RIP kinases: key decision makers in cell death and innate immunity

Decoding ferroptosis: Revealing the hidden assassin behind cardiovascular diseases

The discovery of regulatory cell death processes has driven innovation in cardiovascular disease (CVD) therapeutic strategies. Over the past decade, ferroptosis, an iron-dependent form of regulated cell death driven by excessive lipid peroxidation, has been shown to drive the development of multiple CVDs. This review provides insights into the evolution of the concept of ferroptosis, the similarities and differences with traditional modes of programmed cell death (e.g., apoptosis, autophagy, and necrosis), as well as the core regulatory mechanisms of ferroptosis (including cystine/glutamate transporter blockade, imbalance of iron metabolism, and lipid peroxidation). In addition, it provides not only a detailed review of the role of ferroptosis and its therapeutic potential in widely studied CVDs such as coronary atherosclerotic heart disease, myocardial infarction, myocardial ischemia/reperfusion injury, heart failure, cardiomyopathy, and aortic aneurysm but also an overview of the phenomenon and therapeutic perspectives of ferroptosis in lesser-addressed CVDs such as cardiac valvulopathy, pulmonary hypertension, and sickle cell disease. This article aims to integrate this knowledge to provide a comprehensive view of ferroptosis in a wide range of CVDs and to drive innovation and progress in therapeutic strategies in this field.

Necroptosis in bacterial infections

Necroptosis, a recently discovered form of cell-programmed death that is distinct from apoptosis, has been confirmed to play a significant role in the pathogenesis of bacterial infections in various animal models. Necroptosis is advantageous to the host, but in some cases, it can be detrimental. To understand the impact of necroptosis on the pathogenesis of bacterial infections, we described the roles and molecular mechanisms of necroptosis caused by different bacterial infections in this review.

Mechanisms of intestinal epithelial cell damage by Clostridiumperfringens

Clostridium perfringens, a Gram-positive bacterium, causes intestinal diseases in humans and livestock through its toxins, related to alpha toxin (CPA), beta toxin (CPB), C. perfringens enterotoxin (CPE), epsilon toxin (ETX), Iota toxin (ITX), and necrotic enteritis B-like toxin (NetB). These toxins disrupt intestinal barrier, leading to various cell death mechanisms such as necrosis, apoptosis, and necroptosis. Additionally, non-toxin factors like adhesins and degradative enzymes contribute to virulence by enhancing colonization and survival of C. perfringens. A vicious cycle of intestinal barrier breach, misregulated cell death, and subsequent inflammation is at the heart of chronic inflammatory and infectious gastrointestinal diseases. Understanding these mechanisms is essential for developing targeted therapies against C. perfringens-associated intestinal diseases.

RIP1 kinase inactivation protects against LPS-induced acute respiratory distress syndrome in mice

Acute respiratory distress syndrome (ARDS) is characterized by lung tissue oedema and inflammatory cell infiltration, with limited therapeutic interventions available. Receptor-interacting protein kinase 1 (RIPK1), a critical regulator of cell death and inflammation implicated in many diseases, is not fully understood in the context of ARDS. In this study, we employed RIP1 kinase-inactivated (Rip1K45A/K45A) mice and two distinct RIPK1 inhibitors to investigate the contributions of RIP1 kinase activity in lipopolysaccharide (LPS)-induced ARDS pathology. Our results indicated that RIPK1 kinase inactivation, achieved through both genetic and chemical approaches, significantly attenuated LPS-induced ARDS pathology, as demonstrated by reduced polymorphonuclear neutrophil percentage (PMN%) in alveolar lavage fluid, expression of inflammatory and fibrosis-related factors in lung tissues, as well as histological examination. Results by tunnel staining and qRT-PCR analysis indicated that RIPK1 kinase activity played a role in regulating cell apoptosis and inflammation induced by LPS administration in lung tissue. In summary, employing both pharmacological and genetic approaches, this study demonstrated that targeted RIPK1 kinase inactivation attenuates the pathological phenotype induced by LPS inhalation in an ARDS mouse model. This study enhances our understanding of the therapeutic potential of RIPK1 kinase modulation in ARDS, providing insights for the pathogenesis of ARDS.

Mechanism of PANoptosis in metabolic dysfunction-associated steatotic liver disease

In recent years, the incidence of metabolic dysfunction-associated steatotic liver disease (MASLD) has been steadily rising, emerging as a major chronic liver disease of global concern. The course of MASLD is varied, spanning from MASLD to metabolic dysfunction associated steatohepatitis (MASH). MASH is an important contributor to cirrhosis, which may subsequently lead to hepatocellular carcinoma. It has been found that PANoptosis, an emerging inflammatory programmed cell death (PCD), is involved in the pathogenesis of MASLD and facilitates the development of NASH, eventually resulting in inflammatory fibrosis and hepatocyte death. This paper reviews the latest research progress on PANoptosis and MASLD to understand the mechanism of MASLD and provide new directions for future treatment and drug development.

Practical Three-Component Regioselective Synthesis of Drug-Like 3-Aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnolines as Potential Non-Covalent Multi-Targeting Inhibitors To Combat Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are one of the prominent health challenges facing contemporary society, and many efforts have been made to overcome and (or) control it. In this research paper, we described a practical one-pot two-step three-component reaction between 3,4-dihydronaphthalen-1(2H)-one (1), aryl(or heteroaryl)glyoxal monohydrates (2a-h), and hydrazine monohydrate (NH2NH2•H2O) for the regioselective preparation of some 3-aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnoline derivatives (3a-h). After synthesis and characterization of the mentioned cinnolines (3a-h), the in silico multi-targeting inhibitory properties of these heterocyclic scaffolds have been investigated upon various Homo sapiens-type enzymes, including hMAO-A, hMAO-B, hAChE, hBChE, hBACE-1, hBACE-2, hNQO-1, hNQO-2, hnNOS, hiNOS, hPARP-1, hPARP-2, hLRRK-2(G2019S), hGSK-3β, hp38α MAPK, hJNK-3, hOGA, hNMDA receptor, hnSMase-2, hIDO-1, hCOMT, hLIMK-1, hLIMK-2, hRIPK-1, hUCH-L1, hPARK-7, and hDHODH, which have confirmed their functions and roles in the neurodegenerative diseases (NDs), based on molecular docking studies, and the obtained results were compared with a wide range of approved drugs and well-known (with IC50, EC50, etc.) compounds. In addition, in silico ADMET prediction analysis was performed to examine the prospective drug properties of the synthesized heterocyclic compounds (3a-h). The obtained results from the molecular docking studies and ADMET-related data demonstrated that these series of 3-aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnolines (3a-h), especially hit ones, can really be turned into the potent core of new drugs for the treatment of neurodegenerative diseases (NDs), and/or due to the having some reactionable locations, they are able to have further organic reactions (such as cross-coupling reactions), and expansion of these compounds (for example, with using other types of aryl(or heteroaryl)glyoxal monohydrates) makes a new avenue for designing novel and efficient drugs for this purpose.

Macrophage Tim-3 maintains intestinal homeostasis in DSS-induced colitis by suppressing neutrophil necroptosis

T-cell immunoglobulin domain and mucin domain-3 (Tim-3) is a versatile immunomodulator that protects against intestinal inflammation. Necroptosis is a type of cell death that regulates intestinal homeostasis and inflammation. The mechanism(s) underlying the protective role of macrophage Tim-3 in intestinal inflammation is unclear; thus, we investigated whether specific Tim-3 knockdown in macrophages drives intestinal inflammation via necroptosis. Tim-3 protein and mRNA expression were assessed via double immunofluorescence staining and single-cell RNA sequencing (sc-RNA seq), respectively, in the colonic tissues of patients with inflammatory bowel disease (IBD) and healthy controls. Macrophage-specific Tim3-knockout (Tim-3M-KO) mice were generated to explore the function and mechanism of Tim-3 in dextran sodium sulfate (DSS)-induced colitis. Necroptosis was blocked by pharmacological inhibitors of receptor-interacting protein kinase (RIP)1, RIP3, and reactive oxygen species (ROS). Additionally, in vitro experiments were performed to assess the mechanisms of neutrophil necroptosis induced by Tim-3 knockdown macrophages. Although Tim-3 is relatively inactive in macrophages during colon homeostasis, it is highly active during colitis. Compared to those in controls, Tim-3M-KO mice showed increased susceptibility to colitis, higher colitis scores, and increased pro-inflammatory mediator expression. Following the administration of RIP1/RIP3 or ROS inhibitors, a significant reduction in intestinal inflammation symptoms was observed in DSS-treated Tim-3M-KO mice. Further analysis indicated the TLR4/NF-κB pathway in Tim-3 knockdown macrophages mediates the TNF-α-induced necroptosis pathway in neutrophils. Macrophage Tim-3 regulates neutrophil necroptosis via intracellular ROS signaling. Tim-3 knockdown macrophages can recruit neutrophils and induce neutrophil necroptosis, thereby damaging the intestinal mucosal barrier and triggering a vicious cycle in the development of colitis. Our results demonstrate a protective role of macrophage Tim-3 in maintaining gut homeostasis by inhibiting neutrophil necroptosis and provide novel insights into the pathogenesis of IBD.

