Cav1.2 regulated odontogenic differentiation of NG2+ pericytes during pulp injury

NG2⁺ pericytes, as the possible precursor cells of mesenchymal stem cells (MSCs), have drawn attention due to their ability to differentiate into odontoblasts. Ca_v1.2 is involved in the differentiation process of stem cells, but its role in the differentiation of NG2⁺ pericytes is not clear. The aim of the present study was to examine the role of Ca_v1.2 in the differentiation of NG2⁺ pericytes into odontoblasts. NG2⁺ pericytes were obtained from human dental pulp cells by magnetic-activated cell sorting. During the odontogenic differentiation of NG2⁺ pericytes, the effects of the Ca_v1.2 inhibitors, nimodipine and Ca_v1.2 knockdown shRNA, were analyzed by real-time polymerase chain reaction and alizarin red staining. NG2CreERT2/Rosa26-GFP lineage-tracing mice were established to further investigate the roles of NG2⁺ pericytes and Ca_v1.2 in incisor self-repair after injury in vivo. At 10 min, 1 day, and 3 days after pulp injuries in transgenic mice, NG2-GFP⁺ and Ca_v1.2 immunofluorescence co-staining was performed on the incisors. Nimodipine treatment and Ca_v1.2 knockdown showed similar inhibition of calcium nodule formation and mRNA levels of osteogenic markers (DSPP, DMP1, and Runx2, p < 0.05). NG2⁺ pericytes migrated from their inherent perivascular location to the odontoblast layers after pulp injury. Ca_v1.2 showed a similar response pattern as NG2⁺ pericytes and gradually returned to normal levels. In addition, many co-stained areas of Ca_v1.2 and NG2⁺ pericytes, both near the perivascular and odontoblast layers, were observed. These results indicate that Ca_v1.2 played a vital role in the odontogenic differentiation of NG2⁺ pericytes, and that it might be closely linked to the NG2⁺ pericytes-mediated repair of dental pulp injury in vivo.

Myopericytoma arising from myopericytosis-a hitherto unrecognized entity within the lung

Two cases of myopericytosis combined with pericytoma originating within the lung are reported. These are rare pulmonary tumors. The differential diagnosis for hemangiopericytoma and pericytic tumors with glomus elements is discussed. Both myopericytic lesions mimic other lesions, which are more commonly seen in the lung. Based on the expression of vascular growth factor receptors 2 and 3, an antiangiogenic therapy was suggested for the patient with the myopericytoma. A treatment with an angiogenesis inhibitor resulted in a regression of the tumor, but not the precursor lesion. Probably a more specific therapy using tyrosine kinase inhibitors for VEGFR2/3 might better control these myopericytic proliferations.

Tracing CD34+ Stromal Fibroblasts in Palatal Mucosa and Periodontal Granulation Tissue as a Possible Cell Reservoir for Periodontal Regeneration

The aim of the present research was to trace CD34+ stromal fibroblastic cells (CD34+ SFCs) in the palatal connective tissue harvested for muco-gingival surgical procedures and in granulation tissues from periodontal pockets using immunohistochemical and transmission electron microscopy. Immunohistochemical analysis targeted the presence of three antigens: CD31, α-smooth muscle actin (α-SMA), and CD34. In the palate, CD31 staining revealed a colored inner ring of the vessels representing the endothelium, α-SMA+ was located in the medial layer of the vasculature, and CD34 was intensely expressed by endothelial cells and artery adventitial cells (considered to be CD34+ SFCs). Granulation tissue showed the same pattern for CD31+ and α-SMA, but a different staining pattern for CD34. Ultrastructural examination of the palatal tissue highlighted perivascular cells with fibroblast-like characteristics and pericytes in close spatial relationship to endothelial cells. The ultrastructural evaluation of granulation tissue sections confirmed the presence of neovasculature and the inflammatory nature of this tissue. The present study traced the presence of CD34+ SFCs and of pericytes in the palatal connective tissue thus highlighting once more its intrinsic regenerative capabilities. The clinical and systemic factors triggering mobilization and influencing the fate of local CD34+SCFs and other progenitors are issues to be further investigated.

