Knockdown of wfs1, a fly homolog of Wolfram syndrome 1, in the nervous system increases susceptibility to age- and stress-induced neuronal dysfunction and degeneration in Drosophila

Comprehensive overview of disease models for Wolfram syndrome: toward effective treatments

Wolfram syndrome (OMIM 222300) is a rare autosomal recessive disease with a devastating array of symptoms, including diabetes mellitus, optic nerve atrophy, diabetes insipidus, hearing loss, and neurological dysfunction. The discovery of the causative gene, WFS1, has propelled research on this disease. However, a comprehensive understanding of the function of WFS1 remains unknown, making the development of effective treatment a pressing challenge. To bridge these knowledge gaps, disease models for Wolfram syndrome are indispensable, and understanding the characteristics of each model is critical. This review will provide a summary of the current knowledge regarding WFS1 function and offer a comprehensive overview of established disease models for Wolfram syndrome, covering animal models such as mice, rats, flies, and zebrafish, along with induced pluripotent stem cell (iPSC)-derived human cellular models. These models replicate key aspects of Wolfram syndrome, contributing to a deeper understanding of its pathogenesis and providing a platform for discovering potential therapeutic approaches.

Markers and mechanisms of death in Drosophila

Parameters correlated with age and mortality in Drosophila melanogaster include decreased negative geotaxis and centrophobism behaviors, decreased climbing and walking speed, and darkened pigments in oenocytes and eye. Cessation of egg laying predicts death within approximately 5 days. Endogenous green fluorescence in eye and body increases hours prior to death. Many flies exhibit erratic movement hours before death, often leading to falls. Loss of intestinal barrier integrity (IBI) is assayed by feeding blue dye ("Smurf" phenotype), and Smurf flies typically die within 0-48 h. Some studies report most flies exhibit Smurf, whereas multiple groups report most flies die without exhibiting Smurf. Transgenic reporters containing heat shock gene promoters and innate immune response gene promoters progressively increase expression with age, and partly predict remaining life span. Innate immune reporters increase with age in every fly, prior to any Smurf phenotype, in presence or absence of antibiotics. Many flies die on their side or supine (on their back) position. The data suggest three mechanisms for death of Drosophila. One is loss of IBI, as revealed by Smurf assay. The second is nervous system malfunction, leading to erratic behavior, locomotor malfunction, and falls. The aged fly is often unable to right itself after a fall to a side-ways or supine position, leading to inability to access the food and subsequent dehydration/starvation. Finally, some flies die upright without Smurf phenotype, suggesting a possible third mechanism. The frequency of these mechanisms varies between strains and culture conditions, which may affect efficacy of life span interventions.

Wolfram syndrome 1 regulates sleep in dopamine receptor neurons by modulating calcium homeostasis

Sleep disruptions are quite common in psychological disorders, but the underlying mechanism remains obscure. Wolfram syndrome 1 (WS1) is an autosomal recessive disease mainly characterized by diabetes insipidus/mellitus, neurodegeneration and psychological disorders. It is caused by loss-of function mutations of the WOLFRAM SYNDROME 1 (WFS1) gene, which encodes an endoplasmic reticulum (ER)-resident transmembrane protein. Heterozygous mutation carriers do not develop WS1 but exhibit 26-fold higher risk of having psychological disorders. Since WS1 patients display sleep abnormalities, we aimed to explore the role of WFS1 in sleep regulation so as to help elucidate the cause of sleep disruptions in psychological disorders. We found in Drosophila that knocking down wfs1 in all neurons and wfs1 mutation lead to reduced sleep and dampened circadian rhythm. These phenotypes are mainly caused by lack of wfs1 in dopamine 2-like receptor (Dop2R) neurons which act to promote wake. Consistently, the influence of wfs1 on sleep is blocked or partially rescued by inhibiting or knocking down the rate-limiting enzyme of dopamine synthesis, suggesting that wfs1 modulates sleep via dopaminergic signaling. Knocking down wfs1 alters the excitability of Dop2R neurons, while genetic interactions reveal that lack of wfs1 reduces sleep via perturbation of ER-mediated calcium homeostasis. Taken together, we propose a role for wfs1 in modulating the activities of Dop2R neurons by impinging on intracellular calcium homeostasis, and this in turn influences sleep. These findings provide a potential mechanistic insight for pathogenesis of diseases associated with WFS1 mutations.

