A unique exonic splice enhancer mutation in a family with X-linked mental retardation and epilepsy points to a novel role of the renin receptor

The genetic landscape of autism spectrum disorder in an ancestrally diverse cohort

Autism spectrum disorder (ASD) comprises neurodevelopmental disorders with wide variability in genetic causes and phenotypes, making it challenging to pinpoint causal genes. We performed whole exome sequencing on a modest, ancestrally diverse cohort of 195 families, including 754 individuals (222 with ASD), and identified 38,834 novel private variants. In 68 individuals with ASD (~30%), we identified 92 potentially pathogenic variants in 73 known genes, including BCORL1, CDKL5, CHAMP1, KAT6A, MECP2, and SETD1B. Additionally, we identified 158 potentially pathogenic variants in 120 candidate genes, including DLG3, GABRQ, KALRN, KCTD16, and SLC8A3. We also found 34 copy number variants in 31 individuals overlapping known ASD loci. Our work expands the catalog of ASD genetics by identifying hundreds of variants across diverse ancestral backgrounds, highlighting convergence on nervous system development and signal transduction. These findings provide insights into the genetic underpinnings of ASD and inform molecular diagnosis and potential therapeutic targets.

V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities

Vacuolar-type ATPase (v-ATPase) is a multimeric protein complex that regulates H+ transport across membranes and intra-cellular organelle acidification. Catabolic processes, such as endocytic degradation and autophagy, strictly rely on v-ATPase-dependent luminal acidification in lysosomes. The v-ATPase complex is expressed at high levels in the brain and its impairment triggers neuronal dysfunction and neurodegeneration. Due to their post-mitotic nature and highly specialized function and morphology, neurons display a unique vulnerability to lysosomal dyshomeostasis. Alterations in genes encoding subunits composing v-ATPase or v-ATPase-related proteins impair brain development and synaptic function in animal models and underlie genetic diseases in humans, such as encephalopathies, epilepsy, as well as neurodevelopmental, and degenerative disorders. This review presents the genetic and functional evidence linking v-ATPase subunits and accessory proteins to various brain disorders, from early-onset developmental epileptic encephalopathy to neurodegenerative diseases. We highlight the latest emerging therapeutic strategies aimed at mitigating lysosomal defects associated with v-ATPase dysfunction.

X-Linked Epilepsies: A Narrative Review

X-linked epilepsies are a heterogeneous group of epileptic conditions, which often overlap with X-linked intellectual disability. To date, various X-linked genes responsible for epilepsy syndromes and/or developmental and epileptic encephalopathies have been recognized. The electro-clinical phenotype is well described for some genes in which epilepsy represents the core symptom, while less phenotypic details have been reported for other recently identified genes. In this review, we comprehensively describe the main features of both X-linked epileptic syndromes thoroughly characterized to date (PCDH19-related DEE, CDKL5-related DEE, MECP2-related disorders), forms of epilepsy related to X-linked neuronal migration disorders (e.g., ARX, DCX, FLNA) and DEEs associated with recently recognized genes (e.g., SLC9A6, SLC35A2, SYN1, ARHGEF9, ATP6AP2, IQSEC2, NEXMIF, PIGA, ALG13, FGF13, GRIA3, SMC1A). It is often difficult to suspect an X-linked mode of transmission in an epilepsy syndrome. Indeed, different models of X-linked inheritance and modifying factors, including epigenetic regulation and X-chromosome inactivation in females, may further complicate genotype-phenotype correlations. The purpose of this work is to provide an extensive and updated narrative review of X-linked epilepsies. This review could support clinicians in the genetic diagnosis and treatment of patients with epilepsy featuring X-linked inheritance.

Identification of Synonymous Pathogenic Variants in Monogenic Disorders by Integrating Exome with Transcriptome Sequencing

Exome sequencing is becoming a first-tier clinical diagnostic test for Mendelian diseases, drastically reducing the time and cost of diagnostic odyssey and improving the diagnosis rate. Despite its success, exome sequencing faces practical challenges in assessing the pathogenicity of numerous intronic and synonymous variants, leaving a significant proportion of patients undiagnosed. In this study, a whole-blood transcriptome database was constructed that showed the expression profile of 2981 Online Mendelian Inheritance in Man disease genes in blood samples. Meanwhile, a workflow integrating exome sequencing, blood transcriptome sequencing, and in silico prediction tools to identify and validate splicing-altering intronic or synonymous variants was proposed. Following this pipeline, seven synonymous variants in eight patients were discovered. Of these, the functional evidence of c.981G>A (PIGN), c.1161A>G (ALPL), c.858G>A (ATP6AP2), and c.1011G>T (MTHFR) have not been reported previously. RNA sequencing validation confirmed that these variants induced aberrant splicing, expanding the disease-causing variant spectrum of these genes. Overall, this study shows the feasibility of combining multi-omics data to identify splicing-altering variants, especially the power of RNA sequencing. It also reveals that synonymous variants, which often are overlooked in standard diagnostic approaches, comprise an important portion of unresolved genetic diseases.

Clinical findings in individuals with duplication of genes associated with X-linked intellectual disability

Duplication of all genes associated with X-linked intellectual disability (XLID) have been reported but the majority of the duplications include more than one XLID gene. It is exceptional for whole XLID gene duplications to cause the same phenotype as sequence variants or deletions of the same gene. Duplication of PLP1, the gene associated with Pelizaeus-Merzbacher syndrome, is the most notable duplication of this type. More commonly, duplication of XLID genes results in very different phenotypes than sequence alterations or deletions. Duplication of MECP2 is widely recognized as a duplication of this type, but a number of others exist. The phenotypes associated with gene duplications are often milder than those caused by deletions and sequence variants. Among some duplications that are clinically significant, marked skewing of X-inactivation in female carriers has been observed. This report describes the phenotypic consequences of duplication of 22 individual XLID genes, of which 10 are described for the first time.

Synonymous variants in the ATP6AP2 gene may lead to developmental and epileptic encephalopathy

Objective

To the literature, variants in the ATP6AP2 gene may cause abnormal nervous system development and associated neurological symptoms.

Methods

We report a patient with developmental and epileptic encephalopathy (DEE) carrying an ATP6AP2 c.858G > A (p.Ala286=) synonymous variant. In addition, an overview of reported patients with the same variant were collected and summarized to compare our findings.

Results

The patient started experiencing tonic seizures at 3.5 months of age, and magnetic resonance imaging (MRI) indicated impaired brain white matter development and reduced left hippocampal volume. Furthermore, electroencephalography showed multifocal interictal epileptiform discharges. Treatment with various anti-seizure medications yielded unsatisfactory results, and the disorder eventually developed into epileptic spasms. An in vitro splicing assay for the ATP6AP2 gene mRNA revealed that the variant caused a deletion in exon 8 and a corresponding protein truncation. A review of previously reported ATP6AP2-related DEE patients found that synonymous variants in the ATP6AP2 gene can cause early DEE onset, progressive changes in early-life MRI, and exon skipping in all ATP6AP2-related DEE patients.

Significance

We found that synonymous variants in ATP6AP2 may have significant pathogenicity and are highly correlated with DEE. Due to increased isoform production, ATP6AP2 synonymous variants may cause nervous system developmental disorders by competitively reducing the generation of full-length transcripts, resulting in defects in ATP6AP2-related physiological processes.

ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy

The vacuolar H+-ATPase is an enzymatic complex that functions in an ATP-dependent manner to pump protons across membranes and acidify organelles, thereby creating the proton/pH gradient required for membrane trafficking by several different types of transporters. We describe heterozygous point variants in ATP6V0C, encoding the c-subunit in the membrane bound integral domain of the vacuolar H+-ATPase, in 27 patients with neurodevelopmental abnormalities with or without epilepsy. Corpus callosum hypoplasia and cardiac abnormalities were also present in some patients. In silico modelling suggested that the patient variants interfere with the interactions between the ATP6V0C and ATP6V0A subunits during ATP hydrolysis. Consistent with decreased vacuolar H+-ATPase activity, functional analyses conducted in Saccharomyces cerevisiae revealed reduced LysoSensor fluorescence and reduced growth in media containing varying concentrations of CaCl2. Knockdown of ATP6V0C in Drosophila resulted in increased duration of seizure-like behaviour, and the expression of selected patient variants in Caenorhabditis elegans led to reduced growth, motor dysfunction and reduced lifespan. In summary, this study establishes ATP6V0C as an important disease gene, describes the clinical features of the associated neurodevelopmental disorder and provides insight into disease mechanisms.

