Gremlin regulates renal inflammation via the vascular endothelial growth factor receptor 2 pathway

Cellular crosstalk of mesangial cells and tubular epithelial cells in diabetic kidney disease

Diabetic kidney disease (DKD) is a major cause of end-stage renal disease and imposes a heavy global economic burden; however, little is known about its complicated pathophysiology. Investigating the cellular crosstalk involved in DKD is a promising avenue for gaining a better understanding of its pathogenesis. Nonetheless, the cellular crosstalk of podocytes and endothelial cells in DKD is better understood than that of mesangial cells (MCs) and renal tubular epithelial cells (TECs). As the significance of MCs and TECs in DKD pathophysiology has recently become more apparent, we reviewed the existing literature on the cellular crosstalk of MCs and TECs in the context of DKD to acquire a comprehensive understanding of their cellular communication. Insights into the complicated mechanisms underlying the pathophysiology of DKD would improve its early detection, care, and prognosis. Video Abstract.

GREM1 signaling in cancer: tumor promotor and suppressor?

GREMLIN1 (GREM1) is member of a family of structurally and functionally related secreted cysteine knot proteins, which act to sequester and inhibit the action of multifunctional bone morphogenetic proteins (BMPs). GREM1 binds directly to BMP dimers, thereby preventing BMP-mediated activation of BMP type I and type II receptors. Multiple reports identify the overexpression of GREM1 as a contributing factor in a broad range of cancers. Additionally, the GREM1 gene is amplified in a rare autosomal dominant inherited form of colorectal cancer. The inhibitory effects of GREM1 on BMP signaling have been linked to these tumor-promoting effects, including facilitating cancer cell stemness and the activation of cancer-associated fibroblasts. Moreover, GREM1 has been described to bind and signal to vascular endothelial growth factor receptor (VEGFR) and stimulate angiogenesis, as well as epidermal and fibroblast growth factor receptor (EGFR and FGFR) to elicit tumor-promoting effects in breast and prostate cancer, respectively. In contrast, a 2022 report revealed that GREM1 can promote an epithelial state in pancreatic cancers, thereby inhibiting pancreatic tumor growth and metastasis. In this commentary, we will review these disparate findings and attempt to provide clarity around the role of GREM1 signaling in cancer.

GREM1 is a potential biomarker for the progression and prognosis of bladder cancer

BACKGROUND

Gremlin-1 (GREM1) is a protein closely related to tumor growth, although its function in bladder cancer (BCa) is currently unknown. Our first objective was to study the GREM1 treatment potential in BCa.

METHODS

BCa tissue samples were collected for the detection of GREM1 expression using Western blot analysis and Immunofluorescence staining. Association of GREM1 expression with clinicopathology and prognosis as detected by TCGA (The Cancer Genome Atlas) database. The functional investigation was tested by qRT-PCR, western blot analysis, CCK-8, cell apoptosis, wound healing, and transwell assays. The interaction between GREM1 and the downstream PI3K/AKT signaling pathway was assessed by Western blot analysis.

RESULTS

GREM1 exhibited high expression in BCa tissues and was linked to poor prognosis. Stable knockdown of GREM1 significantly inhibited BCa cell (T24 and 5637) proliferation, apoptosis, migratory, invasive, as well as epithelial-mesenchymal transition (EMT) abilities. GREM1 promotes the progression in BCa via PI3K/AKT signaling pathway.

CONCLUSION

Findings demonstrate that the progression-promoting effect of GREM1 in BCa, providing a novel biomarker for BCa-targeted therapy.

Role of gremlin-1 in the pathophysiology of the adipose tissues

Gremlin-1 is a secreted bone morphogenetic protein (BMP) antagonist playing a pivotal role in the regulation of tissue formation and embryonic development. Since its first identification in 1997, gremlin-1 has been shown to be a multifunctional factor involved in wound healing, inflammation, cancer and tissue fibrosis. Among others, the activity of gremlin-1 is mediated by its interaction with BMPs or with membrane receptors such as the vascular endothelial growth factor receptor 2 (VEGFR2) or heparan sulfate proteoglycans (HSPGs). Growing evidence has highlighted a central role of gremlin-1 in the homeostasis of the adipose tissue (AT). Of note, gremlin-1 is involved in AT dysfunction during type 2 diabetes, obesity and non-alcoholic fatty liver disease (NAFLD) metabolic disorders. In this review we discuss recent findings on gremlin-1 involvement in AT biology, with particular attention to its role in metabolic diseases, to highlight its potential as a prognostic marker and therapeutic target.

Understanding the role of alternative macrophage phenotypes in human atherosclerosis

INTRODUCTION

Atherosclerosis-based ischemic heart disease is still the primary cause of death throughout the world. Over the past decades there has been no significant changes in the therapeutic approaches to atherosclerosis, which are mainly based on lipid lowering therapies and management of comorbid conditions such as diabetes and hypertension. The involvement of macrophages in atherosclerosis has been recognized for decades. More recently, a more detailed and sophisticated understanding of their various phenotypes and roles in the atherosclerotic process has been recognized. This new data is revealing how specific subtypes of macrophage-induced inflammation may have distinct effects on atherosclerosis progression and may provide new approaches for treatment, based upon targeting of specific macrophage subtypes.

AREAS COVERED

We will comprehensively review the spectrum of macrophage phenotypes and how they contribute to atherosclerotic plaque development and progression.

EXPERT OPINION

Various signals derived from atherosclerotic lesions drive macrophages into complex subsets with different gene expression profiles, phenotypes, and functions, not all of which are understood. Macrophage phenotypes include those that enhance, heal, and regress the atherosclerotic lesions though various mechanisms. Targeting of specific macrophage phenotypes may provide a promising and novel approach to prevent atherosclerosis progression.

Exosomal miR-150 derived from BMSCs inhibits TNF-α-mediated osteoblast apoptosis in osteonecrosis of the femoral head by GREM1/NF-κB signaling

Aim: The purpose of this study was to investigate the functions of exosomal miR-150 derived from bone marrow mesenchymal stem cells in osteonecrosis of the femoral head (ONFH). Materials & methods: Cell viability and apoptosis were detected using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and flow cytometry. Alizarin red staining was performed to detect calcium deposits. A rat model was established to assess the effects of exosomal miR-150 on ONFH in vivo. Results: Exosomes or exosomal miR-150 derived from bone marrow mesenchymal stem cells inhibited TNF-α-induced osteoblast apoptosis and promoted osteogenic differentiation and autophagy. Exosomal miR-150 suppressed apoptosis and induced autophagy in TNF-α-treated osteoblasts by regulating the GREM1/NF-κB axis. Exosomal miR-150 also improved the pathological features of ONFH in vivo. Conclusion: Exosomal miR-150 alleviates ONFH by mediating the GREM1/NF-κB axis. This study provides a potential therapeutic strategy for ONFH.

Gremlin-1 Promotes Colorectal Cancer Cell Metastasis by Activating ATF6 and Inhibiting ATF4 Pathways

Cancer cell survival, function and fate strongly depend on endoplasmic reticulum (ER) proteostasis. Although previous studies have implicated the ER stress signaling network in all stages of cancer development, its role in cancer metastasis remains to be elucidated. In this study, we investigated the role of Gremlin-1 (GREM1), a secreted protein, in the invasion and metastasis of colorectal cancer (CRC) cells in vitro and in vivo. Firstly, public datasets showed a positive correlation between high expression of GREM1 and a poor prognosis for CRC. Secondly, GREM1 enhanced motility and invasion of CRC cells by epithelial–mesenchymal transition (EMT). Thirdly, GREM1 upregulated expression of activating transcription factor 6 (ATF6) and downregulated that of ATF4, and modulation of the two key players of the unfolded protein response (UPR) was possibly through activation of PI3K/AKT/mTOR and antagonization of BMP2 signaling pathways, respectively. Taken together, our results demonstrate that GREM1 is an invasion-promoting factor via regulation of ATF6 and ATF4 expression in CRC cells, suggesting GREM1 may be a potential pharmacological target for colorectal cancer treatment.

