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

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

Absence of stearoyl-CoA desaturase-1 does not promote DSS-induced acute colitis

Absence of stearoyl-CoA desaturase-1 (SCD1) in mice leads to chronic inflammation of the skin and increased susceptibility to atherosclerosis, while also increasing plasma inflammatory markers. A recent report suggested that SCD1 deficiency also increases disease severity in a mouse model of inflammatory bowel disease, induced by dextran sulfate sodium (DSS). However, SCD1-deficient mice are known to consume increased amounts of water, which would also be expected to increase the intake of DSS-treated water. The aim of this study was to determine the effect of SCD1 deficiency on DSS-induced acute colitis with DSS dosing adjusted to account for genotype differences in fluid consumption. Wild-type controls were treated with 3.5% DSS for 5 days to induce moderately severe colitis, while the concentration of DSS given to SCD1-deficient mice was lowered to 2.5% to control for increased fluid consumption. Colonic inflammation was assessed by clinical and histological scoring. Although SCD1-deficient mice consumed a total intake of DSS that was greater than that of wild-type controls, colonic inflammation, colon length and fecal blood were not altered by SCD1-deficiency in DSS-induced colitis, while diarrhea and total weight loss were modestly improved. Despite SCD1 deficiency leading to chronic inflammation of the skin and increased susceptibility to atherosclerosis, it does not accelerate inflammation in the DSS-induced model of acute colitis when DSS intake is controlled. These observations suggest that SCD1 deficiency does not play a significant role in colonic inflammation in this model. [The original version of this article, along with updated information and services is located on the World Wide Web at: http://dx.doi.org/10.1016/j.bbalip.2009.08.001]Medicine, Faculty ofMedical Genetics, Department ofReviewedFacultyResearcherOthe

Complete functional rescue of the ABCA1(-/-) mouse by human BAC transgenesis

Humanized mouse models are useful tools to explore the functional and regulatory differences between human and murine orthologous genes. We have combined a bioinformatics approach and an in vivo approach to assess the functional and regulatory differences between the human and mouse ABCA1 genes. Computational analysis identified significant differences in potential regulatory sites between the human and mouse genes. The effect of these differences was assessed in vivo, using a bacterial artificial chromosome transgenic humanized ABCA1 mouse model that expresses the human gene in the absence of mouse ABCA1. Humanized mice expressed human ABCA1 protein at levels similar to wild-type mice and fully compensated for cholesterol efflux activity and lipid levels seen in ABCA1-deficient mice. Liver X receptor agonist administration resulted in significant increases in HDL values associated with parallel increases in the hepatic ABCA1 protein and mRNA levels in the humanized ABCA1 mice, as seen in the wildtype animals. Our studies indicate that despite differences in potential regulatory regions, the human ABCA1 gene is able to functionally fully compensate for the mouse gene. Our humanized ABCA1 mice can serve as a useful model system for functional analysis of the human ABCA1 gene in vivo and can be used for the generation of potential new therapeutics that target HDL metabolis

Mice lacking caspase-2 are protected from behavioral changes, but not pathology, in the YAC128 model of Huntington disease

Background: Huntington Disease (HD) is a neurodegenerative disorder in which caspase activation and cleavage of substrates, including the huntingtin protein, has been invoked as a pathological mechanism. Specific changes in caspase-2 (casp2) activity have been suggested to contribute to the pathogenesis of HD, however unique casp2 cleavage substrates have remained elusive. We thus utilized mice completely lacking casp2 (casp2-/-) to examine the role played by casp2 in the progression of HD. This 'substrate agnostic' approach allows us to query the effect of casp2 on HD progression without pre-defining proteolytic substrates of interest. Results YAC128 HD model mice lacking casp2 show protection from well-validated motor and cognitive features of HD, including performance on rotarod, swimming T-maze, pre-pulse inhibition, spontaneous alternation and locomotor tasks. However, the specific pathological features of the YAC128 mice including striatal volume loss and testicular degeneration are unaltered in mice lacking casp2. The application of high-resolution magnetic resonance imaging (MRI) techniques validates specific neuropathology in the YAC128 mice that is not altered by ablation of casp2. Conclusions The rescue of behavioral phenotypes in the absence of pathological improvement suggests that different pathways may be operative in the dysfunction of neural circuitry in HD leading to behavioral changes compared to the processes leading to cell death and volume loss. Inhibition of caspase-2 activity may be associated with symptomatic improvement in HD.Medical Genetics, Department ofMedicine, Faculty ofMolecular Medicine and Therapeutics, Centre forNon UBCReviewedFacult

Increased ABCA1 activity protects against atherosclerosis

The ABC transporter ABCA1 plays a key role in the first steps of the reverse cholesterol transport pathway by mediating lipid efflux from macrophages. Previously, it was demonstrated that human ABCA1 overexpression in vivo in transgenic mice results in a mild elevation of plasma HDL levels and increased efflux of cholesterol from macrophages. In this study, we determined the effect of overexpression of ABCA1 on atherosclerosis development. Human ABCA1 transgenic mice (BAC(+)) were crossed with ApoE(–/–) mice, a strain that spontaneously develop atherosclerotic lesions. BAC(+)ApoE(–/–) mice developed dramatically smaller, less-complex lesions as compared with their ApoE(–/–) counterparts. In addition, there was increased efflux of cholesterol from macrophages isolated from the BAC(+)ApoE(–/–) mice. Although the increase in plasma HDL cholesterol levels was small, HDL particles from BAC(+)ApoE(–/–) mice were significantly better acceptors of cholesterol. Lipid analysis of HDL particles from BAC(+)ApoE(–/–) mice revealed an increase in phospholipid levels, which was correlated significantly with their ability to enhance cholesterol efflux