Recombinant N-Terminal Slit2 Inhibits TGF-β-Induced Fibroblast Activation and Renal Fibrosis

A first-in-human study of quantitative ultrasound to assess transplant kidney fibrosis

Kidney transplantation is the optimal treatment for renal failure. In the United States, a biopsy at the time of organ procurement is often used to assess kidney quality to decide whether it should be used for transplant. This assessment is focused on renal fibrotic burden, because fibrosis is an important measure of irreversible kidney injury. Unfortunately, biopsy at the time of transplant is plagued by problems, including bleeding risk, inaccuracies introduced by sampling bias and rapid sample preparation, and the need for round-the-clock pathology expertise. We developed a quantitative algorithm, called renal H-scan, that can be added to standard ultrasound workflows to quickly and noninvasively measure renal fibrotic burden in preclinical animal models and human transplant kidneys. Furthermore, we provide evidence that biopsy-based fibrosis estimates, because of their highly localized nature, are inaccurate measures of whole-kidney fibrotic burden and do not associate with kidney function post-transplant. In contrast, we show that whole-kidney H-scan fibrosis estimates associate closely with post-transplant renal function. Taken together, our data suggest that the addition of H-scan to standard ultrasound workflows could provide a safe, rapid and easy-to-perform method for accurate quantification of transplant kidney fibrotic burden, and thus better prediction of post-transplant renal outcomes.

The neurorepellent SLIT2 inhibits LPS-induced proinflammatory signaling in macrophages

Macrophages are important mediators of immune responses with critical roles in the recognition and clearance of pathogens, as well as in the resolution of inflammation and wound healing. The neuronal guidance cue SLIT2 has been widely studied for its effects on immune cell functions, most notably directional cell migration. Recently, SLIT2 has been shown to directly enhance bacterial killing by macrophages, but the effects of SLIT2 on inflammatory activation of macrophages are less known. Using RNA sequencing analysis, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay, we determined that in murine bone marrow-derived macrophages challenged with the potent proinflammatory mediator lipopolysaccharide (LPS), exposure to the bioactive N-terminal fragment of SLIT2 (NSLIT2) suppressed production of proinflammatory cytokines interleukin (IL)-6 and IL-12 and concurrently increased the anti-inflammatory cytokine IL-10. We found that NSLIT2 inhibited LPS-induced MyD88- and TRIF-mediated signaling cascades and did not inhibit LPS-induced internalization of Toll-like receptor 4 (TLR4), but instead inhibited LPS-induced upregulation of macropinocytosis. Inhibition of macropinocytosis in macrophages attenuated LPS-induced production of proinflammatory IL-6 and IL-12 and concurrently enhanced anti-inflammatory IL-10. Taken together, our results indicate that SLIT2 can selectively modulate macrophage response to potent proinflammatory stimuli, such as LPS, by attenuating proinflammatory activation and simultaneously enhancing anti-inflammatory activity. Our results highlight the role of macropinocytosis in proinflammatory activation of macrophages exposed to LPS. Given that LPS-producing bacteria cause host illness through synergistic direct bacterial infection and excessive LPS-induced systemic inflammation, our work suggests a novel therapeutic role for SLIT2 in combatting the significant morbidity and mortality of patients with Gram-negative bacterial sepsis.

Cell membrane-camouflaged nanoparticles activate fibroblast-myofibroblast transition to promote skin wound healing

The fibroblast-myofibroblast transition marked by extracellular matrix (ECM) secretion and contraction of actomyosin-based stress fibers, plays central roles in the wound healing process. This work aims to utilize the cell membrane-based nanoplatform to improve the outcomes of dysregulated wound healing. The cell membranes of myofibroblasts isolated from mouse skin are used as the camouflage for gold nanoparticles loaded with IL-4 cytokine. The membrane-modified nanoparticles show effective in situ clearance of bacterial infection, and act as the activator in IL-4Rα signaling pathway to induce pro-inflammatory M1 macrophages into the anti-inflammatory M2 phenotype. Thus, the poor bacteria-clearance and non-stop inflammation in refractory wounds are improved and accelerated. Furthermore, the nanoplatform releases myofibroblast membranes to propel primitive fibroblasts toward the fibroblast-myofibroblast transition in an epigenetic manner. Matrix-production, vascularization, and epithelial regeneration are then initiated, leading to the satisfactory wound closure. Our study devises a new strategy for activating fibroblasts into myofibroblasts under prolonged and continuous exposure to the fibrotic environment, and develops a promising biomimetic nanoplatform for effective treatment of dysregulated chronic wound healing.

