👤 Mi-ran Seong

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory loss, cognitive decline, and neuroinflammation, primarily mediated by microglia. In this study, we investigate the role of adenylate kinase 5 (AK5) in microglial function and its association with AD-related pathology. Analysis of brain tissues from AD patients and AD model mice revealed a significant reduction in AK5 expression. In vitro knockdown of AK5 in microglial cells attenuated lipopolysaccharide-induced pro-inflammatory responses, including decreased nitric oxide and tumor necrosis factor-alpha production, while enhancing phagocytic activity. Moreover, AK5 silencing induced metabolic reprogramming, evidenced by reduced lipid droplet accumulation and adipose triglyceride lipase mRNA levels, alongside increased farnesoid X receptor mRNA expression. Genome-wide association studies further identified two AK5 single nucleotide polymorphisms (SNPs), rs59556669 and rs75224576, significantly associated with hippocampal and amygdala atrophy as well as increased AD risk. Notably, these SNPs were not in linkage disequilibrium with the apolipoprotein E (APOE) locus, suggesting that AK5 may represent an independent genetic risk factor for AD. Collectively, our findings identify AK5 as a key regulator of microglial immune and metabolic function. The presence of AK5 variants may contribute to AD susceptibility, and AK5 expression or genetic status could serve as a potential biomarker for early risk assessment. Further exploration of AK5-targeted interventions may provide new therapeutic avenues for AD prevention or treatment. Show less

KMT2A (11q23.3) gene rearrangements are found in acute leukemia and are associated with a poor or intermediate prognosis. MLLT10 is the fourth most common gene fusion partner for KMT2A. A reciprocal translocation t(10;11) is insufficient to produce an in-frame KMT2A/MLLT10 fusion, because the genes involved in the rearrangement have opposite transcriptional orientations. In order to bring KMT2A and MLLT10 into juxtaposition, complex rearrangements are required. Until now, conventional chromosome, fluorescence in situ hybridization (FISH), and reverse transcriptase-polymerase chain reaction (RT-PCR) studies have been used to detect KMT2A/MLLT10 fusions. However, conventional studies have limitations, such as poor and inconsistent resolution, when compared to next-generation sequencing (NGS). In this study, we report a pediatric patient with acute megakaryoblastic leukemia, in whom the cryptic KMT2A/MLLT10 fusion was not detected by KMT2A break-apart probe FISH and chromosome analysis, but detected by NGS. In this patient, NGS showed cryptic insertion of MLLT10 exons 9-24 into intron 9 of KMT2A, resulting in a KMT2A/MLLT10 fusion. Therefore, NGS is a valuable complementary option for the evaluation of structural aberrations, especially those with a cryptic size. Show less

Non-alcoholic fatty liver disease (NAFLD) associated with type 2 diabetes may more easily progress towards severe forms of non-alcoholic steatohepatitis (NASH) and cirrhosis. Although the Wnt effector transcription factor 7-like 2 (TCF7L2) is closely associated with type 2 diabetes risk, the role of TCF7L2 in NAFLD development remains unclear. Here, we investigated how changes in TCF7L2 expression in the liver affects hepatic lipid metabolism based on the major risk factors of NAFLD development. Tcf7l2 was selectively ablated in the liver of C57BL/6N mice by inducing the albumin (Alb) promoter to recombine Tcf7l2 alleles floxed at exon 5 (liver-specific Tcf7l2-knockout [KO] mice: Alb-Cre;Tcf7l2 Alb-Cre;Tcf7l2 In mice, loss of hepatic Tcf7l2 contributes to liver steatosis by inducing preferential metabolism of carbohydrates via DNL activation. Therefore, TCF7L2 could be a promising regulator of the NAFLD associated with high-carbohydrate diets and diabetes since TCF7L2 deficiency may lead to development of NAFLD by promoting utilisation of excess glucose pools through activating DNL. RNA-sequencing data have been deposited into the NCBI GEO under the accession number GSE162449 ( www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE162449 ). Show less

