Pulmonary fibrosis in vivo displays increased p21 expression reduced by 5-HT2B receptor antagonists in vitro - a potential pathway affecting proliferation

Pathology of idiopathic pulmonary fibrosis with particular focus on vascular endothelium and epithelial injury and their therapeutic potential

Idiopathic pulmonary fibrosis (IPF) remains a challenging disease with no drugs available to change the trajectory. It is a condition associated with excessive and highly progressive scarring of the lungs with remodelling and extracellular matrix deposition. It is a highly "destructive" disease of the lungs. The diagnosis of IPF is challenging due to continuous evolution of the disease, which also makes early interventions very difficult. The role of vascular endothelial cells has not been explored in IPF in great detail. We do not know much about their contribution to arterial or vascular remodelling, extracellular matrix changes and contribution to pulmonary hypertension and lung fibrosis in general. Endothelial to mesenchymal transition appears to be central to such changes in IPF. Similarly, for epithelial changes, the process of epithelial to mesenchymal transition seem to be the key both for airway epithelial cells and type-2 pneumocytes. We focus here on endothelial and epithelial cell changes and its contributions to IPF. In this review we revisit the pathology of IPF, mechanistic signalling pathways, clinical definition, update on diagnosis and new advances made in treatment of this disease. We discuss ongoing clinical trials with mode of action. A multidisciplinary collaborative approach is needed to understand this treacherous disease for new therapeutic targets.

Fibroblast Upregulation of Vitamin D Receptor Represents a Self-Protective Response to Limit Fibroblast Proliferation and Activation during Pulmonary Fibrosis

Dysregulation of vitamin D receptor (VDR) is implicated in chronic obstructive pulmonary disease. However, whether VDR dysregulation contributes to the development of pulmonary fibrosis remains largely unknown. Analysis of bulk and single-cell RNA profiling datasets revealed VDR upregulation in lung fibroblasts from patients with pulmonary fibrosis or fibrotic mice, which was validated in lung fibroblasts from bleomycin-exposed mice and bleomycin-treated fibroblasts. Stable VDR knockdown promoted, whereas the VDR agonist paricalcitol suppressed lung fibroblast proliferation and activation. Gene set enrichment analysis (GSEA) showed that the JAK/STAT pathway and unfolded protein response (UPR), a process related to endoplasmic reticulum (ER) stress, were enriched in lung fibroblasts of fibrotic lungs. Stable VDR knockdown stimulated, but paricalcitol suppressed ER stress and JAK1/STAT3 activation in lung fibroblasts. The STAT3 inhibitor blocked bleomycin- or stable VDR knockdown-induced ER stress. Paricalcitol inhibited the bleomycin-induced enrichment of STAT3 to the ATF6 promoter, thereby suppressing ATF6 expression in fibroblasts. Paricalcitol or intrapulmonary VDR overexpression inactivated JAK1/STAT3 and suppressed ER stress in bleomycin-treated mice, thus resulting in the inhibition of fibroblast proliferation and activation. Collectively, this study suggests that fibroblast VDR upregulation may be a self-protective response to limit fibroblast proliferation and activation during pulmonary fibrosis by suppressing the JAK1/STAT3/ER stress pathway.

Differential Gene and Protein Expression of Conjunctival Bleb Hyperfibrosis in Early Failure of Glaucoma Surgery

The early failure of glaucoma surgery is mainly caused by over-fibrosis at the subconjunctival space, causing obliteration of the filtration bleb. Because fibrosis has a suspected basis of genetic predisposition, we have undertaken a prospective study to identify upregulated profibrotic genes in a population of glaucoma patients with signs of conjunctival fibrosis and early postoperative surgical failure. Clinical data of re-operated fibrosis patients, hyperfibrosis patients who re-operated more than once in a short time, and control patients with no fibrosis were recorded and analyzed at each follow-up visit. Conjunctival-Tenon surgical specimens were obtained intraoperatively to evaluate the local expression of a panel of genes potentially associated with fibrosis. In order to correlate gene expression signatures with protein levels, we quantified secreted proteins in primary cultures of fibroblasts from patients. Expression of VEGFA, CXCL8, MYC, and CDKN1A was induced in the conjunctiva of hyperfibrosis patients. VEGFA and IL8 protein levels were also increased in fibroblast supernatants. We propose that an increase in these proteins could be useful in detecting conjunctival fibrosis in glaucoma patients undergoing filtering surgery. Molecular markers could be crucial for early detection of patients at high risk of failure of filtration surgery, leading to more optimal and personalized treatments.