Large-Scale Functional Assessment of Genes Involved in Rare Diseases with Intellectual Disabilities Unravels Unique Developmental and Behaviour Profiles in Mouse Models

Major progress has been made over the last decade in identifying novel genes involved in neurodevelopmental disorders, although the task of elucidating their corresponding molecular and pathophysiological mechanisms, which are an essential prerequisite for developing therapies, has fallen far behind. We selected 45 genes for intellectual disabilities to generate and characterize mouse models. Thirty-nine of them were based on the frequency of pathogenic variants in patients and literature reports, with several corresponding to de novo variants, and six other candidate genes. We used an extensive screen covering the development and adult stages, focusing specifically on behaviour and cognition to assess a wide range of functions and their pathologies, ranging from basic neurological reflexes to cognitive abilities. A heatmap of behaviour phenotypes was established, together with the results of selected mutants. Overall, three main classes of mutant lines were identified based on activity phenotypes, with which other motor or cognitive deficits were associated. These data showed the heterogeneity of phenotypes between mutation types, recapitulating several human features, and emphasizing the importance of such systematic approaches for both deciphering genetic etiological causes of ID and autism spectrum disorders, and for building appropriate therapeutic strategies.

A rigorous in silico genomic interrogation at 1p13.3 reveals 16 autosomal dominant candidate genes in syndromic neurodevelopmental disorders

Genome-wide chromosomal microarray is extensively used to detect copy number variations (CNVs), which can diagnose microdeletion and microduplication syndromes. These small unbalanced chromosomal structural rearrangements ranging from 1 kb to 10 Mb comprise up to 15% of human mutations leading to monogenic or contiguous genomic disorders. Albeit rare, CNVs at 1p13.3 cause a variety of neurodevelopmental disorders (NDDs) including development delay (DD), intellectual disability (ID), autism, epilepsy, and craniofacial anomalies (CFA). Most of the 1p13.3 CNV cases reported in the pre-microarray era encompassed a large number of genes and lacked the demarcating genomic coordinates, hampering the discovery of positional candidate genes within the boundaries. In this study, we present four subjects with 1p13.3 microdeletions displaying DD, ID, autism, epilepsy, and CFA. In silico comparative genomic mapping with three previously reported subjects with CNVs and 22 unreported DECIPHER CNV cases has resulted in the identification of four different sub-genomic loci harboring five positional candidate genes for DD, ID, and CFA at 1p13.3. Most of these genes have pathogenic variants reported, and their interacting genes are involved in NDDs. RT-qPCR in various human tissues revealed a high expression pattern in the brain and fetal brain, supporting their functional roles in NDDs. Interrogation of variant databases and interacting protein partners led to the identification of another set of 11 potential candidate genes, which might have been dysregulated by the position effect of these CNVs at 1p13.3. Our studies define 1p13.3 as a genomic region harboring 16 NDD candidate genes and underscore the critical roles of small CNVs in in silico comparative genomic mapping for disease gene discovery. Our candidate genes will help accelerate the isolation of pathogenic heterozygous variants from exome/genome sequencing (ES/GS) databases.

Reduced gene dosage is a common mechanism of neuropathologies caused by ATP6AP2 splicing mutations

BACKGROUND

Mutations that alter splicing of X-linked ATP6AP2 cause a spectrum of neurodevelopmental and neurodegenerative pathologies including parkinsonism in affected males. All previously reported splicing mutations increase the level of a minor isoform with skipped exon 4 (Δe4) that encodes a functionally deficient protein.

OBJECTIVES

We investigated the pathogenic mechanism of a novel c.168+6T>A variant reported in a family with X-linked intellectual disability, epilepsy, and parkinsonism. We also analyzed ATP6AP2 splicing defects in brains of carriers of a c.345C>T variant associated with X-linked spasticity and parkinsonism.

METHODS

We generated induced pluripotent stem cells from patients with c.168+6T>A, reprogrammed them to neural progenitor cells and analyzed them by RNA-Seq and qRT-PCR. We also quantified ATP6AP2 isoforms in the brains of c.345C>T carriers by Nanostring nCounter.

RESULTS

The c.168+6T>A increased skipping of ATP6AP2 exon 2 and usage of cryptic intronic donor splice sites. This results in out-of-frame splicing products and a reciprocal 50% reduction in functional full-length ATP6AP2 transcripts. Neural progenitors of patients with c.168+6T>A exhibited downregulated neural development gene networks. Analysis of blood transcriptomes of c.168+6T>A carriers identified potential biomarkers of ATP6AP2 deficiency in non-neural tissues. The c.345C>T variant increased exon 4 skipping with concomitant decrease of full length ATP6AP2 in brains of carriers.

CONCLUSION

A common pathogenic consequence of splicing mutations affecting inclusion of different ATP6AP2 exons is reduction of the functional full-length transcript. The exacerbated ATP6AP2 splicing defect in brains of c.345C>T carriers is consistent with their CNS-restricted clinical presentations.

(Pro)renin Receptor and Blood Pressure Regulation: A Focus on the Central Nervous System

The renin-angiotensin system (RAS) is classically described as a hormonal system in which angiotensin II (Ang II) is one of the main active peptides. The action of circulating Ang II on its cognate Ang II type-1 receptor (AT1R) in circumventricular organs has important roles in regulating the autonomic nervous system, blood pressure (BP) and body fluid homeostasis, and has more recently been implicated in cardiovascular metabolism. The presence of a local or tissue RAS in various tissues, including the central nervous system (CNS), is well established. However, because the level of renin, the rate-limiting enzyme in the systemic RAS, is very low in the brain, how endogenous angiotensin peptides are generated in the CNS-the focus of this review-has been the subject of considerable debate. Notable in this context is the identification of the (pro)renin receptor (PRR) as a key component of the brain RAS in the production of Ang II in the CNS. In this review, we highlight cellular and anatomical locations of the PRR in the CNS. We also summarize studies using gain- and loss-of function approaches to elucidate the functional importance of brain PRR-mediated Ang II formation and brain RAS activation, as well as PRR-mediated Ang II-independent signaling pathways, in regulating BP. We further discuss recent developments in PRR involvement in cardiovascular and metabolic diseases and present perspectives for future directions.

Diabetes and Renin-Angiotensin-Aldosterone System: Pathophysiology and Genetics

Diabetes mellitus (DM) is a metabolic disorder and characterized by hyperglycemia. Being a concern of both the developed and developing world, diabetes is a global health burden and is a major cause of mortality world-wide. The most common is the type 2 diabetes mellitus (T2DM), which is mainly caused by resistance to insulin. Long-term complications of diabetes cause microvascular related problems (eg. nephropathy, neuropathy and retinopathy) along with macrovascular complications (eg. cardiovascular diseases, ischemic heart disease, peripheral vascular disease). Renin-angiotensin-aldosterone system (RAAS) regulates homeostasis of body fluid that in turn, maintains blood pressure. Thus, RAAS plays pivotal role in the pathogenesis of long-term DM complications like cardiovascular diseases and chronic kidney diseases. T2DM is a polygenic disease, and the roles of RAAS components in insulin signaling pathway and insulin resistance have been well documented. Hyperglycemia has been found to be associated with the increased plasma renin activity, arterial pressure and renal vascular resistance. Several studies have reported involvement of single variants within particular genes in initiation and development of T2D using different approaches. This chapter aims to investigate and discuss potential genetic polymorphisms underlying T2D identified through candidate gene studies, genetic linkage studies, genome wide association studies.

Functions of the (pro)renin receptor (Atp6ap2) at molecular and system levels: pathological implications in hypertension, renal and brain development, inflammation, and fibrosis

The (pro)renin receptor [(P)RR, Atp6ap2] was initially discovered as a membrane-bound binding partner of prorenin and renin. A soluble (P)RR has additional paracrine effects and is involved in metabolic syndrome and kidney damage. Meanwhile it is clear that most of the effects of the (P)RR are independent of prorenin. In the kidney, (P)RR plays an important role in renal dysfunction by activating proinflammatory and profibrotic molecules. In the brain, (P)RR is expressed in cardiovascular regulatory nuclei and is linked to hypertension. (P)RR is known to be an essential component of the v-ATPase as a key accessory protein and plays an important role in kidney, brain and heart via regulating the pH of the extracellular space and intracellular compartments. V-ATPase and (P)RR together act on WNT and mTOR signalling pathways, which are responsible for cellular homeostasis and autophagy. (P)RR through its role in v-ATPase assembly and function is also important for fast recycling endocytosis by megalin. In the kidney, megalin together with v-ATPase and (P)RR is crucial for endocytic uptake of components of the RAS and their intracellular processing. In the brain, (P)RR, v-ATPases and megalin are important regulators both during development and in the adult. All three proteins are associated with diseases such as XLMR, XMRE, X-linked parkinsonism and epilepsy, cognitive disorders with Parkinsonism, spasticity, intellectual disability, and Alzheimer's Disease which are characterized by impaired neuronal function and/or neuronal loss. The present review focusses on the relevant effects of Atp6ap2 without assigning them necessarily to the RAS. Mechanistically, many effects can be well explained by the role of Atp6ap2 for v-ATPase assembly and function. Furthermore, application of a soluble (P)RR analogue as new therapeutic option is discussed.

