Integrin-mediated type II TGF-β receptor tyrosine dephosphorylation controls SMAD-dependent profibrotic signaling

Integrins in the kidney - beyond the matrix

The development and proper functioning of the kidney is dependent on the interaction of kidney cells with the surrounding extracellular matrix (ECM). These interactions are mediated by heterodimeric membrane-bound receptors called integrins, which bind to the ECM via their extracellular domain and via their cytoplasmic tail to intracellular adaptor proteins, to assemble large macromolecular adhesion complexes. These interactions enable integrins to control cellular functions such as intracellular signalling and organization of the actin cytoskeleton and are therefore crucial to organ function. The different nephron segments and the collecting duct system have unique morphologies, functions and ECM environments and are thus equipped with unique sets of integrins with distinct specificities for the ECM with which they interact. These cell-type-specific functions are facilitated by specific intracellular integrin binding proteins, which are critical in determining the integrin activation status, ligand-binding affinity and the type of ECM signals that are relayed to the intracellular structures. The spatiotemporal expression of integrins and their specific interactions with binding partners underlie the proper development, function and repair processes of the kidney. This Review summarizes our current understanding of how integrins, their binding partners and the actin cytoskeleton regulate kidney development, physiology and pathology.

Integrin alpha1 beta1 promotes interstitial fibrosis in a mouse model of polycystic kidney disease

Fibrosis is the cause of end-stage kidney failure in patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD). The molecular and cellular mechanisms involved in fibrosis are complex and anti-fibrotic therapies have so far failed to make an impact on patient welfare. Using unbiased proteomics analysis on the Pkd1 nl/nl mouse, we found that expression of the integrin α1 subunit is increased in this model of ADPKD. In human ADPKD tissue and two single cell RNA kidney disease datasets, ITGA1 was also upregulated. To investigate the functional role of this integrin subunit in ADPKD, we generated a Pkd1 nl/nl Itga1 -/- mouse. We observed a significant reduction in kidney volume and kidney dysfunction in mice lacking the integrin α1 subunit. Kidneys from Pkd1 nl/nl Itga1 -/- mice had smaller cysts and reduced interstitial expansion and tubular atrophy. Picrosirius red staining identified a restriction in collagen staining in the interstitium and the myofibroblast marker α smooth muscle actin was also downregulated. Myofibroblast cell proliferation was reduced in Pkd1 nl/nl Itga1 -/- mice and primary fibroblast cultures demonstrated an abrogated fibrogenic phenotype in integrin α1-depleted fibroblasts. These results highlight a previously unrecognised role for the integrin α1 subunit in kidney fibrosis.

LRG1-Targeted Nintedanib Delivery for Enhanced Renal Fibrosis Mitigation

Renal fibrosis lacks effective nephroprotective drugs in clinical settings due to poor accumulation of therapeutic agents in damaged kidneys, underscoring the urgent need for advanced renal-targeted delivery systems. Herein, we exploited the significantly increased expression of the leucine-rich α-2 glycoprotein 1 (LRG1) protein during renal fibrosis to develop a novel drug delivery system. Our engineered nanocarrier, DENNM, preferentially targets fibrotic kidneys via the decorated ET peptide's high affinity for LRG1. Once internalized by damaged renal cells, DENNM releases its encapsulated nintedanib, triggered by the active caspase-3 protease, disrupting the nanomedicine's structural integrity. The released nintedanib effectively reduces the level of expression of the extracellular matrix and impedes the progression of renal fibrosis by inhibiting the transforming growth factor-β (TGF-β)-Smad2/3 pathway. Our comprehensive in vitro and in vivo studies validate DENNM's antifibrotic efficacy, emphasizing LRG1's potential in renal targeted drug delivery and introducing an innovative approach to nanomedicine for treating renal fibrosis.

TMEM176B Prevents and alleviates bleomycin-induced pulmonary fibrosis via inhibiting transforming growth factor β-Smad signaling

Pulmonary fibrosis is a severe and progressive lung disease characterized by the abnormal accumulation of extracellular matrix, leading to scarring and loss of normal lung function. Recent bioinformatics analysis through the Gene Expression Omnibus (GEO) database identified a significant downregulation of Transmembrane Protein 176B (TMEM176B), previously unexplored in the context of fibrotic lung tissues. To investigate the functional role of TMEM176B, we induced pulmonary fibrosis in mice using bleomycin, TGFβ1, and silica, which consistently resulted in a marked decrease in TMEM176B expression. Intriguingly, overexpression of TMEM176B via adenoviral vectors prior to the induction of fibrosis led to significant improvements in fibrotic manifestations and lung function. Mechanistically, TMEM176B appears to mitigate pulmonary fibrosis by inhibiting the TGFβ1-SMAD signaling pathway, which is a critical mediator of fibroblast proliferation and differentiation and promotes extracellular matrix production. These findings suggest that TMEM176B plays an inhibitory role in the pathophysiological processes of pulmonary fibrosis, highlighting its potential as a therapeutic target.

TGF‑β/Smad signaling in chronic kidney disease: Exploring post‑translational regulatory perspectives (Review)

The TGF‑β/Smad signaling pathway plays a pivotal role in the onset of glomerular and tubulointerstitial fibrosis in chronic kidney disease (CKD). The present review delves into the intricate post‑translational modulation of this pathway and its implications in CKD. Specifically, the impact of the TGF‑β/Smad pathway on various biological processes was investigated, encompassing not only renal tubular epithelial cell apoptosis, inflammation, myofibroblast activation and cellular aging, but also its role in autophagy. Various post‑translational modifications (PTMs), including phosphorylation and ubiquitination, play a crucial role in modulating the intensity and persistence of the TGF‑β/Smad signaling pathway. They also dictate the functionality, stability and interactions of the TGF‑β/Smad components. The present review sheds light on recent findings regarding the impact of PTMs on TGF‑β receptors and Smads within the CKD landscape. In summary, a deeper insight into the post‑translational intricacies of TGF‑β/Smad signaling offers avenues for innovative therapeutic interventions to mitigate CKD progression. Ongoing research in this domain holds the potential to unveil powerful antifibrotic treatments, aiming to preserve renal integrity and function in patients with CKD.

TGFβ Signaling Dysregulation May Contribute to COL4A1-Related Glaucomatous Optic Nerve Damage

Purpose

Mutations in the genes encoding type IV collagen alpha 1 (COL4A1) and alpha 2 (COL4A2) cause a multisystem disorder that includes ocular anterior segment dysgenesis (ASD) and glaucoma. We previously showed that transforming growth factor beta (TGFβ) signaling was elevated in developing anterior segments from Col4a1 mutant mice and that reducing TGFβ signaling ameliorated ASD, supporting a role for the TGFβ pathway in disease pathogenesis. Here, we tested whether altered TGFβ signaling also contributes to glaucoma-related phenotypes in Col4a1 mutant mice.

Methods

To test the role of TGFβ signaling in glaucoma-relevant phenotypes, we genetically reduced TGFβ signaling using mice with mutated Tgfbr2, which encodes the common receptor for all TGFβ ligands in Col4a1+/G1344D mice. We performed slit-lamp biomicroscopy and optical coherence tomography for qualitative and quantitative analyses of anterior and posterior ocular segments, histological analyses of ocular tissues and optic nerves, and intraocular pressure assessments using rebound tonometry.

Results

Col4a1+/G1344D mice showed defects of the ocular drainage structures, including iridocorneal adhesions, and phenotypes consistent with glaucomatous neurodegeneration, including thinning of the nerve fiber layer, retinal ganglion cell loss, optic nerve head excavation, and optic nerve degeneration. We found that reducing TGFβ receptor 2 (TGFBR2) was protective for ASD, ameliorated ocular drainage structure defects, and protected against glaucomatous neurodegeneration in Col4a1+/G1344D mice.

Conclusions

Our results suggest that elevated TGFβ signaling contributes to glaucomatous neurodegeneration in Col4a1 mutant mice.

