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Hack JB, Horning K, Juroske Short DM, Schreiber JM, Watkins JC, Hammer MF. Distinguishing Loss-of-Function and Gain-of-Function SCN8A Variants Using a Random Forest Classification Model Trained on Clinical Features. Neurol Genet 2023; 9:e200060. [PMID: 37152443 PMCID: PMC10160958 DOI: 10.1212/nxg.0000000000200060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Accepted: 01/12/2023] [Indexed: 05/09/2023]
Abstract
Background and Objectives Pathogenic variants at the voltage-gated sodium channel gene, SCN8A, are associated with a wide spectrum of clinical disease outcomes. A critical challenge for neurologists is to determine whether patients carry gain-of-function (GOF) or loss-of-function (LOF) variants to guide treatment decisions, yet in vitro studies to infer channel function are often not feasible in the clinic. In this study, we develop a predictive modeling approach to classify variants based on clinical features present at initial diagnosis. Methods We performed an exhaustive search for individuals deemed to carry SCN8A GOF and LOF variants by means of in vitro studies in heterologous cell systems, or because the variant was classified as truncating, and recorded clinical features. This resulted in a total of 69 LOF variants: 34 missense and 35 truncating variants, including 9 nonsense, 13 frameshift, 6 splice site, 6 indels, and 1 large deletion. We then assembled a truth set of variants with known functional effects, excluding individuals carrying variants at other loci associated with epilepsy. We then trained a predictive model based on random forest using this truth set of 45 LOF variants and 45 GOF variants randomly selected from a set of variants tested by in vitro methods. Results Phenotypic categories assigned to individuals correlated strongly with GOF or LOF variants. All patients with GOF variants experienced early-onset seizures (mean age at onset = 4.5 ± 3.1 months) while only 64.4% patients with LOF variants had seizures, most of which were late-onset absence seizures (mean age at onset = 40.0 ± 38.1 months). With high accuracy (95.4%), our model including 5 key clinical features classified individuals with GOF and LOF variants into 2 distinct cohorts differing in age at seizure onset, development of seizures, seizure type, intellectual disability, and developmental and epileptic encephalopathy. Discussion The results support the hypothesis that patients with SCN8A GOF and LOF variants represent distinct clinical phenotypes. The clinical model developed in this study has great utility because it provides a rapid and highly accurate platform for predicting the functional class of patient variants during SCN8A diagnosis, which can aid in initial treatment decisions and improve prognosis.
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Affiliation(s)
- Joshua B Hack
- BIO5 Institute (J.B.H., M.F.H.), University of Arizona, Tucson; CombinedBrain (K.H.), Brentwood; DenGen Consulting (D.M.J.S.), Rocky Top, TN; Children's National Medical Center (J.M.S.), Department of Neurology, Washington, DC; Department of Mathematics (J.C.W.), University of Arizona; and Neurology Department (M.F.H.), University of Arizona, Tucson
| | - Kyle Horning
- BIO5 Institute (J.B.H., M.F.H.), University of Arizona, Tucson; CombinedBrain (K.H.), Brentwood; DenGen Consulting (D.M.J.S.), Rocky Top, TN; Children's National Medical Center (J.M.S.), Department of Neurology, Washington, DC; Department of Mathematics (J.C.W.), University of Arizona; and Neurology Department (M.F.H.), University of Arizona, Tucson
| | - Denise M Juroske Short
- BIO5 Institute (J.B.H., M.F.H.), University of Arizona, Tucson; CombinedBrain (K.H.), Brentwood; DenGen Consulting (D.M.J.S.), Rocky Top, TN; Children's National Medical Center (J.M.S.), Department of Neurology, Washington, DC; Department of Mathematics (J.C.W.), University of Arizona; and Neurology Department (M.F.H.), University of Arizona, Tucson
| | - John M Schreiber
- BIO5 Institute (J.B.H., M.F.H.), University of Arizona, Tucson; CombinedBrain (K.H.), Brentwood; DenGen Consulting (D.M.J.S.), Rocky Top, TN; Children's National Medical Center (J.M.S.), Department of Neurology, Washington, DC; Department of Mathematics (J.C.W.), University of Arizona; and Neurology Department (M.F.H.), University of Arizona, Tucson
| | - Joseph C Watkins
- BIO5 Institute (J.B.H., M.F.H.), University of Arizona, Tucson; CombinedBrain (K.H.), Brentwood; DenGen Consulting (D.M.J.S.), Rocky Top, TN; Children's National Medical Center (J.M.S.), Department of Neurology, Washington, DC; Department of Mathematics (J.C.W.), University of Arizona; and Neurology Department (M.F.H.), University of Arizona, Tucson
| | - Michael F Hammer
- BIO5 Institute (J.B.H., M.F.H.), University of Arizona, Tucson; CombinedBrain (K.H.), Brentwood; DenGen Consulting (D.M.J.S.), Rocky Top, TN; Children's National Medical Center (J.M.S.), Department of Neurology, Washington, DC; Department of Mathematics (J.C.W.), University of Arizona; and Neurology Department (M.F.H.), University of Arizona, Tucson
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Zhang L, Wang X, Chen J, Sheng S, Kleyman TR. Extracellular intersubunit interactions modulate epithelial Na + channel gating. J Biol Chem 2023; 299:102914. [PMID: 36649907 PMCID: PMC9975279 DOI: 10.1016/j.jbc.2023.102914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 12/13/2022] [Accepted: 01/12/2023] [Indexed: 01/15/2023] Open