Evaluation of MMP-1, MMP-10, TIMP-1, a-SMA and TGF-b1 in angiofibromas of tuberous sclerosis

AIM

Tuberous sclerosis is a neurocutaneous syndrome characterized by affect multiple organs such as brain, kidneys, heart, eyes, lungs and skin. The aim of this study was to analyze the pattern of immunolocalization of markers MMP-1, MMP-10, TIMP-1, α-SMA and TGF-β1 in oral and facial angiofibromas in individuals affected by tuberous sclerosis.

METHODS

Microscopical analyses on hematoxilin-eosin and immunohistochemistry reactions were performed to analyze the previously cited biological markers pattern in orofacial angiofibromas.

RESULTS

Reactivity was observed for MMP-1, MMP-10 and TGF-β1, in addition to negative for TIMP-1 and α-SMA, except perivascular and epithelial staining for this. Concerning the intensity, a strong marking for MMP-1 in the basal layer of the epithelium, and a slight positivity in the suprabasal layers predominated. MMP-10 was slightly expressed in all epithelial layers. The connective tissue showed slight to moderate reactivity for MMP-1 and MMP-10. TIMP-1 demonstrated slight to moderate marking in the various layers of a single lesion and to TGF-β1 expression showed varied in intensity staining both between lesions and between tissue layers.

CONCLUSION

MMP-1, MMP-10 and TGF-β1 exhibited reactivity in oral and cutaneous angiofibromas with heterogeneous distribution patterns among both tissue elements analyzed in the intensity of marking the same among the specimens. TIMP-1 showed reactivity predominantly negative in the specimens analyzed and α-SMA presented restricted to epithelial and perivascular regions of these lesions.

Hepatocyte growth factor and c-Met expression in pericytes: implications for atherosclerotic plaque development

Intraplaque neovascularization contributes to the progression of atherosclerosis. Our aim is to understand the mobilization of cells and factors involved in this process. We investigated the localization of hepatocyte growth factor (HGF) and its receptor, c-Met, in human atherosclerotic plaques, together with the effects of HGF on pericyte migration in vitro. Atherosclerotic femoral arterial segments were collected and analysed from 13 subjects who were undergoing lower limb amputation. Pericytes were identified in human lesions using a 3G5 antibody. Immunohistochemical analysis localized HGF mainly around microvessels, in association with some, but not all, CD31-positive endothelial cells. c-Met expression was mainly associated with smooth muscle cells and pericytes, around some, but not all, microvessels within the atherosclerotic lesions; no detection was apparent in normal internal mammary arteries. Using RT-PCR, we demonstrated expression of HGF and c-Met in a rat pericyte cell-line, TR-PCT1, and in primary pericytes. HGF treatment of TR-PCT1 cells induced their migration, but not their proliferation, in a dose-dependent manner (10-100 ng/ml, p<0.01), an effect mediated by activation of the serine/threonine kinase Akt, shown by western blot analysis. Treating the cells with the PI3K inhibitors Wortmannin (0.1 microM) or LY294002 (10 microM) abolished these effects. This work demonstrates the expression of c-Met and HGF in human atherosclerotic arteries, in association with SM-actin-positive cells and CD-31-positive cells, respectively. HGF induces pericyte migration via PI3-kinase and Akt activation in vitro. HGF and c-Met may be involved in neovascularization during plaque development, and may recruit pericytes to neovessels. Since pericytes are thought to mechanically stabilize new blood vessels, these factors may function to protect against haemorrhage.

