Shunmoogum A. Patten

Pharmacological reduction of ER stress protects against TDP-43 neuronal toxicity in vivo.

C. elegans and D. rerio expressing mutant TAR DNA Binding Protein 43 (TDP-43) are powerful in vivo animal models for the genetics and pharmacology of amyotrophic lateral sclerosis (ALS). Using these small-animal models of ALS, we previously identified methylene blue (MB) as a potent suppressor of TDP-43 toxicity. Consequently here we investigated how MB might exert its neuroprotective properties and found that it acts through reduction of the endoplasmic reticulum (ER) stress response. We tested other compounds known to be active in the ER unfolded protein response in worms and zebrafish expressing mutant human TDP-43 (mTDP-43). We identified three compounds: salubrinal, guanabenz and a new structurally related compound phenazine, which also reduced paralysis, neurodegeneration and oxidative stress in our mTDP-43 models. Using C. elegans genetics, we showed that all four compounds act as potent suppressors of mTDP-43 toxicity through reduction of the ER stress response. Interestingly, these compounds operate through different branches of the ER unfolded protein pathway to achieve a common neuroprotective action. Our results indicate that protein-folding homeostasis in the ER is an important target for therapeutic development in ALS and other TDP-43-related neurodegenerative diseases.

Methylene blue protects against TDP-43 and FUS neuronal toxicity in C. elegans and D. rerio.

The DNA/RNA-binding proteins TDP-43 and FUS are found in protein aggregates in a growing number of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and related dementia, but little is known about the neurotoxic mechanisms. We have generated Caenorhabditis elegans and zebrafish animal models expressing mutant human TDP-43 (A315T or G348C) or FUS (S57Δ or R521H) that reflect certain aspects of ALS including motor neuron degeneration, axonal deficits, and progressive paralysis. To explore the potential of our humanized transgenic C. elegans and zebrafish in identifying chemical suppressors of mutant TDP-43 and FUS neuronal toxicity, we tested three compounds with potential neuroprotective properties: lithium chloride, methylene blue and riluzole. We identified methylene blue as a potent suppressor of TDP-43 and FUS toxicity in both our models. Our results indicate that methylene blue can rescue toxic phenotypes associated with mutant TDP-43 and FUS including neuronal dysfunction and oxidative stress.

Role of Chd7 in Zebrafish: A Model for CHARGE Syndrome

CHARGE syndrome is caused by mutations in the CHD7 gene. Several organ systems including the retina, cranial nerves, inner ear and heart are affected in CHARGE syndrome. However, the mechanistic link between mutations in CHD7 and many of the organ systems dysfunction remains elusive. Here, we show that Chd7 is required for the organization of the neural retina in zebrafish. We observe an abnormal expression or a complete absence of molecular markers for the retinal ganglion cells and photoreceptors, indicating that Chd7 regulates the differentiation of retinal cells and plays an essential role in retinal cell development. In addition, zebrafish with reduced Chd7 display an abnormal organization and clustering of cranial motor neurons. We also note a pronounced reduction in the facial branchiomotor neurons and the vagal motor neurons display aberrant positioning. Further, these fish exhibit a severe loss of the facial nerves. Knock-down of Chd7 results in a curvature of the long body axis and these fish develop irregular shaped vertebrae and have a reduction in bone mineralization. Chd7 knockdown also results in a loss of proper segment polarity illustrated by flawed efnb2a and ttna expression, which is associated with later vascular segmentation defects. These critical roles for Chd7 in retinal and vertebral development were previously unrecognized and our results provide new insights into the role of Chd7 during development and in CHARGE syndrome pathogenesis.

Functional variants of POC5 identified in patients with idiopathic scoliosis

Idiopathic scoliosis (IS) is a spine deformity that affects approximately 3% of the population. The underlying causes of IS are not well understood, although there is clear evidence that there is a genetic component to the disease. Genetic mapping studies suggest high genetic heterogeneity, but no IS disease-causing gene has yet been identified. Here, genetic linkage analyses combined with exome sequencing identified a rare missense variant (p.A446T) in the centriolar protein gene POC5 that cosegregated with the disease in a large family with multiple members affected with IS. Subsequently, the p.A446T variant was found in an additional set of families with IS and in an additional 3 cases of IS. Moreover, POC5 variant p.A455P was present and linked to IS in one family and another rare POC5 variant (p.A429V) was identified in an additional 5 cases of IS. In a zebrafish model, expression of any of the 3 human IS-associated POC5 variant mRNAs resulted in spine deformity, without affecting other skeletal structures. Together, these findings indicate that mutations in the POC5 gene contribute to the occurrence of IS.

Fishing for causes and cures of motor neuron disorders.

Motor neuron disorders (MNDs) are a clinically heterogeneous group of neurological diseases characterized by progressive degeneration of motor neurons, and share some common pathological pathways. Despite remarkable advances in our understanding of these diseases, no curative treatment for MNDs exists. To better understand the pathogenesis of MNDs and to help develop new treatments, the establishment of animal models that can be studied efficiently and thoroughly is paramount. The zebrafish (Danio rerio) is increasingly becoming a valuable model for studying human diseases and in screening for potential therapeutics. In this Review, we highlight recent progress in using zebrafish to study the pathology of the most common MNDs: spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS) and hereditary spastic paraplegia (HSP). These studies indicate the power of zebrafish as a model to study the consequences of disease-related genes, because zebrafish homologues of human genes have conserved functions with respect to the aetiology of MNDs. Zebrafish also complement other animal models for the study of pathological mechanisms of MNDs and are particularly advantageous for the screening of compounds with therapeutic potential. We present an overview of their potential usefulness in MND drug discovery, which is just beginning and holds much promise for future therapeutic development.

