A potent far-upstream enhancer in the mouse pro alpha 2(I) collagen gene regulates expression of reporter genes in transgenic mice

NKX2-5 regulates vessel remodeling in scleroderma-associated pulmonary arterial hypertension

NKX2-5 is a member of the homeobox-containing transcription factors critical in regulating tissue differentiation in development. Here, we report a role for NKX2-5 in vascular smooth muscle cell phenotypic modulation in vitro and in vascular remodeling in vivo. NKX2-5 is upregulated in scleroderma patients with pulmonary arterial hypertension. Suppression of NKX2-5 expression in smooth muscle cells halted vascular smooth muscle proliferation and migration, enhanced contractility, and blocked the expression of extracellular matrix genes. Conversely, overexpression of NKX2-5 suppressed the expression of contractile genes (ACTA2, TAGLN, CNN1) and enhanced the expression of matrix genes (COL1) in vascular smooth muscle cells. In vivo, conditional deletion of NKX2-5 attenuated blood vessel remodeling and halted the progression to hypertension in a mouse chronic hypoxia model. This study revealed that signals related to injury such as serum and low confluence, which induce NKX2-5 expression in cultured cells, is potentiated by TGF-β and further enhanced by hypoxia. The effect of TGF-β was sensitive to ERK5 and PI3K inhibition. Our data suggest a pivotal role for NKX2-5 in the phenotypic modulation of smooth muscle cells during pathological vascular remodeling and provide proof of concept for therapeutic targeting of NKX2-5 in vasculopathies.

Human Skin Aging and the Anti-Aging Properties of Retinol

The skin is the most-extensive and -abundant tissue in the human body. Like many organs, as we age, human skin experiences gradual atrophy in both the epidermis and dermis. This can be primarily attributed to the diminishing population of epidermal stem cells and the reduction in collagen, which is the primary structural protein in the human body. The alterations occurring in the epidermis and dermis due to the aging process result in disruptions to the structure and functionality of the skin. This creates a microenvironment conducive to age-related skin conditions such as a compromised skin barrier, slowed wound healing, and the onset of skin cancer. This review emphasizes the recent molecular discoveries related to skin aging and evaluates preventive approaches, such as the use of topical retinoids. Topical retinoids have demonstrated promise in enhancing skin texture, diminishing fine lines, and augmenting the thickness of both the epidermal and dermal layers.

Fibrocytes: A Critical Review and Practical Guide

Fibrocytes are hematopoietic-derived cells that directly contribute to tissue fibrosis by producing collagen following injury, during disease, and with aging. The lack of a fibrocyte-specific marker has led to the use of multiple strategies for identifying these cells in vivo. This review will detail how past studies were performed, report their findings, and discuss their strengths and limitations. The motivation is to identify opportunities for further investigation and promote the adoption of best practices during future study design.

Leucine rich amelogenin peptide prevents ovariectomy-induced bone loss in mice

Amelogenins, major extra cellular matrix proteins of developing tooth enamel, are predominantly expressed by ameloblasts and play significant roles in the formation of enamel. Recently, amelogenin has been detected in various epithelial and mesenchymal tissues, implicating that it might have distinct functions in various tissues. We have previously reported that leucine rich amelogenin peptide (LRAP), one of the alternate splice forms of amelogenin, regulates receptor activator of NF-kappa B ligand (RANKL) expression in cementoblast/periodontal ligament cells, suggesting that the amelogenins, especially LRAP, might function as a signaling molecule in bone metabolism. The objective of this study was to identify and define LRAP functions in bone turnover. We engineered transgenic (TgLRAP) mice using a murine 2.3kb α1(I)-collagen promoter to drive expression of a transgene consisting of LRAP, an internal ribosome entry site (IRES) and enhanced green fluorescent protein (EGFP) to study functions of LRAP in bone formation and resorption. Calvarial cell cultures from the TgLRAP mice showed increased alkaline phosphatase (ALP) activity and increased formation of mineralized nodules compared to the cells derived from wild-type (WT) mice. The TgLRAP calvarial cells also showed an inhibitory effect on osteoclastogenesis in vitro. Gene expression comparison by quantitative polymerase chain reaction (Q-PCR) in calvarial cells indicated that bone formation makers such as Runx2, Alp, and osteocalcin were increased in TgLRAP compared to the WT cells. Meanwhile, Rankl expression was decreased in the TgLRAP cells in vitro. The ovariectomized (OVX) TgLRAP mice resisted bone loss induced by ovariectomy resulting in higher bone mineral density in comparison to OVX WT mice. The quantitative analysis of calcein intakes indicated that the ovariectomy resulted in increased bone formation in both WT and TgLRAP mice; OVX TgLRAP appeared to show the most remarkably increased bone formation. The parameters for bone resorption in tissue sections showed increased number of osteoclasts in OVX WT, but not in OVX TgLRAP over that of sham operated WT or TgLRAP mice, supporting the observed bone phenotypes in OVX mice. This is the first report identifying that LRAP, one of the amelogenin splice variants, affects bone turnover in vivo.

Postembryonic development and aging of the appendicular skeleton in Ambystoma mexicanum

BACKGROUND

The axolotl is a key model to study appendicular regeneration. The limb complexity resembles that of humans in structure and tissue components; however, axolotl limbs develop postembryonically. In this work, we evaluated the postembryonic development of the appendicular skeleton and its changes with aging.

RESULTS

The juvenile limb skeleton is formed mostly by Sox9/Col1a2 cartilage cells. Ossification of the appendicular skeleton starts when animals reach a length of 10 cm, and cartilage cells are replaced by a primary ossification center, consisting of cortical bone and an adipocyte-filled marrow cavity. Vascularization is associated with the ossification center and the marrow cavity formation. We identified the contribution of Col1a2-descendants to bone and adipocytes. Moreover, ossification progresses with age toward the epiphyses of long bones. Axolotls are neotenic salamanders, and still ossification remains responsive to l-thyroxine, increasing the rate of bone formation.

CONCLUSIONS

In axolotls, bone maturation is a continuous process that extends throughout their life. Ossification of the appendicular bones is slow and continues until the complete element is ossified. The cellular components of the appendicular skeleton change accordingly during ossification, creating a heterogenous landscape in each element. The continuous maturation of the bone is accompanied by a continuous body growth.

Distinct Murine Pancreatic Transcriptomic Signatures during Chronic Pancreatitis Recovery

We have previously demonstrated that the pancreas can recover from chronic pancreatitis (CP) lesions in the cerulein-induced mouse model. To explore how pancreatic recovery is achieved at the molecular level, we used RNA-sequencing (seq) and profiled transcriptomes during CP transition to recovery. CP was induced by intraperitoneally injecting cerulein in C57BL/6 mice. Time-matched controls (CON) were given normal saline. Pancreata were harvested from mice 4 days after the final injections (designated as CP and CON) or 4 weeks after the final injections (designated as CP recovery (CPR) and control recovery (CONR)). Pancreatic RNAs were extracted for RNA-seq and quantitative (q) PCR validation. Using RNA-seq, we identified a total of 3,600 differentially expressed genes (DEGs) in CP versus CON and 166 DEGs in CPR versus CONR. There are 132 DEGs overlapped between CP and CPR and 34 DEGs unique to CPR. A number of selected pancreatic fibrosis-relevant DEGs were validated by qPCR. The top 20 gene sets enriched from DEGs shared between CP and CPR are relevant to extracellular matrix and cancer biology, whereas the top 10 gene sets enriched from DEGs specific to CPR are pertinent to DNA methylation and specific signaling pathways. In conclusion, we identified a distinct set of DEGs in association with extracellular matrix and cancer cell activities to contrast CP and CPR. Once during ongoing CP recovery, DEGs relevant to DNA methylation and specific signaling pathways were induced to express. The DEGs shared between CP and CPR and the DEGs specific to CPR may serve as the unique transcriptomic signatures and biomarkers for determining CP recovery and monitoring potential therapeutic responses at the molecular level to reflect pancreatic histological resolution.