Role of integrin β1 and tenascin C mediate TGF-SMAD2/3 signaling in chondrogenic differentiation of BMSCs induced by type I collagen hydrogel

Cartilage defects may lead to severe degenerative joint diseases. Tissue engineering based on type I collagen hydrogel that has chondrogenic potential is ideal for cartilage repair. However, the underlying mechanisms of chondrogenic differentiation driven by type I collagen hydrogel have not been fully clarified. Herein, we explored potential collagen receptors and chondrogenic signaling pathways through bioinformatical analysis to investigate the mechanism of collagen-induced chondrogenesis. Results showed that the super enhancer-related genes induced by collagen hydrogel were significantly enriched in the TGF-β signaling pathway, and integrin-β1 (ITGB1), a receptor of collagen, was highly expressed in bone marrow mesenchymal stem cells (BMSCs). Further analysis showed genes such as COL2A1 and Tenascin C (TNC) that interacted with ITGB1 were significantly enriched in extracellular matrix (ECM) structural constituents in the chondrogenic induction group. Knockdown of ITGB1 led to the downregulation of cartilage-specific genes (SOX9, ACAN, COL2A1), SMAD2 and TNC, as well as the downregulation of phosphorylation of SMAD2/3. Knockdown of TNC also resulted in the decrease of cartilage markers, ITGB1 and the SMAD2/3 phosphorylation but overexpression of TNC showed the opposite trend. Finally, in vitro and in vivo experiments confirmed the involvement of ITGB1 and TNC in collagen-mediated chondrogenic differentiation and cartilage regeneration. In summary, we demonstrated that ITGB1 was a crucial receptor for chondrogenic differentiation of BMSCs induced by collagen hydrogel. It can activate TGF-SMAD2/3 signaling, followed by impacting TNC expression, which in turn promotes the interaction of ITGB1 and TGF-SMAD2/3 signaling to enhance chondrogenesis. These may provide concernful support for cartilage tissue engineering and biomaterials development.

Depleting transforming growth factor beta receptor 2 signalling in the cartilage of itga1-null mice attenuates spontaneous knee osteoarthritis

Objectives

Integrin α1β1 protects against osteoarthritis (OA) when it is upregulated in the superficial zone of cartilage in the early stages of disease. However, the mechanism behind this protection is unknown. Integrin α1β1 moderates transforming growth factor β receptor II (TGFBR2) signalling, a critical regulator of chondrocyte anabolic activity. To this end, mice lacking integrin α1β1 have increased baseline activation of TGFBR2 signalling and overall fibrosis. The purpose of this study was to evaluate the interplay between integrin α1β1 and TGFBR2 in the development of spontaneous OA. We hypothesized that dampening TGFBR2 signalling in the cartilage of itga1-null mice would attenuate OA.

Methods

Behavioural and histological manifestations of spontaneous knee OA were measured at 4, 8, 12 and 16 months in mice with and without a ubiquitous itga1 deletion and with and without a tamoxifen-induced cartilage specific TGFBR2 depletion.

Results

Knee cartilage degeneration, collateral ligament ossification and pain responses increased with age. Itga1-null mice with intact TGFBR2 signalling developed earlier and more severe OA compared to controls. In agreement with our hypothesis, depleting TGFBR2 signalling in the cartilage of itga1-null mice attenuated OA progression.

Conclusion

Intact TGFBR2 signalling drives early and worse knee OA in itga1-null mice. This result supports the hypothesis that the increased expression of integrin α1β1 by superficial zone chondrocytes early in OA development dampens TGFBR2 signalling and thus protects against degeneration.

Carbon Dots' Potential in Wound Healing: Inducing M2 Macrophage Polarization and Demonstrating Antibacterial Properties for Accelerated Recovery

Bacterial infections and persistent inflammation can impede the intrinsic healing process of wounds. To combat this issue, researchers have delved into the potential use of carbon dots (CDs) in the regulation of inflammation and counteract infections. These CDs were synthesized using a microwave-assisted hydrothermal process and have demonstrated outstanding antibacterial and antibiofilm properties against Gram-positive and Gram-negative bacteria. Additionally, CDs displayed biocompatibility at therapeutic concentrations and the ability to specifically target mitochondria. CD treatment effectively nullified lipopolysaccharide-triggered reactive oxygen species production by macrophages, while simultaneously promoting macrophage polarization toward an anti-inflammatory phenotype (M2), leading to a reduction in inflammation and an acceleration in wound healing. In vitro scratch assays also revealed that CDs facilitated the tissue-repairing process by stimulating epithelial cell migration during reepithelialization. In vivo studies using CDs topically applied to lipopolysaccharide (LPS)-stimulated wounds in C57/BL6 mice demonstrated significant improvements in wound healing due to enhanced fibroblast proliferation, angiogenesis, and collagen deposition. Crucially, histological investigations showed no indications of systemic toxicity in vital organs. Collectively, the application of CDs has shown immense potential in speeding up the wound-healing process by regulating inflammation, preventing bacterial infections, and promoting tissue repair. These results suggest that further clinical translation of CDs should be considered.

Role of integrins in the development of fibrosis in the trabecular meshwork

Primary open angle glaucoma (POAG) is a progressive and chronic disease exhibiting many of the features of fibrosis. The extracellular matrix (ECM) in the trabecular meshwork (TM) undergoes extensive remodeling and enhanced rigidity, resembling fibrotic changes. In addition, there are changes associated with myofibroblast activation and cell contractility that further drives tissue fibrosis and stiffening. This review discusses what is known about the integrins in the TM and their involvement in fibrotic processes.

Chondrocyte primary cilia lengthening and shortening in response to mediators of osteoarthritis; a role for integrin α1β1 and focal adhesions

Objective

Integrin α1β1 protects against osteoarthritis when it is upregulated in the early stages of disease, however, the mechanism behind this is currently unknown. Hypo-osmotic stress, interleukin-1 (IL-1) and transforming growth factor β (TGFβ) influence chondrocyte signaling and are important mediators of osteoarthritis. Evidence for primary cilia as a signaling hub for these factors and the involvement of the F-actin cytoskeleton in this response is growing. The purpose of this study was to investigate the role of integrin α1β1 in the response of primary cilia and the F-actin cytoskeleton to these osteoarthritic mediators.

Design

Primary cilia length and the number of F-actin peaks were measured in ex vivo wild type and itga1-null chondrocytes in response to hypo-osmotic stress, IL-1, and TGFβ alone or in combination, and with or without focal adhesion kinase inhibitor.

Results

We show that integrin α1β1 and focal adhesions are necessary for cilial lengthening and increases in F-actin peaks with hypo-osmotic stress and IL-1, but are not required for cilial shortening with TGFβ. Furthermore, we established that the chondrocyte primary cilium has a resting length of 2.4 ​μm, a minimum length of 2.1 ​μm corresponding to the thickness of the pericellular matrix, and a maximum length of 3.0 ​μm.

Conclusions

While integrin α1β1 is not necessary for the formation of chondrocyte primary cilia and cilial shortening in response to TGFβ, it is necessary for the mediation of cilial lengthening and the formation of F-actin peaks in response to hypo-osmotic stress and IL-1.

Nanofiber-based glaucoma drainage implant improves surgical outcomes by modulating fibroblast behavior

Biomaterials are implanted in millions of individuals worldwide each year. Both naturally derived and synthetic biomaterials induce a foreign body reaction that often culminates in fibrotic encapsulation and reduced functional lifespan. In ophthalmology, glaucoma drainage implants (GDIs) are implanted in the eye to reduce intraocular pressure (IOP) in order to prevent glaucoma progression and vision loss. Despite recent efforts towards miniaturization and surface chemistry modification, clinically available GDIs are susceptible to high rates of fibrosis and surgical failure. Here, we describe the development of synthetic, nanofiber-based GDIs with partially degradable inner cores. We evaluated GDIs with nanofiber or smooth surfaces to investigate the effect of surface topography on implant performance. We observed in vitro that nanofiber surfaces supported fibroblast integration and quiescence, even in the presence of pro-fibrotic signals, compared to smooth surfaces. In rabbit eyes, GDIs with a nanofiber architecture were biocompatible, prevented hypotony, and provided a volumetric aqueous outflow comparable to commercially available GDIs, though with significantly reduced fibrotic encapsulation and expression of key fibrotic markers in the surrounding tissue. We propose that the physical cues provided by the surface of the nanofiber-based GDIs mimic healthy extracellular matrix structure, mitigating fibroblast activation and potentially extending functional GDI lifespan.

Sexual dimorphism in reactive oxygen species production and a role for integrin α1β1 in estrogen receptor α and β expression in articular cartilage

BACKGROUND

Osteoarthritis (OA) is a debilitating disease involving cartilage degradation. A need remains for the discovery of new molecular targets in cartilage for pharmaceutical intervention of OA. One potential target is integrin α1β1 that protects against OA when it is upregulated by chondrocytes early in the disease process. Integrin α1β1 offers this protection by dampening epidermal growth factor receptor (EGFR) signaling, and its effects are more robust in females compared to males. The aim of this study, therefore, was to measure the impact of itga1 on chondrocyte EGFR activity and downstream reactive oxygen species (ROS) production in male and female mice. Furthermore, chondrocyte expression of estrogen receptor (ER) α and ERβ was measured to investigate the mechanism for sexual dimorphism in the EGFR/integrin α1β1 signaling axis. We hypothesized that integrin α1β1 would decrease ROS production and pEGFR and 3-nitrotyrosine expression, with this effect being greater in females. We further hypothesized that chondrocyte expression of ERα and ERβ would be greater in females compared to males, with a greater effect seen in itga1-null compared to wild-type mice.

