Single-cell immune profiling of mouse liver aging reveals Cxcl2+ macrophages recruit neutrophils to aggravate liver injury.

BACKGROUND AND AIMS: Immune cells play a crucial role in liver aging. However, the impact of dynamic changes in the local immune microenvironment on age-related liver injury remains poorly understood. We aimed to characterize intrahepatic immune cells at different ages to investigate key mechanisms associated with liver aging. APPROACH AND RESULTS: We carried out single-cell RNA sequencing on mouse liver tissues at 4 different ages, namely, the newborn, suckling, young, and aged stages. The transcriptomic landscape, cellular classification, and intercellular communication were analyzed. We confirmed the findings by multiplex immunofluorescence staining, flow cytometry, in vitro functional experiments, and chimeric animal models. Nine subsets of 89,542 immune cells with unique properties were identified, of which Cxcl2+ macrophages within the monocyte/macrophage subset were preferentially enriched in the aged liver. Cxcl2+ macrophages presented a senescence-associated secretory phenotype and recruited neutrophils to the aged liver through the CXCL2-CXCR2 axis. Through the secretion of IL-1ß and TNF-α, Cxcl2+ macrophages stimulated neutrophil extracellular traps formation. Targeting the CXCL2-CXCR2 axis limited the neutrophils migration toward the liver and attenuated age-related liver injury. Moreover, the relationship between Cxcl2+ macrophages and neutrophils in age-related liver injury was further validated by human liver transplantation samples. CONCLUSIONS: This in-depth study illustrates that the mechanism of Cxcl2+ macrophage-driven neutrophil activation involves the CXCL2-CXCR2 axis and provides a potential therapeutic strategy for age-related liver injury.

Combined inhibition of surface CD51 and γ-secretase-mediated CD51 cleavage improves therapeutic efficacy in experimental metastatic hepatocellular carcinoma.

BACKGROUND & AIMS: Integrin αv (ITGAV, CD51) is regarded as a key component in multiple stages of tumor progression. However, the clinical failure of cilengitide, a specific inhibitor targeting surface CD51, suggests the importance of yet-unknown mechanisms by which CD51 promotes tumor progression. METHODS: In this study, we used several hepatocellular carcinoma (HCC) cell lines and murine hepatoma cell lines. To investigate the role of CD51 on HCC progression, we used a 3D invasion assay and in vivo bioluminescence imaging. We used periostin-knockout transgenic mice to uncover the role of the tumor microenvironment on CD51 cleavage. Moreover, we used several clinically relevant HCC models, including patient-derived organoids and patient-derived xenografts, to evaluate the therapeutic efficacy of cilengitide in combination with the γ-secretase inhibitor LY3039478. RESULTS: We found that CD51 could undergo transmembrane cleavage by γ-secretase to produce a functional intracellular domain (CD51-ICD). The cleaved CD51-ICD facilitated HCC invasion and metastasis by promoting the transcription of oxidative phosphorylation-related genes. Furthermore, we identified cancer-associated fibroblast-derived periostin as the major driver of CD51 cleavage. Lastly, we showed that cilengitide-based therapy led to a dramatic therapeutic effect when supplemented with LY3039478 in both patient-derived organoid and xenograft models. CONCLUSIONS: In summary, we revealed previously unrecognized mechanisms by which CD51 is involved in HCC progression and uncovered the underlying cause of cilengitide treatment failure, as well as providing evidence supporting the translational prospects of combined CD51-targeted therapy in the clinic. IMPACT AND IMPLICATIONS: Integrin αv (CD51) is a widely recognized pro-tumoral molecule that plays a crucial role in various stages of tumor progression, making it a promising therapeutic target. However, despite early promising results, cilengitide, a specific antagonist of CD51, failed in a phase III clinical trial. This prompted further investigation into the underlying mechanisms of CD51's effects. This study reveals that the γ-secretase complex directly cleaves CD51 to produce an intracellular domain (CD51-ICD), which functions as a pro-tumoral transcriptional regulator and can bypass the inhibitory effects of cilengitide by entering the nucleus. Furthermore, the localization of CD51 in the nucleus is significantly associated with the prognosis of patients with HCC. These findings provide a theoretical basis for re-evaluating cilengitide in clinical settings and highlight the importance of identifying a more precise patient subpopulation for future clinical trials targeting CD51.

Expeditious chemical synthesis of xylomannans disproves the proposed antifreeze activities.