Dermal Fibroblast CCN1 Expression in Mice Recapitulates Human Skin Dermal Aging

The aging process deleteriously alters the structure and function of dermal collagen. These alterations result in thinning, fragility, wrinkles, laxity, impaired wound healing, and a microenvironment conducive to cancer. However, the key factors responsible for these changes have not been fully elucidated, and relevant models for the study of skin aging progression are lacking. CCN1, a secreted extracellular matrix‒associated matricellular protein, is elevated in dermal fibroblasts in aged human skin. Toward constructing a mouse model to study the key factors involved in skin-aging progression, we demonstrate that transgenic mice, with selective expression of CCN1 in dermal fibroblasts (COL1A2-CCN1), display accelerated skin dermal aging. The aged phenotype in COL1A2-CCN1 mice resembles aged human dermis: the skin is wrinkled and the dermis is thin and composed of loose, disorganized, and fragmented collagen fibrils. These dermal alterations reflect reduced production of collagen due to impaired TGFβ signaling and increased expression of matrix metalloproteinases driving the induction of c-Jun/activator protein-1. Importantly, similar mechanisms drive human dermal aging. Taken together, the data demonstrate that elevated expression of CCN1 by dermal fibroblasts functions as a key mediator of dermal aging. The COL1A2-CCN1 mouse model provides a novel tool for understanding and studying the mechanisms of skin aging and age-related skin disorders.

Aggrecanase-selective tissue inhibitor of metalloproteinase-3 (TIMP3) protects articular cartilage in a surgical mouse model of osteoarthritis

A key feature of osteoarthritis is the gradual loss of articular cartilage and bone deformation, resulting in the impairment of joint function. The primary cause of cartilage destruction is considered to be the presence of elevated proteases, such as matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs). However, clinically tested global MMP inhibitors have low efficacy that may be due to their lack of selectivity. We previously demonstrated in vitro that a variant of tissue inhibitor of metalloproteinase-3 ([-1A]TIMP3) inhibits ADAMTSs but not MMPs. In this study, we tested whether the selectivity of [-1A]TIMP3 is beneficial compared with that of the wild-type TIMP3 in preventing or delaying the onset of the degenerative effects in a mouse model of osteoarthritis. We generated transgenic mice that overexpressed TIMP3 or [-1A]TIMP3 driven by a chondrocyte-specific type II collagen promoter. TIMP3 transgenic mice showed compromised bone integrity as opposed to [-1A]TIMP3 mice. After surgically induced joint instability, TIMP3 overexpression proved to be less protective in cartilage destruction than [-1A]TIMP3 at late stages of OA. The selective inhibition of ADAMTSs provides the possibility of modifying TIMP3 to specifically target a class of cartilage-degrading proteinases and to minimize adverse effects on bone and possibly other tissues.

A Novel Composite Biomaterial Made of Jellyfish and Porcine Collagens Accelerates Dermal Wound Healing by Enhancing Reepithelization and Granulation Tissue Formation in Mice

Background and Objective: Impaired dermal wound healing represents a major medical issue in today's aging populations. Granulation tissue formation in the dermis and reepithelization of the epidermis are both important and necessary for proper wound healing. Although a number of artificial dermal grafts have been used to treat full-thickness dermal loss in humans, they do not induce reepithelization of the wound, requiring subsequent epithelial transplantation. In the present study, we sought a novel biomaterial that accelerates the wound healing process. Approach: We prepared a composite biomaterial made of jellyfish and porcine collagens and developed a hybrid-type dermal graft that composed of the upper layer film and the lower layer sponge made of this composite biomaterial. Its effect on dermal wound healing was examined using a full-thickness excisional wound model. Structural properties of the dermal graft and histological features of the regenerating skin tissue were characterized by electron microscopic observation and immunohistological examination, respectively. Results: The composite biomaterial film stimulated migration of keratinocytes, leading to prompt reepithelization. The regenerating epithelium consisted of two distinct cell populations: keratin 5-positive basal keratinocytes and more differentiated cells expressing tight junction proteins such as claudin-1 and occludin. At the same time, the sponge made of the composite biomaterial possessed a significantly enlarged intrinsic space and enhanced infiltration of inflammatory cells and fibroblasts, accelerating granulation tissue formation. Innovation: This newly developed composite biomaterial may serve as a dermal graft that accelerates wound healing in various pathological conditions. Conclusion: We have developed a novel dermal graft composed of jellyfish and porcine collagens that remarkably accelerates the wound healing process.

FAK signaling in cancer-associated fibroblasts promotes breast cancer cell migration and metastasis by exosomal miRNAs-mediated intercellular communication

Cancer-associated fibroblasts (CAFs) are activated fibroblasts that constitute the major components of tumor microenvironment (TME) and play crucial roles in tumor development and metastasis. Here, we generated fibroblast-specific inducible focal adhesion kinase (FAK) knockout (cKO) mice in a breast cancer model to study potential role and mechanisms of FAK signaling in CAF to promote breast cancer metastasis in vivo. While not affecting primary tumor development and growth, FAK deletion significantly suppressed breast cancer metastasis in vivo. Analyses of CAFs derived from cKO mice as well as human CAFs showed that FAK is required for their activity to promote mammary tumor cell migration. We further showed that FAK ablation in CAFs decreased their exosome amount and functions to promote tumor cell migration and other activities, which could contribute to the reduced metastasis observed in cKO mice. Lastly, profiling of miRs from CAF exosomes showed alterations of several exosomal miRs in FAK-null CAFs, and further analysis suggested that miR-16 and miR-148a enriched in exosomes from FAK-null CAFs contribute to the reduced tumor cell activities and metastasis. Together, these results identify a new role for FAK signaling in CAFs that regulate their intercellular communication with tumor cells to promote breast cancer metastasis.

Insights into Fibroblast Plasticity: Cellular Communication Network 2 Is Required for Activation of Cancer-Associated Fibroblasts in a Murine Model of Melanoma

Tumor stroma resembles a fibrotic microenvironment, being characterized by the presence of myofibroblast-like cancer-associated fibroblasts (CAFs). In wild-type mice injected with melanoma cells, we show that the stem cell transcription factor Sox2 is expressed by tumor cells and induced in CAFs derived from synthetic fibroblasts. These fibroblasts were labeled postnatally with green fluorescent protein using mice expressing a tamoxifen-dependent Cre recombinase under the control of a fibroblast-specific promoter/enhancer. Conversely, fibroblast activation was impaired in mice with a fibroblast-specific deletion of cellular communication network 2 (Ccn2), associated with reduced expression of α-smooth muscle actin and Sox2. Multipotent Sox2-expressing skin-derived precursor (SKP) spheroids were cultured from murine back skin. Using lineage tracing and flow cytometry, approximately 40% of SKPs were found to be derived from type I collagen-lineage cells and acquired multipotency in culture. Inhibition of mechanotransduction pathways prevented myofibroblast differentiation of SKPs and expression of Ccn2. In SKPs deleted for Ccn2, differentiation into a myofibroblast, but not an adipocyte or neuronal phenotype, was also impaired. In human melanoma, CCN2 expression was associated with a profibrotic integrin alpha (ITGA) 11-expressing subset of CAFs that negatively associated with survival. These results suggest that synthetic dermal fibroblasts are plastic, and that CCN2 is required for the differentiation of dermal progenitor cells into a myofibroblast/CAF phenotype and is, therefore, a therapeutic target in melanoma.

