Iekaisums Inflammation

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IekaisumsInflammation
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Inflammation

• Defense reaction to tissue damage
• Redness, heat, swelling, pain
• Structural changes in capillaries and venules,
  contraction of endothelial cells,,dilation,
  increase blood flow, escape of plasma proteins
• Signals sent to bone marrow to produce more
  neutrophils and monocytes.Neutrophil and monocyte
  cell counts increase.
• Leukocyte adhesion cascade.
• Leukocyte transmigration through endothelium and
  accumulation at the site of injury.
• Active phagocytosis by neutrophils and
  macrophages.
• Invasion by fibroblasts,synthesis of collagen
  ,repair of wound.
• Termination of acute inflammation.

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Leukocyte adhesion cascade

• A sequence of activation and adhesion events
  leading to the extravasation of leukocytes at the
  site of inflammation.
• Capture and Rolling (Fast-slow)-Selectins
• Firm Adhesion-Integrins
• Transmigration
• Block in any one of them greatly reduces
  leukocyte accummulation in the damaged tissue.

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Distribution of Vascular Selectins

• L-Selectin-most leukocytes (early)
• P-Selectin-Activated Endothelial Cells (early)
• E-Selectin-Activated Endothelial Cells (late)
• All known vascular selectins bind to carbohydrate
  ligands on transmembrane glycoproteins of
  interacting cells.

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Leukocyte Adhesion Cascade. Capture and Rolling

• Cytokines released by injury activate venular
  endothelial cells and induce them to express
  P-selectin (stored in Weibel-Palade bodies) on
  their surface which interacts with a glycoprotein
  on leukocytes.
• As a result the leukocytes roll along the
  endothelium forming bonds at the leading edge and
  breaking them at the trailing one.
• L-selectin expressed by leukocytes also
  participates in the rolling process.It may be
  necessary for the initial attachment to the
  endothelium. In absence of P-selectin rolling is
  less efficiently mediated by L-selectin.
• E-selectin expressed by by activated endothelial
  cells is required to slow down rolling of
  leukocytes and initiates stronger adhesion.

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Capture and Rolling

• Evidence-
• Inhibition of rolling by specific antibodies.
• Leukocytes roll on purified P-selectin in flow
  chambers
• In absence of E-selectin the number of firmly
  adhering leukocytes is reduced
• During rolling leukocyte integrins remain
  inactivated and endothelial immunoglobulins like
  CAMs remain at control levels

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Rolling velocities of leukocytes in mouse mutants
after trauma

• P-selectin (-E-L mutated) 40 um/sec
• L-selectin (-E-P mutated) 120 um/sec
• E-selectin (-L-P mutated) no rolling
• alpha-integrin(-P-L-E mutated) no rolling
• Wild type 43um/sec

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Capture and Rolling

• Selectins mediate transient reversible adhesive
  interactions.
• May allow the leukocytes to interact with
  cytokines, chemoattractants and adhesion
  molecules on the endothelial cell surface which
  in turn may be necessary to activate leukocyte
  integrins and induce firmer cell adhesion later.

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Integrins

• Large family of heterodimeric transmembrane
  glycoproteins that attach cells to extracellular
  matrix proteins of the basement membrane or to
  ligands on other cells having the RGD sequence of
  amino acids.

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LC
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Some integrins require activation to bind to
ligand
EC
LC
Example of inside-out signal transduction e.g.
Platelet Plug Formation White Blood cells
transmigration across ECs
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EC
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Integrins and Ig like CAMs

• After rolling on endothelial cell surface b1
  integrins and b2 integrins (expressed
  exclusively on leukocytes) are activated and
  undergo conformational change.
• At the same time vascular endothelial cells
  express Ig like CAMs on their surface which act
  as counter receptors for leukocyte integrins.
• The leukocyte integrins bind to Ig like CAMs on
  endothelial cells.
• This stops the rolling and induces strong
  adhesion to the endothelial cell surface.

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• A mutation in the b2 integrin results in LAD
  characterized by recurrent bacterial infections
  due to reduction in the ability of neutrophils to
  adhere to venule walls and to exit from the
  blood stream. The absence of this integrin is
  lethal.

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Transmigration

• Locally produced cytokines released as a result
  of tissue injury activate the endothelium.
• Adhesion molecules such as Ig like CAMs , B1 and
  B2 integrins are upregulated.
• Chemoattractants such as fMLP released by
  bacteria induce leukcocyte migration.

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• Migration through the basal lamina requires the
  activation of various digestive enzymes.
• Once through the basal lamina the neutrophils
  migrate up a concentration gradient of fMLP
  released by bacteria. A cell can detect very
  slight differences in the concentration of this
  peptide in different regions of the cell surface.
• These peptides are detected by receptors on the
  surface of neutrophils and their occupancy by the
  formyl peptides polarizes the neutrophil for
  migration by reorganizing its microfilament
  system.

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Once neutrophils have migrated through the
endothelium they find bacteria and dead cells
through chemotaxis
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• Similar mechanisms are thought to be involved in
  migration of lymphocytes through the specialized
  endothelium of lymph node capilaries and by
  metastatic tumor cells to migrate out of venules
  and capillaries .

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Brucu DzianaWound Repair

• .

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EpitelijaEpithelium
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• Epithelial cells change in integrin expression
  allowing them to change from strongly adherent
  cells to less adhesive migrating cells better
  able to adhere to and interact with the
  extracellular components of the blood clot.
• Blood clot is used as a provisional matrix for
  migration of epithelial cells into the wound to
  establish epithelial continuity.
• Synthesis of macromolecules specific for basal
  lamina and their assembly.
• Proliferation of epithelial cells along the wound
  edge to provide more cells.

