LOXL1Defficient Mice Is Susceptible To Chronic Ocular Hypertension

Glaucoma is the second major cause of blindness in the world. Clinical findings show progressive eoss of visual field and excavation of the tissues, or "cupping", of the optic nerve head (ONH). Elevated intraocular pressure (IOP) remains the primary risk factor for development of glaucomatous optic neuropathy. elevated IOP exerts force on the ocular tissue, producing mechnial stress and strain, triggerring cellular reponse cascade, causing tissue remodeling and damage to the RGC axons and finally leading to the loss of retina ganglion cells. The eyeball is closed by a corneo-scleral shell which is abundant of colleagen and elastic fibers. The ONH is more vunerable to ocular hypertension as a "weak spot" or discontinuity in the corneo-sclecral shell. The circumferential mechanical stresses produced by IOP are magnified at the transition between the stiffer sclera and more compliant ONH. Indeed, ONH is the primary site of the RGC axonal insult in glaucoma. Elastic fiber confers resiliency and deformability to the lamina cribrosa and peripapillary tissues, which must undergo constant stretch and relaxation cycles to buffer the constant fluctuations in IOP. Patients of pseudoexfoliation glaucoma (PEXG) are more susceptible to glaucomatous neuropathy. PEXG was found to have the largest area of elastosis in lamina cribrosa among various types of glaucoma. Recent studies highly emphasis a high association between LOXL1polymorphisms and PEXG. Elevation of IOP and defficience in LOXLl expression both are major risk factors of optic neuropathy in PEXG. The interaction between ocular hypertension and LOXLl in glaucomatous neuropathy is an insterest of study. The behavior of elastin in the related leision remains unclear. Thus, we conducted a chronic glaucoma model using microbead injections on the LOXL1difficient mice (Loxl1-/-in brief), with C57/BL6mice (the wildtype, WT) as a control group, studied the different susceptibility to the elevation of IOP and observed the pathophysiological alteration of elastin in the disease.This study was a part of the sino-American joint Ph.D. training program, support by the Chinese Scholarship Committee and the National Institute of Health. Our study devoted to the application of microbead technique in mouse glaucoma model studie, improved the phenotype studies in Loxl1-/-eyes and revealed a new clue of the pathogenesis of PEXG.The thesis is composed of four major parts. The first part, foreword, put up the importance of elasic fiber in remain the resilience and plasticity in tissues, explained the mechanism of elastogenesis and elastolysis under a physical and pathological condition in vivo and vitro. LOXL1was considered essential for the homeostasis of elastic fiber. Difficience of LOXL1leads to impaired elastic fiber system, which plays a role in the biomechnics of glaucomatous neuropathy. The forword also briefly introduced the gross phenotype of Loxll-/-mice and the development of mouse glaucoma model. Finally, put up the major object of this study.The second part talks about using microbead technique to induce chornic ocular hypertension in wildtype and Loxl1-/-mice (n=25for each group). Anterior chamber injection of2μl microbeads(6μm)+3μl viscoelastic induced a moderate and persistent elevation of IOP in mouse eyes. The IOP profile was similar between WT and Ldxl1-/-groups, with more fluctuation in WT eyes.The third part of the thesis mainly studied the global elongation of bead eyes and the axonal degenerations in the optic nerves. We measured the alteration of axial length, evaluated the ONH ’cupping’ and conducted RGC axon countings in cross sections of optic nerves. We found that Loxl1-/-eyes showed a IOP-dependent elongation in globes; severer optic neuropathy was seen both in the ONH and the ON cross sections. Loxl1-/-eyes were more susceptible to chronic ocular hypertension.The last part of our work is the morphological and molecular studies of the protein elastin under a chornic leision led by ocular hypertension. A loose packed structure of elasin was found in the posterior and peripapillary tissues of Loxl1-/-eyes. A block in regeneration and progressive elastolysis co-existed in the Loxl1-/-eyes, leading to substantial accumulation of tropoelastin and the degradated elastin.By conclusion, chronic elevation of IOP accelerated the pathological process of impaired homeostasis of elastic fiber in the afftected eye of LOXL1defficient mouse. The optic nerve was more susceptible to mechanical stress without an appropriate protection of the elastic tissues in the peripapillary area of the ONH. The degradation products of elastin, famous for ’elastin-dervied peptides’, may also play an important role in the pathogenesis of the optic neuropathy.