Bio

Bio


As a Siebel Investigator at the Institute for Stem Cell Biology & Regenerative Medicine, my group is broadly interested in understanding how different human cell-types form from stem cells. To this end, we have delineated a comprehensive roadmap that describes how embryonic stem cells can develop into a spectrum of over twenty different human cell types. This roadmap enabled us to generate rather uniform populations of human liver progenitors, human bone progenitors and human heart progenitors from embryonic stem cells, each of which could regenerate their cognate tissue upon injection into respective mouse models. This platform to produce these engraftable human tissue progenitors provides fundamental building blocks for regenerative medicine and provides an ideal venue to understand human developmental biology.

Academic Appointments


  • Instructor, Institute for Stem Cell Biology and Regenerative Medicine

Honors & Awards


  • Siebel Investigatorship, Stanford School of Medicine (2016)
  • A*STAR Investigatorship, Singapore Agency for Science, Technology & Research (A*STAR) (2016)
  • Harold Weintraub Graduate Student Award, Fred Hutchinson Cancer Research Center (2015)
  • Hertz Foundation Graduate Fellowship Award, The Fannie and John Hertz Foundation (2011)
  • NSF Graduate Research Fellowship, U.S. National Science Foundation (2011)
  • Davidson Laureate Fellowship, Davidson Institute for Talent Development (2010)
  • Harvard Stem Cell Institute Internship Program, Harvard Stem Cell Institute (2008)
  • Rutgers University School of Arts & Sciences Excellence Award, Rutgers University (2007-2010)
  • Research & Development Council of New Jersey Scholarship, New Jersey Research & Development Council (2007)

Research & Scholarship

Current Research and Scholarly Interests


Embryonic stem cells can produce any type of human cell in a dish. Thus they afford an opportunity to recreate, and thus study, basic developmental phenomena (lineage diversification, tissue self-organization and multilineage competence) that are difficult to probe in a developing embryo. However, this opportunity has yet to be fully realized because stem-cell differentiation often yields heterogeneous mixtures of cells that are ill-suited for molecular analysis or cell therapy.

We have developed a reductionist system to define the minimal essential inductive and repressive signals necessary for the developmental induction of a given embryonic lineage from differentiating ESCs. These efforts culminated in systematic roadmaps describing the extrinsic signals that guide human ESCs into a variety of endoderm and mesoderm germ layer derivatives (including liver, intestinal, bone and heart progenitors) through a series of bifurcating intermediate steps. The overarching goal is to exploit the resultant highly-pure populations of human tissue progenitors to explore classic questions in developmental biology, using stem-cell differentiation as a technological platform.

Publications

All Publications


  • Generating Cellular Diversity and Spatial Form: Wnt Signaling and the Evolution of Multicellular Animals. Developmental cell Loh, K. M., van Amerongen, R., Nusse, R. 2016; 38 (6): 643-655

    Abstract

    There were multiple prerequisites to the evolution of multicellular animal life, including the generation of multiple cell fates ("cellular diversity") and their patterned spatial arrangement ("spatial form"). Wnt proteins operate as primordial symmetry-breaking signals. By virtue of their short-range nature and their capacity to activate both lineage-specifying and cell-polarizing intracellular signaling cascades, Wnts can polarize cells at their site of contact, orienting the axis of cell division while simultaneously programming daughter cells to adopt diverging fates in a spatially stereotyped way. By coupling cell fate to position, symmetry-breaking Wnt signals were pivotal in constructing the metazoan body by generating cellular diversity and spatial form.