Small-molecule agents for treating skin diseases

Skin diseases are a class of common and frequently occurring diseases that significantly impact daily lives. Currently, the limited effective therapeutic drugs are far from meeting the clinical needs; most drugs typically only provide symptomatic relief rather than a cure. Developing small-molecule drugs with improved efficacy holds paramount importance for treating skin diseases. This review aimed to systematically introduce the pathogenesis of common skin diseases in daily life, list related drugs applied in the clinic, and summarize the clinical research status of candidate drugs and the latest research progress of candidate compounds in the drug discovery stage. Also, it statistically analyzed the number of publications and global attention trends for the involved skin diseases. This review might provide practical information for researchers engaged in dermatological drugs and further increase research attention to this disease area.

Dopaminergic neuronal death via necroptosis in Parkinson's disease: A review of the literature

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive dysfunction and loss of dopaminergic neurons of the substantia nigra pars compacta (SNc). Several pathways of programmed cell death are likely to play a role in dopaminergic neuron death, such as apoptosis, necrosis, pyroptosis and ferroptosis, as well as cell death associated with proteasomal and mitochondrial dysfunction. A better understanding of the molecular mechanisms underlying dopaminergic neuron death could inform the design of drugs that promote neuron survival. Necroptosis is a recently characterized regulated cell death mechanism that exhibits morphological features common to both apoptosis and necrosis. It requires activation of an intracellular pathway involving receptor-interacting protein 1 kinase (RIP1 kinase, RIPK1), receptor-interacting protein 3 kinase (RIP3 kinase, RIPK3) and mixed lineage kinase domain-like pseudokinase (MLKL). The potential involvement of this programmed cell death pathway in the pathogenesis of PD has been studied by analysing biomarkers for necroptosis, such as the levels and oligomerization of phosphorylated RIPK3 (pRIPK3) and phosphorylated MLKL (pMLKL), in several PD preclinical models and in PD human tissue. Although there is evidence that other types of cell death also have a role in DA neuron death, most studies support the hypothesis that this cell death mechanism is activated in PD tissues. Drugs that prevent or reduce necroptosis may provide neuroprotection for PD. In this review, we summarize the findings from these studies. We also discuss how manipulating necroptosis might open a novel therapeutic approach to reduce neuronal degeneration in PD.

Tlr4 Deletion Modulates Cytokine and Extracellular Matrix Expression in Chronic Spinal Cord Injury, Leading to Improved Secondary Damage and Functional Recovery

Toll-like receptors (TLRs) play an important role in the innate immune response after CNS injury. Although TLR4 is one of the best characterized, its role in chronic stages after spinal cord injury (SCI) is not well understood. We examined the role of TLR4 signaling in injury-induced responses at 1 d, 7 d, and 8 weeks after spinal cord contusion injury in adult female TLR4 null and wild-type mice. Analyses include secondary damage, a range of transcriptome and protein analyses of inflammatory, cell death, and extracellular matrix (ECM) molecules, as well as immune cell infiltration and changes in axonal sprouting and locomotor recovery. Lack of TLR4 signaling results in reduced neuronal and myelin loss, reduced activation of NFκB, and decreased expression of inflammatory cytokines and necroptotic cell death pathway at a late time point (8 weeks) after injury. TLR4 null mice also showed reduction of scar-related ECM molecules at 8 weeks after SCI, accompanied by increase in ECM molecules associated with perineuronal nets, increased sprouting of serotonergic fibers, and improved locomotor recovery. These findings reveal novel effects of TLR4 signaling in chronic SCI. We show that TLR4 influences inflammation, cell death, and ECM deposition at late-stage post-injury when secondary injury processes are normally considered to be over. This highlights the potential for late-stage targeting of TLR4 as a potential therapy for chronic SCI.

Effects of fine particulate matter on bone marrow-conserved hematopoietic and mesenchymal stem cells: a systematic review

The harmful effects of fine particulate matter ≤2.5 µm in size (PM2.5) on human health have received considerable attention. However, while the impact of PM2.5 on the respiratory and cardiovascular systems has been well studied, less is known about the effects on stem cells in the bone marrow (BM). With an emphasis on the invasive characteristics of PM2.5, this review examines the current knowledge of the health effects of PM2.5 exposure on BM-residing stem cells. Recent studies have shown that PM2.5 enters the circulation and then travels to distant organs, including the BM, to induce oxidative stress, systemic inflammation and epigenetic changes, resulting in the reduction of BM-residing stem cell survival and function. Understanding the broader health effects of air pollution thus requires an understanding of the invasive characteristics of PM2.5 and its direct influence on stem cells in the BM. As noted in this review, further studies are needed to elucidate the underlying processes by which PM2.5 disturbs the BM microenvironment and inhibits stem cell functionality. Strategies to prevent or ameliorate the negative effects of PM2.5 exposure on BM-residing stem cells and to maintain the regenerative capacity of those cells must also be investigated. By focusing on the complex relationship between PM2.5 and BM-resident stem cells, this review highlights the importance of specific measures directed at safeguarding human health in the face of rising air pollution.

Cyclosorus Terminans Extract Alleviates Neuroinflammation in Insulin Resistant Rats

High-fat diet consumption for an extended period causes obesity, systemic metabolic disturbance, and brain insulin resistance, resulting in neuroinflammation. Although the beneficial effect of Cyclosorus terminans extract on obesity-related insulin resistance has been demonstrated, little is known about how it affects neuroinflammation and brain insulin resistance in obese rats. Male Wistar rats were given either a normal diet (ND, n = 6) or a high-fat diet (HFD, n = 24) for a total of 14 weeks. At the beginning of the week, 13 rats in the ND group were given vehicle orally for 2 weeks, while rats on HFD diets were randomized to one of four groups and given either vehicle, 100 mg/kg/day of Cyclosorus terminans extract, 200 mg/kg/day of Cyclosorus terminans extract, or 20 mg/kg/day of pioglitazone orally for 2 weeks. After the experimental period, blood and brain samples were taken to assess metabolic and brain parameters. HFD-fed rats had obesity, systemic and brain insulin resistance, brain inflammation, microglial and astrocyte hyperactivity, and brain necroptosis. Treatment with 200 mg/kg/day of Cyclosorus terminans extract and pioglitazone equally attenuated obesity, insulin resistance, brain insulin dysfunction, and neuroinflammation in insulin resistant rats. Our findings suggest that Cyclosorus terminans extract may hold promise as a therapeutic agent for insulin resistance and neuroinflammation in obese conditions.

Current insight on the mechanisms of programmed cell death in sepsis-induced myocardial dysfunction

Sepsis is a clinical syndrome characterized by a dysregulated host response to infection, leading to life-threatening organ dysfunction. It is a high-fatality condition associated with a complex interplay of immune and inflammatory responses that can cause severe harm to vital organs. Sepsis-induced myocardial injury (SIMI), as a severe complication of sepsis, significantly affects the prognosis of septic patients and shortens their survival time. For the sake of better administrating hospitalized patients with sepsis, it is necessary to understand the specific mechanisms of SIMI. To date, multiple studies have shown that programmed cell death (PCD) may play an essential role in myocardial injury in sepsis, offering new strategies and insights for the therapeutic aspects of SIMI. This review aims to elucidate the role of cardiomyocyte's programmed death in the pathophysiological mechanisms of SIMI, with a particular focus on the classical pathways, key molecules, and signaling transduction of PCD. It will explore the role of the cross-interaction between different patterns of PCD in SIMI, providing a new theoretical basis for multi-target treatments for SIMI.

