Production of fibronectin by the human alveolar macrophage: mechanism for the recruitment of fibroblasts to sites of tissue injury in interstitial lung diseases.

Because cells of the mononuclear phagocyte system are known to produce fibronectin and because alveolar macrophages are activated in many interstitial lung diseases, the present study was designed to evaluate a role for the alveolar macrophage as a source of the increased levels of fibronectin found in the lower respiratory tract in interstitial lung diseases and to determine if such fibronectin might contribute to the development of the fibrosis found in these disorders by being a chemoattractant for human lung fibroblasts. Production of fibronectin by human alveolar macrophages obtained by bronchoalveolar lavage and maintained in short-term culture in serum-free conditions was demonstrated; de novo synthesis was confirmed by the incorporation of [14C]proline. This fibronectin had a monomer molecular weight of 220,000 and was antigenically similar to plasma fibronectin. Macrophages from patients with idiopathic pulmonary fibrosis produced fibronectin at a rate 20 times higher than did normal macrophages; macrophages from patients with pulmonary sarcoidosis produced fibronectin at 10 times the normal rate. Macrophages from 6 of 10 patients with various other interstitial disorders produced fibronectin at rates greater than the rate of highest normal control. Human alveolar macrophage fibronectin was chemotactic for human lung fibroblasts, suggesting a functional role for this fibronectin in the derangement of the alveolar structures that is characteristic of these disorders.     

Diseases of Wnt signaling

The Wnt signaling pathways play fundamental roles in the differentiation, proliferation, death and function of many cells and as a result are involved in critical developmental, growth and homeostatic processes in animals. There are four currently known pathways of Wnt signaling; the so-called canonical or Wnt/β-catenin pathway, the Wnt/Ca⁺² pathway involving Protein Kinase A, the planar cell polarity pathway and a pathway involving Protein Kinase C that functions in muscle myogenesis. The best studied of these is the Wnt/β-catenin pathway. The Wnts are an evolutionarily highly conserved family of genes/proteins. Control of the Wnt pathways is modulated by a number of the proteins that either interact with the Wnt ligands directly, or with the low density lipoprotein-receptor related proteins (LRP) 5 and 6 that along with one of several Frizzled proteins function as co-receptors for the Wnt ligands. Aberrant regulation resulting as a consequence of mutations in any of several components of the Wnt pathway and/or protein modulators of the pathway have been shown to cause a wide spectrum of diseases. This review will briefly touch on various diseases of Wnt signaling including cancer, aortic valve calcification and several bone related phenotypes. Our emerging understanding of Wnt signaling offers great hope that new molecular based screening tests and pharmaceutical agents that selectively target this pathway will be developed to diagnose and treat these diseases in the future. An erratum to this article can be found at     

Wnt signaling in the vasculature

The Wnt signaling pathway regulates normal development as well as a variety of pathologies. Studies of the Wnt pathway have focused largely on very early development and on tumorigenesis. Recent observations point to a role for Wnt signaling in vessel development and pathology. Although not yet investigated systematically, several Wnt ligands have been demonstrated to be expressed in the cells of blood vessels in vivo and in vitro, including Wnt-2, -5a, -7a and -10b. Mice deficient for Wnt-2 display vascular abnormalities including defective placental vasculature. Wnt receptors, called frizzled (Fz), are also expressed by vascular cells in culture and in situ. Of the 10 murine Fz identified to date, Fz-1, -2, -3, and -5 have been demonstrated in endothelial and vascular smooth muscle cells; mice deficient for Fz-5 display vascular abnormalities and are embryonic lethal. Two soluble, naturally occurring Wnt antagonists, frizzled-related proteins (FRP)-1 and -3, are also expressed by vascular cells. Stabilization of the downstream signaling component -catenin in blood vessels has been demonstrated in several developmental and pathologic states, further supporting the idea that Wnt signaling plays an important regulatory role in the vasculature.     

