Unveiling the critical role of K+ for xanthorhodopsin expression in E. coli.

Xanthorhodopsin (XR), a retinal-binding 7-transmembrane protein isolated from the eubacterium Salinibacter ruber, utilizes two chromophores (retinal and salinixanthin (SAL)) as an outward proton pump and energy-donating carotenoid. However, research on XR has been impeded owing to limitations in achieving heterogeneous expression of stable forms and high production levels of both wild-type and mutants. We successfully expressed wild-type and mutant XRs in Escherichia coli in the presence of K+. Achieving XR expression requires significant K+ and a low inducer concentration. In particular, we highlight the significance of Ser-159 in helix E located near Gly-156 (a carotenoid-binding position) as a critical site for XR expression. Our findings indicate that replacing Ser-159 with a smaller amino acid, alanine, can enhance XR expression in a manner comparable to K+, implying that Ser-159 poses a steric hindrance for pigment formation in XR. In the presence of K+, the proton pumping and photocycle of the wild-type and mutants were characterized and compared; the wild-type result suggests similar properties to the first reported XR isolation from the S. ruber membrane fraction. We propose that the K+ gradient across the cell membrane of S. ruber serves to uphold the membrane potential of the organism and plays a role in the expression of proteins, such as XR, as demonstrated in our study. Our findings deepen the understanding of adaptive protein expression, particularly in halophilic organisms. We highlight salt selection as a promising strategy for improving protein yield and functionality.

Engineering bionanoreactor in bacteria for efficient hydrogen production.

Hydrogen production through water splitting is a vital strategy for renewable and sustainable clean energy. In this study, we developed an approach integrating nanomaterial engineering and synthetic biology to establish a bionanoreactor system for efficient hydrogen production. The periplasmic space (20 to 30 nm) of an electroactive bacterium, Shewanella oneidensis MR-1, was engineered to serve as a bionanoreactor to enhance the interaction between electrons and protons, catalyzed by hydrogenases for hydrogen generation. To optimize electron transfer, we used the microbially reduced graphene oxide (rGO) to coat the electrode, which improved the electron transfer from the electrode to the cells. Native MtrCAB protein complex on S. oneidensis and self-assembled iron sulfide (FeS) nanoparticles acted in tandem to facilitate electron transfer from an electrode to the periplasm. To enhance proton transport, S. oneidensis MR-1 was engineered to express Gloeobacter rhodopsin (GR) and the light-harvesting antenna canthaxanthin. This led to efficient proton pumping when exposed to light, resulting in a 35.6% increase in the rate of hydrogen production. The overexpression of native [FeFe]-hydrogenase further improved the hydrogen production rate by 56.8%. The bionanoreactor engineered in S. oneidensis MR-1 achieved a hydrogen yield of 80.4 µmol/mg protein/day with a Faraday efficiency of 80% at a potential of -0.75 V. This periplasmic bionanoreactor combines the strengths of both nanomaterial and biological components, providing an efficient approach for microbial electrosynthesis.

Photoisomerization pathway of the microbial rhodopsin chromophore in solution.

Photoisomerization is a key photochemical reaction in microbial and animal rhodopsins. It is well established that such photoisomerization is highly selective; all-trans to 13-cis, and 11-cis to all-trans forms in microbial and animal rhodopsins, respectively. Nevertheless, unusual photoisomerization pathways have been discovered recently in microbial rhodopsins. In an enzymerhodopsin NeoR, the all-trans chromophore is isomerized into the 7-cis form exclusively, which is stable at room temperature. Although, the 7-cis form is produced by illumination of retinal, formation of the 7-cis form was never reported for a protonated Schiff base of all-trans retinal in solution. Present HPLC analysis of retinal oximes prepared by hydroxylamine reaction revealed that all-trans and 7-cis forms cannot be separated from the syn peaks under the standard HPLC conditions, while it is possible by the analysis of the anti-peaks. Consequently, we found formation of the 7-cis form by the photoreaction of all-trans chromophore in solution, regardless of the protonation state of the Schiff base. Upon light absorption of all-trans protonated retinal Schiff base in solution, excited-state relaxation accompanies double-bond isomerization, producing 7-cis, 9-cis, 11-cis, or 13-cis form. In contrast, specific chromophore-protein interaction enforces selective isomerization into the 13-cis form in many microbial rhodopsins, but into 7-cis in NeoR.

Circadian rhythms in the Drosophila eye may regulate adaptation of vision to light intensity.

