A neurodegenerative perspective on mitochondrial optic neuropathies

Publication: www.ncbi.nlm.nih.gov | Publication Date: September 30, 2016

Authors: Patrick Yu-Wai-Man, Marcela Votruba, Florence Burté, Chiara La Morgia, Piero Barboni, and Valerio Carelli

Abstract

Mitochondrial optic neuropathies constitute an important cause of chronic visual morbidity and registrable blindness in both the paediatric and adult population. It is a genetically heterogeneous group of disorders caused by both mitochondrial DNA (mtDNA) mutations and a growing list of nuclear genetic defects that invariably affect a critical component of the mitochondrial machinery. The two classical paradigms are Leber hereditary optic neuropathy (LHON), which is a primary mtDNA disorder, and autosomal dominant optic atrophy (DOA) secondary to pathogenic mutations within the nuclear gene OPA1 that encodes for a mitochondrial inner membrane protein. The defining neuropathological feature is the preferential loss of retinal ganglion cells (RGCs) within the inner retina but, rather strikingly, the smaller calibre RGCs that constitute the papillomacular bundle are particularly vulnerable, whereas melanopsin-containing RGCs are relatively spared. Although the majority of patients with LHON and DOA will present with isolated optic nerve involvement, some individuals will also develop additional neurological complications pointing towards a greater vulnerability of the central nervous system (CNS) in susceptible mutation carriers. These so-called “plus” phenotypes are mechanistically important as they put the loss of RGCs within the broader perspective of neuronal loss and mitochondrial dysfunction, highlighting common pathways that could be modulated to halt progressive neurodegeneration in other related CNS disorders. The management of patients with mitochondrial optic neuropathies still remains largely supportive, but the development of effective disease-modifying treatments is now within tantalising reach helped by major advances in drug discovery and delivery, and targeted genetic manipulation.

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Chemical Chaperones Reduce ER Stress and Restore Glucose Homeostasis in a Mouse Model of Type 2 Diabetes

Publication: www.ncbi.nlm.nih.gov | Publication Date: February 4, 2016

Authors: Umut Özcan, Erkan Yilmaz, Lale Özcan, Masato Furuhashi, Eric Vaillancourt, Ross O. Smith, Cem Z. Görgün, and Gökhan S. Hotamisligil

Abstract

Endoplasmic reticulum (ER) stress is a key link between obesity, insulin resistance, and type 2 diabetes. Here, we provide evidence that this mechanistic link can be exploited for therapeutic purposes with orally active chemical chaperones. 4-Phenyl butyric acid and taurine-conjugated ursodeoxycholic acid alleviated ER stress in cells and whole animals. Treatment of obese and diabetic mice with these compounds resulted in normalization of hyperglycemia, restoration of systemic insulin sensitivity, resolution of fatty liver disease, and enhancement of insulin action in liver, muscle, and adipose tissues. Our results demonstrate that chemical chaperones enhance the adaptive capacity of the ER and act as potent antidiabetic modalities with potential application in the treatment of type 2 diabetes.

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Wolfram Syndrome: Diagnosis, Management, and Treatment

Publication: www.ncbi.nlm.nih.gov | Publication Date: January 7, 2016

Authors: Fumihiko Urano

Abstract

Wolfram syndrome is a rare genetic disorder characterized by juvenile-onset diabetes mellitus, diabetes insipidus, optic nerve atrophy, hearing loss, and neurodegeneration. Although there are currently no effective treatments that can delay or reverse the progression of Wolfram syndrome, the use of careful clinical monitoring and supportive care can help relieve the suffering of patients and improve their quality of life. The prognosis of this syndrome is currently poor, and many patients die prematurely with severe neurological disabilities, raising the urgency for developing novel treatments for Wolfram syndrome. In this article, we describe natural history and etiology, provide recommendations for diagnosis and clinical management, and introduce new treatments for Wolfram syndrome.

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Enhancing the Utility of Adeno-Associated Virus Gene Transfer through Inducible Tissue-Specific Expression

Publication: www.ncbi.nlm.nih.gov | Publication Date: August 13, 2014

Authors: Shu-Jen Chen, Julie Johnston, Arbans Sandhu, Lawrence T. Bish, Ruben Hovhannisyan, Odella Jno-Charles, H. Lee Sweeney, and James M. Wilson

Abstract

The ability to regulate both the timing and specificity of gene expression mediated by viral vectors will be important in maximizing its utility. We describe the development of an adeno-associated virus (AAV)-based vector with tissue-specific gene regulation, using the ARGENT dimerizer-inducible system. This two-vector system based on AAV serotype 9 consists of one vector encoding a combination of reporter genes from which expression is directed by a ubiquitous, inducible promoter and a second vector encoding transcription factor domains under the control of either a heart- or liver-specific promoter, which are activated with a small molecule. Administration of the vectors via either systemic or intrapericardial injection demonstrated that the vector system is capable of mediating gene expression that is tissue specific, regulatable, and reproducible over induction cycles. Somatic gene transfer in vivo is being considered in therapeutic applications, although its most substantial value will be in basic applications such as target validation and development of animal models.

