Intravitreal administration of HA-1077, a ROCK inhibitor, improves retinal function in a mouse model of huntington disease

New insights on the regulators and inhibitors of RhoA-ROCK signalling in Parkinson's disease

A multifaceted and widely prevalent neurodegenerative disease, Parkinson's disease (PD) is typified by the loss of dopaminergic neurons in the midbrain. The discovery of novel treatment(s) that can reverse or halt the course of the disease progression along with identifying the most reliable biomarker(s) in PD remains the crucial concern. RhoA in its active state has been demonstrated to interact with three distinct domains located in the central coiled-coil region of ROCK. RhoA appears to activate effectors most frequently by breaking the intramolecular autoinhibitory connections, which releases functional domains from the effector protein. Additionally, RhoA is highly expressed in the nervous system and it acts as a central molecule for its several downstream effector proteins in multiple signalling pathways both in neurons and glial cells. Mitochondrial dysfunction, vesicle transport malfunction and aggregation of α-Synuclein, a presynaptic neuronal protein genetically and neuropathologically associated with PD. While the RhoA-ROCK signalling pathway appears to have a significant role in PD symptoms, suggesting it could be a promising target for therapeutic interventions. Thus, this review article addresses the potential involvement of the RhoA-ROCK signalling system in the pathophysiology of neurodegenerative illnesses, with an emphasis on its biology and function. We also provide an overview of the state of research on RhoA regulation and its downstream biological activities, focusing on the role of RhoA signalling in neurodegenerative illnesses and the potential benefits of RhoA inhibition as a treatment for neurodegeneration.

Role of Rho-associated kinases and their inhibitor fasudil in neurodegenerative diseases

Neurodegenerative diseases (NDDs) are prevalent in the elderly. The pathogenesis of NDDs is complex, and currently, there is no cure available. With the increase in aging population, over 20 million people are affected by common NDDs alone (Alzheimer's disease and Parkinson's disease). Therefore, NDDs have profound negative impacts on patients, their families, and society, making them a major global health concern. Rho-associated kinases (ROCKs) belong to the serine/threonine protein kinases family, which modulate diverse cellular processes (e.g., apoptosis). ROCKs may elevate the risk of various NDDs (including Huntington's disease, Parkinson's disease, and Alzheimer's disease) by disrupting synaptic plasticity and promoting inflammatory responses. Therefore, ROCK inhibitors have been regarded as ideal therapies for NDDs in recent years. Fasudil, one of the classic ROCK inhibitor, is a potential drug for treating NDDs, as it repairs nerve damage and promotes axonal regeneration. Thus, the current review summarizes the relationship between ROCKs and NDDs and the mechanism by which fasudil inhibits ROCKs to provide new ideas for the treatment of NDDs.

Axon guidance genes are regulated by TDP-43 and RGNEF through long-intron removal

Rho guanine nucleotide exchange factor (RGNEF) is a guanine nucleotide exchange factor (GEF) mainly involved in regulating the activity of Rho-family GTPases. It is a bi-functional protein, acting both as a guanine exchange factor and as an RNA-binding protein. RGNEF is known to act as a destabilizing factor of neurofilament light chain RNA (NEFL) and it could potentially contribute to their sequestration in nuclear cytoplasmic inclusions. Most importantly, RGNEF inclusions in the spinal motor neurons of ALS patients have been shown to co-localize with inclusions of TDP-43, the major well-known RNA-binding protein aggregating in the brain and spinal cord of human patients. Therefore, it can be hypothesized that loss-of-function of both proteins following aggregation may contribute to motor neuron death/survival in ALS patients. To further characterize their relationship, we have compared the transcriptomic profiles of neuronal cells depleted of TDP-43 and RGNEF and show that these two factors predominantly act in an antagonistic manner when regulating the expression of axon guidance genes. From a mechanistic point of view, our experiments show that the effect of these genes on the processivity of long introns can explain their mode of action. Taken together, our results show that loss-of-function of factors co-aggregating with TDP-43 can potentially affect the expression of commonly regulated neuronal genes in a very significant manner, potentially acting as disease modifiers. This finding further highlights that neurodegenerative processes at the RNA level are the result of combinatorial interactions between different RNA-binding factors that can be co-aggregated in neuronal cells. A deeper understanding of these complex scenarios may lead to a better understanding of pathogenic mechanisms occurring in patients, where more than one specific protein may be aggregating in their neurons.

Retinal dysfunction in Huntington's disease mouse models concurs with local gliosis and microglia activation

Huntington's disease (HD) is caused by an aberrant expansion of CAG repeats in the HTT gene that mainly affects basal ganglia. Although striatal dysfunction has been widely studied in HD mouse models, other brain areas can also be relevant to the pathology. In this sense, we have special interest on the retina as this is the most exposed part of the central nervous system that enable health monitoring of patients using noninvasive techniques. To establish the retina as an appropriate tissue for HD studies, we need to correlate the retinal alterations with those in the inner brain, i.e., striatum. We confirmed the malfunction of the transgenic R6/1 retinas, which underwent a rearrangement of their transcriptome as extensive as in the striatum. Although tissue-enriched genes were downregulated in both areas, a neuroinflammation signature was only clearly induced in the R6/1 retina in which the observed glial activation was reminiscent of the situation in HD patient's brains. The retinal neuroinflammation was confirmed in the slow progressive knock-in zQ175 strain. Overall, these results demonstrated the suitability of the mouse retina as a research model for HD and its associated glial activation.

Retina Oculomics in Neurodegenerative Disease

Ophthalmic biomarkers have long played a critical role in diagnosing and managing ocular diseases. Oculomics has emerged as a field that utilizes ocular imaging biomarkers to provide insights into systemic diseases. Advances in diagnostic and imaging technologies including electroretinography, optical coherence tomography (OCT), confocal scanning laser ophthalmoscopy, fluorescence lifetime imaging ophthalmoscopy, and OCT angiography have revolutionized the ability to understand systemic diseases and even detect them earlier than clinical manifestations for earlier intervention. With the advent of increasingly large ophthalmic imaging datasets, machine learning models can be integrated into these ocular imaging biomarkers to provide further insights and prognostic predictions of neurodegenerative disease. In this manuscript, we review the use of ophthalmic imaging to provide insights into neurodegenerative diseases including Alzheimer Disease, Parkinson Disease, Amyotrophic Lateral Sclerosis, and Huntington Disease. We discuss recent advances in ophthalmic technology including eye-tracking technology and integration of artificial intelligence techniques to further provide insights into these neurodegenerative diseases. Ultimately, oculomics opens the opportunity to detect and monitor systemic diseases at a higher acuity. Thus, earlier detection of systemic diseases may allow for timely intervention for improving the quality of life in patients with neurodegenerative disease.

