Structural basement membrane components and corresponding integrins in Schlemm's canal endothelia.
OBJECTIVE
The conventional outflow pathway provides the primary source of resistance to aqueous humor drainage, regulating intraocular pressure. Despite large pressure gradients across the inner wall of Schlemm's canal (SC), cells remain attached to their basement membrane. The goal of this study was to examine integrin-extracellular matrix binding partners of the inner wall basement membrane that facilitate attachment.


METHODS
Human outflow tissues and cultured cells were analyzed by immunofluorescence and western blotting, respectively. Radial sections of human donor eyes or en face preparations of human SC inner wall were probed with antibodies that specifically recognize collagens (Type I, III, and IV), laminins (LM-332 and LM-511) and laminin-specific integrin subunits, α3, α6, β1, and β4, typical of vascular endothelia.


RESULTS
Immunofluorescence studies showed collagens Type I and IV in the SC basement membrane but not collagen III. As expected with mature vascular endothelia, SC cells in situ expressed LM-511 but not LM-332. Significantly, the integrin α6 subunit was expressed uniquely by SC. En face labeling of the inner wall displayed integrin α6 colocalizing with LM α5 at the cell periphery. Western blots of cultured human SC endothelial cell monolayers confirmed expression of Type I collagen, collagen IV, LM-511, and the α6 integrin subunit. Interestingly, LM-332 was present in cultured SC cells up to 60 days post-confluence.


CONCLUSIONS
Even though cells of the inner wall endure pressure gradients in the basal to apical direction, opposite of other endothelia, human SC cells express basement membrane proteins and their cognate integrins typical of vascular endothelia.
Biomedical Engineering Graduate Inter-Disciplinary Program, University of Arizona, Tucson, AZ 85719, USA.
Saumya S
SS
VanderWyst
Kristin M
KM
Perkumas
A Thomas
AT
Read
Darryl R
DR
Overby
W Daniel
WD
Stamer
D000328:Adult; D000368:Aged; D001082:Aqueous Humor / Q000378:metabolism*; D001485:Basement Membrane / Q000378:metabolism*; D024042:Collagen Type I / Q000096:biosynthesis; D024141:Collagen Type IV / Q000096:biosynthesis; D005109:Extracellular Matrix / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007223:Infant; D039503:Integrin alpha6 / Q000096:biosynthesis; D016023:Integrins / Q000737:chemistry*; D007429:Intraocular Pressure; D018613:Microscopy, Confocal / Q000379:methods; D008856:Microscopy, Fluorescence / Q000379:methods; D008875:Middle Aged
D024042:Collagen Type I; D024141:Collagen Type IV; D039503:Integrin alpha6; D016023:Integrins
Exp Eye Res. 2006 Jun;82(6):974-85
16325178
Invest Ophthalmol Vis Sci. 2006 Mar;47(3):794-801
16505009
Mol Biol Cell. 1994 Apr;5(4):389-93
8054683
Exp Eye Res. 1989 Jan;48(1):139-47
2920781
Circ Res. 2001 Sep 28;89(7):566-72
11577021
Invest Ophthalmol Vis Sci. 1992 Apr;33(5):1670-5
1559767
Cell Mol Life Sci. 2010 Sep;67(17):2879-95
20428923
Circ Res. 2005 Nov 25;97(11):1093-107
16306453
Exp Eye Res. 2009 Apr;88(4):656-70
19103197
Curr Eye Res. 1995 Jul;14(7):611-7
7587308
Curr Eye Res. 1993 Aug;12(8):765-70
8222738
Invest Ophthalmol Vis Sci. 1998 Sep;39(10):1804-12
9727403
Exp Eye Res. 1992 Sep;55(3):479-88
1426078
Dev Dyn. 2000 Jun;218(2):213-34
10842354
Arterioscler Thromb Vasc Biol. 2008 Oct;28(10):1703-13
18658045
Exp Eye Res. 1992 Jun;54(6):879-83
1521580
Invest Ophthalmol Vis Sci. 2001 Jul;42(8):1795-802
11431444
Curr Eye Res. 2002 Nov;25(5):299-308
12658549
Ophthalmic Res. 2001 Nov-Dec;33(6):314-24
11721183
Br J Ophthalmol. 1993 Aug;77(8):515-24
8025051
Exp Eye Res. 2004 Jul;79(1):61-74
15183101
Graefes Arch Clin Exp Ophthalmol. 2007 Jan;245(1):74-81
16612638
Invest Ophthalmol Vis Sci. 1979 Jan;18(1):44-51
103860
J Physiol. 2005 Dec 1;569(Pt 2):359-66
16195317
Invest Ophthalmol Vis Sci. 2007 Nov;48(11):4989-99
17962449
J Glaucoma. 2007 Jun-Jul;16(4):391-405
17571003
Exp Eye Res. 2009 Dec;89(6):980-8
19715693
Invest Ophthalmol Vis Sci. 2004 Jul;45(7):2246-54
15223802
Exp Biol Med (Maywood). 2007 Oct;232(9):1121-9
17895520
Eur J Biochem. 1989 Apr 1;180(3):487-502
2653817
J Biomed Mater Res A. 2004 May 1;69(2):294-304
15058002
Graefes Arch Clin Exp Ophthalmol. 1995 May;233(5):291-5
7622078
Science. 2009 Sep 4;325(5945):1230-4
19729652
Curr Eye Res. 2001 Mar;22(3):235-44
11462161
Arch Ophthalmol. 1963 Jun;69:783-801
13949877
Cancer Res. 2009 Jun 15;69(12):5007-14
19491258
Exp Eye Res. 1990 Dec;51(6):691-9
2265680
Matrix Biol. 1994 Aug;14(4):275-81
7827749
Methods Enzymol. 2007;426:47-67
17697879
Trans Am Acad Ophthalmol Otolaryngol. 1951 Nov-Dec;55:774-81
14893332
Surv Ophthalmol. 1996 Mar-Apr;40(5):379-90
8779084
Ann N Y Acad Sci. 1998 Oct 23;857:194-211
9917842
Ophthalmic Res. 1998;30(6):380-7
9731120
Exp Eye Res. 2008 Apr;86(4):543-61
18313051
Matrix Biol. 2005 Aug;24(5):326-32
15979864
Curr Eye Res. 1989 Dec;8(12):1233-40
2627793
Am J Ophthalmol. 1973 Mar;75(3):365-83
4633234