Modeling disrupted synapse formation in wolfram syndrome using hESCs-derived neural cells and cerebral organoids identifies Riluzole as a therapeutic molecule

Dysregulated neurite outgrowth and synapse formation underlie many psychiatric disorders, which are also manifested by wolfram syndrome (WS). Whether and how the causative gene WFS1 deficiency affects synapse formation remain elusive. By mirroring human brain development with cerebral organoids, WFS1-deficient cerebral organoids not only recapitulate the neuronal loss in WS patients, but also exhibit significantly impaired synapse formation and function associated with reduced astrocytes. WFS1 deficiency in neurons autonomously delays neuronal differentiation with altered expressions of genes associated with psychiatric disorders, and impairs neurite outgrowth and synapse formation with elevated cytosolic calcium. Intriguingly, WFS1 deficiency in astrocytes decreases the expression of glutamate transporter EAAT2 by NF-κB activation and induces excessive glutamate. When co-cultured with wildtype neurons, WFS1-deficient astrocytes lead to impaired neurite outgrowth and increased cytosolic calcium in neurons. Importantly, disrupted synapse formation and function in WFS1-deficient cerebral organoids and impaired neurite outgrowth affected by WFS1-deficient astrocytes are efficiently reversed with Riluzole treatment, by restoring EAAT2 expression in astrocytes. Furthermore, Riluzole rescues the depressive-like behavior in the forced swimming test and the impaired recognition and spatial memory in the novel object test and water maze test in Wfs1 conditional knockout mice. Altogether, our study provides novel insights into how WFS1 deficiency affects synapse formation and function, and offers a strategy to treat this disease.

Case Report: A novel mutation in WFS1 gene (c.1756G>A p.A586T) is responsible for early clinical features of cognitive impairment and recurrent ischemic stroke

Wolfram syndrome 1 (WFS1) gene mutations can be dominantly or recessively inherited, and the onset of the clinical picture is highly heterogeneity in both appearance and degree of severity. Different types of WFS1 mutations have been identified. Autosomal recessive mutations in the WFS1 gene will underlie Wolfram syndrome 1 (WS1), a rare and severe neurodegenerative disease characterized by diabetes insipidus, diabetes mellitus, optic atrophy, deafness, and other neurological, urological and psychiatric abnormalities. Other WFS1-related disorders such as low-frequency sensorineural hearing impairment (LFSNHI) and Wolfram syndrome-like disease with autosomal dominant transmission have been described. It is difficult to establish genotype-phenotype correlations because of the molecular complexity of wolframin protein. In this report, we presented a case of WSF1 gene mutation-related disease with cognitive impairment as the initial symptom and recurrent cerebral infarction in the course of the disease. Brain structural imaging results suggested decreased intracranial volume, dramatically reduced in cerebral cortex and cerebellum regions. Multimodal molecular imaging results suggested Tau protein deposition in the corresponding brain regions without Aβ pathology changes. These pathological changes may indicate a role of WFS1 in neuronal vulnerability to tau pathology associated with neurodegeneration and ischemia-induced damage.

Drosophila Toll-9 is induced by aging and neurodegeneration to modulate stress signaling and its deficiency exacerbates tau-mediated neurodegeneration

Drosophila Toll-9 is most closely related to mammalian Toll-like receptors; however, physiological functions of Toll-9 remain elusive. We examined the roles of Toll-9 in fly brains in aging and neurodegeneration. Toll-9 mRNA levels were increased in aged fly heads accompanied by activation of nuclear factor-kappa B (NF-kB) and stress-activated protein kinase (SAPK) signaling, and many of these changes were modulated by Toll-9 in glial cells. The loss of Toll-9 did not affect lifespan or brain integrity, whereas it exacerbated hydrogen peroxide-induced lethality. Toll-9 expression was also induced by nerve injury but did not affect acute stress response or glial engulfment activity, suggesting Toll-9 may modulate subsequent neurodegeneration. In a fly tauopathy model, Toll-9 deficiency enhanced neurodegeneration and disease-related tau phosphorylation with reduced SAPK activity, and blocking SAPK enhanced tau phosphorylation and neurodegeneration. In sum, Toll-9 is induced upon aging and nerve injury and affects neurodegeneration by modulating stress kinase signaling.

Wolfram syndrome 1b mutation suppresses Mauthner-cell axon regeneration via ER stress signal pathway

Wolfram Syndrome (WS) is a fatal human inherited disease with symptoms of diabetes, vision decreasing, and neurodegeneration caused by mutations in the endoplasmic reticulum (ER)-resident protein WFS1. WFS1 has been reported to play an important role in glucose metabolism. However, the role of WFS1 in axonal regeneration in the central nervous system has so far remained elusive. Herein, we established a model of the wfs1b globally deficient zebrafish line. wfs1b deficiency severely impeded the Mauthner-cell (M-cell) axon regeneration, which was partly dependent on the ER stress response. The administration of ER stress inhibitor 4-Phenylbutyric acid (4-PBA) promoted M-cell axon regeneration in wfs1b^-/- zebrafish larvae, while the ER stress activator Tunicamycin (TM) inhibited M-cell axon regeneration in wfs1b^+/+ zebrafish larvae. Moreover, complementation of wfs1b at the single-cell level stimulated M-cell axon regeneration in the wfs1b^-/- zebrafish larvae. Altogether, our results revealed that wfs1b promotes M-cell axon regeneration through the ER stress signal pathway and provide new evidence for a therapeutic target for WS and axon degeneration.