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The therapeutic potential of chemical chaperones in protein folding diseases

Publication: www.ncbi.nlm.nih.gov | Publication Date: May 12, 2014

Authors: Leonardo Cortez and Valerie Sim

Abstract

Several neurodegenerative diseases are caused by defects in protein folding, including Alzheimer, Parkinson, Huntington, and prion diseases. Once a disease-specific protein misfolds, it can then form toxic aggregates which accumulate in the brain, leading to neuronal dysfunction, cell death, and clinical symptoms. Although significant advances have been made toward understanding the mechanisms of protein aggregation, there are no curative treatments for any of these diseases. Since protein misfolding and the accumulation of aggregates are the most upstream events in the pathological cascade, rescuing or stabilizing the native conformations of proteins is an obvious therapeutic strategy. In recent years, small molecules known as chaperones have been shown to be effective in reducing levels of misfolded proteins, thus minimizing the accumulation of aggregates and their downstream pathological consequences. Chaperones are classified as molecular, pharmacological, or chemical. In this mini-review we summarize the modes of action of different chemical chaperones and discuss evidence for their efficacy in the treatment of protein folding diseases in vitro and in vivo.

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Wolfram Syndrome iPS Cells: The First Human Cell Model of Endoplasmic Reticulum Disease

Publication: American Diabetes Association | Publication Date: March 2014

Authors: Fumihiko Urano

Wolfram syndrome is a rare autosomal recessive genetic disorder with clinical signs apparent in early childhood. This condition is characterized by childhood-onset diabetes, optic nerve atrophy, deafness, diabetes insipidus, and neurodegeneration, and it results in death in middle adulthood (1–3). Genetic and experimental evidence strongly suggest that endoplasmic reticulum (ER) dysfunction is a critical pathogenic component of Wolfram syndrome (4,5). However, there is a lack of complete understanding of the pathways and biomarkers involved in the disease process due to the limitations of animal models that do not accurately reflect human patients. As a result, despite the underlying importance of ER dysfunction in Wolfram syndrome, there are currently no therapies that target the ER, a deficiency that points to the urgent need to develop a human cell model of this condition. In this issue, Shang et al. (6) report that this has been successfully accomplished.

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β-Cell Dysfunction Due to Increased ER Stress in a Stem Cell Model of Wolfram Syndrome

Publication: www.ncbi.nlm.nih.gov | Publication Date: February 13, 2014

Authors: Linshan Shang, Haiqing Hua, Kylie Foo, Hector Martinez, Kazuhisa Watanabe, Matthew Zimmer, David J. Kahler, Matthew Freeby, Wendy Chung, Charles LeDuc, Robin Goland, Rudolph L. Leibel, and Dieter Egli

Abstract

Wolfram syndrome is an autosomal recessive disorder caused by mutations in WFS1 and is characterized by insulin-dependent diabetes mellitus, optic atrophy, and deafness. To investigate the cause of β-cell failure, we used induced pluripotent stem cells to create insulin-producing cells from individuals with Wolfram syndrome. WFS1-deficient β-cells showed increased levels of endoplasmic reticulum (ER) stress molecules and decreased insulin content. Upon exposure to experimental ER stress, Wolfram β-cells showed impaired insulin processing and failed to increase insulin secretion in response to glucose and other secretagogues. Importantly, 4-phenyl butyric acid, a chemical protein folding and trafficking chaperone, restored normal insulin synthesis and the ability to upregulate insulin secretion. These studies show that ER stress plays a central role in β-cell failure in Wolfram syndrome and indicate that chemical chaperones might have therapeutic relevance under conditions of ER stress in Wolfram syndrome and other forms of diabetes.

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Valproate, a Mood Stabilizer, Induces WFS1 Expression and Modulates Its Interaction with ER Stress Protein GRP94

Publication: journals.plos.org | Publication Date: January 6, 2009

Authors: Chihiro Kakiuchi, Shinsuke Ishigaki, Christine M. Oslowski, Sonya G. Fonseca, Tadafumi Kato, Fumihiko Urano

Abstract

Background

Valproate is a standard treatment for bipolar disorder and a first-line mood stabilizer. The molecular mechanisms underlying its actions in bipolar disorder are unclear. It has been suggested that the action of valproate is linked to changes in gene expression and induction of endoplasmic reticulum (ER) stress-response proteins.

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