Modulation of Cellular Signaling Pathways in P23H Rhodopsin Photoreceptors.

Article (PDF Available)inCellular Signalling 26(4) · December 2013with38 Reads
DOI: 10.1016/j.cellsig.2013.12.008 · Source: PubMed
Abstract
We previously reported activation of the unfolded protein response (UPR) in P23H rhodopsin (RHO) retinas with autosomal dominant retinitis pigmentosa (ADRP). Knowing that the UPR can trigger Ca(2+) release from the endoplasmic reticulum and regulate cellular signaling we examined the level of Ca(2+)-regulated proteins. We also looked for changes in the expression of Bcl2 family proteins, autophagy proteins and the mTOR/AKT pathways, as well as for the induction of mitochondria-associated apoptosis in the P23H RHO retina. Our data demonstrated that the elevation of calpain and caspase-12 activity was concomitantly observed with a decrease in the BCL2-XL/BAX ratio and an increase in mTor levels in the P23H-3 RHO retina suggesting a vulnerability of P23H RHO photoreceptors to apoptosis. The translocation of BAX to the mitochondria, as well as the release of cytochrome C and AIF into the cytosol supports this conclusion and indicates the involvement of mitochondria-induced apoptosis in the progression of ADRP. The level of autophagy proteins in general was found to be decreased in the P21-P30 P23H RHO retina. Injections of rapamycin, however, protected the P23H RHO rod photoreceptors from experiencing physiological decline. Despite this fact, the downregulation of mTOR did not alter the level of autophagy proteins. Our results imply that in addition to activation of the UPR during ADRP progression, photoreceptors also experience alterations in major proapoptotic pathways.

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Available from: Marina S Gorbatyuk, Feb 13, 2014
    • " well established that EPO can also block cell death by increasing levels of BclXL, which would counteract the increase in Bax induced in this model (for review see [13] ). Finally, levels of autophagic proteins are increased in the P23H mutant rat and photoreceptor degeneration is inhibited by treating with the mTOR signaling inhibitor, rapamycin.[39] It is feasible that the photoreceptors ultimately succumbed to autophagic cell death regardless of EPO treatment. In summary , although EPO can block cell death pathways activated in the hP23H RHO +/-,mRHO +/+ retina, cell death still progressed potential due to an incomplete block of all possible cell death pathways. In addition to the"
    [Show abstract] [Hide abstract] ABSTRACT: Purpose: To test the efficacy of systemic gene delivery of a mutant form of erythropoietin (EPO-R76E) that has attenuated erythropoietic activity, in a mouse model of autosomal dominant retinitis pigmentosa. Methods: Ten-day old mice carrying one copy of human rhodopsin with the P23H mutation and both copies of wild-type mouse rhodopsin (hP23H RHO+/-,mRHO+/+) were injected into the quadriceps with recombinant adeno-associated virus (rAAV) carrying either enhanced green fluorescent protein (eGFP) or EpoR76E. Visual function (electroretinogram) and retina structure (optical coherence tomography, histology, and immunohistochemistry) were assessed at 7 and 12 months of age. Results: The outer nuclear layer thickness decreased over time at a slower rate in rAAV.EpoR76E treated as compared to the rAAV.eGFP injected mice. There was a statistically significant preservation of the electroretinogram at 7, but not 12 months of age. Conclusions: Systemic EPO-R76E slows death of the photoreceptors and vision loss in hP23H RHO+/-,mRHO+/+ mice. Treatment with EPO-R76E may widen the therapeutic window for retinal degeneration patients by increasing the number of viable cells. Future studies might investigate if co-treatment with EPO-R76E and gene replacement therapy is more effective than gene replacement therapy alone.
    Full-text · Article · Jun 2016
    • "Analyzing degenerating retinas, we found partial mislocalization of NNAT in the ONL of the retina compared to wild-type SD rat and C57BL6 mouse retinas (Fig. 1Band E). Rodent models of ADRP expressing S334ter, P23H and T17M rhodopsin experience severe retinal degeneration characterized by activated ER stress, oxidative stress, calcium dysregulation and mitochondrial dysfunction (Kunte et al., 2012; Shinde et al., 2012; Sizova et al., 2014). Taking this into account, we next tested a hypothesis that stress can alter NNAT expression in these photoreceptors. "
    [Show abstract] [Hide abstract] ABSTRACT: Neuronatin (NNAT) is a small transmembrane proteolipid that is highly expressed in the embryonic developing brain and several other peripheral tissues. This study is the first to provide evidence that NNAT is detected in the adult retina of various adult rod-dominant mammals, including wild-type (WT) rodents, transgenic rodents expressing mutant S334ter, P23H, or T17M rhodopsin, non-human primates, humans, and cone-dominant tree shrews. Immunohistochemical and qRT-PCR analyses were applied to detect NNAT. Confocal microscopy analysis revealed that NNAT immunofluorescence is restricted to the outer segments (OS) of photoreceptors without evidence of staining in other retinal cell types across all mammalian species. Moreover, in tree shrew retinas, we found NNAT to be co-localized with rhodopsin, indicating its predominant expression in rods. The rod-derived expression of NNAT was further confirmed by qRT-PCR in isolated rod photoreceptor cells. We also used these cells to mimic cellular stress in transgenic retinas by treating them with the endoplasmic reticulum stress inducer, tunicamycin. Thus, our data revealed accumulation of NNAT around the nucleus as compared to dispersed localization of NNAT within control cells. This distribution coincided with the partial intracellular mislocalization of NNAT to the outer nuclear layer observed in transgenic retinas. In addition, stressed retinas demonstrated an increase of NNAT mRNA and protein levels. Therefore, our study demonstrated that NNAT is a novel stress responsive protein with a potential structural and/or functional role in adult mammalian retinas.
    Full-text · Article · Apr 2016
    • "Bcl-2 is the best-characterized protein family involved in the progression of apoptosis in photoreceptor cells. A decrease in the ratio of Bcl-XL to Bax (Bcl-2-associated X protein) has been evidenced in RP animal models carrying mutations in the rhodopsin gene, thus indicating the implication of mitochondria in the progress of apoptosis [93,101]. In this context, preserving the integrity of the mitochondrial membrane by preventing the formation of mitochondrial outer membrane pores (MOMP) and the modulation of existing mitochondrial channels, such as the mitochondrial permeability transition pore complex, could be good anti-apoptotic strategies to protect cells from death [102,103]. "
    [Show abstract] [Hide abstract] ABSTRACT: All retinal disorders, regardless of their aetiology, involve the activation of oxidative stress and apoptosis pathways. The administration of neuroprotective factors is crucial in all phases of the pathology, even when vision has been completely lost. The retina is one of the most susceptible tissues to reactive oxygen species damage. On the other hand, proper development and functioning of the retina requires a precise balance between the processes of proliferation, differentiation and programmed cell death. The life-or-death decision seems to be the result of a complex balance between pro- and anti-apoptotic signals. It has been recently shown the efficacy of natural products to slow retinal degenerative process through different pathways. In this review, we assess the neuroprotective effect of two compounds used in the ancient pharmacopoeia. On one hand, it has been demonstrated that administration of the saffron constituent safranal to P23H rats, an animal model of retinitis pigmentosa, preserves photoreceptor morphology and number, the capillary network and the visual response. On the other hand, it has been shown that systemic administration of tauroursodeoxycholic acid (TUDCA), the major component of bear bile, to P23H rats preserves cone and rod structure and function, together with their contact with postsynaptic neurons. The neuroprotective effects of safranal and TUDCA make these compounds potentially useful for therapeutic applications in retinal degenerative diseases.
    Full-text · Article · Aug 2015
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