Trophic support delays but does not prevent cell-intrinsic degeneration of neurons deficient for munc18-1

• Published in: The European journal of neuroscience 2004-08, Vol.20 (3), p.623-634
• Main Authors: Heeroma, Joost H., Roelandse, Martijn, Wierda, Keimpe, Van Aerde, Karlijn I., Toonen, Ruud F. G., Hensbroek, Robert A., Brussaard, Arjen, Matus, Andrew, Verhage, Matthijs
• Format: Article
• Language: English
• Subjects: Action Potentials - genetics; Action Potentials - physiology; Action Potentials - radiation effects; Animals; apoptosis; Brain-Derived Neurotrophic Factor - therapeutic use; Calbindins; Cell Survival - genetics; Cells, Cultured; Coculture Techniques - methods; Electric Stimulation - methods; Embryo, Mammalian; Glial Fibrillary Acidic Protein - metabolism; Glutamate Decarboxylase - metabolism; Hippocampus - pathology; Hippocampus - physiopathology; Immunohistochemistry - methods; Insulin - therapeutic use; loxP; Membrane Proteins - metabolism; Mice; Mice, Knockout; Microtubule-Associated Proteins - metabolism; mouse; Munc18 Proteins; Nerve Degeneration - drug therapy; Nerve Degeneration - genetics; Nerve Degeneration - physiopathology; Nerve Growth Factors - metabolism; Nerve Tissue Proteins - deficiency; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - physiology; Neuroglia - drug effects; Neuroglia - metabolism; Neurons - drug effects; Neurons - physiology; Neurotransmitter Agents - genetics; Neurotransmitter Agents - secretion; Patch-Clamp Techniques - methods; Phenothiazines; Qa-SNARE Proteins; regulated secretion; S100 Calcium Binding Protein beta Subunit; S100 Calcium Binding Protein G - metabolism; S100 Proteins - metabolism; Synapses - drug effects; Synapses - genetics; Synapses - metabolism; Time Factors; trophic support; Vesicular Transport Proteins - deficiency; Vesicular Transport Proteins - genetics; Vesicular Transport Proteins - physiology
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/j.1460-9568.2004.03503.x

The stability of neuronal networks is thought to depend on synaptic transmission which provides activity‐dependent maintenance signals for both synapses and neurons. Here, we tested the relationship between presynaptic secretion and neuronal maintenance using munc18‐1‐null mutant mice as a model. These mutants have a specific defect in secretion from synaptic and large dense‐cored vesicles [Verhage et al. (2000), Science, 287, 864–869; Voets et al. (2001), Neuron, 31, 581–591]. Neuronal networks in these mutants develop normally up to synapse formation but eventually degenerate. The proposed relationship between secretion and neuronal maintenance was tested in low‐density and organotypic cultures and, in vivo, by conditional cell‐specific inactivation of the munc18‐1 gene. Dissociated munc18‐1‐deficient neurons died within 4 days in vitro (DIV). Application of trophic factors, insulin or BDNF delayed degeneration up to 7 DIV. In organotypic cultures, munc18‐1‐deficient neurons survived until 9 DIV. On glial feeders, these neurons survived up to 10 DIV and 14 DIV when insulin was applied. Co‐culturing dissociated mutant neurons with wild‐type neurons did not prolong survival beyond 4 DIV, but coculturing mutant slices with wild‐type slices prolonged survival up to 19 DIV. Cell‐specific deletion of munc18‐1 expression in cerebellar Purkinje cells in vivo resulted in the specific loss of these neurons without affecting connected or surrounding neurons. Together, these data allow three conclusions. First, the lack of synaptic activity cannot explain the degeneration in munc18‐1‐null mutants. Second, trophic support delays but cannot prevent degeneration. Third, a cell‐intrinsic yet unknown function of munc18‐1 is essential for prolonged survival.