The sensitivity of the eye at night would lead to complete saturation of the eye during the day. Therefore, the sensitivity of the eye must be down-regulated during the day to maintain visual acuity. In the Drosophila eye, the opening of TRP and TRPL channels leads to an influx of Ca++ that triggers down-regulation of further responses to light, including the movement of the TRPL channel and Gα proteins out of signaling complexes found in actin-mediated microvillar extensions of the photoreceptor cells (the rhabdomere). The eye also exhibits a light entrained-circadian rhythm, and we have recently observed that one component of this rhythm (BDBT) becomes undetectable by antibodies after exposure to light even though immunoblot analyses still detect it in the eye. BDBT is necessary for normal circadian rhythms, and in several circadian and visual mutants this eye-specific oscillation of detection is lost. Many phototransduction signaling proteins (e.g., Rhodopsin, TRP channels and Gα) also become undetectable shortly after light exposure, most likely due to a light-induced compaction of the rhabdomeric microvilli. The circadian protein BDBT might be involved in light-induced changes in the rhabdomere, and if so this could indicate that circadian clocks contribute to the daily adaptations of the eye to light. Likewise, circadian oscillations of clock proteins are observed in photoreceptors of the mammalian eye and produce a circadian oscillation in the ERG. Disruption of circadian rhythms in the eyes of mammals causes neurodegeneration in the eye, demonstrating the importance of the rhythms for normal eye function.

Unique hydrogen-bonding network in a viral channelrhodopsin.

Channelrhodopsins (CRs) are used as key tools in optogenetics, and novel CRs, either found from nature or engineered by mutation, have greatly contributed to the development of optogenetics. Recently CRs were discovered from viruses, and crystal structure of a viral CR, OLPVR1, reported a very similar water-containing hydrogen-bonding network near the retinal Schiff base to that of a light-driven proton-pump bacteriorhodopsin (BR). In both OLPVR1 and BR, nearly planar pentagonal cluster structures are comprised of five oxygen atoms, three oxygens from water molecules and two oxygens from the Schiff base counterions. The planar pentagonal cluster stabilizes a quadrupole, two positive charges at the Schiff base and an arginine, and two negative charges at the counterions, and thus plays important roles in light-gated channel function of OLPVR1 and light-driven proton pump function of BR. Despite similar pentagonal cluster structures, present FTIR analysis revealed different hydrogen-bonding networks between OLPVR1 and BR. The hydrogen bond between the protonated Schiff base and a water is stronger in OLPVR1 than in BR, and internal water molecules donate hydrogen bonds much weaker in OLPVR1 than in BR. In OLPVR1, the bridged water molecule between the Schiff base and counterions forms hydrogen bonds to D76 and D200 equally, while the hydrogen-bonding interaction is much stronger to D85 than to D212 in BR. The present interpretation is supported by the mutation results, where D76 and D200 equally work as the Schiff base counterions in OLPVR1, but D85 is the primary counterion in BR. This work reports highly sensitive hydrogen-bonding network in the Schiff base region, which would be closely related to each function through light-induced alterations of the network.

Mutant dominant-negative rhodopsin∆I256 causes protein aggregates degraded via ERAD and prevents normal rhodopsin from proper membrane trafficking.

Dominant mutations in the rhodopsin gene (Rho) contribute to 25% of autosomal dominant retinitis pigmentosa (adRP), characterized by photoreceptor loss and progressive blindness. One such mutation, Rho ∆I256 , carries a 3-bp deletion, resulting in the loss of one of two isoleucines at codons 255 and 256. Our investigation, using recombinant expression in HEK293 and COS-7 cells, revealed that Rho ∆I256, akin to the known adRP mutation Rho P23H, induces the formation of rhodopsin protein (RHO) aggregates at the perinuclear region. Co-expression of Rho ∆I256 or Rho P23H with wild-type Rho WT, mimicking the heterozygous genotype of adRP patients, demonstrated the dominant-negative effect, as all isoforms were retained in perinuclear aggregates, impeding membrane trafficking. In retinal explants from WT mice, mislocalization of labeled adRP isoforms at the outer nuclear layer was observed. Further analysis revealed that RHO∆I256 aggregates are retained at the endoplasmic reticulum (ER), undergo ER-associated degradation (ERAD), and colocalize with the AAA-ATPase escort chaperone valosin-containing protein (VCP). These aggregates are polyubiquitinated and partially colocalized with the 20S proteasome subunit beta-5 (PSMB5). Pharmacological inhibition of proteasome- or VCP activity increased RHO∆I256 aggregate size. In summary, RHO∆I256 exhibits dominant pathogenicity by sequestering normal RHOWT in ER aggregates, preventing its membrane trafficking and following the ERAD degradation.

