Apolipoprotein D and Platelet-Derived Growth Factor-BB Synergism Mediates Vascular Smooth Muscle Cell Migration

A SERPINE1-Based Immune Gene Signature Predicts Prognosis and Immunotherapy Response in Gastric Cancer

Immune checkpoint inhibitors (ICIs) therapy has been successfully utilized in the treatment of multiple tumors, but only a fraction of patients with gastric cancer (GC) could greatly benefit from it. A recent study has shown that the tumor microenvironment (TME) can greatly affect the effect of immunotherapy in GC. In this study, we established a novel immune risk signature (IRS) for prognosis and predicting response to ICIs in GC based on the TCGA-STAD dataset. Characterization of the TME was explored and further validated to reveal the underlying survival mechanisms and the potential therapeutic targets of GC. The GC patients were stratified into high- and low-risk groups based on the IRS. Patients in the high-risk group, associated with poorer outcomes, were characterized by significantly higher immune function. Further analysis showed higher T cell immune dysfunction and probability of potential immune escape. In vivo, we detected the expressions of SERPINE1 by the quantitative real-time polymerase chain reaction (qPCR)in tumor tissues and adjacent normal tissues. In vitro, knockdown of SERPINE1 significantly attenuated malignant biological behaviors of tumor cells in GC. Our signature can effectively predict the prognosis and response to immunotherapy in patients with GC.

The Lipocalin Apolipoprotein D Functional Portrait: A Systematic Review

Apolipoprotein D is a chordate gene early originated in the Lipocalin protein family. Among other features, regulation of its expression in a wide variety of disease conditions in humans, as apparently unrelated as neurodegeneration or breast cancer, have called for attention on this gene. Also, its presence in different tissues, from blood to brain, and different subcellular locations, from HDL lipoparticles to the interior of lysosomes or the surface of extracellular vesicles, poses an interesting challenge in deciphering its physiological function: Is ApoD a moonlighting protein, serving different roles in different cellular compartments, tissues, or organisms? Or does it have a unique biochemical mechanism of action that accounts for such apparently diverse roles in different physiological situations? To answer these questions, we have performed a systematic review of all primary publications where ApoD properties have been investigated in chordates. We conclude that ApoD ligand binding in the Lipocalin pocket, combined with an antioxidant activity performed at the rim of the pocket are properties sufficient to explain ApoD association with different lipid-based structures, where its physiological function is better described as lipid-management than by long-range lipid-transport. Controlling the redox state of these lipid structures in particular subcellular locations or extracellular structures, ApoD is able to modulate an enormous array of apparently diverse processes in the organism, both in health and disease. The new picture emerging from these data should help to put the physiological role of ApoD in new contexts and to inspire well-focused future research.

The diversity of lipocalin receptors

Lipocalins are important carriers of preferentially hydrophobic molecules, but they can also bind other ligands, like highly polar siderophores or intact proteins. Consequently, they are involved in a variety of physiological processes in many species. Since lipocalins are mainly extracellular proteins, they have to interact with cell receptors to exert their biological effects. In contrast to the large number of lipocalins identified in the last years, the number of receptors known is still limited. Nevertheless, some novel findings concerning the molecules involved in cellular uptake or signaling effects of lipocalins have been made recently. This review presents a detailed overview of the receptors identified so far. The methods used for isolation or identification are described and structural as well as functional information on these proteins is presented essentially in chronological order of their initial discovery.

Combining gene expression signature with clinical features for survival stratification of gastric cancer

The AJCC staging system is considered as the golden standard in clinical practice. However, it remains some pitfalls in assessing the prognosis of gastric cancer (GC) patients with similar clinicopathological characteristics. We aim to develop a new clinic and genetic risk score (CGRS) to improve the prognosis prediction of GC patients. We established genetic risk score (GRS) based on nine-gene signature including APOD, CCDC92, CYS1, GSDME, ST8SIA5, STARD3NL, TIMEM245, TSPYL5, and VAT1 based on the gene expression profiles of the training set from the Asian Cancer Research Group (ACRG) cohort by LASSO-Cox regression algorithms. CGRS was established by integrating GRS with clinical risk score (CRS) derived from Surveillance, Epidemiology, and End Results (SEER) database. GRS and CGRS dichotomized GC patients into high and low risk groups with significantly different prognosis in four independent cohorts with different data types, such as microarray, RNA sequencing and qRT-PCR (all HR > 1, all P < 0.001). Both GRS and CGRS were prognostic signatures independent of the AJCC staging system. Receiver operating characteristic (ROC) analysis showed that area under ROC curve of CGRS was larger than that of the AJCC staging system in most cohorts we studied. Nomogram and web tool (http://39.100.117.92/CGRS/) based on CGRS were developed for clinicians to conveniently assess GC prognosis in clinical practice. CGRS integrating genetic signature with clinical features shows strong robustness in predicting GC prognosis, and can be easily applied in clinical practice through the web application.

