The cytoplasmic nuclear receptor RARγ controls RIP1 initiated cell death when cIAP activity is inhibited

Identification of a marine-derived sesquiterpenoid, Compound-8, that inhibits tumour necrosis factor-induced cell death by blocking complex II assembly

BACKGROUND AND PURPOSE

Tumour necrosis factor (TNF) is a pleiotropic inflammatory cytokine that not only directly induces inflammatory gene expression but also triggers apoptotic and necroptotic cell death, which leads to tissue damage and indirectly exacerbates inflammation. Thus, identification of inhibitors for TNF-induced cell death has broad therapeutic relevance for TNF-related inflammatory diseases. In the present study, we isolated and identified a marine fungus-derived sesquiterpenoid, 9α,14-dihydroxy-6β-p-nitrobenzoylcinnamolide (named as Cpd-8), that inhibits TNF receptor superfamily-induced cell death by preventing the formation of cytosolic death complex II.

EXPERIMENTAL APPROACH

Marine sponge-associated fungi were cultured and the secondary metabolites were extracted to yield pure compounds. Cell viability was measured by ATP-Glo cell viability assay. The effects of Cpd-8 on TNF signalling pathway were investigated by western blotting, immunoprecipitation, and immunofluorescence assays. A mouse model of acute liver injury (ALI) was employed to explore the protection effect of Cpd-8, in vivo.

KEY RESULTS

Cpd-8 selectively inhibits TNF receptor superfamily-induced apoptosis and necroptosis. Cpd-8 prevents the formation of cytosolic death complex II and subsequent RIPK1-RIPK3 necrosome, while it has no effect on TNF receptor I (TNFR1) internalization and the formation of complex I in TNF signalling pathway. In vivo, Cpd-8 protects mice against TNF-α/D-GalN-induced ALI.

CONCLUSION AND IMPLICATIONS

A marine fungus-derived sesquiterpenoid, Cpd-8, inhibits TNF receptor superfamily-induced cell death, both in vitro and in vivo. This study not only provides a useful research tool to investigate the regulatory mechanisms of TNF-induced cell death but also identifies a promising lead compound for future drug development.

HNEAP Regulates Necroptosis of Cardiomyocytes by Suppressing the m5 C Methylation of Atf7 mRNA

PIWI-interacting RNAs (piRNAs) are highly expressed in various cardiovascular diseases. However, their role in cardiomyocyte death caused by ischemia/reperfusion (I/R) injury, especially necroptosis, remains elusive. In this study, a heart necroptosis-associated piRNA (HNEAP) is found that regulates cardiomyocyte necroptosis by targeting DNA methyltransferase 1 (DNMT1)-mediated 5-methylcytosine (m5 C) methylation of the activating transcription factor 7 (Atf7) mRNA transcript. HNEAP expression level is significantly elevated in hypoxia/reoxygenation (H/R)-exposed cardiomyocytes and I/R-injured mouse hearts. Loss of HNEAP inhibited cardiomyocyte necroptosis and ameliorated cardiac function in mice. Mechanistically, HNEAP directly interacts with DNMT1 and attenuates m5 C methylation of the Atf7 mRNA transcript, which increases Atf7 expression level. ATF7 can further downregulate the transcription of Chmp2a, an inhibitor of necroptosis, resulting in the reduction of Chmp2a level and the progression of cardiomyocyte necroptosis. The findings reveal that piRNA-mediated m5 C methylation is involved in the regulation of cardiomyocyte necroptosis. Thus, the HNEAP-DNMT1-ATF7-CHMP2A axis may be a potential target for attenuating cardiac injury caused by necroptosis in ischemic heart disease.

Inhibition of autophagy and RIP1/RIP3/MLKL-mediated necroptosis by edaravone attenuates blood spinal cord barrier disruption following spinal cord injury

The disruption of the blood spinal cord barrier (BSCB) after spinal cord injury (SCI) can trigger secondary tissue damage. Edaravone is likely to protect the BSCB as a free radical scavenger, whereas it has been rarely reported thus far. In this study, the protective effect of edaravone was investigated with the use of compression spinal cord injured rats and human brain microvascular endothelial cells (HBMECs) injury. As indicated by the result of this study, edaravone treatment facilitated functional recovery after rats were subjected to SCI, ameliorated the vascular damage, and up-regulated the expression of BSCB-associated proteins. In vitro results, edaravone improved HBMECs viability, restored intercellular junctions, and promoted cellular angiogenic activities. It is noteworthy that autophagy was activated and RIP1/RIP3/MLKL phosphorylation was notably up-regulated. However, edaravone treatment exhibited the capability of mitigating above-mentioned tendency in vivo and in vitro. Moreover, rapamycin (Rapa) treatment deteriorated the protective effect of edaravone while aggravating the phosphorylation of RIP1/RIP3/MLKL expression. In the model of necrotic activator-induced HBMECs, autophagic expression was increased, whereas edaravone prevented autophagy and phosphorylation of RIP1/RIP3/MLKL. In general, our results suggested that edaravone is capable of reducing the destruction of BSCB and promoting functional recovery after SCI. The possible underlying mechanism is that edaravone is capable of protecting angiogenic activity and improving autophagy and the phosphorylation of RIP1/RIP3/MLKL, as well as their mutual deterioration. Accordingly, edaravone can be a favorable option for the treatment of SCI.

A multidisciplinary approach disclosing unexplored Aflatoxin B1 roles in severe impairment of vitamin D mechanisms of action

Aflatoxin B1 (AFB1), produced by fungi of the genus Aspergillus, is the most toxic and carcinogenic mycotoxin among the classes of aflatoxins. Previous research showed that AFB1 affects vitamin D receptor (VDR) expression. In the present study, integrated computational and experimental studies were carried out to investigate how AFB1 can interfere with Vitamin D signalling. A competitive antagonism of AFB1 toward RXRα and VDR was hypothesized by comparing the docked complex of AFB1/RXRα and AFB1/VDR ligand-binding domain (LBD) with the X-ray structures of RXRα and VDR bound to known ligands. Accordingly, we demonstrated that AFB1 can affect vitamin D-mediated transcriptional activation of VDR by impairing the formation of protein complexes containing both VDR-RXRα and RXRα/RAR and affecting the subcellular localization of VDR and RXRα. As a whole, our data indicate that AFB1 can interfere with different molecular pathways triggered by vitamin D with an antagonistic mechanism of action.

