Scleroderma-like properties of skin from caveolin-1-deficient mice: implications for new treatment strategies in patients with fibrosis and systemic sclerosis

Mitochondrial DNA copy number in patients with systemic sclerosis

Introduction: Systemic scleroderma (SSc) is a chronic autoimmune disease of inflammatory origin. Mitochondrial dysfunction is considered as an important mechanism in the pathogenesis of SSc. Currently mitochondrial DNA (mtDNA) copy number is used as a surrogate marker of mitochondrial dysfunction. Previous studies demonstrate that innate immune cells are important participants in inflammatory and fibrotic processes in SSc. The aim of the study was to evaluate the number of mtDNA copies in CD14+ monocytes and whole blood of patients with SSc in comparison with healthy individuals. Methods: Absolute mtDNA copy number was measured using digital PCR. It was found that the number of mtDNA copies in CD14+ monocytes was significantly higher in patients with SSc compared to control, while the number of mtDNA copies in the whole blood did not have significant differences. Results: The correlation analysis revealed an inverse association of mtDNA copy number with disease duration and the relationship between pro-inflammatory activation of CD14+ monocytes in terms of LPS-stimulated IL-6 secretion and mtDNA copy number. At the same time, basal and LPS-stimulated secretion of IL-6 by cultured CD+ monocytes were significantly higher in SSc group in comparison with control. Discussion: The study results suggest that increase of mtDNA copy number in CD14+ monocytes is a possible mechanism to maintain the reduced function of defective mitochondria in monocytes from patients with SSc associated with the development and progression of SSc.

Immunometabolism changes in fibrosis: from mechanisms to therapeutic strategies

Immune cells are essential for initiating and developing the fibrotic process by releasing cytokines and growth factors that activate fibroblasts and promote extracellular matrix deposition. Immunometabolism describes how metabolic alterations affect the function of immune cells and how inflammation and immune responses regulate systemic metabolism. The disturbed immune cell function and their interactions with other cells in the tissue microenvironment lead to the origin and advancement of fibrosis. Understanding the dysregulated metabolic alterations and interactions between fibroblasts and the immune cells is critical for providing new therapeutic targets for fibrosis. This review provides an overview of recent advances in the pathophysiology of fibrosis from the immunometabolism aspect, highlighting the altered metabolic pathways in critical immune cell populations and the impact of inflammation on fibroblast metabolism during the development of fibrosis. We also discuss how this knowledge could be leveraged to develop novel therapeutic strategies for treating fibrotic diseases.

The Role of SOX9 in IGF-II-Mediated Pulmonary Fibrosis

Pulmonary fibrosis (PF) associated with systemic sclerosis (SSc) results in significant morbidity and mortality. We previously reported that insulin-like growth factor-II (IGF-II) is overexpressed in lung tissues and fibroblasts from SSc patients, and IGF-II fosters fibrosis by upregulating collagen type I, fibronectin, and TGFβ. We now show that IGF-II augments mRNA levels of profibrotic signaling molecules TGFβ2 (p ≤ 0.01) and TGFβ3 (p ≤ 0.05), collagen type III (p ≤ 0.01), and the collagen posttranslational modification enzymes P4HA2 (p ≤ 0.05), P3H2 (p ≤ 0.05), LOX (p = 0.065), LOXL2 (p ≤ 0.05), LOXL4 (p ≤ 0.05) in primary human lung fibroblasts. IGF-II increases protein levels of TGFβ2 (p ≤ 0.01), as well as COL3A1, P4HA2, P4Hβ, and LOXL4 (p ≤ 0.05). In contrast, IGF-II decreases mRNA levels of the collagen degradation enzymes cathepsin (CTS) K, CTSB, and CTSL and protein levels of CTSK (p ≤ 0.05). The SRY-box transcription factor 9 (SOX9) is overexpressed in SSc lung tissues at the mRNA (p ≤ 0.05) and protein (p ≤ 0.01) levels compared to healthy controls. IGF-II induces SOX9 in lung fibroblasts (p ≤ 0.05) via the IGF1R/IR hybrid receptor, and SOX9 regulates TGFβ2 (p ≤ 0.05), TGFβ3 (p ≤ 0.05), COL3A1 (p ≤ 0.01), and P4HA2 (p ≤ 0.001) downstream of IGF-II. Our results identify a novel IGF-II signaling axis and downstream targets that are regulated in a SOX9-dependent and -independent manner. Our findings provide novel insights on the role of IGF-II in promoting pulmonary fibrosis.

The Role of Autophagy and Apoptosis in Affected Skin and Lungs in Patients with Systemic Sclerosis

Systemic sclerosis (SSc) is a complex autoimmune inflammatory disorder with multiple organ involvement. Skin changes present the hallmark of SSc and coincide with poor prognosis. Interstitial lung diseases (ILD) are the most widely reported complications in SSc patients and the primary cause of death. It has been proposed that the processes of autophagy and apoptosis could play a significant role in the pathogenesis and clinical course of different autoimmune diseases, and accordingly in SSc. In this manuscript, we review the current knowledge of autophagy and apoptosis processes in the skin and lungs of patients with SSc. Profiling of markers involved in these processes in skin cells can be useful to recognize the stage of fibrosis and can be used in the clinical stratification of patients. Furthermore, the knowledge of the molecular mechanisms underlying these processes enables the repurposing of already known drugs and the development of new biological therapeutics that aim to reverse fibrosis by promoting apoptosis and regulate autophagy in personalized treatment approach. In SSc-ILD patients, the molecular signature of the lung tissues of each patient could be a distinctive criterion in order to establish the correct lung pattern, which directly impacts the course and prognosis of the disease. In this case, resolving the role of tissue-specific markers, which could be detected in the circulation using sensitive molecular methods, would be an important step toward development of non-invasive diagnostic procedures that enable early and precise diagnosis and preventing the high mortality of this rare disease.

Animal Models of Systemic Sclerosis: Using Nailfold Capillaroscopy as a Potential Tool to Evaluate Microcirculation and Microangiopathy: A Narrative Review

Systemic sclerosis (SSc) is an autoimmune disease with three pathogenic hallmarks, i.e., inflammation, vasculopathy, and fibrosis. A wide plethora of animal models have been developed to address the complex pathophysiology and for the development of possible anti-fibrotic treatments. However, no current model comprises all three pathological mechanisms of the disease. To highlight the lack of a complete model, a review of some of the most widely used animal models for SSc was performed. In addition, to date, no model has accomplished the recreation of primary or secondary Raynaud’s phenomenon, a key feature in SSc. In humans, nailfold capillaroscopy (NFC) has been used to evaluate secondary Raynaud’s phenomenon and microvasculature changes in SSc. Being a non-invasive technique, it is widely used both in clinical studies and as a tool for clinical evaluation. Because of this, its potential use in animal models has been neglected. We evaluated NFC in guinea pigs to investigate the possibility of applying this technique to study microcirculation in the nailfold of animal models and in the future, development of an animal model for Raynaud’s phenomenon. The applications are not only to elucidate the pathophysiological mechanisms of vasculopathy but can also be used in the development of novel treatment options.

