MCB I Block 3

CELL MEMBRANE DISORDERS

Acanthocytosis/Spur Cell Anemia: Too much alcohol or cholesterol → extra cholesterol accumulate in outer leaflet → increases surface area of outer bilayer → Less deformable → thorny → RBC destroyed by spleen → anemia Destruction of liver → can’t produce albumin anymore → albumin usually keeps fluids in the bloods. Can’t keep fluid in the blood anymore, and fluid seeps out into peritoneal cavity → ascites   Glanzmann’s Thrombasthenia: Autosomal recessive Missing glycoprotein IIb or IIIa (“glue”) → platelets can’t stick together → hemophilia Malaria: Plasmodium falciparum attacks Glycophorin A → cells adhese → anemia, hepatosplenomegaly, ischemia. Hereditary Spherocytosis Autosomal dominant Non-functional spectrin, ankyrin, or protein 4.1 → RBCs become round → anemia, jaundice, splenomegaly. Tx: folate, splenectomy.

• A possible cancer treatment is to attack tumor glycocalyx

• Liposomes can be used for Drug Delivery – 3 components needed within the liposome:

• • Drug (either hydrophilic, or lipid-soluble)
  • Antibody (homing peptide) to bring the entire liposome to the antigen
  • PEG – protect from phagocytes.

 

MITOCHONDRIAL DISORDERS

 

Barth Syndrome (x-linked): cardiolipin synthesis defect → inner membrane of mitochondria defective → H+ leak out more easily → less ATP made → muscle weakness, cardiomyopathy, neutropenia, mitochondrial cristae squished together

• BAD, BAX in cytosol → poke hole in mitochondria (MPTP) → cyt c leaks out → apoptosome forms → caspase cascade → apoptosis. Bcl-2 prevents Apoptosis.

• mtDNA vs nuclear DNA
  • Mito imports: RNA polymerase, amino acids, mitochondrial DNA replication enzymes, mitochondrial aminoacyl-tRNA synthases, and mitochondrial ribosomal proteins
  • Mito makes its own: rRNA subunits, tRNA

• Hsp70 and signal translocation sequence target protein to TOM → TIM → signal sequence cleaved → hsp60 help fold the rest inside mito.

• SOD2 vs. GPX
  • SOD2 before peroxide step, GPX after peroxide step.
  • Similar to Oxidase (before) and Catalase (after) in Peroxisome

MITOCHONDRIAL GENETIC DISORDERS

PEO (progressive external ophthalmoplegia)(autosomal dominant): mutation in POLG2 (Pol Gamma) or TWINKLE (mt helicase) → ptosis, weak eye muscles Alpers Syndrome (autosomal recessive): no pol gamma → less mtDNA made → mental deterioration, seizure, blind, deaf, death Kearns-Sayre Syndrome (KSS) – giant deletions of mtDNA in muscles (heart, eyes) Pearson Syndrome – KSS + bone marrow derivatives → pancytopenia (decrease in all blood cells), sideroblastic anemia MELAS (Mitochondrial Encephalomyopathy Lactic Acidosis Stroke-Like Episodes)(maternally-transmitted): mutated tRNA-Leu → can’t make proper mitochondrial proteins. MERRF (Myoclonus Epilepsy and Ragged Red Fibers)(maternally transmitted): mutated tRNA-Lys → can’t make proper mitochondrial proteins. LHON (Leber’s Hereditary Optic Neuropathy): missense mutation of Complex I in optic nerve → blindness, occur more in males (because only have one X chrom) NARP (Neurogenic Muscle Weakness, Ataxia (lack of muscle coordination), Retinitis Pigmentosa): mutated ATPase 6 gene → retinitis pigmentosa Leigh Syndrome: more severe form of NARP. Accumulated mutations over generations.

• Mitochondrial Diseases Summary
  • Diseases involved in deleted nuclear DNA that goes into mito (Alpers, PEO) – only one that’s not maternally transmitted)
  • Diseases involved in deleted parts of mtDNA (KSS, Pearsons)
  • Diseases involved in mutations in tRNA genes (i.e. MELAS, MERFF)
  • Diseases involved in protein coding nuclear genes (i.e. LHON, NARP, Leigh)

NUCLEAR DISORDERS

• Phosphorylation vs. Dephosphorylation of lamin
  • Phosphorylation disassembles lamin (by cdk1 during prophase)
  • Dephosphorylation assembles lamin

Emery-Dreifuss Muscular Dystrophy: mutated lamin A/C (autosomal) or Emerin (x-linked) → chromatin goes into cytoplasm → muscle weakness, arrhythmias, can’t flex elbows and neck well. Dilated Cardiomyopathy: mutated lamin A/C → congestive heart failure Lipodystrophy: mutated lamin A/C → pre-Lamin A interact with adipocyte TF → impairs adipocyte differentiation → fat neck and face, thin body, diabetes Autosomal Dominant Leukodystrophy (ADLD): Lamin B Duplication → demyelination of CNS →MS Hutchinson-Gilford Progeria: mutated lamin A → unstable nuclear envelope, bleb, NPC clustering → nuclear damage → cells die fast → accelerated aging.