CAF-derived exosomes transmitted Gremlin-1 promotes cancer progression and decreases the sensitivity of hepatoma cells to sorafenib

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies worldwide because of metastasis. An increasing number of studies have reported that cancer-associated fibroblasts (CAFs) have emerged as the largest component of the stroma and play a critical role in tumor-promoting processes. However, the effects of CAFs on cancer progression and the sensitivity of hepatoma cells to sorafenib are not well characterized. Here, we identified the proteome of CAF-derived exosomes, and unveiled that exosomal Gremlin-1 derived from CAFs contributes to epithelial-mesenchymal transition (EMT) of hepatoma cells and the decrease of the sorafenib sensitivity through regulating Wnt/β-catenin and BMP signaling pathways. Compared to control subjects, the level of plasma exosomal Gremlin-1 was significantly increased in HCC patients. Further studies indicated that plasma exosomal Gremlin-1 may predict sorafenib response in HCC patients. Collectively, our findings uncover CAFs-derived Gremlin-1-rich exosomes promote EMT and decrease the sensitivity of hepatoma cells to sorafenib by Wnt/β-catenin and BMP signaling.

CCN2 Binds to Tubular Epithelial Cells in the Kidney

Cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), is considered a fibrotic biomarker and has been suggested as a potential therapeutic target for kidney pathologies. CCN2 is a matricellular protein with four distinct structural modules that can exert a dual function as a matricellular protein and as a growth factor. Previous experiments using surface plasmon resonance and cultured renal cells have demonstrated that the C-terminal module of CCN2 (CCN2(IV)) interacts with the epidermal growth factor receptor (EGFR). Moreover, CCN2(IV) activates proinflammatory and profibrotic responses in the mouse kidney. The aim of this paper was to locate the in vivo cellular CCN2/EGFR binding sites in the kidney. To this aim, the C-terminal module CCN2(IV) was labeled with a fluorophore (Cy5), and two different administration routes were employed. Both intraperitoneal and direct intra-renal injection of Cy5-CCN2(IV) in mice demonstrated that CCN2(IV) preferentially binds to the tubular epithelial cells, while no signal was detected in glomeruli. Moreover, co-localization of Cy5-CCN2(IV) binding and activated EGFR was found in tubules. In cultured tubular epithelial cells, live-cell confocal microscopy experiments showed that EGFR gene silencing blocked Cy5-CCN2(IV) binding to tubuloepithelial cells. These data clearly show the existence of CCN2/EGFR binding sites in the kidney, mainly in tubular epithelial cells. In conclusion, these studies show that circulating CCN2(IV) can directly bind and activate tubular cells, supporting the role of CCN2 as a growth factor involved in kidney damage progression.

Production and Biochemical Characterization of Dimeric Recombinant Gremlin-1

Gremlin-1 is a secreted cystine-knot protein that acts as an antagonist of bone morphogenetic proteins (BMPs), and as a ligand of heparin and the vascular endothelial growth factor receptor 2 (VEGFR2), thus regulating several physiological and pathological processes, including embryonic development, tissue fibrosis and cancer. Gremlin-1 exerts all these biological activities only in its homodimeric form. Here, we propose a multi-step approach for the expression and purification of homodimeric, fully active, histidine-tagged recombinant gremlin-1, using mammalian HEK293T cells. Ion metal affinity chromatography (IMAC) of crude supernatant followed by heparin-affinity chromatography enables obtaining a highly pure recombinant dimeric gremlin-1 protein, exhibiting both BMP antagonist and potent VEGFR2 agonist activities.

Epigenetic Modulation of Gremlin-1/NOTCH Pathway in Experimental Crescentic Immune-Mediated Glomerulonephritis

Crescentic glomerulonephritis is a devastating autoimmune disease that without early and properly treatment may rapidly progress to end-stage renal disease and death. Current immunosuppressive treatment provides limited efficacy and an important burden of adverse events. Epigenetic drugs are a source of novel therapeutic tools. Among them, bromodomain and extraterminal domain (BET) inhibitors (iBETs) block the interaction between bromodomains and acetylated proteins, including histones and transcription factors. iBETs have demonstrated protective effects on malignancy, inflammatory disorders and experimental kidney disease. Recently, Gremlin-1 was proposed as a urinary biomarker of disease progression in human anti-neutrophil cytoplasmic antibody (ANCA)-associated crescentic glomerulonephritis. We have now evaluated whether iBETs could regulate Gremlin-1 in experimental anti-glomerular basement membrane nephritis induced by nephrotoxic serum (NTS) in mice, a model resembling human crescentic glomerulonephritis. In NTS-injected mice, the iBET JQ1 inhibited renal Gremlin-1 overexpression and diminished glomerular damage, restoring podocyte numbers. Chromatin immunoprecipitation assay demonstrated BRD4 enrichment of the Grem-1 gene promoter in injured kidneys, consistent with Gremlin-1 epigenetic regulation. Moreover, JQ1 blocked BRD4 binding and inhibited Grem-1 gene transcription. The beneficial effect of iBETs was also mediated by modulation of NOTCH pathway. JQ1 inhibited the gene expression of the NOTCH effectors Hes-1 and Hey-1 in NTS-injured kidneys. Our results further support the role for epigenetic drugs, such as iBETs, in the treatment of rapidly progressive crescentic glomerulonephritis.

Gremlin aggravates periodontitis via activating the NF-κB signaling pathway

BACKGROUND

Gremlin has been reported to regulate inflammation and osteogenesis. Periodontitis is a destructive disease degenerating periodontal tissues, therefore leads to alveolar bone resorption and tooth loss. Based on the importance of Gremlin's bio-activity, the aim of this study is to, in vivo and in vitro, unveil the function of Gremlin in regulating the development of periodontitis and its consequent effects on alveolar bone loss.

METHODS

Clinical specimens were used to determine the expression of Gremlin in periodontal tissues by immunohistochemical staining and western blot. Then utilizing the rat periodontitis model to investigate the function of gremlin-regulated nuclear factor-kappa B (NF-κB) pathway during the development of periodontal inflammation and the alveolar bone loss. Lastly, the regulation of the osteogenesis of human periodontal ligament stem cells (hPDLSCs) by Gremlin under inflamed condition was analyzed by alkaline phosphatase (ALP) and alizarin red staining (ARS).

RESULTS

We found clinically and experimentally that the expression of Gremlin is markedly increased in periodontitis tissues. Interestingly, we revealed that Gremlin regulated the progress of periodontitis via regulating the activities of NF-κB pathway and interleukin-1β (IL-1β). Notably, we observed that Gremlin influenced the osteogenesis of hPDLSCs. Thus, our present study identified Gremlin as a new key regulator for development of periodontitis.

CONCLUSIONS

Our current study illustrated that Gremlin acts as a crucial mediator and possibly serves as a potential diagnostic marker for periodontitis. Discovery of new factors involved in the pathophysiology of periodontitis could contribute to the development of novel therapeutic treatment for the disease. This article is protected by copyright. All rights reserved.

Impact of the COVID-19 pandemic on patients receiving intravitreal injections

We analyzed the economic benefits versus safety risks of sharing anti-vascular endothelial growth factor (VEGF) vials during the coronavirus disease (COVID-19) pandemic. This single-center retrospective study analyzed the data of patients with neovascular age-related macular degeneration (nAMD), proliferative diabetic retinopathy (PDR) and retinal vein occlusion (RVO) who received anti- VEGF between January 2016 and July 2021 at Renmin Hospital, Wuhan University, China. Costs were compared of the two protocols of intravitreal injections (IVIs) of ranibizumab, aflibercept and conbercept after (i) splitting the vial content for use in two patients and after (ii) disposal of the remaining vial content after use in a single patient, with the COVID-19 outbreak considered as the demarcation point. The incidence rates of post-injection endophthalmitis (PIE) pre- and post-outbreak were analyzed. The mean cost of a single IVI increased by 33.3%, from 3917.67?71.69 to 5222.67?84.98 Chinese Yuan during the pandemic. The incidences of IVI-related culture-positive PIE were 0.0134% (3 in 22448) and 0.0223% (1 in 4479), respectively, before and after the pandemic (P=0.6532). We conclude that vial sharing of IVIs in a large clinical institution is not associated with increased PIE risk and can significantly reduce the cost of therapy.

