Honors & Awards
T32 Training Grant, NIH (2019 - 2020)
Dean's Fellowship, School of Medicine, Stanford University (2018)
1st Exemplary Graduate Student Award, University of Florida (2016)
Statewide Graduate Research Symposium (1st Place in Health Science), Florida (2016)
Nominated by Dean in College of Medicine, 1st Annual Graduate Student Appreciation Week Research Day, University of Florida (2016)
41st Medical Guild Competition Award (Silver), University of Florida (2016)
Travel Award, College of Medicine, Office of Research, Graduate Student Council, University of Florida (2016)
Travel Award, University of Florida (2015)
Graduate Scholarship Award, KSEA-GFC (Gainesville Florida Chapter) (2015)
21st Annual Outstanding International Student Award, University of Florida (2015)
Graduate Scholarship Award, KSEA-KUSCO (Korea-U.S. Science Cooperation Center) (2014)
Travel Award, University of Florida (2013)
Boards, Advisory Committees, Professional Organizations
Student/Trainee Member, American Heart Association (AHA) (2017 - 2018)
Graduate Student Member, American Physiological Society (APS) (2016 - 2017)
Bachelor of Engineering, Handong Global University (2001)
Master of Science, Handong Global University (2005)
Doctor of Philosophy, University of Florida (2016)
H+ transport is an integral function of the mitochondrial ADP/ATP carrier
2019; 571 (7766): 515-+
The mitochondrial ADP/ATP carrier (AAC) is a major transport protein of the inner mitochondrial membrane. It exchanges mitochondrial ATP for cytosolic ADP and controls cellular production of ATP. In addition, it has been proposed that AAC mediates mitochondrial uncoupling, but it has proven difficult to demonstrate this function or to elucidate its mechanisms. Here we record AAC currents directly from inner mitochondrial membranes from various mouse tissues and identify two distinct transport modes: ADP/ATP exchange and H+ transport. The AAC-mediated H+ current requires free fatty acids and resembles the H+ leak via the thermogenic uncoupling protein 1 found in brown fat. The ADP/ATP exchange via AAC negatively regulates the H+ leak, but does not completely inhibit it. This suggests that the H+ leak and mitochondrial uncoupling could be dynamically controlled by cellular ATP demand and the rate of ADP/ATP exchange. By mediating two distinct transport modes, ADP/ATP exchange and H+ leak, AAC connects coupled (ATP production) and uncoupled (thermogenesis) energy conversion in mitochondria.
View details for DOI 10.1038/s41586-019-1400-3
View details for Web of Science ID 000477016700061
View details for PubMedID 31341297
View details for PubMedCentralID PMC6662629
Expansion of myeloid-derived suppressor cells with aging in the bone marrow of mice through a NF-?B-dependent mechanism.
2017; 16 (3): 480-487
With aging, there is progressive loss of tissue homeostasis and functional reserve, leading to an impaired response to stress and an increased risk of morbidity and mortality. A key mediator of the cellular response to damage and stress is the transcription factor NF-κB. We demonstrated previously that NF-κB transcriptional activity is upregulated in tissues from both natural aged mice and in a mouse model of a human progeroid syndrome caused by defective repair of DNA damage (ERCC1-deficient mice). We also demonstrated that genetic reduction in the level of the NF-κB subunit p65(RelA) in the Ercc1(-/∆) progeroid mouse model of accelerated aging delayed the onset of age-related pathology including muscle wasting, osteoporosis, and intervertebral disk degeneration. Here, we report that the largest fraction of NF-κB -expressing cells in the bone marrow (BM) of aged (>2 year old) mice (C57BL/6-NF-κB(EGFP) reporter mice) are Gr-1(+) CD11b(+) myeloid-derived suppressor cells (MDSCs). There was a significant increase in the overall percentage of MDSC present in the BM of aged animals compared with young, a trend also observed in the spleen. However, the function of these cells appears not to be compromised in aged mice. A similar increase of MDSC was observed in BM of progeroid Ercc1(-/∆) and BubR1(H/H) mice. The increase in MDSC in Ercc1(-/∆) mice was abrogated by heterozygosity in the p65/RelA subunit of NF-κB. These results suggest that NF-κB activation with aging, at least in part, drives an increase in the percentage of MDSCs, a cell type able to suppress immune cell responses.
