MMP and TIMP expression in quiescent, dividing, and differentiating human lens cells.
OBJECTIVE
Matrix metalloproteinases (MMPs) and the tissue inhibitors of the MMPs (TIMPs) have been implicated in lens differentiation, growth, remodeling, and cataract. Hence, a gene expression analysis was undertaken in epithelial and fiber cells dissected from clear human donor lenses.


METHODS
The human lens was dissected into three regions: anterior epithelial, equatorial, and fiber cells. Primary lens cell cultures were also analyzed. cDNA was generated by reverse transcription of the mRNA portion of the total RNA isolated from each sample. Gene expression data were generated using quantitative real-time reverse transcription PCR. Data were analyzed in terms of cycle threshold number (C(T)) and were normalized to endogenous 18S expression. Western blot analyses were carried out to confirm the presence of two critical MMPs.


RESULTS
Anterior and equatorial samples were uncontaminated by fiber cells because they showed high expression of alpha-crystallin genes but low expression of beta- and gamma-crystallins. The fibers had high expression of these genes and of MIP. MMP genes were expressed at uniformly low levels in the native tissues except for MMP-14 and -15 (MT1- and MT2-MMP, respectively). In fact, MT1-MMP declined in expression from the anterior epithelium to fibers, whereas MT2-MMP increased. The presence of MT1 and MT2-MMP proforms and faster migrating bands, indicating processed or activated forms, was confirmed at the protein level. TIMP genes were uniformly highly expressed in native tissues, with TIMP-3 having the highest expression in the epithelial tissues and TIMP-2 in the fibers. MMP expression was generally elevated in both sets of cultured cells, including MMP-2 and -9. TIMP genes were also relatively highly expressed in the cultured cells.


CONCLUSIONS
MMP expression is generally well regulated in native tissues, with relatively low expression of MMPs and high expression of TIMPs. Membrane-type MMPs (MT1 and 2-MMPs) were the most highly expressed; this is important in a tissue with relatively high membrane content but low extracellular space. The striking reciprocal patterns of expression of MT1-MMP and MT2-MMP indicate that these enzymes are of particular significance in lens function.
Hodgkinson
Lisa M
LM
School of Biological Sciences, University of East Anglia, Norwich, United Kingdom. l.hodgkinson@uea.ac.uk
Duncan
George
G
Wang
Lixin
L
Pennington
Caroline J
CJ
Edwards
Dylan R
DR
Wormstone
I Michael
IM
D000368:Aged; D015153:Blotting, Western; D002454:Cell Differentiation / Q000235:genetics; D002455:Cell Division / Q000235:genetics; D002478:Cells, Cultured; D015870:Gene Expression / Q000502:physiology*; D006801:Humans; D007908:Lens, Crystalline / Q000166:cytology* / Q000378:metabolism*; D020782:Matrix Metalloproteinases / Q000235:genetics*; D008875:Middle Aged; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014019:Tissue Donors; D019714:Tissue Inhibitor of Metalloproteinases / Q000235:genetics*
D012333:RNA, Messenger; D019714:Tissue Inhibitor of Metalloproteinases; D020782:Matrix Metalloproteinases