C23, an oligopeptide derived from cold-inducible RNA-binding protein, suppresses inflammation and reduces lung injury in neonatal sepsis

Intracellular CIRP promotes liver regeneration via STAT3 signaling pathway activation after partial hepatectomy in mice

Cold‑inducible RNA‑binding protein (CIRP) is a cold shock protein implicated in the regulation of multiple biological processes depending on its cellular localization. However, to the best of our knowledge, the role of CIRP in liver regeneration and injury after hepatectomy has not been investigated. The present study was therefore designed to explore whether CIRP is involved in liver regeneration after hepatectomy and its specific role and underlying molecular mechanism. The overall involvement of CIRP in liver regeneration and injury after hepatectomy was evaluated in CIRP‑deficient mice. C23, an antagonist of extracellular CIRP, was used to assess the effect of extracellular CIRP on liver regeneration and injury after hepatectomy. CIRP overexpression and short hairpin RNA plasmids were transfected into HepG2 cells to study the effect of intracellular CIRP on cell proliferation. The effects of extracellular CIRP on cell proliferation and injury were determined via the use of recombinant CIRP protein to stimulate HepG2 cells in vitro. The results indicated that both hepatic and serum CIRP levels significantly increased after partial hepatectomy. Additionally, CIRP deficiency impaired liver regeneration but alleviated liver injury after partial hepatectomy in mice. C23 administration attenuated liver injury and suppressed endoplasmic reticulum (ER) stress and oxidative stress. Loss‑ and gain‑of‑function analyses in HepG2 cells indicated that an increase in intracellular CIRP promoted cell proliferation via signal transducers and activation of transcription 3 (STAT3) signaling pathway activation. Moreover, recombinant CIRP had no effect on cell proliferation or STAT3 phosphorylation but induced ER stress, which was blocked by TAK242, an inhibitor of Toll‑like receptor 4 (TLR4), in HepG2 cells. Taken together, the results of the present study demonstrated that intracellular CIRP promotes liver regeneration by activating the STAT3 pathway, whereas extracellular CIRP induces ER stress possibly via the TLR4 signaling pathway after hepatectomy.

Extracellular cold-inducible RNA-binding protein in CNS injury: molecular insights and therapeutic approaches

Central nervous system (CNS) injuries, such as ischemic stroke (IS), intracerebral hemorrhage (ICH) and traumatic brain injury (TBI), are a significant global burden. The complex pathophysiology of CNS injury is comprised of primary and secondary injury. Inflammatory secondary injury is incited by damage-associated molecular patterns (DAMPs) which signal a variety of resident CNS cells and infiltrating immune cells. Extracellular cold-inducible RNA-binding protein (eCIRP) is a DAMP which acts through multiple immune and non-immune cells to promote inflammation. Despite the well-established role of eCIRP in systemic and sterile inflammation, its role in CNS injury is less elucidated. Recent literature suggests that eCIRP is a pleiotropic inflammatory mediator in CNS injury. eCIRP is also being evaluated as a clinical biomarker to indicate prognosis in CNS injuries. This review provides a broad overview of CNS injury, with a focus on immune-mediated secondary injury and neuroinflammation. We then review what is known about eCIRP in CNS injury, and its known mechanisms in both CNS and non-CNS cells, identifying opportunities for further study. We also explore eCIRP's potential as a prognostic marker of CNS injury severity and outcome. Next, we provide an overview of eCIRP-targeting therapeutics and suggest strategies to develop these agents to ameliorate CNS injury. Finally, we emphasize exploring novel molecular mechanisms, aside from neuroinflammation, by which eCIRP acts as a critical mediator with significant potential as a therapeutic target and prognostic biomarker in CNS injury.

An eCIRP inhibitor attenuates fibrosis and ferroptosis in ischemia and reperfusion induced chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a leading cause of death in the United States, and renal fibrosis represents a pathologic hallmark of CKD. Extracellular cold-inducible RNA-binding protein (eCIRP) is a stress response protein involved in acute inflammation, tissue injury and regulated cell death. However, the role of eCIRP in chronic inflammation and tissue injury has not been elucidated. We hypothesize that eCIRP is involved in renal ischemia/reperfusion (RIR)-induced CKD and that C23, an antagonist to eCIRP, is beneficial in attenuating renal fibrosis and ferroptosis in RIR-induced CKD.

METHODS

C57BL/6 (WT) or CIRP-/- mice underwent renal injury with total blockage of blood perfusion by clamping bilateral renal pedicles for 28 min. In the WT mice at the time of reperfusion, they were treated with C23 (8 mg/kg) or vehicle. Blood and kidneys were harvested for further analysis at 21 days thereafter. In a separate cohort, mice underwent bilateral RIR and treatment with C23 or vehicle and were then subjected to left nephrectomy 72 h thereafter. Mice were then monitored for additional 19 days, and glomerular filtration rate (GFR) was assessed using a noninvasive transcutaneous method.

