Abstract
PEX stems from a pathologic elastotic process involving the cross-linking gene lysyl oxidase-like-1 (LOXL1), and is associated with abnormal formation of elastic extracellular matrix. We previously described a protein sink model to explain PEX material deposition on the lens capsule and other intraocular surfaces. Recent research findings not only provide evidence to support this hypothesis, but also further our understanding of the fundamental disease process. A key aspect of the pathogenic process is the compromise of blood-aqueous barrier integrity in PEXG. Decreased level of LOXL1 is associated with decreased elastin incorporation into elastic tissues, including the elastic lamina of blood vessels. This results in unincorporated elastin that is released as soluble elastin, and leakage of serum proteins, inflammatory cytokines, and extracellular matrix components into aqueous humor. This ultimately leads to aggregation and precipitation of large protein complexes, or PEX material, throughout intraocular surfaces as described in the protein sink model. The pathologic PEX process also affects the biomechanical properties of elastic tissues, such as the trabecular meshwork, lens zonules, and lamina cribrosa. This may be part of the primary pathologic process with intrinsically altered extracellular matrix proteins. This fundamental change in the structural composition of these tissues may alter their rigidity, elasticity, and other biomechanical properties. This likely contributes to increased trabecular meshwork outflow resistance and high intraocular pressure, and mechanical injury to retinal ganglion cell axons at the lamina cribrosa, which are conducive to glaucoma. These pathophysiologic processes combined may underlie some of the clinical hallmarks observed in PEXG.