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Neural stem cells continuously generate newborn neurons that integrate into and modify neural circuitry in the adult hippocampus. The molecular mechanisms that regulate or perturb neural stem cell proliferation and differentiation, however, remain poorly understood. Here, we have found that mouse hippocampal radial glia-like (RGL) neural stem cells express the synaptic cochaperone cysteine string protein-α (CSP-α). Remarkably, in CSP-α knockout mice, RGL stem cells lose quiescence postnatally and enter into a high-proliferation regime that increases the production of neural intermediate progenitor cells, thereby exhausting the hippocampal neural stem cell pool. In cell culture, stem cells in hippocampal neurospheres display alterations in proliferation for which hyperactivation of the mechanistic target of rapamycin (mTOR) signaling pathway is the primary cause of neurogenesis deregulation in the absence of CSP-α. In addition, RGL cells lose quiescence upon specific conditional targeting of CSP-α in adult neural stem cells. Our findings demonstrate an unanticipated cell-autonomic and circuit-independent disruption of postnatal neurogenesis in the absence of CSP-α and highlight a direct or indirect CSP-α/mTOR signaling interaction that may underlie molecular mechanisms of brain dysfunction and neurodegeneration., This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) and Fondo Europeo de Desarrollo Regional (Grants BFU2013-47493-P and BFU2016-76050-P, Juan de la Cierva Contract, and Fellowships BES2008-002858 and BES2014-070405), the Junta de Andalucía (Grants P12-CTS-2232 and CTS-600), and the Instituto de Salud Carlos III.

Skeletal muscle regeneration by muscle satellite cells is a physiological mechanism activated upon muscle damage and regulated by Notch signaling. In a family with autosomal recessive limbgirdle muscular dystrophy, we identified a missense mutation in POGLUT1 (protein O-glucosyltransferase 1), an enzyme involved in Notch posttranslational modification and function. In vitro and in vivo experiments demonstrated that the mutation reduces Oglucosyltransferase activity on Notch and impairs muscle development. Muscles from patients revealed decreased Notch signaling, dramatic reduction in satellite cell pool and a muscle-specific adystroglycan hypoglycosylation not present in patients’ fibroblasts. Primary myoblasts from patients showed slow proliferation, facilitated differentiation, and a decreased pool of quiescent PAX7+ cells. A robust rescue of the myogenesis was demonstrated by increasing Notch signaling. None of these alterations were found in muscles from secondary dystroglycanopathy patients. These data suggest that a key pathomechanism for this novel form of muscular dystrophy is Notch-dependent loss of satellite cells. Junta de Andalucía PI-0017-2014

HD (Huntington's disease) is produced by the expression of mutant forms of the protein htt (huntingtin) containing a pathologically expanded poly-glutamine repeat. For unknown reasons, in HD patients and HD mouse models, neurons from the striatum and cerebral cortex degenerate and lead to motor dysfunction and dementia. Synaptic transmission in those neurons becomes progressively altered during the course of the disease. However, the relationship between synaptic dysfunction and neurodegeneration in HD is not yet clear. Are there early specific functional synaptic changes preceding symptoms and neurodegeneration? What is the role of those changes in neuronal damage? Recent experiments in a Drosophila model of HD have showed that abnormally increased neurotransmitter release might be a leading cause of neurodegeneration. In the present review, we summarize recently described synaptic alterations in HD animal models and discuss potential underlying molecular mechanisms.

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).Wehave 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. Copyright©2011 the authors., Instituto de Salud Carlos III (Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas), the Spanish Ministry of Science and Innovation (BFU2007-66008 to R.F-C., SAF2009-08233 to J.J.L., and Juan de la Cierva contracts to J.L.R. and C.T.-Z.), Junta de Andalucía (P07-CVI- 02854, P06-CVI-02392), Comunidad Autónoma de Madrid, Fundación Ramón Areces, and Fondo Europeo de Desarrollo Regional

The continuous release of neurotransmitter could be seen to place a persistent burden on presynaptic proteins, one that could compromise nerve terminal function. This supposition and the molecular mechanisms that might protect highly active synapses merit investigation. In hippocampal cultures from knock-out mice lacking the presynaptic cochaperone cysteine string protein-α (CSP-α), we observe progressive degeneration of highly active synaptotagmin 2 (Syt2)-expressing GABAergic synapses, but surprisingly not of glutamatergic terminals. In CSP-α knock-out mice, synaptic degeneration of basket cell terminals occursin vivoin the presence of normal glutamatergic synapses onto dentate gyrus granule cells. Consistent with this, in hippocampal cultures from these mice, the frequency of miniature IPSCs, caused by spontaneous GABA release, progressively declines, whereas the frequency of miniature excitatory AMPA receptor-mediated currents (mEPSCs), caused by spontaneous release of glutamate, is normal. However, the mEPSC amplitude progressively decreases. Remarkably, long-term block of glutamatergic transmission in cultures lacking CSP-α substantially rescues Syt2-expressing GABAergic synapses from neurodegeneration. These findings demonstrate that elevated neural activity increases synapse vulnerability and that CSP-α is essential to maintain presynaptic function under a physiologically high-activity regimen.

Cysteine string protein-α (CSP-α) is a synaptic vesicle protein that prevents activity-dependent neurodegeneration by poorly understood mechanisms. We have studied the synaptic vesicle cycle at the motor nerve terminals of CSP-α knock-out mice expressing the synaptopHluorin transgene. Mutant nerve terminals fail to sustain prolonged release and the number of vesicles available to be released decreases. Strikingly, the SNARE protein SNAP-25 is dramatically reduced. In addition, endocytosis during the stimulus fails to maintain the size of the recycling synaptic vesicle pool during prolonged stimulation. Upon depolarization, the styryl dye FM 2-10 becomes trapped and poorly releasable. Consistently with the functional results, electron microscopy analysis revealed characteristic features of impaired synaptic vesicle recycling. The unexpected defect in vesicle recycling in CSP-α knock-out mice provides insights into understanding molecular mechanisms of degeneration in motor nerve terminals. Cysteine string protein-α (CSP-α) is a synaptic vesicle protein that prevents activity-dependent neurodegeneration. Rozas et al. have used synaptopHluorin imaging and electrophysiology to find alterations in synaptic vesicle priming and recycling at motor nerve terminals of CSP-α KO mice. © 2012 Elsevier Inc., This work has been supported by Spanish MINECO (Juan de la Cierva and FPU Programs, BES2008-002858, BFU2007-66008, BFU2010-15713, ERA-NET NEURON EUI2009-04084, CTQ2009-14431/BQU, SAF2010-20822-C02), Junta de Andalucía (P06-CVI-02392, P07-CVI-02854), Xunta de Galicia (INCITE09 209 084PR), HFSP (RGP 0045/2002-C and CDA0032/2005-C), Instituto de Salud Carlos III and FEDER.