Pulmonary 5-HT2B receptor expression in fibrotic interstitial lung diseases

Pulmonary fibrosis is a severe condition in interstitial lung diseases (ILD) such as idiopathic pulmonary fibrosis (IPF) and systemic sclerosis-ILD, where the underlying mechanism is not well defined and with no curative treatments available. Serotonin (5-HT) signaling via the 5-HT_2B receptor has been recognized as a promising preclinical target for fibrosis. Despite this, the involvement of the 5-HT_2B receptor in fibrotic ILD is widely unexplored. This work highlights the spatial pulmonary distribution of the 5-HT_2B receptor in patients with IPF and systemic sclerosis-ILD. We show that the 5-HT_2B receptor is located in typical pathological structures e.g. honeycomb cysts and weakly in fibroblast foci. Together with immunohistochemistry and immunofluorescence stainings of patient derived distal lung tissues, we identified cell targets for 5-HT_2B receptor interference in type II alveolar epithelial cells, endothelial cells and M2 macrophages. Our results emphasize the role of 5-HT_2B receptor as a target in lung fibrosis, warranting further consideration in targeting fibrotic ILDs.

Development of Pharmacophore Models for the Important Off-Target 5-HT2B Receptor

Toxicity is a major cause of attrition in the development of pharmaceuticals, and the off-target effects are a frequent contributor. The 5-HT_2B receptor agonism is known to be responsible for a variety of safety concerns including valvular heart disease which was the cause for the withdrawal of several compounds from the market. An early detection of potential binding to this receptor is thus desirable. Herein, we present the identification of key amino acid residues in the active site of 5-HT_2B by molecular dynamics simulations, the development of pharmacophore models and their performance on in-house data, and a structurally highly diverse subset of Enamine REAL labeled for 5-HT_2B activity by a machine learning model. These models may be used as filters employed on screening compound sets for the early filtration of compounds with potential 5-HT_2B off-target liabilities.

Altered serotonin metabolism in Takeda G protein-coupled receptor 5 knockout mice protects against diet-induced hepatic fibrosis

Background and aims

Diet-induced obesity and metabolic syndrome can trigger the progression of fatty liver disease to non-alcoholic steatohepatitis and fibrosis, which is a major public health concern. Bile acids regulate metabolic homeostasis and inflammation in the liver and gut via the activation of nuclear farnesoid X receptor (Fxr) and the membrane receptor Takeda G protein-coupled receptor 5 (Tgr5). Tgr5 is highly expressed in the gut and skeletal muscle, and in cholangiocytes and Kupffer cells of the liver. Tgr5 is implicated in the mediation of liver and gut inflammation, as well as the maintenance of energy homeostasis. Here, we used a high fat, high fructose, and high sucrose (HFS) diet to determine how bile acid signaling through Tgr5 may regulate metabolism during the progression from fatty liver to non-alcoholic steatohepatitis and fibrosis.

Materials and methods

Female C57BL/6J control wild type (WT) and Tgr5 knockout (Tgr5 -/-) mice were fed HFS (high fat (40% kcal), high fructose, and 20% sucrose water) diet for 20 weeks. Metabolic phenotypes were characterized through examination of bile acid synthesis pathways, lipid and cholesterol metabolism pathways, and fibrosis and inflammation pathways.

Results

Tgr5 -/- mice were more glucose intolerant when fed HFS diet, despite gaining the same amount of weight as WT mice. Tgr5 -/- mice accumulated significantly more hepatic cholesterol and triglycerides on HFS diet compared to WT mice, and gene expression of lipogenic genes was significantly upregulated. Hepatic cholesterol 7alpha-hydroxylase (Cyp7a1) gene expression was consistently elevated in Tgr5 -/- mice, while oxysterol 7alpha-hydroxylase (Cyp7b1), sterol 27-hydroxylase (Cyp27a1), Fxr, and small heterodimer partner (Shp) were downregulated by HFS diet. Surprisingly, hepatic inflammation and fibrosis were also significantly reduced in Tgr5 -/- mice fed HFS diet, which may be due to altered serotonin signaling in the liver.