    View details for DOI 10.1016/j.devcel.2016.08.011

    View details for PubMedID 27676437

  • Mapping the Pairwise Choices Leading from Pluripotency to Human Bone, Heart, and Other Mesoderm Cell Types CELL Loh, K. M., Chen, A., Koh, P. W., Deng, T. Z., Sinha, R., Tsai, J. M., Barkal, A. A., Shen, K. Y., Jain, R., Morganti, R. M., Shyh-Chang, N., Fernhoff, N. B., George, B. M., Wernig, G., Salomon, R. E., Chen, Z., Vogel, H., Epstein, J. A., Kundaje, A., Talbot, W. S., Beachy, P. A., Ang, L. T., Weissman, I. L. 2016; 166 (2): 451-467

    Abstract

    Stem-cell differentiation to desired lineages requires navigating alternating developmental paths that often lead to unwanted cell types. Hence, comprehensive developmental roadmaps are crucial to channel stem-cell differentiation toward desired fates. To this end, here, we map bifurcating lineage choices leading from pluripotency to 12 human mesodermal lineages, including bone, muscle, and heart. We defined the extrinsic signals controlling each binary lineage decision, enabling us to logically block differentiation toward unwanted fates and rapidly steer pluripotent stem cells toward 80%-99% pure human mesodermal lineages at most branchpoints. This strategy enabled the generation of human bone and heart progenitors that could engraft in respective in vivo models. Mapping stepwise chromatin and single-cell gene expression changes in mesoderm development uncovered somite segmentation, a previously unobservable human embryonic event transiently marked by HOPX expression. Collectively, this roadmap enables navigation of mesodermal development to produce transplantable human tissue progenitors and uncover developmental processes. VIDEO ABSTRACT.

    View details for DOI 10.1016/j.cell.2016.06.011

    View details for Web of Science ID 000380255400021

    View details for PubMedID 27419872

  • EX UNO PLURES: MOLECULAR DESIGNS FOR EMBRYONIC PLURIPOTENCY PHYSIOLOGICAL REVIEWS Loh, K. M., Lim, B., Lay Teng Ang, L. T. 2015; 95 (1): 245-295

    Abstract

    Pluripotent cells in embryos are situated near the apex of the hierarchy of developmental potential. They are capable of generating all cell types of the mammalian body proper. Therefore, they are the exemplar of stem cells. In vivo, pluripotent cells exist transiently and become expended within a few days of their establishment. Yet, when explanted into artificial culture conditions, they can be indefinitely propagated in vitro as pluripotent stem cell lines. A host of transcription factors and regulatory genes are now known to underpin the pluripotent state. Nonetheless, how pluripotent cells are equipped with their vast multilineage differentiation potential remains elusive. Consensus holds that pluripotency transcription factors prevent differentiation by inhibiting the expression of differentiation genes. However, this does not explain the developmental potential of pluripotent cells. We have presented another emergent perspective, namely, that pluripotency factors function as lineage specifiers that enable pluripotent cells to differentiate into specific lineages, therefore endowing pluripotent cells with their multilineage potential. Here we provide a comprehensive overview of the developmental biology, transcription factors, and extrinsic signaling associated with pluripotent cells, and their accompanying subtypes, in vitro heterogeneity and chromatin states. Although much has been learned since the appreciation of mammalian pluripotency in the 1950s and the derivation of embryonic stem cell lines in 1981, we will specifically emphasize what currently remains unclear. However, the view that pluripotency factors capacitate differentiation, recently corroborated by experimental evidence, might perhaps address the long-standing question of how pluripotent cells are endowed with their multilineage differentiation potential.

    View details for DOI 10.1152/physrev.00001.2014

    View details for Web of Science ID 000352194500008

    View details for PubMedID 25540144

  • Stem cell signaling. An integral program for tissue renewal and regeneration: Wnt signaling and stem cell control. Science Clevers, H., Loh, K. M., Nusse, R. 2014; 346 (6205)

    Abstract

    Stem cells fuel tissue development, renewal, and regeneration, and these activities are controlled by the local stem cell microenvironment, the "niche." Wnt signals emanating from the niche can act as self-renewal factors for stem cells in multiple mammalian tissues. Wnt proteins are lipid-modified, which constrains them to act as short-range cellular signals. The locality of Wnt signaling dictates that stem cells exiting the Wnt signaling domain differentiate, spatially delimiting the niche in certain tissues. In some instances, stem cells may act as or generate their own niche, enabling the self-organization of patterned tissues. In this Review, we discuss the various ways by which Wnt operates in stem cell control and, in doing so, identify an integral program for tissue renewal and regeneration.

