Fibroblast Activation Protein (FAP) Accelerates Collagen Degradation and Clearance from Lungs in Mice

Floating electrode-dielectric barrier discharge-based plasma promotes skin regeneration in a full-thickness skin defect mouse model

Wound healing involves a complex and dynamic interplay among various cell types, cytokines, and growth factors. Macrophages and transforming growth factor-β1 (TGF-β1) play an essential role in different phases of wound healing. Cold atmospheric plasma has a wide range of applications in the treatment of chronic wounds. Hence, we aimed to investigate the safety and efficacy of a custom-made plasma device in a full-thickness skin defect mouse model. Here, we investigated the wound tissue on days 6 and 12 using histology, qPCR, and western blotting. During the inflammation phase of wound repair, macrophages play an important role in the onset and resolution of inflammation, showing decreased F4/80 on day 6 of plasma treatment and increased TGF-β1 levels. The plasma-treated group showed better epidermal epithelialization, dermal fibrosis, collagen maturation, and reduced inflammation than the control group. Our findings revealed that floating electrode-dielectric barrier discharge (FE-DBD)-based atmospheric-pressure plasma promoted significantly faster wound healing in the plasma-treated group than that in the control group with untreated wounds. Hence, plasma treatment accelerated wound healing processes without noticeable side effects and suppressed pro-inflammatory genes, suggesting that FE-DBD-based plasma could be a potential therapeutic option for treating various wounds.

Progressive changes in the protein expression profile of alveolar septa in early-stage lung adenocarcinoma

BACKGROUND

Adenocarcinomas show a stepwise progression from atypical adenomatous hyperplasia (AAH) through adenocarcinoma in situ (AIS) to invasive adenocarcinoma (IA). Immunoglobulin superfamily containing leucine-rich repeat (ISLR) is a marker of tumor-restraining cancer-associated fibroblasts (CAFs), which are distinct from conventional, strongly α-smooth muscle actin (αSMA)-positive CAFs. Fibroblast activation protein (FAP) has been focused on as a potential therapeutic and diagnostic target of CAFs.

METHODS

We investigated the changes in protein expression during adenocarcinoma progression in the pre-existing alveolar septa by assessing ISLR, αSMA, and FAP expression in normal lung, AAH, AIS, and IA. Fourteen AAH, seventeen AIS, and twenty IA lesions were identified and randomly sampled. Immunohistochemical analysis was performed to evaluate cancer-associated changes and FAP expression in the pre-existing alveolar structures.

RESULTS

Normal alveolar septa expressed ISLR. The ISLR level in the alveolar septa decreased in AAH and AIS tissues when compared with that in normal lung tissue. The αSMA-positive area gradually increased from the adjacent lung tissue (13.3% ± 15%) to AIS (87.7% ± 14%), through AAH (70.2% ± 21%). Moreover, the FAP-positive area gradually increased from AAH (1.69% ± 1.4%) to IA (11.8% ± 7.1%), through AIS (6.11% ± 5.3%). Protein expression changes are a feature of CAFs in the pre-existing alveolar septa that begin in AAH. These changes gradually progressed from AAH to IA through AIS.

CONCLUSIONS

FAP-positive fibroblasts may contribute to tumor stroma formation in early-stage lung adenocarcinoma, and this could influence the development of therapeutic strategies targeting FAP-positive CAFs for disrupting extracellular matrix formation.

Fibroblast activating protein promotes the proliferation, migration, and activation of fibroblasts in oral submucous fibrosis

OBJECTIVES

Fibroblast activating protein (FAP) is associated with various organ fibrosis. However, the expression and molecular function of FAP in oral submucous fibrosis (OSF) is still unclear.

MATERIALS AND METHODS

The high-performance liquid chromatography was used to detect the presence of alkaloids in areca nut extract (ANE). Real-time qPCR, Western blot, and Immunohistochemistry assay were used to analyze the expression of FAP mRNA or protein in OSF and normal oral tissue. A chi-squared test analyzed the relationship between FAP protein expression and clinicopathological data of OSF patients. CCK-8, Wound-healing, and Transwell migration assay were employed to assess the effect of the proliferation and migration ability of hOMF cells with FAP overexpression or knockdown. The expression level of a-SMA, FSP1, and P13K-Akt signaling pathways-related protein in hOMF cells transfected with FAP overexpression or knockdown plasmid was verified by western blot assay.

RESULTS

The four specific areca alkaloids (Arecoline, Guvacine, Arecaidine, and Guvacoline) were successfully detected in the ANE. The viability of hOMF cells was significantly improved in the 50 μg/mL ANE group and was inhibited in the 5 and 50 mg/mL ANE groups. The expression of FAP was upregulated in OSF tissues, and hOMF cells treated with 50 μg/mL ANE and was related to pathology grade, clinical stage, and history of chewing betel nut. Additionally, FAP may promote the proliferation, migration, and activation of hOMF cells through the P13K-Akt signaling pathway.

CONCLUSIONS

This study found that ANE had a bidirectional effect on the viability of hOMF cells, and the FAP gene was a potential therapeutic target in OSF.

Genome-wide screens identify SEL1L as an intracellular rheostat controlling collagen turnover

Accumulating evidence has implicated impaired extracellular matrix (ECM) clearance as a key factor in fibrotic disease. Despite decades of research elucidating the effectors of ECM clearance, relatively little is understood regarding the upstream regulation of this process. Collagen is the most abundant constituent of normal and fibrotic ECM in mammalian tissues. Its catabolism occurs through extracellular proteolysis and cell-mediated uptake of collagen fragments for intracellular degradation. Given the paucity of information regarding the regulation of this latter process, here we execute unbiased genome-wide screens to understand the molecular underpinnings of cell-mediated collagen clearance. Using this approach, we discover a mechanism through which collagen biosynthesis is sensed by cells internally and directly regulates clearance of extracellular collagen. The sensing mechanism appears to be dependent on endoplasmic reticulum-resident protein SEL1L and occurs via a noncanonical function of this protein. This pathway functions as a homeostatic negative feedback loop that limits collagen accumulation in tissues. In human fibrotic lung disease, the induction of this collagen clearance pathway by collagen synthesis is impaired, thereby contributing to the pathological accumulation of collagen in lung tissue. Thus, we describe cell-autonomous, rheostatic collagen clearance as an important pathway of tissue homeostasis.

Mechanical stiffness promotes skin fibrosis through FAPα-AKT signaling pathway

BACKGROUND

Myofibroblasts contribute to the excessive production, remodeling and cross-linking of the extracellular matrix that characterizes the progression of skin fibrosis. An important insight into the pathogenesis of tissue fibrosis has been the discovery that increased matrix stiffness during fibrosis progression is involved in myofibroblast activation. However, mechanistic basis for this phenomenon remains elusive.

OBJECTIVE

To explore the role of fibroblast activation protein-α (FAPα) in mechanical stiffness-induced skin fibrosis progression.

METHODS

RNA-seq was performed to compare differential genes of mouse dermal fibroblasts (MDFs) grown on low or high stiffness plates. This process identified FAPα, which is a membrane protein usually overexpressed in activated fibroblasts, as a suitable candidate. In vitro assay, we investigate the role of FAPα in mechanical stiffness-induced MDFs activation and downstream pathway. By establishing mouse skin fibrosis model and intradermally administrating FAPα adeno-associated virus (AAV) or a selective Fap inhibitor FAPi, we explore the role of FAPα in skin fibrosis in vivo.

RESULTS

We show that FAPα, a membrane protein highly expressed in myofibroblasts of skin fibrotic tissues, is regulated by increased matrix stiffness. Genetic deletion or pharmacological inhibition of FAPα significantly inhibits mechanical stiffness-induced activation of myofibroblasts in vitro. Mechanistically, FAPα promotes myofibroblast activation by stimulating the PI3K-Akt pathway. Furthermore, we showed that administration of the inhibitor FAPi or FAPα targeted knockdown ameliorated the progression of skin fibrosis.

CONCLUSION

Taken together, we identify FAPα as an important driver of mechanical stiffness-induced skin fibrosis and a potential therapeutic target for the treatment of skin fibrosis.

