AAV-mediated ERdj5 overexpression protects against P23H rhodopsin toxicity.

Rhodopsin misfolding caused by the P23H mutation is a major cause of autosomal dominant retinitis pigmentosa (adRP). To date, there are no effective treatments for adRP. The BiP co-chaperone and reductase ERdj5 (DNAJC10) is part of the endoplasmic reticulum (ER) quality control machinery, and previous studies have shown that overexpression of ERdj5 in vitro enhanced the degradation of P23H rhodopsin, whereas knockdown of ERdj5 increased P23H rhodopsin ER retention and aggregation. Here, we investigated the role of ERdj5 in photoreceptor homeostasis in vivo by using an Erdj5 knockout mouse crossed with the P23H knock-in mouse and by adeno-associated viral (AAV) vector-mediated gene augmentation of ERdj5 in P23H-3 rats. Electroretinogram (ERG) and optical coherence tomography of Erdj5-/- and P23H+/-:Erdj5-/- mice showed no effect of ERdj5 ablation on retinal function or photoreceptor survival. Rhodopsin levels and localization were similar to those of control animals at a range of time points. By contrast, when AAV2/8-ERdj5-HA was subretinally injected into P23H-3 rats, analysis of the full-field ERG suggested that overexpression of ERdj5 reduced visual function loss 10 weeks post-injection (PI). This correlated with a significant preservation of photoreceptor cells at 4 and 10 weeks PI. Assessment of the outer nuclear layer (ONL) morphology showed preserved ONL thickness and reduced rhodopsin retention in the ONL in the injected superior retina. Overall, these data suggest that manipulation of the ER quality control and ER-associated degradation factors to promote mutant protein degradation could be beneficial for the treatment of adRP caused by mutant rhodopsin.

The role of the ER stress-response protein PERK in rhodopsin retinitis pigmentosa.

Mutations in rhodopsin, the light-sensitive protein of rod cells, are the most common cause of dominant retinitis pigmentosa (RP), a type of inherited blindness caused by the dysfunction and death of photoreceptor cells. The P23H mutation, the most frequent single cause of RP in the USA, causes rhodopsin misfolding and induction of the unfolded protein response (UPR), an adaptive ER stress response and signalling network that aims to enhance the folding and degradation of misfolded proteins to restore proteostasis. Prolonged UPR activation, and in particular the PERK branch, can reduce protein synthesis and initiate cell death through induction of pro-apoptotic pathways. Here, we investigated the effect of pharmacological PERK inhibition on retinal disease process in the P23H-1 transgenic rat model of retinal degeneration. PERK inhibition with GSK2606414A led to an inhibition of eIF2α phosphorylation, which correlated with reduced ERG function and decreased photoreceptor survival at both high and low doses of PERK inhibitor. Additionally, PERK inhibition increased the incidence of inclusion formation in cultured cells overexpressing P23H rod opsin, and increased rhodopsin aggregation in the P23H-1 rat retina, suggesting enhanced P23H misfolding and aggregation. In contrast, treatment of P23H-1 rats with an inhibitor of eIF2α phosphatase, salubrinal, led to improved photoreceptor survival. Collectively, these data suggest the activation of PERK is part of a protective response to mutant rhodopsin that ultimately limits photoreceptor cell death.

Arl3 and RP2 regulate the trafficking of ciliary tip kinesins.

Ciliary trafficking defects are the underlying cause of many ciliopathies, including Retinitis Pigmentosa (RP). Anterograde intraflagellar transport (IFT) is mediated by kinesin motor proteins; however, the function of the homodimeric Kif17 motor in cilia is poorly understood, whereas Kif7 is known to play an important role in stabilizing cilia tips. Here we identified the ciliary tip kinesins Kif7 and Kif17 as novel interaction partners of the small GTPase Arl3 and its regulatory GTPase activating protein (GAP) Retinitis Pigmentosa 2 (RP2). We show that Arl3 and RP2 mediate the localization of GFP-Kif17 to the cilia tip and competitive binding of RP2 and Arl3 with Kif17 complexes. RP2 and Arl3 also interact with another ciliary tip kinesin, Kif7, which is a conserved regulator of Hedgehog (Hh) signaling. siRNA-mediated loss of RP2 or Arl3 reduced the level of Kif7 at the cilia tip. This was further validated by reduced levels of Kif7 at cilia tips detected in fibroblasts and induced pluripotent stem cell (iPSC) 3D optic cups derived from a patient carrying an RP2 nonsense mutation c.519C > T (p.R120X), which lack detectable RP2 protein. Translational read-through inducing drugs (TRIDs), such as PTC124, were able to restore Kif7 levels at the ciliary tip of RP2 null cells. Collectively, our findings suggest that RP2 and Arl3 regulate the trafficking of specific kinesins to cilia tips and provide additional evidence that TRIDs could be clinically beneficial for patients with this retinal degeneration.

