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Evidence for a functional adrenomedullin signaling pathway in the mouse retina.

Blom J, Giove TJ, Pong WW, Blute TA, Eldred WD - Mol. Vis. (2012)

Bottom Line: We found that calcitonin-receptor-like receptor and receptor activity modifying protein 2 had localization patterns similar to ADM, especially in somata in the inner nuclear and ganglion cell layers.These results are the first to show that ADM and functional ADM receptors are present in the retina.Since ADM is increased in eyes with ocular pathologies such as diabetic retinopathy, glaucoma, retinitis pigmentosa, and uveitis, the ADM signaling pathway may provide a new target for ameliorating these retinal pathologies.

View Article: PubMed Central - PubMed

Affiliation: Boston University, Laboratory of Visual Neurobiology, Department of Biology, Boston, MA 02215, USA.

ABSTRACT

Purpose: Adrenomedullin (ADM) is a small, secreted peptide often associated with vasodilation. However, ADM can also function as a neurotransmitter/neuromodulator, and studies suggest ADM is upregulated in the eye in several ocular diseases. However, no studies to date have described an ADM signaling pathway in the retina.

Methods: PCR, immunocytochemistry, nitric oxide imaging, western blots, and a nitrite assay were used to determine the localization of the components of the ADM signaling pathway in the mouse retina.

Results: We used reverse-transcriptase polymerase chain reaction to show that ADM and its primary receptor, calcitonin-receptor-like receptor, along with its associated receptor activity modifying proteins 2 and 3 are expressed in the retina. Using immunocytochemistry, we detected ADM staining throughout the retina in the photoreceptor outer segments, the outer nuclear layer, Müller and amacrine cell somata in the inner nuclear layer, and some somata in the ganglion cell layer. We found that calcitonin-receptor-like receptor and receptor activity modifying protein 2 had localization patterns similar to ADM, especially in somata in the inner nuclear and ganglion cell layers. Finally, we showed that the ADM receptor was functional in the retina. Stimulation of isolated retinas with ADM increased cyclic adenosine monophosphate- and cyclic guanosine monophosphate-like immunoreactivity, as well as nitric oxide production.

Conclusions: These results are the first to show that ADM and functional ADM receptors are present in the retina. Since ADM is increased in eyes with ocular pathologies such as diabetic retinopathy, glaucoma, retinitis pigmentosa, and uveitis, the ADM signaling pathway may provide a new target for ameliorating these retinal pathologies.

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Related in: MedlinePlus

Summary diagram of the proposed adrenomedullin (ADM) signaling pathway in the retina. Protein kinase C (PKC) activation can lead to increased transcription of the ADM gene via a PKC enhancer element. The ADM precursor preproadrenomedullin is cleaved to proadrenomedullin, which is then cleaved into the secreted peptide ADM and the proadrenomedullin NH2-terminal peptide (PAMP). ADM is secreted and binds to the G-protein coupled receptor calcitonin receptor like receptor (CRLR) that is associated with either the receptor activity modifying protein RAMP2 or RAMP3 to activate a signaling cascade that increases cyclic adenosine monophosphate (cAMP) by activating adenylyl cyclase. Increases in cAMP levels activate protein kinase A (PKA), which increases calcium levels by opening membrane calcium channels or by releasing intracellular calcium stores. The overall increase in intracellular calcium can increase nitric oxide (NO) production by directly stimulating nNOS or by activating nNOS through the activation of the calcium-activated phosphatase, calcineurin (CaN), which dephosphorylates nNOS at an inhibitory phosphorylation site at serine847. Increases in NO production can then increase in cGMP synthesis by activating soluble guanylyl cyclase (sGC).
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f8: Summary diagram of the proposed adrenomedullin (ADM) signaling pathway in the retina. Protein kinase C (PKC) activation can lead to increased transcription of the ADM gene via a PKC enhancer element. The ADM precursor preproadrenomedullin is cleaved to proadrenomedullin, which is then cleaved into the secreted peptide ADM and the proadrenomedullin NH2-terminal peptide (PAMP). ADM is secreted and binds to the G-protein coupled receptor calcitonin receptor like receptor (CRLR) that is associated with either the receptor activity modifying protein RAMP2 or RAMP3 to activate a signaling cascade that increases cyclic adenosine monophosphate (cAMP) by activating adenylyl cyclase. Increases in cAMP levels activate protein kinase A (PKA), which increases calcium levels by opening membrane calcium channels or by releasing intracellular calcium stores. The overall increase in intracellular calcium can increase nitric oxide (NO) production by directly stimulating nNOS or by activating nNOS through the activation of the calcium-activated phosphatase, calcineurin (CaN), which dephosphorylates nNOS at an inhibitory phosphorylation site at serine847. Increases in NO production can then increase in cGMP synthesis by activating soluble guanylyl cyclase (sGC).

Mentions: Most importantly, we found that the primary receptor for ADM, CRLR, and its associated RAMP2 had largely overlapping expression with ADM, especially in Müller cell somata and in presumptive ganglion cell somata in the GCL. The increased levels of cAMP-LI, cGMP-LI, and nitrite in response to stimulation with the ADM peptide provided further evidence of a functional ADM receptor and an ADM/NO signaling pathway in the mouse retina (Figure 8).