Differential induction of T-cell tolerance by tumour fibroblast subsets

T-cell immunotherapy is now a first-line cancer treatment for metastatic melanoma and some lung cancer subtypes, which is a welcome clinical success. However, the response rates observed in these diseases are not yet replicated across other prominent solid tumour types, particularly stromal-rich subtypes with a complex microenvironment that suppresses infiltrating T cells. Cancer-associated fibroblasts (CAFs) are one of the most abundant and pro-pathogenic players in the tumour microenvironment, promoting tumour neogenesis, persistence and metastasis. Accumulating evidence is clear that CAFs subdue anti-tumour T-cell immunity and interfere with immunotherapy. CAFs can be grouped into different subtypes that operate synergistically to suppress T-cell function, including myofibroblastic CAFs, inflammatory CAFs and antigen-presenting CAFs, among other nomenclatures. Here, we review the mechanisms used by CAFs to induce T- cell tolerance and how these functions are likely to affect immunotherapy outcomes.

Fibroblast activation protein: Pivoting cancer/chemotherapeutic insight towards heart failure

An important mechanism for cancer progression is degradation of the extracellular matrix (ECM) which is accompanied by the emergence and proliferation of an activated fibroblast, termed the cancer associated fibroblast (CAF). More specifically, an enzyme pathway identified to be amplified with local cancer progression and proliferation of the CAF, is fibroblast activation protein (FAP). The development and progression of heart failure (HF) irrespective of the etiology is associated with left ventricular (LV) remodeling and changes in ECM structure and function. As with cancer, HF progression is associated with a change in LV myocardial fibroblast growth and function, and expresses a protein signature not dissimilar to the CAF. The overall goal of this review is to put forward the postulate that scientific discoveries regarding FAP in cancer as well as the development of specific chemotherapeutics could be pivoted to target the emergence of FAP in the activated fibroblast subtype and thus hold translationally relevant diagnostic and therapeutic targets in HF.

Stiffness-dependent MSC homing and differentiation into CAFs - implications for breast cancer invasion

Cellular heterogeneity and extracellular matrix (ECM) stiffening have been shown to be drivers of breast cancer invasiveness. Here, we examine how stiffness-dependent crosstalk between cancer cells and mesenchymal stem cells (MSCs) within an evolving tumor microenvironment regulates cancer invasion. By analyzing previously published single-cell RNA sequencing datasets, we establish the existence of a subpopulation of cells in primary tumors, secondary sites and circulatory tumor cell clusters of highly aggressive triple-negative breast cancer (TNBC) that co-express MSC and cancer-associated fibroblast (CAF) markers. By using hydrogels with stiffnesses of 0.5, 2 and 5 kPa to mimic different stages of ECM stiffening, we show that conditioned medium from MDA-MB-231 TNBC cells cultured on 2 kPa gels, which mimic the pre-metastatic stroma, drives efficient MSC chemotaxis and induces stable differentiation of MSC-derived CAFs in a TGFβ (TGFB1)- and contractility-dependent manner. In addition to enhancing cancer cell proliferation, MSC-derived CAFs on 2 kPa gels maximally boost local invasion and confer resistance to flow-induced shear stresses. Collectively, our results suggest that homing of MSCs at the pre-metastatic stage and their differentiation into CAFs actively drives breast cancer invasion and metastasis in TNBC.

Extracellular Matrix Deposition Defines the Duration of Cell Sheet Assembly from Human Adipose-Derived MSC

Cell sheet (CS) engineering using mesenchymal stromal cells (MSC) draws significant interest for regenerative medicine and this approach translates to clinical use for numerous indications. However, little is known of factors that define the timing of CS assembly from primary cultures. This aspect is important for planning CS delivery in autologous and allogeneic modes of use. We used a comparative in vitro approach with primary donors' (n = 14) adipose-derived MSCs and evaluated the impact of healthy subject's sex, MSC culture features (population doubling time and lag-phase), and extracellular matrix (ECM) composition along with factors related to connective tissue formations (α-SMA and FAP-α) on CS assembly duration. Using qualitative and quantitative analysis methods, we found that, in seeded MSCs, high contents of collagen I and collagen IV had a direct correlation with longer CS assembly duration. We found that short lag-phase cultures faster turned to a ready-to-use CS, while age, sex, fibronectin, laminin, α-SMA, and FAP-α failed to provide a significant correlation with the timing of assembly. In detachable CSs, FAP-α was negatively correlated with the duration of assembly, suggesting that its concentration rose over time and contributed to MSC activation, transitioning to α-SMA-positive myofibroblasts and ECM turnover. Preliminary data on cell density and collagen I deposition suggested that the TGF-β1 signaling axis is of pivotal importance for ECM composition and construct maturation.

Fibroblast Activation Protein Alpha (FAPα) in Fibrosis: Beyond a Perspective Marker for Activated Stromal Cells?

The development of tissue fibrosis is a complex process involving the interaction of multiple cell types, which makes the search for antifibrotic agents rather challenging. So far, myofibroblasts have been considered the key cell type that mediated the development of fibrosis and thus was the main target for therapy. However, current strategies aimed at inhibiting myofibroblast function or eliminating them fail to demonstrate sufficient effectiveness in clinical practice. Therefore, today, there is an unmet need to search for more reliable cellular targets to contribute to fibrosis resolution or the inhibition of its progression. Activated stromal cells, capable of active proliferation and invasive growth into healthy tissue, appear to be such a target population due to their more accessible localization in the tissue and their high susceptibility to various regulatory signals. This subpopulation is marked by fibroblast activation protein alpha (FAPα). For a long time, FAPα was considered exclusively a marker of cancer-associated fibroblasts. However, accumulating data are emerging on the diverse functions of FAPα, which suggests that this protein is not only a marker but also plays an important role in fibrosis development and progression. This review aims to summarize the current data on the expression, regulation, and function of FAPα regarding fibrosis development and identify promising advances in the area.

Radiotracers for Imaging of Fibrosis: Advances during the Last Two Decades and Future Directions

Fibrosis accompanies various pathologies, and there is thus an unmet medical need for non-invasive, sensitive, and quantitative methods for the assessment of fibrotic processes. Currently, needle biopsy with subsequent histological analysis is routinely used for the diagnosis along with morphological imaging techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US). However, none of these imaging techniques are sufficiently sensitive and accurate to detect minor changes in fibrosis. More importantly, they do not provide information on fibrotic activity on the molecular level, which is critical for fundamental understanding of the underlying biology and disease course. Molecular imaging technology using positron emission tomography (PET) offers the possibility of imaging not only physiological real-time activity, but also high-sensitivity and accurate quantification. This diagnostic tool is well established in oncology and has exhibited exponential development during the last two decades. However, PET diagnostics has only recently been widely applied in the area of fibrosis. This review presents the progress of development of radiopharmaceuticals for non-invasive detection of fibrotic processes, including the fibrotic scar itself, the deposition of new fibrotic components (fibrogenesis), or the degradation of existing fibrosis (fibrolysis).

Molecular profiling of gingival crevicular fluid fails to distinguish between infrabony and suprabony periodontal defects

AIM

To assess the differential molecular profiling of gingival crevicular fluid (GCF) from infrabony and suprabony periodontal defects compared with healthy sites.

MATERIALS AND METHODS

Seventy-five samples from 25 patients with untreated periodontitis stage III-IV were included. Clinical and radiological parameters as well as GCF samples were collected from an infrabony defect, a suprabony defect and a periodontally healthy site per patient. A multiplex bead immunoassay was performed to assess the level of 18 biomarkers associated with inflammation, connective tissue degradation and regeneration/repair.

RESULTS

GCF volume was higher in periodontal sites compared with healthy sites, with no significant difference between infrabony and suprabony defects. Fourteen biomarkers were elevated in infrabony and suprabony sites compared with healthy sites (p < .05). Only interleukin-1α levels were increased in infrabony compared with suprabony sites, whereas there was no difference in probing pocket depth.

CONCLUSIONS

Although the GCF molecular profile clearly differentiates periodontally affected sites from healthy sites, the different architecture between infrabony and suprabony defects is not reflected in GCF biomarker changes.

