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Transcriptomic and RNAi analyses reveal chloride channel 3-associated osmoregulation in Litopenaeus vannamei under low-salinity stress.

Chloride channels and transporters are important for cellular volume regulation and salinity adaptation in euryhaline crustaceans, yet the intestinal transcriptional relationship between plasma-membrane and intracellular chloride pathways remains unclear in Litopenaeus vannamei. In this study, RNA interference of anoctamin 1 (ANO1) was combined with intestinal transcriptome sequencing under the production-relevant low-salinity condition of salinity 3. ANO1 silencing produced a focused transcriptional response, with 16 differentially expressed genes (DEGs) identified (11 upregulated and 5 downregulated). Functional enrichment indicated that these genes were associated with transporter activity, cytoskeletal organization, extracellular matrix-receptor interaction, membrane lipid metabolism, and vesicular processes. Notably, a transcript encoding chloride channel protein 3 (CLC-3) was significantly upregulated following ANO1 knockdown, suggesting a potential transcriptional relationship between ANO1 and CLC-3 in chloride homeostasis. Based on this finding, CLC-3 was selected for full-length cDNA cloning, sequence characterization, salinity-gradient expression analysis, and RNAi-based functional assessment. The cloned CLC-3 cDNA was 2883 bp in length and encoded an 850 amino acid protein containing a conserved voltage-gated chloride channel (Voltage-CLC) domain and two cystathionine β-synthase domains. Phylogenetic analysis placed LvCLC-3 within the intracellular CLC-c clade, and tissue distribution analysis showed the highest CLC-3 expression in the intestine. Intestinal CLC-3 expression responded nonlinearly to salinity variation, peaking at salinity 20. Under salinity 3, CLC-3 knockdown reduced ANO1, Na+/K+-ATPase alpha subunit, and Na+-K+-2Cl- cotransporter transcript levels, whereas glutamate-gated chloride channel expression increased. Mild hepatopancreatic structural alterations were also observed after CLC-3 knockdown. These findings suggest that CLC-3 is a salinity-responsive intracellular chloride-transporter candidate associated with intestinal ion-transport-related transcriptional responses after ANO1 suppression in L. vannamei, although the underlying physiological mechanism requires further validation.

Animals

Causal effect of chloride intracellular channel protein 5 on chronic periodontitis: A Mendelian randomization study.

This study aimed to evaluate the potential causal effect of chloride intracellular channel protein 5 (CLIC5) on the risk of chronic periodontitis (CP) using a Mendelian randomization (MR) approach. MR analysis was conducted utilizing publicly available summary statistics from genome-wide association studies summary statistics for CLIC5 and CP. Multiple MR methods, including inverse variance weighted, MR Egger, weighted median and weighted mode, were employed to estimate the causal effects. Sensitivity analyses, comprising leave-one-out and heterogeneity assessments were performed to evaluate the robustness of our findings. This MR analysis consistently revealed a negative association between CLIC5 and CP, with statistical significance achieved using the inverse variance weighted and weighted median methods. The concordant effect estimates obtained from all methodological approaches collectively indicated a potential protective effect of CLIC5 against CP. The sensitivity analyses further confirmed the robustness of these findings. This study provides genetic evidence suggesting a potential causal association between increased CLIC5 levels and decreased risk of CP. These findings augment the existing literature implicating chloride channel proteins in modulating the inflammatory processes pertinent to periodontal health. Further investigation is warranted to decipher the underlying biological mechanisms and to explore the potential of CLIC5 as a therapeutic target for CP.

Chloride Channels

Elimination of myotonia improves myopathy in a muscleblind knockout model of myotonic dystrophy.

A cardinal sign of myotonic dystrophy type 1 (DM1) is slow of muscle relaxation after voluntary contraction known as myotonia. Myotonia results from mis-regulated splicing of chloride channel 1 (ClC-1), leading to loss of channel function and runs of involuntary action potentials in muscle fibers. Heralding the onset of weakness, myotonia is often the first symptom of DM1, and raising the possibility that muscle hyperexcitability promotes the subsequent development of myopathy. We used genome editing to test this possibility by deleting the alternatively spliced and frameshift inducing ClC-1 exon 7a (E7a) in the Mbnl1 knockout model of DM1. Although several ClC-1 exons exhibit mis-regulated splicing in DM1, deletion of this single cryptic exon was sufficient to restore ClC-1 function and eliminate myotonia systemically and permanently. As determined by long-read sequencing, deletion of E7a reduced the frequency of other splicing defects in ClC-1 transcripts, likely as a passive consequence of restoring reading frame and nonsense surveillance. Furthermore, we observed significantly improved muscle force generation, fiber-type distribution, and histology, and partial restoration of the muscle transcriptome, including differential gene expression and alternative splicing, in non-myotonic Mbnl1 knockout mice. These results suggest that E7a inclusion is a lynchpin splice event that contributes to skeletal myopathy, highlighting myotonia as a therapeutic target and an outcome of interest in DM1.

