Distinct fibroblast subsets drive inflammation and damage in arthritis

The identification of lymphocyte subsets with non-overlapping effector functions has been pivotal to the development of targeted therapies in immune-mediated inflammatory diseases (IMIDs)1,2. However, it remains unclear whether fibroblast subclasses with non-overlapping functions also exist and are responsible for the wide variety of tissue-driven processes observed in IMIDs, such as inflammation and damage3-5. Here we identify and describe the biology of distinct subsets of fibroblasts responsible for mediating either inflammation or tissue damage in arthritis. We show that deletion of fibroblast activation protein-α (FAPα)+ fibroblasts suppressed both inflammation and bone erosions in mouse models of resolving and persistent arthritis. Single-cell transcriptional analysis identified two distinct fibroblast subsets within the FAPα+ population: FAPα+THY1+ immune effector fibroblasts located in the synovial sub-lining, and FAPα+THY1- destructive fibroblasts restricted to the synovial lining layer. When adoptively transferred into the joint, FAPα+THY1- fibroblasts selectively mediate bone and cartilage damage with little effect on inflammation, whereas transfer of FAPα+ THY1+ fibroblasts resulted in a more severe and persistent inflammatory arthritis, with minimal effect on bone and cartilage. Our findings describing anatomically discrete, functionally distinct fibroblast subsets with non-overlapping functions have important implications for cell-based therapies aimed at modulating inflammation and tissue damage.

Transcriptional and Cellular Diversity of the Human Heart

BACKGROUND

The human heart requires a complex ensemble of specialized cell types to perform its essential function. A greater knowledge of the intricate cellular milieu of the heart is critical to increase our understanding of cardiac homeostasis and pathology. As recent advances in low-input RNA sequencing have allowed definitions of cellular transcriptomes at single-cell resolution at scale, we have applied these approaches to assess the cellular and transcriptional diversity of the nonfailing human heart.

METHODS

Microfluidic encapsulation and barcoding was used to perform single nuclear RNA sequencing with samples from 7 human donors, selected for their absence of overt cardiac disease. Individual nuclear transcriptomes were then clustered based on transcriptional profiles of highly variable genes. These clusters were used as the basis for between-chamber and between-sex differential gene expression analyses and intersection with genetic and pharmacologic data.

RESULTS

We sequenced the transcriptomes of 287 269 single cardiac nuclei, revealing 9 major cell types and 20 subclusters of cell types within the human heart. Cellular subclasses include 2 distinct groups of resident macrophages, 4 endothelial subtypes, and 2 fibroblast subsets. Comparisons of cellular transcriptomes by cardiac chamber or sex reveal diversity not only in cardiomyocyte transcriptional programs but also in subtypes involved in extracellular matrix remodeling and vascularization. Using genetic association data, we identified strong enrichment for the role of cell subtypes in cardiac traits and diseases. Intersection of our data set with genes on cardiac clinical testing panels and the druggable genome reveals striking patterns of cellular specificity.

CONCLUSIONS

Using large-scale single nuclei RNA sequencing, we defined the transcriptional and cellular diversity in the normal human heart. Our identification of discrete cell subtypes and differentially expressed genes within the heart will ultimately facilitate the development of new therapeutics for cardiovascular diseases.

Keratocyte and fibroblast phenotypes in the repairing cornea

In mammals, tissue damage is usually repaired by activation of a fibrotic response which saves the life of the organism, but which can never restore function to the damaged organ. In addition, fibrotic responses form the basis for diverse pathologies, including many that occur in the eye. It is intriguing, therefore, to observe the occasional circumstances in which repair in mammals appears to take on a regenerative character, such as during fetal wound healing or in certain types of corneal wounds. The thesis of this chapter is that the choice between regeneration or fibrosis lies in the control of fibroblast phenotype. The cornea of the eye has several features which make it a particularly useful model for the study of fibroblast phenotype. Studies discussed herein, identify failure to activate the transcription factor NF-kappaB as a control mechanism for inhibiting fibroblast activation in the cornea. Evidence is further presented for the view that transition in fibroblast phenotype in repair tissue is not simply a matter of differential gene expression, but is a developmental event which reflects changes in the hard wiring of signalling pathways by which the cell responds to environmental input.

