Social and natural environmental factors cause the birth-cohort phenomenon of peptic ulcers by superposition mechanism.

The widely believed Helicobacter pylori infection has never explained the birth-cohort phenomenon of peptic ulcers. Although numerous studies have observed that environmental factors are associated with peptic ulcers, their role in the disease has yet to be identified. A new etiological theory proposed that environmental factors cause peptic ulcers via inducing psychological stress. Starting from this etiology, an integration of the mortality rates caused by social and natural environmental factors reproduced a representative fluctuation curve in the birth-cohort phenomenon, where a causal role of environmental factors in peptic ulcers was hidden. The reproduced fluctuation curve revealed that multiple environmental factors caused the birth-cohort phenomenon by Superposition Mechanism, and the causal role of each individual environmental factor surfaced if the fluctuation curves in the birth-cohort phenomenon were properly differentiated. A full understanding of the birth-cohort phenomenon highlights the importance of environmental management in improving clinical outcomes, and suggests that the Superposition Mechanism is an indispensable methodological concept for life science and medicine.

Role of RIPK1 in SMAC mimetics-induced apoptosis in primary human HIV-infected macrophages.

Macrophages serve as viral reservoirs due to their resistance to apoptosis and HIV-cytopathic effects. We have previously shown that inhibitor of apoptosis proteins (IAPs) confer resistance to HIV-Vpr-induced apoptosis in normal macrophages. Herein, we show that second mitochondrial activator of caspases (SMAC) mimetics (SM) induce apoptosis of monocyte-derived macrophages (MDMs) infected in vitro with a R5-tropic laboratory strain expressing heat stable antigen, chronically infected U1 cells, and ex-vivo derived MDMs from HIV-infected individuals. To understand the mechanism governing SM-induced cell death, we show that SM-induced cell death of primary HIV-infected macrophages was independent of the acquisition of M1 phenotype following HIV infection of macrophages. Instead, SM-induced cell death was found to be mediated by IAPs as downregulation of IAPs by siRNAs induced cell death of HIV-infected macrophages. Moreover, HIV infection caused receptor interacting protein kinase-1 (RIPK1) degradation which in concert with IAP1/2 downregulation following SM treatment may result in apoptosis of macrophages. Altogether, our results show that SM selectively induce apoptosis in primary human macrophages infected in vitro with HIV possibly through RIPK1. Moreover, modulation of the IAP pathways may be a potential strategy for selective killing of HIV-infected macrophages in vivo.

Selective Induction of Cell Death in Human M1 Macrophages by Smac Mimetics Is Mediated by cIAP-2 and RIPK-1/3 through the Activation of mTORC.

Inflammatory macrophages have been implicated in many diseases, including rheumatoid arthritis and inflammatory bowel disease. Therefore, targeting macrophage function and activation may represent a potential strategy to treat macrophage-associated diseases. We have previously shown that IFN-γ-induced differentiation of human M0 macrophages toward proinflammatory M1 state rendered them highly susceptible to the cytocidal effects of second mitochondria-derived activator of caspases mimetics (SMs), antagonist of the inhibitors of apoptosis proteins (IAPs), whereas M0 and anti-inflammatory M2c macrophages were resistant. In this study, we investigated the mechanism governing SM-induced cell death during differentiation into M1 macrophages and in polarized M1 macrophages. IFN-γ stimulation conferred on M0 macrophages the sensitivity to SM-induced cell death through the Jak/STAT, IFN regulatory factor-1, and mammalian target of rapamycin complex-1 (mTORC-1)/ribosomal protein S6 kinase pathways. Interestingly, mTORC-1 regulated SM-induced cell death independent of M1 differentiation. In contrast, SM-induced cell death in polarized M1 macrophages is regulated by the mTORC-2 pathway. Moreover, SM-induced cell death is regulated by cellular IAP (cIAP)-2, receptor-interacting protein kinase (RIPK)-1, and RIPK-3 degradation through mTORC activation during differentiation into M1 macrophages and in polarized M1 macrophages. In contrast to cancer cell lines, SM-induced cell death in M1 macrophages is independent of endogenously produced TNF-α, as well as the NF-κB pathway. Collectively, selective induction of cell death in human M1 macrophages by SMs may be mediated by cIAP-2, RIPK-1, and RIPK-3 degradation through mTORC activation. Moreover, blocking cIAP-1/2, mTORC, or IFN regulatory factor-1 may represent a promising therapeutic strategy to control M1-associated diseases.

