Q: Compare abetalipoproteinemia with hypobetalipoproteinemia. A: In abeta there is an absence of plasma lipoproteins due to mutations in the microsomal triglyceride transfer protein (MTP) gene. In hypo plasma lipoprotein levels are low due to mutations in apoB. Q: MTP and apoB physically interact during lipoprotein biogenesis and MTPs lipid transfer activity is required for lipoprotein assembly. Describe MTP activity during this process. A: MTP enhances rate of lipid transfer between vesicles by a shuttle mechanism. The MTP molecule interacts with a memebrane, extracts lipid molecules, dissociates from the membrane and then delivers lipids to a second membrane or lipoprotein particle. Q: What step is rate limiting for VLDL synthesis? A: MTP - Genetic variants that impact lipid metabolism also impact human lifespan. People whose lipid profiles have higher levels of HDL and lower levels of LDL exhibit significantly lower risks of heart disease and stroke. Q: Where is HDL synthesized? A: Synthesized in a nascent form in the liver and to a minor extent in the gut. Q: What are the main apoproteins of HDL? A: apoAI and apoAII, although it also contains apoCand apoE, which it exchanges with other lipoproteins. Q: Describe HDL when it is secreted into the blood. A: small, discoid in shape, and are nearly devoid of cholesterol ester and triacylglycerols. Q: Describe what happens to HDL as it picks up cholesterol from other lipoproteins and from cell membranes. A: The cholesterol is converted to cholesterol esters by the LCAT reaction (which is stimulated by apoAI). The HDL particles fill with cholesterol esters and triacyglycerol and become large and spherical in shape. Q: What does HDL do with the particles it picks up? A: The cholesterol esters are ultimately returned to the liver. "reverse cholesterol transport" Q: HDL transfers apoCII and apoE to chylomicrons and VLDL. What does ApoCII do? A: SpoCII stimulates the degradation of the triacylglycerols by activating LPL producing chylomicron remnants and IDL (from VLDL). Q: HDL transfers apoCII and apoE to chylomicrons and VLDL. What does ApoE do? A: ApoE serves as a ligand for receptors on liver cell membranes that are involved in the uptake of chylomicron remnants and IDL. Q: What two diseases do mutations in the human LCAT gene result in? A: Familial LCAT deficiency (FLD) and fish eye disease (FED). Q: What happens and why in patients with fish eye disease? A: FED patients have a partial deficiency of LCAT function leading to the development of corneal opacities. Q: Describe the disease state of patients with FLD. A: Total deficiency of LCAT function, corneal opacities, mild anemia, proteinuria, and/or renal dysfunction. Glomerulosclerosis, the major cause of morbidity and mortality, may lead to renal failure in the 4th or 5th decade of life. Q: Describe the role of LPL (lipoprotein lipase) in lipoprotein metabolism. A: Binds to heparan sulfate proteoglycans on the surface of the vascular endothelial cells. May hydrolyze up to 10g of triglycerides per hour. Can also anchor lipoproteins to the cell surface and to the extracellular matrix. (HL, hepatic lipase, is associated with liver plasma membranes) Q: What is CETP and where is it expressed? A: Cholesterol Ester Transfer Protein, hydrophobic glycoprotein expressed primarily by the liver, spleen, and adipose tissue. Q: What is the primary role of CETP and how is it accomplished? A: transfer of neutral lipids such as cholesterol esters and triglycerides between lipoproteins. It catalyzes the transfer of CE from HDL to apo B-containing lipoproteins (VLDL, LDL), and also transfers TG and sometimes CE in the opposite direction from VLDL to HDL. Q: Describe the proatherogenic and antiatherogenic roles of CETP. A: High levels of plasma VLDL, then CETP mediated CE transfer results in high levels of CE rich VLDL. The high levels of CE-rich LDL's that result then contribute to atherosclerosis. High levels of HDL results in reverse cholesterol transport facilitated by CETP. Q: What is the structure of lipoprotein (a)? A: cholesterol-phopholipid core and a closely associated protein called apoB100. Q: How does Lp(a) differ from LDL? A: each Lp(a) particle contains one copy of an additional proein of the apoprotein 9a) family bound to apoB100 by a single