A cold-water extracted polysaccharide-protein complex from Grifola frondosa exhibited anti-tumor activity via TLR4-NF-κB signaling activation and gut microbiota modification in H22 tumor-bearing mice

Grifola frondosa polysaccharide-protein complex (G. frondosa PPC) is a polymer which consists of polysaccharides and proteins/peptides linked by covalent bonds. In our previous ex vivo research, it has been demonstrated that a cold-water extracted G. frondosa PPC has stronger antitumor activity than a G. frondosa PPC extracted from boiling water. The main purpose of the current study was to further evaluate the anti-hepatocellular carcinoma and gut microbiota regulation effects of two PPCs isolated from G. frondosa at 4 °C (GFG-4) and 100 °C (GFG-100) in vivo. The results exhibited that GFG-4 remarkably upregulated the expression of related proteins in TLR4-NF-κB and apoptosis pathway, thereby inhibiting the development of H22 tumors. Additionally, GFG-4 increased the abundance of norank_f__Muribaculaceae and Bacillus and reduced the abundance of Lactobacillus. Short chain fatty acids (SCFAs) analysis suggested that GFG-4 promoted SCFAs production, particularly butyric acid. Conclusively, the present experiments revealed GFG-4 has the potential of anti-hepatocellular carcinoma growth via activating TLR4-NF-κB pathway and regulating gut microbiota. Therefore, G. frondosa PPCs could be considered as safe and effective natural ingredient for treatment of hepatocellular carcinoma. The present study also provides a theoretical foundation for the regulation of gut microbiota by G. frondosa PPCs.

Natural and synthetic compounds for glioma treatment based on ROS-mediated strategy

Glioma is the most frequent and most malignant tumor of the central nervous system (CNS)，accounting for about 50% of all CNS tumor and approximately 80% of the malignant primary tumors in the CNS. Patients with glioma benefit from surgical resection, chemo- and radio-therapy. However these therapeutical strategies do not significantly improve the prognosis, nor increase survival rates owing to restricted drug contribution in the CNS and to the malignant characteristics of glioma. Reactive oxygen species (ROS) are important oxygen-containing molecules that regulate tumorigenesis and tumor progression. When ROS accumulates to cytotoxic levels, this can lead to anti-tumor effects. Multiple chemicals used as therapeutic strategies are based on this mechanism. They regulate intracellular ROS levels directly or indirectly, resulting in the inability of glioma cells to adapt to the damage induced by these substances. In the current review, we summarize the natural products, synthetic compounds and interdisciplinary techniques used for the treatment of glioma. Their possible molecular mechanisms are also presented. Some of them are also used as sensitizers: they modulate ROS levels to improve the outcomes of chemo- and radio-therapy. In addition, we summarize some new targets upstream or downstream of ROS to provide ideas for developing new anti-glioma therapies.

Targeting the Retinoic Acid Pathway to Eradicate Cancer Stem Cells

All-trans retinoic acid is a morphogen during embryogenesis and a teratogen. Cancer is an error of development, and the retinoic acid receptors (RAR) for all-trans retinoic acid play a role in cancer. Expression of the cytosolic aldehyde dehydrogenases, which mediate the last step to the synthesis of all-trans retinoic acid, is deregulated in various human cancers. Inhibiting these enzymes using a variety of agents reduced the proliferation of lung cancer cells, reduced the proliferation and induced apoptosis of ovarian, prostate, squamous, and uterine cancer cells, and sensitised breast, colorectal and ovarian cancer cells to chemotherapeutic agents. RARγ is an oncogene within some cases of AML, cholangiocarcinoma, colorectal cancer, clear cell renal cell carcinoma, hepatocellular carcinoma, pancreatic ductal adenocarcinoma, prostate cancer, and ovarian cancer. Pan-RAR and RARγ antagonist inhibition of the action of RARγ led to necroptosis of human prostate and pediatric brain tumour cancer stem cells. Treatment of hepatocellular carcinoma cells with the flavenoid acacetin, which interferes with the action of RARγ, decreased cell growth and induced apoptosis. Targeting the retinoic acid pathway is promising regarding the development of new drugs to eradicate cancer stem cells.

Effect of 3-caffeoylquinic acid on growth performance, nutrient digestibility, and intestinal functions in weaned pigs

Phenolic acid like with the 3-caffeoylquini acid (3-CQA) is formed by caffeic acid and qunic acid. This study was conducted to explore the effect of 3-CQA on growth performance and intestinal functions in weaned pigs. A total of 180 weaned pigs were randomly allocated into five treatments with 6 replicate pens per treatment (6 pigs per pen). Pigs in the control group (CON) were fed with basal diet (BD), and the others in the experimental groups were fed with BD and supplemented with 12.5, 25, 50, and 100 mg/kg 3-CQA. On day 43, the blood sample-collected pigs in the CON and optimal-dose group (only based on growth performance) were picked, and housed in metabolism cages (a total of 12 pigs, N = 6). 3-CQA increased the feed efficiency from days 21 to 42 of the trial and throughout the trial (P < 0.05). 3-CQA increased the serum concentrations of total protein, albumin, and total cholesterol (P < 0.05). Moreover, 3-CQA supplementation at 25 mg/kg increased the apparent digestibility of DM, energy, and ash (P < 0.05). Interestingly, 3-CQA decreased the crypt depth but increased the ratio of villus height to crypt depth in the jejunum and ileum (P < 0.05). Moreover, 3-CQA also increased the activities of sucrase, lactase, and catalase in the jejunal mucosa, and increased the activities of alkaline phosphatase and superoxide dismutase in the ileal mucosa (P < 0.05). 3-CQA also increased the abundance of secretory immunoglobulin A in the ileal mucosa (P < 0.05). Importantly, 3-CQA not only elevated the expression levels of critical functional genes such as the zonula occludens-1 , occludin, solute carrier family 7 , and nuclear factor erythroid 2-related factor 2 (Nrf2) in the duodenum but also elevated the expression levels of divalent metal transporter-1 and Nrf2 in the jejunum (P < 0.05). These results suggested a positive effect of 3-CQA supplementation on the growth and intestinal functions of weaned pigs. The mechanisms of action may be associated with elevated anti-oxidant capacity and improved intestinal barrier functions.

