Novel NAXE variants as a cause for neurometabolic disorder: implications for treatment

Differential interactions between gene expressions and stressors across the lifespan in major depressive disorder

BACKGROUND

Both genetic predispositions and exposures to stressors have collectively contributed to the development of major depressive disorder (MDD). To deep dive into their roles in MDD, our study aimed to examine which susceptible gene expression interacts with various dimensions of stressors in the MDD risk among a large population cohort.

METHODS

Data analyzed were from a longitudinal community-based cohort from Southwest Montreal, Canada (N = 1083). Latent profile models were used to identify distinct patterns of stressors for the study cohort. A transcriptome-wide association study (TWAS) method was performed to examine the interactive effects of three dimensions of stressors (threat, deprivation, and cumulative lifetime stress) and gene expression on the MDD risk in a total of 48 tissues from GTEx. Additional analyses were also conducted to further explore and specify these associations including colocalization, and fine-mapping analyses, in addition to enrichment analysis investigations based on TWAS.

RESULTS

We identified 3321 genes linked to MDD at the nominal p-value <0.05 and found that different patterns of stressors can amplify the genetic susceptibility to MDD. We also observed specific genes and pathways that interacted with deprivation and cumulative lifetime stressors, particularly in specific brain tissues including basal ganglia, prefrontal cortex, brain amygdala, brain cerebellum, brain cortex, and the whole blood. Colocalization analysis also identified these genes as having a high probability of sharing MDD causal variants.

LIMITATIONS

The study cohort was composed exclusively of individuals of Caucasians, which restricts the generalizability of the findings to other ethnic population groups.

CONCLUSIONS

The findings of the study unveiled significant interactions between potential tissue-specific gene expression × stressors in the MDD risk and shed light on the intricate etiological attributes of gene expression and specific stressors across the lifespan in MDD. These genetic and environmental attributes in MDD corroborate the vulnerability-stress theory and direct future stress research to have a closer examination of genetic predisposition and potential involvements of omics studies to specify the intricate relationships between genes and stressful environments.

Transient response to high-dose niacin therapy in a patient with NAXE deficiency

Background

NAXE-encephalopathy or early-onset progressive encephalopathy with brain edema and/or leukoencephalopathy-1 (PEBEL-1) and NAXD-encephalopathy (PEBEL-2) have been described recently as mitochondrial disorders causing psychomotor regression, hypotonia, ataxia, quadriparesis, ophthalmoparesis, respiratory insufficiency, encephalopathy, and seizures with the onset being usually within the first three years of life. It usually leads to rapid disease progression and death in early childhood. Anecdotal reports suggest that niacin, through its role in nicotinamide adenine dinucleotinde (NAD) de novo synthesis, corrects biochemical derangement, and slows down disease progression. Reports so far have supported this observation.

Methods

We describe a patient with a confirmed PEBEL-1 diagnosis and report his clinical response to niacin therapy. Moreover, we systematically searched the literature for PEBEL-1 and PEBEL-2 patients treated with niacin and details about response to treatment and clinical data were reviewed. Furthermore, we are describing off-label use of a COX2 inhibitor to treat niacin-related urticaria in NAXE-encephalopathy.

Results

So far, seven patients with PEBEL-1 and PEBEL-2 treated with niacin were reported, and all patients showed a good response for therapy or stabilization of symptoms. We report a patient exhibiting PEBEL-1 with an unfavorable outcome despite showing initial stabilization and receiving the highest dose of niacin reported to date. Niacin therapy failed to halt disease progression or attain stabilization of the disease in this patient.

Conclusion

Despite previous positive results for niacin supplementation in patients with PEBEL-1 and PEBEL-2, this is the first report of a patient with PEBEL-1 who deteriorated to fatal outcome despite being started on the highest dose of niacin therapy reported to date.

Identification and Validation of Nicotinamide Metabolism-Related Gene Signatures as a Novel Prognostic Model for Hepatocellular Carcinoma

Background

Nicotinamide (NAM+) regulates redox and metabolic activities in the mitochondria. The intention of the research was to identify key genes that relate to nicotinamide in hepatocellular carcinoma (HCC).

