The E50K optineurin mutation impacts autophagy-mediated degradation of TDP-43 and leads to RGC apoptosis in vivo and in vitro

Normal-Tension Glaucoma and Potential Clinical Links to Alzheimer's Disease

Glaucoma is a group of optic neuropathies and the world's leading cause of irreversible blindness. Normal-tension glaucoma (NTG) is a subtype of glaucoma that is characterized by a typical pattern of peripheral retinal loss, in which the patient's intraocular pressure (IOP) is considered within the normal range (<21 mmHg). Currently, the only targetable risk factor for glaucoma is lowering IOP, and patients with NTG continue to experience visual field loss after IOP-lowering treatments. This demonstrates the need for a better understanding of the pathogenesis of NTG and underlying mechanisms leading to neurodegeneration. Recent studies have found significant connections between NTG and cerebral manifestations, suggesting NTG as a neurodegenerative disease beyond the eye. Gaining a better understanding of NTG can potentially provide new Alzheimer's Disease diagnostics capabilities. This review identifies the epidemiology, current biomarkers, altered fluid dynamics, and cerebral and ocular manifestations to examine connections and discrepancies between the mechanisms of NTG and Alzheimer's Disease.

[Optineurin and mitochondrial dysfunction in neurodegeneration]

Optineurin (OPTN) is a multifunctional protein playing a crucial role as a receptor in selective autophagy. OPTN gene mutations are linked to diseases such as normal-tension glaucoma and amyotrophic lateral sclerosis. Recognized as a critical receptor for mitophagy, OPTN is pivotal in selectively degrading damaged mitochondria. This process is essential to prevent their accumulation, the generation of reactive oxygen species, and the release of pro-apoptotic factors. Mitophagy's quality control is governed by the PINK1 kinase and the cytosolic ubiquitin ligase Parkin, whose mutations are associated with Parkinson's disease. This review highlights recent insights emphasizing OPTN's role in mitophagy and its potential involvement in neurodegenerative diseases.

Genetic rodent models of glaucoma in representing disease phenotype and insights into the pathogenesis

Genetic rodent models are widely used in glaucoma related research. With vast amount of information revealed by human studies about genetic correlations with glaucoma, use of these models is relevant and required. In this review, we discuss the glaucoma endophenotypes and importance of their representation in an experimental animal model. Mice and rats are the most popular animal species used as genetic models due to ease of genetic manipulations in these animal species as well as the availability of their genomic information. With technological advances, induction of glaucoma related genetic mutations commonly observed in human is possible to achieve in rodents in a desirable manner. This approach helps to study the pathobiology of the disease process with the background of genetic abnormalities, reveals potential therapeutic targets and gives an opportunity to test newer therapeutic options. Various genetic manipulation leading to appearance of human relevant endophenotypes in rodents indicate their relevance in glaucoma pathology and the utility of these rodent models for exploring various aspects of the disease related to targeted mutation. The molecular pathways involved in the pathophysiology of glaucoma leading to elevated intraocular pressure and the disease hallmark, apoptosis of retinal ganglion cells and optic nerve degeneration, have been extensively explored in genetic rodent models. In this review, we discuss the consequences of various genetic manipulations based on the primary site of pathology in the anterior or the posterior segment. We discuss how these genetic manipulations produce features in rodents that can be considered a close representation of disease phenotype in human. We also highlight several molecular mechanisms revealed by using genetic rodent models of glaucoma including those involved in increased aqueous outflow resistance, loss of retinal ganglion cells and optic neuropathy. Lastly, we discuss the limitations of the use of genetic rodent models in glaucoma related research.