RESULTS

In the RIR-induced CKD, CIRP-/- mice showed decreased collagen deposition, fibronectin staining, and renal injury as compared to the WT mice. Administration of C23 ameliorated renal fibrosis by decreasing the expression of active TGF-β1, α-SMA, collagen deposition, fibronectin and macrophage infiltration to the kidneys. Furthermore, intervention with C23 significantly decreased renal ferroptosis by reducing iron accumulation, increasing the expression of glutathione peroxidase 4 (GPX4) and lipid peroxidation in the kidneys of RIR-induced CKD mice. Treatment with C23 also attenuated BUN and creatinine. Finally, GFR was significantly decreased in RIR mice with left nephrectomy and C23 treatment partially prevented their decrease.

CONCLUSION

Our data show that eCIRP plays an important role in RIR-induced CKD. Treatment with C23 decreased renal inflammation, alleviated chronic renal injury and fibrosis, and inhibited ferroptosis in the RIR-induced CKD mice.

An anti-eCIRP strategy for necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disease characterized by intestinal inflammation and injury, with high mortality risk. Extracellular cold-inducible RNA-binding protein (eCIRP) is a recently discovered damage-associated molecular pattern that propagates inflammation and tissue injury; however, the role of eCIRP in NEC remains unknown. We hypothesize that eCIRP exacerbates NEC pathogenesis and the novel eCIRP-scavenging peptide, milk fat globule-epidermal growth factor-factor VIII (MFG-E8)-derived oligopeptide 3 (MOP3), attenuates NEC severity, serving as a new therapeutic strategy to treat NEC.

METHODS

Stool samples from premature neonates were collected prospectively and eCIRP levels were measured. Wild-type (WT) and CIRP-/- mouse pups were subjected to NEC utilizing a combination of hypoxia and hypercaloric formula orogastric gavage with lipopolysaccharide supplementation. In parallel, WT pups were treated with MOP3 or vehicle. Endpoints including NEC severity, intestinal injury, barrier dysfunction, lung injury, and overall survival were determined.

RESULTS

Stool samples from NEC neonates had elevated eCIRP levels compared to healthy age-matched controls (p < 0.05). CIRP-/- pups were significantly protected from NEC severity, intestinal injury, bowel inflammation, intestinal barrier dysfunction, lung injury, and systemic inflammation. NEC survival was 100% for CIRP-/- pups compared to 65% for WT (p < 0.05). MOP3 treatment recapitulated the benefits afforded by CIRP-knockdown, preventing NEC severity, improving inflammatory profiles, and attenuating organ injury. MOP3 treatment improved NEC survival to 80% compared to 50% for vehicle treatment (p < 0.05).

CONCLUSIONS

eCIRP exacerbates NEC evidenced by protection with CIRP-deficiency and administration of MOP3, a CIRP-directed therapeutic, in a murine model. Thus, eCIRP is a novel target with human relevance, and MOP3 is a promising treatment for lethal NEC.

The Novel MFG-E8-derived Oligopeptide, MOP3, Improves Outcomes in a Preclinical Murine Model of Neonatal Sepsis

INTRODUCTION

Neonatal sepsis is a devastating inflammatory condition that remains a leading cause of morbidity and mortality. Milk fat globule-EGF-factor VIII (MFG-E8) is a glycoprotein that reduces inflammation, whereas extracellular cold-inducible RNA binding protein (eCIRP) worsens inflammation. This study aimed to determine the therapeutic potential of a novel MFG-E8-derived oligopeptide 3 (MOP3) designed to clear eCIRP and protect against inflammation, organ injury, and mortality in neonatal sepsis.

METHODS

C57BL6 mouse pups were injected intraperitoneally with cecal slurry (CS) and treated with MOP3 (20 μg/g) or vehicle. 10 h after injection, blood, lungs, and intestines were collected for analyses, and in a 7-day experiment, pups were monitored for differences in mortality.

RESULTS

MOP3 treatment protected septic pups from inflammation by reducing eCIRP, IL-6, TNFα, and LDH. MOP3 reduced lung and intestinal inflammation and injury as assessed by reductions in tissue mRNA levels of inflammatory markers, histopathologic injury, and apoptosis in lung and intestines. MOP3 also significantly improved 7-day overall survival for CS-septic mouse pups compared to vehicle (75% vs. 46%, respectively).

CONCLUSION

Deriving from MFG-E8 and designed to clear eCIRP, MOP3 protects against sepsis-induced inflammation, organ injury, and mortality in a preclinical model of neonatal sepsis, implicating it as an exciting potential new therapeutic.

LEVEL OF EVIDENCE

Level 1.

Chromatin as alarmins in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disease primarily affecting premature neonates, marked by poorly understood pro-inflammatory signaling cascades. Recent advancements have shed light on a subset of endogenous molecular patterns, termed chromatin-associated molecular patterns (CAMPs), which belong to the broader category of damage-associated molecular patterns (DAMPs). CAMPs play a crucial role in recognizing pattern recognition receptors and orchestrating inflammatory responses. This review focuses into the realm of CAMPs, highlighting key players such as extracellular cold-inducible RNA-binding protein (eCIRP), high mobility group box 1 (HMGB1), cell-free DNA, neutrophil extracellular traps (NETs), histones, and extracellular RNA. These intrinsic molecules, often perceived as foreign, have the potential to trigger immune signaling pathways, thus contributing to NEC pathogenesis. In this review, we unravel the current understanding of the involvement of CAMPs in both preclinical and clinical NEC scenarios. We also focus on elucidating the downstream signaling pathways activated by these molecular patterns, providing insights into the mechanisms that drive inflammation in NEC. Moreover, we scrutinize the landscape of targeted therapeutic approaches, aiming to mitigate the impact of tissue damage in NEC. This in-depth exploration offers a comprehensive overview of the role of CAMPs in NEC, bridging the gap between preclinical and clinical insights.

