IKBKAP Gene Research Articles

Combinatorial treatment increases IKAP levels in human cells generated from Familial Dysautonomia patients.

Familial Dysautonomia (FD) is an autosomal recessive congenital neuropathy that results from a point mutation at the 5’ splice site of intron 20 in the IKBKAP gene. This mutation decreases production of the IKAP protein, and treatments that increase the level of the full-length IKBKAP transcript are likely to be of therapeutic value. We previously found that phosphatidylserine (PS), an FDA-approved food supplement, elevates IKAP levels in cells generated from FD patients. Here we demonstrate that combined treatment of cells generated from FD patients with PS and kinetin or PS and the histone deacetylase inhibitor trichostatin A (TSA) resulted in an additive elevation of IKAP compared to each drug alone. This indicates that the compounds influence different pathways. We also found that pridopidine enhances production of IKAP in cells generated from FD patients. Pridopidine has an additive effect on IKAP levels when used in combination with kinetin or TSA, but not with PS; suggesting that PS and pridopidine influence IKBKAP levels through the same mechanism. Indeed, we demonstrate that the effect of PS and pridopidine is through sigma-1 receptor-mediated activation of the BDNF signaling pathway. A combination treatment with any of these drugs with different mechanisms has potential to benefit FD patients.

Frequency and Burden of Gastrointestinal Symptoms in Patients With Familial Dysautonomia

Introduction: Familial dysautonomia (FD) is a rare hereditary neuropathy caused by a mutation in the IKBKAP gene. Despite sensory impairments, patients with FD report a range of gastrointestinal symptoms. As the type and frequency of GI disorders has never been systematically studied, we aimed to establish the frequency of GI symptoms in FD patients relative to the average US population, with the long-term goal of gaining mechanistic insight into the cause of GI symptoms in FD and potentially broader populations. Methods: We distributed a modified version of the validated GI National Institute of Health (NIH) PROMIS questionnaire to 202 FD patients from the NYU FD Registry (the largest known prospective registry). The survey included 61 questions of eight domains (swallowing, nausea, constipation, fecal incontinence, diarrhea, belly pain, reflux, bloating). In addition, participants were asked to identify which bodily system was associated with the most bothersome symptoms, and their use of gastrostomy tubes, which are commonly used in FD patients. The questionnaire was completed by patients, or when appropriate by their primary caregivers. Raw PROMIS scores were normalized against a published validation cohort of 1177 American adults representative of the general population. Results: Seventy-nine (40%) of surveys were returned, with 53% completed by patients directly. Median age of subjects was 24 years old, and 53% were female (Table 1). A quarter of patients received nutrition by gastrostomy solely, while 53% were reliant on them only for liquid intake. Demographics and G tube use were similar between survey responders and non-responders from the FD registry. GI symptoms were more bothersome (42%) than orthopedic (23%), respiratory (14%), visual (13%), or psychiatric (4%) manifestations of the disease. In the previous week, 42% of patients reported watery or loose stools, 25% reported fecal incontinence, 52% reported nausea, and 52% reported borborygmus (Figure 1). Compared to the average American population (mean age 46), patients with FD reported more frequent and severe gastrointestinal symptoms of incontinence, nausea, bloating, and diarrhea (all in second highest quartile) (Figure 2).474_A Figure 1. Demographics. This is a representative sample of the demographics contained in the FD registry.474_B Figure 2. Percentages of FD patients (n=79) reporting gastrointestinal symptoms within the last seven days.Conclusion: Our results show that despite a variety of significant disease complications, GI symptoms are most commonly identified as the worst problem among FD patients. Further research is needed to better understand the underlying mechanism of these GI symptoms in order to improve quality of life.474_C Figure 3. Comparison of severity and frequency of gastrointestinal complaints in FD patients (n=79) versus average American population (n=1177).