Spread of pathological human Tau from neurons to oligodendrocytes and loss of high-firing pyramidal neurons in aging mice

Intracellular aggregation of hyperphosphorylated Tau (pTau) in the brain is associated with cognitive and motor impairments, and ultimately neurodegeneration. We investigate how human pTau affects cells and network activity in the hippocampal formation of the THY-Tau22 tauopathy model mice in vivo. We find that pTau preferentially accumulates in deep-layer pyramidal neurons, leading to neurodegeneration, and we establish that pTau spreads to oligodendrocytes. During goal-directed virtual navigation in aged transgenic mice, we detect fewer high-firing prosubicular pyramidal cells, but the firing population retains its coupling to theta oscillations. Analysis of network oscillations and firing patterns of pyramidal and GABAergic neurons recorded in head-fixed and freely moving mice suggests preserved neuronal coordination. In spatial memory tests, transgenic mice have reduced short-term familiarity, but spatial working and reference memory are surprisingly normal. We hypothesize that unimpaired subcortical network mechanisms maintain cortical neuronal coordination, counteracting the widespread pTau aggregation, loss of high-firing cells, and neurodegeneration.

NCS1 overexpression restored mitochondrial activity and behavioral alterations in a zebrafish model of Wolfram syndrome

Wolfram syndrome (WS) is a rare neurodegenerative disease resulting in deafness, optic atrophy, diabetes, and neurological disorders. Currently, no treatment is available for patients. The mutated gene, WFS1, encodes an endoplasmic reticulum (ER) protein, Wolframin. We previously reported that Wolframin regulated the ER-mitochondria Ca²⁺ transfer and mitochondrial activity by protecting NCS1 from degradation in patients' fibroblasts. We relied on a zebrafish model of WS, the wfs1ab ^KO line, to analyze the functional and behavioral impact of NCS1 overexpression as a novel therapeutic strategy. The wfs1ab ^KO line showed an increased locomotion in the visual motor and touch-escape responses. The absence of wfs1 did not impair the cellular unfolded protein response, in basal or tunicamycin-induced ER stress conditions. In contrast, metabolic analysis showed an increase in mitochondrial respiration in wfs1ab ^KO larvae. Interestingly, overexpression of NCS1 using mRNA injection restored the alteration of mitochondrial respiration and hyperlocomotion. Taken together, these data validated the wfs1ab ^KO zebrafish line as a pertinent experimental model of WS and confirmed the therapeutic potential of NCS1. The wfs1ab ^KO line therefore appeared as an efficient model to identify novel therapeutic strategies, such as gene or pharmacological therapies targeting NCS1 that will correct or block WS symptoms.

A conserved long-distance telomeric silencing mechanism suppresses mTOR signaling in aging human fibroblasts

Telomeres are repetitive nucleotide sequences at the ends of each chromosome. It has been hypothesized that telomere attrition evolved as a tumor suppressor mechanism in large long-lived species. Long telomeres can silence genes millions of bases away through a looping mechanism called telomere position effect over long distances (TPE-OLD). The function of this silencing mechanism is unknown. We determined a set of 2322 genes with high positional conservation across replicatively aging species that includes known and candidate TPE-OLD genes that may mitigate potentially harmful effects of replicative aging. Notably, we identified PPP2R2C as a tumor suppressor gene, whose up-regulation by TPE-OLD in aged human fibroblasts leads to dephosphorylation of p70S6 kinase and mammalian target of rapamycin suppression. A mechanistic link between telomeres and a tumor suppressor mechanism supports the hypothesis that replicative aging fulfills a tumor suppressor function and motivates previously unknown antitumor and antiaging strategies.

Dysregulated Ca2+ Homeostasis as a Central Theme in Neurodegeneration: Lessons from Alzheimer's Disease and Wolfram Syndrome

Calcium ions (Ca²⁺) operate as important messengers in the cell, indispensable for signaling the underlying numerous cellular processes in all of the cell types in the human body. In neurons, Ca²⁺ signaling is crucial for regulating synaptic transmission and for the processes of learning and memory formation. Hence, the dysregulation of intracellular Ca²⁺ homeostasis results in a broad range of disorders, including cancer and neurodegeneration. A major source for intracellular Ca²⁺ is the endoplasmic reticulum (ER), which has close contacts with other organelles, including mitochondria. In this review, we focus on the emerging role of Ca²⁺ signaling at the ER–mitochondrial interface in two different neurodegenerative diseases, namely Alzheimer’s disease and Wolfram syndrome. Both of these diseases share some common hallmarks in the early stages, including alterations in the ER and mitochondrial Ca²⁺ handling, mitochondrial dysfunction and increased Reactive oxygen species (ROS) production. This indicates that similar mechanisms may underly these two disease pathologies and suggests that both research topics might benefit from complementary research.