Regulation of cold-inducible RNA-binding protein (CIRBP) in response to cellular stresses

Cold-inducible RNA-Binding Protein (CIRBP) is a general stress-response factor in vertebrates harboring two domains: an RNA-recognition motif and a regulatory domain rich in RG/RGG motifs. CIRBP has been described to bind mRNAs upon various stress conditions (cold, infections, UV, hypoxia …) and regulate their stability and translation. The proteins encoded by its targets are involved in key stress-responsive cellular pathways including apoptosis, inflammation, cell proliferation or translation, thus allowing their coordination. Due to its role in regulating central cellular functions, the expression of CIRBP is tightly controlled. We review here current understanding of the multiple mechanistic layers affecting CIRBP expression and function. Beyond transcriptional regulation by cold-responsive elements and the use of alternative promoters and transcription start sites, CIRBP undergoes various alternative splicing (AS) events which, depending on conditions, modulate the stability of CIRBP transcripts and/or impact the sequence of the encoded polypeptide. Typically, whilst CIRBP expression is induced in the context of hypothermia or viral infection, AS events preferentially address alternative isoforms towards mRNA degradation pathways in response to heat stress or to bacterial-secreted pore forming toxins. Post-translational modifications of CIRBP, mostly in its RGG domain, also condition CIRBP subcellular localization and access to its targets, thereby promoting or inhibiting their expression. For instance, phosphorylation and methylation events gate CIRBP nuclear to cytoplasmic translocation and control its recruitment to stress granules. Considering the therapeutic potential of modulating the expression and function of this central player in stress responses, a fine understanding of CIRBP regulation mechanisms deserves further attention.

A novel opsonic eCIRP inhibitor for lethal sepsis

Sepsis is a life-threatening inflammatory condition partly orchestrated by the release of various damage-associated molecular patterns such as extracellular cold-inducible RNA-binding protein (eCIRP). Despite advances in understanding the pathogenic role of eCIRP in inflammatory diseases, novel therapeutic strategies to prevent its excessive inflammatory response are lacking. Milk fat globule-epidermal growth factor-VIII (MFG-E8) is critical for the opsonic clearance of apoptotic cells, but its potential involvement in the removal of eCIRP was previously unknown. Here, we report that MFG-E8 can strongly bind eCIRP to facilitate αvβ3-integrin-dependent internalization and lysosome-dependent degradation of MFG-E8/eCIRP complexes, thereby attenuating excessive inflammation. Genetic disruption of MFG-E8 expression exaggerated sepsis-induced systemic accumulation of eCIRP and other cytokines, and consequently exacerbated sepsis-associated acute lung injury. In contrast, MFG-E8-derived oligopeptide recapitulated its eCIRP binding properties, and significantly attenuated eCIRP-induced inflammation to confer protection against sepsis. Our findings suggest a novel therapeutic approach to attenuate eCIRP-induced inflammation to improve outcomes of lethal sepsis.

PAMPs and DAMPs in Sepsis: A Review of Their Molecular Features and Potential Clinical Implications

Sepsis is a serious organ dysfunction caused by a dysregulated immune host reaction to a pathogen. The innate immunity is programmed to react immediately to conserved molecules, released by the pathogens (PAMPs), and the host (DAMPs). We aimed to review the molecular mechanisms of the early phases of sepsis, focusing on PAMPs, DAMPs, and their related pathways, to identify potential biomarkers. We included studies published in English and searched on PubMed® and Cochrane®. After a detailed discussion on the actual knowledge of PAMPs/DAMPs, we analyzed their role in the different organs affected by sepsis, trying to elucidate the molecular basis of some of the most-used prognostic scores for sepsis. Furthermore, we described a chronological trend for the release of PAMPs/DAMPs that may be useful to identify different subsets of septic patients, who may benefit from targeted therapies. These findings are preliminary since these pathways seem to be strongly influenced by the peculiar characteristics of different pathogens and host features. Due to these reasons, while initial findings are promising, additional studies are necessary to clarify the potential involvement of these molecular patterns in the natural evolution of sepsis and to facilitate their transition into the clinical setting.

Targeting of cold-inducible RNA-binding protein alleviates sepsis via alleviating inflammation, apoptosis and oxidative stress in heart

A systemic inflammatory response is observed in patients undergoing shock and sepsis. This study aimed to explore the effects of cold-inducible RNA-binding protein (CIRP) on sepsis-associated cardiac dysfunction and the underlying mechanism. In vivo and in vitro lipopolysaccharide (LPS)-induced sepsis models were established in mice and neonatal rat cardiomyocytes (NRCMs), respectively. CRIP expressions were increased in the mouse heart and NRCMs treated with LPS. CIRP knockdown alleviated LPS-induced decreases of left ventricular ejection fraction and fractional shortening. CIRP downregulation attenuated the increases of inflammatory factors in the LPS-induced septic mouse heart, and NRCMs. The enhanced oxidative stress in the LPS-induced septic mouse heart and NRCMs was suppressed after CIRP knockdown. By contrast, CIRP overexpression yielded the opposite results. Our current study indicates that the knockdown of CIRP protects against sepsis-induced cardiac dysfunction through alleviating inflammation, apoptosis and oxidative stress of cardiomyocytes.