Gastrointestinal Bleeding Is Common in Children With Familial Dysautonomia: A Case-Control Study (1980-2017): Presidential Poster Award

Introduction: Familial dysautonomia (FD) is a rare hereditary disorder caused by mutations in the IKBKAP gene. The disease is characterized by sensory and afferent autonomic abnormalities. Clinical observations suggest that GI bleeds are not infrequent in patients with FD, but their actual frequency is unknown. We aimed to define the incidence of GI bleeding in patients with FD and its associated risk factors. Methods: Cases and age/sex matched controls were retrospectively identified using the NYU FD registry, which includes over 600 patients with genetically confirmed FD. Cases were defined as patients with FD with at least one episode of GI bleeding between January 1, 1980 and September 25, 2017. For each case we selected one to two age-matched controls with FD and no history of GI bleeding. Data on medication use, gastrostomy (G) tube placement, fundoplication, and ambulatory laboratory values obtained within one year before the GI bleed (or matched time period) were compared using univariate logistic regression models. Retinal fundus tortuosity scores (a noninvasive surrogate marker for the microcirculation) were collected from the most recent clinical visit. Continuous variables were evaluated with t-test and categorical variables by Chi squared test. Multivariate analysis was performed. Results: Thirty-nine FD patients with Gl bleeding and 52 controls were included. 62 GI bleeds occurred in 2,144 observed years (28.0 per 1000 person year) with a median age of bleeding at 11 years old (Figure 1). Fifty-three cases (85.5%) were upper GI bleeds from gastric and duodenal ulcers (Figure 2). Bleeds in patients with FD were more likely to occur in those with a G tube (p<0.01) or with a fundoplication (p<0.01) (Table 1). There were no differences in NSAID or SSRI use, age at fundoplication, or age of G tube placement. For a subset of the FD cohort with available ophthalmic fundus imaging (n=61), cases with GI bleeding had no difference in average arteriolar tortuosity score. Conclusion: The incidence of GI bleeding in FD is considerably higher than in the general pediatric population, which has been reported as 0.2 per 1000 person year. Rather than medications, G-tube and fundoplication appear to be the most important risk factors for gastrointestinal bleeding in patients with FD. Moreover, these procedures did not appear to be direct complications of these procedures. The potential role of other factors leading to mucosal injury remain important targets for study and potential interventions.1054_A Demographics. Bleeds in FD patients were more likely to occur in those with a G tube (p<0.01) and in those with a fundoplication (p<0.01). Statistical tests were not performed to compare medications given that zero cases had history of NSAID or SSRI use.1054_B Distribution of gastrointestinal bleed by age frequency. A total of 62 GI bleeds occurred with a median age of bleeding at 13.09 years old.1054_C Location of gastric ulcers. Fifty-three cases (85.5%) were upper GI bleeds from gastric and duodenal ulcers.

Blocking of an intronic splicing silencer completely rescues IKBKAP exon 20 splicing in familial dysautonomia patient cells.

Familial dysautonomia (FD) is a severe genetic disorder causing sensory and autonomic dysfunction. It is predominantly caused by a c.2204+6T>C mutation in the IKBKAP gene. This mutation decreases the 5′ splice site strength of IKBKAP exon 20 leading to exon 20 skipping and decreased amounts of full-length IKAP protein. We identified a binding site for the splicing regulatory protein hnRNP A1 downstream of the IKBKAP exon 20 5′-splice site. We show that hnRNP A1 binds to this splicing regulatory element (SRE) and that two previously described inhibitory SREs inside IKBKAP exon 20 are also bound by hnRNP A1. Knockdown of hnRNP A1 in FD patient fibroblasts increases IKBKAP exon 20 inclusion demonstrating that hnRNP A1 is a negative regulator of IKBKAP exon 20 splicing. Furthermore, by mutating the SREs in an IKBKAP minigene we show that all three SREs cause hnRNP A1-mediated exon repression. We designed splice switching oligonucleotides (SSO) that blocks the intronic hnRNP A1 binding site, and demonstrate that this completely rescues splicing of IKBKAP exon 20 in FD patient fibroblasts and increases the amounts of IKAP protein. We propose that this may be developed into a potential new specific treatment of FD.

Antisense oligonucleotides correct the familial dysautonomia splicing defect in IKBKAP transgenic mice.