Slit1 Promotes Hypertrophic Scar Formation Through the TGF-β Signaling Pathway

Background and objectives: Slit1 is a secreted protein that is closely related to cell movement and adhesion. Few studies related to fibrosis exist, and the preponderance of current research is confined to the proliferation and differentiation of neural systems. Hypertrophic scars (HTSs) are delineated by an overproduction of the extracellular matrix (ECM) by activated fibroblasts, leading to anomalous fibrosis, which is a severe sequela of burns. However, the functionality of Slit1 in HTS formation remains unknown. We aimed to investigate whether Slit1 regulates fibroblasts through a fibrosis-related mechanism derived from post-burn HTS tissues and normal patient tissues. Methods: Human normal fibroblasts (HNFs) and hypertrophic scar fibroblasts (HTSFs) were extracted from normal skin and post-burn HTS tissues, with settings grouped according to the patient of origin. Cell proliferation was evaluated using a CellTiter-Glo Luminescent Cell Viability Assay Kit. Cell migration experiments were carried out using a μ-Dish insert system. Protein and mRNA expression levels were quantified by Western blot and quantitative real-time polymerase chain reaction. Results: We found increased expressions of Slit1 in HTS tissues and HTSFs compared to normal tissues and HNFs. The treatment of human recombinant Slit1 protein (rSlit1) within HNFs promoted cell proliferation and differentiation, leading to an upregulation in ECM components such as α-SMA, type I and III collagen, and fibronectin. The treatment of rSlit1 in HNFs facilitated cell migration, concurrent with enhanced levels of N-cadherin and vimentin, and a diminished expression of E-cadherin. Treatment with rSlit1 resulted in the phosphorylation of SMAD pathway proteins, including SMAD2, SMAD3, and SMAD1/5/8, and non-SMAD pathway proteins, including TAK1, JNK1, ERK1/2, and p38, in HNFs. Conclusions: Exogenous Slit1 potentiates the epithelial-mesenchymal transition and upregulates SMAD and non-SMAD signaling pathways in HNFs, leading to the development of HTS, suggesting that Slit1 is a promising new target for the treatment of post-burn HTS.

Recombinant Slit2 attenuates tracheal fibroblast activation in benign central airway obstruction by inhibiting the TGF-β1/Smad3 signaling pathway

Airway fibrosis is among the pathological manifestations of benign central airway obstruction noted in the absence of effective treatments and requires new drug targets to be developed. Slit guidance ligand 2-roundabout guidance receptor 1 (Slit2-Robo1) is involved in fibrosis and organ development. However, its significance in airway fibrosis has not yet been reported. The study explored how the recombinant protein Slit2 functions in transforming growth factor-β1 (TGF-β1)-mediated airway fibrosis in vivo and in vitro. In this study, Slit2 expression initially increased in the tracheal granulation tissues of patients with tracheobronchial stenosis but decreased in the fibrotic tissue. In primary rat tracheal fibroblasts (RTFs), recombinant Slit2 inhibited the expression of extracellular matrices such as Timp1, α-SMA, and COL1A2, whereas recombinant TGF-β1 promoted the expression of Robo1, α-SMA, and COL1A2. Slit2 and TGF-β1 played a mutual inhibitory role in RTFs. Slit2 supplementation and Robo1 downregulation inhibited excessive extracellular matrix (ECM) deposition induced by TGF-β1 in RTFs via the TGF-β1/Smad3 pathway. Ultimately, exogenous Slit2 and Robo1 knockdown-mediated attenuation of airway fibrosis were validated in a trauma-induced rat airway obstruction model. These findings demonstrate that recombinant Slit2 alleviated pathologic tracheobronchial healing by attenuating excessive ECM deposition. Slit2-Robo1 is an attractive target for further exploring the mechanisms and treatment of benign central airway obstruction.

Downregulation of Roundabout guidance receptor 2 suppresses hepatocellular carcinoma progression by interacting with Y-box binding protein 1

Roundabout guidance receptor 2 (Robo2) is closely related to malignant tumors such as pancreatic cancer and liver fibrosis, but there is no relevant research on the role of Robo2 in HCC. The study will further explore the function and mechanism of Robo2 and its downstream target genes in HCC. Firstly, Robo2 protein levels in human HCC tissues and paired adjacent normal liver tissues were detected. Then we established HepG2 and Huh7 hepatoma cell lines with knock-down Robo2 by transfection with lentiviral vectors, and examined the occurrence of EMT, proliferation and apoptosis abilities in HCC cells by western blot, flow cytometry, wound healing assay and TUNEL staining. Then we verified the interaction between Robo2 and its target gene by Co-IP and immunofluorescence co-staining, and further explored the mechanism of Robo2 and YB-1 by rescue study. The protein expression level of Robo2 in HCC was considerably higher than that in the normal liver tissues. After successfully constructing hepatoma cells with knock-down Robo2, it was confirmed that down-regulated Robo2 suppressed EMT and proliferation of hepatoma cells, and accelerated the cell apoptosis. High-throughput sequencing and validation experiments verified that YB-1 was the downstream target gene of Robo2, and over-expression of YB-1 could reverse the apoptosis induced by Robo2 down-regulation and its inhibitory effect on EMT and proliferation. Robo2 deficiency inhibits EMT and proliferation of hepatoma cells and augments the cell apoptosis by regulating YB-1, thus inhibits the occurrence of HCC and provides a new strategy for the treatment of HCC.

TGF-β, EMT, and resistance to anti-cancer treatment

Transforming growth factor-β (TGF-β) signaling regulates cell-specific programs involved in embryonic development, wound-healing, and immune homeostasis. Yet, during tumor progression, these TGF-β-mediated programs are altered, leading to epithelial cell plasticity and a reprogramming of epithelial cells into mesenchymal lineages through epithelial-to-mesenchymal transition (EMT), a critical developmental program in morphogenesis and organogenesis. These changes, in turn, lead to enhanced carcinoma cell invasion, metastasis, immune cell differentiation, immune evasion, and chemotherapy resistance. Here, we discuss EMT as one of the critical programs associated with carcinoma cell plasticity and the influence exerted by TGF-β on carcinoma status and function. We further explore the composition of carcinoma and other cell populations within the tumor microenvironment, and consider the relevant outcomes related to the programs associated with cancer treatment resistance.