Characterization of Krt19 CreERT allele for targeting the nucleus pulposus cells in the postnatal mouse intervertebral disc

Intervertebral disc degeneration and associated back pain are relatively common but sparsely understood conditions, affecting over 70% of the population during some point of life. Disc degeneration is often associated with a loss of nucleus pulposus (NP) cells. Genetic mouse models offer convenient avenues to understand the cellular and molecular regulation of the disc during its formation, growth, maintenance, and aging. However, due to the lack of inducible driver lines to precisely target NP cells in the postnatal mouse disc, progress in this area of research has been moderate. NP cells are known to express cytokeratin 19 (Krt19), and tamoxifen (Tam)‐inducible Krt19^CreERT allele is available. The current study describes the characterization of Krt19^CreERT allele to specifically and efficiently target NP cells in neonatal, skeletally mature, middle‐aged, and aged mice using two independent fluorescent reporter lines. The efficiency of recombination at all ages was validated by immunostaining for KRT19. Results show that following Tam induction, Krt19^CreERT specifically drives recombination of NP cells in the spine of neonatal and aged mice, while no recombination was detected in the surrounding tissues. Knee joints from skeletally mature Tam‐treated Krt19^CreERT/+; R26^tdTOM mouse show the absence of recombination in all tissues and cells of the knee joint. Thus, this study provides evidence for the use of Krt19^CreERT allele for genetic characterization of NP cells at different stages of the mouse life.

Regulation of Proliferation, Differentiation and Functions of Osteoblasts by Runx2

Runx2 is essential for osteoblast differentiation and chondrocyte maturation. During osteoblast differentiation, Runx2 is weakly expressed in uncommitted mesenchymal cells, and its expression is upregulated in preosteoblasts, reaches the maximal level in immature osteoblasts, and is down-regulated in mature osteoblasts. Runx2 enhances the proliferation of osteoblast progenitors by directly regulating Fgfr2 and Fgfr3. Runx2 enhances the proliferation of suture mesenchymal cells and induces their commitment into osteoblast lineage cells through the direct regulation of hedgehog (Ihh, Gli1, and Ptch1), Fgf (Fgfr2 and Fgfr3), Wnt (Tcf7, Wnt10b, and Wnt1), and Pthlh (Pthr1) signaling pathway genes, and Dlx5. Runx2 heterozygous mutation causes open fontanelle and sutures because more than half of the Runx2 gene dosage is required for the induction of these genes in suture mesenchymal cells. Runx2 regulates the proliferation of osteoblast progenitors and their differentiation into osteoblasts via reciprocal regulation with hedgehog, Fgf, Wnt, and Pthlh signaling molecules, and transcription factors, including Dlx5 and Sp7. Runx2 induces the expression of major bone matrix protein genes, including Col1a1, Spp1, Ibsp, Bglap2, and Fn1, in vitro. However, the functions of Runx2 in differentiated osteoblasts in the expression of these genes in vivo require further investigation.

Live imaging of collagen deposition during experimental hepatic schistosomiasis and recovery: a view on a dynamic process

Hepatic fibrosis is the central cause of chronic clinical pathology resulting from infection by the blood flukes Schistosoma japonicum or S. mansoni. Much has been elucidated regarding the molecular, cellular and immunological responses that correspond to the formation of the granulomatous response to trapped schistosome eggs. A central feature of this Th2 response is the deposition of collagen around the periphery of the granuloma. To date, traditional histology and transcriptional methods have been used to quantify the deposition of collagen and to monitor the formation of the hepatic granuloma during experimental animal models of schistosomiasis. We have investigated the dynamic nature of granuloma formation through the use of a transgenic mouse model (B6.Collagen 1(A) luciferase mice (B6.Coll 1A-luc⁺)). With this model and whole-animal bioluminescence imaging, we followed the deposition of collagen during an active schistosome infection with Chinese and Philippines geographical strains of S. japonicum and after clearance of the adult parasites by the drug praziquantel. Individual mice were re-imaged over the time course to provide robust real-time quantitation of the development of chronic fibrotic disease. This model provides an improved method to follow the course of hepatic schistosomiasis-induced hepatic pathology and effectively supports the current dogma of the formation of hepatic fibrosis, originally elucidated from static traditional histology. This study demonstrates the first use of the B6.Coll 1A-luc⁺ mouse to monitor the dynamics of disease development and the treatment of pathogen-induced infection with the underlying pathology of fibrosis.

Broad applicability of a streamlined ethyl cinnamate-based clearing procedure

Turbidity and opaqueness are inherent properties of tissues that limit the capacity to acquire microscopic images through large tissues. Creating a uniform refractive index, known as tissue clearing, overcomes most of these issues. These methods have enabled researchers to image large and complex 3D structures with unprecedented depth and resolution. However, tissue clearing has been adopted to a limited extent due to a combination of cost, time, complexity of existing methods and potential negative impact on fluorescence signal. Here, we describe 2Eci (2nd generation ethyl cinnamate-based clearing), which can be used to clear a wide range of tissues in several species, including human organoids, Drosophila melanogaster, zebrafish, axolotl and Xenopus laevis, in as little as 1-5 days, while preserving a broad range of fluorescent proteins, including GFP, mCherry, Brainbow and Alexa-conjugated fluorophores. Ethyl cinnamate is non-toxic and can easily be used in multi-user microscope facilities. This method opens up tissue clearing to a much broader group of researchers due to its ease of use, the non-toxic nature of ethyl cinnamate and broad applicability.

Single-cell analysis uncovers convergence of cell identities during axolotl limb regeneration

Amputation of the axolotl forelimb results in the formation of a blastema, a transient tissue where progenitor cells accumulate prior to limb regeneration. However, the molecular understanding of blastema formation had previously been hampered by the inability to identify and isolate blastema precursor cells in the adult tissue. We have used a combination of Cre-loxP reporter lineage tracking and single-cell messenger RNA sequencing (scRNA-seq) to molecularly track mature connective tissue (CT) cell heterogeneity and its transition to a limb blastema state. We have uncovered a multiphasic molecular program where CT cell types found in the uninjured adult limb revert to a relatively homogenous progenitor state that recapitulates an embryonic limb bud-like phenotype including multipotency within the CT lineage. Together, our data illuminate molecular and cellular reprogramming during complex organ regeneration in a vertebrate.

