Mechanotransduction Across Networks

Cells sense a wide variety of mechanical inputs from their environment that drive processes such as growth, migration, synthesis, and inflammation. Integrin based adhesions form the basis for extracellular matrix mechanosensing and remodeling. However, they are just one linkage in a series of force networks that allow for transmission and sensing within the cell. Extracellular matrix (ECM) forces are directly transmitted through force sensitive focal adhesion adaptor molecules (talin, vinculin) to the force generating actomyosin cytoskeleton which connects to the nuclear envelope via the linker of nucleoskeleton and cytoskeleton (LINC) complex (nesprin, sun, lamin). While the core components of many mechanosensing networks have been well described over the last ~30 years, there remains gaps in our understanding of the internetwork transmission of forces and its importance in activation of downstream signaling. We use a variety of fluorescence imaging techniques to disect force transfer networks within the cell that drive mechanotransduction.

Directional Mechanosensing

Mechanical signals are known to play a central role in tissue morphogenesis, homeostasis, and degeneration. One critical mechanosensing process, is the sensing of directionality of forces and force gradients. Cells exposed to a stiffness gradient display directional migration up this gradient (durotaxis). Cells seeded on aligned matrices orient parallel to alignment direction (contact guidance). Additionally, external mechanical forces such as tensile stress, fluid shear stress, and asymmetric boundary conditions can induce cellular reorientation and alignment (mechanical polarization). These types of directional mechanosensing are known to occur both in vitro and in vivo, with important contributions to several physiologic processes and diseases such as cancer and fibrosis. While in some cases, this sensing appears to be an emergent behavior at the population scale, there are also indications that individual cells and individual mechanosensitive molecules within the cells can sense and alter their activity in response to force direction. We are focused on understanding how directionally force sensative domains within cellular adhesion proteins regulate and enable directional mechanosensing.

Dynamic Forces in Mechanosensing

While cells do eventually reach steady state with regards to a given mechanical input (stiffness, stretch, fluid shear stress), the process of sensing itself occurs through a dynamic network of proteins on the molecular scale. While studying mechanosensitive pathways using downstream readouts (translocation, transcription, protein expression) provides an understanding of what the cells do in response to a given stimulus, it does not provide the upstream molecular mechanisms by which this occurs.  Realistically, it is these upstream biophysical events, at the molecular scale, that will provide a clear picture of mechanosensing.  Our techniques enable us to measure forces and dynamics in living cells.

Fibrosis and Tissue Homeostasis

Mechanosensing plays a critical role in tissue homeostasis, which when perturbed often results in a fibrotic disease process. These fibrotic diseases are the result of tissue remodeling that drives a progressive and irreversible stiffening of the extracellular matrix. The normal homeostatic processes that maintain tissue mechanical properties under healthy conditions require both positive and negative feedback mechanisms. We study how post translational regulation through miRNAs provides negative feedback that allows for tissue homeostasis.  We also focus on approaches for delivery of antifibrotic miRNA to mitigate disease progression. In particular, we are interested in understanding how integrin based mechanosensing regulates fibrotic and inflammatory feedback loops that are activated during degeneration of the intervertebral disc of the spine.