Familial dysautonomia (FD) is a rare inherited neurodegenerative disorder caused by a point mutation in the IKBKAP gene that results in defective splicing of its pre-mRNA. The mutation weakens the 5′ splice site of exon 20, causing this exon to be skipped, thereby introducing a premature termination codon. Though detailed FD pathogenesis mechanisms are not yet clear, correcting the splicing defect in the relevant tissue(s), thus restoring normal expression levels of the full-length IKAP protein, could be therapeutic. Splice-switching antisense oligonucleotides (ASOs) can be effective targeted therapeutics for neurodegenerative diseases, such as nusinersen (Spinraza), an approved drug for spinal muscular atrophy. Using a two-step screen with ASOs targeting IKBKAP exon 20 or the adjoining intronic regions, we identified a lead ASO that fully restored exon 20 splicing in FD patient fibroblasts. We also characterized the corresponding cis-acting regulatory sequences that control exon 20 splicing. When administered into a transgenic FD mouse model, the lead ASO promoted expression of full-length human IKBKAP mRNA and IKAP protein levels in several tissues tested, including the central nervous system. These findings provide insights into the mechanisms of IKBKAP exon 20 recognition, and pre-clinical proof of concept for an ASO-based targeted therapy for FD.

Founder mutation in IKBKAP gene causes vestibular impairment in familial dysautonomia

ObjectiveTo assess vestibular function in patients with familial dysautonomia (FD), a hereditary sensory and autonomic neuropathy – caused by a mutation in the IKBKAP gene (c.2204 + 6 T>C) – and characterized by marked gait ataxia. MethodsCervical and vestibular evoked myogenic potentials (cVEMPs and oVEMPs) were recorded from the sternocleidomastoid (SCM) and extraocular muscles in 14 homozygous patients, 2 heterozygous patients, and 15 healthy controls during percussion of the forehead. ResultscVEMP and oVEMP amplitudes were significantly lower, and peak latencies significantly delayed, in the FD patients. There were no differences in overall EMG during attempted maximal voluntary contractions of the SCM muscle, suggesting intact efferent function. The two heterozygotes with a minor haplotype missense (R696P) mutation in exon 19 of the IKBKAP gene had cVEMP responses less affected than the homozygous. ConclusionsThe founder mutation in the IKBKAP gene affects the development of vestibular afferent pathways, leading to attenuated cVEMPs. SignificanceVestibular abnormalities may contribute to the gait ataxia in FD.

ORAL FACTITIAL INJURY ASSOCIATED WITH FAMILIAL DYSAUTONOMIA

Familial dysautonomia (FD), known as Riley-Day syndrome or hereditary sensory and autonomic neuropathy type III (HSAN3), is a rare autosomal recessive disorder occurring almost exclusively in individuals of Ashkenazi Jewish (AJ) descent (estimated carrier incidence 1:27). Mutations in the IKBKAP gene have recently been shown to be responsible for FD. Signs and symptoms of FD include: reduced sensitivity to pain and thermal extremes, absence of fungiform papillae, the inability to produce tears upon emotional crying, absence of axon flare after injection of intradermal histamine, and absent deep tendon reflexes. There is a high incidence of self-inflicted or accidental traumas to the oral cavity, including crown fractures, luxation or avulsion injuries, and ulceration of the oral and perioral soft tissues.

Proteasome inhibitors to alleviate aberrant IKBKAP mRNA splicing and low IKAP/hELP1 synthesis in familial dysautonomia

FD is a rare neurodegenerative disorder caused by a mutation of the IKBKAP gene, which induces low expression levels of the Elongator subunit IKAP/hELP1 protein. A rational strategy for FD treatment could be to identify drugs increasing IKAP/hELP1 expression levels by blocking protein degradation pathways such as the 26S proteasome. Proteasome inhibitors are promising molecules emerging in cancer treatment and could thus constitute an enticing pharmaceutical strategy for FD treatment. Therefore, we tested three proteasome inhibitors on FD human olfactory ecto-mesenchymal stem cells (hOE-MSCs): two approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA), bortezomib and carfilzomib, as well as epoxomicin. Although all 3 inhibitors demonstrated activity in correcting IKBKAP mRNA aberrant splicing, carfilzomib was superior in enhancing IKAP/hELP1 quantity. Moreover, we observed a synergistic effect of suboptimal doses of carfilzomib on kinetin in improving IKBKAP isoforms ratio and IKAP/hELP1 expression levels allowing to counterbalance carfilzomib toxicity. Finally, we identified several dysregulated miRNAs after carfilzomib treatment that target proteasome-associated mRNAs and determined that IKAP/hELP1 deficiency in FD pathology is correlated to an overactivity of the 26S proteasome. Altogether, these results reinforce the rationale for using chemical compounds inhibiting the 26S proteasome as an innovative option for FD and a promising therapeutic pathway for many other neurodegenerative diseases.