Apolipoprotein D

ApoD is a 25 to 30 kDa glycosylated protein, member of the lipocalin superfamily. As a transporter of several small hydrophobic molecules, its known biological functions are mostly associated to lipid metabolism and neuroprotection. ApoD is a multi-ligand, multi-function protein that is involved lipid trafficking, food intake, inflammation, antioxidative response and development and in different types of cancers. An important aspect of ApoD's role in lipid metabolism appears to involve the transport of arachidonic acid, and the modulation of eicosanoid production and delivery in metabolic tissues. ApoD expression in metabolic tissues has been associated positively and negatively with insulin sensitivity and glucose homeostasis in a tissue dependent manner. ApoD levels rise considerably in association with aging and neuropathologies such as Alzheimer's disease, stroke, meningoencephalitis, moto-neuron disease, multiple sclerosis, schizophrenia and Parkinson's disease. ApoD is also modulated in several animal models of nervous system injury/pathology.

Apolipoprotein D overexpression alters hepatic prostaglandin and omega fatty acid metabolism during the development of a non-inflammatory hepatic steatosis

Apolipoprotein D (ApoD) is a secreted lipocalin associated with neuroprotection and lipid metabolism. Overexpression of ApoD in mouse neural tissue induces the development of a non-inflammatory hepatic steatosis in 12-month-old transgenic animals. Previous data indicates that accumulation of arachidonic acid, ApoD's preferential ligand, and overactivation of PPARγ are likely the driving forces in the development of the pathology. However, the lack of inflammation under those conditions is surprising. Hence, we further investigated the apparent repression of inflammation during hepatic steatosis development in aging transgenic animals. The earliest modulation of lipid metabolism and inflammation occurred at 6 months with a transient overexpression of L-PGDS and concomitant overproduction of 15d-PGJ₂, a PPARγ agonist. Hepatic lipid accumulation was detectable as soon as 9 months. Inflammatory polarization balance varied in time, with a robust anti-inflammatory profile at 6 months coinciding with 15d-PGJ₂ overproduction. Omega-3 and omega-6 fatty acids were preferentially stored in the liver of 12-month-old transgenic mice and resulted in a higher omega-3/omega-6 ratio compared to wild type mice of the same age. Thus, inflammation seems to be controlled by several mechanisms in the liver of transgenic mice: first by an increase in 15d-PGJ₂ production and later by a beneficial omega-3/omega-6 ratio. PPARγ seems to play important roles in these processes. The accumulation of several omega fatty acids species in the transgenic mouse liver suggests that ApoD might bind to a broader range of fatty acids than previously thought.

Expression Pattern of Myelin-Related Apolipoprotein D in Human Multiple Sclerosis Lesions

Apolipoprotein D (Apo D) is a key molecule in the lipid transport during homeostasis and repair processes in normal and pathological conditions of the nervous system with a putative neuroprotective effect. In the last decades, huge experimental efforts have been made to know the exact mechanism of action of Apo D, even though, it remains an open question. In this regard, studies in mammals and flies have suggested that Apo D seems to act through a variety of cellular mechanisms related with its ability to selectively bind different lipid ligands. For instance, this apolipoprotein is required to myelin compaction, it participates in axon regeneration/remyelination, and it can control the magnitude and timing of the inflammatory response after injury, promoting myelin clearance, and regulating the number of immune cells recruited to the damaged area. These, among others, are some of the reasons to study Apo D in multiple sclerosis (MS) pathology, where it could be particularly important since the autoimmune reaction against oligodendrocytes (OLGs) and myelin is generally assumed as the most plausible cause of this pathology. The aim of this work was to investigate the Apo D expression pattern in MS lesions, including active and inactive demyelinating plaques, and also remyelinating ones. Human brain tissues with inflammatory demyelination consistent with MS were used to quantify Apo D immunosignal in different lesions. Our results show a clear decrease of Apo D expression in all sclerosis plaques, being lower in the inactive than in active areas but recovers in the remyelination ones. Apo D is mainly produced by the matured OLGs of white matter and is located in cell processes surrounding the myelin sheath. All these data seem to indicate an important role of Apo D in myelination/remyelination processes as a molecule with a neuroprotective potential, and may serve as a good starting point for its study in MS.

