Ovarian cancer is the deadliest gynecological malignant tumor and is known as the “silent killer”. PARP inhibitors are being increasingly used for their excellent efficacy in the treatment of ovarian cancer. While PARP inhibitors are known to interfere with DNA repair and cause DNA damage, the fates of cancer cells and associated metabolic features in response to PARP inhibition are not well characterized. We herein show that ovarian cancer cells treated with PARP inhibitors exhibit a senescence-like phenotype that is characterized by cell cycle arrest, positive staining of senescence-associated β-gal, and increased accumulation of dysfunctional mitochondria. The survival of senescence-like cells is sustained by glycolysis that is driven by an augmented axis of mitochondrial reactive oxygen species (mtROS) and HIF1α. Mitochondrial antioxidant, inhibition of HIF1α activation and restriction of glycolysis can each block the entry into and the sustenance of the senescence-like state in PARP-inhibited ovarian cancer cells. The senescence-like phenotype, HIF1α activation and lactate production were attenuated in tumor xenografts co-treated with PARP inhibitor Rucaparib and mitochondrial antioxidant. The metabolic reliance on mtROS-driven glycolysis in ovarian cancer cells treated with PARP inhibitors has implications in cancer treatment.

Dermal adipocytes have emerged as active participants in cutaneous host defense. In parallel, adipocyte hypertrophy and hyperplasia-driven obesity has become a global public health priority and is strongly associated with increased risk and severity of bacterial infections. Here, we established and optimized two complementary S. aureus infection models-epidermal and subcutaneous-and in combination with diet-induced (HFD) and genetic (ob/ob) obesity, to systematically evaluate cathelin-related antimicrobial peptide (CRAMP) expression in adipocytes and its crosstalk with neutrophils. Obese mice displayed impaired cutaneous defense despite marked thickening of the fat layer, characterized by attenuated induction of adipocyte CRAMP and reduced local antibacterial activity. In vitro, CRAMP followed a biphasic pattern during adipocyte differentiation-upregulated at early stages but diminished with advanced maturation and lipid accumulation. Mechanistically, neutrophils processed adipocyte-derived CRAMP via serine proteases to generate shorter peptides with enhanced antibacterial activity. Collectively, these findings identify a CRAMP-neutrophil (serine protease) interaction axis as a key amplifier of cutaneous innate immunity and provide mechanistic insight into obesity-associated susceptibility to skin infection, suggesting potential avenues for targeted intervention.

Acute lung injury is a life-threatening inflammatory syndrome characterised by disruption of the alveolar–capillary barrier, pulmonary oedema and impaired gas exchange. Effective targeted therapies remain limited, partly because the metabolic requirements that sustain pathogenic inflammation are incompletely understood. Here we identify nicotinamide phosphoribosyltransferase (NAMPT)-dependent NAD⁺ salvage as an important regulator of inflammatory macrophage function in acute lung injury. Integrated analysis of human and mouse single-cell transcriptomic datasets showed that NAMPT was enriched in recruited inflammatory macrophages. In an LPS-induced acute lung injury model, pharmacological NAMPT inhibition with FK866 and Lyz2-Cre-mediated myeloid Nampt deletion attenuated pulmonary oedema, inflammatory-cell accumulation, alveolar injury and cytokine production and prolonged survival. In primary macrophages, pharmacological or genetic disruption of NAMPT reduced intracellular NAD⁺ availability, suppressed inflammatory effector responses and impaired responsiveness to secondary inflammatory challenge; the latter effect was reversible after NAD⁺ recovery. Metabolic analyses showed coordinated impairment of glycolysis and mitochondrial respiration, together with depletion of tricarboxylic acid cycle intermediates. These changes were accompanied by reduced mTORC1 downstream signalling and diminished HIF-1α abundance, and were partially restored by nicotinamide mononucleotide supplementation. Together, these findings identify NAMPT-dependent NAD⁺ metabolism as a key requirement for inflammatory macrophage bioenergetics and support temporally restricted, cell-selective NAMPT targeting as a potential strategy for acute inflammatory lung injury.

