Essential role for TMEM100 in vascular integrity but limited contributions to the pathogenesis of hereditary haemorrhagic telangiectasia

Genetic parameters and genome-wide association studies for mozzarella and milk production traits, lactation length, and lactation persistency in Murrah buffaloes

Genetic and genomic analyses of longitudinal traits related to milk production efficiency are paramount for optimizing water buffaloes breeding schemes. Therefore, this study aimed to (1) compare single-trait random regression models under a single-step genomic BLUP setting based on alternative covariance functions (i.e., Wood, Wilmink, and Ali and Schaeffer) to describe milk (MY), fat (FY), protein (PY), and mozzarella (MZY) yields, fat-to-protein ratio (FPR), somatic cell score (SCS), lactation length (LL), and lactation persistency (LP) in Murrah dairy buffaloes (Bubalus bubalis); (2) combine the best functions for each trait under a multiple-trait framework; (3) estimate time-dependent SNP effects for all the studied longitudinal traits; and (4) identify the most likely candidate genes associated with the traits. A total of 323,140 test-day records from the first lactation of 4,588 Murrah buffaloes were made available for the study. The model included the average curve of the population nested within herd-year-season of calving, systematic effects of number of milkings per day, and age at first calving as linear and quadratic covariates, and additive genetic, permanent environment, and residual as random effects. The Wood model had the best goodness of fit based on the deviance information criterion and posterior model probabilities for all traits. Moderate heritabilities were estimated over time for most traits (0.30 ± 0.02 for MY; 0.26 ± 0.03 for FY; 0.45 ± 0.04 for PY; 0.28 ± 0.05 for MZY; 0.13 ± 0.02 for FPR; and 0.15 ± 0.03 for SCS). The heritability estimates for LP ranged from 0.38 ± 0.02 to 0.65 ± 0.03 depending on the trait definition used. Similarly, heritabilities estimated for LL ranged from 0.10 ± 0.01 to 0.14 ± 0.03. The genetic correlation estimates across days in milk (DIM) for all traits ranged from -0.06 (186-215 DIM for MY-SCS) to 0.78 (66-95 DIM for PY-MZY). The SNP effects calculated for the random regression model coefficients were used to estimate the SNP effects throughout the lactation curve (from 5 to 305 d). Numerous relevant genomic regions and candidate genes were identified for all traits, confirming their polygenic nature. The candidate genes identified contribute to a better understanding of the genetic background of milk-related traits in Murrah buffaloes and reinforce the value of incorporating genomic information in their breeding programs.

Role and new insights of microfibrillar-associated protein 4 in fibrotic diseases

Fibrosis is one of the most worrisome complications of chronic inflammatory diseases, leading to tissue damage, organ failure, and ultimately, death. The most notable pathological characteristic of fibrosis is the excessive accumulation of extracellular matrix (ECM) components such as collagen and fibronectin adjacent to foci of inflammation or damage. The human microfibrillar-associated protein 4 (MFAP4), an important member of the superfamily of fibrinogen-related proteins, is considered to have an extremely important role in ECM transformation of fibrogenesis. This review summarizes the structure, characteristics, and physiological functions of MFAP4 and the importance of MFAP4 in various fibrotic diseases. Meanwhile, we elaborated the underlying actions and mechanisms of MFAP4 in the development of fibrosis, suggesting that a better understand of MFAP4 broadens novel perspective for early screening, diagnosis, prognostic risk assessment, and treatment of fibrotic diseases.

Splenic stromal niches in homeostasis and immunity

The spleen is a gatekeeper of systemic immunity where immune responses against blood-borne pathogens are initiated and sustained. Non-haematopoietic stromal cells construct microanatomical niches in the spleen that make diverse contributions to physiological spleen functions and regulate the homeostasis of immune cells. Additional signals from spleen autonomic nerves also modify immune responses. Recent insight into the diversity of the splenic fibroblastic stromal cells has revised our understanding of how these cells help to orchestrate splenic responses to infection and contribute to immune responses. In this Review, we examine our current understanding of how stromal niches and neuroimmune circuits direct the immunological functions of the spleen, with a focus on T cell immunity.

