Gremlin 1 - small protein, big impact: the multiorgan consequences of disrupted BMP antagonism†

New insights into Gremlin-1: A tumour microenvironment landscape re-engineer and potential therapeutic target

Gremlin-1 (GREM1), a well-known bone morphogenetic protein (BMP) antagonist, is highly expressed in various malignant tumours. However, the specific role of GREM1 in tumours remains controversial and may be attributed to the heterogeneity and complexity of the tumour microenvironment (TME). It is currently believed that GREM1 regulates the complex landscape of the TME, primarily by antagonising BMP signalling or BMP-independent pathways. Both GREM1 and BMP play dual roles in tumour progression. Therefore, the mutual crosstalk between tumour cells and tumour-associated fibroblasts and the regulation of various secreted factors in the TME affect the secretion level of GREM1, which in turn regulates the amplitude balance between GREM1 and BMP, affecting tumour progression. The inhibition of GREM1 activity in the TME can disrupt this amplitude balance and prevent the formation of a tumour-supportive microenvironment, demonstrating that GREM1 is a potential therapeutic target. In this study, we reviewed the specific signalling pathways via which GREM1 in the TME regulates epithelial-mesenchymal transition, construction of the tumour immune microenvironment, and maintenance of tumour cell stemness via BMP-dependent and BMP-independent regulation, and also summarised the latest clinical progress of GREM1.

Emerging Role of NAT10 as ac4C Writer in Inflammatory Diseases: Mechanisms and Therapeutic Applications

The incidence of inflammatory diseases, including infections, autoimmune disorders, and tumors, is consistently increasing year by year, posing a significant and growing threat to human health on a global scale. Recent research has indicated that RNA acetylation modification, a specific type of post-transcriptional modification, may play a critical role in the pathogenesis of these diseases. Among the various mechanisms of RNA modification, N-acetyltransferase 10 (NAT10) has been identified as the sole cytidine acetyltransferase in eukaryotes. NAT10 is responsible for acetylating mRNA cytosine, which leads to the formation of N4-acetylcytidine (ac4C), a modification that subsequently influences mRNA stability and translation efficiency. Despite these insights, the specific roles and underlying mechanisms by which RNA acetylation contributes to the onset and progression of inflammatory diseases remain largely unclear. This review aimed to elucidate the alterations in NAT10 expression, the modifications it induces in target genes, and its overall contribution to the pathogenesis of various inflammatory conditions. It has been observed that NAT10 expression tends to increase in most inflammatory conditions, thereby affecting the expression and function of target genes through the formation of ac4C. Furthermore, inhibitors targeting NAT10 present promising therapeutic avenues for treating inflammatory diseases by selectively blocking NAT10 activity, thereby preventing the modification of target genes and suppressing immune cell activation and inflammatory responses. This potential for therapeutic intervention underscores the critical importance of further research on NAT10's role in inflammatory disease pathogenesis, as understanding these mechanisms could lead to significant advancements in treatment strategies, potentially transforming the therapeutic landscape for these conditions.

Gremlin1: a BMP antagonist with therapeutic potential in Oncology

Gremlins, originating from early 20th-century Western folklore, are mythical creatures known for causing mechanical malfunctions and electronic failures, aptly dubbed "little devils". Analogously, GREM1 acts like a horde of these mischievous entities by antagonizing the bone morphogenetic protein (BMP signaling) pathway or through other non-BMP dependent mechanisms (such as binding to Fibroblast Growth Factor Receptor 1and Epidermal Growth Factor Receptor) contributing to the malignant progression of various cancers. The overexpression of GREM1 promotes tumor cell growth and survival, enhances angiogenesis within the tumor microenvironment, and creates favorable conditions for tumor development and dissemination. Consequently, inhibiting the activity of GREM1 or blocking its interaction with BMP presents a promising strategy for suppressing tumor growth and metastasis. However, the role of GREM1 in cancer remains a subject of debate, with evidence suggesting both oncogenic and tumor-suppressive functions. Currently, several pharmaceutical companies are researching the GREM1 target, with some advancing to Phase I/II clinical trials. This article will provide a detailed overview of the GREM1 target and explore its potential role in cancer therapy.

