Stem cell mechanobiology and tissue engineering

Tissue engineering is a promising approach for the replacement and regeneration of damaged or diseased tissues and organs. Typical tissue engineering strategies seek to replicate components of the natural cellular microenvironment, including the extracellular matrix and soluble proteins. In the case of load-bearing tissues, mechanical stimulation is likely also required to engineer functional tissues. By providing specific complementary cues, the phenotype of host or transplanted cells can be regulated to guide tissue and organ regeneration. A critical step to defining design criteria for the next generation of functional tissue engineering systems is to determine how multiple exogenous cues integrate intracellularly to regulate cell function.

Using a variety of cell culture models and in vivo experimentation, we are systematically and quantitatively investigating the integrated response of cells to combinations of relevant mechanobiological stimuli. The focus of our work is skeletal tissue engineering using mesenchymal stem cells (MSCs). MSCs have the ability to differentiate to several musculoskeletal cell types, and therefore are a promising autologous source for cell-based skeletal regeneration. We have identified several regulators of MSC osteogenic and chondrogenic differentiation of relevance to skeletal tissue engineering, including matrix-mediated signals, osteogenic growth factors, and mechanical stimuli.

We are currently extending this work to determine relationships between multiple mechanobiological cues and the integrated response of MSCs. Our goal is to identify combinations of stimuli that guide cell function predictably and optimally, and in collaboration with biomaterial scientists apply these design criteria to develop novel 'mechanoactive' tissue engineering systems, bioreactors, and ex vivo growth protocols for functional skeletal tissue engineering.

Heart valve mechanobiology and disease

Cardiovascular diseases are the underlying cause of one third of all deaths in Canada. Sclerosis (thickening and calcification) of the aortic valve is one of the most common cardiovascular diseases and is associated with significant morbidity. While traditionally believed to be a degenerative 'wear and tear' disease, recent evidence suggests the etiology of valvular calcification is far more complex, involving active cell-mediated processes, such as inflammation, lipid modification, and actual bone tissue formation within the valve matrix. However, until the cellular and molecular regulators of these processes are identified, the only treatment available for valve sclerosis is surgical replacement.

Notably, the regions of the valve most susceptible to calcification are exposed to distinct hemodynamic and biomechanical stimuli, suggesting a previously unrecognized mechanobiological basis for the disease. Using state-of-the-art microgenomics approaches, we are profiling spatial variations in gene expression by endothelial and interstitial cells from disease-prone versus disease-protected regions of the valve. This approach has generated novel insights and several hypotheses regarding the molecular regulators of valvular calcification. We are investigating many of these hypotheses using in vitro co-culture systems that allow us to mechanically stimulate valves cells and probe their phenotypic expression. In support of the cell culture studies, we are developing multiscale finite element approaches to relate tissue-level deformations to cellular-level deformations, thereby allowing better characterization of the mechanical stimuli experienced by valve interstitial cells.

By integrating functional genomics studies in vivo, mechanistic experiments in vitro, and computational biomechanics, we aim to determine cause-effect relationships between mechanobiological stimuli, the molecular regulators of valvular calcification, and the progression of the disease. In doing so, we hope to better understand the cellular and molecular basis for valvular calcification, with the goal of identifying therapeutic targets for its prevention and treatment.

BioMEMS for high-throughput mechanobiology

The phenotypic expression and function of cells are regulated by their integrated response to their microenvironmental cues. This implies, for instance, that the response of a cell to a mechanical stimulus may be modulated by a biochemical signal it is experiencing and vice versa. Being able to predict and ultimately control the integrated cellular response is the basis of all therapeutic strategies, and therefore is of broad scientific importance. However, conventional approaches to investigate the effects of mechanobiological stimuli on cell fate tend to be cumbersome, require large amounts of costly reagents, and have limited throughput. These limitations have prevented systematic investigations of the effects of multiple mechanobiological stimuli on cell phenotype.

To address the limitations of current approaches and improve the capacity for discovery, we are developing new platforms for mechanobiological research. In conjunction with collaborators in the Department of Mechanical & Industrial Engineering, we are developing microfabricated arrays of miniaturized mechanobioreactors that permit perturbation of small populations of cells with mechanical and non-mechanical (e.g., cytokines, matrix components) stimuli in a combinatorial, highly parallel fashion. The miniaturized cell-based arrays minimize reagent requirements and will be coupled with advanced biological tools to permit rapid, high content, real-time monitoring of biological effects.

The integration of microfabrication, cell mechanics, and advanced biology will provide a versatile platform for discovery-based science with which relationships between multiple cues and integrated cellular responses can be determined in a rapid, systematic manner. This approach may therefore lead to unexpected discoveries and control strategies that could not be predicted a priori based on knowledge of the phenotypic effects of an isolated stimulus.

2011/09/08 16:40