Assistant Professor - University Medical Line, Pediatrics - Neonatal and Developmental Medicine
Member, Wu Tsai Neurosciences Institute
Honors & Awards
Inaugural Bhatt-Ramanathan Scholarship Award, California Association of Neonatologists (CAN)
2017 STAT Wunderkinds Award, STAT News
Pediatric Scientist Development Program Award, The Association of Medical School Pediatric Department Chairs (AMSPDC)
Bechtel Endowed Fellow in Pediatric Translational Medicine, Child Health Research Institute, Stanford University
Board Certification: American Board of Pediatrics, Pediatrics (2019)
Fellowship: Stanford University Neonatology Fellowship (2018) CA
Residency: Stanford University Hospital and Clinics, Lucile Packard Children's Hospital (2013) CA
Medical Education: Iuliu Hatieganu University of Medicine (2007) Romania
Neonatology Fellowship, Lucile Packard Children's Hospital, Stanford University, Neonatology (2018)
PSDP Scholar, Lucile Packard Children's Hospital, Stanford University, Perinatal Brain Development (2016)
Board Certification, Pediatrics, American Board of Pediatrics (2013)
Pediatrics Residency, Lucile Packard Children's Hospital, Stanford University, Pediatrics (2013)
Pediatrics Internship, Lucile Packard Children's Hospital, Stanford University, Pediatrics (2011)
ECFMG Certification, Educational Commission for Foreign Medical Graduates, Medicine (2009)
M.D., Iuliu Hatieganu University of Medicine and Pharmacy, Romania, Medicine (2007)
Current Research and Scholarly Interests
The research focus of the lab is to understand molecular mechanisms underlying neurodevelopmental disorders associated with premature birth, neonatal and fetal brain injury with the long-term goal of translating the lab’s findings into therapeutics. The research team employs a multidisciplinary approach involving genetics, molecular and developmental neurobiology, animal models and neural cells differentiated from patient-derived induced pluripotent stem (iPS) cells. In particular, the lab is using a powerful 3D human brain-region specific organoid system developed at Stanford (Nature Methods, 2015; Nature Protocols, 2018) to ask questions about brain injury during development.
Independent Studies (1)
- Undergraduate Directed Reading/Research
PEDS 199 (Aut, Win, Spr)
- Undergraduate Directed Reading/Research
Postdoctoral Faculty Sponsor
Jong Bin Choi, Yusuke Hori, Li Li, Dhriti Nagar
Graduate and Fellowship Programs
Anatomical and functional maturation of the mid-gestation human enteric nervous system.
2023; 14 (1): 2680
Immature gastrointestinal motility impedes preterm infant survival. The enteric nervous system controls gastrointestinal motility, yet it is unknown when the human enteric nervous system matures enough to carry out vital functions. Here we demonstrate that the second trimester human fetal enteric nervous system takes on a striped organization akin to the embryonic mouse. Further, we perform ex vivo functional assays of human fetal tissue and find that human fetal gastrointestinal motility matures in a similar progression to embryonic mouse gastrointestinal motility. Together, this provides critical knowledge, which facilitates comparisons with common animal models to advance translational disease investigations and testing of pharmacological agents to enhance gastrointestinal motility in prematurity.
View details for DOI 10.1038/s41467-023-38293-z
View details for PubMedID 37160892
View details for PubMedCentralID PMC10170115
Single-cell transcriptomic landscape of the developing human spinal cord.
Understanding spinal cord assembly is essential to elucidate how motor behavior is controlled and how disorders arise. The human spinal cord is exquisitely organized, and this complex organization contributes to the diversity and intricacy of motor behavior and sensory processing. But how this complexity arises at the cellular level in the human spinal cord remains unknown. Here we transcriptomically profiled the midgestation human spinal cord with single-cell resolution and discovered remarkable heterogeneity across and within cell types. Glia displayed diversity related to positional identity along the dorso-ventral and rostro-caudal axes, while astrocytes with specialized transcriptional programs mapped into white and gray matter subtypes. Motor neurons clustered at this stage into groups suggestive of alpha and gamma neurons. We also integrated our data with multiple existing datasets of the developing human spinal cord spanning 22 weeks of gestation to investigate the cell diversity over time. Together with mapping of disease-related genes, this transcriptomic mapping of the developing human spinal cord opens new avenues for interrogating the cellular basis of motor control in humans and guides human stem cell-based models of disease.