Wolframin is a novel regulator of tau pathology and neurodegeneration

Selective neuronal vulnerability to protein aggregation is found in many neurodegenerative diseases including Alzheimer's disease (AD). Understanding the molecular origins of this selective vulnerability is, therefore, of fundamental importance. Tau protein aggregates have been found in Wolframin (WFS1)-expressing excitatory neurons in the entorhinal cortex, one of the earliest affected regions in AD. The role of WFS1 in Tauopathies and its levels in tau pathology-associated neurodegeneration, however, is largely unknown. Here we report that WFS1 deficiency is associated with increased tau pathology and neurodegeneration, whereas overexpression of WFS1 reduces those changes. We also find that WFS1 interacts with tau protein and controls the susceptibility to tau pathology. Furthermore, chronic ER stress and autophagy-lysosome pathway (ALP)-associated genes are enriched in WFS1-high excitatory neurons in human AD at early Braak stages. The protein levels of ER stress and autophagy-lysosome pathway (ALP)-associated proteins are changed in tau transgenic mice with WFS1 deficiency, while overexpression of WFS1 reverses those changes. This work demonstrates a possible role for WFS1 in the regulation of tau pathology and neurodegeneration via chronic ER stress and the downstream ALP. Our findings provide insights into mechanisms that underpin selective neuronal vulnerability, and for developing new therapeutics to protect vulnerable neurons in AD.

The pattern of retinal ganglion cell loss in Wolfram syndrome is distinct from mitochondrial optic neuropathies

PURPOSE

To describe the clinical phenotype of a cohort of Wolfram syndrome (WS) patients, focusing on the pattern of optic atrophy correlated with brain MRI measurements, as compared to OPA1-associated mitochondrial optic neuropathy.

DESIGN

Retrospective, comparative cohort study METHODS: 25 WS patients and 33 age-matched patients affected by OPA1-related Dominant Optic Atrophy (DOA). Ophthalmological, neurological, endocrinological and MRI data from WS patients were retrospectively retrieved. Ophthalmological data were compared to OPA1-related DOA and further analyzed for age dependency dividing patients in age quartiles. In a subgroup of WS patients, we correlated the structural damage assessed by optical coherence tomography (OCT) with brain MRI morphological measurements. Visual acuity (VA), visual field mean defect (MD), retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL) thickness assessed by OCT, MRI morphological measurements of anterior and posterior visual pathways.

RESULTS

In our cohort optic atrophy was present in 100% of WS patients. VA, MD and RNFL thickness loss were worse in WS patients with a faster decline since early age as compared to DOA patients, who displayed a more stable visual function over the years. Conversely, GCL sectors were overall thinner in DOA patients since early age compared to WS, in which GCL thickness started to decline later in life. The neuroradiological sub-analysis on 11 WS patients exhibited bilateral thinning of the anterior optic pathway, especially prechiasmatic optic nerves and optic tracts. Optic tract thinning was significantly correlated with the GCL thickness but not with RNFL parameters.

CONCLUSIONS

Our results showed a generally more severe and diffuse degeneration of both anterior and posterior visual pathways in WS, with fast deterioration of visual function and structural OCT parameters since early age. The pattern observed at OCT suggests that retinal ganglion cells axonal degeneration (i.e. RNFL) precedes of about a decade the cellular body atrophy (i.e. GCL). This differs substantially from DOA, in which a more stable visual function is evident with predominant early loss of GCL, indirectly supporting the lack of a primary mitochondrial dysfunction in WS.

Effect of Riluzole on the Expression of HCN2 in Dorsal Root Ganglion Neurons of Diabetic Neuropathic Pain Rats

Neuropathic pain since early diabetes swamps patients' lives, and diabetes mellitus has become an increasingly worldwide epidemic. No agent, so far, can terminate the ongoing diabetes. Therefore, strategies that delay the process and the further complications are preferred, such as diabetic neuropathic pain (DNP). Dysfunction of ion channels is generally accepted as the central mechanism of diabetic associated neuropathy, of which hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2) ion channel has been verified the involvement of neuropathic pain in dorsal root ganglion (DRG) neurons. Riluzole is a benzothiazole compound with neuroprotective properties on intervention to various ion channels, including hyperpolarization-activated voltage-dependent channels. To investigate the effect of riluzole within lumbar (L3-5) DRG neurons from DNP models, streptozocin (STZ, 70 mg/kg) injection was recruited subcutaneously followed by paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL), which both show significant reduction, whilst relieved by riluzole (4 mg/kg/d) administration, which was performed once daily for 7 consecutive days for 14 days. HCN2 expression was also decreased in line with alleviated behavioral tests. Our results indicate riluzole as the alleviator to STZ-induced DNP with involvement of downregulated HCN2 in lumbar DRG by continual systemic administration in rats.

