Abstract
Purpose::
To demonstrate that significant changes in the protein levels occur for cochlin and collagen in the extracellular matrix (ECM) of glaucomatous, but not in normal trabecular meshwork (TM); to demonstrate that observed ECM changes are likely due to new interactions of TM matrix proteins with cochlin.
Methods::
Normal human and POAG donor eyes (n=20 for each group) were obtained from NDRI in compliance with the Declaration of Helsinki. Dissected TM tissues were subjected to protein extraction in buffer containing 1% SDS or fixed in 4% paraformaldehyde in DEPC water and subjected to Immunohistochemical analyses with custom generated polyclonal antibodies to cochlin and commercially available antibodies to collagen (type I-IV) and annexin or in-situ hybridization with digoxigenin-labeled sense and antisense riboprobes complementary to cochlin and collagen type II gene sequences.
Results::
A significantly elevated level of cochlin was observed in glaucomatous TM (n=20) but not in controls (n=20 matched in age and race from either gender), concomitant with a significantly decreased level of collagen type II. Cochlin and collagen type II mRNAs were detected in the TM by in-situ hybridization. Reciprocal immunoprecipitation and mass spectrometry confirmed interaction of annexin A2 with cochlin.
Conclusions::
Glaucomatous TM in contrast to normal TM showed altered levels of ECM proteins, namely cochlin and collagen (particularly type II). It is likely that cochlin competes with collagen for interaction with annexin and leads to the degradation of "free" collagen type II in the TM ECM.
Keywords: trabecular meshwork • extracellular matrix • proteomics