Retinoic acid receptor gamma is required for proliferation of pancreatic cancer cells

Despite the expectation that retinoic acid receptor could be the potential therapeutic targets for pancreatic cancers, there has been the lack of information about the role and the impact of retinoic acid receptor gamma (RARγ, RARG) on pancreatic cancer, unlike other two RARs. Herein, we applied TCGA and GEO database to show that the expression and prognosis of RARG is closely related to pancreatic cancer, which demonstrates that RARG is commonly overexpressed in human pancreatic cancer and is an independent diagnostic marker predicting the poor prognosis of pancreatic cancer patients. In addition, we demonstrated that the reduction in the expression of RARG in human pancreatic cancer cells dramatically suppress their proliferation and tumor growth in vivo, partially attributable to the downregulation of tumor-supporting biological processes such as cell proliferation, antiapoptosis and metabolism and the decreased expression of various oncogenes like MYC and STAT3. Mechanistically, RARG binds on the promoters of MYC, STAT3, and SLC2A1 which is distinguished from well-known conventional Retinotic acid response elements (RAREs) and that the binding is likely to be responsible for the epigenetic activation in the level of chromatin, assessed by the measurement of deposition of the gene activation marker histone H3 K27 acetylation (H3K27ac) using ChIP-qPCR. In this study, we reveal that RARG plays important role in the tumorigenesis of pancreatic cancer and represents new therapeutic targets for human pancreatic cancer.

Bombesin receptor-activated protein exacerbates cisplatin-induced AKI by regulating the degradation of SIRT2

BACKGROUND

Acute kidney injury (AKI) is a public health problem with no specific therapies in the clinic and the underlying pathogenesis of AKI remains obscure. Bombesin receptor-activated protein (BRAP, C6ORF89 protein) was initially discovered as a ligand for a previously orphan G-protein-coupled receptor bombesin-like receptor-3. At present, accepted biological effects of BRAP include cell cycle progression, wound repair and the activation of histone deacetylases. However, its role in kidney disease is unknown. In this study we have investigated the role of BRAP and underlying mechanisms involved in cisplatin (CP)-induced AKI.

METHODS

Here we used Bc004004 (homologous of C6ORF89 in mice) knockout mice and HK2 cells to investigate the effect of BRAP on AKI in vitro and in vivo. We analyzed ChIP-Seq and RNA-Seq data to search for the upstream regulators of BRAP and downstream mediators of BRAP action in AKI. Immunostaining, real-time polymerase chain reaction (PCR), co-immunoprecipitation, a dual-luciferase reporter assay and ChIP-PCR assay were applied to reveal the upstream and downstream regulation mechanism of BRAP during cisplatin-induced AKI.

RESULTS

BRAP was downregulated in mice and human kidneys with AKI. Global Bc004004 deletion alleviated tubular cell apoptosis and necroptosis in CP-induced AKI mice, whereas local overexpression of BRAP in kidneys aggravated them. Pan-caspase inhibitor Z-VAD pretreatment attenuated CP-induced blood creatinine increase and kidney injury in wild-type mice but not in BRAP -/- mice. The activation of mixed lineage kinase like-domain was magnified by Z-VAD in CP-treated mice, especially in BRAP -/- mice. The cytoprotective effect of Z-VAD was more substantial than necrostatin-1 (Nec-1, an inhibitor of necroptosis) in CP-treated human kidney proximal tubular epithelial (HK2) cells. Furthermore, Nec-1 pretreatment reduced the CP-induced cell death in BRAP overexpression HK2 cells but did not work in cells with normal BRAP levels. We determined that CP treatment activated the nuclear factor-κB subunit P65 and inhibition of P65 increased the messenger RNA (mRNA) levels of BRAP in HK2 cells. The chromatin immunoprecipitation assay and dual-luciferase reporter gene assay verified P65 binding to the C6ORF89 promoter and reduced its mRNA expression upon CP treatment. Next we found that sirtuin 2 (SIRT2) was downregulated in CP-induced AKI and BRAP levels directly impacted the protein levels of SIRT2. Our findings further confirmed that BRAP regulates the SIRT2 protein levels by affecting SIRT2's interactions with E3 ubiquitin ligase HRD1 and subsequent proteasomal degradation.

CONCLUSIONS

Our results demonstrated that BRAP played an important role in tubular cell apoptosis and necroptosis during CP-induced AKI. Safe and efficient BRAP inhibitors might be effective therapeutic options for AKI.

Retinoic Acid Receptor Gamma (RARγ) Promotes Cartilage Destruction through Positive Feedback Activation of NF-κB Pathway in Human Osteoarthritis

Osteoarthritis (OA) is a severe inflammation-related disease which leads to cartilage destruction. The retinoic acid receptor gamma (RARγ) has been indicated to be involved in many inflammation processes. However, the role and mechanism of RARγ in cartilage destruction caused by inflammation in OA are still unknown. Here, we demonstrated that the RARγ was highly expressed in chondrocytes of OA patients compared with healthy people and was positively correlated with the damage degree of cartilage in OA. Cytokine TNF-α promoted the transcription and expression of RARγ through activating the NF-κB pathway in OA cartilage. In addition, the overexpression of RARγ resulted in the upregulation of matrix degradation and inflammation associated genes and downregulation of differentiation and collagen production genes in human normal chondrocyte C28/I2 cells. Mechanistically, overexpression of RARγ could increase the level of p-IκBα and p-P65 to regulate the expression of downstream genes. RARγ and IκBα also could interact with each other and had the same localization in C28/I2 cells. Moreover, the SD rats OA model induced by monosodium iodoacetate indicated that CD437 (RARγ agonist) and TNF-α accelerated the OA progression, including more severe cartilage layer destruction, larger knee joint diameter, and higher serum ALP levels, while LY2955303 (RARγ inhibitor) showed the opposite result. RARγ was also highly expressed in OA group and even higher in TNF-α group. In conclusion, RARγ/NF-κB positive feedback loop was activated by TNF-α in chondrocyte to promote cartilage destruction. Our data not only propose a novel and precise molecular mechanism for OA disease but also provide a prospective strategy for the treatment.

