Question

For up to 3 extra credit points Use MIM or other sources on the Internet to look up the following proteins that affect cardiovascular health and explain what the proteins do: apolipoprotein E; LDL receptor; apolipoprotein A; angiotensinogen; beta-2 adrenergic receptor; toll-like receptor; C-reactive protein.

Answer 1

Answer: A number of proteins are known to play a major role in cardiovascular health.

1. Apolipoprotein E: It is a transport protein involved in the transport od lipids, vitamins and cholestrol in to the blood through lymph system. It belongs to the family of apolipoproteins (Fat-binding proteins) and is known to paly a major role in the fat metabolism in the body and implicated in cardiovascular disease. In the blood, this protein binds to several lipoprotein classes such as chylomicrons, high density lipoproteins (HDL), very low density lipoproteins (VLDL), low density lipoproteins (LDL). Increased levles of LDL-cholesterol leads to atherosclerosis that is responsible for development of cardiovascular diseases. This protein clears chlomicrons, LDL and VLDL from the blood through it interaction with LDL receptors that are involved in the catabolism of triacylglycide-rich lipoproteins and hence decreases plasma cholestrol and triacylglyceride levels. Defects in this protein causes a condition called as type III hyperlipoproteinemia (increased plasma and triglycerides).

2. LDL receptor: Low density lipoprotein (LDL) receptor is a protein that mediated the endocytosis of LDL-cholesterol attached to apolipoproteins (Apo B100 and ApoE). By clearing the LDL-cholesterol from the blood, this protein maintains the healthy levels of LDL in the plasma and hence prevents cardiovascular diseases.

3. Apolipoprotein A: It is a protein involved in lipid metabolism and is implicated in cardiovascular diseases. This protein binds to HDL cholesterol and helps in the efflux of fat molecules present within the cells of blood (Macrophages) to LDL particles or liver for excretion. In this way, this protein play a major role in reducing the cardiovascular disease risk.

4. Angiotensinogen: It is an alpha-globulin protein and is a precursor of angiotensin proteins. This protein is synthesied in the liver. Renin is an enzyme that acts on angiotensinogen and produce angiotensin I protein. This protein play a major role in vasoconstriction and increase in the blood pressure and also involved in the predisposition of hypertension.

5. Beta-2-adrenergic receptor: It is an membrane spanning g-protein coupled receptor that play a major role in regulation heart health. It interacts with the hormone epinephrine  and stimulates β-adrenoceptor-adenylylcyclase-protein kinase A signalling cascade and mediated contraction of smooth muscles in the heart. It also involved increasing cardiac output.

6. Toll-like receptors : They are membrane spaning receptor proteins that are involved in innate immune system. They are expressed on immune cells such as macrophages and dendritic cells and identifies microbes. They are also found to express in cardovascular tissues such as vascular and myocardial cells. Activation of these receptors on myocardial cells leads to atherosclerosis development and progression and congestive heart failure.

7. C-reactive protein: It is an pentameric circular shaped protein found in the plamsa of the blood. The protein is synthesized in the liver. Its concentration increases in the blood plamsa upon inflammation and secretion of IL-6 by macrophages. High levles of this protein in the blood plasma, indicates that the arteries are inflammed and there is a high risk of cardiovascular diseases such as stroke and peripheral arterial disease.