Roles of thrombospondin-1 and -2 in regulating corneal and iris angiogenesis.
OBJECTIVE
Thrombospondin (TSP)-1 and -2 are important antiangiogenic factors thought to be involved in maintaining corneal avascularity (angiogenic privilege). This study was undertaken to investigate whether deficiencies of these factors altered developmental and inflammation-induced angiogenesis in the cornea and developmental angiogenesis of the iris of mice.


METHODS
Expression of TSP-1 and -2 mRNA and protein was assayed in cornea and iris stroma by RT-PCR and Western blot. Corneas and irides of TSP-1(-/-), TSP-2(-/-), and TSP-1,2(-/-) mice aged 2, 3, and 6 months, and wild-type control mice, were analyzed for spontaneous angiogenesis biomicroscopically, histologically, and with CD31 immunohistochemistry. The mouse model of suture-induced, inflammatory corneal neovascularization was used to evaluate the lack of TSP-1,2 and both TSPs on induced-corneal angiogenesis. Seven days after intrastromal placement of three 11-0 sutures, vascularized areas were analyzed morphometrically on CD31-stained corneal flatmounts.


RESULTS
Corneas and irises from normal mouse eyes constitutively expressed TSP-1 and -2 mRNAs and proteins. Corneas of TSP-1(-/-), -2(-/-), and -1,2(-/-) mice displayed no evidence of spontaneous developmental-postnatal angiogenesis, although irises of these mice contained significantly increased iris vessel density compared with wild-type animals (P < 0.01). One week after suturing, corneas of all TSP(-/-) mice had significantly greater corneal angiogenesis than those of control mice (P < 0.05). TSP-1(-/-) had a significantly greater effect on induced corneal neovascularization than did TSP-2(-/-), with the opposite being the case in developmental iris angiogenesis (P < 0.01).


CONCLUSIONS
Corneal avascularity during development is redundantly regulated, shown by the fact that lack of the antiangiogenic factors TSP-1 and/or -2 resulted in no spontaneous corneal angiogenesis. By contrast, TSP-1, more than TSP-2, helps to suppress inflammation-induced corneal angiogenesis postnatally, implying that angiogenic privilege in the cornea is actively maintained.
Cursiefen
Claus
C
Schepens Eye Research Institute, Department of Ophthalmology, Harvard Medical School, Boston Massachusetts 02114, USA.
Masli
Sharmila
S
Ng
Tat Fong
TF
Dana
M Reza
MR
Bornstein
Paul
P
Lawler
Jack
J
Streilein
J Wayne
JW
D000818:Animals; D015153:Blotting, Western; D003315:Cornea / Q000378:metabolism; D016510:Corneal Neovascularization / Q000378:metabolism* / Q000473:pathology; D005260:Female; D017353:Gene Deletion; D007498:Iris / Q000098:blood supply* / Q000473:pathology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009389:Neovascularization, Pathologic / Q000378:metabolism* / Q000473:pathology; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019700:Thrombospondin 1 / Q000235:genetics / Q000502:physiology*; D019699:Thrombospondins / Q000235:genetics / Q000502:physiology*; D000099262:Thrombospondin 2
D019408:Platelet Endothelial Cell Adhesion Molecule-1; D012333:RNA, Messenger; D019700:Thrombospondin 1; D019699:Thrombospondins; D000099262:Thrombospondin 2