Following damage to peripheral nerves, many patients suffer from persistent pain or motor impairments due to inadequate nerve regeneration. In order to develop new therapies to promote nerve regeneration, it is imperative to understand the cellular and molecular mechanisms that drive this process. Many studies have focused on the neuron-intrinsic cues involved in nerve regeneration, however surrounding cell types, such as glial cells, also play an important role in promoting axonal regrowth. Schwann cells are the main glia of the peripheral nervous system and are critical for axonal maintenance and regeneration. Following injury, Schwann cells dedifferentiate to an immature state that promotes axonal regrowth and nerve repair. The process of Schwann cell dedifferentiation is accompanied by drastic morphological changes as well as cell migration. However, exactly how these morphological changes are driven by intracellular events, such as cytoskeletal rearrangements and membrane remodeling via intracellular transport, remains unknown. In addition to behavioral changes, dedifferentiated Schwann cells provide growth factors to regrowing axons and provide directional guidance, allowing axons to regrow along the proper path. The specific guidance molecules that are used by Schwann cells to direct axonal regrowth, however, are unknown. Recent data from our lab demonstrates that mutants for the classical axon guidance receptor, Deleted in Colorectal Carcinoma (DCC), show misguided axonal regrowth similar to that of mutants lacking Schwann cells. This suggests that DCC may play an important role in guiding axonal regrowth, potentially in a Schwann cell-dependent manner. Here, I propose to define the cellular and molecular mechanisms by which Schwann cells promote axonal regrowth. First, I will use live cell imaging to determine how cytoskeletal structure and intracellular transport change in Schwann cells in response to nerve injury. Additionally, I will determine whether intracellular transport is required in Schwan cells during nerve regeneration using cell-type specific rescue of a dynein mutant, which has significant axonal regeneration defects. Next, I will determine how DCC promotes directional axonal regrowth. Using live cell imaging, I will monitor the behavior of axonal growth cones and Schwann cells simultaneously in wild type and DCC mutants following nerve transection. Additionally, I will determine in which cell type(s) DCC is required to direct axonal regrowth using cell-type specific rescue of DCC mutant regeneration. Combined, the proposed experiments will provide cellular and molecular mechanisms by which Schwann cells promote nerve regeneration in vivo.
Peripheral nerve damage caused by injury or disease is a significant clinical problem, often resulting in persistent pain and impaired movement due to poor nerve regeneration. Results from this study will elucidate cellular and molecular mechanisms that allow nerves to regrow after injury. Defining these mechanisms will ultimately help in developing therapies that promote nerve regeneration.
