Discrete expression and distribution pattern of TIMP-3 in the human retina and choroid.
OBJECTIVE
Extracellular matrix homeostasis is dependent in part upon a family of matrix metalloproteinases and their specific inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). Recently, gene defects in TIMP-3 have been identified in the affected individuals of several families with Sorsby's fundus dystrophy (SFD). Very little information is available regarding TIMP-3 function or even its existence in the retina or choroid.


METHODS
We used reverse transcription-polymerase chain reaction and Northern analysis to evaluate the expression of TIMP mRNA and Western immunoblots to evaluate TIMP protein produced by select cells of the human retina and choroid. We also used these methods and immunohistochemistry to localize the TIMPs in the retina and choroid.


RESULTS
TIMP-3 transcripts are found in cultured human retinal pigment epithelium (RPE), choroidal microcapillary endothelium and pericytes. RPE cells also express and secrete TIMP-3 protein, which is localized to the extracellular matrix and is not found in culture medium; TIMP-1 and -2 are found almost exclusively in the medium. Immunohistochemistry of human retina/choroid sections shows pronounced TIMP-3 immunostaining in Bruch's membrane, particularly near the surface of the RPE and endothelial cells, presumably in their basement membranes, with minimal staining in other portions of the retina. Immunostaining for TIMP-1 is absent and for TIMP-2 is much less prevalent, but detectable in Bruch's membrane.


CONCLUSIONS
TIMP-1, -2 and -3 exhibit distinctive expression patterns in the retina and choroid. This distribution and expression pattern partially explains why TIMP-3 mutations result in SFD, rather than other retinal pathologies, such as those associated with proliferative diabetic retinopathy.
Vranka
J A
JA
Department of Ophthalmology, Casey Eye Institute, Oregon Health Sciences University, Portland 97201, USA.
Johnson
E
E
Zhu
X
X
Shepardson
A
A
Alexander
J P
JP
Bradley
J M
JM
Wirtz
M K
MK
Weleber
R G
RG
Klein
M L
ML
Acott
T S
TS
D002478:Cells, Cultured; D002829:Choroid / Q000378:metabolism*; D046508:Culture Techniques; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D016133:Polymerase Chain Reaction; D011480:Protease Inhibitors / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000378:metabolism*; D014018:Tissue Distribution; D019717:Tissue Inhibitor of Metalloproteinase-3; D019714:Tissue Inhibitor of Metalloproteinases; D014158:Transcription, Genetic
D006023:Glycoproteins; D011480:Protease Inhibitors; D011506:Proteins; D012333:RNA, Messenger; D019717:Tissue Inhibitor of Metalloproteinase-3; D019714:Tissue Inhibitor of Metalloproteinases