miR-584-5p / Ykt6 - mediated autophagy - lysosome - exosome pathway as a critical route affecting the toxic effects of lead on HK-2 cells

Lead is a widespread environmental pollutant with serious adverse effects on human health, but the mechanism underlying its toxicity remains elusive. This study aimed to investigate the role of miR-584-5p / Ykt6 axis in the toxic effect of lead on HK-2 cells and the related mechanism. Our data suggested that lead exposure caused significant cytotoxicity, DNA and chromosome damage to HK-2 cells. Mechanistically, lead exposure down-regulated miR-584-5p and up-regulated Ykt6 expression, consequently, autophagosomal number and autophagic flux increased, lysosomal number and activity decreased, exosomal secretion increased. Interestingly, when miR-584-5p level was enhanced with mimic, autophagosomal number and autophagic flux decreased, lysosomal number and activity increased, ultimately, exosomal secretion was down-regulated, which resulted in significant aggravated toxic effects of lead. Further, directly blocking exosomal secretion with inhibitor GW4869 also resulted in exacerbated toxic effects of lead. Herein, we conclude that miR-584-5p / Ykt6 - mediated autophagy - lysosome - exosome pathway may be a critical route affecting the toxic effects of lead on HK-2 cells. We provide a novel insight into the mechanism underlying the toxicity of lead on human cells.

Generation of an induced pluripotent stem cell line (SYSUSCi004-A) from a patient with Infantile Malignant Osteopetrosis

Infantile Malignant Osteopetrosis (IMO) is a rare, severe autosomal recessive form of osteopetrosis. Here, the peripheral blood mononuclear cells (PBMCs) extracted from a patient with IMO carrying a compound heterozygous mutation in T cell immune regulator 1, ATPase H + transporting V0 subunit a3 (TCIRG1) gene (c.242delC; c.1114C > T) were successfully reprogrammed using Sendai virus encoding the four Yamanaka factors. The generated hiPSCs, IMO-hiPSCs, displayed typical embryonic stem cell-like morphology and were verified by expression of pluripotency markers such as OCT4, SOX2, NANOG, TRA-1-60 and SSEA4, as well as in vivo and in vitro differentiation into derivatives of three germ layers.

Osteopetrorickets: two contradictory patterns-one unifying diagnosis

A 5-month-old infant with bone findings on x-ray presented an apparent contradiction including findings of both diffusely dense bones and rickets in the context of a history and laboratory investigation that suggested leukemia. Next generation gene panel sequencing revealed a TCIRG1 mutation which is consistent with autosomal recessive osteopetrosis. The paradoxical x-ray findings underscore a recently elucidated mechanism for the pathogenesis of a TCIRG mutation. This case highlights the importance of recognizing this radiographic, seeming contradictory, association in the context of a confusing clinical presentation. Failure to recognize this pattern promptly may lead to a delay in diagnosis, thus potentially permanent organ failure.

Distal renal tubular acidosis as presenting manifestation of Wilson disease in a 11-year-old girl

A 11-year-old girl was referred to the pediatric nephrology services of our hospital for evaluation of vitamin-D-refractory rickets. She was born to second-degree consanguineous parents. On examination, she had wrist widening and bilateral genu varum. She had normal anion gap metabolic acidosis, hypokalemia, and hyperchloremia. The fractional excretion of bicarbonate was 3% and the urine anion gap was positive. She also had hypercalciuria, but no phosphaturia, glucosuria or aminoaciduria. In view of a family history of an elder sister having rigidity with cognitive and speech impairment, an ophthalmic evaluation by slit lamp examination was performed in the index case that revealed bilateral Kayser-Fleischer rings. Serum ceruloplasmin was low and 24-h urine copper was elevated in the index case. Whole exome sequencing unveiled a novel pathogenic variant in exon 2 of the ATP7B gene (chr13: c.470del; Depth: 142x) (homozygous) that resulted in a frameshift and premature truncation of the protein, 15 amino acids downstream to codon 157 (p. Cys157LeufsTer15; NM_000053.4) confirming Wilson disease. There were no mutations in the ATP6V0A4, ATP6V1B1, SLC4A1, FOXI1, WDR72 genes or other genes that are known to cause distal RTA. Therapy with D-penicillamine and zinc supplements was initiated. A low dose of 2.5 mEq/kg/day of potassium citrate supplementation normalized the serum bicarbonate levels. This case was notable for the absence of hepatic or neurological involvement at admission. Wilson disease is well known to cause proximal renal tubular acidosis and Fanconi syndrome, with relatively lesser involvement of the distal renal tubules in the literature. However, isolated distal renal tubular involvement as presenting manifestation of Wilson disease (without hepatic or neurological involvement) is rare and can lead to diagnostic confusion.

Human soluble prorenin receptor expressed in mouse renal collecting duct shows sex-specific effect on cardiorenal function

Soluble prorenin receptor (sPRR), a component of the renin-angiotensin system (RAS), has been identified as a plasma biomarker for hypertension and cardiovascular diseases in humans. Despite studies showing that sPRR in the kidney is produced by tubular cells in the renal collecting duct (CD), its biological actions modulating cardiorenal function in physiological conditions remain unknown. Therefore, the objective of our study was to investigate whether CD-derived human sPRR (HsPRR) expression influences cardiorenal function and examine sex and circadian differences. Thus, we investigated the status of the intrarenal RAS, water and electrolyte balance, renal filtration capacity, and blood pressure (BP) regulation in CD-HsPRR and control (CTL) mice. CD-HsPRR mice were generated by breeding human sPRR-Myc-tag mice with Hoxb7/Cre mice. Renal sPRR expression increased in CD-HsPRR mice, but circulating sPRR and RAS levels were unchanged compared with CTL mice. Only female littermates expressing CD-HsPRR showed 1) increased 24-h BP, 2) an impaired BP response to an acute dose of losartan and attenuated angiotensin II (ANG II)-induced hypertension, 3) reduced angiotensin-converting enzyme activity and ANG II content in the renal cortex, and 4) decreased glomerular filtration rate, with no changes in natriuresis and kaliuresis despite upregulation of the β-subunit of the epithelial Na+ channel in the renal cortex. These cardiorenal alterations were displayed only during the active phase of the day. Taken together, these data suggest that HsPRR could interact with ANG II type 1 receptors mediating sex-specific, ANG II-independent renal dysfunction and a prohypertensive phenotype in a sex-specific manner.NEW & NOTEWORTHY We successfully generated a humanized mouse model that expresses human sPRR in the collecting duct. Collecting duct-derived human sPRR did not change circulating sPRR and RAS levels but increased daytime BP in female mice while showing an attenuated angiotensin II-dependent pressor response. These findings may aid in elucidating the mechanisms by which women show uncontrolled BP in response to antihypertensive treatments targeting the RAS, improving approaches to reduce uncontrolled BP and chronic kidney disease incidences in women.

A pH imbalance is linked to autophagic dysregulation of inner ear hair cells in Atp6v1ba-deficient zebrafish

V-ATPase is an ATP hydrolysis-driven proton pump involved in the acidification of intracellular organelles and systemic acid-base homeostasis through H+ secretion in the renal collecting ducts. V-ATPase dysfunction is associated with hereditary distal renal tubular acidosis (dRTA). ATP6V1B1 encodes the B1 subunit of V-ATPase that is integral to ATP hydrolysis and subsequent H+ transport. Patients with pathogenic ATP6V1B1 mutations often exhibit an early onset of sensorineural hearing loss. However, the mechanisms underlying this association remain unclear. We employed morpholino oligonucleotide-mediated knockdown and CRISPR/Cas9 gene editing to generate Atp6v1ba-deficient (atp6v1ba-/-) zebrafish as an ortholog model for ATP6V1B1. The atp6v1ba-/- zebrafish exhibited systemic acidosis and significantly smaller otoliths compared to wild-type siblings. Moreover, deficiency in Atp6v1ba led to degeneration of inner ear hair cells, with ultrastructural changes indicative of autophagy. Our findings indicate a critical role of ATP6V1B1 in regulating lysosomal pH and autophagy in hair cells, and the results provide insights into the pathophysiology of sensorineural hearing loss in dRTA. Furthermore, this study demonstrates that the atp6v1ba-/- zebrafish model is a valuable tool for further investigation into disease mechanisms and potential therapies for acidosis-related hearing impairment.

ATP6V1A variants are associated with childhood epilepsy with favorable outcome

PURPOSE

ATP6V1A variants have been identified in patients with highly variable phenotypes such as autosomal dominant epileptic encephalopathy and autosomal recessive cutis laxa. However, the mechanism underlying phenotype variation is unknown. We screened ATP6V1A variants in patients with epilepsy and analyzed the genotype-phenotype correlation to explain the mechanism underlying phenotypic variations.

METHODS

We performed trio-based whole-exome sequencing in people with epilepsy without acquired causes. All previously reported ATP6V1A variants were systematically retrieved from the HGMD and PubMed databases.