Mesenchymal stromal cells facilitate resolution of pulmonary fibrosis by miR-29c and miR-129 intercellular transfer

To date, pulmonary fibrosis remains an unmet medical need. In this study, we evaluated the potency of mesenchymal stromal cell (MSC) secretome components to prevent pulmonary fibrosis development and facilitate fibrosis resolution. Surprisingly, the intratracheal application of extracellular vesicles (MSC-EVs) or the vesicle-depleted secretome fraction (MSC-SF) was not able to prevent lung fibrosis when applied immediately after the injury caused by bleomycin instillation in mice. However, MSC-EV administration induced the resolution of established pulmonary fibrosis, whereas the vesicle-depleted fraction did not. The application of MSC-EVs caused a decrease in the numbers of myofibroblasts and FAPa⁺ progenitors without affecting their apoptosis. Such a decrease likely occurred due to their dedifferentiation caused by microRNA (miR) transfer by MSC-EVs. Using a murine model of bleomycin-induced pulmonary fibrosis, we confirmed the contribution of specific miRs (miR-29c and miR-129) to the antifibrotic effect of MSC-EVs. Our study provides novel insights into possible antifibrotic therapy based on the use of the vesicle-enriched fraction of the MSC secretome.

Establishment of FAP-overexpressing Cells for FAP-targeted Theranostics

OBJECTIVE

Fibroblast activation protein (FAP) has been widely studied and exploited for its clinical applications. One of the difficulties in interpreting reports of FAP-targeted theranostics is due to the lack of accurate controls, making the results less specific and less confirmative. This study aimed to establish a pair of cell lines, in which one highly expresses FAP (HT1080-hFAP) and the other has no detectable FAP (HT1080-vec) as control, to accurately evaluate the specificity of the FAP-targeted theranostics in vitro and in vivo.

METHODS

The cell lines of the experimental group (HT1080-hFAP) and no-load group (HT1080-vec) were obtained by molecular construction of the recombinant plasmid pIRES-hFAP. The expression of hFAP in HT1080 cells was detected by PCR, Western blotting and flow cytometry. CCK-8, Matrigel transwell invasion assay, scratch test, flow cytometry and immunofluorescence were used to verify the physiological function of FAP. The activities of human dipeptidyl peptidase (DPP) and human endopeptidase (EP) were detected by ELISA in HT1080-hFAP cells. PET imaging was performed in bilateral tumor-bearing nude mice models to evaluate the specificity of FAP.

RESULTS

RT-PCR and Western blotting demonstrated the mRNA and protein expression of hFAP in HT1080-hFAP cells but not in HT1080-vec cells. Flow cytometry confirmed that nearly 95% of the HT1080-hFAP cells were FAP positive. The engineered hFAP on HT1080 cells had its ability to retain enzymatic activities and a variety of biological functions, including internalization, proliferation-, migration-, and invasion-promoting activities. The HT1080-hFAP xenografted tumors in nude mice bound and took up ⁶⁸GA-FAPI-04 with superior selectivity. High image contrast and tumor-organ ratio were obtained by PET imaging. The HT1080-hFAP tumor retained the radiotracer for at least 60 min.

CONCLUSION

This pair of HT1080 cell lines was successfully established, making it feasible for accurate evaluation and visualization of therapeutic and diagnostic agents targeting the hFAP.

Senescent cell population with ZEB1 transcription factor as its main regulator promotes osteoarthritis in cartilage and meniscus

OBJECTIVES

Single-cell level analysis of articular cartilage and meniscus tissues from human healthy and osteoarthritis (OA) knees.

METHODS

Single-cell RNA sequencing (scRNA-seq) analyses were performed on articular cartilage and meniscus tissues from healthy (n=6, n=7) and OA (n=6, n=6) knees. Expression of genes of interest was validated using immunohistochemistry and RNA-seq and function was analysed by gene overexpression and depletion.

RESULTS

scRNA-seq analyses of human knee articular cartilage (70 972 cells) and meniscus (78 017 cells) identified a pathogenic subset that is shared between both tissues. This cell population is expanded in OA and has strong OA and senescence gene signatures. Further, this subset has critical roles in extracellular matrix (ECM) and tenascin signalling and is the dominant sender of signals to all other cartilage and meniscus clusters and a receiver of TGFβ signalling. Fibroblast activating protein (FAP) is also a dysregulated gene in this cluster and promotes ECM degradation. Regulons that are controlled by transcription factor ZEB1 are shared between the pathogenic subset in articular cartilage and meniscus. In meniscus and cartilage cells, FAP and ZEB1 promote expression of genes that contribute to OA pathogenesis, including senescence.

CONCLUSIONS

These single-cell studies identified a senescent pathogenic cell cluster that is present in cartilage and meniscus and has FAP and ZEB1 as main regulators which are novel and promising therapeutic targets for OA-associated pathways in both tissues.

Comprehensive Analysis of Fibroblast Activation Protein Expression in Interstitial Lung Diseases

Rationale: Sustained activation of lung fibroblasts and the resulting oversynthesis of the extracellular matrix are detrimental events for patients with interstitial lung diseases (ILDs). Lung biopsy is a primary evaluation technique for the fibrotic status of ILDs, and is also a major risk factor for triggering acute deterioration. Fibroblast activation protein (FAP) is a long-known surface biomarker of activated fibroblasts, but its expression pattern and diagnostic implications in ILDs are poorly defined. Objectives: The present study aims to comprehensively investigate whether the expression intensity of FAP could be used as a potential readout to estimate or measure the amounts of activated fibroblasts in ILD lungs quantitatively. Methods: FAP expression in human primary lung fibroblasts as well as in clinical lung specimens was first tested using multiple experimental methods, including real-time quantitative PCR (qPCR), Western blot, immunofluorescence staining, deep learning measurement of whole slide immunohistochemistry, as well as single-cell sequencing. In addition, FAP-targeted positron emission tomography/computed tomography imaging PET/CT was applied to various types of patients with ILD, and the correlation between the uptake of FAP tracer and pulmonary function parameters was analyzed. Measurements and Main Results: Here, it was revealed, for the first time, FAP expression was upregulated significantly in the early phase of lung fibroblast activation event in response to a low dose of profibrotic cytokine. Single-cell sequencing data further indicate that nearly all FAP-positive cells in ILD lungs were collagen-producing fibroblasts. Immunohistochemical analysis validated that FAP expression level was closely correlated with the abundance of fibroblastic foci on human lung biopsy sections from patients with ILDs. We found that the total standard uptake value (SUV) of FAP inhibitor (FAPI) PET (SUVtotal) was significantly related to lung function decline in patients with ILD. Conclusions: Our results strongly support that in vitro and in vivo detection of FAP can assess the profibrotic activity of ILDs, which may aid in early diagnosis and the selection of an appropriate therapeutic window.

Inhibition of fibroblast activation protein ameliorates cartilage matrix degradation and osteoarthritis progression

Fibroblast activation protein (Fap) is a serine protease that degrades denatured type I collagen, α2-antiplasmin and FGF21. Fap is highly expressed in bone marrow stromal cells and functions as an osteogenic suppressor and can be inhibited by the bone growth factor Osteolectin (Oln). Fap is also expressed in synovial fibroblasts and positively correlated with the severity of rheumatoid arthritis (RA). However, whether Fap plays a critical role in osteoarthritis (OA) remains poorly understood. Here, we found that Fap is significantly elevated in osteoarthritic synovium, while the genetic deletion or pharmacological inhibition of Fap significantly ameliorated posttraumatic OA in mice. Mechanistically, we found that Fap degrades denatured type II collagen (Col II) and Mmp13-cleaved native Col II. Intra-articular injection of rFap significantly accelerated Col II degradation and OA progression. In contrast, Oln is expressed in the superficial layer of articular cartilage and is significantly downregulated in OA. Genetic deletion of Oln significantly exacerbated OA progression, which was partially rescued by Fap deletion or inhibition. Intra-articular injection of rOln significantly ameliorated OA progression. Taken together, these findings identify Fap as a critical pathogenic factor in OA that could be targeted by both synthetic and endogenous inhibitors to ameliorate articular cartilage degradation.

Covert actions of growth hormone: fibrosis, cardiovascular diseases and cancer

Since its discovery nearly a century ago, over 100,000 studies of growth hormone (GH) have investigated its structure, how it interacts with the GH receptor and its multiple actions. These include effects on growth, substrate metabolism, body composition, bone mineral density, the cardiovascular system and brain function, among many others. Recombinant human GH is approved for use to promote growth in children with GH deficiency (GHD), along with several additional clinical indications. Studies of humans and animals with altered levels of GH, from complete or partial GHD to GH excess, have revealed several covert or hidden actions of GH, such as effects on fibrosis, cardiovascular function and cancer. In this Review, we do not concentrate on the classic and controversial indications for GH therapy, nor do we cover all covert actions of GH. Instead, we stress the importance of the relationship between GH and fibrosis, and how fibrosis (or lack thereof) might be an emerging factor in both cardiovascular and cancer pathologies. We highlight clinical data from patients with acromegaly or GHD, alongside data from cellular and animal studies, to reveal novel phenotypes and molecular pathways responsible for these actions of GH in fibrosis, cardiovascular function and cancer.