The application of PROTAC in HDAC

Inducing protein degradation by proteolysis targeting chimera (PROTAC) has provided great opportunities for scientific research and industrial applications. Histone deacetylase (HDAC)-PROTAC has been widely developed since the first report of its ability to induce the degradation of SIRT2 in 2017. To date, ten of the eighteen HDACs (HDACs 1-8, HDAC10, and SIRT2) have been successfully targeted and degraded by HDAC-PROTACs. HDAC-PROTACs surpass traditional HDAC inhibitors in many aspects, such as higher selectivity, more potent antiproliferative activity, and the ability to disrupt the enzyme-independent functions of a multifunctional protein and overcome drug resistance. Rationally designing HDAC-PROTACs is a main challenge in development because slight variations in chemical structure can lead to drastic effects on the efficiency and selectivity of the degradation. In the future, HDAC-PROTACs can potentially be involved in clinical research with the support of the increased amount of in vivo data, pharmacokinetic evaluation, and pharmacological studies.

RIPK2 inhibitors for disease therapy: Current status and perspectives

Receptor-interacting protein kinase 2 (RIPK2) belongs to the receptor-interacting protein family (RIPs), which is mainly distributed in the cytoplasm. RIPK2 is widely expressed in human tissues, and its mRNA level is highly expressed in the spleen, leukocytes, placenta, testis, and heart. RIPK2 is a dual-specificity kinase with multiple domains, which can interact with tumor necrosis factor receptor (TNFR), and participate in the Toll-like receptor (TLR) and nucleotide-binding oligomerization domain (NOD) signaling pathways. It is considered as a vital adapter molecule involved in the innate immunity, adaptive immunity, and apoptosis. Functionally, RIPK2 and its targeted small molecules are of great significance in inflammatory responses, autoimmune diseases and tumors. The present study reviews the molecule structure and biological functions of RIPK2, and its correlation between human diseases. In addition, we focus on the structure-activity relationship of small molecule inhibitors of RIPK2 and their therapeutic potential in human diseases.

Structure shows that the BIR2 domain of E3 ligase XIAP binds across the RIPK2 kinase dimer interface

RIPK2 is an essential adaptor for NOD signalling and its kinase domain is a drug target for NOD-related diseases, such as inflammatory bowel disease. However, recent work indicates that the phosphorylation activity of RIPK2 is dispensable for signalling and that inhibitors of both RIPK2 activity and RIPK2 ubiquitination prevent the essential interaction between RIPK2 and the BIR2 domain of XIAP, the key RIPK2 ubiquitin E3 ligase. Moreover, XIAP BIR2 antagonists also block this interaction. To reveal the molecular mechanisms involved, we combined native mass spectrometry, NMR, and cryo-electron microscopy to determine the structure of the RIPK2 kinase BIR2 domain complex and validated the interface with in cellulo assays. The structure shows that BIR2 binds across the RIPK2 kinase antiparallel dimer and provides an explanation for both inhibitory mechanisms. It also highlights why phosphorylation of the kinase activation loop is dispensable for signalling while revealing the structural role of RIPK2-K209 residue in the RIPK2-XIAP BIR2 interaction. Our results clarify the features of the RIPK2 conformation essential for its role as a scaffold protein for ubiquitination.

Macrophage polarization and metabolism in atherosclerosis

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of fatty deposits in the inner walls of vessels. These plaques restrict blood flow and lead to complications such as heart attack or stroke. The development of atherosclerosis is influenced by a variety of factors, including age, genetics, lifestyle, and underlying health conditions such as high blood pressure or diabetes. Atherosclerotic plaques in stable form are characterized by slow growth, which leads to luminal stenosis, with low embolic potential or in unstable form, which contributes to high risk for thrombotic and embolic complications with rapid clinical onset. In this complex scenario of atherosclerosis, macrophages participate in the whole process, including the initiation, growth and eventually rupture and wound healing stages of artery plaque formation. Macrophages in plaques exhibit high heterogeneity and plasticity, which affect the evolving plaque microenvironment, e.g., leading to excessive lipid accumulation, cytokine hyperactivation, hypoxia, apoptosis and necroptosis. The metabolic and functional transitions of plaque macrophages in response to plaque microenvironmental factors not only influence ongoing and imminent inflammatory responses within the lesions but also directly dictate atherosclerotic progression or regression. In this review, we discuss the origin of macrophages within plaques, their phenotypic diversity, metabolic shifts, and fate and the roles they play in the dynamic progression of atherosclerosis. It also describes how macrophages interact with other plaque cells, particularly T cells. Ultimately, targeting pathways involved in macrophage polarization may lead to innovative and promising approaches for precision medicine. Further insights into the landscape and biological features of macrophages within atherosclerotic plaques may offer valuable information for optimizing future clinical treatment for atherosclerosis by targeting macrophages.

Saikosaponin A protects against uremic toxin indole‑3 acetic acid‑induced damage to the myocardium

Chronic kidney disease (CKD)‑associated cardiac injury is a common complication in patients with CKD. Indole‑3 acetic acid (IAA) is a uremic toxin that injures the cardiovascular system. Saikosaponin A (SSA) protects against pressure overload‑induced cardiac fibrosis. However, the role and molecular mechanisms of IAA and SSA in CKD‑associated cardiac injury remain unclear. The present study investigated the effects of IAA and SSA on CKD‑associated cardiac injury in neonatal mouse cardiomyocytes and a mouse model of CKD. The expression of tripartite motif‑containing protein 16 (Trim16), receptor interacting protein kinase 2 (RIP2) and phosphorylated‑p38 were assessed using western blotting. The ubiquitination of RIP2 was measured by coimmunoprecipitation, and mouse cardiac structure and function were evaluated using hematoxylin and eosin staining and echocardiography. The results demonstrated that, SSA inhibited IAA‑induced cardiomyocyte hypertrophy, upregulated Trim16 expression, downregulated RIP2 expression and decreased p38 phosphorylation. Furthermore, Trim16 mediated SSA‑induced degradation of RIP2 by ubiquitination. In a mouse model of IAA‑induced CKD‑associated cardiac injury, SSA upregulated the protein expression levels of Trim16 and downregulated those of RIP2. Moreover, SSA alleviated heart hypertrophy and diastolic dysfunction in IAA‑treated mice. Taken together, these results suggest that SSA is a protective agent against IAA‑induced CKD‑associated cardiac injury and that Trim16‑mediated ubiquitination‑related degradation of RIP2 and p38 phosphorylation may contribute to the development of CKD‑associated cardiac injury.

Leucine-rich repeat kinase 2 at a glance

Leucine-rich repeat kinase 2 (LRRK2) is a multidomain scaffolding protein with dual guanosine triphosphatase (GTPase) and kinase enzymatic activities, providing this protein with the capacity to regulate a multitude of signalling pathways and act as a key mediator of diverse cellular processes. Much of the interest in LRRK2 derives from mutations in the LRRK2 gene being the most common genetic cause of Parkinson's disease, and from the association of the LRRK2 locus with a number of other human diseases, including inflammatory bowel disease. Therefore, the LRRK2 research field has focused on the link between LRRK2 and pathology, with the aim of uncovering the underlying mechanisms and, ultimately, finding novel therapies and treatments to combat them. From the biochemical and cellular functions of LRRK2, to its relevance to distinct disease mechanisms, this Cell Science at a Glance article and the accompanying poster deliver a snapshot of our current understanding of LRRK2 function, dysfunction and links to disease.

