Kruppel-like factor KLF4 facilitates cutaneous wound healing by promoting fibrocyte generation from myeloid-derived suppressor cells

The Recovery of Epidermal Proliferation Pattern in Human Skin Xenograft

Abnormalities in epidermal keratinocyte proliferation are a characteristic feature of a range of dermatological conditions. These include hyperproliferative states in psoriasis and dermatitis as well as hypoproliferative states in chronic wounds. This emphasises the importance of investigating the proliferation kinetics under conditions of healthy skin and identifying the key regulators of epidermal homeostasis, maintenance, and recovery following wound healing. Animal models contribute to our understanding of human epidermal self-renewal. Human skin xenografting overcomes the ethical limitations of studying human skin during regeneration. The application of this approach has allowed for the identification of a single population of stem cells and both slowly and rapidly cycling progenitors within the epidermal basal layer and the mapping of their location in relation to rete ridges and hair follicles. Furthermore, we have traced the dynamics of the proliferation pattern reorganization that occurs during epidermal regeneration, underlining the role of YAP activity in epidermal relief formation.

Myeloid-Derived Suppressor Cell Accumulation Drives Intestinal Fibrosis through mCCL6/hCCL15 Chemokine-Mediated Fibroblast Activation

Intestinal fibrosis, a severe complication of Crohn's disease (CD), is linked to chronic inflammation, but the precise mechanism by which immune-driven intestinal inflammation leads to fibrosis development is not fully understood. This study investigates the role of myeloid-derived suppressor cells (MDSCs) in intestinal fibrosis in CD patients and a 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced mouse model. Elevated MDSCs are observed in inflamed intestinal tissues prior to fibrosis and their sustained presence in fibrotic tissues of both CD patients and murine models. Depletion of MDSCs significantly reduces fibrosis, highlighting their key role in the fibrotic process. Mechanistically, MDSC-derived mCCL6 activates fibroblasts via the CCR1-MAPK signaling, and interventions targeting this axis, including neutralizing antibodies, a CCR1 antagonist, or fibroblast-specific Ccr1 knockout mice reduce fibrosis. In CD patients with stenosis, human CCL15, analogous to mCCL6, is found to be elevated in MDSCs and activated fibroblasts. Additionally, CXCR2 and CCR2 ligands are identified as key mediators of MDSC recruitment in intestinal fibrosis. Blocking MDSC recruitment with CXCR2 and CCR2 antagonists alleviates intestinal fibrosis. These findings suggest that strategies targeting MDSC recruitment and mCCL6/hCCL15 signaling could offer therapeutic benefits for intestinal fibrosis.

MCC950 promotes diabetic wound healing through modulating macrophage polarization in an MDSC-dependent manner

Diabetic foot ulcers (DFUs) are serious skin injuries whereby the wound healing process is frequently stalled in the inflammatory phase. Currently, there is a lack of effective therapeutic strategies. MCC950, a highly selective nod-like receptor family pyrin domain containing 3 (NLRP3) inhibitor, has been reported to show strong anti-inflammation effects in many diseases. In this study, we unveiled the role of MCC950 in DFU mice model and its underlying molecular mechanisms. MCC950 could significantly accelerate diabetic wound healing, as shown by shortened healing time and better healing quality. Moreover, increased M2 phenotype macrophages and decreased pro-inflammatory genes were observed in MCC950-treated DFU mice. Additionally, myeloid-derived suppressor cells (MDSCs) were significantly increased in blood, spleen and wound tissues at different time courses. Specifically, MCC950 could recruit more MDSCs in an early phase in DFU mice, exerting an anti-inflammation effect. We identified the cell crosstalk between macrophages and MDSCs with MCC950 treatment process. Depleting MDSCs in vivo could eliminate the therapeutic effect of MCC950 on diabetic wound healing through inhibiting M2 macrophage polarization. Besides, MDSCs isolated from the wounds of MCC950 or saline treated mice were cocultured with bone marrow derived macrophage (BMDM) in a transwell system. Results confirmed that MDSCs sorted from MCC950 treated mice caused a significant increased percentage of M2 macrophages. Collectively, our findings suggest that the administration of MCC950 has the potential to accelerate diabetic wound healing by promoting M2 macrophage polarization in an MDSC-dependent manner. This study provides valuable insights into the utilization of pharmacological agents for DFU treatment.

Extracellular vesicles from 3D cultured dermal papilla cells improve wound healing via Krüppel-like factor 4/vascular endothelial growth factor A -driven angiogenesis

Background

Non-healing wounds are an intractable problem of major clinical relevance. Evidence has shown that dermal papilla cells (DPCs) may regulate the wound-healing process by secreting extracellular vesicles (EVs). However, low isolation efficiency and restricted cell viability hinder the applications of DPC-EVs in wound healing. In this study, we aimed to develop novel 3D-DPC spheroids (tdDPCs) based on self-feeder 3D culture and to evaluate the roles of tdDPC-EVs in stimulating angiogenesis and skin wound healing.

Methods

To address the current limitations of DPC-EVs, we previously developed a self-feeder 3D culture method to construct tdDPCs. DPCs and tdDPCs were identified using immunofluorescence staining and flow cytometry. Subsequently, we extracted EVs from the cells and compared the effects of DPC-EVs and tdDPC-EVs on human umbilical vein endothelial cells (HUVECs) in vitro using immunofluorescence staining, a scratch-wound assay and a Transwell assay. We simultaneously established a murine model of full-thickness skin injury and evaluated the effects of DPC-EVs and tdDPC-EVs on wound-healing efficiency in vivo using laser Doppler, as well as hematoxylin and eosin, Masson, CD31 and α-SMA staining. To elucidate the underlying mechanism, we conducted RNA sequencing (RNA-seq) of tdDPC-EV- and phosphate-buffered saline-treated HUVECs. To validate the RNA-seq data, we constructed knockdown and overexpression vectors of Krüppel-like factor 4 (KLF4). Western blotting, a scratch-wound assay, a Transwell assay and a tubule-formation test were performed to detect the protein expression, cell migration and lumen-formation ability of KLF4 and vascular endothelial growth factor A (VEGFA) in HUVECs incubated with tdDPC-EVs after KLF4 knockdown or overexpression. Dual-luciferase reporter gene assays were conducted to verify the activation effect of KLF4 on VEGFA.