Gremlin: a complex molecule regulating wound healing and fibrosis

Gremlin-1 is part of the TGF-β superfamily and is a BMP antagonist that blocks BMP signalling to precisely control BMP gradients. Gremlin-1 is primarily involved in organogenesis and limb patterning however, has recently been described as being involved in fibrotic diseases. Initially described as a key factor involved in diabetic kidney fibrosis due to being induced by high glucose, it has now been described as being associated with lung, liver, eye, and skin fibrosis. This suggests that it is a key conserved molecule mediating fibrotic events irrespective of organ. It appears that Gremlin-1 may have effects mediated by BMP-dependent and independent pathways. The aim of this review is to evaluate the role of Gremlin-1 in fibrosis, its mechanisms and if this can be targeted therapeutically in fibrotic diseases, which currently have very limited treatment options and are highly prevalent.

Effects of bone morphogenetic protein 4, gremlin, and connective tissue growth factor on estradiol and progesterone production by bovine granulosa cells

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β family of proteins that have been implicated in the paracrine regulation of granulosa cell (GC) function, but whether responses to BMPs change with follicular size or interact with connective tissue growth factor (CTGF) or BMP antagonists (e.g., gremlin [GREM]) to directly affect GC function of cattle is unknown. Therefore, to determine the effects of BMP4 on proliferation and steroidogenesis of GCs and its interaction with GREM or CTGF, experiments were conducted using bovine GC cultures. In vitro, BMP4 (30 ng/mL) inhibited (P < 0.05) follicle-stimulating hormone (FSH) plus insulin-like growth factor 1 (IGF1)-induced progesterone and estradiol production by large- and small-follicle GCs, but the inhibitory effect of BMP4 on estradiol production was much more pronounced in large-follicle GCs. In small-follicle GCs, BMP4 had no effect (P > 0.10) on IGF1-induced proliferation, but GREM inhibited (P < 0.05) cell proliferation and estradiol and progesterone production in IGF1 plus FSH-treated GCs. In large-follicle GCs, BMP4 (10 to 30 ng/mL) increased (P < 0.05) GC numbers and GREM (100 ng/mL) blocked this effect. In large-follicle GCs, CTGF inhibited (P < 0.05) FSH plus IGF1-induced progesterone and estradiol production, and CTGF blocked the stimulatory effect of BMP4 on GC proliferation. These results indicate that BMP4, GREM, and CTGF inhibit GC aromatase activity and progesterone production. Also, the stimulatory effect of BMP4 on GC proliferation and the inhibitory effects of BMP4 on GC steroidogenesis are more pronounced in large vs. small follicles.

Gremlin1 and TGF-β1 protect kidney tubular epithelial cells from ischemia-reperfusion injury through different pathways

BACKGROUND

Gremlin1 belongs to the superfamily members of transforming growth factor (TGF)-β1, playing a profibrotic role in chronic kidney diseases (CKD) and the transition from the late stage of acute kidney injury (AKI) to CKD, but the effect it plays in the early stage of AKI is unclear. This study aimed to investigate the role of Gremlin1on apoptosis in renal tubular epithelial cells under ischemia-reperfusion (I/R) induction.

METHODS

We detected Gremlin1 and TGF-β1 expression in the kidneys of mice undergoing renal ischemia-reperfusion injury bilaterally. We induced apoptosis through depletion and reperfusion of oxygen and serum in human kidney tubular epithelial cells (HKCs), mimicking I/R injury in vivo, and detected the role and pathways of Gremlin1 and TGF-β1on HKCs injury.

RESULTS

Mice undergoing bilateral I/R surgery presented AKI with a significant increase in serum creatinine, obvious renal tubular injuries, and increased macrophage cell and T-cell infiltration in interstitial areas. Gremlin1 expression was significantly increased along with TGF-β1 in the kidneys of AKI mice compared to sham mice. Exogenous Gremlin1 inhibited I/R-induced caspase3 expression in HKCs, which was blocked by a VEGFR2 kinase inhibitor III (SU5416). TGF-β1 also inhibited I/R-induced cell apoptosis in HKCs but had no synergic effect with Gremlin1. The TGF-β1's inhibitory effect could be blocked by the TGF-β1 type I receptor (activin receptor-like kinase 5, and ALK5)-specific inhibitor SB431542.

CONCLUSIONS

Gremlin1 and TGF- β1 protect kidney tubular epithelial cells from ischemia-reperfusion-induced apoptosis through VEGFR2 and Smad2 signaling pathways.

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

Development of a prognostic risk model for clear cell renal cell carcinoma by systematic evaluation of DNA methylation markers

BACKGROUND

Current risk models for renal cell carcinoma (RCC) based on clinicopathological factors are sub-optimal in accurately identifying high-risk patients. Here, we perform a head-to-head comparison of previously published DNA methylation markers and propose a potential prognostic model for clear cell RCC (ccRCC).

PATIENTS AND METHODS

Promoter methylation of PCDH8, BNC1, SCUBE3, GREM1, LAD1, NEFH, RASSF1A, GATA5, SFRP1, CDO1, and NEURL was determined by nested methylation-specific PCR. To identify clinically relevant methylated regions, The Cancer Genome Atlas (TCGA) was used to guide primer design. Formalin-fixed paraffin-embedded (FFPE) tissue samples from 336 non-metastatic ccRCC patients from the prospective Netherlands Cohort Study (NLCS) were used to develop a Cox proportional hazards model using stepwise backward elimination and bootstrapping to correct for optimism. For validation purposes, FFPE ccRCC tissue of 64 patients from the University Hospitals Leuven and a series of 232 cases from The Cancer Genome Atlas (TCGA) were used.

RESULTS

Methylation of GREM1, GATA5, LAD1, NEFH, NEURL, and SFRP1 was associated with poor ccRCC-specific survival, independent of age, sex, tumor size, TNM stage or tumor grade. Moreover, the association between GREM1, NEFH, and NEURL methylation and outcome was shown to be dependent on the genomic region. A prognostic biomarker model containing GREM1, GATA5, LAD1, NEFH and NEURL methylation in combination with clinicopathological characteristics, performed better compared to the model with clinicopathological characteristics only (clinical model), in both the NLCS and the validation population with a c-statistic of 0.71 versus 0.65 and a c-statistic of 0.95 versus 0.86 consecutively. However, the biomarker model had limited added prognostic value in the TCGA series with a c-statistic of 0.76 versus 0.75 for the clinical model.

CONCLUSION

In this study we performed a head-to-head comparison of potential prognostic methylation markers for ccRCC using a novel approach to guide primers design which utilizes the optimal location for measuring DNA methylation. Using this approach, we identified five methylation markers that potentially show prognostic value in addition to currently known clinicopathological factors.

Gender-dependent bladder response to one-day bladder outlet obstruction

BACKGROUND

Development of bladder fibrosis, loss of compliance, and voiding dysfunction are among the severe consequences of various lower urinary conditions, for example, bladder outlet obstruction (BOO), neurogenic bladder, and radiotherapy to the pelvic area. The bladder remodelling results in significant changes in bladder function and architecture, and may ultimately be deleterious for kidney function. The molecular signals underlying pathologic bladder remodelling, as well as the impact of gender, remain poorly understood.

OBJECTIVE

To investigate the bladder remodelling after one day BOO, whether the remodelling is different between different bladder sections, and whether genders may affect the remodelling.

STUDY DESIGN

Thirty male and 30 female C57BL/6NRj mice were randomly divided into Control, Sham and BOO groups with ten mice per group. A 24-h total urethral obstruction was performed at the proximal urethra. Histological changes were observed via H&E, trichrome and immunohistochemistry staining. Harvested bladders were divided into upper and lower sections for analysis. Protein and gene expression were detected by Western blotting and qPCR.

RESULTS

No significant changes in bladder wall thickness were observed following BOO, while increased bladder mass after BOO was found in female mice only. We detected FN and ⍺-SMA upregulation in the male upper bladder segment. Female BOO mice bladders showed increased α-SMA expression in both bladder segments, but no difference of FN was observed in either bladder segments. BOO-induced upregulation of TGF-β and Gremlin were detected in both male and female bladders, while downregulation of BMP-7 was detected only in male bladders. Furthermore, phosphorylation of both SMAD2/3 and SMAD1/5/9 were increased in male bladders following BOO, whereas female mice exhibited increased pSMAD2/3 in the upper and increased pSMAD1/5/9 in the lower bladder segment.

