I am a physician-scientist in the Division of Gastroenterology at Stanford University. My clinical and research interest has been in neurogastroenterology. Specifically, my research has been exploring the interplay between immune cells and the enteric nervous system, and evaluating how perturbations of this interaction as a result of aging disrupts gastrointestinal neuromuscular function. Ultimately, my hope is that insights from this research provide novel therapies for treating patients with motility disorders like constipation and irritable bowel syndrome.
Clinical Instructor, Medicine - Gastroenterology & Hepatology
Instructor in Medicine, Stanford University (2009 - Present)
Clinical and Research Fellow in Gastroenterology, Beth Israel Deaconess, Harvard Medical School (2005 - 2009)
Honors & Awards
GEMSSTAR Scholar, NIA/NIH (2013-2015)
Neurogastroenterology & Motility Distinguished Abstract Plenary, DDW (2013)
Fellowship to Faculty Transition Award, AGA (2012)
Albert Einstein College of Medicine Medical Scientist Training Program, MSTP (1994)
Golden Key National Honor Society, University of California, Berkeley (1994)
Phi Beta Kappa, University of California, Berkeley (1994)
Boards, Advisory Committees, Professional Organizations
Member, American Gastroenterologic Association (2005 - Present)
Medical Education: Albert Einstein College of Medicine (2002) NY
Fellowship: Beth Israel Deaconess Medical Center Dept of Gastroenterology (2009) MA
Residency: Beth Israel Deaconess Medical Center Internal Medicine Residency (2005) MA
Board Certification: Gastroenterology, American Board of Internal Medicine (2009)
Graduate and Fellowship Programs
Gastroenterology & Hepatology (Fellowship Program)
Dysbiosis-Induced Secondary Bile Acid Deficiency Promotes Intestinal Inflammation.
Cell host & microbe
Secondary bile acids (SBAs) are derived from primary bile acids (PBAs) in a process reliant on biosynthetic capabilities possessed by few microbes. To evaluate the role of BAs in intestinal inflammation, we performed metabolomic, microbiome, metagenomic, and transcriptomic profiling of stool from ileal pouches (surgically created resevoirs) in colectomy-treated patients with ulcerative colitis (UC) versus controls (familial adenomatous polyposis [FAP]). We show that relative to FAP, UC pouches have reduced levels of lithocholic acid and deoxycholic acid (normally the most abundant gut SBAs), genes required to convert PBAs to SBAs, and Ruminococcaceae (one of few taxa known to include SBA-producing bacteria). In three murine colitis models, SBA supplementation reduces intestinal inflammation. This anti-inflammatory effect is in part dependent on the TGR5 bile acid receptor. These data suggest that dysbiosis induces SBA deficiency in inflammatory-prone UC patients, which promotes a pro-inflammatory state within the intestine that may be treated by SBA restoration.
View details for DOI 10.1016/j.chom.2020.01.021
View details for PubMedID 32101703
Mass cytometry reveals systemic and local immune signatures that distinguish inflammatory bowel diseases.
2019; 10 (1): 2686
Inflammatory bowel disease (IBD) includes Crohn's disease and ulcerative colitis. Each disease is characterized by a diverse set of potential manifestations, which determine patients' disease phenotype. Current understanding of phenotype determinants is limited, despite increasing prevalence and healthcare costs. Diagnosis and monitoring of disease requires invasive procedures, such as endoscopy and tissue biopsy. Here we report signatures of heterogeneity between disease diagnoses and phenotypes. Using mass cytometry, we analyze leukocyte subsets, characterize their function(s), and examine gut-homing molecule expression in blood and intestinal tissue from healthy and/or IBD subjects. Some signatures persist in IBD despite remission, and many signatures are highly represented by leukocytes that express gut trafficking molecules. Moreover, distinct systemic and local immune signatures suggest patterns of cell localization in disease. Our findings highlight the importance of gut tropic leukocytes in circulation and reveal that blood-based immune signatures differentiate clinically relevant subsets of IBD.