Rescue of mutant rhodopsin traffic by metformin-induced AMPK activation accelerates photoreceptor degeneration.

Protein misfolding caused by inherited mutations leads to loss of protein function and potentially toxic 'gain of function', such as the dominant P23H rhodopsin mutation that causes retinitis pigmentosa (RP). Here, we tested whether the AMPK activator metformin could affect the P23H rhodopsin synthesis and folding. In cell models, metformin treatment improved P23H rhodopsin folding and traffic. In animal models of P23H RP, metformin treatment successfully enhanced P23H traffic to the rod outer segment, but this led to reduced photoreceptor function and increased photoreceptor cell death. The metformin-rescued P23H rhodopsin was still intrinsically unstable and led to increased structural instability of the rod outer segments. These data suggest that improving the traffic of misfolding rhodopsin mutants is unlikely to be a practical therapy, because of their intrinsic instability and long half-life in the outer segment, but also highlights the potential of altering translation through AMPK to improve protein function in other protein misfolding diseases.

Translational read-through of the RP2 Arg120stop mutation in patient iPSC-derived retinal pigment epithelium cells.

Mutations in the RP2 gene lead to a severe form of X-linked retinitis pigmentosa. RP2 patients frequently present with nonsense mutations and no treatments are currently available to restore RP2 function. In this study, we reprogrammed fibroblasts from an RP2 patient carrying the nonsense mutation c.519C>T (p.R120X) into induced pluripotent stem cells (iPSC), and differentiated these cells into retinal pigment epithelial cells (RPE) to study the mechanisms of disease and test potential therapies. RP2 protein was undetectable in the RP2 R120X patient cells, suggesting a disease mechanism caused by complete lack of RP2 protein. The RP2 patient fibroblasts and iPSC-derived RPE cells showed phenotypic defects in IFT20 localization, Golgi cohesion and Gß1 trafficking. These phenotypes were corrected by over-expressing GFP-tagged RP2. Using the translational read-through inducing drugs (TRIDs) G418 and PTC124 (Ataluren), we were able to restore up to 20% of endogenous, full-length RP2 protein in R120X cells. This level of restored RP2 was sufficient to reverse the cellular phenotypic defects observed in both the R120X patient fibroblasts and iPSC-RPE cells. This is the first proof-of-concept study to demonstrate successful read-through and restoration of RP2 function for the R120X nonsense mutation. The ability of the restored RP2 protein level to reverse the observed cellular phenotypes in cells lacking RP2 indicates that translational read-through could be clinically beneficial for patients.

The co-chaperone and reductase ERdj5 facilitates rod opsin biogenesis and quality control.

Mutations in rhodopsin, the light-sensitive protein of rod cells, are the most common cause of autosomal dominant retinitis pigmentosa (ADRP). Many rod opsin mutations, such as P23H, lead to misfolding of rod opsin with detrimental effects on photoreceptor function and viability. Misfolded P23H rod opsin and other mutations in the intradiscal domain are characterized by the formation of an incorrect disulphide bond between C185 and C187, as opposed to the correct and highly conserved C110-C187 disulphide bond. Therefore, we tested the hypothesis that incorrect disulphide bond formation might be a factor that affects the biogenesis of rod opsin by studying wild-type (WT) or P23H rod opsin in combination with amino acid substitutions that prevent the formation of incorrect disulphide bonds involving C185. These mutants had altered traffic dynamics, suggesting a requirement for regulation of disulphide bond formation/reduction during rod opsin biogenesis. Here, we show that the BiP co-chaperone and reductase protein ERdj5 (DNAJC10) regulates this process. ERdj5 overexpression promoted the degradation, improved the endoplasmic reticulum mobility and prevented the aggregation of P23H rod opsin. ERdj5 reduction by shRNA delayed rod opsin degradation and promoted aggregation. The reductase and co-chaperone activity of ERdj5 were both required for these effects on P23H rod opsin. Furthermore, mutations in these functional domains acted as dominant negatives that affected WT rod opsin biogenesis. Collectively, these data identify ERdj5 as a member of the proteostasis network that regulates rod opsin biogenesis and supports a role for disulphide bond formation/reduction in rod opsin biogenesis and disease.

