Dickkopf Homolog 3 Induces Stem Cell Differentiation into Smooth Muscle Lineage via ATF6 Signalling

The tunicamycin derivative TunR2 exhibits potent antibiotic properties with low toxicity in an in vivo Mycobacterium marinum-zebrafish TB infection model

Tunicamycins (TUN) are well-defined, Streptomyces-derived natural products that inhibit protein N-glycosylation in eukaryotes, and by a conserved mechanism also block bacterial cell wall biosynthesis. TUN inhibits the polyprenylphosphate-N-acetyl-hexosamine-1-phospho-transferases (PNPT), an essential family of enzymes found in both bacteria and eukaryotes. We have previously published the development of chemically modified TUN, called TunR1 and TunR2, that have considerably reduced activity on eukaryotes but that retain the potent antibacterial properties. A mechanism for this reduced toxicity has also been reported. TunR1 and TunR2 have been tested against mammalian cell lines in culture and against live insect cells but, until now, no in vivo evaluation has been undertaken for vertebrates. In the current work, TUN, TunR1, and TunR2 are investigated for their relative toxicity and antimycobacterial activity in zebrafish using a well-established Mycobacterium marinum (M. marinum) infection system, a model for studying human Mycobacterium tuberculosis infections. We also report the relative ability to activate the unfolded protein response (UPR), the known mechanism for the eukaryotic toxicity observed with TUN treatment. Importantly, TunR1 and TunR2 retained their antimicrobial properties, as evidenced by a reduction in M. marinum bacterial burden, compared to DMSO-treated zebrafish. In summary, findings from this study highlight the characteristics of recently developed TUN derivatives, mainly TunR2, and its potential for use as a novel anti-bacterial agent for veterinary and potential medical purposes.

The Multifaceted Role of Human Dickkopf-3 (DKK-3) in Development, Immune Modulation and Cancer

The human Dickkopf (DKK) family includes four main secreted proteins, DKK-1, DKK-2, DKK-3, and DKK-4, as well as the DKK-3 related protein soggy (Sgy-1 or DKKL1). These glycoproteins play crucial roles in various biological processes, and especially modulation of the Wnt signaling pathway. DKK-3 is distinct, with its multifaceted roles in development, stem cell differentiation and tissue homeostasis. Intriguingly, DKK-3 appears to have immunomodulatory functions and a complex role in cancer, acting as either a tumor suppressor or an oncogene, depending on the context. DKK-3 is a promising diagnostic and therapeutic target that can be modulated by epigenetic reactivation, gene therapy and DKK-3-blocking agents. However, further research is needed to optimize DKK-3-based therapies. In this review, we comprehensively describe the known functions of DKK-3 and highlight the importance of context in understanding and exploiting its roles in health and disease.

Dickkopf-3: An Update on a Potential Regulator of the Tumor Microenvironment

Dickkopf-3 (Dkk-3) is a member of the Dickkopf family protein of secreted Wingless-related integration site (Wnt) antagonists that appears to modulate regulators of the host microenvironment. In contrast to the clear anti-tumorigenic effects of Dkk-3-based gene therapies, the role of endogenous Dkk-3 in cancer is context-dependent, with elevated expression associated with tumor promotion and suppression in different settings. The receptors and effectors that mediate the diverse effects of Dkk-3 have not been characterized in detail, contributing to an ongoing mystery of its mechanism of action. This review compares the various functions of Dkk-3 in the tumor microenvironment, where Dkk-3 has been found to be expressed by subpopulations of fibroblasts, endothelial, and immune cells, in addition to epithelial cells. We also discuss how the activation or inhibition of Dkk-3, depending on tumor type and context, might be used to treat different types of cancers.

Endothelial repair by stem and progenitor cells

The integrity of the endothelial barrier is required to maintain vascular homeostasis and fluid balance between the circulatory system and surrounding tissues and to prevent the development of vascular disease. However, the origin of the newly developed endothelial cells is still controversial. Stem and progenitor cells have the potential to differentiate into endothelial cell lines and stimulate vascular regeneration in a paracrine/autocrine fashion. The one source of new endothelial cells was believed to come from the bone marrow, which was challenged by the recent findings. By administration of new techniques, including genetic cell lineage tracing and single cell RNA sequencing, more solid data were obtained that support the concept of stem/progenitor cells for regenerating damaged endothelium. Specifically, it was found that tissue resident endothelial progenitors located in the vessel wall were crucial for endothelial repair. In this review, we summarized the latest advances in stem and progenitor cell research in endothelial regeneration through findings from animal models and discussed clinical data to indicate the future direction of stem cell therapy.