Evidence of fibroblast heterogeneity and the role of fibroblast subpopulations in fibrosis

This review article highlights the evidence supporting the concept that, like lymphocytes, fibroblasts also consist of subpopulations with unique phenotypes and functions. A new view of the fibroblast is that they are dynamic and consist of subsets which produce cytokines and interact with the immune system. For example, murine lung fibroblasts separated by fluorescence-activated cell sorting on the basis of the thymocyte-1 antigen are heterogeneous in their morphology, expression of surface markers, antigen presentation to T lymphocytes, ability to synthesize collagen, and cytokine production. Human lung fibroblasts have also been found to be heterogeneous in surface marker expression, proliferation, and collagen production. Investigation of pulmonary fibroblast heterogeneity is important since the lung is particularly susceptible to fibrosis induced by chemotherapy and radiation, inhaled particles, systemic autoimmune disease, etc. The inflammatory responses which typically precede fibrotic induction may be controlled by a subset of resident fibroblasts. Another subset may be important for the fibroblast hyperplasia and extensive extracellular matrix production which are hallmarks of fibrosis. In another model system, periodontal fibroblasts, namely those from periodontal ligament (PDL) and gingiva, also reveal heterogeneity. For example, PDL fibroblasts are composed of subpopulations based on collagen production, morphology, and glycogen pools. Subsets of gingival fibroblasts have also been obtained based on receptors for cyclosporin A and C1q. Specific fibroblast subsets may be involved in gingival repair and hyperplasia. Studies comparing fibroblasts from normal skin vs skin involved with scleroderma have found that scleroderma fibroblasts are activated and able to participate in an inflammatory response. How these fibroblasts become activated is unclear, but it is believed that a subset of fibroblasts is selectively recruited by cytokines at the inflammation site. Finally, investigation and identification of fibroblast subsets from various tissues and their interaction with the immune system could lead to strategies to prevent or reverse debilitating and potentially fatal fibrotic development.

Fibroblast network in rabbit sinoatrial node: structural and functional identification of homogeneous and heterogeneous cell coupling

Cardiomyocytes form a conducting network that is assumed to be electrically isolated from nonmyocytes in vivo. In cell culture, however, cardiac fibroblasts can contribute to the spread of excitation via functional gap junctions with cardiomyocytes. To assess the ability of fibroblasts to form gap junctions in vivo, we combine in situ detection of connexins in rabbit sinoatrial node (a tissue that is particularly rich in fibroblasts) with identification of myocytes and fibroblasts using immunohistochemical labeling and confocal microscopy. We distinguish two spatially distinct fibroblast populations expressing different connexins: fibroblasts surrounded by other fibroblasts preferentially express connexin40, whereas fibroblasts that are intermingled with myocytes largely express connexin45. Functionality of homogeneous and heterogeneous cell coupling was investigated by dye transfer in sinoatrial node tissue explants. These studies reveal spread of Lucifer yellow, predominantly along extended threads of interconnected fibroblasts (probably via connexin40), and occasionally between neighboring fibroblasts and myocytes (probably via connexin45). Our findings show that cardiac fibroblasts form a coupled network of cells, which may be functionally linked to myocytes in rabbit SAN.

Thy-1 expression in human fibroblast subsets defines myofibroblastic or lipofibroblastic phenotypes

Fibroblasts represent a dynamic population of cells, exhibiting functional heterogeneity within and among tissues. Fibroblast heterogeneity also results from phenotypic differences and may arise from activation or differentiation processes taking place in the cells. We previously reported that human fibroblasts were heterogeneous with respect to surface Thy-1 expression and that separation into Thy-1(+) and Thy-1(-) subsets resulted in functionally distinct subpopulations, leading to the concept of fibroblast subset specialization. In this report we investigated whether Thy-1(+) and/or Thy-1(-) fibroblasts were capable of differentiating into myofibroblasts or lipofibroblasts. Fibroblast subsets were used from human myometrium and orbit to test this hypothesis. Only Thy-1(+) human myometrial and orbital fibroblasts were capable of myofibroblast differentiation after treatment with TGFbeta or platelet concentrate supernatant, assessed by alpha smooth muscle actin expression. Interestingly, only Thy-1(-), but not Thy-1(+) subsets differentiated to lipofibroblasts, as determined by the accumulation of cytoplasmic lipid droplets after treatment with 15-deoxy-Delta(12, 14)-PGJ(2) or ciglitazone. We propose that fibroblast Thy-1 display pre-determines lineage to a contractile or lipid-like phenotype in the human myometrium and orbit. This additional distinction between Thy-1(+) and Thy-1(-) human fibroblast subtypes has important consequences in normal tissue homeostasis and in pathogenesis of orbital and myometrial diseases characterized by persistent myofibroblasts or fat accumulation, such as occurs in Graves' ophthalmopathy, tissue fibrosis, abnormal wound healing, and scarring.