Cold-adapted species are able to generate cryoprotective proteins and glycoproteins to prevent freezing damage. The [→4)-ß-D-Manp-(1→4)-ß-D-Xylp-(1→] n xylomannan from the Alaska beetle Upis ceramboides was disclosed by Walters and co-workers in 2009 as the first glycan-based antifreeze agent, which was later reported to be found in diverse taxa. Here, we report the rapid synthesis of four types of xylomannans, including the proposed antifreeze xylomannan up to a 64-mer (Type I), the regioisomeric [→3)-ß-D-Manp-(1→4)-ß-D-Xylp-(1→] n 16-mer (Type II), the diastereomeric [→4)-ß-L-Manp-(1→4)-ß-D-Xylp-(1→] n 16-mer (Type III) and the block-wise [→4)-ß-D-Manp-(1→] m [→4)-ß-D-Xylp-(1→] n 32-mer (Type IV), by employing a strategic iterative exponential glycan growth (IEGG) process. The nuclear magnetic resonance spectral data of the alleged natural xylomannan are in accordance only to those of the block-wise Type IV glycan and none of these synthetic xylomannans has been found to be capable of inducing thermal hysteresis. These results disprove the previous reports about the natural occurrence of antifreeze xylomannans.

Cold-induced FOXO1 nuclear transport aids cold survival and tissue storage.

Cold-induced injuries severely limit opportunities and outcomes of hypothermic therapies and organ preservation, calling for better understanding of cold adaptation. Here, by surveying cold-altered chromatin accessibility and integrated CUT&Tag/RNA-seq analyses in human stem cells, we reveal forkhead box O1 (FOXO1) as a key transcription factor for autonomous cold adaptation. Accordingly, we find a nonconventional, temperature-sensitive FOXO1 transport mechanism involving the nuclear pore complex protein RANBP2, SUMO-modification of transporter proteins Importin-7 and Exportin-1, and a SUMO-interacting motif on FOXO1. Our conclusions are supported by cold survival experiments with human cell models and zebrafish larvae. Promoting FOXO1 nuclear entry by the Exportin-1 inhibitor KPT-330 enhances cold tolerance in pre-diabetic obese mice, and greatly prolongs the shelf-life of human and mouse pancreatic tissues and islets. Transplantation of mouse islets cold-stored for 14 days reestablishes normoglycemia in diabetic mice. Our findings uncover a regulatory network and potential therapeutic targets to boost spontaneous cold adaptation.

FTO deficiency in older livers exacerbates ferroptosis during ischaemia/reperfusion injury by upregulating ACSL4 and TFRC.

Older livers are more prone to hepatic ischaemia/reperfusion injury (HIRI), which severely limits their utilization in liver transplantation. The potential mechanism remains unclear. Here, we demonstrate older livers exhibit increased ferroptosis during HIRI. Inhibiting ferroptosis significantly attenuates older HIRI phenotypes. Mass spectrometry reveals that fat mass and obesity-associated gene (FTO) expression is downregulated in older livers, especially during HIRI. Overexpressing FTO improves older HIRI phenotypes by inhibiting ferroptosis. Mechanistically, acyl-CoA synthetase long chain family 4 (ACSL4) and transferrin receptor protein 1 (TFRC), two key positive contributors to ferroptosis, are FTO targets. For ameliorative effect, FTO requires the inhibition of Acsl4 and Tfrc mRNA stability in a m6A-dependent manner. Furthermore, we demonstrate nicotinamide mononucleotide can upregulate FTO demethylase activity, suppressing ferroptosis and decreasing older HIRI. Collectively, these findings reveal an FTO-ACSL4/TFRC regulatory pathway that contributes to the pathogenesis of older HIRI, providing insight into the clinical translation of strategies related to the demethylase activity of FTO to improve graft function after older donor liver transplantation.

Mesenchymal Stem Cell Membrane-Camouflaged Liposomes for Biomimetic Delivery of Cyclosporine A for Hepatic Ischemia-Reperfusion Injury Prevention.

