alpha 6 beta 4 integrin and dystroglycan cooperate to stabilize the myelin sheath

Schwann cells integrate signals deriving from the axon and the basal lamina to myelinate peripheral nerves. Integrin alpha 6 beta 4 is a laminin receptor synthesized by Schwann cells and displayed apposed to the basal lamina. alpha 6 beta 4 integrin expression in Schwann cells is induced by axons at the onset of myelination, and rises in adulthood. The beta 4 chain has a uniquely long cytoplasmic domain that interacts with intermediate filaments such as dystonin, important in peripheral myelination. Furthermore, alpha 6 beta 4 integrin binds peripheral myelin protein 22, whose alteration causes the most common demyelinating hereditary neuropathy. All these data suggest a role for alpha 6 beta 4 integrin in peripheral nerve myelination. Here we show that ablating alpha 6 beta 4 integrin specifically in Schwann cells of transgenic mice does not affect peripheral nerve development, myelin formation, maturation, or regeneration. However, consistent with maximal expression in adult nerves, alpha 6 beta 4 integrin-null myelin is more prone to abnormal folding with aging. When the laminin receptor dystroglycan is also ablated, major folding abnormalities occur, associated with acute demyelination in some peripheral nervous system districts. These data indicate that, similar to its role in skin, alpha 6 beta 4 integrin confers stability to myelin in peripheral nerves.