ABSTRACT
Interferons (IFNs) potentiate macrophage activation typically via a STAT1-dependent pathway. Recent studies suggest a functioning of STAT1-independent pathway in the regulation of gene expression by IFN-γ, thus pointing to the diversity in cellular responses to IFNs. Many functions of IFNs rely on cross-regulation of the responses to exogenous inflammatory mediators such as TLR ligands. Here we investigated the contribution of STAT1-independent pathway to macrophage activation and its underlying mechanism in the context of combined stimulation of IFN and TLR. We found that TLR-induced production of inflammatory cytokines (TNF-α, IL-12) was not simply nullified but was significantly suppressed by signaling common to IFN-γ and IFN-ß in STAT1-null macrophages. Such a shift in the suppression of TLR response correlated with a sustained STAT3 activation and attenuation of NF-κB signaling. Using a JAK2/STAT3 pathway inhibitor or STAT3-specific siRNA, blocking STAT3 in that context restored TNF-α production and NF-κB signaling, thus indicating a functional cross-regulation among STAT1, STAT3, and NF-κB. Our results suggest that STAT1 deficiency reprograms IFN signaling from priming toward suppression of TLR response via feedback regulation of STAT3, which may provide a new insight into the host defense response against microbial pathogens in a situation of STAT1 deficiency.
Subject(s)
Feedback, Physiological , Interferon-gamma/metabolism , STAT1 Transcription Factor/deficiency , STAT3 Transcription Factor/metabolism , Signal Transduction , Toll-Like Receptors/metabolism , Animals , Female , Gene Expression Regulation , Interleukin-12/biosynthesis , Macrophages/metabolism , Mice, Inbred C57BL , NF-kappa B/metabolism , STAT1 Transcription Factor/metabolism , Transcription, Genetic , Tumor Necrosis Factor-alpha/biosynthesisABSTRACT
Accumulation of ß-amyloid (Aß) and resultant inflammation are critical pathological features of Alzheimer disease (AD). Microglia, a primary immune cell in brain, ingests and degrades extracellular Aß fibrils via the lysosomal system. Autophagy is a catabolic process that degrades native cellular components, however, the role of autophagy in Aß degradation by microglia and its effects on AD are unknown. Here we demonstrate a novel role for autophagy in the clearance of extracellular Aß fibrils by microglia and in the regulation of the Aß-induced NLRP3 (NLR family, pyrin domain containing 3) inflammasome using microglia specific atg7 knockout mice and cell cultures. We found in microglial cultures that Aß interacts with MAP1LC3B-II via OPTN/optineurin and is degraded by an autophagic process mediated by the PRKAA1 pathway. We anticipate that enhancing microglial autophagy may be a promising new therapeutic strategy for AD.
Subject(s)
Amyloid beta-Peptides/metabolism , Autophagy , Carrier Proteins/metabolism , Extracellular Space/metabolism , Inflammasomes/metabolism , Microglia/metabolism , Microglia/pathology , AMP-Activated Protein Kinases/metabolism , Adaptor Proteins, Signal Transducing/metabolism , Aged , Aged, 80 and over , Alzheimer Disease/metabolism , Alzheimer Disease/pathology , Animals , Autophagy-Related Protein 7 , Cell Cycle Proteins , Cell Line , Eye Proteins/metabolism , Female , Heat-Shock Proteins/metabolism , Humans , Inflammation/pathology , Integrases/metabolism , Male , Membrane Transport Proteins , Mice , Microtubule-Associated Proteins/metabolism , Models, Biological , NLR Family, Pyrin Domain-Containing 3 Protein , Neurons/pathology , Proteolysis , Sequestosome-1 Protein , Transcription Factor TFIIIA/metabolismABSTRACT
Composite nanofiber mats (HA/TiO2) consisting of hydroxyapatite (HA) and titania (TiO2) were fabricated via an electrospinning technique and then collagen (type I) was immobilized on the surface of the HA/TiO2 composite nanofiber mat to improve tissue compatibility. The structure and morphology of the collagen-immobilized composite nanofiber mat (HA/TiO2-col) was investigated using an X-ray diffractometer, electron spectroscopy for chemical analysis, and scanning electron microscope. The potential of the HA/TiO2-col composite nanofiber mat for use as a bone scaffold was assessed by an experiment with osteoblastic cells (MC3T3-E1) in terms of cell adhesion, proliferation, and differentiation. The results showed that the HA/TiO2-col composite nanofiber mats possess better cell adhesion and significantly higher proliferation and differentiation than untreated HA/TiO2 composite nanofiber mats. This result suggests that the HA/TiO2-col composite nanofiber mat has a high-potential for use in the field of bone regeneration and tissue engineering.