Recombinant Slit2 suppresses neuroinflammation and Cdc42-mediated brain infiltration of peripheral immune cells via Robo1-srGAP1 pathway in a rat model of germinal matrix hemorrhage

BACKGROUND

Germinal matrix hemorrhage (GMH) is a devastating neonatal stroke, in which neuroinflammation is a critical pathological contributor. Slit2, a secreted extracellular matrix protein, plays a repulsive role in axon guidance and leukocyte chemotaxis via the roundabout1 (Robo1) receptor. This study aimed to explore effects of recombinant Slit2 on neuroinflammation and the underlying mechanism in a rat model of GMH.

METHODS

GMH was induced by stereotactically infusing 0.3 U of bacterial collagenase into the germinal matrix of 7-day-old Sprague Dawley rats. Recombinant Slit2 or its vehicle was administered intranasally at 1 h after GMH and daily for 3 consecutive days. A decoy receptor recombinant Robo1 was co-administered with recombinant Slit2 after GMH. Slit2 siRNA, srGAP1 siRNA or the scrambled sequences were administered intracerebroventricularly 24 h before GMH. Neurobehavior, brain water content, Western blotting, immunofluorescence staining and Cdc42 activity assays were performed.

RESULTS

The endogenous brain Slit2 and Robo1 expressions were increased after GMH. Robo1 was expressed on neuron, astrocytes and infiltrated peripheral immune cells in the brain. Endogenous Slit2 knockdown by Slit2 siRNA exacerbated brain edema and neurological deficits following GMH. Recombinant Slit2 (rSlit2) reduced neurological deficits, proinflammatory cytokines, intercellular adhesion molecules, peripheral immune cell markers, neuronal apoptosis and Cdc42 activity in the brain tissue after GMH. The anti-neuroinflammation effects were reversed by recombinant Robo1 co-administration or srGAP1 siRNA.

CONCLUSIONS

Recombinant Slit2 reduced neuroinflammation and neuron apoptosis after GMH. Its anti-neuroinflammation effects by suppressing onCdc42-mediated brain peripheral immune cells infiltration was at least in part via Robo1-srGAP1 pathway. These results imply that recombinant Slit2 may have potentials as a therapeutic option for neonatal brain injuries.

Role of the SLIT-ROBO signaling pathway in renal pathophysiology and various renal diseases

SLIT ligand and its receptor ROBO were initially recognized for their role in axon guidance in central nervous system development. In recent years, as research has advanced, the role of the SLIT-ROBO signaling pathway has gradually expanded from axonal repulsion to cell migration, tumor development, angiogenesis, and bone metabolism. As a secreted protein, SLIT regulates various pathophysiological processes in the kidney, such as proinflammatory responses and fibrosis progression. Many studies have shown that SLIT-ROBO is extensively involved in various aspects of kidney development and maintenance of structure and function. The SLIT-ROBO signaling pathway also plays an important role in different types of kidney disease. This article reviews the advances in the study of the SLIT-ROBO pathway in various renal pathophysiological and kidney disorders and proposes new directions for further research in this field.

MicroRNA-29a-3p prevents Schistosoma japonicum-induced liver fibrosis by targeting Roundabout homolog 1 in hepatic stellate cells

BACKGROUND

Schistosomiasis is a serious but neglected parasitic disease in humans that may lead to liver fibrosis and death. Activated hepatic stellate cells (HSCs) are the principal effectors that promote the accumulation of extracellular matrix (ECM) proteins during hepatic fibrosis. Aberrant microRNA-29 expression is involved in the development of fibrotic diseases. However, less is known about the role of miR-29 in Schistosoma japonicum (S. japonicum)-induced hepatic fibrosis.

METHODS

The levels of microRNA-29a-3p (miR-29a-3p) and Roundabout homolog 1 (Robo1) were examined in liver tissues during S. japonicum infection. The possible involvement of the miR-29a-3p-Robo1 signaling pathway was determined. We used MIR29A conditional knock-in mice and mice injected with an miR-29a-3p agomir to investigate the role of miR-29a-3p in schistosomiasis-induced hepatic fibrosis. The functional contributions of miR-29a-3p-Robo1 signaling in liver fibrosis and HSC activation were investigated using primary mouse HSCs and the human HSC cell line LX-2.

RESULTS

MiR-29a-3p was downregulated in humans and mice with schistosome-induced fibrosis, and Robo1 was upregulated in liver tissues. The miR-29a-3p targeted Robo1 and negatively regulated its expression. Additionally, the expression level of miR-29a-3p in schistosomiasis patients was highly correlated with the portal vein and spleen thickness diameter, which represent the severity of fibrosis. Furthermore, we demonstrated that efficient and sustained elevation of miR-29a-3p reversed schistosome-induced hepatic fibrosis. Notably, we showed that miR-29a-3p targeted Robo1 in HSCs to prevent the activation of HSCs during infection.

CONCLUSIONS

Our results provide experimental and clinical evidence that the miR-29a-3p-Robo1 signaling pathway in HSCs plays an important role in the development of hepatic fibrosis. Therefore, our study highlights the potential of miR-29a-3p as a therapeutic intervention for schistosomiasis and other fibrotic diseases.