RESULTS

Three novel de novo ATP6V1A variants, including c.749G>C/p.Gly250Ala, c.782A>G/p.Gln261Arg, and c.1103T>C/p.Met368Thr, were identified in three unrelated cases with childhood focal (partial) epilepsy. None of the variants were listed in any public population database and evaluated as likely pathogenic according to the criteria of the American College of Medical Genetics and Genomics (ACMG). All persons showed good responses to anti-seizure medication and psychomotor development was normal. Further analysis showed that monoallelic missense variants were associated with epilepsy with variable severity, whereas biallelic variants resulted in developmental abnormalities of multisystem that may result in early lethality.

CONCLUSION

Childhood focal epilepsy with favorable outcome was probably a novel phenotype of ATP6V1A. ATP6V1A variants are associated with a range of phenotypes that correlate with genotypes. The relationship between phenotype severity and the genotype (genetic impairment) of ATP6V1A variants helps explain the phenotypic variations.

ATP6AP1 as a potential prognostic biomarker in CRC by comprehensive analysis and verification

The role of ATP6AP1 in colorectal cancer (CRC) remains elusive despite its observed upregulation in pan-cancer. Therefore, the current study aimed to assess the clinical significance of ATP6AP1 and its relationship with the immune infiltration in CRC. Transcriptome data of CRC were obtained from The Cancer Genome Atlas (TCGA) database and analyzed using the combination of R packages and tumor-related databases, including TIMER2, TISIDB, cBioPortal, and MethSurv. The tissue arrays and immunohistochemical staining were performed to verify the expression and clinical characteristics of ATP6AP1. The results revealed that ATP6AP1 expression was significantly elevated in CRC and associated with poor clinicopathological characteristics and prognosis. Furthermore, the analysis demonstrated ATP6AP1 expression was correlated with the infiltration of immune cells and cancer-associated fibroblasts in the microenvironment of CRC. Moreover, ATP6AP1 was found to be linked to various immune checkpoints and chemokines, with enrichment of cytoplasmic vesicle lumen, endopeptidase regulator activity, and endopeptidase inhibitor activity observed in the high ATP6AP1 expressional group. In conclusion, the findings of this study suggest that ATP6AP1 upregulation may serve as a biomarker for poor diagnosis in CRC and offer a potential target for immunotherapy in CRC.

Atp6v1h Deficiency Blocks Bone Loss in Simulated Microgravity Mice through the Fos-Jun-Src-Integrin Pathway

The microgravity conditions in outer space are widely acknowledged to induce significant bone loss. Recent studies have implicated the close relationship between Atp6v1h gene and bone loss. Despite this, the role of Atp6v1h in bone remodeling and its molecular mechanisms in microgravity have not been fully elucidated. To address this, we used a mouse tail suspension model to simulate microgravity. We categorized both wild-type and Atp6v1h knockout (Atp6v1h+/-) mice into two groups: regular feeding and tail-suspension feeding, ensuring uniform feeding conditions across all cohorts. Analysis via micro-CT scanning, hematoxylin-eosin staining, and tartrate-resistant acid phosphatase assays indicated that wild-type mice underwent bone loss under simulated microgravity. Atp6v1h+/- mice exhibited bone loss due to Atp6v1h deficiency but did not present aggravated bone loss under the same simulated microgravity. Transcriptomic sequencing revealed the upregulation of genes, such as Fos, Src, Jun, and various integrin subunits in the context of simulated microgravity and Atp6v1h knockout. Real-time quantitative polymerase chain reaction (RT-qPCR) further validated the modulation of downstream osteoclast-related genes in response to interactions with ATP6V1H overexpression cell lines. Co-immunoprecipitation indicated potential interactions between ATP6V1H and integrin beta 1, beta 3, beta 5, alpha 2b, and alpha 5. Our results indicate that Atp6v1h level influences bone loss in simulated microgravity by modulating the Fos-Jun-Src-Integrin pathway, which, in turn, affects osteoclast activity and bone resorption, with implications for osteoporosis. Therefore, modulating Atp6v1h expression could mitigate bone loss in microgravity conditions. This study elucidates the molecular mechanism of Atp6v1h's role in osteoporosis and positions it as a potential therapeutic target against environmental bone loss. These findings open new possibilities for the treatment of multifactorial osteoporosis.

Engineering yeast with a light-driven proton pump system in the vacuolar membrane

BACKGROUND

The supply of ATP is a limiting factor for cellular metabolism. Therefore, cell factories require a sufficient ATP supply to drive metabolism for efficient bioproduction. In the current study, a light-driven proton pump in the vacuolar membrane was constructed in yeast to reduce the ATP consumption required by V-ATPase to maintain the acidification of the vacuoles and increase the intracellular ATP supply for bioproduction.

RESULTS

Delta rhodopsin (dR), a microbial light-driven proton-pumping rhodopsin from Haloterrigena turkmenica, was expressed and localized in the vacuolar membrane of Saccharomyces cerevisiae by conjugation with a vacuolar membrane-localized protein. Vacuoles with dR were isolated from S. cerevisiae, and the light-driven proton pumping activity was evaluated based on the pH change outside the vacuoles. A light-induced increase in the intracellular ATP content was observed in yeast harboring vacuoles with dR.

CONCLUSIONS

Yeast harboring the light-driven proton pump in the vacuolar membrane developed in this study are a potential optoenergetic cell factory suitable for various bioproduction applications.

TFEB-vacuolar ATPase signaling regulates lysosomal function and microglial activation in tauopathy

Transcription factor EB (TFEB) mediates gene expression through binding to the coordinated lysosome expression and regulation (CLEAR) sequence. TFEB targets include subunits of the vacuolar ATPase (v-ATPase), which are essential for lysosome acidification. Single-nucleus RNA sequencing of wild-type and PS19 (Tau) transgenic mice expressing the P301S mutant tau identified three unique microglia subclusters in Tau mice that were associated with heightened lysosome and immune pathway genes. To explore the lysosome-immune relationship, we specifically disrupted the TFEB-v-ATPase signaling by creating a knock-in mouse line in which the CLEAR sequence of one of the v-ATPase subunits, Atp6v1h, was mutated. CLEAR mutant exhibited a muted response to TFEB, resulting in impaired lysosomal acidification and activity. Crossing the CLEAR mutant with Tau mice led to higher tau pathology but diminished microglia response. These microglia were enriched in a subcluster low in mTOR and HIF-1 pathways and were locked in a homeostatic state. Our studies demonstrate a physiological function of TFEB-v-ATPase signaling in maintaining lysosomal homeostasis and a critical role of the lysosome in mounting a microglia and immune response in tauopathy and Alzheimer's disease.

Long Noncoding RNA lnc-TCEA1-3 Affects Osteoclastic Function by Regulating ATP6V1H

H subunit of V-ATPase (ATP6V1H) is specifically expressed in osteoclasts and its deficiency lead to osteoporosis. Our group previously found four intronic SNPs of ATP6V1H related to reduced bone mineral density, but the mechanisms was not clear. In this study, we found that the above four SNPs were located at lncRNA lnc-TCEA1-3 by using bioinformatics analysis. We further detected the function of lnc-TCEA1-3 on regulating ATP6V1H and osteoclast function using Atp6v1h knockout mice, lentivirus transfection and qPCR analysis. Over expression of lnc-TCEA1-3 up regulated the expression of ATP6V1H in HEK293 cells, HOS cells and primarily cultured osteoclasts, and increased the number of primarily cultured osteoclasts. In addition, over expression of lnc-TCEA1-3 exerted distinct effect on two transcripts of ATP6V1H in HEK293, HOS and osteoclasts. This study will facilitate the in-depth analysis of the effects of ATP6V1H on bone diseases, and discover new therapeutic strategies.

Vacuolar H+-ATPase and BZR1 form a feedback loop to regulate the homeostasis of BR signaling in Arabidopsis

Brassinosteroid (BR) is a vital plant hormone that regulates plant growth and development. BRASSINAZOLE RESISTANT 1 (BZR1) is a key transcription factor in BR signaling, and its nucleocytoplasmic localization is crucial for BR signaling. However, the mechanisms that regulate BZR1 nucleocytoplasmic distribution and thus the homeostasis of BR signaling remain largely unclear. The vacuole is the largest organelle in mature plant cells and plays a key role in maintenance of cellular pH, storage of intracellular substances, and transport of ions. In this study, we uncovered a novel mechanism of BR signaling homeostasis regulated by the vacuolar H+-ATPase (V-ATPase) and BZR1 feedback loop. Our results revealed that the vha-a2 vha-a3 mutant (vha2, lacking V-ATPase activity) exhibits enhanced BR signaling with increased total amount of BZR1, nuclear-localized BZR1, and the ratio of BZR1/phosphorylated BZR1 in the nucleus. Further biochemical assays revealed that VHA-a2 and VHA-a3 of V-ATPase interact with the BZR1 protein through a domain that is conserved across multiple species. VHA-a2 and VHA-a3 negatively regulate BR signaling by interacting with BZR1 and promoting its retention in the tonoplast. Interestingly, a series of molecular analyses demonstrated that nuclear-localized BZR1 could bind directly to specific motifs in the promoters of VHA-a2 and VHA-a3 to promote their expression. Taken together, these results suggest that V-ATPase and BZR1 may form a feedback regulatory loop to maintain the homeostasis of BR signaling in Arabidopsis, providing new insights into vacuole-mediated regulation of hormone signaling.

