Polyionic regulation of cartilage development: promotion of chondrogenesis in vitro by polylysine is associated with altered glycosaminoglycan biosynthesis and distribution.

The development of cartilage nodules in cultures of chick limb bud mesenchyme (Hamburger-Hamilton stages 23/24) is significantly promoted when the culture medium is supplemented with (poly-L-lysine (PL) (M(r) greater than or equal to 14K) (San Antonio and Tuan, 1986. Dev. Biol. 115: 313). Here we present findings consistent with the hypothesis that PL may promote chondrogenesis by interacting electrostatically with sulfated glycosaminoglycans (GAGs): (1) poly-L-ornithine, poly-L-histidine, poly-D,L-lysine, and lysine-containing heteropolypeptides stimulate chondrogenesis in proportion to their contents of cationic residues; (2) the effects of PL are diminished when limb mesenchyme cultures are supplemented with exogenous GAGs, including heparin, dermatan sulfate, and chondroitin sulfate; (3) in high density cultures of limb bud mesenchyme, the release of sulfated macromolecules, but not of proteins in general, into the culture medium was significantly inhibited by PL (398K M(r)) treatment, and a net increase in total GAG content of the PL-treated cultures was observed; and (4) in monolayer cultures of cells derived from other chick embryonic tissues, including liver, skeletal muscle, and calvaria, PL treatment promoted the cell layer-associated retention of sulfated GAG. These effects were not observed using the nonstimulatory, low M(r) PL (4K). Based on the above findings and those from previous studies, it is proposed that PL may promote chondrogenesis by interacting electrostatically with cartilage GAGs, thus trapping the extracellular matrix around the newly emerging cartilage nodules and thereby stabilizing their growth and differentiation.