MiR-424/TGIF2-Mediated Pro-Fibrogenic Responses in Oral Submucous Fibrosis

Oral submucous fibrosis (OSF) has been recognized as a potentially malignant disorder and is characterized by inflammation and the deposition of collagen. Among various regulators of fibrogenesis, microRNAs (miR) have received great attention but the detailed mechanisms underlying the miR-mediated modulations remain largely unknown. Here, we showed that miR-424 was aberrantly overexpressed in OSF tissues, and then we assessed its functional role in the maintenance of myofibroblast characteristics. Our results demonstrated that the suppression of miR-424 markedly reduced various myofibroblast activities (such as collagen contractility and migration ability) and downregulated the expression of fibrosis markers. Moreover, we showed that miR-424 exerted this pro-fibrosis property via direct binding to TGIF2, an endogenous repressor of the TGF-β signaling. In addition, our findings indicated that overexpression of miR-424 activated the TGF-β/Smad pathway, leading to enhanced myofibroblast activities. Altogether, our data revealed how miR-424 contributed to myofibroblast transdifferentiation, and targeting the miR-424/TGIF2 axis may be a viable direction for achieving satisfactory results from OSF treatment.

Myofibroblast YAP/TAZ activation is a key step in organ fibrogenesis

Fibrotic diseases account for nearly half of all deaths in the developed world. Despite its importance, the pathogenesis of fibrosis remains poorly understood. Recently, the two mechanosensitive transcription cofactors YAP and TAZ have emerged as important profibrotic regulators in multiple murine tissues. Despite this growing recognition, a number of important questions remain unanswered, including which cell types require YAP/TAZ activation for fibrosis to occur and the time course of this activation. Here, we present a detailed analysis of the role that myofibroblast YAP and TAZ play in organ fibrosis and the kinetics of their activation. Using analyses of cells, as well as multiple murine and human tissues, we demonstrated that myofibroblast YAP and TAZ were activated early after organ injury and that this activation was sustained. We further demonstrated the critical importance of myofibroblast YAP/TAZ in driving progressive scarring in the kidney, lung, and liver, using multiple transgenic models in which YAP and TAZ were either deleted or hyperactivated. Taken together, these data establish the importance of early injury-induced myofibroblast YAP and TAZ activation as a key event driving fibrosis in multiple organs. This information should help guide the development of new antifibrotic YAP/TAZ inhibition strategies.

The Therapeutic Role of Slit2 in Anti-fibrosis, Anti-inflammation and Anti-oxidative Stress in Rats with Coronary Heart Disease

To investigate the efficacy of Slit2 in the rats with coronary heart disease (CHD). CHD model were constructed by feeding high-fat food and injecting with pituitrin in rat, followed by recombinant Slit2 treatment, and then the cardiac function was evaluated by echocardiography, and the indicators concerning the cardiomyocyte injury markers and lipoprotein status and oxidative stress were measured. The Slit2 expression in the heart tissues was identified by immunofluorescence. Enzyme-linked immunosorbent assay (ELISA) was carried out to detect inflammatory cytokines, H2DCFDA staining to determine the ROS generation in heart tissues, Masson trichrome staining to observe myocardial fibrosis, and qRT-PCR and Western blotting to detect gene and protein expressions. Slit2 decreased the levels of LDH, CK-MB, cTnI, TG, TC and LDL-C and increased HDL-C level in CHD rats. In the normal heart tissues, Slit2 expression was significantly lower in cardiomyocytes than cardiac fibroblasts. Furthermore, the expressions of VCAM-1, ICAM-1, fibronectin and TGF-β1 were increased in the heart tissues of CHD rats with the obvious myocardial fibrosis, which were dose-dependently reversed by recombinant Slit2. In addition, recombinant Slit2 also dose-dependently increased the activity of NO, SOD, CAT and GSH-Px, and decreased TNF-α, IL-6, MCP-1, MDA and ROS in CHD rats. Slit2 was downregulated in myocardial tissue and plasma of CHD rats. Recombinant Slit2, by regulating the level of blood lipid, can relieve the myocardial fibrosis, inflammation and oxidative stress in CHD.

Soluble TREM-1, as a new ligand for the membrane receptor Robo2, promotes hepatic stellate cells activation and liver fibrosis

Triggering receptor expressed on myeloid cells‐1 (TREM‐1) exists in two forms: a transmembrane form and a soluble form (sTREM‐1). The levels of sTREM‐1 are elevated in supernatants of activated HSCs. However, the role of sTREM‐1 in HSC activation and liver fibrosis remains undefined. Previous studies have primarily focused on the transmembrane form of TREM‐1; we innovatively observed the function of sTREM‐1 as a ligand in liver fibrosis and screened its receptor. Here, recombinant sTREM‐1 was used as a stimulator which induced HSC activation and further aggravated liver fibrosis. Then, screening for sTREM‐1 interacting membrane receptors was performed using pull‐down assay followed by mass spectrometry, and the membrane receptor roundabout guidance receptor 2 (Robo2) was identified as a candidate receptor for sTREM‐1. The interaction between sTREM‐1 and Robo2 was verified by pull‐down and immunofluorescence. The role of Robo2 on sTREM‐1‐induced HSC activation and its downstream signal pathways was assessed by knockdown of Robo2 in LX‐2 cells. Furthermore, HSC‐specific knockdown of Robo2 was achieved in a mouse model of liver fibrosis by using a recombinant adeno‐associated virus (AAV) vector to confirm the role of the receptor, and we proved that Robo2 knockdown inhibited the activation of HSC and liver fibrosis, which also led to the inactivation of Smad2/3 and PI3K/Akt pathways in sTREM‐1‐induced HSC activation and liver fibrosis. In conclusion, sTREM‐1 acts as a new ligand of Robo2; the binding of sTREM‐1 to Robo2 initiates the activation of the downstream Smad2/3 and PI3K/Akt signalling pathways, thereby promoting HSC activation and liver fibrosis.

