Receptor-interacting protein (RIP) kinase family

Renoprotective Effects of a Novel Receptor-Interacting Protein Kinase 2 Inhibitor, AS3334034, in Uninephrectomized Adriamycin-Induced Chronic Kidney Disease Rats

Renal inflammation is a final common pathway of chronic kidney disease (CKD), and its progression can be used to effectively gauge the degree of renal dysfunction. Inflammatory mechanisms contribute to glomerulosclerosis and tubulointerstitial fibrosis, which are hallmarks of CKD leading to end-stage renal disease. Receptor-interacting protein kinase 2 (RIP2) is largely committed to nucleotide-binding oligomerization domain signaling as a direct effector and transmits nuclear factor-κB (NF-κB)-mediated proinflammatory cytokine production. In the present study, we hypothesized that if inflammation via RIP2 and NF-κB signaling plays an important role in renal failure, then the anti-inflammatory effect of RIP2 inhibitors should be effective in improving CKD. To determine its pharmacologic potency, we investigated the renoprotective properties of the novel RIP2 inhibitor AS3334034 [7-methoxy-6-(2-methylpropane-2-sulfonyl)-N-(4-methyl-1H-pyrazol-3-yl)quinolin-4-amine] in uninephrectomized adriamycin-induced CKD rats. Six weeks' repeated administration of AS3334034 (10 mg/kg, once daily) significantly reduced urinary protein excretion and prevented the development of glomerulosclerosis and tubulointerstitial fibrosis. In addition, AS3334034 showed beneficial effects on renal function, as demonstrated by a decrease in levels of plasma creatinine and blood urea nitrogen and attenuation of a decline in creatinine clearance. Furthermore, AS3334034 significantly attenuated inflammation, renal apoptosis, and glomerular podocyte loss. These results suggest that the RIP2 inhibitor AS3334034 suppresses the progression of chronic renal failure via an anti-inflammatory effect and is therefore potentially useful in treating patients with CKD. SIGNIFICANCE STATEMENT: The receptor-interacting protein kinase 2 (RIP2) inhibitor AS3334034 suppresses the progression of chronic renal failure via an anti-inflammatory effect, suggesting that the nucleotide-binding oligomerization domain-RIP2 axis might play a crucial role in the pathogenesis of inflammatory kidney diseases. AS3334034 is expected to be potentially useful in the treatment of patients with chronic kidney disease.

Compound Prunetin Induces Cell Death in Gastric Cancer Cell with Potent Anti-Proliferative Properties: In Vitro Assay, Molecular Docking, Dynamics, and ADMET Studies

Gastric cancer is the common type of malignancy positioned at second in mortality rate causing burden worldwide with increasing treatment options. Prunetin (PRU) is an O-methylated flavonoid that belongs to the group of isoflavone executing beneficial activities. In the present study, we investigated the anti-proliferative and cell death effect of the compound PRU in AGS gastric cancer cell line. The in vitro cytotoxic potential of PRU was evaluated and significant proliferation was observed. We identified that the mechanism of cell death was due to necroptosis through double staining and was confirmed by co-treatment with inhibitor necrostatin (Nec-1). We further elucidated the mechanism of action of necroptosis via receptor interacting protein kinase 3 (RIPK3) protein expression and it has been attributed by ROS generation through JNK activation. Furthermore, through computational analysis by molecular docking and dynamics simulation, the efficiency of compound prunetin against RIPK3 binding was validated. In addition, we also briefed the pharmacokinetic properties of the compound by in silico ADMET analysis.

RIP1 Is a Novel Component of γ-ionizing Radiation-Induced Invasion of Non-Small Cell Lung Cancer Cells

Abstract: Previously, we demonstrated that γ-ionizing radiation (IR) triggers the invasion/migration of A549 cells via activation of an EGFR-p38/ERK-STAT3/CREB-1-EMT pathway. Here, we have demonstrated the involvement of a novel intracellular signaling mechanism in γ-ionizing radiation (IR)-induced migration/invasion. Expression of receptor-interacting protein (RIP) 1 was initially increased upon exposure of A549, a non-small cell lung cancer (NSCLC) cell line, to IR. IR-induced RIP1 is located downstream of EGFR and involved in the expression/activity of matrix metalloproteases (MMP-2 and MMP-9) and vimentin, suggesting a role in epithelial-mesenchymal transition (EMT). Our experiments showed that IR-induced RIP1 sequentially induces Src-STAT3-EMT to promote invasion/migration. Inhibition of RIP1 kinase activity and expression blocked induction of EMT by IR and suppressed the levels and activities of MMP-2, MMP-9 and vimentin. IR-induced RIP1 activation was additionally associated with stimulation of the transcriptional factor NF-κB. Specifically, exposure to IR triggered NF-κB activation and inhibition of NF-κB suppressed IR-induced RIP1 expression, followed by a decrease in invasion/migration as well as EMT. Based on the collective results, we propose that IR concomitantly activates EGFR and NF-κB and subsequently triggers the RIP1-Src/STAT3-EMT pathway, ultimately promoting metastasis.

RIPK3: A New Player in Renal Fibrosis

Chronic kidney disease (CKD) is the end result of a plethora of renal insults, including repeated episodes of acute or toxic kidney injury, glomerular, or diabetic kidney disease. It affects a large number of the population worldwide, resulting in significant personal morbidity and mortality and economic cost to the community. Hence it is appropriate to focus on treatment strategies that interrupt the development of kidney fibrosis, the end result of all forms of CKD, in addition to upstream factors that may be specific to certain diseases. However, the current clinical approach to prevent or manage renal fibrosis remains unsatisfactory. The rising importance of receptor-interacting serine/threonine-protein kinase (RIPK) 3 in the inflammatory response and TGF-β1 signaling is increasingly recognized. We discuss here the biological functions of RIPK3 and its role in the development of renal fibrosis.

Toxicity of Necrostatin-1 in Parkinson's Disease Models

Parkinson’s disease (PD) is a neurodegenerative disorder that is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. This neuronal loss, inherent to age, is related to exposure to environmental toxins and/or a genetic predisposition. PD-induced cell death has been studied thoroughly, but its characterization remains elusive. To date, several types of cell death, including apoptosis, autophagy-induced cell death, and necrosis, have been implicated in PD progression. In this study, we evaluated necroptosis, which is a programmed type of necrosis, in primary fibroblasts from PD patients with and without the G2019S leucine-rich repeat kinase 2 (LRRK2) mutation and in rotenone-treated cells (SH-SY5Y and fibroblasts). The results showed that programmed necrosis was not activated in the cells of PD patients, but it was activated in cells exposed to rotenone. Necrostatin-1 (Nec-1), an inhibitor of the necroptosis pathway, prevented rotenone-induced necroptosis in PD models. However, Nec-1 affected mitochondrial morphology and failed to protect mitochondria against rotenone toxicity. Therefore, despite the inhibition of rotenone-mediated necroptosis, PD models were susceptible to the effects of both Nec-1 and rotenone.

Prevention of brain damage after traumatic brain injury by pharmacological enhancement of KCNQ (Kv7, "M-type") K+ currents in neurons

Nearly three million people in the USA suffer traumatic brain injury (TBI) yearly; however, there are no pre- or post-TBI treatment options available. KCNQ2-5 voltage-gated K⁺ channels underlie the neuronal "M current", which plays a dominant role in the regulation of neuronal excitability. Our strategy towards prevention of TBI-induced brain damage is predicated on the suggested hyper-excitability of neurons induced by TBIs, and the decrease in neuronal excitation upon pharmacological augmentation of M/KCNQ K⁺ currents. Seizures are very common after a TBI, making further seizures and development of epilepsy disease more likely. Our hypothesis is that TBI-induced hyperexcitability and ischemia/hypoxia lead to metabolic stress, cell death and a maladaptive inflammatory response that causes further downstream morbidity. Using the mouse controlled closed-cortical impact blunt TBI model, we found that systemic administration of the prototype M-channel "opener", retigabine (RTG), 30 min after TBI, reduces the post-TBI cascade of events, including spontaneous seizures, enhanced susceptibility to chemo-convulsants, metabolic stress, inflammatory responses, blood-brain barrier breakdown, and cell death. This work suggests that acutely reducing neuronal excitability and energy demand via M-current enhancement may be a novel model of therapeutic intervention against post-TBI brain damage and dysfunction.

