HNF 461 1st Edition Lecture 20 Outline of Last Lecture I General Structure of a Lipoprotein II Functions of Apolipoproteins III Major Lipoproteins in Circulation IV Major Apolipoproteins in Circulation V Transport of Chylomicrons VI Metabolism of Chylomicrons VII LPL Km VIII Lipid Metabolism in Adipocyte IX Lipid Metabolism in Hepatocyte Outline of Current Lecture I Lipoprotein System II Structure of VLDL III In the Hepatocyte a Fed State b Fasting State IV Formation of VLDL V LPL Regulation VI Regulation of VLDL VII In the Adipocyte a Fed State b Fasting State VIII Albumin Bound Fatty Acids Current Lecture VLDL 1 Lipoprotein System These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute a Function of VLDL Intracellular transport of triglycerides and cholesterol i TG Provide Energy ii Cholesterol Structural element of cell membranes and precursor of hormones b VLDL is always in the blood at fasting state will be predominant 2 Structure of VLDL a Very similar to that of chylomicrons b Integral Protein B100 able to bind to receptors directly i Chylomicron as B48 a shorter protein that can t bind to receptors so apoE binds to chylomicron 3 In the Hepatocyte a Fed State i Glucose is absorbed and enters glycolysis pathway produces glycerol which can act as the backbone for triglycerides 1 Extra glucose becomes fat in the liver packed into VLDL for distribution ii Short chain fatty acids can be formed into longer fatty acids and packed into VLDL b Fasting State i No glucose short chain fatty acids in blood Chylomicron remnants components will be used to make VLDL 4 Formation of VLDL a Nascent VLDL is made in the liver b 1 VLDL has 1 B100 protein c apoE and apoC 2 are transferred to VLDL from HDL d Fatty acids are hydrolyzed by lipoprotein lipase LPL VLDL becomes VLDL remnant IDL which is taken up by liver about 2 3 that is made e Further loss of TAG from IDL LDL which binds to B100 and is absorbed by liver 5 LPL Regulation a Adipose tissue Sensitive to fasting and feeding regulated by insulin i In fasting state LPL is low b Mammary Gland Induced during late pregnancy and lactation c Brown Fat Increased during cold temperature d Heart Complex regulation carried out by multiple mechanism i LPL activity increases during fasting e Stress will decrease LPL is adipose tissue and increase LPL in heart skeletal muscle 6 Regulation of VLDL a Insulin inhibits VLDL secretion by the liver i Promotes apoB degradation b Insulin stimulates LDL IDL uptake by the liver i Diabetics have higher levels in blood because of insulin resistance 7 In the Adipocyte a Fed State i Chylomicrons present in blood ii High VLDL in blood iii Fat cells use TG from VLDL and break down to free fatty acids to synthesize TAG in the cell iv 2 3 IDL is absorbed into liver b Fasting State i Low VLDL in blood ii Glucose levels low in blood iii Chylomicrons not present in blood iv LPL concentration is low so breaking down of TG from VLDL to free fatty acids decreases v Phosphorylation by glucagon initiates HSL to release fatty acids into blood 8 Albumin Bound Fatty Acids a In blood b Free fatty acids bind to albumin c Scavenger receptor CD36 is responsible for taking up and transporting fatty acids and is also responsible for taking up oxidized LDL
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