Different Roles of Stem/Progenitor Cells in Vascular Remodeling

Significance: Since the discovery of vascular stem cells, there has been considerable advancement in comprehending the nature and functions of these cells. Due to their differentiation potential to repair endothelial cells and to participate in lesion formation during vascular remodeling, it is crucial to elucidate vascular stem cell behaviors and the mechanisms underlying this process, which could provide new chances for the design of clinical therapeutic application of stem cells. Recent Advances: Over the past decades, major progress has been made on progenitor/vascular stem cells in the field of cardiovascular research. Vascular stem cells are mostly latent in their niches and can be bioactivated in response to damage and get involved in endothelial repair and smooth muscle cell aggregation to generate neointima. Accumulating evidence has been shown recently, using genetic lineage tracing mouse models, to particularly provide solutions to the nature of vascular stem cells and to monitor both cell migration and the process of differentiation during physiological angiogenesis and in vascular diseases. Critical Issues: This article reviews and summarizes the current research progress of vascular stem cells in this field and highlights future prospects for stem cell research in regenerative medicine. Future Directions: Despite recent advances and achievements of stem cells in cardiovascular research, the nature and cell fate of vascular stem cells remain elusive. Further comprehensive studies using new techniques including genetic cell lineage tracing and single-cell RNA sequencing are essential to fully illuminate the role of stem cells in vascular development and diseases. Antioxid. Redox Signal. 35, 192-203.

Functional Genomic Screening During Somatic Cell Reprogramming Identifies DKK3 as a Roadblock of Organ Regeneration

Somatic cell reprogramming and tissue repair share relevant factors and molecular programs. Here, Dickkopf-3 (DKK3) is identified as novel factor for organ regeneration using combined transcription-factor-induced reprogramming and RNA-interference techniques. Loss of Dkk3 enhances the generation of induced pluripotent stem cells but does not affect de novo derivation of embryonic stem cells, three-germ-layer differentiation or colony formation capacity of liver and pancreatic organoids. However, DKK3 expression levels in wildtype animals and serum levels in human patients are elevated upon injury. Accordingly, Dkk3-null mice display less liver damage upon acute and chronic failure mediated by increased proliferation in hepatocytes and LGR5+ liver progenitor cell population, respectively. Similarly, recovery from experimental pancreatitis is accelerated. Regeneration onset occurs in the acinar compartment accompanied by virtually abolished canonical-Wnt-signaling in Dkk3-null animals. This results in reduced expression of the Hedgehog repressor Gli3 and increased Hedgehog-signaling activity upon Dkk3 loss. Collectively, these data reveal Dkk3 as a key regulator of organ regeneration via a direct, previously unacknowledged link between DKK3, canonical-Wnt-, and Hedgehog-signaling.

MBTPS2, a membrane bound protease, underlying several distinct skin and bone disorders

The MBTPS2 gene on the X-chromosome encodes the membrane-bound transcription factor protease, site-2 (MBTPS2) or site-2 protease (S2P) which cleaves and activates several signaling and regulatory proteins from the membrane. The MBTPS2 is critical for a myriad of cellular processes, ranging from the regulation of cholesterol homeostasis to unfolded protein responses. While its functional role has become much clearer in the recent years, how mutations in the MBTPS2 gene lead to several human disorders with different phenotypes including Ichthyosis Follicularis, Atrichia and Photophobia syndrome (IFAP) with or without BRESHECK syndrome, Keratosis Follicularis Spinulosa Decalvans (KFSD), Olmsted syndrome, and Osteogenesis Imperfecta type XIX remains obscure. This review presents the biological role of MBTPS2 in development, summarizes its mutations and implicated disorders, and discusses outstanding unanswered questions.

Perivascular tissue stem cells are crucial players in vascular disease

Perivascular tissue including adipose layer and adventitia have been considered to play pivotal roles in vascular development and disease progression. Recent studies showed that abundant stem/progenitorcells (SPCs) are present in perivascular tissues. These SPCs exhibit capability to proliferate and differentiate into specific terminal cells. Adult perivascular SPCs are quiescent in normal condition, once activated by specific molecules (e.g., cytokines), they migrate toward the lumen side where they differentiate into both smooth muscle cells (SMCs) and endothelial cells (ECs), thus promoting intima hyperplasia or endothelial regeneration. In addition, perivascular SPCs can also regulate vascular diseases via other ways including but not limited to paracrine effects, matrix protein modulation and microvessel formation. Perivascular SPCs have also been shown to possess therapeutic potentials due to the capability to differentiate into vascular cells and regenerate vascular structures. This review summarizes current knowledge on resident SPCs features and discusses the potential benefits of SPCs therapy in vascular diseases.

tRNA-derived fragments tRFGlnCTG induced by arterial injury promote vascular smooth muscle cell proliferation

tRNA-derived fragments (tRFs) and tRNA halves (tiRNAs) are originated from the specific cleavage of endogenous tRNAs or their precursors and regulate gene expression when the cells are in stressful circumstances. Here, we replicated the rat common carotid artery (CCA) intimal hyperplasia model and investigated the expression of tRFs/tiRNAs in the artery. The normal and the balloon-injured rat CCAs were subjected to small RNA sequencing, and then the differentially expressed tRFs/tiRNAs were identified and analyzed. The expression profiles of tRFs/tiRNAs in the healthy and injured CCAs were remarkably different. tRNA^GlnCTG-derived fragments (tRF^GlnCTG) were found to be overexpressed with a high abundance in the injured CCA. In in vitro experiments, the synthetic tRF^GlnCTG mimetics elevated the proliferation and migration of rat vascular smooth muscle cells (VSMCs). Through bioinformatics analysis and an overexpression experiment, tRF^GlnCTG was found to negatively regulate the expression of FAS cell surface death receptor (FAS). This study revealed that tRF^GlnCTG is a crucial regulator in promoting VSMC proliferation. The investigation of the roles of tRFs/tiRNAs is of significance for understanding the mechanism, diagnosis, and treatment of intimal hyperplasia.

