IN SEARCH OF MOUSE MODELS FOR EXFOLIATION SYNDROME

Abstract

Exfoliation syndrome (XFS) is a systemic connective tissue disorder with elusive pathophysiology. We hypothesize that a mouse model with elastic fiber defects caused by lack of lysyl oxidase like 1 (LOXL1 encoded by Loxl1), combined with microfibril deficiency due to Fbn1 mutation (encoding fibrillin-1, Fbn1C1041G/+) will display ocular and systemic phenotypes of XFS. Loxl1-/- was crossed with Fbn1C1041G/+ to create double mutant (dbm) mice. Intraocular pressure (IOP), visual acuity (VA), electroretinogram (ERG) and biometry were characterized in 4 genotypes (wt, Fbn1C1041G/+, Loxl1-/-, dbm) at 16 weeks old. Optic nerve area was measured by ImageJ and axon counting was achieved by AxonJ. Deep whole-body phenotyping was performed in wt and dbm mice. Two-tailed Student's t-test was used for statistical analysis. There was no difference in IOP between the 4 genotypes. VA was significantly reduced only in dbm mice. The majority of biometric parameters showed significant differences in all 3 mutant genotypes compared to wt, and dbm had exacerbated anomalies compared to single mutants. Dbm mice showed reduced retinal function and significantly enlarged ON area when compared with wt. Dbm mice exhibited severe systemic phenotypes related to abnormal elastic fibers, such as pelvic organ prolapse, cardiovascular and pulmonary abnormalities. Ocular and systemic findings in dbm mice support functional overlap between fibrillin-1 and LOXL1, two prominent components of exfoliation material. Although no elevated IOP or reduction of axon numbers was detected in dbm mice at 16-week-old, their reduced retinal function and enlarged ON area indicate early retinal ganglion cell dysfunction. Dbm mice also provide insight on the link between XFS and systemic diseases in humans.