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, 2nd messenger= cAMP , activates = PKA
    • Gq: effector = PLC, 2nd messenger= DAG/IP3, activates = PKC

 

  • RTK RECEPTORS
    • RTK – PLC: eff = PLC, 2nd = DAG/IP3, activates = PKC
    • RTK – PI3K: eff = PI3K, 2nd= 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: 1st messenger= cytokine, Eff=JAK Phosph’d → STAT Phosph’d →STAT dimerized → transcription
    • Integrin receptors: 1st messenger=collagen → Eff=ILK (integrin-linked kinase) or FAK (focal adhesion kinase) →prolif, growth, differentiation, apoptosis
  • SERINE-THREONINE KINASE RECEPTOR
    • Serine-Threonine Kinase Receptor: 1st messenger=TGFbeta → Eff=S/T domain → 2nd 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