Advantages of Rho-associated kinases and their inhibitor fasudil for the treatment of neurodegenerative diseases

Ras homolog (Rho)-associated kinases (ROCKs) belong to the serine-threonine kinase family, which plays a pivotal role in regulating the damage, survival, axon guidance, and regeneration of neurons. ROCKs are also involved in the biological effects of immune cells and glial cells, as well as the development of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Previous studies by us and others confirmed that ROCKs inhibitors attenuated the symptoms and progression of experimental models of the abovementioned neurodegenerative diseases by inhibiting neuroinflammation, regulating immune imbalance, repairing the blood-brain barrier, and promoting nerve repair and myelin regeneration. Fasudil, the first ROCKs inhibitor to be used clinically, has a good therapeutic effect on neurodegenerative diseases. Fasudil increases the activity of neural stem cells and mesenchymal stem cells, thus optimizing cell therapy. This review will systematically describe, for the first time, the effects of abnormal activation of ROCKs on T cells, B cells, microglia, astrocytes, oligodendrocytes, and pericytes in neurodegenerative diseases of the central nervous system, summarize the therapeutic potential of fasudil in several experimental models of neurodegenerative diseases, and clarify the possible cellular and molecular mechanisms of ROCKs inhibition. This review also proposes that fasudil is a novel potential treatment, especially in combination with cell-based therapy. Findings from this review add support for further investigation of ROCKs and its inhibitor fasudil for the treatment of neurodegenerative diseases.

RhoA Signaling in Neurodegenerative Diseases

Ras homolog gene family member A (RhoA) is a small GTPase of the Rho family involved in regulating multiple signal transduction pathways that influence a diverse range of cellular functions. RhoA and many of its downstream effector proteins are highly expressed in the nervous system, implying an important role for RhoA signaling in neurons and glial cells. Indeed, emerging evidence points toward a role of aberrant RhoA signaling in neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, and amyotrophic lateral sclerosis. In this review, we summarize the current knowledge of RhoA regulation and downstream cellular functions with an emphasis on the role of RhoA signaling in neurodegenerative diseases and the therapeutic potential of RhoA inhibition in neurodegeneration.

Profilin Isoforms in Health and Disease - All the Same but Different

Profilins are small actin binding proteins, which are structurally conserved throughout evolution. They are probably best known to promote and direct actin polymerization. However, they also participate in numerous cell biological processes beyond the roles typically ascribed to the actin cytoskeleton. Moreover, most complex organisms express several profilin isoforms. Their cellular functions are far from being understood, whereas a growing number of publications indicate that profilin isoforms are involved in the pathogenesis of various diseases. In this review, we will provide an overview of the profilin family and "typical" profilin properties including the control of actin dynamics. We will then discuss the profilin isoforms of higher animals in detail. In terms of cellular functions, we will focus on the role of Profilin 1 (PFN1) and Profilin 2a (PFN2a), which are co-expressed in the central nervous system. Finally, we will discuss recent findings that link PFN1 and PFN2a to neurological diseases, such as amyotrophic lateral sclerosis (ALS), Fragile X syndrome (FXS), Huntington's disease and spinal muscular atrophy (SMA).

Rho-Kinase Inhibitors for the Treatment of Refractory Diabetic Macular Oedema

Diabetic macular oedema (DMO) is one of the leading causes of vision loss associated with diabetic retinopathy (DR). New insights in managing this condition have changed the paradigm in its treatment, with intravitreal injections of antivascular endothelial growth factor (anti-VEGF) having become the standard therapy for DMO worldwide. However, there is no single standard therapy for all patients DMO refractory to anti-VEGF treatment; thus, further investigation is still needed. The key obstacles in developing suitable therapeutics for refractory DMO lie in its complex pathophysiology; therefore, there is an opportunity for further improvements in the progress and applications of new drugs. Previous studies have indicated that Rho-associated kinase (Rho-kinase/ROCK) is an essential molecule in the pathogenesis of DMO. This is why the Rho/ROCK signalling pathway has been proposed as a possible target for new treatments. The present review focuses on the recent progress on the possible role of ROCK and its therapeutic potential in DMO. A systematic literature search was performed, covering the years 1991 to 2021, using the following keywords: "rho-Associated Kinas-es", "Diabetic Retinopathy", "Macular Edema", "Ripasudil", "Fasudil" and "Netarsudil". Better insight into the pathological role of Rho-kinase/ROCK may lead to the development of new strategies for refractory DMO treatment and prevention.

Protein Aggregation Inhibitors as Disease-Modifying Therapies for Polyglutamine Diseases

The polyglutamine (polyQ) diseases are a group of inherited neurodegenerative diseases caused by the abnormal expansion of a CAG trinucleotide repeat that are translated into an expanded polyQ stretch in the disease-causative proteins. The expanded polyQ stretch itself plays a critical disease-causative role in the pathomechanisms underlying polyQ diseases. Notably, the expanded polyQ stretch undergoes a conformational transition from the native monomer into the β-sheet-rich monomer, followed by the formation of soluble oligomers and then insoluble aggregates with amyloid fibrillar structures. The intermediate soluble species including the β-sheet-rich monomer and oligomers exhibit substantial neurotoxicity. Therefore, protein conformation stabilization and aggregation inhibition that target the upstream of the insoluble aggregate formation would be a promising approach toward the development of disease-modifying therapies for polyQ diseases. PolyQ aggregation inhibitors of different chemical categories, such as intrabodies, peptides, and small chemical compounds, have been identified through intensive screening methods. Among them, recent advances in the brain delivery methods of several peptides and the screening of small chemical compounds have brought them closer to clinical utility. Notably, the recent discovery of arginine as a potent conformation stabilizer and aggregation inhibitor of polyQ proteins both in vitro and in vivo have paved way to the clinical trial for the patients with polyQ diseases. Meanwhile, expression reduction of expanded polyQ proteins per se would be another promising approach toward disease modification of polyQ diseases. Gene silencing, especially by antisense oligonucleotides (ASOs), have succeeded in reducing the expression of polyQ proteins in the animal models of various polyQ diseases by targeting the aberrant mRNA with expanded CAG repeats. Of note, some of these ASOs have recently been translated into clinical trials. Here we overview and discuss these recent advances toward the development of disease modifying therapies for polyQ diseases. We envision that combination therapies using aggregation inhibitors and gene silencing would meet the needs of the patients with polyQ diseases and their caregivers in the near future to delay or prevent the onset and progression of these currently intractable diseases.