Dark continuous noise from mutant G90D-rhodopsin predominantly underlies congenital stationary night blindness.

Congenital stationary night blindness (CSNB) is an inherited retinal disease that causes a profound loss of rod sensitivity without severe retinal degeneration. One well-studied rhodopsin point mutant, G90D-Rho, is thought to cause CSNB because of its constitutive activity in darkness causing rod desensitization. However, the nature of this constitutive activity and its precise molecular source have not been resolved for almost 30 y. In this study, we made a knock-in (KI) mouse line with a very low expression of G90D-Rho (equal in amount to ~0.1% of normal rhodopsin, WT-Rho, in WT rods), with the remaining WT-Rho replaced by REY-Rho, a mutant with a very low efficiency of activating transducin due to a charge reversal of the highly conserved ERY motif to REY. We observed two kinds of constitutive noise: one being spontaneous isomerization (R*) of G90D-Rho at a molecular rate (R* s-1) 175-fold higher than WT-Rho and the other being G90D-Rho-generated dark continuous noise comprising low-amplitude unitary events occurring at a very high molecular rate equivalent in effect to ~40,000-fold of R* s-1 from WT-Rho. Neither noise type originated from G90D-Opsin because exogenous 11-cis-retinal had no effect. Extrapolating the above observations at low (0.1%) expression of G90D-Rho to normal disease exhibited by a KI mouse model with RhoG90D/WTand RhoG90D/G90D genotypes predicts the disease condition very well quantitatively. Overall, the continuous noise from G90D-Rho therefore predominates, constituting the major equivalent background light causing rod desensitization in CSNB.

The Impact of Terminal Peptide Extensions of Retinal Inosine 5´Monophosphate Dehydrogenase 1 Isoforms on their DNA-binding Activities.

The main structural difference between the mutation-susceptible retinal isoforms of inosine 5´-monophosphate dehydrogenase-1 (IMPDH-1) with the canonical form resides in the C- and N-terminal peptide extensions with unknown structural/functional impacts. In this report, we aimed to experimentally evaluate the functional impact of these extensions on the specific/non-specific single-stranded DNA (ssDNA)-binding activities relative to those of the canonical form. Our in silico findings indicated the possible contribution of the C-terminal segment to the reduced flexibility of the Bateman domain of the enzyme. In addition, the in silico data indicated that the N-terminal tail acts by altering the distance between the tetramers in the concave octamer complex (the native form) of the enzyme. The overall impact of these predicted structural variations became evident, first, through higher Km values with respect to either of the substrates relative to the canonical isoform, as reported previously (Andashti et al. in Mol Cell Biochem 465(1):155-164, 2020). Secondary, the binding of the recombinant mouse retinal isoform IMPDH1 (603) to its specific Rhodopsin target gene was significantly augmented while its binding to non-specific ssDNA was lower than that of the canonical isoform. The DNA-binding activity of the other mouse retinal isoform, IMPDH1(546), to specific and non-specific ssDNA was lower than that of the canonical form most probably due to the in silico predicted rigidity created in the Bateman domain by the C-terminal peptide extension. Furthermore, the DNA binding to the Rhodopsin target gene by each of the IMPDH isoforms influenced in the presence of GTP (Guanosine triphosphate) and ATP (Adenosine triphosphate).

Theoretical study on the structure, spectroscopic, and current-voltage behavior of 11-Cis and Trans retinal isomers in rhodopsin.

In this study, the electronic transport properties of 11-Cis and Trans retinal, components of rhodopsin, were investigated as optical molecular switches using the nonequilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT). These isomers, which can be reversibly converted into each other, were examined in detail. The structural and spectroscopic properties, including infrared (IR), Raman, nuclear magnetic resonance (NMR), and ultraviolet (UV) spectra, were analyzed using the hybrid B3LYP/6-311 + + G** level of theory. Complete vibrational assignments were performed for both forms utilizing the scaled quantum mechanical force field (SQMFF) methodology. To evaluate the conductivity of these molecules, we utilized current-voltage (I-V) characteristics, transmission spectra, molecular projected self-consistent Hamiltonian (MPSH), HOMO-LUMO gap, and second-order interaction energies (E2). The trendline extrapolation of the current-voltage plots confirmed our findings. We investigated the effect of different electrodes (Ag, Au, Pt) and various connection sites (hollow, top, bridge) on conductivity. The Ag electrode with the hollow site exhibited the highest efficiency. Our results indicate that the Cis form has higher conductivity than the Trans form.