The perivascular space as a path of hematopoietic progenitor cells and mature T cells between the blood circulation and the thymic parenchyma

It is known that selected populations of lymphoid cells migrate into and from the adult thymus through blood vessels at the cortico-medullary junction and in the medulla. Here, we show that in the perivascular spaces (PVS) of mice surrounding large blood vessels, CD117-positive hematopoietic progenitor cells, CD4 single-positive (SP) and CD8SP T cells are located. However, developing thymocytes, CD25-positive cells and CD4 and CD8 double-positive cells, are not detectable in the PVS. After intravenous (i.v.) injection of CD117-positive bone marrow (BM) cells from C57BL/6 mice into non-irradiated RAG2 mutant mice i.v., donor-derived cells first preferentially migrate into the PVS within 30 min, and then the number of donor-derived cells in the thymic parenchyma increases. Likewise, newly developed mature T cells in the thymic parenchyma of RAG2 mutant mice transferred with wild-type BM cells migrate to the PVS, before leaving the thymus to the circulation. Accumulation of mature T cells was observed after treatment with sphingosine-1 phosphate receptor agonist FTY720 not only in the medulla but also in the thymic PVS. These results suggest that the PVS is a transit pathway for progenitor cells to immigrate into the thymus and for mature T cells to emigrate from the thymus.

Pericyte coverage of abnormal blood vessels in myelofibrotic bone marrows

BACKGROUND AND OBJECTIVES

Myelofibrotic bone marrow displays abnormal angiogenesis but the pathogenic mechanisms of this are poorly understood. Since pericyte abnormalities are described on solid tumor vessels we studied whether vessel morphology and pericyte coverage in bone marrow samples from patients with myelofibrosis differed from that in samples from controls.

DESIGN AND METHODS

We assessed the microvascular density (MVD), vessel morphology and pericyte coverage in bone marrows from 19 myelofibrosis patients and nine controls. We also studied the same parameters in two mouse models of myelofibrosis, with genetic alterations affecting megakaryocyte differentiation (i.e. one model with low GATA-1 expression and the other with over-expression of thrombopoietin).

RESULTS

In myelofibrotic marrows, MVD was 3.8-fold greater than in controls (p<0.001) and vessels displayed 5.9-fold larger mean perimeters (p<0.001). MVD was 1.8-fold greater in JAK2 V617F-positive than in negative patients (p=0.026). Moreover, 92+/-11 % of vessels in patients with myelofibrosis were pericyte-coated but only 51+/-20 % of vessels in controls (p<0.001). In the two mouse models of myelofibrosis caused by targeting megakaryocytopoesis, wide, pericyte-coated and morphologically aberrant vessels were detected. MVD was significantly greater in bone marrow and spleen samples from animals with myelofibrosis than in wild-type mice.

INTERPRETATION AND CONCLUSIONS

We conclude that angiogenesis is similarly abnormal in human and murine myelofibrosis with intense pericyte coating, presumably related to abnormal megakaryocytopoiesis.

Pericytes of human skeletal muscle are myogenic precursors distinct from satellite cells

Cells derived from blood vessels of human skeletal muscle can regenerate skeletal muscle, similarly to embryonic mesoangioblasts. However, adult cells do not express endothelial markers, but instead express markers of pericytes, such as NG2 proteoglycan and alkaline phosphatase (ALP), and can be prospectively isolated from freshly dissociated ALP(+) cells. Unlike canonical myogenic precursors (satellite cells), pericyte-derived cells express myogenic markers only in differentiated myotubes, which they form spontaneously with high efficiency. When transplanted into severe combined immune deficient-X-linked, mouse muscular dystrophy (scid-mdx) mice, pericyte-derived cells colonize host muscle and generate numerous fibres expressing human dystrophin. Similar cells isolated from Duchenne patients, and engineered to express human mini-dystrophin, also give rise to many dystrophin-positive fibres in vivo. These data show that myogenic precursors, distinct from satellite cells, are associated with microvascular walls in the human skeletal muscle, may represent a correlate of embryonic 'mesoangioblasts' present after birth and may be a promising candidate for future cell-therapy protocols in patients.