Protein quality control of cell stemness

Protein quality control (PQC) systems play essential roles in the recognition, refolding and clearance of aberrant proteins, thus ensuring cellular protein homeostasis, or proteostasis. Especially, continued proliferation and differentiation of stem cells require a high rate of translation; therefore, accurate PQC systems are essential to maintain stem cell function. Growing evidence suggested crucial roles of PQC systems in regulating the stemness and differentiation of stem cells. This review focuses on current knowledge regarding the components of the proteostasis network in stem cells, and the importance of proteostasis in maintaining stem cell identity and regenerative functions. A complete understanding of this process might uncover potential applications in aging intervention and aging-related diseases.

Identification of key genes in ruptured atherosclerotic plaques by weighted gene correlation network analysis

The rupture of atherosclerotic plaques is essential for cardiovascular and cerebrovascular events. Identification of the key genes related to plaque rupture is an important approach to predict the status of plaque and to prevent the clinical events. In the present study, we downloaded two expression profiles related to the rupture of atherosclerotic plaques (GSE41571 and GSE120521) from GEO database. 11 samples in GSE41571 were used to identify the differentially expressed genes (DEGs) and to construct the weighted gene correlation network analysis (WGCNA) by R software. The gene oncology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment tool in DAVID website, and the Protein-protein interactions in STRING website were used to predict the functions and mechanisms of genes. Furthermore, we mapped the hub genes extracted from WGCNA to DEGs, and constructed a sub-network using Cytoscape 3.7.2. The key genes were identified by the molecular complex detection (MCODE) in Cytoscape. Further validation was conducted using dataset GSE120521 and human carotid endarterectomy (CEA) plaques. Results: In our study, 868 DEGs were identified in GSE41571. Six modules with 236 hub genes were identified through WGCNA analysis. Among these six modules, blue and brown modules were of the highest correlations with ruptured plaques (with a correlation of 0.82 and −0.9 respectively). 72 hub genes were identified from blue and brown modules. These 72 genes were the most likely ones being related to cell adhesion, extracellular matrix organization, cell growth, cell migration, leukocyte migration, PI₃K-Akt signaling, focal adhesion, and ECM-receptor interaction. Among the 72 hub genes, 45 were mapped to the DEGs (logFC > 1.0, p-value < 0.05). The sub-network of these 45 hub genes and MCODE analysis indicated 3 clusters (13 genes) as key genes. They were LOXL1, FBLN5, FMOD, ELN, EFEMP1 in cluster 1, RILP, HLA-DRA, HLA-DMB, HLA-DMA in cluster 2, and SFRP4, FZD6, DKK3 in cluster 3. Further expression detection indicated EFEMP1, BGN, ELN, FMOD, DKK3, FBLN5, FZD6, HLA-DRA, HLA-DMB, HLA-DMA, and RILP might have potential diagnostic value.

Post-Transcriptional Regulation of Homeostatic, Stressed, and Malignant Stem Cells

Cellular identity is not driven by differences in genomic content but rather by epigenomic, transcriptomic, and proteomic heterogeneity. Although regulation of the epigenome plays a key role in shaping stem cell hierarchies, differential expression of transcripts only partially explains protein abundance. The epitranscriptome, translational control, and protein degradation have emerged as fundamental regulators of proteome complexity that regulate stem cell identity and function. Here, we discuss how post-transcriptional mechanisms enable stem cell homeostasis and responsiveness to developmental cues and environmental stressors by rapidly shaping the content of their proteome and how these processes are disrupted in pre-malignant and malignant states.

Establishment and validation of an endoplasmic reticulum stress reporter to monitor zebrafish ATF6 activity in development and disease

Induction of endoplasmic reticulum (ER) stress is associated with diverse developmental and degenerative diseases. Modified ER homeostasis causes activation of conserved stress pathways at the ER called the unfolded protein response (UPR). ATF6 is a transcription factor activated during ER stress as part of a coordinated UPR. ATF6 resides at the ER and, upon activation, is transported to the Golgi apparatus, where it is cleaved by proteases to create an amino-terminal cytoplasmic fragment (ATF6f). ATF6f translocates to the nucleus to activate transcriptional targets. Here, we describe the establishment and validation of zebrafish reporter lines for ATF6 activity. These transgenic lines are based on a defined and multimerized ATF6 consensus site, which drives either eGFP or destabilized eGFP, enabling dynamic study of ATF6 activity during development and disease. The results show that the reporter is specific for the ATF6 pathway, active during development and induced in disease models known to engage UPR. Specifically, during development, ATF6 activity is highest in the lens, skeletal muscle, fins and gills. The reporter is also activated by common chemical inducers of ER stress, including tunicamycin, thapsigargin and brefeldin A, as well as by heat shock. In models for amyotrophic lateral sclerosis and cone dystrophy, ATF6 reporter expression is induced in spinal cord interneurons or photoreceptors, respectively, suggesting a role for ATF6 response in multiple neurodegenerative diseases. Collectively our results show that these ATF6 reporters can be used to monitor ATF6 activity changes throughout development and in zebrafish models of disease.