Graph-based algorithms to dissect long-distance water-mediated H-bond networks for conformational couplings in GPCRs.

Changes in structure and dynamics elicited by agonist ligand binding at the extracellular side of G protein coupled receptors (GPCRs) must be relayed to the cytoplasmic G protein binding side of the receptors. To decipher the role of water-mediated hydrogen-bond networks in this relay mechanism, we have developed graph-based algorithms and analysis methodologies applicable to datasets of static structures of distinct GPCRs. For a reference dataset of static structures of bovine rhodopsin solved at the same resolution, we show that graph analyses capture the internal protein-water hydrogen-bond network. The extended analyses of static structures of rhodopsins and opioid receptors suggest a relay mechanism whereby inactive receptors have in place much of the internal core hydrogen-bond network required for long-distance relay of structural change, with extensive local H-bond clusters observed in structures solved at high resolution and with internal water molecules.

The Logistical Backbone of Photoreceptor Cell Function: Complementary Mechanisms of Dietary Vitamin A Receptors and Rhodopsin Transporters.

In this review, we outline our current understanding of the mechanisms involved in the absorption, storage, and transport of dietary vitamin A to the eye, and the trafficking of rhodopsin protein to the photoreceptor outer segments, which encompasses the logistical backbone required for photoreceptor cell function. Two key mechanisms of this process are emphasized in this manuscript: ocular and systemic vitamin A membrane transporters, and rhodopsin transporters. Understanding the complementary mechanisms responsible for the generation and proper transport of the retinylidene protein to the photoreceptor outer segment will eventually shed light on the importance of genes encoded by these proteins, and their relationship on normal visual function and in the pathophysiology of retinal degenerative diseases.

Disease modeling and pharmacological rescue of autosomal dominant retinitis pigmentosa associated with RHO copy number variation.

Retinitis pigmentosa (RP), a heterogenous group of inherited retinal disorder, causes slow progressive vision loss with no effective treatments available. Mutations in the rhodopsin gene (RHO) account for ~25% cases of autosomal dominant RP (adRP). In this study, we describe the disease characteristics of the first-ever reported mono-allelic copy number variation (CNV) in RHO as a novel cause of adRP. We (a) show advanced retinal degeneration in a male patient (68 years of age) harboring four transcriptionally active intact copies of rhodopsin, (b) recapitulated the clinical phenotypes using retinal organoids, and (c) assessed the utilization of a small molecule, Photoregulin3 (PR3), as a clinically viable strategy to target and modify disease progression in RP patients associated with RHO-CNV. Patient retinal organoids showed photoreceptors dysgenesis, with rod photoreceptors displaying stunted outer segments with occasional elongated cilia-like projections (microscopy); increased RHO mRNA expression (quantitative real-time PCR [qRT-PCR] and bulk RNA sequencing); and elevated levels and mislocalization of rhodopsin protein (RHO) within the cell body of rod photoreceptors (western blotting and immunohistochemistry) over the extended (300 days) culture time period when compared against control organoids. Lastly, we utilized PR3 to target NR2E3, an upstream regulator of RHO, to alter RHO expression and observed a partial rescue of RHO protein localization from the cell body to the inner/outer segments of rod photoreceptors in patient organoids. These results provide a proof-of-principle for personalized medicine and suggest that RHO expression requires precise control. Taken together, this study supports the clinical data indicating that RHO-CNV associated adRPdevelops as a result of protein overexpression, thereby overloading the photoreceptor post-translational modification machinery.

Dinoflagellate Proton-Pump Rhodopsin Genes in Long Island Sound: Diversity and Spatiotemporal Distribution.

