Honors & Awards
Postdoctoral Fellowship, Fragile X syndrome FRAXA research foundation (2013-2015)
Dean Postdoctoral Fellowship, Stanford University (2009)
Predoctoral Fellowship, European Molecular Biology Organization (EMBO) (2008)
Doctor of Philosophy, Universita Degli Studi Di Torino (2008)
Marius Wernig, Postdoctoral Faculty Sponsor
Transdifferentiation of mouse fibroblasts and hepatocytes to functional neurons.
Methods in molecular biology (Clifton, N.J.)
2014; 1150: 237-246
Nuclear reprogramming by defined transcription factors became of broad interest in 2006 with the work of Takahashi and Yamanaka (Cell 126:663-676, 2006), but the first example of cell fate reshaping via ectopic expression of transcription factor was provided back in 1987 when Davis and colleagues induced features of a muscle cell in fibroblast using the muscle transcription factor MyoD (Davis et al., Cell 51:987-1000, 1987). In 2010 our laboratory described how forced expression of the three neuronal transcription factors Ascl1, Brn2, and Myt1l rapidly converts mouse fibroblasts into neuronal cells that exhibit biochemical and electrophysiological properties of neurons. We named these cells induced neuronal cells (iN cells) (Vierbuchen et al., Nature 463:1035-1041, 2010; Vierbuchen and Wernig, Nat Biotechnol 29:892-907, 2011). Interestingly, iN cells can also be derived from defined endodermal cells such as primary hepatocytes, suggesting the existence of a more general reprogramming paradigm (Marro et al., Cell Stem Cell 9:374-382, 2011). In this chapter we describe the detailed methods used to attain the direct conversion.
View details for DOI 10.1007/978-1-4939-0512-6_16
View details for PubMedID 24744003
Hierarchical Mechanisms for Direct Reprogramming of Fibroblasts to Neurons
2013; 155 (3): 621-635
Direct lineage reprogramming is a promising approach for human disease modeling and regenerative medicine, with poorly understood mechanisms. Here, we reveal a hierarchical mechanism in the direct conversion of fibroblasts into induced neuronal (iN) cells mediated by the transcription factors Ascl1, Brn2, and Myt1l. Ascl1 acts as an "on-target" pioneer factor by immediately occupying most cognate genomic sites in fibroblasts. In contrast, Brn2 and Myt1l do not access fibroblast chromatin productively on their own; instead, Ascl1 recruits Brn2 to Ascl1 sites genome wide. A unique trivalent chromatin signature in the host cells predicts the permissiveness for Ascl1 pioneering activity among different cell types. Finally, we identified Zfp238 as a key Ascl1 target gene that can partially substitute for Ascl1 during iN cell reprogramming. Thus, a precise match between pioneer factors and the chromatin context at key target genes is determinative for transdifferentiation to neurons and likely other cell types.
View details for DOI 10.1016/j.cell.2013.09.028
View details for Web of Science ID 000326571800016
Neurons generated by direct conversion of fibroblasts reproduce synaptic phenotype caused by autism-associated neuroligin-3 mutation.
Proceedings of the National Academy of Sciences of the United States of America
2013; 110 (41): 16622-16627
Recent studies suggest that induced neuronal (iN) cells that are directly transdifferentiated from nonneuronal cells provide a powerful opportunity to examine neuropsychiatric diseases. However, the validity of using this approach to examine disease-specific changes has not been demonstrated. Here, we analyze the phenotypes of iN cells that were derived from murine embryonic fibroblasts cultured from littermate wild-type and mutant mice carrying the autism-associated R704C substitution in neuroligin-3. We show that neuroligin-3 R704C-mutant iN cells exhibit a large and selective decrease in AMPA-type glutamate receptor-mediated synaptic transmission without changes in NMDA-type glutamate receptor- or in GABAA receptor-mediated synaptic transmission. Thus, the synaptic phenotype observed in R704C-mutant iN cells replicates the previously observed phenotype of R704C-mutant neurons. Our data show that the effect of the R704C mutation is applicable even to neurons transdifferentiated from fibroblasts and constitute a proof-of-concept demonstration that iN cells can be used for cellular disease modeling.