Cardiac Fibroblast Diversity

Cardiac fibrosis is a pathological condition that occurs after injury and during aging. Currently, there are limited means to effectively reduce or reverse fibrosis. Key to identifying methods for curbing excess deposition of extracellular matrix is a better understanding of the cardiac fibroblast, the cell responsible for collagen production. In recent years, the diversity and functions of these enigmatic cells have been gradually revealed. In this review, I outline current approaches for identifying and classifying cardiac fibroblasts. An emphasis is placed on new insights into the heterogeneity of these cells as determined by lineage tracing and single-cell sequencing in development, adult, and disease states. These recent advances in our understanding of the fibroblast provide a platform for future development of novel therapeutics to combat cardiac fibrosis.

Fibroblast pathology in inflammatory diseases

Fibroblasts are important cells for the support of homeostatic tissue function. In inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease, fibroblasts take on different roles (a) as inflammatory cells themselves and (b) in recruiting leukocytes, driving angiogenesis, and enabling chronic inflammation in tissues. Recent advances in single-cell profiling techniques have transformed the ability to examine fibroblast states and populations in inflamed tissues, providing evidence of previously underappreciated heterogeneity and disease-associated fibroblast populations. These studies challenge the preconceived notion that fibroblasts are homogeneous and provide new insights into the role of fibroblasts in inflammatory pathology. In addition, new molecular insights into the mechanisms of fibroblast activation reveal powerful cell-intrinsic amplification loops that synergize with primary fibroblast stimuli to result in striking responses. In this Review, we focus on recent developments in our understanding of fibroblast heterogeneity and fibroblast pathology across tissues and diseases in rheumatoid arthritis and inflammatory bowel diseases. We highlight new approaches to, and applications of, single-cell profiling techniques and what they teach us about fibroblast biology. Finally, we address how these insights could lead to the development of novel therapeutic approaches to targeting fibroblasts in disease.

The myofibroblast: an assessment of controversial issues and a definition useful in diagnosis and research

Some interpretational problems associated with the myofibroblast, which affect how this cell is identified, are discussed. Questions addressed include distinguishing between "external" lamina ("basement membrane") and the fibronectin fibril of the fibronexus; the nature of stress fibers (bundles of smooth-muscle myofilaments with focal densities); the utility of some of these features to distinguish between myofibroblastic and smooth-muscle cell surfaces; and cytoskeletal immunophenotype. The following points are emphasized. Myofibroblasts have a surface characterized by prominent fibronectin fibrils and fibronexus junctions, which are distinct from lamina ("basement membrane"). This can permit a distinction to be made between smooth-muscle and myofibroblastic lesions and tumors. Myofibroblasts are typically positive for vimentin and alpha-smooth-muscle actin, but desmin is not a useful discriminant between smooth-muscle and myofibroblastic lesions. The main features for defining the myofibroblast are abundant rough endoplasmic reticulum; modestly developed peripheral myofilaments with focal densities (stress fibers); fibronexus junctions; vimentin and smooth-muscle actin immunostaining. Other features include a Golgi apparatus and collagen secretion granules, gap junctions, and actin-associated nondesmosomal junctions. Illustrations of the usefulness of these criteria in the diagnosis of soft-tissue lesions (myofibrosarcoma, so-called myofibroblastoma) are given.

Hypoxic activation of adventitial fibroblasts: role in vascular remodeling

Substantial experimental evidence supports the idea that the fibroblast may play a significant role in the vascular response to injury, especially under hypoxic conditions. Fibroblasts have the ability to rapidly respond to hypoxic stress and to modulate their function to adapt rapidly to local vascular needs. Fibroblasts appear to be uniquely equipped to proliferate, transdifferentiate, and migrate under hypoxic conditions. Proliferative responses to hypoxia depend on the activation of Galpha(i) and Gq kinase family members, and on the subsequent stimulation of protein kinase C and mitogen-activated protein kinase family members. Extracellular nucleotides (eg, adenosine triphosphate [ATP]) are likely to be increased in the hypoxic adventitial compartment and can act as autocrine/paracrine modifiers of the hypoxia-induced proliferative response. The proliferative effects of ATP appear to be mediated largely through G-protein-coupled P2Y receptors in fetal and neonatal fibroblasts. Hypoxia, acting through Galpha(iota)-coupled pathways, also can directly up-regulate alpha-smooth muscle actin expression in fibroblast subpopulations, suggesting that hypoxia may play a direct role in mediating the "transdifferentiation" of fibroblasts into myofibroblasts in the vessel wall. In addition, chronic hypoxia causes stable (at least in vitro) phenotypic changes in fibroblasts that appear to be associated with changes in the signaling pathways used to elicit proliferation. However, it is also becoming clear that, similar to the heterogeneity described for vascular smooth muscle cells, numerous fibroblast subtypes exist in the vessel wall, and that each may respond in unique ways to hypoxia and other stimuli and thus serve special functions in response to injury. In fact, adventitia may be considered to be compartments in which cells with "stem-cell-like" characteristics reside. Future work is needed to determine more precisely the role of the fibroblast in the wide variety of vascular complications observed in many humans diseases, and in the genes and gene products that confer unique properties to this important vascular cell.