Far upstream regulatory elements enhance position-independent and uterus-specific expression of the murine alpha1(I) collagen promoter in transgenic mice

The stage- and tissue-specific expression of many eukaryotic genes is regulated by cis-regulatory elements, some of which are located in proximity to the start site of transcription whereas others have been identified at considerable distances. In previous studies we have identified far upstream DNase I-hypersensitive sites in the murine alpha1(I) collagen (Col1a1) gene, which may play a role in the regulation of this abundantly expressed gene. Here we have cloned several of these sites into reporter gene constructs containing the Col1a1 promoter driving the green fluorescent protein (GFP) reporter gene and tested their possible functions in transfection experiments and transgenic mice. In transient and stable transfections none of the hypersensitive sites had a significant effect on Col1a1 promoter activity, indicating that they do not contain a classical transcriptional enhancer. In transgenic animals one element located at -18 to -19.5 kb enhanced the position-independent activity of the linked Col1a1 promoter and may be part of a locus control region. Another element located at -7 to -8 kb specifically enhanced reporter gene expression in the uteri of transgenic mice, suggesting that it contains a novel transcriptional enhancer that may be involved in the regulation of type I collagen expression in tissue remodeling in the uterus during the estrous cycle. Our studies also demonstrate the versatility of the GFP reporter gene for use in transgenic animals because it can be analyzed in live animals, whole mount embryos, histological thin sections, or primary cell cultures, and it can be quantified very sensitively in tissue or cell extracts using a fluorometer.

Layer-specific chromatin accessibility landscapes reveal regulatory networks in adult mouse visual cortex

Mammalian cortex is a laminar structure, with each layer composed of a characteristic set of cell types with different morphological, electrophysiological, and connectional properties. Here, we define chromatin accessibility landscapes of major, layer-specific excitatory classes of neurons, and compare them to each other and to inhibitory cortical neurons using the Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq). We identify a large number of layer-specific accessible sites, and significant association with genes that are expressed in specific cortical layers. Integration of these data with layer-specific transcriptomic profiles and transcription factor binding motifs enabled us to construct a regulatory network revealing potential key layer-specific regulators, including Cux1/2, Foxp2, Nfia, Pou3f2, and Rorb. This dataset is a valuable resource for identifying candidate layer-specific cis-regulatory elements in adult mouse cortex.

Characterization of Mesenchymal-Fibroblast Cells Using the Col1a2 Promoter/Enhancer

Excessive deposition of extracellular matrix (ECM) is a common hallmark of fibrotic diseases in various organs. Chiefly among this ECM are collagen types I and III, secreted by local fibroblasts, and other mesenchymal cells recruited for repair purposes. In the last two decades, the search for a fibroblast-specific promoter/enhancer has intensified in order to control the regulation of ECM in these cells and limit the scarring of the fibrotic process. In our previous work, we characterized an enhancer region 17 kb upstream of the Col1a2 gene transcription start site. This enhancer in transgenic mice is expressed mainly in mesenchymal cells during development and in adults upon injury. When driving transgenes such as beta-galactosidase or luciferase, this construct acts as an informative reporter of collagen transcription and is predictive of collagen type I deposition. In this chapter, we provide detailed protocols for identifying similar enhancers and using the sequence to generate a construct for transfection and producing transgenic animals. We also provided information on the use of luminescence in transgenic mice, tissue processing, as well as using cre/lox system to obtain conditional gain and loss of function in mice.

Targeting the annulus fibrosus of the intervertebral disc: Col1a2-Cre(ER)T mice show specific activity of Cre recombinase in the outer annulus fibrosus

Degeneration of the intervertebral disc (IVD) is a major underlying contributor to back pain-the single leading cause of disability worldwide. However, we possess a limited understanding of the etiology underlying IVD degeneration. To date, there are a limited number of mouse models that have been used to target proteins in specific compartments of the IVD to explore their functions in disc development, homeostasis and disease. Furthermore, the majority of reports exploring the composition and function of the outer encapsulating annulus fibrosus (AF) of the IVD have considered it as one tissue, without considering the numerous structural and functional differences existing between the inner and outer AF. In addition, no mouse models have yet been reported that enable specific targeting of genes within the outer AF. In the current report, we discuss these issues and demonstrate the localized activity of Cre recombinase in the IVD of Col1a2-Cre(ER)T;ROSA26mTmG mice possessing a tamoxifen-dependent Cre recombinase driven by a Cola2 promoter and distal enhancer and the mTmG fluorescent reporter. Following tamoxifen injection of 3-week-old Col1a2-Cre(ER)T;ROSA26mTmG mice, we show Cre activity specifically in the outer AF of the IVD, as indicated by expression of the GFP reporter. Thus, Col1a2-Cre(ER)T;ROSA26mTmG mice may prove to be a valuable tool in delineating the function of proteins in this unique compartment of the IVD, and in further exploring the compositional differences between the inner and outer AF in disc homeostasis, aging and disease.

Inflammatory and fibrotic responses of cardiac fibroblasts to myocardial damage associated molecular patterns (DAMPs)

Cardiac fibroblasts (CF) are well-established as key regulators of extracellular matrix (ECM) turnover in the context of myocardial remodelling and fibrosis. Recently, this cell type has also been shown to act as a sensor of myocardial damage by detecting and responding to damage-associated molecular patterns (DAMPs) upregulated with cardiac injury. CF express a range of innate immunity pattern recognition receptors (TLRs, NLRs, IL-1R1, RAGE) that are stimulated by a host of different DAMPs that are evident in the injured or remodelling myocardium. These include intracellular molecules released by necrotic cells (heat shock proteins, high mobility group box 1 protein, S100 proteins), proinflammatory cytokines (interleukin-1α), specific ECM molecules up-regulated in response to tissue injury (fibronectin-EDA, tenascin-C) or molecules modified by a pathological environment (advanced glycation end product-modified proteins observed with diabetes). DAMP receptor activation on fibroblasts is coupled to altered cellular function including changes in proliferation, migration, myofibroblast transdifferentiation, ECM turnover and production of fibrotic and inflammatory paracrine factors, which directly impact on the heart's ability to respond to injury. This review gives an overview of the important role played by CF in responding to myocardial DAMPs and how the DAMP/CF axis could be exploited experimentally and therapeutically.

Mesenchymal deficiency of Notch1 attenuates bleomycin-induced pulmonary fibrosis

Notch signaling pathway is involved in the regulation of cell fate, differentiation, proliferation, and apoptosis in development and disease. Previous studies suggest the importance of Notch1 in myofibroblast differentiation in lung alveogenesis and fibrosis. However, direct in vivo evidence of Notch1-mediated myofibroblast differentiation is lacking. In this study, we examined the effects of conditional mesenchymal-specific deletion of Notch1 on pulmonary fibrosis. Crossing of mice bearing the floxed Notch1 gene with α2(I) collagen enhancer-Cre-ER(T)-bearing mice successfully generated progeny with a conditional knockout (CKO) of Notch1 in collagen I-expressing (mesenchymal) cells on treatment with tamoxifen (Notch1 CKO). Because Notch signaling is known to be activated in the bleomycin model of pulmonary fibrosis, control and Notch1 CKO mice were analyzed for their responses to bleomycin treatment. The results showed significant attenuation of pulmonary fibrosis in CKO relative to control mice, as examined by collagen deposition, myofibroblast differentiation, and histopathology. However, there were no significant differences in inflammatory or immune cell influx between bleomycin-treated CKO and control mouse lungs. Analysis of isolated lung fibroblasts confirmed absence of Notch1 expression in cells from CKO mice, which contained fewer myofibroblasts and significantly diminished collagen I expression relative to those from control mice. These findings revealed an essential role for Notch1-mediated myofibroblast differentiation in the pathogenesis of pulmonary fibrosis.

