Sem Phan, Ph.D, M.D.
Academic Training: PhD Chemistry 1975 Indiana University; MD 1976 Indiana University
Residency Training: Anatomic Pathology 1976-1980 University of Connecticut Health Center; Board Certified 1979
Current Positions: Member, National Advisory Environmental Health Sciences Council, National Institute of Environmental health Sciences - National Institute of Health
Research in this laboratory is directed at understanding the cellular and molecular mechanisms of tissue repair and fibrosis. Current projects are directed at 5 major interrelated directions. First, recent studies document a contribution by bone marrow progenitor cells to fibrosis in a rodent model of pulmonary fibrosis induced by bleomycin. Phenotypic and functional characterization reveal that these bone marrow derived cells express low levels of collagen type I, high levels of telomerase and have distinctive morphology that distinguish them from endogenous lung fibroblasts. Moreover these cells do not differentiate to myofibroblasts, even when treated with TGFβ. The role of these cells in fibrosis is currently being further elucidated. Second, in the course of the bone marrow progenitor cell studies, the expression of induced telomerase reverse transcriptase (TERT) in these cells is noted. Previously we have shown the induction of telomerase in the bleomycin model of pulmonary fibrosis and recently have examined the role of this induction using TERT null mice. These studies in conjunction with bone marrow chimera mice reveal a key role for a bone marrow derived fibroblast-like cell population for fibrosis in this model. Furthermore the findings reveal that this population is responsible for a major part of the telomerase induction in the lung in this model. The role of TERT induction appears not to have much to do with maintenance of telomere length in this model. The mechanism of TERT induction is being studied by assessing the role of growth factor ligands and transcriptional regulation of the TERT gene itself. These findings in conjunction with the bone marrow progenitor cell studies argue for a critical role of the bone marrow in fibrotic lung disease. Future therapies must deal with this key contribution by bone marrow derived fibroblast like cells in a selective manner that do not interfere with the normal, beneficial epithelial repair process in the injured lung tissue itself. Third, previous cDNA microarray analysis reveals marked induction of found in inflammatory zone 1 (FIZZ1 or resistin-like molecule α [RELMα]) in the bleomycin model in epithelial cells and macrophages, but which is not expressed by lung fibroblasts. Subsequently it is shown that FIZZ1 is an inducer of myofibroblast differentiation, and current studies suggest mediation by Notch1 signaling resulting in activation of CBF with direct transcriptional activation of the α-smooth muscle actin gene. These studies are continuing with development of the FIZZ1 knockout mouse and attempts at identification of the FIZZ1 receptor. FIZZ1 in rodents appear to have similar functional activities as FIZZ2 in humans. Fourth, analysis of the mechanisms of myofibroblast differentiation focuses on transcriptional and epigenetic regulation of the α-smooth muscle actin gene, a key marker of myofibroblast differentiation. We have identified the importance of several interacting transcription factors, including Smad3, GKLF (KLF4), and C/EBPβ, in regulation of the α-actin promoter, and are currently working on additional putative repressors of expression. Epigenetic studies revealed highly methylated CpG islands on the promoter, while the downstream intronic regions are also highly methylated in alveolar epithelial cells, which do not normally express this actin isoform. Analysis of the various DNMTs indicates important roles for certain isoforms in regulating induction of myofibroblast differentiation. Finally, studies of the role Hedgehog signaling in pulmonary fibrosis have been initiated to concentrate on its role in epithelial-mesenchymal cross-talk of potential importance to induction of myofibroblast differentiation and epithelial regeneration.