• Lamin A binds to :
  • Architectural partners
  • Chromatin partners
  • Gene-regulatory partners
  • Signalling partners

• snRNP vs. snoRNP
  • snRNP used in slicing
  • snoRNP used in rRNA assembly

Spinal Muscular Atrophy: mutated SMN (in gems) → can’t make snRNP right → can’t splice → lose motor neurons → muscle atrophy

• PARTS OF THE NUCLEOLUS
  • Fibrillar Center – inactive DNA (has “fibrils” of DNA)
  • Dense fibrillar components (pars fibrosa) – active DNA (dense because you also got rRNAs here and snoRNPs)
  • Granular Component (pars granulosa) – maturing ribosomal precursor particles here (ribosomal subunits look like “granules”)

 

 

 

 

ER/GOLGI DISORDERS

 

Angelman Syndrome: mutation chrom 15 for ubiquitin ligase (only maternal active, while father’s is imprinted) → can’t polyubiquinate stuff for degradation →happy baby, epilepsies, jerkiness. Cystic Fibrosis: mutation in CTFR (Cl ion channel), class 2 mutation (Cl ion channel not folded properly) → rhonchi, crackles in lungs, bronchiectasis (find Cl- in sweat test) Familial Hypercholesterolemia: defective LDL-R (doesn’t make it to membrane)(class II)→ LDL can’t be taken up from the plasma (blood) so stay in circulation → premature atherosclerosis, corneal arcus, xanthomata (cholesterol lumps in tendons), xanthelasmata (cholesterol lumps under skin)   Creutzfeld Jacob Disease: GPI-link’s alpha helix becomes beta sheet → prion → accumulates → shrink brain. I-Cell Disease: GlcNac Phosphotransferase is deficient, so M6P tag is COMPLETELY missing! (remember M6P tag usually added in cis-Golgi)→ acid hydrolases don’t go to lysosome → waste products accumulate in cells as inclusion bodies →lack of growth, psychomotor retardation, death CHF.

 

EXOCYTOSIS DISORDERS

Botulin Toxin: synaptobrevin cleaved → Ach can’t fuse at NMJ → flaccid paralysis Tetanospasmin: synaptobrevin cleaved → GABA/Gly (inhibitory NT) can’t fuse at NMJ → spastic paralysis

• Direct vs. Indirect Pathway
  • Direct Pathway = protein Golgi directly to the apical/basolateral side of plasma membrane
  • Indirect Pathway = protein goes from golgi to some random side, then gets sorted to apical/basolateral later.
  • Transcytosis is indirect pathway!

ENDOCYTOSIS DISORDERS

• Pinocytosis = only one that all cells do (constitutive); remodeling of cytoskeleton; vesicles travel via microtubules.

TB: macrophage swallows TB → TB prevents phagolysosome formation by interfering with Rab (phagosome can’t fuse with lysosome for digestion)→ hemoptysis (coughing blood), chest pain, fever

• Clathrin used in exocytosis and receptor-mediated endocytosis (remember not in phagocytosis or pinocytosis)

Legionnaire’s Disease: spread by aerosol → spreads through lungs. Familial Hypercholesterolemia: I: can’t make LDL-R II: makes LDL-R, but can’t transfer to the plasma membrane III: LDL-R makes it to the plasma membrane, but LDL cannot bind to it. IV: LDL can bind to LDL-R, but it can’t cluster to form coated pits for vesicle budding (because coated-pit binding site defective). V: You form vesicles, but the LDL-R’s cannot be recycled

 

LYSOSOME DISORDERS

• M6P Tag is put on in Cis-Golgi by GlcNAc phosphotransferase. Mnemonic: M-“cis”-P
• V-Type ATPase maintains H+ content inside lysosome so Acid Hydrolases can stay active.
• Lysosomal membrane lipids & proteins are heavily glycosylated to protect them from digestion

• Polyubiquitination vs. Monoubiquitination
  • Polyubiquitination is used for proteins that are made in the cell to go to proteasome.
  • Monoubiquitination is used for proteins that are endocytosed from outside the cell to go to lysosome.