Expression of caveolin family proteins in serum of patients with systemic lupus erythematosus

OBJECTIVES

Caveolin family proteins, including caveolin-1 (Cav-1), caveolin-2 (Cav-2), and caveolin-3 (Cav-3), are identified as the principal protein components of caveolae in mammalian cells. Circulating form of caveolin family proteins can be used as a good potential biomarker for predicting disease.

METHODS

To investigate the clinical significance of the serological levels of caveolin family proteins in patients with systemic lupus erythematosus (SLE), we evaluated the soluble serum levels of caveolin family proteins in patients with SLE by enzyme-linked immunosorbent assay (ELISA) and assessed their associations with various known clinical variables.

RESULTS

The major findings of our study are as follows: Cav-2 was not detected in serum of SLE patients and normal controls (NCs). Serum Cav-1 and Cav-3 levels were higher in SLE patients compared with NCs. There were no significant correlations between serum Cav-1 and Cav-3 levels and SLE disease activity. Further analysis showed that serum Cav-3 may be more valuable as a marker than serum Cav-1 in SLE patients.

CONCLUSION

Serum levels of Cav-1 and Cav-3 might have a diagnostic role in patients with SLE. However, their predictive and prognostic value was not determined. Further studies are necessary to determine the potential clinical significance of these assays in SLE.

Pharmacological inhibition of GLUT1 as a new immunotherapeutic approach after myocardial infarction

Myocardial infarction (MI) is one of the major contributors to cardiovascular morbidity and mortality. Excess inflammation significantly contributes to cardiac remodeling and heart failure after MI. Accumulating evidence has shown the central role of cellular metabolism in regulating the differentiation and function of cells. Metabolic rewiring is particularly relevant for proinflammatory responses induced by ischemia. Hypoxia reduces mitochondrial oxidative phosphorylation (OXPHOS) and induces increased reliance on glycolysis. Moreover, activation of a proinflammatory transcriptional program is associated with preferential glucose metabolism in leukocytes. An improved understanding of the mechanisms that regulate metabolic adaptations holds the potential to identify new metabolic targets and strategies to reduce ischemic cardiac damage, attenuate excess local inflammation and ultimately prevent the development of heart failure. Among possible drug targets, glucose transporter 1 (GLUT1) gained considerable interest considering its pivotal role in regulating glucose availability in activated leukocytes and the availability of small molecules that selectively inhibit it. Therefore, we summarize current evidence on the role of GLUT1 in leukocytes (focusing on macrophages and T cells) and non-leukocytes, including cardiomyocytes, endothelial cells and fibroblasts regarding ischemic heart disease. Beyond myocardial infarction, we can foresee the role of GLUT1 blockers as a possible pharmacological approach to limit pathogenic inflammation in other conditions driven by excess sterile inflammation.

Metformin ameliorates scleroderma via inhibiting Th17 cells and reducing mTOR-STAT3 signaling in skin fibroblasts

Scleroderma is an autoimmune disease that causes dermal fibrosis. It occurs when collagen accumulates in tissue as a result of persistent inflammation. Th17 cells and pro-inflammatory cytokines such as IL-1β, IL-6, IL-17, and TNF-α play important roles in the pathogenesis of scleroderma. Because metformin, a medication used to treat diabetes, has effective immunoregulatory functions, we investigated its therapeutic function in scleroderma. Mice in a model of bleomycin-induced scleroderma were treated with metformin for 2 weeks. Histological assessment demonstrated protective effects of metformin against scleroderma. Metformin decreased the expression of pro-inflammatory factors in dermal tissue and lymphocytes. It also decreased mRNA expression of pro-inflammatory cytokines (IL-1β, IL-6, IL-17, and TNF-α) and fibrosis-inducing molecules both in vivo and in vitro. These results suggest that metformin treatment has anti-inflammatory effects on lymphocytes via the inhibition of IL-17 and cytokines related to Th17 differentiation, such as IL-1β, IL-6, and TNF-α. To investigate how metformin modulates the inflammatory process in skin fibroblasts, we measured mTOR-STAT3 signaling in skin fibroblasts and found that phosphorylated mTOR and phosphorylated STAT3 protein expression were decreased by metformin treatment. These results suggest that metformin has potential to treat scleroderma by inhibiting pro-inflammatory cytokines and anti-inflammatory activity mediated by mTOR-STAT3 signaling.

Engineering Advanced In Vitro Models of Systemic Sclerosis for Drug Discovery and Development

Systemic sclerosis (SSc) is a complex multisystem disease with the highest case-specific mortality among all autoimmune rheumatic diseases, yet without any available curative therapy. Therefore, the development of novel therapeutic antifibrotic strategies that effectively decrease skin and organ fibrosis is needed. Existing animal models are cost-intensive, laborious and do not recapitulate the full spectrum of the disease and thus commonly fail to predict human efficacy. Advanced in vitro models, which closely mimic critical aspects of the pathology, have emerged as valuable platforms to investigate novel pharmaceutical therapies for the treatment of SSc. This review focuses on recent advancements in the development of SSc in vitro models, sheds light onto biological (e.g., growth factors, cytokines, coculture systems), biochemical (e.g., hypoxia, reactive oxygen species) and biophysical (e.g., stiffness, topography, dimensionality) cues that have been utilized for the in vitro recapitulation of the SSc microenvironment, and highlights future perspectives for effective drug discovery and validation.

Serum lactate dehydrogenase level is associated with in-hospital mortality in critically Ill patients with acute kidney injury

Objective

Sixty percent of critically ill patients suffer from acute kidney injury (AKI) and 12% of them require renal replacement therapy during their ICU stay. However, we lack effective biomarkers to predict the mortality of critically ill patients with AKI. Few studies have investigated the association between lactate dehydrogenase levels and mortality in patients with AKI.

Methods

We conducted a retrospective cohort study with large samples, using a large database, the Multi parameter Intelligent Monitoring in Intensive Care III project. Clinical and demographic data were collected from the database by structure query language. Multiple models were constructed by stepwise methods to examine the association between lactate dehydrogenase (LDH) and in-hospital mortality. The predictive performance of LDH was assessed by ROC analysis and p values were calculated for trends.

