Radicicol but not geldanamycin evokes oxidative stress response and efflux protein inhibition in ARPE-19 human retinal pigment epithelial cells

Systems biology reveals anatabine to be an NRF2 activator

Anatabine, an alkaloid present in plants of the Solanaceae family (including tobacco and eggplant), has been shown to ameliorate chronic inflammatory conditions in mouse models, such as Alzheimer’s disease, Hashimoto’s thyroiditis, multiple sclerosis, and intestinal inflammation. However, the mechanisms of action of anatabine remain unclear. To understand the impact of anatabine on cellular systems and identify the molecular pathways that are perturbed, we designed a study to examine the concentration-dependent effects of anatabine on various cell types by using a systems pharmacology approach. The resulting dataset, consisting of measurements of various omics data types at different time points, was analyzed by using multiple computational techniques. To identify concentration-dependent activated pathways, we performed linear modeling followed by gene set enrichment. To predict the functional partners of anatabine and the involved pathways, we harnessed the LINCS L1000 dataset’s wealth of information and implemented integer linear programming on directed graphs, respectively. Finally, we experimentally verified our key computational predictions. Using an appropriate luciferase reporter cell system, we were able to demonstrate that anatabine treatment results in NRF2 (nuclear factor-erythroid factor 2-related factor 2) translocation, and our systematic phosphoproteomic assays showed that anatabine treatment results in activation of MAPK signaling. While there are certain areas to be explored in deciphering the exact anti-inflammatory mechanisms of action of anatabine and other NRF2 activators, we believe that anatabine constitutes an interesting molecule for its therapeutic potential in NRF2-related diseases.

Maize Anthracnose Stalk Rot in the Genomic Era

Anthracnose stalk rot (ASR) of maize results in millions of dollars in losses annually in the United States. ASR, together with anthracnose leaf blight and anthracnose top dieback, is caused by the fungus Colletotrichum graminicola. Current ASR management recommendations emphasize host resistance and reduction of plant stressors (e.g., drought, heat, low fertility, or soil acidity). Stress reduction may be more difficult to achieve in the future due to more high-intensity production protocols and climate change. Moreover, cultural and chemical management practices may conflict with other important goals, including environmental sustainability and maximization of yield potential. Thus, future ASR management may rely more heavily on host resistance, for which there are relatively few highly effective sources. The last comprehensive review of C. graminicola and maize anthracnose was written over two decades ago. The genomic age has brought important new insights into mechanisms governing the host-pathogen interaction from the application of molecular and cytological technologies. This review provides a summary of our current model of maize anthracnose etiology, including how increased knowledge of molecular and cellular events could contribute to better ASR management. Improved understanding of C. graminicola taxonomy has confirmed that the fungus is specific to Zea mays, and that it colonizes living maize tissues via a critical biotrophic phase. Successful biotrophic establishment relies on an array of secreted protein effectors and secondary metabolites produced at different stages of infection and dispersed to multiple locations. These molecules could provide therapeutic targets for the next generation of transgenic or gene-edited ASR-resistant hybrids.

Relationship between heat shock proteins and cellular resistance to drugs and ageing

BACKGROUND AND AIMS

Ageing is a multifactorial degenerative process which causes a decrease in the cellular capacity for repair and adaptation to external stressors. In this way, it is important to maintain the proper balance of the proteome. Heat shock proteins (HSP) will intervene in this balance, which are responsible for the correct assembly, folding and translocation of other proteins when cells are subjected to stressors. This type of protein is overexpressed in human tumor cells, while its deficit, both in function and quantity, contributes to ageing processes. The present work aims to analyze the response of cells from studies carried out in normal and tumor cells that are subjected to stressors.