• Mucopolysaccharidoses vs. Sphingolipidoses vs. Mucolipidoses
  • Mucopolysaccharidoses – accumulate GAG
  • Sphingolipidoses – accumulate sphingolipid
  • Mucolipidoses – accumulate glycoprotein and glycolipid

• Melanosome = specialized lysosome

I-Cell Disease (Mucolipidosis II): GlcNac Phosphotransferase is deficient, so M6P tag is COMPLETELY missing! → acid hydrolases don’t go to lysosome but accumulate extracellularly as inclusion bodies →lack of growth, psychomotor retardation, death CHF. Pseudo-Hurler Polydystrophy (Mucolipidosis III): Milder I-Cell Disease, later onset

Gaucher’s Disease: most common lysosomal storage disease. Deficiency of glucocerebrosidase → accumulation of glucocerebroside (a glycosphingolipid) in macrophages = Gaucher’s cells → hepatomegaly & splenomegaly, Hypersplenism, anaemia, neutropenia & thrombocytopenia Type II has Hypertonia = inability of muscle to stretch. Also MR, Type III has Myoclonus = twitching of muscles Erlenmeyer flask deformity of distal femur Hurler’s Syndrome: most severe MPS. Deficiency of α-L-iduronidase → accumulation of dermatan sulphate & heparan sulphate (GAGs) → Physical & mental deterioration, hirsutism, deafness, AND CORNEAL CLOUDING!!! Hunter’s Syndrome: just like Hurler’s syndrome except missing iduronodate sulphatase and NO CORNEAL CLOUDING and is X-LINKED!!!! Sanfilippo syndrome (MPS III): like Hurler’s except kids live longer and severe behavior problem Morquio syndrome (MPS IV): Normal IQ. Accumulate keratan sulphate. Chediak-Higashi Syndrome: Mutation CHS1/LYST (gene for lysosomal trafficking regulatory protein). Vesicles can’t walk on microtubules to get to lysosomes properly → Delayed fusion of phagosome with lysosome in leukocytes Side Effect: Autophagocytosis of melanosomes in melanocytes → albinism Granular defects in NK cells & platelets

PEROXISOMAL DISORDERS Oxidase vs. Catalase Oxidases used to make H2O2 Catalase use H2O2 to oxidise toxins Catalase in peroxisome and GPX in mito do the same thing. β-oxidation of very long chain fatty acids (VLCFA) VLCFA (≥ C24) can only be degraded in peroxisome Initiated in peroxisome until C10, completed in mitochondria Energy released as heat Fatty acid oxidation = Major source of metabolic energy Fatty acids → AcetylCoA → cytosol; used for biosynthesis of cholesterol & bile acids Nucleic acid purines (A, G) = degraded to uric acid then urate by Xanthine oxidase → excreted Gout: a lot of xanthine oxidase activity → lotta purines converted to uric acid (hyperurecemia) (too much uric acid) → arthritis. Tx: Allopurinol (xanthine oxidase inhibitor) Humans don’t have uric acid oxidase in our peroxisomes → eat too much purines → Gout Zellweger Syndrome: peroxins stop recognizes SKL→ can’t import peroxisomal enzymes → liver failure (because trying to filter all the junk), muscle weakness (because bile acids can’t be produced→lipids not digested→less ATP), VLCFA accumulate in blood and tissues, hypomyelination (because can’t make plasmologen), Big Forehead! XALD (X-Linked Adrenoleukodystrophy): most common peroxisomal disorder. Can’t transport VLCFA into peroxisome → VLCFA accumulate in brain (myelin breakdown) and adrenal cortex (adrenal atrophy)→ apathy, ataxia

• Plasmalogens (made in peroxisome) are the most abundant phospholipids in myelin. The products of VLCFA beta oxidation are used for biosynthesis of cholesterol, bile acids, and other compounds.

• Zellweger vs. XALD
  • Zellweger = peroxisome can’t import peroxisomal enzymes
  • XALD = peroxisome can’t import VLCFA

SIGNAL TRANSDUCTION DISORDERS

Cholera Toxin: keeps Gs in active state → too much cAMP made → prolonged stimulation → too much Cl and Na transported across membrane → water follows salt → diarrhea Pertussis Toxin: blocks Gi → Gi inhibited → too much cAMP → prolonged stimulation Retinitis Pigmentosa 4: mutated rhodopsin → GPCR defective →lose peripheral vision (because rods here). Tx – Vitamin A slows down process.

• G-Proteins (and what they’re involved in):
  • Ran = nuclear translocation
  • Arf = vesicle budding
  • Rab = vesicle fusion
  • Ras = signal transduction (as in GRB2-Sos-Ras)
  • Rho = actin polymerisation – stress fibers
  • Rac = actin polymerisation – lamellipodia
  • Cdc42 = actin polymerisation – filipodia

NIDDM (Non-Insulin-Dependent Diabetes Mellitus): Obesity → insulin receptor defect → no PI3K(effector) → no PIP2 to PIP3 (2nd messenger) → no PKB activation → GLUT4 vesicles cannot fuse with Plasma Membrane → hyperglycemia → affects eyes, muscles, blood vessels, liver, kidney.