Identification of a muscle-specific isoform of VMA21 as a potent actor in X-linked myopathy with excessive autophagy pathogenesis

Defective lysosomal acidification is responsible for a large range of multi-systemic disorders associated with impaired autophagy. Diseases caused by mutations in the VMA21 gene stand as exceptions, specifically affecting skeletal muscle (X-linked Myopathy with Excessive Autophagy, XMEA) or liver (Congenital Disorder of Glycosylation). VMA21 chaperones vacuolar (v-) ATPase assembly, which is ubiquitously required for proper lysosomal acidification. The reason VMA21 deficiencies affect specific, but divergent tissues remains unknown. Here, we show that VMA21 encodes a yet-unreported long protein isoform, in addition to the previously described short isoform, which we name VMA21-120 and VMA21-101, respectively. In contrast to the ubiquitous pattern of VMA21-101, VMA21-120 was predominantly expressed in skeletal muscle, and rapidly up-regulated upon differentiation of mouse and human muscle precursors. Accordingly, VMA21-120 accumulated during development, regeneration and denervation of mouse skeletal muscle. In contrast, neither induction nor blockade of autophagy, in vitro and in vivo, strongly affected VMA21 isoform expression. Interestingly, VMA21-101 and VMA21-120 both localized to the sarcoplasmic reticulum of muscle cells, and interacted with the v-ATPase. While VMA21 deficiency impairs autophagy, VMA21-101 or VMA21-120 overexpression had limited impact on autophagic flux in muscle cells. Importantly, XMEA-associated mutations lead to both VMA21-101 deficiency and loss of VMA21-120 expression. These results provide important insights into the clinical diversity of VMA21-related diseases and uncover a muscle-specific VMA21 isoform that potently contributes to XMEA pathogenesis.

Generation of Atp6v1g3-Cre mice for investigation of intercalated cells and the collecting duct

Kidney intercalated cells (ICs) maintain acid-base homeostasis and recent studies have demonstrated that they function in the kidney's innate defense. To study kidney innate immune function, ICs have been enriched using vacuolar ATPase (V-ATPase) B1 subunit (Atp6v1b1)-Cre (B1-Cre) mice. Although Atp6v1b1 is considered kidney specific, it is expressed in multiple organ systems, both in mice and humans, raising the possibility of off-target effects when using the Cre-lox system. We have recently shown using single-cell RNA sequencing that the gene that codes for the V-ATPase G3 subunit (mouse gene: Atp6v1g3; human gene: ATP6V1G3; protein abbreviation: G3) mRNA is selectively enriched in human kidney ICs. In this study, we generated Atp6v1g3-Cre (G3-Cre) reporter mice using CRISPR/CAS technology and crossed them with Tdtomatoflox/flox mice. The resultant G3-Cre+Tdt+ progeny was evaluated for kidney specificity in multiple tissues and found to be highly specific to kidney cells with minimal or no expression in other organs evaluated compared with B1-Cre mice. Tdt+ cells were flow sorted and were enriched for IC marker genes on RT-PCR analysis. Next, we crossed these mice to ihCD59 mice to generate an IC depletion mouse model (G3-Cre+ihCD59+/+). ICs were depleted in these mice using intermedilysin, which resulted in lower blood pH, suggestive of a distal renal tubular acidosis phenotype. The G3-Cre mice were healthy, bred normally, and produce regular-sized litter. Thus, this new "IC reporter" mice can be a useful tool to study ICs.NEW & NOTEWORTHY This study details the development, validation, and experimental use of a new mouse model to study the collecting duct and intercalated cells. Kidney intercalated cells are a cell type increasingly recognized to be important in several human diseases including kidney infections, acid-base disorders, and acute kidney injury.

Cellular senescence triggers intracellular acidification and lysosomal pH alkalinized via ATP6AP2 attenuation in breast cancer cells

Several chemotherapeutic drugs induce senescence in cancer cells; however, the mechanisms underlying intracellular pH dysregulation in senescent cells remain unclear. Adenosine triphosphatase H+ transporting accessory protein 2 (ATP6AP2) plays a critical role in maintaining pH homeostasis in cellular compartments. Herein, we report the regulatory role of ATP6AP2 in senescent breast cancer cells treated with doxorubicin (Doxo) and abemaciclib (Abe). A decline in ATP6AP2 triggers aberrant pH levels that impair lysosomal function and cause immune profile changes in senescent breast cancer cells. Doxo and Abe elicited a stable senescent phenotype and altered the expression of senescence-related genes. Additionally, senescent cells show altered inflammatory and immune transcriptional profiles due to reprogramming of the senescence-associated secretory phenotype. These findings elucidate ATP6AP2-mediated cellular pH regulation and suggest a potential link in immune profile alteration during therapy-induced senescence in breast cancer cells, providing insights into the mechanisms involved in the senescence response to anticancer therapy.

[Analysis of clinical presentation and genetic characteristics of malignant infantile osteopetrosis]

Objective: To investigate the clinical presentation and genetic characteristics of malignant infantile osteopetrosis. Methods: This was a retrospective case study. Thirty-seven children with malignant infantile osteopetrosis admitted into Beijing Children's Hospital from January 2013 to September 2022 were enrolled in this study. According to the gene mutations, the patients were divided into the CLCN7 group and the TCIRG1 group. Clinical characteristics, laboratory tests, and prognosis were compared between two groups. Wilcoxon test or Fisher exact test were used in inter-group comparison. The survival rate was estimated with the Kaplan-Meier method and the Log-Rank test was used to compare the difference in survival between groups. Results: Among the 37 cases, there were 22 males and 15 females. The age of diagnosis was 0.5 (0.2, 1.0) year. There were 13 patients (35%) and 24 patients (65%) with mutations in CLCN7 and TCIRGI gene respectively. Patients in the CLCN7 group had an older age of diagnosis than those in the TCIRGI group (1.2 (0.4, 3.6) vs. 0.4 (0.2, 0.6) years, Z=-2.60, P=0.008). The levels of serum phosphorus (1.7 (1.3, 1.8) vs. 1.1 (0.8, 1.6) mmol/L, Z=-2.59, P=0.010), creatine kinase isoenzyme (CK-MB) (457 (143, 610) vs. 56 (37, 82) U/L, Z=-3.38, P=0.001) and the level of neutrophils (14.0 (9.9, 18.1) vs. 9.2 (6.7, 11.1) ×109/L, Z=-2.07, P=0.039) at diagnosis were higher in the CLCN7 group than that in the TCIRG1 group. However, the level of D-dimer in the CLCN7 group was lower than that in the TCIRGI group (2.7 (1.0, 3.1) vs. 6.3 (2.5, 9.7) μg/L, Z=2.83, P=0.005). After hematopoietic stem cell transplantation, there was no significant difference in 5-year overall survival rate between the two groups (92.3%±7.4% vs. 83.3%±7.6%, χ²=0.56, P=0.456). Conclusions: TCIRGI gene mutations are more common in children with osteopetrosis. Children with TCIRGI gene mutations have younger age, lower levels of phosphorus, CK-MB, and neutrophils and higher level of D-dimer at the onset. After hematopoietic stem cell transplantation, patients with CLCN7 or TCIRGI gene mutations have similar prognosis.

Circular RNAs and inflammation: Epigenetic regulators with diagnostic role

Circular RNAs (circRNAs) are a group of transcripts generally known to be non-coding transcripts, but occasionally producing short peptides. Circ_Ttc3/miR-148a, circ_TLK1/miR-106a-5p, circ_VMA21/miR-9-3p, circ_0068,888/miR-21-5p, circ_VMA21/miR-199a-5p, circ_AFF2/miR-375, circ_0008360/miR-135b-5p and circ-FBXW7/miR-216a-3p are examples of circRNA/miRNA pairs that contribute in the pathogenesis of immune-related conditions. CircRNAs have been found to regulate function of immune system and participate in the pathophysiology of immune-related disorders. In the current study, we searched PubMed and Google Scholar databases until July 2022 with the key words "circRNA" OR "circular RNA" AND "inflammation". Then, we assessed the abstract of retrieved articles to include original articles that assessed contribution of circRNAs in the pathoetiology of inflammation and related disorders. Finally, we went through the main texts of the articles and tabulated the available information. Therefore, the current study summarizes the role of circRNAs in the pathoetiology of sepsis, atherosclerosis, rheumatoid arthritis and osteoarthritis, immune-related cardiovascular, pulmonary, gastrointestinal and nervous system disorders.