Exosome-derived CIRP: An amplifier of inflammatory diseases

Cold-inducible RNA-binding protein (CIRP) is an intracellular stress-response protein and a type of damage-associated molecular pattern (DAMP) that responds to various stress stimulus by altering its expression and mRNA stability. Upon exposure to ultraviolet (UV) light or low temperature, CIRP get translocated from the nucleus to the cytoplasm through methylation modification and stored in stress granules (SG). During exosome biogenesis, which involves formation of endosomes from the cell membrane through endocytosis, CIRP also gets packaged within the endosomes along with DNA, and RNA and other proteins. Subsequently, intraluminal vesicles (ILVs) are formed following the inward budding of the endosomal membrane, turning the endosomes into multi-vesicle bodies (MVBs). Finally, the MVBs fuse with the cell membrane to form exosomes. As a result, CIRP can also be secreted out of cells through the lysosomal pathway as Extracellular CIRP (eCIRP). Extracellular CIRP (eCIRP) is implicated in various conditions, including sepsis, ischemia-reperfusion damage, lung injury, and neuroinflammation, through the release of exosomes. In addition, CIRP interacts with TLR4, TREM-1, and IL-6R, and therefore are involved in triggering immune and inflammatory responses. Accordingly, eCIRP has been studied as potential novel targets for disease therapy. C23 and M3, polypeptides that oppose eCIRP binding to its receptors, are beneficial in numerous inflammatory illnesses. Some natural molecules such as Luteolin and Emodin can also antagonize CIRP, which play roles similar to C23 in inflammatory responses and inhibit macrophage-mediated inflammation. This review aims to provide a better understanding on CIRP translocation and secretion from the nucleus to the extracellular space and the mechanisms and inhibitory roles of eCIRP in diverse inflammatory illnesses.

A chronotherapeutics-applicable multi-target therapeutics based on AI: Example of therapeutic hypothermia

Nowadays, the complexity of disease mechanisms and the inadequacy of single-target therapies in restoring the biological system have inevitably instigated the strategy of multi-target therapeutics with the analysis of each target individually. However, it is not suitable for dealing with the conflicts between targets or between drugs. With the release of high-precision protein structure prediction artificial intelligence, large-scale high-precision protein structure prediction and docking have become possible. In this article, we propose a multi-target drug discovery method by the example of therapeutic hypothermia (TH). First, we performed protein structure prediction for all protein targets of each group by AlphaFold2 and RoseTTAFold. Then, QuickVina 2 is used for molecular docking between the proteins and drugs. After docking, we use PageRank to rank single drugs and drug combinations of each group. The ePharmaLib was used for predicting the side effect targets. Given the differences in the weights of different targets, the method can effectively avoid inhibiting beneficial proteins while inhibiting harmful proteins. So it could minimize the conflicts between different doses and be friendly to chronotherapeutics. Besides, this method also has potential in precision medicine for its high compatibility with bioinformatics and promotes the development of pharmacogenomics and bioinfo-pharmacology.

Extracellular CIRP Upregulates Proinflammatory Cytokine Expression via the NF-kappaB and ERK1/2 Signaling Pathways in Psoriatic Keratinocytes

Psoriasis is a chronic inflammatory skin disease, and elevation of proinflammatory cytokine levels is a critical driver of the pathogenesis of psoriasis. Extracellular cold-inducible RNA-binding protein (eCIRP) has been shown to play a role in various acute and chronic inflammatory diseases. C23, a short peptide derived from CIRP, competitively binds CIRP receptors and reduces damage in inflammatory diseases. However, the effect of eCIRP in psoriasis has not been studied. In the present study, we investigated the role of eCIRP in the expression of proinflammatory cytokines in keratinocytes. Our data show that eCIRP expression was increased in the sera of psoriasis patients and imiquimod- (IMQ-) induced psoriatic mice and cells stimulated with proinflammatory cytokines (IL-1α, IL-17A, IL-22, oncostatin M, and TNF-α; mix M5). Recombinant human CIRP (rhCIRP) promoted the expression of the proinflammatory cytokines TNF-α, IL-6, and IL-8 and the activation of NF-kappaB (NF-κB) and ERK1/2 in cultured keratinocytes. We then found that the above effects of eCIRP could be blocked by C23 in both normal keratinocytes and M5-stimulated psoriatic keratinocytes. In addition, in vivo experiments revealed that C23 could effectively ameliorate IMQ-induced psoriatic dermatitis. TNF-α and IL-6 mRNA expressions were reduced in the skin lesions of mice with C23-treated IMQ-induced psoriasis, and this effect was accompanied by inhibition of the NF-κB and ERK1/2 signaling pathways. In summary, eCIRP plays an important role in the pathogenesis of psoriasis and may become a new target for psoriasis treatment.