View details for DOI 10.1038/s41593-023-01311-w
View details for PubMedID 37095394
View details for PubMedCentralID 8353162
Carnitine octanoyltransferase is important for the assimilation of exogenous acetyl-L-carnitine into acetyl-CoA in mammalian cells.
The Journal of biological chemistry
In eukaryotes carnitine is best known for its ability to shuttle esterified fatty acids across mitochondrial membranes for β-oxidation. It also returns to the cytoplasm, in the form of acetyl-L-carnitine (LAC), some of the resulting acetyl groups for post-translational protein modification and lipid biosynthesis. While dietary LAC supplementation has been clinically investigated, its effects on cellular metabolism are not well understood. To explain how exogenous LAC influences mammalian cell metabolism, we synthesized isotope-labeled forms of LAC and its analogs. In cultures of glucose-limited U87MG glioma cells, exogenous LAC contributed more robustly to intracellular acetyl-CoA pools than did β-hydroxybutyrate, the predominant circulating ketone body in mammals. The fact that most LAC-derived acetyl-CoA is cytosolic is evident from strong labeling of fatty acids in U87MG cells by exogenous 13C2-acetyl-L-carnitine. We found that the addition of d3-acetyl-L-carnitine increases the supply of acetyl-CoA for cytosolic post-translational modifications due to its strong kinetic isotope effect on acetyl-CoA carboxylase, the first committed step in fatty acid biosynthesis. Surprisingly, whereas cytosolic carnitine acetyltransferase (CRAT) is believed to catalyze acetyl group transfer from LAC to Coenzyme A, CRAT-/- U87MG cells were unimpaired in their ability to assimilate exogenous LAC into acetyl-CoA. We identified carnitine octanoyltransferase (CROT) as the key enzyme in this process, implicating a role for peroxisomes in efficient LAC utilization. Our work has opened the door to further biochemical investigations of a new pathway for supplying acetyl-CoA to certain glucose-starved cells.
View details for DOI 10.1016/j.jbc.2022.102848
View details for PubMedID 36587768
Perinatal infection, inflammation, preterm birth, and brain injury: A review with proposals for future investigations.
Preterm newborns are exposed to several risk factors for developing brain injury. Clinical studies have suggested that the presence of intrauterine infection is a consistent risk factor for preterm birth and white matter injury. Animal models have confirmed these associations by identifying inflammatory cascades originating at the maternofetal interface that penetrate the fetal blood-brain barrier and result in brain injury. Acquired diseases of prematurity further potentiate the risk for cerebral injury. Systems biology approaches incorporating ante- and post-natal risk factors and analyzing omic and multiomic data using machine learning are promising methodologies for further elucidating biologic mechanisms of fetal and neonatal brain injury.
View details for DOI 10.1016/j.expneurol.2022.113988
View details for PubMedID 35081400
Dissecting the molecular basis of human interneuron migration in forebrain assembloids from Timothy syndrome.
Cell stem cell
Defects in interneuron migration can disrupt the assembly of cortical circuits and lead to neuropsychiatric disease. Using forebrain assembloids derived by integration of cortical and ventral forebrain organoids, we have previously discovered a cortical interneuron migration defect in Timothy syndrome (TS), a severe neurodevelopmental disease caused by a mutation in the L-type calcium channel (LTCC) Cav1.2. Here, we find that acute pharmacological modulation of Cav1.2 can regulate the saltation length, but not the frequency, of interneuron migration in TS. Interestingly, the defect in saltation length is related to aberrant actomyosin and myosin light chain (MLC) phosphorylation, while the defect in saltation frequency is driven by enhanced γ-aminobutyric acid (GABA) sensitivity and can be restored by GABA-A receptor antagonism. Finally, we describe hypersynchronous hCS network activity in TS that is exacerbated by interneuron migration. Taken together, these studies reveal a complex role of LTCC function in human cortical interneuron migration and strategies to restore deficits in the context of disease.