disulfide linkage. Q: What are the 3 things Lp(a) is implicated in doing? A: implicated in the delivery of cholesterol to injured blood vessels, blockade of plasmin generation on fibrin and cell surfaces, and stimulus for smooth muscle cell proliferation. Q: What is familial hypercholesterolemia? A: Inherited condition in which too much LDL circulates in the blood. Q: What is Tangier disease? A: Rare, recessive disorder characterized by a reduced efflux of cholesterol from cells resulting in macrophages becoming engorged with cholesterol esters. They have NO HDL due to a defect in an ATP binding cassette transporter gene which encodes the cholesterol-efflux regulatory protein (CERP). Mature HDL is not formed and apoAI is rapidly destroyed. Q: What are the symptoms associated with Tangier disease? A: symptoms range from orange tonsils to coronary heart disease. Q: Describe HDL biosynthesis. A: Assembly of nascent HDL from apolipoprotein-AI, and phospholipid and free cholesterol discs, secreted from the liver and intestine. Q: What happens to cholesterol in mature HDL? A: free cholesterol is esterified to form cholesterol ester which can be either transferred to LDL or delivered to the liver and sterol-metabolizing tissures. Cholesterol is removed from the tissues and cholesterol engorged macrophages are discouraged from accumulating in the artery wall. Normal cells pump out free cholesterol at a rate of 0.1% per minute. Q: Where is apoE abundant and what is it's function? A: In the brain, serves as the principal lipid transport vehicle in CSF, plays a key role in repair by redistributing lipids to regenerating axons. Q: What disease has apoE4 been implicated in? A: sporadic and familial alzheimers' desease, also associated with poor clinical outcome in patients with acute head trauma and stroke. Q: It has been hypothesized that the apoE isoform differentially affect amyloid plaque formation. How is this done? A: lipidated apoE3 binds to the Abeta peptide with a 20 fold higher affinity than lipidated apoE4. The increased binding of apoE3 could enhance the clearance of the Abeta peptide, preventing the accumulation of the neurotoxic Abeta species. ApoE4 has been shown to result in the formation of insoluble, high-molecular-weight complexes with the Abeta peptide. Q: What is the most common cause of senile dementia in the elderly? A: Alzheimer Disease Q: Alzheimer Disease is characterized by GLOBAL cognitive decline and what two distinguishing histopathologies? A: 1. amyloid plaques (composed of extracellular beta-amyloid protein aggregates) and 2. Neurofibrillary tangles consisting mostly of hyperphosphorylated tau protein. Q: What is the main risk factor for Alz Disease? A: Aging Q: What is the main component of amyloid plaques in AD? Mutations in what enzyme result in the problem protein? A: The amyloid Beta protein, when cleaved to a length of 42 aa (versus 40) by gamma-secretase, is believed to be the main toxic component. Q: The process of endoproteolysis cleaves and releases the amyloid beta protein from what large protein? A: The Beta-amyloid precursor protein, a type I transmembrane domain protein Q: The proteases involved in generating amyloid beta are called _________? A: Secretases Q: PPT What are the four findings that implicate cholesterol in Alz. Disease? A: 1. Certain ApoE alleles (eg. epsilion4 [e4]) correlate with AD risk 2. Statin use lowers AD risk 3. A certain CYP46 allele (CYP46 helps remove cholesterol) can predispose to AD and 4. Cholesterol esters correlate with amyloid beta production Q: What are the roles of the 3 secretases in ABeta production? A: 1. Beta-ecretase generates the amino terminus of the ABeta domain 2. Alpha-secretase cleaves between the beta and gamma sites (functional result wasn't discussed) 3. Gamma-secretase (and aspartyl protease) mediates the carboxy-terminal cleavage of BetaAPP at a site almost in the center of the transmembrane domain and finally liberates ABeta Q: What are two cholesterol-lowering drugs whose use is also associated with decrease Alz. D incidence? A: Simvastatin and lovastatin Q: Elevated levels of what protein and the epsilon4 (e4) allele of what carrier protein are risk factors for both familial and sporadic Alz D? A: High levels of ABeta and the e4 allele of the