Renal fibrosis is not reduced by blocking transforming growth factor-β signaling in matrix-producing interstitial cells

Transforming growth factor-β (TGF-β) strongly promotes renal tubulointerstitial fibrosis, but the cellular target that mediates its profibrotic actions has not been clearly identified. While in vitro data suggest that TGF-β-induced matrix production is mediated by renal fibroblasts, the role of these cells in TGF-β-dependent tubulointerstitial fibrosis following renal injury is not well defined. To address this, we deleted the TGF-β type II receptor in matrix-producing interstitial cells using two different inducible Cre models: COL1A2-Cre with a mesenchymal enhancer element and tenascin-Cre which targets medullary interstitial cells and either the mouse unilateral ureteral obstruction or aristolochic acid renal injury model. Renal interstitial cells lacking the TGF-β receptor had significantly impaired collagen I production, but unexpectedly, overall tissue fibrosis was unchanged in the conditional knockouts after renal injury. Thus, abrogating TGF-β signaling in matrix-producing interstitial cells is not sufficient to reduce fibrosis after renal injury.

Animal models of systemic sclerosis: their utility and limitations

Without doubt, animal models have provided significant insights into our understanding of the rheumatological diseases; however, no model has accurately replicated all aspects of any autoimmune disease. Recent years have seen a plethora of knockouts and transgenics that have contributed to our knowledge of the initiating events of systemic sclerosis, an autoimmune disease. In this review, the focus is on models of systemic sclerosis and how they have progressed our understanding of fibrosis and vasculopathy, and whether they are relevant to the pathogenesis of systemic sclerosis.

Tunable delivery of siRNA from a biodegradable scaffold to promote angiogenesis in vivo

A system has been engineered for temporally controlled delivery of siRNA from biodegradable tissue regenerative scaffolds. Therapeutic application of this approach to silence prolyl hydroxylase domain 2 promoted expression of pro-angiogenic genes controlled by HIF1α and enhanced scaffold vascularization in vivo. This technology provides a new standard for efficient and controllable gene silencing to modulate host response within regenerative biomaterials.

Biphasic recruitment of microchimeric fetal mesenchymal cells in fibrosis following acute kidney injury

Fetal microchimeric cells (FMCs) enter the maternal circulation and persist in tissue for decades. They have capacity to home to injured maternal tissue and differentiate along that tissue's lineage. This raises the question of the origin(s) of cells transferred to the mother during pregnancy. FMCs with a mesenchymal phenotype have been documented in several studies, which makes mesenchymal stem cells an attractive explanation for their broad plasticity. Here we assessed the recruitment and mesenchymal lineage contribution of FMCs in response to acute kidney fibrosis induced by aristolochic acid injection. Serial in vivo bioluminescence imaging revealed a biphasic recruitment of active collagen-producing FMCs during the repair process of injured kidney in post-partum wild-type mothers that had delivered transgenic pups expressing luciferase under the collagen type I-promoter. The presence of FMCs long-term post injury (day 60) was associated with profibrotic molecules (TGF-β/CTGF), serum urea levels, and collagen deposition. Immunostaining confirmed FMCs at short term (day 15) using post-partum wild-type mothers that had delivered green fluorescent protein-positive pups and suggested a mainly hematopoietic phenotype. We conclude that there is biphasic recruitment to, and activity of, FMCs at the injury site. Moreover, we identified five types of FMC, implicating them all in the reparative process at different stages of induced renal interstitial fibrosis.

Extracellular matrix synthesis in vascular disease: hypertension, and atherosclerosis

Extracellular matrix (ECM) within the vascular network provides both a structural and regulatory role. The ECM is a dynamic composite of multiple proteins that form structures connecting cells within the network. Blood vessels are distended by blood pressure and, therefore, require ECM components with elasticity yet with enough tensile strength to resist rupture. The ECM is involved in conducting mechanical signals to cells. Most importantly, ECM regulates cellular function through chemical signaling by controlling activation and bioavailability of the growth factors. Cells respond to ECM by remodeling their microenvironment which becomes dysregulated in vascular diseases such hypertension, restenosis and atherosclerosis. This review examines the cellular and ECM components of vessels, with specific emphasis on the regulation of collagen type I and implications in vascular disease.

Activated alveolar epithelial cells initiate fibrosis through secretion of mesenchymal proteins

Fibrosis is characterized by accumulation of activated fibroblasts and pathological deposition of fibrillar collagens. Activated fibroblasts overexpress matrix proteins and release factors that promote further recruitment of activated fibroblasts, leading to progressive fibrosis. The contribution of epithelial cells to this process remains unknown. Epithelium-directed injury may lead to activation of epithelial cells with phenotypes and functions similar to activated fibroblasts. Prior reports that used a reporter gene fate-mapping strategy are limited in their ability to investigate the functional significance of epithelial cell-derived mesenchymal proteins during fibrogenesis. We found that lung epithelial cell-derived collagen I activates fibroblast collagen receptor discoidin domain receptor-2, contributes significantly to fibrogenesis, and promotes resolution of lung inflammation. Alveolar epithelial cells undergoing transforming growth factor-β-mediated mesenchymal transition express several other secreted profibrotic factors and are capable of activating lung fibroblasts. These studies provide direct evidence that activated epithelial cells produce mesenchymal proteins that initiate a cycle of fibrogenic effector cell activation, leading to progressive fibrosis. Therapy targeted at epithelial cell production of type I collagen offers a novel pathway for abrogating this progressive cycle and for limiting tissue fibrosis but may lead to sustained lung injury/inflammation.

Distant mesenchymal progenitors contribute to skin wound healing and produce collagen: evidence from a murine fetal microchimerism model

The contribution of distant and/or bone marrow-derived endogenous mesenchymal stem cells (MSC) to skin wounds is controversial. Bone marrow transplantation experiments employed to address this have been largely confounded by radiation-resistant host-derived MSC populations. Gestationally-acquired fetal MSC are known to engraft in maternal bone marrow in all pregnancies and persist for decades. These fetal cells home to damaged maternal tissues, mirroring endogenous stem cell behavior. We used fetal microchimerism as a tool to investigate the natural homing and engraftment of distant MSC to skin wounds. Post-partum wild-type mothers that had delivered transgenic pups expressing luciferase under the collagen type I-promoter were wounded. In vivo bioluminescence imaging (BLI) was then used to track recruitment of fetal cells expressing this mesenchymal marker over 14 days of healing. Fetal cells were detected in 9/43 animals using BLI (Fisher exact p = 0.01 versus 1/43 controls). These collagen type I-expressing fetal cells were specifically recruited to maternal wounds in the initial phases of healing, peaking on day 1 (n = 43, p<0.01). This was confirmed by detection of Y-chromosome+ve fetal cells that displayed fibroblast-like morphology. Histological analyses of day 7 wounds revealed vimentin-expressing fetal cells in dermal tissue. Our results demonstrate the participation of distant mesenchymal cells in skin wounds. These data imply that endogenous MSC populations are likely recruited from bone marrow to wounds to participate in healing.