TMEM100 Regulates Neuropathic Pain by Reducing the Expression of Inflammatory Factors

There is no effective treatment for peripheral nerve injury-induced chronic neuropathic pain (NP), which profoundly impacts the quality of life of those affected. Transmembraneprotein100 (TMEM100) is considered to be a pain regulatory protein and is expressed in the dorsal root ganglion (DRG) of rats. However, the mechanism of pain regulation and the expression of TMEM100 following various peripheral nerve injuries are unclear. In this study, we constructed two pain models of peripheral nerve injury: tibial nerve injury (TNI) and chronic constriction injury (CCI). This study found that the Paw Withdrawal Mechanical Threshold (PWMT) and Paw Withdraw Thermal Latency (PWTL) of the rats in the two pain models decreased significantly, and the expression of TMEM100 in the DRG of two groups also decreased significantly. Furthermore, the decrease in the CCI group was more obvious than in the TNI group. There was no significant statistical significance (P > 0.05). We constructed an adeno-associated virus 6 (AAV6) vector expressing recombinant fluorescent TMEM100 protein and injected it into the sciatic nerve (SN) of two pain models: CCI and TNI. PWMT and PWTL were significantly increased in the two groups, along with the expression of TMEM100 in the spinal cord and DRG. It also significantly inhibited the activation of microglia, astrocytes, and several inflammatory mediators (TNF- α, IL-1 β, and IL-6). In summary, the results of this study suggested that TMEM100 might be a promising molecular strategy for the treatment of NP, and its anti-inflammatory effects might play an important role in pain relief.

The Role of a Lung Vascular Endothelium Enriched Gene TMEM100

Transmembrane protein 100 (TMEM100) is a crucial factor in the development and maintenance of the vascular system. The protein is involved in several processes such as angiogenesis, vascular morphogenesis, and integrity. Furthermore, TMEM100 is a downstream target of the BMP9/10 and BMPR2/ALK1 signaling pathways, which are key regulators of vascular development. Our recent studies have shown that TMEM100 is a lung endothelium enriched gene and plays a significant role in lung vascular repair and regeneration. The importance of TMEM100 in endothelial cells' regeneration was demonstrated when Tmem100 was specifically deleted in endothelial cells, causing an impairment in their regenerative ability. However, the role of TMEM100 in various conditions and diseases is still largely unknown, making it an interesting area of research. This review summarizes the current knowledge of TMEM100, including its expression pattern, function, molecular signaling, and clinical implications, which could be valuable in the development of novel therapies for the treatment of cardiovascular and pulmonary diseases.

Upregulation of DRG protein TMEM100 facilitates dry-skin-induced pruritus by enhancing TRPA1 channel function

The dry skin tortures numerous patients with severe itch. The transient receptor potential cation channel V member 1 (TRPV1) and A member 1 (TRPA1) are two essential receptors for peripheral neural coding of itch sensory, mediating histaminergic and nonhistaminergic itch separately. In the dorsal root ganglion, transmembrane protein 100 (TMEM100) is structurally related to both TRPV1 and TRPA1 receptors, but the exact role of TMEM100 in itch sensory coding is still unknown. Here, in this study, we find that TMEM100 ⁺ DRG neurons account for the majority of activated neurons in an acetone-ether-water (AEW)-induced dry skin itch model, and some TMEM100 ⁺ DRG neurons are colocalized with both TRPA1 and the chloroquine-related Mrgpr itch receptor family. Both the expression and function of TRPA1 channels, but not TRPV1 channels, are upregulated in the AEW model, and specific DRG Tmem100 gene knockdown alleviates AEW-induced itch and rescues the expression and functional changes of TRPA1. Our results strongly suggest that TMEM100 protein in DRG is the main facilitating factor for dry-skin-related chronic itch, and specific suppression of TMEM100 in DRG could be a novel effective treatment strategy for patients who suffer from dry skin-induced itch.

Neurovascular Manifestations in Pediatric Patients With Hereditary Haemorrhagic Telangiectasia

BACKGROUND

Hereditary hemorrhagic telangiectasia (HHT) is a multiorgan vascular dysplasia with limited data regarding its neurovascular manifestations and genotype-phenotype correlation in children. The objective of this study was to describe the neurovascular findings in a large cohort of children with HHT and correlate between phenotype and genotype.