lipid-carrier apolipoprotein E Q: Simvastatin and lovastatin reduce intracellular and extracellular levels of ABeta42 and ABeta40 peptides in cultures of what type of neurons? A: Hippocampal. (The hippocampus plays a key role in learning and memory.) Q: CYP refers to what enzymes? A: The cytochrome p450s. Q: What groups of compounds do CYPs oxidize (4)? A: 1. Xenobiotic agents such as drugs (so they can be disposed of) and 2. physiologically occurring chemicals such as arachidonic acid (eicosonioid synthesis), fatty acids, and sterols (to form oxysterols). Q: About how many CYPs are known? A: 100, each with varying degrees of specificity for different substrates. Q: What induces the P450 enzymes? A: Their most specific substrate and by substrates of some of the other CYP450 enzymes. Q: Which CYP is associated with LATE-onset Alz D.? To what does this enzyme convert cholesterol? A: CYP46, which converts cholesterol to 24-hydroxycholesterol which more easily leaves the brain. (Remember, increased cholesterol is associated with increased AD.) Q: In what organ is CYP46 EXCLUSIVELY expressed? A: The brain Q: Cholesterol-rich rafts in neuronal cell membranes promote increased production of what protein? A: ABeta42, which aggregates to form plaques as in Alz D. Q: In the brain, extracellular aggregates of ___ protein are thought to interact with plasma membrane receptors, leading to _______ activation and neuron death. A: Amyloid Beta (ABeta); caspase activation Q: Does (hyper)phosphorylation of tau occur upstream or downstream from caspase activation in the signal transduction that leads to neuronal death in Alz D? A: Downstream Q: What are the two enzymes that esterify cholesterol? A: 1. lecithin:cholesterol acyltransferase (LCAT) (I think lecithin=phosphotidylcholine) 2. acyl:cholesterol acyltransferase (ACAT) Q: Where is lecithin:cholesterol acyltransferase located? A: In the blood. Q: Lecithin:cholesterol acyltransferase esterifies cholesterol associated with _____ density lipoprotein particles. A: HDL particles Q: Acyl:cholesterol acyltransferase (ACAT) is found where particularly in what cells? A: In those that need to store cholesterol for the synthesis of steroid hormones. Q: What functional group on cholesterol to ACAT and LCAT use for esterification? A: The hydroxyl group at carbon 3. Q: Which is more hydrophobic, cholesterol or esters thereof? Based on this, where do they each tend to be found? A: Esterified cholesterols are more hydrophobic and are thus more readily packed into lipid droplets or lipoprotein particles. Cholesterol is found in PLipid bilayers Q: What are two functions of Acyl-coenzyme A acyltransferase (ACAT; yes the name has "coenzyme A" added in one part of the notes)? A: 1. It catalyses the formation of cholesterol esters and 2. it "modulates" the generation of ABeta 42 (Alz D) Q: Inhibitors of ACAT were developed for the treatment of ________ but are also potent modulators of ____ generation. A: Atherosclerosis; ABeta generation Q: In the synthesis of bile salts, cholesterol is converted to what 2 groups of acids? A: Cholic acids (hydroxyls at carbons 3, 7, and 12) and chenocholic acids (-OH at carbons 3 and 7). Q: What two modifications generally occur to cholesterol to synthesize bile salts? A: 1. hydroxylation of the steroid nucleus 2. cleavage of the side chain Q: What is the rate limiting enzyme in cholesterol synthesis? A: 7-alpha-hydroxylase. Q: What are the (4) steps in bile salt synthesis (not including conjugation)? A: 1. Hydroxylation at the 7 carbon 2. reduction of the double bond 3. additional hydroxylations (at 3 and 12 for cholic acids; at 3 for chenocholic acids) 4. 3 side chain carbons are removed by oxidation, leaving a COOH Q: What are the two additional steps in forming a CONJUGATED bile salt? A: 1. Activation of the side chain COOH (requires ATP and CoA) 2. Rxn of the acylCoA derivative with either glycine or taurine Q: What % of bile salts are absorbed in the ileum and returned to the liver via enterohepatic circulation? A: >95% Q: What is a secondary bile salt? A: One that lacks a hydroxyl group at position 7. Q: T/F Secondary bile salts may be recongugated in the liver, but they are not rehydroxylated (at C7). A: True Q: What two things do intestinal bacteria remove from conjugated bile salts? A: 