Methods

Relevant clinical information were collected as well as RNA-seq data using the Cancer Genome Atlas (TCGA) database. Differential analysis was used to discover the genes that were differently expressed. On the key genes associated with NAM, functional enrichment analysis was carried out. Next, receiver operating characteristic (ROC) and prognosis Kaplan-Meier (K-M) curve analyses were used to evaluate the importance of important gene expression, respectively. The immune cell signatures were estimated using the CIBERSORT algorithm. Finally, the anticancer impact of NAM on HCC was experimentally confirmed, and important genes NADSYN1 and NT5C were validated at the protein level in clinical specimens.

Results

Six prognostic key genes (NAXE, NADSYN1, NT5C, NT5C3A, PNP and NT5E) were identified. There is an association between the level of key gene expression and the clinical prognosis. Four key genes (NAXE, NADSYN1, NT5C and NT5C3A) have statistical significance of survival prognosis. Finally, the expression of NAM-related genes and the inhibitory effect of NAM on HCC were verified by experiments.

Conclusion

The study first found some Nicotinamide metabolism-related differentially expressed genes (NMRDEGs) that are related to HCC can contribute to predicting survival and monitoring the treatment.

Effects of a Tailored Pediatric Rehabilitation Protocol on Children With Neurometabolic Disorder: A Case Report

Neurometabolic disorders encompass a diverse group of conditions characterized by inborn errors of metabolism, affecting various aspects of neurological function. This case report focuses on an 11-year-old male child with a neurometabolic disorder who presents with walking difficulties, speech impairment, and neurological symptoms. The background emphasizes the heterogeneity of neurometabolic disorders, their genetic and clinical complexity, and the need for tailored interventions to address specific manifestations. The primary aim of this study is to implement a comprehensive physiotherapy intervention plan for an 11-year-old male child with a neurometabolic disorder, targeting the improvement of gait abnormalities, regaining developmental milestones, and addressing associated challenges such as fatigue. The physiotherapy intervention plan employs a multifaceted approach, incorporating principles of neuroplasticity, motor learning, and adaptive strategies. A comprehensive gait training protocol involves proper orthotic fitting, forearm support walker training, treadmill exercises, and parallel bar training. Developmental milestones are addressed through motor and fine motor skill exercises. Coping strategies and energy conservation techniques are integrated to manage fatigue. The study utilizes outcome measures, including the Gross Motor Function Measure, Manual Ability Classification System, and Functional Independence Measure, to assess the impact of the intervention on the patient's functional abilities. Preliminary findings suggest promising improvements in gait, motor skills, and overall functional independence following the implemented physiotherapy intervention. The study underscores the potential effectiveness of a tailored approach rooted in neuroplasticity and motor learning principles for individuals with neurometabolic disorders. The patient-centered care model, encompassing coping strategies and energy conservation techniques, contributes to holistic well-being. While specific literature on these interventions in neurometabolic disorders is limited, the study provides valuable insights and calls for further research to refine and expand tailored therapeutic approaches in this challenging clinical context.

Apolipoprotein A-I Binding Protein Inhibits the Formation of Infantile Hemangioma through Cholesterol-Regulated Hypoxia-Inducible Factor 1α Activation

Infantile hemangioma (IH) is the most frequent vascular tumor of infancy with unclear pathogenesis; disordered angiogenesis is considered to be involved in its formation. Apolipoprotein A-I binding protein (AIBP)-also known as NAXE (NAD [P]HX epimerase)-a regulator of cholesterol metabolism, plays a critical role in the pathological angiogenesis of mammals. In this study, we found that AIBP had much lower expression levels in both tissues from patients with IH and hemangioma endothelial cells (HemECs) than in adjacent normal tissues and human dermal vascular endothelial cells, respectively. Knockout of NAXE by CRISPR-Cas9 in HemECs enhanced tube formation and migration, and NAXE overexpression impaired tube formation and migration of HemECs. Interestingly, AIBP suppressed the proliferation of HemECs in hypoxia. We then found that reduced expression of AIBP correlated with increased hypoxia-inducible factor 1α levels in tissues from patients with IH and HemECs. Further mechanistic investigation demonstrated that AIBP disrupted hypoxia-inducible factor 1α signaling through cholesterol metabolism under hypoxia. Notably, AIBP significantly inhibited the development of IH in immunodeficient mice. Furthermore, using the validated mouse endothelial cell (ie, EOMA cells) and Naxe-/- mouse models, we demonstrated that both endogenous AIBP from tumors and AIBP in the tumor microenvironment limit the formation of hemangioma. These findings suggested that AIBP was a player in the pathogenesis of IH and could be a potential pharmacological target for treating IH.