MATERIALS AND METHODS

Femoral and tibial cartilage of male and female, wild-type and itga1-null mice were processed for ex vivo confocal imaging of ROS, immunohistochemical analysis of 3-nitrotyrosine, or immunofluorescence of pEGFR and ERα and ERβ.

RESULTS

We show that ROS-producing chondrocytes are more abundant in female itga1-null compared to wild-type mice ex vivo; however, itga1 had limited influence on the percent of chondrocytes stained positively for 3-nitrotyrosine or pEGFR in situ. In addition, we found that itga1 influenced ERα and ERβ expression in femoral cartilage from female mice, and that ERα and ERβ were coexpressed as well as colocalized in chondrocytes. Finally, we show sexual dimorphism in ROS and 3-nitrotyrosine production, but surprisingly not in pEGFR expression.

CONCLUSIONS

Together these data highlight sexual dimorphism in the EGFR/integrin α1β1 signaling axis and underline the need for further investigation into the role of ERs in this biological paradigm. Understanding the molecular mechanisms underlying the development of OA is essential for the development of individualized, sex-specific treatments in this age of personalized medicine.

Application of hybrid biophysical-biochemical methods to unravel the molecular basis for auto-inhibition and activation of protein tyrosine phosphatase TCPTP/PTPN2

Since the discovery of protein tyrosine phosphorylation as one of the critical post-translational modifications, it has been well known that the activity of protein tyrosine kinases (PTKs) is tightly regulated. On the other hand, protein tyrosine phosphatases (PTPs) are often regarded to act constitutively active, but recently we and others have shown that many PTPs are expressed in an inactive form due to allosteric inhibition by their unique structural features. Furthermore, their cellular activity is highly regulated in a spatiotemporal manner. In general, PTPs share a conserved catalytic domain comprising about 280 residues that is flanked by either an N-terminal or a C-terminal non-catalytic segment, which differs significantly in size and structure from each other and is known to regulate specific PTP's catalytic activity. The well-characterized non-catalytic segments can be globular or intrinsically disordered. In this work, we have focused on the T-Cell Protein Tyrosine Phosphatase (TCPTP/PTPN2) and demonstrated how the hybrid biophysical-biochemical methods can be applied to unravel the underlying mechanism through which TCPTP's catalytic activity is regulated by the non-catalytic C-terminal segment. Our analysis showed that TCPTP is auto-inhibited by its intrinsically disordered tail and trans-activated by Integrin alpha-1's cytosolic region.

Elevated TGFβ signaling contributes to cerebral small vessel disease in mouse models of Gould syndrome

Cerebral small vessel disease (CSVD) is a leading cause of stroke and vascular cognitive impairment and dementia. Studying monogenic CSVD can reveal pathways that are dysregulated in common sporadic forms of the disease and may represent therapeutic targets. Mutations in collagen type IV alpha 1 (COL4A1) and alpha 2 (COL4A2) cause highly penetrant CSVD as part of a multisystem disorder referred to as Gould syndrome. COL4A1 and COL4A2 form heterotrimers [a1α1α2(IV)] that are fundamental constituents of basement membranes. However, their functions are poorly understood and the mechanism(s) by which COL4A1 and COL4A2 mutations cause CSVD are unknown. We used histological, molecular, genetic, pharmacological, and in vivo imaging approaches to characterize central nervous system (CNS) vascular pathologies in Col4a1 mutant mouse models of monogenic CSVD to provide insight into underlying pathogenic mechanisms. We describe developmental CNS angiogenesis abnormalities characterized by impaired retinal vascular outgrowth and patterning, increased numbers of mural cells with abnormal morphologies, altered contractile protein expression in vascular smooth muscle cells (VSMCs) and age-related loss of arteriolar VSMCs in Col4a1 mutant mice. Importantly, we identified elevated TGFβ signaling as a pathogenic consequence of Col4a1 mutations and show that genetically suppressing TGFβ signaling ameliorated CNS vascular pathologies, including partial rescue of retinal vascular patterning defects, prevention of VSMC loss, and significant reduction of intracerebral hemorrhages in Col4a1 mutant mice aged up to 8 months. This study identifies a novel biological role for collagen α1α1α2(IV) as a regulator of TGFβ signaling and demonstrates that elevated TGFβ signaling contributes to CNS vascular pathologies caused by Col4a1 mutations. Our findings suggest that pharmacologically suppressing TGFβ signaling could reduce the severity of CSVD, and potentially other manifestations associated with Gould syndrome and have important translational implications that could extend to idiopathic forms of CSVD.

The type II TGF-β receptor phosphorylates Tyr 182 in the type I receptor to activate downstream Src signaling

Transforming growth factor–β (TGF-β) signaling has important roles during embryonic development and in tissue homeostasis. TGF-β ligands exert cellular effects by binding to type I (TβRI) and type II (TβRII) receptors and inducing both SMAD-dependent and SMAD-independent intracellular signaling pathways, the latter of which includes the activation of the tyrosine kinase Src. We investigated the mechanism by which TGF-β stimulation activates Src in human and mouse cells. Before TGF-β stimulation, inactive Src was complexed with TβRII. Upon TGF-β1 stimulation, TβRII associated with and phosphorylated TβRI at Tyr 182 . Binding of Src to TβRI involved the interaction of the Src SH2 domain with phosphorylated Tyr 182 and the interaction of the Src SH3 domain with a proline-rich region in TβRI and led to the activation of Src kinase activity and Src autophosphorylation. TGF-β1–induced Src activation required the kinase activities of TβRII and Src but not that of TβRI. Activated Src also phosphorylated TβRI on several tyrosine residues, which may stabilize the binding of Src to the receptor. Src activation was required for the ability of TGF-β to induce fibronectin production and migration in human breast carcinoma cells and to induce α–smooth muscle actin and actin reorganization in mouse fibroblasts. Thus, TGF-β induces Src activation by stimulating a direct interaction with TβRI that depends on tyrosine phosphorylation of TβRI by TβRII.

Arginine Methylation of Integrin Alpha-4 Prevents Fibrosis Development in Alcohol-Associated Liver Disease

BACKGROUND & AIMS

Alcohol-associated liver disease (ALD) comprises a spectrum of disorders including steatosis, steatohepatitis, fibrosis, and cirrhosis. We aimed to study the role of protein arginine methyltransferase 6 (PRMT6), a new regulator of liver function, in ALD progression.

METHODS

Prmt6-deficient mice and wild-type littermates were fed Western diet with alcohol in the drinking water for 16 weeks. Mice fed standard chow diet or Western diet alone were used as a control.

RESULTS

We found that PRMT6 expression in the liver is down-regulated in 2 models of ALD and negatively correlates with disease severity in mice and human liver specimens. Prmt6-deficient mice spontaneously developed liver fibrosis after 1 year and more advanced fibrosis after high-fat diet feeding or thioacetamide treatment. In the presence of alcohol Prmt6 deficiency resulted in a dramatic increase in fibrosis development but did not affect lipid accumulation or liver injury. In the liver PRMT6 is primarily expressed in macrophages and endothelial cells. Transient replacement of knockout macrophages with wild-type macrophages in Prmt6 knockout mice reduced profibrotic signaling and prevented fibrosis progression. We found that PRMT6 decreases profibrotic signaling in liver macrophages via methylation of integrin α-4 at R464 residue. Integrin α-4 is predominantly expressed in infiltrating monocyte derived macrophages. Blocking monocyte infiltration into the liver with CCR2 inhibitor reduced fibrosis development in knockout mice and abolished differences between genotypes.

CONCLUSIONS

Taken together, our data suggest that alcohol-mediated loss of Prmt6 contributes to alcohol-associated fibrosis development through reduced integrin methylation and increased profibrotic signaling in macrophages.

Elevated TGFβ signaling contributes to ocular anterior segment dysgenesis in Col4a1 mutant mice

Ocular anterior segment dysgenesis (ASD) refers to a collection of developmental disorders affecting the anterior structures of the eye. Although a number of genes have been implicated in the etiology of ASD, the underlying pathogenetic mechanisms remain unclear. Mutations in genes encoding collagen type IV alpha 1 (COL4A1) and alpha 2 (COL4A2) cause Gould syndrome, a multi-system disorder that often includes ocular manifestations such as ASD and glaucoma. COL4A1 and COL4A2 are abundant basement membrane proteins that provide structural support to tissues and modulate signaling through interactions with other extracellular matrix proteins, growth factors, and cell surface receptors. In this study, we used a combination of histological, molecular, genetic and pharmacological approaches to demonstrate that altered TGFβ signaling contributes to ASD in mouse models of Gould syndrome. We show that TGFβ signaling was elevated in anterior segments from Col4a1 mutant mice and that genetically reducing TGFβ signaling partially prevented ASD. Notably, we identified distinct roles for TGFβ1 and TGFβ2 in ocular defects observed in Col4a1 mutant mice. Importantly, we show that pharmacologically promoting type IV collagen secretion or reducing TGFβ signaling ameliorated ocular pathology in Col4a1 mutant mice. Overall, our findings demonstrate that altered TGFβ signaling contributes to COL4A1-related ocular dysgenesis and implicate this pathway as a potential therapeutic target for the treatment of Gould syndrome.

