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Deshea L Harris, Maria J Lopez, Arsia Jamali, Pedram Hamrah; Expression of the Neuropeptide Adrenomedullin and its Receptors in Normal and Inflamed Murine Corneas. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4038.
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© ARVO (1962-2015); The Authors (2016-present)
Adrenomedullin (ADM) is a small, secreted peptide that can function as a neurotransmitter/modulator. Recent reports suggest ADM is upregulated in the aqueous humor, vitreous humor or plasma in several ocular diseases including open-angle glaucoma, diabetes, uveitis and retinitis pigmentosa. However, no group to date has described ADM in the cornea. The purpose of this study is to investigate the expression and localization of ADM in the cornea.
RT-qPCR, immunoblotting, and immunocytochemistry were used to determine the presence and localization of the components of the ADM signalling pathways, including ADM and its receptors calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein 2 (RAMP2) in the murine cornea at steady state (SS), after suture-induced inflammation on days 7 and 14, after cautery-induced inflammation on day 5, and axotomy of the trigeminal nerve on days 1, 3, 7.
We demonstrate that ADM mRNA is detected in the naive cornea, and that inflammation induces an increase by 1.7 fold for cautery (p<0.01) and 6.4 fold (p<0.05) for suture-induced models of inflammation over SS. The axotomy model showed a significant 1.6 fold increase (p<0.01) at day 7. In the SS cornea, ADM protein levels by Western blot were found to be more prevalent in the epithelium versus the stroma plus endothelium by 4.5 fold. In the axotomy model at day 3, ADM protein levels were 2.4 fold higher and CRLR was 9.5 fold higher than in SS. In sutured corneas at day 14, only CRLR increased 1.8 fold compared to SS. Immunohistochemistry of fresh frozen cross sections confirmed the primary localization of ADM in the central and peripheral epithelium of the SS cornea, although there is also a presence of ADM+ cells in anterior stroma and endothelium. CRLR and RAMP2 show colocalization with ADM in the epithelium, anterior stroma and endothelium. In the cautery model at day 5, the ADM levels in the central epithelium where the burn is placed are down-regulated, whereas the peripheral ADM levels are similar to those in SS.
This is the first study showing expression and localization of adrenomedullin and its receptors CRLR and RAMP2 in the murine cornea. Since ADM is considered a pleiotropic molecule, further investigations are required to elucidate its potential role in modulating corneal immune responses.
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