Results

In the final analysis, 8436 patients met the inclusion criteria, and 1519 patients died during their hospital stay. The mortality rate increased with increasing LDH levels. The association between LDH and in-hospital mortality was almost linear (p < 0.001). A multiple logistic regression model indicated that LDH level was an independent predictor of in-hospital mortality (OR = 1.56, 95% CI (1.39–1.73), p < 0.001) and this effect remained stable in the subgroup analysis. Moreover, the combined AUC of LDH and SAPSII was 0.83.

Conclusions

The LDH level, which can be easily assessed, is significantly and independently associated with in-hospital mortality, and could increase the predictive ability of SAPSII for in-hospital mortality in our study.

Glycolysis-derived acidic microenvironment as a driver of endothelial dysfunction in systemic sclerosis

OBJECTIVES

Systemic sclerosis (SSc) is an autoimmune disease characterized by peripheral vasculopathy and skin and internal organ fibrosis. Accumulating evidence underlines a close association between a metabolic reprogramming of activated fibroblasts and fibrosis. This prompted us to determine the metabolism of SSc dermal fibroblasts and the effect on the vasculopathy characterizing the disease.

METHODS

Seahorse XF96 Extracellular Flux Analyzer was exploited to evaluate SSc fibroblast metabolism. In vitro invasion and capillary morphogenesis assays were used to determine the angiogenic ability of endothelial cells (EC). Immunofluorescence, flow cytometer and real time PCR techniques provided evidence of the molecular mechanism behind the impaired vascularization that characterizes SSc patients.

RESULTS

SSc fibroblasts, compared with control, showed a boosted glycolytic metabolism with increased lactic acid release and subsequent extracellular acidification, that in turn was found to impair EC invasion and organization in capillary-like networks without altering cell viability. A molecular link between extracellular acidosis and endothelial dysfunction was identified as acidic EC up-regulated MMP-12 which cleaves and inactivates uPAR, impairing angiogenesis in SSc. Moreover, the acidic environment was found to induce the loss of endothelial markers and the acquisition of mesenchymal-like features in EC, thus promoting the endothelial-to-mesenchymal transition (EndoMT) process that contributes to both capillary rarefaction and tissue fibrosis in SSc.

CONCLUSION

This study disclosed a liaison among the metabolic reprogramming of SSc dermal fibroblasts, extracellular acidosis and endothelial dysfunction that may contribute to the impairment and loss of peripheral capillary networks in SSc disease.

Chemical characterization and effects of volatile oil of Alpinia zerumbet on the quality of collagen deposition and caveolin-1 expression in a muscular fibrosis murine model

Abstract This study evaluated the effect of the volatile oil of Alpinia zerumbet (VOAz) on caveolin-1 gene expression and muscular fibrosis. The rats were immobilized to induce fibrosis of the gastrocnemius muscle, and they were treated with VOAz. Collagen quality was assessed by histology and the expression of the caveolin-1 (CAV-1) gene was evaluated using qPCR. Histomorphological analysis indicated a significant reduction in the perimeter, width, and intensity of collagen in the treated groups, thus showing that the oil was effective in regulating the quality of collagen at the three concentrations. The results of expression levels suggested a decrease in the lesioned group and in two treatment groups (0.0115 µg/g and 0.009 µg/g). However, with the lowest concentration (0.0065 µg/g), no significant difference was observed, with levels similar to those found in healthy tissue. Therefore, the results showed that VOAz has the potential to be a non-invasive and low-cost alternative to aid in the treatment of muscular fibrosis.

Mesenchymal stem cell as a novel approach to systemic sclerosis; current status and future perspectives

Systemic sclerosis is a rare chronic autoimmune disease with extensive microvascular injury, damage of endothelial cells, activation of immune responses, and progression of tissue fibrosis in the skin and various internal organs. According to epidemiological data, women's populations are more susceptible to systemic sclerosis than men. Until now, various therapeutic options are employed to manage the symptoms of the disease. Since stem cell-based treatments have developed as a novel approach to rescue from several autoimmune diseases, it seems that stem cells, especially mesenchymal stem cells as a powerful regenerative tool can also be advantageous for systemic sclerosis treatment via their remarkable properties including immunomodulatory and anti-fibrotic effects. Accordingly, we discuss the contemporary status and future perspectives of mesenchymal stem cell transplantation for systemic sclerosis.

Autophagy mediates 2-methoxyestradiol-inhibited scleroderma collagen synthesis and endothelial-to-mesenchymal transition induced by hypoxia

OBJECTIVES

To investigate whether autophagy mediates 2-methoxyestradiol (2-ME)-inhibited hypoxia-induced fibrosis and endothelial-to-mesenchymal transition (endoMT) in SSc.

METHODS

Autophagy in the skin of SSc patients was assessed by transmission electron microscopy. SSc skin fibroblasts and human umbilical vein endothelial cells (HUVECs) were cultured under hypoxic (1% O2) conditions with 2-ME or autophagy inhibitor. Collagen I and connective tissue growth factor (CTGF) in fibroblasts and vascular endothelial (VE)-cadherin, CD31, vimentin and α-smooth muscle actin (α-SMA) in HUVECs were examined by western blotting. Autophagic markers were evaluated by confocal microscopy and immunofluorescence.

RESULTS

SSc skins presented increased autolysosomes, LC3-II, collagen I and CTGF. Hypoxia-challenged fibroblasts and HUVECs formed more autophagosomes and autolysosomes, with increased LC3 and decreased P62. Meanwhile, hypoxia increased collagen I and CTGF in fibroblasts and increased vimentin and α-SMA but decreased VE-cadherin and CD31 in HUVECs. Bafilomycin A1 increased LC3-II and P62 in fibroblasts and HUVECs and decreased collagen I and CTGF in fibroblasts and vimentin and α-SMA in HUVECs, while upregulating VE-cadherin and CD31. 3-methyladenine decreased autophagy and fibrosis in fibroblasts and endothelial-to-mesenchymal transition in HUVECs. 2-ME-treated HUVECs showed more autophagosomes and fewer autolysosomes while 2-ME-treated fibroblasts showed fewer of both. Moreover, 2-ME decreased LC3-II and increased P62 in fibroblasts and increased both in HUVECs. Inhibition of autophagy by 2-ME showed the same effect with bafilomycin A1 on fibroblast collagen synthesis as well as endothelial and mesenchymal markers in HUVECs.

CONCLUSION

Autophagy mediated hypoxia-induced fibroblast collagen synthesis and endoMT in SSc, which could be reversed by 2-ME.

