Fabio Rossi, M.D., Ph.D.
Professor, Department of Medical Genetics
Co-Director, Biomedical Research Centre
Hematopoietic stem cell migration
Transplantation of mobilized Hematopoietic Stem Cells (HSCs) is the best example of cellular therapy available today, and the only one to be routinely used worldwide. Yet, the mechanisms underlying the ability of HSCs, after their infusion in the bloodstream, to find niches that support their self-renewal are nearly completely unknown. Furthermore much of the current research is based on infusion of stem cells in lethally irradiated recipients, a poor model for the low-conditioning protocols in use in human patients. The elucidation of these homing mechanisms may lead to strategies to improve HSC engrafting efficiency and thus to a reduction of the number of stem cells required for transplantation. This would not only greatly improve the prospects for successful gene therapy by reducing the number of engineered stem cells required for engraftment. It may also enable us to use banked cord blood for transplantation of adult patients, which may in the future obviate the need for allogenic transplants. During the past year we have developed novel assays for stem cell migration that will allow us to study the molecular mechanisms underlying this important phenomenon. In collaboration with Dr. Ziltener’s group at the BRC we have used these assays to demonstrate a role of P-selectin as the effector of a previously unreported feedback loop linking stromal niche availability with T-cell progenitor recruitment to the thymus. In the coming year we will expand these studies to hematopoietic stem cells.
Stem cell plasticity
Adult stem cells are present in every tissue and play a major role in the maintenance and repair of all the major body systems. Their tasks range from the daily production of the massive numbers of cells required for maintaining blood homeostasis to the occasional repair of injury in adult muscle. Recently, we and others have proposed that a subset of adult stem cells originating in one tissue may cross organ “boundaries” and “transdifferentiate” to participate in the repair of tissues different than the one they originate from. It is clear from work from a number of groups including ours that within the progeny of hematopoietic stem cells some cells are capable of integrating into damaged myotubes, potentially participating in their repair. It has been proposed that these cells enter the damaged myotube by fusion, and that only subsequently they are reprogrammed from to a myogenic fate. This suggests that, similarly to what take place during “cloning”, nuclear reprogramming can take place in somatic cells in vivo. Despite this progress, several questions are left unanswered:
- Which lineage among the several that spawn from hematopoietic stem cells is responsible for this phenomenon?
- Is direct fusion into mature myotubes a requirement, or can circulating cells fuse into mononucleated precursors yielding a myogenic cell that can still expand?
- Can fusion be enhanced to the point that it becomes therapeutically useful?
The role of microglial cells in neurodegenerative disease
The early activation and proliferation of microglia is a hallmark of many neurodegenerative diseases, and in many cases it is evident prior to the beginning of overt symptoms. Microglial cells are the functional counterparts of tissutal macrophages in the central nervous system and they share the same origins from hematopoietic stem cells. The role of microglia in the progression of these diseases is debated. While on one hand they clear potentially toxic debris through their scavenger action, they also produce pro-inflammatory molecules some of which, such as TNFa, have a direct deleterious effect on neuronal survival. Using a mouse model of amyotrophic lateral sclerosis we will assess the influence of microglia on the pathogenesis of this disease. Furthermore, we will take advantage of the recruitment of microglial precursors to deliver therapeutic neurotrophins locally to the ailing motorneurons.
Chromatin organization and lineage choice
Ultimately, the fate that a given cell will acquire is controlled by the combination of transcription factors active in its nucleus. As more of these transcriptional regulators are identified, it is now becoming clear that they act in concert, instead of individually, to determine a cell’s phenotype. A second level of transcriptional regulation is provided by the organization of chromatin in permissive or repressive domains. How is this organization achieved? It is currently thought that posttranslational modifications of histones may establish a combinatorial code of that ultimately controls the access of transcription factors to whole families of genes (transcriptional memory). To investigate the role of specific histone modifications in cell fate determination within hematopoiesis we are now beginning to use functional genetics and lentiviral mediated RNA interference. Our efforts are focused on SET domain-containing proteins. SET domains are associated with methyltransferase activity, and many members of this family can methylate histones as well as key transcription factors. As methylation is thought to be one of the most stable chromatin modifications, it is a good candidate to mediate the establishment and maintenance of “transcriptional memory” and thus for ensuring lineage fidelity.