This article has an associated First Person interview with the first author of the paper.

Summary: In this study, we validate transgenic zebrafish generated to specifically report the activity of ATF6, representing a major branch of the endoplasmic reticulum stress pathway with functions in development and disease.

DKK3 (Dikkopf-3) Transdifferentiates Fibroblasts Into Functional Endothelial Cells-Brief Report

Objective- To determine the role of a cytokine-like protein DKK3 (dikkopf-3) in directly transdifferentiating fibroblasts into endothelial cells (ECs) and the underlying mechanisms. Approach and Results- DKK3 overexpression in human fibroblasts under defined conditions for 4 days led to a notable change in cell morphology and progenitor gene expression. It was revealed that these cells went through mesenchymal-to-epithelial transition and subsequently expressed KDR (kinase insert domain receptor) at high levels. Further culture in EC defined media led to differentiation of these progenitors into functional ECs capable of angiogenesis both in vitro and in vivo, which was regulated by the VEGF (vascular endothelial growth factor)/miR (microRNA)-125a-5p/Stat3 (signal transducer and activator of transcription factor 3) axis. More importantly, fibroblast-derived ECs showed the ability to form a patent endothelium-like monolayer in tissue-engineered vascular grafts ex vivo. Conclusions- These data demonstrate that DKK3 is capable of directly differentiating human fibroblasts to functional ECs under defined media and provides a novel potential strategy for endothelial regeneration.

Serum dickkopf-3 is associated with death and vascular events after ischemic stroke: an observational study from CATIS

BACKGROUND

Dickkopf-3 (Dkk-3) is implicated in the progression of atherosclerosis. This study aimed to investigate the association between serum Dkk-3 and the prognosis of ischemic stroke.

METHODS

We measured serum Dkk-3 levels in 3344 ischemic stroke patients from CATIS (China Antihypertensive Trial in Acute Ischemic Stroke). The primary outcome was a combination of death and vascular events within 3 months after ischemic stroke.

RESULTS

During 3 months of follow-up, the cumulative incidence rates of primary outcome among ischemic stroke patients in five quintiles of serum Dkk-3 (from low to high) were 4.49%, 3.74%, 2.54%, 5.23%, and 6.73%, respectively (log-rank p = 0.004). Multivariable Cox proportional hazards regression analyses showed that compared with the third quintile of serum Dkk-3, the adjusted hazard ratios (95% confidence intervals) associated with the first and fifth quintile were 3.49 (1.46-8.34) and 4.23 (1.86-9.64) for primary outcome, 3.47 (1.06-11.36) and 5.30 (1.81-15.51) for death, and 2.66 (1.01-7.01) and 3.35 (1.33-8.40) for vascular events, respectively. Multivariable-adjusted Cox proportional hazards regression model with restricted cubic splines showed a U-shaped association between serum Dkk-3 and the risk of primary outcome (p for nonlinearity = 0.030). Moreover, adding serum Dkk-3 to conventional risk factors could improve the predictive power for primary outcome (net reclassification improvement 28.44%, p < 0.001; integrated discrimination improvement 0.48%, p = 0.001).

CONCLUSIONS

Both low and high serum Dkk-3 levels are associated with increased risks of death and vascular events within 3 months after ischemic stroke, indicating that serum Dkk-3 may have a special effect on the prognosis of ischemic stroke. We also found that serum Dkk-3 might be a prognostic biomarker for ischemic stroke. Further studies are needed to replicate our findings and to determine the optimal levels of serum Dkk-3.

Dickkopf-3 in aberrant endothelial secretome triggers renal fibroblast activation and endothelial-mesenchymal transition

Background

Our laboratory has previously demonstrated that Sirt1endo-/- mice show endothelial dysfunction and exaggerated renal fibrosis, whereas mice with silenced endothelial transforming growth factor beta (TGF-β) signaling are resistant to fibrogenic signals. Considering the fact that the only difference between these mutant mice is confined to the vascular endothelium, this indicates that secreted substances contribute to these contrasting responses.

Methods

We performed an unbiased proteomic analysis of the secretome of renal microvascular endothelial cells (RMVECs) isolated from these two mutants. We cultured renal fibroblasts and RMVECs and used microfluidic devices for coculturing.