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

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

5-Iodotubercidin sensitizes cells to RIPK1-dependent necroptosis by interfering with NFκB signaling

Receptor-interacting protein kinases (RIPK)-1 and -3 play crucial roles in cell fate decisions and are regulated by multiple checkpoint controls. Previous studies have identified IKK1/2- and p38/MK2-dependent checkpoints that phosphorylate RIPK1 at different residues to inhibit its activation. In this study, we investigated TNF-induced death in MAPK-activated protein kinase 2 (MK2)-deficient cells and found that MK2 deficiency or inactivation predominantly leads to necroptotic cell death, even without caspase inhibition. While RIPK1 inhibitors can rescue MK2-deficient cells from necroptosis, inhibiting RIPK3 seems to switch the process to apoptosis. To understand the underlying mechanism of this switch, we screened a library of 149 kinase inhibitors and identified the adenosine analog 5-Iodotubercidin (5-ITu) as the most potent compound that sensitizes MK2-deficient MEFs to TNF-induced cell death. 5-ITu also enhances LPS-induced necroptosis when combined with MK2 inhibition in RAW264.7 macrophages. Further mechanistic studies revealed that 5-ITu induces RIPK1-dependent necroptosis by suppressing IKK signaling in the absence of MK2 activity. These findings highlight the role for the multitarget kinase inhibitor 5-ITu in TNF-, LPS- and chemotherapeutics-induced necroptosis and its potential implications in RIPK1-targeted therapies.

Grouper RIP2 inhibits Singapore grouper iridovirus infection by modulating ASC-caspase-1 interaction

Introduction

Receptor interacting protein 2 (RIP2), serves as a vital sensor of cell stress, is able to respond to cell survival or inflammation, and is involved in antiviral pathways. However, studies on the property of RIP2 in viral infections in fish have not been reported.

Methods

In this paper, we cloned and characterized RIP2 homolog from orange-spotted grouper (Epinephelus coioides) (EcRIP2) and further discussed the relevance of EcRIP2 to EcASC, comparing the influences of EcRIP2 and EcASC on the modulation of inflammatory factors and the NF-κB activation to reveal the mechanism of EcRIP2 in fish DNA virus infection.

Results

Encoded a 602 amino acid protein, EcRIP2 contained two structural domains: S-TKc and CARD. Subcellular localization signified that EcRIP2 existed in cytoplasmic filaments and dot aggregation patterns. After SGIV infection, the EcRIP2 filaments aggregated into larger clusters near the nucleus. The infection of SGIV could notably up-regulate the transcription level of the EcRIP2 gene compared with lipopolysaccharide (LPS) and red grouper nerve necrosis virus (RGNNV). Overexpression of EcRIP2 impeded SGIV replication. The elevated expression levels of inflammatory cytokines induced by SGIV were remarkably hindered by EcRIP2 treatment in a concentration-dependent manner. In contrast, EcASC treatment could up-regulate SGIV-induced cytokine expression in the presence of EcCaspase-1. Enhancing amounts of EcRIP2 could overcome the down regulatory effect of EcASC on NF-κB. Nevertheless, increasing doses of EcASC failed to restrain the NF-κB activation in the existence of EcRIP2. Subsequently, it was validated by a co-immunoprecipitation assay that EcRIP2 dose-dependently competed with EcASC binding to EcCaspase-1. With increasing time to SGIV infection, EcCaspase-1 gradually combined with more EcRIP2 than EcASC.

Discussion

Collectively, this paper highlighted that EcRIP2 may impede SGIV-induced hyperinflammation by competing with EcASC for binding EcCaspase-1, thereby suppressing viral replication of SGIV. Our work supplies novel viewpoints into the modulatory mechanism of RIP2-associated pathway and offers a novel view of RIP2-mediated fish diseases.

A Metabolic Driven Bio-Responsive Hydrogel Loading Psoralen for Therapy of Rheumatoid Arthritis

Overexpressed matrix metalloproteinases, hypoxia microenvironment, and metabolic abnormality are important pathological signs of rheumatoid arthritis (RA). Designing a delivery carrier according to the pathological characteristics of RA that can control drug release in response to disease severity may be a promising treatment strategy. Psoralen is the main active ingredient isolated from Psoralea corylifolia L. and possesses excellent anti-inflammatory activities as well as improving bone homeostasis. However, the specific underlying mechanisms, particularly the possible relationships between the anti-RA effects of psoralen and related metabolic network, remain largely unexplored. Furthermore, psoralen shows systemic side effects and has unsatisfactory solubility. Therefore, it is desirable to develop a novel delivery system to maximize psoralen's therapeutic effect. In this study, a self-assembled degradable hydrogel platform is developed that delivers psoralen and calcium peroxide to arthritic joints and controls the release of psoralen and oxygen according to inflammatory stimulation, to regulate homeostasis and the metabolic disorder of the anoxic arthritic microenvironment. Therefore, the hydrogel drug delivery system based on the responsiveness of the inflammatory microenvironment and regulation of metabolism provides a new therapeutic strategy for RA treatment.

HA15 inhibits binding immunoglobulin protein and enhances the efficacy of radiation therapy in esophageal squamous cell carcinoma

Proteomic profiling is a promising approach to identify novel predictors of radiation response. The present study aimed to identify potential biomarkers of radiation response by serum proteomics in esophageal squamous cell carcinoma (ESCC) patients and find efficacious therapeutic drugs to enhance the efficacy of radiation therapy (RT). Serum binding immunoglobulin protein (BIP) was identified and validated as a treatment response predictor in ESCC patients treated with RT. Novel BIP inhibitor HA15 showed antitumor activity in ESCC cells by viability assay. Tumor cell colony formation and apoptosis assay revealed targeting BIP was associated with significant improvements of radiation sensitivity. Further analyses revealed that HA15 enhanced radiation-induced endoplasmic reticulum (ER) stress and immunogenic cell death (ICD) in ESCC. Clinical data indicated that high expression of BIP was associated with poor survival in patients of ESCC. In conclusion, proteomics analysis suggested BIP was a promising predictor of radiation response in locally advanced ESCC. The BIP inhibitor HA15 acted as an ER stress inducer and ICD stimulator; RT combined with HA15 was effective in suppressing the growth of ESCC in vitro and in vivo. Pretreatment BIP was an essential prognostic biomarker in locally advanced ESCC patients treated with RT.

Dermatophagoides farinae Extract Induces Interleukin 33-Mediated Atopic Skin Inflammation via Activation of RIP1

Receptor-interacting protein kinase (RIP) family 1 signaling has complex effects on inflammatory processes and cell death, but little is known concerning allergic skin diseases. We examined the role of RIP1 in Dermatophagoides farinae extract (DFE)-induced atopic dermatitis (AD)-like skin inflammation. RIP1 phosphorylation was increased in HKCs treated with DFE. Nectostatin-1, a selective and potent allosteric inhibitor of RIP1, inhibited AD-like skin inflammation and the expression of histamine, total IgE, DFE-specific IgE, IL-4, IL-5, and IL-13 in an AD-like mouse model. The expression of RIP1 was increased in ear skin tissue from a DFE-induced mouse model with AD-like skin lesions and in the lesional skin of AD patients with high house dust mite sensitization. The expression of IL-33 was down-regulated after RIP1 inhibition, and the levels of IL-33 were increased by over-expression of RIP1 in keratinocytes stimulated with DFE. Nectostatin-1 reduced IL-33 expression in vitro and in the DFE-induced mouse model. These results suggest that RIP1 can be one of the mediators that regulate IL-33-mediated atopic skin inflammation by house dust mites.

Developments of PROTACs technology in immune-related diseases

Traditional chemotherapy and immunotherapy are primary disease-treatment strategies. However, they face numerous challenges, including limited therapeutic benefits, off-target effects, serious adverse effects, drug resistance, long half-life time, poor oral bioavailability, and drugging undruggable proteins. Proteolytic targeted chimeras (PROTACs) were suggested to solve these problems. PROTACs are heterogeneous functional molecules linked by a chemical linker and contain a binding ligand for the protein of interest and a recruiting ligand for the E3 ligand. The binding of a PROTAC to a target protein brings the E3 ligand enzyme into proximity, initiating polyubiquitination of the target protein, followed by protease-mediated degradation. To date, PROTACs against dozens of immunological targets have been successfully developed, many of which have been clinically validated drug targets, and several have entered clinical trials for immune-related diseases. This article reviews the role of PROTACs-mediated degradation of critical proteins in immune disorders and cancer immunotherapy. Chemical structures, cellular and in vivo activities, and pharmacodynamics of these PROTACs are summarized. Lastly, we also discuss the prospects and potential limitations that PROTACs face.