View details for DOI 10.1073/pnas.1316240110
View details for PubMedID 24046374
Rapid Single-Step Induction of Functional Neurons from Human Pluripotent Stem Cells
2013; 78 (5): 785-798
Available methods for differentiating human embryonic stem cells (ESCs) and induced pluripotent cells (iPSCs) into neurons are often cumbersome, slow, and variable. Alternatively, human fibroblasts can be directly converted into induced neuronal (iN) cells. However, with present techniques conversion is inefficient, synapse formation is limited, and only small amounts of neurons can be generated. Here, we show that human ESCs and iPSCs can be converted into functional iN cells with nearly 100% yield and purity in less than 2 weeks by forced expression of a single transcription factor. The resulting ES-iN or iPS-iN cells exhibit quantitatively reproducible properties independent of the cell line of origin, form mature pre- and postsynaptic specializations, and integrate into existing synaptic networks when transplanted into mouse brain. As illustrated by selected examples, our approach enables large-scale studies of human neurons for questions such as analyses of human diseases, examination of human-specific genes, and drug screening.
View details for DOI 10.1016/j.neuron.2013.05.029
View details for Web of Science ID 000320743400006
Generation of oligodendroglial cells by direct lineage conversion.
2013; 31 (5): 434-439
Transplantation of oligodendrocyte precursor cells (OPCs) is a promising potential therapeutic strategy for diseases affecting myelin. However, the derivation of engraftable OPCs from human pluripotent stem cells has proven difficult and primary OPCs are not readily available. Here we report the generation of induced OPCs (iOPCs) by direct lineage conversion. Forced expression of the three transcription factors Sox10, Olig2 and Zfp536 was sufficient to reprogram mouse and rat fibroblasts into iOPCs with morphologies and gene expression signatures resembling primary OPCs. More importantly, iOPCs gave rise to mature oligodendrocytes that could ensheath multiple host axons when co-cultured with primary dorsal root ganglion cells and formed myelin after transplantation into shiverer mice. We propose direct lineage reprogramming as a viable alternative approach for the generation of OPCs for use in disease modeling and regenerative medicine.
View details for DOI 10.1038/nbt.2564
View details for PubMedID 23584610
Cell-specific regulation of Ferroportin transcription following experimentally-induced acute anemia in mice
BLOOD CELLS MOLECULES AND DISEASES
2013; 50 (1): 25-30
Ferroportin (FPN), the sole characterized iron exporter, is mainly controlled by the peptide hormone hepcidin in response to iron, erythroid factors, hypoxia, and inflammation. In addition, intracellular iron level controls FPN translation by modulating the binding of Iron Responsive Proteins at the 5'UTR of FPN mRNA. Recently, hypoxia inducible factor (HIF)2? has been shown to regulate FPN expression in intestinal cells. Here we show that, during experimentally-induced acute anemia in mice, FPN is regulated at transcriptional level in a cell-specific manner. FPN mRNA level increases in duodenum and spleen macrophages, whereas it does not change in liver and is strongly down-regulated in erythroid precursors. These results were confirmed in Caco2, Raw264.7 and K562 cells treated with a hypoxic stimulus. Moreover, we found a differential expression of HIF1? and HIF2? in cells and tissues that might account for the specificity of FPN regulation. Thus, hypoxia, by directly controlling hepcidin and its target FPN, orchestrates a complex regulatory network aimed at ensuring rapid iron recovery from the periphery and efficient iron utilization in the erythroid compartment.
View details for DOI 10.1016/j.bcmd.2012.08.002
View details for Web of Science ID 000312237400004
View details for PubMedID 22921471
The mitochondrial heme exporter FLVCR1b mediates erythroid differentiation
JOURNAL OF CLINICAL INVESTIGATION
2012; 122 (12): 4569-4579
Feline leukemia virus subgroup C receptor 1 (FLVCR1) is a cell membrane heme exporter that maintains the balance between heme levels and globin synthesis in erythroid precursors. It was previously shown that Flvcr1-null mice died in utero due to a failure of erythropoiesis. Here, we identify Flvcr1b, a mitochondrial Flvcr1 isoform that promotes heme efflux into the cytoplasm. Flvcr1b overexpression promoted heme synthesis and in vitro erythroid differentiation, whereas silencing of Flvcr1b caused mitochondrial heme accumulation and termination of erythroid differentiation. Furthermore, mice lacking the plasma membrane isoform (Flvcr1a) but expressing Flvcr1b had normal erythropoiesis, but exhibited hemorrhages, edema, and skeletal abnormalities. Thus, FLVCR1b regulates erythropoiesis by controlling mitochondrial heme efflux, whereas FLVCR1a expression is required to prevent hemorrhages and edema. The aberrant expression of Flvcr1 isoforms may play a role in the pathogenesis of disorders characterized by an imbalance between heme and globin synthesis.