Chromatin-Associated Molecular Patterns (CAMPs) in sepsis

Several molecular patterns have been identified that recognize pattern recognition receptors. Pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) are commonly used terminologies to classify molecules originating from pathogen and endogenous molecules, respectively, to heighten the immune response in sepsis. Herein, we focus on a subgroup of endogenous molecules that may be detected as foreign and similarly trigger immune signaling pathways. These chromatin-associated molecules, i.e., chromatin containing nuclear DNA and histones, extracellular RNA, mitochondrial DNA, telomeric repeat-containing RNA, DNA- or RNA-binding proteins, and extracellular traps, may be newly classified as chromatin-associated molecular patterns (CAMPs). Herein, we review the release of CAMPs from cells, their mechanism of action and downstream immune signaling pathways, and targeted therapeutic approaches to mitigate inflammation and tissue injury in inflammation and sepsis.

The role of Cold-Inducible RNA-binding protein in respiratory diseases

Cold‐inducible RNA‐binding protein (CIRP) is a stress‐response protein that is expressed in various types of cells and acts as an RNA chaperone, modifying the stability of its targeted mRNA. Intracellular CIRP could also be released into extracellular space and once released, extracellular CIRP (eCIRP) acts as a damage‐associated molecular pattern (DAMP) to induce and amplify inflammation. Recent studies have found that eCIRP could promote acute lung injury (ALI) via activation of macrophages, neutrophils, pneumocytes and lung vascular endothelial cells in context of sepsis, haemorrhagic shock, intestinal ischemia/reperfusion injury and severe acute pancreatitis. In addition, CIRP is also highly expressed in the bronchial epithelial cells and its expression is upregulated in the bronchial epithelial cells of patients with chronic obstructive pulmonary diseases (COPD) and rat models with chronic bronchitis. CIRP is a key contributing factor in the cold‐induced exacerbation of COPD by promoting the expression of inflammatory genes and hypersecretion of airway mucus in the bronchial epithelial cells. Besides, CIRP is also involved in regulating pulmonary fibrosis, as eCIRP could directly activate and induce an inflammatory phenotype in pulmonary fibroblast. This review summarizes the findings of CIRP investigation in respiratory diseases and the underlying molecular mechanisms.

Damage-Associated Molecular Patterns As Double-Edged Swords in Sepsis

Significance: Sepsis is defined as a life-threatening organ dysfunction caused by dysregulated host response to infection. This leads to an uncontrolled inflammatory response at the onset of infection, followed by immunosuppression. The development of a specific treatment modality for sepsis is still challenging, reflecting our inadequate understanding of its pathophysiology. Understanding the mechanism and transition of the early hyperinflammation to late stage of immunosuppression in sepsis is critical for developing sepsis therapeutics. Recent Advances: Damage-associated molecular patterns (DAMPs) are intracellular molecules and released upon tissue injury and cell death in sepsis. DAMPs are recognized by pattern recognition receptors to initiate inflammatory cascades. DAMPs not only elicit an inflammatory response but also they subsequently induce immunosuppression, both are equally important for exacerbating sepsis. Recent advances on a new DAMP, extracellular cold-inducible RNA-binding protein for fueling inflammation and immunosuppression in sepsis, have added a new avenue into the dual functions of DAMPs in sepsis. Critical Issues: The molecular modification of DAMPs and their binding to pattern recognition receptors transit dynamically by the cellular environment in pathophysiologic conditions. Correlation between the dynamic changes of the impacts of DAMPs and the clinical outcomes in sepsis still lacks adequate understanding. Here, we focus on the impacts of DAMPs that cause inflammation as well as induce immunosuppression in sepsis. We further discuss the therapeutic potential by targeting DAMPs to attenuate inflammation and immunosuppression for mitigating sepsis. Future Directions: Uncovering pathways of the transition from inflammation to immunosuppression of DAMPs is a potential therapeutic avenue for mitigating sepsis.

Postnatal Sepsis and Bronchopulmonary Dysplasia in Premature Infants: Mechanistic Insights into "New BPD"

Bronchopulmonary dysplasia (BPD) is a debilitating disease in premature infants resulting from lung injury that disrupts alveolar and pulmonary vascular development. Despite the use of lung-protective ventilation and targeted oxygen therapy, BPD rates have not significantly changed over the last decade. Recent evidence suggests that sepsis and conditions initiating the systemic inflammatory response syndrome in preterm infants are key risk factors for BPD. However, the mechanisms by which sepsis-associated systemic inflammation and microbial dissemination program aberrant lung development are not fully understood. Progress has been made within the last 5 years with the inception of animal models allowing mechanistic investigations into neonatal acute lung injury and alveolar remodeling due to endotoxemia and NEC. These recent studies begin to unravel the pathophysiology of early endothelial immune activation via pattern recognition receptors such as Toll Like Receptor 4 and disruption of critical lung developmental processes such as angiogenesis, extracellular matrix deposition, and ultimately alveologenesis. Here we review scientific evidence from preclinical models of neonatal sepsis-induced lung injury to new data emerging from clinical literature.