The mobilization and catabolism of lipid energy is a central function of adipocytes that is under the control of the β-adrenergic signaling pathway, and defects in β-adrenergic signaling in adipocytes have been linked to obesity and obesity-related metabolic diseases. Receptor expression-enhancing proteins (REEPs) are endoplasmic reticulum (ER) proteins that play critical roles in subcellular targeting of receptor signaling complexes. Examination of gene expression profiles indicates that, among REEPs expressed in adipocytes, REEP6 expression is uniquely upregulated by sympathetic nervous system activation, suggesting involvement in regulating adrenergic signal transduction. The aim of this study was to assess the contribution of REEP6 to the thermogenic activation of adipocytes and characterize the metabolic consequences of REEP6 deficiency in vivo. Expression levels of Reep6 in adipose tissue were examined by using public transcriptomic data and validated by Western blot and qPCR analyses. Adipocyte-specific regulatory roles of REEP6 were investigated in vitro in C3H10T1/2 adipocytes and in primary adipocytes obtained from REEP6 KO mice. Effects of in vivo REEP6 deficiency on energy expenditure were measured by indirect calorimetry. Mitochondrial content in adipose tissue was accessed by immunoblot, mitochondrial DNA analysis, and confocal and electron microscopy. Effects of REEP6 KO on obesity-induced metabolic dysfunction were tested in a high-fat diet-induced obesity mouse model by glucose tolerance test, Western blot, and histological analyses. REEP6 expression is highly enriched in murine adipocytes and is sharply upregulated upon adipocyte differentiation and by cold exposure. Inactivation of REEP6 in mice increased adiposity, and reduced energy expenditure and cold tolerance. REEP6 KO severely reduced protein kinase A-mediated signaling in BAT and greatly reduced mitochondrial mass. The effect of REEP6 inactivation on diminished β-adrenergic signaling was reproduced in cultured adipocytes, indicating that this effect is cell-autonomous. REEP6 KO also suppressed expression of adenylate cyclase 3 (Adcy3) in brown adipose tissue and knockdown of REEP6 in adipocytes reduced targeting of ADCY3 to the plasma membrane. Lastly, REEP6 KO exacerbated high-fat diet-induced insulin resistance and inflammation in adipose tissue. This study indicates that REEP6 plays an important role in β-adrenergic signal transduction in adipocytes involving the expression and trafficking of Adcy3. Genetic inactivation of REEP6 reduces energy expenditure, increases adiposity, and the susceptibility to obesity-related metabolic dysfunction. Show less

The melanocortin-4 receptor (MC4R) belongs to the G protein-coupled receptor (GPCR) family and plays an essential role in the control of energy homeostasis. Here, we identified a novel MC4R-interacting protein, glucose-regulated protein 78 (GRP78), from a pulldown assay using hypothalamic protein extracts and the third intracellular loop of MC4R. We found that MC4R interacted with GRP78 in both the cytosol and at the cell surface and that this interaction increased when MC4R was internalized in the presence of the agonist melanotan-II (MTII). Downregulation of GRP78 using a short interfering RNA approach attenuated MTII-mediated receptor internalization. Reduction in GRP78 expression during tunicamycin-induced endoplasmic reticulum stress also suppressed MTII-mediated internalization of MC4R and cAMP-mediated transcriptional activity. Furthermore, lentiviral-mediated short hairpin RNA knockdown of endogenous GRP78 in the paraventricular nucleus (PVN) of the hypothalamus resulted in an increase in body weight in mice fed a high-fat diet. These results suggest that GRP78 in the PVN binds to MC4R and may have a chaperone-like role in the regulation of MC4R trafficking and signaling. Show less

Liver X receptor alpha (LXRα), a member of the nuclear receptor superfamily, plays a pivotal role in hepatic cholesterol and lipid metabolism, regulating the expression of genes associated with hepatic lipogenesis. The additional sex comb-like (ASXL) family was postulated to regulate chromatin function. Here, we investigate the roles of ASXL1 and ASXL2 in regulating LXRα activity. We found that ASXL1 suppressed ligand-induced LXRα transcriptional activity, whereas ASXL2 increased LXRα activity through direct interaction in the presence of the ligand. Chromatin immunoprecipitation (ChIP) assays showed ligand-dependent recruitment of ASXLs to ABCA1 promoters, like LXRα. Knockdown studies indicated that ASXL1 inhibits, while ASXL2 increases, lipid accumulation in H4IIE cells, similar to their roles in transcriptional regulation. We also found that ASXL1 expression increases under fasting conditions, and decreases in insulin-treated H4IIE cells and the livers of high-fat diet-fed mice. Overall, these results support the reciprocal role of the ASXL family in lipid homeostasis through the opposite regulation of LXRα. Show less

The glucagon (GCG) peptide family consists of GCG, glucagon-like peptide 1 (GLP1), and GLP2, which are derived from a common GCG precursor, and the glucose-dependent insulinotropic polypeptide (GIP). These peptides interact with cognate receptors, GCGR, GLP1R, GLP2R, and GIPR, which belong to the secretin-like G protein-coupled receptor (GPCR) family. We used bioinformatics to identify genes encoding a novel GCG-related peptide (GCRP) and its cognate receptor, GCRPR. The GCRP and GCRPR genes were found in representative tetrapod taxa such as anole lizard, chicken, and Xenopus, and in teleosts including medaka, fugu, tetraodon, and stickleback. However, they were not present in mammals and zebrafish. Phylogenetic and genome synteny analyses showed that GCRP emerged through two rounds of whole genome duplication (2R) during early vertebrate evolution. GCRPR appears to have arisen by local tandem gene duplications from a common ancestor of GCRPR, GCGR, and GLP2R after 2R. Biochemical ligand-receptor interaction analyses revealed that GCRP had the highest affinity for GCRPR in comparison to other GCGR family members. Stimulation of chicken, Xenopus, and medaka GCRPRs activated Gαs-mediated signaling. In contrast to chicken and Xenopus GCRPRs, medaka GCRPR also induced Gαq/11-mediated signaling. Chimeric peptides and receptors showed that the K(16)M(17)K(18) and G(16)Q(17)A(18) motifs in GCRP and GLP1, respectively, may at least in part contribute to specific recognition of their cognate receptors through interaction with the receptor core domain. In conclusion, we present novel data demonstrating that GCRP and GCRPR evolved through gene/genome duplications followed by specific modifications that conferred selective recognition to this ligand-receptor pair. Show less

