Morphological and biochemical abnormalities in a model of retinal degeneration: Canine ceroid-lipofuscinosis (CCL)

Use of model organisms for the study of neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinoses are a group of fatal progressive neurodegenerative diseases predominantly affecting children. Identification of mutations that cause neuronal ceroid lipofuscinosis, and subsequent functional and pathological studies of the affected genes, underpins efforts to investigate disease mechanisms and identify and test potential therapeutic strategies. These functional studies and pre-clinical trials necessitate the use of model organisms in addition to cell and tissue culture models as they enable the study of protein function within a complex organ such as the brain and the testing of therapies on a whole organism. To this end, a large number of disease models and genetic tools have been identified or created in a variety of model organisms. In this review, we will discuss the ethical issues associated with experiments using model organisms, the factors underlying the choice of model organism, the disease models and genetic tools available, and the contributions of those disease models and tools to neuronal ceroid lipofuscinosis research. This article is part of a Special Issue entitled: The Neuronal Ceroid Lipofuscinoses or Batten Disease.

English setter model and juvenile ceroid-lipofuscinosis in man

The etiology of the juvenile type of the human ceroid-lipofuscinosis (JCL) is unknown, in spite of the fact that the first report of this disease was given more than 160 years ago. The necessity of good animal models for scientific progress in chronic metabolic diseases in humans is obvious. The inbred strain of English setter with ceroid-lipofuscinosis (CCL) seems to be a perfect model for human JCL. Dogs with CCL and organs for research purposes are available from Dr. Koppang's experimental kennel in Norway.

The English setter with ceroid-lipofuscinosis: a suitable model for the juvenile type of ceroid-lipofuscinosis in humans

Genetic and histological examinations (light and EM) of tissues of an inbred line of English setters have proved that these dogs suffer a general metabolic autosomal recessive disease, canine ceroid-lipofuscinosis (CCL) almost identical to the human Stengel-Batten-Spielmeyer-Vogt disease, or neuronal ceroid-lipofuscinosis (NCL). A controlled longitudinal morphologic study showed that the formation and accumulation of an autofluorescent lipopigment, identified as "ceroid" in the isolated state, appears in the neurons already in 2-day-old puppies and increases linearly with time. Clinical signs and symptoms develop after a distinct loss of neurocytoplasm and its functional organelles is demonstrable. At that time, loss of functional neuronal cytoplasm appears to result from pigment formation. Nerve cells which have suffered this fate will eventually die and disappear. The process leads to severe global neurologic disturbance and cerebral atrophy. By the time of death from the disease at age 20 to 27 months, brain weight is reduced to 60-70% of normal control animals. The English setter with CCL differs somewhat from humans in the degree of morphological damage to various layers of the retina. In human with NCL, there is a pronounced loss of photoreceptors in the end-stage of the disease, but in CCL only minimal structural damage is observed in the retina. For experimental treatment protocols for NCL, the CCL setter is a useful model.

Effects of chloroquine on lysosomal enzymes, NADPH-induced lipid peroxidation, and antioxidant enzymes of rat retina

Chloroquine (1, 5 and 10 mg/kg), given in acute and in chronic (7 and 15 days) treatment schedules, caused characteristic alterations in the lysosomal enzyme system, antioxidant enzymes, NADPH-induced lipid peroxidation, and glutathione content in the retina of the rat. One-half hour and four hours after chloroquine administration, increased free activities of lysosomal enzymes and NADPH-induced lipid peroxidation were observed, associated with a decrease in tissue glutathione content. In contrast to the acute effect, chloroquine, given in 7- and 15-day treatment schedules, had no significant effect on the lysosomal enzyme system, while at the same time a normalization or a decrease in NADPH-induced lipid peroxidation, associated with a significant increase in tissue glutathione content, was noted. Catalase and peroxidase activities were decreased after both the acute and the daily treatment schedules. Superoxide dismutase activity, although increased in the high dose acute study, appeared otherwise little affected by chloroquine treatment.

The distribution of peroxide regulating enzymes in the canine eye

The retina and rod outer segments (ROS), rich in unsaturated lipids, are highly susceptible to autoxidation via free radical mechanisms. In the canine eye, four enzymes, i.e.; p-phenylenediamine (PPD) peroxidase, glutathione peroxidases, catalase and superoxide dismutase which are involved in the production or degradation of peroxides, were measured. All enzymes were present in the retina, ciliary body and iris, but differed in concentration. Superoxide dismutase showed high activity in the ROS. In the retinal pigment epithelium (RPE) a peroxidase utilizing PPD as cosubstrate and superoxide dismutase were both present. The former enzyme was found equally distributed between soluble and insoluble forms. A pigment granule fraction from the RPE only contained PPD-peroxidase. The compartmentalization of peroxide regulating enzymes in the eye is striking. Whereas the retina seems well protected against superoxide free radicals and hydrogen peroxide by virtue of superoxide dismutase, peroxidases and catalase activities, the ROS are only protected by superoxide dismutase. Therefore, after phagocytosis of the ROS, any peroxidized lipids, organic peroxides, or unconverted superoxide radicals contained within the ROS, must be detoxified by a specific RPE peroxidase and superoxide dismutase. Hydrogen peroxide or other peroxidized compounds apparently are not degraded by glutathione peroxidases or catalase, since these enzymes were not measurable in our RPE preparations. The role of antioxidative enzymes in the eye, which retard peroxide and free radical information, appears to be specific and regional.