View details for DOI 10.1016/j.stem.2021.11.011
View details for PubMedID 34990580
Chromatin and gene-regulatory dynamics of the developing human cerebral cortex at single-cell resolution.
Genetic perturbations of cortical development can lead to neurodevelopmental disease, including autism spectrum disorder (ASD). To identify genomic regions crucial to corticogenesis, we mapped the activity of gene-regulatory elements generating a single-cell atlas of gene expression and chromatin accessibility both independently and jointly. This revealed waves of gene regulation by key transcription factors (TFs) across a nearly continuous differentiation trajectory, distinguished the expression programs of glial lineages, and identified lineage-determining TFs that exhibited strong correlation between linked gene-regulatory elements and expression levels. These highly connected genes adopted an active chromatin state in early differentiating cells, consistent with lineage commitment. Base-pair-resolution neural network models identified strong cell-type-specific enrichment of noncoding mutations predicted to be disruptive in a cohort of ASD individuals and identified frequently disrupted TF binding sites. This approach illustrates how cell-type-specific mapping can provide insights into the programs governing human development and disease.
View details for DOI 10.1016/j.cell.2021.07.039
View details for PubMedID 34390642
The CD22-IGF2R interaction is a therapeutic target for microglial lysosome dysfunction in Niemann-Pick type C.
Science translational medicine
2021; 13 (622): eabg2919
[Figure: see text].
View details for DOI 10.1126/scitranslmed.abg2919
View details for PubMedID 34851695
Increased Tau Expression Correlates with Neuronal Maturation in the Developing Human Cerebral Cortex.
Although best known for its role in Alzheimer disease, tau is expressed throughout brain development, though it remains unclear when and which cell types this expression occurs and how it affects disease states in both fetal and neonatal periods. We thus sought to map tau mRNA and protein expression in the developing human brain at the cellular level using a combination of existing single cell RNA sequencing (sc-RNAseq) data, RNA in situ hybridization (RNAscope), and immunohistochemistry (IHC). Using sc-RNAseq, we found that tau mRNA expression begins in radial glia but increases dramatically as migrating neuronal precursors mature. Specifically, TBR1+ maturing neurons and SYN+ mature neurons showed significantly higher mRNA expression than GFAP+/NES+ radial glia or TBR2+ intermediate progenitors. By RNAscope, we found low levels of tau mRNA in subventricular zone radial glia and deep white matter intermediate progenitors, with an increase in more superficially located maturing and mature neurons. By total-tau IHC, the germinal matrix and subventricular zone showed little protein expression, although both RNAscope and sc-RNAseq showed mRNA, and western blotting revealed significantly less protein in those areas compared with more mature regions. Induced pluripotent stem cell (iPSC)-derived cortical organoids showed a similar tau expression pattern by sc-RNAseq and RNAscope. Our results indicate that tau increases with neuronal maturation in both the developing fetal brain and iPSC-derived organoids and forms a basis for future research on regulatory mechanisms triggering the onset of tau gene transcription and translation, which may represent potential therapeutic targets for neurodegenerative tauopathies and neurodevelopmental disorders.Significance Statement Tau is a mediator of neurotoxicity across multiple neurodegenerative diseases, including Alzheimer disease and chronic traumatic encephalopathy. With the recent failure of β-amyloid-targeted therapies in AD to improve cognitive function, there is increasing interest in tau targeted therapies. Tau is expressed throughout brain development, but the function and normal developmental expression remains unclear. Here, we demonstrate that tau expression begins early during neuronal maturation in both human fetal brain and iPSC-derived cortical organoids. This work forms the basis for future research into the developmental regulation of tau expression which may provide future tau-related therapeutic targets.
View details for DOI 10.1523/ENEURO.0058-20.2020
View details for PubMedID 32393582
Human 3D cellular model of hypoxic brain injury of prematurity
2019; 25 (5): 784-+
View details for DOI 10.1038/s41591-019-0436-0
View details for Web of Science ID 000468247800022
Human 3D cellular model of hypoxic brain injury of prematurity.