Rho kinase inhibitor fasudil reduces l-DOPA-induced dyskinesia in a rat model of Parkinson's disease

BACKGROUND AND PURPOSE

Rho kinase (ROCK) activation is involved in neuroinflammatory processes leading to progression of neurodegenerative diseases such as Parkinson's disease. Furthermore, ROCK plays a major role in angiogenesis. Neuroinflammation and angiogenesis are mechanisms involved in developing l-DOPA-induced dyskinesias (LID). However, it is not known whether ROCK plays a role in LID and whether ROCK inhibitors may be useful against LID.

EXPERIMENTAL APPROACH

In rats, we performed short- and long-term dopaminergic lesions using 6-hydroxydopamine and developed a LID model. Effects of dopaminergic lesions and LID on the RhoA/ROCK levels were studied by western blot, real-time PCR analyses and ROCK activity assays in the substantia nigra and striatum. The effects of the ROCK inhibitor fasudil on LID were particularly investigated.

KEY RESULTS

Short-term 6-hydroxydopamine lesions increased nigrostriatal RhoA/ROCK expression, apparently related to the active neuroinflammatory process. However, long-term dopaminergic denervation (completed and stabilized lesions) led to a decrease in RhoA/ROCK levels. Rats with LID showed a significant increase of RhoA and ROCK expression. The development of LID was reduced by the ROCK inhibitor fasudil (10 and 40 mg·kg^-1 ), without interfering with the therapeutic effect of l-DOPA. Interestingly, treatment of 40 mg·kg^-1 of fasudil also induced a significant reduction of dyskinesia in rats with previously established LID.

CONCLUSION AND IMPLICATIONS

The present results suggest that ROCK is involved in the pathophysiology of LID and that ROCK inhibitors such as fasudil may be a novel target for preventing or treating LID. Furthermore, previous studies have revealed neuroprotective effects of ROCK inhibitors.

Protein kinase inhibitors for amyotrophic lateral sclerosis therapy

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that causes the progressive loss of motoneurons and, unfortunately, there is no effective treatment for this disease. Interconnecting multiple pathological mechanisms are involved in the neuropathology of this disease, including abnormal aggregation of proteins, neuroinflammation and dysregulation of the ubiquitin proteasome system. Such complex mechanisms, together with the lack of reliable animal models of the disease have hampered the development of drugs for this disease. Protein kinases, a key pharmacological target in several diseases, have been linked to ALS as they play a central role in the pathology of many diseases. Therefore several inhibitors are being currently trailed for clinical proof of concept in ALS patients. In this review, we examine the recent literature on protein kinase inhibitors currently in pharmaceutical development for this diseaseas future therapy for AS together with their involvement in the pathobiology of ALS. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Neuroblastoma-targeted nanoparticles and novel nanotechnology-based treatment methods

Neuroblastoma is a complicated pediatric tumor, originating from the neural crest, which is the most prevalent in adrenal glands, but may rarely be seen in some other tissues as well. Studies are focused on developing new strategies through novel chemo- and immuno-therapeutic drug targets. Different types of oncogenes such as MYCN, tumor suppressor genes such as p53, and some structural genes such as vascular endothelial growth factor are considered as targets for neuroblastoma therapy. The individual expression patterns in NB cells make them appropriate for this purpose. The combined effect of nano-drug delivery systems and specific drug targets will result in lower systemic side effects, prolonged therapeutic effects, and improvements in the pharmacokinetic properties of the drugs. Some of these novel drug delivery systems with a focus on liposomes as carriers are also discussed. In this review, genes and protein products that are beneficial as drug targets in the treatment of neuroblastoma have been discussed.

Preclinical Nanomedicines for Polyglutamine-Based Neurodegenerative Diseases

Polyglutamine (polyQ) diseases, such as Huntington's disease and several types of spinocerebellar ataxias, are dominantly inherited progressive neurodegenerative disorders and characterized by the presence of expanded CAG trinucleotide repeats in the respective disease locus of the patient genomes. Patients with polyQ diseases currently need to rely on symptom-relieving treatments because disease-modifying therapeutic interventions remain scarce. Many disease-modifying therapeutic agents are now under clinical testing for treating polyQ diseases, but their delivery to the brain is often too invasive (e.g., intracranial injection) or inefficient, owing to in vivo degradation and clearance by physiological barriers (e.g., oral and intravenous administration). Nanoparticles provide a feasible solution for improving drug delivery to the brain, as evidenced by an increasing number of preclinical studies that document the efficacy of nanomedicines for polyQ diseases over the past 5-6 years. In this review, we present the pathogenic mechanisms of polyQ diseases, the common animal models of polyQ diseases for evaluating the efficacy of nanomedicines, and the common administration routes for delivering nanoparticles to the brain. Next, we summarize the recent preclinical applications of nanomedicines for treating polyQ diseases and improving neurological conditions in vivo, placing emphasis on antisense oligonucleotides, small peptide inhibitors, and small molecules as the disease-modifying agents. We conclude with our perspectives of the burgeoning field of "nanomedicines for polyQ diseases", including the use of inorganic nanoparticles and potential drugs as next-generation nanomedicines, development of higher-order animal models of polyQ diseases, and importance of "brain-nano" interactions.

Membrane Fluidity as a New Means to Selectively Target Cancer Cells with Fusogenic Lipid Carriers

Lipid-based carriers such as liposomes represent one of the most advanced classes of drug delivery systems. Their clinical success relies on their composition, similar to that of the cell membrane. Their cellular specificity often relies on a ligand-receptor interaction. Although differences in the physicochemical properties of the cell membrane between tumor and nontumor cells have been reported, they are not systematically used for drug delivery purposes. In this report, a new approach was developed to ensure selective targeting based on physical compatibility between the target and the carrier membranes. By modulating the liposome composition and thus its membrane fluidity, we achieved selective targeting on four cancer cell lines of varying aggressiveness. Furthermore, using membrane-embedded and inner core-encapsulated fluorophores, we assessed the mechanism of this interaction to be based on the fusion of the liposome with the cell membranes. Membrane fluidity is therefore a major parameter to be considered when designing lipid drug carriers as a promising, lower cost alternative to current targeting strategies based on covalent grafting.

Effect of Fasudil on remyelination following cuprizone-induced demyelination

Background

Multiple sclerosis is characterized by demyelination/remyelination, neuroinflammation, and neurodegeneration. Cuprizone (CPZ)‐induced toxic demyelination is an experimental animal model commonly used to study demyelination and remyelination in the central nervous system. Fasudil is one of the most thoroughly studied Rho kinase inhibitors.

