Glaucoma

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Glaucoma

• Salma Kaochar
• Biology 182H
• Research Pre-proposal

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Background

• Number one leading cause of blindness in the
  world.
• Affecting 70 million people worldwide.
• 3 million in the United States
• Currently, there are 150,000 patients in Arizona
  diagnosed with glaucoma.

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Introduction

• Normally, intraocular pressure (IOP) serves to
  maintain its shape for optical purposes. IOP is
  maintained by a balance between production and
  removal of aqueous humor from the eye.
• Aqueous humor nourishes the cornea and lens
• The primary pathway in humans for removal of
  aqueous humor consists of the trabecular meshwork
  (TM) and the canal of Schlemm (SC).

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Human Eye Schematic
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Aqueous Humor Flow
Aqueous fluid is formed in the ciliary body.
After nourishing the lens and cornea, it passes
through a filter called the trabecular meshwork
and a tiny channel known as the Canal of Schlemm.
As the fluid exist the eye, it flows into other
tiny channels and eventually into the eye's blood
vessels.
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The most common form, open-angle glaucoma, is
characterized by elevated intraocular pressure
(IOP) that compresses optic nerve axons resulting
in death of ganglion cells and subsequent loss of
vision.
Open-Angle Glaucoma
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Who is at risk?

• Blacks over age 40.
• Everyone over age 60.
• Disease of the aging eye.
• People with a family history of glaucoma.

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Symptoms

• No symptoms.
• Vision stays normal
• No pain.
• Slowly miss objects to the side and out of the
  corner of their eye.

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Decline Vision
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Diagnosis and Treatment

• Diagnosis
• Visual acuity various distances
• Tonometry fluid pressure
• Pupil dilation optic nerve to check for signs of
  damage
• Visual Field side (peripheral) vision

• Treatment
• Medicine
• Laser surgery burns stretch the drainage holes
  in the meshwork
• Conventional Surgery make a new opening for the
  fluid to leave the eye
• Less than satisfactory.

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Resistance to Outflow

• The majority of resistance to outflow of aqueous
  humor is generated deep in the TM
  (juxtacanalicular region) near or at the inner
  wall of SC

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Tissue Identification

• SC cells are vascular endothelial cell.
• similar intercellular signaling pathways that
  regulate paracellular permeability.
• Cadherin and other cell adhesion molecule (CAM)
  such as PECAM-1.
• Only continuous monolayer of cells in the outflow
  pathway.
• TM cell type undecided.

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Resistance to Outflow

• The majority of resistance to outflow of aqueous
  humor is generated deep in the TM
  (juxtacanalicular region) near or at the inner
  wall of SC

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Cell-cell Junction

• Three different morphological types of cell-cell
  junctions have been described in the outflow
  pathway tight junctions, gap junctions, and
  adherens junctions.
• In contrast, the intercellular junction between
  SC and TM cells contains only gap and adherens
  junctions.

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Why Intercellular Junction?

• Resistance to outflow is in part mediated by the
  intercellular junctions between cells at or near
  the inner wall of SC.
• Three different ways junctions may influence
  outflow function.
• Cell-cell junctional complexes maintain a
  contiguous inner wall of SC and limit
  paracellular fluid flow .
• Because of a discontinuous basal lamina, SC cells
  may rely on cell-cell attachments from
  juxtacanalicular TM cells for support and/or
  communication .
• Cell-cell junctions join cytoskeletal elements
  from cell neighbors, enable the transduction of
  mechanical force between cells and allow the
  outflow tissues to function as a unit .

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Protein in Adherens Junction

• Depletion of extracellular calcium dramatically
  decreases outflow resistance by dissociating
  cell-cell interactions.
• The adhesion of these proteins is highly dynamic
  and regulated by calcium dependent interactions
  of the extracellular domains and the interactions
  of the cytoplasmic domains with the actin
  cytoskeleton .
• Increased expression of the cell adhesion
  protein, endothelial-leukocyte adhesion molecule
  (ELAM-1), was found exclusively in glaucomatous
  eyes compared to age-matched controls .
• Extensive work in vascular endothelium has
  demonstrated the active participation of
  VE-cadherin in maintaining barrier function
  therefore providing a biological precedent.

