Jiahua Xu - US grants

DESCRIPTION (from the application) Interactions between cells and extracellular matrix (ECM) initiate a flow of information that acts to regulate many fundamental processes in development and differentiation and in pathologic events such as wound healing and cancer invasion. Many cellular functions affected by ECM are transduced at the level of gene expression. During cutaneous wound repair, as fibroblasts change the ECM environment with collagen production, the ECM environment can, in turn, alter selectve gene expression as exemplified by the integrin alpha2 and matrix metalloproteinase-1, which are induced by type I collagen. The mechanisms by which ECM regulates cellular functions including gene expression are under intensive study by many investigators. There are at least three mechanisms by which ECM can regulate cell behavior. First, ECM regulates cell function directly through ligation of cell surface receptors. Second, ECM modulates the actions of cytokines and growth factors. Third, the ECM stimulates the cell via mechanico-chemical signals that occur as the cell undergoes shape changes and skeletal reorganization. Using three-dimensional (3D) tissue culture models developed based on the different stages of the wound healing process and different gene outputs, the applicant has been able to separate ECM signals generated by ECM-cell biochemical interactions from those generated by physical force. The stressed collagen (sCOL) lattice simulates the contractile phase of wound repair while the relaxed collagen (rCOL) lattice simulates the normal dermal environment. Compared to conventional tissue culture plastic and collagen-coated surfaces, 3D sCOL and rCOL stimulate integrin alpha2 expression whereas only rCOL stimulates MMP-1 (collagenase-1) expression. As controls, 3D stressed and relaxed fibrin lattices (sFIB and rFIB) do not induce alpha2 production. However, 3D rFIB stimulates collagenase-1 expression. Taken together, the applicant concludes that: 1) the production of both alpha2 integrin and MMP-1 requires specific spatial arrangement; 2) integrin alpha2 expression is controlled by 3D COL signals generated biochemically which are independent of cell shape or physical factors; 3) MMP-1 expression is controlled by 3D ECM signals generated from physical forces which are independent of ECM biochemical components; and 4) 3D rCOL possesses biochemically and physically versatile signalling potential, dependent upon the specific gene output, i.e., integrin alpha2 or MMP-1. The applicant's objective is to assess the mechanisms by which ECM regulates cellular functions. She proposes to use the expression of integrin alpha2 and MMP-1 as gene output to study biochemical and physical signal transduction pathways of 3D ECM. Since 3D culture systems better simulate in vivo physiology, and since the two gene products under study are involved in embryogenesis, morphogenesis, and cancer development, as well as wound healing, understanding the signal transduction pathways of these ECM paradigms to the respective genes is of substantial importance.

Mammalian organs are composed of cells surrounded by extracellular matrix (ECM) components. Interactions between cells and ECM initiate a flow of information that acts to regulate cell growth, cell migration, programmed cell death, and gene expression. These cell functions in turn affect the tissue integrity and destruction. The regulatory mechanisms by which ECM regulates cellular functions are under intensive study. Since ECM in intact tissue can influence cells in many ways: the biochemical interactions between ECM and their integrin receptors, the spatial arrangement of cell-cell interactions, the cell shape, the mechanical tension, and the cell dynamics, three-dimensional (3D) ECM lattices are developed to simulate the ECM-cell interaction in intact tissue. Cells embedded in this system demonstrate morphology and cellular functions usually observed under physiological condition. The regulation of matrix metalloproteinase I (MMP-1) expression is one of these functions. MMP-1 is principally responsible for collagen turnover in most tissues and, in particular, the skin. It has been found that cells grown in relaxed 3D collagen synthesized more MMP-1 than those in stressed 3D collagen. However, the regulation of MMP-1 expression in a tissue-like setting is far from clear. Taking a comparative approach that employs four types of 3D ECM lattices, relaxed collagen, stressed collagen, relaxed fibrin, and stressed fibrin, we were able to dissect mechanical and biochemical signals from 3D ECM. We demonstrated that relaxed, but not stressed 3D ECM (collagen or fibrin), regardless of biochemical nature, can induce MMP-1 expression, suggesting the mechanical nature of the regulation. However, the comparison between cells cultured in relaxed 3D collagen and fibrin showed the modulation of a different set of signaling molecules, suggesting that the physical signal transduction might employ different signaling pathways depending on the ECM environment. The objective of this grant proposal is to assess the mechanisms by which 3D ECM regulates cellular functions. We propose to use 3D collagen and fibrin as model systems to delineate the regulation of MMP-1, a functional output, in near-physiological condition. The mechanically relaxed and stressed 3D ECM lattices provide a physically distinct environment in the constant biochemical recognition between ECM-integrin receptors whereas the comparison between 3D collagen and fibrin lattices will shed light to the biochemical specificity in ECM mechanical signaling. Since 3D ECM is a tissue-equivalent system and MMP-1 is a gene product involved in embryogenesis, morphogenesis, and cancer development, as well as wound healing, understanding the signal transduction pathways from these ECM paradigms to the MMP-1 expression is of substantial importance.