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2016 ; 594
(7
): 1841-54
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Signalling beyond photon absorption: extracellular retinoids and growth factors
modulate rod photoreceptor sensitivity
#MMPMID26691896
McKeown AS
; Pitale PM
; Kraft TW
J Physiol
2016[Apr]; 594
(7
): 1841-54
PMID26691896
show ga
KEY POINTS: We propose that the end product of chromophore bleaching in rod
photoreceptors, all-trans retinol, is part of a feedback loop that increases the
sensitivity of the phototransduction cascade in rods. A previously described
light-induced hypersensitivity in rods, termed adaptive potentiation, is reduced
by exogenously applied all-trans retinol but not all-trans retinal. This
potentiation is produced by insulin-like growth factor-1, whose binding proteins
are located in the extracellular matrix, even in our isolated retina preparation
after removal of the retinal pigmented epithelium. Simple modelling suggests that
the light stimuli used in the present study will produce sufficient all-trans
retinol within the interphotoreceptor matrix to explain the potentiation effect.
ABSTRACT: Photoreceptors translate the absorption of photons into electrical
signals for propagation through the visual system. Mammalian photoreceptor
signalling has largely been studied in isolated cells, and such studies have
necessarily avoided the complex environment of supportive proteins that surround
the photoreceptors. The interphotoreceptor matrix (IPM) contains an array of
proteins that aid in both structural maintenance and cellular homeostasis,
including chromophore turnover. In signalling photon absorption, the chromophore
11-cis retinal is first isomerized to all-trans retinal, followed by conversion
to all-trans retinol (ROL) for removal from the photoreceptor. Interphotoreceptor
retinoid-binding protein (IRBP) is the most abundant protein in the IPM, and it
promotes the removal of bleached chromophores and recycling in the nearby retinal
pigment epithelium. By studying the light responses of isolated mouse retinas, we
demonstrate that ROL can act as a feedback signal onto photoreceptors that
influences the sensitivity of phototransduction. In addition to IRBP, the IPM
also contains insulin-like growth factor-1 (IGF-1) and its associated binding
proteins, although their functions have not yet been described. We demonstrate
that extracellular application of physiological concentrations of IGF-1 can
increase rod photoreceptor sensitivity in mammalian retinas. We also determine
that chromophores and growth factors can limit the range of a newly described
form of photoreceptor light adaptation. Finally, fluorescent antibodies
demonstrate the presence of IRBP and IGFBP-3 in isolated retinas. A simple model
of the formation and release of ROL into the extracellular space quantitatively
describes this novel feedback loop.
|*Photons
[MESH]
|*Sensory Thresholds
[MESH]
|*Vision, Ocular
[MESH]
|Absorption, Radiation
[MESH]
|Animals
[MESH]
|Cells, Cultured
[MESH]
|Extracellular Matrix/metabolism
[MESH]
|Eye Proteins/metabolism
[MESH]
|Insulin-Like Growth Factor I/*metabolism
[MESH]
|Mice
[MESH]
|Mice, Inbred C57BL
[MESH]
|Retinal Rod Photoreceptor Cells/*metabolism/physiology
[MESH]