MLKL-Driven Inflammasome Activation and Caspase-8 Mediate Inflammatory Cell Death in Influenza A Virus Infection

Influenza A virus (IAV) triggers multiple programmed cell death pathways, including MLKL-dependent necroptosis, caspase-8-dependent apoptosis, and caspase-1-dependent pyroptosis in myeloid cells. All three pathways share common upstream regulators, namely, ZBP1 and RIPK3. Yet, the molecular mechanism underlying IAV-induced inflammasome activation remains unclear. Here, we demonstrate that MLKL promotes inflammasome activation and IL-1β processing in IAV-infected macrophages. MLKL drives NLRP3 inflammasome activation through potassium efflux. In the absence of the MLKL-inflammasome axis, caspase-8 coordinates the maturation and secretion of IL-1β. MLKL alone is dispensable for host inflammatory responses to IAV in vivo. Taken together, MLKL and caspase-8 serve as redundant mechanisms by which to drive an inflammatory form of cell death in response to an IAV infection. IMPORTANCE Influenza A virus (IAV) induces multiple types of cell death, which play important roles in the host antiviral responses but can also cause unwanted inflammation and tissue damage. In this study, we dissect the interplay of cell death pathways and demonstrate that macrophages utilize redundant mechanisms to drive an inflammatory form of cell death upon IAV infection. MLKL, the executor of necroptosis, promotes inflammasome activation and pyroptotic cell death. When the MLKL-inflammasome axis is inhibited, cells divert to caspase-8-dependent inflammatory cell death. Our findings advance the current understanding of the innate immune response to IAV infection as well as broader contexts involving multifaceted cell death.

Delta (B1.617.2) variant of SARS-CoV-2 induces severe neurotropic patterns in K18-hACE2 mice

A highly contagious virus, severe acute respiratory syndrome coronavirus 2, caused the coronavirus disease 19 (COVID-19) pandemic (SARS-CoV-2). SARS-CoV-2 genetic variants have been reported to circulate throughout the COVID-19 pandemic. COVID-19 symptoms include respiratory symptoms, fever, muscle pain, and breathing difficulty. In addition, up to 30% of COVID-19 patients experience neurological complications such as headaches, nausea, stroke, and anosmia. However, the neurotropism of SARS-CoV-2 infection remains largely unknown. This study investigated the neurotropic patterns between the B1.617.2 (Delta) and Hu-1 variants (Wuhan, early strain) in K18-hACE2 mice. Despite both the variants inducing similar pathogenic patterns in various organs, B1.617.2-infected K18-hACE2 mice demonstrated a higher range of disease phenotypes such as weight loss, lethality, and conjunctivitis when compared to those in Hu-1-infected mice. In addition, histopathological analysis revealed that B1.617.2 infects the brain of K18-hACE2 mice more rapidly and effectively than Hu-1. Finally, we discovered that, in B1.617.2-infected mice, the early activation of various signature genes involved innate cytokines and that the necrosis-related response was most pronounced than that in Hu-1-infected mice. The present findings indicate the neuroinvasive properties of SARS-CoV-2 variants in K18-hACE2 mice and link them to fatal neuro-dissemination during the disease onset.

PROTACS: A technology with a gold rush-like atmosphere

Abnormally expressed or malfunctioning proteins may affect or even damage cells, leading to the onset of diseases. Proteolysis targeting chimera (PROTAC) technology has been proven to be a fresh therapeutic strategy, superior to conventional small molecule inhibitors for the treatment of diseases caused by pathogenic proteins. Unlike conventional small molecule inhibitors that are occupancy-driven, PROTACs are heterobifunctional small molecules with catalytic properties. They combine with E3 ligases and target proteins to form a ternary complex, rendering the target protein ubiquitous and subsequently degraded by the proteasome. This paper focuses first on significant events in the development of PROTAC technology from 2001 to 2022, followed by a brief overview of various PROTACs categorized by target proteins. In addition, the applications of PROTACs in the treatment of diseases and fundamental biology are also under discussion.

Vemurafenib and Dabrafenib Downregulates RIPK4 Level

Vemurafenib and dabrafenib are BRAF kinase inhibitors (BRAFi) used for the treatment of patients with melanoma carrying the V600E BRAF mutation. However, melanoma cells develop resistance to both drugs when used as monotherapy. Therefore, mechanisms of drug resistance are investigated, and new molecular targets are sought that could completely inhibit melanoma progression. Since receptor-interacting protein kinase (RIPK4) probably functions as an oncogene in melanoma and its structure is similar to the BRAF protein, we analyzed the impact of vemurafenib and dabrafenib on RIPK4 in melanomas. The in silico study confirmed the high similarity of BRAF kinase domains to the RIPK4 protein at both the sequence and structural levels and suggests that BRAFi could directly bind to RIPK4 even more strongly than to ATP. Furthermore, BRAFi inhibited ERK1/2 activity and lowered RIPK4 protein levels in BRAF-mutated melanoma cells (A375 and WM266.4), while in wild-type BRAF cells (BLM and LoVo), both inhibitors decreased the level of RIPK4 and enhanced ERK1/2 activity. The phosphorylation of phosphatidylethanolamine binding protein 1 (PEBP1)-a suppressor of the BRAF/MEK/ERK pathway-via RIPK4 observed in pancreatic cancer did not occur in melanoma. Neither downregulation nor upregulation of RIPK4 in BRAF- mutated cells affected PEBP1 levels or the BRAF/MEK/ERK pathway. The downregulation of RIPK4 inhibited cell proliferation and the FAK/AKT pathway, and increased BRAFi efficiency in WM266.4 cells. However, the silencing of RIPK4 did not induce apoptosis or necroptosis. Our study suggests that RIPK4 may be an off-target for BRAF inhibitors.

PRMT5-mediated regulatory arginine methylation of RIPK3

The TNF receptor-interacting protein kinases (RIPK)-1 and 3 are regulators of extrinsic cell death response pathways, where RIPK1 makes the cell survival or death decisions by associating with distinct complexes mediating survival signaling, caspase activation or RIPK3-dependent necroptotic cell death in a context-dependent manner. Using a mass spectrometry-based screen to find new components of the ripoptosome/necrosome, we discovered the protein-arginine methyltransferase (PRMT)-5 as a direct interaction partner of RIPK1. Interestingly, RIPK3 but not RIPK1 was then found to be a target of PRMT5-mediated symmetric arginine dimethylation. A conserved arginine residue in RIPK3 (R486 in human, R415 in mouse) was identified as the evolutionarily conserved target for PRMT5-mediated symmetric dimethylation and the mutations R486A and R486K in human RIPK3 almost completely abrogated its methylation. Rescue experiments using these non-methylatable mutants of RIPK3 demonstrated PRMT5-mediated RIPK3 methylation to act as an efficient mechanism of RIPK3-mediated feedback control on RIPK1 activity and function. Therefore, this study reveals PRMT5-mediated RIPK3 methylation as a novel modulator of RIPK1-dependent signaling.

Modeling inducible neuropathologies of the retina with differential phenotypes in organoids

Neurodegenerative diseases remain incompletely understood and therapies are needed. Stem cell-derived organoid models facilitate fundamental and translational medicine research. However, to which extent differential neuronal and glial pathologic processes can be reproduced in current systems is still unclear. Here, we tested 16 different chemical, physical, and cell functional manipulations in mouse retina organoids to further explore this. Some of the treatments induce differential phenotypes, indicating that organoids are competent to reproduce distinct pathologic processes. Notably, mouse retina organoids even reproduce a complex pathology phenotype with combined photoreceptor neurodegeneration and glial pathologies upon combined (not single) application of HBEGF and TNF, two factors previously associated with neurodegenerative diseases. Pharmacological inhibitors for MAPK signaling completely prevent photoreceptor and glial pathologies, while inhibitors for Rho/ROCK, NFkB, and CDK4 differentially affect them. In conclusion, mouse retina organoids facilitate reproduction of distinct and complex pathologies, mechanistic access, insights for further organoid optimization, and modeling of differential phenotypes for future applications in fundamental and translational medicine research.