ATP6V1B2-related disorders featuring Lennox-Gastaut-syndrome: A case-based overview

BACKGROUND

ATP6V1B2 (ATPase, H+ transporting, lysosomal VI subunit B, isoform 2) encodes for a subunit of a ubiquitous transmembrane lysosomal proton pump, implicated in the acidification of intracellular organelles and in several additional cellular functions. Variants in ATP6V1B2 have been related to a heterogeneous group of multisystemic disorders sometimes associated with variable neurological involvement. However, our knowledge of genotype-phenotype correlations and the neurological spectrum of ATP6V1B2-related disorders remain limited due to the few numbers of reported cases.

CASE STUDY

We hereby report the case of an 18-year-old male Sicilian patient affected by a global developmental delay, skeletal abnormalities, and epileptic encephalopathy featuring Lennox-Gastaut syndrome (LGS), in which exome sequencing led to the identification of a novel de novo variant in ATP6V1B2 (NM_001693.4: c.973G > C, p.Gly325Arg).

CONCLUSIONS

Our report provides new insights on the inclusion of developmental epileptic encephalopathies (DEEs) within the continuum group of ATP6V1B2-related disorders, expanding the phenotypic and molecular spectrum associated with these conditions.

A heterozygous pathogenic variant in the ATP6V1A gene triggering epilepsy in a large Chinese pedigree

Epilepsy is one of the most common disorders in children, with an incidence rate of approximately 5%. Although an increasing number of genes have been demonstrated to be pathogenic factors in epilepsy, evidence for a potential pathogenic role of ATP6V1A remains limited. Herein, the clinical and genetic data of a 5-year-old boy who experienced seizures at 9 months of age are collected. Genetic variants are screened using whole-exome sequencing (WES), and the effects of the candidate variants are further validated at both the RNA and protein levels. WES reveals a heterozygous variant [NM_001690.4: c .1132 C>T, p.Leu378Phe] of the ATP6V1A gene. This variant is not reported in the public database, but is predicted to be deleterious by multiple software packages, and classified as a variant of unknown significance following the American College of Medical Genetics and Genomics guidelines. Quantitative PCR and western blotting further confirm its down-regulatory role in both the RNA and protein expression of ATP6V1A. This case report confirms the pathogenicity of ATP6V1A in epilepsy with solid experimental evidence, thereby expanding the phenotype spectrum of ATP6V1A variants. More importantly, we show that seizures triggered by ATP6V1A variants could be controlled by Levetiracetam, crucially rescuing the development of the patient.

The hybrid RAVE complex plays V-ATPase-dependent and -independent pathobiological roles in Cryptococcus neoformans

V-ATPase, which comprises 13-14 subunits, is essential for pH homeostasis in all eukaryotes, but its proper function requires a regulator to assemble its subunits. While RAVE (regulator of H+-ATPase of vacuolar and endosomal membranes) and Raboconnectin-3 complexes assemble V-ATPase subunits in Saccharomyces cerevisiae and humans, respectively, the function of the RAVE complex in fungal pathogens remains largely unknown. In this study, we identified two RAVE complex components, Rav1 and Wdr1, in the fungal meningitis pathogen Cryptococcus neoformans, and analyzed their roles. Rav1 and Wdr1 are orthologous to yeast RAVE and human Rabconnectin-3 counterparts, respectively, forming the hybrid RAVE (hRAVE) complex. Deletion of RAV1 caused severe defects in growth, cell cycle control, morphogenesis, sexual development, stress responses, and virulence factor production, while the deletion of WDR1 resulted in similar but modest changes, suggesting that Rav1 and Wdr1 play central and accessary roles, respectively. Proteomics analysis confirmed that Wdr1 was one of the Rav1-interacting proteins. Although the hRAVE complex generally has V-ATPase-dependent functions, it also has some V-ATPase-independent roles, suggesting a unique role beyond conventional intracellular pH regulation in C. neoformans. The hRAVE complex played a critical role in the pathogenicity of C. neoformans, and RAV1 deletion attenuated virulence and impaired blood-brain barrier crossing ability. This study provides comprehensive insights into the pathobiological roles of the fungal RAVE complex and suggests a novel therapeutic strategy for controlling cryptococcosis.

Regulation of V-ATPase by Jasmonic Acid: Possible Role of Persulfidation

Vacuolar H+-translocating ATPase (V-ATPase) is a proton pump crucial for plant growth and survival. For this reason, its activity is tightly regulated, and various factors, such as signaling molecules and phytohormones, may be involved in this process. The aim of this study was to explain the role of jasmonic acid (JA) in the signaling pathways responsible for the regulation of V-ATPase in cucumber roots and its relationship with other regulators of this pump, i.e., H2S and H2O2. We analyzed several aspects of the JA action on the enzyme, including transcriptional regulation, modulation of protein levels, and persulfidation of selected V-ATPase subunits as an oxidative posttranslational modification induced by H2S. Our results indicated that JA functions as a repressor of V-ATPase, and its action is related to a decrease in the protein amount of the A and B subunits, the induction of oxidative stress, and the downregulation of the E subunit persulfidation. We suggest that both H2S and H2O2 may be downstream components of JA-dependent negative proton pump regulation. The comparison of signaling pathways induced by two negative regulators of the pump, JA and cadmium, revealed that multiple pathways are involved in the V-ATPase downregulation in cucumber roots.

ATP6V0C gene variants were identified in individuals with epilepsy, with or without developmental delay

The cause of epilepsy with or without developmental disorders was unidentified in a significant proportion of patients. Whole exome sequencing was performed in three unrelated patients with early-onset epilepsy, with or without developmental delay and intellectual disability. We identified de novo heterozygous variants (p.Arg119Trp, p.Val99_Ser102del, c.260_263 + 11delinsGCCCA) in the ATP6V0C gene, which encodes a subunit of vacuolar ATPase. Three-dimensional protein modeling showed that the variant p.Arg119Trp in ATP6V0C affected the hydrogen bonds with the 115th and 123rd residues, and the protein stability. The p.Val99_Ser102del and c.260_263 + 11delinsGCCCA variants in the other two patients resulted in a loss of function with microdeletion or splicing effects. Their seizures and psychomotor developmental outcomes were different, and all patients had a good prognosis. Our study provides evidence that de novo heterozygous ATP6V0C variants are related to epilepsy and associated with or without developmental delay.

Genotype-Phenotype correlation of distal renal tubular acidosis in Tunisia

INTRODUCTION

Distal renal tubular acidosis (dRTA) is a rare genetic disorder due to the incapacity of the α intercalated cells to excrete protons in the collecting duct. This impaired distal acidification of urine leads to a chronic hyperchloremic metabolic acidosis with a normal plasma anion gap, hypokalemia, and hypercalciuria with hypocitraturia causing nephrocalcinosis. Primary dRTA is inherited either as an autosomal dominant (SLC1A4 gene) or autosomal recessive trait (ATP6V0A1/ATP6V1B1 genes).

AIM

To analyze the genotype-phenotype correlation of dTA in Tunisia.

METHODS

In this study we present all available data of patients followed in our center for dRTA over the last 28 years and who had a genetic study. This was a retrospective descriptive study from January 1991 to December 2018, conducted in the Pediatrics Department of the Charles Nicolle Hospital in Tunis.

RESULTS

Twenty-five cases of dRTA were collected and were offered genetic analysis to confirm the diagnosis. The molecular mutation was confirmed in 13 patients of whom 11 had homozygous mutations in ATP6V1B1(G1) and 2 had homozygous mutations in ATP6V0A4(G2). Median age of diagnosis was 8.9 months. Severe growth retardation was documented in nine children with mutations in ATP6V1B1, in eight children with no genetic mutation and in the two patients with a mutation in ATP6V0A4. All children were found to have metabolic acidosis at initial presentation. Hypokalemia was found in 19 children. All patients were polyuric. Twenty-two patients had nephrocalcinosis (88%). The treatment was based on alkali prescription and substitution of potassium chloride. Sensorineural hearing loss (SNHL) was documented in 12 children. At the last consultation, 14 patients had chronic kidney disease (CKD) stage 2 or higher, 8 of whom were in the group with negative genetic analysis.

CONCLUSION

According to the early onset in patients, the recessive mode seems to be the mode of transmission in Tunisia. dRTA was long considered to not affect renal function, but we note a decline in eDFG.

Significance of the plasma membrane H+-ATPase and V-ATPase for growth and pathogenicity in pathogenic fungi

Pathogenic fungi are widespread and cause a variety of diseases in human beings and other organisms. At present, limited classes of antifungal agents are available to treat invasive fungal diseases. With the wide use of the commercial antifungal agents, drug resistance of pathogenic fungi are continuously increasing. Therefore, exploring effective antifungal agents with novel drug targets is urgently needed to cope with the challenges that the antifungal area faces. pH homeostasis is vital for multiple cellular processes, revealing the potential for defining novel drug targets. Fungi have evolved a number of strategies to maintain a stable pH internal environment in response to rapid metabolism and a dramatically changing extracellular environment. Among them, plasma membrane H+-ATPase (PMA) and vacuolar H+-ATPase (V-ATPase) play a central role in the regulation of pH homeostasis system. In this chapter, we will summarize the current knowledge about pH homeostasis and its regulation mechanisms in pathogenic fungi, especially for the recent advances in PMA and V-ATPase, which would help in revealing the regulating mechanism of pH on cell growth and pathogenicity, and further designing effective drugs and identify new targets for combating fungal diseases.