Hsp90 inhibition protects against inherited retinal degeneration.

The molecular chaperone Hsp90 is important for the functional maturation of many client proteins, and inhibitors are in clinical trials for multiple indications in cancer. Hsp90 inhibition activates the heat shock response and can improve viability in a cell model of the P23H misfolding mutation in rhodopsin that causes autosomal dominant retinitis pigmentosa (adRP). Here, we show that a single low dose of the Hsp90 inhibitor HSP990 enhanced visual function and delayed photoreceptor degeneration in a P23H transgenic rat model. This was associated with the induction of heat shock protein expression and reduced rhodopsin aggregation. We then investigated the effect of Hsp90 inhibition on a different type of rod opsin mutant, R135L, which is hyperphosphorylated, binds arrestin and disrupts vesicular traffic. Hsp90 inhibition with 17-AAG reduced the intracellular accumulation of R135L and abolished arrestin binding in cells. Hsf-1(-/-) cells revealed that the effect of 17-AAG on P23H aggregation was dependent on HSF-1, whereas the effect on R135L was HSF-1 independent. Instead, the effect on R135L was mediated by a requirement of Hsp90 for rhodopsin kinase (GRK1) maturation and function. Importantly, Hsp90 inhibition restored R135L rod opsin localization to wild-type (WT) phenotype in vivo in rat retina. Prolonged Hsp90 inhibition with HSP990 in vivo led to a posttranslational reduction in GRK1 and phosphodiesterase (PDE6) protein levels, identifying them as Hsp90 clients. These data suggest that Hsp90 represents a potential therapeutic target for different types of rhodopsin adRP through distinct mechanisms, but also indicate that sustained Hsp90 inhibition might adversely affect visual function.

Hsp90 as a Potential Therapeutic Target in Retinal Disease.

The molecular chaperone heat shock protein 90 (Hsp90) is a pivotal cellular regulator involved in the folding, activation and assembly of a wide range of proteins. Hsp90 has multiple roles in the retina and the use of different Hsp90 inhibitors has been shown to prevent retinal degeneration in models of retinitis pigmentosa and age-related macular degeneration. Hsp90 is also a potential target in uveal melanoma. Mechanistically, Hsp90 inhibition can evoke a dual response in the retina; stimulating a stress response with molecular chaperone expression. Thereby leading to an improvement in visual function and photoreceptor survival; however, prolonged inhibition can also stimulate the degradation of Hsp90 client proteins potentially deleteriously affect vision. Here, we review the multiple roles of Hsp90 in the retina and the therapeutic potential of Hsp90 as a target.

Differential light-induced responses in sectorial inherited retinal degeneration.

Retinitis pigmentosa (RP) is a group of genetically and clinically heterogeneous inherited degenerative retinopathies caused by abnormalities of photoreceptors or retinal pigment epithelium in the retina leading to progressive sight loss. Rhodopsin is the prototypical G-protein-coupled receptor located in the vertebrate retina and is responsible for dim light vision. Here, novel M39R and N55K variants were identified as causing an intriguing sector phenotype of RP in affected patients, with selective degeneration in the inferior retina. To gain insights into the molecular aspects associated with this sector RP phenotype, whose molecular mechanism remains elusive, the mutations were constructed by site-directed mutagenesis, expressed in heterologous systems, and studied by biochemical, spectroscopic, and functional assays. M39R and N55K opsins had variable degrees of chromophore regeneration when compared with WT opsin but showed no gross structural misfolding or altered trafficking. M39R showed a faster rate for transducin activation than WT rhodopsin with a faster metarhodopsinII decay, whereas N55K presented a reduced activation rate and an altered photobleaching pattern. N55K also showed an altered retinal release from the opsin binding pocket upon light exposure, affecting its optimal functional response. Our data suggest that these sector RP mutations cause different protein phenotypes that may be related to their different clinical progression. Overall, these findings illuminate the molecular mechanisms of sector RP associated with rhodopsin mutations.

Modification of the existing maximum residue levels for dichlorprop-P in cereal grains.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant Nufarm Crop Products UK Ltd. submitted a request to the competent national authority in Italy to modify the existing maximum residue levels (MRLs) for the active substance dichlorprop-P in barley, oat, rye and wheat grain. The data submitted in support of the request were found to be sufficient to derive MRL proposals for these cereal grains. Adequate analytical methods for enforcement are available to control the residues of dichlorprop-P in the commodities under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg and in animal matrices at the validated LOQ of 0.01 mg/kg. Based on the risk assessment results, the European Food Safety Authority (EFSA) concluded that the short-term and long-term intake of residues resulting from the use of dichlorprop-P-2-ethylhexyl (dichlorprop-P 2-EHE) according to the reported agricultural practices is unlikely to present a risk to consumer health.