The catalytic activity of TCPTP is auto-regulated by its intrinsically disordered tail and activated by Integrin alpha-1

T-Cell Protein Tyrosine Phosphatase (TCPTP, PTPN2) is a non-receptor type protein tyrosine phosphatase that is ubiquitously expressed in human cells. TCPTP is a critical component of a variety of key signaling pathways that are directly associated with the formation of cancer and inflammation. Thus, understanding the molecular mechanism of TCPTP activation and regulation is essential for the development of TCPTP therapeutics. Under basal conditions, TCPTP is largely inactive, although how this is achieved is poorly understood. By combining biomolecular nuclear magnetic resonance spectroscopy, small-angle X-ray scattering, and chemical cross-linking coupled with mass spectrometry, we show that the C-terminal intrinsically disordered tail of TCPTP functions as an intramolecular autoinhibitory element that controls the TCPTP catalytic activity. Activation of TCPTP is achieved by cellular competition, i.e., the intrinsically disordered cytosolic tail of Integrin-α1 displaces the TCPTP autoinhibitory tail, allowing for the full activation of TCPTP. This work not only defines the mechanism by which TCPTP is regulated but also reveals that the intrinsically disordered tails of two of the most closely related PTPs (PTP1B and TCPTP) autoregulate the activity of their cognate PTPs via completely different mechanisms.

Involvement of YTHDF1 in renal fibrosis progression via up-regulating YAP

Renal fibrosis is a progressive, fatal renal disease characterized by the aberrant accumulation of myofibroblasts that produce excess extracellular matrix (ECM) in the renal interstitium and glomeruli. Yes-associated protein (YAP) has been regarded as a crucial modulator in myofibroblast transformation, but its upstream regulator remains a mystery. In the present study investigating the participation of m6A methylation during renal fibrosis through bioinformatics analysis, we identified YTHDF1, a modulator of m6A methylation, as a key contributor for renal fibrosis because it was highly expressed in human fibrotic kidneys and had a significant correction with YAP. Their co-localization in human fibrotic kidneys was additionally shown by immunofluorescence. We then found that YTHDF1 was also up-regulated in fibrotic mouse kidneys induced by unilateral ureteral obstruction (UUO), high-dose folic acid administration, or the unilateral ischemia-reperfusion injury, further supporting a causal role of YTHDF1 during renal fibrosis. Consistent with this notion, YTHDF1 knockdown alleviated the progression of renal fibrosis both in cultured cells induced by transforming growth factor-beta administration and in the UUO mouse model. Meanwhile, YAP was accordingly down-regulated when YTHDF1 was inhibited. Furthermore, the specific binding of YTHDF1 to YAP mRNA was detected using RNA Binding Protein Immunoprecipitation, and the up-regulation of fibrotic related molecules in cultured cells induced by YTHDF1 over-expression plasmid was attenuated by YAP siRNA. Taken together, our data highlight the potential utility of YTHDF1 as an indicator for renal fibrosis and suggest that YTHDF1 inhibition might be a promising therapeutic strategy to alleviate renal fibrosis via downregulating YAP.

PTPL1 suppresses lung cancer cell migration via inhibiting TGF-β1-induced activation of p38 MAPK and Smad 2/3 pathways and EMT

Epithelial-mesenchymal transition (EMT) enables dissemination of neoplastic cells and onset of distal metastasis of primary tumors. However, the regulatory mechanisms of EMT by microenvironmental factors such as transforming growth factor-β (TGF-β) remain largely unresolved. Protein tyrosine phosphatase L1 (PTPL1) is a non-receptor protein tyrosine phosphatase that plays a suppressive role in tumorigenesis of diverse tissues. In this study we investigated the role of PTPL1/PTPN13 in metastasis of lung cancer and the signaling pathways regulated by PTPL1 in terms of EMT of non-small cell lung cancer (NSCLC) cells. We showed that the expression of PTPL1 was significantly downregulated in cancerous tissues of 23 patients with NSCLC compared with adjacent normal tissues. PTPL1 expression was positively correlated with overall survival of NSCLC patients. Then we treated A549 cells in vitro with TGF-β1 (10 ng/mL) and assessed EMT. We found that knockdown of PTPL1 enhanced the migration and invasion capabilities of A549 cells, through enhancing TGF-β1-induced EMT. In nude mice bearing A549 cell xenografts, knockdown of PTPL1 significantly promoted homing of cells and formation of tumor loci in the lungs. We further revealed that PTPL1 suppressed TGF-β-induced EMT by counteracting the activation of canonical Smad2/3 and non-canonical p38 MAPK signaling pathways. Using immunoprecipitation assay we demonstrated that PTPL1 could bind to p38 MAPK, suggesting that p38 MAPK might be a direct substrate of PTPL1. In conclusion, these results unravel novel mechanisms underlying the regulation of TGF-β signaling pathway, and have implications for prognostic assessment and targeted therapy of metastatic lung cancer.

Mechanosensitive Regulation of Fibrosis

Cells in the human body experience and integrate a wide variety of environmental cues. A growing interest in tissue mechanics in the past four decades has shown that the mechanical properties of tissue drive key biological processes and facilitate disease development. However, tissue stiffness is not only a potent behavioral cue, but also a product of cellular signaling activity. This review explores both roles of tissue stiffness in the context of inflammation and fibrosis, and the important molecular players driving such processes. During inflammation, proinflammatory cytokines upregulate tissue stiffness by increasing hydrostatic pressure, ECM deposition, and ECM remodeling. As the ECM stiffens, cells involved in the immune response employ intricate molecular sensors to probe and alter their mechanical environment, thereby facilitating immune cell recruitment and potentiating the fibrotic phenotype. This powerful feedforward loop raises numerous possibilities for drug development and warrants further investigation into the mechanisms specific to different fibrotic diseases.

Protein tyrosine phosphatase-α amplifies transforming growth factor-β-dependent profibrotic signaling in lung fibroblasts

Idiopathic pulmonary fibrosis (IPF) is a progressive, often fatal, fibrosing lung disease for which treatment remains suboptimal. Fibrogenic cytokines, including transforming growth factor-β (TGF-β), are central to its pathogenesis. Protein tyrosine phosphatase-α (PTPα) has emerged as a key regulator of fibrogenic signaling in fibroblasts. We have reported that mice globally deficient in PTPα (Ptpra-/-) were protected from experimental pulmonary fibrosis, in part via alterations in TGF-β signaling. The goal of this study was to determine the lung cell types and mechanisms by which PTPα controls fibrogenic pathways and whether these pathways are relevant to human disease. Immunohistochemical analysis of lungs from patients with IPF revealed that PTPα was highly expressed by mesenchymal cells in fibroblastic foci and by airway and alveolar epithelial cells. To determine whether PTPα promotes profibrotic signaling pathways in lung fibroblasts and/or epithelial cells, we generated mice with conditional (floxed) Ptpra alleles (Ptpraf/f). These mice were crossed with Dermo1-Cre or with Sftpc-CreERT2 mice to delete Ptpra in mesenchymal cells and alveolar type II cells, respectively. Dermo1-Cre/Ptpraf/f mice were protected from bleomycin-induced pulmonary fibrosis, whereas Sftpc-CreERT2/Ptpraf/f mice developed pulmonary fibrosis equivalent to controls. Both canonical and noncanonical TGF-β signaling and downstream TGF-β-induced fibrogenic responses were attenuated in isolated Ptpra-/- compared with wild-type fibroblasts. Furthermore, TGF-β-induced tyrosine phosphorylation of TGF-β type II receptor and of PTPα were attenuated in Ptpra-/- compared with wild-type fibroblasts. The phenotype of cells genetically deficient in PTPα was recapitulated with the use of a Src inhibitor. These findings suggest that PTPα amplifies profibrotic TGF-β-dependent pathway signaling in lung fibroblasts.