Results

We successfully cultured tdDPCs and extracted EVs from DPCs and tdDPCs. The tdDPC-EVs significantly promoted the proliferation, lumen formation and migration of HUVECs. Unlike DPC-EVs, tdDPC-EVs exhibited significant advantages in terms of promoting angiogenesis, accelerating wound healing and enhancing wound-healing efficiency both in vitro and in vivo. Bioinformatics analysis and further functional experiments verified that the tdDPC-EV-regulated KLF4/VEGFA axis is pivotal in accelerating wound healing.

Conclusions

3D cultivation can be utilized as an innovative optimization strategy to effectively develop DPC-derived EVs for the treatment of skin wounds. tdDPC-EVs significantly enhance wound healing via KLF4/VEGFA-driven angiogenesis.

The Kruppel-like factor 4-signal transducer and activator of transcription 5A axis promotes pancreatic fibrosis in mice with caerulein-induced chronic pancreatitis

Pancreatic fibrosis (PF) is a hallmark of chronic pancreatitis (CP), but its molecular mechanism remains unclear. This study was conducted to explore the role of Kruppel-like factor 4 (KLF4) in PF in CP mice. The CP mouse model was established using caerulein. After KLF4 interference, pathological changes in pancreatic tissues and fibrosis degree were observed by hematoxylin-eosin staining and Masson staining, and levels of Collagen I, Collagen III, and alpha-smooth muscle actin, inflammatory cytokines, KLF4, signal transducer and activator of transcription 5A (STAT5) in pancreatic tissues were measured by enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, Western blot assay, and immunofluorescence. The enrichment of KLF4 on the STAT5 promoter and the binding of KLF4 to the STAT5 promoter were analyzed. The rescue experiments were performed by co-injection of sh-STAT5 and sh-KLF4 to confirm the regulatory mechanism of KLF4. KLF4 was upregulated in CP mice. Inhibition of KLF4 effectively attenuated pancreatic inflammation and PF in mice. KLF4 was enriched on the STAT5 promoter and enhanced the transcriptional and protein levels of STAT5. Overexpression of STAT5 reversed the inhibitory role of silencing KLF4 in PF. In summary, KLF4 promoted the transcription and expression of STAT5, which further facilitated PF in CP mice.

Suppressive myeloid cells in SARS-CoV-2 and Mycobacterium tuberculosis co-infection

Epidemiologic data show that both current and previous tuberculosis (TB) increase the risk of in-hospital mortality from coronavirus disease-2019 (COVID-19), and there is a similar trend for poor outcomes from Mycobacterium tuberculosis (Mtb) infection after recent SARS-CoV-2. A shared dysregulation of immunity explains the dual risk posed by co-infection, but the specific mechanisms are being explored. While initial attention focused on T cell immunity, more comprehensive analyses revealed a dysfunctional innate immune response in COVID-19, characterized by reduced numbers of dendritic cells, NK cells and a redistribution of mononuclear phagocytes towards intermediate myeloid subsets. During hyper- or chronic inflammatory processes, activation signals from molecules such as growth factors and alarmins lead to the expansion of an immature population of myeloid cells called myeloid-deprived suppressor cells (MDSC). These cells enter a state of pathological activation, lose their ability to rapidly clear pathogens, and instead become broadly immunosuppressive. MDSC are enriched in the peripheral blood of patients with severe COVID-19; associated with mortality; and with higher levels of inflammatory cytokines. In TB, MDSC have been implicated in loss of control of Mtb in the granuloma and ineffective innate and T cell immunity to the pathogen. Considering that innate immune sensing serves as first line of both anti-bacterial and anti-viral defence mechanisms, we propose MDSC as a crucial mechanism for the adverse clinical trajectories of TB-COVID-19 coinfection.

The Role of Krüppel-like Factors in Pancreatic Physiology and Pathophysiology

Krüppel-like factors (KLFs) belong to the family of transcription factors with three highly conserved zinc finger domains in the C-terminus. They regulate homeostasis, development, and disease progression in many tissues. It has been shown that KLFs play an essential role in the endocrine and exocrine compartments of the pancreas. They are necessary to maintain glucose homeostasis and have been implicated in the development of diabetes. Furthermore, they can be a vital tool in enabling pancreas regeneration and disease modeling. Finally, the KLF family contains proteins that act as tumor suppressors and oncogenes. A subset of members has a biphasic function, being upregulated in the early stages of oncogenesis and stimulating its progression and downregulated in the late stages to allow for tumor dissemination. Here, we describe KLFs' function in pancreatic physiology and pathophysiology.

Knowing the myeloid-derived suppressor cells : Another enemy of sarcomas patients

Sarcomas are heterogeneous and aggressive malignant tumors with variable responses to current standard treatments being usually incurable for those patients with metastatic and unresectable diseases. The lack of curative strategies has led to develop new therapies in the treatment of sarcomas where the role of immune system is an evolving field. Most sarcomas often exhibit an immunosuppressive microenvironment, which reduces their capacity to trigger an immune response. Therefore, sarcomas are broadly considered as an "immune cold" tumor, although some studies have described a great immune heterogeneity across sarcoma subtypes. Sarcoma cells, like other tumors, evade their immune destruction through a variety of mechanisms, including expansion and recruitment of myeloid derived suppressor cells (MDSCs). MDSCs are immature myeloid cells that have been correlated with a reduction of the therapeutic efficacy, including immunotherapy, tumor progression and worst prognosis. Consequently, different strategies have been developed in recent years to target MDSCs in cancer treatments. This chapter discusses the role of MDSCs in sarcomas and their current potential as a therapeutic target in these malignancies.