Long-term follow-up of an attenuated presentation of NAXE-related disease, a potentially actionable neurometabolic disease: a case report

Background

Early-onset progressive encephalopathy with brain edema and/or leukoencephalopathy (PEBEL-1) is an autosomal recessive disorder whereby a fluctuating clinical course is exacerbated by febrile illnesses. Pathogenic NAD(P)HX epimerase (NAXE) gene mutations underpin this disorder. This mutation damages the metabolite repair system involved in regenerating crucial redox carriers. Longer survival has rarely been reported in this potentially actionable entity.

Objectives

This case study aims to report a milder phenotype of a patient with NAXE gene mutation and his longitudinal follow-up of more than 20 years.

Case report

A 24-year-old man first became symptomatic in infancy with frequent initial neurological decompensations in the setting of infections with subsequent clinical improvement followed by stability with residual cerebellar dysfunction. Clinical features noted over the years include chronic ataxia, nystagmus, ptosis, mild spasticity of lower limbs, and neuropsychiatric symptoms. Cerebellar and spinal cord atrophy were noted in cranial and spinal MR imaging. Biallelic homozygous variants in the NAXE gene (c.733 A>C) were identified on whole exome sequencing. Symptom management included the initiation of a mitochondrial cocktail with carnitine, coenzyme Q, and thiamine. Subsequently, niacin (Vitamin B3), which is involved in the cellular biosynthesis of NAD+, was added, given its potentially beneficial therapeutic impact.

Conclusion

A missense homozygous variant in the NAXE gene is described in this patient with a milder clinical phenotype of the disease. Supplementation with niacin in addition to a mitochondrial cocktail presents a potential supportive therapeutic option to reduce disease progression.

Nuclear Mitochondrial Disorder Due to a Variant in NAXE in Two Unrelated Indian Children

Progressive encephalopathy with brain edema and/or leukoencephalopathy type 1 (PEBEL1) is a nuclear mitochondrial disorder involving the NAD(P)HX repair mechanism due to a NAXE variation. PEBEL1 is characterized by rapid neurologic deterioration culminating in death following high-grade fever during infancy. Currently, 23 patients from 14 families are described in the literature, with only three survivors. The authors report two living children from unrelated families with PEBEL1. Both children presented in infancy with ptosis, squint, and ataxia with no skin manifestations. Whole-exome sequencing revealed previously reported c.804_807delInsA (p.Lys270del) variation in exon 6 of NAXE. This is the first Indian report of PEBEL1.

De novo mutation of NAXE (APOAIBP)-related early-onset progressive encephalopathy with brain edema and/or leukoencephalopathy-1: A case report

BACKGROUND

Early-onset progressive encephalopathy with brain edema and/or leukoencephalopathy-1 (PEBEL1) is a rare autosomal recessive severe neurometabolic disease. The aim of this study was to investigate the clinical characteristics and genetic pathogenicity of PEBEL1 caused by rare NAXE (or APOA1BP)-related defects.

CASE SUMMARY

The patient was a girl aged 2 years and 10 mo. She was hospitalized due to walking disorder for > 40 d. The clinical manifestations were ataxia, motor function regression, hypotonia, and eyelid ptosis. Within 1 mo of hospitalization, she developed sigh breathing, respiratory failure, cerebellar edema and brain hernia, and finally she died. Changes were found in cranial imaging, including cerebellar edema accompanied by symmetrical myelopathy. Through whole exome sequencing, we detected NAXE compound heterozygous variation (NM 144772.3) c.733A>C (p. Lys245Gln, dbSNP: rs770023429) and novel variation c.370G>T (p.Gly124Cys) in the germline gene. The clinical features and core phenotypes of this case were consistent with 18 previously reported cases of PEBEL1.

CONCLUSION

This is the first case of NAXE-related PEBEL1 with severe clinical phenotype in Mainland China. The p.Gly124Cys mutation discovered in this case has enriched the pathogenic variation spectrum of NAXE.