Journal Article

Treatment updates in myotonic disorders.

Myotonia is delayed muscle relaxation after forceful contraction. It is due to hyperexcitability of the skeletal muscle membrane. It can arise from primary skeletal muscle ion channel dysfunction, involving chloride or sodium channels, but is also a prominent clinical feature in myotonic dystrophies where altered RNA splicing leads to secondary ion channel dysregulation amongst other systemic manifestations. Clinically, myotonia can range from delayed eye opening to a disabling symptom causing impaired mobility, functional difficulty and sometimes pain. It can also be a "hidden disability" with many patients feeling socially embarrassed by "looking healthy", yet being unable to do everyday physical tasks or to do them as effortlessly as their peers. It is a symptom that almost always indicates a genetic diagnosis, although it can occur in acquired conditions, including metabolic and drug-induced causes. To experience myotonia without knowing what it is can be baffling. To receive a genetic diagnosis associated with it can be life changing. Although there is no cure, there are many effective and available symptomatic treatments for myotonia and currently we are in an exciting era of clinical trials for new molecular disease-modifying therapies for myotonic dystrophy type 1. In this review, we consider recent developments in the treatment of myotonic disorders and how they may change clinical practice.

Humans

Longitudinal effects of elexacaftor/tezacaftor/ivacaftor on the oropharyngeal metagenome in adolescents with cystic fibrosis.

BACKGROUND: Triple modulator therapy elexacaftor/tezacaftor/ivacaftor (ETI) improves lung function and impacts upon the respiratory microbiome in people with Cystic fibrosis (pwCF) with advanced lung disease. However, adolescents with cystic fibrosis (CF) are less colonized with bacterial pathogens than adult pwCF but their microbiota already differs from healthy individuals. The aim of this study was to longitudinally analyze the impact of ETI on the respiratory metagenome in adolescents with predominantly mild CF lung disease. METHODS: In this prospective observational study, we included pwCF aged 12-20 years with at least one F508del mutation, who collected oropharyngeal swabs before and after initiation of ETI therapy twice per week to biweekly over three months. We performed whole metagenome shotgun sequencing, followed by host DNA filtering and taxonomic profiling. We used linear and additive mixed effects models adjusted for known confounders and corrected for multiple testing to study longitudinal development of the microbiome. We analyzed bacterial diversity, abundance, and strain-level phylogeny. RESULTS: We analyzed the metagenomic data of 297 swabs of 20 pwCF. Microbiome composition changed after initiation of ETI therapy. We observed a slight diversification of the microbiome over time (Inv Simpson, Coef 0.085, 95 %CI 0.003, 0.17, p = 0.04). Strain-level analysis and clustering showed that strain retention of the most frequent bacterial species is predominant even during ETI therapy. CONCLUSIONS: During three months of ETI therapy, commensal bacteria increased, which may help to prevent overgrowth of bacterial pathogens.

Humans

Abnormal ClC-3/TMEM9-mediated endosomal ion transport in CLCN3-associated neurodevelopmental disease.

Endolysosomal abnormalities are particularly detrimental to the nervous system and have been implicated in neuropsychiatric disorders. Key regulators of the lysosomal and endosomal luminal ion homeostasis are CLC chloride/proton exchangers. We report 15 individuals carrying variants in CLCN3, encoding a ubiquitous endosomal 2Cl-/H+ exchanger, and provide updated clinical information for 5 previously reported individuals. Subjects displayed a broad spectrum of neuropsychiatric symptoms, including developmental delay, intellectual disability, and epilepsy. To reveal the pathogenic mechanism, we investigated ClC-3 variants-mediated ion transport and its regulation by the recently discovered inhibitory beta subunit TMEM9. 12/20 missense variants exhibited altered properties and fell into two classes: those affecting the region binding inhibitory TMEM9 carboxy-termini, and those that broaden the voltage range over which ClC-3 conducts ions. Surprisingly, the latter variants also attenuated TMEM9-mediated inhibition. Both classes produced a toxic gain-of-function, as evident from endolysosomal vacuolization by mutant ClC-3/TMEM9 overexpression. Our results expand the genetic and clinical spectrum of CLCN3-related disease, provide a solid basis for genetic counseling, and uncover an unexpected link between gating-associated conformational changes and inhibition by TMEM9.

