Application of real-time PCR-based multicolor melting curve with automatic analysis system in pregestational and prenatal thalassemia diagnoses.

BACKGROUND: To evaluate the value of the real-time PCR-based multicolor melting curve analysis (MMCA) with an automatic analysis system used in a mass thalassemia screening and prenatal diagnosis program. METHODS: A total of 18,912 peripheral blood samples from 9456 couples and 1150 prenatal samples were detected by MMCA assay. All prenatal samples were also tested by a conventional method. Samples with unknown melting peaks, unusual peak height ratios between a wild allele and a mutant allele, or a discordant phenotype-genotype match were further studied by using multiplex ligation-dependent probe amplification (MLPA) or Sanger sequencing. All MMCA results were automatically analyzed and manually checked. The consistency between MMCA assay and conventional methods among prenatal samples was investigated. RESULTS: Except for initiation codon (T > G) (HBB:c.2T > G), all genotypes of thalassemia inside the scope of conventional methods were detected by MMCA assay. Additionally, 27 carriers with 10 rare HBB variants, 13 with α fusion gene, 1 with a rare deletion in α globin gene, and 1 with rare HBA variant were detected by using MMCA assay. CONCLUSION: MMCA can be an alternative approach used in routine thalassemia carrier screening and prenatal diagnosis for its high throughput, sufficient stability, low cost, and easy operation.

TMEM63 mechanosensitive ion channels: Activation mechanisms, biological functions and human genetic disorders.

The transmembrane 63 (TMEM63) family of proteins are originally identified as homologs of the osmosensitive calcium-permeable (OSCA) channels in plants. Mechanosensitivity of OSCA and TMEM63 proteins are recently demonstrated in addition to their proposed activation mechanism by hyper/hypo-osmolarity. TMEM63 proteins exist in all animals, with a single member in Drosophila (TMEM63) and three members in mammals (TMEM63 A/B/C). In humans, monoallelic variants of TMEM63A have been reported to cause transient hypomyelination during infancy, or severe hypomyelination and global developmental delay. Heterozygous variants of TMEM63B are found in patients with intellectual disability and abnormal motor function and brain morphology. Biallelic variants of TMEM63C are associated with hereditary spastic paraplegias accompanied by mild or no intellectual disability. Physiological functions of TMEM63 proteins clearly recognized so far include detecting food grittiness and environmental humidity in Drosophila, and supporting hearing in mice by regulating survival of cochlear hair cells. In this review, we summarize current knowledge about the activation mechanisms and biological functions of TMEM63 channels, and provide a concise reference for researchers interested in investigating more physiological and pathogenic roles of this family of proteins with ubiquitous expression in the body.

Molecular Determinants for the High-Affinity Blockade of Human Ether-à-go-go-Related Gene K + Channel by Tolterodine.

ABSTRACT: Tolterodine is a first-line antimuscarinic drug used to treat overactive bladder. Adverse cardiac effects including tachycardia and palpitations have been observed, presumably because of its inhibition of the human ether-à-go-go-related gene (hERG) K + channel. However, the molecular mechanism of hERG channel inhibition by tolterodine is largely unclear. In this study, we performed molecular docking to identify potential binding sites of tolterodine in hERG channel, and two-microelectrode voltage-clamp to record the currents of hERG and its mutants expressed in Xenopus oocytes. The results of computational modeling demonstrated that phenylalanine at position 656 (F656) and tyrosine at position 652 (Y652) on the S6 helix of hERG channel are the most favorable binding residues of tolterodine, which was validated by electrophysiological recordings on Y652A and F656A hERG mutants. The Y652A and F656A mutations decreased inhibitory potency of tolterodine 345-fold and 126-fold, respectively. The Y652A mutation significantly altered the voltage dependence of channel inhibition by tolterodine. For both the wild-type and the mutant channels, tolterodine reduced the currents in a time-dependent manner, and the blockade occurred with the channel activated. Tolterodine did not interfere with hERG channel deactivation, whereas channel inactivation greatly impaired its blocking effect. The inhibition of hERG channel by tolterodine is independent of its action on muscarinic acetylcholine receptors. In conclusion, tolterodine is an open-state blocker of hERG K + channel with nanomolar potency. Y652 and F656, 2 aromatic residues on the inner S6 helix, are responsible for the high-affinity binding of tolterodine to hERG channel.