    View details for DOI 10.1126/science.1248012

    View details for PubMedID 25278615

  • Efficient Endoderm Induction from Human Pluripotent Stem Cells by Logically Directing Signals Controlling Lineage Bifurcations CELL STEM CELL Loh, K. M., Ang, L. T., Zhang, J., Kumar, V., Ang, J., Auyeong, J. Q., Lee, K. L., Choo, S. H., Lim, C. Y., Nichane, M., Tan, J., Noghabi, M. S., Azzola, L., Ng, E. S., Durruthy-Durruthy, J., Sebastiano, V., Poellinger, L., Elefanty, A. G., Stanley, E. G., Chen, Q., Prabhakar, S., Weissman, I. L., Lim, B. 2014; 14 (2): 237-252

    Abstract

    Human pluripotent stem cell (hPSC) differentiation typically yields heterogeneous populations. Knowledge of signals controlling embryonic lineage bifurcations could efficiently yield desired cell types through exclusion of alternate fates. Therefore, we revisited signals driving induction and anterior-posterior patterning of definitive endoderm to generate a coherent roadmap for endoderm differentiation. With striking temporal dynamics, BMP and Wnt initially specified anterior primitive streak (progenitor to endoderm), yet, 24 hr later, suppressed endoderm and induced mesoderm. At lineage bifurcations, cross-repressive signals separated mutually exclusive fates; TGF-? and BMP/MAPK respectively induced pancreas versus liver from endoderm by suppressing the alternate lineage. We systematically blockaded alternate fates throughout multiple consecutive bifurcations, thereby efficiently differentiating multiple hPSC lines exclusively into endoderm and its derivatives. Comprehensive transcriptional and chromatin mapping of highly pure endodermal populations revealed that endodermal enhancers existed in a surprising diversity of "pre-enhancer" states before activation, reflecting the establishment of a permissive chromatin landscape as a prelude to differentiation.

    View details for DOI 10.1016/j.stem.2013.12.007

    View details for Web of Science ID 000330835800015

    View details for PubMedID 24412311

  • A Precarious Balance: Pluripotency Factors as Lineage Specifiers CELL STEM CELL Loh, K. M., Lim, B. 2011; 8 (4): 363-369

    Abstract

    Understanding the basis of the unrestricted multilineage differentiation potential of pluripotent cells will be of developmental and translational consequence. We propose that pluripotency transcription factors are lineage specifiers that direct commitment to specific fetal lineages. Individual factors bestow the ability to differentiate into particular cell types, and concomitant expression of multiple lineage specifiers within pluripotent cells enables differentiation into every fetal lineage. Moreover, we speculate that, rather than being an intrinsically stable "ground state," pluripotency is an inherently precarious condition in which rival lineage specifiers continually compete to specify differentiation along mutually exclusive lineages.

    View details for DOI 10.1016/j.stem.2011.03.013

    View details for Web of Science ID 000289707100008

    View details for PubMedID 21474100

  • Inhibition of Apoptosis Overcomes Stage-Related Compatibility Barriers to Chimera Formation in Mouse Embryos. Cell stem cell Masaki, H., Kato-Itoh, M., Takahashi, Y., Umino, A., Sato, H., Ito, K., Yanagida, A., Nishimura, T., Yamaguchi, T., Hirabayashi, M., Era, T., Loh, K. M., Wu, S. M., Weissman, I. L., Nakauchi, H. 2016; 19 (5): 587-592

    Abstract

    Cell types more advanced in development than embryonic stem cells, such as EpiSCs, fail to contribute to chimeras when injected into pre-implantation-stage blastocysts, apparently because the injected cells undergo apoptosis. Here we show that transient promotion of cell survival through expression of the anti-apoptotic gene BCL2 enables EpiSCs and Sox17(+) endoderm progenitors to integrate into blastocysts and contribute to chimeric embryos. Upon injection into blastocyst, BCL2-expressing EpiSCs contributed to all bodily tissues in chimeric animals while Sox17(+) endoderm progenitors specifically contributed in a region-specific fashion to endodermal tissues. In addition, BCL2 expression enabled rat EpiSCs to contribute to mouse embryonic chimeras, thereby forming interspecies chimeras that could survive to adulthood. Our system therefore provides a method to overcome cellular compatibility issues that typically restrict chimera formation. Application of this type of approach could broaden the use of embryonic chimeras, including region-specific chimeras, for basic developmental biology research and regenerative medicine.