Chlorogenic acid improves growth performance of weaned rabbits via modulating the intestinal epithelium functions and intestinal microbiota

This study was conducted to investigate the impacts of chlorogenic acid (CGA) on growth performance, intestinal permeability, intestinal digestion and absorption-related enzyme activities, immune responses, antioxidant capacity and cecum microbial composition in weaned rabbits. One hundred and sixty weaned rabbits were allotted to four treatment groups and fed with a basal diet or a basal diet supplemented with 400, 800, or 1,600 mg/kg CGA, respectively. After a 35-d trial, rabbits on the 800 mg/kg CGA-supplemented group had higher (p < 0.05) ADG and lower (p < 0.05) F/G than those in control (CON) group. According to the result of growth performance, eight rabbits per group were randomly selected from the CON group and 800 mg/kg CGA group to collect serum, intestinal tissue samples and cecum chyme samples. Results showed that compared with the CON group, supplementation with 800 mg/kg CGA decreased (p < 0.05) levels of D-lactate, diamine oxidase, IL-1β, IL-6, and malondialdehyde (MDA), and increased IL-10 concentration in the serum; increased (p < 0.05) jejunal ratio of villus height to crypt depth, enhanced (p < 0.05) activities of maltase and sucrase, increased (p < 0.05) concentrations of IL-10, T-AOC, MHCII and transforming growth factor-α, and decreased (p < 0.05) levels of TNF-α and MDA in the jejunum of weaned rabbits. In addition, results of high-throughput sequencing showed that CGA supplementation elevated (p < 0.05) microbial diversity and richness, and increased (p < 0.05) the abundances of butyrate-producing bacteria (including genera V9D2013_group, Monoglobus, Papillibacter, UCG-005, and Ruminococcus). These results indicated that dietary supplementation with 800 mg/kg CGA could improve the growth performance of weaned rabbits by enhancing intestinal structural integrity, improving the intestinal epithelium functions, and modulating the composition and diversity of gut microbiota.

Combination Treatment of Retinoic Acid Plus Focal Adhesion Kinase Inhibitor Prevents Tumor Growth and Breast Cancer Cell Metastasis

All-trans retinoic acid (RA), the primary metabolite of vitamin A, controls the development and homeostasis of organisms and tissues. RA and its natural and synthetic derivatives, both known as retinoids, are promising agents in treating and chemopreventing different neoplasias, including breast cancer (BC). Focal adhesion kinase (FAK) is a crucial regulator of cell migration, and its overexpression is associated with tumor metastatic behavior. Thus, pharmaceutical FAK inhibitors (FAKi) have been developed to counter its action. In this work, we hypothesize that the RA plus FAKi (RA + FAKi) approach could improve the inhibition of tumor progression. By in silico analysis and its subsequent validation by qPCR, we confirmed RARA, SRC, and PTK2 (encoding RARα, Src, and FAK, respectively) overexpression in all breast cells tested. We also showed a different pattern of genes up/down-regulated between RA-resistant and RA-sensitive BC cells. In addition, we demonstrated that both RA-resistant BC cells (MDA-MB-231 and MDA-MB-468) display the same behavior after RA treatment, modulating the expression of genes involved in Src-FAK signaling. Furthermore, we demonstrated that although RA and FAKi administered separately decrease viability, adhesion, and migration in mammary adenocarcinoma LM3 cells, their combination exerts a higher effect. Additionally, we show that both drugs individually, as well as in combination, induce the expression of apoptosis markers such as active-caspase-3 and cleaved-PARP1. We also provided evidence that RA effects are extrapolated to other cancer cells, including T-47D BC and the human cervical carcinoma HeLa cells. In an orthotopic assay of LM3 tumor growth, whereas RA and FAKi administered separately reduced tumor growth, the combined treatment induced a more potent inhibition increasing mice survival. Moreover, in an experimental metastatic assay, RA significantly reduced metastatic lung dissemination of LM3 cells. Overall, these results indicate that RA resistance could reflect deregulation of most RA-target genes, including genes encoding components of the Src-FAK pathway. Our study demonstrates that RA plays an essential role in disrupting BC tumor growth and metastatic dissemination in vitro and in vivo by controlling FAK expression and localization. RA plus FAKi exacerbate these effects, thus suggesting that the sensitivity to RA therapies could be increased with FAKi coadministration in BC tumors.

Lessons to cancer from studies of leukemia and hematopoiesis

The starting point to describing the origin and nature of any cancer must be knowledge about how the normal counterpart tissue develops. New principles to the nature of hematopoietic stem cells have arisen in recent years. In particular, hematopoietic stem cells can “choose” a cell lineage directly from a spectrum of the end-cell options, and are, therefore, a heterogeneous population of lineage affiliated/biased cells. These cells remain versatile because the developmental trajectories of hematopoietic stem and progenitor cells are broad. From studies of human acute myeloid leukemia, leukemia is also a hierarchy of maturing or partially maturing cells that are sustained by leukemia stem cells at the apex. This cellular hierarchy model has been extended to a wide variety of human solid tumors, by the identification of cancer stem cells, and is termed the cancer stem cell model. At least, two genomic insults are needed for cancer, as seen from studies of human childhood acute lymphoblastic leukemia. There are signature mutations for some leukemia’s and some relate to a transcription factor that guides the cell lineage of developing hematopoietic stem/progenitor cells. Similarly, some oncogenes restrict the fate of leukemia stem cells and their offspring to a single maturation pathway. In this case, a loss of intrinsic stem cell versatility seems to be a property of leukemia stem cells. To provide more effective cures for leukemia, there is the need to find ways to eliminate leukemia stem cells.

