Week 6 Lecture 9 PDF

Week 6 Lecture 9  In more than 75% of cases of familial hypercholesterolemia (FH), the LDL receptor...

Week 6 Lecture 9  In more than 75% of cases of familial hypercholesterolemia (FH), the LDL receptor is defective, owing to mutations in the LDLR gene. Because familial hypercholesterolemia is inherited in an autosomal dominant fashion, most patients who have it are heterozygous, possessing 1 normal allele and 1 mutated allele. The prevalence of heterozygous familial hypercholesterolemia is about 1 in 220, based on large genetic studies. Homozygous familial hypercholesterolemia, in which the patient possesses 2 mutated alleles, is much less prevalent, with a frequency One of the main signs of FH is LDL cholesterol levels over 190 estimated at 1 in 300,000. Patients with mg/dL in adults (and over 160 mg/dL in children). In addition, homozygous disease face a worse most people with FH have a family health history of early heart prognosis. disease or heart attacks. In some cases, elevated LDL levels are found through routine blood cholesterol screening. Structure of LDL cholesterol and its role in atherosclerosis. The major lipoprotein (apolipoprotein B-100) is responsible for LDL binding to cellular receptors. LDL particles are oxidized in the arterial wall, then taken up by tissue macrophages. The lipid laden macrophages coalesce into a fatty streak which then evolves into an atherosclerotic plaque. The plaque may rupture if the fibrous cap thins and fractures, causing a thrombosis and a heart attack.  Stable angina: This is the most common symptom. Stable angina is temporary chest pain or discomfort that comes and goes in a predictable pattern. You’ll usually notice it during physical activity or emotional distress. It goes away when you rest or take nitroglycerin (medicine that treats angina). Shortness of breath (dyspnea): Some people feel short of breath during light physical activity. Sometimes, the first symptom of CAD is a heart attack. Symptoms of a heart attack include: Chest pain or discomfort (angina). Angina can range from mild discomfort to severe pain. It may feel like heaviness, tightness, pressure, aching, burning, numbness, fullness, squeezing or a dull ache. The discomfort may spread to your shoulder, arm, neck, back or jaw. Shortness of breath or trouble breathing. Feeling dizzy or lightheaded. Heart palpitations. Feeling tired. Nausea, stomach discomfort or vomiting. This may feel like indigestion. Weakness. Atherosclerosis is characterized by patchy intimal plaques (atheromas) that encroach on the lumen of medium-sized and large arteries. The plaques contain lipids, inflammatory cells, smooth muscle cells, and connective tissue. Risk factors include dyslipidemia, diabetes, cigarette smoking, family history, sedentary lifestyle, obesity, and hypertension. Symptoms develop when growth or rupture of the plaque reduces or obstructs blood flow; symptoms vary by artery affected. Diagnosis is clinical and confirmed by angiography, ultrasonography, or other imaging tests. Treatment includes risk factor, lifestyle, and dietary modification; physical activity; antiplatelet drugs; and antiatherogenic drugs. HMG-CoA reductase is the rate controlling step in cholesterol biosynthesis and the target of Statin drugs. HMGCR catalyzes the conversion of HMG-CoA to mevalonic acid, a necessary step in the biosynthesis of cholesterol. Normally in mammalian cells this enzyme is competitively suppressed so that its effect is controlled. HMG-CoA reductase is activated by insulin, inhibited by glucagon and oxysterols. Oxysterols are derivatives of cholesterol and accumulate when there is excess cholesterol. When oxysterol levels are high they will also block LDL-receptor mediated endocytosis. When energy levels are low in the cell and [ATP] is decreased, AMPK will be activated and will lead to inhibition of HMG-CoA reductase. Domain structure of HMG CoA reductase. (A) HMG CoA reductase consists of two distinct domains: a hydrophobic N- terminal domain with eight membrane-spanning segments that anchor the protein to ER membranes, and a hydrophilic C- terminal domain that projects into the cytosol and exhibits all of the enzyme's catalytic activity. (B) Amino acid sequence and topology of the membrane domain of hamster HMG CoA reductase. The lysine residues implicated as sites of Insig- dependent, sterol-regulated ubiquitination are highlighted in red and denoted by arrows. The YIYF sequence in the second membrane-spanning helix that mediates Insig binding is highlighted in yellow. If you had to design a sterol sensing domain on HMG CoA reductase, where would you place it? Russel Deboise Boyd PhD Professor UT Southwestern Studies negative feedback regulation of HMG-CoA Reductase How does a cell sense cholesterol and inhibit cholesterol synthesis to fine tune cholesterol levels in the cell? https://www.youtube.com/watch?v=5ORouFPmVJY The lysosomes are small organelles that work as the recycling center in the cells. They are membrane-bounded spheres full of digesting enzymes. These enzymes can break down whatever substance (usually, old cell parts) entering the lysosomes into small molecules (amino acids, nucleotides, fatty acids, and sugars), so the cell can reuse these raw materials to build new organelles. Lysosomes may also be used to destroy invading viruses and bacteria. Acidic with pH of 5.0, which activates hydrolytic enzymes, including proteases, nucleases, lipases, which are all acid hydrolases (which need an acidic pH to be active). If the cell is damaged beyond repair, lysosomes can help it to self-destruct in a process called programmed cell death, or apoptosis. The degradation is carried out by a number of acid hydrolases (phosphatases, nucleases, glycosidases, proteases, peptidases, sulfatases, lipases, etc) capable of digesting all major cellular macromolecules. The best-studied lysosomal hydrolases are the cathepsin proteases which can be divided into three sub-groups according to their active site amino acid, i.e. cysteine (B, C, H, F, K, L, O, S, V, W and X/Z), aspartate (D and E) and serine (G) cathepsins.  