Connective tissue growth factor causes EMT-like cell fate changes in vivo and in vitro

Connective tissue growth factor (CTGF) plays an important role in the pathogenesis of chronic fibrotic diseases. However, the mechanism by which paracrine effects of CTGF control the cell fate of neighboring epithelial cells is not known. In this study, we investigated the paracrine effects of CTGF overexpressed in fibroblasts of Col1a2-CTGF transgenic mice on epithelial cells of skin and lung. The skin and lungs of Col1a2-CTGF transgenic mice were examined for phenotypic markers of epithelial activation and differentiation and stimulation of signal transduction pathways. In addition to an expansion of the dermal compartment in Col1a2-CTGF transgenic mice, the epidermis was characterized by focal hyperplasia, and basal cells stained positive for αSMA, Snail, S100A4 and Sox9, indicating that these cells had undergone a change in their genetic program. Activation of phosphorylated p38 and phosphorylated Erk1/2 was observed in the granular and cornified layers of the skin. Lung fibrosis was associated with a marked increase in cells co-expressing epithelial and mesenchymal markers in the lesional and unaffected lung tissue of Col1a2-CTGF mice. In epithelial cells treated with TGFβ, CTGF-specific siRNA-mediated knockdown suppressed Snail, Sox9, S100A4 protein levels and restored E-cadherin levels. Both adenoviral expression of CTGF in epithelial cells and treatment with recombinant CTGF induced EMT-like morphological changes and expression of α-SMA. Our in vivo and in vitro data supports the notion that CTGF expression in mesenchymal cells in the skin and lungs can cause changes in the differentiation program of adjacent epithelial cells. We speculate that these changes might contribute to fibrogenesis.

Interplay between bone marrow and liver in the pathogenesis of hepatic fibrosis

Recent advances in the technologies of both molecular biology and regenerative medicine have made it possible to identify bone marrow (BM)-derived cells migrating into various fibrotic organs including the liver. A number of studies have reported that BM-derived cells migrating into fibrotic liver tissue exhibit a myofibroblast-like phenotype and may participate in the progression of liver fibrosis. On the other hand, it has also been shown that BM-derived cells express matrix metalloproteinases and contribute to the regression of experimental liver fibrosis. These contradictory results may arise, at least in part, from the uncertainty of various different methods that have been used in those studies. In this review article, we describe the interplay between BM and liver in the progression and regression of liver fibrosis, with an emphasis on the necessity of qualified methods with high specificity and sensitivity to evaluate the role of BM-derived cells in collagen production.

Biology of the renal pericyte

Pericytes are cells of mesenchymal origin that are intimately involved in the development and stabilization of vascular networks. Novel studies of their role in inflammation have identified that pericytes are not only major contributors to the activated matrix depositing myofibroblast populations seen in progressive renal fibrosis but perhaps even more importantly, the detachment of renal pericytes from the vasculature contributes to the microvasculature rarefaction and subsequent hypoxia associated with chronic kidney disease. In this review, our current understanding of the functioning of renal pericytes will be considered and set in the context of the wider literature that is currently available on this neglected population of cells.

Mesenchymal-specific deletion of C/EBPβ suppresses pulmonary fibrosis

The CCAAT/enhancer-binding protein β (C/EBPβ) regulates a variety of factors and cellular responses associated with pulmonary fibrosis. To distinguish its role in the mesenchyme from that in other compartments, the effects of mesenchymal-specific deletion of C/EBPβ on pulmonary fibrosis was examined. Crossing of mice with the floxed C/EBPβ gene with α2(I) collagen enhancer-CreER(T)-bearing mice successfully generated progeny with a conditional knockout (CKO) of C/EBPβ in collagen I-expressing ("mesenchymal") cells only on treatment with tamoxifen (C/EBPβ CKO). When treated with an endotracheal bleomycin injection, C/EBPβ CKO mice showed significant attenuation of pulmonary fibrosis relative to control C/EBPβ-intact mice. C/EBPβ CKO mice also had reduced myofibroblasts in the lung. However, no significant differences in inflammatory/immune cell influx were noted in the mutant mice relative to the control mice. DNA microarray and real-time PCR analyses identified a series of myofibroblast differentiation regulators as novel target genes of C/EBPβ. Interestingly, C/EBPβ deficiency caused a marked induction of matrix metalloproteinase 12 expression, suggesting its potential role as a repressor, which could account for the noted reduction in fibrosis in the C/EBPβ-deficient mice. Thus, these findings indicate an essential role for C/EBPβ in the mesenchymal compartment in pulmonary fibrosis that is independent of its effects on inflammation or immune cell infiltration.

Recent patents on therapeutic applications of the transcription factor decoy approach

INTRODUCTION

Transcription is considered as an important target of drugs employed in biomedicine. Therefore, novel strategies to inhibit the biological effects of transcription factors (TFs) are of interest, such as targeting promoters with triple-helix-forming oligonucleotides and antisense targeting of mRNAs coding for TFs.

AREAS COVERED

The objective of this review is to describe studies considering inhibition of TF functions with molecules mimicking TF binding sites (transcription factor decoy approach, TFD) and to summarize the patents on possible clinical applications of this approach.

EXPERT OPINION

Treatment of cells with TFD molecules leads to inhibition (or activation) of genes regulated by the target transcription factors. The studies and patents on this specific issue have taken in great consideration the delivery strategy, which is a very important parameter. The TFD strategy has been proven effective in vivo. The stability of the TFD molecules in vivo should be carefully considered, as well as the possible toxicity and/or possible effects on innate and adaptive immune response. In order to improve clinical parameters, many patents suggest the use of the TFD molecules in combination with drugs already employed in therapy. We are expecting in the near future relevant clinical trials based on the TFD strategy.

Differential contribution of dermal resident and bone marrow-derived cells to collagen production during wound healing and fibrogenesis in mice

Recent studies show that bone marrow (BM)-derived cells migrating into a dermal wound promote healing by producing collagen type I. However, their contribution to the repair process has not been fully verified yet. It is also unclear whether BM-derived cells participate in dermal fibrogenesis. We have addressed these issues using transgenic mice that harbor tissue-specific enhancer/promoter sequences of α2(I) collagen gene linked to either enhanced green fluorescent protein (COL/EGFP) or the luciferase (COL/LUC) reporter gene. Following dermal excision or subcutaneous bleomycin administration, a large number of EGFP-positive collagen-producing cells appeared in the dermis of COL/EGFP reporter mice. When wild-type mice were transplanted with BM cells from transgenic COL/EGFP animals and subjected to dermal excision, no EGFP-positive BM-derived collagen-producing cells were detected throughout the repair process. Luciferase assays of dermal tissues from COL/LUC recipient mice also excluded collagen production by BM-derived cells during dermal excision healing. In contrast, a limited but significant number of CD45-positive collagen-producing cells migrated from BM following bleomycin injection. These results indicate that resident cells in the skin are the major source of de novo collagen deposition in both physiological and pathological conditions, whereas BM-derived cells participate, in part, in collagen production during dermal fibrogenesis.

Post-transcriptional up-regulation of Tsc-22 by Ybx1, a target of miR-216a, mediates TGF-{beta}-induced collagen expression in kidney cells

Increased accumulation of extracellular matrix proteins and hypertrophy induced by transforming growth factor-β1 (TGF-β) in renal mesangial cells (MC) are hallmark features of diabetic nephropathy. Although the post-transcriptional regulation of key genes has been implicated in these events, details are not fully understood. Here we show that TGF-β increased microRNA-216a (miR-216a) levels in mouse MC, with parallel down-regulation of Ybx1, a miR-216a target and RNA-binding protein. TGF-β also enhanced protein levels of Tsc-22 (TGF-β-stimulated clone 22) and collagen type I α-2 (Col1a2) expression in MC through far upstream enhancer E-boxes by interaction of Tsc-22 with an E-box regulator, Tfe3. Ybx1 colocalized with processing bodies in MC and formed a ribonucleoprotein complex with Tsc-22 mRNA, and this complex formation was reduced by TGF-β, miR-216a mimics, or Ybx1 shRNA to increase Tsc-22 protein levels but enhanced by miR-216a inhibitor oligonucleotides. Chromatin immunoprecipitation (ChIP) assays revealed that TGF-β could increase the occupancies of Tsc-22 and Tfe3 on enhancer E-boxes of Col1a2. Co-immunoprecipitation assays revealed that TGF-β promoted the interaction of Tsc-22 with Tfe3. These results demonstrate that post-transcriptional regulation of Tsc-22 mediated through Ybx1, a miR-216a target, plays a key role in TGF-β-induced Col1a2 in MC related to the pathogenesis of diabetic nephropathy.

