ABSTRACT
BACKGROUND: The majority of patients with Alzheimer's disease (AD) exhibit amyloid-ß (Aß) deposits at the brain vasculature, a process referred to as cerebral amyloid angiopathy (CAA). In over 51% of AD cases, Aß also accumulates in cortical capillaries, which is termed capillary CAA (capCAA). It has been postulated that the presence of capCAA in AD is a specific subtype of AD, although underlying mechanisms are not yet fully understood. Sphingolipids (SLs) are implicated in neurodegenerative disorders, including AD. However, to date it remains unknown whether alterations in the SL pathway are involved in capCAA pathogenesis and if these differ from AD. OBJECTIVE: To determine whether AD cases with capCAA have an altered SL profile compared to AD cases without capCAA. METHODS: Immunohistochemistry was performed to assess the expression and localization of ceramide, acid sphingomyelinase (ASM), and sphingosine-1-phosphate receptors (S1P1, S1P3). In addition, we determined the concentrations of S1P as well as different chain-lengths of ceramides using HPLC-MS/MS. RESULTS: Immunohistochemical analysis revealed an altered expression of ceramide, ASM, and S1P receptors by reactive astrocytes and microglial cells specifically associated with capCAA. Moreover, a shift in the balance of ceramides with different chain-lengths and S1P content is observed in capCAA. CONCLUSION: Here we provide evidence of a deregulated SL balance in capCAA. The increased levels of ASM and ceramide in activated glia cells suggest that the SL pathway is involved in the neuroinflammatory response in capCAA pathogenesis. Future research is needed to elucidate the role of S1P in capCAA.
Subject(s)
Alzheimer Disease/metabolism , Capillaries/metabolism , Cerebral Amyloid Angiopathy/metabolism , Occipital Lobe/metabolism , Sphingolipids/metabolism , Aged , Aged, 80 and over , Alzheimer Disease/complications , Alzheimer Disease/pathology , Amyloid/metabolism , Astrocytes/metabolism , Astrocytes/pathology , Capillaries/pathology , Cerebral Amyloid Angiopathy/complications , Cerebral Amyloid Angiopathy/pathology , Female , Humans , Immunohistochemistry , Male , Microglia/metabolism , Microglia/pathology , Occipital Lobe/pathology , Receptors, Lysosphingolipid/metabolism , Sphingomyelin Phosphodiesterase/metabolismABSTRACT
BACKGROUND: Alzheimer's disease (AD) is the most common neurodegenerative disease. In addition to the occurrence of amyloid deposits and widespread tau pathology, AD is associated with a neuroinflammatory response characterized by the activation of microglia and astrocytes. Protein kinase 2 (CK2, former casein kinase II) is involved in a wide variety of cellular processes. Previous studies on CK2 in AD showed controversial results, and the involvement of CK2 in neuroinflammation in AD remains elusive. METHODS: In this study, we used immunohistochemical and immunofluorescent staining methods to investigate the localization of CK2 in the hippocampus and temporal cortex of patients with AD and non-demented controls. We compared protein levels with Western blotting analysis, and we investigated CK2 activity in human U373 astrocytoma cells and human primary adult astrocytes stimulated with IL-1ß or TNF-α. RESULTS: We report increased levels of CK2 in the hippocampus and temporal cortex of AD patients compared to non-demented controls. Immunohistochemical analysis shows CK2 immunoreactivity in astrocytes in AD and control cases. In AD, the presence of CK2 immunoreactive astrocytes is increased. CK2 immunopositive astrocytes are associated with amyloid deposits, suggesting an involvement of CK2 in the neuroinflammatory response. In U373 cells and human primary astrocytes, the selective CK2 inhibitor CX-4945 shows a dose-dependent reduction of the IL-1ß or TNF-α induced MCP-1 and IL-6 secretion. CONCLUSIONS: This data suggests that CK2 in astrocytes is involved in the neuroinflammatory response in AD. The reduction in pro-inflammatory cytokine secretion by human astrocytes using the selective CK2 inhibitor CX-4945 indicates that CK2 could be a potential target to modulate neuroinflammation in AD.
Subject(s)
Alzheimer Disease/pathology , Astrocytes/enzymology , Brain/pathology , Aged , Aged, 80 and over , Amyloid/metabolism , Astrocytes/drug effects , Blood Vessels/metabolism , Blood Vessels/pathology , Casein Kinase II/metabolism , Cells, Cultured , Cytokines/pharmacology , Dose-Response Relationship, Drug , Enzyme Inhibitors/pharmacology , Female , Glial Fibrillary Acidic Protein/metabolism , Humans , Male , Middle Aged , Naphthyridines/pharmacology , PhenazinesABSTRACT
Alzheimer's disease (AD) is the most common form of dementia and marked by deposition of amyloid-ß (Aß) within the brain. Alterations of Aß transporters at the neurovasculature may play a role in the disease process. We investigated the expression of ABC transporters P-glycoprotein (P-gp) and breast cancer related protein (BCRP) in non-neurologic controls, AD, and severe capillary cerebral amyloid angiopathy (capCAA) cases, which are characterized by deposition of Aß within cerebral capillaries. Our data show that microvascular expression of P-gp and BCRP is strikingly decreased in capCAA-affected vessels but not in AD and control samples. Messenger RNA levels of P-gp, but not of BCRP, were downregulated in brain endothelial cells on exposure to oligomeric Aß42, but not fibrillar Aß42 or Aß40. Coincubating Aß42 together with clusterin, an amyloid-associated protein highly expressed in capCAA-affected vessels, strongly reduced levels of P-gp. In conclusion, accumulation of Aß, in combination with clusterin, within and around cerebral capillaries, may further aggravate the disease process in AD by affecting P-gp expression. Loss of P-gp expression or activity may serve as a selective biomarker for ongoing capCAA.