Lemos DR, Paylor B, Chang C, Sampaio A, Underhill TM, Rossi FM. “Convergent White Adipogenic Progenitors of Different Lineages Participate in a Diffused System Supporting Tissue Regeneration.” 2012. Stem Cells. 13:1082 in press
Le Su, Arthur V. Sampaio, Kevin B. Jones, Marina Pacheco, Angela Goytain, Shujun Lin, Neal Poulin, Lin Yi, Fabio M. Rossi, Juergen Kast, Mario R. Capecchi, T. Michael Underhill, Torsten O. Nielsen. Deconstruction of the SS18-SSX Fusion Oncoprotein Complex: Insights into Disease Etiology and Therapeutics. Cancer Cell, in press
Leslie Ann So Alfaro, Sarah A. Dick, Ashley L. Siegel, Adam S. Anonuevo, Kelly M. McNagny, Lynn A. Megeney, Dawn D.W. Cornelison, Fabio M.V. Rossi. CD34 promotes satellite cell motility and entry into proliferation to facilitate efficient skeletal muscle regeneration. Stem Cells, 2011 Oct 13. doi: 10.1002/stem.759.
Michael Long, Fabio M.V. Rossi. Targeted Cell Fusion Facilitates Stable Heterokaryon Generation In Vitro and In vivo. Plos One 2011, Oct 24 6(10):e26381
Leung DC, Dong KB, Maksakova IA, Goyal P, Appanah R, Lee S, Tachibana M, Shinkai Y, Lehnertz B, Mager DL, Rossi F, Lorincz MC. Lysine methyltransferase G9a is required for de novo DNA methylation and the establishment, but not the maintenance, of proviral silencing.
Proc Natl Acad Sci U S A. 2011 Apr 5;108(14):5718-23.
Sanja Sekulovic, Vala Gylfadottir, Irma Vulto, Maura Gasparetto, Yasmine Even, Christy Brookes, Clayton Smith, Connie J. Eaves, Peter M. Lansdorp, Fabio M. Rossi, and R. Keith Humphries. Prolonged self-renewal activity unmasks telomerase control of telomere homeostasis and function of mouse hematopoietic stem cells. Blood 2011 118:1766-1773
(Sekulovic and Gylfadottir shared first authorship; Rossi and Humphries shared senior authorship)
Bernhard Lehnertz, Felix-M. Schulze and Fabio M. V. Rossi. “The Set7/9 lysine methyltransferase is dispensable for p53 transcriptional activity and tumour suppression in vivo.”
Molecular Cell 2011, 43:673.
Bahareh Ajami, Jami Bennet, Kelly McNagny, Charles Krieger and Fabio MV Rossi. “ Infiltrating monocytes trigger EAE progression but fail to contribute to the resident microglia pool”. Nature Neuroscience, 2011 14:1142
Even Y, Bennett JL, Sekulovic S, So L, Yi L, McNagny KM, Humphries RK, Rossi FMV.. NUP98-HOXA10hd-expanded hematopoietic stem cells efficiently reconstitute bone marrow of mismatched recipients and induce tolerance. Cell Transplant. 2011 Aug 18; 20(7):1099-108.
Hiroyuki Jinno, Olena Morozova, Jeffrey A. Biernaskie, Maryline Paris, Ryoichiro Hosokawa, Michael Rudnicki, Yang Chai, Fabio Rossi, Marco Marra, and Freda D. Miller. Convergent genesis of an adult neural crest-like dermal stem cell from two distinct developmental origins. Stem Cells, 2010 11:2027.
Yi Yang,; Fabio MV Rossi; Edward Putnins. Periodontal Regeneration Using Engineered Bone Marrow Mesenchymal Stromal Cells. Biomaterials. 2010 Nov;31(33):8574-82.
Bernhard Lehnertz, Jeffrey P. Northrop, Frann Antignano, Kyle Burrows, Sima Hadidi, Sarah C. Mullaly, Fabio M.V. Rossi and Colby Zaph. Activating and inhibitory functions for the histone lysine methyltransferase G9a in T helper cell differentiation and function. J. Exp. Med. 2010 May 10;207(5):915-22. Epub 2010 Apr 26.
Anuradha Natarajan, Dario Lemos and Fabio M.V. Rossi Fibro/adipogenic progenitors: A double-edged sword in skeletal muscle regeneration. Cell Cycle 2010 Jun 19;9(11).