Klf4 protects thymus integrity during late pregnancy

Pregnancy causes abrupt thymic atrophy. This atrophy is characterized by a severe decrease in the number of all thymocyte subsets and qualitative (but not quantitative) changes in thymic epithelial cells (TECs). Pregnancy-related thymic involution is triggered by progesterone-induced functional changes affecting mainly cortical TECs (cTECs). Remarkably, this severe involution is rapidly corrected following parturition. We postulated that understanding the mechanisms of pregnancy-related thymic changes could provide novel insights into signaling pathways regulating TEC function. When we analyzed genes whose expression in TECs was modified during late pregnancy, we found a strong enrichment in genes bearing KLF4 transcription factor binding motifs. We, therefore, engineered a Psmb11-iCre : Klf4^lox/lox mouse model to study the impact of TEC-specific Klf4 deletion in steady-state conditions and during late pregnancy. Under steady-state conditions, Klf4 deletion had a minimal effect on TEC subsets and did not affect thymic architecture. However, pregnancy-induced thymic involution was much more pronounced in pregnant females lacking Klf4 expression in TECs. These mice displayed a substantial ablation of TECs with a more pronounced loss of thymocytes. Transcriptomic and phenotypic analyses of Klf4 ^-/- TECs revealed that Klf4 maintains cTEC numbers by supporting cell survival and preventing epithelial-to-mesenchymal plasticity during late pregnancy. We conclude that Klf4 is essential for preserving TEC's integrity and mitigating thymic involution during late pregnancy.

Dynamic changes in myeloid-derived suppressor cells during the menstrual cycle: A pilot study

Various studies have described the roles of myeloid-derived suppressor cells (MDSCs) in pathological conditions, but relatively few have described them under normal physiological conditions. Accumulation of MDSCs is important creating an anti-inflammation environment, which is essential for fertilized egg implantation. This study was designed to record the dynamic changes in MDSC-like cells composition during the menstrual period (MP) and ovulation period (OP) in healthy volunteers over the course of a single menstrual cycle to explore the association between MDSCs and the menstrual cycle under normal physiological conditions. The ratio of MDSC-like cells was higher in MP samples, whereas the activity of Arg-1 was higher during the OP window. There was a negative correlation between the ratio of MDSC-like cells and the percentage of lymphocytes and a positive correlation between MDSC-like cells and prostaglandin E2 (PGE2). Furthermore, regular changes in the ratio and function of MDSC-like cells in the peripheral blood were observed during menstruation, all of which corresponded to the cycle stage. During menstruation, MDSCs may promote endometrial repair, whereas they promote pregnancy during the OP. These findings may help to better understand the pathophysiology of pregnancy-related complications and lay a foundation for improving perinatal outcomes.

The function of myeloid-derived suppressor cells in COVID-19 lymphopenia

Coronavirus disease 2019 (COVID-19) has caused a global pandemic and presents a significant danger to public health. Lymphopenia is considered to be the defining characteristic of severe COVID-19, especially in elderly people. Lymphopenia has been suggested as a pivotal factor in disease severity. To minimize mortality in COVID-19 patients, it is essential to have a deeper understanding of the processes behind lymphocytopenia. Recently, myeloid-derived suppressor cells (MDSCs) have been confirmed as a key mediator of lymphopenia. MDSCs are characterized by their powerful capacity to suppress T cells and eventually contribute to the course of illness. Targeting these cells may improve the disease prognosis. In this article, we analyze the available research on MDSCs in lymphopenia and discuss their immunopathologic changes and prospective therapeutic targets in patients with COVID-19 lymphocytopenia.

Network analysis reveals dysregulated functional patterns in type II diabetic skin

Skin disorders are one of the most common complications of type II diabetes (T2DM). Long-term effects of high blood glucose leave individuals with T2DM more susceptible to cutaneous diseases, but its underlying molecular mechanisms are unclear. Network-based methods consider the complex interactions between genes which can complement the analysis of single genes in previous research. Here, we use network analysis and topological properties to systematically investigate dysregulated gene co-expression patterns in type II diabetic skin with skin samples from the Genotype-Tissue Expression database. Our final network consisted of 8812 genes from 73 subjects with T2DM and 147 non-T2DM subjects matched for age, sex, and race. Two gene modules significantly related to T2DM were functionally enriched in the pathway lipid metabolism, activated by PPARA and SREBF (SREBP). Transcription factors KLF10, KLF4, SP1, and microRNA-21 were predicted to be important regulators of gene expression in these modules. Intramodular analysis and betweenness centrality identified NCOA6 as the hub gene while KHSRP and SIN3B are key coordinators that influence molecular activities differently between T2DM and non-T2DM populations. We built a TF-miRNA-mRNA regulatory network to reveal the novel mechanism (miR-21-PPARA-NCOA6) of dysregulated keratinocyte proliferation, differentiation, and migration in diabetic skin, which may provide new insights into the susceptibility of skin disorders in T2DM patients. Hub genes and key coordinators may serve as therapeutic targets to improve diabetic skincare.

Myeloid-Derived Suppressor Cells and Radiotherapy

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of pathologically activated, mostly immature, myeloid cells that exert robust immunosuppressive functions. MDSCs expand during oncogenesis and have been linked to accelerated disease progression and resistance to treatment in both preclinical tumor models and patients with cancer. Thus, MDSCs stand out as promising targets for the development of novel immunotherapeutic regimens with superior efficacy. Here, we summarize accumulating preclinical and clinical evidence indicating that MDSCs also hamper the efficacy of radiotherapy (RT), as we critically discuss the potential of MDSC-targeting strategies as tools to achieve superior immunotherapeutic tumor control by RT in the clinic.

3D-MSCs A151 ODN-Loaded Exosomes Are Immunomodulatory And Reveal A Proteomic Cargo That Sustains Wound Resolution

•

The MSC-derived secretome from 3D cultures enhances fibroblast and keratinocyte mitogenic and motogenic capacity in vitro, respectively.

•

The cargo of the 3D MSC-derived exosomes (Exo3D) reveals wound healing-related proteins and promotes wound resolution in a wound healing in vivo model.

•

Loading MSC-derived exosomes with A151 ODN further reduces the systemic levels of IL-6 and TNF-α pro-inflammatory cytokines at the late stage of wound healing in vivo, crucial for a full regenerated tissue.

•

A151-loaded Exo3D have a great potential as a noncellular off-the-shelf therapy for non-healing wound treatment.