Endoplasmic reticulum stress: molecular mechanism and therapeutic targets

The endoplasmic reticulum (ER) functions as a quality-control organelle for protein homeostasis, or "proteostasis". The protein quality control systems involve ER-associated degradation, protein chaperons, and autophagy. ER stress is activated when proteostasis is broken with an accumulation of misfolded and unfolded proteins in the ER. ER stress activates an adaptive unfolded protein response to restore proteostasis by initiating protein kinase R-like ER kinase, activating transcription factor 6, and inositol requiring enzyme 1. ER stress is multifaceted, and acts on aspects at the epigenetic level, including transcription and protein processing. Accumulated data indicates its key role in protein homeostasis and other diverse functions involved in various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, achromatopsia, cataracts, ocular tumors, ocular surface diseases, and myopia. This review summarizes the molecular mechanisms underlying the aforementioned ocular diseases from an ER stress perspective. Drugs (chemicals, neurotrophic factors, and nanoparticles), gene therapy, and stem cell therapy are used to treat ocular diseases by alleviating ER stress. We delineate the advancement of therapy targeting ER stress to provide new treatment strategies for ocular diseases.

Mitophagy in the retina: Viewing mitochondrial homeostasis through a new lens

Mitochondrial function is key to support metabolism and homeostasis in the retina, an organ that has one of the highest metabolic rates body-wide and is constantly exposed to photooxidative damage and external stressors. Mitophagy is the selective autophagic degradation of mitochondria within lysosomes, and can be triggered by distinct stimuli such as mitochondrial damage or hypoxia. Here, we review the importance of mitophagy in retinal physiology and pathology. In the developing retina, mitophagy is essential for metabolic reprogramming and differentiation of retina ganglion cells (RGCs). In basal conditions, mitophagy acts as a quality control mechanism, maintaining a healthy mitochondrial pool to meet cellular demands. We summarize the different autophagy- and mitophagy-deficient mouse models described in the literature, and discuss the potential role of mitophagy dysregulation in retinal diseases such as glaucoma, diabetic retinopathy, retinitis pigmentosa, and age-related macular degeneration. Finally, we provide an overview of methods used to monitor mitophagy in vitro, ex vivo, and in vivo. This review highlights the important role of mitophagy in sustaining visual function, and its potential as a putative therapeutic target for retinal and other diseases.

Mitophagy restricts BAX/BAK-independent, Parkin-mediated apoptosis

Degradation of defective mitochondria is an essential process to maintain cellular homeostasis and it is strictly regulated by the ubiquitin-proteasome system (UPS) and lysosomal activities. Here, using genome-wide CRISPR and small interference RNA screens, we identified a critical contribution of the lysosomal system in controlling aberrant induction of apoptosis following mitochondrial damage. After treatment with mitochondrial toxins, activation of the PINK1-Parkin axis triggered a BAX- and BAK-independent process of cytochrome c release from mitochondria followed by APAF1 and caspase 9-dependent apoptosis. This phenomenon was mediated by UPS-dependent outer mitochondrial membrane (OMM) degradation and was reversed using proteasome inhibitors. We found that the subsequent recruitment of the autophagy machinery to the OMM protected cells from apoptosis, mediating the lysosomal degradation of dysfunctional mitochondria. Our results underscore a major role of the autophagy machinery in counteracting aberrant noncanonical apoptosis and identified autophagy receptors as key elements in the regulation of this process.

Ocular protein optineurin shows reversibility from unfolded states and exhibits chaperone-like activity

Optineurin (OPTN) is a multifunctional, ubiquitously expressed cytoplasmic protein, mutants of which are associated with primary open-angle glaucoma (POAG) and amyotrophic lateral sclerosis (ALS). The most abundant heat shock protein crystallin, known for its remarkable thermodynamic stability and chaperoning activity, allows ocular tissues to withstand stress. The presence of OPTN in ocular tissues is intriguing. Interestingly, OPTN also harbors heat shock elements in its promoter region. Sequence analysis of OPTN exhibits intrinsically disordered regions and nucleic acid binding domains. These properties hinted that OPTN might be endowed with sufficient thermodynamic stability and chaperoning activity. However, these attributes of OPTN have not yet been explored. Here, we studied these properties through thermal and chemical denaturation experiments and monitored the processes using CD, fluorimetry, differential scanning calorimetry, and dynamic light scattering. We found that upon heating, OPTN reversibly forms higher-order multimers. OPTN also displayed a chaperone-like function by reducing the thermal aggregation of bovine carbonic anhydrase. It regains its native secondary structure, RNA-binding property, and melting temperature (T _m) after refolding from a thermally as well as chemically denatured state. From our data, we conclude that OPTN, with its unique ability to revert from the stress-mediated unfolded state and its unique chaperoning function, is a valuable protein of the ocular tissues.