METHODS AND RESULTS

A PubMed search was performed using the keywords "cell ageing, cell longevity, resistance, HSP, heat shock proteins, thermal shock proteins". This search generated 212 articles. Subsequently, a series of inclusion and exclusion criteria were applied to select the articles of interest to be evaluated. Normal cells subjected to external stressors at low doses increase the number of HSP, causing them to become more resistant. In addition, tumor cells expressing high levels of HSP show greater resistance to treatment and increased cell replication. HSP intervene in the cellular resistance of both normal and tumor cells.

CONCLUSIONS

In the case of normal cells, the increase in HSP levels makes them respond effectively to an external stressor, increasing their resistance and not causing cell death. In the case of tumor cells, there is an increase in resistance to treatment.

TAS-116, a Well-Tolerated Hsp90 Inhibitor, Prevents the Activation of the NLRP3 Inflammasome in Human Retinal Pigment Epithelial Cells

Chronic inflammation has been associated with several chronic diseases, such as age-related macular degeneration (AMD). The NLRP3 inflammasome is a central proinflammatory signaling complex that triggers caspase-1 activation leading to the maturation of IL-1β. We have previously shown that the inhibition of the chaperone protein, Hsp90, prevents NLRP3 activation in human retinal pigment epithelial (RPE) cells; these are cells which play a central role in the pathogenesis of AMD. In that study, we used a well-known Hsp90 inhibitor geldanamycin, but it cannot be used as a therapy due to its adverse effects, including ocular toxicity. Here, we have tested the effects of a novel Hsp90 inhibitor, TAS-116, on NLRP3 activation using geldanamycin as a reference compound. Using our existing protocol, inflammasome activation was induced in IL-1α-primed ARPE-19 cells with the proteasome and autophagy inhibitors MG-132 and bafilomycin A1, respectively. Intracellular caspase-1 activity was determined using a commercial caspase-1 activity kit and the FLICA assay. The levels of IL-1β were measured from cell culture medium samples by ELISA. Cell viability was monitored by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test and lactate dehydrogenase (LDH) measurements. Our findings show that TAS-116 could prevent the activation of caspase-1, subsequently reducing the release of mature IL-1β. TAS-116 has a better in vitro therapeutic index than geldanamycin. In summary, TAS-116 appears to be a well-tolerated Hsp90 inhibitor, with the capability to prevent the activation of the NLRP3 inflammasome in human RPE cells.

Hydrogen Sulfide: Novel Endogenous and Exogenous Modulator of Oxidative Stress in Retinal Degeneration Diseases

Oxidative stress (OS) damage can cause significant injury to cells, which is related to the occurrence and development of many diseases. This pathological process is considered to be the first step to trigger the death of outer retinal neurons, which is related to the pathology of retinal degenerative diseases. Hydrogen sulfide (H₂S) has recently received widespread attention as a physiological signal molecule and gas neuromodulator and plays an important role in regulating OS in eyes. In this article, we reviewed the OS responses and regulatory mechanisms of H₂S and its donors as endogenous and exogenous regulators in retinal degenerative diseases. Understanding the relevant mechanisms will help to identify the therapeutic potential of H₂S in retinal degenerative diseases.

Unravelling the Role of HSP70 as the Unexplored Molecular Target in Age-Related Macular Degeneration

The motive behind writing this paper was to highlight the relationship between heat shock protein 70 (HSP70) and age-related macular degeneration (AMD) to explore the potential role of HSP70 as a molecular target in AMD therapy. We performed a comprehensive literature search in various databases and finally found 43 relevant studies related to our objective. In our research, we found that in AMD, oxidative stress causes increased inflammation and excessive apoptosis due to the accumulation of aberrant proteins in retinal pigment epithelium (RPE) cells. The long-lasting overstimulation of the defence system leads to RPE degeneration and results in visual impairment or vision loss. However, after thorough research, it was found that HSP70's role as an immunomodulator, the guardian of the proteolytic pathway and regulator of apoptosis makes it a potential therapeutic target in AMD.