Abstract
Epithelial Na+ channels (ENaCs) and related channels have large extracellular domains where specific factors interact and induce conformational changes, leading to altered channel activity. However, extracellular structural transitions associated with changes in ENaC activity are not well defined. Using crosslinking and two-electrode voltage clamp in Xenopus oocytes, we identified several pairs of functional intersubunit contacts where mouse ENaC activity was modulated by inducing or breaking a disulfide bond between introduced Cys residues. Specifically, crosslinking E499C in the β-subunit palm domain and N510C in the α-subunit palm domain activated ENaC, whereas crosslinking βE499C with αQ441C in the α-subunit thumb domain inhibited ENaC. We determined that bridging βE499C to αN510C or αQ441C altered the Na+ self-inhibition response via distinct mechanisms. Similar to bridging βE499C and αQ441C, we found that crosslinking palm domain αE557C with thumb domain γQ398C strongly inhibited ENaC activity. In conclusion, we propose that certain residues at specific subunit interfaces form microswitches that convey a conformational wave during ENaC gating and its regulation.
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Affiliation(s)
- Lei Zhang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Xueqi Wang
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Department of Nephrology, Hunan Key Laboratory of Kidney Disease and Blood Purification, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China; The Third Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Jingxin Chen
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Shaohu Sheng
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
| | - Thomas R Kleyman
- Departments of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA; Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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Kelchtermans J, Pinney SE, Leonard JMM, Mcgrath-Morrow S. Diagnostic and management considerations in pseudohypoaldosteronism type 1b. BMJ Case Rep 2022; 15:e246538. [PMID: 34980640 PMCID: PMC8724702 DOI: 10.1136/bcr-2021-246538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/16/2021] [Indexed: 11/04/2022] Open
Abstract
Pseudohypoaldosteronism type 1B is a rare autosomal recessive disorder caused by dysfunction of amiloride-sensitive epithelial sodium channels (ENaCs). We present the case of a neonate with cardiogenic shock after cardiac arrest due to profound hyperkalaemia. Genetic testing revealed a novel homozygous variant in SCNNIA We review diagnostic considerations including the molecular mechanisms of disease, discuss treatment approaches and highlight the possible significance of the diversity of pulmonary ENaCs.
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Affiliation(s)
- Jelte Kelchtermans
- Division of Pulmonary and Sleep Medicine, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Sara E Pinney
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Division of Endocrinology and Diabetes, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Jacqueline M M Leonard
- Roberts Individualized Medical Genetics Center, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Sharon Mcgrath-Morrow
- Division of Pulmonary and Sleep Medicine, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
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Sheng S, Chen J, Mukherjee A, Yates ME, Buck TM, Brodsky JL, Tolino MA, Hughey RP, Kleyman TR. Thumb domains of the three epithelial Na + channel subunits have distinct functions. J Biol Chem 2018; 293:17582-17592. [PMID: 30228189 PMCID: PMC6231141 DOI: 10.1074/jbc.ra118.003618] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 09/13/2018] [Indexed: 01/10/2023] Open
Abstract
The epithelial Na+ channel (ENaC) possesses a large extracellular domain formed by a β-strand core enclosed by three peripheral α-helical subdomains, which have been dubbed thumb, finger, and knuckle. Here we asked whether the ENaC thumb domains play specific roles in channel function. To this end, we examined the characteristics of channels lacking a thumb domain in an individual ENaC subunit (α, β, or γ). Removing the γ subunit thumb domain had no effect on Na+ currents when expressed in Xenopus oocytes, but moderately reduced channel surface expression. In contrast, ENaCs lacking the α or β subunit thumb domain exhibited significantly reduced Na+ currents along with a large reduction in channel surface expression. Moreover, channels lacking an α or γ thumb domain exhibited a diminished Na+ self-inhibition response, whereas this response was retained in channels lacking a β thumb domain. In turn, deletion of the α thumb domain had no effect on the degradation rate of the immature α subunit as assessed by cycloheximide chase analysis. However, accelerated degradation of the immature β subunit and mature γ subunit was observed when the β or γ thumb domain was deleted, respectively. Our results suggest that the thumb domains in each ENaC subunit are required for optimal surface expression in oocytes and that the α and γ thumb domains both have important roles in the channel's inhibitory response to external Na+ Our findings support the notion that the extracellular helical domains serve as functional modules that regulate ENaC biogenesis and activity.