Aaron W.B. Joe, Lin Yi, Anuradha Natarajan, Fabien Le Grand, Leslie So, Joy Wang, Michael A. Rudnicki, Fabio M.V. Rossi. Muscle injury activates resident fibro/adipogenic progenitors that facilitate myogenesis. Nature Cell Biology, 2010. doi:10.1038/ncb201
Kevin Siggers, Hanspeter Frei, Goran Fernlund and Fabio Rossi. Effect of bone graft substitute on marrow stromal cell proliferation and differentiation. . J Biomed Mater Res A. 2010 Sep 1;94(3):877-85
Joe AW, Yi L, Even Y, Vogl AW, Rossi FMV. Depot specific differences in adipogenic progenitor abundance and proliferative response to high-fat diet. Stem Cells. 2009 Aug 5;27(10):2563-2570. PMID: 19658193
Chiming Yang, Hanspeter Frei, Fabio M. Rossi, Helen M. Burt. The differential in vitro and in vivo responses of bone marrow stromal cells on novel porous gelatin-alginate scaffolds. J Tissue Eng Regen Med. 2009 Epub ahead of print PMID: 19685485
Mike A. Long and Fabio M.V. Rossi. Silencing Inhibits Cre-mediated Recombination of the Z/AP and Z/EG Reporters in Adult Cells. PLoSONE 2009;4(5):e5435. Epub 2009 May 5.
Klaus Gossens, Silvia Naus, Stephane Y. Corbel, Shujun Lin, Fabio M. V. Rossi, Jürgen Kast, & Hermann J. Ziltener. Thymic progenitor homing and lymphocyte homeostasis are linked via S1P controlled expression of thymic P-selectin/CCL25. J. Exp. Med.. 2009 Apr 13;206(4):761-78. Epub 2009 Mar 16.
Chiming Yang; Hanspeter Frei; Helen M Burt; Fabio M. V. Rossi. “Effects of continuous and pulsatile PTH treatments on rat bone marrow stromal cells” Biochem Biophys Res Commun. 2009 Mar 20;380(4):791-6. Epub 2009 Feb 3.
Coral-Ann B. Lewis, Jennifer N. Solomon, Fabio M. Rossi, Charles Krieger “Bone marrow-derived cells in the central nervous system of a mouse model of amyotrophic lateral sclerosis are associated with blood vessels and express CX3CR1”. Glia. 2009 2009 Oct;57(13):1410-9. PMID: 19243075
Kimberly Kadadar; Lin Yi; Yusra Ahmad; Leslie So; Fabio Rossi; Grace K. Pavlath. “Sca-1 expression is required for efficient remodeling of the extracellular matrix during skeletal muscle regeneration”. Dev. Biol. 2009 Feb 1;326(1):47-59. Epub 2008 Nov 6.
Clas B. Johansson, Sawsan Youssef, Kassie Koleckar, Colin Holbrook, Regis Doyonnas, Stephane Y. Corbel, Lawrence Steinman, Fabio M.V. Rossi, and Helen M. Blau. “Extensive fusion of haematopoietic cells with Purkinje neurons in response to chronic inflammation”. Nature Cell Biology 2008 May;10(5):575-83. Epub 2008 Apr 20.
Bahareh Ajami, Jami Bennett, Charles Krieger, Wolfram Tetzlaff, and Fabio M.V. Rossi. “Local self-renewal can sustain CNS microglia maintenance and function throughout adult life”. Nature Neuroscience. 2007 Dec;10(12):1538-43.
Rossi FMV, Corbel SY, Merzaban JS, Carlow DA, Gossens K, Duenas J, So L, Yi L, Ziltener HJ. Homing of adult thymic progenitors is mediated by P-selectin and its ligand PSGL-1. Nature Immunology 6:626-634, 2005.
Corbel SY, Lee A, Yi L, Duenas J, Brazelton TR, Blau HM, Rossi FMV. Contribution of Hematopoietic Stem Cells to Skeletal Muscle. Nature Medicine 9(12):1528-1532, 2003.
Farshad Babaeijandaghi, Graduate Research Assistant
Vittoria Canale, Research Assistant/Technician
Chikai Chang, Research Assistant/Technician
Christine Eisner, Graduate Research Assistant
Elena Groppa, Postdoctoral Fellow
William Kennedy, Lab Assistant
Coral-Ann Lewis PhD, Postdoctoral Fellow
Marcela Low Mansilla PhD, Postdoctoral Fellow
Phuong Nguyen, Graduate Research Assistant
Hesham Soliman, Postdoctoral Fellow
Lin Yi MSc., Research Assistant/Technician
Jack Yuan, Co-op Student
Regan-Heng Zhang, Graduate Research Assistant