Curcumin alleviates experimental colitis in mice by suppressing necroptosis of intestinal epithelial cells

Curcumin, the primary bioactive substance in turmeric, exhibits potential therapeutic effects on ulcerative colitis. However, its mechanism for regulating necroptosis in colitis has not been fully elucidated. In this study, the effect of curcumin on experimental colitis-induced necroptosis of intestinal epithelial cells was investigated, and its molecular mechanism was further explored. We found that curcumin blocked necroptosis in a dose-dependent manner by inhibiting the phosphorylation of RIP3 and MLKL instead of RIP1 in HT-29 cells. Co-Immunoprecipitation assay showed that curcumin weakened the interaction between RIP1 and RIP3, possibly due to the direct binding of curcumin to RIP3 as suggested by drug affinity responsive target stability analysis. In a classical in vivo model of TNF-α and pan-caspase inhibitor-induced necroptosis in C57BL/6 mice, curcumin potently inhibited systemic inflammatory responses initiated by the necroptosis signaling pathway. Then, using a dextran sodium sulfate-induced colitis model in C57BL/6 mice, we found that curcumin inhibited the expression of p-RIP3 in the intestinal epithelium, reduced intestinal epithelial cells loss, improved the function of the intestinal tight junction barrier, and reduced local intestinal inflammation. Collectively, our findings suggest that curcumin is a potent targeted RIP3 inhibitor with anti-necroptotic and anti-inflammatory effects, maintains intestinal barrier function, and effectively alleviates colitis injury.

Recent advances in the development of RIPK2 modulators for the treatment of inflammatory diseases

Receptor-interacting serine/threonine kinase 2 (RIPK2) is a vital immunomodulator that plays critical roles in nucleotide-binding oligomerization domain 1 (NOD1), NOD2, and Toll-like receptors (TLRs) signaling. Stimulated NOD1 and NOD2 interact with RIPK2 and lead to the activation of nuclear factor kappa B (NF-κB) and mitogen-activated protein kinases (MAPK), followed by the production of pro-inflammatory cytokines such as TNF-α, IL-6, and IL-12/23. Defects in NOD/RIPK2 signaling are associated with numerous inflammatory diseases, including asthma, sarcoidosis, inflammatory bowel disease (Crohn's disease and ulcerative colitis), multiple sclerosis, and Blau syndrome. As RIPK2 is a crucial element of innate immunity, small molecules regulating RIPK2 functions are attractive to establish novel immunotherapies. The increased interest in developing RIPK2 inhibitors has led to the clinical investigations of novel drug candidates. In this review, we attempt to summarize recent advances in the development of RIPK2 inhibitors and degraders.

Generative deep learning enables the discovery of a potent and selective RIPK1 inhibitor

The retrieval of hit/lead compounds with novel scaffolds during early drug development is an important but challenging task. Various generative models have been proposed to create drug-like molecules. However, the capacity of these generative models to design wet-lab-validated and target-specific molecules with novel scaffolds has hardly been verified. We herein propose a generative deep learning (GDL) model, a distribution-learning conditional recurrent neural network (cRNN), to generate tailor-made virtual compound libraries for given biological targets. The GDL model is then applied to RIPK1. Virtual screening against the generated tailor-made compound library and subsequent bioactivity evaluation lead to the discovery of a potent and selective RIPK1 inhibitor with a previously unreported scaffold, RI-962. This compound displays potent in vitro activity in protecting cells from necroptosis, and good in vivo efficacy in two inflammatory models. Collectively, the findings prove the capacity of our GDL model in generating hit/lead compounds with unreported scaffolds, highlighting a great potential of deep learning in drug discovery.

Dengue virus downregulates TNFR1- and TLR3-stimulated NF-κB activation by targeting RIPK1

Dengue virus (DENV) infection is the most prevalent arthropod-borne virus disease and is endemic in more than 100 countries. Several DENV proteins have been shown to target crucial human host proteins to evade innate immune responses and establish a productive infection. Here we report that the DENV NS3 protein targets RIPK1 (Receptor Interacting Protein Kinase I), a central mediator of inflammation and cell death, and decreases intracellular RIPK1 levels during DENV infection. The interaction of NS3 with RIPK1 results in the inhibition of NF-κB activation in response to TNFR or TLR3 stimulation. Also, we observed that the effects of NS3 on RIPK1 were independent of NS3 protease activity. Our data demonstrate a novel mechanism by which DENV suppresses normal cellular functions to evade host innate immune responses

Comparative and evolutionary analysis of RIP kinases in immune responses

The group of receptor-interacting protein (RIP) kinases has seven members (RIPK1–7), with one homologous kinase domain but distinct non-kinase regions. Although RIPK1–3 have emerged as key modulators of inflammation and cell death, few studies have connected RIPK4–7 to immune responses. The divergence in domain structures and paralogue information in the Ensembl database have raised question about the phylogeny of RIPK1–7. In this study, phylogenetic trees of RIPK1–7 and paralogues constructed using full-length amino acid sequences or Kinase domain demonstrate that RIPK6 and RIPK7 are distinct from RIPK1–5 and paralogues shown in the Ensembl database are inaccurate. Comparative and evolutionary analyses were subsequently performed to gain new clues about the potential functions of RIPK3–7. RIPK3 gene loss in birds and animals that undergo torpor, a common physiological phenomenon in cold environments, implies that RIPK3 may be involved in ischemia-reperfusion injury and/or high metabolic rate. The negligible expression of RIPK4 and RIPK5 in immune cells is likely responsible for the lack of studies on the direct role of these members in immunity; RIPK6 and RIPK7 are conserved among plants, invertebrates and vertebrates, and dominantly expressed in innate immune cells, indicating their roles in innate immunity. Overall, our results provide insights into the multifaceted and conserved biochemical functions of RIP kinases.

Recent Advances in PROTACs for Drug Targeted Protein Research

Proteolysis-targeting chimera (PROTAC) is a heterobifunctional molecule. Typically, PROTAC consists of two terminals which are the ligand of the protein of interest (POI) and the specific ligand of E3 ubiquitin ligase, respectively, via a suitable linker. PROTAC degradation of the target protein is performed through the ubiquitin–proteasome system (UPS). The general process is that PROTAC binds to the target protein and E3 ligase to form a ternary complex and label the target protein with ubiquitination. The ubiquitinated protein is recognized and degraded by the proteasome in the cell. At present, PROTAC, as a new type of drug, has been developed to degrade a variety of cancer target proteins and other disease target proteins, and has shown good curative effects on a variety of diseases. For example, PROTACs targeting AR, BR, BTK, Tau, IRAK4, and other proteins have shown unprecedented clinical efficacy in cancers, neurodegenerative diseases, inflammations, and other fields. Recently, PROTAC has entered a phase of rapid development, opening a new field for biomedical research and development. This paper reviews the various fields of targeted protein degradation by PROTAC in recent years and summarizes and prospects the hot targets and indications of PROTAC.

Rosin Derivative IDOAMP Inhibits Prostate Cancer Growth via Activating RIPK1/RIPK3/MLKL Signaling Pathway

Rosin derivatives such as dehydroabietic acid and dehydroabietic amine belonging to diterpenoids have similar structure with androgen that inhibited the occurrence and development of prostate cancer. In this study, the effects and possible mechanism of the rosin derivative IDOAMP on prostate cancer were investigated. Our results showed that IDOAMP effectively inhibited cell viabilities of LNCaP, PC3, and DU145 prostate cells. After the treatment with IDOAMP, the levels of cleaved-PARP, LC3BII/I, and HMGB1 were increased, whereas the expression of GPX4 was decreased. Interestingly, cell viability was reversed by the supplements of necrostatin-1 and necrosulfonamide. Meanwhile, the IDOAMP downregulated the expression of human Aurora kinase A that was overexpressed in prostate cancer. In addition, co-IP results showed that IDOAMP inhibited the binding of Aurora kinase A to the receptor-interacting serine/threonine kinase 1 (RIPK1) and RIPK3. However, the binding of RIPK1 to FADD, RIPK3, or MLKL was significantly promoted. Further studies showed that the phosphorylation levels of RIPK1, RIPK, and MLKL were increased in a concentration-dependent manner. In in vivo model, IDOAMP reduced the tumor volumes and weights. In conclusion, IDOAMP directly inhibited Aurora kinase A and promoted the RIPK1/RIPK3/MLKL necrosome activation to inhibit the prostate cancer.