The importance of caveolins and caveolae to dermatology: Lessons from the caves and beyond

Caveolae are flask-shaped invaginations of the cell membrane rich in cholesterol and sphingomyelin, with caveolin proteins acting as their primary structural components that allow compartmentalization and orchestration of various signalling molecules. In this review, we discuss how pleiotropic functions of caveolin-1 (Cav1) and its intricate roles in numerous cellular functions including lipid trafficking, signalling, cell migration and proliferation, as well as cellular senescence, infection and inflammation, are integral for normal development and functioning of skin and its appendages. We then examine how disruption of the homeostatic levels of Cav1 can lead to development of various cutaneous pathophysiologies including skin cancers, cutaneous fibroses, psoriasis, alopecia, age-related changes in skin and aberrant wound healing and propose how levels of Cav1 may have theragnostic value in skin physiology/pathophysiology.

Pharmacological and Genetic Inhibition of Caveolin-1 Promotes Epithelialization and Wound Closure

Chronic wounds-including diabetic foot ulcers, venous leg ulcers, and pressure ulcers-represent a major health problem that demands an urgent solution and new therapies. Despite major burden to patients, health care professionals, and health care systems worldwide, there are no efficacious therapies approved for treatment of chronic wounds. One of the major obstacles in achieving wound closure in patients is the lack of epithelial migration. Here, we used multiple pre-clinical wound models to show that Caveolin-1 (Cav1) impedes healing and that targeting Cav1 accelerates wound closure. We found that Cav1 expression is significantly upregulated in wound edge biopsies of patients with non-healing wounds, confirming its healing-inhibitory role. Conversely, Cav1 was absent from the migrating epithelium and is downregulated in acutely healing wounds. Specifically, Cav1 interacted with membranous glucocorticoid receptor (mbGR) and epidermal growth factor receptor (EGFR) in a glucocorticoid-dependent manner to inhibit cutaneous healing. However, pharmacological disruption of caveolae by MβCD or CRISPR/Cas9-mediated Cav1 knockdown resulted in disruption of Cav1-mbGR and Cav1-EGFR complexes and promoted epithelialization and wound healing. Our data reveal a novel mechanism of inhibition of epithelialization and wound closure, providing a rationale for pharmacological targeting of Cav1 as potential therapy for patients with non-healing chronic wounds.

Caveolin-1 as a target in prevention and treatment of hypertrophic scarring

Reduced expression of caveolin-1 (Cav-1) is an important pathogenic factor in hypertrophic scarring (HTS). Such a reduction can be found in connection with the main known risk factors for HTS, including dark skin, female gender, young age, burn site and severity of the injury. The degree of overexpression of Cav-1 associated with different therapeutic options for HTS correlates with clinical improvements in HTS. This makes endo- or exogenous induction of Cav-1 not only an important therapeutic target for HTS, but also highlights its use as a preventive target to reduce or avoid HTS formation.

Correlation Between Autophagy and Collagen Deposition in Patients With Pelvic Organ Prolapse

OBJECTIVES

The aim of this study was to explore the link between autophagy and collagen metabolism in patients with pelvic organ prolapse (POP) by detecting the expressions of autophagy factors, collagen, desmin, cytokeratin, and vimentin.

METHODS

Histology of anterior vaginal wall and uterosacral ligament was assessed by hematoxylin-eosin staining in POP and non-POP control patients (n = 50 per group). Expressions of collagen types I and III, LC3II, beclin 1, and p62 were examined by Western blot analysis. Expressions of LC3, vimentin, desmin, and cytokeratin were detected by immunohistochemical staining. A linkage between the mean of LC3 integrated option density summation (IOD SUM) and POP clinicopathologic parameters including Pelvic Organ Prolapse Quantification (POP-Q) staging, age, body mass index, gravidity, and parity was analyzed by χ test, respectively.

RESULTS

Compared with the control group, the following differences were found both in the vaginal wall and in the uterosacral ligament of the POP group: hematoxylin-eosin staining showed that collagen was more fragmented and disorganized. Expressions of collagen types I and III, LC3II, and beclin 1 were diminished, whereas the p62 level was elevated in Western blotting. Immunohistochemical staining showed that expression of LC3 was down-regulated, whereas vimentin level was increased. There were no significant differences in the expressions of desmin and cytokeratin in the 2 groups (P > 0.05). Mean of LC3 IOD SUM was highly linked to the POP-Q stage in the POP group (P < 0.05), whereas there was no significant correlation between the mean of LC3 IOD SUM and POP groups in age, body mass index, gravidity, and parity, respectively(P > 0.05).

CONCLUSIONS

Autophagic activity is impaired in the POP group, which may relate to collagen deposition.

Caveolin-1 as a pathophysiological factor and target in psoriasis

Low expression of caveolin-1 (Cav-1) is typical in psoriatic lesions and overexpression of Cav-1 leads to a reduction of inflammation and suppression of epidermal hyperproliferation, thus ameliorating these two well-known hallmarks of psoriasis. At the same time, the interfacial layers of the white adipose tissue (WAT) adjacent to psoriatic lesions demonstrate much higher stiffness, which also points to a modification of Cav-1 expression in this tissue. These processes are connected with each other and regulated via exosomal exchange. Here we discuss the role of Cav-1 expression in inflammatory and hyperproliferative processes and analyze the ways to provide spatially different modulation of Cav-1 expression in the skin and WAT. Such modulation can be induced by different pharmacological and physical factors. These include application of mechanical stress and supra-physiological temperatures. Cav-1 should therefore be considered as an important target in treatment of psoriasis.

Metabolic regulation of dermal fibroblasts contributes to skin extracellular matrix homeostasis and fibrosis

Extracellular matrix (ECM) homeostasis is essential for normal tissue function, and its disruption by iatrogenic injury, trauma, or disease results in fibrosis. Skin ECM homeostasis is maintained by a complex process that involves an integration of cytokine and environmental mediators. However, it is unclear, in both normal and disease states, how these multifactorial processes converge to shift ECM homeostasis towards accumulation or degradation. Here we show a consistent downregulation in fatty acid oxidation (FAO) and upregulation of glycolysis in fibrotic skin and in normal skin with abundant ECM. Perturbation of glycolysis and FAO pathway enzymes reveals their reciprocal effects in ECM upregulation and downregulation, respectively. Increasing peroxisome proliferator-activated receptor (PPAR) signalling, an inducer of the FAO pathway, generates a catabolic fibroblast phenotype characterised by inhibition of ECM transcription and enhanced ECM internalization and lysosomal degradation. In contrast, suppression of glycolysis inhibits ECM gene transcription and protein levels, independently of an intact FAO pathway or PPAR signalling. Moreover, we show that CD36, a multifunctional fatty acid transporter, connects the metabolic state of fibroblasts with their capacity for ECM regulation, as internalization and degradation of collagen-1 is abrogated in fibroblasts lacking CD36. Finally, restoring FAO and upregulating CD36 reduces ECM accumulation in murine skin fibrosis. These findings indicate that metabolic perturbation of ECM homeostasis may have broad implications for therapies aimed at ECM regulation, such as fibrosis, regenerative medicine, and ageing.