Pharmacokinetic aspects of retinal drug delivery

Drug delivery to the posterior eye segment is an important challenge in ophthalmology, because many diseases affect the retina and choroid leading to impaired vision or blindness. Currently, intravitreal injections are the method of choice to administer drugs to the retina, but this approach is applicable only in selected cases (e.g. anti-VEGF antibodies and soluble receptors). There are two basic approaches that can be adopted to improve retinal drug delivery: prolonged and/or retina targeted delivery of intravitreal drugs and use of other routes of drug administration, such as periocular, suprachoroidal, sub-retinal, systemic, or topical. Properties of the administration route, drug and delivery system determine the efficacy and safety of these approaches. Pharmacokinetic and pharmacodynamic factors determine the required dosing rates and doses that are needed for drug action. In addition, tolerability factors limit the use of many materials in ocular drug delivery. This review article provides a critical discussion of retinal drug delivery, particularly from the pharmacokinetic point of view. This article does not include an extensive review of drug delivery technologies, because they have already been reviewed several times recently. Instead, we aim to provide a systematic and quantitative view on the pharmacokinetic factors in drug delivery to the posterior eye segment. This review is based on the literature and unpublished data from the authors' laboratory.

Hypoxia induces cardiac fibroblast proliferation and phenotypic switch: a role for caveolae and caveolin-1/PTEN mediated pathway

BACKGROUND

Cardiac fibrosis following myocardial infarction (MI) results in heart failure. Caveolin-1, the main structural protein of caveolae, regulates signal transduction pathways controlling cell proliferation and apoptosis. Meanwhile, low phosphatase and tensin homolog (PTEN) activity enhances the PI3K/Akt signal pathway to induce cell proliferation. But whether caveolin-1 and PTEN activation regulates cardiac fibroblast proliferation and contributes to cardiac fibrosis from ischemic injury is incompletely understood. This study investigates whether hypoxia inducing cardiac fibroblast proliferation and phenotypic switch is caveolin-dependent.

METHODS

We used in vitro and in vivo models of ischemic injury, immunohistochemical staining, and cell proliferation assays to address this hypothesis.

RESULTS

We found that MI induced collagen deposition and cardiac dysfunction. After MI, mice displayed reduced caveolin-1 and PTEN expression and increased α-smooth muscle actin (α-SMA) expression in the infarct zone. Qualitative and quantitative analyses indicated that caveolin-1 expression was lowest at 7 days after MI, accompanied by increased collagen deposition and attenuated cardiac function. We cultured cardiac fibroblasts of mice were in hypoxia or normoxia conditions for 12, 24 and 48 hours. At all the time points, caveolin-1 and PTEN expression were gradually reduced, whereas, α-SMA was gradually increased. We also observed that cell viability was increased at 12 and 24 h after hypoxia then lightly decreased at 48 h. Additionally, disruption of caveolae with methyl-β-cyclodextrin (MβCD) enhanced p-Akt and α-SMA expression and fibroblast proliferation and phenotypic switch.

CONCLUSIONS

These findings suggest a key role for caveolae, perhaps through the caveolin-1/PTEN signaling pathway, in cardiac fibroblast proliferation and phenotypic switch under hypoxia.

A phase II open-label study of ganetespib, a novel heat shock protein 90 inhibitor for patients with metastatic breast cancer

BACKGROUND

Ganetespib is a small molecule, nongeldanamycin HSP90 inhibitor with potent inhibitory effects on HSP90-dependent oncoproteins of relevance to breast cancer pathogenesis. We therefore tested ganetespib in an unselected cohort of patients with MBC.

PATIENTS AND METHODS

Patients were treated with single agent ganetespib at 200 mg/m(2) once weekly for 3 weeks, on a 28-day cycle. Therapy was continued until disease progression. The primary end point was ORR using Reponse Evaluation Criteria in Solid Tumors version 1.1.

