9/24/14. Anatomy of the Eye. Corneal Anatomy. The Cornea! Transparent Tough Biological Barrier Refractile. The Cornea is an ORGAN

Transcription

1 The Cornea! J Funderburgh Biology of Vision INTBP Sep 2014 Transparent Tough Biological Barrier Refractile 1! Anatomy of the Eye The Cornea is an ORGAN Corneal Anatomy Epithelial Basement Membrane! Bowman s Layer-(Anterior Limiting Lamina)! Descemet s Membrane! 1

2 Epithelial/Stromal Organ! Epithelium/Stroma Organs: Cornea Ovary, lung, pancreas, kidney, cornea, gut, skin.! Epithelium! Cell-cell junctions! Cell polarity! Hemidesmosomes! Basement membrane!! Stroma! Interstitial connective tissue! Mesenchymal cells (fibrocytes)! Fibrous Collagen! Adapter Proteins! Leukocytes! Eye Development Summary Retina & Choroid are derived from central nervous system Lens pinches off from the overlying ectoderm 4 weeks 5 weeks 5 weeks! Hilfer SR, Yang JW.!Anat Rec Aug;197(4): ! Corneal Epithelium forms from ectoderm Corneal Stroma and Endothelium are Neural crest derived periocular mesenchyme forms corneal stroma, endothelium and eyelid mesenchyme Journal of Biology 2005, 4:11 6! 2

3 Corneal surface is a squamous epithelium overlying a stromal connective tissue The corneal epithelium is a SELF RENEWING TISSUE dependent on a population of stem cells at the LIMBAL zone between cornea and sclera. Richard Thoft X-Y-Z Theory of Epithelial Migration Conjunctival epithelium Limbus Corneal Epithelium Stem Cells Transient Amplifying Chimeras with ß-Gal labeled cells show centripetal migration (J West) Limbal Stem Cells Defined as Label Retaining Cells after incorporation of BrdU or 3H-Thymidine Label cell DNA. Wait >2 weeks. Only the basal limbal cells retain BrdU label (red) In response to a central wound, migrating transient amplifying cells incorporate radioactive thymidine R. Lavker 3

4 Corneal epithelium is generated from Limbal Stem Cells Limbal Stem Cell Deficiency Limbus contains unique structures that may provide a stem cell niche The search for a limbal stem cell marker has been long and controversial. ABCG2, Integrin alpha 9, p63 are contenders Nov Funderburgh 12 4

5 ABCG2 is present in basal limbal cells But not in central cornea Nov Funderburgh 13 OCT image by Kira Lathrop Nov Funderburgh 14 You NEED Your Stem-Cells Gut Skin Red Blood Cells Corneal Epithelium 4 days 3 weeks 4 months 2 weeks 15 5

6 Autologous limbal stem cell transplantation is highly successful at restoration of function 1-2 mm piece of limbal epithelium is transplanted from contralateral eye Human Amniotic Membrane supports expansion of limbal stem cells in vitro S. Tseng Nov Funderburgh 17 Epithelial limbal cells are transplantation to the eye on after expansion on human amniotic membrane Nov Funderburgh 18 6

7 Rama P, Matuska S, Paganoni G, Spinelli A, De Luca M, Pellegrini G. Limbal stem-cell therapy and long-term corneal regeneration. N Engl J Med 2010;363: Graziella Pellegrini Nov Funderburgh 19 OCCLUDING JUNCTIONS:! Tight junctions! BARRIER FUNCTION! COMMUNICATING JUNCTIONS:! Gap junctions! ANCHORING JUNCTIONS (cell-cell) Adherens junctions! Desmosomes ANCHORING JUNCTIONS (cell-matrix) Hemidesmosomes (epitheial)! Focal adhesions (fibroblast) 9! Cornea provides an In vivo model! of epithelial wound healing! 5! 7

8 Migrating epithelium moves as a sheet! 8! Rat Corneal Epithelial wound Model! Suzuki et al Invest Ophthalmol Vis Sci 2000, 41:2495! Connexin-gap junctions! Demoglein- desmosomes! Occludin- tiget junctions! Cadherin- Adherens junctions! Laminin- BM! 10! Rat corneal wound healing- Laser Ablation! During healing connexin and desmoglein expression returns with establishment of basement membrane. cadherin and occludin junctions are NOT disrupted.! 11! 8

9 Corneal epithelium migrates without cell division! Migrating epithelial edge- 16 hr after wounding ( BrdU incorporations )! Peripheral cornea- 16 hr after wounding ( BrdU incorporations )! 12! Inhibitors of cell cycle entry are present at the leading edge! TGFß! p15! p15, p27,p21! p27! Peripheral cornea Wound Edge! 13! Expression of Cyclin-dependent Kinase Inhibitors During Corneal Wound Repair James D. Zieske Progress in Retinal and Eye Research Vol. 19, No. 3, pp. 257 to 270, 2000! TGFß Receptors are upregulated in during healing! TGFßR2 concentrated at the leading edge! Zieske, Invest. Ophthalmol. Vis. Sci. June 2001 vol. 42 no

