Generation and Use of Chimeric RIP Kinase Molecules to Study Necroptosis

CD47-SIRPα axis blockade in NASH promotes necroptotic hepatocyte clearance by liver macrophages and decreases hepatic fibrosis

Necroptosis contributes to hepatocyte death in nonalcoholic steatohepatitis (NASH), but the fate and roles of necroptotic hepatocytes (necHCs) in NASH remain unknown. We show here that the accumulation of necHCs in human and mouse NASH liver is associated with an up-regulation of the "don't-eat-me" ligand CD47 on necHCs, but not on apoptotic hepatocytes, and an increase in the CD47 receptor SIRPα on liver macrophages, consistent with impaired macrophage-mediated clearance of necHCs. In vitro, necHC clearance by primary liver macrophages was enhanced by treatment with either anti-CD47 or anti-SIRPα. In a proof-of-concept mouse model of inducible hepatocyte necroptosis, anti-CD47 antibody treatment increased necHC uptake by liver macrophages and inhibited markers of hepatic stellate cell (HSC) activation, which is responsible for liver fibrogenesis. Treatment of two mouse models of diet-induced NASH with anti-CD47, anti-SIRPα, or AAV8-H1-shCD47 to silence CD47 in hepatocytes increased the uptake of necHC by liver macrophages and decreased markers of HSC activation and liver fibrosis. Anti-SIRPα treatment avoided the adverse effect of anemia found in anti-CD47-treated mice. These findings provide evidence that impaired clearance of necHCs by liver macrophages due to CD47-SIRPα up-regulation contributes to fibrotic NASH, and suggest therapeutic blockade of the CD47-SIRPα axis as a strategy to decrease the accumulation of necHCs in NASH liver and dampen the progression of hepatic fibrosis.

The purinergic P2Y14 receptor links hepatocyte death to hepatic stellate cell activation and fibrogenesis in the liver

Fibrosis contributes to ~45% of deaths in western countries. In chronic liver disease, fibrosis is a major factor determining outcomes, but efficient antifibrotic therapies are lacking. Although platelet-derived growth factor and transforming growth factor-β constitute key fibrogenic mediators, they do not account for the well-established link between cell death and fibrosis in the liver. Here, we hypothesized that damage-associated molecular patterns (DAMPs) may link epithelial cell death to fibrogenesis in the injured liver. DAMP receptor screening identified purinergic receptor P2Y14 among several candidates as highly enriched in hepatic stellate cells (HSCs), the main fibrogenic cell type of the liver. Conversely, P2Y14 ligands uridine 5'-diphosphate (UDP)-glucose and UDP-galactose were enriched in hepatocytes and were released upon different modes of cell death. Accordingly, ligand-receptor interaction analysis that combined proteomic and single-cell RNA sequencing data revealed P2Y14 ligands and P2Y14 receptor as a link between dying cells and HSCs, respectively. Treatment with P2Y14 ligands or coculture with dying hepatocytes promoted HSC activation in a P2Y14-dependent manner. P2Y14 ligands activated extracellular signal-regulated kinase (ERK) and Yes-associated protein (YAP) signaling in HSCs, resulting in ERK-dependent HSC activation. Global and HSC-selective P2Y14 deficiency attenuated liver fibrosis in multiple mouse models of liver injury. Functional expression of P2Y14 was confirmed in healthy and diseased human liver and human HSCs. In conclusion, P2Y14 ligands and their receptor constitute a profibrogenic DAMP pathway that directly links cell death to fibrogenesis.

Guidelines for Regulated Cell Death Assays: A Systematic Summary, A Categorical Comparison, A Prospective

Over the past few years, the field of regulated cell death continues to expand and novel mechanisms that orchestrate multiple regulated cell death pathways are being unveiled. Meanwhile, researchers are focused on targeting these regulated pathways which are closely associated with various diseases for diagnosis, treatment, and prognosis. However, the complexity of the mechanisms and the difficulties of distinguishing among various regulated types of cell death make it harder to carry out the work and delay its progression. Here, we provide a systematic guideline for the fundamental detection and distinction of the major regulated cell death pathways following morphological, biochemical, and functional perspectives. Moreover, a comprehensive evaluation of different assay methods is critically reviewed, helping researchers to make a reliable selection from among the cell death assays. Also, we highlight the recent events that have demonstrated some novel regulated cell death processes, including newly reported biomarkers (e.g., non-coding RNA, exosomes, and proteins) and detection techniques.

Clemastine Fumarate Protects Against Myocardial Ischemia Reperfusion Injury by Activating the TLR4/PI3K/Akt Signaling Pathway

Our pilot studies have shown that clemastine fumarate (CLE) can protect against myocardial ischemia-reperfusion injury (MIRI) through regulation of toll like receptor 4 (TLR4). However, the protective mechanism of CLE and related signaling pathways for MIRI remains unclear. The objective of this study is to determine the mechanism by which CLE relieves MIRI in cardiomyocytes and its relationship with the TLR4/PI3K/Akt signaling pathway. CCK8 analysis was used to test the optimal concentration of TLR4 inhibitor CLI-095 and TLR4 agonist lipopolysaccharide (LPS) on MIRI. The expression of inflammatory factors, oxidative stress response, cell damage, and intracellular calcium redistribution of cardiomyocytes were examined using the ELISA kits, Total Superoxide Dismutase Assay Kit with WST-8 and Lipid Peroxidation MDA Assay Kit, LDH Cytotoxicity Assay Kit, and laser scanning confocal microscope. The expression of TLR4/PI3K/Akt and cleaved caspase-3 were determined by Western blotting and immunofluorescent staining. Our results showed that MIRI aggravated the inflammatory response, oxidative stress, cellular damage of cardiomyocytes, and caused redistribution of intracellular calcium, upregulated the expression of TLR4 protein, cleaved caspase-3 protein, and down-regulated the expression of PI3K/Akt protein. After treatment with CLE, the inflammatory response, oxidative stress, and cellular damage of cardiomyocytes were alleviated, and intracellular calcium ion accumulation decreased. The expression of TLR4 protein, cleaved caspase-3 protein declined, but PI3K/Akt protein expression increased in cardiomyocytes treated with CLE. In addition, after treatment with the TLR4 inhibitor CLI-095, the results were similar to those of CLE treatment. The TLR4 agonist LPS aggravated the reactions caused by MIRI. The role of LPS was reversed after CLE treatment. These results suggested that CLE can attenuate MIRI by activating the TLR4/PI3K/Akt signaling pathway.