CONCLUSIONS

Our data indicate that some specific proteins and growth factors were detected as early alterations of tissue which may lead to fibrosis. In addition, the males tended to have more pronounced response than females. However, the causes and consequences of the findings need to be further investigated.

DHA inhibits Gremlin-1-induced epithelial-to-mesenchymal transition via ERK suppression in human breast cancer cells

Docosahexaenoic acid (DHA) is an omega-3 fatty acid abundant in fish oils. It is known to have an inhibitory effect on various diseases such as inflammation, diabetes, and cancer. Epithelial-to-mesenchymal transition (EMT) is a process that epithelial cells gain migratory property to become mesenchymal cells involved in wound healing, organ fibrosis, and cancer progression. Gremlin-1 (GREM1) is a bone morphogenetic protein antagonist known to play a role in EMT. However, the role of GREM1 in the induction of EMT in human breast cancer cells and the effect of DHA on GREM1-induced EMT remain unclear. Establishment of GREM1 knockdown cell lines was performed using lentiviral shRNAs. Expression of EMT markers was determined by qRT-PCR and Western blotting. Effect of GREM1 and/or DHA on cell migration was investigated using wound healing assay. The level of GREM1 expression in human breast cancer tissues was determined by Oncomine database mining. GREM1 induced the expression of genes including N-cadherin, vimentin, and Slug. GREM1 promoted the migration of human breast cancer cells. GREM1 enhanced the expression of phosphorylated extracellular signal-regulated kinase (p-ERK) and the ERK activation was involved in EMT. Interestingly, DHA reduced the expression of GREM1. DHA also inhibited the expression of mesenchymal cell-associated genes and cell migration induced by GREM1. Furthermore, DHA suppressed the expression of p-ERK induced by GREM1. These results indicate that GREM1–ERK axis plays a role in EMT in human breast cancer cells and DHA is a putative compound that can inhibit EMT by inhibiting GREM1 signal transduction.

Analysis of genomics and immune infiltration patterns of epithelial-mesenchymal transition related to metastatic breast cancer to bone

OBJECTIVE

This study aimed to design a weighted co-expression network and a breast cancer (BC) prognosis evaluation system using a specific whole-genome expression profile combined with epithelial-mesenchymal transition (EMT)-related genes; thus, providing the basis and reference for assessing the prognosis risk of spreading of metastatic breast cancer (MBC) to the bone.

METHODS

Four gene expression datasets of a large number of samples from GEO were downloaded and combined with the dbEMT database to screen out EMT differentially expressed genes (DEGs). Using the GSE20685 dataset as a training set, we designed a weighted co-expression network for EMT DEGs, and the hub genes most relevant to metastasis were selected. We chose eight hub genes to build prognostic assessment models to estimate the 3-, 5-, and 10-year survival rates. We evaluated the models' independent predictive abilities using univariable and multivariable Cox regression analyses. Two GEO datasets related to bone metastases from BC were downloaded and used to perform differential genetic analysis. We used CIBERSORT to distinguish 22 immune cell types based on tumor transcripts.

RESULTS

Differential expression analysis showed a total of 304 DEGs, which were mainly related to proteoglycans in cancer, and the PI3K/Akt and the TGF-β signaling pathways, as well as mesenchyme development, focal adhesion, and cytokine binding functionally. The 50 hub genes were selected, and a survival-related linear risk assessment model consisting of eight genes (FERMT2, ITGA5, ITGB1, MCAM, CEMIP, HGF, TGFBR1, F2RL2) was constructed. The survival rate of patients in the high-risk group (HRG) was substantially lower than that of the low-risk group (LRG), and the 3-, 5-, and 10-year AUCs were 0.68, 0.687, and 0.672, respectively. In addition, we explored the DEGs of BC bone metastasis, and BMP2, BMPR2, and GREM1 were differentially expressed in both data sets. In GSE20685, memory B cells, resting memory T cell CD4 cells, T regulatory cells (T_regs), γδ T cells, monocytes, M0 macrophages, M2 macrophages, resting dendritic cells (DCs), resting mast cells, and neutrophils exhibited substantially different distribution between HRG and LRG. In GSE45255, there was a considerable difference in abundance of activated NK cells, monocytes, M0 macrophages, M2 macrophages, resting DCs, and neutrophils in HRG and LRG.

CONCLUSIONS

Based on the weighted co-expression network for breast-cancer-metastasis-related DEGs, we screened hub genes to explore a prognostic model and the immune infiltration patterns of MBC. The results of this study provided a factual basis to bioinformatically explore the molecular mechanisms of the spread of MBC to the bone and the possibility of predicting the survival of patients.

Gremlin-1 activates Akt/STAT3 signaling, which increases the glycolysis rate in breast cancer cells

Gremlin-1 (GREM1), one of the antagonists of bone morphogenetic proteins (BMPs), has recently been reported to be overexpressed in a variety of cancers including breast cancer. GREM1 is involved in tumor promotion, but little is known about its role in the glycolysis of cancer cells. In this study, we investigated the role of GREM1 in glycolysis of breast cancer cells and its underlying molecular mechanisms. We first observed that glucose uptake and lactate production were increased in GREM1-overexpressing breast cancer cells. GREM1 increased the expression of hexokinase-2 (HK2), which catalyzes the phosphorylation of glucose, the first step in glycolysis. In addition, GREM1 activated STAT3 transcription factor through the ROS-Akt signaling pathway. The ROS-Akt-STAT3 axis activated by GREM1 was involved in promoting glucose uptake by increasing the expression of HK2 in breast cancer cells. Therefore, our study suggested a new mechanism by which GREM1 is involved in breast cancer promotion by increasing glycolysis in breast cancer cells.

Gremlin-1 augments the oestrogen-related receptor α signalling through EGFR activation: implications for the progression of breast cancer

BACKGROUND

Gremlin-1 (GREM1), one of the bone morphogenetic protein antagonists, is involved in organogenesis, tissue differentiation and kidney development. However, the role of GREM1 in cancer progression and its underlying mechanisms remain poorly understood.

METHODS

The role of GREM1 in breast cancer progression was assessed by measuring cell viability, colony formation, 3D tumour spheroid formation/invasion and xenograft tumour formation. Chromatin immunoprecipitation, a luciferase reporter assay and flow cytometry were performed to investigate the molecular events in which GREM1 is involved.

RESULTS

GREM1 expression was elevated in breast cancer cells and tissues obtained from breast cancer patients. Its overexpression was associated with poor prognosis in breast cancer patients, especially those with oestrogen receptor (ER)-negative tumours. GREM1 knockdown inhibited the proliferation of breast cancer cells and xenograft mammary tumour growth, while its overexpression enhanced their viability, growth and invasiveness. Oestrogen-related receptor α (ERRα), an orphan nuclear hormone receptor, directly interacted with the GREM1 promoter and increased the expression of GREM1. GREM1 also enhanced the promoter activity of ESRRA encoding ERRα, comprising a positive feedback loop. Notably, GREM1 bound to and activated EGFR, a well-known upstream regulator of ERRα.

CONCLUSIONS

Our study suggests that the GREM1-ERRα axis can serve as a potential therapeutic target in the management of cancer, especially ER-negative tumour.

Extracellular BMP Antagonists, Multifaceted Orchestrators in the Tumor and Its Microenvironment

The bone morphogenetic proteins (BMPs), a subgroup of the transforming growth factor-β (TGF-β) superfamily, are involved in multiple biological processes such as embryonic development and maintenance of adult tissue homeostasis. The importance of a functional BMP pathway is underlined by various diseases, including cancer, which can arise as a consequence of dysregulated BMP signaling. Mutations in crucial elements of this signaling pathway, such as receptors, have been reported to disrupt BMP signaling. Next to that, aberrant expression of BMP antagonists could also contribute to abrogated signaling. In this review we set out to highlight how BMP antagonists affect not only the cancer cells, but also the other cells present in the microenvironment to influence cancer progression.