Evidence in disease and non-disease contexts that nonsense mutations cause altered splicing via motif disruption

Transcripts containing premature termination codons (PTCs) can be subject to nonsense-associated alternative splicing (NAS). Two models have been evoked to explain this, scanning and splice motif disruption. The latter postulates that exonic cis motifs, such as exonic splice enhancers (ESEs), are disrupted by nonsense mutations. We employ genome-wide transcriptomic and k-mer enrichment methods to scrutinize this model. First, we show that ESEs are prone to disruptive nonsense mutations owing to their purine richness and paucity of TGA, TAA and TAG. The motif model correctly predicts that NAS rates should be low (we estimate 5–30%) and approximately in line with estimates for the rate at which random point mutations disrupt splicing (8–20%). Further, we find that, as expected, NAS-associated PTCs are predictable from nucleotide-based machine learning approaches to predict splice disruption and, at least for pathogenic variants, are enriched in ESEs. Finally, we find that both in and out of frame mutations to TAA, TGA or TAG are associated with exon skipping. While a higher relative frequency of such skip-inducing mutations in-frame than out of frame lends some credence to the scanning model, these results reinforce the importance of considering splice motif modulation to understand the etiology of PTC-associated disease.

The (pro)renin receptor (ATP6ap2) facilitates receptor-mediated endocytosis and lysosomal function in the renal proximal tubule

The ATP6ap2 (Pro)renin receptor protein associates with H+-ATPases which regulate organellar, cellular, and systemic acid-base homeostasis. In the kidney, ATP6ap2 colocalizes with H+-ATPases in various cell types including the cells of the proximal tubule. There, H+-ATPases are involved in receptor-mediated endocytosis of low molecular weight proteins via the megalin/cubilin receptors. To study ATP6ap2 function in the proximal tubule, we used an inducible shRNA Atp6ap2 knockdown rat model (Kd) and an inducible kidney-specific Atp6ap2 knockout mouse model. Both animal lines showed higher proteinuria with elevated albumin, vitamin D binding protein, and procathepsin B in urine. Endocytosis of an injected fluid-phase marker (FITC- dextran, 10 kDa) was normal whereas processing of recombinant transferrin, a marker for receptor-mediated endocytosis, to lysosomes was delayed. While megalin and cubilin expression was unchanged, abundance of several subunits of the H+-ATPase involved in receptor-mediated endocytosis was reduced. Lysosomal integrity and H+-ATPase function are associated with mTOR signaling. In ATP6ap2, KO mice mTOR and phospho-mTOR appeared normal but increased abundance of the LC3-B subunit of the autophagosome was observed suggesting a more generalized impairment of lysosomal function in the absence of ATP6ap2. Hence, our data suggests a role for ATP6ap2 for proximal tubule function in the kidney with a defect in receptor-mediated endocytosis in mice and rats.

Urinary soluble (pro)renin receptor excretion is associated with urine pH in humans

The (pro)renin receptor [(P)RR] binds to renin and its precursor prorenin to activate the tissue renin-angiotensin system. It is cleaved to generate soluble (P)RR and M8–9, a residual hydrophobic truncated protein. The (pro)renin receptor also functions as an intracellular accessory protein of vacuolar-type H⁺-ATPase, which plays an essential role in controlling the intracellular vesicular acid environment. Thus, in the kidney, (P)RR may play a role in transporting H⁺ to urine in the collecting duct. Although blood soluble (P)RR has been recognized as a biomarker reflecting the status of the tissue renin-angiotensin system and/or tissue (P)RR, the significance of urinary soluble (P)RR excretion has not been determined. Therefore, this study aimed to investigate the characteristics of urinary soluble (P)RR excretion. Urinary soluble (P)RR excretion was measured, and its association with background factors was investigated in 441 patients. Relationships between changes in urine pH due to vitamin C treatment, which reduce urine pH, and urinary soluble (P)RR excretion were investigated in 10 healthy volunteers. Urinary soluble (P)RR excretion was 1.46 (0.44–2.92) ng/gCre. Urine pH showed a significantly positive association with urinary soluble (P)RR excretion, independent of other factors. Changes in urine pH and urinary soluble (P)RR excretion due to vitamin C treatment were significantly and positively correlated (ρ = 0.8182, p = 0.0038). These data showed an association between urinary soluble (P)RR excretion and urine pH in humans, suggesting that (P)RR in the kidney might play a role in urine pH regulation.

Soluble (pro)renin receptor: a novel ligand for angiotensin II type 1 receptor?

This commentary highlights the study entitled 'Soluble (pro)renin receptor induces endothelial dysfunction and hypertension in mice with diet-induced obesity via activation of angiotensin II type 1 receptor' presented by Fu et al. published in Clinical Science (Clin Sci (Lond) (2021) 135(6), https://doi.org/10.1042/CS20201047). The authors evaluated the role of the soluble (pro)renin receptor (sPRR), a cleavage product of the prorenin receptor (PRR) by the site 1 protease, as a ligand for angiotensin II type 1 receptor (AT1R). They presented for the first time that sPRR directly interacts with AT1R, causing nuclear factor-κB activation, inflammation, apoptosis, and endothelial dysfunction in primary human umbilical vein endothelial cells (HUVECs). Furthermore, the interaction between sPRR and AT1R was responsible for endothelial dysfunction and hypertension in diet-induced obesity mice. These results provide a potential mechanism for obesity-induced endothelial dysfunction and hypertension. Thus, the sPRR/AT1R complex may be a novel therapeutic target for cardiovascular diseases associated with endothelial dysfunction.

X-Linked Parkinsonism: Phenotypic and Genetic Heterogeneity

X-linked parkinsonism encompasses rare heterogeneous disorders mainly inherited as a recessive trait, therefore being more prevalent in males. Recent developments have revealed a complex underlying panorama, including a spectrum of disorders in which parkinsonism is variably associated with additional neurological and non-neurological signs. In particular, a childhood-onset encephalopathy with epilepsy and/or cognitive disability is the most common feature. Their genetic basis is also heterogeneous, with many causative genes and different mutation types ranging from "classical" coding variants to intronic repeat expansions. In this review, we provide an updated overview of the phenotypic and genetic spectrum of the most relevant X-linked parkinsonian syndromes, namely X-linked dystonia-parkinsonism (XDP, Lubag disease), fragile X-associated tremor/ataxia syndrome (FXTAS), beta-propeller protein-associated neurodegeneration (BPAN, NBIA/PARK-WDR45), Fabry disease, Waisman syndrome, methyl CpG-binding protein 2 (MeCP2) spectrum disorder, phosphoglycerate kinase-1 deficiency syndrome (PGK1) and X-linked parkinsonism and spasticity (XPDS). All clinical and radiological features reported in the literature have been reviewed. Epilepsy occasionally represents the symptom of onset, predating parkinsonism even by a few years; action tremor is another common feature along with akinetic-rigid parkinsonism. A focus on the genetic background and its pathophysiological implications is provided. The pathogenesis of these disorders ranges from well-defined metabolic alterations (PGK1) to non-specific lysosomal dysfunctions (XPDS) and vesicular trafficking alterations (Waisman syndrome). However, in other cases it still remains poorly defined. Recognition of the phenotypic and genetic heterogeneity of X-linked parkinsonism has important implications for diagnosis, management, and genetic counseling. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Loss of zebrafish atp6v1e1b, encoding a subunit of vacuolar ATPase, recapitulates human ARCL type 2C syndrome and identifies multiple pathobiological signatures

The inability to maintain a strictly regulated endo(lyso)somal acidic pH through the proton-pumping action of the vacuolar-ATPases (v-ATPases) has been associated with various human diseases including heritable connective tissue disorders. Autosomal recessive (AR) cutis laxa (CL) type 2C syndrome is associated with genetic defects in the ATP6V1E1 gene and is characterized by skin wrinkles or loose redundant skin folds with pleiotropic systemic manifestations. The underlying pathological mechanisms leading to the clinical presentations remain largely unknown. Here, we show that loss of atp6v1e1b in zebrafish leads to early mortality, associated with craniofacial dysmorphisms, vascular anomalies, cardiac dysfunction, N-glycosylation defects, hypotonia, and epidermal structural defects. These features are reminiscent of the phenotypic manifestations in ARCL type 2C patients. Our data demonstrates that loss of atp6v1e1b alters endo(lyso)somal protein levels, and interferes with non-canonical v-ATPase pathways in vivo. In order to gain further insights into the processes affected by loss of atp6v1e1b, we performed an untargeted analysis of the transcriptome, metabolome, and lipidome in early atp6v1e1b-deficient larvae. We report multiple affected pathways including but not limited to oxidative phosphorylation, sphingolipid, fatty acid, and energy metabolism together with profound defects on mitochondrial respiration. Taken together, our results identify complex pathobiological effects due to loss of atp6v1e1b in vivo.