Gefitinib Inhibits Invasion and Metastasis of Osteosarcoma via Inhibition of Macrophage Receptor Interacting Serine-Threonine Kinase 2

Most patients with osteosarcoma have subclinical pulmonary micrometastases at diagnosis. Mounting evidence suggests that macrophages facilitate metastasis. As the EGFR has been implicated in carcinoma-macrophage cross-talk, in this study, we asked whether gefitinib, an EGFR inhibitor, reduces osteosarcoma invasion and metastatic outgrowth using the K7M2-Balb/c syngeneic murine model. Macrophages enhanced osteosarcoma invasion in vitro, which was suppressed by gefitinib. Oral gefitinib inhibited tumor extravasation in the lung and reduced the size of metastatic foci, resulting in reduced metastatic burden. Gefitinib also altered pulmonary macrophage phenotype, increasing MHCII and decreasing CD206 expression compared with controls. Surprisingly, these effects are mediated through inhibition of macrophage receptor interacting protein kinase 2 (RIPK2), rather than EGFR. Supporting this, lapatinib, a highly specific EGFR inhibitor that does not inhibit RIPK2, had no effect on macrophage-promoted invasion, and RIPK2^-/- macrophages failed to promote invasion. The selective RIPK2 inhibitor WEHI-345 blocked tumor cell invasion in vitro and reduced metastatic burden in vivo In conclusion, our results indicate that gefitinib blocks macrophage-promoted invasion and metastatic extravasation by reprogramming macrophages through inhibition of RIPK2.

Comprehensive Evolutionary Analysis of Lamprey TNFR-Associated Factors (TRAFs) and Receptor-Interacting Protein Kinase (RIPKs) and Insights Into the Functional Characterization of TRAF3/6 and RIPK1

TNFR-associated factors (TRAFs) and receptor-interacting protein kinases (RIPKs) are important immunological linker molecules in mammals and play important roles in the TNFα, TLR and IFN signaling pathways. However, the evolutionary origins of these genes in vertebrates have not previously been described in lampreys. In this study, we searched the genomes of Lampetra japonicum, Lethenteron reissneri, and Petromyzon marinus for genes encoding trafs and ripks and performed homologous sequence alignment, phylogenetic tree, functional domain, conserved motif, gene structure, and synteny analyses to determine their evolutionary relationships. The distribution of the lamprey traf and ripk families and the immune response of the gene families in lampreys stimulated by different pathogens were also demonstrated, suggesting a role of structural changes in expression and functional diversification. Additionally, the dual luciferase reporter gene assay showed that the addition of exogenous immunomodulator (TNFα or IFN) to the overexpression of LjLRIPK1a or LjTRAF3/6 significantly downregulated NF-κB or ISRE activation. LjRIPK1a can significantly enhance caspase-8 activity, and overexpression of LjRIPK1a or LjTRAF3a/6 in HEK293T cells results in cell apoptosis. In summary, this study makes an important contribution to the understanding of the traf and ripk gene families in different vertebrates. Our results also provide new evidence for the evolution of vertebrate TRAFs and RIPKs and their impacts on immune regulation.

Ankyrin Repeat and Kinase Domain Containing 1 Gene, and Addiction Vulnerability

The TaqIA single nucleotide variant (SNV) has been tested for association with addictions in a huge number of studies. TaqIA is located in the ankyrin repeat and kinase domain containing 1 gene (ANKK1) that codes for a receptor interacting protein kinase. ANKK1 maps on the NTAD cluster along with the dopamine receptor D2 (DRD2), the tetratricopeptide repeat domain 12 (TTC12) and the neural cell adhesion molecule 1 (NCAM1) genes. The four genes have been associated with addictions, although TTC12 and ANKK1 showed the strongest associations. In silico and in vitro studies revealed that ANKK1 is functionally related to the dopaminergic system, in particular with DRD2. In antisocial alcoholism, epistasis between ANKK1 TaqIA and DRD2 C957T SNVs has been described. This clinical finding has been supported by the study of ANKK1 expression in peripheral blood mononuclear cells of alcoholic patients and controls. Regarding the ANKK1 protein, there is direct evidence of its location in adult and developing central nervous system. Together, these findings of the ANKK1 gene and its protein suggest that the TaqIA SNV is a marker of brain differences, both in structure and in dopaminergic function, that increase individual risk to addiction development.

Leucine Rich Repeat Kinase 2 and Innate Immunity

For more than a decade, researchers have sought to uncover the biological function of the enigmatic leucine rich repeat kinase 2 (LRRK2) enzyme, a large multi-domain protein with dual GTPase and kinase activities. Originally identified as a familial Parkinson's disease (PD) risk gene, variations in LRRK2 are also associated with risk of idiopathic PD, inflammatory bowel disease and susceptibility to bacterial infections. LRRK2 is highly expressed in peripheral immune cells and the potential of LRRK2 to regulate immune and inflammatory pathways has emerged as common link across LRRK2-implicated diseases. This review outlines the current genetic and biochemical evidence linking LRRK2 to the regulation of innate immune inflammatory pathways, including the toll-like receptor and inflammasome pathways. Evidence suggests a complex interplay between genetic risk and protective alleles acts to modulate immune outcomes in a manner dependent on the particular pathogen and cell type invaded.

Necrostatin-1 Alleviates Bleomycin-Induced Pulmonary Fibrosis and Extracellular Matrix Expression in Interstitial Pulmonary Fibrosis

Background

Interstitial pulmonary fibrosis (IPF) is harmful for patients’ life and health. The effective treatment of IPF is lacking because of unclear pathogenesis. Necrostatin-1 has protective effects on lung injury and can suppress the fibrosis development. I this study we investigated whether necrostatin-1 could decrease the proliferation of pulmonary fibroblasts, pulmonary fibrosis and expression of extracellular matrix (ECM) in IPF.

Material/Methods

The IPF mice model was conducted by intra-tracheal injection of bleomycin (BLM) (2 mg/kg) for C57BL/6N mice. Necrostatin-1 treatment was performed with 1 mg/kg necrostatin-1 by an intravenous injection for C57BL/6N mice. Lung tissue structures and collagen deposition were observed by hematoxylin and eosin staining and Masson staining. IPF in vitro model was constructed by MRC-5 cells induced by transforming growth factor beta 1 (TGF-β1). And, 20 μM necrostatin-1 was used to treat the TGF-β1 induced MRC-5 cells. Cell Counting Kit-8 (CCK-8) assay detected the viability of MRC-5 cells. The expression of receptor-interacting protein kinase-1 and -3 (RIPK1 and RIPK3), α smooth muscle actin (α-SMA), collagen IV, collagen I, fibronectin (FN), and transforming growth factor-β (TGF-β) in lung tissues and MRC-5 cells was measured by western blot analysis. The α-SMA expression in lung tissues was also analyzed by immunohistochemistry.

Results

The expression of RIPK1 and RIPK3 in lung tissues of BLM induced mice was increased. The degree of pulmonary fibrosis and expression of α-SMA, collagen IV, collagen I, FN, and TGF-β in lung tissues of BLM induced mice was enhanced. The proliferation of MRC-5 cells was increased when MRC-5 cells were induced by TGF-β. The expression of RIPK1, RIPK3, α-SMA, collagen IV, collagen I, and FN was increased in TGF-β induced MRC-5 cells. And, necrostatin-1 could effectively reverse the changes of pulmonary fibrosis, RIPK1, RIPK3, and ECM in vivo and in vitro experiments.

Conclusions

Necrostatin-1 attenuated pulmonary fibrosis in lung tissues of BLM induced mice and inhibited the fibroblast proliferation. And, necrostatin-1 also decreased the expression of RIPK1, RIPK3, and ECM in lung tissues of BLM induced mice and TGF-β induced fibroblasts. Necrostatin-1 could be a new effective drug for the treatment of IPF.