View details for DOI 10.1111/acel.12571
View details for PubMedID 28229533
View details for PubMedCentralID PMC5418207
Mitochondrial ATP transporter depletion protects mice against liver steatosis and insulin resistance
Non-alcoholic fatty liver disease (NAFLD) is a common metabolic disorder in obese individuals. Adenine nucleotide translocase (ANT) exchanges ADP/ATP through the mitochondrial inner membrane, and Ant2 is the predominant isoform expressed in the liver. Here we demonstrate that targeted disruption of Ant2 in mouse liver enhances uncoupled respiration without damaging mitochondrial integrity and liver functions. Interestingly, liver specific Ant2 knockout mice are leaner and resistant to hepatic steatosis, obesity and insulin resistance under a lipogenic diet. Protection against fatty liver is partially recapitulated by the systemic administration of low-dose carboxyatractyloside, a specific inhibitor of ANT. Targeted manipulation of hepatic mitochondrial metabolism, particularly through inhibition of ANT, may represent an alternative approach in NAFLD and obesity treatment.
View details for DOI 10.1038/ncomms14477
View details for Web of Science ID 000394226400001
View details for PubMedID 28205519
View details for PubMedCentralID PMC5316896
Macrophage-released ADAMTS1 promotes muscle stem cell activation.
2017; 8 (1): 669
Coordinated activation of muscle stem cells (known as satellite cells) is critical for postnatal muscle growth and regeneration. The muscle stem cell niche is central for regulating the activation state of satellite cells, but the specific extracellular signals that coordinate this regulation are poorly understood. Here we show that macrophages at sites of muscle injury induce activation of satellite cells via expression of Adamts1. Overexpression of Adamts1 in macrophages in vivo is sufficient to increase satellite cell activation and improve muscle regeneration in young mice. We demonstrate that NOTCH1 is a target of ADAMTS1 metalloproteinase activity, which reduces Notch signaling, leading to increased satellite cell activation. These results identify Adamts1 as a potent extracellular regulator of satellite cell activation and have significant implications for understanding the regulation of satellite cell activity and regeneration after muscle injury.Satellite cells are crucial for growth and regeneration of skeletal muscle. Here the authors show that in response to muscle injury, macrophages secrete Adamts1, which induces satellite cell activation by modulating Notch1 signaling.
View details for PubMedID 28939843
HoxBlinc RNA Recruits Set1/MLL Complexes to Activate Hox Gene Expression Patterns and Mesoderm Lineage Development
2016; 14 (1): 103-114
Trithorax proteins and long-intergenic noncoding RNAs are critical regulators of embryonic stem cell pluripotency; however, how they cooperatively regulate germ layer mesoderm specification remains elusive. We report here that HoxBlinc RNA first specifies Flk1(+) mesoderm and then promotes hematopoietic differentiation through regulation of hoxb pathways. HoxBlinc binds to the hoxb genes, recruits Setd1a/MLL1 complexes, and mediates long-range chromatin interactions to activate transcription of the hoxb genes. Depletion of HoxBlinc by shRNA-mediated knockdown or CRISPR-Cas9-mediated genetic deletion inhibits expression of hoxb genes and other factors regulating cardiac/hematopoietic differentiation. Reduced hoxb expression is accompanied by decreased recruitment of Set1/MLL1 and H3K4me3 modification, as well as by reduced chromatin loop formation. Re-expression of hoxb2-b4 genes in HoxBlinc-depleted embryoid bodies rescues Flk1(+) precursors that undergo hematopoietic differentiation. Thus, HoxBlinc plays an important role in controlling hoxb transcription networks that mediate specification of mesoderm-derived Flk1(+) precursors and differentiation of Flk1(+) cells into hematopoietic lineages.