The Role of Mitochondria in Optic Atrophy With Autosomal Inheritance

Optic atrophy (OA) with autosomal inheritance is a form of optic neuropathy characterized by the progressive and irreversible loss of vision. In some cases, this is accompanied by additional, typically neurological, extra-ocular symptoms. Underlying the loss of vision is the specific degeneration of the retinal ganglion cells (RGCs) which form the optic nerve. Whilst autosomal OA is genetically heterogenous, all currently identified causative genes appear to be associated with mitochondrial organization and function. However, it is unclear why RGCs are particularly vulnerable to mitochondrial aberration. Despite the relatively high prevalence of this disorder, there are currently no approved treatments. Combined with the lack of knowledge concerning the mechanisms through which aberrant mitochondrial function leads to RGC death, there remains a clear need for further research to identify the underlying mechanisms and develop treatments for this condition. This review summarizes the genes known to be causative of autosomal OA and the mitochondrial dysfunction caused by pathogenic mutations. Furthermore, we discuss the suitability of available in vivo models for autosomal OA with regards to both treatment development and furthering the understanding of autosomal OA pathology.

Human iPSC-derived neurons reveal early developmental alteration of neurite outgrowth in the late-occurring neurodegenerative Wolfram syndrome

Recent studies indicate that neurodegenerative processes that appear during childhood and adolescence in individuals with Wolfram syndrome (WS) occur in addition to early brain development alteration, which is clinically silent. Underlying pathological mechanisms are still unknown. We have used induced pluripotent stem cell-derived neural cells from individuals affected by WS in order to reveal their phenotypic and molecular correlates. We have observed that a subpopulation of Wolfram neurons displayed aberrant neurite outgrowth associated with altered expression of axon guidance genes. Selective inhibition of the ATF6α arm of the unfolded protein response prevented the altered phenotype, although acute endoplasmic reticulum stress response-which is activated in late Wolfram degenerative processes-was not detected. Among the drugs currently tried in individuals with WS, valproic acid was the one that prevented the pathological phenotypes. These results suggest that early defects in axon guidance may contribute to the loss of neurons in individuals with WS.

A mutant wfs1 zebrafish model of Wolfram syndrome manifesting visual dysfunction and developmental delay

Wolfram syndrome (WS) is an ultra-rare progressive neurodegenerative disorder defined by early-onset diabetes mellitus and optic atrophy. The majority of patients harbour recessive mutations in the WFS1 gene, which encodes for Wolframin, a transmembrane endoplasmic reticulum protein. There is limited availability of human ocular and brain tissues, and there are few animal models for WS that replicate the neuropathology and clinical phenotype seen in this disorder. We, therefore, characterised two wfs1 zebrafish knockout models harbouring nonsense wfs1a and wfs1b mutations. Both homozygous mutant wfs1a-/- and wfs1b-/- embryos showed significant morphological abnormalities in early development. The wfs1b-/- zebrafish exhibited a more pronounced neurodegenerative phenotype with delayed neuronal development, progressive loss of retinal ganglion cells and clear evidence of visual dysfunction on functional testing. At 12 months of age, wfs1b-/- zebrafish had a significantly lower RGC density per 100 μm2 (mean ± standard deviation; 19 ± 1.7) compared with wild-type (WT) zebrafish (25 ± 2.3, p < 0.001). The optokinetic response for wfs1b-/- zebrafish was significantly reduced at 8 and 16 rpm testing speeds at both 4 and 12 months of age compared with WT zebrafish. An upregulation of the unfolded protein response was observed in mutant zebrafish indicative of increased endoplasmic reticulum stress. Mutant wfs1b-/- zebrafish exhibit some of the key features seen in patients with WS, providing a versatile and cost-effective in vivo model that can be used to further investigate the underlying pathophysiology of WS and potential therapeutic interventions.

Uniting the divergent Wolfram syndrome-linked proteins WFS1 and CISD2 as modulators of Ca2+ signaling

[Figure: see text].

Novel mutations in the WFS1 gene are associated with Wolfram syndrome and systemic inflammation

Mutations in the WFS1 gene, encoding wolframin (WFS1), cause endoplasmic reticulum (ER) stress and are associated with a rare autosomal-recessive disorder known as Wolfram syndrome (WS). WS is clinically characterized by childhood-onset diabetes mellitus, optic atrophy, deafness, diabetes insipidus and neurological signs. We identified two novel WFS1 mutations in a patient with WS, namely, c.316-1G > A (in intron 3) and c.757A > T (in exon 7). Both mutations, located in the N-terminal region of the protein, were predicted to generate a truncated and inactive form of WFS1. We found that although the WFS1 protein was not expressed in peripheral blood mononuclear cells (PBMCs) of the proband, no constitutive ER stress activation could be detected in those cells. In contrast, WS proband’s PBMCs produced very high levels of proinflammatory cytokines (i.e. TNF-α, IL-1β, and IL-6) in the absence of any stimulus. WFS1 silencing in PBMCs from control subjects by means of small RNA interference also induced a pronounced proinflammatory cytokine profile. The same cytokines were also significantly higher in sera from the WS patient as compared to matched healthy controls. Moreover, the chronic inflammatory state was associated with a dominance of proinflammatory T helper 17 (Th17)-type cells over regulatory T (Treg) lymphocytes in the WS PBMCs. The identification of a state of systemic chronic inflammation associated with WFS1 deficiency may pave the way to innovative and personalized therapeutic interventions in WS.