Inhibitors Targeting RIPK1/RIPK3: Old and New Drugs

The scaffolding function of receptor-interacting protein kinase 1 (RIPK1) regulates prosurvival signaling and inflammatory gene expression, while its kinase activity mediates both apoptosis and necroptosis; the latter involving RIPK3 kinase activity. The mutual transition between the scaffold and kinase functions of RIPK1 is regulated by (de)ubiquitylation and (de)phosphorylation. RIPK1-mediated cell death leads to disruption of epithelial barriers and/or release of damage-associated molecular patterns (DAMPs), cytokines, and chemokines, propagating inflammatory and degenerative diseases. Many drug development programs have pursued targeting RIPK1, and to a lesser extent RIPK3 kinase activity. In this review, we classify existing and novel small-molecule drugs based on their pharmacodynamic (PD) type I, II, and III binding mode. Finally, we discuss their applicability and therapeutic potential in inflammatory and degenerative experimental disease models.

Molecular Insights into the Mechanism of Necroptosis: The Necrosome As a Potential Therapeutic Target

Necroptosis, or regulated necrosis, is an important type of programmed cell death in addition to apoptosis. Necroptosis induction leads to cell membrane disruption, inflammation and vascularization. It plays important roles in various pathological processes, including neurodegeneration, inflammatory diseases, multiple cancers, and kidney injury. The molecular regulation of necroptotic pathway has been intensively studied in recent years. Necroptosis can be triggered by multiple stimuli and this pathway is regulated through activation of receptor-interacting protein kinase 1 (RIPK1), RIPK3 and pseudokinase mixed lineage kinase domain-like (MLKL). A better understanding of the mechanism of regulation of necroptosis will further aid to the development of novel drugs for necroptosis-associated human diseases. In this review, we focus on new insights in the regulatory machinery of necroptosis. We further discuss the role of necroptosis in different pathologies, its potential as a therapeutic target and the current status of clinical development of drugs interfering in the necroptotic pathway.

Small-Molecule Inhibitors of Necroptosis: Current Status and Perspectives

Necroptosis, an important form of programmed cell death (PCD), is a highly regulated caspase-independent type of cell death that plays a critical role in the pathophysiology of various inflammatory, infectious, and degenerative diseases. Currently, receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL) have been widely recognized as critical therapeutic targets of the necroptotic machinery. Targeting RIPK1, RIPK3, and/or MLKL is a promising strategy for necroptosis-related diseases. Following the identification of the first RIPK1 inhibitor Nec-1 in 2005, the antinecroptosis field is attracting increasing research interest from multiple disciplines, including the biological and medicinal chemistry communities. Herein, we will review the functions of necroptosis in human diseases, as well as the related targets and representative small-molecule inhibitors, mainly focusing on research articles published during the past 10 years. Outlooks and perspectives on the associated challenges are also discussed.

Implications of Necroptosis for Cardiovascular Diseases

Necroptosis is a non-apoptotic programmed cell death pathway, which causes necrosis-like morphologic changes and triggers inflammation in the surrounding tissues. Accumulating evidence has demonstrated that necroptosis is involved in a number of pathological processes that lead to cardiovascular diseases. However, the exact molecular pathways linking them remain unknown. Herein, this review summarizes the necroptosis-related pathways involved in the development of various cardiovascular diseases, including atherosclerosis, cardiac ischemia-reperfusion injury, cardiac hypertrophy, dilated cardiomyopathy and myocardial infarction, and may shed light on the diagnosis and treatment of these diseases.

Immunohistochemical expression pattern of RIP5, FGFR1, FGFR2 and HIP2 in the normal human kidney development

AIM

Present study analyses the co-localisation of RIP5 with FGFR1, FGFR2 and HIP2 in the developing kidney, as RIP5 is a major determinant of urinary tract development, downstream of FGF-signaling.

METHODS

Paraffin embedded human kidney tissues of 16 conceptuses between the 6th-22th developmental week were analysed using double-immunofluorescence method with RIP5/FGFR1/FGFR2 and HIP2 markers. Quantification of positive cells were performed using Kruskal-Wallis test.

RESULTS

In the 6th week of kidney development RIP5 (89.6%) and HIP2 (39.6%) are strongly expressed in the metanephric mesenchyme. FGFR1 shows moderate/strong expression in the developing nephrons (87.3%) and collecting ducts (70.5%) (p < 0.05). RIP5/FGFR1 co-localized at the marginal zone and the ureteric bud with predominant FGFR1 expression. FGFR2 (26.1%) shows similar expression pattern as FGFR1 (70.5%) in the same kidney structures. RIP5/FGFR2 co-localized at the marginal zone and the collecting ducts (predominant expression of FGFR2). HIP2 is strongly expressed in collecting ducts (96.7%), and co-localized with RIP5. In 10th week, RIP5 expression decrease (74.2%), while the pattern of expression of RIP5 and FGFR1 in collecting ducts (33.4% and 91.9%) and developing nephrons (21.9% and 32.4%) (p < 0.05) is similar to that in the 6th developmental week. Ureter is moderately expressing RIP5 while FGFR1 is strongly expressed in the ureteric wall. FGFR2 is strongly expressed in the collecting ducts (84.3%) and ureter. HIP2 have 81.1% positive cells in the collecting duct. RIP5/FGFR1 co-localize in collecting ducts and Henley's loop.

CONCLUSIONS

The expression pattern of RIP5, FGFR1, FGFR2 and HIP2 in the human kidney development might indicate their important roles in metanephric development and ureteric muscle layer differentiation through FGF signaling pathways.

RIPK3 mediates renal tubular epithelial cell apoptosis in endotoxin‑induced acute kidney injury

Renal tubular epithelial cell apoptosis is an important pathological mechanism of septic acute kidney injury (AKI). Endotoxin, also known as lipopolysaccharide (LPS), has a key role in septic AKI and can directly induce tubular epithelial cell apoptosis. The upregulation of receptor-interacting protein kinase 3 (RIPK3) in tubular epithelial cells has been reported in septic AKI, with RIPK3 mediating apoptosis in several cell types. In the present study, the effect of RIPK3 on endotoxin-induced AKI was investigated in mouse tubular epithelial cell apoptosis in vitro and in vivo. It was found that the expression of RIPK3 was markedly increased in endotoxin-induced AKI. Endotoxin-induced AKI and tubular epithelial cell apoptosis could be attenuated by GSK′872, a RIPK3 inhibitor. LPS stimulation also upregulated RIPK3 expression in tubular epithelial cells in a time-dependent manner. Both RIPK3 inhibitor and small interfering RNA (siRNA) targeting RIPK3 reduced LPS-induced tubular epithelial cell apoptosis in vitro. The expression of the proapoptotic protein Bax was induced by LPS and reversed by GSK′872 or RIPK3-siRNA. The present study revealed that RIPK3 mediated renal tubular cell apoptosis in endotoxin-induced AKI. RIPK3 may be a potential target for the prevention of renal tubular cell apoptosis in endotoxin-induced AKI.

Dysregulation of Intestinal Epithelial Cell RIPK Pathways Promotes Chronic Inflammation in the IBD Gut

Crohn's disease (CD) and ulcerative colitis (UC) are common intestinal bowel diseases (IBD) characterized by intestinal epithelial injury including extensive epithelial cell death, mucosal erosion, ulceration, and crypt abscess formation. Several factors including activated signaling pathways, microbial dysbiosis, and immune deregulation contribute to disease progression. Although most research efforts to date have focused on immune cells, it is becoming increasingly clear that intestinal epithelial cells (IEC) are important players in IBD pathogenesis. Aberrant or exacerbated responses to how IEC sense IBD-associated microbes, respond to TNF stimulation, and regenerate and heal the injured mucosa are critical to the integrity of the intestinal barrier. The role of several genes and pathways in which single nucleotide polymorphisms (SNP) showed strong association with IBD has recently been studied in the context of IEC. In patients with IBD, it has been shown that the expression of specific dysregulated genes in IECs plays an important role in TNF-induced cell death and microbial sensing. Among them, the NF-κB pathway and its target gene TNFAIP3 promote TNF-induced and receptor interacting protein kinase (RIPK1)-dependent intestinal epithelial cell death. On the other hand, RIPK2 functions as a key signaling protein in host defense responses induced by activation of the cytosolic microbial sensors nucleotide-binding oligomerization domain-containing proteins 1 and 2 (NOD1 and NOD2). The RIPK2-mediated signaling pathway leads to the activation of NF-κB and MAP kinases that induce autophagy following infection. This article will review these dysregulated RIPK pathways in IEC and their role in promoting chronic inflammation. It will also highlight future research directions and therapeutic approaches involving RIPKs in IBD.