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VEGF

• Vascular Endothelial Growth Factor Receptor five
  known isomers.
• Tyrosin kinase receptors
• Expression of VEGFR1, VEGFR2, and VEGFR3 in
  endothelial cell.
• Essential for blood vessel development.

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Continue...

• Formation of new blood vessel --gt weakens
  cell-cell contacts between endothelial cells.
• Involved in vascular permeability.
• Induce the tyrosine phosphorylation of PECAM-1,
  VE-Cadherin, plakoglobin, and catenin.

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In Summary...

• VEGF induces strong increase in tyrosine
  phosphorylation of the adherens junction
  component --gt associated with loss of integrity
  of intercellular adhesion --gt VEGF
  induce-modification of adhesion molecule might
  change the lateral clustering of the
  extracellular domains of junctional protein such
  as VE-cad and alter cadherin adhesive strength.
• No evidence that any of the receptors for VEGF
  are expressed in SC cells

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Questions to be addressed

• What type of VEGF receptors are expressed in SC
  cells?
• What role do they have in outflow regulation, if
  any?

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Experimental Strategy

• RT-PCR

If yes.
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Continue...

• Western Blot and immunofluorescence microscopy

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Continue ...

• Create a virus with VEGF in plasmid--gt over or
  underexpress VEGF.
• And so on...

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Benefit?

• May provide a cellular pathway of potential
  targets for future glaucoma therapy.
• Pharmacological interference with the delivery to
  or turnover of adherens proteins at the cell
  surface.

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Selected References

• 1. Quigley H. Number of people with glaucoma
  worldwide. Br J Ophthalmol 199680389-393.
• 2. Quigley H, Hohman R, Addicks E, Massof R,
  Green W. Morphologic changes in the lamina
  cribrosa correlated with neural loss in
  open-angle glaucoma. Am J Ophthalmol
  198395673-691.
• 3. Rohen J. Why is intraocular pressure elevated
  in chronic simple glaucoma? Anatomical
  considerations. Ophthalmol 198395673-691.
• 4. Grant WM. Experimental aqueous perfusion in
  enucleated human eyes. Arch Ophthalmol
  196369783.
• 5. Bill A, Maepea O. Mechanisms and routes of
  aqueous humor drainage. Philadelphia WB
  Saunders, 1975206-226.
• 6. Underwood J, Murphy C, Chen J, Franse-Carman
  l, Wood I, Epstein D, Alvarado J. Glucocorticoids
  regulate transendothelial fluid flow resistance
  and formation of intercellular junctions. Am J
  Physiol 1999277C330-C342.
• 7. Johnstone M. Pressure-dependent changes in
  nuclei and the process origins of the endothelial
  cells lining Schlemm's canal. Invest Ophthalmol
  Vis Sci 19791844-51.
• 8. Wiederholt M, Thieme H, Stumpff F. The
  regulation of trabecular meshwork and ciliary
  muscle contractility. Prog Retinal Eye Res
  200019271-295.
• 9. Raviola G, Raviola E. Paracellular route of
  aqueous outflow in the trabecular meshwork and
  canal of Schlemm. A freeze-fracture study of the
  endothelial junctions in the sclerocorneal angle
  of the macaque monkey eye. Invest Ophthalmol Vis
  Sci 19812152-72.
• 10. Grierson I, Lee W. The fine structure of the
  trabecular meshwork at graded levels of
  intraocular pressure. Exp Eye Res 197520505-22.

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Thank You!Questions???Comments??
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Quick Definitions

• Epithelia Membranous tissue composed of one or
  more layers of cells separated by very little
  intercellular substance and forming the covering
  of most internal and external surfaces of the
  body and its organs.
• Endothelia a thin layer of flattened cells that
  lines the inside of some body cavities.
• Vascular of or relating to or having vessels
  that conduct and circulate fluids