Expression of dystroglycan and laminin-2 in peripheral nerve under axonal degeneration and regeneration

In Schwann cells, the transmembrane glycoprotein beta-dystroglycan composes the dystroglycan complex, together with the extracellular glycoprotein alp ha-dystroglycan which binds laminin-2, a major component of the Schwann cel l basal lamina. To provide clues to the biological functions of the interac tion of the dystroglycan complex with laminin-2 in peripheral nerve, the ex pression of beta-dystroglycan and laminin-alpha 2 chain was studied in rat sciatic nerves undergoing axonal degeneration and regeneration as well as i n normal condition. In normal sciatic nerve, immunoreactivity for the cytop lasmic domain of beta-dystroglycan was consistently and selectively localiz ed in the Schwann cell cytoplasm underlying the outer (abaxonal) membrane a pposing the basal lamina. While beta-dystroglycan expression was gradually down-regulated in Schwann cells losing contact with axons during axonal deg eneration, it was progressively up-regulated as the regenerating process of ensheathment and myelination proceeded during regeneration. Interestingly, beta-dystroglycan expression, when detectable, was always restricted to th e Schwann cell cytoplasm beneath the outer membrane apposing the basal lami na during both axonal degeneration and regeneration. Furthermore, laminin-a lpha 2 immunoreactivity roughly paralleled that of beta-dystroglycan during both axonal degeneration and regeneration, indicating that the expression of beta-dystroglycan and laminin-alpha 2 is induced and maintained by the S chwann cell contact with axons. Our results indicate that the dystroglycan complex is involved in the adhesion of the Schwann cell outer membrane with the basal lamina and suggest that the dystroglycan complex may play a role in the process of Schwann cell ensheathment and myelination through the in teraction with laminin-2.