An essential role for resident fibroblasts in experimental lung fibrosis is defined by lineage-specific deletion of high-affinity type II transforming growth factor β receptor

RATIONALE

Fibrotic response to lung injury depends on development of a fibrogenic population of myofibroblasts. The importance of resident interstitial fibroblasts and role of transforming growth factor β (TGFβ) in this process is unclear.

OBJECTIVES

To define the importance of TGFβ signaling in resident lung fibroblasts in the development of experimental pulmonary fibrosis.

METHODS

A compound genetic strategy in which mice homozygous for a floxed high-affinity type II TGFβ receptor (TβRII) allele were crossed with a transgenic strain harboring a fibroblast-specific transgene encoding ligand-dependent Cre-recombinase was used. TβRII was deleted by postnatal administration of tamoxifen over 5 days to compound mutant mice with appropriate littermate controls. Illumina microarray gene profiling and quantitative reverse transcriptase-polymerase chain reaction were used to confirm anergy to TGFβ in explanted lung fibroblasts. Bleomycin lung injury was used to induce lung fibrosis, which was analyzed by histology and biochemical methods. Immunofluorescence was used to define cell populations after lung injury.

MEASUREMENTS AND MAIN RESULTS

There was significant attenuation of fibrosis in mice after deletion of TβRII in resident fibroblasts. At 7 days after injury the number of fibrocytes and myofibroblasts was substantially reduced. Potential regulators of fibrosis were suggested by gene expression profiles that identified key candidate profibrotic genes, including connective tissue growth factor and endothelin-1 expressed by wild-type but not mutant lung fibroblasts.

CONCLUSIONS

Intact TGFβ signaling in resident pulmonary fibroblasts is essential for pulmonary fibrosis to develop. Our data support a key regulatory role of these cells in determining fibrocyte recruitment and myofibroblast differentiation.

A sensitive short-term evaluation of antifibrotic effects using newly established type I collagen reporter transgenic rats

Fibrosis is the final common pathway for various tissue lesions that lead to chronic progressive organ failure, and consequently effective antifibrotic drugs are strongly desired. However, there are few animal models in which it is possible to evaluate fibrosis sensitively in a short period of time. We therefore generated two transgenic rats harboring a firefly luciferase reporter gene under the control of the 5'-flanking region of rat α(1)(I) collagen (Col1a1-Luc Tg rats) and α(2)(I) collagen (Col1a2-Luc Tg rats). The luciferase activities of these transgenic rats were highly correlated with the hydroxyproline content in various organs. In unilateral ureteral obstruction (UUO), a well-characterized model of renal fibrosis, the luciferase activity in obstructed kidneys showed a significant increase after even 3 days of UUO, while the hydroxyproline content showed little increase. In addition, the renal hydroxyproline content had a higher correlation with the luciferase activity than α(1)(I) collagen mRNA level for over 2 wk after UUO. Although both an ANG II type 1 receptor blocker (ARB), olmesartan, and a transforming growth factor-β (TGF-β) type I receptor kinase (ALK5) inhibitor, SB-431542, inhibited renal luciferase activities in UUO, only SB-431542 inhibited luciferase activity induced by TGF-β1 in isolated glomeruli. Double immunostaining for luciferase and α-smooth muscle actin (α-SMA) revealed that some α-SMA-positive tubular epithelial cells and tubular interstitial cells produced type I collagen, which would lead to renal fibrosis. Thus collagen reporter transgenic rats would be very useful for the evaluation of antifibrotic effects and analysis of their mechanisms.

Selective expression of connective tissue growth factor in fibroblasts in vivo promotes systemic tissue fibrosis

OBJECTIVE

Connective tissue growth factor (CTGF) is a cysteine-rich secreted matricellular protein involved in wound healing and tissue repair. Enhanced and prolonged expression of CTGF has been associated with tissue fibrosis in humans. However, questions remain as to whether CTGF expression alone is sufficient to drive fibrosis. This study was undertaken to investigate whether CTGF alone is sufficient to cause fibrosis in intact animals and whether its effects are mediated through activation of transforming growth factor beta (TGFbeta) signaling or through distinct signal transduction pathways.

METHODS

We generated mice overexpressing CTGF in fibroblasts under the control of the fibroblast-specific collagen alpha2(I) promoter enhancer. Tissues such as skin, lung, and kidney were harvested for histologic analysis. Mouse embryonic fibroblasts were prepared from embryos (14.5 days postcoitum) for biochemical analysis.

RESULTS

Mice overexpressing CTGF in fibroblasts were susceptible to accelerated tissue fibrosis affecting the skin, lung, kidney, and vasculature, most notably the small arteries. We identified a marked expansion of the myofibroblast cell population in the dermis. RNA analysis of transgenic dermal fibroblasts revealed elevated expression of key matrix genes, consistent with a fibrogenic response. CTGF induced phosphorylation of p38, ERK-1/2, JNK, and Akt, but not Smad3, in transgenic mouse fibroblasts compared with wild-type mouse fibroblasts. Transfection experiments showed significantly increased basal activity of the CTGF and serum response element promoters, and enhanced induction of the CTGF promoter in the presence of TGFbeta.

CONCLUSION

These results demonstrate that selective expression of CTGF in fibroblasts alone causes tissue fibrosis in vivo through specific signaling pathways, integrating cues from the extracellular matrix into signal transduction pathways to orchestrate pivotal biologic responses relevant to tissue repair and fibrosis.

Negligible contribution of bone marrow-derived cells to collagen production during hepatic fibrogenesis in mice

BACKGROUND & AIMS

Recent studies have reported that bone marrow (BM)-derived cells migrating into fibrotic liver tissue exhibit a myofibroblast-like phenotype and may participate in the progression of liver fibrosis. However, their contribution to collagen production has not been fully verified yet. We revisited this issue by using 2 mechanistically distinct liver fibrosis models introduced into transgenic collagen reporter mice and their BM recipients.

METHODS

BM of wild-type mice was replaced by cells obtained from transgenic animals harboring tissue-specific enhancer/promoter sequences of alpha2(I) collagen gene (COL1A2) linked to enhanced green fluorescent protein (EGFP) or firefly luciferase (LUC) gene. Liver fibrosis was introduced into those mice by repeated carbon tetrachloride injections or ligation of the common bile duct. Activation of COL1A2 promoter was assessed by confocal microscopic examination detecting EGFP signals and luciferase assays of liver homogenates.

RESULTS

The tissue-specific COL1A2 enhancer/promoter was activated in hepatic stellate cells following a single carbon tetrachloride injection or during primary culture on plastic. A large number of EGFP-positive collagen-expressing cells were observed in liver tissue of transgenic COL1A2/EGFP mice in both liver fibrosis models. In contrast, there were few EGFP-positive BM-derived collagen-producing cells detected in fibrotic liver tissue of COL1A2/EGFP recipients. Luciferase assays of liver tissues from COL1A2/LUC-recipient mice further indicated that BM-derived cells produced little collagen in response to fibrogenic stimuli.