Immune checkpoint therapy (ICT) has revolutionized cancer treatment by restoring cytotoxic T-cell activity, yet primary and acquired resistance remain pervasive. Increasing evidence reveals that such resistance is not dictated solely by tumor-intrinsic factors but arises from the dynamic interplay between malignant and stromal compartments within the tumor microenvironment. Among these, cancer-associated fibroblasts (CAFs)—the dominant stromal population—have emerged as key orchestrators of immune accessibility and therapeutic outcome. Beyond forming structural barriers through extracellular matrix remodeling, CAFs actively shape immune cell recruitment, polarization, and effector functions via diverse cytokines, chemokines, and metabolic pathways. In turn, immune-derived mediators reprogram CAF states, establishing bidirectional feedback circuits that continuously recalibrate stromal and immune homeostasis. These reciprocal networks transform the immune microenvironment into a self-adaptive ecosystem that governs tumor progression and responsiveness to ICT. This review synthesizes recent advances in understanding CAF–immune crosstalk, emphasizing how such interactions drive both primary and acquired resistance to checkpoint blockade. We further highlight emerging therapeutic strategies aimed at reprogramming the CAF–immune axis—rather than eradicating it—to restore durable and systemic antitumor immunity.

Glucocorticoids are frequently administered to alleviate therapy-related side effects in cancer patients, yet their role in tumor progression remains controversial and mechanistically unresolved. Here, we demonstrate that the long-acting glucocorticoid dexamethasone (Dex) exerts antitumor effects that are mediated by neutrophils. In murine models of Lewis lung carcinoma (LLC) and B16F10 melanoma, Dex markedly suppressed tumor growth and prolonged survival of tumor-bearing mice. These effects were independent of adaptive immunity, macrophages, and tumor cell-intrinsic glucocorticoid signaling, but required functional glucocorticoid receptor (GR) signaling in neutrophils. Dex-treated neutrophils exhibited longer survival and higher cytotoxicity toward tumor cells via increased production of reactive oxygen species (ROS). Disruption of this GR-ROS axis, either through neutrophil-specific GR deletion or pharmacological inhibition of ROS, abolished the antitumor activity of Dex. Together, these findings uncover a neutrophil-mediated tumoricidal function of Dex and suggest that neutrophil GR-ROS signaling may be harnessed for cancer therapy.

Abstract Mammalian tooth development progresses through two principal stages-crown formation and root development-orchestrated by intricate interactions between the oral epithelium and neural crest-derived mesenchyme. After crown formation, Hertwig’s epithelial root sheath (HERS) directs root development. In this phase, Gli1⁺ mesenchymal stem cells (MSCs) give rise to dental pulp, dentin, cementum, and the periodontal ligament (PDL). The root anchors the tooth to the alveolar bone via PDL fibers, forming a dynamic occlusal buffer that mediates mechanosensation and nutrient supply. Although previous work has shown that macrophages are abundant in the dental pulp and follicle, the functional importance of macrophages in tooth development has not been well characterized. Here, we investigated the spatiotemporal dynamics of macrophage populations (identified by CD68, F4/80, CD206, and other markers) in molars and surrounding tissues during postnatal root development in mice. Importantly, Macrophage depletion via clodronate liposomes resulted in shortened root, impaired PDL elongation and retarded alveolar bone shooting surrounding the root. Gli1⁺ MSCs exhibited increased proliferation but impaired osteo/odontogenic differentiation upon macrophage depletion. Single-cell RNA sequencing and in vitro co-culture experiments support a model in which macrophage-derived TGF-β acts on mesenchymal TGF-β receptors to direct MSC fate and thereby regulate root morphogenesis. Collectively, these findings establish macrophages as critical niche components that orchestrate tooth root development through immune–mesenchymal crosstalk.

