Biomedical Sciences Graduate Program(s)
Biomedical Sciences Graduate Programs
There is clear evidence that altered control of the differentiated state of vascular smooth muscle cells (SMC), or SMC phenotypic switching, plays a critical role in development of a number of major human diseases including atherosclerosis, hypertension, asthma, and cancer. However, the mechanisms and factors that regulate SMC phenotypic switching in these diseases are poorly understood. A major long-term goal of our laboratory has been to elucidate cellular and molecular mechanisms that control the growth and differentiation of SMC during normal vascular development, and to determine how these control processes are altered during vascular injury or in disease states [see review by Alexander et al.1]. For example, a major focus of previous studies has been to identify molecular mechanisms that control the coordinate expression of genes such as smooth muscle a–actin (SM ?-actin), SM22?, and smooth muscle myosin heavy chains (SM MHC) that are required for the differentiated function of the SMC. Studies involve use of a wide repertoire of molecular-genetic techniques and include identification of cis elements and trans regulatory factors that regulate cell-type specific expression of SMC differentiation marker genes both in cultured cell systems and in vivo in transgenic mice. In addition, we use a variety of gene knockout, mouse chimeric, and gene over-expression approaches to investigate the role of specific transcription factors and local environmental cues (e.g. growth factors, mechanical factors, cell-cell and cell-matrix interactions, hypoxia, inflammatory cytokines, etc.) in regulation of SMC differentiation in vivo during vascular development, as well as following vascular injury, or with cardiovascular disease 2, 3.
A particularly exciting recent development is that we have employed SMC specific promoters originally cloned and characterized in our laboratory to create mice in which we can target conditional knockout (or over-expression) of genes of interest specifically to SMCs and also perform rigorous SMC-pericyte lineage tracing experiments to define mechanisms that control phenotypic transitions of these cells during injury-repair and in diseases such as atherosclerosis. Remarkably, using these model systems, we have recently shown that SMC-pericytes de-differentiate, give rise to mesenchymal stem cell (MSC)-like cells, and trans-differentiate into alternative cell types during development of experimental atherosclerosis, as well as in models of myocardial infarction, lung injury, skin wounding, and partial hepatectomy. Moreover, we have shown that the phenotypic transitions of SMC-pericytes in these models is regulated by activation of stem cell pluripotency genes, including Oct4 (manuscript in review), and Klf43, 4, factors also shown to be involved in reprogramming of somatic cells into induced pluripotential stem (iPS) cells.
Our lab has also pioneered studies of the role of epigenetic mechanisms in control of SMC differentiation and phenotypic switching5, as well as lineage determination of multiple specialized cell types from embryonic stem cells (ESC)6. Of major interest, we have shown that lineage determination of SMC, as well as other specialized cells from ESC, involves acquisition of locus- and cell-type selective histone modifications that influence chromatin structure and permissiveness of genes for transcriptional activation. Moreover, we have demonstrated that phenotypic switching of SMC into alternative cell types involves reversal of a subset of these histone modifications and transcriptional silencing of SMC marker genes. However, these cells retain certain histone modifications that we hypothesize serve as a mechanism for “cell lineage memory” during reversible phenotypic switching. That is, a mechanism that allows a SMC to undergo transient transitions to alternative phenotypes necessary for vascular repair, but which biases the cell into re-differentiating into a SMC once the repair is complete. Of major significance, we have recently developed a powerful new assay that allows assessment of specific histone modifications within single cells within fixed tissue specimens (i.e. a single cell chromatin immunoprecipitation assay) to further test this hypothesis within our various in vivo model systems.
Finally, a major long term emphasis of the lab is to translate results of our basic science studies into advancing clinical practice. Current projects in this area include testing how inhibition of IL-1? signaling may help promote increased stability of atherosclerotic plaques thus reducing the probability of a heart attack or stroke. In addition, we are investigating ways to therapeutically augment the stem cell like properties of SMC-pericytes as a means to treat a wide range of major human diseases.
(1) Alexander MR, Owens GK. Epigenetic Control of Smooth Muscle Cell Differentiation and Phenotypic Switchingin Vascular Development and Disease. Annu Rev Physiol 2012 February 15;74:13-40.
(2) Wamhoff BR, Hoofnagle MH, Burns A, Sinha S, McDonald OG, Owens GK. A G/C Element Mediates Repression of the SM22a Promoter Within Phenotypically Modulated Smooth Muscle Cells in Experimental Atherosclerosis. Circ Res 2004 November 12;95(10):981-8.
(3) Yoshida T, Kaestner KH, Owens GK. Conditional Deletion of Kruppel-Like Factor 4 Delays Downregulation of Smooth Muscle Cell Differentiation Markers but Accelerates Neointimal Formation Following Vascular Injury. Circ Res 2008 June 20;102(12):1548-57.
(4) Salmon M, Gomez D, Greene E, Shankman L, Owens GK. Cooperative Binding of KLF4, pELK-1, and HDAC2 to a G/C Repressor Element in the SM22alpha Promoter Mediates Transcriptional Silencing During SMC Phenotypic Switching In Vivo. Circ Res 2012 August 31;111(6):685-96.
(5) McDonald OG, Wamhoff BR, Hoofnagle MH, Owens GK. Control of SRF binding to CARG-box chromatin regulates smooth muscle gene expression in vivo. J Clin Invest 2006;116:36-48.
(6) Gan Q, Yoshida T, McDonald OG, Owens GK. Concise review: epigenetic mechanisms contribute to pluripotency and cell lineage determination of embryonic stem cells. Stem Cells 2007 January;25(1):2-9.
Link to PubMed Listings for this Mentor
(Find Out How to Update Your Faculty Profile)
||PO Box 801394 Robert M. Berne Cardiovascular Research Cen,
||+1 434-924-2652, +1 434-924-9173