Conclusions

Tgr5 -/- mice may be protected from high fat, high sugar-induced hepatic inflammation and injury due to altered serotonin metabolism.

Structure, Function, and Pharmaceutical Ligands of 5-Hydroxytryptamine 2B Receptor

Since the first characterization of the 5-hydroxytryptamine 2B receptor (5-HT2BR) in 1992, significant progress has been made in 5-HT2BR research. Herein, we summarize the biological function, structure, and small-molecule pharmaceutical ligands of the 5-HT2BR. Emerging evidence has suggested that the 5-HT2BR is implicated in the regulation of the cardiovascular system, fibrosis disorders, cancer, the gastrointestinal (GI) tract, and the nervous system. Eight crystal complex structures of the 5-HT2BR bound with different ligands provided great insights into ligand recognition, activation mechanism, and biased signaling. Numerous 5-HT2BR antagonists have been discovered and developed, and several of them have advanced to clinical trials. It is expected that the novel 5-HT2BR antagonists with high potency and selectivity will lead to the development of first-in-class drugs in various therapeutic areas.

Crosstalk between Mast Cells and Lung Fibroblasts Is Modified by Alveolar Extracellular Matrix and Influences Epithelial Migration

Mast cells play an important role in asthma, however, the interactions between mast cells, fibroblasts and epithelial cells in idiopathic pulmonary fibrosis (IPF) are less known. The objectives were to investigate the effect of mast cells on fibroblast activity and migration of epithelial cells. Lung fibroblasts from IPF patients and healthy individuals were co-cultured with LAD2 mast cells or stimulated with the proteases tryptase and chymase. Human lung fibroblasts and mast cells were cultured on cell culture plastic plates or decellularized human lung tissue (scaffolds) to create a more physiological milieu by providing an alveolar extracellular matrix. Released mediators were analyzed and evaluated for effects on epithelial cell migration. Tryptase increased vascular endothelial growth factor (VEGF) release from fibroblasts, whereas co-culture with mast cells increased IL-6 and hepatocyte growth factor (HGF). Culture in scaffolds increased the release of VEGF compared to culture on plastic. Migration of epithelial cells was reduced by IL-6, while HGF and conditioned media from scaffold cultures promoted migration. In conclusion, mast cells and tryptase increased fibroblast release of mediators that influenced epithelial migration. These data indicate a role of mast cells and tryptase in the interplay between fibroblasts, epithelial cells and the alveolar extracellular matrix in health and lung disease.

A Novel Fibroblast Reporter Cell Line for in vitro Studies of Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal disease of the lower respiratory tract with restricted therapeutic options. Repetitive injury of the bronchoalveolar epithelium leads to activation of pulmonary fibroblasts, differentiation into myofibroblasts and excessive extracellular matrix (ECM) deposition resulting in aberrant wound repair. However, detailed molecular and cellular mechanisms underlying initiation and progression of fibrotic changes are still elusive. Here, we report the generation of a representative fibroblast reporter cell line (10-4A BFP ) to study pathophysiological mechanisms of IPF in high throughput or high resolution in vitro live cell assays. To this end, we immortalized primary fibroblasts isolated from the distal lung of Sprague-Dawley rats. Molecular and transcriptomic characterization identified clone 10-4A as a matrix fibroblast subpopulation. Mechanical or chemical stimulation induced a reversible fibrotic state comparable to effects observed in primary isolated fibroblasts. Finally, we generated a reporter cell line (10-4A BFP ) to express nuclear blue fluorescent protein (BFP) under the promotor of the myofibroblast marker alpha smooth muscle actin (Acta2) using CRISPR/Cas9 technology. We evaluated the suitability of 10-4A BFP as reporter tool in plate reader assays. In summary, the 10-4A BFP cell line provides a novel tool to study fibrotic processes in vitro to gain new insights into the cellular and molecular processes involved in fibrosis formation and propagation.