Antagonizing RARγ Drives Necroptosis of Cancer Stem Cells

There is a need for agents that eliminate cancer stem cells, which sustain cancer and are also largely responsible for disease relapse and metastasis. Conventional chemotherapeutics and radiotherapy are often highly effective against the bulk of cancer cells, which are proliferating, but spare cancer stem cells. Therapeutics that target cancer stem cells may also provide a bona fide cure for cancer. There are two rationales for targeting the retinoic acid receptor (RAR)γ. First, RARγ is expressed selectively within primitive cells. Second, RARγ is a putative oncogene for a number of human cancers, including cases of acute myeloid leukemia, cholangiocarcinoma, and colorectal, renal and hepatocellular carcinomas. Prostate cancer cells depend on active RARγ for their survival. Antagonizing all RARs caused necroptosis of prostate and breast cancer stem cell-like cells, and the cancer stem cells that gave rise to neurospheres from pediatric patients’ primitive neuroectodermal tumors and an astrocytoma. As tested for prostate cancer, antagonizing RARγ was sufficient to drive necroptosis. Achieving cancer-selectively is a longstanding paradigm for developing new treatments. The normal prostate epithelium was less sensitive to the RARγ antagonist and pan-RAR antagonist than prostate cancer cells, and fibroblasts and blood mononuclear cells were insensitive. The RARγ antagonist and pan-RAR antagonist are promising new cancer therapeutics.

Effect of sialyllactose on growth performance and intestinal epithelium functions in weaned pigs challenged by enterotoxigenic Escherichia Coli

Background

Sialyllactose (SL) is one of the most abundant oligosaccharides present in porcine breast milk. However, little is known about its effect on growth performance and intestinal health in weaned pigs. This study was conducted to explore the protective effect of SL on intestinal epithelium in weaned pigs upon enterotoxigenic Escherichia coli (ETEC) challenge.

Methods

Thirty-two pigs were randomly divided into four treatments. Pigs fed with a basal diet or basal diet containing SL (5.0 g/kg) were orally infused with ETEC or culture medium.

Results

SL supplementation elevated the average daily gain (ADG) and feed efficiency in the ETEC-challenged pigs (P < 0.05). SL also improved the digestibilities of dry matter (DM), gross energy (GE), and ash in non-challenged pigs (P < 0.05). Moreover, SL not only elevated serum concentrations of immunoglobulins (IgA, IgG, and IgM), but also significantly decreased the serum concentrations of inflammatory cytokines (TNF-α, IL-1β, and IL-6) upon ETEC challenge (P < 0.05). Interestingly, SL increased the villus height, the ratio of villus height to crypt depth (V:C), and the activities of mucosal sucrase and maltase in the jejunum and ileum (P < 0.05). SL also elevated the concentrations of microbial metabolites (e.g. acetic acid, propanoic acid, and butyric acid) and the abundance of Lactobacillus, Bifidobacterium, and Bacillus in the cecum (P < 0.05). Importantly, SL significantly elevated the expression levels of jejunal zonula occludins-1 (ZO-1), occluding, and fatty acid transport protein-4 (FATP4) in the ETEC-challenged pigs (P < 0.05).

Conclusions

SL can alleviate inflammation and intestinal injury in weaned pigs upon ETEC challenge, which was associated with suppressed secretion of inflammatory cytokines and elevated serum immunoglobulins, as well as improved intestinal epithelium functions and microbiota.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00673-8.

The evolution of regulated cell death pathways in animals and their evasion by pathogens

The coevolution of host-pathogen interactions underlies many human physiological traits associated with protection from or susceptibility to infections. Among the mechanisms that animals utilize to control infections are the regulated cell death pathways of pyroptosis, apoptosis, and necroptosis. Over the course of evolution these pathways have become intricate and complex, coevolving with microbes that infect animal hosts. Microbes, in turn, have evolved strategies to interfere with the pathways of regulated cell death to avoid eradication by the host. Here, we present an overview of the mechanisms of regulated cell death in Animalia and the strategies devised by pathogens to interfere with these processes. We review the molecular pathways of regulated cell death, their roles in infection, and how they are perturbed by viruses and bacteria, providing insights into the coevolution of host-pathogen interactions and cell death pathways.

Manno-oligosaccharide attenuates inflammation and intestinal epithelium injury in weaned pigs upon enterotoxigenic Escherichia coli K88 challenge

To explore the effect of manno-oligosaccharide (MOS) on intestinal health in weaned pigs upon enterotoxigenic Escherichia coli K88 (ETEC) challenge, thirty-two male weaned pigs were randomly assigned into four groups. Pigs fed with a basal diet or basal diet containing MOS (0·6 g/kg) were orally infused with ETEC or culture medium. Results showed that MOS significantly elevated the digestibility of crude protein and gross energy in both ETEC-challenged and non-challenged pigs (P < 0·05). MOS also elevated serum concentrations of IgA and IgM (P < 0·05), but decreased serum concentrations of TNF-α, IL-1β and IL-6 (P < 0·05) in ETEC-challenged pigs. Interestingly, MOS increased villus height and the ratio of villus height:crypt depth in duodenum and ileum (P < 0·05). MOS also increased duodenal sucrase and ileal lactase activity in ETEC-challenged pigs (P < 0·05). MOS decreased the abundance of E. coli, but increased the abundance of Lactobacillus, Bifidobacterium and Bacillus in caecum (P < 0·05). Importantly, MOS not only elevated the expression levels of zonula occludens-1 (ZO-1), claudin-1 and GLUT-2 in duodenum (P < 0·05) but also elevated the expression levels of ZO-1, GLUT-2 and L-type amino acid transporter-1 in ileum (P < 0·05) upon ETEC challenge. These results suggested that MOS can alleviate inflammation and intestinal injury in weaned pigs upon ETEC challenge, which was associated with suppressed secretion of inflammatory cytokines and elevated serum Ig, as well as improved intestinal epithelium functions and microbiota.

