P23 Acts as Functional RBP in the Macrophage Inflammation Response

Macrophages exert the primary cellular immune response. Pathogen components like bacterial lipopolysaccharides (LPS) stimulate macrophage migration, phagocytotic activity and cytokine expression. Previously, we identified the poly(A)+ RNA interactome of RAW 264.7 macrophages. Of the 402 RNA-binding proteins (RBPs), 32 were classified as unique in macrophages, including nineteen not reported to interact with nucleic acids before. Remarkably, P23 a HSP90 co-chaperone, also known as cytosolic prostaglandin E2 synthase (PTGES3), exhibited differential poly(A)+ RNA binding in untreated and LPS-induced macrophages. To identify mRNAs bound by P23 and to elucidate potential regulatory RBP functions in macrophages, we immunoprecipitated P23 from cytoplasmic extracts of cross-linked untreated and LPS-induced cells. RNAseq revealed that enrichment of 44 mRNAs was reduced in response to LPS. Kif15 mRNA, which encodes kinesin family member 15 (KIF15), a motor protein implicated in cytoskeletal reorganization and cell mobility was selected for further analysis. Noteworthy, phagocytic activity of LPS-induced macrophages was enhanced by P23 depletion. Specifically, in untreated RAW 264.7 macrophages, decreased P23 results in Kif15 mRNA destabilization, diminished KIF15 expression and accelerated macrophage migration. We show that the unexpected RBP function of P23 contributes to the regulation of macrophage phagocytotic activity and migration.

Sensitivity of Rodent Microglia to Kynurenines in Models of Epilepsy and Inflammation In Vivo and In Vitro: Microglia Activation Is Inhibited by Kynurenic Acid and the Synthetic Analogue SZR104

Kynurenic acid is an endogenous modulator of ionotropic glutamate receptors and a suppressor of the immune system. Since glutamate and microglia are important in the pathogenesis of epilepsy, we investigated the possible action of the synthetic kynurenic acid analogue, SZR104, in epileptic mice and the action of kynurenic acid and SZR104 on the phagocytotic activity of cultured microglia cells. Pilocarpine epilepsy was used to test the effects of SZR104 on morphological microglia transformation, as evaluated through ionized calcium-binding adaptor molecule 1 (Iba1) immunohistochemistry. Microglia-enriched rat secondary cultures were used to investigate phagocytosis of fluorescent microbeads and Iba1 protein synthesis in control and lipopolysaccharide-challenged cultures. SZR104 inhibited microglia transformation following status epilepticus. Kynurenic acid and SZR104 inhibited lipopolysaccharide-stimulated phagocytotic activity of microglia cells. Although kynurenic acid and its analogues proved to be glutamate receptor antagonists, their immunosuppressive action was dominant in epilepsy. The inhibition of phagocytosis in vitro raised the possibility of the inhibition of genes encoding inflammatory cytokines in microglial cells.

Tracking tau fibrillogenesis and consequent primary phagocytosis of neurons mediated by microglia in a living tauopathy model

ABSTRACTFibrillary tau pathologies have been implicated in Alzheimer’s and allied neurodegenerative diseases, while mechanisms by which neurons bearing tau tangles die remain enigmatic. To address this issue, we pursued tau and related key pathologies macroscopically by PET and MRI and microscopically by intravital two-photon laser optics. Time-course macroscopic assays of tau transgenic mice demonstrated intimate associations of tau deposition and increase of an inflammatory microglial marker, translocator protein (TSPO), with regional brain atrophy. Longitudinal microscopy of these mice revealed a rapid turnover of tau lesions resulting from continuous generation of new tau aggregates followed by loss of neurons and their fibrillar contents. This technology also allowed the capturing of the disappearance of tangle-bearing neurons several days after being engulfed by activated microglia. Notably, a therapeutic TSPO ligand profoundly suppressed the mobility and phagocytotic activity of microglia and improved neuronal survival in this model, supporting the involvement of primary phagocytosis of viable neurons by microglia in tau-primed neuronal death. Finally, partial depletion of microglia revealed roles of immune factors, MFG-E8 and C1q, as ‘eat-me’ signals for an immediate attraction of phagocytic microglia towards the elimination of tangle-loaded neurons.