Results

Dickkopf-3 (DKK3), a putative ligand of the Wnt/β-catenin pathway, was present exclusively in the fibrogenic secretome. In cultured fibroblasts, DKK3 potently induced myofibroblast activation. In addition, DKK3 antagonized effects of DKK1, a known inhibitor of the Wnt pathway, in conversion of fibroblasts to myofibroblasts. In RMVECs, DKK3 induced endothelial-mesenchymal transition and impaired their angiogenic competence. The inhibition of endothelial outgrowth, enhanced myofibroblast formation and endothelial-mesenchymal transition were confirmed in coculture. In reporter DKK3-eGFP × Col3.6-GFPcyan mice, DKK3 was marginally expressed under basal conditions. Adriamycin-induced nephropathy resulted in upregulation of DKK3 expression in tubular and, to a lesser degree, endothelial compartments. Sulindac sulfide was found to exhibit superior Wnt pathway-suppressive action and decreased DKK3 signals and the extent of renal fibrosis.

Conclusions

In conclusion, this unbiased proteomic screen of the profibrogenic endothelial secretome revealed DKK3 acting as an agonist of the Wnt pathway, enhancing formation of myofibroblasts and endothelial-mesenchymal transition and impairing angiogenesis. A potent inhibitor of the Wnt pathway, sulindac sulfide, suppressed nephropathy-induced DKK3 expression and renal fibrosis.

Binding of Dickkopf-3 to CXCR7 Enhances Vascular Progenitor Cell Migration and Degradable Graft Regeneration

Supplemental Digital Content is available in the text.

Rationale:

Vascular progenitor cells play key roles in physiological and pathological vascular remodeling—a process that is crucial for the regeneration of acellular biodegradable scaffolds engineered as vital strategies against the limited availability of healthy autologous vessels for bypass grafting. Therefore, understanding the mechanisms driving vascular progenitor cells recruitment and differentiation could help the development of new strategies to improve tissue-engineered vessel grafts and design drug-targeted therapy for vessel regeneration.

Objective:

In this study, we sought to investigate the role of Dkk3 (dickkopf-3), recently identified as a cytokine promotor of endothelial repair and smooth muscle cell differentiation, on vascular progenitor cells cell migration and vascular regeneration and to identify its functional receptor that remains unknown.

Methods and Results:

Vascular stem/progenitor cells were isolated from murine aortic adventitia and selected for the Sca-1 (stem cell antigen-1) marker. Dkk3 induced the chemotaxis of Sca-1+ cells in vitro in transwell and wound healing assays and ex vivo in the aortic ring assay. Functional studies to identify Dkk3 receptor revealed that overexpression or knockdown of chemokine receptor CXCR7 (C-X-C chemokine receptor type 7) in Sca-1+ cells resulted in alterations in cell migration. Coimmunoprecipitation experiments using Sca-1+ cell extracts treated with Dkk3 showed the physical interaction between DKK3 and CXCR7, and specific saturation binding assays identified a high-affinity Dkk3-CXCR7 binding with a dissociation constant of 14.14 nmol/L. Binding of CXCR7 by Dkk3 triggered the subsequent activation of ERK1/2 (extracellular signal-regulated kinases 1/2)-, PI3K (phosphatidylinositol 3-kinase)/AKT (protein kinase B)-, Rac1 (Ras-related C3 botulinum toxin substrate 1)-, and RhoA (Ras homolog gene family, member A)-signaling pathways involved in Sca-1+ cell migration. Tissue-engineered vessel grafts were fabricated with or without Dkk3 and implanted to replace the rat abdominal aorta. Dkk3-loaded tissue-engineered vessel grafts showed efficient endothelization and recruitment of vascular progenitor cells, which had acquired characteristics of mature smooth muscle cells. CXCR7 blocking using specific antibodies in this vessel graft model hampered stem/progenitor cell recruitment into the vessel wall, thus compromising vascular remodeling.

Conclusions:

We provide a novel and solid evidence that CXCR7 serves as Dkk3 receptor, which mediates Dkk3-induced vascular progenitor migration in vitro and in tissue-engineered vessels, hence harnessing patent grafts resembling native blood vessels.

CREB3 Transcription Factors: ER-Golgi Stress Transducers as Hubs for Cellular Homeostasis

CREB3 family of transcription factors are ER localized proteins that belong to the bZIP family. They are transported from the ER to the Golgi, cleaved by S1P and S2P proteases and the released N-terminal domains act as transcription factors. CREB3 family members regulate the expression of a large variety of genes and according to their tissue-specific expression profiles they play, among others, roles in acute phase response, lipid metabolism, development, survival, differentiation, organelle autoregulation, and protein secretion. They have been implicated in the ER and Golgi stress responses as regulators of the cell secretory capacity and cell specific cargos. In this review we provide an overview of the diverse functions of each member of the family (CREB3, CREB3L1, CREB3L2, CREB3L3, CREB3L4) with special focus on their role in the central nervous system.

Dynamic expression of tRNA-derived small RNAs define cellular states

Transfer RNA (tRNA)-derived small RNAs (tsRNAs) have recently emerged as important regulators of protein translation and shown to have diverse biological functions. However, the underlying cellular and molecular mechanisms of tsRNA function in the context of dynamic cell-state transitions remain unclear. Expression analysis of tsRNAs in distinct heterologous cell and tissue models of stem vs. differentiated states revealed a differentiation-dependent enrichment of 5'-tsRNAs. We report the identification of a set of 5'-tsRNAs that is upregulated in differentiating mouse embryonic stem cells (mESCs). Notably, interactome studies with differentially enriched 5'-tsRNAs revealed a switch in their association with "effector" RNPs and "target" mRNAs in different cell states. We demonstrate that specific 5'-tsRNAs can preferentially interact with the RNA-binding protein, Igf2bp1, in the RA-induced differentiated state. This association influences the transcript stability and thereby translation of the pluripotency-promoting factor, c-Myc, thus providing a mechanistic basis for how 5'-tsRNAs can modulate stem cell states in mESCs. Together our study highlights the role of 5'-tsRNAs in defining distinct cell states.

