The use of antibodies to treat neurodegenerative diseases has undergone rapid development in the past decade. To date, immunotherapeutic approaches to Alzheimer’s disease have mostly targeted amyloid beta as it is a secreted protein that can be found in plasma and CSF and is consequently accessible to circulating antibodies. Few recent publications have suggested the utility of treatment of tau pathology with monoclonal antibodies to tau. Our laboratory has begun a systematic study of different classes of tau monoclonal antibodies using mutant P301L mice. Three or seven months old mutant tau mice were inoculated weekly with tau monoclonal antibodies at a dose of 10 mg/Kg, until seven or ten months of age were reached respectively. Our data strongly support the notion that in P301L animals treated with MC1, a conformational monoclonal antibody specific for PHF-tau, the rate of development of tau pathology is effectively reduced, while injecting DA31, a high affinity tau sequence antibody, does not exert such benefit. MC1 appears superior to DA31 in overall effects, suggesting that specificity is more important than affinity in therapeutic applications. Unfortunately the survival rate of the P301L treated mice was not improved when immunizing either with MC1 or PHF1, a high affinity phospho-tau antibody previously reported to be efficacious in reducing pathological tau. These data demonstrate that passive immunotherapy in mutant tau models may be efficacious in reducing the development of tau pathology, but a great deal of work remains to be done to carefully select the tau epitopes to target.
The endocannabinoid CB 2 receptor system has been implicated in the neuropathology of Alzheimer's disease (AD). In order to investigate the impact of the CB 2 receptor system on AD pathology, a colony of mice with a deleted CB 2 receptor gene, CNR2, was established on a transgenic human mutant APP background for pathological comparison with CB 2 receptor-sufficient transgenic mice. J20 APP (PDGFB-APPSwInd) mice were bred over two generations with CNR2-/-(Cnr2 tm1Dgen /J) mice to produce a colony of J20 CNR2 +/+ and J20 CNR2-/mice. Seventeen J20 CNR2 +/+ mice (12 females, 5 males) and 16 J20 CNR2-/mice (11 females, 5 males) were killed at 12 months, and their brains were interrogated for AD-related pathology with both biochemistry and immunocytochemistry (ICC). In addition to amyloid-dependent endpoints such as soluble Aβ production and plaque deposition quantified with 6E10 staining, the effect of CB 2 receptor deletion on total soluble mouse tau production was assayed by using a recently developed high-sensitivity assay. Results revealed that soluble Aβ42 and plaque deposition were significantly increased in J20 CNR2-/mice relative to CNR2 +/+ mice. Microgliosis, quantified with ionized calcium-binding adapter molecule 1 (Iba-1) staining, did not differ between groups, whereas plaque associated microglia was more abundant in J20 CNR2-/mice. Total tau was significantly suppressed in J20 CNR2-/mice relative to J20 CNR2 +/+ mice. The results confirm the constitutive role of the CB 2 receptor system both in reducing amyloid plaque pathology in AD and also support tehpotential of cannabinoid therapies targeting CB 2 to reduce Aβ; however, the results suggest that interventions may have a divergent effect on tau pathology.
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