Methods

Following CPZ exposure, the degree of demyelination in the brain of male C57BL/6 mice was assessed by Luxol fast blue, Black Gold II, myelin basic protein immunofluorescent staining, and Western blot. The effect of Fasudil on behavioral change was determined using elevated plus maze test and pole test. The possible mechanisms of Fasudil action were examined by immunohistochemistry, flow cytometry, ELISA, and dot blot.

Results

Fasudil improved behavioral abnormalities, inhibited microglia‐mediated neuroinflammation, and promoted astrocyte‐derived nerve growth factor and ciliary neurotrophic factor, which should contribute to protection and regeneration of oligodendrocytes. In addition, Fasudil inhibited the production of myelin oligodendrocyte glycoprotein antibody and the infiltration of peripheral CD4⁺ T cells and CD68⁺ macrophages, which appears to be related to the integrity of the blood‐brain barrier.

Conclusion

These results provide evidence for the therapeutic potential of Fasudil in CPZ‐induced demyelination. However, how Fasudil acts on microglia, astrocytes, and immune cells remains to be further explored.

AQAMAN, a bisamidine-based inhibitor of toxic protein inclusions in neurons, ameliorates cytotoxicity in polyglutamine disease models

Polyglutamine (polyQ) diseases are a group of dominantly inherited neurodegenerative disorders caused by the expansion of an unstable CAG repeat in the coding region of the affected genes. Hallmarks of polyQ diseases include the accumulation of misfolded protein aggregates, leading to neuronal degeneration and cell death. PolyQ diseases are currently incurable, highlighting the urgent need for approaches that inhibit the formation of disaggregate cytotoxic polyQ protein inclusions. Here, we screened for bisamidine-based inhibitors that can inhibit neuronal polyQ protein inclusions. We demonstrated that one inhibitor, AQAMAN, prevents polyQ protein aggregation and promotes de-aggregation of self-assembled polyQ proteins in several models of polyQ diseases. Using immunocytochemistry, we found that AQAMAN significantly reduces polyQ protein aggregation and specifically suppresses polyQ protein-induced cell death. Using a recombinant and purified polyQ protein (thioredoxin-Huntingtin-Q46), we further demonstrated that AQAMAN interferes with polyQ self-assembly, preventing polyQ aggregation, and dissociates preformed polyQ aggregates in a cell-free system. Remarkably, AQAMAN feeding of Drosophila expressing expanded polyQ disease protein suppresses polyQ-induced neurodegeneration in vivo In addition, using inhibitors and activators of the autophagy pathway, we demonstrated that AQAMAN's cytoprotective effect against polyQ toxicity is autophagy-dependent. In summary, we have identified AQAMAN as a potential therapeutic for combating polyQ protein toxicity in polyQ diseases. Our findings further highlight the importance of the autophagy pathway in clearing harmful polyQ proteins.

Retinal dysfunction in a presymptomatic patient with Huntington's disease

PURPOSE

Huntington's disease (HD) is an autosomal dominant, neurodegenerative disorder characterized by progressive motor dysfunction, cognitive decline, and psychiatric disturbances. Studies have shown retinal abnormalities in patients and mouse models with HD; however, to our knowledge, no prior research papers evaluated retinal structure and function in a presymptomatic patient with HD. The aim of this report is to present a case of retinal dysfunction in a presymptomatic patient with HD.

METHODS

We investigated retinal structure and function in a 25-year-old male who tested positive for the gene that causes HD, but did not have any symptoms normally associated with HD. Vision and ocular testing included a comprehensive dilated ophthalmic examination, 24-2 full-threshold Humphrey visual field, spectral-domain optical coherence tomography (SD-OCT), fundus photography, full-field electroretinogram (ERG), and multifocal electroretinogram (mfERG).

RESULTS

Visual electrophysiology testing showed rod and cone functional anomalies in both eyes. Full-field ERG amplitudes were subnormal in both eyes for the dark-adapted (DA) 0.01 ERG, DA 3 ERG, DA 3 oscillatory potentials (OPs), DA 10 ERG, light-adapted (LA) 3 ERG, and LA 30 Hz flicker, but peak times for the six standard ERG responses were not significantly different from normals. mfERGs revealed functional anomalies of the central retina with attenuated P1 amplitudes for five of the six concentric rings in the right eye and all six rings in the left eye. mfERG P1 peak times were normal at all eccentricities. Dilated fundus examination, SD-OCT, and fundus photography were unremarkable in both eyes. The visual field was normal in the right eye, but there was a mild paracentral field defect in the left eye.

CONCLUSIONS

Our results illustrate that the ERG and mfERG detected early retinal dysfunction in a presymptomatic patient with HD consistent with electroretinogram findings in animal models of HD. However, our report was limited to one patient and additional studies are needed to verify whether the ERG and/or mfERG can uncover neural dysfunction before motor, behavioral, and cognitive abnormalities are discernible in patients with HD.

Profilin reduces aggregation and phase separation of huntingtin N-terminal fragments by preferentially binding to soluble monomers and oligomers

Huntingtin N-terminal fragments (Htt-NTFs) with expanded polyglutamine tracts form a range of neurotoxic aggregates that are associated with Huntington's disease. Here, we show that aggregation of Htt-NTFs, irrespective of polyglutamine length, yields at least three phases (designated M, S, and F) that are delineated by sharp concentration thresholds and distinct aggregate sizes and morphologies. We found that monomers and oligomers make up the soluble M phase, ∼25-nm spheres dominate in the soluble S phase, and long, linear fibrils make up the insoluble F phase. Previous studies showed that profilin, an abundant cellular protein, reduces Htt-NTF aggregation and toxicity in cells. We confirm that profilin achieves its cellular effects through direct binding to the C-terminal proline-rich region of Htt-NTFs. We show that profilin preferentially binds to Htt-NTF M-phase species and destabilizes aggregation and phase separation by shifting the concentration boundaries for phase separation to higher values through a process known as polyphasic linkage. Our experiments, aided by coarse-grained computer simulations and theoretical analysis, suggest that preferential binding of profilin to the M-phase species of Htt-NTFs is enhanced through a combination of specific interactions between profilin and polyproline segments and auxiliary interactions between profilin and polyglutamine tracts. Polyphasic linkage may be a general strategy that cells utilize to regulate phase behavior of aggregation-prone proteins. Accordingly, detailed knowledge of phase behavior and an understanding of how ligands modulate phase boundaries may pave the way for developing new therapeutics against a variety of aggregation-prone proteins.

