The long-term objective of this research is to define molecular mechanisms that are involved in demyelination and re-myelination of the peripheral nervous system (PNS). Demyelination is linked to the loss of all or part of neuronal functions because of the intimate connection between myelinating glial cells and axons. Therefore, the prevention of demyelination or promoting re-myelination is an important therapeutic objective for neurodegenerative diseases of the PNS and the CNS. We and others have shown recently that a function of receptor tyrosine kinase, erbB2, is associated with triggering PNS demyelination. ErbB2 function is also involved in promoting PNS myelination. The mechanisms by which erbB2 elicits two opposing roles in the PNS is unknown. Understanding the receptor signaling mechanisms has important implications for prevention of demyelinating neurodegenerative diseases and regenerative medicines. The broad goal of the present study is to define erbB2 function in initiating injury-induced PNS demyelination.
Three specific aims are proposed: 1) determine the mechanism by which erbB2 promotes PNS demyelination, 2) determine whether erbB2 activation is sufficient to induce PNS demyelination and 3) determine the mechanism of signal transduction that is associated with the demyelinating function of erbB2. The study plan exploits a new in vitro compartmentalized Schwann cell-neuron co-culture system that recapitulates Schwann cell nerve injury responses in vivo. The system serves as a powerful tool for studying signal transduction using both pharmacological and genetic intervention. To investigate erbB2 function (Aim 1), we will use an adenoviral delivery system to express dominant-negative erbB2 mutant in adult myelinating Schwann cells, during different stages of PNS demyelination, which will enable us to achieve a conditional erbB2 inhibition both in vivo and in vitro. For the erbB2 gain-of-function study in Aim 2, we will use an innovative regulated erbB2 homo- and hetero-dimerization system. This system allows us to generate ectopic erbB2 signaling within myelinating Schwann cells, independent of the endogenous receptor and the ligand. For the signaling function raised in Aim 3, we will use both biochemical and imaging approaches to define erbB2-signaling mechanism that is associated with the demyelinating function of the receptor.
Demyelination is a common pathologic feature in many PNS neurodegenerative diseases including Charcot-Marie-Tooth syndrome, Guillian-Barre syndrome, neuropathies secondary to diabetes and cancer chemotherapy, infectious neuropathy and motor deficits related to glial injury. Demyelination is also linked to the loss of all or part of neuronal functions because of the intimate connection between myelinating glial cells and the axons. Therefore, the prevention of demyelination is an important therapeutic objective for neurodegenerative diseases of the PNS and the CNS. Recent studies suggest that erbB2 activation might play a role in mediating PNS demyelination. Therefore, aberrant activation of the receptor or the associated cytoplasmic effectors may underlie a wide range of demyelinating disorders. Understanding the signal mechanism that initiates demyelination may have implications for the development of therapies that block erbB2 activation or diagnostic tests for detecting early demyelination before further progression of neurodegeneration. ? ? ?
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