Review of the existing maximum residue levels for gamma-cyhalothrin according to Article 12 of Regulation (EC) No 396/2005.

According to Article 12 of Regulation (EC) No 396/2005, EFSA has reviewed the maximum residue levels (MRLs) currently established at European level for the pesticide active substance gamma-cyhalothrin. To assess the occurrence of gamma-cyhalothrin residues in plants, processed commodities, rotational crops and livestock, EFSA considered the conclusions derived in the framework of Commission Regulation (EU) No 188/2011, as well as the European authorisations reported by Member States (including the supporting residues data) in the framework of this review. Based on the assessment of the available data, MRL proposals were derived, and a consumer risk assessment was carried out. Although no risk to consumers was identified, some information required by the regulatory framework was missing. The residue definition for monitoring (lambda-cyhalothrin (includes gamma-cyhalothrin) (sum of R, S and S, R isomers)) covers both lambda- and gamma-cyhalothrin. Appropriate enantioselective techniques, which are not commonly used in routine analysis, are required to differentiate gamma-cyhalothrin residues from lambda-cyhalothrin. According to the available data, it is expected that the MRLs currently set in Regulation (EC) No 396/2005 will cover the uses of gamma-cyhalothrin assessed in the present review. Therefore, risk managers can consider maintaining the existing EU MRLs.

Modification of the existing maximum residue levels in various plant commodities resulting from the use of potassium phosphonates.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicants De Sangosse SAS and Tilco-Alginure submitted two requests, respectively, to the competent national authorities in France and Germany to modify the existing maximum residue levels (MRLs) for the active substance potassium phosphonates in various plant commodities. The data submitted in support of the requests were found to be sufficient to derive MRL proposals for the commodities under assessment. For the derived MRL on baby leaf crops, further risk manager consideration is required to decide between two MRL options. Adequate analytical methods for enforcement are available to control the residues of potassium phosphonates in accordance with the residue definition 'phosphonic acid and its salts expressed as phosphonic acid' in the commodities under consideration. Based on the risk assessment results and assuming that the existing MRLs will be amended as proposed by EFSA in previous outputs, EFSA concluded that the long-term intake of residues resulting from the existing uses of fosetyl and phosphonates (previously assessed in a joint MRL review) and new proposed uses of potassium phosphonates is unlikely to present a risk to consumer health. Considering the toxicological profile of the active substance, a short-term dietary risk assessment was not required. The risk assessment shall be regarded as indicative because some MRL proposals derived by EFSA in the framework of the MRL review according to Articles 12 and 43 of Regulation (EC) No 396/2005 require further consideration by risk managers.

Modification of the existing maximum residue level for methoxyfenozide in aubergines.

In accordance with Article 6 of Regulation (EC) No 396/2005, the Federal Public Service (FPS) Health, Food chain Safety and Environment submitted a request on behalf of Belgium (evaluating Member State, EMS) to modify the existing maximum residue level (MRL) for the active substance methoxyfenozide in aubergines/eggplants. The data submitted in support of the request were found to be sufficient to derive an MRL proposal for aubergines/eggplants. Adequate analytical methods for enforcement are available to control the residues of methoxyfenozide in the commodity under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg. Based on the risk assessment results, the EFSA concluded that the short-term and long-term intake of residues resulting from the indoor use of methoxyfenozide according to the reported agricultural practice is unlikely to present a risk to consumer health.

Review of the existing maximum residue levels for difenoconazole according to Article 12 of Regulation (EC) No 396/2005.

According to Article 12 of Regulation (EC) No 396/2005, EFSA has reviewed the maximum residue levels (MRLs) currently established at European level for the pesticide active substance difenoconazole. To assess the occurrence of difenoconazole residues in plants, processed commodities, rotational crops and livestock, EFSA considered the conclusions derived in the framework of Council Directive 91/414/EEC, the MRLs established by the Codex Alimentarius Commission as well as the European authorisations reported by Member States and the UK (including the supporting residues data). Based on the assessment of the available data, MRL proposals were derived, and a consumer risk assessment was carried out. Some information required by the regulatory framework was missing and a possible acute risk to consumers was identified. Hence, the consumer risk assessment is considered indicative only, some MRL proposals derived by EFSA still require further consideration by risk managers and measures for reduction of the consumer exposure should also be considered.