Introduction

Non-healing wounds remain a major burden due to the lack of effective treatments. Mesenchymal stem cell-derived exosomes (MSC-Exo) have emerged as therapeutic options given their pro-regenerative and immunomodulatory features. Still, little is known on the exact mechanisms mediated by MSC-Exo. Importantly, modulation of their efficacy through 3D-physiologic cultures together with loading strategies continues underexplored.

Objectives

To uncover the MSC-Exo-mediated mechanism via proteomic analyses, and to use 3D-culture and loading technologies to expand MSC-Exo efficacy for cutaneous wound healing.

Methods

MSC-Exo were produced in either 3D or 2D cultures (Exo3D/Exo2D) and loaded with an exogenous immunosuppressive oligodeoxynucleotide (A151 ODN). Both, loaded and naïve exosomes were characterised regarding size, morphology and the presence of specific protein markers; while IPA analyses enabled to correlate their protein content with the effects observed in vitro and in vivo. The Exo3D/Exo2D regenerative potential was evaluated in vitro by assessing keratinocyte and fibroblast mitogenicity, motogenicity, and cytokine secretion as well as using an in vivo wound splinting model. Accordingly, the modulation of inflammatory and immune responses by A151-loaded Exo3D/Exo2D was also assessed.

Results

Exo3D stimulated mitogenically and motogenically keratinocytes and fibroblasts in vitro, with upregulation of IL-1α and VEGF-α or increased secretion of TGF-β, TNF-α and IL-10. In vivo, Exo3D reduced the granulation tissue area and promoted complete re-epithelization of the wound. These observations were sustained by the proteomic profiling of the Exo3D cargo that identified wound healing-related proteins, such as TGF-β, ITGA1-3/5, IL-6, CDC151, S100A10 and Wnt5α. Moreover, when loaded with A151 ODN, Exo3D differentially mediated wound healing-related trophic factors reducing the systemic levels of IL-6 and TNF-α at the late stage of wound healing in vivo.

Conclusion

Our results support the potential of A151-loaded Exo3D for the treatment of chronic wounds by promoting skin regeneration, while modulating the systemic levels of the pro-inflammatory cytokines.

The Impact of Iron Chelators on the Biology of Cancer Stem Cells

Neoplastic diseases are still a major medical challenge, requiring a constant search for new therapeutic options. A serious problem of many cancers is resistance to anticancer drugs and disease progression in metastases or local recurrence. These characteristics of cancer cells may be related to the specific properties of cancer stem cells (CSC). CSCs are involved in inhibiting cells’ maturation, which is essential for maintaining their self-renewal capacity and pluripotency. They show increased expression of transcription factor proteins, which were defined as stemness-related markers. This group of proteins includes OCT4, SOX2, KLF4, Nanog, and SALL4. It has been noticed that the metabolism of cancer cells is changed, and the demand for iron is significantly increased. Iron chelators have been proven to have antitumor activity and influence the expression of stemness-related markers, thus reducing chemoresistance and the risk of tumor cell progression. This prompts further investigation of these agents as promising anticancer novel drugs. The article presents the characteristics of stemness markers and their influence on the development and course of neoplastic disease. Available iron chelators were also described, and their effects on cancer cells and expression of stemness-related markers were analyzed.

Six Shades of Vascular Smooth Muscle Cells Illuminated by KLF4 (Krüppel-Like Factor 4)

Multiple layers of vascular smooth muscle cells (vSMCs) are present in blood vessels forming the media of the vessel wall. vSMCs provide a vessel wall structure, enabling it to contract and relax, thus modulating blood flow. They also play a crucial role in the development of vascular diseases, such as atherosclerosis and aortic aneurysm formation. vSMCs display a remarkable high degree of plasticity. At present, the number of different vSMC phenotypes has only partially been characterized. By mapping vSMC phenotypes in detail and identifying triggers for phenotype switching, the relevance of the different phenotypes in vascular disease may be identified. Up until recently, vSMCs were classified as either contractile or dedifferentiated (ie, synthetic). However, single-cell RNA sequencing studies revealed such dedifferentiated arterial vSMCs to be highly diverse. Currently, no consensus exist about the number of vSMC phenotypes. Therefore, we reviewed the data from relevant single-cell RNA sequencing studies, and classified a total of 6 vSMC phenotypes. The central dedifferentiated vSMC type that we classified is the mesenchymal-like phenotype. Mesenchymal-like vSMCs subsequently seem to differentiate into fibroblast-like, macrophage-like, osteogenic-like, and adipocyte-like vSMCs, which contribute differentially to vascular disease. This phenotype switching between vSMCs requires the transcription factor KLF4 (Kruppel-like factor 4). Here, we performed an integrated analysis of the data about the recently identified vSMC phenotypes, their associated gene expression profiles, and previous vSMC knowledge to better understand the role of vSMC phenotype transitions in vascular pathology.

β2-adrenergic receptor signaling regulates metabolic pathways critical to myeloid-derived suppressor cell function within the TME

Myeloid-derived suppressor cells (MDSCs) impede antitumor immunity; however, the precise mechanisms that regulate their suppressive function remain unresolved. Identifying these mechanisms could lead to therapeutic interventions to boost cancer immunotherapy efficacy. Here, we reveal that β2 adrenergic receptor (β2-AR) expression on MDSCs increases with tumor growth and that the β2-AR stress pathway drives the immune suppressive activity of MDSCs by altering their metabolism. We show that β2-AR signaling decreases glycolysis and increases oxidative phosphorylation and fatty acid oxidation (FAO). It also increases expression of the fatty acid transporter CPT1A, which is necessary for the FAO-mediated immunosuppressive function of MDSCs. Moreover, we show that β2-AR signaling increases autophagy and activates the arachidonic acid cycle, both required for increasing the release of the immunosuppressive mediator, PGE2. Our data reveal that β2-AR signaling triggered by stress is an important physiological regulator of key metabolic pathways in MDSCs, driving their immunosuppressive function.

Mohammadpour et al. show that β2-AR signaling in MDSCs alters their metabolic state and increases their immunosuppressive function. Specific processes found to be increased include fatty acid oxidation, oxidative phosphorylation, and autophagy. In addition, these metabolic alterations facilitate an increase in PGE2 production via elevated COX2 expression.

