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M. Kang, D.-J. Oh, D. J. Rhee; Structural and Functional Characterization of Hevin in Trabecular Meshwork. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4882.
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Hevin is a matricellular protein that has anti-adhesive properties and regulates certain extracellular matrix components.1 Phylogenetically, hevin is the result of a gene duplication of SPARC.2 SPARC is highly transcribed by trabecular meshwork (TM) cells, is increased in response to mechanical stress, and its absence results in a lower intraocular pressure (IOP). It is unknown if hevin is expressed in the TM.1,3 We hypothesized that hevin is expressed in the TM and has a functional consequence on IOP. We examined human TM tissue, cultured TM endothelial cells, and anterior segment sections for the expression of hevin and compared the IOPs of hevin-null and wild-type (WT) mice.
Total RNA and protein were isolated from human TM and cultured TM endothelial cells. RT-PCR and Western blotting were performed to identify transcription and protein expression. Confocal microscopy determined the distribution of hevin in human and mouse anterior chamber segments. Intraocular pressure (IOP) was measured in C57BL6x129SvJ and hevin-null mice using both Tonolab and cannulation tonometry.
Hevin mRNA was expressed in TM tissues, but not in cultured TM cells. Although the calculated molecular weight of hevin was 72 kDa, immunoblotting of hevin showed a low mobility in human TM tissues with an observed molecular weight of approximately 115 kDa regardless of the reducing condition (Fig. 1). Confocal microscopy showed that hevin was expressed in human TM tissue at low levels (Fig. 2). IOP between hevin-null and WT mice were not different (16.5±1.75 mmHg, N=32, compared to 16.0±1.84 mmHg, N=30) (p=0.21).
We showed that hevin mRNA and protein are expressed in non-glaucomatous TM tissue as a structurally modified form. Hevin does not appear to be critical to an aqueous outflow resistance which may be related to its low levels of expression or lack of concentration in the juxtacanalicular region.
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