Retinal single-layer analysis with optical coherence tomography shows inner retinal layer thinning in Huntington's disease as a potential biomarker

PURPOSE

There have been ongoing clinical trials of therapeutic agents in Huntington's disease (HD) which requires development of reliable biomarkers of disease progression. There have been studies in the literature with conflicting results on the involvement of retina in HD, and up to date there is not a study evaluating the single retinal layers in HD. We aimed to evaluate the specific retinal changes in HD and their usability as potential disease progression markers.

METHODS

This cross-sectional study used spectral-domain optical coherence tomography with automatic segmentation to measure peripapillary retinal nerve fiber layer (pRNFL) thickness and the thickness and volume of retinal layers in foveal scans of 15 patients with HD and 15 age- and sex-matched controls. Genetic testing results, disease duration, HD disease burden scores and Unified HD Rating Scales motor scores were acquired for the patients.

RESULTS

Temporal pRNFL, macular RNFL (mRNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer and outer plexiform layer thicknesses and IPL, retinal pigment epithelium and outer macular volume were found lower in HD compared to controls, while outer nuclear layer and outer retinal layer thickness were increased (p < 0.05). We found significant correlations between inner retinal layer thicknesses, most significantly with mRNFL and GCL and disease progression markers.

CONCLUSION

The outcomes of this study points out that retinal layers, most significantly mRNFL and GCL, are strongly correlated with the disease progression in HD and could serve as useful biomarkers for disease progression.

Vision in laboratory rodents-Tools to measure it and implications for behavioral research

Mice and rats are nocturnal mammals and their vision is specialized for detection of motion and contrast in dim light conditions. These species possess a large proportion of UV-sensitive cones in their retinas and the majority of their optic nerve axons target superior colliculus rather than visual cortex. Therefore, it was a widely held belief that laboratory rodents hardly utilize vision during day-time behavior. This dogma is being questioned as accumulating evidence suggests that laboratory rodents are able to perform complex visual functions, such as perceiving subjective contours, and that declined vision may affect their performance in many behavioral tasks. For instance, genetic engineering may have unexpected consequences on vision as mouse models of Alzheimer's and Huntington's diseases have declined visual function. Rodent vision can be tested in numerous ways using operant training or reflex-based behavioral tasks, or alternatively using electrophysiological recordings. In this article, we will first provide a summary of visual system and explain its characteristics unique to rodents. Then, we present well-established techniques to test rodent vision, with an emphasis on pattern vision: visual water test, optomotor reflex test, pattern electroretinography and pattern visual evoked potentials. Finally, we highlight the importance of visual phenotyping in rodents. As the number of genetically engineered rodent models and volume of behavioral testing increase simultaneously, the possibility of visual dysfunctions needs to be addressed. Neglect in this matter potentially leads to crude biases in the field of neuroscience and beyond.

Fasudil, a Clinically Used ROCK Inhibitor, Stabilizes Rod Photoreceptor Synapses after Retinal Detachment

Purpose

Retinal detachment disrupts the rod-bipolar synapse in the outer plexiform layer by retraction of rod axons. We showed that breakage is due to RhoA activation whereas inhibition of Rho kinase (ROCK), using Y27632, reduces synaptic damage. We test whether the ROCK inhibitor fasudil, used for other clinical applications, can prevent synaptic injury after detachment.

Methods

Detachments were made in pigs by subretinal injection of balanced salt solution (BSS) or fasudil (1, 10 mM). In some animals, fasudil was injected intravitreally after BSS-induced detachment. After 2 to 4 hours, retinae were fixed for immunocytochemistry and confocal microscopy. Axon retraction was quantified by imaging synaptic vesicle label in the outer nuclear layer. Apoptosis was analyzed using propidium iodide staining. For biochemical analysis by Western blotting, retinal explants, detached from retinal pigmented epithelium, were cultured for 2 hours.

Results

Subretinal injection of fasudil (10 mM) reduced retraction of rod spherules by 51.3% compared to control detachments (n = 3 pigs, P = 0.002). Intravitreal injection of 10 mM fasudil, a more clinically feasible route of administration, also reduced retraction (28.7%, n = 5, P < 0.05). Controls had no photoreceptor degeneration at 2 hours, but by 4 hours apoptosis was evident. Fasudil 10 mM reduced pyknotic nuclei by 55.7% (n = 4, P < 0.001). Phosphorylation of cofilin and myosin light chain, downstream effectors of ROCK, was decreased with 30 μM fasudil (n = 8–10 explants, P < 0.05).

Conclusions

Inhibition of ROCK signaling with fasudil reduced photoreceptor degeneration and preserved the rod-bipolar synapse after retinal detachment.

Translational Relevance

These results support the possibility, previously tested with Y27632, that ROCK inhibition may attenuate synaptic damage in iatrogenic detachments.

Rho Kinase Inhibition with Fasudil in the SOD1G93A Mouse Model of Amyotrophic Lateral Sclerosis-Symptomatic Treatment Potential after Disease Onset

Despite an improved understanding of the genetic background and the pathomechanisms of amyotrophic lateral sclerosis (ALS) no novel disease-modifying therapies have been successfully implemented in clinical routine. Riluzole still remains the only clinically approved substance in human ALS treatment with limited efficacy. We have previously identified pharmacological rho kinase (ROCK) inhibitors as orally applicable substances in SOD1.G93A transgenic ALS mice (SOD1^G93A), which are able to extend survival time and improve motor function after presymptomatic treatment. Here, we have evaluated the therapeutic effect of the orally administered ROCK inhibitor Fasudil starting at a symptomatic disease stage, more realistically reflecting the clinical situation. Oral Fasudil treatment was initiated at a symptomatic stage at 80 days of life (d80) with 30 or 100 mg/kg body weight in both female and male mice. While baseline neurological scoring and survival were not influenced, Fasudil significantly improved motor behavior in male mice. Spinal cord pathology of motoneurons (MN) and infiltrating microglial cells (MG) at disease end-stage were not significantly modified. Although treatment after symptom onset was less potent than treatment in asymptomatic animals, our study shows the therapeutic benefits of this well-tolerated substance, which is already in clinical use for other indications.