Wnt signaling in ankylosing spondylitis

The mechanisms that lead to bony fusion in ankylosing spondylitis (AS) are yet to be fully defined. In recent years, there have been several advances in our understanding of this complex disease. Here, the potential impact of the Wnt signaling pathway will be discussed. This pathway is involved in bone morphogenesis and homeostasis. Perturbations in the normal regulation have been implicated in abnormal bone formation (e.g., osteophytes). Levels of Wnt regulatory proteins like Dickkopf have been investigated as potential biomarkers of disease. This pathway might be involved in other aspects of this disease including T cell activation and differentiation, and in bone marrow adipogenesis. The pathways leading to the unique pathology and bony fusion in AS are complex and the Wnt pathway might play a critical contributing role.     

Wnt signaling in rheumatoid synoviocyte activation

Rheumatoid arthritis (RA) is a joint-specific disease with complex pathogenesis. It is characterized by synovial inflammation, cartilage loss, and joint destruction. The reasons why joint damage recurs when therapy is discontinued are not clearly understood. Several lines of evidence suggest that cartilage damage is promoted by the transformed and invasive fibroblast-like synoviocytes (FLS) of the rheumatoid joint. It has been demonstrated in several systems that aberrant wnt-mediated signaling causes blockade of cartilage differentiation and malformation of joints. In this review, we have discussed the importance of wnt–frizzled-mediated signaling in the autonomous activation of FLS in patients with RA. Anti-wnt/anti-frizzled antibodies, frizzled receptor antagonists, or small molecule inhibitors of wnt–frizzled signaling might be useful for therapeutic interventions in RA. Received: May 15, 2001/Accepted: September 28, 2001     

Wnt/Frizzled signaling in angiogenesis

The roles of growth factors such as angiopoietin (Ang) and vascular endothelial growth factor (VEGF) in angiogenesis have been known for some time, yet we have just an incipient appreciation for the contribution of Wnts to this process. Cellular proliferation and polarity, apoptosis, branching morphogenesis, inductive processes, and the maintenance of stem cells in an undifferentiated, proliferative state are all regulated by Wnt signaling. The development and maintenance of vascular structures are dependent on all these processes, and their orchestration has, to some extent, been revealed in studies of VEGF and Ang receptors. Recent evidence links the Wnt/Frizzled signaling pathway to proper vascular growth in mammals but our knowledge of Wnt function in the vasculature is rudimentary. Further insight into vascular development and the process of angiogenesis depends on evaluating the function of novel endothelial regulatory pathways such as Wnt/Frizzled signaling.     

Wnt signaling in rheumatoid synoviocyte activation

Abstract

Rheumatoid arthritis (RA) is a joint-specific disease with complex pathogenesis. It is characterized by synovial inflammation, cartilage loss, and joint destruction. The reasons why joint damage recurs when therapy is discontinued are not clearly understood. Several lines of evidence suggest that cartilage damage is promoted by the transformed and invasive fibroblast-like synoviocytes (FLS) of the rheumatoid joint. It has been demonstrated in several systems that aberrant wnt-mediated signaling causes blockade of cartilage differentiation and malformation of joints. In this review, we have discussed the importance of wnt–frizzled-mediated signaling in the autonomous activation of FLS in patients with RA. Anti-wnt/anti-frizzled antibodies, frizzled receptor antagonists, or small molecule inhibitors of wnt–frizzled signaling might be useful for therapeutic interventions in RA.     