Extracellular CIRP Activates the IL-6Rα/STAT3/Cdk5 Pathway in Neurons

Extracellular cold-inducible RNA-binding protein (eCIRP) stimulates microglial inflammation causing neuronal damage during ischemic stroke and is a critical mediator of alcohol-induced cognitive impairment. However, the precise role of eCIRP in mediating neuroinflammation remains unknown. In this study, we report that eCIRP activates neurotoxic cyclin-dependent kinase-5 (Cdk5)/p25 through the induction of IL-6Rα/STAT3 pathway in neurons. Amyloid β (Aβ)-mediated neuronal stress, which is associated with Alzheimer's disease, increased the levels of eCIRP released from BV2 microglial cells. The released eCIRP levels from BV2 cells increased 3.2-fold upon stimulation with conditioned medium from Neuro-2a (N2a) cells containing Aβ compared to control N2a supernatant in a time-dependent manner. Stimulation of N2a cells and primary neurons with eCIRP upregulated the neuronal Cdk5 activator p25 expression in a dose- and time-dependent manner. eCIRP directly induced neuronal STAT3 phosphorylation and p25 increase via its novel receptor IL-6Rα. Next, we showed using surface plasmon resonance that eCIRP-derived peptide C23 inhibited the binding of eCIRP to IL-6Rα at 25 μM, with a 40-fold increase in equilibrium dissociation constant (K_d) value (from 8.08 × 10^-8 M to 3.43 × 10^-6 M), and completely abrogated the binding at 50 μM. Finally, C23 reversed the eCIRP-induced increase in neuronal STAT3 phosphorylation and p25 levels. In conclusion, the current study demonstrates that the upregulation of neuronal IL-6Rα/STAT3/Cdk5 pathway is a key mechanism of eCIRP's role in neuroinflammation and that C23 as a potent inhibitor of this pathway has translational potential in neurodegenerative pathologies controlled by eCIRP.

Luteolin Suppresses Sepsis-Induced Cold-Inducible RNA-Binding Protein Production and Lung Injury in Neonatal Mice

Neonatal sepsis is a life-threatening inflammatory condition. Extracellular cold-inducible RNA-binding protein (CIRP), a proinflammatory mediator, plays a critical role in the pathogenesis of sepsis-induced lung injury in neonates. Luteolin, a polyphenolic flavonoid, has potent anti-inflammatory properties. However, the effects of luteolin on CIRP production and neonatal sepsis-induced lung injury remained unknown. We therefore hypothesize that treatment with luteolin suppresses CIRP production and attenuates lung injury in neonatal sepsis. To study this, sepsis was induced in C57BL/6J mouse pups (5-7 days) by intraperitoneal cecal slurry injection (CSI). One hour after CSI, luteolin (10 mg/kg body weight) or vehicle (normal saline) was administered through intraperitoneal injection. CIRP mRNA and protein were determined and lung injury was assessed at 10 h after CSI. Our results showed that administration of luteolin decreased CIRP mRNA and protein, improved lung architecture, reduced lung edema, and apoptosis after CSI. To examine the direct effect of luteolin on CIRP production, peritoneal macrophages were isolated from neonatal mice and stimulated with 100 ng/mL LPS with or without the presence of luteolin. The result indicates that luteolin directly inhibited LPS-induced CIRP production in neonatal macrophages. In addition, luteolin also downregulated hypoxia-inducible factor-1α (HIF-1α) and NOD-like receptor 3 (NLRP3) expression in septic neonates and in LPS-stimulated neonatal macrophages. In conclusion, administration of luteolin suppresses CIRP production and attenuates lung injury in neonatal sepsis. The beneficial effect of luteolin may be related to downregulation of HIF-1α and NLRP3 expression in neonatal macrophages. Luteolin may be developed as an adjunctive therapy for neonatal sepsis.

A Prediction Model of Extubation Failure Risk in Preterm Infants

Objectives: This study aimed to identify variables and develop a prediction model that could estimate extubation failure (EF) in preterm infants. Study Design: We enrolled 128 neonates as a training cohort and 58 neonates as a validation cohort. They were born between 2015 and 2020, had a gestational age between 25^0/7 and 29^6/7 weeks, and had been treated with mechanical ventilation through endotracheal intubation (MVEI) because of acute respiratory distress syndrome. In the training cohort, we performed univariate logistic regression analysis along with stepwise discriminant analysis to identify EF predictors. A monogram based on five predictors was built. The concordance index and calibration plot were used to assess the efficiency of the nomogram in the training and validation cohorts. Results: The results of this study identified a 5-min Apgar score, early-onset sepsis, hemoglobin before extubation, pH before extubation, and caffeine administration as independent risk factors that could be combined for accurate prediction of EF. The EF nomogram was created using these five predictors. The area under the receiver operator characteristic curve was 0.824 (95% confidence interval 0.748-0.900). The concordance index in the training and validation cohorts was 0.824 and 0.797, respectively. The calibration plots showed high coherence between the predicted probability of EF and actual observation. Conclusions: This EF nomogram was a useful model for the precise prediction of EF risk in preterm infants who were between 25^0/7 and 29^6/7 weeks' gestational age and treated with MVEI because of acute respiratory distress syndrome.