View details for DOI 10.1172/JCI62422
View details for Web of Science ID 000311926200030
View details for PubMedID 23187127
Direct Lineage Conversion of Terminally Differentiated Hepatocytes to Functional Neurons
CELL STEM CELL
2011; 9 (4): 374-382
Several recent studies have showed that mouse and human fibroblasts can be directly reprogrammed into induced neuronal (iN) cells, bypassing a pluripotent intermediate state. However, fibroblasts represent heterogeneous mesenchymal progenitor cells that potentially contain neural crest lineages, and the cell of origin remained undefined. This raises the fundamental question of whether lineage reprogramming is possible between cell types derived from different germ layers. Here, we demonstrate that terminally differentiated hepatocytes can be directly converted into functional iN cells. Importantly, single-cell and genome-wide expression analyses showed that fibroblast- and hepatocyte-derived iN cells not only induced a neuronal transcriptional program, but also silenced their donor transcriptome. The remaining donor signature decreased over time and could not support functional hepatocyte properties. Thus, the reprogramming factors lead to a binary lineage switch decision rather than an induction of hybrid phenotypes, but iN cells retain a small but detectable epigenetic memory of their donor cells.
View details for DOI 10.1016/j.stem.2011.09.002
View details for Web of Science ID 000296041200015
View details for PubMedID 21962918
Induction of human neuronal cells by defined transcription factors
2011; 476 (7359): 220-U122
Somatic cell nuclear transfer, cell fusion, or expression of lineage-specific factors have been shown to induce cell-fate changes in diverse somatic cell types. We recently observed that forced expression of a combination of three transcription factors, Brn2 (also known as Pou3f2), Ascl1 and Myt1l, can efficiently convert mouse fibroblasts into functional induced neuronal (iN) cells. Here we show that the same three factors can generate functional neurons from human pluripotent stem cells as early as 6?days after transgene activation. When combined with the basic helix-loop-helix transcription factor NeuroD1, these factors could also convert fetal and postnatal human fibroblasts into iN cells showing typical neuronal morphologies and expressing multiple neuronal markers, even after downregulation of the exogenous transcription factors. Importantly, the vast majority of human iN cells were able to generate action potentials and many matured to receive synaptic contacts when co-cultured with primary mouse cortical neurons. Our data demonstrate that non-neural human somatic cells, as well as pluripotent stem cells, can be converted directly into neurons by lineage-determining transcription factors. These methods may facilitate robust generation of patient-specific human neurons for in vitro disease modelling or future applications in regenerative medicine.