The ATP6V1B2 DDOD/DOORS-Associated p.Arg506* Variant Causes Hyperactivity and Seizures in Mice

The vacuolar H+-ATPase is a multisubunit enzyme which plays an essential role in the acidification and functions of lysosomes, endosomes, and synaptic vesicles. Many genes encoding subunits of V-ATPases, namely ATP6V0C, ATP6V1A, ATP6V0A1, and ATP6V1B2, have been associated with neurodevelopmental disorders and epilepsy. The autosomal dominant ATP6V1B2 p.Arg506* variant can cause both congenital deafness with onychodystrophy, autosomal dominant (DDOD) and deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures syndromes (DOORS). Some but not all individuals with this truncating variant have intellectual disability and/or epilepsy, suggesting incomplete penetrance and/or variable expressivity. To further explore the impact of the p.Arg506* variant in neurodevelopment and epilepsy, we generated Atp6v1b2emR506* mutant mice and performed standardized phenotyping using the International Mouse Phenotyping Consortium (IMPC) pipeline. In addition, we assessed the EEG profile and seizure susceptibility of Atp6v1b2emR506* mice. Behavioral tests revealed that the mice present locomotor hyperactivity and show less anxiety-associated behaviors. Moreover, EEG analyses indicate that Atp6v1b2emR506* mutant mice have interictal epileptic activity and that both heterozygous (like patients) and homozygous mice have reduced seizure thresholds to pentylenetetrazol. Our results confirm that variants in ATP6V1B2 can cause seizures and that the Atp6v1b2emR506* heterozygous mouse model is a valuable tool to further explore the pathophysiology and potential treatments for vacuolar ATPases-associated epilepsy and disorders.

Prevalence of Monogenic Bone Disorders in a Dutch Cohort of Atypical Femur Fracture Patients

Atypical femur fractures (AFFs), considered rare associations of bisphosphonates, have also been reported in patients with monogenic bone disorders without bisphosphonate use. The exact association between AFFs and monogenic bone disorders remains unknown. Our aim was to determine the prevalence of monogenic bone disorders in a Dutch AFF cohort. AFF patients were recruited from two specialist bone centers in the Netherlands. Medical records of the AFF patients were reviewed for clinical features of monogenic bone disorders. Genetic variants identified by whole-exome sequencing in 37 candidate genes involved in monogenic bone disorders were classified based on the American College of Medical Genetics and Genomics (ACMG) classification guidelines. Copy number variations overlapping the candidate genes were also evaluated using DNA array genotyping data. The cohort comprises 60 AFF patients (including a pair of siblings), with 95% having received bisphosphonates. Fifteen AFF patients (25%) had clinical features of monogenic bone disorders. Eight of them (54%), including the pair of siblings, had a (likely) pathogenic variant in either PLS3, COL1A2, LRP5, or ALPL. One patient carried a likely pathogenic variant in TCIRG1 among patients not suspected of monogenic bone disorders (2%). In total, nine patients in this AFF cohort (15%) had a (likely) pathogenic variant. In one patient, we identified a 12.7 Mb deletion in chromosome 6, encompassing TENT5A. The findings indicate a strong relationship between AFFs and monogenic bone disorders, particularly osteogenesis imperfecta and hypophosphatasia, but mainly in individuals with symptoms of these disorders. The high yield of (likely) pathogenic variants in AFF patients with a clinical suspicion of these disorders stresses the importance of careful clinical evaluation of AFF patients. Although the relevance of bisphosphonate use in this relationship is currently unclear, clinicians should consider these findings in medical management of these patients. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Hearing Loss Related to Gene Mutations in Distal Renal Tubular Acidosis

INTRODUCTION

Distal renal tubular acidosis (dRTA) is a disease that may develop either primarily or secondarily, resulting from urinary acidification defects in distal tubules. Hearing loss may accompany primary forms of dRTA. This study aims to determine the characteristics of hearing loss due to different gene mutations in patients with dRTA.

METHODS

Behavioral and electrophysiological audiological evaluations were performed after otolaryngology examination in 21 patients with clinically diagnosed dRTA. Radiological imaging of the inner ear (n = 9) was conducted and results of genetic analyses using next-generation sequencing method (n = 16) were included.

RESULTS

Twenty-one patients with dRTA from 20 unrelated families, aged between 8 months and 33 years (median = 12, interquartile range = 20), participated. All patients with ATP6V1B1 mutations (n = 9) had different degrees of hearing loss. There was one patient with hearing loss in patients with ATP6V0A4 mutations (n = 6). One patient with the WDR72 mutation had normal hearing. Large vestibular aqueduct syndrome (LVAS) was detected in 6 (67%) of 9 patients whose radiological evaluation results were available.

CONCLUSIONS

LVAS is common in patients with dRTA and may influence the type and severity of hearing loss in these patients. The possibility of both congenital and late-onset and progressive hearing loss should be considered in dRTA patients. A regular audiological follow-up is essential for the early detection of a possible late-onset or progressive hearing loss in these patients.

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.

Molecular Characterization of Multifocal Granular Cell Tumors

Granular cell tumors (GrCT) were recently found to be driven by inactivating mutations in vacuolar H + -ATPase (V-ATPase) genes, most frequently ATP6AP1 and ATP6AP2 . Multifocal presentation is present in ~10% of cases; however, the relationship between multifocal tumors in a given patient has not been elucidated. We hypothesized that benign-appearing multifocal GrCT are molecularly distinct whereas paired primary and metastatic malignant GrCT share identical mutations. To test this, we conducted targeted next-generation sequencing of the V-ATPase genes in multifocal GrCT and whole exome and Sanger sequencing in paired primary and metastatic malignant GrCT. Thirteen patients with≥2 GrCT were identified (total of 43 tumors). Forty-two tumors were successfully sequenced. Tumors showed somatic mutations in 3 of the 10 targeted genes in 32 of 42 samples (76%). Twenty tumors showed mutations in ATP6AP1 (48%), 10 tumors had mutations in ATP6AP2 (24%), and 2 tumors showed mutations in ATP6V0A4 (5%). Predicted loss-of-function mutations were found in ATP6AP1 in 17 tumors (40%), in ATP6AP2 in 10 tumors (24%), and in ATP6V0A4 in 1 tumor (2%). In 8 patients, mutually exclusive mutations were detected in at least 2 tumors per patient. Two patients were identified with malignant GrCT with material available from both primary and metastatic sites. Identical frameshift insertions were found in ATP6AP1 in 1 case and the second case showed identical nonsense mutations in ATP6AP1 . In conclusion, multifocal GrCT within an individual patient are molecularly distinct, while paired primary and metastatic GrCT share identical mutations.

Fractionated plasma N-glycan profiling of novel cohort of ATP6AP1-CDG subjects identifies phenotypic association

ATP6AP1-CDG is an X-linked disorder typically characterized by hepatopathy, immunodeficiency, and an abnormal type II transferrin glycosylation pattern. Here, we present 11 new patients and clinical updates with biochemical characterization on one previously reported patient. We also document intrafamilial phenotypic variability and atypical presentations, expanding the symptomatology of ATP6AP1-CDG to include dystonia, hepatocellular carcinoma, and lysosomal abnormalities on hepatic histology. Three of our subjects received successful liver transplantation. We performed N-glycan profiling of total and fractionated plasma proteins for six patients and show associations with varying phenotypes, demonstrating potential diagnostic and prognostic value of fractionated N-glycan profiles. The aberrant N-linked glycosylation in purified transferrin and remaining plasma glycoprotein fractions normalized in one patient post hepatic transplant, while the increases of Man4GlcNAc2 and Man5GlcNAc2 in purified immunoglobulins persisted. Interestingly, in the single patient with isolated immune deficiency phenotype, elevated high-mannose glycans were detected on purified immunoglobulins without glycosylation abnormalities on transferrin or the remaining plasma glycoprotein fractions. Given the diverse and often tissue specific clinical presentations and the need of clinical management post hepatic transplant in ATP6AP1-CDG patients, these results demonstrate that fractionated plasma N-glycan profiling could be a valuable tool in diagnosis and disease monitoring.

Regulation of the V-ATPase subunit ATP6V0D2 and its role in demyelination after peripheral nerve injury

After peripheral nerve injury, demyelinating Schwann cells discharge myelin debris and macrophages execute myelin degradation, leading to demyelination of degenerating axons, which is essential for efficient nerve regeneration. In this study, we show that vacuolar-type proton ATPase subunit d2 (Atp6v0d2) is among the most highly upregulated genes in degenerating mouse sciatic nerves after nerve injury using microarray analysis. ATP6V0D2 is mostly expressed in macrophages of injured nerves. Atp6v0d2 knockout mice display delayed peripheral nerve demyelination and significantly attenuated myelin lipid digestion after nerve injury. However, macrophage recruitment and Schwann cell dedifferentiation are unaffected by loss of Atp6v0d2 expression. Taken together, these data demonstrate that ATP6V0D2 in macrophages is specifically required for demyelination during Wallerian degeneration.