Chloride Channels

Fractures are highly correlated with bone density and inversely correlated with bone turnover markers in autosomal dominant osteopetrosis.

Autosomal dominant osteopetrosis (ADO) is a rare osteosclerotic disorder usually caused by missense variants in the CLCN7 gene, which results in impaired osteoclastic bone resorption. Penetrance is incomplete, and disease severity varies widely, even among relatives within the same family. Although ADO can cause visual loss, osteonecrosis, osteomyelitis, and bone marrow failure, the most common complication of ADO is fracture. We are conducting a natural history study to characterize disease progression and determinants of disease severity. We hypothesized that baseline BMD and bone turnover markers would correlate with self-reported fracture history. We report cross-sectional analysis of baseline data from the natural history study in 54 individuals (42 adults, 12 children). In adults, Z-scores for both volumetric (r&#xa0;=&#x2009;0.87, p&#xa0;<&#x2009;.001) and areal BMD (aBMD) of the LS, and Z-scores for FN, and TH aBMD (r&#xa0;=&#x2009;0.77 to 0.78; p&#xa0;<&#x2009;.001) were correlated with lifetime fracture number. Tartrate resistant acid phosphatase, a marker of osteoclast number, correlated positively with fracture (r&#xa0;=&#x2009;0.52, p&#xa0;=&#x2009;.004) consistent with an adaptive response of higher numbers of osteoclasts among more severely affected individuals. However, fracture number correlated inversely with the bone resorption markers serum C-telopeptide (r&#xa0;=&#x2009;-0.60, p&#xa0;<&#x2009;.001) and urine N-telopeptide/creatinine ratio (r&#xa0;=&#x2009;-0.35, p&#xa0;=&#x2009;.047), suggesting that ADO subjects who have the most reduced osteoclast activity have a greater tendency to fracture. Correlation coefficients between fractures, BMD, and bone turnover markers were similar when limited to the 37 adults with disease-causing CLCN7 variants. There were no statistically significant differences between subjects with the most common CLCN7 variant (G215R), the most common variant in our cohort, compared to other CLCN7 variants with respect to fracture, bone density measures, or biochemical markers of bone turnover. These data demonstrate that bone density and biochemical bone turnover markers are indicators of ADO severity as defined by fracture number.

Humans

Function-informed transcriptome analysis of Drosophila renal tubule.

BACKGROUND: Comprehensive, tissue-specific, microarray analysis is a potent tool for the identification of tightly defined expression patterns that might be missed in whole-organism scans. We applied such an analysis to Drosophila melanogaster Malpighian (renal) tubule, a defined differentiated tissue. RESULTS: The transcriptome of the D. melanogaster Malpighian tubule is highly reproducible and significantly different from that obtained from whole-organism arrays. More than 200 genes are more than 10-fold enriched and over 1,000 are significantly enriched. Of the top 200 genes, only 18 have previously been named, and only 45% have even estimates of function. In addition, 30 transcription factors, not previously implicated in tubule development, are shown to be enriched in adult tubule, and their expression patterns respect precisely the domains and cell types previously identified by enhancer trapping. Of Drosophila genes with close human disease homologs, 50 are enriched threefold or more, and eight enriched 10-fold or more, in tubule. Intriguingly, several of these diseases have human renal phenotypes, implying close conservation of renal function across 400 million years of divergent evolution. CONCLUSIONS: From those genes that are identifiable, a radically new view of the function of the tubule, emphasizing solute transport rather than fluid secretion, can be obtained. The results illustrate the phenotype gap: historically, the effort expended on a model organism has tended to concentrate on a relatively small set of processes, rather than on the spread of genes in the genome.

Animals

A novel frameshift variant leads to familial osteopetrosis with variable phenotypes in a Chinese Han consanguineous family.