Wnt signaling promotes hematoendothelial cell development from human embryonic stem cells

Human embryonic stem cells (hESCs) provide an important means to effectively study soluble and cell-bound mediators that regulate development of early blood and endothelial cells in a human model system. Here, several complementary methods are used to demonstrate canonical Wnt signaling is important for development of hESC-derived cells with both hematopoietic and endothelial potential. Analyses using both standard flow cy-tometry, as well the more detailed high-throughput image scanning flow cytometry, characterizes sequential development of distinct early developing CD34(bright)CD31(+)Flk1(+) cells and a later population of CD34(dim)CD45(+) cells. While the CD34(bright)CD31(+)Flk1(+) have a more complex morphology and can develop into both endothelial cells and hematopoietic cells, the CD34(dim)CD45(+) cells have a simpler morphology and give rise to only hematopoietic cells. Treatment with dickkopf1 to inhibit Wnt signaling results in a dramatic decrease in development of cells with hematoendothelial potential. In addition, activation of the canonical Wnt signaling pathway in hESCs by coculture with stromal cells that express Wnt1, but not use of noncanonical Wnt5-expressing stromal cells, results in an accelerated differentiation and higher percentage of CD34(bright)CD31(+)Flk1(+) cells at earlier stages of differentiation. These studies effectively demonstrate the importance of canonical Wnt signaling to mediate development of early hematoendothelial progenitors during human development.     

A role for interstitial matrix in tissue tension of alveolar wall

Single alveolar walls subjected to length-tension studies in saline and Bicine (0.2 M) undergo a progressive decay in tissue tension (TTD). We have examined the effect of different solutions on this TTD and looked for corresponding changes in the ultrastructure. Lung parenchyma was dissected to single alveolar walls (30 X 30 X 150 microns) in phosphate-buffered saline (0.15 M). Transferred to a length-tension bath, the tissue was immersed in Bicine, saline, fortified Hank's solution, 0.25% Alcian blue in saline, or a sodium dodecyl sulfate solution, for variable periods. Cycled through a given extension with peak force measured over time, these same tissues were fixed in buffered glutaraldehyde/tannic acid and processed for electron microscopy. Single alveolar walls immersed in saline or Bicine showed a progressive TTD. Vacuoles or spaces appeared in the interstitium which with cellular disorganization progressed with the TTD. Seen within 0.3 h, the changes were well advanced at 0.6 h. In sodium dodecyl sulfate (70 mM), however, there was no TTD and structurally there was no interstitium, with only basement membranes and fibrous proteins remaining. In fortified Hank's solution or 0.25% Alcian blue the interstitial matrix, cell morphology and tissue tension were well preserved for 1 h. This study suggest that leaching of the interstitial matrix occurs in saline or Bicine, and an intact matrix is essential for the preservation of tissue tension.     

Studies of up-regulation of androgen receptors in genital skin fibroblasts

Prolonged exposure of genital skin fibroblasts (GSF) to dihydrotestosterone (DHT) increases androgen receptor binding of steroid, a process termed 'up-regulation'. Because the extent of up-regulation appears to be quite variable, we have investigated the optimal conditions and the molecular mechanisms that control this phenomenon in seven strains of normal neonatal GSF. When GSF were incubated for 1-48 h with 3 nM methyltrienolone (R1881), maximal up-regulation was reached by 20 h and remained constant thereafter. With DHT, rapid steroid metabolism required replenishment of DHT for maximum up-regulation. Up-regulation levels following 20 h incubation with DHT (including steroid replenishment) and R1881 were 2.07-fold (range = 1.1-3.3) and 2.35-fold (range = 1.86-3.33), respectively. The greater variability observed with DHT may be related to variable rates of steroid catabolism among cell strains. Half-maximal up-regulation was attained at 0.29 nM R1881, which approximates the Kd. Maximal up-regulation was reached only with continuous exposure to R1881 for 24 h. It was completely inhibited by actinomycin D (0.5 micrograms/ml) or cycloheximide (10 micrograms/ml). Following up-regulation, removal of R1881 for 24 h resulted in a highly variable decline of androgen receptors among cell strains. Maximal up-regulation could be reinduced by exposure to R1881 again for an additional 24 h. During up-regulation, androgen receptor levels in nuclei and nuclear matrix rose with increments comparable to those obtained in whole cells. We conclude that the extent of up-regulation and its rate of decline differ greatly among normal cell strains. Hence, its study in cells of patients with androgen insensitivity may have limited value.(ABSTRACT TRUNCATED AT 250 WORDS)     