Wolfram syndrome: new pathophysiological insights and therapeutic strategies

Wolfram Syndrome (WS) is an ultra-rare, progressive neurodegenerative disease characterized by early-onset diabetes mellitus and irreversible loss of vision, secondary to optic nerve degeneration. Visual loss in WS is an important cause of registrable blindness in children and young adults and the pathological hallmark is the preferential loss of retinal ganglion cells within the inner retina. In addition to optic atrophy, affected individuals frequently develop variable combinations of neurological, endocrinological, and psychiatric complications. The majority of patients carry recessive mutations in the WFS1 (4p16.1) gene that encodes for a multimeric transmembrane protein, wolframin, embedded within the endoplasmic reticulum (ER). An increasingly recognised subgroup of patients harbor dominant WFS1 mutations that usually cause a milder phenotype, which can be limited to optic atrophy. Wolframin is a ubiquitous protein with high levels of expression in retinal, neuronal, and muscle tissues. It is a multifunctional protein that regulates a host of cellular functions, in particular the dynamic interaction with mitochondria at mitochondria-associated membranes. Wolframin has been implicated in several crucial cellular signaling pathways, including insulin signaling, calcium homeostasis, and the regulation of apoptosis and the ER stress response. There is currently no cure for WS; management remains largely supportive. This review will cover the clinical, genetic, and pathophysiological features of WS, with a specific focus on disease models and the molecular pathways that could serve as potential therapeutic targets. The current landscape of therapeutic options will also be discussed in the context of the latest evidence, including the pipeline for repurposed drugs and gene therapy.

Plain language summary

Wolfram syndrome - disease mechanisms and treatment options Wolfram syndrome (WS) is an ultra-rare genetic disease that causes diabetes mellitus and progressive loss of vision from early childhood. Vision is affected in WS because of damage to a specialized type of cells in the retina, known as retinal ganglion cells (RGCs), which converge at the back of the eye to form the optic nerve. The optic nerve is the fast-conducting cable that transmits visual information from the eye to the vision processing centers within the brain. As RGCs are lost, the optic nerve degenerates and it becomes pale in appearance (optic atrophy). Although diabetes mellitus and optic atrophy are the main features of WS, some patients can develop more severe problems because the brain and other organs, such as the kidneys and the bladder, are also affected. The majority of patients with WS carry spelling mistakes (mutations) in the WFS1 gene, which is located on the short arm of chromosome 4 (4p16.1). This gene is highly expressed in the eye and in the brain, and it encodes for a protein located within a compartment of the cell known as the endoplasmic reticulum. For reasons that still remain unclear, WFS1 mutations preferentially affect RGCs, accounting for the prominent visual loss in this genetic disorder. There is currently no effective treatment to halt or slow disease progression and management remains supportive, including the provision of visual aids and occupational rehabilitation. Research into WS has been limited by its relative rarity and the inability to get access to eye and brain tissues from affected patients. However, major advances in our understanding of this disease have been made recently by making use of more accessible cells from patients, such as skin cells (fibroblasts), or animal models, such as mice and zebrafish. This review summarizes the mechanisms by which WFS1 mutations affect cells, impairing their function and eventually leading to their premature loss. The possible treatment strategies to block these pathways are also discussed, with a particular focus on drug repurposing (i.e., using drugs that are already approved for other diseases) and gene therapy (i.e., replacing or repairing the defective WFS1 gene).

Proteomic Characterization of Proliferation Inhibition of Well-Differentiated Laryngeal Squamous Cell Carcinoma Cells Under Below-Background Radiation in a Deep Underground Environment

Background: There has been a considerable concern about cancer induction in response to radiation exposure. However, only a limited number of studies have focused on the biological effects of below-background radiation (BBR) in deep underground environments. To improve our understanding of the effects of BBR on cancer, we studied its biological impact on well-differentiated laryngeal squamous cell carcinoma cells (FD-LSC-1) in a deep underground laboratory (DUGL). Methods: The growth curve, morphological, and quantitative proteomic experiments were performed on FD-LSC-1 cells cultured in the DUGL and above-ground laboratory (AGL). Results: The proliferation of FD-LSC-1 cells from the DUGL group was delayed compared to that of cells from the AGL group. Transmission electron microscopy scans of the cells from the DUGL group indicated the presence of hypertrophic endoplasmic reticulum (ER) and a higher number of ER. At a cutoff of absolute fold change ≥ 1.2 and p < 0.05, 807 differentially abundant proteins (DAPs; 536 upregulated proteins and 271 downregulated proteins in the cells cultured in the DUGL) were detected. KEGG pathway analysis of these DAPs revealed that seven pathways were enriched. These included ribosome (p < 0.0001), spliceosome (p = 0.0001), oxidative phosphorylation (p = 0.0001), protein export (p = 0.0001), thermogenesis (p = 0.0003), protein processing in the endoplasmic reticulum (p = 0.0108), and non-alcoholic fatty liver disease (p = 0.0421). Conclusion: The BBR environment inhibited the proliferation of FD-LSC-1 cells. Additionally, it induced changes in protein expression associated with the ribosome, gene spliceosome, RNA transport, and energy metabolism among others. The changes in protein expression might form the molecular basis for proliferation inhibition and enhanced survivability of cells adapting to BBR exposure in a deep underground environment. RPL26, RPS27, ZMAT2, PRPF40A, SNRPD2, SLU7, SRSF5, SRSF3, SNRPF, WFS1, STT3B, CANX, ERP29, HSPA5, COX6B1, UQCRH, and ATP6V1G1 were the core proteins associated with the BBR stress response in cells.