Skin Conditions and Movement Disorders: Hiding in Plain Sight

Skin manifestations are well-recognized non-motor symptoms of Parkinson's disease (PD) and other hypokinetic and hyperkinetic movement disorders. Skin conditions are usually well visible during routine clinical examination and their recognition may play a major role in diagnostic work-up. In this educational review we: (1) briefly outline skin conditions related to Parkinson's disease, including therapy-related skin complications and their management; (2) discuss the role of skin biopsies in early diagnosis of PD and differential diagnosis of parkinsonian syndromes; and focus more on areas which have not been reviewed in the literature before, including (3) skin conditions related to atypical parkinsonism, and (4) skin conditions related to hyperkinetic movement disorders. In case of rare hyperkinetic movement disorders, specific dermatological manifestations, like presence of angiokeratomas, telangiectasias, Mongolian spots, lipomas, ichthyosis, progeroid skin changes and others may point to a very specific group of disorders and help guide further investigations.

NAXE deficiency: A neurometabolic disorder of NAD(P)HX repair amenable for metabolic correction

The NAD(P)HX repair system is a metabolite damage repair mechanism responsible for restoration of NADH and NADPH after their inactivation by hydration. Deficiency in either of its two enzymes, NAD(P)HX dehydratase (NAXD) or NAD(P)HX epimerase (NAXE), causes a fatal neurometabolic disorder characterized by decompensations precipitated by inflammatory stress. Clinical findings include rapidly progressive muscle weakness, ataxia, ophthalmoplegia, and motor and cognitive regression, while neuroimaging abnormalities are subtle or nonspecific, making a clinical diagnosis challenging. During stress, nonenzymatic conversion of NAD(P)H to NAD(P)HX increases, and in the absence of repair, NAD(P)H is depleted, and NAD(P)HX accumulates, leading to decompensation; however, the contribution of each to the metabolic derangement is not established. Herein, we summarize the clinical knowledge of NAXE deficiency from 30 cases and lessons learned about disease pathogenesis from cell cultures and model organisms and describe a metabolomics signature obtained by untargeted metabolomics analysis in one case at the time of crisis and after initiation of treatment. Overall, biochemical findings support a model of acute depletion of NAD⁺, signs of mitochondrial dysfunction, and altered lipidomics. These findings are further substantiated by untargeted metabolomics six months post-crisis showing that niacin supplementation reverses primary metabolomic abnormalities concurrent with improved clinical status.

Progressive Myoclonus Epilepsies

Background and Objectives

To assess the current diagnostic yield of genetic testing for the progressive myoclonus epilepsies (PMEs) of an Italian series described in 2014 where Unverricht-Lundborg and Lafora diseases accounted for ∼50% of the cohort.

Methods

Of 47/165 unrelated patients with PME of indeterminate genetic origin, 38 underwent new molecular evaluations. Various next-generation sequencing (NGS) techniques were applied including gene panel analysis (n = 7) and/or whole-exome sequencing (WES) (WES singleton n = 29, WES trio n = 7, and WES sibling n = 4). In 1 family, homozygosity mapping was followed by targeted NGS. Clinically, the patients were grouped in 4 phenotypic categories: “Unverricht-Lundborg disease-like PME,” “late-onset PME,” “PME plus developmental delay,” and “PME plus dementia.”

Results

Sixteen of 38 (42%) unrelated patients reached a positive diagnosis, increasing the overall proportion of solved families in the total series from 72% to 82%. Likely pathogenic variants were identified in NEU1 (2 families), CERS1 (1 family), and in 13 nonfamilial patients in KCNC1 (3), DHDDS (3), SACS, CACNA2D2, STUB1, AFG3L2, CLN6, NAXE, and CHD2. Across the different phenotypic categories, the diagnostic rate was similar, and the same gene could be found in different phenotypic categories.

Discussion

The application of NGS technology to unsolved patients with PME has revealed a collection of very rare genetic causes. Pathogenic variants were detected in both established PME genes and in genes not previously associated with PME, but with progressive ataxia or with developmental encephalopathies. With a diagnostic yield >80%, PME is one of the best genetically defined epilepsy syndromes.

NAXE gene mutation-related progressive encephalopathy: A case report and literature review

RATIONALE

Progressive encephalopathy with brain edema and/or leukoencephalopathy-1 is an infantile, lethal neurometabolic disorder caused by a NAD(P)HX epimerase (NAXE) gene mutation. It is characterized by a fluctuating disease course with repeated episodes of improvement and regression. In this report, we present a rare case of NAXE gene mutation-related encephalopathy with unexpected neurological recovery and long survival time.