Cutis laxa syndromes are pleiotropic disorders of the connective tissue, characterized by skin redundancy and variable systemic manifestations. Cutis laxa syndromes are caused by pathogenic variants in genes encoding structural and regulatory components of the extracellular matrix or in genes encoding components of cellular trafficking, metabolism, and mitochondrial function. Pathogenic variants in genes coding for vacuolar-ATPases, a multisubunit complex responsible for the acidification of multiple intracellular vesicles, cause type 2 cutis laxa syndromes, a group of cutis laxa subtypes further characterized by neurological, skeletal, and rarely cardiopulmonary manifestations. To investigate the pathomechanisms of vacuolar-ATPase dysfunction, we generated zebrafish models that lack a crucial subunit of the vacuolar-ATPases. The mutant zebrafish models show morphological and functional features reminiscent of the phenotypic manifestations in cutis laxa patients carrying pathogenic variants in ATP6V1E1. In-depth analysis at multiple -omic levels identified biological signatures that indicate impairment of signaling pathways, lipid metabolism, and mitochondrial respiration. We anticipate that these data will contribute to a better understanding of the pathogenesis of cutis laxa syndromes and other disorders involving defective v-ATPase function, which may eventually improve patient treatment and management.

Emerging insights on the role of V-ATPase in human diseases: Therapeutic challenges and opportunities

The control of the intracellular pH is vital for the survival of all organisms. Membrane transporters, both at the plasma and intracellular membranes, are key players in maintaining a finely tuned pH balance between intra- and extracellular spaces, and therefore in cellular homeostasis. V-ATPase is a housekeeping ATP-driven proton pump highly conserved among prokaryotes and eukaryotes. This proton pump, which exhibits a complex multisubunit structure based on cell type-specific isoforms, is essential for pH regulation and for a multitude of ubiquitous and specialized functions. Thus, it is not surprising that V-ATPase aberrant overexpression, mislocalization, and mutations in V-ATPase subunit-encoding genes have been associated with several human diseases. However, the ubiquitous expression of this transporter and the high toxicity driven by its off-target inhibition, renders V-ATPase-directed therapies very challenging and increases the need for selective strategies. Here we review emerging evidence linking V-ATPase and both inherited and acquired human diseases, explore the therapeutic challenges and opportunities envisaged from recent data, and advance future research avenues. We highlight the importance of V-ATPases with unique subunit isoform molecular signatures and disease-associated isoforms to design selective V-ATPase-directed therapies. We also discuss the rational design of drug development pipelines and cutting-edge methodological approaches toward V-ATPase-centered drug discovery. Diseases like cancer, osteoporosis, and even fungal infections can benefit from V-ATPase-directed therapies.

Immunohistochemistry for (Pro)renin Receptor in Humans

The (pro)renin receptor is a multifunctional protein with roles in angiotensin-II-dependent and -independent intracellular cell signaling and roles as an intracellular accessory protein for the vacuolar H⁺-ATPase, including hormone secretion. While (pro)renin receptor mRNA is widely expressed in various human tissues, localization of (pro)renin receptor protein expression has not yet been systemically determined. Therefore, this study localized (pro)renin receptor protein expression in human organs. Systemic immunohistochemical examination of (pro)renin receptor expression was performed in whole body organs of autopsy cases. (Pro)renin receptor immunostaining was observed in the cytoplasm of cells in almost all human organs. It was observed in thyroid follicular epithelial cells, hepatic cells, pancreatic duct epithelial cells, zona glomerulosa and zona reticularis of the cortex and medulla of the adrenal gland, proximal and distal tubules and collecting ducts of the kidney, cardiomyocytes, and skeletal muscle cells. In the brain, (pro)renin receptor staining was detected in neurons throughout all areas, especially in the medulla oblongata, paraventricular nucleus and supraoptic nucleus of the hypothalamus, cerebrum, granular layer of the hippocampus, Purkinje cell layer of the cerebellum, and the pituitary anterior and posterior lobes. In the anterior lobe of the pituitary gland, all types of anterior pituitary hormone-positive cells showed double staining with (pro)renin receptor. These data showed that (pro)renin receptor protein was expressed in almost all organs of the human body. Its expression pattern was not uniform, and cell-specific expression pattern was observed, supporting the notion that (pro)renin receptor plays numerous physiological roles in each human organ.

Recent developments in gastroesophageal mesenchymal tumours

The pathologist's approach to gastroesophageal mesenchymal tumours has changed dramatically during the last 25 years. In particular, gastrointestinal stromal tumour (GIST) has evolved from a wastebasket mesenchymal tumour category to a precisely defined entity with an increasingly detailed genetic subclassification. This subclassification has brought gastrointestinal mesenchymal neoplasia into the realm of precision medicine, with specific treatments optimised for particular genetic subtypes. Molecular genetic data have also greatly improved our understanding of oesophageal mesenchymal tumours, including the discovery that so-called 'giant fibrovascular polyps' in fact represent a clinically distinctive presentation of well-differentiated liposarcoma. Here, we will focus on gastroesophageal mesenchymal tumours for which there have been recent developments in classification, molecular genetics or tumour biology: granular cell tumour, 'giant fibrovascular polyp'/well-differentiated liposarcoma, plexiform fibromyxoma, gastroblastoma and, of course, GIST.

Interactions of antiepileptic drugs with drugs approved for the treatment of indications other than epilepsy

Introduction: Comorbidities of epilepsy may significantly interfere with its treatment as diseases in the general population are also encountered in epilepsy patients and some of them even more frequently (for instance, depression, anxiety, or heart disease). Obviously, some drugs approved for other than epilepsy indications can modify the anticonvulsant activity of antiepileptics. Areas covered: This review highlights the drug-drug interactions between antiepileptics and aminophylline, some antidepressant, antiarrhythmic (class I-IV), selected antihypertensive drugs and non-barbiturate injectable anesthetics (ketamine, propofol, etomidate, and alphaxalone). The data were reviewed mainly from experimental models of seizures. Whenever possible, clinical data were provided. PUBMED data base was the main search source.Expert opinion: Aminophylline generally reduced the protective activity of antiepileptics, which, to a certain degree, was consistent with scarce clinical data on methylxanthine derivatives and worse seizure control. The only antiarrhythmic with this profile of action was mexiletine when co-administered with VPA. Among antidepressants and non-barbiturate injectable anesthetics, trazodone, mianserin and etomidate or alphaxalone, respectively, negatively affected the anticonvulsant action of some antiepileptic drugs. Clinical data indicate that only amoxapine, bupropion, clomipramine and maprotiline should be used with caution. Possibly, drugs reducing the anticonvulsant potential of antiepileptics should be avoided in epilepsy patients.

Increased soluble (pro)renin receptor protein by autophagy inhibition in cultured cancer cells

(Pro)renin receptor ((P)RR) regulates the renin-angiotensin system and functions as an essential accessory subunit of vacuolar H+ -ATPase. There is accumulating evidence that shows close relationship between (P)RR and autophagy. Soluble (P)RR consisting of the extracellular domain of (P)RR is generated from (P)RR by proteolytic enzymes. The aim of the present study was to clarify the influence of autophagy inhibition on soluble (P)RR expression in cancer cells. Autophagy was inhibited by treatment of bafilomycin A1 or chloroquine in MCF-7 and A549 cells for 72 hr. Western blot analysis showed that protein levels of soluble (P)RR were markedly elevated by autophagy inhibition, whereas no noticeable increases were observed in full-length (P)RR. Secretion of soluble (P)RR into the medium was increased dose-dependently by bafilomycin A1 or chloroquine. Autophagy inhibition was confirmed by enhanced accumulation of autophagy-related proteins, LC3, p62 and LAMP1 in intracellular vesicles. Increased amount of soluble (P)RR by autophagy inhibition was decreased by site-1 protease inhibitor, whereas no noticeable increase in site-1 protease immunoreactivity was observed in cells with autophagy inhibition by immunocytochemistry. These findings suggest that soluble (P)RR protein accumulates by autophagy inhibition, possibly because of the reduced degradation of soluble (P)RR in the intracellular vesicles during autophagy inhibition.

