Gary K. Owens, PhD
Cellular and molecular mechanisms that control growth and differentiation of vascular smooth muscle cells during vasculogenesis/angiogenesis
The major long term goals of research in the Owens laboratory are to elucidate cellular and molecular mechanisms that control growth and differentiation of vascular smooth muscle cells (SMC) during vasculogenesis/angiogenesis, and to identify mechanisms that contribute to alterations in the differentiated state of the SMC that contribute to development of vascular diseases such as hypertension or atherosclerosis, as well as to defective vessel maturation within solid tumors. Current studies are aimed at identifying molecular mechanisms that control the coordinate expression of contractile protein genes such as smooth muscle *-actin and smooth muscle myosin heavy chains that are required for the differentiated function of the smooth muscle cell. 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 smooth muscle differentiation genes both in cultured cell systems and in vivo in transgenic mice. In addition, they use a variety of gene knockout, chimera, 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, etc.) in regulation of smooth muscle differentiation during vascular development, or in cardiovascular disease. A particularly exciting recent development is that they have employed smooth muscle specific promoters originally cloned and characterized in their laboratory to create mice in which they can target knockout (or over-expression) of genes of interest specifically to smooth muscle cells. Such systems will permit development of unique and powerful genetic mouse model systems with which to directly explore mechanisms that contribute to vascular development, and remodeling in vivo, as well as to investigate the etiology of a variety of major cardiovascular diseases including hypertension and atherosclerosis. In addition, they have employed these promoters to develop methods for producing purified populations of smooth muscle cells or smooth muscle cell progenitor cells from both embryonic and adult stem cells. The latter studies have tremendous potential for use in either correcting gene defects that contribute to cardiovascular disease, or alternatively delivering therapeutic genes to treat or possibly cure these diseases.
As an extension of their studies focused on SMC investment of endothelial tubes during vascular development and remodeling, they have begun to characterize abnormalities found in tumor vessels. The vasculature within many solid tumors is highly disorganized and contains tortuous and dilated vessels that are highly leaky due to failure to undergo normal maturation and investment with SMC or pericytes. Of particular importance, endothelial tubes formed in tumors that invest normally with SMCs/pericytes have very low rates of tumor cell shedding such that defective maturation or SMC/pericyte investment of tumor vessels is thought to be a major determinant of the rate of tumor cell shedding and metastatic potential. In addition, there is recent evidence from Mukesh Jain's lab that tumor vascular maturation plays a key role in the efficacy of delivery of chemotherapeutic agents and the failure of many anti-angiogenic agent cancer clinical trials. Studies in their lab are focused on utilizing our unique SMC promoter-reporter transgenic, and SMC targeted gene knockout mice in combination with mouse models for cancer progression (both human and mouse tumor lines) to determine cellular and molecular mechanisms responsible for defective investment of tumor vessels, as well as to identify the relative contributions of circulating progenitor cells versus pre-existing SMC to investment of tumor blood vessels. They are also carrying out studies in SMC:tumor cell co-cultures to determine mechanisms whereby tumor cells may inhibit SMC differentiation. Of major interest, they have demonstrated that highly metastatic tumor cells produce a soluble protein that profoundly inhibits differentiation of SMC/pericytes. They are in the process of identifying and identifying this SMC differentiation repressor protein using a combination of proteomic and genomic approaches. Taken together, their in vitro and in vivo studies are likely to provide valuable new insights into mechanisms that contribute to defective maturation of tumor vessels, and possible clinical interventions to modify this to reduce tumor growth, increase susceptibility to chemotherapeutic agents, and reduce overall metastatic potential.
They are collaborating with Dr. Donald Hunt in studies to identify the soluble protein produced by highly metastatic tumor cells that profoundly inhibits differentiation of SMC and pericytes using high throughput mass spec proteomic methods developed in his laboaratory. They have also collaborated extensively with Dr. Hunt to map phosphorylation sites on the rRNA transcription factor UBF, and shown that this is a key rate limiting step in growth of normal and transformed cells. A paper describing these latter studies has been submitted for publication (Lin et al., 2005).
They are collaborating with Dr. Tom Skalak in studies to determine if circulating bone marrow derived stem cells contribute to investment of tumor vessels with SMCs/pericytes. Of major interest, using a novel whole mount vascular preparation in conjunction with their unique SMC promoter lacZ transgenic mice, they have shown minimal contribution of bone marrow derived cells to either SMC or EC lineages within the tumor vasculature. However, they have shown the presence of large number of bone marrow derived cells in a perivascular location suggesting that they could play a key paracrine role in tumor angiogenesis. A manuscript describing these findings is in preparation and they plan on submitting an NIH BME Partnership grant with Dr. Skalak in this area this fall.