View details for DOI 10.1016/j.celrep.2015.12.007
View details for Web of Science ID 000367792200010
View details for PubMedID 26725110
View details for PubMedCentralID PMC4706800
Mitochondrial ATP transporter Ant2 depletion impairs erythropoiesis and B lymphopoiesis
CELL DEATH AND DIFFERENTIATION
2015; 22 (9): 1437-1450
Adenine nucleotide translocases (ANTs) transport ADP and ATP through mitochondrial inner membrane, thus playing an essential role for energy metabolism of eukaryotic cells. Mice have three ANT paralogs, Ant1 (Slc25a4), Ant2 (Slc25a5) and Ant4 (Slc25a31), which are expressed in a tissue-dependent manner. While knockout mice have been characterized with Ant1 and Ant4 genes, which resulted in exercise intolerance and male infertility, respectively, the role of the ubiquitously expressed Ant2 gene in animal development has not been fully demonstrated. Here, we generated Ant2 hypomorphic mice by targeted disruption of the gene, in which Ant2 expression is largely depleted. The mice showed apparently normal embryonic development except pale phenotype along with a reduced birth rate. However, postnatal growth was severely retarded with macrocytic anemia, B lymphocytopenia, lactic acidosis and bloated stomach, and died within 4 weeks. Ant2 depletion caused anemia in a cell-autonomous manner by maturation arrest of erythroid precursors with increased reactive oxygen species and premature deaths. B-lymphocyte development was similarly affected by Ant2 depletion, and splenocytes showed a reduction in maximal respiration capacity and cellular ATP levels as well as an increase in cell death accompanying mitochondrial permeability transition pore opening. In contrast, myeloid, megakaryocyte and T-lymphocyte lineages remained apparently intact. Erythroid and B-cell development may be particularly vulnerable to Ant2 depletion-mediated mitochondrial dysfunction and oxidative stress.
View details for DOI 10.1038/cdd.2014.230
View details for Web of Science ID 000359295300005
View details for PubMedID 25613378
View details for PubMedCentralID PMC4532771
Purinergic P2Y(14) receptor modulates stress-induced hematopoietic stem/progenitor cell senescence
JOURNAL OF CLINICAL INVESTIGATION
2014; 124 (7): 3159-3171
Purinergic receptors of the P2Y family are G protein-coupled surface receptors that respond to extracellular nucleotides and can mediate responses to local cell damage. P2Y-dependent signaling contributes to thrombotic and/or inflammatory consequences of tissue injury by altering platelet and endothelial activation and immune cell phagocytosis. Here, we have demonstrated that P2Y14 modifies cell senescence and cell death in response to tissue stress, thereby enabling preservation of hematopoietic stem/progenitor cell function. In mice, P2Y14 deficiency had no demonstrable effect under homeostatic conditions; however, radiation stress, aging, sequential exposure to chemotherapy, and serial bone marrow transplantation increased senescence in animals lacking P2Y14. Enhanced senescence coincided with increased ROS, elevated p16(INK4a) expression, and hypophosphorylated Rb and was inhibited by treatment with a ROS scavenger or inhibition of p38/MAPK and JNK. Treatment of WT cells with pertussis toxin recapitulated the P2Y14 phenotype, suggesting that P2Y14 mediates antisenescence effects through Gi/o protein-dependent pathways. Primitive hematopoietic cells lacking P2Y14 were compromised in their ability to restore hematopoiesis in irradiated mice. Together, these data indicate that P2Y14 on stem/progenitor cells of the hematopoietic system inhibits cell senescence by monitoring and responding to the extracellular manifestations of tissue stress and suggest that P2Y14-mediated responses prevent the premature decline of regenerative capacity after injury.
View details for DOI 10.1172/JCI61636
View details for Web of Science ID 000338688400038
View details for PubMedID 24937426
View details for PubMedCentralID PMC4071372
The nucleotide sugar UDP-glucose mobilizes long-term repopulating primitive hematopoietic cells
JOURNAL OF CLINICAL INVESTIGATION
2013; 123 (8): 3420-3435
Hematopoietic stem progenitor cells (HSPCs) are present in very small numbers in the circulating blood in steady-state conditions. In response to stress or injury, HSPCs are primed to migrate out of their niche to peripheral blood. Mobilized HSPCs are now commonly used as stem cell sources due to faster engraftment and reduced risk of posttransplant infection. In this study, we demonstrated that a nucleotide sugar, UDP-glucose, which is released into extracellular fluids in response to stress, mediates HSPC mobilization. UDP-glucose-mobilized cells possessed the capacity to achieve long-term repopulation in lethally irradiated animals and the ability to differentiate into multi-lineage blood cells. Compared with G-CSF-mobilized cells, UDP-glucose-mobilized cells preferentially supported long-term repopulation and exhibited lymphoid-biased differentiation, suggesting that UDP-glucose triggers the mobilization of functionally distinct subsets of HSPCs. Furthermore, co-administration of UDP-glucose and G-CSF led to greater HSPC mobilization than G-CSF alone. Administration of the antioxidant agent NAC significantly reduced UDP-glucose-induced mobilization, coinciding with a reduction in RANKL and osteoclastogenesis. These findings provide direct evidence demonstrating a potential role for UDP-glucose in HSPC mobilization and may provide an attractive strategy to improve the yield of stem cells in poor-mobilizing allogeneic or autologous donors.