Regulation of V-ATPase Activity and Organelle pH by Phosphatidylinositol Phosphate Lipids

Luminal pH and the distinctive distribution of phosphatidylinositol phosphate (PIP) lipids are central identifying features of organelles in all eukaryotic cells that are also critical for organelle function. V-ATPases are conserved proton pumps that populate and acidify multiple organelles of the secretory and the endocytic pathway. Complete loss of V-ATPase activity causes embryonic lethality in higher animals and conditional lethality in yeast, while partial loss of V-ATPase function is associated with multiple disease states. On the other hand, many cancer cells increase their virulence by upregulating V-ATPase expression and activity. The pH of individual organelles is tightly controlled and essential for function, but the mechanisms for compartment-specific pH regulation are not completely understood. There is substantial evidence indicating that the PIP content of membranes influences organelle pH. We present recent evidence that PIPs interact directly with subunit isoforms of the V-ATPase to dictate localization of V-ATPase subpopulations and participate in their regulation. In yeast cells, which have only one set of organelle-specific V-ATPase subunit isoforms, the Golgi-enriched lipid PI(4)P binds to the cytosolic domain of the Golgi-enriched a-subunit isoform Stv1, and loss of PI(4)P binding results in mislocalization of Stv1-containing V-ATPases from the Golgi to the vacuole/lysosome. In contrast, levels of the vacuole/lysosome-enriched signaling lipid PI(3,5)P₂ affect assembly and activity of V-ATPases containing the Vph1 a-subunit isoform. Mutations in the Vph1 isoform that disrupt the lipid interaction increase sensitivity to stress. These studies have decoded “zip codes” for PIP lipids in the cytosolic N-terminal domain of the a-subunit isoforms of the yeast V-ATPase, and similar interactions between PIP lipids and the V-ATPase subunit isoforms are emerging in higher eukaryotes. In addition to direct effects on the V-ATPase, PIP lipids are also likely to affect organelle pH indirectly, through interactions with other membrane transporters. We discuss direct and indirect effects of PIP lipids on organelle pH, and the functional consequences of the interplay between PIP lipid content and organelle pH.

A review of clinically significant drug-drug interactions involving angiotensin II receptor antagonists and antiepileptic drugs

INTRODUCTION

Angiotensin II receptor blockers are widely used for the treatment of arterial hypertension and heart failure. However, recent studies on animal models of seizures showed that in the brain, the renin-angiotensin-aldosterone system might be involved in neuroinflammation; therefore, the administration of angiotensin II receptor blockers that cross the blood/brain barrier, reduces not only blood pressure but reduces neuroinflammation-induced neuronal injury. Apart from this neuroprotective effect, these drugs exhibit anticonvulsant activity in animal models of seizures, and losartan is associated with a probable anti-epileptogenic activity.

AREAS COVERED

In this review, we intended to highlight the role of drug-drug interactions involving angiotensin II receptor antagonists with antiepileptic drugs accompanied by a brief characteristic of the role of RAS in neuroinflammation.

EXPERT OPINION

Some combinations of antiepileptic drugs (lamotrigine or valproate) with sartans are particularly effective in terms of enhanced seizure control. Considering a possible anti-epileptogenic activity of losartan, its combinations with antiepileptic drugs may prove especially beneficial in epileptogenesis inhibition.

The emerging roles of vacuolar-type ATPase-dependent Lysosomal acidification in neurodegenerative diseases

Background

Lysosomes digest extracellular material from the endocytic pathway and intracellular material from the autophagic pathway. This process is performed by the resident hydrolytic enzymes activated by the highly acidic pH within the lysosomal lumen. Lysosome pH gradients are mainly maintained by the vacuolar (H⁺) ATPase (or V-ATPase), which pumps protons into lysosomal lumen by consuming ATP. Dysfunction of V-ATPase affects lysosomal acidification, which disrupts the clearance of substrates and leads to many disorders, including neurodegenerative diseases.

Main body

As a large multi-subunit complex, the V-ATPase is composed of an integral membrane V0 domain involved in proton translocation and a peripheral V1 domain catalyzing ATP hydrolysis. The canonical functions of V-ATPase rely on its H⁺-pumping ability in multiple vesicle organelles to regulate endocytic traffic, protein processing and degradation, synaptic vesicle loading, and coupled transport. The other non-canonical effects of the V-ATPase that are not readily attributable to its proton-pumping activity include membrane fusion, pH sensing, amino-acid-induced activation of mTORC1, and scaffolding for protein-protein interaction. In response to various stimuli, V-ATPase complex can reversibly dissociate into V1 and V0 domains and thus close ATP-dependent proton transport. Dysregulation of pH and lysosomal dysfunction have been linked to many human diseases, including neurodegenerative disorders such as Alzheimer disease, Parkinson’s disease, amyotrophic lateral sclerosis as well as neurodegenerative lysosomal storage disorders.

Conclusion

V-ATPase complex is a universal proton pump and plays an important role in lysosome acidification in all types of cells. Since V-ATPase dysfunction contributes to the pathogenesis of multiple neurodegenerative diseases, further understanding the mechanisms that regulate the canonical and non-canonical functions of V-ATPase will reveal molecular details of disease process and help assess V-ATPase or molecules related to its regulation as therapeutic targets.

Genetic perspective on the synergistic connection between vesicular transport, lysosomal and mitochondrial pathways associated with Parkinson's disease pathogenesis

Parkinson's disease (PD) and atypical parkinsonian syndromes (APS) are symptomatically characterized by parkinsonism, with the latter presenting additionally a distinctive range of atypical features. Although the majority of patients with PD and APS appear to be sporadic, genetic causes of several rare monogenic disease variants were identified. The knowledge acquired from these genetic factors indicated that defects in vesicular transport pathways, endo-lysosomal dysfunction, impaired autophagy-lysosomal protein and organelle degradation pathways, α-synuclein aggregation and mitochondrial dysfunction play key roles in PD pathogenesis. Moreover, membrane dynamics are increasingly recognized as a key player in the disease pathogenesis due lipid homeostasis alterations, associated with lysosomal dysfunction, caused by mutations in several PD and APS genes. The importance of lysosomal dysfunction and lipid homeostasis is strengthened by both genetic discoveries and clinical epidemiology of the association between parkinsonism and lysosomal storage disorders (LSDs), caused by the disruption of lysosomal biogenesis or function. A synergistic coordination between vesicular trafficking, lysosomal and mitochondria defects exist whereby mutations in PD and APS genes encoding proteins primarily involved one PD pathway are frequently associated with defects in other PD pathways as a secondary effect. Moreover, accumulating clinical and genetic observations suggest more complex inheritance patters of familial PD exist, including oligogenic and polygenic inheritance of genes in the same or interconnected PD pathways, further strengthening their synergistic connection.Here, we provide a comprehensive overview of PD and APS genes with functions in vesicular transport, lysosomal and mitochondrial pathways, and highlight functional and genetic evidence of the synergistic connection between these PD associated pathways.

The (pro)renin receptor in health and disease

The (pro)renin receptor ((P)RR) was first identified as a single-transmembrane receptor in human kidneys and initially attracted attention owing to its potential role as a regulator of the tissue renin-angiotensin system (RAS). Subsequent studies found that the (P)RR is widely distributed in organs throughout the body, including the kidneys, heart, brain, eyes, placenta and the immune system, and has multifaceted functions in vivo. The (P)RR has roles in various physiological processes, such as the cell cycle, autophagy, acid-base balance, energy metabolism, embryonic development, T cell homeostasis, water balance, blood pressure regulation, cardiac remodelling and maintenance of podocyte structure. These roles of the (P)RR are mediated by its effects on important biological systems and pathways including the tissue RAS, vacuolar H⁺-ATPase, Wnt, partitioning defective homologue (Par) and tyrosine phosphorylation. In addition, the (P)RR has been reported to contribute to the pathogenesis of diseases such as fibrosis, hypertension, pre-eclampsia, diabetic microangiopathy, acute kidney injury, cardiovascular disease, cancer and obesity. Current evidence suggests that the (P)RR has key roles in the normal development and maintenance of vital organs and that dysfunction of the (P)RR is associated with diseases that are characterized by a disruption of the homeostasis of physiological functions.

