CD44 and primary open angle glaucoma

In our view, primary open-angle glaucoma (POAG) is a common neurodegenerative disease caused by a variety of molecular defects and/or cellular insults that result in cell stress and death of the trabecular meshwork (TM) and retinal ganglion cells (RGC). One potential biological marker of POAG is CD44, which is one of the adhesion/homing molecules. Direct evidence for CD44's very central role in POAG includes: (1) aqueous humor of patients with POAG contains an increased amount of the soluble extracellular 32-kDa fragment of CD44 (sCD44) in comparison with the aqueous humor of age-matched normal individuals; (2) increased levels of sCD44 in the aqueous correlates with the extent of visual field loss in POAG patients; (3) sCD44, particularly hypo-phosphorylated sCD44, is a potent and specific toxic protein to TM and RGC in vitro; and (4) overexpression of both full-length CD44 and truncated sCD44 in transgenic mouse eyes is sufficient to cause ocular hypertension. The increase in intraocular pressure (IOP) lasted more than 90 days accompanied by optic nerve damage. The overexpression of CD44 may thus be the first documented animal model that closely mimics the human disease POAG. Other models have been cytodestructive and nonphysiologic.