View details for DOI 10.1038/s41467-019-10387-7
View details for PubMedID 31217423
Age-Related Changes inGut Microbiota AlterPhenotype of Muscularis Macrophages and Disrupt Gastrointestinal Motility.
Cellular and molecular gastroenterology and hepatology
2019; 7 (1): 243
View details for PubMedID 30585161
Advances in Enteric Neurobiology: The "Brain" in the Gut in Health and Disease.
The Journal of neuroscience : the official journal of the Society for Neuroscience
2018; 38 (44): 9346–54
The enteric nervous system (ENS) is a large, complex division of the peripheral nervous system that regulates many digestive, immune, hormonal, and metabolic functions. Recent advances have elucidated the dynamic nature of the mature ENS, as well as the complex, bidirectional interactions among enteric neurons, glia, and the many other cell types that are important for mediating gut behaviors. Here, we provide an overview of ENS development and maintenance, and focus on the latest insights gained from the use of novel model systems and live-imaging techniques. We discuss major advances in the understanding of enteric glia, and the functional interactions among enteric neurons, glia, and enteroendocrine cells, a large class of sensory epithelial cells. We conclude by highlighting recent work on muscularis macrophages, a group of immune cells that closely interact with the ENS in the gut wall, and the importance of neurological-immune system communication in digestive health and disease.
View details for PubMedID 30381426
Multi-Organ RNA-Sequencing of Patients with Systemic Sclerosis (SSc) Finds That Intrinsic Subsets Are Conserved across Organ Systems
View details for Web of Science ID 000447268902203
Identification of Risk Factors for Gastric Antral Vascular Ectasia (GAVE) Among Systemic Sclerosis Patients
View details for Web of Science ID 000447268901344
DNA methylation, through DNMT1, has an essential role in the development of gastrointestinal smooth muscle cells and disease
CELL DEATH & DISEASE
2018; 9: 474
DNA methylation is a key epigenetic modification that can regulate gene expression. Genomic DNA hypomethylation is commonly found in many gastrointestinal (GI) diseases. Dysregulated gene expression in GI smooth muscle cells (GI-SMCs) can lead to motility disorders. However, the consequences of genomic DNA hypomethylation within GI-SMCs are still elusive. Utilizing a Cre-lox murine model, we have generated SMC-restricted DNA methyltransferase 1 (Dnmt1) knockout (KO) mice and analyzed the effects of Dnmt1 deficiency. Dnmt1-KO pups are born smaller than their wild-type littermates, have shortened GI tracts, and lose peristaltic movement due to loss of the tunica muscularis in their intestine, causing massive intestinal dilation, and death around postnatal day 21. Within smooth muscle tissue, significant CpG hypomethylation occurs across the genome at promoters, introns, and exons. Additionally, there is a marked loss of differentiated SMC markers (Srf, Myh11, miR-133, miR-143/145), an increase in pro-apoptotic markers (Nr4a1, Gadd45g), loss of cellular connectivity, and an accumulation of coated vesicles within SMC. Interestingly, we observed consistent abnormal expression patterns of enzymes involved in DNA methylation between both Dnmt1-KO mice and diseased human GI tissue. These data demonstrate that DNA hypomethylation in embryonic SMC, via congenital Dnmt1 deficiency, contributes to massive dysregulation of gene expression and is lethal to GI-SMC. These results suggest that Dnmt1 has a necessary role in the embryonic, primary development process of SMC with consistent patterns being found in human GI diseased tissue.
View details for PubMedID 29700293
Multi-Organ RNA-Sequencing of Patients with Systemic Sclerosis (SSc) Finds That Intrinsic Subsets Are Conserved across Organ Systems
View details for Web of Science ID 000411824106435
Adult enteric nervous system in health is maintained by a dynamic balance between neuronal apoptosis and neurogenesis
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2017; 114 (18): E3709-E3718
According to current dogma, there is little or no ongoing neurogenesis in the fully developed adult enteric nervous system. This lack of neurogenesis leaves unanswered the question of how enteric neuronal populations are maintained in adult guts, given previous reports of ongoing neuronal death. Here, we confirm that despite ongoing neuronal cell loss because of apoptosis in the myenteric ganglia of the adult small intestine, total myenteric neuronal numbers remain constant. This observed neuronal homeostasis is maintained by new neurons formed in vivo from dividing precursor cells that are located within myenteric ganglia and express both Nestin and p75NTR, but not the pan-glial marker Sox10. Mutation of the phosphatase and tensin homolog gene in this pool of adult precursors leads to an increase in enteric neuronal number, resulting in ganglioneuromatosis, modeling the corresponding disorder in humans. Taken together, our results show significant turnover and neurogenesis of adult enteric neurons and provide a paradigm for understanding the enteric nervous system in health and disease.
