A novel mouse model of Niemann-Pick type C disease carrying a D1005G-Npc1 mutation comparable to commonly observed human mutations.

We have identified a point mutation in Npc1 that creates a novel mouse model (Npc1(nmf164)) of Niemann-Pick type C1 (NPC) disease: a single nucleotide change (A to G at cDNA bp 3163) that results in an aspartate to glycine change at position 1005 (D1005G). This change is in the cysteine-rich luminal loop of the NPC1 protein and is highly similar to commonly occurring human mutations. Genetic and molecular biological analyses, including sequencing the Npc1(spm) allele and identifying a truncating mutation, confirm that the mutation in Npc1(nmf164) mice is distinct from those in other existing mouse models of NPC disease (Npc1(nih), Npc1(spm)). Analyses of lifespan, body and spleen weight, gait and other motor activities, as well as acoustic startle responses all reveal a more slowly developing phenotype in Npc1(nmf164) mutant mice than in mice with the null mutations (Npc1(nih), Npc1(spm)). Although Npc1 mRNA levels appear relatively normal, Npc1(nmf164) brain and liver display dramatic reductions in Npc1 protein, as well as abnormal cholesterol metabolism and altered glycolipid expression. Furthermore, histological analyses of liver, spleen, hippocampus, cortex and cerebellum reveal abnormal cholesterol accumulation, glial activation and Purkinje cell loss at a slower rate than in the Npc1(nih) mouse model. Magnetic resonance imaging studies also reveal significantly less demyelination/dysmyelination than in the null alleles. Thus, although prior mouse models may correspond to the severe infantile onset forms of NPC disease, Npc1(nmf164) mice offer many advantages as a model for the late-onset, more slowly progressing forms of NPC disease that comprise the large majority of human cases.

Age, experience and genetic background influence treadmill walking in mice.

The use of a treadmill to gather data for gait analysis in mice is a convenient, sensitive method to evaluate motor performance. However, evidence from several species, including mice, shows that treadmill locomotion is a novel task that is not equivalent to over ground locomotion and that may be particularly sensitive to the test environment and protocol. We investigated the effects of age, genetic background and repeated trials on treadmill walking in mice and show that these factors are important considerations in the interpretation of gait data. Specifically we report that as C57BL/6J (B6) mice age, the animals use progressively longer, less frequent strides to maintain the same walking speed. The increase is most rapid between 1 and 6 months of age and is explained, in part, by changes in size and weight. We also extended previous findings showing that repeat trials cause mice to modify their treadmill gait pattern. In a second trial B6 mice consistently walk with a shorter swing phase and greater duty factor. Also, with the shortest retest interval (3 min) mice use shorter more frequent steps but the response varies with the number and timing of trials. Finally, we compared the gait pattern of an additional seven inbred strains of mice and found significant variation in the length and frequency of strides used to maintain the same walking speed. The combined results offer the bases for further mechanistic studies and can be used to guide optimal experimental design.

Gait analysis detects early changes in transgenic SOD1(G93A) mice.

The effective treatment or cure of motoneuron disease will require understanding the disease processes that precede irreversible cell loss. To study these early stages, and to evaluate potential treatments in relevant animal models, requires a sensitive functional assay. To this end, we sought to determine whether the gait pattern of SOD1 transgenic mice changed prior to overt symptoms. Using a simplified video-based approach we compared the treadmill gait of C57BL/6J and B6.SOD1 transgenic mice at 8 and 10 weeks of age. B6.SOD1 mice had significantly longer stride and stance times than controls by 8 weeks. Consistent with disease progression, hindpaw measures of B6.SOD1 mice showed larger changes than front paws. Differences between control and B6.SOD1 mice increased at 10 weeks, but only because repeat testing caused habituation in control mice to a greater extent than in B6.SOD1 mice. Together the results demonstrate that simplified gait analysis is sensitive to early processes of motor system disease in mice.

Mdm muscular dystrophy: interactions with calpain 3 and a novel functional role for titin's N2A domain.

Human tibial muscular dystrophy and limb-girdle muscular dystrophy 2J are caused by mutations in the giant sarcomeric protein titin (TTN) adjacent to a binding site for the muscle-specific protease calpain 3 (CAPN3). Muscular dystrophy with myositis (mdm) is a recessive mouse mutation with severe and progressive muscular degeneration caused by a deletion in the N2A domain of titin (TTN-N2ADelta83), disrupting a putative binding site for CAPN3. To determine whether the muscular dystrophy in mutant mdm mice is caused by misregulation of CAPN3 activity, genetic crosses with CAPN3 overexpressing transgenic (C3Tg) and CAPN3 knockout (C3KO) mice were generated. Here, we report that overexpression of CAPN3 exacerbates the mdm disease, leading to a shorter life span and more severe muscular dystrophy. However, in a direct genetic test of CAPN3's role as a mediator of mdm pathology, C3KO;mdm double mutant mice showed no change in the progression or severity of disease indicating that aberrant CAPN3 activity is not a primary mechanism in this disease. To determine whether we could detect a functional deficit in titin in a non-disease state, we examined the treadmill locomotion of heterozygous +/mdm mice and detected a significant increase in stride time with a concomitant increase in stance time. Interestingly, these altered gait parameters were completely corrected by CAPN3 overexpression in transgenic C3Tg;+/mdm mice, supporting a CAPN3-dependent role for the N2A domain of TTN in the dynamics of muscle contraction.