Autophagy in glaucoma pathogenesis: Therapeutic potential and future perspectives

Glaucoma is a common blinding eye disease characterized by progressive loss of retinal ganglion cells (RGCs) and their axons, progressive loss of visual field, and optic nerve atrophy. Autophagy plays a pivotal role in the pathophysiology of glaucoma and is closely related to its pathogenesis. Targeting autophagy and blocking the apoptosis of RGCs provides emerging guidance for the treatment of glaucoma. Here, we provide a systematic review of the mechanisms and targets of interventions related to autophagy in glaucoma and discuss the outlook of emerging ideas, techniques, and multidisciplinary combinations to provide a new basis for further research and the prevention of glaucomatous visual impairment.

Single nucleotide mutation changes the capability of CCN3 in osteosarcoma cell invasion and differentiation

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The frequency of G-to-A mutation in CCN3 is higher than para-carcinoma tissue.

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Mutation in CCN3 change its capacity of osteosarcoma invasion and differentiation.

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Mutant CCN3 decrease nuclear ratio of glycosylated/non-glycosylated isoforms.

This study aimed to identify significant mutations in CCN3 gene in osteosarcoma, and to explore the influence of this gene on cell invasion and differentiation and the underlying mechanism. Sanger sequencing was used to identify CCN3 gene sequence in human osteosarcoma cell lines, peripheral blood mononuclear cells (PBMC), and osteosarcoma tissues. Wild-type and mutant CCN3 (mCCN3) were ectopically expressed by lentivirus in human osteosarcoma cell lines. Tumor cell invasion was measured by trans-well assay. Osteogenic differentiation was induced by osteogenic differentiating medium and evaluated based on alkaline phosphatase activity and collagen type I alpha 1 chain and osteocalcin expression. Western blotting was used to detect protein levels of CCN3 and mCCN3 in cytoplasmic, nuclear and secreted fractions of cells. A G-to-A single nucleotide mutation in the coding region of CCN3 was found in both osteosarcoma cells and tissues. The frequency of this mutation in osteosarcoma tissue was much higher than that in para-carcinoma tissue and PBMC of healthy people. This nucleotide mutation decreased nuclear glycosylated full length protein level of CCN3 and affected osteosarcoma cell invasion and differentiation. A lower nuclear ratio of glycosylated/non-glycosylated isoforms accounted for the different behavior of mCCN3 compared with CCN3. The G-to-A mutation identified in CCN3 resulted in differential glycosylated full-length protein levels and altered the functional role of CCN3 in osteosarcoma cell invasion and differentiation.

Molecular Impact of the Tumor Microenvironment on Multiple Myeloma Dissemination and Extramedullary Disease

Multiple myeloma (MM) is the most common malignant monoclonal disease of plasma cells. Aside from classical chemotherapy and glucocorticoids, proteasome inhibitors, immunomodulatory agents and monoclonal antibodies are used in the current treatment scheme of MM. The tumor microenvironment (TME) plays a fundamental role in the development and progression of numerous solid and non-solid cancer entities. In MM, the survival and expansion of malignant plasma cell clones heavily depends on various direct and indirect signaling pathways provided by the surrounding bone marrow (BM) niche. In a number of MM patients, single plasma cell clones lose their BM dependency and are capable to engraft at distant body sites or organs. The resulting condition is defined as an extramedullary myeloma (EMM). EMMs are highly aggressive disease stages linked to a dismal prognosis. Emerging literature demonstrates that the dynamic interactions between the TME and malignant plasma cells affect myeloma dissemination. In this review, we aim to summarize how the cellular and non-cellular BM compartments can promote plasma cells to exit their BM niche and metastasize to distant intra-or extramedullary locations. In addition, we list selected therapy concepts that directly target the TME with the potential to prevent myeloma spread.