Modification of the existing maximum residue levels for cycloxydim in various crops.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant BASF SE submitted a request to the competent national authority in the Netherlands to modify the existing maximum residue levels (MRLs) for the active substance cycloxydim in pome fruits, apricots/peaches, peas (with pods), maize/corn, sugar beet roots and milk (sheep). The data submitted in support of the request were found to be sufficient to derive MRL proposals for pome fruits, peas (with pods), maize/corn and sugar beet roots while for apricots, peaches and sheep milk no changes to the existing MRLs were considered necessary. Adequate analytical methods for enforcement are available to control the residues of cycloxydim according to the current enforcement residue definition in the commodities under consideration. Based on the risk assessment results, EFSA concluded that the short-term and long-term intake of residues resulting from the uses of cycloxydim according to the reported agricultural practices is unlikely to present a risk to consumer health.

Evaluation of confirmatory data following the Article 12 MRL review and modification of the existing maximum residue levels for aluminium phosphide and magnesium phosphide.

The applicant Detia Freyberg GmbH submitted to the competent national authority in Germany two requests to evaluate the confirmatory data that were identified for tree nuts, oilseeds, cereals and commodities of animal origin in the framework of the maximum residue level (MRL) review under Article 12 of Regulation (EC) No 396/2005 as not available and two requests in accordance with Article 6 of Regulation (EC) No 396/2005 to increase the existing MRL for the active substance aluminium phosphide in peanuts, barley, oat, rye, rice and wheat, roots of herbal infusions, cocoa beans and seed spices and for the active substance magnesium phosphide in oilseeds (except peanuts) and pistachios. The four applications were combined by EFSA under the current assessment. To address the data gaps, validation data for the method of analysis for enforcement of phosphide in high-oil content commodities and new residue trials were submitted. The data gaps on additional residue trials supporting authorisations on oilseeds and cereal grains, on clarifications regarding the discrepancies observed in the residue trial results for pistachios, and on data confirming the negligible occurrence of phosphane and its oxidation products in livestock products were considered addressed. The data gap on independent laboratory validation (ILV) and a confirmatory method for monitoring of phosphide in high-oil content commodities was considered not fully addressed. The information provided justified a lowering of the current tentative MRLs for the whole group of cereals (except rice and 'others'), an increase of the current tentative MRLs for pistachios, the whole group of oilseeds, rice and 'other' cereals, herbal infusions from roots, cocoa beans and seed spices, and a revision of the risk assessment performed for phosphane and its phosphide salts. Based on the risk assessment results, EFSA concluded that the short-term and long-term intake of residues resulting from the use of AlP and Mg3P2 according to the reported agricultural practices is unlikely to present a risk to consumer health. Further risk management considerations are required.

Modification of the existing maximum residue levels for flonicamid in various crops.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant ISK Biosciences Europe N.V. submitted two requests to the competent national authority in Finland and Belgium, respectively, to modify the existing maximum residue levels (MRLs) for the active substance flonicamid in potatoes and in various crops. The data submitted in support of the requests were found to be sufficient to derive MRL proposals for potatoes, lettuces and salad plants, spinaches and similar leaves, beans (without pods), cardoons, celeries, Florence fennels and rhubarbs. Adequate analytical methods for enforcement are available to control the residues according to the residue definition as of the sum of flonicamid, TFNA and TFNG, expressed as flonicamid in the plant matrices under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg for each compound. Based on the risk assessment results, EFSA concluded that the short-term and long-term intake of residues resulting from the uses of flonicamid according to the reported agricultural practices is unlikely to present a risk to consumer health.

Modification of the existing maximum residue level for clopyralid in honey.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant Corteva Agriscience International Sàrl submitted a request to the competent national authority in Finland to modify the existing maximum residue levels (MRLs) for the active substance clopyralid in honey. The data submitted in support of the request were found to be sufficient to derive MRL proposals for honey. Adequate analytical methods for enforcement are available to control the residues of clopyralid (including potential conjugates) in honey at the validated limit of quantification (LOQ) of 0.001 mg/kg. Based on the risk assessment results, EFSA concluded that the short-term and long-term intake of clopyralid residues in honey, resulting from the authorised use of clopyralid on oilseed rape notified in the present MRL assessment, is unlikely to present a risk to consumer health.