View details for DOI 10.1038/nature10202
View details for Web of Science ID 000293731900039
View details for PubMedID 21617644
Heme controls ferroportin1 (FPN1) transcription involving Bach1, Nrf2 and a MARE/ARE sequence motif at position-7007 of the FPN1 promoter
HAEMATOLOGICA-THE HEMATOLOGY JOURNAL
2010; 95 (8): 1261-1268
Macrophages of the reticuloendothelial system play a key role in recycling iron from hemoglobin of senescent or damaged erythrocytes. Heme oxygenase 1 degrades the heme moiety and releases inorganic iron that is stored in ferritin or exported to the plasma via the iron export protein ferroportin. In the plasma, iron binds to transferrin and is made available for de novo red cell synthesis. The aim of this study was to gain insight into the regulatory mechanisms that control the transcriptional response of iron export protein ferroportin to hemoglobin in macrophages.Iron export protein ferroportin mRNA expression was analyzed in RAW264.7 mouse macrophages in response to hemoglobin, heme, ferric ammonium citrate or protoporphyrin treatment or to siRNA mediated knockdown or overexpression of Btb And Cnc Homology 1 or nuclear accumulation of Nuclear Factor Erythroid 2-like. Iron export protein ferroportin promoter activity was analyzed using reporter constructs that contain specific truncations of the iron export protein ferroportin promoter or mutations in a newly identified MARE/ARE element.We show that iron export protein ferroportin is transcriptionally co-regulated with heme oxygenase 1 by heme, a degradation product of hemoglobin. The protoporphyrin ring of heme is sufficient to increase iron export protein ferroportin transcriptional activity while the iron released from the heme moiety controls iron export protein ferroportin translation involving the IRE in the 5'untranslated region. Transcription of iron export protein ferroportin is inhibited by Btb and Cnc Homology 1 and activated by Nuclear Factor Erythroid 2-like involving a MARE/ARE element located at position -7007/-7016 of the iron export protein ferroportin promoter.This finding suggests that heme controls a macrophage iron recycling regulon involving Btb and Cnc Homology 1 and Nuclear Factor Erythroid 2-like to assure the coordinated degradation of heme by heme oxygenase 1, iron storage and detoxification by ferritin, and iron export by iron export protein ferroportin.
View details for DOI 10.3324/haematol.2009.020123
View details for Web of Science ID 000281568000006
View details for PubMedID 20179090
Lack of haptoglobin affects iron transport across duodenum by modulating ferroportin expression
2007; 133 (4): 1261-1271
Haptoglobin is an acute phase protein responsible for the recovery of free hemoglobin from plasma. Haptoglobin-null mice were previously shown to have an altered heme-iron distribution, thus reproducing what occurs in humans in cases of congenital or acquired anhaptoglobinemia. Here, we report the analysis of iron homeostasis in haptoglobin-null mice.Iron absorption was measured in tied-off duodenal segments. Iron stores were evaluated on tissue homogenates and sections. The expression of molecules involved in iron homeostasis was analyzed at the protein and messenger RNA levels both in mice and in murine RAW264.7 macrophages stimulated in vitro with hemoglobin.Analysis of intestinal iron transport reveals that haptoglobin-null mice export significantly more iron from the duodenal mucosa to plasma compared with control counterparts. Increased iron export from the duodenum correlates with increased duodenal expression of ferroportin, both at the protein and messenger RNA levels, whereas hepatic hepcidin expression remains unchanged. Up-regulation of the ferroportin transcript, but not of the protein, also occurs in haptoglobin-null spleen macrophages, which accumulate free hemoglobin-derived iron. Finally, we demonstrate that hemoglobin induces ferroportin expression in RAW264.7 cells.Taking together these data, we suggest that haptoglobin, by controlling plasma levels of hemoglobin, participates in the regulation of ferroportin expression, thus contributing to the regulation of iron transfer from duodenal mucosa to plasma.
View details for DOI 10.1053/j.gastro.2007.07.004
View details for Web of Science ID 000250036200023
View details for PubMedID 17919498
Plasma protein haptoglobin modulates renal iron loading
AMERICAN JOURNAL OF PATHOLOGY
2005; 166 (4): 973-983
Haptoglobin is the plasma protein with the highest binding affinity for hemoglobin. The strength of hemoglobin binding and the existence of a specific receptor for the haptoglobin-hemoglobin complex in the monocyte/macrophage system clearly suggest that haptoglobin may have a crucial role in heme-iron recovery. We used haptoglobin-null mice to evaluate the impact of haptoglobin gene inactivation on iron metabolism. Haptoglobin deficiency led to increased deposition of hemoglobin in proximal tubules of the kidney instead of the liver and the spleen as occurred in wild-type mice. This difference in organ distribution of hemoglobin in haptoglobin-deficient mice resulted in abnormal iron deposits in proximal tubules during aging. Moreover, iron also accumulated in proximal tubules after renal ischemia-reperfusion injury or after an acute plasma heme-protein overload caused by muscle injury, without affecting morphological and functional parameters of renal damage. These data demonstrate that haptoglobin crucially prevents glomerular filtration of hemoglobin and, consequently, renal iron loading during aging and following acute plasma heme-protein overload.
View details for Web of Science ID 000227919500005
View details for PubMedID 15793279