I know that HDLs collect cholesterol from peripheral tissues and transport it back to the liver using SRB1 - Reverse cholesterol transport and dumping it in bile. So the tissue is producing some extra cholesterol (why would it? apart from some atherosclerotic condition) and our HDL gets it back to the liver. This is a bit fine. But then there is CETP which is giving back the cholesterol to VLDLs. So is it not confusing that our HDL took the excess cholesterol from the tissues only to give it back via VLDL?
So my questions -
Q1 - Why would a tissue have extra cholesterol?(when excellent feedback mechanisms exist - eg. SREBP SCAP INSIG path). Does the HDL pathway make sense only when there is some atherosclerosis?
Q2. Reverse Cholesterol transport refers to the SRB1 part only or SRB1 + CETP combined?
Q3. What is the rationale behind handing over the cholesterol back to VLDLs by CETPs? I know that considerable LDLs get back to the liver too but isnt just SRB1 pathway just fine? Why is it so important to equilibriate your lipid content across lipoproteins? I understand this is the mechanism how torectrapib works but presence of CETP in the body signifies that it must have some ulterior motive, right?
please help :)