ZBP1 not RIPK1 mediates tumor necroptosis in breast cancer

Tumor necrosis happens commonly in advanced solid tumors. We reported that necroptosis plays a major role in tumor necrosis. Although several key necroptosis regulators including receptor interacting protein kinase 1 (RIPK1) have been identified, the regulation of tumor necroptosis during tumor development remains elusive. Here, we report that Z-DNA-binding protein 1 (ZBP1), not RIPK1, mediates tumor necroptosis during tumor development in preclinical cancer models. We found that ZBP1 expression is dramatically elevated in necrotic tumors. Importantly, ZBP1, not RIPK1, deletion blocks tumor necroptosis during tumor development and inhibits metastasis. We showed that glucose deprivation triggers ZBP1-depedent necroptosis in tumor cells. Glucose deprivation causes mitochondrial DNA (mtDNA) release to the cytoplasm and the binding of mtDNA to ZBP1 to activate MLKL in a BCL-2 family protein, NOXA-dependent manner. Therefore, our study reveals ZBP1 as the key regulator of tumor necroptosis and provides a potential drug target for controlling tumor metastasis.

Integrative chemogenomic analysis identifies small molecules that partially rescue ΔF508-CFTR for cystic fibrosis

Rare diseases affect 10% of the first‐world population, yet over 95% lack even a single pharmaceutical treatment. In the present age of information, we need ways to leverage our vast data and knowledge to streamline therapeutic development and lessen this gap. Here, we develop and implement an innovative informatic approach to identify therapeutic molecules, using the Connectivity Map and LINCS L1000 databases and disease‐associated transcriptional signatures and pathways. We apply this to cystic fibrosis (CF), the most common genetic disease in people of northern European ancestry leading to chronic lung disease and reduced lifespan. We selected and tested 120 small molecules in a CF cell line, finding 8 with activity, and confirmed 3 in primary CF airway epithelia. Although chemically diverse, the transcriptional profiles of the hits suggest a common mechanism associated with the unfolded protein response and/or TNFα signaling. This study highlights the power of informatics to help identify new therapies and reveal mechanistic insights while moving beyond target‐centric drug discovery.

The RARγ Oncogene: An Achilles Heel for Some Cancers

Cancer "stem cells" (CSCs) sustain the hierarchies of dividing cells that characterize cancer. The main causes of cancer-related mortality are metastatic disease and relapse, both of which originate primarily from CSCs, so their eradication may provide a bona fide curative strategy, though there maybe also the need to kill the bulk cancer cells. While classic anti-cancer chemotherapy is effective against the dividing progeny of CSCs, non-dividing or quiescent CSCs are often spared. Improved anti-cancer therapies therefore require approaches that target non-dividing CSCs, which must be underpinned by a better understanding of factors that permit these cells to maintain a stem cell-like state. During hematopoiesis, retinoic acid receptor (RAR) γ is selectively expressed by stem cells and their immediate progeny. It is overexpressed in, and is an oncogene for, many cancers including colorectal, renal and hepatocellular carcinoma, cholangiocarcinomas and some cases of acute myeloid leukemia that harbor RARγ fusion proteins. In vitro studies suggest that RARγ-selective and pan-RAR antagonists provoke the death of CSCs by necroptosis and point to antagonism of RARγ as a potential strategy to treat metastatic disease and relapse, and perhaps provide a cure for some cancers.

Location, location, location: A compartmentalized view of TNF-induced necroptotic signaling

Necroptosis is a lytic, proinflammatory cell death pathway, which has been implicated in host defense and, when dysregulated, the pathology of many human diseases. The central mediators of this pathway are the receptor-interacting serine/threonine protein kinases RIPK1 and RIPK3 and the terminal executioner, the pseudokinase mixed lineage kinase domain-like (MLKL). Here, we review the chronology of signaling along the RIPK1-RIPK3-MLKL axis and highlight how the subcellular compartmentalization of signaling events controls the initiation and execution of necroptosis. We propose that a network of modulators surrounds the necroptotic signaling core and that this network, rather than acting universally, tunes necroptosis in a context-, cell type-, and species-dependent manner. Such a high degree of mechanistic flexibility is likely an important property that helps necroptosis operate as a robust, emergency form of cell death.

Transition from TNF-Induced Inflammation to Death Signaling

Tumor necrosis factor (TNF) plays a key role in inflammatory responses and in various cellular events such as apoptosis and necroptosis. The interaction of TNF with its receptor, TNFR1, drives the initiation of complex molecular pathways leading to inflammation and cell death. RARγ is released from the nucleus to orchestrate the formation of the cytosolic death complexes, and it is cytosolic RARγ that plays a pivotal role in switching TNF-induced inflammatory responses to RIPK1-initiated cell death. Thus, RARγ provides a checkpoint for the transition from inflammatory signaling to death machinery of RIPK1-initiated cell death in response to TNF. Here, we use techniques to identify RARγ as a downstream mediator of TNFR1 signaling complex. We use confocal imaging to show the localization of RARγ upon activation of cell death. Immunoprecipitation of RARγ identified the interacting proteins.

Receptor-interacting protein kinase 1 is a key mediator in TLR3 ligand and Smac mimetic-induced cell death and suppresses TLR3 ligand-promoted invasion in cholangiocarcinoma

BACKGROUND

Toll-like receptor 3 (TLR3) ligand which activates TLR3 signaling induces both cancer cell death and activates anti-tumor immunity. However, TLR3 signaling can also harbor pro-tumorigenic consequences. Therefore, we examined the status of TLR3 in cholangiocarcinoma (CCA) cases to better understand TLR3 signaling and explore the potential therapeutic target in CCA.

METHODS

The expression of TLR3 and receptor-interacting protein kinase 1 (RIPK1) in primary CCA tissues was assayed by Immunohistochemical staining and their associations with clinicopathological characteristics and survival data were evaluated. The effects of TLR3 ligand, Poly(I:C) and Smac mimetic, an IAP antagonist on CCA cell death and invasion were determined by cell death detection methods and Transwell invasion assay, respectively. Both genetic and pharmacological inhibition of RIPK1, RIPK3 and MLKL and inhibitors targeting NF-κB and MAPK signaling were used to investigate the underlying mechanisms.