TLR-4 Agonist Induces IFN-γ Production Selectively in Proinflammatory Human M1 Macrophages through the PI3K-mTOR- and JNK-MAPK-Activated p70S6K Pathway.

IFN-γ, a proinflammatory cytokine produced primarily by T cells and NK cells, activates macrophages and engages mechanisms to control pathogens. Although there is evidence of IFN-γ production by murine macrophages, IFN-γ production by normal human macrophages and their subsets remains unknown. Herein, we show that human M1 macrophages generated by IFN-γ and IL-12- and IL-18-stimulated monocyte-derived macrophages (M0) produce significant levels of IFN-γ. Further stimulation of IL-12/IL-18-primed macrophages or M1 macrophages with agonists for TLR-2, TLR-3, or TLR-4 significantly enhanced IFN-γ production in contrast to the similarly stimulated M0, M2a, M2b, and M2c macrophages. Similarly, M1 macrophages generated from COVID-19-infected patients' macrophages produced IFN-γ that was enhanced following LPS stimulation. The inhibition of M1 differentiation by Jak inhibitors reversed LPS-induced IFN-γ production, suggesting that differentiation with IFN-γ plays a key role in IFN-γ induction. We subsequently investigated the signaling pathway(s) responsible for TLR-4-induced IFN-γ production in M1 macrophages. Our results show that TLR-4-induced IFN-γ production is regulated by the ribosomal protein S6 kinase (p70S6K) through the activation of PI3K, the mammalian target of rapamycin complex 1/2 (mTORC1/2), and the JNK MAPK pathways. These results suggest that M1-derived IFN-γ may play a key role in inflammation that may be augmented following bacterial/viral infections. Moreover, blocking the mTORC1/2, PI3K, and JNK MAPKs in macrophages may be of potential translational significance in preventing macrophage-mediated inflammatory diseases.

Transfection of hard-to-transfect primary human macrophages with Bax siRNA to reverse Resveratrol-induced apoptosis.

Small interfering RNA (siRNA) is a critical loss-of-function tool for elucidating the role of genes in biomedical studies. The effective use of siRNA needs transfection technology that delivers siRNA into the correct location of target cells, especially those which are extremely difficult to transfect. Macrophages, which play an important role in the pathogenesis of many diseases, are known to be extremely hard to transfect. Thus, to elucidate the functions of genes in human macrophage biology, it is essential to devise technology for efficient siRNA transfection. However, a fast and efficient method for siRNA transfection in primary human macrophages has not been reported. The siRNA transfection is a tug-of-war between transfection rate and cytotoxicity. A higher transfection rate is generally accompanied with increased cytotoxicity, therefore, choosing a transfection reagent that limits cell death while maintain a desirable transfection rate is important. In this study, we employed auto-analysis function of the IncuCyte® to devise a fast and cost-saving technology for efficient transfection of adherent cells and particularly human macrophages. We show that DharmaFECT3 transfection reagent from Dharmacon was the most efficient in transfecting primary human monocyte-derived macrophages and PMA-differentiated U937 cells, whereas other transfection reagents tested were cytotoxic. This method exhibited approximately 85% transfection efficiency in human macrophages. Moreover, siRNA silencing of Bax with this technique effectively protected primary human macrophages and PMA-differentiated U937 cells against Resveratrol-induced cell death. In addition, this method inherently takes the balance between transfection rate and cytotoxicity of siRNA transfection reagents into consideration.