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J. J. Blom, J. Russell, W. D. Eldred; Modulation of the Adrenomedullin Signaling Pathway in in vitro Retinal Organ Culture. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5617.
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Diabetic retinopathy is a leading cause of vision impairment and blindness in adults. Most research has focused on the vascular pathology and its prevention. However, electrophysiological deficits and neurodegeneration occur before these vascular changes and they have a significant impact on vision. The nitric oxide (NO) signaling pathway is integrally involved in many aspects of visual processing, and changes in the NO pathway are measurable in eyes of diabetic patients. The small peptide adrenomedullin (ADM), can activate calcineurin, a Ca2+ activated phosphatase that dephosphorylates neuronal nitric oxide synthase (nNOS) at Ser 847 to increase its enzyme activity. ADM levels are elevated in eyes of diabetic patients, and therefore ADM may play a role in the pathology of diabetic retinopathy. The goal of this research is to examine the role of the ADM signaling pathway in an in vitro retinal organ culture system.
PCR and immunocytochemistry were used to determine the localization and modulation of the components of the ADM signaling pathway in an in vitro retinal organ culture system. Retinal cultures were incubated for 24 to 96 hours in glucose concentrations ranging from 5mM to 30mM glucose.
In retinal cultures incubated in high glucose, there was a decrease in nNOS-like immunoreactivity (LI) and an increase in cGMP-LI. Additionally there were increases in ADM-LI, calcineurin-LI, and a decrease in phospho-nNOS (p-nNOS)-LI. The ADM receptor calcitonin receptor like receptor (CRLR) was localized to the plexiform layers. ADM mRNA levels were lowered by the inhibition of PKC and raised by the activation of PKC. The inhibition of PKC in culture decreased ADM-LI and increased p-nNOS-LI. When calcineurin was inhibited with FK506, there was an increase in p-nNOS-LI in retinas incubated in high glucose.
These results indicated that the ADM/nNOS/NO signaling pathway can be modulated in short term retinal organ cultures by high glucose in ways that closely resemble in vivo diabetic retinopathy. Continued exploration of this pathway will provide information how this signaling pathway can be selectively targeted to reduce the pathological changes in diabetic retinopathy.
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