View details for DOI 10.1172/JCI64060
View details for Web of Science ID 000322750500026
View details for PubMedID 23863713
View details for PubMedCentralID PMC3726149
The purinergic P2Y(14) receptor axis is a molecular determinant for organism survival under in utero radiation toxicity
CELL DEATH & DISEASE
In utero exposure of the embryo and fetus to radiation has been implicated in malformations or fetal death, and often produces lifelong health consequences such as cancers and mental retardation. Here we demonstrate that deletion of a G-protein-coupled purinergic receptor, P2Y14, confers potent resistance to in utero radiation. Intriguingly, a putative P2Y14 receptor ligand, UDP-glucose, phenocopies the effect of P2Y14 deficiency. These data indicate that P2Y14 is a receptor governing in utero tolerance to genotoxic stress that may be pharmacologically targeted to mitigate radiation toxicity in pregnancy.
View details for DOI 10.1038/cddis.2013.218
View details for Web of Science ID 000322512100004
View details for PubMedID 23828566
View details for PubMedCentralID PMC3730399
- Cytotoxicity of recombinant immunotoxin containing lectin A chain from Korean mistletoe MOLECULAR & CELLULAR TOXICOLOGY 2013; 9 (1): 29–36
Cell Autonomous and Nonautonomous Mechanisms Drive Hematopoietic Stem/progenitor Cell Loss in the Absence of DNA Repair
2013; 31 (3): 511-525
Daily, cells incur tens of thousands of DNA lesions caused by endogenous processes. Due to their long-lived nature, adult stem cells may be particularly susceptible to the negative impact of this constant genotoxic stress. Indeed, in murine models of DNA repair deficiencies, there is accumulation of DNA damage in hematopoietic stem cells and premature loss of function. Herein, we demonstrate that mice expressing reduced levels of ERCC1-XPF DNA repair endonuclease (Ercc1-/Δ mice) spontaneously display a progressive decline in the number and function of hematopoietic stem/progenitor cells (HSPCs). This was accompanied by increased cell death, expression of senescence markers, reactive oxygen species, and DNA damage in HSPC populations, illustrating cell autonomous mechanisms that contribute to loss of function. In addition, the bone marrow microenvironment of Ercc1-/Δ mice was not permissive for the engraftment of transplanted normal stem cells. Bones from Ercc1-/Δ mice displayed excessive osteoclastic activity, which alters the microenvironment in a way that is unfavorable to HSPC maintenance. This was accompanied by increased proinflammatory cytokines in the bone marrow of Ercc1-/Δ mice. These data provide novel evidence that spontaneous, endogenous DNA damage, if not repaired, promotes progressive attrition of adult stem cells via both cell autonomous and nonautonomous mechanisms.
View details for DOI 10.1002/stem.1261
View details for Web of Science ID 000315412900010
View details for PubMedID 23097336
View details for PubMedCentralID PMC3582850
Ewing sarcoma gene Ews regulates hematopoietic stem cell senescence
2011; 117 (4): 1156-1166
The longevity of organisms is maintained by stem cells. If an organism loses the ability to maintain a balance between quiescence and differentiation in the stem/progenitor cell compartment due to aging and/or stress, this may result in death or age-associated diseases, including cancer. Ewing sarcoma is the most lethal bone tumor in young patients and arises from primitive stem cells. Here, we demonstrated that endogenous Ewing sarcoma gene (Ews) is indispensable for stem cell quiescence, and that the ablation of Ews promotes the early onset of senescence in hematopoietic stem progenitor cells. The phenotypic and functional changes in Ews-deficient stem cells were accompanied by an increase in senescence-associated β-galactosidase staining and a marked induction of p16(INK4a) compared with wild-type counterparts. With its relevance to cancer and possibly aging, EWS is likely to play a significant role in maintaining the functional capacity of stem cells and may provide further insight into the complexity of Ewing sarcoma in the context of stem cells.
View details for DOI 10.1182/blood-2010-04-279349
View details for Web of Science ID 000286623400013
View details for PubMedID 21030557
View details for PubMedCentralID PMC3056469