Dkk (Dickkopf) Proteins

Clinical and preclinical studies over the past 3 decades have uncovered a multitude of signaling pathways involved in the initiation and progression of atherosclerosis. From these studies, signaling by proteins of the Wnt family has recently emerged as an important player in the development of atherosclerosis. Wnt signaling is characterized by a large number of ligands, receptors, and coreceptors and can be regulated at many different levels. Among Wnt modulators, the evolutionary conserved Dkk (Dickkopf) proteins, and especially Dkk-1, the founding member of the family, are the best characterized. The role of Dkks in the pathophysiology of the arterial wall is only partially understood, but their involvement in atherosclerosis is becoming increasingly evident. This review introduces recent key findings on Dkk proteins and their functions in atherosclerosis and discusses the potential importance of modulating Dkk signaling as part of a novel, improved strategy for preventing and treating atherosclerosis-related diseases.

Visual Overview—

An online visual overview is available for this article.

Fibrogenic Secretome of Sirtuin 1-Deficient Endothelial Cells: Wnt, Notch and Glycocalyx Rheostat

Sirtuins (SIRT) are ubiquitous histone and protein deacetylases and a member of this family, SIRT1, is the best-studied one. Its functions in endothelial cells encompass branching angiogenesis, activation of endothelial nitric oxide synthase, regulation of proapoptotic and proinflammatory pathways, among others. Defective SIRT1 activity has been described in various cardiovascular, renal diseases and in aging-associated conditions. Therefore, understanding of SIRT1-deficient, endothelial dysfunctional phenotype has much to offer clinically. Here, we summarize recent studies by several investigative teams of the characteristics of models of global endothelial SIRT1 deficiency, the causes of facilitative development of fibrosis in these conditions, dissect the protein composition of the aberrant secretome of SIRT1-deficient endothelial cells and present several components of this aberrant secretome that are involved in fibrogenesis via activation of fibroblasts to myofibroblasts. These include ligands of Wnt and Notch pathways, as well as proteolytic fragments of glycocalyx core protein, syndecan-4. The latter finding is crucial for understanding the degradation of glycocalyx that accompanies SIRT1 deficiency. This spectrum of abnormalities associated with SIRT1 deficiency in endothelial cells is essential for understanding the origins and features of endothelial dysfunction in a host of cardiovascular and renal diseases.

Protective effect of stromal Dickkopf-3 in prostate cancer: opposing roles for TGFBI and ECM-1

Aberrant transforming growth factor-β (TGF-β) signaling is a hallmark of the stromal microenvironment in cancer. Dickkopf-3 (Dkk-3), shown to inhibit TGF-β signaling, is downregulated in prostate cancer and upregulated in the stroma in benign prostatic hyperplasia, but the function of stromal Dkk-3 is unclear. Here we show that DKK3 silencing in WPMY-1 prostate stromal cells increases TGF-β signaling activity and that stromal cell-conditioned media inhibit prostate cancer cell invasion in a Dkk-3-dependent manner. DKK3 silencing increased the level of the cell-adhesion regulator TGF-β-induced protein (TGFBI) in stromal and epithelial cell-conditioned media, and recombinant TGFBI increased prostate cancer cell invasion. Reduced expression of Dkk-3 in patient tumors was associated with increased expression of TGFBI. DKK3 silencing reduced the level of extracellular matrix protein-1 (ECM-1) in prostate stromal cell-conditioned media but increased it in epithelial cell-conditioned media, and recombinant ECM-1 inhibited TGFBI-induced prostate cancer cell invasion. Increased ECM1 and DKK3 mRNA expression in prostate tumors was associated with increased relapse-free survival. These observations are consistent with a model in which the loss of Dkk-3 in prostate cancer leads to increased secretion of TGFBI and ECM-1, which have tumor-promoting and tumor-protective roles, respectively. Determining how the balance between the opposing roles of extracellular factors influences prostate carcinogenesis will be key to developing therapies that target the tumor microenvironment.

A lifetime of stress: ATF6 in development and homeostasis

BACKGROUND

Activating transcription factor 6 (ATF6) is an endoplasmic reticulum (ER)-localised protein and member of the leucine zipper family of transcription factors. Best known for its role in transducing signals linked to stress to the endoplasmic reticulum, the 50 kDa activated form of ATF6 is now emerging as a major regulator of organogenesis and tissue homeostasis. Responsible for the correct folding, secretion and membrane insertion of a third of the proteome in eukaryotic cells, the ER encompasses a dynamic, labyrinthine network of regulators, chaperones, foldases and cofactors. Such structures are crucial to the extensive protein synthesis required to undergo normal development and maintenance of tissue homeostasis. When an additional protein synthesis burden is placed on the ER, ATF6, in tandem with ER stress transducers inositol requiring enzyme 1 (IRE1) and PKR-like endoplasmic reticulum kinase (PERK), slows the pace of protein translation and induces the production of stress-reducing chaperones and foldases.