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Affiliation(s)
- Shaohu Sheng
- From the Renal-Electrolyte Division, Department of Medicine and
| | - Jingxin Chen
- From the Renal-Electrolyte Division, Department of Medicine and
| | | | | | | | | | | | - Rebecca P Hughey
- From the Renal-Electrolyte Division, Department of Medicine and
- Cell Biology
- Microbiology and Molecular Genetics, and
| | - Thomas R Kleyman
- From the Renal-Electrolyte Division, Department of Medicine and
- Cell Biology
- Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
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Hanukoglu I, Boggula VR, Vaknine H, Sharma S, Kleyman T, Hanukoglu A. Expression of epithelial sodium channel (ENaC) and CFTR in the human epidermis and epidermal appendages. Histochem Cell Biol 2017; 147:733-748. [PMID: 28130590 DOI: 10.1007/s00418-016-1535-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/23/2016] [Indexed: 02/07/2023]
Abstract
A major function of the skin is the regulation of body temperature by sweat secretions. Sweat glands secrete water and salt, especially NaCl. Excreted water evaporates, cooling the skin surface, and Na+ ions are reabsorbed by the epithelial sodium channels (ENaC). Mutations in ENaC subunit genes lead to a severe multi-system (systemic) form of pseudohypoaldosteronism (PHA) type I, characterized by salt loss from aldosterone target organs, including sweat glands in the skin. In this study, we mapped the sites of localization of ENaC in the human skin by confocal microscopy using polyclonal antibodies generated against human αENaC. Our results reveal that ENaC is expressed strongly in all epidermal layers except stratum corneum, and also in the sebaceous glands, eccrine glands, arrector pili smooth muscle cells, and intra-dermal adipocytes. In smooth muscle cells and adipocytes, ENaC is co-localized with F-actin. No expression of ENaC was detected in the dermis. CFTR is strongly expressed in sebaceous glands. In epidermal appendages noted, except the eccrine sweat glands, ENaC is mainly located in the cytoplasm. In the eccrine glands and ducts, ENaC and CFTR are located on the apical side of the membrane. This localization of ENaC is compatible with ENaC's role in salt reabsorption. PHA patients may develop folliculitis, miliaria rubra, and atopic dermatitis-like skin lesions, due to sweat gland duct occlusion and inflammation of eccrine glands as a result of salt accumulation.
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Affiliation(s)
- Israel Hanukoglu
- Laboratory of Cell Biology, Ariel University, Ariel, 40700, Israel.
| | - Vijay R Boggula
- Laboratory of Cell Biology, Ariel University, Ariel, 40700, Israel.,Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv, Israel
| | - Hananya Vaknine
- Division of Pathology, E. Wolfson Medical Center, Holon, Israel
| | - Sachin Sharma
- Laboratory of Cell Biology, Ariel University, Ariel, 40700, Israel
| | - Thomas Kleyman
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.,Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA, USA.,Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Aaron Hanukoglu
- Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv, Israel.,Division of Pediatric Endocrinology, E. Wolfson Medical Center, Holon, Israel
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Glycosylation-dependent activation of epithelial sodium channel by solnatide. Biochem Pharmacol 2015; 98:740-53. [DOI: 10.1016/j.bcp.2015.08.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 08/03/2015] [Indexed: 12/29/2022]
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Chen J, Ray EC, Yates ME, Buck TM, Brodsky JL, Kinlough CL, Winarski KL, Hughey RP, Kleyman TR, Sheng S. Functional Roles of Clusters of Hydrophobic and Polar Residues in the Epithelial Na+ Channel Knuckle Domain. J Biol Chem 2015; 290:25140-50. [PMID: 26306034 DOI: 10.1074/jbc.m115.665398] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Indexed: 12/21/2022] Open
Abstract
The extracellular regions of epithelial Na(+) channel subunits are highly ordered structures composed of domains formed by α helices and β strands. Deletion of the peripheral knuckle domain of the α subunit in the αβγ trimer results in channel activation, reflecting an increase in channel open probability due to a loss of the inhibitory effect of external Na(+) (Na(+) self-inhibition). In contrast, deletion of either the β or γ subunit knuckle domain within the αβγ trimer dramatically reduces epithelial Na(+) channel function and surface expression, and impairs subunit maturation. We systematically mutated individual α subunit knuckle domain residues and assessed functional properties of these mutants. Cysteine substitutions at 14 of 28 residues significantly suppressed Na(+) self-inhibition. The side chains of a cluster of these residues are non-polar and are predicted to be directed toward the palm domain, whereas a group of polar residues are predicted to orient their side chains toward the space between the knuckle and finger domains. Among the mutants causing the greatest suppression of Na(+) self-inhibition were αP521C, αI529C, and αS534C. The introduction of Cys residues at homologous sites within either the β or γ subunit knuckle domain resulted in little or no change in Na(+) self-inhibition. Our results suggest that multiple residues in the α subunit knuckle domain contribute to the mechanism of Na(+) self-inhibition by interacting with palm and finger domain residues via two separate and chemically distinct motifs.