Pathogenic Pathways and Therapeutic Approaches Targeting Inflammation in Diabetic Nephropathy

Diabetic nephropathy (DN) is associated with an increased morbidity and mortality, resulting in elevated cost for public health systems. DN is the main cause of chronic kidney disease (CKD) and its incidence increases the number of patients that develop the end-stage renal disease (ESRD). There are growing epidemiological and preclinical evidence about the close relationship between inflammatory response and the occurrence and progression of DN. Several anti-inflammatory strategies targeting specific inflammatory mediators (cell adhesion molecules, chemokines and cytokines) and intracellular signaling pathways have shown beneficial effects in experimental models of DN, decreasing proteinuria and renal lesions. A number of inflammatory molecules have been shown useful to identify diabetic patients at high risk of developing renal complications. In this review, we focus on the key role of inflammation in the genesis and progression of DN, with a special interest in effector molecules and activated intracellular pathways leading to renal damage, as well as a comprehensive update of new therapeutic strategies targeting inflammation to prevent and/or retard renal injury.

Targeting the progression of chronic kidney disease

Chronic kidney disease (CKD) is a devastating condition that is reaching epidemic levels owing to the increasing prevalence of diabetes mellitus, hypertension and obesity, as well as ageing of the population. Regardless of the underlying aetiology, CKD is slowly progressive and leads to irreversible nephron loss, end-stage renal disease and/or premature death. Factors that contribute to CKD progression include parenchymal cell loss, chronic inflammation, fibrosis and reduced regenerative capacity of the kidney. Current therapies have limited effectiveness and only delay disease progression, underscoring the need to develop novel therapeutic approaches to either stop or reverse progression. Preclinical studies have identified several approaches that reduce fibrosis in experimental models, including targeting cytokines, transcription factors, developmental and signalling pathways and epigenetic modulators, particularly microRNAs. Some of these nephroprotective strategies are now being tested in clinical trials. Lessons learned from the failure of clinical studies of transforming growth factor β1 (TGFβ1) blockade underscore the need for alternative approaches to CKD therapy, as strategies that target a single pathogenic process may result in unexpected negative effects on simultaneously occurring processes. Additional promising avenues include preventing tubular cell injury and anti-fibrotic therapies that target activated myofibroblasts, the main collagen-producing cells.

VEGFR2 Blockade Improves Renal Damage in an Experimental Model of Type 2 Diabetic Nephropathy

The absence of optimal treatments for Diabetic Nephropathy (DN) highlights the importance of the search for novel therapeutic targets. The vascular endothelial growth factor receptor 2 (VEGFR2) pathway is activated in experimental and human DN, but the effects of its blockade in experimental models of DN is still controversial. Here, we test the effects of a therapeutic anti-VEGFR2 treatment, using a VEGFR2 kinase inhibitor, on the progression of renal damage in the BTBR ob/ob (leptin deficiency mutation) mice. This experimental diabetic model develops histological characteristics mimicking the key features of advanced human DN. A VEGFR2 pathway-activation blockade using the VEGFR2 kinase inhibitor SU5416, starting after kidney disease development, improves renal function, glomerular damage (mesangial matrix expansion and basement membrane thickening), tubulointerstitial inflammation and tubular atrophy, compared to untreated diabetic mice. The downstream mechanisms involved in these beneficial effects of VEGFR2 blockade include gene expression restoration of podocyte markers and downregulation of renal injury biomarkers and pro-inflammatory mediators. Several ligands can activate VEGFR2, including the canonical ligands VEGFs and GREMLIN. Activation of a GREMLIN/VEGFR2 pathway, but not other ligands, is correlated with renal damage progression in BTBR ob/ob diabetic mice. RNA sequencing analysis of GREMLIN-regulated genes confirm the modulation of proinflammatory genes and related-molecular pathways. Overall, these data show that a GREMLIN/VEGFR2 pathway activation is involved in diabetic kidney disease and could potentially be a novel therapeutic target in this clinical condition.

Molecular Regulation of Notch Signaling by Gremlin

Gremlin is a member of the TGF-β superfamily that can act as a BMP antagonist, and recently, has been described as a ligand of the vascular endothelial growth factor receptor 2 (VEGFR2). Gremlin shares properties with the Notch signaling pathway. Both participate in embryonic development and are reactivated in pathological conditions. Gremlin is emerging as a potential therapeutic target and biomarker of renal diseases. Here we review the role of the Gremlin-VEGFR2 axis in renal damage and downstream signaling mechanisms, such as Notch pathway.

MiR-9-5p protects from kidney fibrosis by metabolic reprogramming

MicroRNAs (miRNAs) regulate gene expression posttranscriptionally and control biological processes (BPs), including fibrogenesis. Kidney fibrosis remains a clinical challenge and miRNAs may represent a valid therapeutic avenue. We show that miR-9-5p protected from renal fibrosis in the mouse model of unilateral ureteral obstruction (UUO). This was reflected in reduced expression of pro-fibrotic markers, decreased number of infiltrating monocytes/macrophages, and diminished tubular epithelial cell injury and transforming growth factor-beta 1 (TGF-β1)-dependent de-differentiation in human kidney proximal tubular (HKC-8) cells. RNA-sequencing (RNA-Seq) studies in the UUO model revealed that treatment with miR-9-5p prevented the downregulation of genes related to key metabolic pathways, including mitochondrial function, oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO), and glycolysis. Studies in human tubular epithelial cells demonstrated that miR-9-5p impeded TGF-β1-induced bioenergetics derangement. The expression of the FAO-related axis peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α)-peroxisome proliferator-activated receptor alpha (PPARα) was reduced by UUO, although preserved by the administration of miR-9-5p. We found that in mice null for the mitochondrial master regulator PGC-1α, miR-9-5p was unable to promote a protective effect in the UUO model. We propose that miR-9-5p elicits a protective response to chronic kidney injury and renal fibrosis by inducing reprogramming of the metabolic derangement and mitochondrial dysfunction affecting tubular epithelial cells.

Cancer-associated fibroblast-derived Gremlin 1 promotes breast cancer progression

Background

Bone morphogenetic proteins (BMPs) have been reported to maintain epithelial integrity and to antagonize the transforming growth factor β (TGFβ)-induced epithelial to mesenchymal transition. The expression of soluble BMP antagonists is dysregulated in cancers and interrupts proper BMP signaling in breast cancer.

Methods

In this study, we mined the prognostic role of BMP antagonists GREMLIN 1 (GREM1) in primary breast cancer tissues using in-house and publicly available datasets. We determined which cells express GREM1 RNA using in situ hybridization (ISH) on a breast cancer tissue microarray. The effects of Grem1 on the properties of breast cancer cells were assessed by measuring the mesenchymal/stem cell marker expression and functional cell-based assays for stemness and invasion. The role of Grem1 in breast cancer-associated fibroblast (CAF) activation was measured by analyzing the expression of fibroblast markers, phalloidin staining, and collagen contraction assays. The role of Grem1 in CAF-induced breast cancer cell intravasation and extravasation was studied by utilizing xenograft zebrafish breast cancer (co-) injection models.

Results

Expression analysis of clinical breast cancer datasets revealed that high expression of GREM1 in breast cancer stroma is correlated with a poor prognosis regardless of the molecular subtype. The large majority of human breast cancer cell lines did not express GREM1 in vitro, but breast CAFs did express GREM1 both in vitro and in vivo. Transforming growth factor β (TGFβ) secreted by breast cancer cells, and also inflammatory cytokines, stimulated GREM1 expression in CAFs. Grem1 abrogated bone morphogenetic protein (BMP)/SMAD signaling in breast cancer cells and promoted their mesenchymal phenotype, stemness, and invasion. Moreover, Grem1 production by CAFs strongly promoted the fibrogenic activation of CAFs and promoted breast cancer cell intravasation and extravasation in co-injection xenograft zebrafish models.

Conclusions

Our results demonstrated that Grem1 is a pivotal factor in the reciprocal interplay between breast cancer cells and CAFs, which promotes cancer cell invasion. Targeting Grem1 could be beneficial in the treatment of breast cancer patients with high Grem1 expression.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1194-0) contains supplementary material, which is available to authorized users.

Gremlin and renal diseases: ready to jump the fence to clinical utility?