Microbial proton-pump rhodopsin (PPR)-based phototrophy, a light-harvesting mechanism different from chlorophyll-based photosystems, may contribute significantly to solar energy entry into the marine ecosystem. PPR transforms solar energy into cellular energy that is used for various metabolic processes in the cells or flagellar movement. Although rhodopsins or their encoding genes have been documented in a wide phylogenetic range of cultured dinoflagellates, information is limited about how widespread and how spatiotemporally dynamical dinoflagellate PPR (DiPPR) are in natural marine ecosystems. In this study, we investigated DiPPR in Long Island Sound (LIS), a temperate estuary of the Atlantic Ocean between Connecticut and Long Island, New York, USA. We isolated six novel full-length dinoflagellate proton-pump rhodopsin cDNAs, expanding the DiPPR database that is crucial to PPR research. Based on these new sequences and existing sequences of DiPPR, we designed primers and conducted quantitative PCR and sequencing to determine the abundance and diversity of DiPPR genes spatially and temporally throughout a year in the water samples collected from LIS. DiPPR genes were found year-round and throughout LIS but with higher abundances in the eutrophic Western Sound and in April and July. The gene diversity data suggest that there are at least five distinct rhodopsin-harboring groups of dinoflagellates throughout the year. The abundance of DiPPR genes, measured as copy number per mL of seawater, appeared not to be influenced by water temperature or nitrogen nutrient concentration but exhibited weak negative correlations with orthophosphate concentration and salinity and a positive correlation with the abundance of DiPPR-harboring dinoflagellates. This first quantitative profiling of PPR in natural plankton reveals the prevalence and dynamics of this plastid-independent photoenergy harvesting mechanism in a temperate estuary and provides efficient DiPPR primers potentially useful for future research. Furthermore, this study shed light on the potential role of DiPPR in phosphor nutrition and dinoflagellate population, which warrants further studies.

Accurate Detection of Convergent Mutations in Large Protein Alignments With ConDor.

Evolutionary convergences are observed at all levels, from phenotype to DNA and protein sequences, and changes at these different levels tend to be correlated. Notably, convergent mutations can lead to convergent changes in phenotype, such as changes in metabolism, drug resistance, and other adaptations to changing environments. We propose a two-component approach to detect mutations subject to convergent evolution in protein alignments. The "Emergence" component selects mutations that emerge more often than expected, while the "Correlation" component selects mutations that correlate with the convergent phenotype under study. With regard to Emergence, a phylogeny deduced from the alignment is provided by the user and is used to simulate the evolution of each alignment position. These simulations allow us to estimate the expected number of mutations in a neutral model, which is compared to the observed number of mutations in the data studied. In Correlation, a comparative phylogenetic approach, is used to measure whether the presence of each of the observed mutations is correlated with the convergent phenotype. Each component can be used on its own, for example Emergence when no phenotype is available. Our method is implemented in a standalone workflow and a webserver, called ConDor. We evaluate the properties of ConDor using simulated data, and we apply it to three real datasets: sedge PEPC proteins, HIV reverse transcriptase, and fish rhodopsin. The results show that the two components of ConDor complement each other, with an overall accuracy that compares favorably to other available tools, especially on large datasets.

Modeling autosomal dominant retinitis pigmentosa by using patient-specific retinal organoids with a class-3 RHO mutation.

Rhodopsin-mediated autosomal dominant retinitis pigmentosa (RHO-adRP) causes progressive vision loss and is potentially incurable, accounting for 25% of adRP cases. Studies on RHO-adRP mechanism were at large based on the biochemical and cellular properties, especially class-3. Nonetheless, the absence of an appropriate model for class-3 RHO-adRP has impeded comprehensive exploration. Here, induced pluripotent stem cells (iPSCs) were generated from a healthy control and two sibling RP patients with the same point mutation, c.403C>T (p.R135W). The first three-dimensional (3D) retinal organoid model of a class-3 RHO point mutation from patient-derived iPSCs was generated. Significant defects were observed in rod photoreceptors in terms of localization, morphology, transcriptional profiling and single cell resolution, to better understand the human disease resulting from RHO mutations from a developmental perspective. This first human model of class-3 RHO-adRP provides a representation of patient's retina in vitro and displays features of RHO-adRP retinal organoids relevant for therapeutic development.

Multiple retinal isomerizations during the early phase of the bestrhodopsin photoreaction.

