Addition of purified basal lamina molecules enables Schwann cell ensheathment of sympathetic neurites in culture.

Our aim was to determine the effect of purified basal lamina components on the differentiation of non-myelin-forming Schwann cells accompanying rat sympathetic neurons in culture. Previous work has demonstrated that Schwann cells contacting superior cervical ganglion neurons cultured in the presence of ascorbate and serum fail to effectively deposit matrix and ensheathe neurites unless fibroblasts are also present. We questioned if an increase in the amount of available basal lamina components could mimic fibroblast-induced Schwann cell differentiation. Superior cervical ganglion neuron plus Schwann cell cultures were supplemented with purified basal lamina molecules for up to 7 weeks. The addition of laminin, type IV collagen, heparan sulfate proteoglycan, or a combination of all three components, led to increased basal lamina deposition and increased neurite ensheathment compared with cultures with no additions. In long-term cultures receiving component additions, however, ensheathment was exaggerated, and the Schwann cells were hypertrophic. The ensheathing conformations adopted by these Schwann cells surpassed normal-appearing ensheathment and resembled more unusual unmyelinated nerve morphology found in vivo by others in normal senescence and in several peripheral neuropathies. These experiments show that increased availability of exogenous basal lamina components leads to increased basal lamina deposition and that basal lamina elaboration can have dramatic effects on the morphology of nonmyelinating Schwann cells. These findings suggest that influences of extracellular matrix should be considered when unusual Schwann cell/axon conformations are seen in vivo.