Function of WFS1 and WFS2 in the Central Nervous System: Implications for Wolfram Syndrome and Alzheimer's disease

L.P. Li, L. Venkataraman, S. Chen, and H.J. Fu. Function of WFS1 and WFS2 in the Central Nervous System: Implications for Wolfram Syndrome and Alzheimer's Disease. NEUROSCI BIOBEHAV REVXXX-XXX,2020.-Wolfram syndrome (WS) is a rare monogenetic spectrum disorder characterized by insulin-dependent juvenile-onset diabetes mellitus, diabetes insipidus, optic nerve atrophy, hearing loss, progressive neurodegeneration, and a wide spectrum of psychiatric manifestations. Most WS patients belong to Wolfram Syndrome type 1 (WS1) caused by mutations in the Wolfram Syndrome 1 (WFS1/Wolframin) gene, while a small fraction of patients belongs to Wolfram Syndrome type 2 (WS2) caused by pathogenic variants in the CDGSH Iron Sulfur Domain 2 (CISD2/WFS2) gene. Although currently there is no treatment for this life-threatening disease, the molecular mechanisms underlying the pathogenesis of WS have been proposed. Interestingly, Alzheimer's disease (AD), an age-dependent neurodegenerative disease, shares some common mechanisms with WS. In this review, we focus on the function of WFS1 and WFS2 in the central nervous system as well as their implications in WS and AD. We also propose three future directions for elucidating the role of WFS1 and WFS2 in WS and AD.

Wolfram Syndrome: a Monogenic Model to Study Diabetes Mellitus and Neurodegeneration

Wolfram syndrome (WS) is a rare, progressive disorder characterized by childhood-onset diabetes mellitus, optic nerve atrophy, hearing loss, diabetes insipidus, and neurodegeneration. Currently, there is no effective treatment for WS, and patients typically die between 30 and 40 years of age. WS is primarily caused by autosomal recessive mutations in the Wolfram syndrome 1 (WFS1) gene (OMIM 222300), which encodes for wolframin (WFS1). This disorder is therefore a valuable monogenic model for prevalent diseases, particularly diabetes mellitus and neurodegeneration. Whereas reduced survival and secretion are known cellular impairments causing WS, the underlying molecular pathways and the physiological function of WFS1 remain incompletely described. Here, we characterize WFS1 as a regulator of intracellular calcium homeostasis, review our current understanding of the disease mechanism of WS, and discuss candidate treatment approaches. These insights will facilitate identification of new therapeutic strategies not only for WS but also for diabetes mellitus and neurodegeneration.

Lactate dehydrogenase expression modulates longevity and neurodegeneration in Drosophila melanogaster

Lactate dehydrogenase (LDH) catalyzes the conversion of glycolysis-derived pyruvate to lactate. Lactate has been shown to play key roles in brain energetics and memory formation. However, lactate levels are elevated in aging and Alzheimer's disease patients, and it is not clear whether lactate plays protective or detrimental roles in these contexts. Here we show that Ldh transcript levels are elevated and cycle with diurnal rhythm in the heads of aged flies and this is associated with increased LDH protein, enzyme activity, and lactate concentrations. To understand the biological significance of increased Ldh gene expression, we genetically manipulated Ldh levels in adult neurons or glia. Overexpression of Ldh in both cell types caused a significant reduction in lifespan whereas Ldh down-regulation resulted in lifespan extension. Moreover, pan-neuronal overexpression of Ldh disrupted circadian locomotor activity rhythms and significantly increased brain neurodegeneration. In contrast, reduction of Ldh in neurons delayed age-dependent neurodegeneration. Thus, our unbiased genetic approach identified Ldh and lactate as potential modulators of aging and longevity in flies.