• RTK Signalling Defects:
  • VEGF – Colorectal cancer, NSCLC
  • EGFR (HER1) → Breast Cancer, Colorectal Cancer
  • EGFR2 (HER2) → Breast Cancer

• G-PROTEIN RECEPTORS
  • Gs, Gi: effector = adenyl cyclase, 2^nd messenger= cAMP , activates = PKA
  • Gq: effector = PLC, 2^nd messenger= DAG/IP3, activates = PKC

 

• RTK RECEPTORS
  • RTK – PLC: eff = PLC, 2^nd = DAG/IP3, activates = PKC
  • RTK – PI3K: eff = PI3K, 2^nd= PIP2/3, activates PKB (i.e. AKT/PTEN)
    • (PI3K: PIP2→PIP3 whereas PTEN: PIP3→PIP2 )
    • (AKT is like PKB)
    • Insulin signalling uses the PI3K-PKB pathway → effect vesicles with Glut4 receptors to merge with PM
• RTK – GRB2-SOS-Ras-MapK-TF(Fos/Jun)-GF Pathway

• NON-TK RECEPTORS
  • Cytokine Receptors: 1^st messenger= cytokine, Eff=JAK Phosph’d → STAT Phosph’d →STAT dimerized → transcription
  • Integrin receptors: 1^st messenger=collagen → Eff=ILK (integrin-linked kinase) or FAK (focal adhesion kinase) →prolif, growth, differentiation, apoptosis

• SERINE-THREONINE KINASE RECEPTOR
  • Serine-Threonine Kinase Receptor: 1^st messenger=TGFbeta → Eff=S/T domain → 2^nd messenger → Smad2 or Smad3 dimerase with Smad4 → transcription

• INTRACELLULAR RECEPTORS
  • Steroid Hormone Receptors: Steroid and Zinc → Receptor → HRE → transcription
  • NO Receptors: Acetylecholine →NO synthase → make NO from arginine → NO then goes to smooth muscle cell to convert GTP to cGMP, which relaxes it.

 

 

MICROTUBULES DISORDERS

• MTOC = place where microtubules grow from… so find in migrating cells, mitotic cells, nerve cells, base of cilia and flagella, etc.
  • gamma-tubulin rings in MTOC “seed” sphere
  • Basal bodies = MTOCs under cilia and flagella

• Dynactin complex attach dynein or kinesin to vesicle.

• Viruses can travel on dynein (+→-) or kinesin(-→+) to and fro cell body.

Varicella Zoster Virus: Virus in dorsal root ganglion travel via kinesin to end of nerves at skin. “Chicken Pox”, “Shingles” Rabies: Virus can travel from wound via dynein to CNS→encephalitis → prodromal phase (headache, malaise)→neuro phase (delirium)→coma→ death (respiratory failure)

• MAP vs. Kinesin13
  • MAP (microtubule associated protein) stabilizes microtubules. i.e. tau
  • Kinesin 13 (catastrophe factor) destabilizes microtubules

Alzheimer’s Disease: hyperphosphorylated tau → MT tangles → Neurofillamentary tangles + beta amyloid plaques accumulate. Diagnose: increased tau in CSF. Also see in trisomy 21 Huntington’s Disease: Hungtingtin mutated (CAG repeats at N-terminal) →MT destabilize → accumulate in brain, adhese transcription factors→ neuronal cell death → chorea (jerkiness), dementia, forgetfulness, death Familial Motor Neuron Disease (MND): mutation in Dynactin subunit → lower motor neurons (musc atrophy, weakness), or upper motor neuron (hyperreflexia) Familial Amyotrophic Lateral Sclerosis (ALS): mutation in SOD1 →lower motor neurons (musc atrophy, weakness), upper motor neuron (hyperreflexia) Chediak-Higashi Syndrome: USMLE says it’s a microtubule problem when it really is a lysosomal trafficking problem → lysosome don’t fuse with phagosomes on time in leukocytes. Autophagocytosis of melanosomes → albinism

• Notice you have 2 inner and 3 outer dynein arms in cilia.

Primary Cilia Dyskinesia: Lack/Defective inner dynein arm → Immobile cilia → sperm can’t swim, fallopian tube can’t carry ovum, and you get bronchitis, otitis media, and sinusitis. Kartagener Syndrome

• TX:
  • Colchicine: inhibit polymerization of MT → Cell Death. Treat Gout
  • Vincristine/Vinblastine: inhibit polymerization of MT → Cell Death. Treat cancers w/ high mitotic index
  • Paclitaxel (Taxol): inhibit depolymerization → blocks mitosis → Cell Death. Treat breast, prostate, lung cancer. ODDBALL (only one that inhibits depolymerization).