PATIENT CONCERNS

A 20-month-old girl presented with progressively unsteady gait and bilateral hand tremors after a trivial febrile illness. Her disease rapidly progressed to consciousness disturbance, 4-limb weakness (muscle power: 1/5 on the Medical Research Council scale), and respiratory failure. The patient gradually recovered 2 months later. However, another episode of severe fever-induced encephalopathy developed 2 years after the initial presentation.

DIAGNOSES

Results of laboratory investigations, including complete blood count, blood chemistry, inflammatory markers, and cerebral spinal fluid analysis were unremarkable. Electroencephalography and nerve conduction velocity studies yielded normal results. Brain magnetic resonance imaging on diffusion-weighted imaging revealed abnormal sysmmetric hyperintensity in the bilateral middle cerebellar peduncles. A genetic study using whole exome sequencing confirmed the diagnosis of NAXE gene mutation-related encephalopathy.

INTERVENTIONS

Pulse therapy with methylprednisolone, intravenous immunoglobulin, coenzyme Q10, and carnitine were initially introduced. After a NAXE gene defect was detected, the vitamin B complex and coenzyme Q10 were administered. A continuous rehabilitation program was also implemented.

OUTCOMES

NAXE gene mutation-related encephalopathy is usually regarded as a lethal neurometabolic disorder. However, the outcome in this case is better than that in the previous cases. She showed progressive neurological recovery and a longer survival time. The muscle power of the 4 limbs recovered to grade 4. At present (age of 5.5 years old), she can walk with an unsteady gait and go to school.

LESSONS

Although NAXE gene mutation-related encephalopathy is rare, it should be considered as a differential diagnosis of early onset progressive encephalopathy.

A novel homozygous missense variant in the NAXE gene in an Iranian family with progressive encephalopathy with brain edema and leukoencephalopathy

Homozygous or compound heterozygous mutations in the NAD(P)HX epimerase (NAXE) gene, cause early-onset progressive encephalopathy with brain edema and/or leukoencephalopathy 1. This disorder is characterized by psychomotor regression, hypotonia, ataxia, respiratory insufficiency, tetraparesis, and seizures, leading to coma and death in early childhood. In this study, whole-exome sequencing was used to identify the pathogenic variant, followed by confirmation of identified variant in the proband and segregation analysis in the family by Sanger sequencing. Several in-silico prediction tools were employed to provide additional evidences on the pathogenicity of the identified variant. The proband was an affected 3-year-old boy presented with encephalopathy and developmental regression from Ardebil province, northwest of Iran. Additional clinical features were cognitive regression and a high level of lactate in CSF. The clinical presentation was suggestive of a mitochondrial disorder. In addition, his brother died at the age of 20 months old due to encephalopathy, seizures, developmental regression, and loss of consciousness. We found a novel homozygous missense variant within the NAXE gene, [NM_144772.3:c.565G > A; p.(Gly189Ser)]. Applying different in-silico prediction tools and bioinformatics databases analysis showed that this variant is damaging. So far, seven mutations have been reported in the NAXE gene. In this study, we report the first mutation in the Iranian population and the eighth one in total for this gene.

NAD(P)HX epimerase downregulation promotes tumor progression through ROS/HIF-1α signaling in hepatocellular carcinoma

Reactive oxygen species (ROS) derived from aberrant tumor metabolism could contribute to tumor invasion and metastasis. NAD(P)HX Epimerase (NAXE), an epimerase that allows the repair of damaged forms of antioxidant NADPH, is a potential cellular ROS scavenger and its role in tumor development is still elusive. Here, we found that NAXE is significantly downregulated in hepatocellular carcinoma (HCC) tissues and cell lines. NAXE downregulation is associated with poor clinicopathological characteristics and is an independent risk factor for overall and disease‐free survival of HCC patients after liver resection. In addition, low NAXE expression could identify worse prognosis of HCC patients before vascular invasion or in early stages of disease. In particularly, low NAXE expression in HCC is markedly associated with microvascular invasion (MVI) and its combination with MVI predicts poorer prognosis of HCC patients after liver resection. Furthermore, in vitro and in vivo experiments both showed that knockdown of NAXE expression in HCC cells promoted migration, invasion, and metastasis by inducing epithelial‐mesenchymal transition (EMT), whereas NAXE overexpression causes the opposite effects. Mechanistically, low NAXE expression reduced NADPH levels and further caused ROS level increase and hypoxia‐inducible factor‐1α (HIF‐1α) activation, thereby promoting invasion and metastasis of HCC by facilitating EMT. What is more, the tumor‐promoting effect of NAXE knockdown in HCC xenograft can be abolished by giving mice N‐acetyl‐l‐cysteine (NAC) in drinking water. Taken together, our findings uncovered a tumor suppressor role for NAXE in HCC by scavenging excessive ROS and inhibiting tumor‐promoting signaling pathways, suggesting a new strategy for HCC therapy by targeting redox signaling.