The lysosomal system refers to the autophagic pathway and the endocytic pathway, and mediates the transport and proteolytic degradation of cellular waste. In the endocytic pathway, early endosomes (EE) mature into late endosomes (LE) prior to full acidification (Lysosome). In the autophagic (macroautophagy) pathway, a preautophagosomal structure (PAS) is formed, enveloping an area of cytoplasm or a selected substrate, and developing into a double-membrane autophagosome (AP). Lysosomes fuse with autophagosomes, generating single-membrane autolysosomes (AL), and ultimately lysosomes. Upon fusion with autophagosomes, lysosomes introduce proteolytic enzymes which carry out the degradation of substrates as the compartment becomes more acidic. The acidification of these compartments is mediated by the v-ATPase. Chaperone-mediated autophagy (CMA) is another type of autophagy, during which a chaperone protein complex (Hsc70 Macroautophagy Endocytosis complex) recognizes a cytoplasmic target protein PAS: preautophagosomal structure EE: Early Endosomes via a KFERQ motif, and shuttles the target protein AP: autophagosome LE: Late Endosomes to the lysosomal lumen for digestion via interaction AL: Autolysosome with the LAMP2 protein complex, which serves as the lysosomal CMA receptor.  The maintenance of a highly acidic pH (4.2-5.3) is essential for regulating many functions of lysosomes. With rare exceptions, lysosomal hydrolases of all classes operate optimally below neutral pH, although the pH optimum o individual acidic hydrolases varies considerably. The broadly specific protease cathepsin D, for example, is optimally active at the lowest end of the lysosomal pH range, while some other major cathepsins (such as cathepsin B) operate optimally in the range of pH 6.0. The wide range of pH optima implies that the rises in intraluminal pH that accompany introduction of substrates upon fusion with autophagosomes or endosomes and the gradual reacidification of the lysosomal lumen may coordinate the sequence Macroautophagy Endocytosis of hydrolase activations that is most efficient PAS: preautophagosomal structure EE: Early Endosomes for dismantling and digesting complex AP: autophagosome LE: Late Endosomes substrates, such as a mitochondrion, or for AL: Autolysosome minimizing the generation of amyloidogenic or other potentially deleterious digestion products. Lysosomes are present in almost all eukaryotic cells except red blood cells. Lysosomes locate in the cytoplasm. They display considerable variation in size and shape. In regular cells, lysosomes are spherical bodies about 50-70 nm in diameter. Several hundred lysosomes may be present in a single animal cell. These lysosomes are too small to be seen under a regular light microscope. Electron microscope or fluorescence microscope are required to observe and study lysosomes. A major player in the regulation of lysosomal biogenesis is the basic Helix- Loop-Helix (bHLH) leucine zipper transcription factor, TFEB. Among the identified TFEB transcriptional targets are lysosomal hydrolases that are involved in substrate degradation, lysosomal membrane proteins that mediate the interaction of the lysosome with other cellular structures, and components of the vacuolar H.-ATPase (v-ATPase) complex that participate in lysosomal acidification. TFEB can recognize E-box and M-box sequences of the CLEAR net- work, activate downstream genes and promote their transcription, resulting in an increased num- ber of lysosomes and higher levels of lysosomal enzymes, thereby enhancing lysosomal catabolic activity. The discovery of the coordinated lysosomal expression and regulation (CLEAR) genetic program and its master controller, transcription factor EB (TFEB), has provided an unprecedented tool to study and manipulate lysosomal function. This motif, named the Coordinated Lysosomal Expression and Regulation (CLEAR) element, comprises an E-box (CANNTG) that was recognized by the TFE family transcription factors. TFEB enhances the expression of its target genes by specifically binding to the CLEAR motif present in the target promoters One is to activate the expression of various autophagy-related molecules (e.g., Ag molecules, LC3) through transcription to enhance cell autophagy so that the damaged organelles are degraded by autophagosomes and autolysosomes, which can recycle the degradation products (such as amino acids) for cells. The other is to combine the E-box element of CLEAR to transcriptionally activate the expression of lysosomal pathway- related molecules, especially the expression of lysosomal- associated membrane protein LAMP1, to promote lysosome formation in vitro Under normal conditions (such as low lysosomal pH or high nutrients), the V- ATPase complex activates the small Rag GTPase (Rags), a component of the LYNUS machinery, which recruits mTORC1 to the lysosomal membrane.