Wnt signaling in the stem cell niche

PURPOSE OF REVIEW: All the cells present in the blood are derived from the hematopoietic stem cell (HSC). Because mature blood cells have a limited life span, HSCs must perpetuate themselves through self-renewal to maintain a functional hematopoietic compartment for the lifetime of an organism. This review focuses on studies that identify the Wnt signaling pathway as a mediator of HSC self-renewal and maintenance and analyzes its potential influence in context of the HSC niche. RECENT FINDINGS: The Wnt signaling pathway has emerged as a potential regulator of self-renewal for HSCs. Recent findings have demonstrated that Wnt signaling can directly promote HSC self-renewal and ability to reconstitute the hematopoietic system of lethally irradiated mice. The recent findings that osteoblasts are an important regulatory component of the HSC microenvironment, and that elements of the Wnt signaling pathway can influence osteoblast frequency, raise the possibility that Wnt signaling may influence HSC function indirectly through the niche as well. SUMMARY: In this review, the authors evaluate the experimental evidence for a direct role of Wnt signaling HSCs as well as an indirect role through its influence on the HSC niche. Defining the mechanism of action of Wnt signaling in HSC maintenance in context of the surrounding microenvironment and determining how this signal may integrate with other niche derived signals represents the next challenge HSC biology.     

Targeting Wnt signaling pseudokinases in hematological cancers

Recent studies showed that several pseudokinases from the receptor tyrosine kinase family are important players in regulating cancer cell invasion, metastasis, and drug resistance, suggesting that targeting these proteins can play a therapeutic role in cancer treatment. Receptor Tyr kinase‐like orphan receptors (RORs), protein Tyr kinase 7 (PTK7) (also called colon carcinoma kinase 4 (CCK4)), and receptor‐like Tyr kinase (RYK) are Wnt ligand binding receptors within the non‐canonical Wnt signaling, with important roles in development, tissue homeostasis, and organogenesis. At the cellular level, these receptors transduce signals important for cell survival, migration, polarization, and chemotaxis. Considerable progress has been made in the last decade in the field of pseudokinase signaling, improving our understanding of their structure‐function mechanisms, and intracellular network of transduction components. Consequently, their role in various diseases, including cancer, is now scrutinized for therapeutic interventions to improve treatment outcome. In this article, we review findings regarding molecular mechanisms and targeted therapies for ROR1, PTK7, and RYK in hematological malignancies.     

Uterine Wnt/beta-catenin signaling is required for implantation

Successful implantation relies on precisely orchestrated and reciprocal signaling between the implanting blastocyst and the receptive uterus. We have examined the role of the Wnt/beta-catenin signaling pathway during the process of implantation and demonstrate that this pathway is activated during two distinct stages. Wnt/beta-catenin signaling is first transiently activated in circular smooth muscle forming a banding pattern of activity within the uterus on early day 4. Subsequently, activation is restricted to the luminal epithelium at the prospective site of implantation. Activation at both sites requires the presence of the blastocyst. Furthermore, inhibition of Wnt/beta-catenin signaling interferes with the process of implantation. Our results demonstrate that the Wnt/beta-catenin signaling pathway plays a central role in coordinating uterus-embryo interactions required for implantation.     

非经典Wnt信号在骨稳态中的作用

Wnt信号通路是由经典及非经典两类通路组成的一个复杂的蛋白网络,其在骨代谢疾病和肿瘤疾病等研究中至关重要。对于骨代谢疾病早期报道多集中于经典信号通路,但随着研究的不断深入,非经典Wnt信号通路在调控骨稳态(骨形成和骨吸收)中的作用日益受到关注。本文对非经典Wnt配体及其在骨稳态中的作用进行阐述,了解非经典Wnt信号的靶向调控为治疗骨质疏松症等骨稳态失衡相关疾病提供潜在研究方法及新的靶点。