Histological Evaluation of Diabetic Neurodegeneration in the Retina of Zucker Diabetic Fatty (ZDF) Rats

Abstract

In diabetes, retinal dysfunctions exist prior to clinically detectable vasculopathy, however the pathology behind these functional deficits is still not fully established. Previously, our group published a detailed study on the retinal histopathology of type 1 diabetic (T1D) rat model, where specific alterations were detected. Although the majority of human diabetic patients have type 2 diabetes (T2D), similar studies on T2D models are practically absent. To fill this gap, we examined Zucker Diabetic Fatty (ZDF) rats - a model for T2D - by immunohistochemistry at the age of 32 weeks. Glial reactivity was observed in all diabetic specimens, accompanied by an increase in the number of microglia cells. Prominent outer segment degeneration was detectable with changes in cone opsin expression pattern, without a decrease in the number of labelled elements. The immunoreactivity of AII amacrine cells was markedly decreased and changes were detectable in the number and staining of some other amacrine cell subtypes, while most other cells examined did not show any major alterations. Overall, the retinal histology of ZDF rats shows a surprising similarity to T1D rats indicating that despite the different evolution of the disease, the neuroretinal cells affected are the same in both subtypes of diabetes.

Diabetic Retinopathy: The Role of Mitochondria in the Neural Retina and Microvascular Disease

“…Previous studies have focused primarily on the retinal microvasculature. However, a recent growing body of literature indicates that diabetes causes cellular dysfunction and loss of virtually all retinal cell populations [ 13 , 53 , 54 , 55 , 56 , 57 , 58 ], as measured qualitatively by ERG and quantitatively by optical coherence tomography, revealing a decrease in retinal thickness [ 10 , 59 ]. Diabetes-induced alterations of neuronal cells and photoreceptors are particularly important as the death of these cells is not matched by similar rates of regeneration [ 60 ].…”

Diabetic photoreceptors: Mechanisms underlying changes in structure and function

“…However, it is not known whether long-term light-deprivation likewise increases oxidative stress concomitantly with the reported reduction in inflammation found in phototransduction-deficient diabetic animals. If so, the decoupling of oxidative stress from inflammation and ensuing DR can be (Tarchick et al, 2016) High fat diet & STZ in Balb/c mice 10-30 days of diabetes Reduced ONL thickness (Ren et al, 2017) STZ in C57BL/6 mice 2-12 weeks of diabetes Reduced ONL thickness form 10 weeks of age (Martin et al, 2004) STZ C57BL/6J mice 4-12 weeks of diabetes Progressive thinning of ONL (only peripheral retina) and OPL (central and peripheral retina) from 9-12 weeks (Piano et al, 2016) STZ in C57BL/6J mice 2-7 months of diabetes No difference in ONL thickness and number of ONL cell rows (Liu et al, 2016) Ins2 Akita 3-9 months of age Reduced OS to OPL thickeness, which progresses from 3 to 9 months of age, reduced cone, but not rod density (Hombrebueno et al, 2014) Mouse type 2 diabetes models C57BL/KsJ-db/db mice 8-24 weeks of age Reduced ONL thickness in the central (from 8 weeks) and peripheral retina (from 12 weeks) (Bogdanov et al, 2014) BKS.db/db mice 20-28 weeks of age Reduced ONL from 28 weeks (Yang et al, 2015) High fat diet in C57BL/6J mice 12 months of age No difference in ONL or OPL thickness (Rajagopal et al, 2016) Rat type 1 diabetes model STZ in Sprague-Dawley rats 24 weeks of age Reduced ONL thickness with gradual decline from 1-12 weeks, which accelerated between 12-24 weeks, photoreceptors with apoptotic appearance on EM from 12 weeks (Park et al, 2003) STZ in Wistar rats 24 weeks of diabetes Reduced number of photoreceptor nuclei (Kumar et al, 2013) STZ in Sprague-Dawley rats 7.5 months of diabetes No thinning of ONL + OPL (Barber et al, 1998) Rat type 2 diabetes model ZDF rats 31 weeks of age No difference in number of ONL cell rows, no difference in number of apoptotic cells (Johnson et al, 2013) ZDF rats 32 weeks of age Thickening of the ONL, no difference in number of ONL cell rows, increase in apoptotic cells or cone number, but fragmented OS (Szabó et al, 2017) Nonmurine animal models of diabetes Alloxan-diabetic dogs 5 years of diabetes No reduced retinal thickness, reduced OS/IS thickness or ONL thickness (Tonade & Kern, 2017) Abbreviations: STZ, streptozotocin; ZDF, Zucker diabetic fatty; OS, outer segment; IS, inner segment; ONL, outer nuclear layer; OPL, outer plexiform layer; EM, electron microscopy.…”

Improved Survival and Retinal Function of Aging ZDF Rats in Long-Term, Uncontrolled Diabetes by BGP-15 Treatment

“…Right after the final OGTT, animals were put to sleep with ketamine/xylazine combination (100/10 mg/kg) to carry out electroretinographical screening according to our formerly used method (Wachal et al, 2020). Pupils of both eyes were dilated with one drop of cyclopentolate (Humapent, Teva Ltd., Debrecen, Hungary), and then, a short funduscopic examination took place with a handheld ophthalmoscope (Heine Mini 2000 Ophthalmoscope, HEINE Optotechnik GmbH and Co. KG, Gilching, Germany) to confirm diabetic retinopathy-based on retinal status of ZDF rats with diabetic retinopathy characterized in detail in scientific literature (Kowluru et al, 2016;Mishra et al, 2016;Szabo et al, 2017). For the ERG measurement, five-needle electrodes were inserted into the animal to conduct the lightgenerated currents into an amplifier coupled with an analog-todigital converter (Bridge Amp and PowerLab, ADInstruments, Sydney, Australia) to make waveforms visible on a computer using PowerLab Chart software (version 5.2.2, ADInstruments, Sydney, Australia).…”