Optineurin Deficiency and Insufficiency Lead to Higher Microglial TDP-43 Protein Levels

Mutations in optineurin, a ubiquitin-binding adaptor protein, cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease of motor neurons linked to chronic inflammation and protein aggregation. The majority of ALS patients, including those carrying the optineurin mutations, exhibit cytoplasmic mislocalization, ubiquitination, and aggregation of nuclear TAR DNA-binding protein 43 kDa (TDP-43). To address the crosstalk between optineurin and TDP-43, we generated optineurin knockout (KO) neuronal and microglial cell lines using the CRISPR/Cas9 approach. Interestingly, we observed that loss of optineurin resulted in elevated TDP-43 protein expression in microglial BV2 but not neuronal Neuro 2a and NSC-34 cell lines. No changes were observed at the mRNA level, suggesting that this increase was post-translationally regulated. To confirm this observation in primary cells, we then used microglia and macrophages from an optineurin loss-of-function mouse model that lacks the C-terminal ubiquitin-binding region (Optn^470T), mimicking optineurin truncations in ALS patients. As observed in the BV2 cells, we also found elevated basal levels of TDP-43 protein in Optn^470T microglia and bone marrow-derived macrophages. To test if inflammation could further enhance TDP-43 accumulation in cells lacking functional optineurin, we stimulated them with lipopolysaccharide (LPS), and we observed a significant increase in TDP-43 expression following LPS treatment of WT cells. However, this was absent in both BV2 Optn KO and primary Optn^470T microglia, which exhibited the same elevated TDP-43 levels as in basal conditions. Furthermore, we did not observe nuclear TDP-43 depletion or cytoplasmic aggregate formation in either Optn^470T microglia or LPS-treated WT or Optn^470T microglia. Taken together, our results show that optineurin deficiency and insufficiency post-translationally upregulate microglial TDP-43 protein levels and that elevated TDP-43 levels in cells lacking functional optineurin could not be further increased by an inflammatory stimulus, suggesting the presence of a plateau.

Optineurin in ocular herpes infection

Herpes Simplex Virus-1 (HSV-1) is a neurotropic virus that can infect humans in the eye and travel to the trigeminal ganglion to establish latency. HSV-1 causes various disease states in both the primary and secondary sites of infection including the eye and the nervous system. This DNA virus exploits various adaptive measures to infect host cells, hijack host cell proteins, evade host immune response and spread from cell-to-cell to avoid immune detection. Recent data suggest that Optineurin (OPTN), a host protein, is a key restriction factor that prevents cell-to-cell spread of HSV-1 and guards against serious damage to the nervous system during infection. In recent years OPTN has gained increased attention because of its involvement in cellular mechanisms that promote homeostasis and prevent neurodegeneration. At the center of it all is the role OPTN plays as a receptor for selective autophagy. This review summarizes our latest understanding of the viral lifecycle, disease pathologies, and OPTN-mediated protective mechanisms during HSV-1 infection of the eye and the nervous system. We specifically highlight recent discoveries that implicate OPTN as crucial in the prevention of ocular and neurodegenerative diseases.

Cell interactome in sarcopenia during aging

BACKGROUND

The diversity between the muscle cellular interactome of dependent and independent elderly people is based on the interrelationships established between different cellular mechanisms, and alteration of this balance modulates cellular activity in muscle tissue with important functional implications.

METHODS

Thirty patients (85 ± 8 years old, 23% female) scheduled to undergo hip fracture surgery participated in this study. During the surgical procedures, skeletal muscle tissue was obtained from the Vastus lateralis. Two groups of participants were studied based on their Barthel index: 15 functional-independent individuals (100-90) and 15 severely functional-dependent individuals (40-0). The expression of proteins from the most important cellular mechanisms was studied by western blot.