10 TGFß Signaling after wounding! 4h! 8h! 16h! 16h! 48h! 48h! SMAD2 Nuclear Localization! Invest. Ophthalmol. Vis. Sci. July 2005 vol. 46 no Epithelial Summary 1. Multilayered squamous epithelium 2. Centripital migration 3. Maintained by a population of stem cells in the limbus 4. Forms an impermeable barrier to the interior of the eye via TJ 5. Rapidly migrates to seal wounds 6. Migration maintains barrier function but suppresses cell division 29! Stroma: the MATRIX 10

11 The Corneal Stroma is composed of collagenous layers (lamellae) with cells (keratocytes) sandwiched between. Collagen fibers in each lamella are parallel and tightly packed Structure of collagen!" "It has a triple-helix structure containing three!-polypeptide chains arranged in right-handed supercoil " Glycine, proline, hydroxyproline Telopeptide! 300 nm! 11

12 Fibrillar collagen is an alloy! Birk & Linsenmayer, 1993! Proteoglycan is a protein modified with one or more large sulfated carbohydrates known as glycosaminoglycan! Glycosaminoglycans are linear and negatively charged due to a high density of carboxyl (COOH-) and sulfate (OSO3-) groups. Because of this these charges the GAG chins are typically rigid giving the molecules a bottle brush aspect. PGs occupy a large hydrodynamic volume.! SLRPs in the corneal stroma! 12

13 SLRP Lumican Binds Collagen in cornea and RegulatesCollagen Fibril Spacing!!"#$%&'()#$"*$+',-&./(01.2(3&"*#(( 85."*# /(!,.2#$%*(9:)!;;<( 4*#%&"&.(!5'6&"*( :&-5'&#(-$#.*&'(2,/"#$=>,( 7*#&"&.(!5'6&"*( Matrix Stability-the lego effect! 1." Multiple interactions per molecule! 2." Large number of molecules involved! 3." Crosslinking! 13

14 Connective tissue is a a composite material! High tensile strength rods embedded in a stiff matrix! Fiberglass! Carbon Fiber! Lamellae = Plies! Additionally, corneal cells are filled with abundant soluble proteins that may reduce refraction. Known as corneal crystalines. 14

15 Lumican knockout mice have disrupted collagen fibril diameter and organization as well as stromal haze. Du, et al Stem Cells (7):

16 DC" /%&''E(5.16$#%(-$''&+*.(F0#1'/( 0C" ;."*#&-"1$.(31">(!JK)/( LC" )&#&''*'(-$''&+*.(=&-M*2("1+>"',(=&-M*2( &C" )#$=*#(>,2#&"1$.(( 0C"!=*-1&'1N*2(OPO(-$."*."(!"#$%&'(%&"#1A(1/(=#$25-*2(0,(M*#&"$-,"*/( #$%&'()"*+(%%,&-" ".),&/&'00"(&/")$1"2,0,$&",&"3,)),$&0"1$%)/1,/'" " #(40'/"567" 8%(43(".(+9'%,()"(&/":4&-()";)+'%0" <*=">'%(??0"" " 48! 16

17 Proteoglycans in scars are involved in the altered architecture of the extracellular matrix Beatrice Yue Keratocytes, cells of the corneal stroma Normal keratocytes are highly dendritic, make the transparent connective tissue of the stroma In wounds keratocytes proliferate MYOFIBROBLAST phenotype, producing nontransparent connective tissue associated with haze. In some conditions the tissue becomes fibrotic and forms permanent scars. TGFß induces scar formation in vivo and in vitro. Corneal Stroma Immune privilege allows successful allograft 90% success rate 17

18 *9%$3()"09'3"+'))0"(%'")$+(),C'/"045D(+'&9"9$"9E'"),35()"5(0'3'&9"3'35%(&'""&'(%"FG*#"!!!! Du Y, et al. Stem Cells 2005;23: ! 8E'%'"(%'"I4)?A$9'&9"*9'3"#'))0",&"<43(&"#$%&'()"*9%$3("" <,-E)6"#)$&$-'&,+" Du Y, et al. Stem Cells 2005;23: ! Funderburgh ML et al Faseb J 2005;19: ! #$%&'()"*9%$3("*9'3"#'))0"J'0+4'"#$%&'()"8%(&0A(%'&+6"",&"F43KLK"I,+'" 18

19 ALDH! TKT! Corneal Endothelium is a single cell layer of flattened hexagonal cells Not identical to vascular endothelium. produces a Basement Membrane (basal lamina) known as Descemet s Memembrane 19

20 Corneal endothelial cells never replicate throughout life. Cell death is compensated by spreading Corneal Endothelium Actively Pumps water from the stroma to maintain corneal hydration. Water diffuses back in through leaky junctions. ZO1 stain for TJ Endothelial Pumping Involves: Energy (ATP) Na+ Transporter Aquoporins Bicarbonate/Carbonic anhydrase J. Bonnano Corneal Endothelium 1. Single layer epithelial tissue 2. Not self-renewing. In adult humans does not divide (G1 Arrest) 3. Leaky barrier 4. High metabolic activity- pumps water from stroma ATP-dependent Na/K transporter 5. Loses cells throughout life 6. Endothelial failure (Fuchs Dystrophy) requires transplant 7. Difficult to expand in culture 60! 20