Transcription factors Krüppel-like factor 4 and paired box 5 regulate the expression of the Grainyhead-like genes

Genes from the Grainyhead-like (GRHL) family code for transcription factors necessary for the development and maintenance of various epithelia. These genes are also very important in the development of many types of cancer. However, little is known about the regulation of expression of GRHL genes. Previously, there were no systematic analyses of the promoters of GRHL genes or transcription factors that bind to these promoters. Here we report that the Krüppel-like factor 4 (KLF4) and the paired box 5 factor (PAX5) bind to the regulatory regions of the GRHL genes and regulate their expression. Ectopic expression of KLF4 or PAX5 alters the expression of GRHL genes. In KLF4-overexpressing HEK293 cells, the expression of GRHL1 and GRHL3 genes was upregulated by 32% and 60%, respectively, whereas the mRNA level of GRHL2 gene was lowered by 28% when compared to the respective controls. The levels of GRHL1 and GRHL3 expression were decreased by 30% or 33% in PAX5-overexpressing HEK293 cells. The presence of minor frequency allele of single nucleotide polymorphism rs115898376 in the promoter of the GRHL1 gene affected the binding of KLF4 to this site. The evidence presented here suggests an important role of KLF4 and PAX5 in the regulation of expression of GRHL1-3 genes.

Myeloid-derived suppressor cells (MDSC): When good intentions go awry

MDSC are a heterogeneous population of immature myeloid cells that are released by biological stress such as tissue damage and inflammation. Conventionally, MDSC are known for their detrimental role in chronic inflammation and neoplastic conditions. However, their intrinsic functions in immunoregulation, wound healing, and angiogenesis are intended to protect from over-reactive immune responses, maintenance of immunotolerance, tissue repair, and homeostasis. Paradoxically, under certain conditions, MDSC can impair protective immune responses and exacerbate the disease. The transition from protective to harmful MDSC is most likely driven by environmental and epigenetic mechanisms induced by prolonged exposure to unresolved inflammatory triggers. Here, we review several examples of the dual impact of MDSC in conditions such as maternal-fetal tolerance, self-antigens immunotolerance, obesity-associated cancer, sepsis and trauma. Moreover, we also highlighted the evidence indicating that MDSC have a role in COVID-19 pathophysiology. Finally, we have summarized the evidence indicating epigenetic mechanisms associated with MDSC function.

Mussel-Inspired Surface Immobilization of Heparin on Magnetic Nanoparticles for Enhanced Wound Repair via Sustained Release of a Growth Factor and M2 Macrophage Polarization

Efficient reconstruction of a fully functional skin after wounds requires multiple functionalities of wound dressing due to the complexity of healing. In these regards, topical administration of functionalized nanoparticles capable of sustainably releasing bioactive agents to the wound site may significantly accelerate wound repair. Among the various nanoparticles, superparamagnetic iron oxide (Fe₃O₄) nanoparticles gain increasing attractiveness due to their intrinsic response to an external magnetic field (eMF). Herein, based on the Fe₃O₄ nanoparticle, we developed a fibroblast growth factor (bFGF)-loaded Fe₃O₄ nanoparticle using a simple mussel-inspired surface immobilization method. This nanoparticle, named as bFGF-HDC@Fe₃O₄, could stabilize bFGF in various conditions and exhibited sustained release of bFGF. In addition, an in vitro study discovered that bFGF-HDC@Fe₃O₄ could promote macrophage polarization toward an anti-inflammatory (pro-healing) M2 phenotype especially under eMF. Further, in vivo full-thickness wound animal models demonstrated that bFGF-HDC@Fe₃O₄ could significantly accelerate wound healing through M2 macrophage polarization and increased cell proliferation. Therefore, this approach of realizing sustained the release of the growth factor with magnetically macrophage regulating behavior through modification of Fe₃O₄ nanoparticles offers promising potential to tissue-regenerative applications.

KLF4 Promotes Diabetic Chronic Wound Healing by Suppressing Th17 Cell Differentiation in an MDSC-Dependent Manner

OBJECTIVES

Diabetic wound inflammation deficiencies lead to ulcer development and eventual amputation and disability. Our previous research demonstrates that myeloid-derived suppressor cells (MDSCs) accumulate during inflammation and promote chronic wound healing via the regulation of Kruppel-like factor 4 (KLF4). In this study, we aimed to investigate the potential roles of MDSCs and KLF4 in diabetic wound healing.

METHODS

An ob/ob mouse pressure ulcer (PU) model was used to evaluate the process of wound healing. The expression levels of KLF4 and IL-17A were measured by real-time PCR, and the population of MDSCs and Th17 cells was measured by flow cytometry. The levels of cytokines were determined by an immunosuppression assay.

RESULTS

KLF4 deficiency in the diabetic PU model resulted in decreased accumulation of MDSCs, increased expansion of Th17 cells, and significantly delayed wound healing. Conversely, KLF4 activation by APTO-253 accelerated wound healing accompanied by increased MDSC populations and decreased numbers of Th17 cells. MDSCs have been proven to mediate Th17 differentiation via cytokines, and our in vitro data showed that elevated KLF4 expression in MDSCs resulted in reduced Th17 cell numbers and, thus, decreased levels of cytokines indispensable for Th17 differentiation.

CONCLUSIONS

Our study revealed a previously unreported function of KLF4-regulated MDSCs in diabetic wound healing and identified APTO-253 as a potential agent to improve the healing of pressure ulcers.

Recent Discoveries on the Involvement of Krüppel-Like Factor 4 in the Most Common Cancer Types

Krüppel-like factor 4 (KLF4) is a transcription factor highly conserved in evolution. It is particularly well known for its role in inducing pluripotent stem cells. In addition, KLF4 plays many roles in cancer. The results of most studies suggest that KLF4 is a tumor suppressor. However, the functioning of KLF4 is regulated at many levels. These include regulation of transcription, alternative splicing, miRNA, post-translational modifications, subcellular localization, protein stability and interactions with other molecules. Simple experiments aimed at assaying transcript levels or protein levels fail to address this complexity and thus may deliver misleading results. Tumor subtypes are also important; for example, in prostate cancer KLF4 is highly expressed in indolent tumors where it impedes tumor progression, while it is absent from aggressive prostate tumors. KLF4 is important in regulating response to many known drugs, and it also plays a role in tumor microenvironment. More and more information is available about upstream regulators, downstream targets and signaling pathways associated with the involvement of KLF4 in cancer. Furthermore, KLF4 performs critical function in the overall regulation of tissue homeostasis, cellular integrity, and progression towards malignancy. Here we summarize and analyze the latest findings concerning this fascinating transcription factor.