Slit2 Inhibits Breast Cancer Metastasis by Activating M1-Like Phagocytic and Antifibrotic Macrophages

Tumor-associated macrophages (TAM) are heterogeneous in nature and comprise antitumor M1-like (M1-TAM) or pro-tumor M2-like (M2-TAM) TAMs. M2-TAMs are a major component of stroma in breast tumors and enhance metastasis by reducing their phagocytic ability and increasing tumor fibrosis. However, the molecular mechanisms that regulate phenotypic plasticity of TAMs are not well known. Here we report a novel tumor suppressor Slit2 in breast cancer by regulating TAMs in the tumor microenvironment. Slit2 reduced the in vivo growth and metastasis of spontaneous and syngeneic mammary tumor and xenograft breast tumor models. Slit2 increased recruitment of M1-TAMs to the tumor and enhanced the ability of M1-TAMs to phagocytose tumor cells in vitro and in vivo. This Slit2-mediated increase in M1-TAM phagocytosis occurred via suppression of IL6. Slit2 was also shown to diminish fibrosis in breast cancer mouse models by increasing the expression of matrix metalloproteinase 13 in M1-TAMs. Analysis of patient samples showed high Slit2 expression strongly associated with better patient survival and inversely correlated with the abundance of CD163+ TAMs. Overall, these studies define the role of Slit2 in inhibiting metastasis by activating M1-TAMs and depleting tumor fibrosis. Furthermore, these findings suggest that Slit2 can be a promising immunotherapeutic agent to redirect TAMs to serve as tumor killers for aggressive and metastatic breast cancers. In addition, Slit2 expression along with CD163+ TAMs could be used as an improved prognostic biomarker in patients with breast cancer. SIGNIFICANCE: This study provides evidence that the antitumor effect of Slit2 in breast cancer occurs by activating the phagocytic activity of M1-like tumor-associated macrophages against tumor cells and diminishing fibrosis.

Therapeutic trials in adult FSGS: lessons learned and the road forward

Focal segmental glomerulosclerosis (FSGS) is not a specific disease entity but a lesion that primarily targets the podocyte. In a broad sense, the causes of the lesion can be divided into those triggered by a presumed circulating permeability factor, those that occur secondary to a process that might originate outside the kidneys, those caused by a genetic mutation in a podocyte or glomerular basement membrane protein, and those that arise through an as yet unidentifiable process, seemingly unrelated to a circulating permeability factor. A careful attempt to correctly stratify patients with FSGS based on their clinical presentation and pathological findings on kidney biopsy is essential for sound treatment decisions in individual patients. However, it is also essential for the rational design of therapeutic trials in FSGS. Greater recognition of the pathophysiology underlying podocyte stress and damage in FSGS will increase the likelihood that the cause of an FSGS lesion is properly identified and enable stratification of patients in future interventional trials. Such efforts will facilitate the identification of effective therapeutic agents.

The neurorepellent, Slit2, prevents macrophage lipid loading by inhibiting CD36-dependent binding and internalization of oxidized low-density lipoprotein

Atherosclerosis is characterized by retention of modified lipoproteins, especially oxidized low density lipoprotein (oxLDL) within the sub-endothelial space of affected blood vessels. Recruited monocyte-derived and tissue-resident macrophages subsequently ingest oxLDL by binding and internalizing oxLDL via scavenger receptors, particularly CD36. The secreted neurorepellent, Slit2, acting through its transmembrane receptor, Roundabout-1 (Robo-1), was previously shown to inhibit recruitment of monocytes into nascent atherosclerotic lesions. The effects of Slit2 on oxLDL uptake by macrophages have not been explored. We report here that Slit2 inhibits uptake of oxLDL by human and murine macrophages, and the resulting formation of foam cells, in a Rac1-dependent and CD36-dependent manner. Exposure of macrophages to Slit2 prevented binding of oxLDL to the surface of cells. Using super-resolution microscopy, we observed that exposure of macrophages to Slit2 induced profound cytoskeletal remodeling with formation of a thick ring of cortical actin within which clusters of CD36 could not aggregate, thereby attenuating binding of oxLDL to the surface of cells. By inhibiting recruitment of monocytes into early atherosclerotic lesions, and the subsequent binding and internalization of oxLDL by macrophages, Slit2 could represent a potent new tool to combat individual steps that collectively result in progression of atherosclerosis.

Slit2 is a potential biomarker for renal impairment in systemic lupus erythematosus

Slit2 glycoprotein has been described to regulate the inflammatory response and be involved in autoimmune diseases. Here, we investigated the expression of Slit2 and its potential significance in systemic lupus erythematosus (SLE). A total of 103 patients with SLE participated in our study. The levels of serum Slit2 were measured by enzyme-linked immunosorbent assay, and the expression of Slit2 in renal tissue was detected by immunohistochemistry. Patients with active disease had higher levels of serum Slit2 than patients with inactive disease and controls. Patients with sole skin impairment or sole renal impairment or both skin and renal impairment had higher levels of serum Slit2 than patients with neither skin nor renal impairment. Patients with chronic kidney disease (CKD) had higher levels of serum Slit2 than patients with no CKD. Levels of serum Slit2 in patients with active disease were positively correlated with the SLE Disease Activity Index, complement C4, and anti-dsDNA antibody. Levels of serum Slit2 in patients with CKD were positively correlated with serum creatinine, urine protein, and glomerular filtration rate. The expression of Slit2 and its receptor Roundabout1 (Robo1) in the renal tissue of patients with lupus nephritis were higher than controls. Moreover, renal Slit2 was positively correlated with renal chronic index. Our data indicated that Slit2 may contribute to renal impairment and this may be a potential biomarker for SLE.

