Induction of cholinergic function in cultured sympathetic neurons by periosteal cells: Cellular mechanisms

Periosteum, the connective tissue surrounding bone, alters the transmitter properties of its sympathetic innervation during development in vivo and af ter transplantation. Initial noradrenergic properties are downregulated and the innervation acquires cholinergic and peptidergic properties. To elucid ate the cellular mechanisms responsible, sympathetic neurons were cultured with primary periosteal cells or osteoblast cell lines. Both primary cells and an immature osteoblast cell line, MC3T3-E1, induced choline acetyltrans ferase (ChAT) activity. In contrast, lines representing marrow stromal cell s or mature osteoblasts did not increase ChAT. Growth of periosteal cells w ith sympathetic neurons in transwell cultures that prevent direct contact b etween the neurons and periosteal cells or addition of periosteal cell-cond itioned medium to neuron cultures induced ChAT, indicating that periosteal cells release a soluble cholinergic inducing factor. Antibodies against LIF R beta, a receptor subunit shared by neuropoietic cytokines, prevented ChAT induction in periosteal cell/neuron cocultures, suggesting that a member o f this family is responsible. ChAT activity was increased in neurons grown with periosteal cells or conditioned medium from mice lacking either leukem ia inhibitory factor (LIE) or LIF and ciliary neurotrophic factor (CNTF). T hese results provide evidence that periosteal cells influence sympathetic n euron phenotype by releasing a soluble cholinergic factor that is neither L IF nor CNTF but signals via LIFR beta.