Impact of KLF4 on Cell Proliferation and Epithelial Differentiation in the Context of Cystic Fibrosis

Cystic fibrosis (CF) cells display a more cancer-like phenotype vs. non-CF cells. KLF4 overexpression has been described in CF and this transcriptional factor acts as a negative regulator of wt-CFTR. KLF4 is described as exerting its effects in a cell-context-dependent fashion, but it is generally considered a major regulator of proliferation, differentiation, and wound healing, all the processes that are also altered in CF. Therefore, it is relevant to characterize the differential role of KLF4 in these processes in CF vs. non-CF cells. To this end, we used wt- and F508del-CFTR CFBE cells and their respective KLF4 knockout (KO) counterparts to evaluate processes like cell proliferation, polarization, and wound healing, as well as to compare the expression of several epithelial differentiation markers. Our data indicate no major impact of KLF4 KO in proliferation and a differential impact of KLF4 KO in transepithelial electrical resistance (TEER) acquisition and wound healing in wt- vs. F508del-CFTR cells. In parallel, we also observed a differential impact on the levels of some differentiation markers and epithelial-mesencymal transition (EMT)-associated transcription factors. In conclusion, KLF4 impacts TEER acquisition, wound healing, and the expression of differentiation markers in a way that is partially dependent on the CFTR-status of the cell.

Functional genomics analysis of human colon organoids identifies key transcription factors

Organoids are a valuable three-dimensional (3D) model to study the differentiated functions of the human intestinal epithelium. They are a particularly powerful tool to measure epithelial transport processes in health and disease. Though biological assays such as organoid swelling and intraluminal pH measurements are well established, their underlying functional genomics are not well characterized. Here we combine genome-wide analysis of open chromatin by ATAC-Seq with transcriptome mapping by RNA-Seq to define the genomic signature of human intestinal organoids (HIOs). These data provide an important tool for investigating key physiological and biochemical processes in the intestinal epithelium. We next compared the transcriptome and open chromatin profiles of HIOs with equivalent data sets from the Caco2 colorectal carcinoma line, which is an important two-dimensional (2D) model of the intestinal epithelium. Our results define common features of the intestinal epithelium in HIO and Caco2 and further illustrate the cancer-associated program of the cell line. Generation of Caco2 cysts enabled interrogation of the molecular divergence of the 2D and 3D cultures. Overrepresented motif analysis of open chromatin peaks identified caudal type homeobox 2 (CDX2) as a key activating transcription factor in HIO, but not in monolayer cultures of Caco2. However, the CDX2 motif becomes overrepresented in open chromatin from Caco2 cysts, reinforcing the importance of this factor in intestinal epithelial differentiation and function. Intersection of the HIO and Caco2 transcriptomes further showed functional overlap in pathways of ion transport and tight junction integrity, among others. These data contribute to understanding human intestinal organoid biology.

The Engagement Between MDSCs and Metastases: Partners in Crime

Tumor metastases represent the major cause of cancer-related mortality, confirming the urgent need to identify key molecular pathways and cell-associated networks during the early phases of the metastatic process to develop new strategies to either prevent or control distal cancer spread. Several data revealed the ability of cancer cells to establish a favorable microenvironment, before their arrival in distant organs, by manipulating the cell composition and function of the new host tissue where cancer cells can survive and outgrow. This predetermined environment is termed “pre-metastatic niche” (pMN). pMN development requires that tumor-derived soluble factors, like cytokines, growth-factors and extracellular vesicles, genetically and epigenetically re-program not only resident cells (i.e., fibroblasts) but also non-resident cells such as bone marrow-derived cells. Indeed, by promoting an “emergency” myelopoiesis, cancer cells switch the steady state production of blood cells toward the generation of pro-tumor circulating myeloid cells defined as myeloid-derived suppressor cells (MDSCs) able to sustain tumor growth and dissemination. MDSCs are a heterogeneous subset of myeloid cells with immunosuppressive properties that sustain metastatic process. In this review, we discuss current understandings of how MDSCs shape and promote metastatic dissemination acting in each fundamental steps of cancer progression from primary tumor to metastatic disease.

Safety and Efficacy of Human Adipose-Derived Stromal/Stem Cell Therapy in an Immunocompetent Murine Pressure Ulcer Model

Pressure injuries/ulcers are frequent complications in elderly, paraplegic, and quadriplegic patients, which account for considerable cost to the international health care economy and remain refractory to current treatment options. Autologous or allogeneic adult stromal/stem cells represent an alternative therapeutic approach. The current study extends prior findings by exploring the safety and efficacy of human adipose-derived stromal/stem cell (ASC) therapy in an established immunocompetent murine skin pressure ulcer model where dermal fibroblast cells (DFCs) served as a control. Human adipose tissue was processed using a closed system device designed for point-of-care use in the operating room and on file with the Food and Drug Administration. Cell characterization was performed using colony-forming unit-fibroblast, differentiation, and immunophenotypic assays in vitro. Wound healing was assessed over a 20-day period based on photomicrographs, histology, and immunohistochemistry. The isolated human ASCs displayed significantly greater colony formation relative to DFCs while both populations exhibited comparable immunophenotype and differentiation potential. Both fresh and cryopreserved human ASCs significantly accelerated and enhanced wound healing in young (2 month) mice of both sexes relative to DFC controls based on tissue architecture and CD68⁺ cell infiltration. In contrast, while injection of either fresh or cryopreserved human ASCs was safe in older mice, the fresh ASCs significantly enhanced wound closure relative to the cryopreserved ASCs. Overall, these findings support the safety and efficacy of human ASCs isolated using a closed system device designed for clinical procedures in the future treatment of pressure injuries.