Hepatic ischemia-reperfusion injury (HIRI) is a prevalent issue during liver resection and transplantation, with currently no cure or FDA-approved therapy. A promising drug, Cyclosporin A (CsA), ameliorates HIRI by maintaining mitochondrial homeostasis but has systemic side effects due to its low bioavailability and high dosage requirements. This study introduces a biomimetic CsA delivery system that directly targets hepatic lesions using mesenchymal stem cell (MSC) membrane-camouflaged liposomes. These hybrid nanovesicles (NVs), leveraging MSC-derived proteins, demonstrate efficient inflammatory chemotaxis, transendothelial migration, and drug-loading capacity. In a HIRI mouse model, the biomimetic NVs accumulated at liver injury sites entered hepatocytes, and significantly reduced liver damage and restore function using only one-tenth of the CsA dose typically required. Proteomic analysis verifies the protection mechanism, which includes reactive oxygen species inhibition, preservation of mitochondrial integrity, and reduced cellular apoptosis, suggesting potential for this biomimetic strategy in HIRI intervention.

5-aminolevulinate and CHIL3/CHI3L1 treatment amid ischemia aids liver metabolism and reduces ischemia-reperfusion injury.

Rationale: Liver resection and transplantation surgeries are accompanied by hepatic ischemia-reperfusion (HIR) injury that hampers the subsequent liver recovery. Given that the liver is the main organ for metabolism and detoxification, ischemia-reperfusion in essence bestows metabolic stress upon the liver and disrupts local metabolic and immune homeostasis. Most of the recent and current research works concerning HIR have been focusing on addressing HIR-induced hepatic injury and inflammation, instead of dealing with the metabolic reprogramming and restoration of redox homeostasis. As our previous work uncovers the importance of 5-aminolevulinate (5-ALA) synthesis during stress adaptation, here we evaluate the effects of supplementing 5-ALA to mitigate HIR injury. Methods: 5-ALA was supplemented into the mice or cultured cells during the ischemic or oxygen-glucose deprivation (OGD) phase. Following reperfusion or reoxygenation, cellular metabolism and energy homeostasis, mitochondrial production of reactive oxygen species (ROS) and transcriptomic changes were evaluated in HIR mouse models or cultured hepatocytes and macrophages. Liver injury, hepatocytic functional tests, and macrophagic M1/M2 polarization were assessed. Results: Dynamic changes in the expression of key enzymes in 5-ALA metabolism were first confirmed in donor and mouse liver samples following HIR. Supplemented 5-ALA modulated mouse hepatic lipid metabolism and reduced ATP production in macrophages following HIR, resulting in elevation of anti-inflammatory M2 polarization. Mechanistically, 5-ALA down-regulates macrophagic chemokine receptor CX3CR1 via the repression of RelA following OGD and reoxygenation (OGD/R). Cx3cr1 KO mice demonstrated milder liver injuries and more macrophage M2 polarization after HIR. M2 macrophage-secreted chitinase-like protein 3 (CHIL3; CHI3L1 in human) is an important HIR-induced effector downstream of CX3CR1 deficiency. Addition of CHIL3/CHI3L1 alone improved hepatocellular metabolism and reduced OGD/R-inflicted injuries in cultured mouse and human hepatocytes. Combined treatment with 5-ALA and CHIL3 during the ischemic phase facilitated lipid metabolism and ATP production in the mouse liver following HIR. Conclusion: Our results reveal that supplementing 5-ALA promotes macrophagic M2 polarization via downregulation of RelA and CX3CR1 in mice following HIR, while M2 macrophage-produced CHIL3/CHI3L1 also manifests beneficial effects to the recovery of hepatic metabolism. 5-ALA and CHIL3/CHI3L1 together mitigate HIR-induced mitochondrial dysfunction and hepatocellular injuries, which may be developed into safe and effective clinical treatments to attenuate HIR injuries.

Synergy of 5-aminolevulinate supplement and CX3CR1 suppression promotes liver regeneration via elevated IGF-1 signaling.

Inadequate remnant volume and regenerative ability of the liver pose life-threatening risks to patients after partial liver transplantation (PLT) or partial hepatectomy (PHx), while few clinical treatments focus on safely accelerating regeneration. Recently, we discovered that supplementing 5-aminolevulinate (5-ALA) improves liver cold adaptation and functional recovery, leading us to uncover a correlation between 5-ALA metabolic activities and post-PLT recovery. In a mouse 2/3 PHx model, 5-ALA supplements enhanced liver regeneration, promoting infiltration and polarization of anti-inflammatory macrophages via P53 signaling. Intriguingly, chemokine receptor CX3CR1 functions to counterbalance these effects. Genetic ablation or pharmacological inhibition of CX3CR1 (AZD8797; phase II trial candidate) augmented the macrophagic production of insulin-like growth factor 1 (IGF-1) and subsequent hepatocyte growth factor (HGF) production by hepatic stellate cells. Thus, short-term treatments with both 5-ALA and AZD8797 demonstrated pro-regeneration outcomes superior to 5-ALA-only treatments in mice after PHx. Overall, our findings may inspire safe and effective strategies to better treat PLT and PHx patients.

