👤 Sung Hwan Ki

The spectrum of genetic variants and their clinical significance of Hypertrophic cardiomyopathy (HCM) have been poorly studied in Asian patients. The objectives of this study were to assess the spectrum of genetic variants and genotype-phenotype relationships within a Korean HCM population. Eighty-nine consecutive unrelated HCM patients were included. All patients underwent genotypic analysis for 23 HCM-associated genes. Clinical parameters including echocardiographic and cardiac magnetic resonance (CMR) parameters were evaluated. A composite of major adverse cardiac and cerebrovascular events was assessed. Genetic variants were detected in 55 of 89 subjects. Pathogenic variants or likely pathogenic variants were identified in 27 of HCM patients in Genetic variants in patients with HCM are relatively common and are associated with adverse clinical events and myocardial fibrosis on CMR. Genotypic analysis may add important information to clinical variables in the assessment of long-term risk for HCM patients. Show less

Diagnosis of the urea cycle disorder (USD) carbamoyl-phosphate synthetase 1 (CPS1) deficiency (CPS1D) based on only the measurements of biochemical intermediary metabolites is not sufficient to properly exclude other UCDs with similar symptoms. We report the first Korean CPS1D patient using whole exome sequencing (WES). A four-day-old female neonate presented with respiratory failure due to severe metabolic encephalopathy with hyperammonemia (1,690 μmol/L; reference range, 11.2-48.2 μmol/L). Plasma amino acid analysis revealed markedly elevated levels of alanine (2,923 μmol/L; reference range, 131-710 μmol/L) and glutamine (5,777 μmol/L; reference range, 376-709 μmol/L), whereas that of citrulline was decreased (2 μmol/L; reference range, 10-45 μmol/L). WES revealed compound heterozygous pathogenic variants in the CPS1 gene: one novel nonsense pathogenic variant of c.580C>T (p.Gln194*) and one known pathogenic frameshift pathogenic variant of c.1547delG (p.Gly516Alafs*5), which was previously reported in Japanese patients with CPS1D. We successfully applied WES to molecularly diagnose the first Korean patient with CPS1D in a clinical setting. This result supports the clinical applicability of WES for cost-effective molecular diagnosis of UCDs. Show less

Pathogenic variants in genes related to channelopathy and cardiomyopathy are the most common cause of sudden unexplained cardiac death. However, few reports have investigated the frequency and/or spectrum of pathogenic variants in these genes in Korean sudden cardiac arrest survivors. This study aimed to investigate the causative genetic variants of cardiac-associated genes in Korean sudden cardiac arrest survivors. We performed exome sequencing followed by filtering and validation of variants in 100 genes related to channelopathy and cardiomyopathy in 19 Korean patients who survived sudden cardiac arrest. Five of the 19 patients (26.3%) had either a pathogenic variant or a likely pathogenic variant in MYBPC3 (n=1), MYH7 (n=1), RYR2 (n=2), or TNNT2 (n=1). All five variants were missense variants that have been reported previously in patients with channelopathies or cardiomyopathies. Furthermore, an additional 12 patients (63.2%) had more than one variant of uncertain significance. In conclusion, pathogenic or likely pathogenic variants in genes related to channelopathy and cardiomyopathy are not uncommon in Korean sudden cardiac arrest survivors and cardiomyopathy-related genes should be included in the molecular diagnosis of sudden cardiac arrest in Korea. Show less

Canonical Wnt signals, transduced by stabilized β-catenin, play similar roles across animals in maintaining stem cell pluripotency, regulating cell differentiation, and instructing normal embryonic development. Dysregulated Wnt/β-catenin signaling causes diseases and birth defects, and a variety of regulatory processes control this pathway to ensure its proper function and integration with other signaling systems. We previously identified GTP-binding protein 2 (Gtpbp2) as a novel regulator of BMP signaling, however further exploration revealed that Gtpbp2 can also affect Wnt signaling, which is a novel finding reported here. Knockdown of Gtpbp2 in Xenopus embryos causes severe axial defects and reduces expression of Spemann-Mangold organizer genes. Gtpbp2 knockdown blocks responses to ectopic Wnt8 ligand, such as organizer gene induction in ectodermal tissue explants and induction of secondary axes in whole embryos. However, organizer gene induction by ectopic Nodal2 is unaffected by Gtpbp2 knockdown. Epistasis tests, conducted by activating Wnt signal transduction at sequential points in the canonical pathway, demonstrate that Gtpbp2 is required downstream of Dishevelled and Gsk3β but upstream of β-catenin, which is similar to the previously reported effects of Axin1 overexpression in Xenopus embryos. Focusing on Axin in Xenopus embryos, we find that knockdown of Gtpbp2 elevates endogenous or exogenous Axin protein levels. Furthermore, Gtpbp2 fusion proteins co-localize with Dishevelled and co-immunoprecipitate with Axin and Gsk3b. We conclude that Gtpbp2 is required for canonical Wnt/β-catenin signaling in Xenopus embryos. Our data suggest a model in which Gtpbp2 suppresses the accumulation of Axin protein, a rate-limiting component of the β-catenin destruction complex, such that Axin protein levels negatively correlate with Gtpbp2 levels. This model is supported by the similarity of our Gtpbp2-Wnt epistasis results and previously reported effects of Axin overexpression, the physical interactions of Gtpbp2 with Axin, and the correlation between elevated Axin protein levels and lost Wnt responsiveness upon Gtpbp2 knockdown. A wide variety of cancer-causing Wnt pathway mutations require low Axin levels, so development of Gtpbp2 inhibitors may provide a new therapeutic strategy to elevate Axin and suppress aberrant β-catenin signaling in cancer and other Wnt-related diseases. Show less