Cardiomyocyte death in sepsis: Mechanisms and regulation (Review)

Sepsis‑induced cardiac dysfunction is one of the most common types of organ dysfunction in sepsis; its pathogenesis is highly complex and not yet fully understood. Cardiomyocytes serve a key role in the pathophysiology of cardiac function; due to the limited ability of cardiomyocytes to regenerate, their loss contributes to decreased cardiac function. The activation of inflammatory signalling pathways affects cardiomyocyte function and modes of cardiomyocyte death in sepsis. Prevention of cardiomyocyte death is an important therapeutic strategy for sepsis‑induced cardiac dysfunction. Thus, understanding the signalling pathways that activate cardiomyocyte death and cross‑regulation between death modes are key to finding therapeutic targets. The present review focused on advances in understanding of sepsis‑induced cardiomyocyte death pathways, including apoptosis, necroptosis, mitochondria‑mediated necrosis, pyroptosis, ferroptosis and autophagy. The present review summarizes the effect of inflammatory activation on cardiomyocyte death mechanisms, the diversity of regulatory mechanisms and cross‑regulation between death modes and the effect on cardiac function in sepsis to provide a theoretical basis for treatment of sepsis‑induced cardiac dysfunction.

The RIPK family: expression profile and prognostic value in lung adenocarcinoma

Receptor interacting protein kinases (RIPKs) are a family of serine/threonine kinases which are supposed to regulate tumor generation and progression. Rare study illustrates the roles and functions of RIPKs family in lung adenocarcinoma (LUAD) comprehensively. Our results indicated that the expression of RIPK2 higher in LUAD patients while RIPK5 (encoded by gene DSTYK) expression was lower. Only RIPK2 had a strong correlation with pathological stage in LUAD patients. Kaplan-Meier plotter revealed that LUAD patients with low RIPK2 or RIPK3 level showed better overall survival (OS), but worse when LUAD patients with high RIPK5. Further, lower expression of RIPK2 and higher expression of RIPK1, RIPK4 and RIPK5 prompted a longer disease free survival (DFS). Genetic alterations based on cBioPortal revealing 16% alteration rates of RIPK2, as well as RIPK5. We also found that the functions of RIPKs family were linked to cellular senescence, protein serine/threonine kinase activity, apoptosis process et al. TIMER database indicated that the RIPKs family members had distinct relationships with the infiltration of six types of immune cells (macrophages, neutrophils, CD8+ T-cells, B-cells, CD4+ T-cells and dendritic cells). Moreover, RIPK2 could be observed as an independent prognostic factor with Cox proportional hazard model analysis. DiseaseMeth databases revealed that the global methylation levels of RIPK2 increased in LUAD patients. Thus, the findings above will enhance the understanding of RIPKs family in LUAD pathology and progression, providing novel insights into RIPKs-core therapy for LUAD patients.

Essential Role of the Innate Immune Adaptor RIP2 in the Response to Otitis Media

Intracellular nucleotide binding and oligomerization domain (NOD) and Toll-like (TLR) receptors have emerged as pivotal sensors of infection. Both Nod1 and Nod2 contain a caspase activation and recruitment domain (CARD) that interacts with the adaptor protein RIP2 (receptor-interaction protein-2). This leads to ubiquitination of RIP2 and in turn to the activation of NFκB and MAPK transcription factors, to command the host defensive response against pathogenic infections. RIP2 is also activated by TLRs 2 and 4, although the mechanism of this activation is less. The role of RIP2 in otitis media (OM) pathogenesis has yet to be examined. Herein, we used in vivo animal models including C57BL/6 wild-type (WT) and RIP2^−/− knockout mice inoculated in the middle ear (ME) with non-typeable Haemophilus influenzae (NTHi), a common human OM pathogen, to evaluate the expression of RIP2 and its signaling genes at the cellular level to determine the role of RIP2 in OM pathogenesis and recovery. The Nod1, Nod2, and Ripk2 genes are minimally expressed in the normal ME. However, they are strongly upregulated during acute OM, as are many genes related to RIP2 signaling. However, while signaling genes were expressed by various ME cell types, only mucosal epithelial and stromal cells expressed the NODs, RIP2, and signaling genes required for the activation of the host defensive response. Whereas WT mice clear ME bacteria and recover from OM within 5 days after infection, RIP2-deficient mice show persistent ME bacterial carriage and inflammation to at least 15 days. This includes significantly prolonged mucosal hyperplasia and ME leukocytic infiltration. Recruitment of macrophages is also delayed in comparison to WT mice. Thus, RIP2 is required to elicit a robust innate immune response that promotes bacterial clearance and increases host innate resistance. The results also identify the structural cells of the ME mucosa, as opposed to leukocytes, as the primary sites of NOD/RIP2 activity in the infected ME.

Ca2+/Calmodulin-Dependent Protein Kinase II Regulation by Inhibitor of Receptor Interacting Protein Kinase 3 Alleviates Necroptosis in Glycation End Products-Induced Cardiomyocytes Injury

Necroptosisis a regulatory programmed form of necrosis. Receptor interacting protein kinase 3 (RIPK3) is a robust indicator of necroptosis. RIPK3 mediates myocardial necroptosis through activation of calcium/calmodulin-dependent protein kinase II (CaMKII) in cardiac ischemia-reperfusion (I/R) injury and heart failure. However, the exact mechanism of RIPK3 in advanced glycation end products (AGEs)-induced cardiomyocytes necroptosis is not clear. In this study, cardiomyocytes were subjected to AGEs stimulation for 24 h. RIPK3 expression, CaMKII expression, and necroptosis were determined in cardiomyocytes after AGEs stimulation. Then, cardiomyocytes were transfected with RIPK3 siRNA to downregulate RIPK3 followed by AGEs stimulation for 24 h. CaMKIIδ alternative splicing, CaMKII activity, oxidative stress, necroptosis, and cell damage were detected again. Next, cardiomyocytes were pretreated with GSK′872, a specific RIPK3 inhibitor to assess whether it could protect cardiomyocytes against AGEs stimulation. We found that AGEs increased the expression of RIPK3, aggravated the disorder of CaMKII δ alternative splicing, promoted CaMKII activation, enhanced oxidative stress, induced necroptosis, and damaged cardiomyocytes. RIPK3 downregulation or RIPK3 inhibitor GSK′872 corrected CaMKIIδ alternative splicing disorder, inhibited CaMKII activation, reduced oxidative stress, attenuated necroptosis, and improved cell damage in cardiomyocytes.

All About (NK Cell-Mediated) Death in Two Acts and an Unexpected Encore: Initiation, Execution and Activation of Adaptive Immunity

NK cells are key mediators of immune cell-mediated cytotoxicity toward infected and transformed cells, being one of the main executors of cell death in the immune system. NK cells recognize target cells through an array of inhibitory and activating receptors for endogenous or exogenous pathogen-derived ligands, which together with adhesion molecules form a structure known as immunological synapse that regulates NK cell effector functions. The main and best characterized mechanisms involved in NK cell-mediated cytotoxicity are the granule exocytosis pathway (perforin/granzymes) and the expression of death ligands. These pathways are recognized as activators of different cell death programmes on the target cells leading to their destruction. However, most studies analyzing these pathways have used pure recombinant or native proteins instead of intact NK cells and, thus, extrapolation of the results to NK cell-mediated cell death might be difficult. Specially, since the activation of granule exocytosis and/or death ligands during NK cell-mediated elimination of target cells might be influenced by the stimulus received from target cells and other microenvironment components, which might affect the cell death pathways activated on target cells. Here we will review and discuss the available experimental evidence on how NK cells kill target cells, with a special focus on the different cell death modalities that have been found to be activated during NK cell-mediated cytotoxicity; including apoptosis and more inflammatory pathways like necroptosis and pyroptosis. In light of this new evidence, we will develop the new concept of cell death induced by NK cells as a new regulatory mechanism linking innate immune response with the activation of tumour adaptive T cell responses, which might be the initiating stimulus that trigger the cancer-immunity cycle. The use of the different cell death pathways and the modulation of the tumour cell molecular machinery regulating them might affect not only tumour cell elimination by NK cells but, in addition, the generation of T cell responses against the tumour that would contribute to efficient tumour elimination and generate cancer immune memory preventing potential recurrences.