TGF-β1-induced miR-424 promotes pulmonary myofibroblast differentiation by targeting Slit2 protein expression

Idiopathic pulmonary fibrosis (IPF) is a devastating interstitial lung disease with irreversible loss of lung tissue and function. Myofibroblasts in the lung are key cellular mediators of IPF progression. Transforming growth factor (TGF)-β1, a major profibrogenic cytokine, induces pulmonary myofibroblast differentiation, and emerging evidence has established the importance of microRNAs (miRs) in the development of IPF. The objective of this study was to define the pro-fibrotic roles and mechanisms of miRs in TGF-β1-induced pulmonary myofibroblast differentiation. Using RNA sequencing, we identified miR-424 as an important TGF-β1-induced miR in human lung fibroblasts (HLFs). Quantitative RT-PCR confirmed that miR-424 expression was increased by 2.6-fold in HLFs in response to TGF-β1 and was 1.7-fold higher in human fibrotic lung tissues as compared to non-fibrotic lung tissues. TGF-β1-induced upregulation of miR-424 was blocked by the Smad3 inhibitor SIS3, suggesting the involvement of this canonical TGF-β1 signaling pathway. Transfection of a miR-424 hairpin inhibitor into HLFs reduced TGF-β1-induced expression of classic myofibroblast differentiation markers including ɑ-smooth muscle actin (ɑ-SMA) and connective tissue growth factor (CTGF), whereas a miR-424 mimic significantly enhanced TGF-β1-induced myofibroblast differentiation. In addition, TGF-β1 induced Smad3 phosphorylation in HLFs, and this response was reduced by the miR-424 inhibitor. In silico analysis identified Slit2, a protein that inhibits TGF-β1 profibrogenic signaling, as a putative target of regulation by miR-424. Slit2 is less highly expressed in human fibrotic lung tissues than in non-fibrotic lung tissues, and knockdown of Slit2 by its siRNA enhanced TGF-β1-induced HLF differentiation. Overexpression of a miR-424 mimic down-regulated expression of Slit2 but not the Slit2 major receptor ROBO1 in HLFs. Luciferase reporter assays showed that the miR-424 mimic represses Slit2 3' untranslated region (3'-UTR) reporter activity, and mutations at the seeding regions in the 3'-UTR of Slit2 abolish this inhibition. Together, these data demonstrate a pro-fibrotic role of miR-424 in TGF-β1-induced HLF differentiation. It functions as a positive feed-back regulator of the TGF-β1 signaling pathway by reducing expression of the negative regulator Slit2. Thus, targeting miR-424 may provide a new therapeutic strategy to prevent myofibroblast differentiation and IPF progression.

Tripartite motif-containing 35 (TRIM35) is up-regulated in UUO-induced renal fibrosis animal model

Renal fibrosis has been recognized as a serious health threat in the world because of the high cost of treatment and poor prognosis. However, the molecular mechanism of renal fibrosis is still largely unknown. In this study, we aimed at illustrating the role of TRIM35 in the renal fibrosis process. A UUO mouse model and a TGF-β1-induced tubulointerstitial fibrosis model were constructed for the research of renal fibrosis at animal and cell level, respectively. Hematoxylin-eosin and Masson staining were used for visualizing the pathological change. qRT-PCR, Western blot analysis and immunohistochemical staining were used to detect the expression of fibrosis-associated proteins and TRIM35. The results showed that, after the modeling, the expressions of α-SMA, Collagen I, Collagen III, Fibronectin and Snail1 were up-regulated, while the expression of E-cadherin was down-regulated, indicating the successful construction of animal and cell models. More importantly, TRIM35 was proved to be up-regulated in both animal and cell models. Therefore, this study demonstrates the potential promotional effect of TRIM35 in the renal fibrosis process, which may prove to be a new biomarker for the diagnosis and development of new treatments of renal fibrosis.

SLIT2/ROBO1-signaling inhibits macropinocytosis by opposing cortical cytoskeletal remodeling

Macropinocytosis is essential for myeloid cells to survey their environment and for growth of RAS-transformed cancer cells. Several growth factors and inflammatory stimuli are known to induce macropinocytosis, but its endogenous inhibitors have remained elusive. Stimulation of Roundabout receptors by Slit ligands inhibits directional migration of many cell types, including immune cells and cancer cells. We report that SLIT2 inhibits macropinocytosis in vitro and in vivo by inducing cytoskeletal changes in macrophages. In mice, SLIT2 attenuates the uptake of muramyl dipeptide, thereby preventing NOD2-dependent activation of NF-κB and consequent secretion of pro-inflammatory chemokine, CXCL1. Conversely, blocking the action of endogenous SLIT2 enhances CXCL1 secretion. SLIT2 also inhibits macropinocytosis in RAS-transformed cancer cells, thereby decreasing their survival in nutrient-deficient conditions which resemble tumor microenvironment. Our results identify SLIT2 as a physiological inhibitor of macropinocytosis and challenge the conventional notion that signals that enhance macropinocytosis negatively regulate cell migration, and vice versa.