Expression of Osteopontin and Gremlin 1 Proteins in Cardiomyocytes in Ischemic Heart Failure

A relevant role of osteopontin (OPN) and gremlin 1 (Grem1) in regulating cardiac tissue remodeling and formation of heart failure (HF) are documented, with the changes of OPN and Grem1 levels in blood plasma due to acute ischemia, ischemic heart disease-induced advanced HF or dilatative cardiomyopathy being the primary focus in most of these studies. However, knowledge on the early OPN and Grem1 proteins expression changes within cardiomyocytes during remodeling due to chronic ischemia remains insufficient. The aim of this study was to determine the OPN and Grem1 proteins expression changes in human cardiomyocytes at different stages of ischemic HF. A semi-quantitative immunohistochemical analysis was performed in 105 myocardial tissue samples obtained from the left cardiac ventricles. Increased OPN immunostaining intensity was already detected in the stage A HF group, compared to the control group (p < 0.001), and continued to increase in the stage B HF (p < 0.001), achieving the peak of immunostaining in the stages C/D HF group (p < 0.001). Similar data of Grem1 immunostaining intensity changes in cardiomyocytes were documented. Significantly positive correlations were detected between OPN, Grem1 expression in cardiomyocytes and their diameter as well as the length, in addition to positive correlation between OPN and Grem1 expression changes within cardiomyocytes. These novel findings suggest that OPN and Grem1 contribute significantly to reorganization of cellular geometry from the earliest stage of cardiomyocyte remodeling, providing new insights into the ischemic HF pathogenesis.

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.

Irradiation and lithium treatment alter the global DNA methylation pattern and gene expression underlying a shift from gliogenesis towards neurogenesis in human neural progenitors

Central nervous system (CNS) tumors account for almost a third of pediatric cancers and are the largest contributor to cancer-related death in children. Cranial radiation therapy (CRT) is, often in combination with chemotherapy and surgery, effective in the treatment of high-grade childhood brain cancers, but it has been associated with late complications in 50-90% of survivors, such as decline in cognition and mood, decreased social competence, and fatigue. A leading hypothesis to explain the decline in cognition, at least partially, is injury to the neural stem and progenitor cells (NSPCs), which leads to apoptosis and altered fate choice, favoring gliogenesis over neurogenesis. Hence, treatments harnessing neurogenesis are of great relevance in this context. Lithium, a well-known mood stabilizer, has neuroprotective and antitumor effects and has been found to reverse irradiation-induced damage in rodents, at least in part by regulating the expression of the glutamate decarboxylase 2 gene (Gad2) via promoter demethylation in rat NSPCs. Additionally, lithium was shown to rescue irradiation-induced cognitive defects in mice. Here, we show that irradiation (IR) alone or in combination with lithium chloride (LiCl) caused major changes in gene expression and global DNA methylation in iPSC-derived human NSPCs (hNSPCs) compared to untreated cells, as well as LiCl-only-treated cells. The pattern of DNA methylation changes after IR-treatment alone was stochastic and observed across many different gene groups, whereas differences in DNA methylation after LiCl-treatment of irradiated cells were more directed to specific promoters of genes, including genes associated with neurogenesis, for example GAD2. Interestingly, IR and IR + LiCl treatment affected the promoter methylation and expression of several genes encoding factors involved in BMP signaling, including the BMP antagonist gremlin1. We propose that lithium in addition to promoting neuronal differentiation, also represses glial differentiation in hNSPCs with DNA methylation regulation being a key mechanism of action.

NAT10 Promotes Osteogenic Differentiation of Mesenchymal Stem Cells by Mediating N4-Acetylcytidine Modification of Gremlin 1

Objective

To investigate the function of NAT10 in mesenchymal stem cell (MSC) osteogenic differentiation and study the mechanism by which NAT10 affects MSC osteogenesis by mediating Gremlin 1 N4-acetylcytidine (ac⁴C) modification.

Methods

Osteogenic differentiation of MSCs was induced, and the osteogenic ability was evaluated with alizarin red S (ARS) and alkaline phosphatase (ALP) assays. The NAT10 expression level during MSC osteogenesis was measured by western blot (WB). MSCs were transfected with lentiviruses to inhibit (Sh-NAT10) or overexpress NAT10 (Over-NAT10), and the osteogenic differentiation ability was assessed by ARS, ALP, and osteogenic gene marker assays. β-Catenin, Akt, and Smad signaling pathway component activation levels were assessed, and the expression levels of key Smad signaling pathway molecules were determined by PCR and WB. The Gremlin 1 mRNA ac⁴C levels were analyzed using RIP-PCR, and the Gremlin 1 mRNA degradation rate was determined. Sh-Gremlin 1 was transfected to further investigate the role of NAT10 and Gremlin 1 in MSC osteogenesis.

Results

During MSC osteogenesis, NAT10 expression, ARS staining, and the ALP level gradually increased. Decreasing NAT10 expression inhibited, and increasing NAT10 expression promoted MSC osteogenic differentiation. NAT10 affected the BMP/Smad rather than the Akt and β-Catenin signaling pathway activation by regulating Gremlin 1 expression. The Gremlin 1 mRNA ac⁴C level was positively regulated by NAT10, which accelerated Gremlin 1 degradation. Sh-Gremlin 1 abolished the promotive effect of NAT10 on MSC osteogenic differentiation.

Conclusion

NAT10 positively regulated MSC osteogenic differentiation through accelerating the Gremlin 1 mRNA degradation by increasing its ac⁴C level. These results may provide new mechanistic insight into MSC osteogenesis and bone metabolism in vivo.