Piceatannol-mediated JAK2/STAT3 signaling pathway inhibition contributes to the alleviation of oxidative injury and collagen synthesis during pulmonary fibrosis

Pulmonary fibrosis (PF) is characterized by oxidative injury and excessive collagen synthesis in lung fibroblasts, causing impaired pulmonary function and chronic lung injury. Piceatannol, a dietary polyphenol, possesses vital pharmacological effects in metabolic disorders, cancers, cardiovascular disease and infectious disease; however, its role in PF is still not completely elucidated. Mice (8 to 10 weeks old) were administered bleomycin (BLM) intratracheally (2 U/kg) to establish an in vivo PF model. Murine primary lung fibroblasts were isolated and stimulated with TGF-β (10 ng/mL) for 48 h to induce its activation. Meanwhile, mice or primary lung fibroblasts were treated with different doses of piceatannol to observe its protective roles. Pulmonary function and arterial blood gas were detected to assess pulmonary physiological status. Collagen deposition and the mRNA levels of profibrotic genes were determined by H&E staining and RT-PCR. Meanwhile, the protein and mRNA markers, as well as end-product of oxidative stress were detected in vivo and in vitro. The results showed that pulmonary function was significantly impaired in BLM-induced mice, accompanied by elevated oxidative stress and excessive collagen synthesis. Piceatannol significantly improved pulmonary function and decreased oxidative injury as well as collagen synthesis in mice with PF. Mechanically, piceatannol treatment significantly inhibited the activation of JAK2/STAT3 signaling pathway in BLM-induced mice and TGF-β-induced lung fibroblasts. Additional findings also demonstrated that coumermycin A1 (C-A1), an agonist of JAK2, could abolish the effects of piceatannol on TGF-β-induced lung fibroblasts and reactivated the phosphorylation STAT3. Taken together, our study demonstrated that piceatannol could protect against oxidative injury and collagen synthesis during PF in a JAK2/STAT3 signaling pathway-dependent manner.

Mesoporous Polydopamine Loaded Pirfenidone Target to Fibroblast Activation Protein for Pulmonary Fibrosis Therapy

Recently, fibroblast activation protein (FAP), an overexpressed transmembrane protein of activated fibroblast in pulmonary fibrosis, has been considered as the new target for diagnosing and treating pulmonary fibrosis. In this work, mesoporous polydopamine (MPDA), which is facile prepared and easily modified, is developed as a carrier to load antifibrosis drug pirfenidone (PFD) and linking FAP inhibitor (FAPI) to realize lesion-targeted drug delivery for pulmonary fibrosis therapy. We have found that PFD@MPDA-FAPI is well biocompatible and with good properties of antifibrosis, when ICG labels MPDA-FAPI, the accumulation of the nanodrug at the fibrosis lung in vivo can be observed by NIR imaging, and the antifibrosis properties of PFD@MPDA-FAPI in vivo were also better than those of pure PFD and PFD@MPDA; therefore, the easily produced and biocompatible nanodrug PFD@MPDA-FAPI developed in this study is promising for further clinical translations in pulmonary fibrosis antifibrosis therapy.

[68 Ga]Ga-FAPI-46 PET for non-invasive detection of pulmonary fibrosis disease activity

PURPOSE

The lack of effective molecular biomarkers to monitor idiopathic pulmonary fibrosis (IPF) activity or treatment response remains an unmet clinical need. Herein, we determined the utility of fibroblast activation protein inhibitor for positron emission tomography (FAPI PET) imaging in a mouse model of pulmonary fibrosis.

METHODS

Pulmonary fibrosis was induced by intratracheal administration of bleomycin (1 U/kg) while intratracheal saline was administered to control mice. Subgroups from each cohort (n = 3-5) underwent dynamic 1 h PET/CT after intravenously injecting FAPI-46 radiolabeled with gallium-68 ([⁶⁸ Ga]Ga-FAPI-46) at 7 days and 14 days following disease induction. Animals were sacrificed following imaging for ex vivo gamma counting and histologic correlation. [⁶⁸ Ga]Ga-FAPI-46 uptake was quantified and reported as percent injected activity per cc (%IA/cc) or percent injected activity (%IA). Lung CT density in Hounsfield units (HU) was also correlated with histologic examinations of lung fibrosis.

RESULTS

CT only detected differences in the fibrotic response at 14 days post-bleomycin administration. [⁶⁸ Ga]Ga-FAPI-46 lung uptake was significantly higher in the bleomycin group than in control subjects at 7 days and 14 days. Significantly (P = 0.0012) increased [⁶⁸ Ga]Ga-FAPI-46 lung uptake in the bleomycin groups at 14 days (1.01 ± 0.12%IA/cc) vs. 7 days (0.33 ± 0.09%IA/cc) at 60 min post-injection of the tracer was observed. These findings were consistent with an increase in both fibrinogenesis and FAP expression as seen in histology.

CONCLUSION

CT was unable to assess disease activity in a murine model of IPF. Conversely, FAPI PET detected both the presence and activity of lung fibrogenesis, making it a promising tool for assessing early disease activity and evaluating the efficacy of therapeutic interventions in lung fibrosis patients.

Uncovering Mediators of Collagen Degradation in the Tumor Microenvironment

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Collagen cleavage in tumors is primarily mediated by FAP⁺ cancer-associated fibroblasts.

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Collagen fibers are cleaved in an MMP-dependent manner.

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Released collagen fragments are internalized by M2-like tumor-associated macrophages and cancer-associated fibroblasts.

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The mannose receptor is central in collagen internalization by tumor-associated macrophages.

Increased remodeling of the extracellular matrix in malignant tumors has been shown to correlate with tumor aggressiveness and a poor prognosis. This remodeling involves degradation of the original extracellular matrix (ECM) and deposition of a new tumor-supporting ECM. The main constituent of the ECM is collagen and collagen turnover mainly occurs in a sequential manner, where initial proteolytic cleavage of the insoluble fibers is followed by cellular internalization of large well-defined collagen fragments for lysosomal degradation. However, despite extensive research in the field, a lack of consensus on which cell types within the tumor microenvironment express the involved proteases still exists. Furthermore, the relative contribution of different cell types to collagen internalization is not well-established. Here, we developed quantitative ex vivo collagen degradation assays and show that the proteases responsible for the initial collagen cleavage in two murine syngeneic tumor models are matrix metalloproteinases produced by cancer-associated fibroblasts and that collagen degradation fragments are endocytosed primarily by tumor-associated macrophages and cancer-associated fibroblasts from the tumor stroma. Using tumors from mannose receptor-deficient mice, we show that this receptor is essential for collagen-internalization by tumor-associated macrophages. Together, these findings identify the cell types responsible for the entire collagen degradation pathway, from initial cleavage to endocytosis of fragments for intracellular degradation.

Immune Modulatory Properties of Collagen in Cancer

During tumor growth the extracellular matrix (ECM) undergoes dramatic remodeling. The normal ECM is degraded and substituted with a tumor-specific ECM, which is often of higher collagen density and increased stiffness. The structure and collagen density of the tumor-specific ECM has been associated with poor prognosis in several types of cancer. However, the reason for this association is still largely unknown. Collagen can promote cancer cell growth and migration, but recent studies have shown that collagens can also affect the function and phenotype of various types of tumor-infiltrating immune cells such as tumor-associated macrophages (TAMs) and T cells. This suggests that tumor-associated collagen could have important immune modulatory functions within the tumor microenvironment, affecting cancer progression as well as the efficacy of cancer immunotherapy. The effects of tumor-associated collagen on immune cells could help explain why a high collagen density in tumors is often correlated with a poor prognosis. Knowledge about immune modulatory functions of collagen could potentially identify targets for improving current cancer therapies or for development of new treatments. In this review, the current knowledge about the ability of collagen to influence T cell activity will be summarized. This includes direct interactions with T cells as well as induction of immune suppressive activity in other immune cells such as macrophages. Additionally, the potential effects of collagen on the efficacy of cancer immunotherapy will be discussed.