Nanoparticulate strategies for the treatment of polyglutamine diseases by halting the protein aggregation process

Polyglutamine (polyQ) diseases are a class of neurodegenerative disorders that cause cellular dysfunction and, eventually, neuronal death in specific regions of the brain. Neurodegeneration is linked to the misfolding and aggregation of expanded polyQ-containing proteins, and their inhibition is one of major therapeutic strategies used commonly. However, successful treatment has been limited to date because of the intrinsic properties of therapeutic agents (poor water solubility, low bioavailability, poor pharmacokinetic properties), and difficulty in crossing physiological barriers, including the blood-brain barrier (BBB). In order to solve these problems, nanoparticulate systems with dimensions of 1-1000 nm able to incorporate small and macromolecules with therapeutic value, to protect and deliver them directly to the brain, have recently been developed, but their use for targeting polyQ disease-mediated protein misfolding and aggregation remains scarce. This review provides an update of the polyQ protein aggregation process and the development of therapeutic strategies for halting it. The main features that a nanoparticulate system should possess in order to enhance brain delivery are discussed, as well as the different types of materials utilized to produce them. The final part of this review focuses on the potential application of nanoparticulate system strategies to improve the specific and efficient delivery of therapeutic agents to the brain for the treatment of polyQ diseases.

Discovery of Therapeutic Approaches for Polyglutamine Diseases: A Summary of Recent Efforts

Polyglutamine (PolyQ) diseases are a group of neurodegenerative disorders caused by the expansion of cytosine-adenine-guanine (CAG) trinucleotide repeats in the coding region of specific genes. This leads to the production of pathogenic proteins containing critically expanded tracts of glutamines. Although polyQ diseases are individually rare, the fact that these nine diseases are irreversibly progressive over 10 to 30 years, severely impairing and ultimately fatal, usually implicating the full-time patient support by a caregiver for long time periods, makes their economic and social impact quite significant. This has led several researchers worldwide to investigate the pathogenic mechanism(s) and therapeutic strategies for polyQ diseases. Although research in the field has grown notably in the last decades, we are still far from having an effective treatment to offer patients, and the decision of which compounds should be translated to the clinics may be very challenging. In this review, we provide a comprehensive and critical overview of the most recent drug discovery efforts in the field of polyQ diseases, including the most relevant findings emerging from two different types of approaches-hypothesis-based candidate molecule testing and hypothesis-free unbiased drug screenings. We hereby summarize and reflect on the preclinical studies as well as all the clinical trials performed to date, aiming to provide a useful framework for increasingly successful future drug discovery and development efforts.

Coupling of D2R Short but not D2R Long receptor isoform to the Rho/ROCK signaling pathway renders striatal neurons vulnerable to mutant huntingtin

Huntington's disease, an inherited neurodegenerative disorder, results from abnormal polyglutamine extension in the N-terminal region of the huntingtin protein. This mutation causes preferential degeneration of striatal projection neurons. We previously demonstrated, in vitro, that dopaminergic D2 receptor stimulation acted in synergy with expanded huntingtin to increase aggregates formation and striatal death through activation of the Rho/ROCK signaling pathway. In vivo, in a lentiviral-mediated model of expanded huntingtin expression in the rat striatum, we found that the D2 antagonist haloperidol protects striatal neurons against expanded huntingtin-mediated toxicity. Two variant transcripts are generated by alternative splicing of the of D2 receptor gene, the D2R-Long and the D2R-Short, which are thought to play different functional roles. We show herein that overexpression of D2R-Short, but not D2R-Long in cell lines is associated with activation of the RhoA/ROCK signaling pathway. In striatal neurons in culture, the selective D2 agonist Quinpirole triggers phosphorylation of cofilin, a downstream effector of ROCK, which is abrogated by siRNAs that knockdown both D2R-Long and D2R-Short, but not by siRNAs targeting D2R-Long alone. Aggregate formation and neuronal death induced by expanded huntingtin, were potentiated by Quinpirole. This D2 agonist-mediated effect was selectively inhibited by the siRNA targeting both D2R-Long and D2R-Short but not D2R-Long alone. Our data provide evidence for a specific coupling of D2R-Short to the RhoA/ROCK/cofilin pathway, and its involvement in striatal vulnerability to expanded huntingtin. A new route for targeting Rho-ROCK signaling in Huntington's disease is unraveled with our findings.

Umbelliferone reverses depression-like behavior in chronic unpredictable mild stress-induced rats by attenuating neuronal apoptosis via regulating ROCK/Akt pathway

There is increasing evidence that major depressive disorder (MDD) is also a progressive neurodegeneration disorder and neuronal damage is the major pathology of MDD. Umbelliferone, a coumarin derivative, was found in a range of plants with proved anti-oxidative, anti-inflammatory and neuroprotective effects. The primary purpose of this investigation was to evaluate whether umbelliferone could confer an antidepressant-like effect on the depressive model in rats developed by chronic unpredictable mild stress (CUMS) and explore the possible mechanism involved in its neuroprotective effects. We found that treatments with umbelliferone (15mg/kg, 30mg/kg) significantly ameliorated CUMS-induced depressive-like behaviors, such as decreased sucrose consumption, reduced locomotor activity and prolonged immobility time. Rats under CUMS stimulation treated with umbelliferone (15mg/kg, 30mg/kg) showed reduced neuronal apoptosis, as well as inhibited inflammatory cytokines levels by down-regulating Rho-associated protein kinase (ROCK) signaling and up-regulating protein kinase B (Akt) signaling. In conclusion, umbelliferone showed neuroprotective effects on CUMS-induced model of depression, which was associated with the inhibition of neuronal apoptosis modulated by ROCK/Akt pathway.

HIV-1 Tat Regulates Occludin and Aβ Transfer Receptor Expression in Brain Endothelial Cells via Rho/ROCK Signaling Pathway

HIV-1 transactivator protein (Tat) has been shown to play an important role in HIV-associated neurocognitive disorders. The aim of the present study was to evaluate the relationship between occludin and amyloid-beta (Aβ) transfer receptors in human cerebral microvascular endothelial cells (hCMEC/D3) in the context of HIV-1-related pathology. The protein expressions of occludin, receptor for advanced glycation end products (RAGE), and low-density lipoprotein receptor-related protein 1 (LRP1) in hCMEC/D3 cells were examined using western blotting and immunofluorescent staining. The mRNA levels of occludin, RAGE, and LRP1 were measured using quantitative real-time polymerase chain reaction. HIV-1 Tat at 1 µg/mL and the Rho inhibitor hydroxyfasudil (HF) at 30 µmol/L, with 24 h exposure, had no significant effect on hCMEC/D3 cell viability. Treatment with HIV-1 Tat protein decreased mRNA and protein levels of occludin and LRP1 and upregulated the expression of RAGE; however, these effects were attenuated by HF. These data suggest that the Rho/ROCK signaling pathway is involved in HIV-1 Tat-mediated changes in occludin, RAGE, and LRP1 in hCMEC/D3 cells. HF may have a beneficial influence by protecting the integrity of the blood-brain barrier and the expression of Aβ transfer receptors.