Phosphatidylserine improves axonal transport by inhibition of HDAC and has potential in treatment of neurodegenerative diseases.

Familial dysautonomia (FD) is a rare children neurodegenerative disease caused due to a point mutation in the IKBKAP gene that results in decreased IKK complex-associated protein (IKAP) protein production. The disease affects mostly the dorsal root ganglion (DRG) and the sympathetic ganglion. Recently, we found that the molecular mechanisms underlying neurodegeneration in FD patients are defects in axonal transport of nerve growth factors and microtubule stability in the DRG. Neurons are highly polarized cells with very long axons. In order to survive and maintain proper function, neurons depend on transport of proteins and other cellular components from the neuronal body along the axons. We further demonstrated that IKAP is necessary for axon maintenance and showed that phosphatidylserine acts as an HDAC6 inhibitor to rescue neuronal function in FD cells. In this review, we will highlight our latest research findings.

Phosphatidylserine enhances IKBKAP transcription by activating the MAPK/ERK signaling pathway.

Familial dysautonomia (FD) is a genetic disorder manifested due to abnormal development and progressive degeneration of the sensory and autonomic nervous system. FD is caused by a point mutation in the IKBKAP gene encoding the IKAP protein, resulting in decreased protein levels. A promising potential treatment for FD is phosphatidylserine (PS); however, the manner by which PS elevates IKAP levels has yet to be identified. Analysis of ChIP-seq results of the IKBKAP promoter region revealed binding of the transcription factors CREB and ELK1, which are regulated by the mitogen-activated protein kinase (MAPK)/extracellular-regulated kinase (ERK) signaling pathway. We show that PS treatment enhanced ERK phosphorylation in cells derived from FD patients. ERK activation resulted in elevated IKBKAP transcription and IKAP protein levels, whereas pretreatment with the MAPK inhibitor U0126 blocked elevation of the IKAP protein level. Overexpression of either ELK1 or CREB activated the IKBKAP promoter, whereas downregulation of these transcription factors resulted in a decrease of the IKAP protein. Additionally, we show that PS improves cell migration, known to be enhanced by MAPK/ERK activation and abrogated in FD cells. In conclusion, our results demonstrate that PS activates the MAPK/ERK signaling pathway, resulting in activation of transcription factors that bind the promoter region of IKBKAP and thus enhancing its transcription. Therefore, compounds that activate the MAPK/ERK signaling pathway could constitute potential treatments for FD.

Sensory and autonomic deficits in a new humanized mouse model of familial dysautonomia.

Familial dysautonomia (FD) is an autosomal recessive neurodegenerative disease that affects the development and survival of sensory and autonomic neurons. FD is caused by an mRNA splicing mutation in intron 20 of the IKBKAP gene that results in a tissue-specific skipping of exon 20 and a corresponding reduction of the inhibitor of kappaB kinase complex-associated protein (IKAP), also known as Elongator complex protein 1. To date, several promising therapeutic candidates for FD have been identified that target the underlying mRNA splicing defect, and increase functional IKAP protein. Despite these remarkable advances in drug discovery for FD, we lacked a phenotypic mouse model in which we could manipulate IKBKAP mRNA splicing to evaluate potential efficacy. We have, therefore, engineered a new mouse model that, for the first time, will permit to evaluate the phenotypic effects of splicing modulators and provide a crucial platform for preclinical testing of new therapies. This new mouse model, TgFD9; Ikbkap(Δ20/flox) was created by introducing the complete human IKBKAP transgene with the major FD splice mutation (TgFD9) into a mouse that expresses extremely low levels of endogenous Ikbkap (Ikbkap(Δ20/flox)). The TgFD9; Ikbkap(Δ20/flox) mouse recapitulates many phenotypic features of the human disease, including reduced growth rate, reduced number of fungiform papillae, spinal abnormalities, and sensory and sympathetic impairments, and recreates the same tissue-specific mis-splicing defect seen in FD patients. This is the first mouse model that can be used to evaluate in vivo the therapeutic effect of increasing IKAP levels by correcting the underlying FD splicing defect.