Liver X receptor-α (LXRα), a member of the nuclear receptor superfamily of ligand-activated transcription factors, regulates de novo fatty acid synthesis that leads to stimulate hepatic steatosis. Although, resveratrol has beneficial effects on metabolic disease, it is not known whether resveratrol affects LXRα-dependent lipogenic gene expression. This study investigated the effect of resveratrol in LXRα-mediated lipogenesis and the underlying molecular mechanism. Resveratrol inhibited the ability of LXRα to activate sterol regulatory element binding protein-1c (SREBP-1c) and thereby inhibited target gene expression in hepatocytes. Moreover, resveratrol decreased LXRα-RXRα DNA binding activity and LXRE-luciferase transactivation. Resveratrol is known to activate Sirtuin 1 (Sirt1) and AMP-activated protein kinase (AMPK), although its precise mechanism of action remains controversial. We found that the ability of resveratrol to repress T0901317-induced SREBP-1c expression was not dependent on AMPK and Sirt1. It is well established that hepatic steatosis is associated with antioxidant and redox signaling. Our data showing that expression of Sestrin2 (Sesn2), which is a novel antioxidant gene, was significantly down-regulated in the livers of high-fat diet-fed mice. Moreover, resveratrol up-regulated Sesn2 expression, but not Sesn1 and Sesn3. Sesn2 overexpression repressed LXRα-activated SREBP-1c expression and LXRE-luciferase activity. Finally, Sesn2 knockdown using siRNA abolished the effect of resveratrol in LXRα-induced FAS luciferase gene transactivation. We conclude that resveratrol affects Sesn2 gene induction and contributes to the inhibition of LXRα-mediated hepatic lipogenesis. Show less

Dithiolethiones, a novel class of adenosine monophosphate-activated protein kinase (AMPK) activators, prevent insulin resistance through AMPK-dependent p70 ribosomal S6 kinase-1 (S6K1) inhibition. There is no known effect of S6K1 for liver X receptor-alpha (LXRalpha)-mediated lipogenic gene expression and steatosis, a cause of chronic liver disease. This study investigated the role of S6K1 in LXRalpha activation and the effects of oltipraz (prototype) and other dithiolethiones on LXRalpha-dependent lipogenesis in hepatocytes and high-fat diet animal model. Oltipraz prevented the ability of LXRalpha agonist (T0901317) to activate sterol regulatory element binding protein-1c (SREBP-1c), inhibiting its own mRNA and protein induction. Impaired SREBP-1c activity by oltipraz caused inhibition of LXRalpha-induced transcription of the fatty acid synthase, LXRalpha, acetyl-CoA carboxylase, stearoyl-CoA desaturase-1, and adenosine triphosphate-binding cassette transporter A1 genes. S6K1 activation antagonized the inhibitory effect of oltipraz on SREBP-1c activation, whereas dominant negative (DN) mutant S6K1 and rapamycin inhibited the T0901317-induced SREBP-1c expression. Oltipraz impaired LXRalpha DNA binding activity and LXR agonist-induced CYP7A1-LXRE-luciferase (CYP7A1) transactivation. Moreover, in vitro S6K1 directly phosphorylated LXRalpha at serine residues for gene transactivation, which was antagonized by its DN mutant. S6K1 inhibition antagonized CYP7A1 induction promoted by AMPK inhibition, whereas AMPK activation abrogated S6K1-dependent CYP7A1 induction, supporting the opposing role of S6K1 and AMPK in LXR activity. Finally, oltipraz was found to inhibit hepatic triglyceride accumulation and lipogenic gene induction in mice fed a high-fat diet. Other dithiolethiones also inhibited SREBP-1c induction by T0901317. Our findings showing the role of AMPK-S6K1 pathway in LXR activity and S6K1-dependent inhibition of LXRalpha-induced lipogenic gene transactivation by a novel class of dithiolethiones led to the identification of S6K1 as a particularly attractive target for intervention in hepatic steatosis. Show less