NPC1-/- Mouse Model
Niemann-Pick C1 (NPC1), predominantly expressed in perisynaptic astrocytic glial cells (Patel et al., 1999), is involved in intracellular cholesterol trafficking (Peake et al., 2010). It plays an important role in glial vesicular trafficking, a process crucial for maintaining structural and functional integrity of nerve terminals (Patel et al., 1999).
Defects in NPC1 cause Niemann-Pick disease type C1, an inherited lysosomal storage disorder that affects the viscera and the central nervous system. The disease is caused by defective intracellular processing and transport of low-density lipoprotein derived cholesterol and it causes accumulation of cholesterol in lysosomes, with delayed induction of cholesterol homeostatic reactions (Mattsson et al., 2012).
Interestingly, NPC disease shares similarities with Alzheimer’s disease (AD) showing progressive neurodegeneration, accumulation of amyloid-beta peptides, APP C-terminal fragments (Mattsson et al., 2012) and hyperphosphorylated tau (Ohm et al., 2003). The AD-like pathological features were identified both in the brains of NPC patients and NPC (NPC1-/-) mouse model (Mattsson et al., 2012).
Typical pathological features of Niemann-Pick disease:
- Increased cholesterol levels
- Progressive neuronal loss (especially Purkinje cells of the cerebellum)
- Altered APP expression and accumulation of amyloid-beta peptides
- Motor coordination deficits
Tissue weight of livers and brains were evaluated in 7 weeks old NPC1-/- and wildtype animals. Liver weight in NPC1 knockout animals is about 1.5 times higher compared to wildtype animals (Fig. 1 left side). In contrast, brain weight is significantly decreased in NPC1-/- mice compared to corresponding littermates (Fig. 1 right side).
Figure 1: Absence of NPC1 in 7 weeks old NPC1-/- animals leads to increased liver weight (left side) and decreased brain weight (right side). NPC-/- n=12, NPC+/+ n=6; Statistical analysis: Student`s ttest, **p<0.01; ***p<0.001.
Tissue Cholesterol Levels
Total and free cholesterol levels were assessed in livers and brains of 7 weeks old animals. While total (TC) and free (FC) liver cholesterol levels are about 5.5 times higher (Fig.2, left panel), brain cholesterol levels were similar in NPC1 knockout animals compared to wildtype littermates (Fig.2, right panel). Moreover, Filipin staining of brain lipids revealed enhanced lipid accumulation in the cerebellum and hippocampus of NPC1-/- animals (data not shown).
Figure 2. Absence of NPC1 in 7 weeks old NPC1-/- animals leads to cholesterol accumulation in the liver (left panel) but not in the brain (right panel). NPC-/- n=12, NPC+/+ n=6; Statistical analysis: Student`s t-test, ***p<0.001.
Purkinje Cell Degeneration in NPC1-/- Mice
NPC1 knockout mice show a fast neuronal loss, especially Purkinje cells of the cerebellum are vastly affected (Fig. 3). Additionally to a decreased number of Purkinje cells, expression of APP in NPC1-/- mice is also altered in this cell type.
Figure 3: NPC knockout mice are among other pathological changes characterized by a fast loss of neurons in the cerebellum, including Purkinje cells. Note that especially in anterior parts of the cerebellum the calbindin IR Purkinje cell network largely breaks down. Only small stripes remain as indicated by the arrow (3). Healthy Purkinje cells are furthermore positive for APP (green, ab Y188).
Neuroinflammation in NPC1-/- Mice
NPC1 knockout mice show enhanced neuroinflammation as analyzed by activated microglia and astrocytosis (Fig.4).
Figure 4. NPC knockout mice are among other pathological changes characterized by a fast loss of neurons in the cerebellum (decreased MAP2 labeling (blue), which is accompanied by neuroinflammatory response seen as activated microglia and astrocytosis. Note the strong microgliosis especially in anterior parts of the cerebellum where the calbindin IR Purkinje cell network largely breaks down. CD45 IR activated microglia (red) is absent in wildtype mice. The size of observed microglia is enormous, indicating phagocytic and also hypertrophic microglia. These cells can be found mainly in the white matter but also in the Purkinje cell layer, an area where also an increased number of astrocytes (green) are located.
Motor Coordination Deficits Over Age
RotaRod and gait analysis were used to assess motor coordination. At an age of 5 weeks, NPC-/- animals did not show any differences compared to wildtype animals in both RotaRod and Gait Analysis. However, 7 weeks old NPC-/- showed a significantly decreased latency to fall from the rod compared to 5 weeks old NPC-/- animals and 7 weeks old non-transgenic (ntg) littermates in the RotaRod, as well as increased time of step cycle in gait analysis compared to 7 weeks old ntg animals (Fig.5).
Figure 5: Assessment of motor coordination over age. Latency to fall from the rod of the RotaRod (A) and step cycle the time in gait analysis (B) of 5 and 7 weeks old mice. NPC-/- n=10, NPC+/+ n=5; Statistical analysis: Student`s ttest, **p<0.01.
QPS Austria offers a custom tailored study design for this model and is flexible to accommodate to your special interests. We could also advise you on the study design.
We would be happy to test your compounds in the NPC1-/- mouse model!
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