the formula for calculating the net lipid accretion rate?

Answer 22

Lipogenesis rate minus lipolysis rate

Question 23

What do triacylglycerols do?

Answer 23

• Stores fat as TAGs
• Accumulates FAs to produce TAGs by:
  1) FAS from blood, which comes from diet and hepatic synthesis.
  2) De novo (from new) synthesis of FAs

Question 24

How does diet contribute to lipogenesis?

1. TAGs (From the diet) are transported from the small intestine attached to ________. These structures are called ____________.
2. Endothelial cell walls of capillaries contain the enzyme _______ that hydrolyses TAgs in chylomicrons to glycerol and free fatty acids for uptake by adipocytes.

Answer 24

1. lipoproteins, chylomicrons
2. lipoprotein lipase

Question 25

What are the locations where diet-contributed lipogenesis occurs for cattle, sheep, and pigs? What about for avian species?

Answer 25

- For cattle, sheep, and pigs = occurs mostly in the adipose tissue. - For avian species = occurs mostly in the liver

Question 26

A component of lipogenesis is the dietary fatty acids used to assemble TAGs in adipocytes. What's the difference between ruminants and monogastrics?

Answer 26

- For ruminants, rumen microbes modify FA before absorption - therefore, fatty acids in feed and adipose are DIFFERENT. - For monogastrics, unmodified FAs absorbed from the diet enter the blood stream - therefore, FA in feed and adipose is SIMILAR.

Question 27

A component of lipogenesis is the substrate for de novo synthesis of fatty acids in adipocytes. What's the difference between ruminants and monogastrics?

Answer 27

- For ruminants, they have acetate. - For monogastrics, they have glucose.

Question 28

Lipolysis is the breakdown of TAG within adipocytes and results in diffusion of FA across the cell membrane. What is it controlled and stimulated by?

Answer 28

- Controlled by hormone-sensitive lipases. - Stimulated by hormones with catabolic actions.

Question 29

For the regulation of lipogenesis and lipolysis, ________, _________, and ___________ trigger to increase cAMP, which results in ________ lipolysis and _________ lipogenesis.

Answer 29

Starvation, exercise, catecholamines, increasing, decreasing

Question 30

In lipolysis, fatty acids are targeted to various processes including...

Answer 30

- Catabolized for energy - Used for membrane synthesis

Question 31

For the regulation of lipogenesis and lipolysis, ________, and _________ trigger to decrease cAMP, which results in ________ lipolysis and _________ lipogenesis.

Answer 31

Insulin, feeding, decreasing, increasing