Morphological alterations of the cornea in the mouse model of niemann-pick disease type c1

Lacritin and other autophagy associated proteins in ocular surface health

Advantage may be taken of macroautophagy ('autophagy') to promote ocular health. Autophagy continually captures aged or damaged cellular material for lysosomal degradation and recyling. When autophagic flux is chronically elevated, or alternatively deficient, health suffers. Chronic elevation of flux and stress are the consequence of inflammatory cytokines or of dry eye tears but not normal tears invitro. Exogenous tear protein lacritin transiently accelerates flux to restore homeostasis invitro and corneal health invivo, and yet the monomeric active form of lacritin appears to be selectively deficient in dry eye. Tissue transglutaminase-dependent cross-linking of monomer decreases monomer quantity and monomer affinity for coreceptor syndecan-1 thereby abrogating activity. Tissue transglutaminase is elevated in dry eye. Mutation of arylsulfatase A, arylsulfatase B, ceroid-lipofuscinosis neuronal 3, mucolipin, or Niemann-Pick disease type C1 respectively underlie several diseases of apparently insufficient autophagic flux that affect the eye, including: metachromatic leukodystrophy, mucopolysaccharidosis type VI, juvenile-onset Batten disease, mucolipidosis IV, and Niemann-Pick type C associated with myelin sheath destruction of corneal sensory and ciliary nerves and of the optic nerve; corneal clouding, ocular hypertension, glaucoma and optic nerve atrophy; accumulation of 'ceroid-lipofuscin' in surface conjunctival cells, and in ganglion and neuronal cells; decreased visual acuity and retinal dystrophy; and neurodegeneration. For some, enzyme or gene replacement, or substrate reduction, therapy is proving to be successful. Here we discuss examples of restoring ocular surface homeostasis through alteration of autophagy, with particular attention to lacritin.

Corneal alterations during combined therapy with cyclodextrin/allopregnanolone and miglustat in a knock-out mouse model of NPC1 disease

Background

Niemann Pick disease type C1 is a neurodegenerative disease caused by mutations in the NPC1 gene, which result in accumulation of unesterified cholesterol and glycosphingolipids in the endosomal-lysosomal system as well as limiting membranes. We have previously shown the corneal involvement in NPC1 pathology in form of intracellular inclusions in epithelial cells and keratocytes. The purpose of the present study was to clarify if these inclusions regress during combined substrate reduction- and by-product therapy (SRT and BPT).

Methodology/Principal Findings

Starting at postnatal day 7 (P7) and thereafter, NPC1 knock-out mice (NPC1^−/−) and wild type controls (NPC1^+/+) were injected with cyclodextrin/allopregnanolone weekly. Additionally, a daily miglustat injection started at P10 until P23. Starting at P23 the mice were fed powdered chow with daily addition of miglustat. The sham group was injected with 0.9% NaCl at P7, thereafter daily starting at P10 until P23, and fed powdered chow starting at P23. For corneal examination, in vivo confocal laser-scanning microscopy (CLSM) was performed one day before experiment was terminated. Excised corneas were harvested for lipid analysis (HPLC/MS) and electron microscopy.

In vivo CLSM demonstrated a regression of hyperreflective inclusions in all treated NPC1^−/−mice. The findings varied between individual mice, demonstrating a regression, ranging from complete absence to pronounced depositions. The reflectivity of inclusions, however, was significantly lower when compared to untreated and sham-injected NPC1^−/− mice. These confocal findings were confirmed by lipid analysis and electron microscopy. Another important CLSM finding revealed a distinct increase of mature dendritic cell number in corneas of all treated mice (NPC1^−/− and NPC1^+/+), including sham-treated ones.

Conclusions/Significance

The combined substrate reduction- and by-product therapy revealed beneficial effects on the cornea. In vivo CLSM is a non-invasive tool to monitor disease progression and treatment effects in NPC1 disorder.