CONCLUSIONS

By using a specific and sensitive experimental system, which detects exclusively BM-derived collagen-producing cells, we conclude an unexpectedly limited role of BM-derived cells in collagen production during hepatic fibrogenesis.

Essential roles for early growth response transcription factor Egr-1 in tissue fibrosis and wound healing

The early growth response gene (Egr-1) codes for a zinc finger transcription factor that has important roles in the regulation of cell growth, differentiation, and survival. Aberrant Egr-1 expression is implicated in carcinogenesis, inflammation, atherosclerosis, and ischemic injury. We reported previously that normal fibroblasts stimulated by transforming growth factor-ss showed rapid and transient induction of Egr-1. Moreover, we observed that tissue expression of Egr-1 was elevated in patients with scleroderma, which suggests that Egr-1 may be involved in tissue repair and fibrosis. Here, we investigated matrix remodeling and wound healing in mice harboring gain of function or loss of function mutations of Egr-1. Using the model of bleomycin-induced scleroderma, we found that the early influx of inflammatory cells into the skin and lungs, and the subsequent development of fibrosis in these organs, were markedly attenuated in Egr-1 null mice. Furthermore, full-thickness incisional skin wound healing was impaired, and skin fibroblasts lacking Egr-1 showed reduced migration and myofibroblast transdifferentiation in vitro. In contrast, transgenic mice with fibroblast-specific Egr-1 overexpression showed exuberant tissue repair, with enhanced collagen accumulation and increased tensile strength of incisional wounds. Together, these results point to the fundamental role that Egr-1 plays in the regulation of transforming growth factor-ss-dependent physiological and pathological matrix remodeling.

JunB mediates enhancer/promoter activity of COL1A2 following TGF-beta induction

Transcriptional control of the genes coding for collagen type I is regulated by a complex interaction between a distal enhancer and a proximal promoter. In this study, we have dissected the molecular mechanism of this interaction by defining a specific sequence within the enhancer that respond in fibroblasts to transforming growth factor-β (TGF-β). We show that TGF-β activates COL1A2 gene via a non-canonical (Smad-independent) signalling pathway, which requires enhancer/promoter co-operation. This interaction involves exchange of cJun/Jun B transcription factor occupancy of a critical enhancer site resulting in the stabilization of enhancer/promoter coalescence. Moreover, using transgenesis, we show that interference in this mechanism results in the abolition of COL1A2 fibroblast expression in vivo. These data are therefore relevant to the control of collagen type I in vivo both in embryonic development, in adult connective tissue homeostasis, and in tissue repair and scarring pathologies.

Cell-cell interactions during remodeling of the intestine at metamorphosis in Xenopus laevis

Amphibian metamorphosis is accompanied by extensive intestinal remodeling. This process, mediated by thyroid hormone (TH) and its nuclear receptors, affects every cell type. Gut remodeling in Xenopus laevis involves epithelial and mesenchymal proliferation, smooth muscle thickening, neuronal aggregation, formation of intestinal folds, and shortening of its length by 75%. Transgenic tadpoles expressing a dominant negative TH receptor (TRDN) controlled by epithelial-, fibroblast-, and muscle-specific gene promoters were studied. TRDN expression in the epithelium caused abnormal development of virtually all cell types, with froglet guts displaying reduced intestinal folds, thin muscle and mesenchyme, absence of neurons, and reduced cell proliferation. TRDN expression in fibroblasts caused abnormal epithelia and mesenchyme development, and expression in muscle produced fewer enteric neurons and a reduced inter-muscular space. Gut shortening was inhibited only when TRDN was expressed in fibroblasts. Gut remodeling results from both cell-autonomous and cell-cell interactions.

Rosiglitazone abrogates bleomycin-induced scleroderma and blocks profibrotic responses through peroxisome proliferator-activated receptor-gamma

The nuclear hormone receptor, peroxisome proliferator-activated receptor (PPAR)-gamma, originally identified as a key mediator of adipogenesis, is expressed widely and implicated in diverse biological responses. Both natural and synthetic agonists of PPAR-gamma abrogated the stimulation of collagen synthesis and myofibroblast differentiation induced by transforming growth factor (TGF)-beta in vitro. To characterize the role of PPAR-gamma in the fibrotic process in vivo, the synthetic agonist rosiglitazone was used in a mouse model of scleroderma. Rosiglitazone attenuated bleomycin-induced skin inflammation and dermal fibrosis as well as subcutaneous lipoatrophy and counteracted the up-regulation of collagen gene expression and myofibroblast accumulation in the lesioned skin. Rosiglitazone treatment reduced the induction of the early-immediate transcription factor Egr-1 in situ without also blocking the activation of Smad2/3. In both explanted fibroblasts and skin organ cultures, rosiglitazone prevented the stimulation of collagen gene transcription and cell migration elicited by TGF-beta. Rosiglitazone-driven adipogenic differentiation of both fibroblasts and preadipocytes was abrogated in the presence of TGF-beta; this effect was accompanied by the concomitant down-regulation of cellular PPAR-gamma mRNA expression. Collectively, these results indicate that rosiglitazone treatment attenuates inflammation, dermal fibrosis, and subcutaneous lipoatrophy via PPAR-gamma in a mouse model of scleroderma and suggest that pharmacological PPAR-gamma ligands, widely used as insulin sensitizers in the treatment of type-2 diabetes mellitus, may be potential therapies for scleroderma.

Glycyrrhizin and its metabolite inhibit Smad3-mediated type I collagen gene transcription and suppress experimental murine liver fibrosis

AIMS

Glycyrrhizin has been widely used for the treatment of chronic hepatitis C. It decreases the serum levels of aminotransferases, and suppresses progression of liver fibrosis as well as subsequent occurrence of hepatocellular carcinoma. Although previous studies have shown that glycyrrhizin and its metabolite inhibit collagen gene expression, its underlying mechanisms are virtually unknown. This study was aimed to explore molecular mechanisms responsible for the inhibitory effect of glycyrrhizin on type I collagen gene transcription.

MAIN METHODS

Effects of glycyrrhizin and its metabolite, glycyrrhetinic acid, on collagen promoter activity were examined by using transgenic reporter mice harboring alpha2(I) collagen gene (COL1A2) promoter. Their effects on the TGF-beta/Smad signaling pathway were studied by cell transfection assays and immunofluorescence studies using cultured hepatic stellate cells.

KEY FINDINGS

Administration of glycyrrhizin or its metabolite, glycyrrhetinic acid, significantly suppressed COL1A2 promoter activation and progression of liver fibrosis induced by repeated carbon tetrachloride injections. In cultured hepatic stellate cells, glycyrrhetinic acid, but not glycyrrhizin, inhibited type I collagen synthesis mostly at the level of gene transcription. This inhibitory effect of glycyrrhetinic acid was abolished by a mutation introduced into a Smad3-binding region within the COL1A2 promoter. Glycyrrhetinic acid did not affect gene expression of TGF-beta receptors or Smad proteins, but inhibited nuclear accumulation of Smad3 in activated hepatic stellate cells. In addition to those direct inhibitory effects on COL1A2 transcription, glycyrrhetinic acid also suppressed activation of quiescent hepatic stellate cells in primary culture.

SIGNIFICANCE

The results provide a molecular basis for the anti-fibrotic effect of glycyrrhizin treatment.