RESULTS

Twenty-two patients were enrolled with a median age of 51(range, 38-70) years and a median Eastern Cooperative Oncology Group performance status of 0 (range, 0-1). Most patients had at least 2 previous lines of chemotherapy in the metastatic setting. Most common toxicities, largely grade 1/2, were diarrhea, fatigue, nausea, and hypersensitivity reaction. The ORR in this unselected population was 9%, with all responses coming from the subset of patients with HER2-positive MBC (2/13; 15%). One patient with TNBC had objective tumor regression in the lung metastases. The clinical benefit rate (complete response + partial response + stable disease > 6 months) was 9%, median progression-free survival was 7 weeks (95% confidence interval [CI], 7-19), and median overall survival was 46 weeks (95% CI, 27-not applicable).

CONCLUSION

The study did not meet the prespecified criteria for ORR in the first stage of the Simon 2-stage model in this heavily pretreated unselected population of MBC. However, activity was observed in trastuzumab-refractory HER2-positive and TNBC. Ganetespib was well tolerated and responses in more targeted populations harboring specific HSP90-dependent oncoproteins justifies its further study, particularly as part of rational combinations.

Dry age-related macular degeneration: mechanisms, therapeutic targets, and imaging

Age-related macular degeneration is the leading cause of irreversible visual dysfunction in individuals over 65 in Western Society. Patients with AMD are classified as having early stage disease (early AMD), in which visual function is affected, or late AMD (generally characterized as either "wet" neovascular AMD, "dry" atrophic AMD or both), in which central vision is severely compromised or lost. Until recently, there have been no therapies available to treat the disorder(s). Now, the most common wet form of late-stage AMD, choroidal neovascularization, generally responds to treatment with anti-vascular endothelial growth factor therapies. Nevertheless, there are no current therapies to restore lost vision in eyes with advanced atrophic AMD. Oral supplementation with the Age-Related Eye Disease Study (AREDS) or AREDS2 formulation (antioxidant vitamins C and E, lutein, zeaxanthin, and zinc) has been shown to reduce the risk of progression to advanced AMD, although the impact was in neovascular rather than atrophic AMD. Recent findings, however, have demonstrated several features of early AMD that are likely to be druggable targets for treatment. Studies have established that much of the genetic risk for AMD is associated with complement genes. Consequently, several complement-based therapeutic treatment approaches are being pursued. Potential treatment strategies against AMD deposit formation and protein and/or lipid deposition will be discussed, including anti-amyloid therapies. In addition, the role of autophagy in AMD and prevention of oxidative stress through modulation of the antioxidant system will be explored. Finally, the success of these new therapies in clinical trials and beyond relies on early detection, disease typing, and predicting disease progression, areas that are currently being rapidly transformed by improving imaging modalities and functional assays.

A first in human, safety, pharmacokinetics, and clinical activity phase I study of once weekly administration of the Hsp90 inhibitor ganetespib (STA-9090) in patients with solid malignancies

Background

This phase I study investigated the maximum tolerated dose (MTD), safety, pharmacokinetics and antitumor activity of ganetespib in patients with solid malignancies.

Methods

Patients were enrolled in cohorts of escalating ganetespib doses, given as 1 hour IV infusion, once weekly for 3 weeks, followed by a 1-week rest until disease progression or unacceptable toxicity. Endpoints included safety, pharmacokinetic and pharmacodynamic parameters and preliminary clinical activity.

Results

Fifty-three patients were treated at doses escalating from 7 to 259 mg/m². The most common adverse events were Grade 1 and 2 diarrhea, fatigue, nausea or vomiting. Dose-limiting toxicities (DLT) observed were: one Grade 3 amylase elevation (150 mg/m²), one Grade 3 diarrhea and one Grade 3 and one Grade 4 asthenia (259 mg/m²). The MTD was 216 mg/m² and the recommended phase 2 dose was established at 200 mg/m² given IV at Days 1, 8, and 15 every 4 weeks. There was a linear relationship between dose and exposure. Plasma HSP70 protein levels remained elevated for over a week post treatment. Disease control rate (objective response and stable disease at ≥ 16 weeks) was 24.4%.