Therapeutic molecular targets of SSc-ILD

Systemic sclerosis is a fibrosing chronic connective tissue disease of unknown etiology. A major hallmark of systemic sclerosis is the uncontrolled and persistent activation of fibroblasts, which release excessive amounts of extracellular matrix, lead to organ dysfunction, and cause high mobility and motility of patients. Systemic sclerosis–associated interstitial lung disease is one of the most common fibrotic organ manifestations in systemic sclerosis and a major cause of death. Treatment options for systemic sclerosis–associated interstitial lung disease and other fibrotic manifestations, however, remain very limited. Thus, there is a huge medical need for effective therapies that target tissue fibrosis, vascular alterations, inflammation, and autoimmune disease in systemic sclerosis–associated interstitial lung disease. In this review, we discuss data suggesting therapeutic ways to target different genes in distinct tissues/organs that contribute to the development of SSc.

Buyang Huanwu Tang inhibits cellular epithelial-to-mesenchymal transition by inhibiting TGF-β1 activation of PI3K/Akt signaling pathway in pulmonary fibrosis model in vitro

Background

Pulmonary fibrosis (PF) is a chronic and progressive interstitial lung disease. Buyang Huanwu Tang (BYHWT), a classical traditional Chinese medicine formula, has been widely utilized for the treatment of PF in China. This present study aimed to explore the mechanism of BYHWT in the treatment of PF in vitro.

Methods

TGF-β1 stimulated human alveolar epithelial A549 cells were used as in vitro model for PF. Post the treatment of BYHWT, cell viability was measured by MTT assay, and cell morphology was observed under microscope. The epithelial-to-mesenchymal transition (EMT) markers (E-cadherin, Vimentin) and collagen I (Col I) were detected by western blot, immunofluorescence staining and real-time quantitative polymerase chain reaction. With the co-administration of activators (IGF-1, SC79) and inhibitors (LY294002, MK2206), the effect of BYHWT on PI3K/Akt pathway was analyzed by western blot.

Results

BYHWT inhibited cell growth, and prevented cell morphology changed from epithelial to fibroblasts in TGF-β1 induced A549 cells. BYHWT decreased Vimentin and Col I, while increased E-cadherin at both protein and mRNA levels. Moreover, phosphorylation of PI3K (p-PI3K) and phosphorylation of Akt (p-Akt) were significantly down-regulated by BYHWT in TGF-β1 stimulated A549 cells.

Conclusion

These results indicate that BYHWT suppressed TGF-β1-induced collagen accumulation and EMT of A549 cells by inhibiting the PI3K/Akt signaling pathway. These findings suggest that BYHWT may have potential for the treatment of PF.

Bleomycin inhibits proliferation and induces apoptosis in TPC-1 cells through reversing M2-macrophages polarization

Papillary thyroid carcinoma (PTC) is one of the most common types of thyroid malignancy. Previous studies have demonstrated that the density of tumor-associated macrophages (TAMs) within the tumor microenvironment affects the progression of PTC due to the imbalance in M1/M2 macrophage subtypes. M2 macrophages induce anti-inflammatory effects and promote tumor progression, whereas M1 macrophages destroy tumor cells. Therefore, reversing TAM polarization to M1 may be a novel strategy for the treatment of cancer. Although bleomycin (BLM) is a commonly used anti-cancer drug, which regulates the secretion of relevant cytokines, high dose and long-term treatment with BLM may lead to pulmonary fibrosis. In the present study, flow cytometry data revealed that low dose treatment with BLM (5 or 10 mU/ml) facilitated the expression of the M1 phenotype markers cluster of differentiation (CD)80 and C-C chemokine receptor 7, and concurrently suppressed the M2 marker CD206 on M2-macrophages. Reverse transcription-quantitative polymerase chain reaction data revealed that the expression levels of tumor necrosis factor-α and interleukin-1β markedly increased, whereas the expression of IL-10 decreased in M2 macrophages treated with BLM. A fluorescein isothiocyanate-dextran uptake experiment revealed that BLM increased the phagocytic capacity of M2, however not M1 or M0 macrophages. In addition, to verify the effect of BLM-treated M2 macrophages on thyroid carcinoma cells, a co-culture system of macrophages and the human PTC cell line TPC-1, was established. BLM-treated M2 macrophages increased the number of cells in early and late apoptosis and inhibited the migration, proliferation and invasion of TPC-1 cells. These results suggest that a low dose and indirect effect of BLM may induce suppressive effects on PTC by selectively reversing M2 macrophage polarization to M1, which may provide a novel strategy for cancer treatment.