Adhesion and growth factor receptor crosstalk mechanisms controlling cell migration

Cell migration requires cells to sense and interpret an array of extracellular signals to precisely co-ordinate adhesion dynamics, local application of mechanical force, polarity signalling and cytoskeletal dynamics. Adhesion receptors and growth factor receptors (GFRs) exhibit functional and signalling characteristics that individually contribute to cell migration. Integrins transmit bidirectional mechanical forces and transduce long-range intracellular signals. GFRs are fast acting and highly sensitive signalling machines that initiate signalling cascades to co-ordinate global cellular processes. Syndecans are microenvironment sensors that regulate GTPases to control receptor trafficking, cytoskeletal remodelling and adhesion dynamics. However, an array of crosstalk mechanisms exists, which co-ordinate and integrate the functions of the different receptor families. Here we discuss the nature of adhesion receptor and GFR crosstalk mechanisms. The unifying theme is that efficient cell migration requires precise spatial and temporal co-ordination of receptor crosstalk. However, a higher order of complexity emerges; whereby multiple crosstalk mechanisms are integrated and subject to both positive and negative feedbacks. Exquisite and sensitive control of these mechanisms ensures that mechanical forces and pro-migratory signals are triggered in the right place and at the right time during cell migration. Finally, we discuss the challenges, and potential therapeutic benefits, associated with deciphering this complexity.

N-acetyl-seryl-aspartyl-lysyl-proline is a valuable endogenous antifibrotic peptide for kidney fibrosis in diabetes: An update and translational aspects

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous peptide that has been confirmed to show excellent organ-protective effects. Even though originally discovered as a modulator of hemotopoietic stem cells, during the recent two decades, AcSDKP has been recognized as valuable antifibrotic peptide. The antifibrotic mechanism of AcSDKP is not yet clear; we have established that AcSDKP could target endothelial-mesenchymal transition program through the induction of the endothelial fibroblast growth factor receptor signaling pathway. Also, recent reports suggested the clinical significance of AcSDKP. The aim of this review was to update recent advances of the mechanistic action of AcSDKP and discuss translational research aspects.

Differential Roles of Cysteinyl Cathepsins in TGF-β Signaling and Tissue Fibrosis

Transforming growth factor beta (TGF-β) signaling contributes to tissue fibrosis. Here we demonstrate that TGF-β enhances CatS and CatK expression but reduces CatB and CatL expression in mouse kidney tubular epithelial cells (TECs). CatS- and CatK deficiency reduces TEC nuclear membrane importer importin-β expression, Smad-2/3 activation, and extracellular matrix (ECM) production. Yet CatB- and CatL-deficiency displays the opposite observations with reduced nuclear membrane exporter RanBP3 expression. CatS and CatK form immunocomplexes with the importin-β and RanBP3 more effectively than do CatB and CatL. On the plasma membrane, CatS and CatK preferentially form immunocomplexes with and activate TGF-β receptor-2, whereas CatB and CatL form immunocomplexes with and inactivate TGF-β receptor-1. Unilateral ureteral obstruction-induced renal injury tests differential cathepsin activities in TGF-β signaling and tissue fibrosis. CatB- or CatL-deficiency exacerbates fibrosis, whereas CatS- or CatK-deficiency protects kidneys from fibrosis. These cathepsins exert different effects in the TGF-β signaling cascade independent of their proteolytic properties.

Application of nintedanib and other potential anti-fibrotic agents in fibrotic diseases

Nintedanib, a Food and Drug Administration-approved drug for the treatment of patients with idiopathic pulmonary fibrosis (IPK), inhibits both tyrosine kinase receptors and non-receptor kinases, and block activation of platelet-derived growth factor receptors, fibroblast growth factor receptor, vascular endothelial growth factor receptors, and Src family kinases. Preclinical and clinical studies have revealed the potent anti-fibrotic effect of nintedanib in IPK in human and animal models. Recent preclinical studies have also demonstrated the inhibitory effect of nintedanib on the development and progression of tissue fibrosis in other organs, including liver, kidney, and skin. The anti-fibrotic actions of nintedanib occur through a number of mechanisms, including blocking differentiation of fibroblasts to myofibroblasts, inhibition of epithelial-mesenchymal transition, and suppression of inflammation and angiogenesis. In this article, we summarize the mechanisms and efficacy of nintedanib in the treatment of fibrotic diseases in animal models and clinical trials, provide an update on recent advances in the development of other novel antifibrotic agents in preclinical and clinical study, and offer our perspective about the possible clinical application of these agents in fibrotic diseases.

Specificity, versatility, and control of TGF-β family signaling

Encoded in mammalian cells by 33 genes, the transforming growth factor-β (TGF-β) family of secreted, homodimeric and heterodimeric proteins controls the differentiation of most, if not all, cell lineages and many aspects of cell and tissue physiology in multicellular eukaryotes. Deregulation of TGF-β family signaling leads to developmental anomalies and disease, whereas enhanced TGF-β signaling contributes to cancer and fibrosis. Here, we review the fundamentals of the signaling mechanisms that are initiated upon TGF-β ligand binding to its cell surface receptors and the dependence of the signaling responses on input from and cooperation with other signaling pathways. We discuss how cells exquisitely control the functional presentation and activation of heteromeric receptor complexes of transmembrane, dual-specificity kinases and, thus, define their context-dependent responsiveness to ligands. We also introduce the mechanisms through which proteins called Smads act as intracellular effectors of ligand-induced gene expression responses and show that the specificity and impressive versatility of Smad signaling depend on cross-talk from other pathways. Last, we discuss how non-Smad signaling mechanisms, initiated by distinct ligand-activated receptor complexes, complement Smad signaling and thus contribute to cellular responses.

Autocrine CTHRC1 activates hepatic stellate cells and promotes liver fibrosis by activating TGF-β signaling

BACKGROUND

Hepatic fibrosis is caused by chronic liver injury and may progress toward liver cirrhosis, and even hepatocellular carcinoma. However, current treatment is not satisfactory. Therefore, there is a mandate to find novel therapeutic targets to improve therapy, and biomarkers to monitor therapeutic response.

METHODS

Liver fibrosis was induced by carbon tetrachloride (CCl4) or thioacetamide (TAA) in wild type (WT) or CTHRC1-/- mice, followed by immunofluorescence and immunohistochemical analyses. CTHRC1 monoclonal antibody (mAb) was used to abrogate the effect of CTHRC1 in vitro and in vivo.

RESULTS

Here, we reported that collagen triple helix repeat containing 1 (CTHRC1), a secreted protein derived from hepatic stellate cells (HSCs), was significantly up-regulated in fibrotic liver tissues. CTHRC1 promoted HSCs transformation from a quiescent to an activated state, and enhanced migratory or contractile capacities of HSCs by activating TGF-β signaling. Meanwhile, CTHRC1 competitively bound to Wnt noncononical receptor and promoted the contractility but not activation of HSCs. CCl4 or TAA-induced liver fibrosis was attenuated in CTHRC-/- mice compared with littermate control, while a monoclonal antibody of CTHRC1 suppressed liver fibrosis in WT mice treated with CCl4 or TAA.

INTERPRETATION

We demonstrated that CTHRC1 is a new regulator of liver fibrosis by modulating TGF-β signaling. Targeting CTHRC1 could be a promising therapeutic approach, which can suppress TGF-β signaling and avoid the side effects caused by directly targeting TGF-β. CTHRC1 could also be a potential biomarker for monitoring response to anti-fibrotic therapy. FUND: This study was supported by the National Natural Science Foundation of China (ID 81672358, 81871923, 81872242, 81802890), the Shanghai Municipal Education Commission-Gaofeng Clinical Medicine Grant Support (ID 20181708), the Natural Science Foundation of Shanghai (ID 17ZR1428300, 18ZR1436900), and Shanghai Municipal Health Bureau (ID 2018BR32). The funders did not play a role in manuscript design, data collection, data analysis, interpretation nor writing of the manuscript.

TGF-β and the Tissue Microenvironment: Relevance in Fibrosis and Cancer

Transforming growth factor-β (TGF-β) is a cytokine essential for the induction of the fibrotic response and for the activation of the cancer stroma. Strong evidence suggests that a strong cross-talk exists among TGF-β and the tissue extracellular matrix components. TGF-β is stored in the matrix as part of a large latent complex bound to the latent TGF-β binding protein (LTBP) and matrix binding of latent TGF-β complexes, which is required for an adequate TGF-β function. Once TGF-β is activated, it regulates extracellular matrix remodelling and promotes a fibroblast to myofibroblast transition, which is essential in fibrotic processes. This cytokine also acts on other cell types present in the fibrotic and tumour microenvironment, such as epithelial, endothelial cells or macrophages and it contributes to the cancer-associated fibroblast (CAF) phenotype. Furthermore, TGF-β exerts anti-tumour activity by inhibiting the host tumour immunosurveillance. Aim of this review is to update how TGF-β and the tissue microenvironment cooperate to promote the pleiotropic actions that regulate cell responses of different cell types, essential for the development of fibrosis and tumour progression. We discuss recent evidences suggesting the use of TGF-β chemical inhibitors as a new line of defence against fibrotic disorders or cancer.

