WWOX-Related Neurodevelopmental Disorders: Models and Future Perspectives

The WW domain-containing oxidoreductase (WWOX) gene was originally discovered as a putative tumor suppressor spanning the common fragile site FRA16D, but as time has progressed the extent of its pleiotropic function has become apparent. At present, WWOX is a major source of interest in the context of neurological disorders, and more specifically developmental and epileptic encephalopathies (DEEs). This review article aims to introduce the many model systems used through the years to study its function and roles in neuropathies. Similarities and fundamental differences between rodent and human models are discussed. Finally, future perspectives and promising research avenues are suggested.

Molecular Biology of the WWOX Gene That Spans Chromosomal Fragile Site FRA16D

It is now more than 20 years since the FRA16D common chromosomal fragile site was characterised and the WWOX gene spanning this site was identified. In this time, much information has been discovered about its contribution to disease; however, the normal biological role of WWOX is not yet clear. Experiments leading to the identification of the WWOX gene are recounted, revealing enigmatic relationships between the fragile site, its gene and the encoded protein. We also highlight research mainly using the genetically tractable model organism Drosophila melanogaster that has shed light on the integral role of WWOX in metabolism. In addition to this role, there are some particularly outstanding questions that remain regarding WWOX, its gene and its chromosomal location. This review, therefore, also aims to highlight two unanswered questions. Firstly, what is the biological relationship between the WWOX gene and the FRA16D common chromosomal fragile site that is located within one of its very large introns? Secondly, what is the actual substrate and product of the WWOX enzyme activity? It is likely that understanding the normal role of WWOX and its relationship to chromosomal fragility are necessary in order to understand how the perturbation of these normal roles results in disease.

Neonatal neuronal WWOX gene therapy rescues Wwox null phenotypes

WW domain-containing oxidoreductase (WWOX) is an emerging neural gene regulating homeostasis of the central nervous system. Germline biallelic mutations in WWOX cause WWOX-related epileptic encephalopathy (WOREE) syndrome and spinocerebellar ataxia, and autosomal recessive 12 (SCAR12), two devastating neurodevelopmental disorders with highly heterogenous clinical outcomes, the most common being severe epileptic encephalopathy and profound global developmental delay. We recently demonstrated that neuronal ablation of murine Wwox recapitulates phenotypes of Wwox-null mice leading to intractable epilepsy, hypomyelination and postnatal lethality. Here, we designed and produced an adeno-associated viral vector harboring murine Wwox or human WWOX cDNA and driven by the human neuronal Synapsin I promoter (AAV-SynI-WWOX). Testing the efficacy of AAV-SynI-WWOX delivery in Wwox null mice demonstrated that specific neuronal restoration of WWOX expression rescued brain hyperexcitability and seizures, hypoglycemia, and myelination deficits as well as the premature lethality of Wwox-null mice. These findings provide a proof-of-concept for WWOX gene therapy as a promising approach to curing children with WOREE and SCAR12.

Neurological Disorders Associated with WWOX Germline Mutations—A Comprehensive Overview

The transcriptional regulator WW domain-containing oxidoreductase (WWOX) is a key player in a number of cellular and biological processes including tumor suppression. Recent evidence has emerged associating WWOX with non-cancer disorders. Patients harboring pathogenic germline bi-allelic WWOX variants have been described with the rare devastating neurological syndromes autosomal recessive spinocerebellar ataxia 12 (SCAR12) (6 patients) and WWOX-related epileptic encephalopathy (DEE28 or WOREE syndrome) (56 patients). Individuals with these syndromes present with a highly heterogenous clinical spectrum, the most common clinical symptoms being severe epileptic encephalopathy and profound global developmental delay. Knowledge of the underlying pathophysiology of these syndromes, the range of variants of the WWOX gene and its genotype-phenotype correlations is limited, hampering therapeutic efforts. Therefore, there is a critical need to identify and consolidate all the reported variants in WWOX to distinguish between disease-causing alleles and their associated severity, and benign variants, with the aim of improving diagnosis and increasing therapeutic efforts. Here, we provide a comprehensive review of the literature on WWOX, and analyze the pathogenic variants from published and unpublished reports by collecting entries from the ClinVar, DECIPHER, VarSome, and PubMed databases to generate the largest dataset of WWOX pathogenic variants. We estimate the correlation between variant type and patient phenotype, and delineate the impact of each variant, and used GnomAD to cross reference these variants found in the general population. From these searches, we generated the largest published cohort of WWOX individuals. We conclude with a discussion on potential personalized medicine approaches to tackle the devastating disorders associated with WWOX mutations.