1. The conjugated moiety (glysine or taurine) and 2. the -OH from C7. Q: We have a supply of bile salts (2-4 grams, with .2-.6 g/day being synthesized) that is recycled how many times per day? A: 6-8 Q: T/F Because the steroid nucleus CANNOT be degraded in the body, bile salt excretion is a major route for cholesterol removal from the body. A: True Q: What negatively regulates the rate-limiting enzyme of bile salt synthesis? A: Bile salts exhibit feeback inhibition of 7-alpha hydroxylase Q: What is cholestyramine? A: A positively charged resin that acts as a cholesterol sequestrant, reducing bile salt resorption to 90-92%. Q: What change is induced in hepatocytes by reduction in cellular cholesterol (for example, because of increased bile production as signalled by decreased bile salt resorption like during resin therapy)? A: More LDL RECEPTORS are synthesized which, in turn, will internalize more circulating LDL. This helps lower serum cholesterol. Q: What % of the population in western countries (will) have gallstones? A: 20% Q: Exceeding what ratio of cholesterol to phospholipid in bile in bile salt micelles results in crystallization of the excess cholesterol? A: Greater than 1 cholesterol: 1 phospholipid Q: In general, glucocorticoids and progestins contain how many carbons? A: 21 Q: In general, androgens contain how many carbons? A: 19 Q: In general, estrogens contain how many carbons? A: 18 Q: What determines which hormones an organ can synthesize? A: The specific enzymes present Q: How many CYP450 enzymes are required in the biosynthesis of glucocorticoids, mineralocorticoids, and sex steroids? A: Four Q: What is the action of a CYP450 enzyme in steroid hormone synthesis? A: These monooxygenases transfer electrons from NADPH to molecular oxygen which then oxidizes a variety of the ring carbons of cholesterol. Q: Where is the cytochrome P450scc (side chain cleavage enzyme) located in a cell and what does it do? A: It's located in the inner mitochondrial membrane and removes 6 carbons from the side chain of cholesterol, forming pregnenolone. Q: What enzyme catalyzes the conversion of pregnenolone to progesterone? A: 3beta-hydroxysteroid dehydrogenase Q: Which enzyme in the synthesis of progesterone is not a member of the CYP450 family? A: 3-beta-hydroxysteroid dehydrogenase, which converts pregnenolone to progesterone. Q: Where are the enzymes localized that produce other steroid hormones from progesterone? What type of enzymes are they? A: They are members of the P450 family located in the ER. Q: PP-What is the main hormone involved in the development and progression of breast tumors? A: Estrogen, shame on you if you missed it, this has been known for over a century Q: PP-Estrogen deprivation is a key therapuetic approach for treating breast tumors, what are the two methods of accomplishing this estrogen deprivation? A: 1. Competitive binding of the estrogen receptor (Tamoxifen) 2. Aromatase inhibition (about 2X as effective), aromatase is the enzyme responsible for estrogen synthesis from androgenic substrates. Also oophrectomy was used long ago. Q: PP-What reaction does aromatase catalyze? A: Testosterone to estradiol, also mentioned in the notes androstenedione to estrone Q: What family of molecules is Aromatase? A: A P450 Cytochrome Q: In what tissues is aromatase highly expressed? A: Placenta (granulosa cells of ovarian follicles), it is also present in fat, normal breast tissue and cancer breast tissue Q: In post menopausal women where does residual estrogen production occur? A: In nonglandualar sources, paticularly subcutaneous fat Q: Compare estrogen levels premenopausal plasma, postmenopausal plasma and in postmenopausal breast cancer tissue. A: Pre ~110 pg/ml, post ~7 pg/ml, cancer ~10X plasma levels Q: What significant event happened in the letrozole, aromatase inhibitor, trial? A: Results were so good that it was unblinded and the placebo group was offered the drug Q: What was significant finding in the hormone (estrogen and progesterone) replacement study? A: Those taking hormaone replacement had a slightly higher risk of heart attack, stroke and other problems, and therefore hormone replacement therapy "fell from grace" and stopped being a recommended therapy Q: Besides providing nutrients, what other important