Developmental hypomyelination in Wolfram syndrome: new insights from neuroimaging and gene expression analyses

Wolfram syndrome is a rare multisystem disorder caused by mutations in WFS1 or CISD2 genes leading to brain structural abnormalities and neurological symptoms. These abnormalities appear in early stages of the disease. The pathogenesis of Wolfram syndrome involves abnormalities in the endoplasmic reticulum (ER) and mitochondrial dynamics, which are common features in several other neurodegenerative disorders. Mutations in WFS1 are responsible for the majority of Wolfram syndrome cases. WFS1 encodes for an endoplasmic reticulum (ER) protein, wolframin. It is proposed that wolframin deficiency triggers the unfolded protein response (UPR) pathway resulting in an increased ER stress-mediated neuronal loss. Recent neuroimaging studies showed marked alteration in early brain development, primarily characterized by abnormal white matter myelination. Interestingly, ER stress and the UPR pathway are implicated in the pathogenesis of some inherited myelin disorders like Pelizaeus-Merzbacher disease, and Vanishing White Matter disease. In addition, exploratory gene-expression network-based analyses suggest that WFS1 expression occurs preferentially in oligodendrocytes during early brain development. Therefore, we propose that Wolfram syndrome could belong to a category of neurodevelopmental disorders characterized by ER stress-mediated myelination impairment. Further studies of myelination and oligodendrocyte function in Wolfram syndrome could provide new insights into the underlying mechanisms of the Wolfram syndrome-associated brain changes and identify potential connections between neurodevelopmental disorders and neurodegeneration.

GLP-1 receptor agonist liraglutide has a neuroprotective effect on an aged rat model of Wolfram syndrome

Wolfram syndrome (WS) is a rare neurodegenerative disorder that is mainly characterized by diabetes mellitus, optic nerve atrophy, deafness, and progressive brainstem degeneration. Treatment with GLP-1 receptor agonists has shown a promising anti-diabetic effect in WS treatment in both animal models and in human patients. Since previous research has tended to focus on investigation of the WS first symptom, diabetes mellitus, the aim of the present study was to examine liraglutide effect on WS-associated neurodegeneration. We took 9-month-old Wfs1 knock-out (KO) animals that already had developed glucose intolerance and treated them with liraglutide for 6 months. Our research results indicate that 6-month liraglutide treatment reduced neuroinflammation and ameliorated endoplasmic reticulum (ER) stress in the inferior olive of the aged WS rat model. Liraglutide treatment also protected retinal ganglion cells from cell death and optic nerve axons from degeneration. According to this, the results of the present study provide novel insight that GLP-1 receptor agonist liraglutide has a neuroprotective effect in the WS rat model.

Novel roles of ER stress in repressing neural activity and seizures through Mdm2- and p53-dependent protein translation

Seizures can induce endoplasmic reticulum (ER) stress, and sustained ER stress contributes to neuronal death after epileptic seizures. Despite the recent debate on whether inhibiting ER stress can reduce neuronal death after seizures, whether and how ER stress impacts neural activity and seizures remain unclear. In this study, we discovered that the acute ER stress response functions to repress neural activity through a protein translation-dependent mechanism. We found that inducing ER stress promotes the expression and distribution of murine double minute-2 (Mdm2) in the nucleus, leading to ubiquitination and down-regulation of the tumor suppressor p53. Reduction of p53 subsequently maintains protein translation, before the onset of translational repression seen during the latter phase of the ER stress response. Disruption of Mdm2 in an Mdm2 conditional knockdown (cKD) mouse model impairs ER stress-induced p53 down-regulation, protein translation, and reduction of neural activity and seizure severity. Importantly, these defects in Mdm2 cKD mice were restored by both pharmacological and genetic inhibition of p53 to mimic the inactivation of p53 seen during ER stress. Altogether, our study uncovered a novel mechanism by which neurons respond to acute ER stress. Further, this mechanism plays a beneficial role in reducing neural activity and seizure severity. These findings caution against inhibition of ER stress as a neuroprotective strategy for seizures, epilepsies, and other pathological conditions associated with excessive neural activity.

One-third of epilepsy patients respond poorly to current anti-epileptic drugs. Thus, there is an urgent need to characterize cellular behavior during seizures, and the corresponding molecular mechanisms in order to develop better therapies. Seizures are known to induce ER stress but how the ER stress response functions to modulate seizure activity is unknown. Our study provides evidence to demonstrate a novel and beneficial role for the ER stress response in reducing neural activity and seizure severity. Mechanistically, we found that these beneficial effects are mediated by elevated protein translation, which is triggered by the activation of Mdm2-p53 signaling, during the early ER stress response. Our findings suggest that therapeutic attempts to reduce ER stress in epilepsies may result in worsening seizure activity and therefore caution against inhibition of ER stress as a neuroprotective strategy for epilepsies.

Social behavior and aging: A fly model

The field of behavioral genetics has recently begun to explore the effect of age on social behaviors. Such studies are particularly important, as certain neuropsychiatric disorders with abnormal social interactions, like autism and schizophrenia, have been linked to older parents. Appropriate social interaction can also have a positive impact on longevity, and is associated with successful aging in humans. Currently, there are few genetic models for understanding the effect of aging on social behavior and its potential transgenerational inheritance. The fly is emerging as a powerful model for identifying the basic molecular mechanisms underlying neurological and neuropsychiatric disorders. In this review, we discuss these recent advancements, with a focus on how studies in Drosophila melanogaster have provided insight into the effect of aging on aspects of social behavior, including across generations.