Conclusions

Ganetespib is well tolerated as a weekly infusion for 3 of every 4 weeks cycle. The recommended phase II dose is 200 mg/m², and is associated with an acceptable tolerability profile.

Trial registration

NCT00687934

The ubiquitin-proteasome system in retinal health and disease

The ubiquitin-proteasome system (UPS) is the main intracellular pathway for modulated protein turnover, playing an important role in the maintenance of cellular homeostasis. It also exerts a protein quality control through degradation of oxidized, mutant, denatured, or misfolded proteins and is involved in many biological processes where protein level regulation is necessary. This system allows the cell to modulate its protein expression pattern in response to changing physiological conditions and provides a critical protective role in health and disease. Impairments of UPS function in the central nervous system (CNS) underlie an increasing number of genetic and idiopathic diseases, many of which affect the retina. Current knowledge on the UPS composition and function in this tissue, however, is scarce and dispersed. This review focuses on UPS elements reported in the retina, including ubiquitinating and deubiquitinating enzymes (DUBs), and alternative proteasome assemblies. Known and inferred roles of protein ubiquitination, and of the related, SUMO conjugation (SUMOylation) process, in normal retinal development and adult homeostasis are addressed, including modulation of the visual cycle and response to retinal stress and injury. Additionally, the relationship between UPS dysfunction and human neurodegenerative disorders affecting the retina, including Alzheimer's, Parkinson's, and Huntington's diseases, are dealt with, together with numerous instances of retina-specific illnesses with UPS involvement, such as retinitis pigmentosa, macular degenerations, glaucoma, diabetic retinopathy (DR), and aging-related impairments. This information, though still basic and limited, constitutes a suitable framework to be expanded in incoming years and should prove orientative toward future therapy design targeting sight-affecting diseases with a UPS underlying basis.

Age related macular degeneration and drusen: neuroinflammation in the retina

Inflammation protects from dangerous stimuli, restoring normal tissue homeostasis. Inflammatory response in the nervous system ("neuroinflammation") has distinct features, which are shared in several diseases. The retina is an immune-privileged site, and the tight balance of immune reaction can be disrupted and lead to age-related macular disease (AMD) and to its peculiar sign, the druse. Excessive activation of inflammatory and immunological cascade with subsequent induction of damage, persistent activation of resident immune cells, accumulation of byproducts that exceeds the normal capacity of clearance giving origin to a chronic local inflammation, alterations in the activation of the complement system, infiltration of macrophages, T-lymphocytes and mast-cells from the bloodstream, participate in the mechanisms which originate the drusen. In addition, aging of the retina and AMD involve also para-inflammation, by which immune cells react to persistent stressful stimuli generating low-grade inflammation, aimed at restoring function and maintaining tissue homeostasis by varying the set point in relation to the new altered conditions. This mechanism is also seen in the normal aging retina, but, in the presence of noxious stimuli as in AMD, it can become chronic and have an adverse outcome. Finally, autophagy may provide new insights to understand AMD pathology, due to its contribution in the removal of defective proteins. Therefore, the AMD retina can represent a valuable model to study neuroinflammation, its mechanisms and therapy in a restricted and controllable environment. Targeting these pathways could represent a new way to treat and prevent both exudative and dry forms of AMD.