Adipose stem cell hierarchy was delineated by scRNA-seq analysis, revealing that ICAM-1, a glycoprotein that mediates cell-cell interaction, is a preadipocyte marker. However, the cellular and molecular mechanisms of how ICAM-1+ preadipocytes contribute to adipose tissue homeostasis in vivo remain unclear. To address this, Icam1+/CreERT2 mice were generated, and it was demonstrated that ICAM-1-expressing progenitors actively participated in developing and remodeling white adipose tissue. Under a high-fat diet, both proliferation and adipogenic differentiation of ICAM-1+ preadipocytes increased significantly. Interestingly, ICAM-1 plays a critical role in maintaining the interaction between preadipocytes and immune cells, acting as a checkpoint on white adipogenesis. Mice lacking ICAM-1 specifically in stromal cells exhibited worsened hyperplastic obesity, showing heightened fatty acid synthesis and lipid storage in adipose tissue, and the related insulin resistance. In human adipose tissue, ICAM-1 also marked committed preadipocytes and mediated adhesion between preadipocytes and immune cells. Thus, our study shows that ICAM-1 marks preadipocytes and curbs adipogenesis by facilitating adhesion between preadipocytes and immune cells.

Cancer cells expressing CD47 escape macrophage phagocytosis by binding to the SIRPα ligand expressed on macrophages. CD47 targeted therapy offers a promising approach to cancer treatment. Here we report that two major isoforms of CD47 differ in ovarian cancer and normal tissues. The truncated isoform lacking exon 9 and exon 10 (CD47-S) was exclusively expressed in normal tissues, whereas the full-length isoform (CD47-L) was predominantly expressed in ovarian cancer tissues. Interestingly, CD47-S was unable to locate at the cell surface to bind with SIRPα as CD47-L did, and thereby inactivated “don’t-eat-me” signal. Mechanistic investigations revealed that splicing factor HNRNPA1 promoted splicing switch from CD47-L to CD47-S through exon 9 and exon 10 skipping. We further developed antisense oligonucleotides (ASOs) that effectively switched CD47-L to CD47-S . Importantly, ASOs treatment evoked macrophage-mediated antitumor immune response, thereby triggered pyroptosis of ovarian cancer cells. Moreover, CD47-targeting ASOs significantly reduced tumor growth in patient-derived xenograft. Together, ASO-mediated isoform switch of CD47 has emerged as a promising strategy to improve immune responses against tumors. ### Competing Interest Statement The authors have declared no competing interest.

Insulin-like growth factors (IGFs) are key regulators of the stem cell niche, playing critical roles in the proliferation and differentiation of stem cells into various lineages, including skeletal muscle. While IGF2 is known to influence muscle development, its specific effects and mechanisms in human skeletal muscle remain incompletely understood. In this study, we demonstrate that IGF2 is a key regulator of human satellite cell (huSC) proliferation, differentiation, and mitochondrial bioenergetics. Using primary huSCs cultured under defined myogenic conditions, we show that IGF2 significantly enhances myoblast proliferation and promotes differentiation via upregulation of myogenic regulatory factors and activation of the IGF1 receptor (IGF1R) pathway. Knockdown of endogenous IGF2 impaired these processes, while exogenous supplementation restored myogenic potential. Notably, IGF2 also improved mitochondrial function, evidenced by increased oxygen consumption rate, mitochondrial mass, oxidative phosphorylation protein expression, and intracellular ATP production. These effects were primarily mediated through IGF1R signaling, with IGF2R playing a modulatory role in regulating IGF2 availability. Our findings reveal that IGF2 not only initiates structural differentiation but also drives metabolic reprogramming in huSCs, highlighting its dual role in supporting muscle regeneration and energy homeostasis. These insights highlight IGF2 as a promising therapeutic target for muscle-wasting conditions such as muscular dystrophy and age-related sarcopenia and suggest its broader potential in regenerative medicine strategies.