Mutations in V-ATPase in follicular lymphoma activate autophagic flux creating a targetable dependency

The recent discovery of recurrent gene mutations in chaperones or components of the vacuolar-type H+-translocating ATPase (V-ATPase) in follicular lymphoma (FL) was an unexpected finding. The application of whole exome sequencing and targeted gene re-sequencing has resulted in the identification of mutations in ATP6AP1, ATP6V1B2 and VMA21 in a combined 30% of FL, together constituting a major novel mutated pathway in this disease. Interestingly, no other human hematological malignancy carries these mutations at more than sporadic occurrences, implicating unique aspects of FL biology requiring these mutations. The mutations in ATP6V1B2 and VMA21 through separate mechanisms impair lysosomal V-ATPase activity resulting in an elevated lysosomal pH. The elevated lysosomal pH impairs protein and peptide hydrolysis and associates with reduced cytoplasmic amino acid concentrations resulting in compensatory activation of autophagic flux. The elevated autophagic flux constitutes a survival dependency for FL cells and can be targeted with inhibitors to ULK1 and multiple recently identified cyclin-dependent kinase inhibitors. Targeting autophagy alone or in combination with other targeted therapies constitutes a novel therapeutic opportunity for FL patients.

Osteopetrosis: Gene-based nosology and significance Dysosteosclerosis

Dysosteosclerosis (DSS) refers to skeletal dysplasias that radiographically feature focal appendicular osteosclerosis with variable platyspondyly. Genetic heterogeneity is increasingly reported for the DSS phenotype and now involves mutations of SLC29A3, TNFRSF11A, TCIRG1, LRRK1, and CSF1R. Typical radiological findings are widened radiolucent long bones with thin cortices yet dense irregular metaphyses, flattened vertebral bodies, dense ribs, and multiple fractures. However, the radiographic features of DSS evolve, and the metaphyseal and/or appendicular osteosclerosis variably fades with increasing patient age, likely due to some residual osteoclast function. Fractures are the principal presentation of DSS, and may even occur in infancy with SLC29A3-associated DSS. Cranial base sclerosis can lead to cranial nerve palsies such as optic atrophy, and may be the initial presentation, though not observed with SLC29A3-associated DSS. Gene-specific extra-skeletal features can be the main complication in some forms of DSS such as CSF1R- associated DSS. Further genetic heterogeneity is likely, especially for X-linked recessive DSS and cases currently with an unknown genetic defect. Distinguishing DSS can be challenging due to variable clinical and radiological features and an evolving phenotype. However, defining the DSS phenotype is important for predicting complications, prognosis, and instituting appropriate health surveillance and treatment.

Ras-mutant cancers are sensitive to small molecule inhibition of V-type ATPases in mice

Mutations in Ras family proteins are implicated in 33% of human cancers, but direct pharmacological inhibition of Ras mutants remains challenging. As an alternative to direct inhibition, we screened for sensitivities in Ras-mutant cells and discovered 249C as a Ras-mutant selective cytotoxic agent with nanomolar potency against a spectrum of Ras-mutant cancers. 249C binds to vacuolar (V)-ATPase with nanomolar affinity and inhibits its activity, preventing lysosomal acidification and inhibiting autophagy and macropinocytosis pathways that several Ras-driven cancers rely on for survival. Unexpectedly, potency of 249C varies with the identity of the Ras driver mutation, with the highest potency for KRASG13D and G12V both in vitro and in vivo, highlighting a mutant-specific dependence on macropinocytosis and lysosomal pH. Indeed, 249C potently inhibits tumor growth without adverse side effects in mouse xenografts of KRAS-driven lung and colon cancers. A comparison of isogenic SW48 xenografts with different KRAS mutations confirmed that KRASG13D/+ (followed by G12V/+) mutations are especially sensitive to 249C treatment. These data establish proof-of-concept for targeting V-ATPase in cancers driven by specific KRAS mutations such as KRASG13D and G12V.

Osteoclast rich osteopetrosis due to defects in the TCIRG1 gene

Discovery that mutations in TCIRG1 (also known as Atp6i) gene are responsible for most instances of autosomal recessive osteopetrosis (ARO) heralded a new era for comprehension and treatment of this phenotypically heterogeneous rare bone disease. TCIRG1 encodes the a3 subunit, an essential isoform of the vacuolar ATPase proton pump involved in acidification of the osteoclast resorption lacuna and in secretory lysosome trafficking. TCIRG1 defects lead to inefficient bone resorption by nonfunctional osteoclasts seen in abundance on bone marrow biopsy, delineating this ARO as 'osteoclast-rich'. Presentation is usually in early childhood and features of extramedullary haematopoiesis (hepatosplenomegaly, anaemia, thrombocytopenia) due to bone marrow fibrosis, and cranial nerve impingement (blindness in particular). Impaired dietary calcium uptake due to high pH causes the co-occurrence of rickets, described as "osteopetrorickets". Osteoclast dysfunction leads to early death if untreated, and allogeneic haematopoietic stem cell transplantation is currently the treatment of choice. Studies of patients as well as of mouse models carrying spontaneous (the oc/oc mouse) or targeted disruption of Atp6i (TCIRG1) gene have been instrumental providing insight into disease pathogenesis and development of novel cellular therapies that exploit gene correction.

The interdependent transport of yeast vacuole Ca2+ and H+ and the role of phosphatidylinositol 3,5-bisphosphate

Yeast vacuoles are acidified by the v-type H+-ATPase (V-ATPase) that is comprised of the membrane embedded VO complex and the soluble cytoplasmic V1 complex. The assembly of the V1-VO holoenzyme on the vacuole is stabilized in part through interactions between the VO a-subunit ortholog Vph1 and the lipid phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2). PI(3,5)P2 also affects vacuolar Ca2+ release through the channel Yvc1 and uptake through the Ca2+ pump Pmc1. Here, we asked if H+ and Ca2+ transport activities were connected through PI(3,5)P2. We found that overproduction of PI(3,5)P2 by the hyperactive fab1T2250A mutant augmented vacuole acidification, whereas the kinase-inactive fab1EEE mutant attenuated the formation of a H+ gradient. Separately, we tested the effects of excess Ca2+ on vacuole acidification. Adding micromolar Ca2+ blocked vacuole acidification, whereas chelating Ca2+ accelerated acidification. The effect of adding Ca2+ on acidification was eliminated when the Ca2+/H+ antiporter Vcx1 was absent, indicating that the vacuolar H+ gradient can collapse during Ca2+ stress through Vcx1 activity. This, however, was independent of PI(3,5)P2, suggesting that PI(3,5)P2 plays a role in submicromolar Ca2+ flux but not under Ca2+ shock. To see if the link between Ca2+ and H+ transport was bidirectional, we examined Ca2+ transport when vacuole acidification was inhibited. We found that Ca2+ transport was inhibited by halting V-ATPase activity with Bafilomycin or neutralizing vacuolar pH with chloroquine. Together, these data show that Ca2+ transport and V-ATPase efficacy are connected but not necessarily through PI(3,5)P2.

Novel Intronic Mutation in VMA21 Causing Severe Phenotype of X-Linked Myopathy with Excessive Autophagy-Case Report

X-linked Myopathy with Excessive Autophagy (XMEA) is a rare autophagic vacuolar myopathy caused by mutations in the Vacuolar ATPase assembly factor VMA21 gene; onset usually occurs during childhood and rarely occurs during adulthood. We described a 22-year-old patient with XMEA, whose onset was declared at 11 through gait disorder. He had severe four-limb proximal weakness and amyotrophy, and his proximal muscle MRC score was between 2 and 3/5 in four limbs; creatine kinase levels were elevated (1385 IU/L), and electroneuromyography and muscle MRI were suggestive of myopathy. Muscle biopsy showed abnormalities typical of autophagic vacuolar myopathy. We detected a hemizygous, unreported, intronic, single-nucleotide substitution c.164-20T>A (NM_001017980.4) in intron 2 of the VMA21 gene. Fibroblasts derived from this patient displayed a reduced level of VMA21 transcripts (at 40% of normal) and protein, suggesting a pathogenicity related to an alteration of the splicing efficiency associated with an intron retention. This patient with XMEA displayed a severe phenotype (rapid weakness of upper and lower limbs) due to a new intronic variant of VMA21, related to an alteration in the splicing efficiency associated with intron retention, suggesting that phenotype severity is closely related to the residual expression of the VMA21 protein.