Cecal Slurry Injection in Neonatal and Adult Mice

Studying the pathophysiology of sepsis still requires animal models, and the mouse remains the most commonly used species. Here we discuss the "cecal slurry" (CS) model of polymicrobial, peritoneal sepsis and compare and contrast it to other commonly used methods. Among the different murine models of sepsis, cecal ligation and puncture (CLP), and not the CS, is often considered the "gold standard" to induce polymicrobial sepsis in laboratory animals. CLP is a well-described model involving a simple surgical procedure that closely mimics the clinical course of intra-abdominal sepsis. However, CLP may not be an option for experiments involving newborn pups, where the cecum is indistinguishable from small bowel, where differences in microbiome content may affect the experiment, or where surgical procedures/anesthesia exposure needs to be limited. An important alternative method is the CS model, involving the intraperitoneal injection of cecal contents from a donor animal into the peritoneal cavity of a recipient animal to induce polymicrobial sepsis. Furthermore, CS is an effective alternative model of intraperitoneal polymicrobial sepsis in adult mice and can now be considered the "gold standard" for experiments in neonatal mice.

Targeting the eCIRP/TREM-1 interaction with a small molecule inhibitor improves cardiac dysfunction in neonatal sepsis

Background

Neonatal sepsis and the associated myocardial dysfunction remain a leading cause of infant mortality. Extracellular cold-inducible RNA-binding protein (eCIRP) acts as a ligand of triggering receptor expressed on myeloid cells-1 (TREM-1). M3 is a small CIRP-derived peptide that inhibits the eCIRP/TREM-1 interaction. We hypothesize that the eCIRP/TREM-1 interaction in cardiomyocytes contributes to sepsis-induced cardiac dysfunction in neonatal sepsis, while M3 is cardioprotective.

Methods

Serum was collected from neonates in the Neonatal Intensive Care Unit (NICU). 5–7-day old C57BL/6 mouse pups were used in this study. Primary murine neonatal cardiomyocytes were stimulated with recombinant murine (rm) CIRP with M3. TREM-1 mRNA and supernatant cytokine levels were assayed. Mitochondrial oxidative stress, ROS, and membrane potential were assayed. Neonatal mice were injected with rmCIRP and speckle-tracking echocardiography was conducted to measure cardiac strain. Sepsis was induced by i.p. cecal slurry. Mouse pups were treated with M3 or vehicle. After 16 h, echocardiography was performed followed by euthanasia for tissue analysis. A 7-day survival study was conducted.

Results

Serum eCIRP levels were elevated in septic human neonates. rmCIRP stimulation of cardiomyocytes increased TREM-1 gene expression. Stimulation of cardiomyocytes with rmCIRP upregulated TNF-α and IL-6 in the supernatants, while this upregulation was inhibited by M3. Stimulation of cardiomyocytes with rmCIRP resulted in a reduction in mitochondrial membrane potential (MMP) while M3 treatment returned MMP to near baseline. rmCIRP caused mitochondrial calcium overload; this was inhibited by M3. rmCIRP injection impaired longitudinal and radial cardiac strain. Sepsis resulted in cardiac dysfunction with a reduction in cardiac output and left ventricular end diastolic diameter. Both were improved by M3 treatment. Treatment with M3 attenuated serum, cardiac, and pulmonary levels of pro-inflammatory cytokines compared to vehicle-treated septic neonates. M3 dramatically increased sepsis survival.

Conclusions

Inhibition of eCIRP/TREM-1 interaction with M3 is cardioprotective, decreases inflammation, and improves survival in neonatal sepsis.

Trial registration Retrospectively registered.

Potential Role of Extracellular CIRP in Alcohol-Induced Alzheimer's Disease

Alzheimer's disease (AD) is the sixth leading cause of death in the USA and the most common form of neurodegenerative dementia. In AD, microtubule-associated protein tau becomes pathologically phosphorylated and aggregated, leading to neurodegeneration and the cognitive deficits that characterize the disease. Prospective studies have shown that frequent and heavy alcohol drinking is linked to early onset and increased severity of AD. The precise mechanisms of how alcohol leads to AD, however, remain poorly understood. We have shown that extracellular cold-inducible RNA-binding protein (eCIRP) is a critical mediator of memory impairment induced by exposure to binge-drinking levels of alcohol, leading us to reason that eCIRP may be a key player in the relationship between alcohol and AD. In this review, we first discuss the mechanisms by which alcohol promotes AD. We then review eCIRP's role as a critical mediator of acute alcohol intoxication-induced neuroinflammation and cognitive impairment. Next, we explore the potential contribution of eCIRP to the development of alcohol-induced AD by targeting tau phosphorylation. We also consider the effects of eCIRP on neuronal death and neurogenesis linking alcohol with AD. Finally, we highlight the importance of further studying eCIRP as a critical molecular mechanism connecting acute alcohol intoxication, neuroinflammation, and tau phosphorylation in AD along with the potential of therapeutically targeting eCIRP as a new strategy to attenuate alcohol-induced AD.