Soluble phosphate glasses: in vitro studies using human cells of hard and soft tissue origin

This report describes the short-term response of two typical cellular components of a hard/soft tissue interface such as the periodontal ligament/mandible and patellar tendon/tibia. Tissue engineering of such interfaces requires a contiguous scaffold system with at least two cell types associated with it. Human oral osteoblasts, oral fibroblasts and hand flexor tendon fibroblasts were seeded on phosphate-based glasses of different dissolution rates. Quantitative and morphological assessment of cell adhesion and proliferation for all cell types was assessed, after first elucidating an experimental composition range using MG63 cells. In addition, immunolabelling of bone-specific non-collagenous proteins bone sialoprotein, osteonectin and osteopontin was performed to determine osteoblast phenotype. Fibroblast phenotype was established by immunolabelling for prolyl-4-hydroxylase, an enzyme vital for collagen biosynthesis. Results indicated that both cell types maintained their respective phenotypes over time in culture on glass discs of generic composition (CaO)x-(Na2O)(0.5-x)-(P2O5)0.5, remained attached and proliferated dependent on glass composition and cell type. Glasses containing at least 46 mol% CaO, produced no adverse cell reaction suggesting that these compositions that support both osteoblasts and fibroblasts would be ideal as a scaffold material for engineering the hard/soft tissue interface.

Sphingolipids control dermal fibroblast heterogeneity

Human cells produce thousands of lipids that change during cell differentiation and can vary across individual cells of the same type. However, we are only starting to characterize the function of these cell-to-cell differences in lipid composition. Here, we measured the lipidomes and transcriptomes of individual human dermal fibroblasts by coupling high-resolution mass spectrometry imaging with single-cell transcriptomics. We found that the cell-to-cell variations of specific lipid metabolic pathways contribute to the establishment of cell states involved in the organization of skin architecture. Sphingolipid composition is shown to define fibroblast subpopulations, with sphingolipid metabolic rewiring driving cell-state transitions. Therefore, cell-to-cell lipid heterogeneity affects the determination of cell states, adding a new regulatory component to the self-organization of multicellular systems.

Novel isolation of alkaline phosphatase-positive subpopulation from periodontal ligament fibroblasts

BACKGROUND

Periodontal ligament fibroblasts (PDLFs) are the cells essential for periodontal regeneration. PDLFs comprise a heterogeneous cell population and consist of several cell subsets that differ in their function. It is known that PDLFs produce osteoblast-related extracellular matrix proteins and show higher alkaline phosphatase (ALP) activity compared with gingival fibroblasts (GFs), implying that PDLFs have osteogenic characterisitics. The aim of the present study was to isolate the osteogenic population of PDLFs according to their expression of ALP.

METHODS

PDLFs and gingival fibroblasts were separated into two populations, ALP-positive and ALP-negative, with an immunomagnetic method using a monoclonal antibody against human bone type ALP and magnetic beads conjugated with a secondary antibody. Expression of basic fibroblast growth factor (bFGF) receptor and transforming growth factor (TGF)-beta receptor was investigated in these two populations. Osteoblast-related molecules, osteocalcin, and bone sialoprotein; ALP activity; and effect of bFGF on proliferation were also compared.

RESULTS

Effective separation was confirmed in both PDLFs and GFs by flow cytometry. The expression of FGF receptor (FGFR) and TGF-beta receptor was significantly higher in ALP-positive PDLFs than in ALP-negative PDLFs. ALP-positive PDLFs also expressed higher mRNA levels of osteocalcin and bone sialoprotein compared with ALP-negative PDLFs. The mitogenic effect of bFGF on ALP-positive PDLFs was greater than that of ALP-negative PDLFs.

