Pathologic alterations of the outer retina in streptozotocin-induced diabetes.
OBJECTIVE
Neurodegeneration as an early event of diabetic retinopathy preceding clinically detectable vascular alterations is a widely proven issue today. While there is evidence for the impairment of color vision and contrast sensitivity in early diabetes, suggesting deteriorated photoreceptor function, the underlying neuropathology of these functional alterations is still unknown. The aim of the present study was to investigate the effects of early diabetes on the outer retinal cells.


METHODS
The retinal pigment epithelium, photopigment expression, and density and morphology of photoreceptors were studied using immunocytochemistry in streptozotocin-induced diabetes in two rat strains. The fine structure of photoreceptors and pigment epithelium was also investigated with transmission electron microscopy.


RESULTS
Here we found that retinal thickness was unchanged in diabetic animals and that no significant increase in the number of apoptotic cells was present. Although the density of cones expressing middle (M)- and shortwave (S)-sensitive opsins was similar in diabetic and control retinas, we detected remarkable morphologic signs of degeneration in the outer segments of diabetic rods, most M-cones, and some S-cones. A decrease in thickness and RPE65 protein immunoreactivity of the pigment epithelium were evident. Furthermore, an increased number of dual cones, coexpressing both M- and S-opsins, was detected at the peripheral retina of diabetic rats.


CONCLUSIONS
Degenerative changes of photoreceptors and pigment epithelium shown here prior to apoptotic loss of photoreceptors may contribute to functional alterations reported in diabetic human patients and different animal models, thus may serve as a potential model for testing the efficacy of neuroprotective agents in diabetes.
Department of Ophthalmology, Semmelweis University, Budapest, Hungary Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary.
Anna
A
Énzsöly
Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary.
Arnold
A
Szabó
Department of Anatomy, Histology and Embryology, Semmelweis University, Budapest, Hungary.
Orsolya
O
Kántor
Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary.
Csaba
C
Dávid
Department of Control Engineering and Information Technology, Budapest University of Technology and Economics, Budapest, Hungary.
Péter
P
Szalay
Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary.
Klaudia
K
Szabó
Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary.
Ágoston
Á
Szél
Department of Ophthalmology, Semmelweis University, Budapest, Hungary.
János
J
Németh
Department of Human Morphology and Developmental Biology, Semmelweis University, Budapest, Hungary.
Ákos
Á
Lukáts
D000818:Animals; D017209:Apoptosis; D002452:Cell Count; D003921:Diabetes Mellitus, Experimental / Q000150:complications / Q000378:metabolism / Q000473:pathology*; D003930:Diabetic Retinopathy / Q000209:etiology / Q000378:metabolism / Q000473:pathology*; D018450:Disease Progression; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D037102:Lectins / Q000378:metabolism; D008297:Male; D046529:Microscopy, Electron, Transmission; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D055214:Retinal Photoreceptor Cell Outer Segment / Q000378:metabolism / Q000648:ultrastructure*; D055213:Retinal Pigment Epithelium / Q000378:metabolism / Q000648:ultrastructure
D037102:Lectins
diabetes mellitus; neurodegeneration; photoreceptor morphology; retinal pigment epithelium