METHODS

This retrospective study was conducted on 221 children (<18 years) with a definite or possible diagnosis of HHT based on Curacao criteria, or with positive genetics for the mutated genes of ENG, ACVRL-1, and SMAD-4, who also underwent brain MRI and/or conventional angiography. Demographic and clinical information, imaging findings, and follow up information were gathered.

RESULTS

Two hundred twenty-one children with HHT (70.6% genetically confirmed, and 99.5% positive family history) were included, with a median age of 7 years (interquartile range: 3 to 11 years) and 58.8% male predominance. Neurovascular lesions were found in 64 of 221 (28.9%), with 3.1% prevalence of intracranial hemorrhage. The most commonly observed vascular malformations were developmental venous anomalies (48.5%) and brain arteriovenous malformations (AVMs) (31.2%), followed by capillary malformations (14.1%). Multiple AVMs were seen in 10.0% of the cohort. We found no instances of de novo AVM (1281.8 patient-years).A significantly higher proportion of patients with ENG mutations (19.7%) had brain AVM than those with ACVRL-1 (4.9%) and SMAD-4 (0%) mutations (P < 0.01). There was no significant difference in the hemorrhagic risk of shunting lesions associated with ENG (35.3%) or ACVRL-1 (33.3%) positivity (P = 0.9).

CONCLUSIONS

We describe the neurovascular imaging and genetic findings from a large pediatric cohort of HHT, to enhance clinical awareness and guide management of patients with HHT.

Gene expression profiling using targeted RNA-sequencing to elucidate the progression from histologically normal lung tissues to non-invasive lesions in invasive lung adenocarcinoma

Lung adenocarcinoma (LUAD) shows heterogeneous morphological features and the stepwise progression from adenocarcinoma in situ to minimally invasive adenocarcinoma to invasive LUAD. Although multiple genetic alterations have been linked to the progression, the differences between the gene expression profiles of non-invasive lesions (non-ILs) and adjacent histologically normal lung (aNL) tissues within invasive LUAD have not been investigated. Herein, we analyzed differentially expressed genes (DEGs) specific to early-stage carcinogenesis in LUAD. Invasive LUAD tissue samples containing both non-ILs and aNL tissues were obtained from seven patients with pathological stage I LUAD, and each component was subjected to microdissection. Gene expression profiles of each component were determined using targeted RNA-sequencing. In total, 2536 DEGs, including 863 upregulated and 1673 downregulated genes, were identified in non-ILs. In non-ILs, the expression of SLC44A5, a choline transporter-like protein-coding gene, was significantly upregulated, and that of TMEM100, a gene encoding a transmembrane protein, was significantly downregulated. Reportedly, SLC44A5 plays an important role in the development and progression of hepatocellular carcinoma, whereas TMEM100 functions as a tumor suppressor in non-small cell lung cancer. Gene set enrichment analysis showed that DEGs in non-ILs were negatively enriched in cell death and immune response. Immunohistochemical analysis revealed that increased SLC44A5 expression and decreased TMEM100 expression were maintained in ILs. A protein-protein interaction (PPI) network analysis identified several upregulated and downregulated hub genes with high degrees in non-ILs. In conclusion, several new DEGs and key PPI network hub genes were identified in non-ILs, contributing to understanding of early-stage carcinogenesis in LUAD.

A diverse fibroblastic stromal cell landscape in the spleen directs tissue homeostasis and immunity

[Figure: see text].