Recombinant Slit2 attenuates neuronal apoptosis via the Robo1-srGAP1 pathway in a rat model of neonatal HIE

Apoptosis following hypoxic-ischemic injury to the brain plays a major role in neuronal cell death. The neonatal brain is more susceptible to injury as the cortical neurons are immature and there are lower levels of antioxidants. Slit2, an extracellular matrix protein, has been shown to be neuroprotective in various models of neurological diseases. However, there is no information about the role of Slit2 in neonatal hypoxia-ischemia. In this study, we evaluated the effect of Slit2 and its receptor Robo1 in a rat model with neonatal HIE. 10-day old rat pups were used to create the neonatal HIE model. The right common carotid artery was ligated followed by 2.5 h of hypoxia. Recombinant Slit2 was administered intranasally 1 h post HI, recombinant Robo1 was used as a decoy receptor and administered intranasally 1h before HI and srGAP1-siRNA was administered intracerebroventricularly 24 h before HI. Brain infarct area measurement, short-term and long-term neurological function tests, Western blot, immunofluorescence staining, Fluoro-Jade C staining, Nissl staining and TUNEL staining were the assessments done following drug administration. Recombinant Slit2 administration reduced neuronal apoptosis and neurological deficits after neonatal HIE which were reversed by co-administration of recombinant Robo1 and srGAP1-siRNA administration. Recombinant Slit2 showed improved outcomes possibly via the robo1-srGAP1 pathway which mediated the inhibition of RhoA. In this study, the results suggest that Slit2 may help in attenuation of apoptosis and could be a therapeutic agent for treatment of neonatal hypoxic ischemic encephalopathy.

Lung Tumorigenesis Alters the Expression of Slit2-exon15 Splicing Variants in Tumor Microenvironment

Slit2 expression is downregulated in various cancers, including lung cancer. We identified two Slit2 splicing variants at exon15—Slit2-WT and Slit2-ΔE15. In the RT-PCR analyses, the Slit2-WT isoform was predominantly expressed in all the lung cancer specimens and in their normal lung counterparts, whereas Slit2-ΔE15 was equivalently or predominantly expressed in 41% of the pneumothorax specimens. A kRas^G12D transgenic mice system was used to study the effects of tumorigenesis on the expressions of the Slit2-exon15 isoforms. The results revealed that a kRas^G12D-induced lung tumor increased the Slit2-WT/Slit2-ΔE15 ratio and total Slit2 expression level. However, the lung tumors generated via a tail vein injection of lung cancer cells decreased the Slit2-WT/Slit2-ΔE15 ratio and total Slit2 expression level. Interestingly, the lipopolysaccharide (LPS)-induced lung inflammation also decreased the Slit2-WT/Slit2-ΔE15 ratio. Since Slit2 functions as an anti-inflammatory factor, the expression of Slit2 increases in kRas^G12D lungs, which indicates that Slit2 suppresses immunity during tumorigenesis. However, an injection of lung cancer cells via the tail vein and the LPS-induced lung inflammation both decreased the Slit2 expression. The increased Slit2 in the tumor microenvironment was mostly Slit2-WT, which lacks growth inhibitory activity. Thus, the results of our study suggested that the upregulation of Slit2-WT, but not Slit2-ΔE15, in a cancer microenvironment is an important factor in suppressing immunity while not interfering with cancer growth.

Different Isoforms of the Neuronal Guidance Molecule Slit2 Directly Cause Chemoattraction or Chemorepulsion of Human Neutrophils

The movement of neutrophils between blood and tissues appears to be regulated by chemoattractants and chemorepellents. Compared with neutrophil chemoattractants, relatively little is known about neutrophil chemorepellents. Slit proteins are endogenously cleaved into a variety of N- and C-terminal fragments, and these fragments are neuronal chemorepellents and inhibit chemoattraction of many cell types, including neutrophils. In this report, we show that the ∼140-kDa N-terminal Slit2 fragment (Slit2-N) is a chemoattractant and the ∼110-kDa N-terminal Slit2 fragment (Slit2-S) is a chemorepellent for human neutrophils. The effects of both Slit2 fragments were blocked by Abs to the Slit2 receptor Roundabout homolog 1 or the Slit2 coreceptor Syndecan-4. Slit2-N did not appear to activate Ras but increased phosphatidylinositol 3,4,5-triphosphate levels. Slit2-N-induced chemoattraction was unaffected by Ras inhibitors, reversed by PI3K inhibitors, and blocked by Cdc42 and Rac inhibitors. In contrast, Slit2-S activated Ras but did not increase phosphatidylinositol 3,4,5-triphosphate levels. Slit2-S-induced chemorepulsion was blocked by Ras and Rac inhibitors, not affected by PI3K inhibitors, and reversed by Cdc42 inhibitors. Slit2-N, but not Slit2-S, increased neutrophil adhesion, myosin L chain 2 phosphorylation, and polarized actin formation and single pseudopods at the leading edge of cells. Slit2-S induced multiple pseudopods. These data suggest that Slit2 isoforms use similar receptors but different intracellular signaling pathways and have different effects on the cytoskeleton and pseudopods to induce neutrophil chemoattraction or chemorepulsion.

Nitric oxide deficiency and endothelial-mesenchymal transition of pulmonary endothelium in the progression of 4T1 metastatic breast cancer in mice

Background

Mesenchymal transformation of pulmonary endothelial cells contributes to the formation of a metastatic microenvironment, but it is not known whether this precedes or follows early metastasis formation. In the present work, we characterize the development of nitric oxide (NO) deficiency and markers of endothelial–mesenchymal transition (EndMT) in the lung in relation to the progression of 4T1 metastatic breast cancer injected orthotopically in mice.

