pki-166 and Demyelinating-Diseases

Demyelination is a common pathologic feature in many neurodegenerative diseases including infection with leprosy-causing Mycobacterium leprae. Because of the long incubation time and highly complex disease pathogenesis, the management of nerve damage in leprosy, as in other demyelinating diseases, is extremely difficult. Therefore, an important challenge in therapeutic interventions is to identify the molecular events that occur in the early phase before the progression of the disease. Here we provide evidence that M. leprae-induced demyelination is a result of direct bacterial ligation to and activation of ErbB2 receptor tyrosine kinase (RTK) signaling without ErbB2-ErbB3 heterodimerization, a previously unknown mechanism that bypasses the neuregulin-ErbB3-mediated ErbB2 phosphorylation. MEK-dependent Erk1 and Erk2 (hereafter referred to as Erk1/2) signaling is identified as a downstream target of M. leprae-induced ErbB2 activation that mediates demyelination. Herceptin (trastuzumab), a therapeutic humanized ErbB2-specific antibody, inhibits M. leprae binding to and activation of ErbB2 and Erk1/2 in human primary Schwann cells, and the blockade of ErbB2 activity by the small molecule dual ErbB1-ErbB2 kinase inhibitor PKI-166 (ref. 11) effectively abrogates M. leprae-induced myelin damage in in vitro and in vivo models. These results may have implications for the design of ErbB2 RTK-based therapies for both leprosy nerve damage and other demyelinating neurodegenerative diseases.

Topics: Animals; Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Butadienes; Cells, Cultured; Chlorocebus aethiops; Coculture Techniques; COS Cells; Demyelinating Diseases; Enzyme Activation; Enzyme Inhibitors; HeLa Cells; Humans; Leprosy; Mice; Mice, Knockout; Mice, Nude; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mycobacterium leprae; Nitriles; Pyrimidines; Pyrroles; Rats; Receptor, ErbB-2; Schwann Cells; Sciatic Nerve; Signal Transduction; Trastuzumab

How do myelinated axons signal to the nuclei of cells that enwrap them? The cell bodies of oligodendrocytes and Schwann cells are segregated from axons by multiple layers of bimolecular lipid leaflet and myelin proteins. Conventional signal transduction strategies would seem inadequate to the challenge without special adaptations. Wallerian degeneration provides a model to study axon-to-Schwann cell signaling in the context of nerve injury. We show a hitherto undetected rapid, but transient, activation of the receptor tyrosine kinase erbB2 in myelinating Schwann cells after sciatic nerve axotomy. Deconvolving microscopy using phosphorylation state-specific antibodies shows that erbB2 activation emanates from within the microvilli of Schwann cells, in direct contact with the axons they enwrap. To define the functional role of this transient activation, we used a small molecule antagonist of erbB2 activation (PKI166). The response of myelinating Schwann cells to axotomy is inhibited by PKI166 in vivo. Using neuron/Schwann cell cocultures prepared in compartmentalized cell culture chambers, we show that even transient activation of erbB2 is sufficient to initiate Schwann cell demyelination and that the initiating functions of erbB2 are localized to Schwann cells.

Topics: Analysis of Variance; Animals; Axotomy; Blotting, Western; Bromodeoxyuridine; Cell Proliferation; Cells, Cultured; Coculture Techniques; Demyelinating Diseases; Disease Models, Animal; Embryo, Mammalian; Female; Fluorescent Antibody Technique; Ganglia, Spinal; Gene Expression; Glycoproteins; Immunoprecipitation; Mitogen-Activated Protein Kinase Kinases; Myelin Basic Protein; Myelin Sheath; Neuregulins; Neuroglia; Neurons; Platelet-Derived Growth Factor; Pyrimidines; Pyrroles; Rats; Rats, Sprague-Dawley; Receptor Protein-Tyrosine Kinases; Receptor, ErbB-2; Schwann Cells; Sciatic Neuropathy; Signal Transduction; Sodium Channels; Time Factors; Wallerian Degeneration