Microarray expression profiling identifies genes with altered expression in Adolescent Idiopathic Scoliosis.

PurposeAdolescent Idiopathic Scoliosis (AIS) is considered a complex genetic disease, in which malfunctioning or dysregulation of one or more genes has been proposed to be responsible for the expressed phenotype. However, to date, no disease causing genes has been identified and the pathogenesis of AIS remains unknown. The aim of this study is, therefore, to identify specific molecules with differing expression patterns in AIS compared to healthy individuals.MethodsMicroarray analysis and quantitative RT-PCR have examined differences in the gene transcription profile between primary osteoblasts derived from spinal vertebrae of AIS patients and those of healthy individuals.ResultsThere are 145 genes differentially expressed in AIS osteoblasts. A drastic and significant change has been noted particularly in the expression levels of Homeobox genes (HOXB8, HOXB7, HOXA13, HOXA10), ZIC2, FAM101A, COMP and PITX1 in AIS compared to controls. Clustering analysis revealed the interaction of these genes in biological pathways crucial for bone development, in particular in the differentiation of skeletal elements and structural integrity of the vertebrae.ConclusionsThis study reports on the expression of molecules that have not been described previously in AIS. We also provide for the first time gene interaction pathways in AIS pathogenesis. These genes are involved in various bone regulatory and developmental pathways and many of them can be grouped into clusters to participate in a particular biological pathway. Further studies can be built on our findings to further elucidate the association between different biological pathways and the pathogenesis of AIS.

Could genetic determinants of inner ear anomalies be a factor for the development of idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a condition characterized by a three-dimensional structural deformity of the spine. It is the most common type of spine deformity occurring in children aged 10 to maturity. Although the etiology of AIS still remains unknown, the role of genetic factors in the development of idiopathic scoliosis is widely accepted. However, to date no causative genes of AIS have been identified. Recently, the semicircular canals, which are part of the inner ear, were found to be morphologically abnormal in idiopathic scoliosis patients. Here we hypothesized that genetic predisposition to inner ear anomalies in AIS patients may be a strong factor in the generation of idiopathic scoliosis. The proposed idea is that gene defects could impair the development of the semicircular canals. A malformation of semicircular canals might affect the transmission of sensory signal about rotational movement of the body to the central nervous system; leading to an alteration in the neuronal circuit of balance. This will in turn affect body posture and results in the initiation of the curvature of the spine. This hypothesis may provide new insights in the understanding of the pathophysiologic mechanisms of idiopathic scoliosis. It can also offer hopes for potential early prediction of scoliosis.

Neuroleptics as therapeutic compounds stabilizing neuromuscular transmission in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing, fatal disorder with no effective treatment. We used simple genetic models of ALS to screen phenotypically for potential therapeutic compounds. We screened libraries of compounds in C. elegans, validated hits in zebrafish, and tested the most potent molecule in mice and in a small clinical trial. We identified a class of neuroleptics that restored motility in C. elegans and in zebrafish, and the most potent was pimozide, which blocked T-type Ca2+ channels in these simple models and stabilized neuromuscular transmission in zebrafish and enhanced it in mice. Finally, a short randomized controlled trial of sporadic ALS subjects demonstrated stabilization of motility and evidence of target engagement at the neuromuscular junction. Simple genetic models are, thus, useful in identifying promising compounds for the treatment of ALS, such as neuroleptics, which may stabilize neuromuscular transmission and prolong survival in this disease.

Simple animal models for amyotrophic lateral sclerosis drug discovery.

ABSTRACT Introduction: Simple animal models have enabled great progress in uncovering the disease mechanisms of amyotrophic lateral sclerosis (ALS) and are helping in the selection of therapeutic compounds through chemical genetic approaches. Areas covered: Within this article, the authors provide a concise overview of simple model organisms, C. elegans, Drosophila and zebrafish, which have been employed to study ALS and discuss their value to ALS drug discovery. In particular, the authors focus on innovative chemical screens that have established simple organisms as important models for ALS drug discovery. Expert opinion: There are several advantages of using simple animal model organisms to accelerate drug discovery for ALS. It is the authors’ particular belief that the amenability of simple animal models to various genetic manipulations, the availability of a wide range of transgenic strains for labelling motoneurons and other cell types, combined with live imaging and chemical screens should allow for new detailed studies elucidating early pathological processes in ALS and subsequent drug and target discovery.

Could estrogen impact a new pertinent gene for AIS

Adolescent Idiopathic Scoliosis (AIS) is a complex rotational spinal deformity that occurs during the pubertal growth spurt. Recently, through a stepwise association study a new susceptibility locus on chromosome 6q24.1 was reported in Japanese population. The most significantly associated SNP, rs6570507, was in GPR126. This gene is coding for a protein of the adhesion subfamily of G-protein coupled receptors. We identified variants in another orphan members of the adhesion subfamily of G-protein coupled receptors which that is characterized by a long serine/threonine-rich N-terminus possibly regulated by hormones such as estrogens and consequently involved in the progression of AIS during the pubertal growth. The aim of this study was to investigate the regulation of this gene (GPRCh3) by 17-beta-estradiol.