Apolipoprotein D Overexpression Protects Against Kainate-Induced Neurotoxicity in Mice

Excitotoxicity due to the excessive activation of glutamatergic receptors leads to neuronal dysfunction and death. Excitotoxicity has been implicated in the pathogenesis of a myriad of neurodegenerative diseases with distinct etiologies such as Alzheimer's and Parkinson's. Numerous studies link apolipoprotein D (apoD), a secreted glycoprotein highly expressed in the central nervous system (CNS), to maintain and protect neurons in various mouse models of acute stress and neurodegeneration. Here, we used a mouse model overexpressing human apoD in neurons (H-apoD Tg) to test the neuroprotective effects of apoD in the kainic acid (KA)-lesioned hippocampus. Our results show that apoD overexpression in H-apoD Tg mice induces an increased resistance to KA-induced seizures, significantly attenuates inflammatory responses and confers protection against KA-induced cell apoptosis in the hippocampus. The apoD-mediated protection against KA-induced toxicity is imputable in part to increased plasma membrane Ca2+ ATPase type 2 expression (1.7-fold), decreased N-methyl-D-aspartate receptor (NMDAR) subunit NR2B levels (30 %) and lipid metabolism alterations. Indeed, we demonstrate that apoD can attenuate intracellular cholesterol content in primary hippocampal neurons and in brain of H-apoD Tg mice. In addition, apoD can be internalised by neurons and this internalisation is accentuated in ageing and injury conditions. Our results provide additional mechanistic information on the apoD-mediated neuroprotection in neurodegenerative conditions.

Apolipoprotein D Internalization Is a Basigin-dependent Mechanism

Apolipoprotein D (apoD), a member of the lipocalin family, is a 29-kDa secreted glycoprotein that binds and transports small lipophilic molecules. Expressed in several tissues, apoD is up-regulated under different stress stimuli and in a variety of pathologies. Numerous studies have revealed that overexpression of apoD led to neuroprotection in various mouse models of acute stress and neurodegeneration. This multifunctional protein is internalized in several cells types, but the specific internalization mechanism remains unknown. In this study, we demonstrate that the internalization of apoD involves a specific cell surface receptor in 293T cells, identified as the transmembrane glycoprotein basigin (BSG, CD147); more particularly, its low glycosylated form. Our results show that internalized apoD colocalizes with BSG into vesicular compartments. Down-regulation of BSG disrupted the internalization of apoD in cells. In contrast, overexpression of basigin in SH-5YSY cells, which poorly express BSG, restored the uptake of apoD. Cyclophilin A, a known ligand of BSG, competitively reduced apoD internalization, confirming that BSG is a key player in the apoD internalization process. In summary, our results demonstrate that basigin is very likely the apoD receptor and provide additional clues on the mechanisms involved in apoD-mediated functions, including neuroprotection.

Aging without Apolipoprotein D: Molecular and cellular modifications in the hippocampus and cortex