Influence of Fat on Differential Receptor Interacting Serine/Threonine Protein Kinase 1 Activity Leading to Apoptotic Cell Death in Murine Liver Ischemia Reperfusion Injury Through Caspase 8

Current understanding is that receptor interacting serine/threonine protein kinase 1 (RIPK1) can lead to two distinct forms of cell death: RIPK3‐mediated necroptosis or caspase 8 (Casp8)‐mediated apoptosis. Here, we report that RIPK1 signaling is indispensable for protection from hepatocellular injury in a steatotic liver undergoing ischemia reperfusion injury (IRI) but not in the lean liver. In lean liver IRI, RIPK1‐mediated cell death is operational, leading to protection in RIP1 kinase‐dead knock‐in (RIPK1^K45A) mice and necrostatin‐1s (Nec1s)‐treated lean wild‐type (WT) mice. However, when fed a high‐fat diet (HFD), RIPK1^K45A‐treated and Nec1s‐treated WT mice undergoing IRI demonstrate exacerbated hepatocellular injury along with decreased RIPK1 ubiquitylation. Furthermore, we demonstrate that HFD‐fed RIPK3^–/–/Casp8^–/– mice show protection from IRI, but HFD‐fed RIPK3^–/–/Casp8^–/+ mice do not. We also show that blockade of RIPK1 leads to increased Casp8 activity and decreases mitochondrial viability. Conclusion: Although more studies are required, we provide important proof of concept for RIPK1 inhibition leading to distinctive outcomes in lean and steatotic liver undergoing IRI. Considering the rising incidence of nonalcoholic fatty liver disease (NAFLD) in the general population, it will be imperative to address this critical difference when treating patients with RIPK1 inhibitors. This study also presents a new target for drug therapy to prevent hepatocellular injury in NAFLD.

Innate Immune Signaling and Its Role in Metabolic and Cardiovascular Diseases

The innate immune system is an evolutionarily conserved system that senses and defends against infection and irritation. Innate immune signaling is a complex cascade that quickly recognizes infectious threats through multiple germline-encoded cell surface or cytoplasmic receptors and transmits signals for the deployment of proper countermeasures through adaptors, kinases, and transcription factors, resulting in the production of cytokines. As the first response of the innate immune system to pathogenic signals, inflammatory responses must be rapid and specific to establish a physical barrier against the spread of infection and must subsequently be terminated once the pathogens have been cleared. Long-lasting and low-grade chronic inflammation is a distinguishing feature of type 2 diabetes and cardiovascular diseases, which are currently major public health problems. Cardiometabolic stress-induced inflammatory responses activate innate immune signaling, which directly contributes to the development of cardiometabolic diseases. Additionally, although the innate immune elements are highly conserved in higher-order jawed vertebrates, lower-grade jawless vertebrates lack several transcription factors and inflammatory cytokine genes downstream of the Toll-like receptors (TLRs) and retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) pathways, suggesting that innate immune signaling components may additionally function in an immune-independent way. Notably, recent studies from our group and others have revealed that innate immune signaling can function as a vital regulator of cardiometabolic homeostasis independent of its immune function. Therefore, further investigation of innate immune signaling in cardiometabolic systems may facilitate the discovery of new strategies to manage the initiation and progression of cardiometabolic disorders, leading to better treatments for these diseases. In this review, we summarize the current progress in innate immune signaling studies and the regulatory function of innate immunity in cardiometabolic diseases. Notably, we highlight the immune-independent effects of innate immune signaling components on the development of cardiometabolic disorders.

Gene silencing of receptor-interacting protein 2 protects against cigarette smoke-induced acute lung injury

BACKGROUND AND PURPOSE

Chronic obstructive pulmonary disease (COPD) is characterized by progressive alveolar damage and generally irreversible airflow limitation. Nuclear factor-κB (NF-κB) plays a critical role in COPD pathogenesis. Receptor-interacting protein 2 (Rip2), a 60 kDa adaptor protein, is a positive regulator of NF-κB pathway and also an inducible transcriptional product of NF-κB activation. We sought to investigate if Rip2 gene silencing could protect against cigarette smoke (CS)-induced acute lung injury.

EXPERIMENTAL APPROACH

Gene silencing efficacy of Rip2 siRNA was characterized in mouse macrophage and mouse lung epithelial cell lines, and in a CS-induced acute lung injury mouse model. Bronchoalveolar lavage (BAL) fluid cell counts, levels of pro-inflammatory and oxidative damage markers, lung section inflammatory and epithelium thickness scorings, and nuclear NF-κB translocation were measured.

KEY RESULTS

CS was found to upregulate Rip2 level in mouse lungs. Rip2 siRNA was able to suppress Rip2 levels in both macrophage and lung epithelial cell lines and in mouse lungs, block CS extract (CSE)-induced mediator release by the cultured cells, and abate neutrophil counts in BAL fluid from CS-challenged mice. Rip2 siRNA suppressed CS-induced inflammatory and oxidative damage markers, and nuclear p65 accumulation and transcriptional activation in lung tissues. Besides, Rip2 siRNA was able to disrupt CSE-induced NF-κB activation in a NF-κB reporter gene assay.

CONCLUSIONS AND IMPLICATIONS

Taken together, we report for the first time that Rip2 gene silencing ameliorated CS-induced acute lung injury probably via disruption of the NF-κB activity, postulating that Rip2 may be a novel therapeutic target for COPD.

Protective effect of RIPK1-inhibitory compound in in vivo models for retinal degenerative disease

Receptor interacting protein kinase 1 (RIPK1) plays a key role in necroptosis, which is a type of programmed necrosis that is involved in ocular diseases, including glaucoma and dry age-related macular degeneration (AMD). We previously introduced RIPK1-inhibitory compound (RIC), which has biochemical characteristics and a mode of action that are distinct from those of the prototype RIPK1 inhibitor necrostatin-1. The intraperitoneal administration of RIC exerts a protective effect on retinal ganglion cells against a glaucomatous insult. In this study, we examined the protective effect of RIC on retinal pigment epithelium (RPE) against sodium iodate (SI) insult, which is associated with dry AMD pathogenesis. The eye drop administration of RIC that reached on the retina prevented RPE loss in SI-induced retinal degeneration. RIC consistently demonstrated retinal protection in the funduscopy and electroretinogram analyses in SI-injected rabbits and iodoacetic acid-treated mini-pigs. Moreover, the in vivo protective effects of RIC were superior to those of ACU-4429 and doxycycline, which are other medications investigated in clinical trials for the treatment of dry AMD, and RIC did not induce retinal toxicity following topical administration in rats. Collectively, RIC displayed excellent retinal penetration and prevented retinal degeneration in the pathogenesis of dry AMD with a high in vivo efficacy.

Structural and functional conservation of half-smooth tongue sole Cynoglossus semilaevis RIP3 in cell death signalling

Receptor interacting protein kinase 3 (RIP3) has emerged as an essential molecular regulator in human inflammation with accumulating evidence in vertebrates. However, the structure and functions of RIP3 in teleosts remains elusive. Here we identified one RIP3 homologue from half-smooth tongue sole Cynoglossus semilaevis, designated CsRIP3. The open reading frame (ORF) of CsRIP3 contained 1491 nucleotides and encoded a protein with 496 amino acids (Mw = 55.44 kDa). CsRIP3 expression was detected in various tissues in half-smooth tongue soles. CsRIP3 expression was up-regulated after pathogens i.e. Vibrio and poly (i:c) treatment in vivo, indicating its possible role in teleost immune response. Further analysis using human cells demonstrated that CsRIP3 exhibited highly conserved pro-apoptotic and pro-necroptotic functions in comparison with human RIP3. In conclusion, for the first time we reported the homologous structure and functions of CsRIP3 in inflammatory cell death, which provides novel perspectives on fish immunity studies in future.

