Impeded Interaction between Schwann Cells and Axons in the Absence of Laminin alpha 4

The Schwann cell basal lamina (BL) is required for normal myelination. Loss or mutations of BL constituents, such as laminin-2 ( alpha 2 beta 1 gamma 1), lead to severe neuropathic diseases affecting peripheral nerves. The function of the second known laminin present in Schwann cell BL, laminin-8 ( alpha 4 beta 1 gamma 1), is so far unknown. Here we show that absence of the laminin alpha 4 chain, which distinguishes laminin-8 from laminin-2, leads to a disturbance in radial sorting, impaired myelination, and signs of ataxia and proprioceptive disturbances, whereas the axonal regenerative capacity is not influenced. In vitro studies show poor axon growth of spinal motoneurons on laminin-8, whereas it is extensive on laminin-2. Schwann cells, however, extend longer processes on laminin-8 than on laminin-2, and, in contrast to the interaction with laminin-2, solely use the integrin receptor alpha 6 beta 1 in their interaction with laminin-8. Thus, laminin-2 and laminin-8 have different critical functions in peripheral nerves, mediated by different integrin receptors.