The dome-shaped cornea is a transparent, non-vascularized, and epithelialized highly organized tissue. Physical and chemical injuries may trigger corneal wound healing (CWH) response and result in neovascularization that impairs the visual function. CWH involves not only migration, proliferation, and differentiation of the cells in different layers of cornea, but also the mobilization of immune cells. We demonstrated here that human adipose-derived mesenchymal stromal cells (ADSCs) could effectively inhibit neovascularization during ethanol-induced injury in mouse cornea. Importantly, we found that while neutrophils are essential for CWH, excessive and prolonged neutrophil retention during the granulation stage contributes to neovascularization. ADSCs were found to promote the clearance of neutrophils in the cornea during the granulation stage, likely via increasing the reverse transendothelial cell migration of CXCR4high neutrophils from cornea to the lung. Our results demonstrate that ADSCs are effective in treating CWH-induced neovascularization and modulation of neutrophil clearance could be novel strategies for better vision recovery after injury.

Resistance to chemotherapeutic agents is a critical challenge for the clinical management of ovarian cancer. While curcumin has been reported to possess anti-cancer properties, how it exerts its anti-neoplastic effect on ovarian cancer cells remains to be explored. We here characterized the fate of human ovarian cancer cell lines HO8910 and OVCAR3 treated with curcumin. Cell proliferation, cell death, mitochondrial function, oxidative damage and tumor formation in nude mice were examined. Significant inhibition of proliferation and induction of apoptosis were observed in ovarian cells treated with curcumin. The cancer cells exhibit cell cycle arrest at G2/M phase, mitochondrial accumulation, mitochondrial oxidative stress and high level of DNA damage after curcumin treatment. This effect of curcumin is independent of the BRCA mutation status. Curcumin-induced proliferation inhibition and apoptosis were effectively attenuated by the application of antioxidant N-acetylcysteine (NAC), suggesting that curcumin exerts its anti-cancer effect by inflicting oxidative stress. Curcumin applied at 200 mg/kg intraperitoneal infusion daily also inhibited the growth, oxidative damage, and mitochondrial accumulation of tumor xenografts in vivo. Together, the results indicate that curcumin can exert its anti-tumor effect via inducing mitochondrial dysfunction-associated oxidative DNA damage and can be potentially used in combination with other DNA repair-interfering therapeutics, such as PARP inhibitor, in the treatment of ovarian cancer.

Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is a crucial coactivator that regulates mitochondrial biogenesis and function across diverse tissues, including the brain, heart, skeletal muscle, bone marrow, and liver. The diversity of PGC-1α isoforms in distinct tissues allows this co-transcription factor to exert wide-ranging biological effects, including regulating mitochondrial functions, oxidative stress, and endoplasmic reticulum homeostasis. Here, we focus on the key roles of PGC-1α in cell differentiation. Initially identified in brown adipose tissue in response to cold exposure, PGC-1α regulates cell differentiation by modulating gene expression networks involved in mitochondrial biogenesis. PGC-1α influences cell fate in several cell types, including adipocytes, skeletal muscle cells, and bone marrow-derived cells. A deeper understanding of PGC-1α provides valuable insights into developmental biology, tissue formation, and potential therapeutic targets for regenerative medicine and disease treatment. This review explores recent progress in understanding the roles of PGC-1α in cell differentiation, offering an integrated perspective on its significance in tissue and organism development.

Chemotherapy remains the cornerstone of gastric cancer (GC) treatment, with Oxaliplatin (OXA) being a critical first-line agent. However, chemotherapy resistance, compounded by increased stemness, poses a significant challenge in GC management. In this study, we demonstrate that JMJD3, encoded by KDM6B and catalyzing the demethylation of H3K27me3, is highly expressed in both GC tissues and patient-derived chemotherapy-resistant xenograft (PDX) models and contributes to increased malignancy and chemoresistance. Overexpression of JMJD3 enhanced stemness and chemoresistance in GC cells, while JMJD3 knockdown had opposite effects. Mechanistically, JMJD3 promotes GC cell stemness and chemoresistance by reducing H3K27me3 on the ALOX5 promoter, a histone modification associated with ALOX5 transcriptional activation. Tumorigenesis induced by N-methyl-N-nitrosourea (MNU) was reduced in mice with gastric epithelial cell-specific deletion of Kdm6b. Importantly, ALOX5 upregulation due to the elevated JMJD3 function sensitized GC cells to ferroptosis inducers. These findings suggest that JMJD3 plays a pivotal role in GC chemoresistance by modulating both stemness and ferroptosis sensitivity. Targeting JMJD3 may provide a novel therapeutic strategy for overcoming chemotherapy resistance, with ferroptosis inducers potentially offering a promising adjunctive treatment in GC.