Phenotypic and genotypic characterization of families with complex intellectual disability identified pathogenic genetic variations in known and novel disease genes

Intellectual disability (ID), which presents itself during childhood, belongs to a group of neurodevelopmental disorders (NDDs) that are clinically widely heterogeneous and highly heritable, often being caused by single gene defects. Indeed, NDDs can be attributed to mutations at over 1000 loci, and all type of mutations, ranging from single nucleotide variations (SNVs) to large, complex copy number variations (CNVs), have been reported in patients with ID and other related NDDs. In this study, we recruited seven different recessive NDD families with comorbidities to perform a detailed clinical characterization and a complete genomic analysis that consisted of a combination of high throughput SNP-based genotyping and whole-genome sequencing (WGS). Different disease-associated loci and pathogenic gene mutations were identified in each family, including known (n = 4) and novel (n = 2) mutations in known genes (NAGLU, SLC5A2, POLR3B, VPS13A, SYN1, SPG11), and the identification of a novel disease gene (n = 1; NSL1). Functional analyses were additionally performed in a gene associated with autism-like symptoms and epileptic seizures for further proof of pathogenicity. Lastly, detailed genotype-phenotype correlations were carried out to assist with the diagnosis of prospective families and to determine genomic variation with clinical relevance. We concluded that the combination of linkage analyses and WGS to search for disease genes still remains a fruitful strategy for complex diseases with a variety of mutated genes and heterogeneous phenotypic manifestations, allowing for the identification of novel mutations, genes, and phenotypes, and leading to improvements in both diagnostic strategies and functional characterization of disease mechanisms.

The Renin-Angiotensin System in the Central Nervous System and Its Role in Blood Pressure Regulation

Purpose of the Review

The main goal of this article is to discuss how the development of state-of-the-art technology has made it possible to address fundamental questions related to how the renin-angiotensin system (RAS) operates within the brain from the neurophysiological and molecular perspective.

Recent Findings

The existence of the brain RAS remains surprisingly controversial. New sensitive in situ hybridization techniques and novel transgenic animals expressing reporter genes have provided pivotal information of the expression of RAS genes within the brain. We discuss studies using genetically engineered animals combined with targeted viral microinjections to study molecular mechanisms implicated in the regulation of the brain RAS. We also discuss novel drugs targeting the brain RAS that have shown promising results in clinical studies and trials.

Summary

Over the last 50 years, several new physiological roles of the brain RAS have been identified. In the coming years, efforts to incorporate cutting-edge technologies such as optogenetics, chemogenetics, and single-cell RNA sequencing will lead to dramatic advances in our full understanding of how the brain RAS operates at molecular and neurophysiological levels.

Aggressive behavior in cattle is associated with a polymorphism in the MAOA gene promoter

Molecular mechanisms underlying aggressive behavior are primitive and similar among the subphylum Vertebrata. In humans, a primary goal in the study of aggression is to determine the neurobehavioral molecular factors triggering violence. Although several species have been used to study agonistic responses, researchers are limited by the difficulty of artificially inducing aggression in animals not selected for it. Conversely, the Lidia cattle breed has been selected since the eighteenth century to display agonistic responses based on traits such as aggressiveness, ferocity and mobility, all of them showing significant heritability values. This intensive selection may have driven shifts in specific allele frequencies. In a previous analysis across the autosomes, we revealed long-term selection regions including genes involved in behavioral development. In the present study, we focus on mapping recent signatures of selection associated with aggressiveness at chromosome X, by comparing Lidia cattle samples with two non-specialized Spanish breeds showing tamed behavior. The most significant markers peaked around the monoamine oxidase A (MAOA) gene, and thus the associations of three functionally important regions located near the promoter of this gene were further investigated. A polymorphism consisting of a variable number of tandem repeats of the nucleotide 'C' (BTX:105,462,494) and displaying lower number of repetitions in the Lidia breed when compared with the tamed breeds was detected. In silico analyses predicted that the g.105,462,494delsinsC variant may code for the Sp1 binding motif, one of the major transcription factors controlling the core promoter and expression of the MAOA gene in humans.

Identifying gene mutations of Chinese patients with polycystic kidney disease through targeted next-generation sequencing technology

BACKGROUND

Polycystic kidney disease (PKD) is the most common hereditary kidney disease. The main mutational genes causing autosomal dominant polycystic kidney disease (ADPKD) are PKD1 and PKD2 as well as some rare pathogenic genes. Unilateral PKD is rare in clinics, and its association with gene mutations is unclear.

METHODS

Targeted next-generation sequencing (NGS) was performed to detect the renal ciliopathy-associated genes (targeted NGS panel including 63 genes) in PKD patients.

RESULTS

Forty-eight PKD1 and PKD2 mutation sites were detected in 44 bilateral PKD patients, of which 48 were PKD1 mutation sites (87.5%) and six were PKD2 mutation sites (12.5%). All of which exhibited typical ADPKD. Furthermore, we detected HNF1B heterozygous mutations in three families. Although these three patients showed HNF1B heterozygous mutations, their clinical characteristics differed and showed phenotypic heterogeneity.

CONCLUSIONS

Targeted NGS panel was helpful in detecting typical ADPKD patients and even in non-typical PKD patients. Macromutation in HNF1B may lead to bilateral PKD. The 16 novel PKD gene mutation sites and two novel PKD2 gene mutation sites discovered in this study have some significance in genetic counseling for ADPKD patients, and increase the number of studied families and expand the mutation database of ADPKD.

Conditional ablation of the prorenin receptor in nephron progenitor cells results in developmental programming of hypertension

Nephron induction during kidney development is driven by reciprocal interactions between progenitor cells (NPCs) of the cap mesenchyme (CM) and the ureteric bud (UB). The prorenin receptor (PRR) is a receptor for renin and prorenin, and an accessory subunit of the vacuolar proton pump V‐ATPase. Previously, we demonstrated that conditional ablation of the PRR in Six2⁺NPCs in mice (Six2^PRR−/−) causes early neonatal death. Here, we identified genes that are regulated by PRR in Six2⁺NPCs FACS‐isolated from Six2^PRR−/− and control kidneys on embryonic day E15.5 using whole‐genome expression analysis. Seven genes with expression in CM cells previously shown to direct kidney development, including Notch1, β‐catenin, Lef1, Lhx1, Jag1, and p53, were downregulated. The functional groups within the downregulated gene set included genes involved in embryonic and cellular development, renal regeneration, cellular assembly and organization, cell morphology, death and survival. Double‐transgenic Six2^PRR−/−/BatGal⁺ mice, a reporter strain for β‐catenin transcriptional activity, showed decreased β‐catenin activity in the UB in vivo. Reduced PRR gene dosage in heterozygous Six2^PRR+/− mice was associated with decreased glomerular number, segmental thickening of the glomerular basement membrane with focal podocyte foot process effacement, development of hypertension and increased soluble PRR (sPRR) levels in the urine at 2 months of age. Together, these data demonstrate that NPC PRR performs essential functions during nephrogenesis via control of hierarchy of genes that regulate critical cellular processes. Both reduced nephron endowment and augmented urine sPRR likely contribute to programming of hypertension in Six2^PRR+/− mice.

ATP6AP2 variant impairs CNS development and neuronal survival to cause fulminant neurodegeneration

Vacuolar H+-ATPase-dependent (V-ATPase-dependent) functions are critical for neural proteostasis and are involved in neurodegeneration and brain tumorigenesis. We identified a patient with fulminant neurodegeneration of the developing brain carrying a de novo splice site variant in ATP6AP2 encoding an accessory protein of the V-ATPase. Functional studies of induced pluripotent stem cell-derived (iPSC-derived) neurons from this patient revealed reduced spontaneous activity and severe deficiency in lysosomal acidification and protein degradation leading to neuronal cell death. These deficiencies could be rescued by expression of full-length ATP6AP2. Conditional deletion of Atp6ap2 in developing mouse brain impaired V-ATPase-dependent functions, causing impaired neural stem cell self-renewal, premature neuronal differentiation, and apoptosis resulting in degeneration of nearly the entire cortex. In vitro studies revealed that ATP6AP2 deficiency decreases V-ATPase membrane assembly and increases endosomal-lysosomal fusion. We conclude that ATP6AP2 is a key mediator of V-ATPase-dependent signaling and protein degradation in the developing human central nervous system.