Metabolomic profile of systemic sclerosis patients

Systemic sclerosis (SSc) is an autoimmune disease of unknown aetiology characterized by vascular lesions, immunological alterations and diffuse fibrosis of the skin and internal organs. Since recent evidence suggests that there is a link between metabolomics and immune mediated disease, serum metabolic profile of SSc patients and healthy controls was investigated by ¹H-NMR and GC-MS techniques. The results indicated a lower level of aspartate, alanine, choline, glutamate, and glutarate in SSc patients compared with healthy controls. Moreover, comparing patients affected by limited SSc (lcSSc) and diffuse SSc (dcSSc), 6 discriminant metabolites were identified. The multivariate analysis performed using all the metabolites significantly different revealed glycolysis, gluconeogenesis, energetic pathways, glutamate metabolism, degradation of ketone bodies and pyruvate metabolism as the most important networks. Aspartate, alanine and citrate yielded a high area under receiver-operating characteristic (ROC) curves (AUC of 0.81; CI 0.726–0.93) for discriminating SSc patients from controls, whereas ROC curve generated with acetate, fructose, glutamate, glutamine, glycerol and glutarate (AUC of 0.84; CI 0.7–0.98) discriminated between lcSSc and dcSSc. These results indicated that serum NMR-based metabolomics profiling method is sensitive and specific enough to distinguish SSc from healthy controls and provided a feasible diagnostic tool for the diagnosis and classification of the disease.

Development of tensile strength methodology for murine skin wound healing

In this study, a methodology was evaluated and improved to quickly measure the tensile strength of murine skin in a biomechanical assay for an incisional wound healing model. The aim was to streamline and enhance the wound model, skin specimen preparation, and tensile test so that large numbers of fresh tissue could be tested reliably and rapidly. Linear incisions of 25-mm length were made in the dorsal skin of mice along the spine and metallic staples were used to close the wound. After 20 days, the mice were sacrificed, and a square-shaped section of skin containing the linear incision was excised. Two metallic punches were fabricated and used to punch 15-mm long strips of skin of 2 mm width whose length was orthogonal to the direction of incision. The tensiometer configuration was modified to expedite tensile measurements on fresh skin, and load-to-failure was measured for each strip of skin from the cephalad to the caudal region. We evaluated sources of error in the animal model and the testing protocol and developed procedures to maximize speed and reproducibility in tensile strength measurements. This report provides guidance for efficient and reproducible tensile strength measurement of large numbers of skin specimens from freshly sacrificed animals.

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Tattoo placement to identify the two ends of the healing incisional wound assisted in decreasing error in the position and orientation of tensile strips.

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Custom-made punches to prepare skin strips for tensile testing helped conduct tensile tests of fresh tissue rapidly.

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Alteration of the manual grips of the tensile tester enabled specimens to be gripped rapidly to significantly accelerate testing for each skin strip.

Mesenchymal stromal cells prevent bleomycin-induced lung and skin fibrosis in aged mice and restore wound healing

Fibrosis can develop in nearly any tissue leading to a wide range of chronic fibrotic diseases. However, current treatment options are limited. In this study, we utilized an established aged mouse model of bleomycin-induced lung fibrosis (BLM) to test our hypothesis that fibrosis may develop simultaneously in multiple organs by evaluating skin fibrosis and wound healing. Fibrosis was induced in lung in aged (18-22-month-old) C57BL/6 male mice by intratracheal BLM administration. Allogeneic adipose-derived mesenchymal stromal cells (ASCs) or saline were injected intravenously 24 hr after BLM administration. Full thickness 8-mm punch wounds were performed 7 days later to study potential systemic anti-fibrotic and wound healing effects of intravenously delivered ASCs. Mice developed lung and skin fibrosis as well as delayed wound closure. Moreover, we observed similar changes in the expression of known pro-fibrotic factors in both lung and skin wound tissue, including miR-199 and protein expression of its corresponding target, caveolin-1, as well as phosphorylation of protein kinase B. Importantly, ASC-treated mice exhibited attenuation of BLM-induced lung and skin fibrosis and accelerated wound healing, suggesting that ASCs may prime injured tissues and prevent end-organ fibrosis.

Development and progression of immobilization-induced skin fibrosis through overexpression of transforming growth factor-ß1 and hypoxic conditions in a rat knee joint contracture model

PURPOSE

The purpose of this study was to investigate the pathology and mechanism of immobilization-induced skin fibrosis in a rat joint contracture model.

METHODS

Rats were randomly divided into control and immobilization groups. In the immobilization groups, knee joints of the rats were immobilized for 1, 2, and 4 weeks. After each immobilization, skin was dissected. To assess fibrosis in the skin, the thickness and area of adipocytes and connective tissue fibers were measured. Myofibroblasts were analyzed by immunohistochemistry by using anti-α-SMA as a marker. Gene expression levels of type I and III collagen, TGF-ß1, and HIF-1α were measured by using RT-PCR.

RESULTS

One week after immobilization, there was a marked increase in the area of connective tissue fibers in the immobilization group. Type I and type III collagen were significantly increased with prolonged immobilization. Higher numbers of α-SMA-positive cells were noted in the immobilized group at 2 and 4 weeks after immobilization. The expression level of TGF-β1 mRNA in the immobilization group increased after one week of immobilization. In contrast, the expression level of HIF1-α mRNA increased after 2 weeks of immobilization, and a greater increase was seen at 4 weeks after immobilization.

CONCLUSIONS

These results suggest that immobilization induces skin fibrosis with accumulation of types I and III collagen. These fibrotic changes may be evoked by upregulation of TGF-β1 after one week of immobilization. Additionally, upregulation of HIF-1α may relate to skin fibrosis by accelerating the differentiation of fibroblasts to myofibroblasts starting at 2 weeks after immobilization.