 

INTERMEDIATE FILAMENT DISORDERS

 

• MT vs. IF vs. Actin in assembly energy
  • MT: need GTP to assemble
  • IF: don’t need GTP or ATP to assemble
  • Actin: need ATP to assemble

Epidermolysis Bullosa Simplex (EBS): Rupture of Keratin in cells connected to Basal layer (mutation in Keratin 5 and 14) → blisters (i.e. soon after birth) Epidermolytic Hyperkeratosis (EH): Mutation in Keratins 1 and 10 →keratin proliferates → thickened skin, easy blistering, infections Epidermolytic Plantopalmar Keratoderma (EPPK): Mutation in Keratin 9 (outermost keratinized layer of epidermis)(only in sole and palm) →treebark on hands and feet Desmin Related Myopathy: desmin mutation → desmin aggregates throughout cell → muscles become disorganized → muscle cell apoptosis → muscle weakness, atrophy, cardiac and respiratory failure

• Neurofilament defects found in Alzheimer’s, Parkinson’s, and ALS (amyotrophic lateral sclerosis)

• Different Types of Tangles:
  • Glial Tangles = tangles of GFAP
  • Lewy Bodies = tangles of neurofilament
  • Neurofibrilary Tangles = hyperphosphorylated tau in AD (mitochondria!)

ACTIN DISORDERS

• MT vs Actin
  • MT: + end = grow; – end = breakdown
  • Actin: + end = fast grow; – end = slow grow

• Notice that ATP is in g-actin. ADP is in f-actin

• “Seeds”
  • MT seed: tubulin gamma
  • Seed for branched actin: ARP (actin-related protein) (- end)
  • Seed for unbranched actin: Formin (+ end)

• Profilin exchanges ADP for ATP on the G-actin, making it ready for polymerization.

• High vs. Low concentration of ATP-G-Actin
  • High conc ATP-G-Actin: monomers added at both ends, but faster at +
  • Low conc ATP-G-Actin: monomers added to + and come off – → treadmilling

• TYPES OF ARFs!!
  • ARFs that bind to G-actin
    • Thymosin: binds G-actin→ prevents F-actin assembly (“thanatopsis”)
    • Profilin: Binds G-actin → promotes F-actin assembly (“promotes filament”)
• ARFs that bind to F-actin
  • Cofilin: disassemble at – end (disassemble) (“cuts filament”)
  • Gelsolin: caps + end (prevent further growth) (“gel sol cap”)

• Besides being in muscles, actin are in:
  • Microvilli – they just are.
  • Stress Fibers – contractile bundles of actin
  • Lamellipodia/Filipodia – contract to move cell
  • Cytokinesis – contract to pinch cells apart

• Two types of cross-linking:

• • To form parallel cables (“bundles”) –
    • alpha actinin (contractile, because loose so myosin can insert in it, i.e. stress fibers),
    • fimbrin (non-contractile, because dense, i.e. microvilli), villin
  • To form filament webs (“gel”) –
    • spectrin (remember in RBC),
    • filamin (“filament”)

• Stress fibers (remember they are contractile, so they are crosslinked by alpha-actinin) connect to ECM via focal adhesions (integrin). Remember they are used in cell signaling (collagen effect integrin →effect ILK or FAK → proliferation)

• Stress fibers vs. Microvilli
  • Stress fibers: alpha-actinin and focal adhesions cross-linking/attaching actins to integrins (in ECM)
  • Microvilli: Fimbrin and Villin cross-linking actins

• G-Proteins: Rho vs Rac vs Cdc42
  • Rho = actin polymerisation (via formin “unbranched cables”) – stress fibers
  • Rac = actin polymerisation (via WASP then arp2/3 because branched) – lamellipodia
  • Cdc42 = actin polymerisation (via WASP then arp 2/3 because branched) – filipodia
  • Mnemonic: “Rhostress,” “Raclam,” Cd. Fili”

Wiscott-Aldrich Syndrome: Defective WASP → no Arp2/3 activation → no actin nucleation → no lamellipodia or filipodia → defective signaling pathway (notice acronym almost like “WASP”)

• Drugs that Affect Actin Polymerisation:
  • Cytochalasin D: bind to + end, ends polymerization, depolymerisation at – end
  • Latrunculin: like sponge – soaks up free monomers, prevent polymerization
  • Phalloidin: binds to filament, stops polymerization. Remember Red Texas Phalloidin?

• Myosin:
  • I has I head + calmodulin (“I” looks like a microvilli)
  • II has II heads + essential + regulatory – II looks like squeezing (contractile)
  • V has 2 heads + calmodulin (V for Vesicle!)

• Proteins that attach to Actin/Myosin
  • Cap Z = cap at the Z disc
  • Titin = pulls myosin tight
  • Tropomodulin = “tropo minus end”

• CapZ vs. Tropomodulin
  • CapZ @ + end
  • Tropomodulin @ – end

• Z disc = CapZ + alpha-actinin

• Mechanism for Muscle Contraction
  • ATP-binding detaches myosin head (the reasoning behind rigor mortis)
  • ATP→ADP moves it into the myosin-binding site
  • ADP-detachment does powerstroke

Dilated Cardiomyopathy: besides mutation in lamin A/C, can also be caused by mutation where actin binds Z disc. Familial Hypertrophic Cardiomyopathy: mutation in myosin II → #1 cause of suddencardiac death in athletes!! Just randomly drop dead. Muscular heart with large atrium andsmall ventricle.