Increased PD-1-positive macrophages in the tissue of gastric cancer are closely associated with poor prognosis in gastric cancer patients.

Background: Programmed cell death 1 (PD-1) is one of the immune checkpoint molecules that negatively regulate the function of T cells. Although recent studies indicate that PD-1 is also expressed on other immune cells besides T cells, its role remains unclear. This study aims to evaluate PD-1 expression on macrophages and examine its effect on anti-tumor immunity in gastric cancer (GC) patients. Methods : The frequency of PD-1 + macrophages obtained from GC tissue was determined by multicolor flow cytometry (n = 15). Double immunohistochemistry staining of PD-1 and CD68 was also performed to evaluate the correlations among the frequency of PD-1 + macrophages, clinicopathological characteristicus, and prognosis in GC patients (n = 102). Results: The frequency of PD-1 + macrophages was significantly higher in GC tissue than in non-tumor gastric tissue. The phagocytotic activity of PD-1 + macrophages was severely impaired compared with that of PD-1 - macrophages. The 5-year disease specific survival rates in patients with PD-1 + macrophage Low (the frequency of PD-1 + macrophages; < 0.85%) and those with PD-1 + macrophage High (the frequency of PD-1 + macrophages; ≥ 0.85%) were 85.9% and 65.8%, respectively ( P = 0.008). Finally, multivariate analysis showed the frequency of PD-1 + macrophage to be an independent prognostic factor. Conclusions: The function of PD-1 + macrophage was severely impaired and increased frequency of PD-1 + macrophage worsened the prognosis of GC patients. PD-1–PD-L1 therapies may function through a direct effect on macrophages in GC.

Increased PD-1-positive macrophages in the tissue of gastric cancer are closely associated with poor prognosis in gastric cancer patients.

Background: Programmed cell death 1 (PD-1) is one of the immune checkpoint molecules that negatively regulate the function of T cells. Although recent studies indicate that PD-1 is also expressed on other immune cells besides T cells, its role remains unclear. This study aims to evaluate PD-1 expression on macrophages and examine its effect on anti-tumor immunity in gastric cancer (GC) patients. Methods : The frequency of PD-1 + macrophages obtained from GC tissue was determined by multicolor flow cytometry (n = 15). Double immunohistochemistry staining of PD-1 and CD68 was also performed to evaluate the correlations among the frequency of PD-1 + macrophages, clinicopathological characteristicus, and prognosis in GC patients (n = 102). Results: The frequency of PD-1 + macrophages was significantly higher in GC tissue than in non-tumor gastric tissue. The phagocytotic activity of PD-1 + macrophages was severely impaired compared with that of PD-1 - macrophages. The 5-year disease specific survival rates in patients with PD-1 + macrophage Low (the frequency of PD-1 + macrophages; < 0.85%) and those with PD-1 + macrophage High (the frequency of PD-1 + macrophages; ≥ 0.85%) were 85.9% and 65.8%, respectively ( P = 0.008). Finally, multivariate analysis showed the frequency of PD-1 + macrophage to be an independent prognostic factor. Conclusions: The function of PD-1 + macrophage was severely impaired and increased frequency of PD-1 + macrophage worsened the prognosis of GC patients. PD-1–PD-L1 therapies may function through a direct effect on macrophages in GC.

Increased PD-1-positive macrophages in the tissue of gastric cancer are closely associated with poor prognosis in gastric cancer patients.