The current therapeutic strategy for the treatment of chronic kidney diseases only ameliorates disease progression. During renal injury, developmental genes are re-expressed and could be potential therapeutic targets. Among those genes reactivated in the adult damaged kidney, Gremlin is of particular relevance since recent data suggest that it could be a mediator of diabetic nephropathy and other progressive renal diseases. Earlier studies have shown that Gremlin is upregulated in trans-differentiated renal proximal tubular cells and in several chronic kidney diseases associated with fibrosis. However, not much was known about the mechanisms by which Gremlin acts in renal pathophysiology. The role of Gremlin as a bone morphogenetic protein antagonist has clearly been demonstrated in organogenesis and in fibrotic-related disorders. Gremlin binds to vascular endothelial growth factor receptor 2 (VEGFR2) in endothelial and tubular epithelial cells. Activation of the Gremlin-VEGFR2 axis was found in several human nephropathies. We have recently described that Gremlin activates the VEGFR2 signaling pathway in the kidney, eliciting a downstream mechanism linked to renal inflammatory response. Gremlin deletion improves experimental renal damage, diminishing fibrosis. Overall, the available data identify the Gremlin-VEGFR2 axis as a novel therapeutic target for kidney inflammation and fibrosis and provide a rationale for unveiling new concepts to investigate in several clinical conditions.

Gremlin, A Potential Urinary Biomarker of Anca-Associated Crescentic Glomerulonephritis

Gremlin renal overexpression has been reported in diabetic nephropathy, pauci-immune crescentic glomerulonephritis and chronic allograft nephropathy and has been implicated in the pathophysiology of the progression of renal damage. However, it is unknown whether urinary Gremlin can be associated with renal functional status, renal biopsy findings and outcome. To examine these associations we studied 20 patients with ANCA+ renal vasculitis and very high urinary Gremlin (354 ± 76 ug/gCr), 86 patients with other glomerular diseases and moderately elevated urinary Gremlin (83 ± 14 ug/gCr) and 11 healthy controls (urinary Gremlin 11.3 ± 2.4 ug/gCr). Urinary Gremlin was significantly correlated with renal expression of Gremlin (r = 0.64, p = 0.013) observed in cellular glomerular crescents, tubular epithelial cells and interstitial inflammatory cells. Moreover, urinary Gremlin levels were correlated with the number of glomerular crescents (r = 0.53; p < 0.001), renal CD68 positive cells (r = 0.71; p < 0.005), tubulointerstitial fibrosis (r = 0.50; p < 0.05), and serum creatinine levels (r = 0.60; p < 0.001). Interestingly, Gremlin expression was colocalized with CD68, CD163 (monocyte/macrophage markers) and CCL18 positive cells. ROC curve analysis showed that the cutoff value of urinary Gremlin in glomerular diseases as 43 ug/gCr with 72% of sensitivity and 100% of specificity [AUC: 0.96 (CI 95% 0.92–0.99] (p < 0.001). For ANCA+ renal vasculitis the value of urinary Gremlin of 241 ug/gCr had 55% of sensitivity and 100% of specificity [AUC: 0.81 (CI 95% 0.68–0.94) (p < 0.001]. Based on these results we propose that urinary Gremlin represents a non-invasive biomarker in ANCA+ renal vasculitis, and suggest a role of Gremlin in the formation of crescents.

Excessive mechanical loading promotes osteoarthritis through the gremlin-1-NF-κB pathway

Exposure of articular cartilage to excessive mechanical loading is deeply involved in the pathogenesis of osteoarthritis. Here, we identify gremlin-1 as a mechanical loading-inducible factor in chondrocytes, detected at high levels in middle and deep layers of cartilage after cyclic strain or hydrostatic pressure loading. Gremlin-1 activates nuclear factor-κB signalling, leading to subsequent induction of catabolic enzymes. In mice intra-articular administration of gremlin-1 antibody or chondrocyte-specific deletion of Gremlin-1 decelerates osteoarthritis development, while intra-articular administration of recombinant gremlin-1 exacerbates this process. Furthermore, ras-related C3 botulinum toxin substrate 1 activation induced by mechanical loading enhances reactive oxygen species (ROS) production. Amongst ROS-activating transcription factors, RelA/p65 induces Gremlin-1 transcription, which antagonizes induction of anabolic genes such as Sox9, Col2a1, and Acan by bone morphogenetic proteins. Thus, gremlin-1 plays essential roles in cartilage degeneration by excessive mechanical loading.

Excessive mechanical stress promotes the development of osteoarthritis. Here Chang et al. identify gremlin-1 as a factor expressed in chondrocytes in response to mechanical stress, and contributing to osteoarthritis via activation of the NF-κB pathway.

Gingival fibroblasts prevent BMP-mediated osteoblastic differentiation

Objectives

The inhibitory action of the superficial gingival connective tissues may limit the regenerative potential of alveolar bone in periodontal therapy or dental implant applications. The aims of this study were to investigate the hypothesis that gingival fibroblasts (GF) can inhibit bone morphogenetic protein (BMP)‐induced osteoblastic differentiation, to determine their expression of BMP inhibitors, and finally to determine whether reduction of these inhibitors can relieve suppression of osteoblastic differentiation.

Methods

Gingival fibroblasts were co‐cultured either directly or indirectly with calvarial osteoblasts to assess alkaline phosphatase inhibitory activity, a marker of osteoblastic differentiation. To test total BMP‐inhibitory activity of rat GF, conditioned media (GFCM) were collected from cultures. ROS 17/2.8 osteoblastic cells were stimulated with BMP2, together with GFCM. Inhibitor expression was tested using RT‐qPCR, Western blotting and in situ hybridization. Removal of inhibitors was carried out using immunoprecipitation beads.

Results

Co‐culture experiments showed GF‐secreted factors that inhibit BMP‐stimulated ALP activity. 10 ng/ml BMP2 increased alkaline phosphatase expression in ROS cells by 41%. GFCM blocked BMP activity which was equivalent to the activity of 100 ng/ml Noggin, a well‐described BMP inhibitor. Cultured gingival fibroblasts constitutively expressed BMP antagonist genes from the same subfamily, Grem1, Grem2 and Nbl1 and the Wnt inhibitor Sfrp1. Gremlin1 (6.7 × reference gene expression) had highest levels of basal expression. ISH analysis showed Gremlin1 expression was restricted to the inner half of the gingival lamina propria and the PDL. Removal of Gremlin1 protein from GFCM eliminated the inhibitory effect of GFCM on ALP activity in ROS cells. Subsequent addition of recombinant Gremlin1 restored the inhibitory activity.

Conclusions

Factors secreted by gingival fibroblasts inhibit BMP‐induced bone formation and a range of BMP inhibitors are constitutively expressed in gingival connective tissues. These inhibitors, particularly Gremlin1, may limit coronal alveolar bone regenerative potential during oral and periodontal surgery.

Gremlin Regulates Tubular Epithelial to Mesenchymal Transition via VEGFR2: Potential Role in Renal Fibrosis

Chronic kidney disease (CKD) is emerging as an important health problem due to the increase number of CKD patients and the absence of an effective curative treatment. Gremlin has been proposed as a novel therapeutic target for renal inflammatory diseases, acting via Vascular Endothelial Growth Factor Receptor-2 (VEGFR2). Although many evidences suggest that Gremlin could regulate renal fibrosis, the receptor involved has not been yet clarified. Gremlin, as other TGF-β superfamily members, regulates tubular epithelial to mesenchymal transition (EMT) and, therefore, could contribute to renal fibrosis. In cultured tubular epithelial cells Gremlin binding to VEGFR2 is linked to proinflammatory responses. Now, we have found out that in these cells VEGFR2 is also involved in the profibrotic actions of Gremlin. VEGFR2 blockade by a pharmacological kinase inhibitor or gene silencing diminished Gremlin-mediated gene upregulation of profibrotic factors and restored changes in EMT-related genes. Moreover, VEGFR2 inhibition blocked EMT phenotypic changes and dampened the rate of wound healing in response to Gremlin. The role of VEGFR2 in experimental fibrosis was evaluated in experimental unilateral ureteral obstruction. VEFGR2 inhibition diminished the upregulation of profibrotic genes and EMT changes, as well as the accumulation of extracellular matrix proteins, such as fibronectin and collagens in the obstructed kidneys. Notch pathway activation participates in renal damage progression by regulating cell growth/proliferation, regeneration and inflammation. In cultured tubular epithelial cells, Notch inhibition markedly downregulated Gremlin-induced EMT changes and wound healing speed. These results show that Gremlin regulates the EMT process via VEGFR2 and Notch pathway activation, suggesting that the Gremlin/VEGFR2 axis could be a potential therapeutic target for CKD.

