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Visual Transduction and Age-Related Changes in Lipofuscin

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Małgorzata Rózanowski and Bartosz Rózanowski

CONTENTS

INTRODUCTION: WHAT IS LIPOFUSCIN?

LIPOFUSCIN OF THE RETINAL PIGMENT EPITHELIUM

FACTORS AFFECTING ACCUMULATION OF RPE LIPOFUSCIN

EFFECTS OF LIPOFUSCIN ON RPE FUNCTION AND VIABILITY

APPROACHES TO DIMINISH LIPOFUSCIN ACCUMULATION OR LIPOFUSCIN-INDUCED

DAMAGE

CONCLUSIONS

REFERENCES

INTRODUCTION: WHAT IS LIPOFUSCIN?

With aging, postmitotic cells accumulate brownish-yellow lipophilic granules with fluorescent properties called age pigment or lipofuscin [1–5]. Histochemical identification of lipofuscin is based on its granular appearance enclosed with lipid membrane and on staining with methods used for lipids, proteins, and carbohydrates. These residual bodies can also be stained using traditional methods used for detection of lysosomal enzymes.

Lipofuscin accumulates not only in cells of long-lived primates but also in other mammals with much shorter life spans as well as in phylogenetically lower species, such as insects, crustaceans, and even plants. Chemical composition, physicochemical properties, and the rates of lipofuscin accumulation are dependent on the type of cells in which the accumulation occurs and on the metabolic rate or level of oxidative stress to which the cells are exposed. For example, in human heart muscle cells the rate of accumulation of lipofuscin is about 0.6% of cell volume per decade of life, whereas in motor neurons the accumulation of lipofuscin is much faster, and it reaches up to 75% of cell volume in centenarians.

Despite extensive research, the genesis of lipofuscin and its cellular effects are not fully understood. It is generally believed that lipofuscin is formed as a result of incomplete lysosomal degradation of autophagocytosed or endocytosed material.

From: Ophthalmology Research: Visual Transduction and Non-Visual Light Perception

Edited by: J. Tombran-Tink and C. J. Barnstable © Humana Press, Totowa, NJ

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