Rescue from excitotoxicity and axonal degeneration accompanied by age-dependent behavioral and neuroanatomical alterations in caspase-6-deficient mice.

Apoptosis, or programmed cell death, is a cellular pathway involved in normal cell turnover, developmental tissue remodeling, embryonic development, cellular homeostasis maintenance and chemical-induced cell death. Caspases are a family of intracellular proteases that play a key role in apoptosis. Aberrant activation of caspases has been implicated in human diseases. In particular, numerous findings implicate Caspase-6 (Casp6) in neurodegenerative diseases, including Alzheimer disease (AD) and Huntington disease (HD), highlighting the need for a deeper understanding of Casp6 biology and its role in brain development. The use of targeted caspase-deficient mice has been instrumental for studying the involvement of caspases in apoptosis. The goal of this study was to perform an in-depth neuroanatomical and behavioral characterization of constitutive Casp6-deficient (Casp6-/-) mice in order to understand the physiological function of Casp6 in brain development, structure and function. We demonstrate that Casp6-/- neurons are protected against excitotoxicity, nerve growth factor deprivation and myelin-induced axonal degeneration. Furthermore, Casp6-deficient mice show an age-dependent increase in cortical and striatal volume. In addition, these mice show a hypoactive phenotype and display learning deficits. The age-dependent behavioral and region-specific neuroanatomical changes observed in the Casp6-/- mice suggest that Casp6 deficiency has a more pronounced effect in brain regions that are involved in neurodegenerative diseases, such as the striatum in HD and the cortex in AD.

Natural history of disease in the YAC128 mouse reveals a discrete signature of pathology in Huntington disease.

Models of Huntington disease (HD) recapitulate some neuropathological features of the disease. However, a global natural history of neuroanatomy in a mouse expressing full-length huntingtin has not been conducted. We investigated neuropathological changes in the YAC128 murine model of HD using magnetic resonance imaging (MRI). Structures affected in human HD are reduced in the YAC128 mice both in absolute terms and in terms of percentage of brain volume. Structures resistant to degeneration in HD, including the cerebellum and hippocampus, are spared in the YAC128 mice. Segmentation of major white matter structures confirms specific, progressive, loss of white matter in HD. In parallel with their specific volume loss, the YAC128 mice also show progressive increases in total ventricular volume, similarly to human HD patients. Cortical atrophy in the YAC128 mice is layer specific, which is the observed pattern of cortical loss in human HD patients. Finally, we have used a classification tree analysis to maximize separation of genotypes using all 62 structure volumes in an objective manner. This analysis demonstrates that sub-cortical gray matter structures (striatum, globus pallidus, thalamus) and cerebral white matter structures (corpus callosum, anterior commisure, fimbria) are the most discriminatory. The high resolution of the current study enables robust measurement of subtle early pathological changes. The use of mice furthermore enables us to address questions difficult to address in humans, including the sequential changes of HD from baseline and the relation between MRI and stereological measures.

Low levels of human HIP14 are sufficient to rescue neuropathological, behavioural, and enzymatic defects due to loss of murine HIP14 in Hip14-/- mice.

Huntingtin Interacting Protein 14 (HIP14) is a palmitoyl acyl transferase (PAT) that was first identified due to altered interaction with mutant huntingtin, the protein responsible for Huntington Disease (HD). HIP14 palmitoylates a specific set of neuronal substrates critical at the synapse, and downregulation of HIP14 by siRNA in vitro results in increased cell death in neurons. We previously reported that mice lacking murine Hip14 (Hip14-/-) share features of HD. In the current study, we have generated human HIP14 BAC transgenic mice and crossed them to the Hip14-/- model in order to confirm that the defects seen in Hip14-/- mice are in fact due to loss of Hip14. In addition, we sought to determine whether human HIP14 can provide functional compensation for loss of murine Hip14. We demonstrate that despite a relative low level of expression, as assessed via Western blot, BAC-derived human HIP14 compensates for deficits in neuropathology, behavior, and PAT enzyme function seen in the Hip14-/- model. Our findings yield important insights into HIP14 function in vivo.