Vacuolar H+ -ATPase subunit VAB3 regulates cell growth and ion homeostasis in Arabidopsis

Vacuolar H⁺ -ATPase (V-ATPase) has diverse functions related to plant development and growth. It creates the turgor pressure that drives cell growth by generating the energy needed for the active transport of solutes across the tonoplast. V-ATPase is a large protein complex made up of multiheteromeric subunits, some of which have unknown functions. In this study, a forward genetics-based strategy was employed to identify the vab3 mutant, which displayed resistance to isoxaben, a cellulose synthase inhibitor that could induce excessive transverse cell expansion. Map-based cloning and genetic complementary assays demonstrated that V-ATPase B subunit 3 (VAB3) is associated with the observed insensitivity of the mutant to isoxaben. Analysis of the vab3 mutant revealed defective ionic homeostasis and hypersensitivity to salt stress. Treatment with a V-ATPase inhibitor exacerbated ionic tolerance and cell elongation defects in the vab3 mutant. Notably, exogenous low-dose Ca²⁺ or Na⁺ could partially restore isoxaben resistance of the vab3 mutant, suggesting a relationship between VAB3-regulated cell growth and ion homeostasis. Taken together, the results of this study suggest that the V-ATPase subunit VAB3 is required for cell growth and ion homeostasis in Arabidopsis.

Isoform a4 of the vacuolar ATPase a subunit promotes 4T1-12B breast cancer cell-dependent tumor growth and metastasis in vivo

The vacuolar H+-ATPase (V-ATPase) is an ATP-dependent proton pump that governs the pH of various intracellular compartments and also functions at the plasma membrane in certain cell types, including cancer cells. Membrane targeting of the V-ATPase is controlled by isoforms of subunit a, and we have previously shown that isoforms a3 and a4 are important for the migration and invasion of several breast cancer cell lines in vitro. Using CRISPR-mediated genome editing to selectively disrupt each of the four a subunit isoforms, we also recently showed that a4 is critical to plasma membrane V-ATPase localization, as well as in vitro migration and invasion of 4T1-12B murine breast cancer cells. We now report that a4 is important for the growth of 4T1-12B tumors in vivo. We found that BALB/c mice bearing a4-/- 4T1-12B allografts had significantly smaller tumors than mice in the control group. In addition, we determined that a4-/- allografts showed dramatically reduced metastases to the lung and reduced luminescence intensity of metastases to bone relative to the control group. Taken together, these results suggest that the a4 isoform of the V-ATPase represents a novel potential therapeutic target to limit breast cancer growth and metastasis.

NGF-Induced Upregulation of CGRP in Orofacial Pain Induced by Tooth Movement Is Dependent on Atp6v0a1 and Vesicle Release

The nerve growth factor (NGF) and calcitonin gene-related peptide (CGRP) play a crucial role in the regulation of orofacial pain. It has been demonstrated that CGRP increases orofacial pain induced by NGF. V-type proton ATPase subunit an isoform 1 (Atp6v0a1) is involved in the exocytosis pathway, especially in vesicular transport in neurons. The objective was to examine the role of Atp6v0a1 in NGF-induced upregulation of CGRP in orofacial pain induced by experimental tooth movement. Orofacial pain was elicited by ligating closed-coil springs between incisors and molars in Sprague–Dawley rats. Gene and protein expression levels were determined through real-time polymerase chain reaction, immunostaining, and fluorescence in situ hybridization. Lentivirus vectors carrying Atp6v0a1 shRNA were used to knockdown the expression of Atp6v0a1 in TG and SH-SY5Y neurons. The release of vesicles in SH-SY5Y neurons was observed by using fluorescence dye FM1-43, and the release of CGRP was detected by Enzyme-Linked Immunosorbent Assy. Orofacial pain was evaluated through the rat grimace scale. Our results revealed that intraganglionic administration of NGF and Atp6v0a1 shRNA upregulated and downregulated CGRP in trigeminal ganglia (TG) and trigeminal subnucleus caudalis (Vc), respectively, and the orofacial pain was also exacerbated and alleviated, respectively, following administration of NGF and Atp6v0a1 shRNA. Besides, intraganglionic administration of NGF simultaneously caused the downregulation of Atp6v0a1 in TG. Moreover, the release of vesicles and CGRP in SH-SY5Y neurons was interfered by NGF and Atp6v0a1 shRNA. In conclusion, in the orofacial pain induced by experimental tooth movement, NGF induced the upregulation of CGRP in TG and Vc, and this process is dependent on Atp6v0a1 and vesicle release, suggesting that they are involved in the transmission of nociceptive information in orofacial pain.

Specific KRAS-Mutant Cancers Are Sensitive to Inhibition of V-type ATPases

249C was identified as a selective Ras-mutant cytotoxic agent that binds to and inhibits V-ATPase.

Follicular lymphoma-associated mutations in the V-ATPase chaperone VMA21 activate autophagy creating a targetable dependency

The discovery of recurrent mutations in subunits and regulators of the vacuolar-type H⁺-translocating ATPase (V-ATPase) in follicular lymphoma (FL) highlights a role for macroautophagy/autophagy, amino-acid, and nutrient-sensing pathways in the pathogenesis of this disease. Here, we report on novel mutations in the ER-resident chaperone VMA21, which is involved in V-ATPase assembly in 12% of FL. Mutations in a novel VMA21 hotspot (p.93X) result in the removal of a C-terminal non-canonical ER retrieval signal thus causing VMA21 mislocalization to lysosomes. The resulting impairment in V-ATPase activity prevents full lysosomal acidification and function, including impaired pH-dependent protein degradation as shown via lysosomal metabolomics and ultimately causes a degree of amino acid depletion in the cytoplasm. These deficiencies result in compensatory autophagy activation, as measured using multiple complementary assays in human and yeast cells. Of translational significance, the compensatory activation of autophagy creates a dependency for survival for VMA21-mutated primary human FL as shown using inhibitors to ULK1, the proximal autophagy-regulating kinase. Using high-throughput microscopy-based screening assays for autophagy-inhibiting compounds, we identify multiple clinical grade cyclin-dependent kinase inhibitors as promising drugs and thus provide new rationale for innovative clinical trials in FL harboring aberrant V-ATPase.Abbreviations: ALs: autolysosomes; APs: autophagosomes; ER: endoplasmic reticulum; FL: follicular lymphoma; GFP: green fluorescent protein; IP: immunoprecipitation; LE/LY: late endosomes/lysosomes; Lyso-IP: lysosomal immunoprecipitation; OST: oligosaccharide transferase; prApe1: precursor aminopeptidase I; SEP: super ecliptic pHluorin; V-ATPase: vacuolar-type H⁺-translocating ATPase.

[Genotype-phenotype analysis and prognosis in children with primary distal renal tubular acidosis]

Objective: The purpose of this study was to investigate the relationship between genotypes and clinical phenotypes of primary distal renal tubular acidosis (dRTA) in children. Methods: Clinical information, genetic testing information and follow-up data (until March 2021) of children with dRTA from Children's Hospital of Chongqing Medical University (from January 2010 to December 2020) were analyzed retrospectively. According to different pathogenic genes, patients were divided into SLC4A1 gene and ATP6V0A4+ATP6V1B1 gene groups. Age at onset, clinical manifestations and laboratory findings were compared. Self-comparisons of height standard deviation score (HtSDS), weight standard deviation score (WtSDS), blood pH and serum potassium before and after treatment were tested. T-test, Fisher's exact test and rank sum test were used to analyze among groups. Results: Among 27 children with dRTA (16 boys and 11 girls), the age of onset was 33.4 (10.0, 36.0) months.There were 22 patients (81%) with SLC4A1 gene variation, 3 patients (11%) with ATP6V1B1 gene variation and 2 patients (8%) with ATP6V0A4 gene variation. Totally 22 patients (81%) with renal calcium deposition, 19 patients (70%) hypokalemia, 18 patients (67%) short stature, 16 patients (59%) malnutrition, 16 patients (59%) rickets, and 15 patients (56%) polydipsia and polyuria. Noteworthily, the genotyping results indicated that the age at onset in SLC4A1 gene group was older than that in ATP6V0A4+ATP6V1B1 gene group, with a statistically significant difference (27.3 (12.0, 36.0) vs. 8.2 (2.5, 15.0) months, H=6.33, P=0.012). However, there were no significant differences in clinical manifestations or laboratory test results (all P>0.05). Furthermore, the course of disease was 3.9 (1.3, 6.0) years and the follow-up period was 3.1 (1.0, 4.5) years in 27 patients. In addition, there were no significant differences in recovery rate of clinical manifestations and last laboratory findings between SLC4A1 gene group and ATP6V0A4+ATP6V1B1 gene group (all P>0.05). HtSDS and WtSDS of those patients significantly increased after treatment (-3.2±1.9 vs. -2.1±1.1, -2.5±1.5 vs. 0±1.9, t=-2.94, -5.44, both P<0.01). Serum K⁺ and blood pH were restored eventually ((3.2±0.5) vs. (4.0±0.5) mmol/L, 7.27±0.07 vs. 7.37±0.07, t=-4.92, -5.25, both P<0.01). Totally 14 patients had normalized serum potassium, 12 patients had normalized blood pH, but only 4 patients had normalized serum bicarbonate concentration and normal base excess. Conclusions: The age of onset of patients who had SLC4A1 gene mutation was older than that of patients with ATP6V0A4 gene and ATP6V1B1 gene mutations. However, there was no obvious correlation between the condition and prognosis of the dRTA patients and pathogenic genes. Early diagnosis, early treatment, regular follow-up and timely adjustment of the dosage of medication can significantly improve the prognosis of dRTA in children. Serum bicarbonate concentration and actual base excess might not be the necessory indicators to assess clinical recovery.