ß-Thalassemia Intermedia Caused by the ß-Globin Gene 3' Untranslated Region: Another Case Report.

The 3' untranslated region (3'UTR) is associated with mRNA stability because of its involvement in 3' end processing, polyadenylation, and mRNA capping. Mutations located in this area can cause a phenotype compatible with ß+-thalassemia (ß+-thal). We report a Chinese subject with ß-thal intermedia (ß-TI) who developed transfusion-dependent anemia. Molecular studies revealed that the patient was a compound heterozygote for two ß-thal alleles: codons 41/42 (-TTCT) (HBB: c.126_129delCTTT) and term codon +32 (A>C) (HBB: c.*32A>C).

Severe Hb H Disease Caused by Hb Zürich-Albisrieden (HBA1: c.178G>C): Another Case Report.

Hb Zürich-Albisrieden, [α59(E8)Gly→Arg, HBA1: c.178G>C] is a rare and highly unstable α-globin chain variant. The involved mutation has been reported in both HBA1 and HBA2 genes. A few compound heterozygotes of Hb Zürich-Albisrieden and α0-thalassemia have shown that this variant is associated with severe Hb H disease. We describe here another case of Hb Zürich-Albisrieden who presented with transfusion-dependent anemia beginning shortly after birth.

Hb Westmead (HBA2: c.369C>G): Hematological Characteristics in Heterozygotes with and without α0-Thalassemia.

Hb Westmead (α122(H5)His>Gln) (HBA2: c.369C>G) is a common α-globin variant causing α-thalassemia (α-thal) in Mainland China. In this study, we report the hematological characteristics in Hb Westmead carriers in a Chinese population. There were 546 individuals carrying Hb Westmead based on their molecular diagnosis: 514 Hb Westmead heterozygotes and 32 compound heterozygotes for Hb Westmead and α0-thal. Compared to common deletional α+-thal, Hb Westmead was associated with higher mean corpuscular hemoglobin (Hb) (MCH) values. Compound heterozygotes for Hb Westmead and α0-thal showed significantly higher Hb, mean corpuscular volume (MCV) and MCH values than subjects with deletional Hb H disease. When compared to α0-thal carriers, compound heterozygotes for Hb Westmead and α0-thal showed similar Hb values, but significantly lower MCV and MCH values. Our results indicate that Hb Westmead is a silent nondeletional α+-thal, with a deficiency of α-globin chain milder than deletional α+-thal, and compound heterozygotes for Hb Westmead/α0-thal have a phenotype similar to simple α0-thal.

Hematological Characteristics of Hb Constant Spring (HBA2: c.427T>C) Carriers in Mainland China.

Hb Constant Spring (Hb CS) (HBA2: c.427T>C) is a common α-globin variant causing α-thalassemia (α-thal) phenotypes in mainland China. In this study, we evaluated the efficiency of erythrocyte parameters and capillary electrophoresis (CE) in the determination of Hb CS in blood samples from Hb CS carriers. Based on molecular diagnosis, there were 462 patients carrying Hb CS: 411 Hb CS heterozygotes, seven carried Hb H-Hb CS disease, 18 compound heterozygotes for Hb CS/α+-thal, and 26 double heterozygotes for Hb CS and ß-thalassemia (ß-thal). Forty-three cases had no Hb CS peak visible on CE, including all 26 cases of double heterozygotes for Hb CS and ß-thal, and 17 cases of heterozygotes carrying only Hb CS. Hb CS heterozygotes, those without a Hb CS peak, presented with lower hemoglobin (Hb), mean corpuscular volume (MCV) and mean corpuscular Hb (MCH) values than those with a Hb CS peak. The MCV <80.0 fL yielded a detection rate of 87.8% for screening individuals carrying Hb CS. Therefore, we emphasize that if one partner of a couple has tested positive for α0-thal, the other should be subjected to detailed screening for this nondeletional allele using molecular analysis, regardless of his/her red cell indices and electrophoretic chromatogram.