CONCLUSIONS

These results indicate that osteoblastic and/or cementoblastic PDLF subsets could be isolated from the PDLF populations using an immunomagnetic method. Magnetic isolation of PDLFs may be a useful tool to obtain the cells which will potentially induce mineralization on the root surface.

Fibroblast heterogeneity in the periodontium and other tissues

Fibroblasts are the major resident cells which inhabit the periodontal tissues. As such, they are crucial for maintaining the connective tissues which support and anchor the tooth. Little is known of their origins, synthesis of regulatory cytokines and growth factors in health and disease, and importance in soft tissue regeneration. An emerging concept is that fibroblasts are not homogeneous, but instead consist of subsets of cells which can regulate bone marrow-derived cells such as T lymphocytes. Fibroblasts can be separated into subsets on the basis of morphology, size and expression of intermediate filaments as well as collagen subtypes. Differential surface marker expression has also been a key feature to distinguish fibroblast subsets from many tissues. Antigens such as Thy-1, class II MHC, and C1q are among those surface proteins which have been employed successfully to separate fibroblasts. Importantly, these fibroblast subsets are not only antigenically diverse, but also possess distinct functions. Thy 1+ pulmonary fibroblasts can display class II MHC antigens, synthesize IL-1 and can activate T lymphocytes, whereas the Thy 1+ subset is devoid of these functions. Recently, fibroblasts from the human orbit have also been shown to be separable on the basis of Thy 1 surface marker expression. Fibroblasts derived from human gingiva and periodontal ligament also appear to be composed of subsets with a heritable pattern of surface markers which will permit their separation into functional subpopulations. This paper will review findings of fibroblast heterogeneity in periodontal and other tissues. Evidence will be presented for the use of surface markers to delineate functional subsets. The ability to discriminate subsets of fibroblasts will aid in studies of periodontal disease pathogenesis and wound healing.

Temporal variations in cell migration and traction during fibroblast-mediated gel compaction

Current models used in our laboratory to assess the migration and traction of a population of cells within biopolymer gels are extended to investigate temporal changes in these parameters during compaction of mechanically constrained gels. The random cell migration coefficient, micro (t) is calculated using a windowing technique by regressing the mean-squared displacement of cells tracked at high magnification in three dimensions with a generalized least squares algorithm for a subset of experimental time intervals, and then shifting the window interval-by-interval until all time points are analyzed. The cell traction parameter, tau(0)(t), is determined by optimizing the solution of our anisotropic biphasic theory to tissue equivalent compaction. The windowing technique captured simulated sinusoidal and step changes in cell migration superposed on a persistent random walk in simulated cell movement. The optimization software captured simulated time dependence of compaction on cell spreading. Employment of these techniques on experimental data using rat dermal fibroblasts (RDFs) and human foreskin fibroblasts (HFFs) demonstrated that these cells exhibit different migration-traction relationships. Rat dermal fibroblast migration was negatively correlated to traction, suggesting migration was not the driving force for compaction with these cells, whereas human foreskin fibroblast migration was positively correlated to traction.

Distinct populations of crypt-associated fibroblasts act as signaling hubs to control colon homeostasis

Despite recent progress in recognizing the importance of mesenchymal cells for the homeostasis of the intestinal system, the current picture of how these cells communicate with the associated epithelial layer remains unclear. To describe the relevant cell populations in an unbiased manner, we carried out a single-cell transcriptome analysis of the adult murine colon, producing a high-quality atlas of matched colonic epithelium and mesenchyme. We identify two crypt-associated colonic fibroblast populations that are demarcated by different strengths of platelet-derived growth factor receptor A (Pdgfra) expression. Crypt-bottom fibroblasts (CBFs), close to the intestinal stem cells, express low levels of Pdgfra and secrete canonical Wnt ligands, Wnt potentiators, and bone morphogenetic protein (Bmp) inhibitors. Crypt-top fibroblasts (CTFs) exhibit high Pdgfra levels and secrete noncanonical Wnts and Bmp ligands. While the Pdgfralow cells maintain intestinal stem cell proliferation, the Pdgfrahigh cells induce differentiation of the epithelial cells. Our findings enhance our understanding of the crosstalk between various colonic epithelial cells and their associated mesenchymal signaling hubs along the crypt axis-placing differential Pdgfra expression levels in the spotlight of intestinal fibroblast identity.