A detailed knowledge of the mechanisms underlying brain aging is fundamental to understand its functional decline and the baseline upon which brain pathologies superimpose. Endogenous protective mechanisms must contribute to the adaptability and plasticity still present in the healthy aged brain. Apolipoprotein D (ApoD) is one of the few genes with a consistent and evolutionarily conserved up-regulation in the aged brain. ApoD protecting roles upon stress or injury are well known, but a study of the effects of ApoD expression in the normal aging process is still missing. Using an ApoD-knockout mouse we analyze the effects of ApoD on factors contributing to the functional maintenance of the aged brain. We focused our cellular and molecular analyses in the cortex and hippocampus at an age representing the onset of senescence where mortality risks are below 25%, avoiding bias towards long-lived animals. Lack of ApoD causes a prematurely aged brain without altering lifespan. Age-dependent hyperkinesia and memory deficits are accompanied by differential molecular effects in the cortex and hippocampus. Transcriptome analyses reveal distinct effects of ApoD loss on the molecular age-dependent patterns of the cortex and hippocampus, with different cell-type contributions to age-regulated gene expression. Markers of glial reactivity, proteostasis, and oxidative and inflammatory damage reveal early signs of aging and enhanced brain deterioration in the ApoD-knockout brain. The lack of ApoD results in an age-enhanced significant reduction in neuronal calcium-dependent functionality markers and signs of early reduction of neuronal numbers in the cortex, thus impinging upon parameters clearly differentiating neurodegenerative conditions from healthy brain aging. Our data support the hypothesis that the physiological increased brain expression of ApoD represents a homeostatic anti-aging mechanism.

STAT3 signaling in pulmonary arterial hypertension

Pulmonary artery hypertension (PAH) is a proliferative disorder associated with enhanced pulmonary artery smooth muscle cell proliferation and suppressed apoptosis. The sustainability of this phenotype requires the activation of pro-survival transcription factor like the signal transducers and activators of transcription-3 (STAT3). Using multidisciplinary and translational approaches, we and others have demonstrated that STAT3 activation in both human and experimental models of PAH accounts for the modulation of the expression of several proteins already known as implicated in PAH pathogenesis, as well as for signal transduction to other transcription factors. Furthermore, recent data demonstrated that STAT3 could be therapeutically targeted in different animal models and some molecules are actually in clinical trials for cancer or PAH treatment.

Identification of apolipoprotein D as a cardioprotective gene using a mouse model of lethal atherosclerotic coronary artery disease

Mice with homozygous null mutations in the HDL receptor (scavenger receptor class B, type I, or SR-BI) and apolipoprotein E (apoE) genes [SR-BI/apoE double KO (SR-BI(-/-)/apoE(-/-) or dKO) mice] spontaneously develop occlusive, atherosclerotic coronary artery disease (CAD) and die prematurely (50% mortality at 42 d of age). Using microarray mRNA expression profiling, we identified genes whose expression in the hearts of dKO mice changed substantially during disease progression [at 21 d of age (no CAD), 31 d of age (small myocardial infarctions), and 43 d of age (extensive myocardial infarctions) vs. CAD-free SR-BI(+/-)/apoE(-/-) controls]. Expression of most genes that increased >sixfold in dKO hearts at 43 d also increased after coronary artery ligation. We examined the influence and potential mechanism of action of apolipoprotein D (apoD) whose expression in dKO hearts increased 80-fold by 43 d. Analysis of ischemia/reperfusion-induced myocardial infarction in both apoD KO mice and wild-type mice with abnormally high plasma levels of apoD (adenovirus-mediated hepatic overexpression) established that apoD reduces myocardial infarction. There was a correlation of apoD's ability to protect primary cultured rat cardiomyocytes from hypoxia/reoxygenation injury with its potent ability to inhibit oxidation in a standard antioxidation assay in vitro. We conclude that dKO mice represent a useful mouse model of CAD and apoD may be part of an intrinsic cardioprotective system, possibly as a consequence of its antioxidation activity.

Inhibition of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) reverses experimental pulmonary hypertension

Genetic deletion of TRAIL or antibody blockade prevents the development of pulmonary arterial hypertension and can reverse vascular remodeling in established disease.

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by the progressive narrowing and occlusion of small pulmonary arteries. Current therapies fail to fully reverse this vascular remodeling. Identifying key pathways in disease pathogenesis is therefore required for the development of new-targeted therapeutics. We have previously reported tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) immunoreactivity within pulmonary vascular lesions from patients with idiopathic PAH and animal models. Because TRAIL can induce both endothelial cell apoptosis and smooth muscle cell proliferation in the systemic circulation, we hypothesized that TRAIL is an important mediator in the pathogenesis of PAH. We demonstrate for the first time that TRAIL is a potent stimulus for pulmonary vascular remodeling in human cells and rodent models. Furthermore, antibody blockade or genetic deletion of TRAIL prevents the development of PAH in three independent rodent models. Finally, anti-TRAIL antibody treatment of rodents with established PAH reverses pulmonary vascular remodeling by reducing proliferation and inducing apoptosis, improves hemodynamic indices, and significantly increases survival. These preclinical investigations are the first to demonstrate the importance of TRAIL in PAH pathogenesis and highlight its potential as a novel therapeutic target to direct future translational therapies.