Familial Dysautonomia: Mechanisms and Models.

Hereditary Sensory and Autonomic Neuropathies (HSANs) compose a heterogeneous group of genetic disorders characterized by sensory and autonomic dysfunctions. Familial Dysautonomia (FD), also known as HSAN III, is an autosomal recessive disorder that affects 1/3,600 live births in the Ashkenazi Jewish population. The major features of the disease are already present at birth and are attributed to abnormal development and progressive degeneration of the sensory and autonomic nervous systems. Despite clinical interventions, the disease is inevitably fatal. FD is caused by a point mutation in intron 20 of the IKBKAP gene that results in severe reduction in expression of IKAP, its encoded protein. In vitro and in vivo studies have shown that IKAP is involved in multiple intracellular processes, and suggest that failed target innervation and/or impaired neurotrophic retrograde transport are the primary causes of neuronal cell death in FD. However, FD is far more complex, and appears to affect several other organs and systems in addition to the peripheral nervous system. With the recent generation of mouse models that recapitulate the molecular and pathological features of the disease, it is now possible to further investigate the mechanisms underlying different aspects of the disorder, and to test novel therapeutic strategies.

MicroRNA screening identifies a link between NOVA1 expression and a low level of IKAP in familial dysautonomia.

ABSTRACTFamilial dysautonomia (FD) is a rare neurodegenerative disease caused by a mutation in intron 20 of the IKBKAP gene (c.2204+6T>C), leading to tissue-specific skipping of exon 20 and a decrease in the synthesis of the encoded protein IKAP (also known as ELP1). Small non-coding RNAs known as microRNAs (miRNAs) are important post-transcriptional regulators of gene expression and play an essential role in the nervous system development and function. To better understand the neuronal specificity of IKAP loss, we examined expression of miRNAs in human olfactory ecto-mesenchymal stem cells (hOE-MSCs) from five control individuals and five FD patients. We profiled the expression of 373 miRNAs using microfluidics and reverse transcription coupled to quantitative PCR (RT-qPCR) on two biological replicate series of hOE-MSC cultures from healthy controls and FD patients. This led to the total identification of 26 dysregulated miRNAs in FD, validating the existence of a miRNA signature in FD. We then selected the nine most discriminant miRNAs for further analysis. The signaling pathways affected by these dysregulated miRNAs were largely within the nervous system. In addition, many targets of these dysregulated miRNAs had been previously demonstrated to be affected in FD models. Moreover, we found that four of our nine candidate miRNAs target the neuron-specific splicing factor NOVA1. We demonstrated that overexpression of miR-203a-3p leads to a decrease of NOVA1, counter-balanced by an increase of IKAP, supporting a potential interaction between NOVA1 and IKAP. Taken together, these results reinforce the choice of miRNAs as potential therapeutic targets and suggest that NOVA1 could be a regulator of FD pathophysiology.

Familial Dysautonomia (FD) Human Embryonic Stem Cell Derived PNS Neurons Reveal that Synaptic Vesicular and Neuronal Transport Genes Are Directly or Indirectly Affected by IKBKAP Downregulation.