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) play important roles in insulin secretion through their receptors, GLP1R and GIPR. Although GLP-1 and GIP are attractive candidates for treatment of type 2 diabetes and obesity, little is known regarding the molecular interaction of these peptides with the heptahelical core domain of their receptors. These core domains are important not only for specific ligand binding but also for ligand-induced receptor activation. Here, using chimeric and point-mutated GLP1R/GIPR, we determined that evolutionarily conserved amino acid residues such as Ile(196) at transmembrane helix 2, Leu(232) and Met(233) at extracellular loop 1, and Asn(302) at extracellular loop 2 of GLP1R are responsible for interaction with ligand and receptor activation. Application of chimeric GLP-1/GIP peptides together with molecular modeling suggests that His(1) of GLP-1 interacts with Asn(302) of GLP1R and that Thr(7) of GLP-1 has close contact with a binding pocket formed by Ile(196), Leu(232), and Met(233) of GLP1R. This study may provide critical clues for the development of peptide and/or nonpeptide agonists acting at GLP1R. Show less

Glucagon like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretin hormones released in response to food intake and potentiate insulin secretion from pancreatic beta cells through their distinct yet related G protein-coupled receptors, GLP1R and GIPR. While GLP-1 and GIP exhibit similarity in their N-terminal sequence and overall alpha-helical structure, GLP-1 does not bind to GIPR and vice versa. To determine which amino acid residues of these peptide ligands are responsible for specific interaction with their respective receptors, we generated mutant GIP in which several GLP-1-specific amino acid residues were substituted for the original amino acids. The potency of the mutant ligands was examined using HEK293 cells transfected with GLP1R or GIPR expression plasmids together with a cAMP-responsive element-driven luciferase (CRE-luc) reporter plasmid. A mutated GIP peptide in which Tyr(1), Ile(7), Asp(15), and His(18) were replaced by His, Thr, Glu, and Ala, respectively, was able to activate both GLP1R and GIPR with moderate potency. Replacing the original Tyr(1) and/or Ile(7) in the N-terminal moiety of this mutant peptide allowed full activation of GIPR but not of GLP1R. However, reintroducing Asp(15) and/or His(18) in the central alpha-helical region did not significantly alter the ligand potency. These results suggest that Tyr/His(1) and Ile/Thr(7) of GIP/GLP-1 peptides confer differential ligand selectivity toward GIPR and GLP1R. Show less

Although hepatitis B virus X protein (HBx) has been implicated in abnormal lipid metabolism in hepatitis B virus (HBV)-associated hepatic steatosis, its underlying molecular mechanism remains unclear. Liver X receptor (LXR) plays an important role in regulating the expression of genes involved in hepatic lipogenesis. Here we demonstrate that LXRalpha and LXRbeta mediate HBV-associated hepatic steatosis. We have found that HBx induces the expression of LXR and its lipogenic target genes, such as sterol regulatory element binding protein-1c (SREBP-1c), fatty acid synthase (FAS), and peroxisome proliferator-activated receptor, and this is accompanied by the accumulation of lipid droplets. RNA interference with LXR expression decreases the amount of lipid droplets as well as the expression of the lipogenic genes, and this indicates that HBx-induced lipogenesis is LXR-dependent. LXRalpha and HBx colocalize in the nucleus and are physically associated. HBx induces the transactivation function of LXRalpha by recruiting CREB binding protein to the promoter of the target gene. Furthermore, we have observed that expression of LXR is increased in the livers of HBx-transgenic mice. Finally, there is a significant increase in the expression of LXRbeta (P = 0.036), SREBP-1c (P = 0.008), FAS, and stearoyl-coenyzme A desaturase-1 (P = 0.001) in hepatocellular carcinoma (HCC) in comparison with adjacent nontumorous nodules in human HBV-associated HCC specimens. Our results suggest a novel association between HBx and LXR that may represent an important mechanism explaining HBx-induced hepatic lipogenesis during HBV-associated hepatic carcinogenesis. Show less