RESULTS

TLR3 was significantly higher expressed in tumor than adjacent normal tissues. We demonstrated in a panel of CCA cell lines that TLR3 was frequently expressed in CCA cell lines, but was not detected in a nontumor cholangiocyte. Subsequent in vitro study demonstrated that Poly(I:C) specifically induced CCA cell death, but only when cIAPs were removed by Smac mimetic. Cell death was also switched from apoptosis to necroptosis when caspases were inhibited in CCA cells-expressing RIPK3. In addition, RIPK1 was required for Poly(I:C) and Smac mimetic-induced apoptosis and necroptosis. Of particular interest, high TLR3 or low RIPK1 status in CCA patients was associated with more invasiveness. In vitro invasion demonstrated that Poly(I:C)-induced invasion through NF-κB and MAPK signaling. Furthermore, the loss of RIPK1 enhanced Poly(I:C)-induced invasion and ERK activation in vitro. Smac mimetic also reversed Poly(I:C)-induced invasion, partly mediated by RIPK1. Finally, a subgroup of patients with high TLR3 and high RIPK1 had a trend toward longer disease-free survival (p = 0.078, 28.0 months and 10.9 months).

CONCLUSION

RIPK1 plays a pivotal role in TLR3 ligand, Poly(I:C)-induced cell death when cIAPs activity was inhibited and loss of RIPK1 enhanced Poly(I:C)-induced invasion which was partially reversed by Smac mimetic. Our results suggested that TLR3 ligand in combination with Smac mimetic could provide therapeutic benefits to the patients with CCA. Video abstract.

Necroptosis, tumor necrosis and tumorigenesis

Necroptosis, known as programmed necrosis, is a form of caspase-independent, finely regulated cell death with necrotic morphology. Tumor necrosis, foci of necrotic cell death, occurs in advanced solid tumors and is often associated with poor prognosis of cancer patients. While it is well documented that apoptosis plays a key role in tumor regression and the inactivation of apoptosis is pivotal to tumor development, the role of necroptosis in tumorigenesis is still not fully understood as recent studies have reported both tumor-promoting and tumor-suppressing effects of necroptosis. In this short review, we will discuss some recent studies about the role of necroptosis in tumorigenesis and speculate the implications of these findings in future research and potential novel cancer therapy targeting necroptosis.

Current translational potential and underlying molecular mechanisms of necroptosis

Cell death has a fundamental impact on the evolution of degenerative disorders, autoimmune processes, inflammatory diseases, tumor formation and immune surveillance. Over the past couple of decades extensive studies have uncovered novel cell death pathways, which are independent of apoptosis. Among these is necroptosis, a tightly regulated, inflammatory form of cell death. Necroptosis contribute to the pathogenesis of many diseases and in this review, we will focus exclusively on necroptosis in humans. Necroptosis is considered a backup mechanism of apoptosis, but the in vivo appearance of necroptosis indicates that both caspase-mediated and caspase-independent mechanisms control necroptosis. Necroptosis is regulated on multiple levels, from the transcription, to the stability and posttranslational modifications of the necrosome components, to the availability of molecular interaction partners and the localization of receptor-interacting serine/threonine-protein kinase 1 (RIPK1), receptor-interacting serine/threonine-protein kinase 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL). Accordingly, we classified the role of more than seventy molecules in necroptotic signaling based on consistent in vitro or in vivo evidence to understand the molecular background of necroptosis and to find opportunities where regulating the intensity and the modality of cell death could be exploited in clinical interventions. Necroptosis specific inhibitors are under development, but >20 drugs, already used in the treatment of various diseases, have the potential to regulate necroptosis. By listing necroptosis-modulated human diseases and cataloging the currently available drug-repertoire to modify necroptosis intensity, we hope to kick-start approaches with immediate translational potential. We also indicate where necroptosis regulating capacity should be considered in the current applications of these drugs.

Caspase-8, receptor-interacting protein kinase 1 (RIPK1), and RIPK3 regulate retinoic acid-induced cell differentiation and necroptosis

Among caspase family members, Caspase-8 is unique, with associated critical activities to induce and suppress death receptor-mediated apoptosis and necroptosis, respectively. Caspase-8 inhibits necroptosis by suppressing the function of receptor-interacting protein kinase 1 (RIPK1 or RIP1) and RIPK3 to activate mixed lineage kinase domain-like (MLKL). Disruption of Caspase-8 expression causes embryonic lethality in mice, which is rescued by depletion of either Ripk3 or Mlkl, indicating that the embryonic lethality is caused by activation of necroptosis. Here, we show that knockdown of Caspase-8 expression in embryoid bodies derived from ES cells markedly enhances retinoic acid (RA)-induced cell differentiation and necroptosis, both of which are dependent on Ripk1 and Ripk3; however, the enhancement of RA-induced cell differentiation is independent of Mlkl and necrosome formation. RA treatment obviously enhanced the expression of RA-specific target genes having the retinoic acid response element (RARE) in their promoter regions to induce cell differentiation, and induced marked expression of RIPK1, RIPK3, and MLKL to stimulate necroptosis. Caspase-8 knockdown induced RIPK1 and RIPK3 to translocate into the nucleus and to form a complex with RA receptor (RAR), and RAR interacting with RIPK1 and RIPK3 showed much stronger binding activity to RARE than RAR without RIPK1 or RIPK3. In Caspase-8-deficient as well as Caspase-8- and Mlkl-deficient mouse embryos, the expression of RA-specific target genes was obviously enhanced. Thus, Caspase-8, RIPK1, and RIPK3 regulate RA-induced cell differentiation and necroptosis both in vitro and in vivo.