Alcohol Intoxication and Cognition: Implications on Mechanisms and Therapeutic Strategies

Binge alcohol drinking is highly prevalent in young adults and results in 30% deaths per year in young males. Binge alcohol drinking or acute alcohol intoxication is a risk factor for developing alcohol use disorder (AUD). Three FDA approved drugs are currently in use as therapy for AUD; however, all of them have contra-indications and limitations. Structural brain imaging studies in alcoholics have shown defects in the brain regions involved in memory, cognition and emotional processing. Positron emission tomography (PET) using radiotracers (e.g., 18FDG) and measuring brain glucose metabolism have demonstrated diagnostic and prognostic utility in evaluating patients with cognitive impairment. Using PET imaging, only a few exclusive human studies have addressed the relationship between alcohol intoxication and cognition. Those studies indicate that alcohol intoxication causes reduction in brain activity. Consistent with prior findings, a recent study by us showed that acute alcohol intoxication reduced brain activity in the cortical and subcortical regions including the temporal lobe consisting the hippocampus. Additionally, we have observed a strong correlation between reduction in metabolic activity and spatial cognition impairment in the hippocampus after binge alcohol exposure. We have also demonstrated the involvement of a stress response protein, cold inducible RNA binding protein (CIRP), as a potential mechanistic mediator in acute alcohol intoxication. In this review, we will first discuss in detail prior human PET imaging studies on alcohol intoxication as well as our recent study on acute alcohol intoxication, and review the existing literature on potential mechanisms of acute alcohol intoxication-induced cognitive impairment and therapeutic strategies to mitigate these impairments. Finally, we will highlight the importance of studying brain regions as part of a brain network in delineating the mechanism of acute alcohol intoxication-induced cognitive impairment to aid in the development of therapeutics for such indication.

DAMPs and NETs in Sepsis

Sepsis is a deadly inflammatory syndrome caused by an exaggerated immune response to infection. Much has been focused on host response to pathogens mediated through the interaction of pathogen-associated molecular patterns (PAMPs) and pattern recognition receptors (PRRs). PRRs are also activated by host nuclear, mitochondrial, and cytosolic proteins, known as damage-associated molecular patterns (DAMPs) that are released from cells during sepsis. Some well described members of the DAMP family are extracellular cold-inducible RNA-binding protein (eCIRP), high mobility group box 1 (HMGB1), histones, and adenosine triphosphate (ATP). DAMPs are released from the cell through inflammasome activation or passively following cell death. Similarly, neutrophil extracellular traps (NETs) are released from neutrophils during inflammation. NETs are webs of extracellular DNA decorated with histones, myeloperoxidase, and elastase. Although NETs contribute to pathogen clearance, excessive NET formation promotes inflammation and tissue damage in sepsis. Here, we review DAMPs and NETs and their crosstalk in sepsis with respect to their sources, activation, release, and function. A clear grasp of DAMPs, NETs and their interaction is crucial for the understanding of the pathophysiology of sepsis and for the development of novel sepsis therapeutics.

A novel target to reduce microglial inflammation and neuronal damage after deep hypothermic circulatory arrest

BACKGROUND

Neuroinflammation acts as a contributor to neurologic deficits after deep hypothermic circulatory arrest. However, the molecular mechanism remains unclear. This study postulates that cold-inducible RNA-binding protein can promote deep hypothermic circulatory arrest-induced neuroinflammation.

METHODS

Rats were randomly assigned into 3 groups (n = 5, each group): sham group, deep hypothermic circulatory arrest group, and deep hypothermic circulatory arrest + Cirp^-/- group (Cirp^-/- group). Murine microglial BV2 cells were administered by adeno-associated viral vectors containing cold-inducible RNA-binding protein small interference RNA or negative control small interference RNA at 2 days before 4-hour oxygen-glucose deprivation at 18°C. Microglial activation, cell death, neuroinflammation, and related protein expression were assessed in tissue samples and cell cultures.

RESULTS

Cold-inducible RNA-binding protein was elevated along with evident neuroinflammation and neuronal damage in rats exposed to deep hypothermic circulatory arrest. In Cirp^-/- rats, histologic injury (3.00 [interquartile range, 2.00-3.00] vs 1.00 [interquartile range, 1.00-1.50] neuropathological score, P < .001) and microglial activation (40 ± 4 vs 13 ± 7 CA1 area, P < .001) were alleviated after deep hypothermic circulatory arrest. With RNA-sequencing analysis, this associated with reduction of key proinflammatory cytokines induced by inhibiting Brd2-NF-κB signals. In BV2 cells treated with small interference RNA-cold-inducible RNA-binding protein, similar protective effects were observed, including decreased proinflammatory cytokines and cytotoxicity. Brd2-NF-κB signals were confirmed by the addition of Brd2 inhibitor JQ1. Notably, the conditioned medium from BV2 cells transfected with small interference RNA cold-inducible RNA-binding protein significantly reduced apoptosis in neural SH-SY5Y cells after oxygen-glucose deprivation, which was similar to that after JQ1 administration.

CONCLUSIONS

Enhanced cold-inducible RNA-binding protein in microglia aggravates neuronal injury by promoting the release of proinflammatory cytokines, which might be mediated through Brd2-NF-κB signals during deep hypothermic circulatory arrest.