Bestrhodopsins constitute a class of light-regulated pentameric ion channels that consist of one or two rhodopsins in tandem fused with bestrophin ion channel domains. Here, we report on the isomerization dynamics in the rhodopsin tandem domains of Phaeocystis antarctica bestrhodopsin, which binds all-trans retinal Schiff-base (RSB) absorbing at 661 nm and, upon illumination, converts to the meta-stable P540 state with an unusual 11-cis RSB. The primary photoproduct P682 corresponds to a mixture of highly distorted 11-cis and 13-cis RSB directly formed from the excited state in 1.4 ps. P673 evolves from P682 in 500 ps and contains highly distorted 13-cis RSB, indicating that the 11-cis fraction in P682 converts to 13-cis. Next, P673 establishes an equilibrium with P595 in 1.2 µs, during which RSB converts to 11-cis and then further proceeds to P560 in 48 µs and P540 in 1.0 ms while remaining 11-cis. Hence, extensive isomeric switching occurs on the early ground state potential energy surface (PES) on the hundreds of ps to µs timescale before finally settling on a metastable 11-cis photoproduct. We propose that P682 and P673 are trapped high up on the ground-state PES after passing through either of two closely located conical intersections that result in 11-cis and 13-cis RSB. Co-rotation of C11=C12 and C13=C14 bonds results in a constricted conformational landscape that allows thermal switching between 11-cis and 13-cis species of highly strained RSB chromophores. Protein relaxation may release RSB strain, allowing it to evolve to a stable 11-cis isomeric configuration in microseconds.

Convergent mechanism underlying the acquisition of vertebrate scotopic vision.

High sensitivity of scotopic vision (vision in dim light conditions) is achieved by the rods' low background noise, which is attributed to a much lower thermal activation rate (kth) of rhodopsin compared with cone pigments. Frogs and nocturnal geckos uniquely possess atypical rods containing noncanonical cone pigments that exhibit low kth, mimicking rhodopsin. Here, we investigated the convergent mechanism underlying the low kth of rhodopsins and noncanonical cone pigments. Our biochemical analysis revealed that the kth of canonical cone pigments depends on their absorption maximum (λmax). However, rhodopsin and noncanonical cone pigments showed a substantially lower kth than predicted from the λmax dependency. Given that the λmax is inversely proportional to the activation energy of the pigments in the Hinshelwood distribution-based model, our findings suggest that rhodopsin and noncanonical cone pigments have convergently acquired low frequency of spontaneous-activation attempts, including thermal fluctuations of the protein moiety, in the molecular evolutionary processes from canonical cone pigments, which contributes to highly sensitive scotopic vision.

Light regulation of rhodopsin distribution during outer segment renewal in murine rod photoreceptors.

Vision under dim light relies on primary cilia elaborated by rod photoreceptors in the retina. This specialized sensory structure, called the rod outer segment (ROS), comprises hundreds of stacked, membranous discs containing the light-sensitive protein rhodopsin, and the incorporation of new discs into the ROS is essential for maintaining the rod's health and function. ROS renewal appears to be primarily regulated by extrinsic factors (light); however, results vary depending on different model organisms. We generated two independent transgenic mouse lines where rhodopsin's fate is tracked by a fluorescently labeled rhodopsin fusion protein (Rho-Timer) and show that rhodopsin incorporation into nascent ROS discs appears to be regulated by both external lighting cues and autonomous retinal clocks. Live-cell imaging of the ROS isolated from mice exposed to six unique lighting conditions demonstrates that ROS formation occurs in a periodic manner in cyclic light, constant darkness, and artificial light/dark cycles. This alternating bright/weak banding of Rho-Timer along the length of the ROS relates to inhomogeneities in rhodopsin density and potential points of structural weakness. In addition, we reveal that prolonged dim ambient light exposure impacts not only the rhodopsin content of new discs but also that of older discs, suggesting a dynamic interchange of material between new and old discs. Furthermore, we show that rhodopsin incorporation into the ROS is greatly altered in two autosomal recessive retinitis pigmentosa mouse models, potentially contributing to the pathogenesis. Our findings provide insights into how extrinsic (light) and intrinsic (retinal clocks and genetic mutation) factors dynamically regulate mammalian ROS renewal.

Molecular mechanisms underlying inherited photoreceptor degeneration as targets for therapeutic intervention.

Retinitis pigmentosa (RP) is a form of retinal degeneration characterized by primary degeneration of rod photoreceptors followed by a secondary cone loss that leads to vision impairment and finally blindness. This is a rare disease with mutations in several genes and high genetic heterogeneity. A challenging effort has been the characterization of the molecular mechanisms underlying photoreceptor cell death during the progression of the disease. Some of the cell death pathways have been identified and comprise stress events found in several neurodegenerative diseases such as oxidative stress, inflammation, calcium imbalance and endoplasmic reticulum stress. Other cell death mechanisms appear more relevant to photoreceptor cells, such as high levels of cGMP and metabolic changes. Here we review some of the cell death pathways characterized in the RP mutant retina and discuss preclinical studies of therapeutic approaches targeting the molecular outcomes that lead to photoreceptor cell demise.