Single-cell analysis reveals fibroblast heterogeneity and myeloid-derived adipocyte progenitors in murine skin wounds

During wound healing in adult mouse skin, hair follicles and then adipocytes regenerate. Adipocytes regenerate from myofibroblasts, a specialized contractile wound fibroblast. Here we study wound fibroblast diversity using single-cell RNA-sequencing. On analysis, wound fibroblasts group into twelve clusters. Pseudotime and RNA velocity analyses reveal that some clusters likely represent consecutive differentiation states toward a contractile phenotype, while others appear to represent distinct fibroblast lineages. One subset of fibroblasts expresses hematopoietic markers, suggesting their myeloid origin. We validate this finding using single-cell western blot and single-cell RNA-sequencing on genetically labeled myofibroblasts. Using bone marrow transplantation and Cre recombinase-based lineage tracing experiments, we rule out cell fusion events and confirm that hematopoietic lineage cells give rise to a subset of myofibroblasts and rare regenerated adipocytes. In conclusion, our study reveals that wounding induces a high degree of heterogeneity among fibroblasts and recruits highly plastic myeloid cells that contribute to adipocyte regeneration.

The diversity of fibroblasts contributing to wound healing is unclear. Here, the authors use single-cell RNA-sequencing to identify heterogeneity among murine fibroblasts in the wound and find that recruited myeloid cells contribute to adipocyte regeneration during healing.

Subcutaneously administered adrenomedullin exerts a potent therapeutic effect in a murine model of ulcerative colitis

Adrenomedullin (AM) exerts a potent anti-inflammatory effect. Intrarectal or consecutive intravenous administrations of AM reduce pathological manifestations in rodent colitis models. However, in clinical applications, a safer administration route that provides stronger alleviation of patient burden is preferred. We investigated whether subcutaneously administered AM is effective against dextran sulfate sodium (DSS)-induced colitis. C57BL/6J mice were administered 1% DSS in drinking water and received AM at 8, 40 or 80 nmol/kg subcutaneously once a day for 7 consecutive days. Subcutaneously administered AM significantly and dose-dependently ameliorated body weight loss, diarrhea, and histological severity of colonic inflammation in DSS-treated mice. The AM therapeutic effect was associated with the upregulation of the production of autocrine AM, and expression of cAMP, c-fos, KLF4, and downregulation of STAT3 and NF-κB p65 phosphorylation, as well as a decrease in proinflammatory cytokine expression in the colon. Subcutaneous AM treatment potently attenuated DSS-induced colitis, which suggests that AM administered subcutaneously in ulcerative colitis (UC) patients may decrease diseases burden and improve quality of life.

Effects of Derinat on ischemia-reperfusion-induced pressure ulcer mouse model

Sodium salt of deoxyribonucleic acid (DNA), Derinat, isolated from the soft roes of Russian sturgeon, has been utilized as an immunomodulator for the treatment of reactive oxygen species (ROS)-associated diseases in clinics. Here we show that treatment with Derinat has an anti-inflammatory and anti-oxidative effects on cutaneous ischemia-reperfusion (IR) injury in pressure ulcer (PU) model mice. Dorsal skin damage and dermal edema in mild PU model mice were attenuated by treatment with Derinat. Immunohistochemical and biochemical analyses showed that Derinat suppressed IR-induced oxidative damage, i.e. accumulation of 8-hydroxy-2'-deoxyguanosine (8-OHdG), and related inflammatory factors such as cyclooxygenase 2 (COX-2) and IL-6 receptor (IL-6R) in dorsal skin from PU model mice. We also verified that phospholyated/non-phosphorylated ratio of extracellular signal-regulated kinase (Erk) and p38 mitogen-activated protein kinase (MAPK) increased after IR, which were attenuated by Derinat. We then compared the effect of Derinat with that of salmon DNA and other PU therapeutic agents, prostaglandin E1 (PGE1) and basic fibroblast growth factor (bFGF), by using severe PU model mice. The effects of Derinat and salmon-DNA were compatible with those of PGE1 and bFGF. These results suggest that Derinat other fish-derived DNA formulation could be effective enough and become intriguing new therapeutic options.

Deficiency of KLF4 compromises the lung function in an acute mouse model of allergic asthma

Asthma is a chronic inflammatory disease of the airways and the mechanisms are not fully understood. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of monocytes, granulocyte and myeloid cells at early stage of differentiation. They possess phenotypic plasticity and regulate airway inflammation. We recently reported that Kruppel-like factor 4 (KLF4) regulates MDSC differentiation into fibrocytes, emerging effectors in chronic inflammation. However, the role of KLF4 in asthma is not known. Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived cytokine and a key initiator of allergic airway inflammation. Given the fact that TSLP promotes Th2 cytokine production that increases MDSC differentiation into fibrocytes, we postulate that KLF4 regulates asthma in a TSLP-dependent manner. In this study, we utilized a model of allergic asthma with ovalbumin challenge (OVA). We found that upon OVA treatment the wild type mice had increased MDSC infiltration into the lung, up-regulation of KLF4 and TSLP gene expression, and higher levels of Th2 cytokines including IL4 and IL13. Consistently, lack of KLF4 expression in monocytes and lung epithelial cells resulted in decreased TSLP expression and lower levels of Th2 cytokines in mice, and fibrocyte generation was compromised. KLF4 deficiency in these cells also led to decreased airway hyperresponsiveness (AHR), a cardinal feature of asthma, as assessed by whole body plethysmography. Moreover, lung fibrosis as measured by trichome staining was attenuated and the population of CD45 + COL1A1+ fibrocytes was diminished in this setting. Together, our results suggest that KLF4 regulates asthma development in a TSLP- and fibrocyte-dependent manner.

Heterogeneity of Fibroblasts and Myofibroblasts in Pulmonary Fibrosis

PURPOSE OF REVIEW

Idiopathic Pulmonary Fibrosis (IPF) is the most common form of interstitial lung diseases of unknown eathiopathogenesis, mean survival of 3-5 years and limited therapeutics. Characterized by a loss of alveolar type II epithelial cells and aberrant activation of stromal cells, considerable effort was undertaken to characterize the origin and activation mechanisms of fibroblasts and myofibroblasts in IPF lungs. In this review, the origin and contribution of fibroblast and myofibroblasts in lung fibrosis will be summarized.