Role of Retinoic Acid Receptor-γ in DNA Damage-Induced Necroptosis

DNA-damaging compounds, commonly used as chemotherapeutic drugs, are known to trigger cells to undergo programmed cell death such as apoptosis and necroptosis. However, the molecular mechanism of DNA damage-induced cell death is not fully understood. Here, we report that RARγ has a critical role in DNA damage-induced programmed cell death, specifically in necroptosis. The loss of RARγ abolishes the necroptosis induced by DNA damage. In addition, cells that lack RARγ are less susceptible to extrinsic apoptotic pathway activated by DNA-damaging agents whereas the intrinsic apoptotic pathway is not affected. We demonstrate that RARγ is essential for the formation of RIPK1/RIPK3 death complex, known as Ripoptosome, in response to DNA damage. Furthermore, we show that RARγ plays a role in skin cancer development by using RARγ1 knockout mice and human squamous cell carcinoma biopsies. Hence, our study reveals that RARγ is a critical component of DNA damage-induced cell death.

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RARγ plays a key role in DNA damage-induced cell death

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RARγ is essential for RIPK1-mediated necroptosis and apoptosis following DNA damage

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RARγ is required for the formation of Ripoptosome in response to DNA damage

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Loss of RARγ correlates with skin cancer development

The role of necroptosis in cancer: A double-edged sword?

Necroptosis is a programmed, caspase-independent cell death that is morphologically similar to necrosis. Unlike apoptosis, necroptosis evokes inflammatory responses by releasing damage-associated molecular patterns. Recent studies suggest that tumor undergoes necroptosis in vivo and necroptosis has pro- or anti-tumoral effects in cancer development and progression. Furthermore, triggering necroptosis in tumor cells has been explored as a potential therapeutic strategy against cancer. Here, we will review the recent research progress of necroptosis in conferring anti- or pro-tumoral effects and its potential application in cancer therapy.

Characteristics of the mitochondrial and cellular uptake of MPP+, as probed by the fluorescent mimic, 4'I-MPP

The discovery that 1-methyl-4-phenylpyridinium (MPP⁺) selectively destroys dopaminergic neurons and causes Parkinson’s disease (PD) symptoms in mammals has strengthened the environmental hypothesis of PD. The current model for the dopaminergic toxicity of MPP⁺ is centered on its uptake into dopaminergic neurons, accumulation into the mitochondria, inhibition of the complex-I leading to ATP depletion, increased reactive oxygen species (ROS) production, and apoptotic cell death. However, some aspects of this mechanism and the details of the cellular and mitochondrial accumulation of MPP⁺ are still poorly understood. The aim of this study was to characterize a structural and functional MPP⁺ mimic which is suitable to study the cellular distribution and mitochondrial uptake of MPP⁺ in live cells and use it to identify the molecular details of these processes to advance the understanding of the mechanism of the selective dopaminergic toxicity of MPP⁺. Here we report the characterization of the fluorescent MPP⁺ derivative, 1-methyl-4-(4'-iodophenyl)pyridinium (4'I-MPP⁺), as a suitable candidate for this purpose. Using this novel probe, we show that cytosolic/mitochondrial Ca²⁺ play a critical role through the sodium-calcium exchanger (NCX) in the mitochondrial and cellular accumulation of MPP⁺ suggesting for the first time that MPP⁺ and related mitochondrial toxins may also exert their toxic effects through the perturbation of Ca²⁺ homeostasis in dopaminergic cells. We also found that the specific mitochondrial NCX (mNCX) inhibitors protect dopaminergic cells from the MPP⁺ and 4'I-MPP⁺ toxicity, most likely through the inhibition of the mitochondrial uptake, which could potentially be exploited for the development of pharmacological agents to protect the central nervous system (CNS) dopaminergic neurons from PD-causing environmental toxins.

Retinoic Acid, Leaky Gut, and Autoimmune Diseases

A leaky gut has been observed in a number of autoimmune diseases including type 1 diabetes, multiple sclerosis, inflammatory bowel disease, and systemic lupus erythematosus. Previous studies from our laboratory have shown that lupus mice also bear a leaky gut and that the intestinal barrier function can be enhanced by gut colonization of probiotics such as Lactobacillus spp. Retinoic acid (RA) can increase the relative abundance of Lactobacillus spp. in the gut. Interestingly, RA has also been shown to strengthen the barrier function of epithelial cells in vitro and in the absence of probiotic bacteria. These reports bring up an interesting question of whether RA exerts protective effects on the intestinal barrier directly or through regulating the microbiota colonization. In this review, we will discuss the roles of RA in immunomodulation, recent literature on the involvement of a leaky gut in different autoimmune diseases, and how RA shapes the outcomes of these diseases.

Molecular pathways involved in the transport of nuclear receptors from the nucleus to cytoplasm

Nuclear receptors (NRs) are transcription regulators that direct the expression of many genes linked to cellular processes, such as proliferation, differentiation, and apoptosis. Additionally, some cellular events are also modulated by signaling pathways induced by NRs outside of the nucleus. Hence, the subcellular transport of NRs is dynamic and is modulated by several signals, protein-protein interactions, and posttranslational modifications. Particularly, the exit of NRs from the nucleus to cytoplasm and/or other compartments is transcendental, as it is this export event, which determines their abundance in the cells' compartments, the activation or attenuation of nuclear or extranuclear pathways, and the magnitude and duration of their effects inside or outside of the nucleus. Consequently, an adequate control of the distribution of NRs is critical for homeostasis, because a deregulation in the nucleo-cytoplasmic transport of NRs could be involved in diseases including cancer as well as metabolic and vascular alterations. In this review, we investigated the pathways and molecular and biological aspects that have been described for the nuclear export of NRs so far and their functional relevance in some diseases. This information suggests that the transport of NRs out of the nucleus is a key mechanism for the identification of new therapeutic targets for alterations associated with the deregulation of the function of NRs.

Switching from TNF-induced inflammation to death signaling

TNFR1-mediated cell signaling involves complex molecular pathways leading to inflammation and death. Cytosolic RARγ plays a pivotal role in converting TNF-induced inflammatory responses to RIP1 initiated cell death and this finely regulated function of RARγ serves as a checkpoint to engage death pathways in response to TNF.