MUSCULAR DISORDERS

• Actin – dystrophin – (beta dystroglycan-GRB2-alpha dystroglycan) – laminin2

• Satellite Cell (in basal lamina of mature muscle) → myoblast → +myotube +myofibers → mature muscle
• Stem Cell “Side Population Cells” (in bone marrow) → differentiate into satellite cells

• Muscular Dystrophy → repair cannot keep up with damage → connective tissue + fat accumulation. Detect w/ blood test – find increased serum creatine kinase. Or do PCR deletion screening.

• Absence of dystrophin → loss of DAP (dystrophin associated proteins) at sarcolemma→Absence of physical link → fragile sarcolemma

• Dystrophin = largest gene therefore prone to many mutations. Binds actin cytoskeleton to sarcoglycan-dystroglycan complex.

X-LINKED MUSCULAR DYSTROPHIES: Duchenne’s Muscular Dystrophy: X-linked or gonadal mosaic → TOTAL loss of function of dystrophin → Gower’s Maneuver, calf pseudohypertrophy (calf looks big and muscular but its not, because damage accumulates a lot of fat and connective tissue) → walk on toes, mild cognitive impairment, death by cardiac/resp failure. 8% of female carriers of DMD gene have partial weakness. Called MANIFESTING HETEROZYGOTES. Becker’s Muscular Dystrophy: like DMD but PARTIALLY functioning dystrophin (rather than TOTAL loss of function in dystrophin). Emery-Dreifuss: mutation in A/C or Emerin → early contractures (shortening of muscle, can’t stretch) → cardiomyopathy and arrhythmia. AUTOSOMAL MUSCULAR DYSTROPHIES: Myotonic Muscular Dystrophy: Accumulated CTG repeats (1000’s more too much). Anticipation (accumulates from generation to generation) → facial muscle weakness → ptosis, drooping mouth. Fascioscapulohumeral Muscular Dystrophy: can’t puff cheeks, scapular winging. Normal life expectancy. Limb Girdle Muscular Dystrophy 1: defective Caveolin-3   Limb Girdle Muscular Dystrophy 2: defective assembly of A/B/G/D sarcoglycan. Also can be defect in titin, calpain, etc.   Congenital Muscular Dystrophy: mutation of laminin → muscle weakness, MR, pectoral fold

• Muscular Dystrophy Treatments: physical therapy, pacemaker

• Treatment of DMD:
  • Inject donor myoblast? Difficult because muscle cells don’t divide, so need to inject a lot.
  • Step Cell Therapy – either upregulate utrophin (homologous to dystrophin but in fetus), or inject stem cells that would differentiate into myoblasts, or exon-skipping

 

 

 

EXTRACELLULAR MATRIX DISORDERS

 

Ehlers-Danlos Syndrome: defective fibrillar collagen synthesis →weak connective tissue →stretchy skin, joint hypermobility Marfan’s Syndrome: remember fibrillin binds elastin. Fibrillin defect → weak elastic tissue →arachnodactyly (“spider fingers”), funnel chest, retinal detachment, aortic root dilation. COPD (Emphysema): Absence of A1AT (A1AD “alpha-1-antitrypsin deficiency”) can cause emphysema. Smoking can to because it inhibits A1AT and smoking also recruits neutrophils to lungs releasing elastase. Elastin loss → alveoli collapse → hyperventilation, barrel chest.

• Matrix Metalloproteinases
  • MMP I = Collagenase I (so breaks down collagen I)
  • MMP II = Collagenase IV (so breaks down collagen IV, used by cell to invade basal lamina, as well as chemotaxis)

• Glycoprotein vs. Proteoglycan
  • Glycoproteins = adhesive (Gl for Glue)
  • Proteoglycan/GAG = space filler, compression (Pr for Press)

• Hyaluronan is a type of “space filler – produced during wound healing, which need a lot of cell-free space for repair cells to migrate. Its length is humongous – to create space filler! It is not covalently linked to core protein so it is not compact.

• Gel of Vitreous Humor = collagen suspended in hyaluronan + lots of water → ultimate shock absorber!

• Hyaluronan (a type of proteoglycan) vs. Other Proteoglycan
  • Remember proteoglycan is usually a GAG + core protein
  • Hyaluronan is a special exception! Is a GAG without core protein!

• Proteoglycan complexes can be Aggrecan (Cartilage) or Versican.
• Aggrecan proteoglycans attach to hyaluronan proteoglycan! (like paintbrushes on a string)

• After growth factor binds to Perlecan or Syndecan (heparan sulfate), it has a better and more convenient binding access to receptor on cell surface

Diabetic Nephropathy: Perlecan and Syndecan (HSPG’s) downregulated → no size/charge barrier in glomerulus → hyperglycemia → collagen glycosylated more (sincethere’s more carbs floating around) → glomerular basement membrane thickens with collagen.