Coinheritance of Hb City of Hope (HBB: c.208G>A) and ß-Thalassemia: Compromising the Molecular Diagnosis of the Codons 71/72 (+A) (HBB: c.216_217insA) Mutation by Reverse Dot-Blot Hybridization.

More than 900 abnormal hemoglobin (Hb) ß chain variants have now been characterized. The majority are due to point mutations resulting in a single amino acid substitution within the globin gene involved, with nearly twice as many ß chain variants identified compared to α chain variants. Although most of these variants are clinically and hematologically silent, they can interact with different thalassemia mutations, which could sometimes render laboratory diagnostics in a routine setting difficult. In this study, we present a case of coinheritance of Hb City of Hope [ß69(E13)Gly→Ser; HBB: c.208G>A] and ß-thalassemia (ß-thal), that compromises the molecular diagnosis of ß-thal trait.

Results of Coexistence of ß-Thalassemia Minor in Hb H Disease Patients.

The aim of this study was to determine the hematological characteristics in a large group of Hb H (ß4) patients with or without a coexisting ß-thalassemia (ß-thal), identified by a thalassemia screening program in mainland China. A total of 361 patients with Hb H disease were found, including 343 with deletional types and 18 with nondeletional types. ß-Thalassemia was found in 28 (7.8%) out of the 361 Hb H cases, and all of the 28 cases had the deletional type of Hb H disease. Lower hemoglobin (Hb) levels were detected in cases with the nondeletional type compared to those in cases with the deletional type. ß-Thalassemia significantly increases the Hb levels in Hb H cases. The Hb H and Hb Bart's (γ4) fractions were visible in 270 (85.7%) and 122 (38.7%) out of 315 deletional type cases, respectively, while no Hb H or Hb Bart's fractions were detectable in 28 deletional type cases with ß-thal. Therefore, the diagnosis of Hb H disease in a ß-thal carrier is challenging. Molecular analysis of α- and ß-globin genes is imperative in all cases with a ß-thal trait.

Analysis of the Genotypes in a Chinese Population with Increased Hb A2 and Low Hematological Indices.

Increased Hb A2 is considered the most reliable hematological finding for the identification of ß-thalassemia (ß-thal) carriers. The aim of this study was to determine the underlying genetic factors associated with a high Hb A2 level in a Chinese population. Subjects were recruited from couples preparing for pregnancy who participated in the thalassemia screening program during a 2-year period. DNA analyses were used for diagnosis of ß-thal and other genetic factors. A total of 5985 adults who screened positive for ß-thal were recruited. Of these, 5933 (99.1%) were detected to have a ß-thal mutation. In the remaining 52 (0.9%) individuals without mutations involving the ß-globin gene cluster, 16 were found to have Krüppel-like factor 1 (KLF1) gene variants, and two had an α-globin gene triplication. There were still 34 individuals with unknown genetic factors for their raised Hb A2 values. The results of this study indicate that genetic factors other than ß-thal can rarely contribute to the elevation of Hb A2. These subjects usually have borderline microcytic red cell indices and Hb A2 values.

KFL1 Gene Variants in α-Thalassemia Individuals with Increased Fetal Hemoglobin in a Chinese Population.

Krüppel-like factor 1 (KLF1) is a pleiotropic erythroid transcription factor that is a regulator of definitive erythropoiesis. The aim of this study was to detect KLF1 gene variants in α-thalassemia (α-thal) carriers with an increased Hb F level in a Chinese population, and determine the changes of hematological parameters as a result of interactions between KLF1 gene mutations and α-thal. Subjects with α-thal and Hb F levels of ≥1.0% were selected for further investigation. Direct sequencing was used to detect KLF1 gene mutations. Hematological parameters of subjects with α-thal and concomitant KLF1 gene mutations and those with α-thal alone were compared. The KLF1 gene variants were detected in 46 of 275 (16.7%) individuals with α-thal and Hb F levels of ≥1.0%. The detection rate of KLF1 gene mutations rose correspondingly when the Hb F level increased. For α0-thal carriers, significantly lower mean corpuscular volume (MCV) and mean corpuscular hemoglobin (Hb) (MCH) values were observed in KLF1 gene mutation-positive carriers than that in KLF1 gene mutation-free carriers; conversely, significantly higher Hb A2 and Hb F levels were observed in the former condition rather than in the latter condition. The results of this study indicate that KLF1 gene variants are common in Chinese subjects with α-thal and increased Hb F levels, and KLF1 gene mutations decreased the red blood cell (RBC) indices in α-thal carriers as that in normal adults.