TGF-β and the Tissue Microenvironment: Relevance in Fibrosis and Cancer

Transforming growth factor-β (TGF-β) is a cytokine essential for the induction of the fibrotic response and for the activation of the cancer stroma. Strong evidence suggests that a strong cross-talk exists among TGF-β and the tissue extracellular matrix components. TGF-β is stored in the matrix as part of a large latent complex bound to the latent TGF-β binding protein (LTBP) and matrix binding of latent TGF-β complexes, which is required for an adequate TGF-β function. Once TGF-β is activated, it regulates extracellular matrix remodelling and promotes a fibroblast to myofibroblast transition, which is essential in fibrotic processes. This cytokine also acts on other cell types present in the fibrotic and tumour microenvironment, such as epithelial, endothelial cells or macrophages and it contributes to the cancer-associated fibroblast (CAF) phenotype. Furthermore, TGF-β exerts anti-tumour activity by inhibiting the host tumour immunosurveillance. Aim of this review is to update how TGF-β and the tissue microenvironment cooperate to promote the pleiotropic actions that regulate cell responses of different cell types, essential for the development of fibrosis and tumour progression. We discuss recent evidences suggesting the use of TGF-β chemical inhibitors as a new line of defence against fibrotic disorders or cancer.

Integrins in wound healing, fibrosis and tumor stroma: High potential targets for therapeutics and drug delivery

Wound healing is a complex process, which ultimately leads to fibrosis if not repaired well. Pathologically very similar to fibrosis is the tumor stroma, found in several solid tumors which are regarded as wounds that do not heal. Integrins are heterodimeric surface receptors which control various physiological cellular functions. Additionally, integrins also sense ECM-induced extracellular changes during pathological events, leading to cellular responses, which influence ECM remodeling. The purpose and scope of this review is to introduce integrins as key targets for therapeutics and drug delivery within the scope of wound healing, fibrosis and the tumor stroma. This review provides a general introduction to the biology of integrins including their types, ligands, means of signaling and interaction with growth factor receptors. Furthermore, we highlight integrins as key targets for therapeutics and drug delivery, based on their biological role, expression pattern within human tissues and at cellular level. Next, therapeutic approaches targeting integrins, with a focus on clinical studies, and targeted drug delivery strategies based on ligands are described.

Forkhead box O proteins: Crucial regulators of cancer EMT

The epithelial-mesenchymal transition (EMT) is an acknowledged cellular transition process in which epithelial cells acquire mesenchymal-like properties that endow cancer cells with increased migratory and invasive behavior. Forkhead box O (FOXO) proteins have been shown to orchestrate multiple EMT-associated pathways and EMT-related transcription factors (EMT-TFs), thereby modulating the EMT process. The focus of the current review is to evaluate the latest research progress regarding the roles of FOXO proteins in cancer EMT. First, a brief overview of the EMT process in cancer and a general background on the FOXO family are provided. Next, we present the interactions between FOXO proteins and multiple EMT-associated pathways during malignancy development. Finally, we propose several novel potential directions for future research. Collectively, the information compiled herein should serve as a comprehensive repository of information on this topic and should aid in the design of additional studies and the future development of FOXO proteins as therapeutic targets.

Opposing Actions of Fibroblast and Cardiomyocyte Smad3 Signaling in the Infarcted Myocardium

BACKGROUND

Transforming growth factor-βs regulate a wide range of cellular responses by activating Smad-dependent and Smad-independent cascades. In the infarcted heart, Smad3 signaling is activated in both cardiomyocytes and interstitial cells. We hypothesized that cell-specific actions of Smad3 regulate repair and remodeling in the infarcted myocardium.

METHODS

To dissect cell-specific Smad3 actions in myocardial infarction, we generated mice with Smad3 loss in activated fibroblasts or cardiomyocytes. Cardiac function was assessed after reperfused or nonreperfused infarction using echocardiography. The effects of cell-specific Smad3 loss on the infarcted heart were studied using histological studies, assessment of protein, and gene expression levels. In vitro, we studied Smad-dependent and Smad-independent actions in isolated cardiac fibroblasts.

RESULTS

Mice with fibroblast-specific Smad3 loss had accentuated adverse remodeling after reperfused infarction and exhibited an increased incidence of late rupture after nonreperfused infarction. The consequences of fibroblast-specific Smad3 loss were not a result of effects on acute infarct size but were associated with unrestrained fibroblast proliferation, impaired scar remodeling, reduced fibroblast-derived collagen synthesis, and perturbed alignment of myofibroblast arrays in the infarct. Polarized light microscopy in Sirius red-stained sections demonstrated that the changes in fibroblast morphology were associated with perturbed organization of the collagenous matrix in the infarcted area. In contrast, α-smooth muscle actin expression by infarct myofibroblasts was not affected by Smad3 loss. Smad3 critically regulated fibroblast function, activating integrin-mediated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-2 (NOX-2) expression. Smad3 loss in cardiomyocytes attenuated remodeling and dysfunction after infarction. Cardiomyocyte-specific Smad3 loss did not affect acute infarct size but was associated with attenuated cardiomyocyte apoptosis in the remodeling myocardium, accompanied by decreased myocardial NOX-2 levels, reduced nitrosative stress, and lower matrix metalloproteinase-2 expression.

CONCLUSIONS

In healing myocardial infarction, myofibroblast- and cardiomyocyte-specific activation of Smad3 has contrasting functional outcomes that may involve activation of an integrin/reactive oxygen axis.

Protein Tyrosine Phosphatases in Systemic Sclerosis: Potential Pathogenic Players and Therapeutic Targets

PURPOSE OF REVIEW

The pathogenesis of systemic sclerosis depends on a complex interplay between autoimmunity, vasculopathy, and fibrosis. Reversible phosphorylation on tyrosine residues, in response to growth factors and other stimuli, critically regulates each one of these three key pathogenic processes. Protein tyrosine kinases, the enzymes that catalyze addition of phosphate to tyrosine residues, are known players in systemic sclerosis, and tyrosine kinase inhibitors are undergoing clinical trials for treatment of this disease. Until recently, the role of tyrosine phosphatases-the enzymes that counteract the action of tyrosine kinases by removing phosphate from tyrosine residues-in systemic sclerosis has remained largely unknown. Here, we review the function of tyrosine phosphatases in pathways relevant to the pathogenesis of systemic sclerosis and their potential promise as therapeutic targets to halt progression of this debilitating rheumatic disease.

RECENT FINDINGS

Protein tyrosine phosphatases are emerging as important regulators of a multitude of signaling pathways and undergoing validation as molecular targets for cancer and other common diseases. Recent advances in drug discovery are paving the ways to develop new classes of tyrosine phosphatase modulators to treat human diseases. Although so far only few reports have focused on tyrosine phosphatases in systemic sclerosis, these enzymes play a role in multiple pathways relevant to disease pathogenesis. Further studies in this field are warranted to explore the potential of tyrosine phosphatases as drug targets for systemic sclerosis.

mTOR inhibition reduces growth and adhesion of hepatocellular carcinoma cells in vitro

Mechanistic target of rapamycin (mTOR) signaling is typically increased in hepatocellular carcinoma (HCC). A panel of HCC cell lines (HepG2, Hep3B and HuH6) was exposed to various concentrations of the mTOR inhibitors, everolimus and temsirolimus, in order to investigate their effects on cell growth, clonal formation, cell cycle progression, and adhesion and chemotactic migration using MTT and clonal cell growth assays, fluorometric detection of cell cycle phases and a Boyden chamber assay. In addition, integrin α and β adhesion receptors were analyzed by flow cytometry and blocking studies using function blocking monoclonal antibodies were conducted to explore functional relevance. The results demonstrated that everolimus and temsirolimus significantly suppressed HCC cell growth and clonal formation, at 0.1 or 1 nM (depending on the cell line). In addition, the number of cells in G0/G1 phase was increased in response to drug treatment, whereas the number of G2/M phase cells was decreased. Drug treatment also considerably suppressed HCC cell adhesion to immobilized collagen. Integrin profiling revealed strong expression of integrin α1, α2, α6 and β1 subtypes; and integrin α1 was upregulated in response to mTOR inhibition. Suppression of integrin α1 did not affect cell growth; however, it did significantly decrease adhesion and chemotaxis, with the influence on adhesion being greater than that on motility. Due to a positive association between integrin α1 expression and the extent of adhesion, whereby reduced receptor expression was correlated to decreased cell adhesion, it may be hypothesized that the adhesion‑blocking effects of mTOR inhibitors are not associated with mechanical contact inhibition of the α1 receptor but with integrin α1‑dependent suppression of oncogenic signaling, thus preventing tumor cell‑matrix interaction.