Intrinsic directionality of migrating vascular smooth muscle cells is regulated by NAD(+) biosynthesis

Cell migration is central to tissue repair and regeneration but must proceed with precise directionality to be productive. Directional migration requires external cues but also depends on the extent to which cells can inherently maintain their direction of crawling. We report that the NAD(+) biosynthetic enzyme, nicotinamide phosphoribosyltransferase (Nampt/PBEF/visfatin), mediates directionally persistent migration of vascular smooth muscle cells (SMCs). Time-lapse microscopy of human SMCs subjected to Nampt inhibition revealed chaotic motility whereas SMCs transduced with the Nampt gene displayed highly linear migration paths. Ordered motility conferred by Nampt was associated with downsizing of the lamellipodium, reduced lamellipodium wandering around the cell perimeter, and increased lamellipodial protrusion rates. These protrusive and polarity-stabilizing effects also enabled spreading SMCs to undergo bipolar elongation to an extent not typically observed in vitro. Nampt was found to localize to lamellipodia and fluorescence recovery of Nampt-eGFP after photobleaching revealed microtubule-dependent transport of Nampt to the leading edge. In addition, Nampt was found to associate with, and activate, Cdc42, and Nampt-driven directional persistence and lamellipodium anchoring required Cdc42. We conclude that high-fidelity SMC motility is coordinated by a Nampt-Cdc42 axis that yields protrusive but small and anchored lamellipodia. This novel, NAD(+)-synthesis-dependent control over motility may be crucial for efficient repair and regeneration of the vasculature, and possibly other tissues.

Endothelial cells downregulate apolipoprotein D expression in mural cells through paracrine secretion and Notch signaling

Endothelial and mural cell interactions are vitally important for proper formation and function of blood vessels. These two cell types communicate to regulate multiple aspects of vessel function. In studying genes regulated by this interaction, we identified apolipoprotein D (APOD) as one gene that is downregulated in mural cells by coculture with endothelial cells. APOD is a secreted glycoprotein that has been implicated in governing stress response, lipid metabolism, and aging. Moreover, APOD is known to regulate smooth muscle cells and is found in abundance within atherosclerotic lesions. Our data show that the regulation of APOD in mural cells is bimodal. Paracrine secretion by endothelial cells causes partial downregulation of APOD expression. Additionally, cell contact-dependent Notch signaling plays a role. NOTCH3 on mural cells promotes the downregulation of APOD, possibly through interaction with the JAGGED-1 ligand on endothelial cells. Our results show that NOTCH3 contributes to the downregulation of APOD and by itself is sufficient to attenuate APOD transcript expression. In examining the consequence of decreased APOD expression in mural cells, we show that APOD negatively regulates cell adhesion. APOD attenuates adhesion by reducing focal contacts; however, it has no effect on stress fiber formation. These data reveal a novel mechanism in which endothelial cells control neighboring mural cells through the downregulation of APOD, which, in turn, influences mural cell function by modulating adhesion.

BMP promotes motility and represses growth of smooth muscle cells by activation of tandem Wnt pathways

We present a novel cell-signaling paradigm in which bone morphogenetic protein 2 (BMP-2) consecutively and interdependently activates the wingless (Wnt)-β-catenin (βC) and Wnt-planar cell polarity (PCP) signaling pathways to facilitate vascular smooth muscle motility while simultaneously suppressing growth. We show that BMP-2, in a phospho-Akt-dependent manner, induces βC transcriptional activity to produce fibronectin, which then activates integrin-linked kinase 1 (ILK-1) via α4-integrins. ILK-1 then induces the Wnt-PCP pathway by binding a proline-rich motif in disheveled (Dvl) and consequently activating RhoA-Rac1-mediated motility. Transfection of a Dvl mutant that binds βC without activating RhoA-Rac1 not only prevents BMP-2-mediated vascular smooth muscle cell motility but promotes proliferation in association with persistent βC activity. Interfering with the Dvl-dependent Wnt-PCP activation in a murine stented aortic graft injury model promotes extensive neointima formation, as shown by optical coherence tomography and histopathology. We speculate that, in response to injury, factors that subvert BMP-2-mediated tandem activation of Wnt-βC and Wnt-PCP pathways contribute to obliterative vascular disease in both the systemic and pulmonary circulations.