Stromal prorenin receptor is critical for normal kidney development

Formation of the metanephric kidney requires coordinated interaction among the stroma, ureteric bud, and cap mesenchyme. The transcription factor Foxd1, a specific marker of renal stromal cells, is critical for normal kidney development. The prorenin receptor (PRR), a receptor for renin and prorenin, is also an accessory subunit of the vacuolar proton pump V-ATPase. Global loss of PRR is embryonically lethal in mice, indicating an essential role of the PRR in embryonic development. Here, we report that conditional deletion of the PRR in Foxd1⁺ stromal progenitors in mice (cKO) results in neonatal mortality. The kidneys of surviving mice show reduced expression of stromal markers Foxd1 and Meis1 and a marked decrease in arterial and arteriolar development with the subsequent decreased number of glomeruli, expansion of Six2⁺ nephron progenitors, and delay in nephron differentiation. Intrarenal arteries and arterioles in cKO mice were fewer and thinner and showed a marked decrease in the expression of renin, suggesting a central role for the PRR in the development of renin-expressing cells, which in turn are essential for the proper formation of the renal arterial tree. We conclude that stromal PRR is crucial for the appropriate differentiation of the renal arterial tree, which in turn may restrict excessive expansion of nephron progenitors to promote a coordinated and proper morphogenesis of the nephrovascular structures of the mammalian kidney.

The (pro)renin receptor: an emerging player in hypertension and metabolic syndrome

The (pro)renin receptor (PRR) is a multifunctional protein that is expressed in multiple organs. Binding of prorenin/renin to the PRR activates angiotensin II-dependent and angiotensin II-independent pathways. The PRR is also involved in autophagy and Wnt/ß catenin signaling, functions that are not contingent on prorenin binding. Emerging evidence suggests that the PRR plays an important role in blood pressure regulation and glucose and lipid metabolism. Herein, we review PRR function in health and disease, with particular emphasis on hypertension and the metabolic syndrome.

Role of the Angiotensin Pathway and its Target Therapy in Epilepsy Management

Despite extensive research on epileptogenesis, there is still a need to investigate new pathways and targeted therapeutic approaches in this complex process. Inflammation, oxidative stress, neurotoxicity, neural cell death, gliosis, and blood–brain barrier (BBB) dysfunction are the most common causes of epileptogenesis. Moreover, the renin–angiotensin system (RAS) affects the brain’s physiological and pathological conditions, including epilepsy and its consequences. While there are a variety of available pharmacotherapeutic approaches, information on new pathways is in high demand and the achievement of treatment goals is greatly desired. Therefore, targeting the RAS presents an interesting opportunity to better understand this process. This has been supported by preclinical studies, primarily based on RAS enzyme, receptor-inhibition, and selective agonists, which are characterized by pleiotropic properties. Although there are some antiepileptic drugs (AEDs) that interfere with RAS, the main targeted therapy of this pathway contributes in synergy with AEDs. However, the RAS-targeted treatment alone, or in combination with AEDs, requires clinical studies to contribute to, and clarify, the evidence on epilepsy management. There is also a genetic association between RAS and epilepsy, and an involvement of pharmacogenetics in RAS, so there are possibilities for the development of new diagnostic and personalized treatments for epilepsy.

Loss-of-function mutations in ATP6AP1 and ATP6AP2 in granular cell tumors

Granular cell tumors (GCTs) are rare tumors that can arise in multiple anatomical locations, and are characterized by abundant intracytoplasmic granules. The genetic drivers of GCTs are currently unknown. Here, we apply whole-exome sequencing and targeted sequencing analysis to reveal mutually exclusive, clonal, inactivating somatic mutations in the endosomal pH regulators ATP6AP1 or ATP6AP2 in 72% of GCTs. Silencing of these genes in vitro results in impaired vesicle acidification, redistribution of endosomal compartments, and accumulation of intracytoplasmic granules, recapitulating the cardinal phenotypic characteristics of GCTs and providing a novel genotypic–phenotypic correlation. In addition, depletion of ATP6AP1 or ATP6AP2 results in the acquisition of oncogenic properties. Our results demonstrate that inactivating mutations of ATP6AP1 and ATP6AP2 are likely oncogenic drivers of GCTs and underpin the genesis of the intracytoplasmic granules that characterize them, providing a genetic link between endosomal pH regulation and tumorigenesis.

Granular cell tumors (GCTs) are rare tumors that arise in multiple anatomical locations. Here, the authors investigate the genomics of GCTs, finding inactivating somatic mutations in ATP6AP1 or ATP6AP2 in 72% of the 82 GCTs analyzed. In vitro manipulation of these genes recapitulated GCT phenotypes in cellular models.

Essential role of ATP6AP2 enrichment in caveolae/lipid raft microdomains for the induction of neuronal differentiation of stem cells

Background

The subcellular distribution of prorenin receptor and adaptor protein ATP6AP2 may affect neurogenesis. In this study, we hypothesized that ATP6AP2 expression and subcellular relocalization from caveolae/lipid raft microdomains (CLR-Ms) to intracellular sites may correlate with neuronal differentiation (Neu-Dif) of adipose-derived mesenchymal stem cells (ADSCs).

Methods

Human ADSCs isolated from 24 healthy donors and 24 patients with neurological disorders (ND) were cultured and induced for Neu-Dif. The mechanism of action of ATP6AP2 and the impact of its localization within the plasma membrane (particularly CLR-Ms) and intracellular sites on several pathways (mitogen-activated protein kinase, Wnt(s) signaling and others) and intracellular calcium and exosome release were evaluated. The impact of CLR-Ms on ATP6AP2 or vice versa was determined by pharmacological disruption of CLR-Ms or siATP6AP2 assays.

Results

In patients with ND, loss of ATP6AP2 from CLR-Ms correlated with an inhibition of Neu-Dif and signaling. However, its relocalization in CLR-Ms was positively correlated to induction of Neu-Dif in healthy subjects. An apparent switch from canonical to noncanonical Wnt signaling as well as from caveolin to flotillin occurs concurrently with the increases of ATP6AP2 expression during neurogenesis. Stimulation by renin activates ERK/JNK/CREB/c-Jun but failed to induce β-catenin. Wnt5a enhanced the renin-induced JNK responsiveness. Gα proteins crosslink ATP6AP2 to caveolin where a switch from Gαi to Gαq is necessary for Neu-Dif. In ATP6AP2-enriched CLR-Ms, the release of exosomes was induced dependently from the intracellular Ca²⁺ and Gαq. Pharmacological disruption of CLR-M formation/stability impairs both ATP6AP2 localization and Neu-Dif in addition to reducing exosome release, indicating an essential role of ATP6AP2 enrichment in CLR-Ms for the induction of Neu-Dif. The mechanism is dependent on CLR-M dynamics, particularly the membrane fluidity. Knockdown of ATP6AP2 inhibited Neu-Dif but increased astrocytic-Dif, depleted ATP6AP2/flotillin/Gαq but accumulated caveolin/Gαi in CLR-Ms, and blocked the activation of JNK/ERK/c-Jun/CREB/exosome release. siATP6AP2 cells treated with sphingomyelinase/methyl-β-cyclodextrin reversed the levels of caveolin/flotillin in CLR-Ms but did not induce Neu-Dif, indicating the crucial relocalization of ATP6AP2 in CLR-Ms for neurogenesis. Treatment of ND-derived cells with nSMase showed reversibility in ATP6AP2 abundance in CLR-Ms and enhanced Neu-Dif.

Conclusions

This study gives evidence of the determinant role of CLR-M ATP6AP2 localization for neuronal and oligodendrocyte differentiation involving mechanisms of switches from Gαi/caveolin/canonical to Gαq/flotillin/PCP, the ERK/JNK pathway and Ca²⁺-dependent release of exosomes and as a potential target of drug therapy for neurodegenerative disorders.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0862-9) contains supplementary material, which is available to authorized users.

