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The collagen network within the heart, produced by cardiac fibroblasts, provides a structural framework and transmits mechanical information during contraction. Synthesis and organization of collagen increases during neonatal development as the heart adapts to increased hemodynamic load. How fibroblasts organize collagen within the heart is unknown. A three-dimensional fibrin gel model was used to begin to elucidate the mechanisms whereby fibroblasts organize the collagenous matrix. Fibrin gels containing neonatal fibroblasts were fixed after 24-72 hours in culture and examined by confocal microscopy to determine the distribution of fibroblasts, localization of discoidin domain receptor 2 (DDR2) and collagen. Collagen synthesis, measured at both protein and RNA levels, increased indicating that cardiac fibroblasts were laying down new collagen matrix. No significant changes in MMP2 activity in conditioned media were observed. Confocal microscopy revealed that fibroblasts were randomly distributed throughout the fibrin gels and the type I collagen distribution paralleled that of the fibroblasts and overlapped somewhat with the expression of DDR2 on the fibroblast cell surface. These studies demonstrate that fibrin gels are an excellent model system in which to examine collagen organization by cardiac fibroblasts. [ABSTRACT FROM AUTHOR]

The foreign body response to medical devices and materials implanted in the human body, including scarring, fibrous encapsulation, and potential rejection, is a longstanding and serious clinical issue. There are no widely acceptable or safe therapies for ameliorating the foreign body response. Clinical complications resulting from the response include disfigurement of silicone prostheses and loss of function of devices such as implanted pacemakers, stents, and shunts. Cellularized implants and stem cells placed in the body are also subject to the foreign body response with the added issue that the regenerative repair intended to be prompted by the graft may be inhibited. Beneficial modification of the body's reaction to implanted materials, medical devices, engineered constructs, or stem cells would be a fundamentally important therapeutic advance.As part of investigating the cellular response, we have developed a model which uses cells isolated from skeletal muscle biopsy, cultured, and proliferated in vitro. These satellite cells, which are mononucleated progenitor cells, reside between the plasma membrane of the muscle fiber and the basal membrane that encompasses the fiber. While usually quiescent, these cells become activated following muscle damage. Once activated, the satellite cells proliferate, migrate to injured muscle, and participate in repair by fusing with existing muscle fibers or by differentiating into new skeletal muscle fibers. Satellite cells have been shown to be heterogeneous populations of stem cells and progenitor cells. We have developed an explant method for isolating, sorting, enriching, and culturing these cells for use in skeletal muscle regenerative medicine to determine if the foreign body response can be inhibited by manipulating the cell-cell communication.