Treatable inherited metabolic disorders causing intellectual disability: 2021 review and digital app

BACKGROUND

The Treatable ID App was created in 2012 as digital tool to improve early recognition and intervention for treatable inherited metabolic disorders (IMDs) presenting with global developmental delay and intellectual disability (collectively 'treatable IDs'). Our aim is to update the 2012 review on treatable IDs and App to capture the advances made in the identification of new IMDs along with increased pathophysiological insights catalyzing therapeutic development and implementation.

METHODS

Two independent reviewers queried PubMed, OMIM and Orphanet databases to reassess all previously included disorders and therapies and to identify all reports on Treatable IDs published between 2012 and 2021. These were included if listed in the International Classification of IMDs (ICIMD) and presenting with ID as a major feature, and if published evidence for a therapeutic intervention improving ID primary and/or secondary outcomes is available. Data on clinical symptoms, diagnostic testing, treatment strategies, effects on outcomes, and evidence levels were extracted and evaluated by the reviewers and external experts. The generated knowledge was translated into a diagnostic algorithm and updated version of the App with novel features.

RESULTS

Our review identified 116 treatable IDs (139 genes), of which 44 newly identified, belonging to 17 ICIMD categories. The most frequent therapeutic interventions were nutritional, pharmacological and vitamin and trace element supplementation. Evidence level varied from 1 to 3 (trials, cohort studies, case-control studies) for 19% and 4-5 (case-report, expert opinion) for 81% of treatments. Reported effects included improvement of clinical deterioration in 62%, neurological manifestations in 47% and development in 37%.

CONCLUSION

The number of treatable IDs identified by our literature review increased by more than one-third in eight years. Although there has been much attention to gene-based and enzyme replacement therapy, the majority of effective treatments are nutritional, which are relatively affordable, widely available and (often) surprisingly effective. We present a diagnostic algorithm (adjustable to local resources and expertise) and the updated App to facilitate a swift and accurate workup, prioritizing treatable IDs. Our digital tool is freely available as Native and Web App (www.treatable-id.org) with several novel features. Our Treatable ID endeavor contributes to the Treatabolome and International Rare Diseases Research Consortium goals, enabling clinicians to deliver rapid evidence-based interventions to our rare disease patients.

Systemic metabolite profiling reveals sexual dimorphism of AIBP control of metabolism in mice

Emerging studies indicate that APOA-I binding protein (AIBP) is a secreted protein and functions extracellularly to promote cellular cholesterol efflux, thereby disrupting lipid rafts on the plasma membrane. AIBP is also present in the mitochondria and acts as an epimerase, facilitating the repair of dysfunctional hydrated NAD(P)H, known as NAD(P)H(X). Importantly, AIBP deficiency contributes to lethal neurometabolic disorder, reminiscent of the Leigh syndrome in humans. Whereas cyclic NADPHX production is proposed to be the underlying cause, we hypothesize that an unbiased metabolic profiling may: 1) reveal new clues for the lethality, e.g., changes of mitochondrial metabolites., and 2) identify metabolites associated with new AIBP functions. To this end, we performed unbiased and profound metabolic studies of plasma obtained from adult AIBP knockout mice and control littermates of both genders. Our systemic metabolite profiling, encompassing 9 super pathways, identified a total of 640 compounds. Our studies demonstrate a surprising sexual dimorphism of metabolites affected by AIBP deletion, with more statistically significant changes in the AIBP knockout female vs male when compared with the corresponding controls. AIBP knockout trends to reduce cholesterol but increase the bile acid precursor 7-HOCA in female but not male. Complex lipids, phospholipids, sphingomyelin and plasmalogens were reduced, while monoacylglycerol, fatty acids and the lipid soluble vitamins E and carotene diol were elevated in AIBP knockout female but not male. NAD metabolites were not significantly different in AIBP knockout vs control mice but differed for male vs female mice. Metabolites associated with glycolysis and the Krebs cycle were unchanged by AIBP knockout. Importantly, polyamine spermidine, critical for many cellular functions including cerebral cortex synapses, was reduced in male but not female AIBP knockout. This is the first report of a systemic metabolite profile of plasma samples from AIBP knockout mice, and provides a metabolic basis for future studies of AIBP regulation of cellular metabolism and the pathophysiological presentation of AIBP deficiency in patients.