Osteopetrosis, a group of highly heterogeneous genetic bone disorders, is characterized by deafness, increased bone density, hepatosplenomegaly, pancytopenia and intellectual disability. Osteopetrosis can be divided into three subtypes: autosomal recessive osteopetrosis (ARO), intermediate autosomal recessive osteopetrosis (IARO), and autosomal dominant osteopetrosis (ADO). CLCN7 has been reported to be the most common gene responsible for the ADO-II subtype. In this study, a novel variant, c.175dupA (p.Met59Asnfs*8), of CLCN7 was identified in a Chinese Han consanguineous family with suspected ADO-II. The proband was homozygous for the p.Met59Asnfs*8 variant and exhibited multiple severe phenotypes, including deafness, short stature, brittle bones, optic atrophy, hepatosplenomegaly, intellectual disability, cleft palate and recurrent infection. However, except for the mother of the proband, who presented a series of clinical phenotypes caused by bone marrow failure, all the other family members who were heterozygous had no obvious abnormal phenotypes. Our study suggested that the novel variant p.Met59Asnfs*8 in CLCN7 was very likely pathogenic factor in our suspected ADO-II family. The phenotypes of heterozygous carriers may be affected by incomplete penetrance. Loss of function of CLCN7 caused by nonsense-mediated mRNA decay (NMD) due to the frameshift variant was likely the underlying pathogenic mechanism. This study broadened the mutation spectrum of CLCN7, provided a foundation for timely and effective clinical intervention for related diseases, and demonstrates the importance of genetic counselling.

Adult

Protein sorting and proteostasis mechanisms in CFTR-related exocrine pancreas dysfunction: A systematic narrative review.

The pancreas consists of exocrine and endocrine compartments. In the exocrine pancreas, cystic fibrosis transmembrane conductance regulator (CFTR) functions mainly in ductal epithelial cells as a chloride and bicarbonate channel. Its activity depends on proper protein folding, trafficking, and localization to the apical membrane. This systematic narrative review aims to synthesize the available evidence on the role of protein sorting machinery in CFTR channelopathies and its contribution to exocrine pancreatic dysfunction. A thorough search was conducted using PRISMA criteria on PubMed, Wiley Online Library, and Scopus for studies published in English between January 2000 and November 2025. Twenty studies that met the inclusion criteria were included in this review. Pathogenic CFTR variants impair protein folding, endoplasmic reticulum (ER) exit, and endosomal recycling, resulting in reduced apical membrane expression and stability. These defects disrupt the localization of associated transporters and secretory proteins, impair ductal bicarbonate secretion, alter zymogen handling, and promote acinar injury, although these claims are supported mainly by indirect experimental models and therefore require clinical confirmation. CFTR channelopathies in the exocrine pancreas encompass both ion transport defects and broader disruptions of protein sorting machinery. CFTR may contribute to the assembly, stabilization, or localization of selected apical transport complexes, and its loss can secondarily alter epithelial organization. Therapeutic approaches targeting both channel correction and intracellular trafficking may improve pancreatic function and mitigate disease progression.

Humans

Thick Ascending Limb Specific Inactivation of Myh9 and Myh10 Myosin Motors Results in Progressive Kidney Disease and Drives Sex-specific Cellular Adaptation in the Distal Nephron and Collecting Duct.

Our previous work established a role for myosin motor proteins MYH9 and MYH10 in trafficking of thick ascending limb (TAL) cargoes uromodulin and Na+-K+-2Cl- cotransporter NKCC2. We have generated a TAL-specific Myh9&10 conditional knockout (Myh9&10 TAL-cKO) mouse model to determine the cell autonomous roles for MYH9&10 in TAL cargo trafficking and to understand the consequence of TAL dysfunction in adult kidney. Myh9&10 TAL-cKO mice develop progressive kidney disease with pathological tubular injury confirmed by histological changes, tubular injury markers, upregulated endoplasmic reticulum (ER) stress/unfolded protein response, and higher blood urea nitrogen and serum creatinine. However, male mice survive twice as long as female mice. We have determined this sexual dimorphism in morbidity is due to adaptation of the distal nephron and collecting duct in response to TAL dysfunction and lower NKCC2 expression. We demonstrate that this triggers a compensatory mechanism involving sex-specific cellular adaptation within the distal nephron and collecting duct to boost sodium reabsorption. While both sexes overcompensate by activating epithelial sodium channel (ENaC) expression in medullary collecting ducts resulting in hypernatremia, this is initially subdued in male Myh9&10 TAL-cKO mice through higher sodium chloride cotransporter (NCC) expression within the distal nephron. Our results indicate that compromised TAL function ultimately results in maladaptation of medullary collecting duct cells which acquire cortical-like properties including ENaC expression. This work further confirms a cell autonomous role for MYH9&10 in maintenance of NKCC2 expression in the TAL and uncover distal nephron and collecting duct adaptive mechanisms which respond to TAL dysfunction.

Animals