EXPRESS: Gremlin1 blocks vascular endothelial growth factor signalling in the pulmonary microvascular endothelium

The bone morphogenetic protein (BMP) antagonist gremlin 1 plays a central role in the pathogenesis of hypoxic pulmonary hypertension (HPH). Recently, non-canonical functions of gremlin 1 have been identified, including specific binding to the vascular endothelial growth factor receptor-2 (VEGFR2). We tested the hypothesis that gremlin 1 modulates VEGFR2 signaling in the pulmonary microvascular endothelium.

We examined the effect of gremlin 1 haploinsufficiency on the expression of VEGF responsive genes and proteins in the hypoxic (10% O2) murine lung in vivo. Using human microvascular endothelial cells in vitro we examined the effect of gremlin 1 on VEGF signaling.

Gremlin 1 haploinsufficiency (Grem1+/–) attenuated the hypoxia-induced increase in gremlin 1 observed in the wild-type mouse lung. Reduced gremlin 1 expression in hypoxic Grem1+/– mice restored VEGFR2 expression and endothelial nitric oxide synthase (eNOS) expression and activity to normoxic values. Recombinant monomeric gremlin 1 inhibited VEGFA-induced VEGFR2 activation, downstream signaling, and VEGF-induced increases in Bcl-2, cell number, and the anti-apoptotic effect of VEGFA in vitro.

These results show that the monomeric form of gremlin 1 acts as an antagonist of VEGFR2 activation in the pulmonary microvascular endothelium. Given the previous demonstration that inhibition of VEGFR2 causes marked worsening of HPH, our results suggest that increased gremlin 1 in the hypoxic lung, in addition to blocking BMP receptor type-2 (BMPR2) signaling, contributes importantly to the development of PH by a non-canonical VEGFR2 blocking activity.

Gremlin activates the Notch pathway linked to renal inflammation

Preclinical studies suggest that Gremlin participates in renal damage and could be a potential therapeutic target for human chronic kidney diseases. Inflammation is a common characteristic of progressive renal disease, and therefore novel anti-inflammatory therapeutic targets should be investigated. The Notch signaling pathway is involved in kidney development and is activated in human chronic kidney disease, but whether Gremlin regulates the Notch pathway has not been investigated. In cultured tubular cells, Gremlin up-regulated gene expression of several Notch pathway components, increased the production of the canonical ligand Jagged-1, and caused the nuclear translocation of active Notch-1 (N1ICD). In vivo administration of Gremlin into murine kidneys elicited Jagged-1 production, increased N1ICD nuclear levels, and up-regulated the gene expression of the Notch effectors hes-1 and hey-1 All these data clearly demonstrate that Gremlin activates the Notch pathway in the kidney. Notch inhibition using the γ-secretase inhibitor DAPT impaired renal inflammatory cell infiltration and proinflammatory cytokines overexpression in Gremlin-injected mice and in experimental models of renal injury. Moreover, Notch inhibition blocked Gremlin-induced activation of the canonical and noncanonical nuclear factor-κB (NF-κB) pathway, identifying an important mechanism involved in the anti-inflammatory actions of Notch inhibition. In conclusion, Gremlin activates the Notch pathway in the kidney and this is linked to NF-κB-mediated inflammation, supporting the hypothesis that Notch inhibition could be a potential anti-inflammatory strategy for renal diseases.

Acute Kidney Injury and Progression of Diabetic Kidney Disease

Diabetic kidney disease, commonly termed diabetic nephropathy (DN), is the most common cause of end-stage kidney disease (ESKD) worldwide. The characteristic histopathology of DN includes glomerular basement membrane thickening, mesangial expansion, nodular glomerular sclerosis, and tubulointerstitial fibrosis. Diabetes is associated with a number of metabolic derangements, such as reactive oxygen species overproduction, hypoxic state, mitochondrial dysfunction, and inflammation. In the past few decades, our knowledge of DN has advanced considerably although much needs to be learned. The traditional paradigm of glomerulus-centered pathophysiology has expanded to the tubule-interstitium, the immune response and inflammation. Biomarkers of proximal tubule injury have been shown to correlate with DN progression, independent of traditional glomerular injury biomarkers such as albuminuria. In this review, we summarize mechanisms of increased susceptibility to acute kidney injury in diabetes mellitus and the roles played by many kidney cell types to facilitate maladaptive responses leading to chronic and end-stage kidney disease.

REST upregulates gremlin to modulate diffuse intrinsic pontine glioma vasculature

Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive glial tumor that occurs in children. The extremely poor median and 5-year survival in children afflicted with DIPG highlights the need for novel biology-driven therapeutics. Here, we have implicated the chromatin remodeler and regulator of brain development called RE1 Silencing Transcription Factor (REST), in DIPG pathology. We show that REST protein is aberrantly elevated in at least 21% of DIPG tumors compared to normal controls. Its knockdown in DIPG cell lines diminished cell growth and decreased their tumorigenicity in mouse intracranial models. DIPGs are vascularized tumors and interestingly, REST loss in DIPG cells also caused a substantial decline in tumor vasculature as measured by a decrease in CD31 and VEGFR2 staining. These observations were validated in vitro, where a significant decline in tube formation by human umbilical vein endothelial cells (HUVEC) was seen following REST-loss in DIPG cells. Mechanistically, REST controlled the secretion of a pro-angiogenic molecule and ligand for VEGFR2 called Gremlin-1 (GREM-1), and was associated with enhanced AKT activation. Importantly, the decline in tube formation caused by REST loss could be rescued by addition of recombinant GREM-1, which also caused AKT activation in HUVECs and human brain microvascular endothelial cells (HBMECs). In summary, our study is the first to demonstrate autocrine and paracrine functions for REST in DIPG development. It also provides the foundation for future investigations on anti-angiogenic therapies targeting GREM-1 in combination with drugs that target REST-associated chromatin remodeling activities.

Monomeric gremlin is a novel vascular endothelial growth factor receptor-2 antagonist

Angiogenesis plays a key role in various physiological and pathological conditions, including inflammation and tumor growth. The bone morphogenetic protein (BMP) antagonist gremlin has been identified as a novel pro-angiogenic factor. Gremlin promotes neovascular responses via a BMP-independent activation of the vascular endothelial growth factor (VEGF) receptor-2 (VEGFR2). BMP antagonists may act as covalent or non-covalent homodimers or in a monomeric form, while VEGFRs ligands are usually dimeric. However, the oligomeric state of gremlin and its role in modulating the biological activity of the protein remain to be elucidated.

Here we show that gremlin is expressed in vitro and in vivo both as a monomer and as a covalently linked homodimer. Mutagenesis of amino acid residue Cys141 prevents gremlin dimerization leading to the formation of gremlin^C141A monomers. Gremlin^C141A monomer retains a BMP antagonist activity similar to the wild-type dimer, but is devoid of a significant angiogenic capacity. Notably, we found that gremlin^C141A mutant engages VEGFR2 in a non-productive manner, thus acting as receptor antagonist. Accordingly, both gremlin^C141A and wild-type monomers inhibit angiogenesis driven by dimeric gremlin or VEGF-A₁₆₅. Moreover, by acting as a VEGFR2 antagonist, gremlin^C141A inhibits the angiogenic and tumorigenic potential of murine breast and prostate cancer cells in vivo.

In conclusion, our data show that gremlin exists in multiple forms endowed with specific bioactivities and provide new insights into the molecular bases of gremlin dimerization. Furthermore, we propose gremlin monomer as a new inhibitor of VEGFR2 signalling during tumor growth.