[18F]FAPI-42 PET imaging in cancer patients: optimal acquisition time, biodistribution, and comparison with [68Ga]Ga-FAPI-04

PURPOSE

[¹⁸F]FAPI-42 is a new fibroblast activation protein (FAP)-specific tracer used for cancer imaging. Here, we describe the optimal acquisition time and in vivo evaluation of [¹⁸F]FAPI-42 and compared intra-individual biodistribution, tumor uptake, and detection ability to [⁶⁸Ga]Ga-FAPI-04.

METHODS

A total of 22 patients with various types of cancer received [¹⁸F]FAPI-42 whole-body positron emission tomography/computed tomography (PET/CT). Among them, 4 patients underwent PET/CT scans, including an early dynamic 20-min, static 1-h, and static 2-h scans. The in vivo biodistribution in normal organs and tumor uptake were semiquantitatively evaluated using the standardized uptake value (SUV) and tumor-to-background ratio (TBR). Furthermore, both [¹⁸F]FAPI-42 and [⁶⁸Ga]Ga-FAPI-04 PET/CT were performed in 12 patients to compare biodistribution, tumor uptake, and tumor detection ability.

RESULTS

[¹⁸F]FAPI-42 uptake in the tumors was rapid and reached a high level with an average SUVmax of 15.8 at 18 min, which stayed at a similarly high level to 2 h. The optimal image acquisition time for [¹⁸F]FAPI-42 was determined to be 1 h postinjection. For tumor detection, [¹⁸F]FAPI-42 had a high uptake and could be clearly visualized in the lesions. Compared to [⁶⁸Ga]Ga-FAPI-04, [¹⁸F]FAPI-42 had the same detectability for 144 positive lesions. In addition, [¹⁸F]FAPI-42 showed a higher SUVmax in liver and bone lesions (P < 0.05) and higher TBRs in liver, bone, lymph node, pleura, and peritoneal lesions (all P < 0.05).

CONCLUSION

The present study demonstrates that the optimal image acquisition time of [¹⁸F]FAPI-42 is 1 h postinjection and that [¹⁸F]FAPI-42 exhibits comparable lesion detectability to [⁶⁸Ga]Ga-FAPI-04.

TRIAL REGISTRATION

Chinese Clinical Trial Registry (ChiCTR2100045757).

New Frontiers in Cancer Imaging and Therapy Based on Radiolabeled Fibroblast Activation Protein Inhibitors: A Rational Review and Current Progress

Over the past decade, the tumor microenvironment (TME) has become a new paradigm of cancer diagnosis and therapy due to its unique biological features, mainly the interconnection between cancer and stromal cells. Within the TME, cancer-associated fibroblasts (CAFs) demonstrate as one of the most critical stromal cells that regulate tumor cell growth, progression, immunosuppression, and metastasis. CAFs are identified by various biomarkers that are expressed on their surfaces, such as fibroblast activation protein (FAP), which could be utilized as a useful target for diagnostic imaging and treatment. One of the advantages of targeting FAP-expressing CAFs is the absence of FAP expression in quiescent fibroblasts, leading to a controlled targetability of diagnostic and therapeutic compounds to the malignant tumor stromal area using radiolabeled FAP-based ligands. FAP-based radiopharmaceuticals have been investigated strenuously for the visualization of malignancies and delivery of theranostic radiopharmaceuticals to the TME. This review provides an overview of the state of the art in TME compositions, particularly CAFs and FAP, and their roles in cancer biology. Moreover, relevant reports on radiolabeled FAP inhibitors until the year 2021 are highlighted-as well as the current limitations, challenges, and requirements for those radiolabeled FAP inhibitors in clinical translation.

Cholecystokinin Receptor Antagonist Improves Efficacy of Chemotherapy in Murine Models of Pancreatic Cancer by Altering the Tumor Microenvironment

Pancreatic cancer is resistant to chemotherapy in part due to the dense desmoplastic fibrosis surrounding the tumor, the immunosuppressive cells in the tumor microenvironment (TME), and the early rate of metastases. In this study, we examined the effects of a CCK receptor antagonist, proglumide, alone and in combination with gemcitabine in murine models of pancreatic cancer. Tumor growth rate, metastases, and survival were assessed in mice bearing syngeneic murine or human pancreatic tumors treated with PBS (control), gemcitabine, proglumide, or the combination of gemcitabine and proglumide. Excised tumors were evaluated histologically for fibrosis, immune cells, molecular markers, and uptake of chemotherapy by mass spectroscopy. Peripheral blood was analyzed with a microRNAs biomarker panel associated with fibrosis and oncogenesis. Differentially expressed genes between tumors of mice treated with gemcitabine monotherapy and combination therapy were compared by RNAseq. When given in combination the two compounds exhibited inhibitory effects by decreasing tumor growth rate by 70%, metastases, and prolonging survival. Proglumide monotherapy altered the TME by decreasing fibrosis, increasing intratumoral CD8+ T-cells, and decreasing arginase-positive cells, thus rendering the tumor sensitive to chemotherapy. Proglumide altered the expression of genes involved in fibrosis, epithelial-mesenchymal transition, and invasion. CCK-receptor antagonism with proglumide renders pancreatic cancer susceptible to chemotherapy.

Development of a Bispecific Antibody-Based Platform for Retargeting of Capsid Modified AAV Vectors

A major limiting factor for systemically delivered gene therapies is the lack of novel tissue specific AAV (Adeno-associated virus) derived vectors. Bispecific antibodies can be used to redirect AAVs to specific target receptors. Here, we demonstrate that the insertion of a short linear epitope “2E3” derived from human proprotein-convertase subtilisin/kexin type 9 (PCSK9) into different surface loops of the VP capsid proteins can be used for AAV de-targeting from its natural receptor(s), combined with a bispecific antibody-mediated retargeting. We chose to target a set of distinct disease relevant membrane proteins—fibroblast activation protein (FAP), which is upregulated on activated fibroblasts within the tumor stroma and in fibrotic tissues, as well as programmed death-ligand 1 (PD-L1), which is strongly upregulated in many cancers. Upon incubation with a bispecific antibody recognizing the 2E3 epitope and FAP or PD-L1, the bispecific antibody/rAAV complex was able to selectively transduce receptor positive cells. In summary, we developed a novel, rationally designed vector retargeting platform that can target AAVs to a new set of cellular receptors in a modular fashion. This versatile platform may serve as a valuable tool to investigate the role of disease relevant cell types and basis for novel gene therapy approaches.

The functional cross talk between cancer cells and cancer associated fibroblasts from a cancer mechanics perspective

The function of biological tissues in health and disease is regulated at cellular level and is highly influenced by the physical microenvironment, through the interaction of forces between cells and ECM, which are perceived through mechanosensing pathways. In cancer, both chemical and physical signaling cascades and their interactions are involved during cell-cell and cell-ECM communications to meet requirements of tumor growth. Among stroma cells, cancer associated fibroblasts (CAFs) play key role in tumor growth and pave the way for cancer cells to initiate metastasis and invasion to other tissues, and without recruitment of CAFs, the process of cancer invasion is dysfunctional. This is through an intense chemical and physical cross talks with tumor cells, and interactive remodeling of ECM. During such interaction CAFs apply traction forces and depending on the mechanical properties, deform ECM and in return receive physical signals from the micromechanical environment. Such interaction leads to ECM remodeling by manipulating ECM structure and its mechanical properties. The results are in form of deposition of extra fibers, stiffening, rearrangement and reorganization of fibrous structure, and degradation which are due to a complex secretion and expression of different markers triggered by mechanosensing of tumor cells, specially CAFs. Such events define cancer progress and invasion of cancer cells. A systemic knowledge of chemical and physical factors provides a holistic view of how cancer process and enhances the current treatment methods to provide more diversity among targets that involves tumor cells and ECM structure.

Oncogenesis, Microenvironment Modulation and Clinical Potentiality of FAP in Glioblastoma: Lessons Learned from Other Solid Tumors

Currently, glioblastoma (GBM) is the most common malignant tumor of the central nervous system in adults. Fibroblast activation protein (FAP) is a member of the dipeptidyl peptidase family, which has catalytic activity and is engaged in protein recruitment and scaffolds. Recent studies have found that FAP expression in different types of cells within the GBM microenvironment is typically upregulated compared with that in lower grade glioma and is most pronounced in the mesenchymal subtype of GBM. As a marker of cancer-associated fibroblasts (CAFs) with tumorigenic activity, FAP has been proven to promote tumor growth and invasion via hydrolysis of molecules such as brevican in the extracellular matrix and targeting of downstream pathways and substrates, such as fibroblast growth factor 21 (FGF21). In addition, based on its ability to suppress antitumor immunity in GBM and induce temozolomide resistance, FAP may be a potential target for immunotherapy and reversing temozolomide resistance; however, current studies on therapies targeting FAP are still limited. In this review, we summarized recent progress in FAP expression profiling and the understanding of the biological function of FAP in GBM and raised the possibility of FAP as an imaging biomarker and therapeutic target.

Identification of BR102910 as a selective fibroblast activation protein (FAP) inhibitor

Fibroblast activation protein (FAP) belongs to the family of prolyl-specific serine proteases and displays both exopeptidase and endopeptidase activities. FAP expression is undetectable in most normal adult tissues, but is greatly upregulated in sites of tissue remodeling, which include fibrosis, inflammation and cancer. Due to its restricted expression pattern and dual enzymatic activities, FAP inhibition is investigated as a therapeutic option for several diseases. In the present study, we described the structure-activity relationship of several synthesized compounds against DPPIV and prolyl oligopeptidase (PREP). In particular, BR102910 (compound 24) showed nanomolar potency and high selectivity. Moreover, the in vivo FAP inhibition study of BR102910 (compound 24) using C57BL/6J mice demonstrated exceptional profiles and satisfactory FAP inhibition efficacy. Based on excellent in vitro and in vivo profiles, the potential of BR102910 (compound 24) as a lead candidate for the treatment of type 2 diabetes is considered.

The role of fibroblast activation protein in health and malignancy

Fibroblast activation protein-α (FAP) is a type-II transmembrane serine protease expressed almost exclusively to pathological conditions including fibrosis, arthritis, and cancer. Across most cancer types, elevated FAP is associated with worse clinical outcomes. Despite the clear association between FAP and disease severity, the biological reasons underlying these clinical observations remain unclear. Here we review basic FAP biology and FAP's role in non-oncologic and oncologic disease. We further explore how FAP may worsen clinical outcomes via its effects on extracellular matrix remodeling, intracellular signaling regulation, angiogenesis, epithelial-to-mesenchymal transition, and immunosuppression. Lastly, we discuss the potential to exploit FAP biology to improve clinical outcomes.

You Say You Want a Resolution (of Fibrosis)

In pathological fibrosis, aberrant tissue remodeling with excess extracellular matrix leads to organ dysfunction and eventual morbidity. Diseases of fibrosis create significant global health and economic burdens and are often deadly. Although fibrosis has traditionally been thought of as an irreversible process, a growing body of evidence demonstrates that organ fibrosis can reverse in certain circumstances, especially if an underlying cause of injury can be removed. This body of evidence has uncovered more and more contributors to persistent and nonresolving tissue fibrosis. Here, we review the present knowledge on resolution of organ fibrosis and restoration of near-normal tissue architecture. We emphasize three critical areas of tissue homeostasis that are necessary for fibrosis resolution, namely, the elimination of matrix-producing cells, the clearance of excess matrix, and the regeneration of normal tissue constituents. In so doing, we also highlight how profibrotic pathways interact with one another and where there may be therapeutic opportunities to intervene and remediate pathological persistent fibrosis.

Human Autopsy-Derived Scalp Fibroblast Biobanking for Age-Related Neurodegenerative Disease Research

The Arizona Study of Aging and Neurodegenerative Disorders/Brain and Body Donation Program at Banner Sun Health Research Institute (BSHRI) is a longitudinal clinicopathological study with a current enrollment of more than 900 living subjects for aging and neurodegenerative disease research. Annual clinical assessments are done by cognitive and movement neurologists and neuropsychologists. Brain and body tissues are collected at a median postmortem interval of 3.0 h for neuropathological diagnosis and banking. Since 2018, the program has undertaken banking of scalp fibroblasts derived from neuropathologically characterized donors with Alzheimer’s disease, Parkinson’s disease, and other neurodegenerative diseases. Here, we describe the procedure development and cell characteristics from 14 male and 15 female donors (mean ± SD of age: 83.6 ± 12.2). Fibroblasts from explant cultures were banked at passage 3. The results of mRNA analysis showed positive expression of fibroblast activation protein, vimentin, fibronectin, and THY1 cell surface antigen. We also demonstrated that the banked fibroblasts from a postmortem elderly donor were successfully reprogramed to human-induced pluripotent stem cells (hiPSCs). Taken together, we have demonstrated the successful establishment of a human autopsy-derived fibroblast banking program. The cryogenically preserved cells are available for request at the program website of the BSHRI.

Three Distinct Stroma Types in Human Pancreatic Cancer Identified by Image Analysis of Fibroblast Subpopulations and Collagen

PURPOSE

Cancer-associated fibroblasts have emerged to be highly heterogenous and can play multifaceted roles in dictating pancreatic ductal adenocarcinoma (PDAC) progression, immunosuppression, and therapeutic response, highlighting the need for a deeper understanding of stromal heterogeneity between patients and even within a single tumor. We hypothesized that image analysis of fibroblast subpopulations and collagen in PDAC tissues might guide stroma-based patient stratification to predict clinical outcomes and tumor characteristics.

EXPERIMENTAL DESIGN

A novel multiplex IHC-based image analysis system was established to digitally differentiate fibroblast subpopulations. Using whole-tissue slides from 215 treatment-naïve PDACs, we performed concurrent quantification of principal fibroblast subpopulations and collagen and defined three stroma types: collagen-rich stroma, fibroblast activation protein α (FAP)-dominant fibroblast-rich stroma, and α smooth muscle actin (ACTA2)-dominant fibroblast-rich stroma. These stroma types were assessed for the associations with cancer-specific survival by multivariable Cox regression analyses and with clinicopathologic factors, including CD8⁺ cell density.

RESULTS

FAP-dominant fibroblasts and ACTA2-dominant fibroblasts represented the principal distinct fibroblast subpopulations in tumor stroma. Stroma types were associated with patient survival, SMAD4 status, and transcriptome signatures. Compared with FAP-dominant fibroblast-rich stroma, collagen-rich stroma correlated with prolonged survival [HR, 0.57; 95% confidence interval (CI), 0.33-0.99], while ACTA2-dominant fibroblast-rich stroma exhibited poorer prognosis (HR, 1.65; 95% CI, 1.06-2.58). FAP-dominant fibroblast-rich stroma was additionally characterized by restricted CD8⁺ cell infiltrates and intense neutrophil infiltration.

CONCLUSIONS

This study identified three distinct stroma types differentially associated with survival, immunity, and molecular features, thereby underscoring the importance of stromal heterogeneity in subtyping pancreatic cancers and supporting the development of antistromal therapies.

Molecular recognition of fibroblast activation protein for diagnostic and therapeutic applications

Fibroblast activation protein (FAP) is a non-classical serine protease expressed predominantly in conditions accompanied by tissue remodeling, particularly cancer. Due to its plasma membrane localization, FAP represents a promising molecular target for tumor imaging and treatment. The unique enzymatic activity of FAP facilitates development of diagnostic and therapeutic tools based on molecular recognition of FAP by substrates and small-molecule inhibitors, in addition to conventional antibody-based strategies. In this review, we provide background on the pathophysiological role of FAP and discuss its potential for diagnostic and therapeutic applications. Furthermore, we present a detailed analysis of the structural patterns crucial for substrate and inhibitor recognition by the FAP active site and determinants of selectivity over the related proteases dipeptidyl peptidase IV and prolyl endopeptidase. We also review published data on targeting of the tumor microenvironment with FAP antibodies, FAP-targeted prodrugs, activity-based probes and small-molecule inhibitors. We describe use of a recently developed, selective FAP inhibitor with low-nanomolar potency in inhibitor-based targeting strategies including synthetic antibody mimetics based on hydrophilic polymers and inhibitor conjugates for PET imaging. In conclusion, recent advances in understanding of the molecular structure and function of FAP have significantly contributed to the development of several tools with potential for translation into clinical practice.

Fibroblast Activation Protein Regulates Lesion Burden and the Fibroinflammatory Response in Apoe-Deficient Mice in a Sexually Dimorphic Manner

Fibroblast activation protein (FAP) has been established as an inducible and mesenchymal cell-specific mediator of disease progression in cancer and fibrosis. Atherosclerosis is a fibroinflammatory disease, and FAP was previously reported to be up-regulated in human atherosclerotic plaques compared with normal vessel. We investigated the spatial and temporal distribution of Fap-expressing cells in a murine model of atherosclerosis and used a genetic approach to determine if and how Fap affected disease progression. Fap was found to be expressed predominantly on vascular smooth muscle cells in lesions of athero-prone Apoe^-/- mice. Global deletion of Fap (Fap^-/-) in Apoe^-/- mice accelerated atherosclerotic disease progression in both males and females, with the effect observed earlier in males. Sex-specific effects on lesion morphology were observed. Relative levels of extracellular matrix, fibrotic, and inflammatory cell content were comparable in lesions in male mice regardless of Fap status. In contrast, lesions in Fap^-/- female mice were characterized by a more fibrotic composition due to a reduction in inflammation, specifically a reduction in Mox macrophages. Combined, these data suggest that Fap restrains the progression of atherosclerosis and may contribute to the sexually dimorphic susceptibility to atherosclerosis by regulating the balance between inflammation (an indicator of vulnerability to plaque rupture) and fibrosis (an indicator of plaque stability).

The role of fibroblast activation protein in progression and development of osteosarcoma cells

To investigate the expression levels of fibroblast activation protein (FAP) in human osteosarcoma tissues and its possible correlations with clinical pathological characteristics of patients with osteosarcoma, and to explore the potential effects of FAP on progression and development of osteosarcoma. Immunohistochemistry (IHC) assay was initially performed to detect the expression levels of FAP in 66 tumor tissues and adjacent non-tumor tissues. Patients were sequentially divided into two groups based on different expression levels of FAP. The correlations between the expression levels of FAP and the clinical pathological characteristics were investigated, and the role of FAP in proliferation, migration, and invasion of osteosarcoma cells was assessed via colony formation, MTT, wound healing, and transwell assays, respectively. The possible effects of FAP on tumor growth and metastasis were evaluated in vivo. We further attempted to reveal the underlying mechanism of FAP involved in tumor growth through bioinformatics and IHC assays. High expression levels of FAP were noted in human osteosarcoma tissues. It also was unveiled that FAP was significantly associated with the tumor size (P = 0.005*) and clinical stage (P = 0.017*). Our data further confirmed that knockdown of FAP remarkably blocked proliferation, migration, and invasion of osteosarcoma cells in vitro, and suppressed tumor growth and metastasis in mice via AKT signaling pathway. The possible role of FAP in progression and development of osteosarcoma could be figured out. Our data may be helpful to develop a novel therapeutic target for the treatment of osteosarcoma.

microRNA-30a attenuates TGF-β1-induced activation of pulmonary fibroblast cell by targeting FAP-α

Idiopathic interstitial pulmonary fibrosis is a common diffuse interstitial lung disease and has poor prognosis. And one of the pathological features of it is persistent fibroblast activation. It was reported that microRNA‐30a was down‐regulated in bronchoalveolar lavage fluid from idiopathic pulmonary fibrosis patients. But whether miR‐30a is involved in fibroblast activation and its specific mechanism is unclear. In this study, we aimed to investigate the role of miR‐30a in fibroblast activation induced by TGF‐β1. We found miR‐30a could targetedly suppress FAP‐α expression. In MRC5 cells, miR‐30a was not only involved in regulating the expression of FAP‐α, col1a and α‐SMA induced by TGF‐β1 but also had a role in cell proliferation with or without TGF‐β1 treatment via regulating FAP‐α expression. Thus, the results indicated that miR‐30a alleviated fibroblast activation by regulating the expression of FAP‐α.

Chimeric Antigen Receptor T Cell Therapy: A Novel Modality for Immune Modulation

Cancer remains a leading cause of death, despite multimodal treatment approaches. Even in patients with a healthy immune response, cancer cells can escape the immune system during tumorigenesis. Cancer cells incapacitate the normal cell-mediated immune system by expressing immune modulation ligands such as programmed death (PD) ligand 1, the B7 molecule, or secreting activators of immune modulators. Chimeric antigen receptor (CAR) T cells were originally designed to target cancer cells. Engineered approaches allow CAR T cells, which possess a simplified yet specific receptor, to be easily activated in limited situations. CAR T cell treatment is a derivative of the antigen-antibody reaction and can be applied to various diseases. In this review, the current successes of CAR T cells in cancer treatment and the therapeutic potential of CAR T cells are discussed.

Dental Tissue and Stem Cells Revisited: New Insights From the Expression of Fibroblast Activation Protein-Alpha

Fibroblast activation protein-α (FAPα) is a membrane protein with dipeptidyl-peptidase and type I collagenase activity and is expressed during fetal growth. At the age of adolescence, FAPα expression is greatly reduced, only emerging in pathologies associated with extracellular matrix remodeling. We determined whether FAPα is expressed in human dental tissue involved in root maturation i.e., dental follicle and apical papilla and in dental pulp tissue. The dental follicle revealed a high concentration of FAPα and vimentin-positive cells within the stromal tissue. A similar observation was made in cell culture and FACS analysis confirmed these as dental follicle stem cells. Within the remnants of the Hertwigs’ epithelial root sheath, we observed FAPα staining in the E-cadherin positive and vimentin-negative epithelial islands. FAPα- and vimentin-positive cells were encountered at the periphery of the islands suggesting an epithelial mesenchymal transition process. Analysis of the apical papilla revealed two novel histological regions; the periphery with dense and parallel aligned collagen type I defined as cortex fibrosa and the inner stromal tissue composed of less compacted collagen defined as medulla. FAPα expression was highly present within the medulla suggesting a role in extracellular matrix remodeling. Dental pulp tissue uncovered a heterogeneous FAPα staining but strong staining was noted within odontoblasts. In vitro studies confirmed the presence of FAPα expression in stem cells of the apical papilla and dental pulp. This study identified the expression of FAPα expression in dental stem cells which could open new perspectives in understanding dental root maturation and odontoblast function.

Fibroblast Activation Protein is a GH Target: A Prospective Study of Patients with Acromegaly Before and After Treatment

BACKGROUND

Fibroblast growth factor 21 (FGF21) is a circulating hormone with pleiotropic metabolic effects, which is inactivated by fibroblast activation protein (FAP). Data regarding interaction between FGF21, FAP, and growth hormone (GH) are limited, but it is noteworthy that collagens are also FAP substrates, since GH potently stimulates collagen turnover.

AIM

To measure circulating FGF21 components, including FAP, in patients with acromegaly before and after disease control.

METHODS

Eighteen patients with active acromegaly were studied at the time of diagnosis and ≥ 6 months after disease control by either surgery or medical treatment. Serum levels of total and active FGF21, β-klotho, FAP, and collagen turnover markers were measured by immunoassays. Expression of putative FGF21-dependent genes were measured in adipose tissue by reverse transcriptase-polymerase chain reaction, body composition assessed by dual-energy x-ray absorptiometry scan, and insulin sensitivity estimated with homeostatic model assessment of insulin resistance (HOMA-IR).

RESULTS

Total FGF21, active FGF21 and β-klotho remained unchanged. Insulin sensitivity and body fat mass increased after disease control but neither correlated with active FGF21. Expression of FGF21-dependent genes did not change after treatment. FAP levels (µg/L) were markedly reduced after treatment [105.6 ± 29.4 vs 62.2 ± 32.4, P < 0.000]. Collagen turnover markers also declined significantly after treatment and ΔFAP correlated positively with ΔProcollagen Type I (P < 0.000) and Type III (P < 0.000).

CONCLUSION

1) Circulating FGF21 and β-klotho do not change in response to acromegaly treatment, 2) FAP concentrations in serum decrease after disease control and correlate positively with collagen turnover markers, and 3) FAP is a hitherto unrecognized GH target linked to collagen turnover.

CLINICAL TRIALS REGISTRATION

NCT00647179.