PKK deletion in basal keratinocytes promotes tumorigenesis after chemical carcinogenesis

Squamous cell carcinoma (SCC) of the skin is a keratinocyte malignancy characterized by tumors presenting on sun-exposed areas with surgery being the mainstay treatment. Despite advances in targeted therapy in other skin cancers, such as basal cell carcinoma and melanoma, there have been no such advances in the treatment of SCC. This is partly due to an incomplete knowledge of the pathogenesis of SCC. We have recently identified a protein kinase C-associated kinase (PKK) as a potential tumor suppressor in SCC. We now describe a novel conditional PKK knockout mouse model, which demonstrates that PKK deficiency promotes SCC formation during chemically induced tumorigenesis. Our results further support that PKK functions as a tumor suppressor in skin keratinocytes and is important in the pathogenesis of SCC of the skin. We further define the interactions of keratinocyte PKK with TP63 and NF-κB signaling, highlighting the importance of this protein as a tumor suppressor in SCC development.

Receptors and Signaling Pathways for Recognition of Bacteria in Livestock and Crops: Prospects for Beneficial Microbes in Healthy Growth Strategies

Modern animal and crop production practices are associated with the regular use of antimicrobials, potentially increasing selection pressure on bacteria to become resistant. Alternative approaches are needed in order to satisfy the demands of the growing human population without the indiscriminate use of antimicrobials. Researchers have brought a different perspective to solve this problem and have emphasized the exploitation of animal- and plant-associated microorganisms that are beneficial to their hosts through the modulation of the innate immune system. There is increasing evidence that plants and animals employ microbial perception and defense pathways that closely resemble each other. Formation of pattern recognition receptor (PRR) complexes involving leucine-rich repeat (LRR)-containing proteins, mitogen-activated protein kinase (MAPK)-mediated activation of immune response genes, and subsequent production of antimicrobial products and reactive oxygen species (ROS) and nitric oxide (NO) to improve defenses against pathogens, add to the list of similarities between both systems. Recent pioneering work has identified that animal and plant cells use similar receptors for sensing beneficial commensal microbes that are important for the maintenance of the host's health. Here, we reviewed the current knowledge about the molecular mechanisms involved in the recognition of pathogenic and commensal microbes by the innate immune systems of animal and plants highlighting their differences and similarities. In addition, we discuss the idea of using beneficial microbes to modulate animal and plant immune systems in order to improve the resistance to infections and reduce the use of antimicrobial compounds.

ALA-mediated biphasic downregulation of α-7nAchR/HIF-1α along with mitochondrial stress modulation strategy in mammary gland chemoprevention

The study elucidates the effect of ɑ-linolenic acid (ALA) on mitochondrial stress, hypoxic cancer microenvironment, and intervention of cholinergic anti-inflammatory pathway using N-methyl-N-nitrosourea (MNU) induced estrogen receptor (ER+) mammary gland carcinoma and Caenorhabditis elegans model, respectively. The efficacy of ALA was scrutinized in vivo and in vitro using various experiments like hemodynamic studies, morphological analysis, antioxidants parameters, immunoblotting, and quantitative reverse transcription polymerase chain reaction. The effect of ALA was also validated using C. elegans worms. ALA administration had a positive effect on tissue architecture of the malignancy when scrutinized through the whole mount carmine staining, hematoxylin and eosin staining, and scanning electron microscopy. The proteomic and genomic checkpoint revealed the participation of mitochondrial dysfunction, alteration of hypoxic microenvironment, and involvement of cholinergic anti-inflammatory response after treatment with ALA. ALA treatment has also increased the level of synaptic acetylcholine and acetylcholine esterase with a significant decrease in lipid content. It was concluded that ALA persuaded the mitochondrial stress, activation of downstream cholinergic anti-inflammatory markers, and favorable regulation of hypoxia microenvironment through inhibition of fatty acid synthase and sterol regulatory element-binding protein.

Insights into the Influence of Specific Splicing Events on the Structural Organization of LRRK2

Leucine-rich repeat kinase 2 (LRRK2) is a large protein of unclear function. Rare mutations in the LRRK2 gene cause familial Parkinson's disease (PD) and inflammatory bowel disease. Genome-wide association studies (GWAS) have revealed significant association of the abovementioned diseases at the LRRK2 locus. Cell and systems biology research has led to potential roles that LRRK2 may have in PD pathogenesis, especially the kinase domain (KIN). Previous human expression studies showed evidence of mRNA expression and splicing patterns that may contribute to our understanding of the function of LRRK2. In this work, we investigate and identified significant regional differences in LRRK2 expression at the mRNA level, including a number of splicing events in the Ras of complex protein (Roc) and C-terminal of Roc domain (COR) of LRRK2, in the substantia nigra (SN) and occipital cortex (OCTX). Our findings indicate that the predominant form of LRRK2 mRNA is full length, with shorter isoforms present at a lower copy number. Our molecular modelling study suggests that splicing events in the ROC/COR domains will have major consequences on the enzymatic function and dimer formation of LRRK2. The implications of these are highly relevant to the broader effort to understand the biology and physiological functions of LRRK2, and to better characterize the role(s) of LRRK2 in the underlying mechanism leading to PD.

RIG-I-Like Receptors as Novel Targets for Pan-Antivirals and Vaccine Adjuvants Against Emerging and Re-Emerging Viral Infections

Emerging and re-emerging viruses pose a significant public health challenge around the world, among which RNA viruses are the cause of many major outbreaks of infectious diseases. As one of the early lines of defense in the human immune system, RIG-I-like receptors (RLRs) play an important role as sentinels to thwart the progression of virus infection. The activation of RLRs leads to an antiviral state in the host cells, which triggers the adaptive arm of immunity and ultimately the clearance of viral infections. Hence, RLRs are promising targets for the development of pan-antivirals and vaccine adjuvants. Here, we discuss the opportunities and challenges of developing RLR agonists into antiviral therapeutic agents and vaccine adjuvants against a broad range of viruses.

Potentiating effect of acetaminophen and carbon tetrachloride-induced hepatotoxicity is mediated by activation of receptor interaction protein in mice

When multiple drugs or chemicals are used in combination, it is important to understand the risk of their interactions and predict potential additive effects. The aim of the current study was to investigate the molecular mechanism(s) accounting for the additive/synergistic effect of combination treatment with acetaminophen (APAP) and carbon tetrachloride (CCl₄). Mice were intraperitoneally administered vehicle or 100 mg/kg (5 mL/kg) APAP and 30 min after vehicle or 15 mg/kg (5 mL/kg) CCl₄. Sixteen hours after treatment, mice from each group were sacrificed and the livers were removed. CCl₄ administration caused slight glycogen depletion; this effect was more pronounced following co-administration of APAP and CCl₄. ATP and NADPH levels showed the same trend as glycogen levels. The levels of receptor interacting protein 1 and 3 increased following combination treatment with APAP and CCl₄. In contrast, levels of the glutamate cysteine ligase catalytic subunit and glutamate cysteine ligase modifier subunits were not significantly affected by combination treatment. APAP and CCl₄ co-administration potentiated the phosphorylation of c-Jun N-terminal kinase and p38 kinases, although phosphorylated activation of extracellular signal-regulated kinase was not changed. Our results suggest that APAP and CCl₄ co-administration potentiates hepatotoxicity in an additive/synergistic manner via receptor interacting protein activation.

Is Receptor-Interacting Protein Kinase 3 a Viable Therapeutic Target for Mycobacterium tuberculosis Infection?

