Engineering the cellular fluidic microenvironment

Our group develops microfluidic biomimetic platforms to study the physical interactions between cells and their microenvironment. We use these platforms to study the biology of cell adhesion and mechanotransduction, the process by which cells sense and respond to physical forces.

 

Defects in adhesion and mechanotransduction contribute to a wide variety of diseases, and our areas of research focus on cardiovascular disease, cancer, and fibrosis. As engineers, we are interested in applying the biological insights learned through implementing our platforms to design and build tissues for regenerative medicine.

Cardiovascular disease - How do the cells of the vasculature regulate what gets into and out of the blood?

Human microvessel on a chip model that led to the discovery of the Notch mechanosensory complex as reported in Polacheck, Kutys et al. Nature 2017.

The vascular endothelium serves as a selective barrier between blood and surrounding tissue, preventing tissue edema and maintaining plasma volume, while enabling the exchange of nutrients and cells to meet tissue demands. Maintenance of the vascular barrier is critical for homeostasis, and barrier dysfunction is a hallmark of cardiovascular disease. Pathologies of vascular permeability present a clinical challenge because of the lack of targeted therapies that stimulate vascular barrier function.

 

Studying vascular permeability is difficult in living animals because of the poor experimental control over pressures and because flows in blood vessels, and traditional tissue culture methods influence the cell-cell and cell-matrix signaling that are thought to regulate permeability. To address these experimental shortcomings, we are working to develop perfusable engineered human blood vessels that demonstrate physiologic barrier function. We are implementing these models to investigate the molecular pathways that regulate barrier function and to define the role of these pathways in cardiovascular disease such as atherosclerosis, reperfusion injury, and stroke with the long-term goal of identifying new molecular targets and strategies for manipulating vascular permeability in the clinic. 

Cancer - How does interstitial transport in the tumor microenvironment contribute to disease progression?

During solid tumor growth, tumor-induced angiogenesis, desmoplasia, and the collapse of draining lymphatics cause increased interstitial fluid pressure (IFP) in the tumor microenvironment. This elevated pressure causes large pressure gradients and elevated interstitial fluid flow at the tumor margin. This interstitial fluid flow is different than the flow of blood in the vasculature. The fluid originates within the tumor and creeps through the tissue, between cells and proteins in the tumor to drain in normal tissue surrounding the tumor. Clinically, elevated IFP correlates with increased metastasis and poor prognosis. Metastasis is the leading cause of cancer-related death, so IFP is a potential tool for clinicians to judge severity of cancer, but the mechanisms by which these pressures and flows contribute to the molecular and cellular events of the metastasis remain unknown.

 

To investigate the role of IFP and interstitial flow in cancer progression and metastasis, we are developing human vascularized tumor models and leveraging these models to study how flow alters cell-cell and cell-matrix adhesion signaling in tumor cells and stromal cells, including fibroblasts. We are also interested in understanding the effects of interstitial flow on immune cell trafficking and surveillance in the tumor microenvironment. The long-term goals of this work are to understand the molecular basis for the connection between IFP and patient prognosis and to inform interventional strategies for preventing metastatic disease.  

Microfluidic breast cancer model that enabled the discovery that interstitial flow guides tumor cell migration as reported in Polacheck et al. PNAS 2011.

Fibrosis - How does vascular leak and pathologic transport contribute to the fibrotic cascade?

3D vascularized tissue models developed to investigate molecular pathogenesis of fibrotic disease, modified from Polacheck et al. PNAS 2014.

Fibrosis related diseases account for roughly 45% of deaths in the developed world. Despite this prevalence and the poor quality of life suffered by patients with fibrotic disease, treatment strategies remain poor to nonexistent. This lack of effective treatment is due in part to a poor understanding of the molecular and cellular events that lead to excessive extracellular matrix deposition, which defines the disease and ultimately impairs organ function. Furthermore, because the events that lead to fibroblast activation and matrix synthesis are unknown, there are no effective markers to detect early stage disease, and thus diagnosis typically occurs after irreversible changes to the matrix structure and density have already occurred.

 

A growing body of work indicates that chronic vascular leak precedes fibroblast activation in idiopathic pulmonary fibrosis, kidney fibrosis, and scleroderma, but how this leak and associated endothelial dysfunction contribute to disease progression is unknown. We are developing 3D vascularized models of fibrosis to investigate the cellular crosstalk among the vascular, stromal, and tissue-specific cells that lead to fibroblast activation, with a specific focus on the role of pathologic fluid transport induced by vascular leak. The long-term goals of this work are to understand the molecular pathogenesis of fibrosis and to develop platforms for screening molecular targets to halt the fibrotic cascade to maintain organ function and improve patient quality of life.

Regenerative medicine - Can we develop mature tissues in vitro for implantation to supplement or repair organ function?

A major hurdle in the development of tissue engineered therapy for organ replacement is generating stable vasculature that provides nutrients and removes waste from engineered tissues. In addition to developing vascularized human microtissues for basic science and disease modeling as described above, we are working to improve the stability of the vascular component of these tissues to learn the molecular cues necessary to engineer vascular networks that function in vivo. We are also implanting these in vitro microtissues into animal models to investigate how the engineered vasculature interfaces with the native host vasculature. The long-term goal of this work is to define the biological parameters that govern vascular tissue engineering to inform the development of vascularized tissue engineered therapies.  

By controlling the local environment, hemodynamics, and gene expression in endothelial cells we can control whether vessels grow (left) or remain stable (right).

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© 2018 by William Polacheck.

UNC NC State BME