ITGA1 is a pre-malignant biomarker that promotes therapy resistance and metastatic potential in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has single-digit 5-year survival rates at <7%. There is a dire need to improve pre-malignant detection methods and identify new therapeutic targets for abrogating PDAC progression. To this end, we mined our previously published pseudopodium-enriched (PDE) protein/phosphoprotein datasets to identify novel PDAC-specific biomarkers and/or therapeutic targets. We discovered that integrin alpha 1 (ITGA1) is frequently upregulated in pancreatic cancers and associated precursor lesions. Expression of ITGA1-specific collagens within the pancreatic cancer microenvironment significantly correlates with indicators of poor patient prognosis, and depleting ITGA1 from PDAC cells revealed that it is required for collagen-induced tumorigenic potential. Notably, collagen/ITGA1 signaling promotes the survival of ALDH1-positive stem-like cells and cooperates with TGFβ to drive gemcitabine resistance. Finally, we report that ITGA1 is required for TGFβ/collagen-induced EMT and metastasis. Our data suggest that ITGA1 is a new diagnostic biomarker and target that can be leveraged to improve patient outcomes.

FGFR1 is critical for the anti-endothelial mesenchymal transition effect of N-acetyl-seryl-aspartyl-lysyl-proline via induction of the MAP4K4 pathway

Endothelial-to-mesenchymal transition (EndMT) has been shown to contribute to organ fibrogenesis, and we have reported that the anti-EndMT effect of N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is associated with restoring expression of diabetes-suppressed fibroblast growth factor receptor (FGFR), the key anti-EndMT molecule. FGFR1 is the key inhibitor of EndMT via the suppression of the transforming growth factor β (TGFβ) signaling pathway, and mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4) inhibits integrin β1, a key factor in activating TGFβ signaling and EndMT. Here, we showed that the close proximity between AcSDKP and FGFR1 was essential for the suppression of TGFβ/smad signaling and EndMT associated with MAP4K4 phosphorylation (P-MAP4K4) in endothelial cells. In cultured human dermal microvascular endothelial cells (HMVECs), the anti-EndMT and anti-TGFβ/smad effects of AcSDKP were lost following treatment with a neutralizing FGFR1 antibody (N-FGFR1) or transfection of FRS2 siRNA. The physical interaction between FGFR1 and P-MAP4K4 in HMVECs was confirmed by proximity ligation analysis and an immunoprecipitation assay. AcSDKP induced P-MAP4K4 in HMVECs, which was significantly inhibited by treatment with either N-FGFR1 or FRS2 siRNA. Furthermore, MAP4K4 knockdown using specific siRNAs induced smad3 phosphorylation and EndMT in HMVECs, which was not suppressed by AcSDKP. Streptozotocin-induced diabetic CD-1 mice exhibited suppression of both FGFR1 and P-MAP4K4 expression levels associated with the induction of TGFβ/smad3 signaling and EndMT in their hearts and kidneys; those were restored by AcSDKP treatment. These data demonstrate that the AcSDKP-FGFR1-MAP4K4 axis has an important role in combating EndMT-associated fibrotic disorders.

Nintedanib, a triple tyrosine kinase inhibitor, attenuates renal fibrosis in chronic kidney disease

Nintedanib (BIBF1120) is a triple kinase inhibitor of platelet-derived growth factor receptor (PDGFR), fibroblast growth factor receptors (FGFR), vascular endothelial growth factor receptor (VEGFR), and Src family kinase, which has recently been approved by FDA to treat idiopathic pulmonary fibrosis. Whether it affects renal fibrosis remains unknown. Here, we demonstrated that administration of nintedanib immediately or 3 days after unilateral ureteral obstruction (UUO) injury and with folic acid (FA) injection attenuated renal fibrosis and inhibited activation of renal interstitial fibroblasts. Delayed administration of nintedanib also partially reversed established renal fibrosis. Treatment with nintedanib blocked UUO-induced phosphorylation of PDGFRβ, FGFR1, FGFR2, VEGFR2, and several Src family kinases including Src, Lck, Lyn as well as activation of signal transducer and activator of transcription-3 (STAT3), nuclear factor-κB (NF-κB), and Smad-3 in the kidney. Furthermore, nintedanib inhibited UUO-elicited renal proinflammatory cytokine expression and macrophage infiltration. These data indicate that nintedanib is a potent anti-fibrotic agent in the kidney and may hold therapeutic potential as a treatment of chronic fibrotic kidney disease.

Transforming Growth Factor-β: Master Regulator of the Respiratory System in Health and Disease

In this article, we review the biology and physiological importance of transforming growth factor-β (TGF-β) to homeostasis in the respiratory system, its importance to innate and adaptive immune responses in the lung, and its pathophysiological role in various chronic pulmonary diseases including pulmonary arterial hypertension, chronic obstructive pulmonary disease, asthma, and pulmonary fibrosis. The TGF-β family is responsible for initiation of the intracellular signaling pathways that direct numerous cellular activities including proliferation, differentiation, extracellular matrix synthesis, and apoptosis. When TGF-β signaling is dysregulated or essential control mechanisms are unbalanced, the consequences of organ and tissue dysfunction can be profound. The complexities and myriad checkpoints built into the TGF-β signaling pathways provide attractive targets for the treatment of these disease states, many of which are currently being investigated. This review focuses on those aspects of TGF-β biology that are most relevant to pulmonary diseases and that hold promise as novel therapeutic targets.

Activation of FXR protects against renal fibrosis via suppressing Smad3 expression

Renal fibrosis is the common pathway of most chronic kidney disease progression to end-stage renal failure. The nuclear receptor FXR (farnesoid X receptor), a multiple functional transcription factor, plays an important role in protecting against fibrosis. The TGFβ-Smad signaling has a central role in kidney fibrosis. However, it remains unclear whether FXR plays direct anti-fibrotic effect in renal fibrosis via regulating TGFβ-Smad pathway. In this study, we found that the level of FXR was negatively correlated with that of Smad3 and fibronectin (a marker of fibrosis) in human fibrotic kidneys. Activation of FXR suppressed kidney fibrosis and downregulated Smad3 expression, which was markedly attenuated by FXR antagonist. Moreover, the FXR-mediated repression of fibrosis was significantly alleviated by ectopic expression of Smad3. Luciferase reporter assay revealed that FXR activation inhibited the transcriptional activity of Smad3 gene promoter. The in vivo experiments showed that FXR agonist protected against renal fibrosis and downregulated Smad3 expression in UUO mice. These results suggested that FXR may serve as an important negative regulator for manipulating Smad3 expression, and the FXR/Smad3 pathway may be a novel target for the treatment of renal fibrosis.

Sulfur Dioxide Protects Against Collagen Accumulation in Pulmonary Artery in Association With Downregulation of the Transforming Growth Factor β1/Smad Pathway in Pulmonary Hypertensive Rats

BACKGROUND

We aimed to explore the role of endogenous sulfur dioxide (SO2) in pulmonary vascular collagen remodeling induced by monocrotaline and its mechanisms.

METHODS AND RESULTS

A rat model of monocrotaline-induced pulmonary vascular collagen remodeling was developed and administered with l-aspartate-β-hydroxamate or SO2 donor. The morphology of small pulmonary arteries and collagen metabolism were examined. Cultured pulmonary arterial fibroblasts stimulated by transforming growth factor β1 (TGF-β1) were used to explore the mechanism. The results showed that in monocrotaline-treated rats, mean pulmonary artery pressure increased markedly, small pulmonary arterial remodeling developed, and collagen deposition in lung tissue and pulmonary arteries increased significantly in association with elevated SO2 content, aspartate aminotransferase (AAT) activity, and expression of AAT1 compared with control rats. Interestingly, l-aspartate-β-hydroxamate, an inhibitor of SO2 generation, further aggravated pulmonary vascular collagen remodeling in monocrotaline-treated rats, and inhibition of SO2 in pulmonary artery smooth muscle cells activated collagen accumulation in pulmonary arterial fibroblasts. SO2 donor, however, alleviated pulmonary vascular collagen remodeling with inhibited collagen synthesis, augmented collagen degradation, and decreased TGF-β1 expression of pulmonary arteries. Mechanistically, overexpression of AAT1, a key enzyme of SO2 production, prevented the activation of the TGF-β/type I TGF-β receptor/Smad2/3 signaling pathway and abnormal collagen synthesis in pulmonary arterial fibroblasts. In contrast, knockdown of AAT1 exacerbated Smad2/3 phosphorylation and deposition of collagen types I and III in TGF-β1-treated pulmonary arterial fibroblasts.