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Affiliation(s)
- Jingxin Chen
- From the Renal-Electrolyte Division, Department of Medicine
| | - Evan C Ray
- From the Renal-Electrolyte Division, Department of Medicine
| | | | | | | | | | | | - Rebecca P Hughey
- From the Renal-Electrolyte Division, Department of Medicine, the Department of Cell Biology, the Department of Microbiology and Molecular Genetics, and
| | - Thomas R Kleyman
- From the Renal-Electrolyte Division, Department of Medicine, the Department of Cell Biology, the Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Shaohu Sheng
- From the Renal-Electrolyte Division, Department of Medicine
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Chinigarzadeh A, Muniandy S, Salleh N. Estrogen, progesterone, and genistein differentially regulate levels of expression of α-, β-, and γ-epithelial sodium channel (ENaC) and α-sodium potassium pump (Na⁺/K⁺-ATPase) in the uteri of sex steroid-deficient rats. Theriogenology 2015; 84:911-26. [PMID: 26154487 DOI: 10.1016/j.theriogenology.2015.05.029] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Revised: 04/18/2015] [Accepted: 05/28/2015] [Indexed: 12/22/2022]
Abstract
Estrogen, progesterone, and genistein could induce changes in uterine fluid volume and Na(+) concentration. Progesterone upregulates expression of epithelial sodium channel (ENaC) and Na(+)/K(+)-ATPase which contributed toward these changes. However, effects of estrogen and genistein were unknown. This study therefore investigated changes in expression of these proteins in the uterus under estrogen, progesterone, and genistein influences to further understand mechanisms underlying sex steroids and phytoestrogen effects on uterine fluid Na(+) regulation. In this study, uteri of ovariectomized female rats receiving 7-day treatment with genistein (25, 50, and 100 mg/kg/day), estrogen (0.8 × 10(-4) mg/kg/day), or progesterone (4 mg/kg/day) were harvested, and expression levels of α-, β-, and γ-ENaC proteins and messenger RNAs (mRNAs) and α-Na(+)/K(+)-ATPase protein were determined by Western blotting (proteins) and real-time polymerase chain reaction (mRNA). Meanwhile, distribution of α-, β-, and γ-ENaC and α-Na(+)/K(+)-ATPase proteins in the uterus was identified by immunohistochemistry. Our findings indicated that expression of α-, β-, and γ-ENaC proteins and mRNAs and α-Na(+)/K(+)-ATPase protein were enhanced under progesterone influence. Lower expressions were noted under estrogen and genistein influences compared to progesterone. Under estrogen, progesterone, and genistein influences, α- and β-ENaC were distributed at apical membrane and γ-ENaC was distributed at apical and basolateral membranes of uterine luminal epithelia. Under progesterone influence, α-Na(+)/K(+)-ATPase was highly expressed at basolateral membrane. In conclusion, high expression of α-, β-, and γ-ENaC and α-Na(+)/K(+)-ATPase under progesterone influence would contribute toward increased uterine fluid Na(+) reabsorption, whereas lesser expression of these proteins under estrogen and genistein influences would contribute toward lower reabsorption of uterine fluid Na(+).
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Affiliation(s)
- Asma Chinigarzadeh
- Department of Physiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
| | - Sekaran Muniandy
- Department of Molecular Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
| | - Naguib Salleh
- Department of Physiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
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