In situ structural basis of human axonopathies

ongoing

Myelinated axons propagate action potentials across otherwise unsurmountable distances. The overarching hypothesis of the cryoNERVE project is that membrane morphology crucially determines axonal health and function. Mutations in genes coding for membrane-shaping proteins are the major cause of familial axonopathies like hereditary spastic paraplegia (HSP) and Charcot-Marie-Tooth (CMT) disease. However, current techniques lack the resolution to ascertain the functions of these proteins and their pathological dysfunction within native nerves. At the same time, the highly specialized architecture of axons and their delicate interplay with glia can only be studied in situ. I have shown how cryo-electron tomography (cryo-ET) reveals the structural basis of neuronal function and disease within intact cells. However, cryo-ET imaging of tissues remains a major challenge. In cryoNERVE, we will develop cryo-ET workflows to image native nerve tissue at unprecedented resolution. We will build on these advances to study the function of HSP and CMT proteins within truly physiological environments. Specifically, we will investigate (i) how these proteins shape axonal organelles and their cross-talk, (ii) the mechanisms allowing myelin sheath formation and neuron-glia communication, and (iii) the alterations introduced by axonopathy-causing mutants. Lastly, we will pioneer the first cryo-ET analyses of vitrified human tissues. Frustratingly, peripheral nerve biopsies from axonopathy patients often cannot be diagnosed with existing methods. We will examine patient biopsies at molecular resolution, and capitalize on our findings in flies and mice to reveal hitherto obscured pathological abnormalities. Thus, cryoNERVE will provide a holistic molecular and structural basis of human axonopathies like HSP and CMT, pave the way for high-resolution analyses of native human tissues and explore the potential of cryo-ET as a diagnostic tool with nanometric precision.