MAIN TEXT

In the context of development and tissue homeostasis, however, distinct cellular impacts have been attributed to ATF6. Drawing on data published from human, rodent, fish, goat and bovine research, this review first focuses on ATF6-mediated regulation of osteo- and chondrogenesis, ocular development as well as neuro- and myelinogenesis. The purported role of ATF6 in development of the muscular and reproductive systems as well as adipo- and lipogenesis is then described. With relevance to cardiac disease, cancer and brain disorders, the importance of ATF6 in maintaining tissue homeostasis is the subject of the final section.

CONCLUSION

In conclusion, the review encourages further elucidation of ATF6 regulatory operations during organogenesis and tissue homeostasis, to spawn the development of ATF6-targeted therapeutic strategies.

Role of Resident Stem Cells in Vessel Formation and Arteriosclerosis

Vascular, resident stem cells are present in all 3 layers of the vessel wall; they play a role in vascular formation under physiological conditions and in remodeling in pathological situations. Throughout development and adult early life, resident stem cells participate in vessel formation through vasculogenesis and angiogenesis. In adults, the vascular stem cells are mostly quiescent in their niches but can be activated in response to injury and participate in endothelial repair and smooth muscle cell accumulation to form neointima. However, delineation of the characteristics and of the migration and differentiation behaviors of these stem cells is an area of ongoing investigation. A set of genetic mouse models for cell lineage tracing has been developed to specifically address the nature of these cells and both migration and differentiation processes during physiological angiogenesis and in vascular diseases. This review summarizes the current knowledge on resident stem cells, which has become more defined and refined in vascular biology research, thus contributing to the development of new potential therapeutic strategies to promote endothelial regeneration and ameliorate vascular disease development.

DKK3 (Dickkopf 3) Alters Atherosclerotic Plaque Phenotype Involving Vascular Progenitor and Fibroblast Differentiation Into Smooth Muscle Cells

OBJECTIVE

DKK3 (dickkopf 3), a 36-kD secreted glycoprotein, has been shown to be involved in the differentiation of partially reprogrammed cells and embryonic stem cells to smooth muscle cells (SMCs), but little is known about its involvement in vascular disease. This study aims to assess the effects of DKK3 on atherosclerotic plaque composition.

APPROACH AND RESULTS

In the present study, we used a murine model of atherosclerosis (ApoE^-/-) in conjunction with DKK3^-/- and performed tandem stenosis of the carotid artery to evaluate atherosclerotic plaque development. We found that the absence of DKK3 leads to vulnerable atherosclerotic plaques, because of a reduced number of SMCs and reduced matrix protein deposition, as well as increased hemorrhage and macrophage infiltration. Further in vitro studies revealed that DKK3 can induce differentiation of Sca1⁺ (stem cells antigen 1) vascular progenitors and fibroblasts into SMCs via activation of the TGF-β (transforming growth factor-β)/ATF6 (activating transcription factor 6) and Wnt signaling pathways. Finally, we assessed the therapeutic potential of DKK3 in mouse and rabbit models and found that DKK3 altered the atherosclerotic plaque content via increasing SMC numbers and reducing vascular inflammation.

CONCLUSIONS

Cumulatively, we provide the first evidence that DKK3 is a potent SMC differentiation factor, which might have a therapeutic effect in reducing intraplaque hemorrhage related to atherosclerotic plaque phenotype.

A Cytokine-Like Protein Dickkopf-Related Protein 3 Is Atheroprotective

Supplemental Digital Content is available in the text.

Background:

Dickkopf-related protein 3 (DKK3) is a secreted protein that is involved in the regulation of cardiac remodeling and vascular smooth muscle cell differentiation, but little is known about its role in atherosclerosis.

Methods:

We tested the hypothesis that DKK3 is atheroprotective using both epidemiological and experimental approaches. Blood DKK3 levels were measured in the Bruneck Study in 2000 (n=684) and then in 2005 (n=574). DKK3-deficient mice were crossed with apolipoprotein E^-/- mice to evaluate atherosclerosis development and vessel injury-induced neointimal formation. Endothelial cell migration and the underlying mechanisms were studied using in vitro cell culture models.

Results:

In the prospective population-based Bruneck Study, the level of plasma DKK3 was inversely related to carotid artery intima-media thickness and 5-year progression of carotid atherosclerosis independently from standard risk factors for atherosclerosis. Experimentally, we analyzed the area of atherosclerotic lesions, femoral artery injury-induced reendothelialization, and neointima formation in both DKK3^-/-/apolipoprotein E^-/- and DKK3^+/+/apolipoprotein E^-/- mice. It was demonstrated that DKK3 deficiency accelerated atherosclerosis and delayed reendothelialization with consequently exacerbated neointima formation. To explore the underlying mechanisms, we performed transwell and scratch migration assays using cultured human endothelial cells, which exhibited a significant induction in cell migration in response to DKK3 stimulation. This DKK3-induced migration activated ROR2 and DVL1, activated Rac1 GTPases, and upregulated JNK and c-jun phosphorylation in endothelial cells. Knockdown of the ROR2 receptor using specific siRNA or transfection of a dominant-negative form of Rac1 in endothelial cells markedly inhibited cell migration and downstream JNK and c-jun phosphorylation.

