ABSTRACT
CCAAT-enhancer binding proteins are transcription factors that help to regulate a wide range of inflammatory mediators, as well as several key elements of energy metabolism. Because C/EBPs are expressed by rodent astrocytes and microglia, and because they are induced by pro-inflammatory cytokines that are chronically upregulated in the Alzheimer's disease (AD) cortex, we have investigated whether C/EBPs are expressed and upregulated in the AD cortex. Here, we demonstrate for the first time that C/EBPß can be detected by Western blots in AD and nondemented elderly (ND) cortex, and that it is significantly increased in AD cortical samples. In situ, C/EBPß localizes immunohistochemically to microglia. In microglia cultured from rapid autopsies of elderly patient's brains and in the BV-2 murine microglia cell line, we have shown that C/EBPß can be upregulated by C/EBP-inducing cytokines or lipopolysaccharide and exhibits nuclear translocation possibly indicating functional activity. Given the known co-regulatory role of C/EBPs in pivotal inflammatory mechanisms, many of which are present in AD, we propose that upregulation of C/EBPs in the AD brain could be an important orchestrator of pathogenic changes.
Subject(s)
Alzheimer Disease/metabolism , CCAAT-Enhancer-Binding Protein-beta/metabolism , Microglia/metabolism , Alzheimer Disease/genetics , Amyloid beta-Peptides/metabolism , Animals , Autopsy , Brain/metabolism , Brain/pathology , CCAAT-Enhancer-Binding Protein-beta/genetics , Cell Line , Cell Nucleus , Cells, Cultured , Frontal Lobe/metabolism , Frontal Lobe/pathology , Gene Expression , Humans , Immunohistochemistry , Mice , Protein Binding , Protein TransportABSTRACT
The CCAAT-enhancer binding protein (C/EBP) family of transcription factors, particularly C/EBPdelta, is well known to regulate or co-regulate a wide range of inflammatory mediators and mechanisms in the periphery, including interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). These cytokines, in turn, can induce C/EBPdelta expression and translocation to the nucleus as an active transcription factor. Because IL-1, IL-6, and TNF-alpha are increased in pathologically vulnerable regions of the Alzheimer's disease (AD) brain, we sought to determine if C/EBPdelta might be expressed in AD cortex. Immunohistochemistry of AD tissue sections revealed profuse C/EBPdelta staining of astrocytes, particularly reactive astrocytes surrounding amyloid beta peptide deposits. Substantially less immunoreactivity was observed in comparable sections from nondemented elderly control (ND) patients. These qualitative findings were consistent with quantitative Western blot densitometry results showing significant increases in C/EBPdelta in AD compared to ND cortex samples. Additional in vitro studies were pursued in order to characterize functional activity of C/EBPdelta in human elderly astrocytes. Consistent with a functionally active transcription factor, C/EBPdelta immunoreactivity predominated in the nucleus of cultured AD and ND astrocytes, and exhibited increases and nuclear localization, as determined by Western blots and electrophoretic mobility shifts after exposure to C/EBPdelta-inducing cytokines.
Subject(s)
Alzheimer Disease/genetics , Alzheimer Disease/metabolism , CCAAT-Enhancer-Binding Proteins/genetics , CCAAT-Enhancer-Binding Proteins/metabolism , Cerebral Cortex/metabolism , Cytokines/metabolism , Transcription Factors/genetics , Transcription Factors/metabolism , Up-Regulation/genetics , Active Transport, Cell Nucleus/physiology , Aged , Aged, 80 and over , Alzheimer Disease/physiopathology , Astrocytes/cytology , Astrocytes/metabolism , CCAAT-Enhancer-Binding Protein-delta , Cell Nucleus/metabolism , Cerebral Cortex/pathology , Cerebral Cortex/physiopathology , Female , Humans , Immunohistochemistry , Male , Plaque, Amyloid/metabolismABSTRACT
Factor H, a regulatory protein of the alternative pathway of complement (APC), is present in amyloid-beta (Abeta) plaques in Alzheimer's disease (AD). Abeta plaques also contain significant amounts of heparan sulfate proteoglycans (HSPGs), such as agrin, as well as numerous activated microglia expressing increased levels complement receptor 3 (CR3). Here, we show the colocalization of each of these molecules in the AD brain and the functional capacity for these molecules to bind to one another in vitro. We propose that CR3 receptors expressed by microglia are used for ligand binding to factor H bound to HSPGs and Abeta in plaques in the AD brain.
Subject(s)
Agrin/analysis , Alzheimer Disease/immunology , Brain/immunology , Complement Factor H/analysis , Macrophage-1 Antigen/analysis , Aged , Agrin/metabolism , Alzheimer Disease/metabolism , Alzheimer Disease/pathology , Amyloid beta-Peptides/analysis , Amyloid beta-Peptides/metabolism , Blotting, Western , Brain/metabolism , Brain Chemistry , Complement Factor H/immunology , Complement Factor H/metabolism , Complement Pathway, Alternative , Humans , Immunohistochemistry , Neuroglia/immunologyABSTRACT
There is now abundant evidence that brain microglia, when activated, have the lineage, receptors, and synthetic capacity to participate in both potentially neurotoxic inflammatory responses and potentially beneficial phagocytic responses. Amyloid beta peptide (Abeta) forms highly insoluble, beta-pleated aggregates that are widely deposited in the Alzheimer's disease (AD) cortex and limbic system. Aggregated Abeta also activates the classical and alternative complement cascades. These properties make Abeta an excellent target for microglial phagocytosis, a view supported by multiple reports, through well established mechanisms of phagocyte clearance.