Caveolin-1 Controls Hyperresponsiveness to Mechanical Stimuli and Fibrogenesis-Associated RUNX2 Activation in Keloid Fibroblasts

Keloids are pathological scars characterized by excessive extracellular matrix production that are prone to form in body sites with increased skin tension. CAV1, the principal coat protein of caveolae, has been associated with the regulation of cell mechanics, including cell softening and loss of stiffness sensing ability in NIH3T3 fibroblasts. Although CAV1 is present in low amounts in keloid fibroblasts (KFs), the causal association between CAV1 down-regulation and its aberrant responses to mechanical stimuli remain unclear. In this study, atomic force microscopy showed that KFs were softer than normal fibroblasts with a loss of stiffness sensing. The decrease of CAV1 contributed to the hyperactivation of fibrogenesis-associated RUNX2, a transcription factor germane to osteogenesis/chondrogenesis, and increased migratory ability in KFs. Treatment of KFs with trichostatin A, which increased the acetylation level of histone H3, increased CAV1 and decreased RUNX2 and fibronectin. Trichostatin A treatment also resulted in cell stiffening and decreased migratory ability in KFs. Collectively, these results suggest a role for CAV1 down-regulation in linking the aberrant responsiveness to mechanical stimulation and extracellular matrix accumulation with the progression of keloids, findings that may lead to new developments in the prevention and treatment of keloid scarring.

Caveolin-1 in the Pathogenesis of Diabetic Nephropathy: Potential Therapeutic Target?

PURPOSE OF REVIEW

Diabetic nephropathy, a major microvascular complication of diabetes and the most common cause of end-stage renal disease, is characterized by prominent accumulation of extracellular matrix. The membrane microdomains caveolae, and their integral protein caveolin-1, play critical roles in the regulation of signal transduction. In this review we discuss current knowledge of the contribution of caveolin-1/caveolae to profibrotic signaling and the pathogenesis of diabetic kidney disease, and assess its potential as a therapeutic target.

RECENT FINDINGS

Caveolin (cav)-1 is key to facilitating profibrotic signal transduction induced by several stimuli known to be pathogenic in diabetic nephropathy, including the most prominent factors hyperglycemia and angiotensin II. Phosphorylation of cav-1 on Y14 is an important regulator of these responses. In vivo studies support a pathogenic role for caveolae in the progression of diabetic nephropathy. Targeting caveolin-1/caveolae would enable inhibition of multiple profibrotic pathways, representing a novel and potentially potent therapeutic option for diabetic nephropathy.

Loss of caveolin-1 alters extracellular matrix protein expression and ductal architecture in murine mammary glands

The extracellular matrix (ECM) is abnormal in breast tumors and has been reported to contribute to breast tumor progression. One factor, which may drive ongoing matrix synthesis in breast tumors, is the loss of stromal caveolin-1 (cav-1), a scaffolding protein of caveolae, which has been linked to breast tumor aggressiveness. To determine whether loss of cav-1 results in the abnormal expression of matrix proteins, mammary glands from cav- 1-/- and cav- 1 +/+ mice were investigated for differences in expression of several ECM proteins. In addition, the presence of myofibroblasts, changes in the vessel density, and differences in duct number and size were assessed in the mammary glands of both animal models. Using immunohistochemistry, expression of fibronectin, tenascin-C, collagens and αSMA were significantly increased in the mammary glands of cav-1-/- mice. Second harmonic generation revealed more organized collagen fibers in cav-1 -/- glands and supported immunohistochemical analyses of increased collagen abundance in the glands of cav-1 -/- mice. Analysis of the ductal structure demonstrated a significant increase in the number of proliferating ducts in addition to significant increases in the duct circumference and area in cav-1 -/- glands compared to cav- 1 +/+ glands. Differences in microvessel density weren't apparent between the animal models. In summary, we found that the loss of cav-1 resulted in increased ECM and α-SMA protein expression in murine mammary glands. Furthermore, we found that an abnormal ductal architecture accompanied the loss of cav-1. These data support a role for cav-1 in maintaining mammary gland structure.

Ultrastructural evaluation of gingival connective tissue in hereditary gingival fibromatosis

OBJECTIVE

To describe the ultrastructural features of hereditary gingival fibromatosis (HGF) in affected family members and compare microscopic findings with normal gingival (NG) tissue.

STUDY DESIGN

Gingival tissue samples from nine patients with HGF from five unrelated families were evaluated by transmission electron microscopy. Nine NG tissue samples were used for comparison.

RESULTS

Areas containing collagen fibrils forming loops and folds were observed in both groups, whereas oxytalan fibers were frequently identified in the HGF group. The diameter of collagen fibrils and the interfibrillar space among them were more uniform in the NG group than in the HGF group. Fibroblasts were the most common cells found in both the HGF and NG groups and exhibited enlarged, rough endoplasmic reticulum, mitochondria with well-preserved crests, conspicuous nucleoli, and euchromatic chromatin. Other cells, such as mast cells, plasma cells, and macrophages, were also observed.

CONCLUSIONS

HGF tissues had ultrastructural characteristics that were very similar to those of NG tissues. Oxytalan fibers were observed more frequently in the HGF samples than in the NG samples. Other studies of HGF in patients from different families should be performed to better understand the pathogenesis of this hereditary condition.

Metabolic fingerprints of human primary endothelial and fibroblast cells

INTRODUCTION

Human primary cells originating from different locations within the body could differ greatly in their metabolic phenotypes, influencing both how they act during physiological/pathological processes and how susceptible/resistant they are to a variety of disease risk factors. A novel way to monitor cellular metabolism is through cell energetics assays, so we explored this approach with human primary cell types, as models of sclerotic disorders.

OBJECTIVES

In order to better understand pathophysiological processes at the cellular level, our goals were to measure metabolic pathway activities of endothelial cells and fibroblasts, and determine their metabolic phenotype profiles.

METHODS

Biolog Phenotype MicroArray™ technology was used for the first time to characterize metabolic phenotypes of diverse primary cells. These colorimetric assays enable detection of utilization of 367 specific biochemical substrates by human endothelial cells from the coronary artery (HCAEC), umbilical vein (HUVEC) and normal, healthy lung fibroblasts (NHLF).

RESULTS

Adenosine, inosine, d-mannose and dextrin were strongly utilized by all three cell types, comparable to glucose. Substrates metabolized solely by HCAEC were mannan, pectin, gelatin and prevalently tricarballylic acid. HUVEC did not show any uniquely metabolized substrates whereas NHLF exhibited strong utilization of sugars and carboxylic acids along with amino acids and peptides.

CONCLUSION

Taken together, we show for the first time that this simple energetics assay platform enables metabolic characterization of primary cells and that each of the three human cell types examined gives a unique and distinguishable profile.

