Calpain inhibition mediates autophagy-dependent protection against polyglutamine toxicity.

Over recent years, accumulated evidence suggests that autophagy induction is protective in animal models of a number of neurodegenerative diseases. Intense research in the field has elucidated different pathways through which autophagy can be upregulated and it is important to establish how modulation of these pathways impacts upon disease progression in vivo and therefore which, if any, may have further therapeutic relevance. In addition, it is important to understand how alterations in these target pathways may affect normal physiology when constitutively modulated over a long time period, as would be required for treatment of neurodegenerative diseases. Here we evaluate the potential protective effect of downregulation of calpains. We demonstrate, in Drosophila, that calpain knockdown protects against the aggregation and toxicity of proteins, like mutant huntingtin, in an autophagy-dependent fashion. Furthermore, we demonstrate that, overexpression of the calpain inhibitor, calpastatin, increases autophagosome levels and is protective in a mouse model of Huntington's disease, improving motor signs and delaying the onset of tremors. Importantly, long-term inhibition of calpains did not result in any overt deleterious phenotypes in mice. Thus, calpain inhibition, or activation of autophagy pathways downstream of calpains, may be suitable therapeutic targets for diseases like Huntington's disease.

Alpha-helix targeting reduces amyloid-beta peptide toxicity.

The amyloid-beta peptide (Abeta) can generate cytotoxic oligomers, and their accumulation is thought to underlie the neuropathologic changes found in Alzheimer's disease. Known inhibitors of Abeta polymerization bind to undefined structures and can work as nonspecific aggregators, and inhibitors that target conformations that also occur in larger Abeta assemblies may even increase oligomer-derived toxicity. Here we report on an alternative approach whereby ligands are designed to bind and stabilize the 13-26 region of Abeta in an alpha-helical conformation, inspired by the postulated Abeta native structure. This is achieved with 2 different classes of compounds that also reduce Abeta toxicity to cells in culture and to hippocampal slice preparations, and that do not show any nonspecific aggregatory properties. In addition, when these inhibitors are administered to Drosophila melanogaster expressing human Abeta(1-42) in the central nervous system, a prolonged lifespan, increased locomotor activity, and reduced neurodegeneration is observed. We conclude that stabilization of the central Abeta alpha-helix counteracts polymerization into toxic assemblies and provides a strategy for development of specific inhibitors of Abeta polymerization.

Defective neurogenesis in citron kinase knockout mice by altered cytokinesis and massive apoptosis.

Citron-kinase (Citron-K) has been proposed by in vitro studies as a crucial effector of Rho in regulation of cytokinesis. To further investigate in vivo its biologic functions, we have inactivated Citron-K gene in mice by homologous recombination. Citron-K-/- mice grow at slower rates, are severely ataxic, and die before adulthood as a consequence of fatal seizures. Their brains display defective neurogenesis, with depletion of specific neuronal populations. These abnormalities arise during development of the central nervous system due to altered cytokinesis and massive apoptosis. Our results indicate that Citron-K is essential for cytokinesis in vivo but only in specific neuronal precursors. Moreover, they suggest a novel molecular mechanism for a subset of human malformative syndromes of the CNS.