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SaistaudiConnective Tissue
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• Fibroblasts become activated by growth factors
  especially TGF beta released by cells in the
  wounded region.
• Fibroblasts migrate into the wound and synthesize
  and secrete collagen the major component of
  scars.
• TGF beta also induces the fibroblasts to
  differentiate into a more contractile type of
  fibroblast(myofibroblast).
• By pulling on the collagen fibers the
  myofibroblasts induce wound contraction which
  brings the two sides of the wound closer
  together.

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• The size of the scar depends on the time it takes
  to repair the wound and on the amount of
  hyaluronan present in the wounded area.
• In newborns because the ECM has large amounts of
  hyaluronan the wounds heal very rapidly and scars
  are small or absent altogether.
• If tension tending to pull the sides of the wound
  apart is exerted on the wound more collagen is
  secreted by the fibroblasts to resist this
  tension and scars formed tend to be larger.
• Once the mechanical stress on the wound is
  relieved by synthesis of collagen and wound
  contraction, fibroblasts in the wounded area
  become quiescent and stop proliferating.

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MetastazeanasMetastasis

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• Cancer cells
• Are genetically unstable
• Disregard signals that regulate cell
  proliferation.
• Avoid suicide by apoptosis.
• Avoid differentiation which normally limits
  proliferation.
• Escape from primary tumor.(invasive)
• Can survive and proliferate in foreign
  sites.(metastasize)

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• Normally cells recognize and adhere to
  neighbouring cells by cell-cell junctions and
  cell- cell adhesion molecules.
• This recognition- adhesion system breaks down in
  cancer.
• Moreover normally cells which fail to adhere are
  destroyed by apoptosis.This mechanism is also
  defective in tumor cells.
• This allows the tumor cells to migrate and form
  metastasis.This requires changes in cell-cell and
  cell -substratum adhesiveness.

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Steps in Metastasis

• Carcinoma cells loose adhesiveness to each other.
• Overcome restraints imposed by the basal lamina
• Migrate through connective tissue.
• Penetrate blood vessels.(basal lamina)
• Migrate out of blood vessels(basal lamina)
• Migrate through connective tissue and establish a
  metastasis.

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Cadherins

• Cadherins and associated molecules are important
  in oncogenesis and metastasis.
• E-Cadherin is down regulated in most carcinomas
  and is therefore a tumor suppressor.
• The greater the loss of E-cadherin the greater
  the metastatic potential of the carcinoma.
• Loss of cadherin is accompanied by a loss of
  zonula adherens junctions and a dramatic
  reduction in cell-cell adhesion.
• Because zonula adherens is necessary for the
  maintenance of tight junctions ,they are also
  disrupted resulting in the loss of cell polarity.

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Cadherins

• Experimentally increasing the levels of
  E-cadherin can restore many of the normal
  epithelial properties of carcinoma cells
  including loss of their ability to cause tumors
  when injected into animals.
• In a family in New Zealand 25 members have died
  from stomach cancer.All of these individuals
  carried a mutation in the gene for E-cadherin.

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Cadherins

• Down regulation of cadherins also occurs normally
  when cells separate and migrate away from the
  ectoderm.
• Fibroblasts induced to express E-cadherin
  resemble epihelial cells.

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Beta-Catenin

• When dephosphorylated on its tyrosine beta
  catenin is located in zonula adherens junction
  and participates in cell-cell adhesion.
• Upon phosphorylation it can leave this site and
  move into the cytosol or into the nucleus.
• In the nucleus it can act as a transcription
  factor for genes that stimulate cell replication.

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Beta-Catenin

• In the cytosol beta-catenin is bound by APC
  (Adematous polyposis coli) a protein coded by a
  tumor supressor gene.
• Normally the Beta catenin APC complex is then
  ubiquinated and degraded.
• Defects in gene coding for APC greatly increase
  the risk of colon cancer.
• This is likely because cytosolic beta-catenin is
  not removed and is free to stimulate cell
  proliferation after moving to the nucleus.
• A high incidence of carcinomas is also found in
  families with mutations in the beta -catenin.

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Adenomatous Polyposis Coli
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• To break through the basal lamina cancer cells
  first upregulate integrins allowing them to
  adhere strongly to laminin in the basal lamina.
• They then secrete enzymes or activate enzymes (
  e.g.metalloproteases ) in the ECM that digest the
  basal lamina allowing the cancer cells to pass
  through. Similar mechanism may allow them to pass
  through the basal laminas of blood vessels.
• Enzyme inhibitors could interfere with these
  stages.

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Degradation/Turnover of ECM components
Transfection of DNA coding for a defective MPP
might inhibit tumor cell metastasis
Matrix Metalloproteases FunctionTurnover,
Reorganization of ECM Cell Migration Activity
of MMPs restricted to local sites by limiting the
actvating metalloproteases to the cell surface of
the cell that needs to migrate.
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• In the blood vessels the metastizing carcinoma
  cells must also slow down before they can
  extravasate
• They probably use mechanisms similar to those
  used by leukocytes,an integrin present on some
  carcinoma cells that can mediate this has been
  identified.
• Alternately the tumor cells could become stuck in
  the smaller blood vessels and then migrate out.

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• Most tumor cells then use integrins to migrate on
  fibronectin after penetrating the basal lamina.
• They also use proteases to help them move through
  the connective tissue.
• Attempts are being made to use peptides with the
  RGD sequence to inhibit these stages in
  formation of metasasis.

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Fibronectin
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