TMEM100 expression suppresses metastasis and enhances sensitivity to chemotherapy in gastric cancer

The gene encoding transmembrane protein 100 (TMEM100) was first discovered to be transcribed by the murine genome. It has been recently proven that TMEM100 contributes to hepatocellular carcinoma and non-small-cell lung carcinoma (NSCLC). This study investigates the impact of TMEM100 expression on gastric cancer (GC). TMEM100 expression was remarkably downregulated in GC samples compared to the surrounding non-malignant tissues (p < 0.01). Excessive TMEM100 expression prohibited the migration and invasion of GC cells without influencing their growth. However, TMEM100 knockdown restored their migration and invasion potential. Additionally, TMEM100 expression restored the sensitivity of GC cells to chemotherapeutic drugs such as 5-fluouracil (5-FU) and cisplatin. In terms of TMEM100 modulation, it was revealed that BMP9 rather than BMP10, is the upstream modulator of TM3M100. HIF1α downregulation modulated the impact of TMEM100 on cell migration, chemotherapy sensitivity and invasion in GC cells. Eventually, the in vivo examination of TMEM100 activity revealed that its upregulation prohibits the pulmonary metastasis of GC cells and increases the sensitivity of xenograft tumors to 5-FU treatment. In conclusion, TMEM100 serves as a tumor suppressor in GC and could be used as a promising target for the treatment of GC and as a predictor of GC clinical outcome.

Tmem100-BAC-EGFP mice to selectively mark and purify embryonic endothelial cells of large caliber arteries in mid-gestational vascular formation

Embryonic vascular development is achieved through the complex arrays of differentiation, proliferation, migration and mutual interaction of different cell types, and visualization as well as purification of unique cell populations are fundamental in studying its detailed mechanisms using in vivo experimental models. We previously demonstrated that Tmem100 was a novel endothelial gene encoding a small transmembrane protein, and that Tmem100 null mice showed embryonic lethality due to severe impairment of vascular formation. In the present study, we generated an EGFP reporter mouse line using a 216 kb genomic region containing mouse Tmem100 gene. A novel line designated as Tmem100-BAC-EGFP mice precisely recapitulated the Tmem100 expression profile at the mid-gestational stage, which was highly enriched in endothelial cells of large caliber arteries in mouse embryos. FACS experiments demonstrated that Tmem100-BAC-EGFP mice served to selectively purify a specific population of arterial endothelial cells, indicating their usefulness not only for the research concerning Tmem100 expression and function but also for comparative analysis of multiple endothelial cell subgroups in embryonic vascular development.

Conjugation of vascular endothelial growth factor to poly lactic-co-glycolic acid nanospheres enhances differentiation of embryonic stem cells to lymphatic endothelial cells

OBJECTIVE

Pluripotent stem cell-derived lymphatic endothelial cells (LECs) show great promise in their therapeutic application in the field of regenerative medicine related to lymphatic vessels. We tested the approach of forced differentiation of mouse embryonal stem cells into LECs using biodegradable poly lactic-co-glycolic acid (PLGA) nanospheres in conjugation with growth factors (vascular endothelial growth factors [VEGF-A and VEGF-C]).

METHODS

We evaluated the practical use of heparin-conjugated PLGA nanoparticles (molecular weight ~15,000) in conjugation with VEGF-A/C, embryoid body (EB) formation, and LEC differentiation using immunofluorescence staining followed by quantification and quantitative real-time polymerase chain reaction analysis.

RESULTS

We showed that formation and differentiation of EB with VEGF-A/C-conjugated PLGA nanospheres, compared to direct supplementation of VEGF-A/C to the EB differentiation media, greatly improved yield of LYVE1(+) LECs. Our analyses revealed that the enhanced potential of LEC differentiation using VEGF-A/C-conjugated PLGA nanospheres was mediated by elevation of expression of the genes that are important for lymphatic vessel formation.

CONCLUSION

Together, we not only established an improved protocol for LEC differentiation using PLGA nanospheres but also provided a platform technology for the mechanistic study of LEC development in mammals.

Cell Fate Determination of Lymphatic Endothelial Cells

The lymphatic vasculature, along with the blood vasculature, is a vascular system in our body that plays important functions in fluid homeostasis, dietary fat uptake, and immune responses. Defects in the lymphatic system are associated with various diseases such as lymphedema, atherosclerosis, fibrosis, obesity, and inflammation. The first step in lymphangiogenesis is determining the cell fate of lymphatic endothelial cells. Several genes involved in this commitment step have been identified using animal models, including genetically modified mice. This review provides an overview of these genes in the mammalian system and related human diseases.

Statistical and Functional Studies Identify Epistasis of Cardiovascular Risk Genomic Variants From Genome-Wide Association Studies

Background

Epistasis describes how gene‐gene interactions affect phenotypes, and could have a profound impact on human diseases such as coronary artery disease (CAD). The goal of this study was to identify gene‐gene interactions in CAD using an easily generalizable multi‐stage approach.

Methods and Results

Our forward genetic approach consists of multiple steps that combine statistical and functional approaches, and analyze information from global gene expression profiling, functional interactions, and genetic interactions to robustly identify gene‐gene interactions. Global gene expression profiling shows that knockdown of ANRIL (DQ485454) at 9p21.3 GWAS (genome‐wide association studies) CAD locus upregulates TMEM100 and TMEM106B. Functional studies indicate that the increased monocyte adhesion to endothelial cells and transendothelial migration of monocytes, 2 critical processes in the initiation of CAD, by ANRIL knockdown are reversed by knockdown of TMEM106B, but not of TMEM100. Furthermore, the decreased monocyte adhesion to endothelial cells and transendothelial migration of monocytes induced by ANRIL overexpression was reversed by overexpressing TMEM106B. TMEM106B expression was upregulated by >2‐fold in CAD coronary arteries. A significant association was found between variants in TMEM106B (but not in TMEM100) and CAD (P=1.9×10⁻⁸). Significant gene‐gene interaction was detected between ANRIL variant rs2383207 and TMEM106B variant rs3807865 (P=0.009). A similar approach also identifies significant interaction between rs6903956 in ADTRP and rs17465637 in MIA3 (P=0.005).

Conclusions

We demonstrate 2 pairs of epistatic interactions between GWAS loci for CAD and offer important insights into the genetic architecture and molecular mechanisms for the pathogenesis of CAD. Our strategy has broad applicability to the identification of epistasis in other human diseases.

TMEM100 is a key factor for specification of lymphatic endothelial progenitors

BACKGROUND

TMEM100 is identified as a downstream gene of bone morphogenetic protein 9 (BMP9) signaling via activin receptor-like kinase 1 (ALK1), which is known to participate in lymphangiogenesis as well as angiogenesis. TMEM100 has been shown to be important for blood vessel formation and maintenance, but its role in the development of lymphatic vasculature remains unknown. The objective is to investigate the role of TMEM100 in development of the lymphatic system.

METHODS AND RESULTS

Global Tmem100 gene deletion was induced by tamoxifen on 10.5 days post-coitus. Tmem100-inducible knockout (iKO) embryos in embryonic days (E)14.5-16.5 exhibited edema and blood-filled enlarged lymphatics with misconnections between veins and lymphatic vessels. For a reciprocal approach, we have generated a novel mouse line in which TMEM100 overexpression (OE) can be induced in endothelial cells by intercrossing with Tie2-Cre driver. TMEM100-OE embryos at E12.5-14.5 exhibited edema with small size and number of lymphatic vessels, the exact opposite phenotypes of Tmem100-iKOs. In Tmem100-iKO embryos, the number of progenitors of lymphatic endothelial cells (LECs) in the cardinal vein was increased, while it was decreased in TMEM100-OE embryos. The activity of NOTCH signaling, which limits the number of progenitors of LECs in the cardinal vein, was decreased in Tmem100-iKO embryos, whereas it was increased in TMEM100-OE embryos.

CONCLUSION

TMEM100 plays an important role in the specification of LECs in the cardinal veins, at least in part, by regulating the NOTCH signaling.

TMEM100 mediates inflammatory cytokines secretion in hepatic stellate cells and its mechanism research

Recent studies have shown that Transmembrane protein 100 (TMEM100) is a gene at locus 17q32 encoding a 134-amino acid protein with two hypothetical transmembrane domainsa, and first identified as a transcript from the mouse genome. As a downstream target gene of bone morphogenetic protein (BMP)-activin receptor-like kinase 1 (ALK1) signaling, it was activated to participate in inducing arterial endothelium differentiation, maintaining vascular integrity, promoting cell apoptosis, inhibiting metastasis and proliferation of cancer cells. However, evidence for the function of TMEM100 in inflammation is still limited. In this study, we explore the role of TMEM100 in inflammatory cytokine secretion and the role of MAPK signaling pathways in tumor necrosis factor-alpha (TNF-α)-induced TMEM100 expression in LX-2 cells. We found that the expression of TMEM100 was decreased markedly in human liver fibrosis tissues, and its expression was also inhibited in LX-2 cells induced by TNF-α, suggesting that it might be associated with the development of inflammation. Therefore, we demonstrated that overexpression of TMEM100 by transfecting pEGFP-C2-TMEM100 could lead to the down-regulation of IL-1β and IL-6 secretion. Moreover, we found that expression changes of TMEM100 could be involved in inhibition or activation of MAPK signaling pathways accompanied with regulating phosphorylation levels of ERK and JNK protein in response to TNF-α. These results suggested that TMEM100 might play an important role in the secretion of inflammatory cytokines (IL-1β and IL-6) of LX-2 cells induced by TNF-α, and MAPK (ERK and JNK) signaling pathways might participate in its induction of expression.

Transmembrane protein 100 is expressed in neurons and glia of dorsal root ganglia and is reduced after painful nerve injury

Introduction

Tmem100 modulates interactions between TRPA1 and TRPV1. The cell specificity of Tmem100 expression in dorsal root ganglia (DRGs) is not well defined, nor is the effect of peripheral nerve injury on Tmem100 expression.

Objective

This study was designed to determine the cell specificity of Tmem100 expression in DRG and its subcellular localization, and to examine how Tmem100 expression may be altered in painful conditions.

Methods

Dorsal root ganglion Tmem100 expression was determined by immunohistochemistry, immunoblot, and quantitative real-time PCR, and compared between various experimental rat pain models and controls.

Results

Tmem100 is expressed in both neurons and perineuronal glial cells in the rat DRG. The plasma membrane and intracellular localization of Tmem100 are identified in 83% ± 6% of IB4-positive and 48% ± 6% of calcitonin gene-related peptide-positive neurons, as well as in medium- and large-sized neurons, with its immunopositivity colocalized to TRPV1 (94% ± 5%) and TRPA1 (96% ± 3%). Tmem100 is also detected in the perineuronal satellite glial cells and in some microglia. Tmem100 protein is significantly increased in the lumbar DRGs in the complete Freund adjuvant inflammatory pain. By contrast, peripheral nerve injury by spinal nerve ligation diminishes Tmem100 expression in the injured DRG, with immunoblot and immunohistochemistry experiments showing reduced Tmem100 protein levels in both neurons and satellite glial cells of DRGs proximal to injury, whereas Tmem100 is unchanged in adjacent DRGs. The spared nerve injury model also reduces Tmem100 protein in the injured DRGs.

Conclusion

Our data demonstrate a pain pathology-dependent alteration of DRG Tmem100 protein expression, upregulated during CFA inflammatory pain but downregulated during neuropathic pain.

The expression of Transmembrane Protein 100 is regulated by alterations in calcium signaling rather than endoplasmic reticulum stress

Transmembrane protein 100 (TMEM100) comprises 134 amino acid residues and is highly conserved among vertebrates. Tmem100 has been recently reported as a key factor in angiogenesis, pain transmission, and tumor suppression. Although the importance of TMEM100 function is well supported, few studies have elucidated its expression mechanism. In the current study, we found that activating transcription factor 6α, a transcription factor activated by endoplasmic reticulum (ER) stress, enhanced Tmem100 promoter activity. Two ER stress response element-like motifs were identified in the mouse Tmem100 promoter region. However, additional experiments using another type of ER stress inducer demonstrated that calcium signaling was more important than ER stress in the regulation of TMEM100 expression. Intracellular calcium signaling controls biological processes such as cell proliferation and embryonic development. This study suggested that TMEM100 performs various functions in response to alterations in calcium signaling in addition to those in response to ER stress.

ALK1 signaling in development and disease: new paradigms

Activin A receptor like type 1 (ALK1) is a transmembrane serine/threonine receptor kinase in the transforming growth factor-beta receptor family that is expressed on endothelial cells. Defects in ALK1 signaling cause the autosomal dominant vascular disorder, hereditary hemorrhagic telangiectasia (HHT), which is characterized by development of direct connections between arteries and veins, or arteriovenous malformations (AVMs). Although previous studies have implicated ALK1 in various aspects of sprouting angiogenesis, including tip/stalk cell selection, migration, and proliferation, recent work suggests an intriguing role for ALK1 in transducing a flow-based signal that governs directed endothelial cell migration within patent, perfused vessels. In this review, we present an updated view of the mechanism of ALK1 signaling, put forth a unified hypothesis to explain the cellular missteps that lead to AVMs associated with ALK1 deficiency, and discuss emerging roles for ALK1 signaling in diseases beyond HHT.

Deregulated TGF-β/BMP Signaling in Vascular Malformations

Correct organization of the vascular tree requires the balanced activities of several signaling pathways that regulate tubulogenesis and vascular branching, elongation, and pruning. When this balance is lost, the vessels can be malformed and fragile, and they can lose arteriovenous differentiation. In this review, we concentrate on the transforming growth factor (TGF)-β/bone morphogenetic protein (BMP) pathway, which is one of the most important and complex signaling systems in vascular development. Inactivation of these pathways can lead to altered vascular organization in the embryo. In addition, many vascular malformations are related to deregulation of TGF-β/BMP signaling. Here, we focus on two of the most studied vascular malformations that are induced by deregulation of TGF-β/BMP signaling: hereditary hemorrhagic telangiectasia (HHT) and cerebral cavernous malformation (CCM). The first of these is related to loss-of-function mutation of the TGF-β/BMP receptor complex and the second to increased signaling sensitivity to TGF-β/BMP. In this review, we discuss the potential therapeutic targets against these vascular malformations identified so far, as well as their basis in general mechanisms of vascular development and stability.

Bone Morphogenetic Protein 9 Protects against Neonatal Hyperoxia-Induced Impairment of Alveolarization and Pulmonary Inflammation

Aim: Effective treatment of premature infants with bronchopulmonary dysplasia (BPD) is lacking. We hypothesize that bone morphogenetic protein 9 (BMP9), a ligand of the TGF-β family that binds to the activin receptor-like kinase 1 (ALK1)-BMP receptor type 2 (BMPR2) receptor complex, may be a novel therapeutic option for BPD. Therefore, we investigated the cardiopulmonary effects of BMP9 in neonatal Wistar rats with hyperoxia-induced BPD.

Methods: Directly after birth Wistar rat pups were exposed to 100% oxygen for 10 days. From day 2 rat pups received BMP9 (2.5 μg/kg, twice a day) or 0.9% NaCl by subcutaneous injection. Beneficial effects of BMP9 on aberrant alveolar development, lung inflammation and fibrosis, and right ventricular hypertrophy (RVH) were investigated by morphometric analysis and cytokine production. In addition, differential mRNA expression of BMP9 and its receptor complex: ALK1, BMPR2, and Endoglin, and of the ALK1 downstream target transmembrane protein 100 (TMEM100) were studied during the development of experimental BPD. Expression of the BMP9 receptor complex and TMEM100 was studied in human endothelial and epithelial cell cultures and the effect of BMP9 on inflammatory cytokine production and TMEM100 expression was studied in endothelial cell cultures.

Results:ALK1, ALK2, BMPRII, TMEM100, and Endoglin were differentially expressed in experimental BPD, suggesting a role for BMP9-dependent signaling in the development of (experimental) BPD. TMEM100 was expressed in the wall of blood vessels, showing an elastin-like expression pattern in arterioles. Expression of TMEM100 mRNA and protein was decreased after exposure to hyperoxia. BMP9 treatment of rat pups with hyperoxia-induced experimental BPD reduced alveolar enlargement, lung septal thickness and fibrosis, and prevented inflammation, but did not attenuate vascular remodeling and RVH. The anti-inflammatory effect of BMP9 was confirmed in vitro. Highest expression of ALK1, BMPR2, and TMEM100 was observed in human endothelial cell cultures. Stimulation of human endothelial cell cultures with BMP9 reduced their pro-inflammatory cytokine response and induced TMEM100 expression in pulmonary arterial endothelial cells.

Conclusion: BMP9 protects against neonatal hyperoxia-induced BPD by improving aberrant alveolar development, inflammation and fibrosis, demonstrating its therapeutic potential for premature infants with severe BPD.

Low-expression of TMEM100 is associated with poor prognosis in non-small-cell lung cancer

Transmembrane protein 100 (TMEM100) was first identified as a transcript from the mouse genome. Recent studies have demonstrated that TMEM100 is involved in hepatocellular carcinoma (HCC) malignancy. However, the distribution and clinical significance of TMEM100 in non-small-cell lung carcinoma (NSCLC) remains poorly understood. This study aims to explore the significance of TMEM100 expression in NSCLC. We found that TMEM100 expression was significantly reduced in NSCLC tissues when compared with that in adjacent normal lung tissues (P<0.001). Kaplan-Meier survival analysis showed that overall survival of patients with lower expressions of TMEM100 was significantly shorter (n=152, P<0.05). In addition, TMEM100 overexpression in NSCLC cell lines inhibited cell proliferation in vitro and in vivo. Transwell migration and invasion assay showed that TMEM100 significantly suppressed the migration and invasion of NSCLC cell lines. In contrast, knocking down TMEM100 promoted NSCLC proliferation and migration. Finally, we found that TMEM100 worked as a cancer suppressor gene mainly by inhibiting the TNF signaling pathway. In conclusion, TMEM100 acted as a tumor suppressor in NSCLC and may prove to be a potential prognostic biomarker and therapeutic target for NSCLC.

Mutual interaction between endothelial cells and mural cells enhances BMP9 signaling in endothelial cells

Hereditary hemorrhagic telangiectasia is characterized by the formation of abnormal vascular networks and caused by the mutation of genes involved in BMP9 signaling. It is also known that the interaction between endothelial cells (ECs) and mural cells (MCs) is critical to maintain vessel integrity. However, it has not yet fully been uncovered whether the EC–MC interaction affects BMP9 signaling or not. To elucidate this point, we analyzed BMP9 signaling in a co-culture of several types of human primary culture ECs and MCs. The co-culture activated the Notch pathway in both types of cells in a co-culture- and BMP9-dependent manner. In HUVECs, the genes induced by BMP9 were significantly and synergistically induced in the presence of pericytes, fibroblasts or mesenchymal stem cells. The synergistic induction was greatly reduced in a non-contact condition. In fibroblasts, PDGFRB expression was potently induced in the presence of HUVECs, and BMP9 additively increased this response. Taken together, these results suggest that the EC–MC interaction potentiates BMP9 signaling both in ECs and MCs and plays a critical role in the maintenance of proper vessel functions.

Summary: A mutual interaction between endothelial cells and mural cells enhances BMP9 signaling in endothelial cells, with implications for the maintenance of vascular integrity and vascular disease research.

Arteriovenous malformations in hereditary haemorrhagic telangiectasia: looking beyond ALK1-NOTCH interactions

Hereditary haemorrhagic telangiectasia (HHT) is characterized by the development of arteriovenous malformations--enlarged shunts allowing arterial flow to bypass capillaries and enter directly into veins. HHT is caused by mutations in ALK1 or Endoglin; however, the majority of arteriovenous malformations are idiopathic and arise spontaneously. Idiopathic arteriovenous malformations differ from those due to loss of ALK1 in terms of both location and disease progression. Furthermore, while arteriovenous malformations in HHT and Alk1 knockout models have decreased NOTCH signalling, some idiopathic arteriovenous malformations have increased NOTCH signalling. The pathogenesis of these lesions also differs, with loss of ALK1 causing expansion of the shunt through proliferation, and NOTCH gain of function inducing initial shunt enlargement by cellular hypertrophy. Hence, we propose that idiopathic arteriovenous malformations are distinct from those of HHT. In this review, we explore the role of ALK1-NOTCH interactions in the development of arteriovenous malformations and examine a possible role of two signalling pathways downstream of ALK1, TMEM100 and IDs, in the development of arteriovenous malformations in HHT. A nuanced understanding of the precise molecular mechanisms underlying idiopathic and HHT-associated arteriovenous malformations will allow for development of targeted treatments for these lesions.