Background Atherosclerosis, a leading cause of heart attack and stroke, involves intricate immune cell dynamics within arterial plaques, yet their spatial organization and functional roles remain elusive. Methods We combined Visium HD spatial transcriptomics, imaging mass cytometry, and single-cell RNA-seq across fatty-streak, advanced, and restenotic plaques to map myeloid architectures and relate them to lesion geography and extracellular matrix features. Slingshot trajectory analysis resolved macrophages differentiation path. In vitro , we tested microenvironmental and lipid cues separately: fibronectin (FN) exposure during PMA-driven THP-1 differentiation and oxidized LDL (oxLDL)-induced foam cell formation in murine bone-marrow derived macrophages (BMDMs). Results Our analysis identified seven macrophage subsets and two neutrophil populations with distinct spatial distribution and functional roles. In early lesions, neutrophils expressing MMP9, MPO, p47phox, TGF-β1 and arachidonate 5-lipoxygenase (ALOX5), aligned with proteolysis, inflammatory processes, and endothelial-mesenchymal transition features. In advanced plaques, macrophage subsets exhibit specialized functions: Ki67+ proliferative macrophages localized near necrotic cores, sustaining local population; SPP1+ macrophages, enriched in lipid handling and tissue remodeling, are prone to apoptosis/ferroptosis, potentially promoting necrotic core expansion; and C3aR+ macrophages form antigen-presenting niches with elevated HLA-DR and CD74, engaging T cells possibly through CXCL12–CXCR4 signaling. Slingshot trajectories indicated progression from C3aR⁺ toward SPP1⁺ remodeling states concentrated at fibronectin-rich rims. In vitro , FN increased MMP9 and TIMP1 in THP-1-derived macrophages, consistent with FN imprinting remodeling features characteristic of SPP1⁺ macrophages in situ . Concurrently, oxLDL-treated BMDMs showed enhanced lipid-handling and remodeling modules consistent with the SPP1 program. Conclusions These findings define conserved myeloid niches and support a microenvironment-imprinting model that links ECM composition and lipid loading to macrophage state transitions, providing a framework for microenvironment-targeted therapies to stabilize plaques and mitigate cardiovascular risk. ### Competing Interest Statement The authors have declared no competing interest.

BACKGROUND:Liver fibrosis is an aberrant wound-healing process in response to chronic hepatic injury. Functional plasticity of macrophages is crucial in this pathological process. How the pro-fibrotic function of macrophages is sustained metabolically and whether it can be targeted for therapy remain to be explored. PURPOSE:This study investigates the impact of spermidine, a natural polyamine, on macrophage function and its potential in treating hepatic fibrosis. METHODS:Chronic liver disease datasets and single-cell RNA sequencing (scRNA-seq) data were analyzed for the characteristics of spermidine metabolism in hepatic macrophage function and liver fibrosis. Mice undergoing liver fibrosis caused by carbon tetrachloride (CCl4) were treated with spermidine through daily drinking water. Macrophage-specific PGC1α knockout mice were used to determine the requirement of mitochondrial fitness in the anti-fibrotic function of macrophages. Furthermore, spermidine-treated macrophages were adoptively transferred to mice with liver fibrosis to test their therapeutic potential. RESULTS:Analysis of chronic liver disease datasets revealed a dysregulated polyamine metabolism in diseased liver tissues, particularly in distinct subsets of macrophages. Spermidine supplementation protected mice from CCl4-induced liver fibrosis through endowing macrophages a persistent anti-inflammatory and pro-resolving function that is characterized by elevated matrix metalloproteinase expression and enhanced mitochondrial function. Spermidine-treated macrophages (SPDMs) exhibited increased mitochondrial mass, augmented oxidative phosphorylation, and altered fatty acid metabolism. The markers characteristic of tolerogenic and liver-regenerative macrophages were upregulated in SPDMs in a manner dependent on peroxisome proliferator-activated receptor-γ coactivator (PGC) -1α, a key regulator of mitochondrial homeostasis. Interestingly, oleate generated by stearoyl-CoA desaturase 1 (SCD1) was essential for SPDMs to acquire the increased mitochondrial fitness. Notably, adoptive transfer of SPDMs to fibrotic mice significantly attenuated disease progression. The anti-fibrotic effect was compromised in mice with myeloid cell-specific deletion of PGC1α, highlighting the importance of mitochondrial biogenesis in mediating macrophage phenotype plasticity. CONCLUSIONS:Our study implicates dysregulation of spermidine metabolism in hepatic macrophages in the development of chronic liver diseases. We demonstrated an anti-fibrotic function of spermidine that is attributed to its action on macrophages. PGC1α-mediated mitochondrial fitness is required for spermidine to confer macrophages an enhanced anti-inflammatory and anti-fibrotic capacity. Meanwhile, we provide novel insights into the role of fatty acid metabolism in modifying the biological function of macrophages. This study opens new avenues for treating fibrotic diseases by targeting macrophage plasticity through spermidine-mediated metabolic reprogramming and demonstrate the potential of spermidine-trained macrophages as approaches for inflammatory and fibrotic conditions.