The dwindling list of antimicrobial agents exhibiting broad efficacy against clinical strains of Mycobacterium tuberculosis (Mtb) has forced the medical community to redefine current approaches to the treatment of tuberculosis (TB). Host receptor-interacting protein kinase 3 (RIPK3) has been flagged recently as a potential target, given that it is believed to regulate necroptosis-independent signaling pathways, which have been implicated in exacerbating several inflammatory conditions and which reportedly play a role in the necrosis of Mtb-infected macrophages. To examine the therapeutic potential of inhibiting RIPK3, we infected RIPK3-deficient mice with aerosolized Mtb. We found that the loss of RIPK3 did not alter overall disease outcomes, with deficient animals harboring similar bacterial numbers in the lungs and spleens compared to their wild-type counterparts. Mtb-infected macrophages were not rescued from dying by Ripk3 deletion, nor did this affect production of the pro-inflammatory cytokine IL-1β, both in vitro and in vivo. Infiltration of immune cells into the lungs, as well as the activation of adaptive immunity, similarly was not overtly affected by the loss of RIPK3 signaling. Collectively, our data argue against a role of RIPK3 in mediating pathological inflammation or macrophage necrosis during Mtb disease pathogenesis and thus suggest that this host protein is unlikely to be an attractive therapeutic target for TB.

ANKK1 is found in myogenic precursors and muscle fibers subtypes with glycolytic metabolism

Ankyrin repeat and kinase domain containing 1 (ANKK1) gene has been widely related to neuropsychiatry disorders. The localization of ANKK1 in neural progenitors and its correlation with the cell cycle has suggested its participation in development. However, ANKK1 functions still need to be identified. Here, we have further characterized the ANKK1 localization in vivo and in vitro, by using immunolabeling, quantitative real-time PCR and Western blot in the myogenic lineage. Histologic investigations in mice and humans revealed that ANKK1 is expressed in precursors of embryonic and adult muscles. In mice embryos, ANKK1 was found in migrating myotubes where it shows a polarized cytoplasmic distribution, while proliferative myoblasts and satellite cells show different isoforms in their nuclei and cytoplasm. In vitro studies of ANKK1 protein isoforms along the myogenic progression showed the decline of nuclear ANKK1-kinase until its total exclusion in myotubes. In adult mice, ANKK1 was expressed exclusively in the Fast-Twitch muscles fibers subtype. The induction of glycolytic metabolism in C2C12 cells with high glucose concentration or treatment with berberine caused a significant increase in the ANKK1 mRNA. Similarly, C2C12 cells under hypoxic conditions caused the increase of nuclear ANKK1. These results altogether show a relationship between ANKK1 gene regulation and the metabolism of muscles during development and in adulthood. Finally, we found ANKK1 expression in regenerative fibers of muscles from dystrophic patients. Future studies in ANKK1 biology and the pathological response of muscles will reveal whether this protein is a novel muscle disease biomarker.

A20 regulates canonical wnt-signaling through an interaction with RIPK4

A20 is a ubiquitin-editing enzyme that is known to regulate inflammatory signaling and cell death. However, A20 mutations are also frequently found in multiple malignancies suggesting a potential role as a tumor suppressor as well. We recently described a novel role for A20 in regulating the wnt-beta-catenin signaling pathway and suppressing colonic tumor development in mice. The underlying mechanisms for this phenomenon are unclear. To study this, we first generated A20 knockout cell lines by genome-editing techniques. Using these cells, we show that loss of A20 causes dysregulation of wnt-dependent gene expression by RNAseq. Mechanistically, A20 interacts with a proximal signaling component of the wnt-signaling pathway, receptor interacting protein kinase 4 (RIPK4), and regulation of wnt-signaling by A20 occurs through RIPK4. Finally, similar to the mechanism by which A20 regulates other members of the receptor interacting protein kinase family, A20 modifies ubiquitin chains on RIPK4 suggesting a possible molecular mechanism for A20’s control over the wnt-signaling pathway.

Extracellular Hsp70 induces inflammation and modulates LPS/LTA-stimulated inflammatory response in THP-1 cells

Extracellular Hsp70 (eHsp70) can act as damage-associated molecular pattern (DAMP) via Toll-like receptors TLR2 and TLR4, and stimulate immune and inflammatory responses leading to sterile inflammation and propagation of already existing inflammation. It was found elevated in the blood of patients with chronic obstructive pulmonary disease (COPD), who might suffer occasional bacterial colonizations and infections. We used a monocytic THP-1 cell line as a cellular model of systemic compartment of COPD to assess inflammatory effects of eHsp70 when present alone or together with bacterial products lypopolysaccharide (LPS) and lypoteichoic acid (LTA). THP-1 cells were differentiated into macrophage-like cells and treated with various concentrations of recombinant human Hsp70 protein (rhHsp70), LPS (TLR4 agonist), LTA (TLR2 agonist), and their combinations for 4, 12, 24, and 48 h. Concentrations of IL-1α, IL-6, IL-8, and TNF-α were determined by ELISA. Cell viability was assessed by MTS assay, and mode of cell death by luminometric measurements of caspases-3/7, -8, and -9 activities. rhHsp70 showed cell protecting effect by suppressing caspases-3/7 activation, while LPS provoked cytotoxicity through caspases-8 and -3/7 pathway. Regarding inflammatory processes, rhHsp70 alone induced secretion of IL-1α and IL-8, but had modulatory effects on release of all four cytokines when applied together with LPS or LTA. Combined effect with LPS was mainly synergistic, and with LTA mainly antagonistic, although it was cytokine- and time-dependent. Our results confirmed pro-inflammatory function of extracellular Hsp70, and suggest its possible implication in COPD exacerbations caused by bacterial infection through desensitization or inappropriate activation of TLR2 and TLR4 receptors.

Corosolic Acid Induces Non-Apoptotic Cell Death through Generation of Lipid Reactive Oxygen Species Production in Human Renal Carcinoma Caki Cells

Corosolic acid is one of the pentacyclic triterpenoids isolated from Lagerstroemia speciose and has been reported to exhibit anti-cancer and anti-proliferative activities in various cancer cells. In the present study, we investigated the molecular mechanisms of corosolic acid in cancer cell death. Corosolic acid induces a decrease of cell viability and an increase of cell cytotoxicity in human renal carcinoma Caki cells. Corosolic acid-induced cell death is not inhibited by apoptosis inhibitor (z-VAD-fmk, a pan-caspase inhibitor), necroptosis inhibitor (necrostatin-1), or ferroptosis inhibitors (ferrostatin-1 and deferoxamine (DFO)). Furthermore, corosolic acid significantly induces reactive oxygen species (ROS) levels, but antioxidants (N-acetyl-l-cysteine (NAC) and trolox) do not inhibit corosolic acid-induced cell death. Interestingly, corosolic acid induces lipid oxidation, and α-tocopherol markedly prevents corosolic acid-induced lipid peroxidation and cell death. Anti-chemotherapeutic effects of α-tocopherol are dependent on inhibition of lipid oxidation rather than inhibition of ROS production. In addition, corosolic acid induces non-apoptotic cell death in other renal cancer (ACHN and A498), breast cancer (MDA-MB231), and hepatocellular carcinoma (SK-Hep1 and Huh7) cells, and α-tocopherol markedly inhibits corosolic acid-induced cell death. Therefore, our results suggest that corosolic acid induces non-apoptotic cell death in cancer cells through the increase of lipid peroxidation.

RIP2 Is a Critical Regulator for NLRs Signaling and MHC Antigen Presentation but Not for MAPK and PI3K/Akt Pathways

RIP2 is an adaptor protein which is essential for the activation of NF-κB and NOD1- and NOD2-dependent signaling. Although NOD-RIP2 axis conservatively existed in the teleost, the function of RIP2 was only reported in zebrafish, goldfish, and rainbow trout in vitro. Very little is known about the role and mechanisms of piscine NOD-RIP2 axis in vivo. Our previous study showed the protective role of zebrafish NOD1 in larval survival through CD44a-mediated activation of PI3K-Akt signaling. In this study, we examined whether RIP2 was required for larval survival with or without pathogen infection, and determined the signaling pathways modulated by RIP2. Based on our previous report and the present study, our data demonstrated that NOD1-RIP2 axis was important for larval survival in the early ontogenesis. Similar to NOD1, RIP2 deficiency significantly affected immune system processes. The significantly enriched pathways were mainly involved in immune system, such as “Antigen processing and presentation” and “NOD-like receptor signaling pathway” and so on. Furthermore, both transcriptome analysis and qRT-PCR revealed that RIP2 was a critical regulator for expression of NLRs (NOD-like receptors) and those genes involved in MHC antigen presentation. Different from NOD1, the present study showed that NOD1, but not RIP2 deficiency significantly impaired protein levels of MAPK pathways. Although RIP2 deficiency also significantly impaired the expression of CD44a, the downstream signaling of CD44a-Lck-PI3K-Akt pathway remained unchanged. Collectively, our works highlight the similarity and discrepancy of NOD1 and RIP2 in the regulation of immune signaling pathways in the zebrafish early ontogenesis, and confirm the crucial role of RIP2 in NLRs signaling and MHC antigen presentation, but not for MAPK and PI3K/Akt pathways.