CONCLUSIONS

Endogenous SO2 plays a protective role in pulmonary artery collagen accumulation induced by monocrotaline via inhibition of the TGF-β/type I TGF-β receptor/Smad2/3 pathway.

Integrin α1β1 protects against signs of post-traumatic osteoarthritis in the female murine knee partially via regulation of epidermal growth factor receptor signalling

OBJECTIVE

To investigate the role of integrin α1β1 in the progression of post-traumatic osteoarthritis (PTOA), and elucidate the contribution of epidermal growth factor receptor (EGFR) signalling to the mechanism by which integrin α1β1 might control PTOA. We hypothesised that integrin α1β1 plays a protective role in the course of PTOA and that the effect of PTOA (e.g., synovitis, loss of cartilage and growth of osteophytes) would be exacerbated in mice lacking integrin α1β1 at every time point post destabilisation of medial meniscus (DMM).

METHODS

DMM or sham surgery was performed on integrin α1-null and wild type (WT) mice and the progression of PTOA analysed at 2, 4, 8 and 12 weeks post-surgery (PS) using micro-computed tomography (microCT), histology, and immunohistochemistry. In addition, the effects of EGFR blockade were examined by treating the mice with the EGFR inhibitor erlotinib.

RESULTS

Integrin α1-null female, but not male, mice showed earlier cartilage degradation post DMM surgery compared to WT controls. Furthermore, erlotinib treatment resulted in significantly less cartilage damage in integrin α1-null but not WT mice. Independent of genotype, erlotinib treatment significantly mitigated the effects of PTOA on many tissues of female mice including meniscal and fabella bone volume, subchondral bone thickness and density and cartilage degradation. In contrast, reduced EGFR signalling had little effect on signs of PTOA in male mice.

CONCLUSION

Integrin α1β1 protects against PTOA-induced cartilage degradation in female mice partially via the reduction of EGFR signalling. Furthermore, reduction of EGFR signalling protects against the development of PTOA in female, but not male mice.

Signaling Receptors for TGF-β Family Members

Transforming growth factor β (TGF-β) family members signal via heterotetrameric complexes of type I and type II dual specificity kinase receptors. The activation and stability of the receptors are controlled by posttranslational modifications, such as phosphorylation, ubiquitylation, sumoylation, and neddylation, as well as by interaction with other proteins at the cell surface and in the cytoplasm. Activation of TGF-β receptors induces signaling via formation of Smad complexes that are translocated to the nucleus where they act as transcription factors, as well as via non-Smad pathways, including the Erk1/2, JNK and p38 MAP kinase pathways, and the Src tyrosine kinase, phosphatidylinositol 3'-kinase, and Rho GTPases.

Development of an In Vitro Assay to Evaluate Contractile Function of Mesenchymal Cells that Underwent Epithelial-Mesenchymal Transition

Fibrosis is often involved in the pathogenesis of various chronic progressive diseases such as interstitial pulmonary disease. Pathological hallmark is the formation of fibroblastic foci, which is associated with the disease severity. Mesenchymal cells consisting of the fibroblastic foci are proposed to be derived from several cell sources, including originally resident intrapulmonary fibroblasts and circulating fibrocytes from bone marrow. Recently, mesenchymal cells that underwent epithelial-mesenchymal transition (EMT) have been also supposed to contribute to the pathogenesis of fibrosis. In addition, EMT can be induced by transforming growth factor β, and EMT can be enhanced by pro-inflammatory cytokines like tumor necrosis factor α. The gel contraction assay is an ideal in vitro model for the evaluation of contractility, which is one of the characteristic functions of fibroblasts and contributes to wound repair and fibrosis. Here, the development of a gel contraction assay is demonstrated for evaluating contractile ability of mesenchymal cells that underwent EMT.

COL11A1 is overexpressed in recurrent non-small cell lung cancer and promotes cell proliferation, migration, invasion and drug resistance

Collagen type XI α1 (COL11A1), a minor fibrillar collagen, has been demonstrated to be involved in cell proliferation, migration and the tumorigenesis of many human malignancies. Previous studies have shown that COL11A1 may be a valuable diagnostic marker for non-small cell lung carcinoma (NSCLC). However, its biological function in NSCLC progression remains largely unclear. In the present study, we investigated the expression levels of COL11A1 in different human NSCLC samples, and found that COL11A1 was overexpressed in NSCLC with lymph node metastasis and in recurrent NSCLC tissues. We also revealed that COL11A1 promoted the cell proliferation, migration and invasion of NSCLC cell lines in vitro. Furthermore, our results highlighted the importance of COL11A1 in chemoresistance to cisplatin. Mechanistically, we found that the effects of the overexpression of COL11A1 in NSCLC cells were mediated by Smad signaling. Collectively, our findings suggest that COL11A1 may sever as a biomarker for metastatic NSCLC, and can be used to predict recurrence after surgical resection. Therapeutic approaches targeting COL11A1 may facilitate the optimization of cisplatin treatment of NSCLC by overcoming chemoresistance.

Knockdown of lncRNA-ATB suppresses autocrine secretion of TGF-β2 by targeting ZNF217 via miR-200c in keloid fibroblasts

Abnormally high activation of transforming growth factor-β (TGF-β) signaling has been demonstrated to be involved in the initiation and progression of keloids. However, the functional role of long non-coding RNA (lncRNA)-activated by TGF-β (lncRNA-ATB) in keloids has not been documented. Here we investigated the role of lncRNA-ATB in the autocrine secretion of TGF-β in keloid fibroblasts (KFs) and explored the underlying molecular mechanism. Using immunohistochemistry and quantitative RT-PCR analysis, we showed that lncRNA-ATB and ZNF217, a transcriptional activator of TGF-β, were overexpressed and miR-200c, which targets ZNF217, was under-expressed in keloid tissue and keloid fibroblasts. Through gain- and loss-of-function studies, we demonstrated that knockdown of lncRNA-ATB decreased autocrine secretion of TGF-β2 and ZNF217 expression but upregulated expression of miR-200c in KFs. Stable downregulation of ZNF217 expression decreased the autocrine secretion of TGF-β2. miR-200c was endogenously associated with lncRNA-ATB, and inhibition of miR-200c overcame the decrease in ZNF217 expression in KFs. Taken together, these findings indicate that lncRNA-ATB governs the autocrine secretion of TGF-β2 in KFs, at least in part, by downregulating the expression level of ZNF217 via miR-200c, suggesting a signaling axis consisting of lncRNA-ATB/miR-200c/ZNF217/TGF-β2. These findings may provide potential biomarkers and targets for novel diagnostic and therapeutic approaches for keloids.

Intermedin is upregulated and attenuates renal fibrosis by inhibition of oxidative stress in rats with unilateral ureteral obstruction

AIM

Transforming growth factor-β1 (TGF-β1) plays a pivotal role in the progression of renal fibrosis. Reactive oxygen species mediate profibrotic action of TGF-β1. Intermedin (IMD) has been shown to inhibit oxidative stress, but its role in renal fibrosis remains unclear. Here, we investigated the effects of IMD on renal fibrosis in a rat model of unilateral ureteral obstruction (UUO).

METHODS

The expression of IMD and its receptors, calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMP1/2/3), in the obstructed kidney was detected by real-time polymerase chain reaction (PCR), western blotting and immunohistochemistry. To evaluate the effects of IMD on renal fibrosis, we locally overexpressed exogenous IMD in the obstructed kidney using an ultrasound-microbubble-mediated delivery system. Renal fibrosis was determined by Masson trichrome staining. The expression of TGF-β1, connective tissue growth factor (CTGF), α-smooth muscle actin (α-SMA) and fibronectin was measured. Smad2/3 activation and macrophage infiltration were evaluated. We also studied oxidative stress by measuring superoxide dismutase (SOD) activity and malondialdehyde (MDA) content.

RESULTS

mRNA and protein expression of IMD increased after UUO. CRLR, RAMP1, RAMP2 and RAMP3 were also induced by ureteral obstruction. IMD overexpression remarkably attenuated UUO-induced tubular injury and blunted fibrotic response as shown by decreased interstitial collagen deposition and downregulation of fibronectin. Macrophage infiltration, α-SMA and CTGF upregulation caused by UUO were all relieved by IMD, whereas TGF-β1 upregulation and Smad2/3 activation were not affected. Meanwhile, we noted increased oxidative stress in obstruction, which was also attenuated by IMD gene delivery.

CONCLUSIONS

Our results indicate that IMD is upregulated after UUO. IMD plays a protective role in renal fibrosis via its antioxidant effects.