Heat shock protein 70 upregulation by geldanamycin reduces brain injury in a mouse model of intracerebral hemorrhage

This study investigated the effect of geldanamycin post-treatment on the development of secondary brain injury and neurological deficits in a mouse model of intracerebral hemorrhage. CD-1 mice received stereotactic injection of collagenase type VII into the right basal ganglia. Treatment groups were administered 1 mg/kg (low dose) or 10 mg/kg (high dose) of geldanamycin. Mice were euthanized at two time-points: 24 h or 72 h. Blood-brain-barrier permeability, brain edema, and neurobehavioral deficits were assessed. Additionally, the effects of geldanamycin on heat shock protein 27 and 72; tumor necrosis factor-alpha and interleukin 1 beta expressions were evaluated. High dose geldanamycin significantly attenuated blood-brain barrier disruption and brain edema after intracerebral hemorrhage. Neurobehavioral outcomes were significantly improved in some parameters by high dose treatment. Molecular results showed a marked increase in heat shock protein 72 expression in ipsilateral brain of geldanamycin treated groups with a reduction in the pro-inflammatory tumor necrosis factor-alpha.

CONCLUSION

Geldanamycin post-treatment is neuroprotective in the mouse model of intracerebral hemorrhage. Geldanamycin administration results in reduction of inflammation, preservation of blood-brain-barrier and amelioration of neurobehavioral deficits after an insult possibly by upregulation of heat shock protein 72.

Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin inhibits the proliferation of ARPE-19 cells

BACKGROUND

The antiproliferative effect of the Hsp90 inhibitor 17-AAG (17-allylamino-17-demethoxygeldanamycin) on human retinal pigment epithelial cells is investigated.

METHODS

MTT and flow cytometry were used to study the antiproliferative effects of the 17-AAG treatment of ARPE-19 cells. 2D gel electrophoresis (2-DE) and mass spectrometry were applied to detect the altered expression of proteins, which was verified by real-time PCR. Gene Ontology analysis and Ingenuity Pathway Analysis (IPA) were utilized to analyze the signaling pathways, cellular location, function, and network connections of the identified proteins. And SOD assay was employed to confirm the analysis.

RESULTS

17-AAG suppressed the proliferation of ARPE-19 cells by inducing cell cycle arrest and apoptosis. Proteomic analysis revealed that the expression of 94 proteins was altered by a factor of more than 1.5 following exposure to 17-AAG. Of these 94, 87 proteins were identified. Real-time PCR results indicated that Hsp90 and Hsp70, which were not identified by proteomic analysis, were both upregulated upon 17-AAG treatment. IPA revealed that most of the proteins have functions that are related to oxidative stress, as verified by SOD assay, while canonical pathway analysis revealed glycolysis/gluconeogenesis.

CONCLUSIONS

17-AAG suppressed the proliferation of ARPE-19 cells by inducing cell cycle arrest and apoptosis, and possibly by oxidative stress.

Regulatory role of HIF-1alpha in the pathogenesis of age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is a leading cause of irreversible blindness in the elderly throughout the world. AMD is attributed to a complex interaction of genetic and environmental factors. It is characterized by degeneration involving the retinal photoreceptors, retinal pigment epithelium (RPE), and Bruch's membrane, as well as alterations in choroidal capillaries. Aging and age-associated degenerative diseases, such as AMD, are intimately associated with decreased levels of tissue oxygenation and hypoxia that may induce accumulation of detrimental RPE-associated deposits, inflammation and neovascularization processes in retina. Hypoxia-inducible factor (HIF) is the master regulator for hypoxia-induced cellular adaptation that is involved in NF-kappaB signaling and the autophagic protein clearance system. In this review, we discuss role of HIF in AMD pathology and as a possible therapeutic target.

HSP90alpha and HSP90beta isoforms selectively modulate MHC class II antigen presentation in B cells

