Rubiarbonol B induces RIPK1-dependent necroptosis via NOX1-derived ROS production

The activation of receptor-interacting protein kinase 1 (RIPK1) by death-inducing signaling complex (DISC) formation is essential for triggering the necroptotic mode of cell death under apoptosis-deficient conditions. Thus, targeting the induction of necroptosis by modulating RIPK1 activity could be an effective strategy to bypass apoptosis resistance in certain types of cancer. In this study, we screened a series of arborinane triterpenoids purified from Rubia philippinesis and identified rubiarbonol B (Ru-B) as a potent caspase-8 activator that induces DISC-mediated apoptosis in multiple types of cancer cells. However, in RIPK3-expressing human colorectal cancer (CRC) cells, the pharmacological or genetic inhibition of caspase-8 shifted the mode of cell death by Ru-B from apoptosis to necroptosis though upregulation of RIPK1 phosphorylation. Conversely, Ru-B-induced cell death was almost completely abrogated by RIPK1 deficiency. The enhanced RIPK1 phosphorylation and necroptosis triggered by Ru-B treatment occurred independently of tumor necrosis factor receptor signaling and was mediated by the production of reactive oxygen species via NADPH oxidase 1 in CRC cells. Thus, we propose Ru-B as a novel anticancer agent that activates RIPK1-dependent cell death via ROS production, and suggest its potential as a novel necroptosis-targeting compound in apoptosis-resistant CRC.

Fisetin alleviates cellular senescence through PTEN mediated inhibition of PKCδ-NOX1 pathway in vascular smooth muscle cells

Reactive oxygen species (ROS) are a key risk factor of cellular senescence and age-related diseases, and protein kinase C (PKC) has been shown to activate NADPH oxidases (NOXs), which generate ROS. Although PKC activation induces oxidative stress, leading to the cellular dysfunction in various cell types, the correlation between PKC and senescence has not been reported in vascular smooth muscle cell (VSMC). Several studies have indicated cellular senescence is accompanied by phosphatase and tensin homolog (PTEN) loss and that an interaction exists between PTEN and PKC. Therefore, we aimed to determine whether PTEN and PKC are associated with VSMC senescence and to investigate the mechanism involved. We found hydrogen peroxide (H₂O₂) decreased PTEN expression and increased PKCδ phosphorylation. Moreover, H₂O₂ upregulated the NOX1 subunits, p22^phox and p47^phox, and induced VSMC senescence via p53-p21 signaling pathway. We identified PKCδ activation contributed to VSMC senescence through activation of NOX1 and ROS production. However, fisetin inhibited cellular senescence induced by the PTEN-PKCδ-NOX1-ROS signaling pathway, and this anti-aging effect was attributed to reduced ROS production caused by suppressing NOX1 activation. These results suggest that the PTEN-PCKδ signaling pathway is directly related to senescence via NOX1 activation and that the downregulation of PKCδ by flavonoids provides a potential means of treating age-associated diseases.

Chronic infusion of ELABELA alleviates vascular remodeling in spontaneously hypertensive rats via anti-inflammatory, anti-oxidative and anti-proliferative effects

Inflammatory activation and oxidative stress promote the proliferation of vascular smooth muscle cells (VSMCs), which accounts for pathological vascular remodeling in hypertension. ELABELA (ELA) is the second endogenous ligand for angiotensin receptor-like 1 (APJ) receptor that has been discovered thus far. In this study, we investigated whether ELA regulated VSMC proliferation and vascular remodeling in spontaneously hypertensive rats (SHRs). We showed that compared to that in Wistar-Kyoto rats (WKYs), ELA expression was markedly decreased in the VSMCs of SHRs. Exogenous ELA-21 significantly inhibited inflammatory cytokines and NADPH oxidase 1 expression, reactive oxygen species production and VSMC proliferation and increased the nuclear translocation of nuclear factor erythroid 2-related factor (Nrf2) in VSMCs. Osmotic minipump infusion of exogenous ELA-21 in SHRs for 4 weeks significantly decreased diastolic blood pressure, alleviated vascular remodeling and ameliorated vascular inflammation and oxidative stress in SHRs. In VSMCs of WKY, angiotensin II (Ang II)-induced inflammatory activation, oxidative stress and VSMC proliferation were attenuated by pretreatment with exogenous ELA-21 but were exacerbated by ELA knockdown. Moreover, ELA-21 inhibited the expression of matrix metalloproteinase 2 and 9 in both SHR-VSMCs and Ang II-treated WKY-VSMCs. We further revealed that exogenous ELA-21-induced inhibition of proliferation and PI3K/Akt signaling were amplified by the PI3K/Akt inhibitor LY294002, while the APJ receptor antagonist F13A abolished ELA-21-induced PI3K/Akt inhibition and Nrf2 activation in VSMCs. In conclusion, we demonstrate that ELA-21 alleviates vascular remodeling through anti-inflammatory, anti-oxidative and anti-proliferative effects in SHRs, indicating that ELA-21 may be a therapeutic agent for treating hypertension.