View details for DOI 10.1073/pnas.1619406114
View details for PubMedID 28420791
Age-dependent shift in macrophage polarisation causes inflammation-mediated degeneration of enteric nervous system.
The enteric nervous system (ENS) undergoes neuronal loss and degenerative changes with age. The cause of this neurodegeneration is poorly understood. Muscularis macrophages residing in close proximity to enteric ganglia maintain neuromuscular function via direct crosstalk with enteric neurons and have been implicated in the pathogenesis of GI motility disorders like gastroparesis and postoperative ileus. The aim of this study was to assess whether ageing causes alterations in macrophage phenotype that contributes to age-related degeneration of the ENS.Longitudinal muscle and myenteric plexus from small intestine of young, mid-aged and old mice were dissected and prepared for whole mount immunostaining, flow cytometry, Luminex immunoassays, western blot analysis, enteric neural stem cell (ENSC) isolation or conditioned media. Bone marrow derived macrophages were prepared and polarised to classic (M1) or alternative (M2) activation states. Markers for macrophage phenotype were measured using quantitative RT-PCR.Ageing causes a shift in macrophage polarisation from anti-inflammatory 'M2' to proinflammatory 'M1' that is associated with a rise in cytokines and immune cells in the ENS. This phenotypic shift is associated with a neural response to inflammatory signals, increase in apoptosis and loss of enteric neurons and ENSCs, and delayed intestinal transit. An age-dependent decrease in expression of the transcription factor FoxO3, a known longevity gene, contributes to the loss of anti-inflammatory behaviour in macrophages of old mice, and FoxO3-deficient mice demonstrate signs of premature ageing of the ENS.A shift by macrophages towards a proinflammatory phenotype with ageing causes inflammation-mediated degeneration of the ENS.
View details for DOI 10.1136/gutjnl-2016-312940
View details for PubMedID 28228489
Intestinal pseudo-obstruction in patients with systemic sclerosis: an analysis of the Nationwide Inpatient Sample.
2016; 55 (4): 654-658
Intestinal pseudo-obstruction is a rare gastrointestinal complication in patients with SSc without large studies examining its prevalence or outcomes. We aimed to compare outcomes in SSc patients with intestinal pseudo-obstruction to patients with intestinal pseudo-obstruction secondary to other causes, and SSc patients without intestinal pseudo-obstruction.This is a case-control study using the Healthcare Cost and Utilization Project Nationwide Inpatient Sample for the period 2002-2011. We included patients with the previously validated International Classification of Diseases-Clinical Modification-9 code 710.1 for SSc in combination with codes for intestinal pseudo-obstruction, and determined length of hospitalization and the risks for surgical procedures, use of total parenteral nutrition (TPN) and in-hospital mortality.A total of 193 610 SSc hospitalizations occurred in the USA between 2002 and 2011, of which 5.4% (n = 10 386) were associated with a concurrent intestinal pseudo-obstruction diagnosis (cases). In-hospital mortality was 7.3%. In multivariate analyses, cases were more likely to die during the inpatient stay and to receive TPN than patients with idiopathic intestinal pseudo-obstruction (control group 1), patients with intestinal pseudo-obstruction and diabetes (control group 2), and SSc patients without intestinal pseudo-obstruction (control group 3). Cases had longer in-hospital stay than control groups 2 and 3, and were less likely to undergo surgical procedures than control groups 1 and 2.Intestinal pseudo-obstruction is a rare cause of hospitalization in patients with SSc, but is associated with high in-hospital mortality in comparison with other SSc patients and those with intestinal pseudo-obstruction secondary to other causes.