Methyl-β-cyclodextrin up-regulates collagen I expression in chronologically-aged skin via its anti-caveolin-1 activity

Caveolin-1 (Cav-1) is one of the key molecules to modulate collagen metabolism in the skin. This study aimed to unravel the relationship between Cav-1 and collagen levels in the aged skin, and also to evaluate a new role of anti-Cav-1 agent as a collagen-modulating agent. A negative correlation between Cav-1 and collagen I (COL I) was detected in chronologically aged skin of humans and mice, which was further confirmed by Cav-1 knock-down or knock-out experiments. Next, we tested whether methyl-β-cyclodextrin (MβCD) as a chemical Cav-1 inhibitor could be developed as a collagen-modulating agent in the skin. Testing different conditions of MβCD injection via the intra-dermal route revealed that 2.5% MβCD administered twice per week for two months showed a potent COL I-up-regulating activity, leading to the increase of skin thickness (P < 0.05) without adverse reactions such as skin fibrosis. In human dermal fibroblasts, MβCD treatment induced up-regulated COL I and down-regulated Cav-1, supporting the results of mouse experiments. Collectively, MβCD has a COL I-enhancing activity in chronologically-aged skin, where Cav-1 acts as a brake in COL I expression, suggesting its potential role for an anti-aging agent.

Caveolin-1 is a negative regulator of NADPH oxidase-derived reactive oxygen species

Changes in the expression and function of caveolin-1 (Cav-1) have been proposed as a pathogenic mechanism underlying many cardiovascular diseases. Cav-1 binds to and regulates the activity of numerous signaling proteins via interactions with its scaffolding domain. In endothelial cells, Cav-1 has been shown to reduce reactive oxygen species (ROS) production, but whether Cav-1 regulates the activity of NADPH oxidases (Noxes), a major source of cellular ROS, has not yet been shown. Herein, we show that Cav-1 is primarily expressed in the endothelium and adventitia of pulmonary arteries (PAs) and that Cav-1 expression is reduced in isolated PAs from multiple models of pulmonary artery hypertension (PH). Reduced Cav-1 expression correlates with increased ROS production in the adventitia of hypertensive PA. In vitro experiments revealed a significant ability of Cav-1 and its scaffolding domain to inhibit Nox1-5 activity and it was also found that Cav-1 binds to Nox5 and Nox2 but not Nox4. In addition to posttranslational actions, in primary cells, Cav-1 represses the mRNA and protein expression of Nox2 and Nox4 through inhibition of the NF-κB pathway. Last, in a mouse hypoxia model, the genetic ablation of Cav-1 increased the expression of Nox2 and Nox4 and exacerbated PH. Together, these results suggest that Cav-1 is a negative regulator of Nox function via two distinct mechanisms, acutely through direct binding and chronically through alteration of expression levels. Accordingly, the loss of Cav-1 expression in cardiovascular diseases such as PH may account for the increased Nox activity and greater production of ROS.

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.

Fibrosis--a lethal component of systemic sclerosis

Fibrosis is a pathological process characterized by excessive accumulation of connective tissue components in an organ or tissue. Fibrosis is produced by deregulated wound healing in response to chronic tissue injury or chronic inflammation, the hallmarks of rheumatic diseases. Progressive fibrosis, which distorts tissue architecture and results in progressive loss of organ function, is now recognized to be one of the major causes of morbidity and mortality in individuals with one of the most lethal rheumatic disease, systemic sclerosis (SSc). In this Review, we discuss the pathological role of fibrosis in SSc. We discuss the involvement of endothelium and pericyte activation, aberrant immune responses, endoplasmic reticulum stress and chronic tissue injury in the initiation of fibrosis in SSc. We then discuss fibroblast activation and myofibroblast differentiation that occurs in response to these initiating processes and is responsible for excessive accumulation of extracellular matrix. Finally, we discuss the chemical and mechanical signals that drive fibroblast activation and myofibroblast differentiation, which could serve as targets for new therapies for fibrosis in SSc.

Interaction of caveolin-1 with ATG12-ATG5 system suppresses autophagy in lung epithelial cells

Autophagy plays a pivotal role in cellular homeostasis and adaptation to adverse environments, although the regulation of this process remains incompletely understood. We have recently observed that caveolin-1 (Cav-1), a major constituent of lipid rafts on plasma membrane, can regulate autophagy in cigarette smoking-induced injury of lung epithelium, although the underlying molecular mechanisms remain incompletely understood. In the present study we found that Cav-1 interacted with and regulated the expression of ATG12-ATG5, an ubiquitin-like conjugation system crucial for autophagosome formation, in lung epithelial Beas-2B cells. Deletion of Cav-1 increased basal and starvation-induced levels of ATG12-ATG5 and autophagy. Biochemical analyses revealed that Cav-1 interacted with ATG5, ATG12, and their active complex ATG12-ATG5. Overexpression of ATG5 or ATG12 increased their interactions with Cav-1, the formation of ATG12-ATG5 conjugate, and the subsequent basal levels of autophagy but resulted in decreased interactions between Cav-1 and another molecule. Knockdown of ATG12 enhanced the ATG5-Cav-1 interaction. Mutation of the Cav-1 binding motif on ATG12 disrupted their interaction and further augmented autophagy. Cav-1 also regulated the expression of ATG16L, another autophagy protein associating with the ATG12-ATG5 conjugate during autophagosome formation. Altogether these studies clearly demonstrate that Cav-1 competitively interacts with the ATG12-ATG5 system to suppress the formation and function of the latter in lung epithelial cells, thereby providing new insights into the molecular mechanisms by which Cav-1 regulates autophagy and suggesting the important function of Cav-1 in certain lung diseases via regulation of autophagy homeostasis.

Altered MCM protein levels and autophagic flux in aged and systemic sclerosis dermal fibroblasts

Aging is a common risk factor of many disorders. With age, the level of insoluble extracellular matrix increases leading to increased stiffness of a number of tissues. Matrix accumulation can also be observed in fibrotic disorders, such as systemic sclerosis (SSc). Although the intrinsic aging process in skin is phenotypically distinct from SSc, here we demonstrate similar behavior of aged and SSc skin fibroblasts in culture. We have used quantitative proteomics to characterize the phenotype of dermal fibroblasts from healthy subjects of various ages and from patients with SSc. Our results demonstrate that proteins involved in DNA and RNA processing decrease with age and in SSc, while those involved in mitochondrial and other metabolic processes behave the opposite. Specifically, mini-chromosome maintenance (MCM) helicase proteins are less abundant with age and SSc, and they exhibit an altered subcellular distribution. We observed that lower levels of MCM7 correlate with reduced cell proliferation, lower autophagic capacity and higher intracellular protein expression phenotypes of aged and SSc cells. Additionally, we show that SSc fibroblasts exhibit higher levels of senescence than their healthy counterparts, suggesting further similarities between the fibrotic disorder and the aging process. Hence, at the molecular level, SSc fibroblasts exhibit intrinsic characteristics of fibroblasts from aged skin.