Stimulation of Skin Repair Is Dependent on Fibroblast Source and Presence of Extracellular Matrix

In this study in vitro and in vivo functions were compared between cultured dermal equivalents produced with human fibroblasts isolated either from papillary dermis or adipose tissue of the same donors. Papillary dermal fibroblasts had a normal spindle cell shape; in contrast, adipose tissue fibroblasts had a stellate cell shape, actin stress fibers containing alpha-smooth muscle actin, multiple narrow extensions at their edges, and longer focal adhesion plaques. After dynamic culture for 14 days in PEGT/PBT carrier scaffolds, cell numbers between the two cell sources were comparable, but tissue morphology was different between the cultured groups. In addition, papillary fibroblasts had deposited significantly more glycosaminoglycans (214 +/- 15 versus 159 +/- 21 microg, p < 0.001) and a lower amount of collagen (49 +/- 14 versus 111 +/- 25 microg of hydroxyproline, p < 0.001) than had adipose fibroblasts. Moreover, the latter constructs were significantly more contracted than the papillary fibroblast-cultured constructs (78 +/- 6 versus 96 +/- 3%, p < 0.001). In comparison with the influence of cultured dermal equivalents on wound healing, the transplantation of five groups (control acellular carrier, papillary fibroblast-seeded construct, adipose fibroblast-seeded construct, papillary fibroblast-cultured construct, and adipose fibroblast-cultured construct) to full-thickness wounds on the backs of athymic mice showed clear differences in angiogenesis and tissue ingrowth after 10 days, and in reepithelialization after 21 days. After 10 days, the level of vascular ingrowth in the carrier (von Willebrand staining) for the five groups was as follows: adipose fibroblast-cultured > papillary fibroblast-cultured = adipose fibroblast-seeded > papillary fibroblast-seeded > acellular carrier. After 21 days, only the acellular carriers were not vascularized and the papillary fibroblast-seeded constructs were not completely vascularized. Complete wound reepithelialization (92 +/- 12%) was observed only in the group treated with adipose cultured constructs. Wound contraction was not observed. Staining for HLA-ABC and alpha-smooth muscle actin showed that human fibroblasts had survived and that adipose fibroblasts continued to express the actin isoform. These results showed not only stimulation of skin repair when fibroblasts were present in the carrier, but also significant positive effects of the deposited extracellular matrix (ECM) in the carrier. In addition, the adipose fibroblast-seeded construct, and especially the adipose fibroblast-cultured construct, significantly stimulated angiogenesis and reepithelialization when compared with their corresponding papillary fibroblast constructs. Apparently, tissue source or fibroblast phenotype and the presence of ECM play a crucial role in the stimulation of (impaired) healing and engineering of dermal equivalents.

Thy1 (+) and (-) lung fibrosis subpopulations in LEW and F344 rats

Appreciation of the potential of fibroblasts as effector cells in inflammation has led to the recognition of fibroblast subpopulations, the most stable of which are the Thy1 (+) and Thy1 (-) subpopulations in mouse lung fibroblasts. We investigated the presence of Thy1 (+) and (-) fibroblasts in rats, comparing the percentage in primary cultures from rats with different susceptibility to fibrosis, and whether the characteristics were similar in mice and rats, and between normal and fibrotic rats lungs. Using primary cultures of rat fibroblasts obtained both from normal and fibrotic lungs, we analysed the percentage of Thy1 (+) and (-) fibroblasts by fluorescence-activated cell sorter (FACS) analysis. We sorted the fibroblasts to evaluate immune region associated antigen (Ia) expression, which tends to be raised in tissues involved in inflammation, and other characteristics. We found that Thy1 (+) and (-) fibroblasts: 1) are distinct subpopulations in rat lungs; 2) are found in different proportions in rat strains with different propensity towards lung fibrosis; and 3) have similar but not identical characteristics in mice and rats. We also found that bleomycin-induced fibrosis increases the percentage of Ia expression in Thy1 (-), but not Thy1 (+) fibroblasts. The presence of these stable fibroblast supopulations in multiple species, and the fact that these fibroblasts differ in their response to a fibrosing agent, suggests the importance of considering fibroblast subpopulations in development and disease.