Cancer development is associated with adaptation to various stressful conditions, such as extracellular acidosis. The adverse tumor microenvironment also selects for increased malignancy. Mitochondria are integral in stress sensing to allow for tumor cells to adapt to stressful conditions. Here, we show that colorectal cancer cells adapted to acidic microenvironment (CRC-AA) are more reliant on oxidative phosphorylation than their parental cells, and the acetyl-CoA in CRC-AA cells are generated from fatty acids and glutamine, but not from glucose. Consistently, CRC-AA cells exhibit increased mitochondrial mass and fitness that depends on an upregulated autophagic flux-lipid droplet axis. Lipid droplets (LDs) function as a buffering system to store the fatty acids derived from autophagy and to protect mitochondria from lipotoxicity in CRC-AA cells. Blockade of LD biogenesis causes mitochondrial dysfunction that can be rescued by inhibiting carnitine palmitoyltransferase 1 α (CPT1α). High level of mitochondrial superoxide is essential for the AMPK activation, resistance to apoptosis, high autophagic flux and mitochondrial function in CRC-AA cells. Thus, our results demonstrate that the cascade of autophagic flux and LD formation plays an essential role in sustaining mitochondrial fitness to promote cancer cell survival under chronic acidosis. Our findings provide insight into the pro-survival metabolic plasticity in cancer cells under microenvironmental or therapeutic stress and imply that this pro-survival cascade may potentially be targeted in cancer therapy.

Mesenchymal stem/stromal cells (MSCs) have garnered attention for their potential in cancer therapy due to their ability to home to tumor sites. Engineered MSCs have been developed to deliver therapeutic proteins, microRNAs, prodrugs, chemotherapy drugs, and oncolytic viruses directly to the tumor microenvironment, with the goal of enhancing therapeutic efficacy while minimizing off-target effects. Despite promising results in preclinical studies and clinical trials, challenges such as variability in delivery efficiency and safety concerns persist. Ongoing research aims to optimize MSC-based cancer eradication and immunotherapy, enhancing their specificity and efficacy in cancer treatment. This review focuses on advancements in engineering MSCs for tumor-targeted therapy.