    View details for DOI 10.1016/j.stem.2016.10.013

    View details for PubMedID 27814480

  • Stem cells: Equilibrium established. Nature Loh, K. M., Lim, B. 2015; 521 (7552): 299-300

    View details for DOI 10.1038/521299a

    View details for PubMedID 25993958

  • Differentiation of trophoblast cells from human embryonic stem cells: to be or not to be? REPRODUCTION Roberts, R. M., Loh, K. M., Amita, M., Bernardo, A. S., Adachi, K., Alexenko, A. P., Schust, D. J., Schulz, L. C., Telugu, B. P., Ezashi, T., Pedersen, R. A. 2014; 147 (5): D1-D12
  • Rapid and Efficient Conversion of Integration-Free Human Induced Pluripotent Stem Cells to GMP-Grade Culture Conditions PLOS ONE Durruthy-Durruthy, J., Briggs, S. F., Awe, J., Ramathal, C. Y., Karumbayaram, S., Lee, P. C., Heidmann, J. D., Clark, A., Karakikes, I., Loh, K. M., Wu, J. C., Hoffman, A. R., Byrne, J., Pera, R. A., Sebastiano, V. 2014; 9 (4)
  • Rapid and efficient conversion of integration-free human induced pluripotent stem cells to GMP-grade culture conditions. PloS one Durruthy-Durruthy, J., Briggs, S. F., Awe, J., Ramathal, C. Y., Karumbayaram, S., Lee, P. C., Heidmann, J. D., Clark, A., Karakikes, I., Loh, K. M., Wu, J. C., Hoffman, A. R., Byrne, J., Reijo Pera, R. A., Sebastiano, V. 2014; 9 (4)

    Abstract

    Data suggest that clinical applications of human induced pluripotent stem cells (hiPSCs) will be realized. Nonetheless, clinical applications will require hiPSCs that are free of exogenous DNA and that can be manufactured through Good Manufacturing Practice (GMP). Optimally, derivation of hiPSCs should be rapid and efficient in order to minimize manipulations, reduce potential for accumulation of mutations and minimize financial costs. Previous studies reported the use of modified synthetic mRNAs to reprogram fibroblasts to a pluripotent state. Here, we provide an optimized, fully chemically defined and feeder-free protocol for the derivation of hiPSCs using synthetic mRNAs. The protocol results in derivation of fully reprogrammed hiPSC lines from adult dermal fibroblasts in less than two weeks. The hiPSC lines were successfully tested for their identity, purity, stability and safety at a GMP facility and cryopreserved. To our knowledge, as a proof of principle, these are the first integration-free iPSCs lines that were reproducibly generated through synthetic mRNA reprogramming that could be putatively used for clinical purposes.

    View details for DOI 10.1371/journal.pone.0094231

    View details for PubMedID 24718618

  • Clonal precursor of bone, cartilage, and hematopoietic niche stromal cells PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chan, C. K., Lindau, P., Jiang, W., Chen, J. Y., Zhang, L. F., Chen, C., Seita, J., Sahoo, D., Kim, J., Lee, A., Park, S., Nag, D., Gong, Y., Kulkarni, S., Luppen, C. A., Theologis, A. A., Wan, D. C., DeBoer, A., Seo, E. Y., Vincent-Tompkins, J. D., Loh, K., Walmsley, G. G., Kraft, D. L., Wu, J. C., Longaker, M. T., Weissman, I. L. 2013; 110 (31): 12643-12648