Necroptosis and Viral Myocarditis: Tumor Necrosis Factor α as a Novel Biomarker for the Diagnosis of Viral Myocarditis

Programmed cell death (PCD), including necroptosis, has emerged as a significant pathway in cardiovascular diseases. The infection of viral myocarditis (VMC) could cause cardiomyocytes degeneration, necrosis, and immune-inflammatory myocardial response. In this review, we summarized and evaluated the available evidence on the pathogenesis, molecule mechanism, diagnosis, and potential treatment strategies of viral myocarditis, with a special focus on the novel mechanism of necroptosis for cardiomyocytes death. Studies have shown that tumor necrosis factor-alpha (TNF-α) is an important cytokine involved in the activation of necroptosis; an elevated level of TNF-α is continually reported in patients suffering from VMC, implicating its involvement in the pathogenesis of VMC. It is of great interest to explore the clinical implication of TNF-α. We subsequently conducted a meta-analysis on the efficacy of serum TNF-α expression level and its diagnostic accuracy on acute viral myocarditis detection. Taken together, the review demonstrates a compelling role of necroptosis involved in the pathogenesis of VMC. Further, applying TNF-α as a serological marker for the diagnosis of VMC may be a useful strategy.

Gene expression profiling of RIP2-knockdown in HD11 macrophages - elucidation of potential pathways (gene network) when challenged with avian pathogenic E.coli (APEC)

BACKGROUND

Receptor interacting serine/threonine kinase 2 (RIP2), ubiquitous in many tissue/cell types, is the key regulator of immune and inflammatory responses for many diseases, including avian pathogenic E. coli (APEC), which causes a wide variety of localized or systemic infections. However, the molecular mechanisms by which RIP2 drives its transcriptional program to affect immune and inflammatory response upon APEC infection remains poorly understood.

RESULTS

In this study, RNA-seq and bioinformatics analyses were used to detect gene expression and new direct/indirect RIP2 targets in the treatments of wild type HD11 cells (WT), RIP2 knockdown cells (shRIP2), APEC stimulation cells (APEC), and RIP2 knockdown cells combined with APEC infection (shRIP2 + APEC). The results revealed that a total of 4691 and 2605 differentially expressed genes (DEGs) were screened in shRIP2 + APEC vs. APEC and shRIP2 vs. WT, respectively. Functional annotation analysis showed that apoptosis, MAPK, p53, Toll-like receptor, and Nod-like receptor signaling pathways were involved in APEC-induced RIP2 knockdown HD11 cells. By analyzing the enriched pathway and gene networks, we identified that several DEGs, including HSP90AB1, BID, and CASP9 were targeted by RIP2 upon APEC infection.

CONCLUSION

As a whole, this study can not only provide data support for constructing gene networks of RIP2 knockdown with APEC challenge but also provide new ideas for improving the immune and inflammatory response.

The Signaling Pathway of TNF Receptors: Linking Animal Models of Renal Disease to Human CKD

Chronic kidney disease (CKD) has been recognized as a global public health problem. Despite the current advances in medicine, CKD-associated morbidity and mortality remain unacceptably high. Several studies have highlighted the contribution of inflammation and inflammatory mediators to the development and/or progression of CKD, such as tumor necrosis factor (TNF)-related biomarkers. The inflammation pathway driven by TNF-α, through TNF receptors 1 (TNFR1) and 2 (TNFR2), involves important mediators in the pathogenesis of CKD. Circulating levels of TNFRs were associated with changes in other biomarkers of kidney function and injury, and were described as predictors of disease progression, cardiovascular morbidity, and mortality in several cohorts of patients. Experimental studies describe the possible downstream signaling pathways induced upon TNFR activation and the resulting biological responses. This review will focus on the available data on TNFR1 and TNFR2, and illustrates their contributions to the pathophysiology of kidney diseases, their cellular and molecular roles, as well as their potential as CKD biomarkers. The emerging evidence shows that TNF receptors could act as biomarkers of renal damage and as mediators of the disease. Furthermore, it has been suggested that these biomarkers could significantly improve the discrimination of clinical CKD prognostic models.

Synthesis and characterization of potent RIPK3 inhibitors based on a tricyclic scaffold

Background: Necroptosis is an important form of regulated cell death involved in inflammatory diseases, degenerative diseases and cancer. RIPK3 is an interesting target for intervention of necroptosis-associated diseases. Methodology: Herein the authors report the synthesis of a series RIPK3 inhibitors under the guidance of structure-based drug design which leads to the identification of compound 37. Results: Compound 37 potently rescued human and mouse cells from necroptotic stimuli TNFα, Smac mimetic, z-VAD and LPS + z-VAD, displayed high affinity to RIPK3 (Kd = 14 nM) but no observable affinity to RIPK1 and inhibited RIPK3 kinase function. Importantly, compound 37 significantly alleviated TNF-induced systemic inflammatory response syndrome in the mouse model. Conclusion: These results support compound 37 as a prototype RIPK3 inhibitor for lead optimization.

Ankk1 Loss of Function Disrupts Dopaminergic Pathways in Zebrafish

Ankyrin repeat and kinase domain containing 1 (ANKK1) is a member of the receptor-interacting protein serine/threonine kinase family, known to be involved in cell proliferation, differentiation and activation of transcription factors. Genetic variation within the ANKK1 locus is suggested to play a role in vulnerability to addictions. However, ANKK1 mechanism of action is still poorly understood. It has been suggested that ANKK1 may affect the development and/or functioning of dopaminergic pathways. To test this hypothesis, we generated a CRISPR-Cas9 loss of function ankk1 zebrafish line causing a 27 bp insertion that disrupts the ankk1 sequence introducing an early stop codon. We found that ankk1 transcript levels were significantly lower in ankk1 mutant (ankk127ins) fish compared to their wild type (ankk1+/+) siblings. In ankk1+/+ adult zebrafish brain, ankk1 protein was detected in isocortex, hippocampus, basolateral amygdala, mesencephalon, and cerebellum, resembling the mammalian distribution pattern. In contrast, ankk1 protein was reduced in the brain of ankk127ins/27ins fish. Quantitative polymerase chain reaction analysis revealed an increase in expression of drd2b mRNA in ankk127ins at both larval and adult stages. In ankk1+/+ adult zebrafish brain, drd2 protein was detected in cerebral cortex, cerebellum, hippocampus, and caudate homolog regions, resembling the pattern in humans. In contrast, drd2 expression was reduced in cortical regions of ankk127ins/27ins being predominantly found in the hindbrain. No differences in the number of cell bodies or axonal projections detected by anti-tyrosine hydroxylase immunostaining on 3 days post fertilization (dpf) larvae were found. Behavioral analysis revealed altered sensitivity to effects of both amisulpride and apomorphine on locomotion and startle habituation, consistent with a broad loss of both pre and post synaptic receptors. Ankk127ins mutants showed reduced sensitivity to the effect of the selective dopamine receptor antagonist amisulpride on locomotor responses to acoustic startle and were differentially sensitive to the effects of the non-selective dopamine agonist apomorphine on both locomotion and habituation. Taken together, our findings strengthen the hypothesis of a functional relationship between ANKK1 and DRD2, supporting a role for ANKK1 in the maintenance and/or functioning of dopaminergic pathways. Further work is needed to disentangle ANKK1’s role at different developmental stages.