Abstract 16915: Potential Role of Endothelial Cell WWOX in the Pulmonary Vascular Response to Hypoxia

Introduction: Pulmonary arterial hypertension (PAH) is characterized by abnormal proliferation and dysfunction of pulmonary artery smooth muscle and endothelial cells (PASMC, PAEC). The WWOX/ Wwox gene encodes a tumor suppressor WW domain-containing oxidoreductase, known as WWOX. WWOX has been linked to several protein networks, highlighting its functions in cell homeostasis, survival and proliferation. Loss of WWOX gene expression is observed in human cancer cells, as lung cancer. We hypothesize that during hypoxia, WWOX expression is modulated in PAECs, regulating cell proliferation and selecting apoptosis-resistant cells, thus causing vascular remodeling. Methods and Results: Endothelial cell specific Wwox knockout mice were developed by a conditional ablation of Wwox gene expression using the Cre -Lox site-specific recombination system. We crossed Wwox flox/flox mice with CDH5 Cre+ mice, generating Wwox floxed, CDH-Cre+ specific mice that are tamoxifen-inducible (EC- WWOX KO). EC-WWOX KO mice were treated daily with tamoxifen or vehicle for 5 days and exposed to 10% hypoxia. After four weeks of hypoxia exposure, EC-WWOX KO mice showed increased right ventricular systolic pressure (RVSP) (P=0.0003) and Fulton index (RV (LV+S)) ( P=0.049), when compared to controls, suggesting PH development. In vitro , PAECs exposure to 3% hypoxia for 6 hours showed an increase of WWOX mRNA (P=0.0154) and protein (P<0.05) expression levels, decreased of cell proliferation detected by CyQUANT assay and PCNA protein expression (P=0.0024). These effects did not extend to cells exposed to 3% hypoxia for 24h. Immunoblots showed activation of apoptotic markers, such as cleaved caspase 3, PARP and Bax, suggesting that in hypoxia there is a potential controlled balance between increased WWOX expression, decreased cell proliferation and stimulation of apoptosis in these cells. Conclusion: Loss of EC WWOX expression plays a significant role in the development of PH in mice exposed to chronic hypoxia. We speculate that increased WWOX expression with acute hypoxia exposure could contribute to the selection of proliferative and pro-apoptotic PAECs, characteristic of PAH. Studies seeking to understand the mechanisms surrounding WWOX expression in PAECs are ongoing.

WWOX is a Risk Factor for Alzheimer’s Disease: How and Why?

A recent large genome-wide association meta-analysis revealed that the human WWOX gene is regarded as one of the five newly identified risk factors for Alzheimer’s disease (AD). However, this study did not functionally characterize how WWOX protein deficiency affects AD initiation, progression and neurodegeneration. In this review, evidence and perspectives are provided regarding how WWOX works in limiting neurodegeneration. Firstly, loss of WWOX/Wwox gene leads to severe neural diseases with degeneration, metabolic disorder and early death in the newborns. Downregulation of pY33-WWOX may start at middle ages, and this leads to slow aggregation of a cascade of proteins, namely TRAPPC6A[Formula: see text], TIAF1 and SH3GLB2, that leads to amyloid-beta (A[Formula: see text]) formation and tau tangle formation in old-aged AD patients. Secondly, functional antagonism between tumor suppressors p53 and WWOX may occur in vivo, in which p53-mediated inflammation is blocked by WWOX. Loss of balance in the functional antagonism leads to aggregation of pathogenic proteins for AD such as tau and A[Formula: see text] in the brain cortex and hippocampus. Thirdly, downregulation of pY33-WWOX is accompanied by upregulation of pS14-WWOX. The event frequently correlates with enhanced AD progression and cancer cell growth in vivo. A small peptide Zfra4-10 dramatically suppresses pS14-WWOX and restores memory loss in triple transgenic (3xTg) mice, and inhibits cancer growth in mice as well. Finally, a supporting scenario is that WWOX deficiency induces enhanced cell migration and loss of cell-to-cell recognition. This allows the generation of neuronal heterotopia and associated epileptic seizure in WWOX-deficient newborn patients.

The WWOX gene in brain development and pathology

Shortly after its discovery in 2000, WWOX was hailed as a tumor suppressor gene. In subsequent years of research, this function was confirmed indisputably. Majority of tumors show high rate of loss of heterozygosity and decreased expression of WWOX. Nevertheless, over the years, the range of its known functions, at the cellular, organ and system levels, has expanded to include metabolism and endocrine system control and CNS differentiation and functioning. Despite of its function as a tumor suppressor gene, WWOX genetic alternations were found in a number of metabolic and neural diseases. A lack of WWOX protein as a consequence of germline mutations results in brain development disturbances and malfunctions. Impact statement WW domain-containing oxidoreductase encoded by the WWOX gene is a transcription regulator and a key player in a number of cellular and biological processes such as tumor suppression, cell proliferation, apoptosis induction, steroid metabolism, and central nervous system development. This review provides a comprehensive summary of currently known roles and discusses the importance of WWOX gene for CNS development and functioning.