Background: Programmed cell death 1 (PD-1) is one of the immune checkpoint molecules that negatively regulate the function of T cells. Although recent studies indicate that PD-1 is also expressed on other immune cells besides T cells, its role remains unclear. This study aims to evaluate PD-1 expression on macrophages and examine its effect on anti-tumor immunity in gastric cancer (GC) patients. Methods: The frequency of PD-1+ macrophages obtained from GC tissue was determined by multicolor flow cytometry (n = 15). Double immunohistochemistry staining of PD-1 and CD68 was also performed to evaluate the correlations among the frequency of PD-1+ macrophages, clinicopathological characteristicus, and prognosis in GC patients (n = 102). Results: The frequency of PD-1+ macrophages was significantly higher in GC tissue than in non-tumor gastric tissue. The phagocytotic activity of PD-1+ macrophages was severely impaired compared with that of PD-1- macrophages. The 5-year disease specific survival rates in patients with PD-1+ macrophageLow (the frequency of PD-1+ macrophages; < 0.85%) and those with PD-1+ macrophageHigh (the frequency of PD-1+ macrophages; ≥ 0.85%) were 85.9% and 65.8%, respectively (P = 0.008). Finally, multivariate analysis showed the frequency of PD-1+ macrophage to be an independent prognostic factor. Conclusions: The function of PD-1+ macrophage was severely impaired and increased frequency of PD-1+ macrophage worsened the prognosis of GC patients. PD-1–PD-L1 therapies may function through a direct effect on macrophages in GC.

Pharmacological inhibition of APP processing and knock-down of APP in primary human macrophages impairs the secretion of cytokines

Background The amyloid precursor protein (APP) and amyloid β (Aβ) peptides support the innate immune defense as an immune receptor, an antimicrobial peptide and an opsonine. In APP-deficient mouse models, a reduced secretion of cytokines has been observed. It is unclear whether this can be attributed to the lack of APP or to the missing secretion of Aβ peptides.Methods In primary human monocyte derived macrophages the secretion of Aβ peptides was inhibited by the γ-secretase inhibitor DAPT or by the β-secretase inhibitor GL-189, applied as a tripartite substance. Alternatively, APP was knocked down by transfection with siRNA. TNFα, IL-6 and IL-10 were measured by ELISA and the phagocytotic activity was evaluated by flow cytometry.Results Reduced concentrations of TNFα and IL-6 were observed in the media of APPk/d macrophages and after inhibition of the β-, or γ-secretase, especially after additional immunological activation with LPS. Secretion of IL-10 was increased after pharmacological inhibition of APP processing when the macrophages were not immunologically activated but was decreased during LPS-induced inflammation in APPk/d macrophages. No changes of the phagocytotic activity were observed.Conclusion We conclude that macrophage APP and Aβ peptides support the initiation of an immune response and are involved in the secretion of TNFα, IL-6 and IL-10.

The innate immune receptor Dectin-2 mediates the phagocytosis of cancer cells by Kupffer cells for the suppression of liver metastasis

Tumor metastasis is the cause of most cancer deaths. Although metastases can form in multiple end organs, the liver is recognized as a highly permissive organ. Nevertheless, there is evidence for immune cell-mediated mechanisms that function to suppress liver metastasis by certain tumors, although the underlying mechanisms for the suppression of metastasis remain elusive. Here, we show that Dectin-2, a C-type lectin receptor (CLR) family of innate receptors, is critical for the suppression of liver metastasis of cancer cells. We provide evidence that Dectin-2 functions in resident macrophages in the liver, known as Kupffer cells, to mediate the uptake and clearance of cancer cells. Interestingly, Kupffer cells are selectively endowed with Dectin-2–dependent phagocytotic activity, with neither bone marrow-derived macrophages nor alveolar macrophages showing this potential. Concordantly, subcutaneous primary tumor growth and lung metastasis are not affected by the absence of Dectin-2. In addition, macrophage C-type lectin, a CLR known to be complex with Dectin-2, also contributes to the suppression of liver metastasis. Collectively, these results highlight the hitherto poorly understood mechanism of Kupffer cell-mediated control of metastasis that is mediated by the CLR innate receptor family, with implications for the development of anticancer therapy targeting CLRs.