Evidence for a functional adrenomedullin signaling pathway in the mouse retina.

Blom J, Giove TJ, Pong WW, Blute TA, Eldred WD - Mol. Vis. (2012)

Summary diagram of the proposed adrenomedullin (ADM) signaling pathway in the retina. Protein kinase C (PKC) activation can lead to increased transcription of the ADM gene via a PKC enhancer element. The ADM precursor preproadrenomedullin is cleaved to proadrenomedullin, which is then cleaved into the secreted peptide ADM and the proadrenomedullin NH2-terminal peptide (PAMP). ADM is secreted and binds to the G-protein coupled receptor calcitonin receptor like receptor (CRLR) that is associated with either the receptor activity modifying protein RAMP2 or RAMP3 to activate a signaling cascade that increases cyclic adenosine monophosphate (cAMP) by activating adenylyl cyclase. Increases in cAMP levels activate protein kinase A (PKA), which increases calcium levels by opening membrane calcium channels or by releasing intracellular calcium stores. The overall increase in intracellular calcium can increase nitric oxide (NO) production by directly stimulating nNOS or by activating nNOS through the activation of the calcium-activated phosphatase, calcineurin (CaN), which dephosphorylates nNOS at an inhibitory phosphorylation site at serine847. Increases in NO production can then increase in cGMP synthesis by activating soluble guanylyl cyclase (sGC).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC3369892&req=5

f8: Summary diagram of the proposed adrenomedullin (ADM) signaling pathway in the retina. Protein kinase C (PKC) activation can lead to increased transcription of the ADM gene via a PKC enhancer element. The ADM precursor preproadrenomedullin is cleaved to proadrenomedullin, which is then cleaved into the secreted peptide ADM and the proadrenomedullin NH2-terminal peptide (PAMP). ADM is secreted and binds to the G-protein coupled receptor calcitonin receptor like receptor (CRLR) that is associated with either the receptor activity modifying protein RAMP2 or RAMP3 to activate a signaling cascade that increases cyclic adenosine monophosphate (cAMP) by activating adenylyl cyclase. Increases in cAMP levels activate protein kinase A (PKA), which increases calcium levels by opening membrane calcium channels or by releasing intracellular calcium stores. The overall increase in intracellular calcium can increase nitric oxide (NO) production by directly stimulating nNOS or by activating nNOS through the activation of the calcium-activated phosphatase, calcineurin (CaN), which dephosphorylates nNOS at an inhibitory phosphorylation site at serine847. Increases in NO production can then increase in cGMP synthesis by activating soluble guanylyl cyclase (sGC).
Mentions: Most importantly, we found that the primary receptor for ADM, CRLR, and its associated RAMP2 had largely overlapping expression with ADM, especially in Müller cell somata and in presumptive ganglion cell somata in the GCL. The increased levels of cAMP-LI, cGMP-LI, and nitrite in response to stimulation with the ADM peptide provided further evidence of a functional ADM receptor and an ADM/NO signaling pathway in the mouse retina (Figure 8).

Bottom Line: We found that calcitonin-receptor-like receptor and receptor activity modifying protein 2 had localization patterns similar to ADM, especially in somata in the inner nuclear and ganglion cell layers.These results are the first to show that ADM and functional ADM receptors are present in the retina.Since ADM is increased in eyes with ocular pathologies such as diabetic retinopathy, glaucoma, retinitis pigmentosa, and uveitis, the ADM signaling pathway may provide a new target for ameliorating these retinal pathologies.

View Article: PubMed Central - PubMed

Affiliation: Boston University, Laboratory of Visual Neurobiology, Department of Biology, Boston, MA 02215, USA.

ABSTRACT

Purpose: Adrenomedullin (ADM) is a small, secreted peptide often associated with vasodilation. However, ADM can also function as a neurotransmitter/neuromodulator, and studies suggest ADM is upregulated in the eye in several ocular diseases. However, no studies to date have described an ADM signaling pathway in the retina.

Methods: PCR, immunocytochemistry, nitric oxide imaging, western blots, and a nitrite assay were used to determine the localization of the components of the ADM signaling pathway in the mouse retina.

Results: We used reverse-transcriptase polymerase chain reaction to show that ADM and its primary receptor, calcitonin-receptor-like receptor, along with its associated receptor activity modifying proteins 2 and 3 are expressed in the retina. Using immunocytochemistry, we detected ADM staining throughout the retina in the photoreceptor outer segments, the outer nuclear layer, Müller and amacrine cell somata in the inner nuclear layer, and some somata in the ganglion cell layer. We found that calcitonin-receptor-like receptor and receptor activity modifying protein 2 had localization patterns similar to ADM, especially in somata in the inner nuclear and ganglion cell layers. Finally, we showed that the ADM receptor was functional in the retina. Stimulation of isolated retinas with ADM increased cyclic adenosine monophosphate- and cyclic guanosine monophosphate-like immunoreactivity, as well as nitric oxide production.

Conclusions: These results are the first to show that ADM and functional ADM receptors are present in the retina. Since ADM is increased in eyes with ocular pathologies such as diabetic retinopathy, glaucoma, retinitis pigmentosa, and uveitis, the ADM signaling pathway may provide a new target for ameliorating these retinal pathologies.

Show MeSH
Related in: MedlinePlus