First Report of the Rare IVS-II-705 (T>G) ß-Thalassemia Mutation in a Chinese Family.

We have found an example of the mutation at the intronic region of the second intervening sequence of the ß-globin gene, IVS-II-705 (T>G) (HBB: c.316-146T>G), in a Chinese family. The two subjects heterozygous for this mutation presented with typical ß-thalassemia (ß-thal) trait.

Hb A2-Tianhe (HBD: c.323G>A): First Report in a Chinese Family with Normal Hb A2-ß-Thalassemia Trait.

Coinheritance of δ-globin variants along with ß-globin gene defects can interfere with correct diagnosis of ß-thalassemia (ß-thal) trait. In this report, we present the coinheritance of a δ-globin variant, Hb A2-Tianhe [δ107(G9)Gly→Asp; HBD: c.323G>A] and a heterozygous ß-thal in a Chinese individual with microcytosis, hypochromia and a normal Hb A2 level.

A Novel Frameshift Mutation at Codons 138/139 (HBB: c.417_418insT) on the ß-Globin Gene Leads to ß-Thalassemia.

We describe a new ß-thalassemic mutation in a Chinese subject. This allele develops by insertion of one nucleotide (+T) between codons 138 and 139 in the third exon of the ß-globin gene. The mutation causes a frameshift that leads to a termination codon at codon 139. In the heterozygote, this allele has the phenotype of classical ß-thalassemia (ß-thal) minor.

Pre Gestational Thalassemia Screening in Mainland China: The First Two Years of a Preventive Program.

In this study, we report the experience of a pre gestational thalassemia screening program at a single center in Southern China. Free thalassemia screening, genetic counseling and prenatal diagnosis (PND) for couples planning pregnancy were implemented over a 2-year period. Among a total of 83,062 screened individuals (41,531 couples), the allele frequencies of ß-thalassemia (ß-thal), - -SEA and - -THAI deletions were 3.79, 5.75 and 0.028%, respectively. Out of the 41,531 couples, 11,039 couples had at least one partner who had a positive screening test; of these, 455 at-risk couples (1.07%) were identified, including 68 (0.16%) for ß-thal, 162 (0.39%) for Hb Bart's (γ4) hydrops fetalis, 190 (0.46%) for deletional Hb H (ß4) disease and 25 (0.06%) for nondeletional Hb H disease. Of the 455 at-risk couples, 90 were already pregnant and 66 underwent PND at 10-13 weeks' gestation, resulting in 15 affected fetuses. The remaining 355 at-risk couples were still preparing for pregnancy, and they were on the list for follow-up. There is considerable scope for facilitating timely PND through improved organization and screening strategy. The pre pregnancy screening is a feasible and effective approach to thalassemia prevention.

Upregulation of Transient Receptor Potential Canonical Channels Contributes to Endotoxin-Induced Pulmonary Arterial Stenosis.

BACKGROUND Septic shock is a pathologic condition caused by endotoxin-producing bacteria, and often associated with severe pulmonary hypertension. Inflammation is a major systemic response to endotoxin; however, it is unknown whether endotoxin has a direct impact on pulmonary arteries that contributes to pathogenesis of pulmonary hypertension. MATERIAL AND METHODS Rat pulmonary arteries and primary pulmonary arterial smooth muscle cells (PASMCs) were cultured in vitro and treated with lipopolysaccharide (LPS) and blockers of transient receptor potential canonical (TRPC) channels. Neointimal growth and arterial stenosis were observed on cryosections of cultured pulmonary arteries. Proliferation of PASMCs was examined by a WST-1 (water-soluble tetrazolium salt) assay. Expression of TRPC genes in pulmonary arteries and PASMCs were detected and quantified by real-time polymerase chain reaction and Western blotting. RESULTS LPS significantly induced neointimal growth and stenosis of pulmonary arteries and promoted proliferation of PASMCs. TRPC channel blockers 2-aminoethoxydiphenyl borate and SKF-96365 inhibited LPS-induced remodeling of pulmonary arteries and PASMC proliferation. Expression of TRPC1/3/4/6 was detected in pulmonary arteries and PASMCs. LPS treatment dramatically increased the expression of TRPC3 and TRPC4 at both messenger RNA and protein levels. CONCLUSIONS LPS stimulates stenosis of pulmonary arteries through enhancement of TRPC-mediated Ca2+ entry into PASMCs, which is caused by upregulation of TRPC3 and TRPC4 channels.