Neuroprotective effect of apolipoprotein D against human coronavirus OC43-induced encephalitis in mice

Apolipoprotein D (apoD) is a lipocalin upregulated in the nervous system after injury or pathologies such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. We previously demonstrated that apoD protects against neuropathology by controlling the level of peroxidated lipids. Here, we further investigated the biological function of apoD in a mouse model of acute encephalitis. Our results show that apoD transcript and protein are upregulated during acute encephalitis induced by the human coronavirus OC43 (HCoV-OC43) infection. The apoD upregulation coincides with glial activation, and its expression returns to normal levels when the virus is cleared, concomitantly to a resolved glial reactivity. In addition, the overexpression of human apoD in the neurons of Thy-1/ApoD transgenic mice results in a threefold increase of the number of mice surviving to HCoV-OC43 infection. This increased survival rate is correlated with an upregulated glial activation associated with a limited innate immune response (cytokines, chemokines) and T-cell infiltration into infected brains. Moreover, the protection seems to be associated with a restricted phospholipase A2 activity. These data reveal a role for apoD in the regulation of inflammation and suggest that it protects from HCoV-OC43-induced encephalitis, most likely through the phospholipase A2 signaling pathways.

SM22alpha-targeted deletion of bone morphogenetic protein receptor 1A in mice impairs cardiac and vascular development, and influences organogenesis

Expression of bone morphogenetic protein receptor 1A (BMPR1A) is attenuated in the lung vessels of patients with pulmonary arterial hypertension, but the functional impact of this abnormality is unknown. We ablated Bmpr1a in cardiomyocytes and vascular smooth muscle cells (VSMCs) by breeding mice possessing a loxP allele of Bmpr1a (Bmpr1aflox) expressing R26R with SM22alpha-Cre mice. SM22alpha-Cre;R26R;Bmpr1aflox/flox mice died soon after embryonic day 11 (E11) with massive vascular and pericardial hemorrhage and impaired brain development. At E10.5, SM22alpha-Cre;R26R;Bmpr1aflox/flox embryos showed thinning of the myocardium associated with reduced cell proliferation. These embryos also had severe dilatation of the aorta and large vessels with impaired investment of SMCs that was also related to reduced proliferation. SM22alpha-Cre;R26R;Bmpr1aflox/flox mice showed collapsed telencephalon in association with impaired clearing of brain microvessels in areas where reduced apoptosis was observed. Transcript and protein levels of matrix metalloproteinase (MMP) 2 and 9 were reduced in E9.5 and E10.5 SM22alpha-Cre;R26R;Bmpr1aflox/flox embryos, respectively. Knock-down of BMPR1A by RNA interference in human pulmonary artery SMCs reduced MMP2 and MMP9 activity, attenuated serum-induced proliferation, and impaired PDGF-BB-directed migration. RNA interference of MMP2 or MMP9 recapitulated these abnormalities, supporting a functional interaction between BMP signaling and MMP expression. In human brain microvascular pericytes, knock-down of BMPR1A reduced MMP2 activity and knock-down of either BMPR1A or MMP2 caused resistance to apoptosis. Thus, loss of Bmpr1a, by decreasing MMP2 and/or MMP9 activity, can account for vascular dilatation and persistence of brain microvessels, leading to the impaired organogenesis documented in the brain.

Evidence of a role for osteoprotegerin in the pathogenesis of pulmonary arterial hypertension

Pulmonary artery smooth muscle cell (PA-SMC) migration and proliferation are key processes in the pathogenesis of pulmonary arterial hypertension (PAH). Recent information suggests that abnormalities in the bone morphogenetic protein (BMP) receptor 2 (BMP-R2) signaling pathway are important in PAH pathogenesis. It remains unclear whether and how this pathway interacts with, for example, serotonin (5-HT) and inflammation to trigger and/or sustain the development of PAH. The secreted glycoprotein osteoprotegerin (OPG) is emerging as an important regulatory molecule in vascular biology and is modulated by BMPs, 5-HT, and interleukin-1 in other cell types. However, whether OPG is expressed by PA-SMCs within PAH lesions and plays a role in PAH is unknown. Immunohistochemistry of human PAH lesions demonstrated increased OPG expression, and OPG was significantly increased in idiopathic PAH patient serum. Recombinant OPG stimulated proliferation and migration of PA-SMCs in vitro, and BMP-R2 RNA interference increased OPG secretion. Additionally, both 5-HT and interleukin-1 also increased OPG secretion. These data are the first to demonstrate that OPG is increased in PAH and that it can regulate PA-SMC proliferation and migration. OPG may provide a common link between the different pathways associated with the disease, potentially playing an important role in the pathogenesis of PAH.

Breast cancer and metabolic syndrome linked through the plasminogen activator inhibitor-1 cycle

Plasminogen activator inhibitor-1 (PAI-1) is a physiological inhibitor of urokinase (uPA), a serine protease known to promote cell migration and invasion. Intuitively, increased levels of PAI-1 should be beneficial in downregulating uPA activity, particularly in cancer. By contrast, in vivo, increased levels of PAI-1 are associated with a poor prognosis in breast cancer. This phenomenon is termed the "PAI-1 paradox". Many factors are responsible for the upregulation of PAI-1 in the tumor microenvironment. We hypothesize that there is a breast cancer predisposition to a more aggressive stage when PAI-1 is upregulated as a consequence of Metabolic Syndrome (MetS). MetS exerts a detrimental effect on the breast tumor microenvironment that supports cancer invasion. People with MetS have an increased risk of coronary heart disease, stroke, peripheral vascular disease and hyperinsulinemia. Recently, MetS has also been identified as a risk factor for breast cancer. We hypothesize the existence of the "PAI-1 cycle". Sustained by MetS, adipocytokines alter PAI-1 expression to promote angiogenesis, tumor-cell migration and procoagulant microparticle formation from endothelial cells, which generates thrombin and further propagates PAI-1 synthesis. All of these factors culminate in a chemotherapy-resistant breast tumor microenvironment. The PAI-1 cycle may partly explain the PAI-1 paradox. In this hypothesis paper, we will discuss further how MetS upregulates PAI-1 and how an increased level of PAI-1 can be linked to a poor prognosis.

Lentiviral Gene Delivery of vMIP-II to Transplanted Endothelial Cells and Endothelial Progenitors Is Proangiogenic In Vivo

Therapies that stimulate angiogenesis show promise in revascularization of transplanted or ischemic tissues. Viral macrophage inflammatory protein-II (vMIP-II) is encoded by human herpesvirus 8, and it can be both immunosuppressive and proangiogenic. However, little has been done to characterize the potential of vMIP-II-induced angiogenesis. We engineered a vMIP-II lentiviral gene vector, transduced both mature endothelial cells and progenitors, and transplanted these in Matrigel templates as an in vivo angiogenesis model. Our results show that vMIP-II promotes new, functional, branching, and segmented vessels associated with smooth muscle cells and connected with the host vasculature. Angiogenesis is enhanced through host cells as well as through transplanted vMIP-expressing endothelial cells. As a proof-of-concept for using vMIP-II in clinical applications, we showed that islets co-transplanted with endothelial cells expressing vMIP-II were revascularized and survived in Matrigel templates, whereas no islets survived under control conditions. vMIP-II up-regulates the expression of multiple proangiogenic factors that can have a synergistic effect. These include vascular endothelial growth factor (VEGF), kinase insert domain receptor, neuropilin 2, carcinoembryonic antigen-related cell adhesion molecule 1, interleukin-1alpha, fibronectin, and integrins alpha3, alpha4, and alpha5. These results provide the first demonstration that vMIP-II is proangiogenic in vivo and can deliver this function to endothelial progenitors as well as to mature endothelial cells through vector-mediated gene delivery.