Intracellular AIBP (Apolipoprotein A-I Binding Protein) Regulates Oxidized LDL (Low-Density Lipoprotein)-Induced Mitophagy in Macrophages

OBJECTIVE

Atherosclerotic lesions are often characterized by accumulation of OxLDL (oxidized low-density lipoprotein), which is associated with vascular inflammation and lesion vulnerability to rupture. Extracellular AIBP (apolipoprotein A-I binding protein; encoded by APOA1BP gene), when secreted, promotes cholesterol efflux and regulates lipid rafts dynamics, but its role as an intracellular protein in mammalian cells remains unknown. The aim of this work was to determine the function of intracellular AIBP in macrophages exposed to OxLDL and in atherosclerotic lesions. Approach and Results: Using a novel monoclonal antibody against human and mouse AIBP, which are highly homologous, we demonstrated robust AIBP expression in human and mouse atherosclerotic lesions. We observed significantly reduced autophagy in bone marrow-derived macrophages, isolated from Apoa1bp-/- compared with wild-type mice, which were exposed to OxLDL. In atherosclerotic lesions from Apoa1bp-/- mice subjected to Ldlr knockdown and fed a Western diet, autophagy was reduced, whereas apoptosis was increased, when compared with that in wild-type mice. AIBP expression was necessary for efficient control of reactive oxygen species and cell death and for mitochondria quality control in macrophages exposed to OxLDL. Mitochondria-localized AIBP, via its N-terminal domain, associated with E3 ubiquitin-protein ligase PARK2 (Parkin), MFN (mitofusin)1, and MFN2, but not BNIP3 (Bcl2/adenovirus E1B 19-kDa-interacting protein-3), and regulated ubiquitination of MFN1 and MFN2, key components of mitophagy.

CONCLUSIONS

These data suggest that intracellular AIBP is a new regulator of autophagy in macrophages. Mitochondria-localized AIBP augments mitophagy and participates in mitochondria quality control, protecting macrophages against cell death in the context of atherosclerosis.

Current progress in the therapeutic options for mitochondrial disorders

Mitochondrial disorders manifest enormous genetic and clinical heterogeneity - they can appear at any age, present with various phenotypes affecting any organ, and display any mode of inheritance. What mitochondrial diseases do have in common, is impairment of respiratory chain activity, which is responsible for more than 90% of energy production within cells. While diagnostics of mitochondrial disorders has been accelerated by introducing Next-Generation Sequencing techniques in recent years, the treatment options are still very limited. For many patients only a supportive or symptomatic therapy is available at the moment. However, decades of basic and preclinical research have uncovered potential target points and numerous compounds or interventions are now subjects of clinical trials. In this review, we focus on current and emerging therapeutic approaches towards the treatment of mitochondrial disorders. We focus on small compounds, metabolic interference, such as endurance training or ketogenic diet and also on genomic approaches.

A Proposed Diagnostic Algorithm for Inborn Errors of Metabolism Presenting With Movements Disorders

Inherited metabolic diseases or inborn errors of metabolism frequently manifest with both hyperkinetic (dystonia, chorea, myoclonus, ataxia, tremor, etc.) and hypokinetic (rigid-akinetic syndrome) movement disorders. The diagnosis of these diseases is in many cases difficult, because the same movement disorder can be caused by several diseases. Through a literature review, two hundred and thirty one inborn errors of metabolism presenting with movement disorders have been identified. Fifty-one percent of these diseases exhibits two or more movement disorders, of which ataxia and dystonia are the most frequent. Taking into account the wide range of these disorders, a methodical evaluation system needs to be stablished. This work proposes a six-step diagnostic algorithm for the identification of inborn errors of metabolism presenting with movement disorders comprising red flags, characterization of the movement disorders phenotype (type of movement disorder, age and nature of onset, distribution and temporal pattern) and other neurological and non-neurological signs, minimal biochemical investigation to diagnose treatable diseases, radiological patterns, genetic testing and ultimately, symptomatic, and disease-specific treatment. As a strong action, it is emphasized not to miss any treatable inborn error of metabolism through the algorithm.