Mechanosensitive channels TMEM63A and TMEM63B mediate lung inflation-induced surfactant secretion.

Pulmonary surfactant is a lipoprotein complex lining the alveolar surface to decrease the surface tension and facilitate inspiration. Surfactant deficiency is often seen in premature infants and in children and adults with respiratory distress syndrome. Mechanical stretch of alveolar type 2 epithelial (AT2) cells during lung expansion is the primary physiological factor that stimulates surfactant secretion; however, it is unclear whether there is a mechanosensor dedicated to this process. Here, we show that loss of the mechanosensitive channels TMEM63A and TMEM63B (TMEM63A/B) resulted in atelectasis and respiratory failure in mice due to a deficit of surfactant secretion. TMEM63A/B were predominantly localized at the limiting membrane of the lamellar body (LB), a lysosome-related organelle that stores pulmonary surfactant and ATP in AT2 cells. Activation of TMEM63A/B channels during cell stretch facilitated the release of surfactant and ATP from LBs fused with the plasma membrane. The released ATP evoked Ca2+ signaling in AT2 cells and potentiated exocytic fusion of more LBs. Our study uncovered a vital physiological function of TMEM63 mechanosensitive channels in preparing the lungs for the first breath at birth and maintaining respiration throughout life.

To Be or Not to Be an Ion Channel: Cryo-EM Structures Have a Say.

Ion channels are the second largest class of drug targets after G protein-coupled receptors. In addition to well-recognized ones like voltage-gated Na/K/Ca channels in the heart and neurons, novel ion channels are continuously discovered in both excitable and non-excitable cells and demonstrated to play important roles in many physiological processes and diseases such as developmental disorders, neurodegenerative diseases, and cancer. However, in the field of ion channel discovery, there are an unignorable number of published studies that are unsolid and misleading. Despite being the gold standard of a functional assay for ion channels, electrophysiological recordings are often accompanied by electrical noise, leak conductance, and background currents of the membrane system. These unwanted signals, if not treated properly, lead to the mischaracterization of proteins with seemingly unusual ion-conducting properties. In the recent ten years, the technical revolution of cryo-electron microscopy (cryo-EM) has greatly advanced our understanding of the structures and gating mechanisms of various ion channels and also raised concerns about the pore-forming ability of some previously identified channel proteins. In this review, we summarize cryo-EM findings on ion channels with molecular identities recognized or disputed in recent ten years and discuss current knowledge of proposed channel proteins awaiting cryo-EM analyses. We also present a classification of ion channels according to their architectures and evolutionary relationships and discuss the possibility and strategy of identifying more ion channels by analyzing structures of transmembrane proteins of unknown function. We propose that cross-validation by electrophysiological and structural analyses should be essentially required for determining molecular identities of novel ion channels.

Sphingosine-1-Phosphate Signaling in Cardiovascular Diseases.

Sphingosine-1-phosphate (S1P) is an important sphingolipid molecule involved in regulating cardiovascular functions in physiological and pathological conditions by binding and activating the three G protein-coupled receptors (S1PR1, S1PR2, and S1PR3) expressed in endothelial and smooth muscle cells, as well as cardiomyocytes and fibroblasts. It exerts its actions through various downstream signaling pathways mediating cell proliferation, migration, differentiation, and apoptosis. S1P is essential for the development of the cardiovascular system, and abnormal S1P content in the circulation is involved in the pathogenesis of cardiovascular disorders. This article reviews the effects of S1P on cardiovascular function and signaling mechanisms in different cell types in the heart and blood vessels under diseased conditions. Finally, we look forward to more clinical findings with approved S1PR modulators and the development of S1P-based therapies for cardiovascular diseases.