H+-ATPases in Plant Growth and Stress Responses

H⁺-ATPases, including the phosphorylated intermediate-type (P-type) and vacuolar-type (V-type) H⁺-ATPases, are important ATP-driven proton pumps that generate membrane potential and provide proton motive force for secondary active transport. P- and V-type H⁺-ATPases have distinct structures and subcellular localizations and play various roles in growth and stress responses. A P-type H⁺-ATPase is mainly regulated at the posttranslational level by phosphorylation and dephosphorylation of residues in its autoinhibitory C terminus. The expression and activity of both P- and V-type H⁺-ATPases are highly regulated by hormones and environmental cues. In this review, we summarize the recent advances in understanding of the evolution, regulation, and physiological roles of P- and V-type H⁺-ATPases, which coordinate and are involved in plant growth and stress adaptation. Understanding the different roles and the regulatory mechanisms of P- and V-type H⁺-ATPases provides a new perspective for improving plant growth and stress tolerance by modulating the activity of H⁺-ATPases, which will mitigate the increasing environmental stress conditions associated with ongoing global climate change.

Transcriptomic and functional studies reveal miR-431-5p as a tumour suppressor in pancreatic ductal adenocarcinoma cells

The lactate receptor HCAR1 (hydroxycarboxylic acid receptor 1) is highly expressed in pancreatic ductal adenocarcinoma (PDAC), where it regulates lactate transport between the cancer cells. Little is known about the underlying cause of high HCAR1 expression in PDAC, and in the present study, we investigated whether HCAR1 could be a target of miRNA regulation. By searching for predicted miRNA candidates in silico, we identified miR-431-5p as a possible regulator of HCAR1. We found miR-431-5p to repress HCAR1 expression through direct binding to the 3' UTR. The endogenous expression of miR-431-5p and HCAR1 was found to be negatively related in the PDAC cell lines BxPC-3, Capan-2, and PANC-1. Overexpression of miR-431-5p inhibited cell proliferation in all the cell lines, and a shift in cell cycle progression and induction of apoptosis were found in the BxPC-3 cells. Transcriptomic analysis of mRNA from BxPC-3 cells revealed numerous differentially expressed genes (DEGs), including HCAR1, in response to miR-431-5p overexpression. A significant proportion of these DEGs was enriched in cancer-related processes and signalling pathways. Among the most significantly repressed DEGs was ATP6V0E1, encoding the integral subunit e of vacuolar ATPase (V-ATPase), an enzyme that is important for cancer cell survival. Small interfering RNA (siRNA)-mediated knockdown of HCAR1 and ATP6V0E1 showed that only knockdown of ATP6V0E1 mimicked the effect of miR-431-5p overexpression on cell viability. Our findings indicate that miR-431-5p acts as a tumour suppressor in PDAC cells, with BxPC-3 cells being most responsive.

The congenital dyserythropoieitic anemias: genetics and pathophysiology

PURPOSE OF REVIEW

The congenital dyserythropoietic anemias (CDA) are hereditary disorders characterized by ineffective erythropoiesis. This review evaluates newly developed CDA disease models, the latest advances in understanding the pathogenesis of the CDAs, and recently identified CDA genes.

RECENT FINDINGS

Mice exhibiting features of CDAI were recently generated, demonstrating that Codanin-1 (encoded by Cdan1) is essential for primitive erythropoiesis. Additionally, Codanin-1 was found to physically interact with CDIN1, suggesting that mutations in CDAN1 and CDIN1 result in CDAI via a common mechanism. Recent advances in CDAII (which results from SEC23B mutations) have also been made. SEC23B was found to functionally overlap with its paralogous protein, SEC23A, likely explaining the absence of CDAII in SEC23B-deficient mice. In contrast, mice with erythroid-specific deletion of 3 or 4 of the Sec23 alleles exhibited features of CDAII. Increased SEC23A expression rescued the CDAII erythroid defect, suggesting a novel therapeutic strategy for the disease. Additional recent advances included the identification of new CDA genes, RACGAP1 and VPS4A, in CDAIII and a syndromic CDA type, respectively.

SUMMARY

Establishing cellular and animal models of CDA is expected to result in improved understanding of the pathogenesis of these disorders, which may ultimately lead to the development of new therapies.

Vacuolar ATPase subunit F is critical for larval survival in Henosepilachna vigintioctopunctata

Vacuolar ATPase (vATPase) is an important proton pump in insect tissues including gut and Malpighian tubule. Subunit F, one of the 16 subunits of the vATPase holoenzyme, is not well characterized. Here, we found that two HvvATPaseF isoforms were highly expressed in the hindgut and Malpighian tubules (MT) in the 28-spotted lady-beetle Henosepilachna vigintioctopunctata, an agricultural pest that feeds on Solanaceae and Cucurbitaceae. Knockdown of both HvvATPaseF variants by RNA interference (RNAi) delayed larval growth and negatively affected ecdysis and adult emergence. In the midgut, RNAi treatment resulted in the disappearance of peritrophic membrane, the reduction in the size and the impaired integrity of the gut, which was associated with sparse principle cells and an increase in TUNEL- and EdU-positive cells. Whereas the MT were opaque and the tubule lumens were full of urine in dsegfp-fed larvae, the tubules were clear and the tubule lumens were empty in the dsvATPaseF-fed larvae. HvvATPaseF knockdown was also associated with a decrease in the abundance of the fat body and the levels of glucose, trehalose, triglyceride, total soluble amino acids and proteins, and an increase in glycogen. Consistent with the known effects of sugars on chitin formation, both the expression level of a chitin biosynthesis gene and the thickness of the head capsule cuticle were reduced in the HvvATPaseF-depleted beetles. Our results demonstrated that subunit F plays an essential role in H. vigintioctopunctata development.

V-ATPase subunit a is required for survival and midgut development of Locusta migratoria

The vacuolar-type H⁺ -ATPase (V-ATPase) is an ATP-dependent proton pump, which regulates various cellular processes. To date, most functional studies on V-ATPases of insects have focused on subunits of the V1 complex, and there is little information on the VO genes. In this study, two cDNA sequences of LmV-ATPase a were identified in Locusta migratoria. RT-qPCR analysis revealed that LmV-ATPase a1 and LmV-ATPase a2 are differentially expressed in various tissues and developmental stages. Injection of dsRNA for the common region of LmV-ATPase a1 and LmV-ATPase a2 into third-instar nymphs resulted in a significant suppression of LmV-ATPase a. The injected nymphs ceased feeding, lost body weight and finally died at a mortality of 98.6%. Furthermore, aberrations of midgut epithelial cells, the accumulation of electron-lucent vesicles in the cytoplasm, and a partially damaged brush border were observed in dsLmV-ATPase a-injected nymphs using transmission electron microscopy. Especially, the mRNA level of wingles, and notch genes were dramatically down-regulated in the dsLmV-ATPase a-injected nymphs. Taken together, our results suggest that LmV-ATPase a is required for survival and midgut development of L. migratoria. Hence, this gene could be a good target for RNAi-based control against locusts.

Clinical presentation and analysis of genotype-phenotype correlations in patients with malignant infantile osteopetrosis

Malignant infantile osteopetrosis (MIOP) is the autosomal recessive, severe form of osteopetrosis. This rare genetic syndrome usually presents soon after birth and is often fatal if left untreated. Early diagnosis is key for proper management but clinical presentation is diverse, and oftentimes diagnosis may be challenging. In this study, we retrospectively collected data of genetic mutations and phenotypic characteristics at the initial presentation of 81 MIOP patients and analyzed genotype-phenotype correlations. The most common genetic mutation was in the TCIRG1 gene (n = 46, 56.8%), followed by SNX10 (n = 20, 25%). Other genetic mutations included RANK (n = 7, 8.7%), CLCN7 (n = 5, 6.2%) and CA2 (n = 3, 3.7%). More than half of the patients presented with growth retardation (n = 46, 56.8%). Twenty-one of the patients were blind (26%) and thirty-seven patients had other neurological deficits (45.7%) at the time of initial presentation. Most patients presented with hematological signs of bone marrow failure including anemia (n = 69, 85.2%) and thrombocytopenia (n = 33, 40.7%). Thrombocytopenia at initial presentation was significantly more prevalent in patients with mutations in the TCIRG1 gene (p = 0.036). Other phenotypic presenting features were not found to be significantly correlated to specific gene mutations. In conclusion, the initial presentation of MIOP is variable, but some features are common such as growth retardation, visual impairment, and cytopenias. High awareness of MIOP presenting signs is essential for prompt diagnosis of this challenging disease.