    Abstract

    Organs are composites of tissue types with diverse developmental origins, and they rely on distinct stem and progenitor cells to meet physiological demands for cellular production and homeostasis. How diverse stem cell activity is coordinated within organs is not well understood. Here we describe a lineage-restricted, self-renewing common skeletal progenitor (bone, cartilage, stromal progenitor; BCSP) isolated from limb bones and bone marrow tissue of fetal, neonatal, and adult mice. The BCSP clonally produces chondrocytes (cartilage-forming) and osteogenic (bone-forming) cells and at least three subsets of stromal cells that exhibit differential expression of cell surface markers, including CD105 (or endoglin), Thy1 [or CD90 (cluster of differentiation 90)], and 6C3 [ENPEP glutamyl aminopeptidase (aminopeptidase A)]. These three stromal subsets exhibit differential capacities to support hematopoietic (blood-forming) stem and progenitor cells. Although the 6C3-expressing subset demonstrates functional stem cell niche activity by maintaining primitive hematopoietic stem cell (HSC) renewal in vitro, the other stromal populations promote HSC differentiation to more committed lines of hematopoiesis, such as the B-cell lineage. Gene expression analysis and microscopic studies further reveal a microenvironment in which CD105-, Thy1-, and 6C3-expressing marrow stroma collaborate to provide cytokine signaling to HSCs and more committed hematopoietic progenitors. As a result, within the context of bone as a blood-forming organ, the BCSP plays a critical role in supporting hematopoiesis through its generation of diverse osteogenic and hematopoietic-promoting stroma, including HSC supportive 6C3(+) niche cells.

    View details for DOI 10.1073/pnas.1310212110

    View details for Web of Science ID 000322441500042

    View details for PubMedID 23858471

  • Rejuvenating tithonus. EMBO reports Loh, K. M., Lim, B. 2013; 14 (7): 583-584

    View details for DOI 10.1038/embor.2013.81

    View details for PubMedID 23764924

  • EPIGENETICS Actors in the cell reprogramming drama NATURE Loh, K. M., Lim, B. 2012; 488 (7413): 599-600

    View details for Web of Science ID 000308095100043

    View details for PubMedID 22932382

  • Investigating the bona fide differentiation capacity of human pluripotent stem cells CELL RESEARCH Heng, J. D., Loh, K. M., Ng, H. 2012; 22 (1): 6-8

    View details for DOI 10.1038/cr.2011.142

    View details for Web of Science ID 000299312900003

    View details for PubMedID 21876556

  • Recreating Pluripotency? CELL STEM CELL Loh, K. M., Lim, B. 2010; 7 (2): 137-139

    Abstract

    Two Matters Arising articles in this issue challenge the conclusions of a previous Cell Stem Cell paper that found extensive transcriptional differences between hESCs and hiPSCs. The original authors provide a response and set in motion a discussion in the field about appropriate methods for microarray data analysis.

    View details for DOI 10.1016/j.stem.2010.07.005

    View details for Web of Science ID 000281107400002

    View details for PubMedID 20682438

  • A Small-Molecule Inhibitor of Tgf-beta Signaling Replaces Sox2 in Reprogramming by Inducing Nanog CELL STEM CELL Ichida, J. K., Blanchard, J., Lam, K., Son, E. Y., Chung, J. E., Egli, D., Loh, K. M., Carter, A. C., Di Giorgio, F. P., Koszka, K., Huangfu, D., Akutsu, H., Liu, D. R., Rubin, L. L., Eggan, K. 2009; 5 (5): 491-503

    Abstract

    The combined activity of three transcription factors can reprogram adult cells into induced pluripotent stem cells (iPSCs). However, the transgenic methods used for delivering reprogramming factors have raised concerns regarding the future utility of the resulting stem cells. These uncertainties could be overcome if each transgenic factor were replaced with a small molecule that either directly activated its expression from the somatic genome or in some way compensated for its activity. To this end, we have used high-content chemical screening to identify small molecules that can replace Sox2 in reprogramming. We show that one of these molecules functions in reprogramming by inhibiting Tgf-beta signaling in a stable and trapped intermediate cell type that forms during the process. We find that this inhibition promotes the completion of reprogramming through induction of the transcription factor Nanog.

    View details for DOI 10.1016/j.stem.2009.09.012

    View details for Web of Science ID 000272019500011

    View details for PubMedID 19818703

Footer Links:

Stanford Medicine Resources: