The pericyte antigen RGS5 in perivascular soft tissue tumors

Mesenchymal Tumors of the Skin: A Review

Mesenchymal tumors of the skin are rare and clinically heterogeneous, and can represent diagnostic challenge for pathologists. Most of these lesions have overlapping clinical and histological features, thus the understanding of architectural patterns, cytoplasmic and stromal features can facilitate proper diagnosis. Anatomic site may be an important factor in the differential diagnosis, as are patient's age and sex. Ancillary tests are often required and can be useful to rule out other entities. Molecular diagnostics is playing an increasingly important role in the diagnosis of soft tissue neoplasms. Here, we review clinical, histological, and molecular features of some of the most common of these uncommon entities including benign and malignant lesions.

Single-cell landscape of undifferentiated pleomorphic sarcoma

Undifferentiated pleomorphic sarcoma (UPS) is a highly aggressive malignant soft tissue tumor with a poor prognosis; however, the identity and heterogeneity of tumor populations remain elusive. Here, eight major cell clusters were identified through the RNA sequencing of 79,569 individual cells of UPS. UPS originates from mesenchymal stem cells (MSCs) and features undifferentiated subclusters. UPS subclusters were predicted to exist in two bulk RNA datasets, and had a prognostic value in The Cancer Genome Atlas (TCGA) dataset. The functional heterogeneity of malignant UPS cells and the immune microenvironment were characterized. Additionally, the fused cells were innovatively detected by expressing both monocyte/macrophage markers and other subcluster-associated genes. Based on the ligand-receptor interaction analysis, cellular interactions with epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) were abundant. Furthermore, 73% of patients with UPS (48/66) showed positive EGFR expression, which was associated with a poor prognosis. EGFR blockade with cetuximab inhibited tumor growth in a patient-derived xenograft model. Our transcriptomic studies delineate the landscape of UPS intratumor heterogeneity and serve as a foundational resource for further discovery and therapeutic exploration.

Differential pericyte marker expression in craniofacial benign and malignant vascular tumors

BACKGROUND

Vascular anomalies and tumors are common in the head, neck, and craniofacial areas and are associated with abnormalities in the angiomatous architecture. However, the etiology and molecular basis for the pathogenesis of most vascular lesions are still unknown. Pericytes are mural cells that surround endothelial cells. Besides angiogenesis and other physiological functions, pericytes play an important role in vascularized tissue repair and as resident mesenchymal stem/progenitor cells. Perivascular cells demonstrate a distinct immunohistochemical profile, including expression of alpha-smooth muscle actin (α-SMA), CD146, CD105, and PDGFRβ, without endothelial differentiation (absence of CD31 and CD34 immunoreactivity). These pericyte markers have been shown to be expressed in soft tissue hemangiomas. However, they have not been fully examined in intraosseous hemangiomas.

METHODS

In this study, we compared mesenchymal stem cell (MSC) expression of CD146 and α-SMA markers in pericytes from hemangiomas from different tissues and malignant vascular tumors.

RESULTS

The results demonstrated an increased expression of pericyte markers in perivascular cells of benign hemangiomas, especially intraosseous hemangiomas and a significantly reduced expression of pericyte markers in malignant angiosarcomas.

CONCLUSION

The evidence provides insight into the function of pericytes in vascular tumors and suggests their role in vascular tumor disease types.

Dysregulation of murine long noncoding single-cell transcriptome in nonalcoholic steatohepatitis and liver fibrosis

LncRNAs comprise a heterogeneous class of RNA-encoding genes typified by low expression, nuclear enrichment, high tissue-specificity, and functional diversity, but the vast majority remain uncharacterized. Here, we assembled the mouse liver noncoding transcriptome from >2000 bulk RNA-seq samples and discovered 48,261 liver-expressed lncRNAs, a majority novel. Using these lncRNAs as a single-cell transcriptomic reference set, we elucidated lncRNA dysregulation in mouse models of high fat diet-induced nonalcoholic steatohepatitis and carbon tetrachloride-induced liver fibrosis. Trajectory inference analysis revealed lncRNA zonation patterns across the liver lobule in each major liver cell population. Perturbations in lncRNA expression and zonation were common in several disease-associated liver cell types, including nonalcoholic steatohepatitis-associated macrophages, a hallmark of fatty liver disease progression, and collagen-producing myofibroblasts, a central feature of liver fibrosis. Single-cell-based gene regulatory network analysis using bigSCale2 linked individual lncRNAs to specific biological pathways, and network-essential regulatory lncRNAs with disease-associated functions were identified by their high network centrality metrics. For a subset of these lncRNAs, promoter sequences of the network-defined lncRNA target genes were significantly enriched for lncRNA triplex formation, providing independent mechanistic support for the lncRNA-target gene linkages predicted by the gene regulatory networks. These findings elucidate liver lncRNA cell-type specificities, spatial zonation patterns, associated regulatory networks, and temporal patterns of dysregulation during hepatic disease progression. A subset of the liver disease-associated regulatory lncRNAs identified have human orthologs and are promising candidates for biomarkers and therapeutic targets.

RGS proteins and their roles in cancer: friend or foe?

As negative modulators of G-protein-coupled receptors (GPCRs) signaling, regulators of G protein signaling (RGS) proteins facilitate various downstream cellular signalings through regulating kinds of heterotrimeric G proteins by stimulating the guanosine triphosphatase (GTPase) activity of G-protein α (Gα) subunits. The expression of RGS proteins is dynamically and precisely mediated by several different mechanisms including epigenetic regulation, transcriptional regulation -and post-translational regulation. Emerging evidence has shown that RGS proteins act as important mediators in controlling essential cellular processes including cell proliferation, survival -and death via regulating downstream cellular signaling activities, indicating that RGS proteins are fundamentally involved in sustaining normal physiological functions and dysregulation of RGS proteins (such as aberrant expression of RGS proteins) is closely associated with pathologies of many diseases such as cancer. In this review, we summarize the molecular mechanisms governing the expression of RGS proteins, and further discuss the relationship of RGS proteins and cancer.

Single-Cell RNA-Seq Reveals Transcriptomic Heterogeneity and Post-Traumatic Osteoarthritis-Associated Early Molecular Changes in Mouse Articular Chondrocytes

Articular cartilage is a connective tissue lining the surfaces of synovial joints. When the cartilage severely wears down, it leads to osteoarthritis (OA), a debilitating disease that affects millions of people globally. The articular cartilage is composed of a dense extracellular matrix (ECM) with a sparse distribution of chondrocytes with varying morphology and potentially different functions. Elucidating the molecular and functional profiles of various chondrocyte subtypes and understanding the interplay between these chondrocyte subtypes and other cell types in the joint will greatly expand our understanding of joint biology and OA pathology. Although recent advances in high-throughput OMICS technologies have enabled molecular-level characterization of tissues and organs at an unprecedented resolution, thorough molecular profiling of articular chondrocytes has not yet been undertaken, which may be in part due to the technical difficulties in isolating chondrocytes from dense cartilage ECM. In this study, we profiled articular cartilage from healthy and injured mouse knee joints at a single-cell resolution and identified nine chondrocyte subtypes with distinct molecular profiles and injury-induced early molecular changes in these chondrocytes. We also compared mouse chondrocyte subpopulations to human chondrocytes and evaluated the extent of molecular similarity between mice and humans. This work expands our view of chondrocyte heterogeneity and rapid molecular changes in chondrocyte populations in response to joint trauma and highlights potential mechanisms that trigger cartilage degeneration.

Single-Cell Transcriptomic Analysis of Tumor-Derived Fibroblasts and Normal Tissue-Resident Fibroblasts Reveals Fibroblast Heterogeneity in Breast Cancer

Cancer-associated fibroblasts (CAFs) are a prominent stromal cell type in solid tumors and molecules secreted by CAFs play an important role in tumor progression and metastasis. CAFs coexist as heterogeneous populations with potentially different biological functions. Although CAFs are a major component of the breast cancer stroma, molecular and phenotypic heterogeneity of CAFs in breast cancer is poorly understood. In this study, we investigated CAF heterogeneity in triple-negative breast cancer (TNBC) using a syngeneic mouse model, BALB/c-derived 4T1 mammary tumors. Using single-cell RNA sequencing (scRNA-seq), we identified six CAF subpopulations in 4T1 tumors including: 1) myofibroblastic CAFs, enriched for α-smooth muscle actin and several other contractile proteins; 2) ‘inflammatory’ CAFs with elevated expression of inflammatory cytokines; and 3) a CAF subpopulation expressing major histocompatibility complex (MHC) class II proteins that are generally expressed in antigen-presenting cells. Comparison of 4T1-derived CAFs to CAFs from pancreatic cancer revealed that these three CAF subpopulations exist in both tumor types. Interestingly, cells with inflammatory and MHC class II-expressing CAF profiles were also detected in normal breast/pancreas tissue, suggesting that these phenotypes are not tumor microenvironment-induced. This work enhances our understanding of CAF heterogeneity, and specifically targeting these CAF subpopulations could be an effective therapeutic approach for treating highly aggressive TNBCs.

Sarcoma Tumor Microenvironment

Components of the tumor microenvironment (TME) are known to play an essential role during malignant progression, but often in a context-dependent manner. In bone and soft tissue sarcomas, disease-regulatory activities in the TME remain largely uncharacterized. This chapter introduces the cellular, structural, and chemical composition of the sarcoma TME from a pathobiological and therapeutic perspective.Sarcomas are malignant tumors with diverse features when it comes to primary tumor appearance, metastatic potential, and response to treatment. Many of the classic subtypes are mainly composed of malignant cells and are therefore assumed to be committed to autocrine signaling. Some of the tumors are infiltrated by immune cells and contain necrotic areas or excessive amounts of extracellular matrix (ECM) that regulates tissue stiffness and interstitial fluid pressure. Vascular invasion and blood vessel characteristics can in some instances be considered in the prognostic setting.Further insights into the disease-regulatory activities of the sarcoma TME will provide essential knowledge on how to develop successful combination treatments targeting not only malignant cells, but also their routes of nutrition and ability to shield themselves toward existing therapy.

Single cell RNA-seq study of wild type and Hox9,10,11 mutant developing uterus

The uterus is a remarkable organ that must guard against infections while maintaining the ability to support growth of a fetus without rejection. The Hoxa10 and Hoxa11 genes have previously been shown to play essential roles in uterus development and function. In this report we show that the Hoxa9,10,11, Hoxc9,10,11, Hoxd9,10,11 genes play a redundant role in the formation of uterine glands. In addition, we use single cell RNA-seq to create a high resolution gene expression atlas of the developing wild type mouse uterus. Cell types and subtypes are defined, for example dividing endothelial cells into arterial, venous, capillary, and lymphatic, while epithelial cells separate into luminal and glandular subtypes. Further, a surprising heterogeneity of stromal and myocyte cell types are identified. Transcription factor codes and ligand/receptor interactions are characterized. We also used single cell RNA-seq to globally define the altered gene expression patterns in all developing uterus cell types for two Hox mutants, with 8 or 9 mutant Hox genes. The mutants show a striking disruption of Wnt signaling as well as the Cxcl12/Cxcr4 ligand/receptor axis.

Pericytes in Sarcomas and Other Mesenchymal Tumors

Tumors of mesenchymal origin are a diverse group, with >130 distinct entities currently recognized by the World Health Organization. A subset of mesenchymal tumors grow or invade in a perivascular fashion, and their potential relationship to pericytes is a matter of ongoing interest. In fact, multiple intersections exist between pericytes and tumors of mesenchymal origin. First, pericytes are the likely cell of origin for a group of mesenchymal tumors with a common perivascular growth pattern. These primarily benign tumors grow in a perivascular fashion and diffusely express canonical pericyte markers such as CD146, smooth muscle actin (SMA), platelet-derived growth factor receptor beta (PDGFR-β), and RGS5. These benign tumors include glomus tumor, myopericytoma, angioleiomyoma, and myofibroma. Second and as suggested by animal models, pericytes may give rise to malignant sarcomas. This is not a suggestion that all sarcomas within a certain subtype arise from pericytes, but that genetic modifications within a pericyte cell type may give rise to sarcomas. Third, mesenchymal tumors that are likely not a pericyte derivative co-opt pericyte markers in certain contexts. These include the PEComa family of tumors and liposarcoma. Fourth and finally, as "guardians" that enwrap the microvasculature, nonneoplastic pericytes may be important in sarcoma disease progression.

Mesenchymal Neoplasms of the Genitourinary System: A Selected Review with Recent Advances in Clinical, Diagnostic, and Molecular Findings

Mesenchymal neoplasms of the genitourinary (GU) tract often pose considerable diagnostic challenges due to their wide morphologic spectrum, relative rarity, and unexpected incidence at GU sites. Soft tissue tumors arise throughout the GU tract, whether from adventitia surrounding or connective tissues within the kidneys, urinary bladder, and male and female genital organs. This selected article focuses on a subset of these lesions, ranging from benign to malignant and encompassing a range of patterns of mesenchymal differentiation, where recent scholarship has lent greater insight into their clinical, molecular, or diagnostic features.

Regulator of G protein signaling 5 restricts neutrophil chemotaxis and trafficking

Neutrophils are white blood cells that are mobilized to damaged tissues and to sites of pathogen invasion, providing the first line of host defense. Chemokines displayed on the surface of blood vessels promote migration of neutrophils to these sites, and tissue- and pathogen-derived chemoattractant signals, including N-formylmethionylleucylphenylalanine (fMLP), elicit further migration to sites of infection. Although nearly all chemoattractant receptors use heterotrimeric G proteins to transmit signals, many of the mechanisms lying downstream of chemoattractant receptors that either promote or limit neutrophil motility are incompletely defined. Here, we show that regulator of G protein signaling 5 (RGS5), a protein that modulates G protein activity, is expressed in both human and murine neutrophils. We detected significantly more neutrophils in the airways of Rgs5^-/- mice than WT counterparts following acute respiratory virus infection and in the peritoneum in response to injection of thioglycollate, a biochemical proinflammatory stimulus. RGS5-deficient neutrophils responded with increased chemotaxis elicited by the chemokines CXC motif chemokine ligand 1 (CXCL1), CXCL2, and CXCL12 but not fMLP. Moreover, adhesion of these cells was increased in the presence of both CXCL2 and fMLP. In summary, our results indicate that RGS5 deficiency increases chemotaxis and adhesion, leading to more efficient neutrophil mobilization to inflamed tissues in mice. These findings suggest that RGS5 expression and activity in neutrophils determine their migrational patterns in the complex microenvironments characteristic of inflamed tissues.

Myopericytoma/myopericytomatosis of the lower extremity in two young patients: a recently designated rare soft tissue neoplasm

Myopericytomas are rare, slow-growing benign perivascular tumors most commonly arising within the superficial subcutaneous soft tissues of the lower extremity. They represent one of several related perivascular tumors of myoid lineage with similar morphology and shared immunohistochemical profile including positive staining for smooth muscle actin. Histologically, myopericytoma exhibit concentric, perivascular proliferation of spindled myoid cells with bland elongated nuclei and associated blood vessels. A solitary well-demarcated nodule or mass is typically referred to as myopericytoma, whereas an infiltrative multinodular lesion has more recently been termed myopericytomatosis. At magnetic resonance imaging, tumors are most commonly superficial, may be well-defined (myopericytoma) or ill-defined (myopericytomatosis), and demonstrate highly vascularized, avidly enhancing soft tissue often with areas of internal hemorrhage. We report 2 cases involving the lower extremity (1 myopericytoma and 1 myopericytomatosis) occurring in young patients, focusing on the clinical, histopathologic, and radiologic characteristics of this relatively new distinct entity.

Post-surgery fluids promote transition of cancer stem cell-to-endothelial and AKT/mTOR activity, contributing to relapse of giant cell tumors of bone

Giant cell tumors of bone (GCTB) are rare sarcomas with a high rate of unpredictable local relapse. Studies suggest that surgical methods affect recurrence, supporting the idea that local disease develops from re-growth of residual cancer cells. To identify early prognostic markers of individual risk of recurrence, we evaluated the effect of post-surgery fluids from a cohort of GCTB patients on growth of primary and established sarcoma cell lines, and mice xenograph. Post-surgery fluids increased cell growth and enhanced expression of CD44⁺⁺, the principal receptor for the extracellular matrix component hyaluronan and the mesenchymal stem marker CD117⁺. Cancer cells became highly invasive and tumorigenic, acquiring stemness properties, and activated AKT/mTOR pathway. Prolonged stimulation with post-surgery fluids down-regulated the mesenchymal gene TWIST1 and Vimentin protein, and transdifferentiated cells into tubule-like structures positive to the endothelial markers VE-Cadherin and CD31⁺. In mice, post-surgery fluids gave rise to larger and more vascularized tumors than control, while in patients AKT/mTOR pathway activation was associated with recurrence by logistic regression (Kaplan-Meier; P<0.001). These findings indicate that post-surgery fluids are an adjuvant in mechanisms of tumor regrowth, increasing stem cell growth and AKT/mTOR activity.

Ang-2 but not Ang-1 expression in perivascular soft tissue tumors

Perivascular soft tissue tumors are relatively uncommon neoplasms of unclear line of differentiation, although most are presumed to originate from pericytes. Previously, we reported a shared immunophenotype across these related tumor types. Here, we extend these findings to examine the expression of the pericyte markers angiopoietin-1 and -2 (Ang-1 and -2) among perivascular soft tissue tumors. Results showed consistent Ang-2 but not Ang-1 expression across tumor types. In summary, the absence of Ang-1 expression distinguishes perivascular from vascular soft tissue tumors. Ang-2 expression is present across perivascular soft tissue tumors, with some variation between histologic subtypes.