No abstract

Neurovascular-glymphatic dysfunction plays an important role in Alzheimer’s disease and has been analyzed mainly in association with amyloid-beta (Aβ) pathology. The neurovascular-glymphatic link with tauopathies has not been well elucidated. Here, we aimed to investigate the alterations in the neurovasculature and map the aquaporin 4 (AQP4) distribution and depolarization associated with tau and Aβ. Perfusion, susceptibility weighted imaging and structural magnetic resonance imaging (MRI) were performed in the pR5 P301L mouse model of 4-repeat tau and the arcAβ mouse model of amyloidosis. Immunofluorescence staining was performed using antibodies against AQP4, CD31, astroglia (GFAP, s100β), phospho-tau (AT-8) and Aβ (6E10) in brain tissue slices from P301L, arcAβ and nontransgenic mice. P301L mice showed regional atrophy, preserved cerebral blood flow and reduced cerebral vessel density compared to nontransgenic mice, while arcAβ mice showed cerebral microbleeds and reduced cerebral vessel density. AQP4 depolarization and peri-tau enrichment in the hippocampus and increased AQP4 levels in the forebrain and hippocampus were detected in P301L mice compared to nontransgenic mice. In comparison, cortical AQP4 depolarization and cortical/hippocampal peri-plaque increases were observed in arcAβ mice. Increased s100β-GFAP fluorescence intensities indicative of reactive astrocytes were detected surrounding tau inclusions in P301L mice and Aβ plaques in arcAβ mice. In conclusion, we observed a divergent region-specific AQP4 increase and association with phospho-tau and Aβ pathologies.

Neuroinflammation plays an important role in the pathophysiology of Alzheimer’s disease. The cannabinoid type 2 receptor (CB2R) is an emerging target for neuroinflammation and therapeutics of Alzheimer’s disease. Here, we aim to assess the alterations in brain CB2R levels and evaluate novel CB2R imaging tracers in the arcAß mouse model of Alzheimer’s disease amyloidosis. Immunohistochemical staining for amyloid-ß deposits (6E10), microgliosis (anti-Iba1 and anti-CD68 antibodies), astrocytes (GFAP) and the anti-CB2R antibody was performed on brain slices from 17-month-old arcAß mice. Autoradiography using the CB2R imaging probes [18F]RoSMA-18-d6, [11C]RSR-056, and [11C]RS-028 and mRNA analysis were performed in brain tissue from arcAß and non-transgenic littermate (NTL) mice at 6, 17, and 24 months of age. Specific increased CB2R immunofluorescence intensities on the increased number of GFAP-positive astrocytes and Iba1-positive microglia were detected in the hippocampus and cortex of 17-month-old arcAß mice compared to NTL mice. CB2R immunofluorescence was higher in glial cells inside 6E10-positive amyloid-ß deposits than peri-plaque glial cells, which showed low background immunofluorescence in the hippocampus and cortex of 17-month-old arcAß mice. Ex vivo autoradiography showed that the specific binding of [18F]RoSMA-18-d6 and [11C]RSR-056 was comparable in arcAß and NTL mice at 6, 17, and 24 months of age. The level of Cnr2 mRNA expression in the brain was not significantly different between arcAß and NTL mice at 6, 17, or 24 months of age. In conclusion, we demonstrated pronounced specific increases in microglial and astroglial CB2R expression levels in a mouse model of AD-related cerebral amyloidosis, emphasizing CB2R as a suitable target for imaging neuroinflammation.

Neuroinflammation plays an important role in the pathophysiology of Alzheimer′s disease. The cannabinoid type 2 receptor (CB2R) is an emerging target for neuroinflammation and therapeutics of Alzheimer′s disease. Here, we aimed to assess the alterations in brain CB2R levels and evaluate novel CB2R imaging tracers in the arcAβ mouse model of Alzheimer′s disease amyloidosis. Immunohistochemical staining for Aβ deposits (6E10), microgliosis (anti-Iba1 and anti-CD68 antibodies), astrocytes (GFAP) and the anti-CB2R antibody was performed on brain slices from arcAβ mice 17 months of age. Autoradiography using the CB2R imaging probes [18F]RoSMA-18-d6, [11C]RSR-056 and [11C]RS-028 and mRNA analysis were performed in brain tissue from arcAβ and nontransgenic littermate (NTL) mice at 6, 17, and 24 months of age. Specific increased CB2R immunofluorescence intensities on the increased number of GFAP-positive astrocytes and Iba1-positive microglia were detected in the hippocampus and cortex of 17-month-old arcAβ mice compared to NTL mice. CB2R immunofluorescence was higher in the glial cells inside 6E10-positive amyloid-β deposits than peri-plaque with a low background. Ex vivo autoradiography showed that the binding of [18F]RoSMA-18-d6 and [11C]RSR-056 was comparable in arcAβ and NTL mice at 6, 17 and 24 months. The level of Cnr2 mRNA expression in the brain was not significantly different between arcAβ and NTL mice at 6, 17 or 24 months. In conclusion, we demonstrated pronounced specific increases in microglial and astroglial CB2R expression levels in a model of AD-related cerebral amyloidosis/AD mouse model, emphasizing CB2R as a suitable target for imaging neuroinflammation.