RESULTS

Compared with independent elderly patients, dependent elderly showed an abrupt decrease in the capacity of protein synthesis; this decrease was only partially compensated for at the response to unfolded or misfolded proteins (UPR) level due to the increase in IRE1 (P < 0.001) and ATF6 (P < 0.05), which block autophagy, an essential mechanism for cell survival, by decreasing the expression of Beclin-1, LC3, and p62 (P < 0.001) and the antioxidant response. This lead to increased oxidative damage to lipids (P < 0.001) and that damage was directly associated with the mitochondrial impairment induced by the significant decreases in the I, III, IV, and V mitochondrial complexes (P < 0.01), which drastically reduced the energy capacity of the cell. The essential cellular mechanisms were generally impaired and the triggering of apoptosis was induced, as shown by the significantly elevated levels of most proapoptotic proteins (P < 0.05) and caspase-3/7 (P < 0.001) in dependents. The death of highly damaged cells is not detrimental to organs as long as the regenerative capacity remains unaltered, but in the dependent patients, this ability was also significantly altered, which was revealed by the reduction in the myogenic regulatory factors and satellite cell marker (P < 0.001), and the increase in myostatin (P < 0.01). Due to the severely disturbed cell interactome, the muscle contractile capacity showed significant damage.

CONCLUSIONS

Functionally dependent patients exhibited severe alterations in their cellular interactome at the muscle level. Cell apoptosis was caused by a decrease in successful protein synthesis, to which the cellular control systems did not respond adequately; autophagy was simultaneously blocked, the mitochondrion malfunctioned, and as the essential recovery mechanisms failed, these cells could not be replaced, resulting in the muscle being condemned to a loss of mass and functionality.

Age-related visual impairments and retinal ganglion cells axonal degeneration in a mouse model harboring OPTN (E50K) mutation

Retinal ganglion cells (RGCs) axons are the signal carriers of visual information between retina and brain. Therefore, they play one of the important roles affected in many optic neurodegenerative diseases like glaucoma. Among the genetic risks associated with glaucoma, the E50K mutation in the Optineurin (OPTN) gene are known to result in glaucoma in the absence of increased intraocular pressure (IOP), whereas the relevant pathological mechanism and neurological issues remain to be further investigated. In this study, the OPTN (E50K) mutant mouse model was established through CRISPR/Cas9-mediated genome editing, and aging-related RGCs loss and the visual dysfunction were identified. In E50K mice 16 months old, the axonal transport decreased comparing to wild-type (WT) mice at the same age. Furthermore, results of electron microscopy demonstrated significant morphological anomaly of mitochondria in RGCs axons of young E50K mice 3 months old, and these changes were aggravated with age. These indicated that the damaged mitochondria-associated dysfunction of RGCs axon should play an etiological role in glaucoma as an age-related outcome of OPTN (E50K) mutation. The findings of this study have potential implications for the targeted prevention and treatment of NTG.

The interplay of autophagy and oxidative stress in the pathogenesis and therapy of retinal degenerative diseases

Oxidative stress is mainly caused by intracellular reactive oxygen species (ROS) production, which is highly associated with normal physiological homeostasis and the pathogenesis of diseases, particularly ocular diseases. Autophagy is a self-clearance pathway that removes oxidized cellular components and regulates cellular ROS levels. ROS can modulate autophagy activity through transcriptional and posttranslational mechanisms. Autophagy further triggers transcription factor activation and degrades impaired organelles and proteins to eliminate excessive ROS in cells. Thus, autophagy may play an antioxidant role in protecting ocular cells from oxidative stress. Nevertheless, excessive autophagy may cause autophagic cell death. In this review, we summarize the mechanisms of interaction between ROS and autophagy and their roles in the pathogenesis of several ocular diseases, including glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR), and optic nerve atrophy, which are major causes of blindness. The autophagy modulators used to treat ocular diseases are further discussed. The findings of the studies reviewed here might shed light on the development and use of autophagy modulators for the future treatment of ocular diseases.

