Hyaluronan is a fundamental component of the extracellular matrix (ECM), having essential roles in embryonic development, tissue hydration, and cell homeostasis. However, in many disease states hyaluronan can have a deleterious effect on tissue remodeling and function. To investigate the cell-mediated role of HA within the ECM, cells overexpressing the hyaluronan synthases (has-1, has-2, has-3) or the empty vector control (LXSN), were seeded within collagen gel scaffolds. In Specific Aim I, gels were grown under static tension for 6 weeks. The collagen gels containing has overexpressing cells had significantly increased retention and secretion of hyaluronan; reduced contraction; reduced collagen density; and significantly altered material properties vs. LXSN controls. These results indicate that the endogenous overproduction of hyaluronan within collagen gels alters their material, morphological and biochemical characteristics.
In Specific Aim II, collagen gels containing has overexpressing cells and LXSN control cells were grown in a cyclic strain environment. Cyclic strain caused a significant elevation in the collagen fibril density, cell number, and hyaluronan content of the resulting collagen gels compared to those grown under a static strain regimen. The material behavior of collagen gels containing has overexpressing cells were weakened compared to controls. Transmission electron microscopy and immunohistochemistry showed that proteoglycan distribution was influenced by both strain and the specific has isozyme overexpressed.
In Specific Aim III the effects of exogenous HA addition were examined in collagen gels containing either LXSN or has overexpressing cells. It was found that while exogenous high molecular weight HA reduced the diameter of collagen gels containing LXSN cells, the endogenous overproduction of HA (also of high molecular weight) caused the opposite effect. Furthermore, HA oligosaccharides caused an increase in the diameter of collagen gels containing LXSN cells, but had no effect in the has overexpressing groups. Similarly, the ultimate tensile strength was increased upon the addition of exogenous high molecular weight HA to collagen gels containing LXSN cells, but not has overexpressing cells.
In this research collagen gels were used to simulate the impact of endogenously produced hyaluronan on overall extracellular matrix organization. This research provides an important step in understanding the role of hyaluronan within soft tissues, and offers insight into hyaluronan mediated pathological remodeling.