Proteomic Analysis of the Human Olfactory Bulb

The importance of olfaction to human health and disease is often underappreciated. Olfactory dysfunction has been reported in association with a host of common complex diseases, including neurological diseases such as Alzheimer's disease and Parkinson's disease. For health, olfaction or the sense of smell is also important for most mammals, for optimal engagement with their environment. Indeed, animals have developed sophisticated olfactory systems to detect and interpret the rich information presented to them to assist in day-to-day activities such as locating food sources, differentiating food from poisons, identifying mates, promoting reproduction, avoiding predators, and averting death. In this context, the olfactory bulb is a vital component of the olfactory system receiving sensory information from the axons of the olfactory receptor neurons located in the nasal cavity and the first place that processes the olfactory information. We report in this study original observations on the human olfactory bulb proteome in healthy subjects, using a high-resolution mass spectrometry-based proteomic approach. We identified 7750 nonredundant proteins from human olfactory bulbs. Bioinformatics analysis of these proteins showed their involvement in biological processes associated with signal transduction, metabolism, transport, and olfaction. These new observations provide a crucial baseline molecular profile of the human olfactory bulb proteome, and should assist the future discovery of biomarker proteins and novel diagnostics associated with diseases characterized by olfactory dysfunction.

Roles and functions of Atp6ap2 in the brain

The classical renin-angiotensin system (RAS) in the body has been studied intensively in the last decades, since it is known that this system is involved in the regulation of blood pressure. Since nearly all members of the classical RAS have also been identified within the brain in the last decades and due to the existence of the blood-brain barrier, a RAS within the brain (bRAS) that is largely independent from the peripheral RAS has been postulated. All members of the angiotensin family as e.g., angiotensin II, angiotensin IV and angiotensin II (1-7) along with the respective receptors (e.g., angiotensin II receptor type 1 (AT1), angiotensin II receptor type 2 (AT2), angiotensin IV receptor (AT4), angiotensin II (1-7) receptor (Mas)) have been identified within the brain. Moreover, a receptor capable of binding renin and the renin precursor prorenin with high affinity has also been detected within the brain. This protein functions as a membrane receptor for (pro)renin and also represents a V-ATPase subunit and is therefore termed (P)RR or Atp6ap2, respectively. In this review we shed light on the (known as well as putative) roles and functions of Atp6ap2 in the brain under physiological and pathophysiological conditions.

Homeostatic effect of laughter on diabetic cardiovascular complications: The myth turned to fact

AIMS

Laughter has been used for centuries to alleviate pain in morbid conditions. It was not until 1976 that scientists thought about laughter as a form of therapy that can modulate hormonal and immunological parameters that affect the outcome of many serious diseases. Moreover, laughter therapy was shown to be beneficial in type 2 diabetes mellitus (T2DM) by delaying the onset of many diabetic complications. Laughter is also described to influence the cardiovascular and endothelial functions and thus may protect against diabetic cardiovascular complications. In this review, we outline the different biochemical, physiological and immunological mechanisms by which laughter may influence the overall state of wellbeing and enhance disease prognosis. We also focus on the biological link between laughter therapy and diabetic cardiovascular complications as well as the underlying mechanisms involved in T2DM.

METHODS

Reviewing all the essential databases for "laughter" and "type 2 diabetes mellitus".

RESULTS

Although laughter therapy is still poorly investigated, recent studies show that laughter may retard the onset of diabetic complications, enhance cardiovascular functions and rectify homeostatic abnormalities associated with T2DM.

CONCLUSIONS

Laughter therapy is effective in delaying diabetic complications and should be used as an adjuvant therapy.

Increased (pro)renin receptor expression in the subfornical organ of hypertensive humans

The central nervous system plays an important role in essential hypertension in humans and in animal models of hypertension through modulation of sympathetic activity and Na⁺ and body fluid homeostasis. Data from animal models of hypertension suggest that the renin-angiotensin system in the subfornical organ (SFO) of the brain is critical for hypertension development. We recently reported that the brain (pro)renin receptor (PRR) is a novel component of the brain renin-angiotensin system and could be a key initiator of the pathogenesis of hypertension. Here, we examined the expression level and cellular distribution of PRR in the SFO of postmortem human brains to assess its association with the pathogenesis of human hypertension. Postmortem SFO tissues were collected from hypertensive and normotensive human subjects. Immunolabeling for the PRR and a retrospective analysis of clinical data were performed. We found that human PRR was prominently expressed in most neurons and microglia, but not in astrocytes, in the SFO. Importantly, PRR levels in the SFO were elevated in hypertensive subjects. Moreover, PRR immunoreactivity was significantly correlated with systolic blood pressure but not body weight, age, or diastolic blood pressure. Interestingly, this correlation was independent of antihypertensive drug therapy. Our data indicate that PRR in the SFO may be a key molecular player in the pathogenesis of human hypertension and, as such, could be an important focus of efforts to understand the neurogenic origin of hypertension. NEW & NOTEWORTHY This study provides evidence that, in the subfornical organ of the human brain, the (pro)renin receptor is expressed in neurons and microglia cells but not in astrocytes. More importantly, (pro)renin receptor immunoreactivity in the subfornical organ is increased in hypertensive humans and is significantly correlated with systolic blood pressure.

Mutations in the X-linked ATP6AP2 cause a glycosylation disorder with autophagic defects

Rujano et al. report mutations in ATP6AP2 leading to liver disease, immunodeficiency, and psychomotor impairment. ATP6AP2 deficiency impairs the assembly and function of the V-ATPase proton pump, causing defects in protein glycosylation and autophagy.

The biogenesis of the multi-subunit vacuolar-type H⁺-ATPase (V-ATPase) is initiated in the endoplasmic reticulum with the assembly of the proton pore V0, which is controlled by a group of assembly factors. Here, we identify two hemizygous missense mutations in the extracellular domain of the accessory V-ATPase subunit ATP6AP2 (also known as the [pro]renin receptor) responsible for a glycosylation disorder with liver disease, immunodeficiency, cutis laxa, and psychomotor impairment. We show that ATP6AP2 deficiency in the mouse liver caused hypoglycosylation of serum proteins and autophagy defects. The introduction of one of the missense mutations into Drosophila led to reduced survival and altered lipid metabolism. We further demonstrate that in the liver-like fat body, the autophagic dysregulation was associated with defects in lysosomal acidification and mammalian target of rapamycin (mTOR) signaling. Finally, both ATP6AP2 mutations impaired protein stability and the interaction with ATP6AP1, a member of the V0 assembly complex. Collectively, our data suggest that the missense mutations in ATP6AP2 lead to impaired V-ATPase assembly and subsequent defects in glycosylation and autophagy.

Atp6ap2 ablation in adult mice impairs viability through multiple organ deficiencies

ATP6AP2 codes for the (pro)renin receptor and is an essential component of vacuolar H+ ATPase. Activating (pro)renin for conversion of Angiotensinogen to Angiotensin makes ATP6AP2 attractive for drug intervention. Tissue-specific ATP6AP2 inactivation in mouse suggested a strong impact on various organs. Consistent with this, we found that embryonic ablation of Atp6ap2 resulted in both male hemizygous lethality and female haploinsufficiency. Next, we examined the phenotype of an induced inactivation in the adult animal, most akin to detect potential effect of functional interference of ATP6AP2 through drug therapy. Induced ablation of Atp6ap2, even without equal efficiency in all tissues (aorta, brain and kidney), resulted in rapid lethality marked by weight loss, changes in nutritional as well as blood parameters, leukocyte depletion, and bone marrow hypoplasia. Upon Atp6ap2 ablation, the colon demonstrated a rapid disruption of crypt morphology, aberrant proliferation, cell-death activation, as well as generation of microadenomas. Consequently, disruption of ATP6AP2 is extremely poorly tolerated in the adult, and severely affects various organ systems demonstrating that ATP6AP2 is an essential gene implicated in basic cellular mechanisms and necessary for multiple organ function. Accordingly, any potential drug targeting of this gene product must be strictly assessed for safety.

Soluble (Pro)renin Receptor and Obstructive Sleep Apnea Syndrome: Oxidative Stress in Brain?

(Pro)renin receptor ((P)RR) is a multi-functional molecule that is related to both the renin-angiotensin system (RAS) and vacuolar H⁺-ATPase (v-ATPase), an ATP-dependent multi-subunit proton pump. Soluble (P)RR (s(P)RR), which consists of the extracellular domain of (P)RR, is present in blood and urine. Elevated plasma s(P)RR concentrations are reported in patients with chronic kidney disease and pregnant women with hypertension or diabetes mellitus. In addition, we have shown that plasma s(P)RR concentrations are elevated in patients with obstructive sleep apnea syndrome (OSAS). Interestingly, the levels are elevated in parallel with the severity of OSAS, but are not related to the presence of hypertension or the status of the circulating RAS in OSAS. It is known that v-ATPase activity protects cells from endogenous oxidative stress, and loss of v-ATPase activity results in chronic oxidative stress. We hypothesize that hypoxia and subsequent oxidative stress, perhaps in the brain, may be one of the factors that elevate plasma s(P)RR levels in OSAS.