Conclusions:

This study provides the evidence for a role of DKK3 in the protection against atherosclerosis involving endothelial migration and repair, with great therapeutic potential implications against atherosclerosis.

Dickkopf-3 Ablation Attenuates the Development of Atherosclerosis in ApoE-Deficient Mice

Background

Dickkopf‐3 (DKK3) is a negative regulator of the Wnt/β‐catenin signaling pathway, which is involved in inflammation. However, little is known about the relationship between DKK3 expression and the progression of atherosclerosis. The aim of the present study was to define the role of DKK3 and its potential mechanism in the development of atherosclerosis.

Methods and Results

Immunofluorescence analysis showed that DKK3 was strongly expressed in macrophages of atherosclerotic plaques from patients with coronary heart disease and in hyperlipidemic mice. The expression level was significantly increased in atherogenesis. DKK3^−/−ApoE^−/− mice exhibited a significant decrease in atherosclerotic lesions in the entire aorta, aortic sinus, and brachiocephalic arteries. Transplantation of bone marrow from DKK3^−/−ApoE^−/− mice into lethally irradiated ApoE^−/− recipients resulted in a reduction of atherosclerotic lesions, compared with the lesions in recipients transplanted with ApoE^−/− donor cells, suggesting that the effect of DKK3 deficiency was largely mediated by bone marrow–derived cells. A reduction in the necrotic core size, accompanied by increased collagen content and smooth muscle cells and decreased accumulation of macrophages and lipids, contributed to the stability of plaques in DKK3^−/−ApoE^−/− mice. Furthermore, multiple proinflammatory cytokines exhibited marked decreases in DKK3^−/−ApoE^−/− mice. Finally, we observed that DKK3 ablation increased β‐catenin expression in the nuclei of macrophages both in vivo and in vitro.

Conclusions

DKK3 expression in macrophages is involved in the pathogenesis of atherosclerosis through modulation of inflammation and inactivation of the Wnt/β‐catenin pathway.

Assessing the contribution of thrombospondin-4 induction and ATF6α activation to endoplasmic reticulum expansion and phenotypic modulation in bladder outlet obstruction

Phenotypic modulation of smooth muscle cells is a hallmark of disease. The associated expansion of endoplasmic reticulum (ER) volume remains unexplained. Thrombospondin-4 was recently found to promote ATF6α activation leading to ER expansion. Using bladder outlet obstruction as a paradigm for phenotypic modulation, we tested if thrombospondin-4 is induced in association with ATF6α activation and ER expansion. Thrombospondin-4 was induced and ATF6α was activated after outlet obstruction in rodents. Increased abundance of spliced of Xbp1, another ER-stress sensor, and induction of Atf4 and Creb3l2 was also seen. Downstream of ATF6α, Calr, Manf, Sdf2l1 and Pdi increased as did ER size, whereas contractile markers were reduced. Overexpression of ATF6α, but not of thrombospondin-4, increased Calr, Manf, Sdf2l1 and Pdi and caused ER expansion, but the contractile markers were inert. Knockout of thrombospondin-4 neither affected bladder growth nor expression of ATF6α target genes, and repression of contractile markers was the same, even if ATF6α activation was curtailed. Increases of Xbp1s, Atf4 and Creb3l2 were similar. Our findings demonstrate reciprocal regulation of the unfolded protein response, including ATF6α activation and ER expansion, and reduced contractile differentiation in bladder outlet obstruction occurring independently of thrombospondin-4, which however is a sensitive indicator of obstruction.

New insights into the unfolded protein response in stem cells

The unfolded protein response (UPR) is an evolutionarily conserved adaptive mechanism to increase cell survival under endoplasmic reticulum (ER) stress conditions. The UPR is critical for maintaining cell homeostasis under physiological and pathological conditions. The vital functions of the UPR in development, metabolism and immunity have been demonstrated in several cell types. UPR dysfunction activates a variety of pathologies, including cancer, inflammation, neurodegenerative disease, metabolic disease and immune disease. Stem cells with the special ability to self-renew and differentiate into various somatic cells have been demonstrated to be present in multiple tissues. These cells are involved in development, tissue renewal and certain disease processes. Although the role and regulation of the UPR in somatic cells has been widely reported, the function of the UPR in stem cells is not fully known, and the roles and functions of the UPR are dependent on the stem cell type. Therefore, in this article, the potential significances of the UPR in stem cells, including embryonic stem cells, tissue stem cells, cancer stem cells and induced pluripotent cells, are comprehensively reviewed. This review aims to provide novel insights regarding the mechanisms associated with stem cell differentiation and cancer pathology.