A splicing mutation in the IKBKAP gene causes Familial Dysautonomia (FD), affecting the IKAP protein expression levels and proper development and function of the peripheral nervous system (PNS). Here we found new molecular insights for the IKAP role and the impact of the FD mutation in the human PNS lineage by using a novel and unique human embryonic stem cell (hESC) line homozygous to the FD mutation originated by pre implantation genetic diagnosis (PGD) analysis. We found that IKBKAP downregulation during PNS differentiation affects normal migration in FD-hESC derived neural crest cells (NCC) while at later stages the PNS neurons show reduced intracellular colocalization between vesicular proteins and IKAP. Comparative wide transcriptome analysis of FD and WT hESC-derived neurons together with the analysis of human brains from FD and WT 12 weeks old embryos and experimental validation of the results confirmed that synaptic vesicular and neuronal transport genes are directly or indirectly affected by IKBKAP downregulation in FD neurons. Moreover we show that kinetin (a drug that corrects IKBKAP alternative splicing) promotes the recovery of IKAP expression and these IKAP functional associated genes identified in the study. Altogether, these results support the view that IKAP might be a vesicular like protein that might be involved in neuronal transport in hESC derived PNS neurons. This function seems to be mostly affected in FD-hESC derived PNS neurons probably reflecting some PNS neuronal dysfunction observed in FD.

Involvement of IKAP in peripheral target innervation and in specific JNK and NGF signaling in developing PNS neurons.

A splicing mutation in the ikbkap gene causes Familial Dysautonomia (FD), affecting the IKAP protein expression levels and proper development and function of the peripheral nervous system (PNS). Here we attempted to elucidate the role of IKAP in PNS development in the chick embryo and found that IKAP is required for proper axonal outgrowth, branching, and peripheral target innervation. Moreover, we demonstrate that IKAP colocalizes with activated JNK (pJNK), dynein, and β-tubulin at the axon terminals of dorsal root ganglia (DRG) neurons, and may be involved in transport of specific target derived signals required for transcription of JNK and NGF responsive genes in the nucleus. These results suggest the novel role of IKAP in neuronal transport and specific signaling mediated transcription, and provide, for the first time, the basis for a molecular mechanism behind the FD phenotype.

Familial dysautonomia (FD) patients have reduced levels of the modified wobble nucleoside mcm5s2U in tRNA

Familial dysautonomia (FD) is a recessive neurodegenerative genetic disease. FD is caused by a mutation in the IKBKAP gene resulting in a splicing defect and reduced levels of full length IKAP protein. IKAP homologues can be found in all eukaryotes and are part of a conserved six subunit protein complex, Elongator complex. Inactivation of any Elongator subunit gene in multicellular organisms cause a wide range of phenotypes, suggesting that Elongator has a pivotal role in several cellular processes. In yeast, there is convincing evidence that the main role of Elongator complex is in formation of modified wobble uridine nucleosides in tRNA and that their absence will influence translational efficiency. To date, no study has explored the possibility that FD patients display defects in formation of modified wobble uridine nucleosides as a consequence of reduced IKAP levels. In this study, we show that brain tissue and fibroblast cell lines from FD patients have reduced levels of the wobble uridine nucleoside 5-methoxycarbonylmethyl-2-thiouridine (mcm5s2U). Our findings indicate that FD could be caused by inefficient translation due to lower levels of wobble uridine nucleosides.

IKAP deficiency in an FD mouse model and in oligodendrocyte precursor cells results in downregulation of genes involved in oligodendrocyte differentiation and myelin formation.

The splice site mutation in the IKBKAP gene coding for IKAP protein leads to the tissue-specific skipping of exon 20, with concomitant reduction in IKAP protein production. This causes the neurodevelopmental, autosomal-recessive genetic disorder - Familial Dysautonomia (FD). The molecular hallmark of FD is the severe reduction of IKAP protein in the nervous system that is believed to be the main reason for the devastating symptoms of this disease. Our recent studies showed that in the brain of two FD patients, genes linked to oligodendrocyte differentiation and/or myelin formation are significantly downregulated, implicating IKAP in the process of myelination. However, due to the scarcity of FD patient tissues, these results awaited further validation in other models. Recently, two FD mouse models that faithfully recapitulate FD were generated, with two types of mutations resulting in severely low levels of IKAP expression. Here we demonstrate that IKAP deficiency in these FD mouse models affects a similar set of genes as in FD patients' brains. In addition, we identified two new IKAP target genes involved in oligodendrocyte cells differentiation and myelination, further underscoring the essential role of IKAP in this process. We also provide proof that IKAP expression is needed cell-autonomously for the regulation of expression of genes involved in myelin formation since knockdown of IKAP in the Oli-neu oligodendrocyte precursor cell line results in similar deficiencies. Further analyses of these two experimental models will compensate for the lack of human postmortem tissues and will advance our understanding of the role of IKAP in myelination and the disease pathology.