• Cross-Links
  • Collagen 6 cross-links Collagen 1
  • Collagen 9 cross-links Collagen 2
  • Fibrillin cross-links elastin

• Basal Lamina is a Specialized type of ECM:
  • Integrin – Laminin – Perlecan/Entactin – Collagen IV

• ECM Composed of:
  • Structural: collagen, elastin, fibrillin
  • Glycoprotein Adhesives: laminin, fibronectin, entactin
  • Proteoglycan Filler: proteoglycan (perlecan/syndecan), Hyaluron
  • Two Organizations:
    • Interstitial Matrix
    • Basal Lamina

• Basal Lamina vs. Other types of ECM!
  • Basal Lamina: Integrin II – (Glycoprotein) Laminin – Perlecan (Proteoglycan) – CollagenIV (Structure)
  • Unspecialized ECM or stress fibers: Actin – Vinculin/Talin – Integrin I – (Glycoprotein) Fibronectin – Syndecan (Proteoglycan) – CollagenI/III/V (Structure)

• Fibronectin has these binding sites:
  • For collagen
  • For cell surface integrins (binding sequence is RGD)
  • For heparin (Proteoglycan)
  • For Fibrin

• Plasma membrane is weak, so need strong matrix on each side, hence ECM on the outside of the cell membrane and actin matrix on the inside.

• Interaction between fibronectin and actin
  • Integrin creates interaction between actin (inside cell) with fibronectin (outside cell). So actin and fibronectin can align in same direction!
  • So fibronectin is involved in cell spreading and migration (in the right direction), as it creates a “paste” of cells that are properly aligned. Embryogenesis and wound healing both need this direction and “paste” created by fibronectin.

• Fibronectin: 2 forms:
  • Soluble = for blood coagulation
  • Insoluble = for the “paste” that guide cell migration and growth (w/ alignment)

 

 

CELL-MATRIX INTERACTIONS DISORDERS

• Remember Vinculin is a focal adhesion (“foot hold”) protein, on the cytosolic side of the cell – connect actin filament of stress fibers to ECM

• Integrins attach glycoproteins via its RGD sequence

• Integrin is the telephone between ECM and Cell, but they’re also the connection. So if signals tell them to cluster, they will adhese the cell more and cause anchorage-dependent growth. The reverse will cause cell motility.

• Remember glycoprotein IIb and IIIa in Glanzmann’s Thrombasthenia? They are platelet integrins!!(β₃)

• Focal Adhesion vs. Hemidesmosome:
  • Focal Adhesion: actin stress fibers – vinculin/talin – integrin – fibronectin – collagen (I, III, V)
  • Hemidesmosome: keratin – plectin (“plaque”) – integrin – laminin – collagen VII – Collagen IV (of basal lamina)

Bullous Pemphigoid: autoimmune attack on hemidesmosomes → epidermis detach from dermis → blistering.

• Filapodia vs. Lamellipodia
  • Notice filopodia are “filament feet”
  • Lamellipodia are “lamellar feet”

• Old actin filaments are disassembled in back, and new ones are created in front → crawling of cell. Contraction at back propels cell body forward.

• Chemotaxis:
  • It’s interesting how the MMP and TIMPs are stored in ECM (Basal Lamina), as if ECM has the keys to its own doors to allow cell to enter.
  • Remember MMP is collagenase. MMPI digests Collagen I, MMPII digests Collagen IV (basal lamina)

 

CELL-CELL INTERACTIONS DISORDERS

 

• Cell Junctions:
  • Tight Jxns Occlude
  • Adherens and Desmosomes anchor
  • Gap junctions communicate

• TADG = from apex to base = tight jxn → adherens jxn → desmosomes → gap jxn

• Adherens vs. Desmosomes
  • Adherens – connect via actin. A for “Actin”
  • Desmosomes – connect via intermediate filaments

• Cadherins = “Calcium-Dependent Adherens”

• T vs A vs D vs G
  • Tight Junction: Claudin/Occludin – ZO – actin
  • Adherins: Cadherin – catenin/alpha actinin – actin
  • Desmosomes: Cadherins (desmoglein/desmocollin) – Plakoglobin/Desmoplakin – intermediate filaments
  • Gap Junctions: 1000s channels = 2 connexons = 6 connexins

• So both desmosome and hemidesmosome have “plaques” (Have parts of it named plec-something or plak-something)

• You can tell which side of the cell is which by looking at where the zonula occludens is.

• Paracellular pathway = passage of free molecules between the cells. Zonula occludens is the door to this pathway.

