Glycosaminoglycans in the basal lamina and extracellular matrix of serially aged mouse mammary ducts.

The synthesis and accumulation of specific glycosaminoglycans into proteoglycans of the basal lamina and extracellular matrix is an important aspect of ductal growth and branching morphogenesis in the mouse mammary gland. The present study was undertaken to determine whether serially aged mammary gland, which has lost most of its growth potential during repeated transplantation, displays altered ability to synthesize and accumulate glycosaminoglycans into the extracellular matrix or basal lamina. Using histochemical and autoradiographic procedures coupled with enzymatic digestion, it is now shown that serially aged mammary ductal tissue synthesizes and incorporates hyaluronate into the basal lamina at the leading edge of the end bud, where growth takes place, and sulfated glycosaminoglycans are accumulated in the extracellular matrix along the end bud flanks, associated with ductal morphogenesis. These patterns of synthesis and accumulation are similar to those associated with the growth of young gland. In non-growing regions, regardless of whether growth termination resulted from serial aging or from normal growth regulatory mechanisms operating in the young gland, sulfated glycosaminoglycans were distributed in the extracellular matrix around the ductal tips. Again, the pattern was similar in young and serially aged gland. We conclude that glycosaminoglycan metabolism and distribution are related to growth status rather than tissue age, and are unlikely to be an important component of mammary senescence.