Protein clearance strategies for disease intervention

Protein homeostasis, or proteostasis, is essential for cell function and viability. Unwanted, damaged, misfolded and aggregated proteins are degraded by the ubiquitin–proteasome system (UPS) and the autophagy-lysosome pathway. Growing evidence indicates that alterations in these major proteolytic mechanisms lead to a demise in proteostasis, contributing to the onset and development of distinct diseases. Indeed, dysregulation of the UPS or autophagy is linked to several neurodegenerative, infectious and inflammatory disorders as well as cancer. Thus, modulation of protein clearance pathways is a promising approach for therapeutics. In this review, we discuss recent findings and open questions on how targeting proteolytic mechanisms could be applied for disease intervention.

Neuroprotective effects of bone marrow Sca-1+ cells against age-related retinal degeneration in OPTN E50K mice

Glaucoma is characterized by retinal ganglion cell (RGC) death, the underlying mechanisms of which are still largely unknown. An E50K mutation in the Optineurin (OPTN) gene is a leading cause of normal-tension glaucoma (NTG), which directly affects RGCs in the absence of high intraocular pressure and causes severe glaucomatous symptoms in patients. Bone marrow (BM) stem cells have been demonstrated to play a key role in regenerating damaged tissue during ageing and disease through their trophic effects and homing capability. Here, we separated BM stem cells into Sca-1⁺ and Sca-1^- cells and transplanted them into lethally irradiated aged OPTN E50K mice to generate Sca-1⁺ and Sca-1^- chimaeras, respectively. After 3 months of BM repopulation, we investigated whether Sca-1⁺ cells maximized the regenerative effects in the retinas of NTG model mice with the OPTN E50K mutation. We found that the OPTN E50K mutation aggravated age-related deficiency of neurotrophic factors in both retinas and BM during NTG development, leading to retinal degeneration and BM dysfunction. Sca-1⁺ cells from young healthy mice had greater paracrine trophic effects than Sca-1^- cells and Sca-1⁺ cells from young OPTN E50K mice. In addition, Sca-1⁺ chimaeras demonstrated better visual functions than Sca-1^- chimaeras and untreated OPTN E50K mice. More Sca-1⁺ cells than Sca-1^- cells were recruited to repair damaged retinas and reverse visual impairment in NTG resulting from high expression levels of neurotrophic factors. These findings indicated that the Sca-1⁺ cells from young, healthy mice may have exhibited an enhanced ability to repair retinal degeneration in NTG because of their excellent neurotrophic capability.

Proteomic analysis of aged and OPTN E50K retina in the development of normal tension glaucoma

Progressive degeneration of retinal ganglion cells (RGCs) is a major characteristic of glaucoma, whose underlying mechanisms are still largely unknown. An E50K mutation in the Optineurin (OPTN) gene is a leading cause of normal tension glaucoma (NTG), directly affecting RGCs without high intraocular pressure and causing severe glaucomatous symptoms in clinical settings. A systematic analysis of the NTG mouse model is crucial for better understanding of the underlying pathological mechanisms for glaucoma. To elucidate proteomic and biochemical pathway alterations during NTG development, we established an OPTN E50K mutant mouse model through CRISPR/Cas9. Retinal proteins from resulting mice exhibiting glaucomatous phenotypes were subject to tandem mass tag-labeled quantitative proteomics and then analyzed through bioinformatics methods to characterize the molecular and functional signatures of NTG. We identified 6364 quantitative proteins in our proteomic analysis. Bioinformatics analysis revealed that OPTN E50K mice experienced protein synthesis dysregulation, age-dependent energy defects and autophagy-lysosome pathway dysfunction. Certain biological features, including amyloid deposition, RNA splicing, microglia activation and reduction of crystallin production, were similar to Alzheimer's disease. Our study is the first to describe proteomic and biochemical pathway alterations in NTG pathogenesis during disease advancement. Several proteomic signatures overlapped with retinal changes found in the ad mice model, suggesting the presence of common mechanisms between age-related degenerative disorders, as well as prospective new targets for diagnostic and therapeutic strategies.