2017 update on the relationship between diabetes and colorectal cancer: epidemiology, potential molecular mechanisms and therapeutic implications

Worldwide deaths from diabetes mellitus (DM) and colorectal cancer increased by 90% and 57%, respectively, over the past 20 years. The risk of colorectal cancer was estimated to be 27% higher in patients with type 2 DM than in non-diabetic controls. However, there are potential confounders, information from lower income countries is scarce, across the globe there is no correlation between DM prevalence and colorectal cancer incidence and the association has evolved over time, suggesting the impact of additional environmental factors. The clinical relevance of these associations depends on understanding the mechanism involved. Although evidence is limited, insulin use has been associated with increased and metformin with decreased incidence of colorectal cancer. In addition, colorectal cancer shares some cellular and molecular pathways with diabetes target organ damage, exemplified by diabetic kidney disease. These include epithelial cell injury, activation of inflammation and Wnt/β-catenin pathways and iron homeostasis defects, among others. Indeed, some drugs have undergone clinical trials for both cancer and diabetic kidney disease. Genome-wide association studies have identified diabetes-associated genes (e.g. TCF7L2) that may also contribute to colorectal cancer. We review the epidemiological evidence, potential pathophysiological mechanisms and therapeutic implications of the association between DM and colorectal cancer. Further studies should clarify the worldwide association between DM and colorectal cancer, strengthen the biological plausibility of a cause-and-effect relationship through characterization of the molecular pathways involved, search for specific molecular signatures of colorectal cancer under diabetic conditions, and eventually explore DM-specific strategies to prevent or treat colorectal cancer.

Gremlin1 plays a key role in kidney development and renal fibrosis

Gremlin1 (Grem1), an antagonist of bone morphogenetic proteins, plays a key role in embryogenesis. A highly specific temporospatial gradient of Grem1 and bone morphogenetic protein signaling is critical to normal lung, kidney, and limb development. Grem1 levels are increased in renal fibrotic conditions, including acute kidney injury, diabetic nephropathy, chronic allograft nephropathy, and immune glomerulonephritis. We demonstrate that a small number of grem1^−/− whole body knockout mice on a mixed genetic background (8%) are viable, with a single, enlarged left kidney and grossly normal histology. The grem1^−/− mice displayed mild renal dysfunction at 4 wk, which recovered by 16 wk. Tubular epithelial cell-specific targeted deletion of Grem1 (TEC-grem1-cKO) mice displayed a milder response in the acute injury and recovery phases of the folic acid model. Increases in indexes of kidney damage were smaller in TEC-grem1-cKO than wild-type mice. In the recovery phase of the folic acid model, associated with renal fibrosis, TEC-grem1-cKO mice displayed reduced histological damage and an attenuated fibrotic gene response compared with wild-type controls. Together, these data demonstrate that Grem1 expression in the tubular epithelial compartment plays a significant role in the fibrotic response to renal injury in vivo.

Gremlin-1 Overexpression in Mouse Lung Reduces Silica-Induced Lymphocyte Recruitment - A Link to Idiopathic Pulmonary Fibrosis through Negative Correlation with CXCL10 Chemokine

Idiopathic pulmonary fibrosis (IPF) is characterized by activation and injury of epithelial cells, the accumulation of connective tissue and changes in the inflammatory microenvironment. The bone morphogenetic protein (BMP) inhibitor protein gremlin-1 is associated with the progression of fibrosis both in human and mouse lung. We generated a transgenic mouse model expressing gremlin-1 in type II lung epithelial cells using the surfactant protein C (SPC) promoter and the Cre-LoxP system. Gremlin-1 protein expression was detected specifically in the lung after birth and did not result in any signs of respiratory insufficiency. Exposure to silicon dioxide resulted in reduced amounts of lymphocyte aggregates in transgenic lungs while no alteration in the fibrotic response was observed. Microarray gene expression profiling and analyses of bronchoalveolar lavage fluid cytokines indicated a reduced lymphocytic response and a downregulation of interferon-induced gene program. Consistent with reduced Th1 response, there was a downregulation of the mRNA and protein expression of the anti-fibrotic chemokine CXCL10, which has been linked to IPF. In human IPF patient samples we also established a strong negative correlation in the mRNA expression levels of gremlin-1 and CXCL10. Our results suggest that in addition to regulation of epithelial-mesenchymal crosstalk during tissue injury, gremlin-1 modulates inflammatory cell recruitment and anti-fibrotic chemokine production in the lung.

Parathyroid Hormone-Related Protein Interacts With the Transforming Growth Factor-β/Bone Morphogenetic Protein-2/Gremlin Signaling Pathway to Regulate Proinflammatory and Profibrotic Mediators in Pancreatic Acinar and Stellate Cells

OBJECTIVES

Transforming growth factor β (TGF-β) regulates immune and fibrotic responses of chronic pancreatitis. The bone morphogenetic protein 2 (BMP-2) antagonist gremlin is regulated by TGF-β. Parathyroid hormone-related protein (PTHrP) levels are elevated in chronic pancreatitis. Here, we investigated the cross-talk between TGF-β/BMP-2/gremlin and PTHrP signaling.

METHODS

Reverse transcription/real-time polymerase chain reaction, chromatin immunoprecipitation, Western blotting, and transient transfection were used to investigate PTHrP regulation by TGF-β and BMP-2 and gremlin regulation by PTHrP. The PTHrP antagonist PTHrP (7-34) and acinar cells with conditional Pthrp gene deletion (PTHrP) were used to assess PTHrP's role in the proinflammatory and profibrotic effects of TGF-β and gremlin.

RESULTS

Transforming growth factor β increased PTHrP levels in acinar cells and pancreatic stellate cells (PSCs) through a Smad3-dependent pathway. Transforming growth factor β's effects on levels of IL-6 and intercellular adhesion molecule 1 (ICAM-1) (acinar cells) and procollagen I and fibronectin (PSCs) were inhibited by PTHrP (7-34). PTHrP suppressed TGF-β's effects on IL-6 and ICAM-1. Parathyroid hormone-related hormone increased gremlin in acinar cells, and inhibiting gremlin action suppressed TGF-β's and PTHrP's effects on IL-6 and ICAM-1. Transforming growth factor β-mediated gremlin up-regulation was suppressed in PTHrP cells. Bone morphogenetic protein 2 suppressed PTHrP levels in PSCs.

CONCLUSIONS

Parathyroid hormone-related hormone functions as a novel mediator of the proinflammatory and profibrotic effects of TGF-β. Transforming growth factor β and BMP-2 regulate PTHrP expression, and PTHrP regulates gremlin levels.

Tubular overexpression of Gremlin in transgenic mice aggravates renal damage in diabetic nephropathy

Diabetic nephropathy (DN) is currently a leading cause of end-stage renal failure worldwide. Gremlin was identified as a gene differentially expressed in mesangial cells exposed to high glucose and in experimental diabetic kidneys. We have described that Gremlin is highly expressed in biopsies from patients with diabetic nephropathy, predominantly in areas of tubulointerstitial fibrosis. In streptozotocin (STZ)-induced experimental diabetes, Gremlin deletion using Grem1 heterozygous knockout mice or by gene silencing, ameliorates renal damage. To study the in vivo role of Gremlin in renal damage, we developed a diabetic model induced by STZ in transgenic (TG) mice expressing human Gremlin in proximal tubular epithelial cells. The albuminuria/creatinuria ratio, determined at week 20 after treatment, was significantly increased in diabetic mice but with no significant differences between transgenic (TG/STZ) and wild-type mice (WT/STZ). To assess the level of renal damage, kidney tissue was analyzed by light microscopy (periodic acid-Schiff and Masson staining), electron microscopy, and quantitative PCR. TG/STZ mice had significantly greater thickening of the glomerular basement membrane, increased mesangial matrix, and podocytopenia vs. WT/STZ. At the tubulointerstitial level, TG/STZ showed increased cell infiltration and mild interstitial fibrosis. In addition, we observed a decreased expression of podocin and overexpression of monocyte chemoattractant protein-1 and fibrotic-related markers, including transforming growth factor-β1, Col1a1, and α-smooth muscle actin. Together, these results show that TG mice overexpressing Gremlin in renal tubules develop greater glomerular and tubulointerstitial injury in response to diabetic-mediated damage and support the involvement of Gremlin in diabetic nephropathy.

Targeting the Gremlin-VEGFR2 axis - a promising strategy for multiple diseases?

Published recently in the Journal of Pathology, Lavoz et al. show that Gremlin promotes renal inflammation directly via VEGFR2. As Gremlin has been implicated in many other diseases, such as heart, lung and liver fibrosis, osteogenesis, angiogenesis and cancer, the new findings provide a rationale for novel concepts to investigate and potentially treat several pathologies.