Dynamic changes in IKBKAP mRNA levels during crisis of familial dysautonomia patients

Familial dysautonomia is a neurodegenerative, genetic disorder caused by an autosomal recessive mutation in the IKBKAP gene, which encodes the IkB kinase complex-associated protein. Familial dysautonomia patients have recurrent crises characterized by bouts of nausea, vomiting, hypertension, tachycardia, sweating, blotching and personality changes. The dysautonomia crisis is usually triggered by stressful physiological or emotional events, however the pathophysiology of the crisis is not yet fully clear and little is known about the molecular mechanisms involved in onset and consequences of the crisis. We have investigated the dysautonomia crisis by evaluating the expression of the familial dysautonomia gene - IKBKAP, in patients during different crisis stages. Baseline IKBKAP mRNA levels in white blood cells were evaluated in thirteen FD patients (fourteen crisis events) and compared to mRNA levels at the onset, during, and after recovery from the crisis. We have found a significant decrease in IKBKAP mRNA level during the crisis, which is restored to a baseline level after recovery from the crisis. We speculate that the familial dysautonomia crisis pathophysiology might be related, at least in part, to the down regulation of the IKBKAP gene. Yet, it is still unclear whether the down regulation in IKBKAP mRNA is caused by the physiological stress events which have triggered the crisis or whether this molecular change is a consequence of the crisis.

Cardiac glycosides correct aberrant splicing of IKBKAP‐encoded mRNA in familial dysautonomia derived cells by suppressing expression of SRSF3

The ability to modulate the production of the wild-type transcript in cells bearing the splice-altering familial dysautonomia (FD) causing mutation in the IKBKAP gene prompted a study of the impact of a panel of pharmaceuticals on the splicing of this transcript, which revealed the ability of the cardiac glycoside digoxin to increase the production of the wild-type, exon-20-containing, IKBKAP-encoded transcript and the full-length IκB-kinase-complex-associated protein in FD-derived cells. Characterization of the cis elements and trans factors involved in the digoxin-mediated effect on splicing reveals that this response is dependent on an SRSF3 binding site(s) located in the intron 5' of the alternatively spliced exon and that digoxin mediates its effect by suppressing the level of the SRSF3 protein. Characterization of the digoxin-mediated effect on the RNA splicing process was facilitated by the identification of several RNA splicing events in which digoxin treatment mediates the enhanced inclusion of exonic sequence. Moreover, we demonstrate the ability of digoxin to impact the splicing process in neuronal cells, a cell type profoundly impacted by FD. This study represents the first demonstration that digoxin possesses splice-altering capabilities that are capable of reversing the impact of the FD-causing mutation. These findings support the clinical evaluation of the impact of digoxin on the FD patient population.

Ikbkap/Elp1 Deficiency Causes Male Infertility by Disrupting Meiotic Progression

Mouse Ikbkap gene encodes IKAP—one of the core subunits of Elongator—and is thought to be involved in transcription. However, the biological function of IKAP, particularly within the context of an animal model, remains poorly characterized. We used a loss-of-function approach in mice to demonstrate that Ikbkap is essential for meiosis during spermatogenesis. Absence of Ikbkap results in defects in synapsis and meiotic recombination, both of which result in increased apoptosis and complete arrest of gametogenesis. In Ikbkap-mutant testes, a few meiotic genes are down-regulated, suggesting IKAP's role in transcriptional regulation. In addition, Ikbkap-mutant testes exhibit defects in wobble uridine tRNA modification, supporting a conserved tRNA modification function from yeast to mammals. Thus, our study not only reveals a novel function of IKAP in meiosis, but also suggests that IKAP contributes to this process partly by exerting its effect on transcription and tRNA modification.