Owing to recent medical and technological advances in neonatal care, infants born extremely premature have increased survival rates1,2. After birth, these infants are at high risk of hypoxic episodes because of lung immaturity, hypotension and lack of cerebral-flow regulation, and can develop a severe condition called encephalopathy of prematurity3. Over 80% of infants born before post-conception week 25 have moderate-to-severe long-term neurodevelopmental impairments4. The susceptible cell types in the cerebral cortex and the molecular mechanisms underlying associated gray-matter defects in premature infants remain unknown. Here we used human three-dimensional brain-region-specific organoids to study the effect of oxygen deprivation on corticogenesis. We identified specific defects in intermediate progenitors, a cortical cell type associated with the expansion of the human cerebral cortex, and showed that these are related to the unfolded protein response and changes. Moreover, we verified these findings in human primary cortical tissue and demonstrated that a small-molecule modulator of the unfolded protein response pathway can prevent the reduction in intermediate progenitors following hypoxia. We anticipate that this human cellular platform will be valuable for studying the environmental and genetic factors underlying injury in the developing human brain.
View details for PubMedID 31061540
Reliability of human cortical organoid generation
2019; 16 (1): 75-+
View details for DOI 10.1038/s41592-018-0255-0
View details for Web of Science ID 000454162400033
Reliability of human cortical organoid generation.
2019; 16 (1): 75–78
The differentiation of pluripotent stem cells in three-dimensional cultures can recapitulate key aspects of brain development, but protocols are prone to variable results. Here we differentiated multiple human pluripotent stem cell lines for over 100 d using our previously developed approach to generate brain-region-specific organoids called cortical spheroids and, using several assays, found that spheroid generation was highly reliable and consistent. We anticipate the use of this approach for large-scale differentiation experiments and disease modeling.
View details for PubMedID 30573846
Generation and assembly of human brain region-specific three-dimensional cultures.
The ability to generate region-specific three-dimensional (3D) models to study human brain development offers great promise for understanding the nervous system in both healthy individuals and patients. In this protocol, we describe how to generate and assemble subdomain-specific forebrain spheroids, also known as brain region-specific organoids, from human pluripotent stem cells (hPSCs). We describe how to pattern the neural spheroids toward either a dorsal forebrain or a ventral forebrain fate, establishing human cortical spheroids (hCSs) and human subpallial spheroids (hSSs), respectively. We also describe how to combine the neural spheroids in vitro to assemble forebrain assembloids that recapitulate the interactions of glutamatergic and GABAergic neurons seen in vivo. Astrocytes are also present in the human forebrain-specific spheroids, and these undergo maturation when the forebrain spheroids are cultured long term. The initial generation of neural spheroids from hPSCs occurs in <1 week, with regional patterning occurring over the subsequent 5 weeks. After the maturation stage, brain region-specific spheroids are amenable to a variety of assays, including live-cell imaging, calcium dynamics, electrophysiology, cell purification, single-cell transcriptomics, and immunohistochemistry studies. Once generated, forebrain spheroids can also be matured for >24 months in culture.
View details for PubMedID 30202107
Functional cortical neurons and astrocytes from human pluripotent stem cells in 3D cultures.
The human cerebral cortex develops through an elaborate succession of cellular events that, when disrupted, can lead to neuropsychiatric disease. The ability to reprogram somatic cells into pluripotent cells that can be differentiated in vitro provides a unique opportunity to study normal and abnormal corticogenesis. Here, we present a simple and reproducible 3D culture approach for generating a laminated cerebral cortex-like structure, named human cortical spheroids (hCSs), from pluripotent stem cells. hCSs contain neurons from both deep and superficial cortical layers and map transcriptionally to in vivo fetal development. These neurons are electrophysiologically mature, display spontaneous activity, are surrounded by nonreactive astrocytes and form functional synapses. Experiments in acute hCS slices demonstrate that cortical neurons participate in network activity and produce complex synaptic events. These 3D cultures should allow a detailed interrogation of human cortical development, function and disease, and may prove a versatile platform for generating other neuronal and glial subtypes in vitro.
