Lecture 8

Question 1

2 types of dyslipidemias.

Answer 1

Acquired (requires an overload) and genetic.

Question 2

How can we observe the metabolism of cholesterol in fibroblasts?

Answer 2

Through the use of radioactive tracers.

Question 3

Biosynthesis of cholesterol begins with what molecule?

Answer 3

Acetyl-CoA.

Question 4

HMGR activity in normal and fibroblast cells.

Answer 4

Looking at HMG-CoA reductase. When LDL is removed, normal cells show an increase in HMG-CoA reductase (increase in cholesterol synthesis); FH cells always have a high level of HMG-CoA reductase activity (the cell cannot sense things properly).

Question 5

FH is caused by the absence of LDL receptor (LDLR) function.

Answer 5

4 classes of LDLR gene variations: Class I (variation in the protein itself), Class II (protein can be made, but transport from ER to Golgi is defected so it is degraded), Class III (the receptor is there, but cannot bind LDL), Class IV (internalization of bound LDL is defective).

Question 6

LDLR is…

Answer 6

A multidomain protein.

Question 7

Protein responsible for moving cholesterol to the membrane in reverse cholesterol transport.

Answer 7

ABCA1.

Question 8

Sterol response element (SRE).

Answer 8

DNA sequence in the promoter region of genes whose expression is increased by cholesterol depletion and decreased by cholesterol excess. Examples: HMG-CoA reductase and LDLR genes.

Question 9

Adding SRE to a gene.

Answer 9

The gene now becomes sensitive to cholesterol.

Question 10

Regulatory element.

Answer 10

Allows a gene to respond to a specific condition.

Question 11

SREBP (SRE binding protein).

Answer 11

A protein that binds to the SRE sequence and stimulates transcription. Binding is dictated by concentration of unesterified cholesterol within the cell.

Question 12

SREBPs are activated in response to…

Answer 12

Decreased cellular cholesterol concentration.

Question 13

SREBP synthesis.

Answer 13

Synthesized as a membrane-bound precursor protein that must be proteolytically processed to release the DNA-binding domain. It is a multi-domain protein with a DNA binding domain.

Question 14

Proteolysis of SREBP.

Answer 14

Allows it to leave the membrane, go to the nucleus, and bind to DNA.

Question 15

Domains of SREBP.

Answer 15

Transmembrane regions, cytoplasmic regions, and the ER luminal domain.

Question 16

3 isoforms of SREBPs in mammalian cells.

Answer 16

SREBP-1a and SREBP-1c (encoded by the same gene, result of alternate splicing), and SREBP-2 (encoded by a different gene).

Question 17

SREBP-1a.

Answer 17

Activator of all SREBP responsive genes; genes containing an SRE region in the promoter must answer to SREBP-1a. Strongest activator of the SREBPs.

Question 18

SREBP-1c.

Answer 18

Regulates genes involved in fatty acid synthesis; it is a weaker activator than SREBP-1a.

Question 19

SREBP-2.

Answer 19

Preferentially regulates genes involved in cholesterol synthesis; weaker activator than SREBP-1a.

Question 20

SCAP.

Answer 20

SREBP cleavage activating protein.

Question 21

Insigs (insulin induced genes).

Answer 21

ER resident proteins.

Question 22

S1P.

Answer 22

A protease within the Golgi complex.

Question 23

mTORC1.

Answer 23

A master regulator; it can sense nutrient concentration, energy status, and growth factors.

Question 24

PCSK9 inhibitors.

Answer 24

PCSK9 is an enzyme. This class of cholesterol-lowering drugs are injectables (biologics). Based on monoclonal antibodies against PCSK9.

Question 25

Which PCSK9 inhibitor was withdrawn from the market?

Answer 25

Bococizumab due to economic reasons (did not make enough money).

Question 26

What are PCSK6 inhibitors used in conjunction with?

Answer 26

Dietary and lifestyle changes.

Question 27

Frequency of PCSK9 inhibitor administration.

Answer 27

Once every 2 weeks or once a month.

Question 28

PCSK9 (proprotein convertase subtilisin/kexin type 9).

Answer 28

It is a protein secrete dmainly by the liver; expression is regulated by SREBP-2.

Question 29

Which class of SREBP regulates expression of PCSK9?

Answer 29

SREBP-2.

Question 30

Hypercholesterolemia and PCSK9.

Answer 30

Gain-of-fucntion variants of PCSK9.

Question 31

Hypocholesterolemia of PCSK9.

Answer 31

Loss-of-function variants of PCSK9.

Question 32

Effects of PCSK9 on LDLR function.

Answer 32

PCSK9 passes through the ER to the Golgi and is secreted. It then binds to the LDL receptor along with the LDL particle.

Question 33

LDL receptor in the absence of PCSK9.

Answer 33

Much more recycling of LDLR.

Question 34

Inhibition of PCSK9 pathway.

Answer 34

More LDL receptors are present in the liver (not recycled), which allows the liver to dispose of more cholesterol.

Question 35

Which type of cells makes PCSK9?

Answer 35

Mainly liver cells.