View details for DOI 10.1093/rheumatology/kev393
View details for PubMedID 26615031
Serum Response Factor Is Essential for Prenatal Gastrointestinal Smooth Muscle Development and Maintenance of Differentiated Phenotype.
Journal of neurogastroenterology and motility
2015; 21 (4): 589-602
Smooth muscle cells (SMCs) characteristically express serum response factor (SRF), which regulates their development. The role of SRF in SMC plasticity in the pathophysiological conditions of gastrointestinal (GI) tract is less characterized.We generated SMC-specific Srf knockout mice and characterized the prenatally lethal phenotype using ultrasound biomicroscopy and histological analysis. We used small bowel partial obstruction surgeries and primary cell culture using cell-specific enhanced green fluorescent protein (EGFP) mouse lines to study phenotypic and molecular changes of SMCs by immunofluorescence, Western blotting, and quantitative polymerase chain reaction. Finally we examined SRF change in human rectal prolapse tissue by immunofluorescence.Congenital SMC-specific Srf knockout mice died before birth and displayed severe GI and cardiac defects. Partial obstruction resulted in an overall increase in SRF protein expression. However, individual SMCs appeared to gradually lose SRF in the hypertrophic muscle. Cells expressing low levels of SRF also expressed low levels of platelet-derived growth factor receptor alpha (PDGFRα(low)) and Ki67. SMCs grown in culture recaptured the phenotypic switch from differentiated SMCs to proliferative PDGFRα(low) cells. The immediate and dramatic reduction of Srf and Myh11 mRNA expression confirmed the phenotypic change. Human rectal prolapse tissue also demonstrated significant loss of SRF expression.SRF expression in SMCs is essential for prenatal development of the GI tract and heart. Following partial obstruction, SMCs down-regulate SRF to transition into proliferative PDGFRα(low) cells that may represent a phenotype responsible for their plasticity. These findings demonstrate that SRF also plays a critical role in the remodeling process following GI injury.
View details for DOI 10.5056/jnm15063
View details for PubMedID 26424044
View details for PubMedCentralID PMC4622142
Ex Vivo Neurogenesis within Enteric Ganglia Occurs in a PTEN Dependent Manner
2013; 8 (3)
A population of multipotent stem cells capable of differentiating into neurons and glia has been isolated from adult intestine in humans and rodents. While these cells may provide a pool of stem cells for neurogenesis in the enteric nervous system (ENS), such a function has been difficult to demonstrate in vivo. An extensive study by Joseph et al. involving 108 rats and 51 mice submitted to various insults demonstrated neuronal uptake of thymidine analog BrdU in only 1 rat. Here we introduce a novel approach to study neurogenesis in the ENS using an ex vivo organotypic tissue culturing system. Culturing longitudinal muscle and myenteric plexus tissue, we show that the enteric nervous system has tremendous replicative capacity with the majority of neural crest cells demonstrating EdU uptake by 48 hours. EdU(+) cells express both neuronal and glial markers. Proliferation appears dependent on the PTEN/PI3K/Akt pathway with decreased PTEN mRNA expression and increased PTEN phosphorylation (inactivation) corresponding to increased Akt activity and proliferation. Inhibition of PTEN with bpV(phen) augments proliferation while LY294002, a PI3K inhibitor, blocks it. These data suggest that the ENS is capable of neurogenesis in a PTEN dependent manner.