role do cholesterol, fatty acids, fat-soluble vitamins and other lipids serve? A: They are precursors for ligands that bing to transcription factor receptors in the nucleus. Q: What four steps are necessary for cholesterol, fatty acids, fat-soluble vitamins and other lipids to form biologically active ligands? A: 1. Absorbtion in the intestine 2. Processing and transformation by metabolid enzymes 3. delivery and binding to receptors 4. elimination to maintain physiological state Q: We have 48 members ligand-activated transciption factor nuclear receptors, what are the two main classes of theses nuclear receptors? A: 1. Classical endocrine receptors - mediate steroid hormones, thyroid hormones and vitamins A & D (fat soluble) 2. Orphan nuclear receptors - lipid sensors that protect the body from lipid overload Q: Describe the structural organization of nuclear receptors? A: Amino terminous has a ligand independent transcriptional activation function (AF-1); Core DNA binding domain with 2 DNA sequence specific Zn fingers; Large COOH terminus that encompasses the ligand binding domain Q: What happens to nuclear receptors (structurally) upon ligand binding? A: Conformational change that coordinately dissociates coreppressors and facilitates recruitment of coactivator proteins to enable transcriptional activation Q: What are some examples of nuclear steroid hormone receptors and how are they controlled? A: Receptors for glucocorticoid, mineralcorticoid, estrogen, androgen and progesterone. They are controlled via negative feedback control Q: What are some examples of adopted orphan nuclear receptors, what is their function and how are they controlled? A: Examples include receptors for: Fatty acids (PPARs), Oxsterols (LXRs), bile acids (FXRs) and xenobiotics. Their purpose is to maintain lipid hormaone homeostasis. They are controlled via Feedforward control Q: Why can't adopted orphan nuclear receptors be regulated by feedback control? A: They are receptors for dietary lipids, whose concentrations are determined by the number of twinkies you eat, therefore negative feedback control won't work, fatty! Q: What are are the general effects of genes activated by adopted orphan nuclear receptors? A: Lipid metabolism, storage, transport and elimination Q: PP-What are the three major FAMILIES OF PROTEINS for lipid metabolism (cascade of nuclear orphan receptors)? A: 1. Cytochrome P450 (CYPs or POXs); 2. ABC Pumps; 3. Nuclear Receptors Q: Describe the process of feedforward regulation? A: Lipid is introduced to receptor, which binds it with a low affinity, binding activates transcription of metabolic enzymes which will maintain lipid nutrient homeostasis via lipid metabolism, storage, transport and elimination Q: PP-What is the general function of Cytochrome P450 (CYPs or POXs) in lipid metabolism? A: Oxidize and inactivate lipids or xenobiotics (relatively slow process) Q: PP-What is the general function of lipid binding proteins in lipid metabolism? A: Bind to lipids or xenobiotics and buffer their action Q: PP-What is the general function of ABC pumps in lipid metabolism? A: Pump lipid or xenobiotic out of cell or into peroxisomes for destruction Q: PP-What are the three PROTEINS ENCODED BY mRNA acivated by adopted orphan nuclear receptors? A: 1. CYPs (listed as a major protein family); 2. ABC pumps (also listed as a major protein family); 3. Lipid binding proteins Q: What are PPARs? A: Peroxisome Proliferator-Activated Receptors, they are sensors for fatty acids, eicosanoids and synthetic ligands Q: What proteins does PPARa (alpha) upregulate and what do they do? A: Fatty acid binding protein, which buffers fatty acid effects; 2 specific ABC proteins which pump fatty acids in to peroxisomes for B-oxidation; and CYP4A for w-oxidation and fatty acid clearance. Overall they buffer and degrade fatty acids Q: What roles do PPARy (gamma) play? A: Regulates adipogenesis; and plays a role in cellular differentiation, insulin sensitization, athersclerosis and cancer Q: Name some possible ligands for PPARy (gamma). A: Fatty acids, other arachidonic derivatives and antidiabetic drugs Q: Does PPARy (gamma) cause lipid degradation? A: No, PPARy (gamma) promotes fat storage by increasing adipocyte differentiations and the transcription of many lipogenic proteins