RIPK4/PEBP1 axis promotes pancreatic cancer cell migration and invasion by activating RAF1/MEK/ERK signaling

Pancreatic cancer is a lethal disease with a high metastatic potential. In our previous study, we identified a specific subgroup of patients with pancreatic cancer with a serum signature of carcinoembryonic antigen (CEA)+/cancer antigen (CA)125+/CA19-9 ≥1,000 U/ml. In this study, by using high-throughput screening analysis, we found that receptor-interacting protein kinases 4 (RIPK4) may be a key molecule involved in the high metastatic potential of this subgroup of patients with pancreatic cancer. A high RIPK4 expression predicted a poor prognosis and promoted pancreatic cancer cell migration and invasion via the RAF1/MEK/ERK pathway. Moreover, RIPK4 activated the RAF1/MEK/ERK pathway by regulating proteasome-mediated phosphatidylethanolamine binding protein 1 (PEBP1) degradation. The suppression of PEBP1 degradation eliminated the RIPK4-induced activation of RAF1/MEK/ERK signaling and pancreatic cancer cell migration or invasion. Thus, on the whole, the findings of this study indicated that RIPK4 was upregulated in the subgroup of pancreatic cancer with a high metastatic potential. RIPK4 overexpression promoted pancreatic cancer cell migration and invasion via the PEBP1 degradation-induced activation of the RAF1/MEK/ERK pathway.

The Receptor Interacting Protein Kinases in the Liver

The receptor interacting serine/threonine kinase1 and 3 (RIPK1, RIPK3) are regulators of cell death and survival. RIPK1 kinase activity is required for necroptosis and apoptosis, while its scaffolding function is necessary for survival. Although both proteins can mediate apoptosis, RIPK1 and RIPK3 are most well-known for their role in the execution of necroptosis via the mixed lineage domain like pseudokinase. Necroptosis is a caspase-independent regulated cell death program which was first described in cultured cells with unknown physiologic relevance in the liver. Many recent reports have suggested that RIPK1 and/or RIPK3 participate in liver disease pathogenesis and cell death. Notably, both proteins have been shown to mediate inflammation independent of cell death. Whether necroptosis occurs in hepatocytes, and how it is executed in the presence of an intact caspase machinery is controversial. In spite of this controversy, it is evident that RIPK1 and RIPK3 participate in many experimental liver disease models. Therefore, in addition to cell death signaling, their necroptosis-independent role warrants further examination.

Keratinocyte-Specific Ablation of RIPK4 Allows Epidermal Cornification but Impairs Skin Barrier Formation

In humans, receptor-interacting protein kinase 4 (RIPK4) mutations can lead to the autosomal recessive Bartsocas-Papas and popliteal pterygium syndromes, which are characterized by severe skin defects, pterygia, as well as clefting. We show here that the epithelial fusions observed in RIPK4 full knockout (KO) mice are E-cadherin dependent, as keratinocyte-specific deletion of E-cadherin in RIPK4 full KO mice rescued the tail-to-body fusion and fusion of oral epithelia. To elucidate RIPK4 function in epidermal differentiation and development, we generated epidermis-specific RIPK4 KO mice (RIPK4^EKO). In contrast to RIPK4 full KO epidermis, RIPK4^EKO epidermis was normally stratified and the outside-in skin barrier in RIPK4^EKO mice was largely intact at the trunk, in contrast to the skin covering the head and the outer end of the extremities. However, RIPK4^EKO mice die shortly after birth due to excessive water loss because of loss of tight junction protein claudin-1 localization at the cell membrane, which results in tight junction leakiness. In contrast, mice with keratinocyte-specific RIPK4 deletion during adult life remain viable. Furthermore, our data indicate that epidermis-specific deletion of RIPK4 results in delayed keratinization and stratum corneum maturation and altered lipid organization and is thus indispensable during embryonic development for the formation of a functional inside-out epidermal barrier.

Twist1 induces distinct cell states depending on TGFBR1-activation

Basic helix-loop-helix transcription factor Twist1 is a master regulator of Epithelial-Mesenchymal Transition (EMT), a cellular program implicated in different stages of development as well as metastatic dissemination of carcinomas. Here, we show that Twist1 requires TGF-beta type-I receptor (TGFBR1)-activation to bind an enhancer region of downstream effector ZEB1, thereby inducing ZEB1 transcription and EMT. When TGFBR1-phosphorylation is inhibited, Twist1 generates a distinct cell state characterized by collective invasion, simultaneous proliferation and expression of endothelial markers. By contrast, TGFBR1-activation directs Twist1 to induce stable mesenchymal transdifferentiation through EMT, thereby generating cells that display single-cell invasion, but lose their proliferative capacity. In conclusion, preventing Twist1-induced EMT by inhibiting TGFβ-signaling does not generally block acquisition of invasion, but switches mode from single-cell/non-proliferative to collective/proliferative. Together, these data reveal that transient Twist1-activation induces distinct cell states depending on signaling context and caution against the use of TGFβ-inhibitors as a therapeutic strategy to target invasiveness.

Influence of protein kinase RIPK4 expression on the apoptosis and proliferation of chondrocytes in osteoarthritis

The present study aimed to investigate the expression of receptor‑interacting protein kinase 4 (RIPK4) and its effect on the apoptosis and proliferation of chondrocytes in osteoarthritis (OA). A total of 28 OA cartilage tissues and 20 normal cartilage tissues were collected to detect the expression of RIPK4 by using reverse transcription‑quantitative polymerase chain reaction and western blot analysis. Chondrocytes were isolated from OA cartilage tissues and divided into OA, NC, si‑RIPK4, Wnt3a, and si‑RIPK4+Wnt3a groups, and those isolated from normal cartilage tissues were considered the Normal group. Chondrocytes proliferation was detected by MTT assay, cell apoptosis was indicated using flow cytometry and Wnt/β‑catenin signaling pathway related‑proteins were investigated using western blot analysis. RIPK4 mRNA and protein expression levels in OA cartilage tissues and OA chondrocytes were increased compared with normal controls (all P<0.05). Additionally, OA chondrocytes showed reduced cell proliferation, increased cell apoptosis and upregulated expression levels of Wnt/β‑catenin signaling pathway related‑proteins (all P<0.05). Once transfected with si‑RIPK4, the proliferation ability of chondrocytes was enhanced, but apoptosis was notably decreased. Furthermore, the expression levels of Wnt/β‑catenin signaling pathway related‑proteins were significantly downregulated (all P<0.05). Results indicated that Wnt3a reversed the effect of si‑RIPK4 on chondrocyte proliferation and apoptosis (all P<0.05). Thus, silencing RIPK4 promoted the proliferation and inhibited the apoptosis of chondrocytes. In addition, silencing RIPK4 blocked the Wnt/β‑catenin signaling pathway, thus contributing to alleviating the OA pathogenesis.

Necrostatin-1 attenuates lipopolysaccharide-induced acute lung injury in mice

AIM OF THE STUDY

Receptor-interacting protein (RIP) kinase family members are involved in several biological processes. However, their role in acute lung injury (ALI) is still unclear. In the present study, we aim to determine the expression and function of RIP kinase family in ALI.