View details for DOI 10.1371/journal.pone.0059452
View details for Web of Science ID 000317562100136
View details for PubMedID 23527198
View details for PubMedCentralID PMC3602370
Divergent fate and origin of neurosphere-like bodies from different layers of the gut
AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY
2012; 302 (9): G958-G965
Enteric neural stem cells (ENSCs) are a population of neural crest-derived multipotent stem cells present in postnatal gut that may play an important role in regeneration of the enteric nervous system. In most studies, these cells have been isolated from the layer of the gut containing the myenteric plexus. However, a recent report demonstrated that neurosphere-like bodies (NLBs) containing ENSCs could be isolated from mucosal biopsy specimens from children, suggesting that ENSCs are present in multiple layers of the gut. The aim of our study was to assess whether NLBs isolated from layers of gut containing either myenteric or submucosal plexus are equivalent. We divided the mouse small intestine into two layers, one containing myenteric plexus and the other submucosal plexus, and assessed for NLB formation. Differences in NLB density, proliferation, apoptosis, neural crest origin, and phenotype were investigated. NLBs isolated from the myenteric plexus layer were present at a higher density and demonstrated greater proliferation, lower apoptosis, and higher expression of nestin, p75, Sox10, and Ret than those from submucosal plexus. Additionally, they contained a higher percentage of neural crest-derived cells (99.4 ± 1.5 vs. 0.7 ± 1.19% of Wnt1-cre:tdTomato cells; P < 0.0001) and produced more neurons and glial cells than those from submucosal plexus. NLBs from the submucosal plexus layer expressed higher CD34 and produced more smooth muscle-like cells. NLBs from the myenteric plexus layer contain more neural crest-derived ENSCs while those from submucosal plexus appear more heterogeneous, likely containing a population of mesenchymal stem cells.
View details for DOI 10.1152/ajpgi.00511.2011
View details for Web of Science ID 000303593900007
View details for PubMedID 22361728
View details for PubMedCentralID PMC3362075
Stem cell transplantation in neurodegenerative disorders of the gastrointestinal tract: future or fiction?
2012; 61 (4): 613-621
Current advances in our understanding of stem and precursor cell biology and in the protocols of stem cell isolation and transplantation have opened up the possibility of transplanting neural stem cells for the treatment of gastrointestinal motility disorders. This review summarises the current status of research in this field, identifies the major gaps in our knowledge and discusses the potential opportunities and hurdles for clinical application.
View details for DOI 10.1136/gut.2010.235614
View details for Web of Science ID 000300955000020
View details for PubMedID 21816959
View details for PubMedCentralID PMC4119942
Gut-derived factors promote neurogenesis of CNS-neural stem cells and nudge their differentiation to an enteric-like neuronal phenotype
AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY
2011; 301 (4): G644-G655
Recent studies have explored the potential of central nervous system-derived neural stem cells (CNS-NSC) to repopulate the enteric nervous system. However, the exact phenotypic fate of gut-transplanted CNS-NSC has not been characterized. The aim of this study was to investigate the effect of the gut microenvironment on phenotypic fate of CNS-NSC in vitro. With the use of Transwell culture, differentiation of mouse embryonic CNS-NSC was studied when cocultured without direct contact with mouse intestinal longitudinal muscle-myenteric plexus preparations (LM-MP) compared with control noncocultured cells, in a differentiating medium. Differentiated cells were analyzed by immunocytochemistry and quantitative RT-PCR to assess the expression of specific markers and by whole cell patch-clamp studies for functional characterization of their phenotype. We found that LM-MP cocultured cells had a significant increase in the numbers of cells that were immune reactive against the panneuronal marker β-tubulin, neurotransmitters neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT), and neuropeptide vasoactive intestinal peptide (VIP) and showed an increase in expression of these genes, compared with control cells. Whole cell patch-clamp analysis showed that coculture with LM-MP decreases cell excitability and reduces voltage-gated Na(+) currents but significantly enhances A-current and late afterhyperpolarization (AHP) and increases the expression of the four AHP-generating Ca(2+)-dependent K(+) channel genes (KCNN), compared with control cells. In a separate experiment, differentiation of LM-MP cocultured CNS-NSC produced a significant increase in the numbers of cells that were immune reactive against the neurotransmitters nNOS, ChAT, and the neuropeptide VIP compared with CNS-NSC differentiated similarly in the presence of neonatal brain tissue. Our results show that the gut microenvironment induces CNS-NSC to produce neurons that share some of the characteristics of classical enteric neurons, further supporting the therapeutic use of these cells for gastrointestinal disorders.
View details for DOI 10.1152/ajpgi.00123.2011
View details for Web of Science ID 000295253900006
View details for PubMedID 21817062
View details for PubMedCentralID PMC3191554