Differential Thy-1 expression by splenic fibroblasts defines functionally distinct subsets

Fibroblasts have an important structural role in the spleen, as they provide a scaffold of extracellular matrix in which cells of the immune system reside. Aside from their vague recognition as "stromal" or "reticular" components of the spleen, these cells have not been characterized. In this study, normal fibroblast lines from mouse [B6D2(F1)] spleen were established. The fibroblast phenotype of these lines was confirmed by their morphology, expression of vimentin, as well as their lack of epithelial and endothelial cell markers, their failure to display the hematopoietic marker CD45, and their inability to phagocytize. Interestingly, 50-65% of the splenic fibroblasts expressed the Thy-1 antigen, while a subpopulation of Thy-1-negative fibroblasts existed. FACS on the basis of Thy-1, as well as limiting dilution cloning, yielded stable lines and clones of Thy-1+ and Thy-1- splenic fibroblasts. Phenotypic characterization revealed that both subsets synthesized collagen and expressed class I MHC, ICAM-1, VCAM-1, and CD44 constitutively. However, intriguing differences existed between the fibroblast subpopulations. Thy-1+ splenic fibroblasts produced significantly greater levels of IL-6 than did their Thy-1- counterparts. After treatment with IFN-gamma (150 U/ml, 72 hr), Thy-1-, but not Thy-1+, splenic fibroblasts expressed class II MHC and presented antigen to an I-A(b)-restricted T cell line. This suggests that the Thy-1- fibroblasts may present antigen to T lymphocytes in vivo under inflammatory conditions. Thus, splenic fibroblasts are a heterogeneous and dynamic cell type poised in an immunologically relevant location to interact with bone marrow-derived cells under normal and fibrotic conditions.

Expression of tumour necrosis factor-alpha (TNF-alpha) mRNA and protein in pathological thyroid tissue and carcinoma cell lines

There has been much controversy about the presence of TNF-alpha within thyroid tissue. We therefore conducted a study to determine if TNF-alpha mRNA is present in thyroid tissue and thyroid-derived cells. Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was employed with a heterologous competitor fragment. Significantly lower levels of TNF-alpha mRNA were found in the autonomous nodules from patients with thyroid autonomy (TA; n = 4; 5.7 +/- 1.3 arbitrary units (AU) (mean +/- s.e.m.); P < 0.03) and in normal thyroid tissue (n = 2, 7.0 +/- 3.1 AU) compared with tissue from patients with Graves' disease (GD; n = 13; 27.9 +/- 10.3 AU), non-toxic multinodular goitre (NTG; n = 5; 20.9 +/- 5.8 AU) and perinodular tissue from TA patients (20.3 +/- 4.0 AU). Higher levels were detected in tissues from patients with Hashimoto's thyroiditis (HT; n = 2; 51.3 +/- 10.3 AU). Cultures of pure thyroid-derived fibroblasts (46 +/- 18 AU thyrocytes (33 +/- 8 AU), and the anaplastic thyroid carcinoma cell lines 8505 C (39 +/- 11 AU), SW 1736 (214 +/- 16 AU) and C643 (3 +/- 1 AU) showed significantly lower TNF-alpha mRNA levels than thyroid-derived lymphocytes (1650 +/- 32 AU). TNF-alpha was detected in the supernatants of unstimulated lymphocytes (22.1 +/- 1.1 pg/ml) and SW 1736 cells (3.5 +/- 0.9 pg/ml), but not in unstimulated fibroblasts and thyrocytes. Using an intracellular labelling technique in flow cytometry, the immunophenotype of stimulated TNF-alpha-positive lymphocytes was determined as predominantly CD3+CD45RO+. Our results suggest that TNF-alpha is present in the thyroid tissue of different thyroid disorders. Thyroid-derived lymphocytes are potential TNF-alpha producers and may thus locally influence thyroid function.

Protective Effects of Sesamin against UVB-Induced Skin Inflammation and Photodamage In Vitro and In Vivo

Ultraviolet (UV) exposure has been demonstrated as the most critical factor causing extrinsic skin aging and inflammation. This study explored the protective effects and mechanisms of sesamin against skin photodamage. Sesamin reduced intracellular reactive oxygen species production after UVB irradiation in human dermal fibroblasts. The sesamin treatment attenuated mitogen-activated protein (MAP) kinase phosphorylation and matrix metalloproteinase (MMPs) overexpression induced by UVB exposure, and it significantly enhanced the tissue inhibitor of metalloproteinase-1 protein expression. Sesamin also elevated the total collagen content in human fibroblasts by inhibiting UVB-induced mothers against decapentaplegic homolog 7 (Smad7) protein expression. Sesamin reduced UVB-induced inducible nitric oxide synthase (i-NOS) and cyclooxygenase-2 (COX-2) overexpression and inhibited nuclear factor-kappa B (NF-κB) translocation. Moreover, sesamin may regulate the c-Jun N-terminal kinases (JNK) and p38 MAP kinase pathways, which inhibit COX-2 expression. Sesamin could reduce UVB-induced inflammation, epidermal hyperplasia, collagen degradation, and wrinkle formation in hairless mice. It also reduced MMP-1, interleukin (IL-1), i-NOS, and NF-κB in the mouse skin. These results demonstrate that sesamin had antiphotodamage and anti-inflammatory activities. Sesamin has potential for use as a skin protection agent in antiphotodamage and skin care products.