MSC-derived extracellular vesicles as nanotherapeutics for promoting aged liver regeneration.

Aging is one of the critical factors to impair liver regeneration leading to a high incidence of severe complications after hepatic surgery in the elderly population without any effective treatment for clinical administration. As cell-free nanotherapeutics, mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have been demonstrated the therapeutic potentials on liver diseases. However, the effects of MSC-EVs on the proliferation of aged hepatocytes are largely unclear. In this study, we found MSCs could reduce the expression of senescence-associated markers in the liver and stimulate its regeneration in aged mice after receiving a two-thirds partial hepatectomy (PHx) through their secreted MSC-EVs. Using RNA-Seq and AAV9 vector, we mechanistically found that these effects of UC-MSC-EVs partially attributed to inducing Atg4B-related mitophagy. This effect repairs the mitochondrial status and functions of aged hepatocytes to promote their proliferation. And protein mass spectrum analysis uncovered that DEAD-Box Helicase 5 (DDX5) enriches in UC-MSC-EVs, which interacts with E2F1 to facilitate its nuclear translocation for activating the expression of Atg4B. Collectively, our data show that MSC-EVs act nanotherapeutic potentials in anti-senescence and promoting regeneration of aged liver by transferring DDX5 to regulate E2F1-Atg4B signaling pathway that induce mitophagy, which highlights the clinical application valuation of MSC-EVs for preventing severe complications in aged population receiving liver surgery.

Extracellular vesicles derived from mesenchymal stromal cells as nanotherapeutics for liver ischaemia-reperfusion injury by transferring mitochondria to modulate the formation of neutrophil extracellular traps.

As nanotherapeutics, mesenchymal stromal cell-derived extracellular vesicles (MSC-EVs) are considered a potent alternative for whole-cell therapy and are gradually entering the clinical field of liver diseases. In this study, neutrophil extracellular traps (NETs) formation in liver tissue was verified as a critical factor for liver ischaemia-reperfusion injury (IRI) in both clinical samples and animal models. Human umbilical cord-derived MSC-EVs (hUC-MSC-EVs) might function to reduce the NETs formation and subsequently improve liver IRI. Mechanistically, we showed that hUC-MSC-EVs contain functional mitochondria that are transferred to intrahepatic neutrophils. This effect triggers mitochondrial fusion and subsequently restores the mitochondrial status and functions in neutrophils to reduce NETs formation. Collectively, our findings suggest that MSC-EVs exert a nanotherapeutic effect on inhibiting local NETs formation by transferring functional mitochondria to intrahepatic neutrophils and repairing their mitochondrial function, which highlights the therapeutic value of hUC-MSC-EVs for liver IRI.

MiR-34a regulates mitochondrial content and fat ectopic deposition induced by resistin through the AMPK/PPARα pathway in HepG2 cells.

Resistin is an adipocyte-derived cytokine and was named for its role in the development of insulin resistance. Increased serum resistin levels are also associated with steatohepatitis and non-alcoholic fatty liver disease. In a previous study, resistin was observed to reduce mitochondrial content and upregulate miR-34a significantly in the liver. In this study, male C57BL/6 mice were injected with agomir-34a or control agomir, and HepG2 cells were transfected with miR-34a mimics or inhibitors to assess their role in resistin-induced fat deposition. The overexpression of miR-34a increased liver and HepG2 cell TAG content, decreased mitochondrial content, changed mitochondrial morphology and impaired mitochondrial function. In contrast, a miR-34a inhibitor significantly restored the TAG content and mitochondrial transmembrane potential. A study of transcriptional regulation revealed that C/EBPß is essential for upregulating miR-34a by resistin. Furthermore, miR-34a inhibited the PPARα signaling pathway by binding to sites in the 3'UTR of AdipoR2 genes and the AMPK pathway. Consequently, this increased the fat content and decreased the mitochondrial content in HepG2 cells. This paper reveals a novel mechanism for mitochondrial regulation, which suggests that normal mitochondrial content and function is crucial for lipid metabolism in the liver.