Protective Effect of Total Flavones from Hippophae rhamnoides L. against Visible Light-Induced Retinal Degeneration in Pigmented Rabbits

Sea buckthorn (Hippophae rhamnoides L.) flavones have been used as candidate functional food ingredients because of their bioactivities, such as treating cardiovascular disorders, lowering plasma cholesterol level, and regulating immune function. However, the protective effects of sea buckthorn flavones against retinal degeneration remain unclear to date. This study investigated the protective effects of total flavones from H. rhamnoides (TFH) against visible light-induced retinal damage and explored the related mechanisms in pigmented rabbits. Rabbits were treated with TFH (250 and 500 mg/kg) for 2 weeks pre-illumination and 1 week post-illumination until sacrifice. Retinal function was quantified by performing electroretinography 1 day before and 1, 3, and 7 days after light exposure (18000 lx for 2 h). Retinal degeneration was evaluated by measuring the thickness of the outer nuclear layer (ONL) and performing the TUNEL assay 7 days after light exposure. Enzyme-linked immunosorbent assay, Western blot analysis, and immunohistochemistry were used to explore the antioxidant, anti-inflammatory, and anti-apoptotic mechanisms of TFH during visible light-induced retinal degeneration. Light exposure produced a degenerative effect primarily on the ONL, inner nuclear layer (INL), and ganglion cell layer (GCL). TFH significantly attenuated the destruction of electroretinograms caused by light damage, maintained ONL thickness, and decreased the number of TUNEL-positive cells in the INL and GCL. TFH ameliorated the retinal oxidative stress (GSH-Px, CAT, T-AOC, and MDA), inflammation (IL-1β and IL-6), angiogenesis (VEGF), and apoptosis (Bax, Bcl2, and caspase-3) induced by light exposure. Therefore, TFH exhibited protective effects against light-induced retinal degeneration by increasing the antioxidant defense mechanisms, suppressing pro-inflammatory and angiogenic cytokines, and inhibiting retinal cell apoptosis.

Retinoprotective Effects of Bilberry Anthocyanins via Antioxidant, Anti-Inflammatory, and Anti-Apoptotic Mechanisms in a Visible Light-Induced Retinal Degeneration Model in Pigmented Rabbits

Excessive visible light exposure can induce damage to retinal cells and contribute to the development or progression of age-related macular degeneration. In this study we created a model of phototoxicity in pigmented rabbits. Furthermore, we investigated the protective effect of bilberry anthocyanin extract (BAE, Table A1) and explored the possible mechanisms of action in this model. The model of light-induced retinal damage was established by the pigmented rabbits exposed to light at 18,000 lx for 2 h, and they were sacrificed on day 7. After administration of BAE at dosages of 250 and 500 mg/kg/day, retinal dysfunction was significantly inhibited in terms of electroretinograms, and the decreased thicknesses of retinal outer nuclear layer and lengths of the outer segments of the photoreceptor cells were suppressed in rabbits with retinal degeneration. BAE attenuated the changes caused by light to certain apoptotic proteins (Bax, Bcl-2, and caspase-3). The extract increased the levels of superoxide dismutase, glutathione peroxidase, and catalase, as well as the total antioxidant capacity, but decreased the malondialdehyde level in the retinal cells. BAE inhibited the light-induced elevation in the levels of proinflammatory cytokines and angiogenic parameters (IL-1β and VEGF). Results showed that visible light-induced retinal degeneration model in pigmented rabbits was successfully established and BAE exhibited protective effects by increasing the antioxidant defense mechanisms, suppressing lipid peroxidation and proinflammatory cytokines, and inhibiting retinal cells apoptosis.

The role of the Rho/ROCK signaling pathway in inhibiting axonal regeneration in the central nervous system

The Rho/Rho-associated coiled-coil containing protein kinase (Rho/ROCK) pathway is a major signaling pathway in the central nervous system, transducing inhibitory signals to block regeneration. After central nervous system damage, the main cause of impaired regeneration is the presence of factors that strongly inhibit regeneration in the surrounding microenvironment. These factors signal through the Rho/ROCK signaling pathway to inhibit regeneration. Therefore, a thorough understanding of the Rho/ROCK signaling pathway is crucial for advancing studies on regeneration and repair of the injured central nervous system.

[Ophthalmic manifestations of Huntington's disease]

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by a mutation in the huntingtin gene. The whole nervous system, including visual analyzer, is involved in the pathogenesis of the disease. Various ocular sings can be found in both preclinical and clinical stages of HD. Specific retinal damage, namely, abnormal proteins formation, photoreceptor degeneration and retinal remodeling, has been studied in animal models. Functional changes in occipital lobe activity and its atrophy as well as degeneration of visual pathways can already be present in the early stages of the disease. Oculomotor symptoms of HD include disturbed visual fixation, slower tracking eye movements and saccades, and suppressed vestibulo-ocular reflex. Visual perceptual disorders, such as visuospatial difficulties, problems of stimulus identification and motion perception, along with decreased contrast sensitivity, have also been described. The possibility of using certain ophthalmic parameters as biomarkers of HD is being discussed.

Optical coherence tomography findings in Huntington's disease: a potential biomarker of disease progression

Previous reports of ocular abnormalities in Huntington's disease (HD) have detailed eye movement disorders. The objective of this case-control study was to investigate optic nerve and macular morphology in HD using optical coherence tomography (OCT). A total of 26 HD patients and 29 controls underwent a thorough ophthalmic examination including spectral domain OCT scans of the macula and peripapillary retinal nerve fibre layer (RNFL). Genetic testing results, disease duration, HD disease burden scores and Unified HD Rating Scale motor scores were acquired for HD patients. Temporal RNFL thickness was significantly reduced in the HD group (62.3 vs. 69.8 μm, p = 0.005), and there was a significant negative correlation between temporal RNFL thickness and disease duration (R (2) = -0.51, p = 0.04). Average peripapillary RNFL thickness was not significantly different between the HD and control groups. There was a significant negative correlation between macular volume and disease duration (R (2) = -0.71, p = 0.002), and motor scores (R (2) = -0.56, p = 0.01). Colour vision was significantly poorer in the HD group. Temporal RNFL is preferentially thinned in HD patients, possibly implicating mitochondrial dysfunction as the temporal RNFL is reduced in the patients with some mitochondrial disorders, including Leber's hereditary optic neuropathy. The correlation between the decrease in macular volume and temporal RNFL, and increasing disease severity suggests that OCT may be a useful biomarker for disease progression in HD. Larger, longitudinal studies are required.