Inflammatory Bowel Disease (i.e. Chron’s Disease or Ulcerative Colitis): occludin (intight jxn) downregulated → paracellular pathway opened up → PMN (neutrophils) get through Pemphigus: autoimmune attack on desmosomal cadherins (desmoglein/desmocollin) → blistering → deadly infections

• Bullous Pemphigoid vs. Pemphigus
  • Bullous Pemphigoid – autoimmune attack on hemidesmosomes
  • Pemphigus – autoimmune attack on desmosomal cadherins

• Gap Junction:
  • Electrical: Peristalsis, Coordinated depolarization of heart muscles, uterine contraction
  • Chemical: cAMP passes between cells so can respond the same way to a hormone

• High Calcium level (from damaged cell) → closes gap junction, to prevent damage.

• Connexins
  • Connexin 26 Mutation (in cochlea): deafness
  • Connexin 50 Mutation (in lens): cataracts → blindness
  • Connexin 32 Mutation (in peripheral myelin): Chargot-Marie-Tooth → degeneration of peripheral nerves → atrophy of distant muscles, decreased deep tendon reflex, “foot drop,” “high-stepping gait,” “high-arched foot,” “hammer toes” (really mean nicknames for CMT!)

• Connexin 32 is unique in that it is actually an INTRAcellular gap junction, because it is the communication between the different onion layers of schwann cells.

• Selectins:
  • L-Selectin for leukocyte – for lymphocyte homing (addressins on lymphocytes attach to the L-selectins on lymphoid organs, homing)
  • P-Selectin for platelet
  • E-Selectin for endothelial cell – leukocyte can “roll” on the E-selectin in the bloodstream.

• Lymphocyte Rolling, Trapping, and Extravasation
  • Rolls on E-selectin – WEAK ADHESION SO IT CAN ROLL
  • Then, eventually rolls onto ICAM , which binds to the lymphocyte’s integrin – STRONG ADHESION, so it can stop and migrate through

Leukocyte Adhesion Deficiency (LAD): β2 integrin mutation → impaired leukocyte chemotaxis, extravasation, and therefore phagocytosis → life-threatening bacterial infections.

COLLAGEN DISORDERS

 

• Collagen Structure:
  • 3 residues/turn, L hand helix
  • 3 stranded helix, R hand helix

• PXG repeats:
  • Proline (P) – remember that it is bulky from Block 1?
  • Hydroxyproline (X) – remember hydroxylated proline from Block 2?
  • Glycine – connects all 3 strands with each other via H-bonding.

• MAKING A COLLAGEN:

1. Make 2 a₁ & 1 a₂ chains + signal peptide (preprocollagen)
2. Cleave signal peptide (procollagen)
3. Hydroxylate proline and lysine (via Vitamin C)
4. Glycosylate hydroxylysine
5. Disulfide bond aligns chain and initiates triple helix formation from C→N
6. H bonds form between hydroxyproline of procollagens.
7. Procollagen Peptidase removes Propeptides on both C and N end.

Scurvy: Lack Vitamin C →can’t hydroxylate proline → can’t H bond → can’t form collagen → weak connective tissue → bleeding gums, nails, loose teeth, fatigue, etc.

• Remember:
  • Collagen I = skin/bone/tendon
  • Collagen II = Cartilage
  • Collagen III = blood vessels, fetal skin
  • Collagen IV (sheet-forming) = Basal Lamina
  • Collagen VII = Anchoring

Osteogenesis Imperfecta: Mutation in Collagen I (Glycine mutation at C-terminal) → fragile bones, tooth abnormal, blue sclera. Ehlers-Danlos Syndrome: Mostly defect in Collagen I or V, but sometimes III, lysyl hydroxylase (needed for procollagen bonding), or in converting procollagen to collagen. Alport Syndrome: defective Collagen IV → basal lamina defective →basal lamina in kidney doesn’t filter well → protein and blood in urine → kidney failure Goodpasture Syndrome: like Alport except autoimmune Epidermolysis Bullosa: Simplex: mutation in Keratin 5 and 14 Junctional: mutation in laminin, integrins, hemidesmosomal proteins (@ junction) Dystrophic: mutation in Collagen VII (anchoring of hemidesmosomes to basal lamina). “boy whose skin fell off” Achondroplasia: FGFR3 Mutation → FGFR3 (chondrocyte inhibitor) keeps getting expressed! → chondrocyte proliferation is inhibited → no grow. Mnemonic: “Figs for Three.” FGFR = fibroblast growth factor receptor is a Receptor Tyrosine Kinase

• Other Collagenopathies:

• • Achondrogenesis type II
  • Kniest dysplasia – dwarf, enlarged joints
  • Spondyloepimetaphyseal dysplasia
  • Stickler syndrome – underdeveloped facial bones
  • Campomelic Dysplasia – Mutation in SOX9 → decrease Collagen II
  • Thanatophoric Dysplasia – born dead. FGFR3 mutation, like achondroplasia
  • Hypochondroplasia – also FGFR3 mutation, like achondroplasia