RECENT FINDINGS

Lineage tracing experiments suggested that interstitial lung fibroblasts and lipofibroblasts, pericytes and mesothelial cells differentiate into myofibroblasts. However, epithelial and bone marrow derived cells may give rise to collagen expressing fibroblasts but do not differentiate into myofibroblasts.

SUMMARY

There is great heterogeneity in fibroblasts and myofibroblasts in fibrotic lungs. Further, there is evidence for the expansion of pericyte derived myofibroblasts and loss of lipofibroblasts and lipofibroblast derived myofibroblasts in IPF.

Role of carbonic anhydrases in skin wound healing

Skin wound closure occurs when keratinocytes migrate from the edge of the wound and re-epithelialize the epidermis. Their migration takes place primarily before any vascularization is established, that is, under hypoxia, but relatively little is known regarding the factors that stimulate this migration. Hypoxia and an acidic environment are well-established stimuli for cancer cell migration. The carbonic anhydrases (CAs) contribute to tumor cell migration by generating an acidic environment through the conversion of carbon dioxide to bicarbonate and a proton. On this basis, we explored the possible role of CAs in tissue regeneration using mouse skin wound models. We show that the expression of mRNAs encoding CA isoforms IV and IX are increased (~25 × and 4 ×, respectively) during the wound hypoxic period (days 2-5) and that cells expressing CAs form a band-like structure beneath the migrating epidermis. RNA-Seq analysis suggested that the CA IV-specific signal in the wound is mainly derived from neutrophils. Due to the high level of induction of CA IV in the wound, we treated skin wounds locally with recombinant human CA IV enzyme. Recombinant CA IV significantly accelerated wound re-epithelialization. Thus, CA IV could contribute to wound healing by providing an acidic environment in which the migrating epidermis and neutrophils can survive and may offer novel opportunities to accelerate wound healing under compromised conditions.

Krüppel-like factor 4 (KLF4): What we currently know

Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger-containing transcription factor that regulates diverse cellular processes such as cell growth, proliferation, and differentiation. Since its discovery in 1996, KLF4 has been gaining a lot of attention, particularly after it was shown in 2006 as one of four factors involved in the induction of pluripotent stem cells (iPSCs). Here we review the current knowledge about the different functions and roles of KLF4 in various tissue and organ systems.

Pharmacological activation of cannabinoid 2 receptor attenuates inflammation, fibrogenesis, and promotes re-epithelialization during skin wound healing

Previous studies showed that cannabinoid 2 (CB2) receptor is expressed in multiple effector cells during skin wound healing. Meanwhile, its functional involvement in inflammation, fibrosis, and cell proliferation in other organs and skin diseases implied CB2 receptor might also regulate skin wound healing. To verify this hypothesis, mice excisional wounds were created and treated with highly selective CB2 receptor agonist GP1a (1-(2,4-dichlorophenyl)-6-methyl- N-piperidin-1-yl-4H-indeno[1,2-c]pyrazole-3-carboxamide) and antagonist AM630 ([6-iodo-2- methyl-1-(2-morpholin-4-ylethyl)indol-3-yl]-(4-methoxyphenyl)methanone) respectively. The inflammatory infiltration, cytokine expression, fibrogenesis, and wound re-epithelialization were analyzed. After CB2 receptor activation, neutrophil and macrophage infiltrations were reduced, and expressions of monocyte chemotactic protein (MCP)-1, stromal cell-derived factor (SDF)-1, Interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-β1 and vascular endothelial growth factor (VEGF)-A were decreased. Keratinocyte proliferation and migration were enhanced. Wound re-epithelialization was accelerated. Fibroblast accumulation and fibroblast-to-myofibroblast transformation were attenuated, and expression of pro-collagen I was decreased. Furthermore, HaCaT cells in vitro were treated with GP1a or AM630, which revealed that CB2 receptor activation promoted keratinocyte migration by inducing the epithelial to mesenchymal transition. These results, taken together, indicate that activating CB2 receptor could ameliorate wound healing by reducing inflammation, accelerating re-epithelialization, and attenuating scar formation. Thus, CB2 receptor agonist might be a novel perspective for skin wound therapy.

Heme Oxygenase-1 Induction Prevents Autoimmune Diabetes in Association With Pancreatic Recruitment of M2-Like Macrophages, Mesenchymal Cells, and Fibrocytes

Immunoregulatory and regenerative processes are activated in the pancreas during the development of type 1 diabetes (T1D) but are insufficient to prevent the disease. We hypothesized that the induction of cytoprotective heme oxygenase-1 (HO-1) by cobalt protophoryrin (CoPP) would prevent T1D by promoting anti-inflammatory and pro-repair processes. Diabetes-prone BioBreeding rats received ip CoPP or saline twice per week for 3 weeks, starting at 30 days and were monitored for T1D. Immunohistochemistry, confocal microscopy, quantitative RT-PCR, and microarrays were used to evaluate postinjection pancreatic changes at 51 days, when islet inflammation is first visible. T1D was prevented in CoPP-treated rats (29% vs 73%). Pancreatic Hmox1 was up-regulated along with islet-associated CD68(+)HO-1(+) cells, which were also observed in a striking peri-lobular interstitial infiltrate. Most interstitial cells expressed the mesenchymal marker vimentin and the hematopoietic marker CD34. Spindle-shaped, CD34(+)vimentin(+) cells coexpressed collagen V, characteristic of fibrocytes. M2 macrophage factors Krüppel-like factor 4, CD163, and CD206 were expressed by interstitial cells, consistent with pancreatic upregulation of several M2-associated genes. CoPP upregulated islet-regenerating REG genes and increased neogenic REG3β(+) and insulin(+) clusters. Thus, short-term induction of HO-1 promoted a protective M2-like milieu in the pancreas and recruited mesenchymal cells, M2 macrophages, and fibrocytes that imparted immunoregulatory and pro-repair effects, preventing T1D.