FTIR microspectroscopy of malignant fibroblasts transformed by mouse sarcoma virus

Fourier transform infrared microspectroscopy (FTIR-MSP), which is based on the characteristic molecular vibrational spectra of cells, was used to investigate spectral differences between normal primary rabbit bone marrow (BM) cells and bone marrow cells transformed (BMT) by murine sarcoma virus (MuSV). Primary cells, rather than cell lines, were used for this research because primary cells are similar to normal tissue cells in most of their characteristics. Our results showed dramatic changes in absorbance between the control cells and MuSV124-transformed cells. Various biological markers, such as the phosphate level and the RNA/DNA obtained, based on the analysis of the FTIR-MSP spectra, also displayed significant differences between the control and transformed cells. Preliminary results suggested that the cluster analysis performed on the FTIR-MSP spectra yielded 100% accuracy in classifying both types of cells.

Diversity of dermal fibroblasts as major determinant of variability in cell reprogramming

Induced pluripotent stem cells (iPSCs) are adult somatic cells genetically reprogrammed to an embryonic stem cell-like state. Notwithstanding their autologous origin and their potential to differentiate towards cells of all three germ layers, iPSC reprogramming is still affected by low efficiency. As dermal fibroblast is the most used human cell for reprogramming, we hypothesize that the variability in reprogramming is, at least partially, because of the skin fibroblasts used. Human dermal fibroblasts harvested from five different anatomical sites (neck, breast, arm, abdomen and thigh) were cultured and their morphology, proliferation, apoptotic rate, ability to migrate, expression of mesenchymal or epithelial markers, differentiation potential and production of growth factors were evaluated in vitro. Additionally, gene expression analysis was performed by real-time PCR including genes typically expressed by mesenchymal cells. Finally, fibroblasts isolated from different anatomic sites were reprogrammed to iPSCs by integration-free method. Intriguingly, while the morphology of fibroblasts derived from different anatomic sites differed only slightly, other features, known to affect cell reprogramming, varied greatly and in accordance with anatomic site of origin. Accordingly, difference also emerged in fibroblasts readiness to respond to reprogramming and ability to form colonies. Therefore, as fibroblasts derived from different anatomic sites preserve positional memory, it is of great importance to accurately evaluate and select dermal fibroblast population prior to induce reprogramming.

Immunocytochemical characterisation of cell cultures grown from dissociated 1-2-day post-natal rat cerebral tissue. A developmental study

A range of cell-specific markers have been employed with immunocytochemical methods to characterise and quantitate the cell types present in mixed brain cell cultures derived from dissociated 1-2-day post-natal rat cerebral hemispheres and grown in the presence of FCS. Protoplasmic astrocytes (GFAP+, A2B5-) were the major cell type to develop in culture, a confluent monolayer forming in 5-8 days. A population of smaller round cells of oligodendrocyte-like morphology appeared on this astrocyte layer. Greater than 70% of these smaller cells were GC- and thus were not oligodendrocytes. The GC- cells were A2B5+ and, in early cultures, may therefore be progenitor glial cells. Examination of GFAP and A2B5 co-expression by these smaller cells was difficult due to the dense underlying GFAP+ astrocyte layer. In less dense areas of older cultures these smaller cells with processes were GFAP+ and A2B5+: these are Type 2, fibrous astrocytes. GC+ oligodendrocytes, comprising 5-10% of the total identified cell population, were initially distributed over the astrocyte monolayer; in older cultures (after about 8 days) GC+ cells were observed in clumps over places where NF+ cells were identifiable. Such GC+ cells mostly became MBP+. Neurones accounted for about 6% of the identifiable cells in early cultures but a lower percentage in older cultures. Minor populations of ependymal cells and macrophages were present; cells displaying fibronectin, fibroblasts, were rarely identified. Use of horse serum in place of FCS gave lower yields of GC+ cells in cultures, slowed down astrocyte development, and resulted in the formation of trunks of GFAP+ cells throughout cultures. Other sera gave lower numbers of GC+ cells.