Modulation of apolipoprotein D expression and translocation under specific stress conditions

Apolipoprotein D is a lipocalin, primarily associated with high density lipoproteins in human plasma. Its expression is induced in several pathological and stressful conditions including growth arrest suggesting that it could act as a nonspecific stress protein. A survey of cellular stresses shows those causing an extended growth arrest, as hydrogen peroxide and UV light increase apoD expression. Alternatively, lipopolysaccharide (LPS), a pro-inflammatory agonist showed a time- and dose-dependent effect on apoD expression that correlates with an increase in proliferation. At the promoter level, NF-kB, AP-1 and APRE-3 proved to be the elements implicated in the LPS response. Colocalization of apoDh-GFP fusion constructs with DNA and Golgi markers, immunocytochemistry of the endogenous protein and cell fractionation showed that both serum starvation and LPS treatment caused a displacement of apoD localization. In normal conditions, apoD is mainly perinuclear but it accumulates in cytoplasm and nucleus under these stress conditions. Since nuclear apoD appears derived from the secreted protein, it may act as an extracellular ligand transporter as well as a transcriptional regulator depending on its location. This role of apoD inside the cell is not only dependent of endogenous apoD but may also be provided by exogenous apoD entering the cell.

Interdependent Serotonin Transporter and Receptor Pathways Regulate S100A4/Mts1, a Gene Associated With Pulmonary Vascular Disease

Heightened expression of the S100 calcium–binding protein, S100A4/Mts1, is observed in pulmonary vascular disease. Loss of serotonin (5-hydroxytryptamine [5-HT]) receptors or of the serotonin transporter (SERT) attenuates pulmonary hypertension in animals, and polymorphisms causing gain of SERT function are linked to clinical pulmonary vascular disease. Because 5-HT induces release of S100β, we investigated the codependence of 5-HT receptors and SERT in regulating S100A4/Mts1 in human pulmonary artery smooth muscle cells (hPA-SMC). 5-HT elevated S100A4/Mts1 mRNA levels and increased S100A4/Mts1 protein in hPA-SMC lysates and culture media. S100A4/Mts1 in the culture media stimulated proliferation and migration of hPA-SMC in a manner dependent on the receptor for advanced glycation end products. Treatment with SB224289 (selective antagonist of 5-HT 1B ), fluoxetine (SERT inhibitor), SERT RNA-interference, and iproniazid (monoamine oxidase-A inhibitor), blocked 5-HT–induced S100A4/Mts1. 5-HT signaling mediated phosphorylation (p) of extracellular signal–regulated kinase 1/2 (pERK1/2), but pERK1/2 nuclear translocation depended on SERT, monoamine oxidase activity, and reactive oxygen species. Nuclear translocation of pERK1/2 was required for pGATA-4–mediated transcription of S100A4/Mts1. These data provide evidence for a mechanistic link between the 5-HT pathway and S100A4/Mts1 in pulmonary hypertension and explain how the 5-HT 1B receptor and SERT are codependent in regulating S100A4/Mts1.

Molecular markers distinguish bone marrow mesenchymal stem cells from fibroblasts

To characterize mesenchymal stem cells (MSC), we compared gene expression profiles in human bone marrow MSC (11 lines) and human fibroblasts (4 lines) by RT-PCR and real time PCR. Messenger RNA levels of MHC-DR-alpha, MHC-DR-beta, MHC-DR-associated protein CD74, tissue factor pathway inhibitor-2, and neuroserpin were much higher in MSC than in fibroblasts, even in the presence of large interindividual variations. Those of adrenomedullin, apolipoprotein D, C-type lectin superfamily member-2, collagen type XV alpha1, CUG triplet repeat RNA-binding protein, matrix metalloproteinase-1, protein tyrosine kinase-7, and Sam68-like phosphotyrosine protein/T-STAR were lower in MSC than in fibroblasts. FACS analysis showed that cell surface expression of MHC-DR was also higher in MSC than in fibroblasts. MHC-DR expression decreased after osteogenic differentiation, whereas the expression of adrenomedullin-a potent stimulator of osteoblast activity-along with collagen XV alpha1 and apolipoprotein D increased after osteogenic differentiation. The marker genes identified in this study should be useful for characterization of MSC both in basic and clinical studies.