MATERIALS AND METHODS

In the present study, ALI was induced in BALB/c male mice by intravenously injecting lipopolysaccharide (LPS). The expression levels of the RIP kinase family in ALI mice were determined using western blotting and immunohistochemical staining. The specific RIP-1 inhibitor, necrostatin-1, was used to treat LPS-induced ALI mice, followed by survival time recording, as well as histopathological and immunohistochemical staining of lung tissues, western blotting, myeloperoxidase (MPO) assay and enzyme-linked immunosorbent assay (ELISA) of related cytokines and downstream target expression.

RESULTS

We found that RIP-1 expression was upregulated in the lung of ALI mice and inhibition of RIP-1 by necrostatin-1 significantly prolonged the survival time of mice, which was accompanied by less serve lung injury. Furthermore, lower expression of pro-inflammatory cytokines (interleukin [IL]-6, tumor necrosis factor [TNF]-α, IL-8, cyclooxygenase [COX]-2, monocyte chemoattractant protein [MCP]-1, and IL-1β), MPO and nuclear factor (NF)-κB activation were found in bronchoalveolar lavage fluid (BALF) and lung tissues of necrostatin-1-treated ALI mice. Necrostatin-1 also attenuated LPS-induced pro-inflammatory cytokine expression and NF-κB activation in RAW 264.7 cells.

CONCLUSIONS

In summary, necrostatin-1 protected against LPS-induced ALI in mice by inhibiting inflammation and pulmonary NF-κB activation. Thus, necrostatin-1 could be a novel therapeutic strategy for ALI.

Kinase-independent role of nuclear RIPK1 in regulating parthanatos through physical interaction with PARP1 upon oxidative stress

Regulated necrosis occurs in various pathophysiological conditions under oxidative stress. Here, we report that receptor-interacting protein kinase 1 (RIPK1), a key player in one type of regulated necrosis (necroptosis), also participates in another type of poly (ADP-ribose) polymerase 1 (PARP1)-dependent regulated necrosis (parthanatos). Various biological signatures of parthanatos were significantly attenuated in Ripk1^-/- mouse embryonic fibroblasts, including PARylation, nuclear translocation of apoptosis-inducing factor, and PARP1-dependent cell death under H₂O₂ exposure. Hence, we investigated whether RIPK1 regulates the activity of PARP1. RIPK1 activated PARP1 via an interaction with the catalytic domain of PARP1 in the nucleus. Of note, both wild type and kinase-dead mutant RIPK1 induced PARP1 activation and led to PARP1-mediated cell death upon H₂O₂ insult, demonstrating the kinase-independent regulation of RIPK1 in PARP1 activation. Collectively, our results demonstrate the existence of a kinase-independent role of nuclear RIPK1 in the regulation of PARP1.

The implication of neuronimmunoendocrine (NIE) modulatory network in the pathophysiologic process of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder implicitly marked by the substantia nigra dopaminergic neuron degeneration and explicitly characterized by the motor and non-motor symptom complexes. Apart from the nigrostriatal dopamine depletion, the immune and endocrine study findings are also frequently reported, which, in fact, have helped to broaden the symptom spectrum and better explain the pathogenesis and progression of PD. Nevertheless, based on the neural, immune, and endocrine findings presented above, it is still difficult to fully recapitulate the pathophysiologic process of PD. Therefore, here, in this review, we have proposed the neuroimmunoendocrine (NIE) modulatory network in PD, aiming to achieve a more comprehensive interpretation of the pathogenesis and progression of this disease. As a matter of fact, in addition to the classical motor symptoms, NIE modulatory network can also underlie the non-motor symptoms such as gastrointestinal, neuropsychiatric, circadian rhythm, and sleep disorders in PD. Moreover, the dopamine (DA)-melatonin imbalance in the retino-diencephalic/mesencephalic-pineal axis also provides an alternative explanation for the motor complications in the process of DA replacement therapy. In conclusion, the NIE network can be expected to deepen our understanding and facilitate the multi-dimensional management and therapy of PD in future clinical practice.

RIPK1 binds to vitamin D receptor and decreases vitamin D-induced growth suppression

Receptor interacting protein kinase 1 (RIPK1) is an enzyme acting downstream of tumor necrosis factor alpha to control cell survival and death. RIPK1 expression has been reported to cause drug resistance in cancer cells, but so far, no published studies have investigated the role of RIPK1 in vitamin D signaling. In the present study, we investigated whether RIPK1 plays any roles in 1,25-dihydroxyvitamin D3 (1,25D3)-induced growth suppression. In our studies, RIPK1 decreased the transcriptional activity of vitamin D receptor (VDR) in luciferase reporter assays independent of its kinase activity, suggesting a negative role of RIPK1 in 1,25D3 action. RIPK1 also formed a complex with VDR, and deletion analyses mapped the RIPK1 binding region to the C-terminal ligand-binding domain of the VDR. Subcellular fractionation analyses indicated that RIPK1 increased VDR retention in the cytoplasm, which may account for its inhibition of VDR transcriptional activity. Consistent with the reporter analyses, 1,25D3-induced growth suppression was more pronounced in RIPK1-null MEFs and RIPK1-knockdown ovarian cancer cells than in control cells. Our studies have defined RIPK1 as a VDR repressor, projecting RIPK1 depletion as a potential strategy to increase the potency of 1,25D3 and its analogs for cancer intervention.

Necrostatin-1 protects hippocampal neurons against ischemia/reperfusion injury via the RIP3/DAXX signaling pathway in rats

Global cerebral ischemia/reperfusion (I/R) induces selective neuronal injury in CA1 region of hippocampus, leading to severe impairment in behavior, learning and memory functions. However, the molecular mechanism underlying the processes was not elucidated clearly. RIP3 is a key molecular switch connecting apoptosis, necrosis and necroptosis. DAXX, as a novel substrate of RIP3, plays a vital role in ischemia-induced neuronal death. The aim of this study is to investigate the role and mechanism of RIP3/DAXX signaling pathway on neurons in CA1 region of the rat hippocampus after cerebral I/R. Global cerebral ischemia was induced by the method of four-vessel occlusion. RIP1 specific inhibitor Necrostatin-1 was administered by intracerebroventricular injection 1h before ischemia. Open-field, closed-field, and Morris water maze tests were performed respectively to examine the anxiety and cognitive behavior in each group. Hematoxylin and eosinstaining was used to examine the survival of hippocampal CA1 pyramidal neurons. Western blot or immunoprecipitation were carried to detect protein expression, phosphorylation, and interaction. We found that pre-treatment with Nec-1 protected locomotive ability, relieved anxiety behavior, and improved cognitive ability in the rats subjected to cerebral I/R. In addition Moreover, Nec-1 decreased significantly the dead rate of neurons in hippocampal CA1 region after cerebral I/R through suppressing RIP1-RIP3 interaction and RIP3 activation along with RIP3-DAXX interaction, and then blocked DAXX translocation from nucleaus to cytoplasm, which resulted in the inactiviation of DAXX. We concluded that pre-treatment with Nec-1 can protect neurons in the hippocampal CA1 region against ischemic damage through the RIP3-DAXX signaling pathway.

RIP1-dependent reactive oxygen species production executes artesunate-induced cell death in renal carcinoma Caki cells

Artesunate is a well-known anti-malarial drug originated from artemisinin as a Chinese herb and has been reported to have anti-cancer potential in many cancer cells. In the present study, we examined the efficacy of artesunate against the renal carcinoma Caki cells and explored its mechanism of cytotoxicity. A steep decline in cell viability within 18 h was recorded upon artesunate exposure, but pretreatment of z-VAD-FMK had no effect on the loss of the cell viability by artesunate. On the other hand, necrostatin-1 pretreatment and knockdown of RIP-1 significantly reduced the cytotoxicity of artesunate against Caki cell. Moreover, the generation of mitochondrial ROS prompted by artesunate was found to be the principle mechanism of cell death. Pretreatment with necrostatin-1 or knockdown of RIP-1 inhibited the generation of ROS by artesunate, resulting in the protection of the cells from artesunate toxicity. Moreover, the similar results were observed in the case of other renal carcinoma cell lines (ACHN and A498). The results suggest that artesunate induces the generation of ROS and cell death in RIP1-dependent manner. Therefore, our data suggest that artesunate could induce RIP1-dependent cell death in human renal carcinoma.