View details for DOI 10.1038/nmeth.3415
View details for PubMedCentralID PMC4489980
PLACENTAL HORMONE CONTRIBUTION TO FETAL BRAIN DAMAGE
Joint Meeting of the International-Federation-of-Placenta-Associations (IFPA) and European-Placenta-Group (EPG)
W B SAUNDERS CO LTD. 2014: A52–A52
View details for Web of Science ID 000342961400184
Neonatal CSF oxytocin levels are associated with parent report of infant soothability and sociability.
2013; 38 (7): 1208-1212
Oxytocin (OT) has been linked to social behavior in rodents, non-human primates, and adult humans, but almost nothing is known about brain OT activity in human newborns or its impact on social development. To better understand the role of OT biology in human social functioning, a multi-disciplinary, longitudinal study was conducted. Cerebral spinal fluid (CSF) OT levels from 18 human neonates were evaluated and examined in relationship to social-seeking behavior at term, at 3 months, and at 6 months of age. Higher neonatal CSF OT levels were consistently associated with solicitation of parental soothing and interest in social engagement with others. This is the first study to link CSF OT levels to normative human social functioning. Research is now required to test whether early OT levels serve as a biomarker for subsequent social abnormalities.
View details for DOI 10.1016/j.psyneuen.2012.10.017
View details for PubMedID 23507187
Using iPSC-derived neurons to uncover cellular phenotypes associated with Timothy syndrome
2011; 17 (12): 1657-U176
Monogenic neurodevelopmental disorders provide key insights into the pathogenesis of disease and help us understand how specific genes control the development of the human brain. Timothy syndrome is caused by a missense mutation in the L-type calcium channel Ca(v)1.2 that is associated with developmental delay and autism. We generated cortical neuronal precursor cells and neurons from induced pluripotent stem cells derived from individuals with Timothy syndrome. Cells from these individuals have defects in calcium (Ca(2+)) signaling and activity-dependent gene expression. They also show abnormalities in differentiation, including decreased expression of genes that are expressed in lower cortical layers and in callosal projection neurons. In addition, neurons derived from individuals with Timothy syndrome show abnormal expression of tyrosine hydroxylase and increased production of norepinephrine and dopamine. This phenotype can be reversed by treatment with roscovitine, a cyclin-dependent kinase inhibitor and atypical L-type-channel blocker. These findings provide strong evidence that Ca(v)1.2 regulates the differentiation of cortical neurons in humans and offer new insights into the causes of autism in individuals with Timothy syndrome.
View details for DOI 10.1038/nm.2576
View details for PubMedID 22120178
Using induced pluripotent stem cells to investigate cardiac phenotypes in Timothy syndrome
2011; 471 (7337): 230-U120
Individuals with congenital or acquired prolongation of the QT interval, or long QT syndrome (LQTS), are at risk of life-threatening ventricular arrhythmia. LQTS is commonly genetic in origin but can also be caused or exacerbated by environmental factors. A missense mutation in the L-type calcium channel Ca(V)1.2 leads to LQTS in patients with Timothy syndrome. To explore the effect of the Timothy syndrome mutation on the electrical activity and contraction of human cardiomyocytes, we reprogrammed human skin cells from Timothy syndrome patients to generate induced pluripotent stem cells, and differentiated these cells into cardiomyocytes. Electrophysiological recording and calcium (Ca(2+)) imaging studies of these cells revealed irregular contraction, excess Ca(2+) influx, prolonged action potentials, irregular electrical activity and abnormal calcium transients in ventricular-like cells. We found that roscovitine, a compound that increases the voltage-dependent inactivation of Ca(V)1.2 (refs 6-8), restored the electrical and Ca(2+) signalling properties of cardiomyocytes from Timothy syndrome patients. This study provides new opportunities for studying the molecular and cellular mechanisms of cardiac arrhythmias in humans, and provides a robust assay for developing new drugs to treat these diseases.
View details for DOI 10.1038/nature09855
View details for PubMedID 21307850
- The Placenta: The Lost Neuroendocrine Organ Neoreviews 2010; 11 (2)