Protection of photoreceptors by intravitreal injection of the Y-27632 Rho-associated protein kinase inhibitor in Royal College of Surgeons rats

Retinitis pigmentosa (RP) is an inherited retinal disease, which is characteristic by degeneration of the rod and cone photoreceptors. The present study aimed to assess the protective effects on photoreceptors of intravitreal injection of Y‑27632, a specific inhibitor of Rho‑associated protein kinase (ROCK), in a Royal College of Surgeons (RCS) rat model. Different concentrations of Y‑27632 (1‑50 mM) were administered by intravitreal injection into the RCS rats. The effects of Y‑27632 were recorded using electroretinography (ERG), measuring the thicknesses of the retinal outer nuclear layer (ONL) and examination of apoptotic markers using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and western blot analysis. Treatment of the eyes with Y27632 at 10 or 50 mM, led to a 30% increase in a‑ and b‑wave amplitudes in ERG, and an increase in ONL thickness by 10%, compared with the 1 mM Y‑27632‑treated and vehicle (phosphate‑buffered saline; PBS)‑treated groups. In addition, eyes treated with 10 mM Y27632 exhibited a 90% decrease in TUNEL‑positive cells, accompanied by decreased protein expression levels of active caspase 3 and Bax by 50%, and a 90% increase in the ratio of Bcl‑2/Bax, compared with the PBS‑treated groups. These data suggested that Y‑27632 protected retinal function by inhibiting the apoptosis of photoreceptor cells in the RCS rat model. The present study demonstrated for the first time, to the best of our knowledge, to report the use of Y‑27632 for protection against RP in an RCS rat model. Y‑27632 may be a potential candidate for the treatment of human RP.

Chatting with the neighbors: crosstalk between Rho-kinase (ROCK) and other signaling pathways for treatment of neurological disorders

ROCK inhibition has been largely applied as a strategy to treat neurodegenerative diseases (NDDs) and promising results have been obtained in the recent years. However, the underlying molecular and cellular mechanisms are not fully understood and different models have been proposed for neurodegenerative disorders. Here, we aim to review the current knowledge obtained for NDDs identifying common mechanisms as well as disease-specific models. In addition to the role of ROCK in different cell types such as neurons and microglia, we focus on the molecular signaling-pathways which mediate the beneficial effects of ROCK. Besides canonical ROCK signaling, modulation of neighboring pathways by non-canonical ROCK-crosstalk is a recurrent pattern in many NDD-model systems and has been suggested to mediate beneficial effects of ROCK-inhibition.

Early retinal function deficit without prominent morphological changes in the R6/2 mouse model of Huntington's disease

Huntington’s disease (HD) is an inherited neurodegenerative disorder that primarily affects the medium-size GABAergic neurons of striatum. The R6/2 mouse line is one of the most widely used animal models of HD. Previously the hallmarks of HD-related pathology have been detected in photoreceptors and interneurons of R6/2 mouse retina. Here we aimed to explore the survival of retinal ganglion cells (RGCs) and functional integrity of distinct retinal cell populations in R6/2 mice. The pattern electroretinography (PERG) signal was lost at the age of 8 weeks in R6/2 mice in contrast to the situation in wild-type (WT) littermates. This defect may be attributable to a major reduction in photopic ERG responses in R6/2 mice which was more evident in b- than a-wave amplitudes. At the age of 4 weeks R6/2 mice had predominantly the soluble form of mutant huntingtin protein (mHtt) in the RGC layer cells, whereas the aggregated form of mHtt was found in the majority of those cells from the 12-week-old R6/2 mice and onwards. Retinal astrocytes did not contain mHtt deposits. The total numbers of RGC layer cells, retinal astrocytes as well as optic nerve axons did not differ between 18-week-old R6/2 mice and their WT controls. Our data indicate that mHtt deposition does not cause RGC degeneration or retinal astrocyte loss in R6/2 mice even at a late stage of HD-related pathology. However, due to functional deficits in the rod- and cone-pathways, the R6/2 mice suffer progressive deficits in visual capabilities starting as early as 4 weeks; at 8 weeks there is severe impairment. This should be taken into account in any behavioral testing conducted in R6/2 mice.

Upregulation of Nogo receptor expression induces apoptosis of retinal ganglion cells in diabetic rats

The Nogo receptor is an essential factor for neuronal apoptosis, but the changes in Nogo receptor expression in the retina and the effects of the Nogo receptor on retinal ganglion cell apoptosis in diabetes mellitus remain unclear. We found that Nogo receptor expression was mainly visible in retinal ganglion cells of a rat model of diabetes mellitus induced by streptozotocin. At 12 weeks after onset of diabetes mellitus, Nogo receptor and Rho kinase expression significantly increased in the retina, and retinal ganglion cell apoptosis was apparent. When RNA interference was used to suppress Nogo receptor expression in rat retina, Rho kinase expression was obviously inhibited, and retinal ganglion cell apoptosis was evidently reduced in rats with diabetes mellitus. These results indicate that upregulation of Nogo receptor expression is an important mechanism of retinal ganglion cell apoptosis in rats with diabetes mellitus.

Experimental models for identifying modifiers of polyglutamine-induced aggregation and neurodegeneration

Huntington's disease (HD) typifies a class of inherited neurodegenerative disorders in which a CAG expansion in a single gene leads to an extended polyglutamine tract and misfolding of the expressed protein, driving cumulative neural dysfunction and degeneration. HD is invariably fatal with symptoms that include progressive neuropsychiatric and cognitive impairments, and eventual motor disability. No curative therapies yet exist for HD and related polyglutamine diseases; therefore, substantial efforts have been made in the drug discovery field to identify potential drug and drug target candidates for disease-modifying treatment. In this context, we review here a range of early-stage screening approaches based in in vitro, cellular, and invertebrate models to identify pharmacological and genetic modifiers of polyglutamine aggregation and induced neurodegeneration. In addition, emerging technologies, including high-content analysis, three-dimensional culture models, and induced pluripotent stem cells are increasingly being incorporated into drug discovery screening pipelines for protein misfolding disorders. Together, these diverse screening strategies are generating novel and exciting new probes for understanding the disease process and for furthering development of therapeutic candidates for eventual testing in the clinical setting.