Vaccine against gastrin, a polyclonal antibody stimulator, decreases pancreatic cancer metastases

Growth of pancreatic cancer is stimulated by gastrin in both a paracrine and an autocrine fashion. Traditional therapies have not significantly improved survival, and recently pancreatic cancer has been deemed a "cold" tumor due to its poor response to immunotherapy. Strategies to improve survival of pancreatic cancer are desperately needed. In the current investigation, we studied the effects of an anti-gastrin cancer vaccine, polyclonal antibody stimulator (PAS; formerly called G17DT and Gastrimmune), used alone or in combination with a programmed cell death receptor (PD)-1 immune checkpoint antibody on pancreatic cancer growth, metastases, and the tumor microenvironment (TME). Immune-competent female C57BL/6 mice bearing syngeneic orthotopic murine pancreatic cancer treated with PAS had significantly smaller tumors and fewer metastases. Examination of the TME demonstrated decreased fibrosis with fewer M2 and more M1 tumor-associated macrophages. Expression of the E-cadherin gene was significantly increased and expression of the TGFβR2 gene was decreased compared with controls. Mice treated with PAS or the combination of PAS and PD-1 antibody exhibited significantly less tumor expression of phospho-paxillin, the focal adhesion protein β-catenin, and matrix metalloproteinase-7. This study suggests that inhibition of the cancer-promoting effects of gastrin in pancreatic cancer can decrease metastases by altering the TME and decreasing pathways that activate the epithelial mesenchymal transition. The PAS vaccine appears to change the TME, making it more susceptible to therapy with an immune checkpoint antibody. This novel combination of two immunotherapies may improve survival of pancreatic cancer by decreasing both tumor growth and metastasis formation.NEW & NOTEWORTHY Survival from advanced pancreatic cancer is poor, in part due to dense fibrosis of the tumor microenvironment, increased number of M2-polarized macrophages that promote angiogenesis and invasion, and lack of "target-specific" therapy. Herein, we report that a tumor vaccine that selectively targets gastrin decreases pancreatic cancer growth and metastases. Furthermore, the gastrin vaccine polyclonal antibody stimulator alters the tumor microenvironment rendering it more responsive to immunotherapy with a programmed cell death receptor-1 immune checkpoint antibody.

Novel Small Molecule-Derived, Highly Selective Substrates for Fibroblast Activation Protein (FAP)

Fibroblast activation protein (FAP) is a proline-selective serine protease. It is hardly expressed in healthy adult tissue but upregulated in tissue remodeling sites associated with several diseases including epithelial cancer types, atherosclerosis, arthritis and fibrosis. Ongoing research aims at clinical implementation of FAP as a biomarker for these diseases. Several immunochemical methods that quantify FAP expression have been reported. An alternative/complementary approach focuses on quantification of FAP's enzymatic activity. Developing an activity-based assay for FAP has nonetheless proven challenging because of selectivity issues with respect to prolyl oligopeptidase (PREP). Here, we present substrate-type FAP probes that are structurally derived from a FAP-inhibitor (UAMC1110) that we published earlier. Both cleavage efficiency and FAP-selectivity of the best compounds in the series equal or surpass the most advanced peptide-based FAP substrates reported to date. Finally, proof-of-concept is provided that 4-aminonaphthol containing probes can spatially localize FAP activity in biological samples.

Fibroblast activation protein restrains adipogenic differentiation and regulates matrix-mediated mTOR signaling

Obesity is a risk factor for multiple diseases, including diabetes, cardiovascular disease, and cancer. Within obese adipose tissue, multiple factors contribute to creating a disease-promoting environment, including metabolic dysfunction, inflammation, and fibrosis. Recent evidence points to fibrotic responses, particularly extracellular matrix remodeling, in playing a highly functional role in the pathogenesis of obesity. Fibroblast activation protein plays an essential role in remodeling collagen-rich matrices in the context of fibrosis and cancer. We observed that FAP-null mice have increased weight compared to wild-type controls, and so investigated the role of FAP in regulating diet-induced obesity. Using genetically engineered mouse models and in-vitro cell-derived matrices, we demonstrate that FAP expression by pre-adipocytes restrains adipogenic differentiation. We further show that FAP-mediated matrix remodeling alters lipid metabolism in part by regulating mTOR signaling. The impact of FAP on adipogenic differentiation and mTOR signaling together confers resistance to diet-induced obesity. The critical role of ECM remodeling in regulating obesity offers new potential targets for therapy.

Loss of cells expressing fibroblast activation protein has variable effects in models of TGF-β and chronic bleomycin-induced fibrosis

Fibroblast activation protein (FAP), a cell surface serine protease, is upregulated on a subset of activated fibroblasts (often distinct from α-smooth muscle actin-expressing myofibroblasts) associated with matrix remodeling, including fibroblasts in idiopathic pulmonary fibrosis (Acharya PS, Zukas A, Chandan V, Katzenstein AL, Puré E. Hum Pathol 37: 352-360, 2006.). As FAP⁺ fibroblasts could be pivotal in either breakdown and/or production of collagen and other matrix components, the goal of this study was to define the role of FAP⁺ cells in pulmonary fibrosis in two established, but different, mouse models of chronic lung fibrosis: repetitive doses of intratracheal bleomycin and a single dose of an adenoviral vector encoding constitutively active TGF-β1 (Ad-TGFβ). To determine their role in fibrotic remodeling, FAP-expressing cells were depleted by injection of T cells expressing a chimeric antigen receptor specific for murine FAP in mice with established fibrosis. The contribution of FAP to the function of FAP-expressing cells was assessed in FAP knockout mice. Using histological analyses, quantification of soluble collagen content, and flow cytometry, we found that loss of FAP⁺ cells exacerbated fibrosis in the bleomycin model, a phenotype largely recapitulated by the genetic deletion of FAP, indicating that FAP plays a role in this model. In contrast, depletion of FAP⁺ cells or genetic deletion of FAP had little effect in the Ad-TGFβ model highlighting the potential for distinct mechanisms driving fibrosis depending on the initiating insult. The role of FAP in human lung fibrosis will need to be well understood to guide the use of FAP-targeted therapeutics that are being developed.

IL-33-mediated IL-13 secretion by ST2+ Tregs controls inflammation after lung injury

Acute respiratory distress syndrome is an often fatal disease that develops after acute lung injury and trauma. How released tissue damage signals, or alarmins, orchestrate early inflammatory events is poorly understood. Herein we reveal that IL-33, an alarmin sequestered in the lung epithelium, is required to limit inflammation after injury due to an unappreciated capacity to mediate Foxp3+ Treg control of local cytokines and myeloid populations. Specifically, Il33-/- mice are more susceptible to lung damage-associated morbidity and mortality that is typified by augmented levels of the proinflammatory cytokines and Ly6Chi monocytes in the bronchoalveolar lavage fluid. Local delivery of IL-33 at the time of injury is protective but requires the presence of Treg cells. IL-33 stimulates both mouse and human Tregs to secrete IL-13. Using Foxp3Cre × Il4/Il13fl/fl mice, we show that Treg expression of IL-13 is required to prevent mortality after acute lung injury by controlling local levels of G-CSF, IL-6, and MCP-1 and inhibiting accumulation of Ly6Chi monocytes. Our study identifies a regulatory mechanism involving IL-33 and Treg secretion of IL-13 in response to tissue damage that is instrumental in limiting local inflammatory responses and may shape the myeloid compartment after lung injury.

Delayed resolution of bleomycin-induced pulmonary fibrosis in absence of MMP13 (collagenase 3)

Matrix metalloprotease 13 (MMP13) deficiency in pulmonary fibrosis has described contradictory phenotypes on inflammatory and fibrotic responses after lung injury, and its role during lung fibrosis resolution is still undefined. MMP13 has been considered the main collagenase in rodents, and the remodeling of fibrillar collagen is widely attributed to the action of this enzyme. In this study we aimed to explore the role of MMP13 during lung fibrosis progression and resolution. Lung fibrosis was induced by intratracheal instillation, and inflammatory, fibrotic, and resolution stages were evaluated in Mmp13-null and wild-type (WT) mice. Bronchoalveolar lavage fluid was taken for cytokine array analysis and activity of gelatinases. Our results showed that MMP13 is upregulated mainly during two stages after lung injury, inflammation and resolution of fibrosis, and it is mainly expressed by alveolar and interstitial macrophages. Mmp13-null mice exhibited more extensive inflammation at 7 days after bleomycin treatment, and it was characterized by increased macrophage infiltration and significant alterations in proinflammatory cytokines. We also documented that Mmp13-deficient mice experienced more severe and prolonged lung fibrosis compared with WT mice. Delayed resolution in Mmp13-deficient lungs was characterized by a decreased overall collagenolytic activity and persistent fibrotic foci associated with emphysema-like areas. Together, our findings indicate that MMP13 plays an antifibrotic role and its activity is crucial in lung repair and restoration of tissue integrity during fibrosis resolution.