Caveolin-1 deficiency protects against mesangial matrix expansion in a mouse model of type 1 diabetic nephropathy

AIMS/HYPOTHESIS

Glomerular matrix protein accumulation, mediated largely by resident mesangial cells (MCs), is central to the pathogenesis of diabetic nephropathy. We previously showed that caveolin (CAV)-1/caveolae mediate matrix upregulation by MCs in response to high glucose and TGFβ, two important pathogenic mediators of diabetic glomerular sclerosis. Here, we evaluated the in vivo role of CAV-1/caveolae in the development of diabetic nephropathy.

METHODS

Diabetes was induced in Cav1-knockout (KO) mice and their wild-type (WT) counterparts by streptozotocin injection. After 10 months, kidneys were evaluated for the development of nephropathy, including glomerular sclerosis and upregulation of matrix proteins. Parallel experiments assessing glucose-induced matrix upregulation were carried out in MCs isolated from KO mice.

RESULTS

KO diabetic mice developed hyperglycaemia and renal hypertrophy, but were protected from developing albuminuria and glomerular sclerosis compared with WT mice. KO mice were significantly protected from the upregulation of glomerular collagen I, fibronectin, connective tissue growth factor (CTGF) and TGFβ. In vitro, glucose induced collagen I A1 promoter activation and collagen I, fibronectin and CTGF protein upregulation in WT but not KO MCs. Re-expression of Cav1 in KO cells restored this response.

CONCLUSIONS/INTERPRETATION

Cav1 deletion rendered significant protection from glomerular matrix accumulation and albuminuria in a mouse model of type 1 diabetes. These studies provide a foundation for the development of renal-targeted interference with CAV-1/caveolae as a novel approach to the treatment of diabetic nephropathy.

Autophagy is a key feature in the pathogenesis of systemic sclerosis

Autophagosomes are formed during autophagy, which is activated by hypoxia and starvation. Autophagy is important for mast cell degranulation. We hypothesized that autophagy is a key feature in the pathogenesis of systemic sclerosis (SSc). We examined SSc clinical features and mast cell density across the presence and severity of autophagy. Skin punch biopsy was performed on 33 SSc patients and 6 healthy controls (HC). Autophagy was evaluated by immunofluorescence on paraffin sections using LC3-FITC staining on these patients. The intensity of staining and mast cell density was examined across clinical features in 19 of the SSc patients. Presence of autophagosome formation was assessed by EM in 17 of the SSc patients and 4 HC. In our SSc study population, 29 of subjects were female and 23 were limited cutaneous. Twenty-nine of 33 SSc patients had autophagy by LC3-FITC staining. Intensity of staining decreased with longer duration of SSc (p = 0.09) and RP (p = 0.10). Bloating and distention differed across level of intensity staining (Wilcoxon signed-rank test, p = 0.05), with the greatest levels among those with moderate intensity. On EM, autophagosome formation was present in 16 of 17 SSc patients and no HC. All SSc patients had perivascular mast cells. Autophagy was present in 29 of 33 SSc patients, and none of our HC suggesting importance in pathogenesis. Autophagy staining was greater among those with shorter duration of SSc. Bloating and distention were higher in patients with moderate autophagy staining. Perivascular mast cells were present in all SSc patients. The role of autophagy in vasculopathy and mast cell activation in SSc warrants further studies.

Interstitial lung diseases-can pathologists arrive at an etiology-based diagnosis? A critical update

Interstitial lung diseases (ILD) encompass a group of diseases with a wide range of etiologies and a variety of tissue reactions within the lung. In many instances, a careful evaluation of the tissue reactions will result in a specific diagnosis or at least in a narrow range of differentials, which will assist the clinician to arrive at a definite diagnosis, when combining our interpretation with the clinical presentation of the patient and high-resolution computed tomography. In this review, we will exclude granulomatous pneumonias as well as vascular diseases (primary arterial pulmonary hypertension and vasculitis); however, pulmonary hypertension as a complication of interstitial processes will be mentioned. Few entities of pneumoconiosis presenting as an interstitial process will be included, whereas those with granulomatous reactions will be excluded. Drug reactions will be touched on within interstitial pneumonias, but will not be a major focus. In contrast to the present-day preferred descriptive pattern recognition, it is the author's strong belief that pathologists should always try to dig out the etiology from a tissue specimen and not being satisfied with just a pattern description. It is the difference of sorting tissue reactions into boxes by their main pattern, without recognizing minor or minute reactions, which sometimes will guide one to the correct etiology-oriented interpretation. In the author's personal perspective, tissue reactions can even be sorted by their timeliness, and therefore, ordered by the time of appearance, providing an insight into the pathogenesis and course of a disease. Also, underlying immune mechanisms will be discussed briefly as far as they are essential to understand the disease.

Autophagy and mesenchymal cell fibrogenesis

Autophagy is a catabolic pathway essential for cellular energy homeostasis that involves the self-degradation of intracellular components in lysosomes. This process has been implicated in the pathophysiology of many human disorders, including infection, cancer, and fibrosis. Autophagy is also recognized as a mediator of survival and proliferation, and multiple pathways induce autophagy under conditions of cellular stress, including nutrient and energy depletion. High autophagic activity has been detected in fibrogenic cells from several tissues; however the role of autophagy in fibrogenesis and mesenchymal cells varies greatly in different tissues and settings, with contributions uncovered to energy metabolism and collagen turnover by fibrogenic cells. Because several chemical modulators of autophagy have already been identified, autophagy regulation constitutes a potential target for antifibrotic therapy. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Caveolin-1, cellular senescence and age-related diseases

According to the "free radical theory" of aging, normal aging occurs as the result of tissue damages inflicted by reactive oxygen species (ROS) when ROS production exceeds the antioxidant capacity of the cell. ROS induce cellular dysfunctions such as stress-induced premature senescence (SIPS), which is believed to contribute to normal organismal aging and play a role in age-related diseases. Consistent with this hypothesis, increased oxidative damage of DNA, proteins, and lipids have been reported in aged animals and senescent cells accumulate in vivo with advancing age. Caveolin-1 acts as a scaffolding protein that concentrates and functionally regulates signaling molecules. Recently, great progress has been made toward understanding of the role of caveolin-1 in stress-induced premature senescence. Data show that caveolin-mediated signaling may contribute to explain, at the molecular level, how oxidative stress promotes the deleterious effects of cellular senescence such as aging and age-related diseases. In this review, we discuss the cellular mechanisms and functions of caveolin-1 in the context of SIPS and their relevance to the biology of aging.