Methods

NO production, endothelial nitric oxide synthase (eNOS) phosphorylation status, markers of EndMT in the lung, pulmonary endothelium permeability, and platelet activation/reactivity were analyzed in relation to the progression of 4T1 breast cancer metastasis to the lung, as well as to lung tissue remodeling, 1–5 weeks after 4T1 cancer cell inoculation in Balb/c mice.

Results

Phosphorylation of eNOS and NO production in the lungs of 4T1 breast cancer-bearing mice was compromised prior to the development of pulmonary metastasis, and was associated with overexpression of Snail transcription factor in the pulmonary endothelium. These changes developed prior to the mesenchymal phenotypic switch in the lungs evidenced by a decrease in vascular endothelial-cadherin (VE-CAD) and CD31 expression, and the increase in pulmonary endothelial permeability, phenomena which coincided with early pulmonary metastasis. Increased activation of platelets was also detected prior to the early phase of metastasis and persisted to the late phase of metastasis, as evidenced by the higher percentage of unstimulated platelets binding fibrinogen without changes in von Willebrand factor and fibrinogen binding in response to ADP stimulation.

Conclusions

Decreased eNOS activity and phosphorylation resulting in a low NO production state featuring pulmonary endothelial dysfunction was an early event in breast cancer pulmonary metastasis, preceding the onset of its phenotypic switch toward a mesenchymal phenotype (EndMT) evidenced by a decrease in VE-CAD and CD31 expression. The latter coincided with development of the first metastatic nodules in the lungs. These findings suggest that early endothelial dysfunction featured by NO deficiency rather than EndMT, might represent a primary regulatory target to prevent early pulmonary metastasis.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1013-z) contains supplementary material, which is available to authorized users.

Identification of direct negative cross-talk between the SLIT2 and bone morphogenetic protein-Gremlin signaling pathways

Slit guidance ligand 2 (SLIT2) is a large, secreted protein that binds roundabout (ROBO) receptors on multiple cell types, including neurons and kidney podocytes. SLIT2-ROBO-mediated signaling regulates neuronal migration and ureteric bud (UB) outgrowth during kidney development as well as glomerular filtration in adult kidneys. Additionally, SLIT2 binds Gremlin, an antagonist of bone morphogenetic proteins (BMPs), and BMP-Gremlin signaling also regulates UB formation. However, direct cross-talk between the ROBO2-SLIT2 and BMP-Gremlin signaling pathways has not been established. Here, we report the discovery of negative feedback between the SLIT2 and BMP-Gremlin signaling pathways. We found that the SLIT2-Gremlin interaction inhibited both SLIT2-ROBO2 signaling in neurons and Gremlin antagonism of BMP activity in myoblasts and fibroblasts. Furthermore, BMP2 down-regulated SLIT2 expression and promoter activity through canonical BMP signaling. Gremlin treatment, BMP receptor inhibition, and SMAD family member 4 (SMAD4) knockdown rescued BMP-mediated repression of SLIT2. BMP2 treatment of nephron progenitor cells derived from human embryonic stem cells decreased SLIT2 expression, further suggesting an interaction between the BMP2-Gremlin and SLIT2 pathways in human kidney cells. In conclusion, our study has revealed direct negative cross-talk between two pathways, previously thought to be unassociated, that may regulate both kidney development and adult tissue maintenance.

Slit2 ameliorates renal inflammation and fibrosis after hypoxia-and lipopolysaccharide-induced epithelial cells injury in vitro

Hypoxic acute kidney injury (AKI) is often incompletely repaired and leads to chronic kidney disease (CKD), which is characterized by tubulointerstitial inflammation and fibrosis. The Slit2 family of secreted glycoproteins is expressed in the kidney, it has been shown to exert an anti-inflammatory activity and prevent ischemic renal injury in vivo. However, whether Slit2 reduces renal fibrosis and inflammation after hypoxic and inflammatory epithelial cells injury in vitro remains unknown. In this study, we aimed to evaluate whether Slit2 ameliorated fibrosis and inflammation in two renal epithelial cells line challenged with hypoxia and lipopolysaccharide (LPS). Renal epithelial cells were treated with hypoxia and LPS to induce cell injury. Hoechst staining and Western blot analysis was conducted to examine epithelial cells injury. Immunofluorescence staining and Western blot analysis was performed to evaluate tubulointerstitial fibrosis. Real-time polymerase chain reaction (PCR) tested the inflammatory factor interleukin (IL)-1β and tumor necrosis factor (TNF)-α, and Western blot analysis determined the hypoxia-inducible factor (HIF)-1α, Toll-like receptor 4 (TLR4) and nuclear factor (NF)-κB. Results revealed that hypoxia induced epithelial cells apoptosis, inflammatory factor IL-1β and TNF-α release and tubulointerstitial fibrosis. LPS could exacerbate hypoxia -induced epithelial cells apoptosis, IL-1β and TNF-α release and fibrosis. Slit2 reduced the expression of fibronectin, the rate of epithelial cell apoptosis, and the expression of inflammatory factor. Slit2 could also inhibit the expression of TLR4 and NF-κB, but not the expression of HIF-1α. Therefore, Slit2 attenuated inflammation and fibrosis after LPS- and hypoxia-induced epithelial cells injury via the TLR4/NF-κB signaling pathway, but not depending on the HIF-1α signaling pathway.