Increased neurotransmitter release at the neuromuscular junction in a mouse model of polyglutamine disease.
In Huntington's disease (HD), the expansion of polyglutamine (polyQ) repeats at the N terminus of the ubiquitous protein huntingtin (htt) leads to neurodegeneration in specific brain areas. Neurons degenerating in HD develop synaptic dysfunctions. However, it is unknown whether mutant htt impacts synaptic function in general. To investigate that, we have focused on the nerve terminals of motor neurons that typically do not degenerate in HD. Here, we have studied synaptic transmission at the neuromuscular junction of transgenic mice expressing a mutant form of htt (R6/1 mice). We have found that the size and frequency of miniature endplate potentials are similar in R6/1 and control mice. In contrast, the amplitude of evoked endplate potentials in R6/1 mice is increased compared to controls. Consistent with a presynaptic increase of release probability, synaptic depression under high-frequency stimulation is higher in R6/1 mice. In addition, no changes were detected in the size and dynamics of the recycling synaptic vesicle pool. Moreover, we have found increased amounts of the synaptic vesicle proteins synaptobrevin 1,2/VAMP 1,2 and cysteine string protein-α, and the SNARE protein SNAP-25, concomitant with normal levels of other synaptic vesicle markers. Our results reveal that the transgenic expression of a mutant form of htt leads to an unexpected gain of synaptic function. That phenotype is likely not secondary to neurodegeneration and might be due to a primary deregulation in synaptic protein levels. Our findings could be relevant to understand synaptic toxic effects of proteins with abnormal polyQ repeats.
Instituto de Biomedicina de Sevilla Hospital Universitario Virgen del Rocío/Consejo Superior de Investigaciones Científicas (CSIC)/Universidad de Sevilla, Departamento de Fisiología Médica y Biofísica Universidad de Sevilla, 41009 Sevilla, Spain.
José L
JL
Rozas
Leonardo
L
Gómez-Sánchez
Cristina
C
Tomás-Zapico
José J
JJ
Lucas
Rafael
R
Fernández-Chacón
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D015153:Blotting, Western; D004195:Disease Models, Animal; D004594:Electrophysiology; D005071:Evoked Potentials / Q000502:physiology; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D006816:Huntington Disease / Q000378:metabolism / Q000503:physiopathology*; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D009469:Neuromuscular Junction / Q000378:metabolism / Q000503:physiopathology*; D009473:Neuronal Plasticity / Q000502:physiology; D009474:Neurons / Q000378:metabolism; D010455:Peptides; D050683:R-SNARE Proteins / Q000378:metabolism; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism; D050987:Vesicle-Associated Membrane Protein 1 / Q000378:metabolism
D050956:HSP40 Heat-Shock Proteins; D008565:Membrane Proteins; D010455:Peptides; D050683:R-SNARE Proteins; D050825:Synaptosomal-Associated Protein 25; D050987:Vesicle-Associated Membrane Protein 1; C088460:cysteine string protein; C097188:polyglutamine
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