Two isoforms of heat shock protein (HSP) 90, alpha and beta, are abundantly expressed in the cytoplasm of cells, yet only HSP90alpha serves as a chaperone to potentiate epitope presentation in the context of MHC class I molecules. By contrast, the role of HSP90 isoforms in MHC class II presentation of exogenous and endogenous Ags remains less clear. Studies here using human B lymphoblasts demonstrate the importance of HSP90alpha and HSP90beta isoforms in selectively regulating class II presentation of the diabetes autoantigen glutamic acid decarboxylase (GAD). Inactivation of HSP90 function using geldanamycin or radicicol inhibited MHC class II presentation of exogenous and endogenous GAD, but did not perturb the presentation of several other intra- and extracellular Ags. Treatment of human B cells with geldanamycin and radicicol did not alter cellular MHC class II expression, but did induce a stress response in these APCs. Yet, cell stress alone failed to perturb MHC class II presentation of GAD. HSP90 was found to associate with select Ags such as GAD in cells and ex vivo. Knockdown of HSP90alpha or HSP90beta expression using small interfering RNA decreased the abundance of each isoform, respectively, but did not affect MHC class II expression or induce a stress response. Notably, disruption of HSP90alpha or HSP90beta expression specifically inhibited class II presentation of the exogenous and endogenous GAD Ag. Precomplexing HSP90 with GAD Ag enhanced exogenous GAD Ag presentation. These results demonstrate a requirement for HSP90alpha and HSP90beta in regulating class II presentation of select Ags.

Heat shock proteins as gatekeepers of proteolytic pathways-Implications for age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is the major diagnosis for severe and irreversible central loss of vision in elderly people in the developed countries. The loss of vision involves primarily a progressive degeneration and cell death of postmitotic retinal pigment epithelial cells (RPE), which secondarily evokes adverse effects on photoreceptor cells. The RPE cells are exposed to chronic oxidative stress from three sources: their high levels of oxygen consumption, their exposure to the high levels of lipid peroxidation derived from the photoreceptor outer segments and their exposure to constant light stimuli. Cells increase the expression of heat shock proteins (HSPs) in order to normalize their growth conditions in response to various environmental stress factors, e.g. oxidative stress. The HSPs function as molecular chaperones by preventing the accumulation of cellular cytotoxic protein aggregates and assisting in correct folding of both nascent and misfolded proteins. Increased HSPs levels are observed in the retina of AMD patients, evidence of stressed tissue. A hallmark of RPE cell aging is lysosomal lipofuscin accumulation reflecting a weakened capacity to degrade proteins in lysosomes. The presence of lipofuscin increases the misfolding of intracellular proteins, which evokes additional stress in the RPE cells. If the capacity of HSPs to repair protein damages is overwhelmed, then the proteins are mainly cleared in proteasomes or in lysosomes. In this review, we discuss the role of heat shock proteins, proteasomes, and lysosomes and autophagic processes in RPE cell proteolysis and how these might be involved in development of AMD. In addition to classical lysosomal proteolysis, we focus on the increasing evidence that, HSPs, proteasomes and autophagy regulate protein turnover in the RPE cells and thus have important roles in AMD disease.

Identification of common and unique modifiers of zebrafish midline bifurcation and cyclopia

Loss of the zebrafish Nodal-related protein Squint causes a spectrum of phenotypes including cyclopia and midline bifurcations (MB). Here we examine MBs and their relation to cyclopia in maternal-zygotic squint (MZsqt) mutants. There is a concordance of MB with cyclopia in MZsqt embryos. Heat treatment and depletion of Hsp90a are "common" risk factors, each of which increases the incidence of both phenotypes. Midline identity is specified on both sides of MBs, and deep-layer cells are initially lacking within bifurcations, whereas enveloping layer cells are intact. Bifurcations do not appear until the completion of gastrulation and are preceded by gaps in the expression of wnt5b, an essential regulator of dorsal convergence. The incidence of early MBs and wnt5b expression defects in heated MZsqt embryos is high, but there is also substantial recovery. Wnt5b depletion increases the incidence of MB, but not cyclopia, and as such Wnt5b is a "unique" risk factor for MB. Reciprocally, depletion of Wnt11 or Hsp90b increases cyclopia only. In summary, we find that MB arises after gastrulation in regions that fail to express wnt5b, and we show that two complex dysmorphologies - MB and cyclopia - can be promoted by either common or unique risk factors.