Mesenchymal stem/stromal cells (MSCs) are integral components of the tumor microenvironment and critical for the colonization of disseminated cancer cells; specifically, stem cell antigen (Sca-1) is recognized as a surface marker of MSCs. In this study, we found that MSCs highly expressing Sca-1 are positively associated with lung metastasis. MSCs derived from the lungs of mice bearing metastasized breast tumors (LMSCs) exhibited higher level of Sca-1 compared to those with adenoma. When co-injected with 4T1 cells intravenously, Sca-1high LMSCs resulted in more tumor nodules in lung tissue than Sca-1low LMSCs. Furthermore, Sca-1high LMSCs expressed higher levels of CCL2, CCL7, and CXCL1 than Sca-1low LMSCs. Sca-1high LMSCs can directly recruit 4T1 cells through producing CXCL1. Additionally, Sca-1high LMSCs are highly potent in recruiting immune cells of the myeloid lineage (neutrophils and macrophages) to the lungs. Inhibition of macrophage chemotaxis by Bindarit, an inhibitor of CCL2/7/8 transcription, decreased the lung tumor burden induced by Sca-1high MSCs. Using Ccr5-/- mice, it was further confirmed that Sca-1high LMSCs promote tumorigenesis by recruiting macrophages, further supporting that the increased recruitment of macrophages mediates the pro-metastasis effect of Sca-1high LMSCs. Collectively, this study demonstrated that Sca-1high LMSCs and their effectors could be targeted to inhibit breast cancer metastasis to the lung.

Mesenchymal stem/stromal cells (MSCs) have shown significant therapeutic effects in a range of autoimmune and hyperinflammatory diseases through their strong immunomodulatory properties, both in animal models and clinical settings. Exposure to inflammatory cytokines is crucial for MSCs to acquire immunoregulatory functions; however, the detailed mechanisms underlying this process remain largely unexplored. MSCs with pharmacological inhibition or genetic knockout of poly ADP-ribose polymerase1 (PARP1) were treated with the inflammatory factors IFNγ and TNFα for 24 h. The mRNA and protein expression of chemokines and immunosuppressive molecules were detected by qRT-PCR and Western blotting, respectively. The therapeutic efficacy of MSCs was evaluated using a mouse concanavalin A-induced acute liver injury model and a dextran sulfate sodium-induced inflammatory bowel disease model. The phosphorylation of signal transducer and activator of transcription 1 (STAT1) was analyzed in activated MSCs, and STAT1 inhibition through either a STAT1 inhibitor or STAT1 knockout was employed to confirm the role of STAT1 in enhancing the immunoregulatory function of MSCs during PARP inhibition. PARP inhibition or genetic knockout of PARP1 further enhanced the immunoregulatory function of MSCs elicited by inflammatory cytokines IFNγ and TNFα, as evidenced by the upregulation of genes associated with immunoregulation in MSCs, augmentation of immunosuppressive functions of MSCs on T cells, and increased therapeutic effects of MSCs in mouse models of autoimmune and hyperinflammatory diseases. PARP inhibition was further shown to enhance the expression of immunosuppressive factors in primed MSCs through increased phosphorylation at the tyrosine 701 site on STAT1. Our study indicates that like its pro-inflammatory role in macrophages, PARP also functions to undermine the immunosuppressive effects of MSCs, and PARP inhibition represents a strategy to further unleash the immunoregulatory power of MSCs.

Apoptosis has been reported to drive regeneration in many species. Executioner caspases, the key effectors in apoptosis, are responsible for production and secretion of various pro-regenerative signals from apoptotic cells to the surrounding cells. However, whether executioner caspase activation (ECA) can promote regeneration without inducing apoptosis is poorly understood. Here, by generating transgenic mice carrying a lineage tracing system for cells that have experienced ECA, we demonstrate that ECA occurs in a few hepatocytes in homeostatic livers. The fraction of hepatocytes with ECA dramatically expands during regeneration after partial hepatectomy (PHx) or carbon tetrachloride (CCl4) treatment. Interestingly, rather than undergoing apoptosis, the majority of hepatocytes with ECA survive and proliferate during liver regeneration. Inhibition of ECA in livers results in reduced hepatocyte proliferation and impaired regeneration, whereas increasing ECA to a level sufficient to kill hepatocytes also impedes regeneration, suggesting that ECA needs to be precisely controlled at a sublethal level. Mechanistically, we show that ECA promotes hepatocyte proliferation through enhancing JAK/STAT3 activity. Our work reveals an essential apoptosis-independent role of executioner caspases in liver regeneration.