Characterization of freshly isolated and cultured cells derived from the fatty and fluid portions of liposuction aspirates

Liposuction aspirates (primarily saline solution, blood, and adipose tissue fragments) separate into fatty and fluid portions. Cells isolated from the fatty portion are termed processed lipoaspirate (PLA) cells and contain adipose-derived adherent stromal cells (ASCs). Here we define cells isolated from the fluid portion of liposuction aspirates as liposuction aspirate fluid (LAF) cells. Stromal vascular fractions (SVF) were isolated separately from both portions and characterized under cultured and non-cultured conditions. A comparable number of LAF and PLA cells were freshly isolated, but fewer LAF cells were adherent. CD34+ CD45- cells from fresh LAF isolates were expanded by adherent culture, suggesting that LAF cells contain ASCs. Although freshly isolated PLA and LAF cells have distinct cell surface marker profiles, adherent PLA and LAF cells have quite similar characteristics with regard to growth kinetics, morphology, capacity for differentiation, and surface marker profiles. After plating, both PLA and LAF cells showed significant increased expression of CD29, CD44, CD49d, CD73, CD90, CD105, and CD151 and decreased expression of CD31 and CD45. Multicolor FACS analysis revealed that SVF are composed of heterogeneous cell populations including blood-derived cells (CD45+), ASCs (CD31- CD34+ CD45- CD90+ CD105- CD146-), endothelial (progenitor) cells (CD31+ CD34+ CD45- CD90+ CD105low CD146+), pericytes (CD31- CD34- CD45- CD90+ CD105- CD146+), and other cells. After plating, ASCs showed a dramatic increase in CD105 expression. Although some adherent ASCs lost CD34 expression with increasing culture time, our culture method maintained CD34 expression in ASCs for at least 10-20 weeks. These results suggest that liposuction-derived cells may be useful and valuable for cell-based therapies.

Microarray analysis of blood microvessels from PDGF-B and PDGF-Rbeta mutant mice identifies novel markers for brain pericytes

Normal blood microvessels are lined by pericytes, which contribute to microvessel development and stability through mechanisms that are poorly understood. Pericyte deficiency has been implicated in the pathogenesis of microvascular abnormalities associated with diabetes and tumors. However, the unambiguous identification of pericytes is still a problem because of cellular heterogeneity and few available molecular markers. Here we describe an approach to identify pericyte markers based on transcription profiling of pericyte-deficient brain microvessels isolated from platelet-derived growth factor (PDGF-B)-/- and PDGF beta receptor (PDGFRbeta)-/- mouse mutants. The approach was validated by the identification of known pericyte markers among the most down-regulated genes in PDGF-B-/- and PDGFRbeta-/- microvessels. Of candidates for novel pericyte markers, we selected ATP-sensitive potassium-channel Kir6.1 (also known as Kcnj8) and sulfonylurea receptor 2, (SUR2, also known as Abcc9), both part of the same channel complex, as well as delta homologue 1 (DLK1) for in situ hybridization, which demonstrated their specific expression in brain pericytes of mouse embryos. We also show that Kir6.1 is highly expressed in pericytes in brain but undetectable in pericytes in skin and heart. The three new brain pericyte markers are signaling molecules implicated in ion transport and intercellular signaling, potentially opening new windows on pericyte function in brain microvessels.

N-cadherin deficiency impairs pericyte recruitment, and not endothelial differentiation or sprouting, in embryonic stem cell-derived angiogenesis

Endothelial cells express two classical cadherins, VE-cadherin and N-cadherin. VE-cadherin is absolutely required for vascular morphogenesis, but N-cadherin is thought to participate in vessel stabilization by interacting with periendothelial cells during vessel formation. However, recent data suggest a more critical role for N-cadherin in endothelium that would regulate angiogenesis, in part by controlling VE-cadherin expression. In this study, we have assessed N-cadherin function in vascular development using an in vitro model derived from embryonic stem (ES) cell differentiation. We show that pluripotent ES cells genetically null for N-cadherin can differentiate normally into endothelial cells. In addition, sprouting angiogenesis was unaltered, suggesting that N-cadherin is not essential for the early events of angiogenesis. However, the lack of N-cadherin led to an impairment in pericyte covering of endothelial outgrowths. We conclude that N-cadherin is necessary neither for vasculogenesis nor proliferation and migration of endothelial cells but is required for the subsequent maturation of endothelial sprouts by interacting with pericytes.

Absence of smooth muscle actin-positive pericyte coverage of tumor vessels correlates with hematogenous metastasis and prognosis of colorectal cancer patients

OBJECTIVES

Immature microvessels, which are not covered by pericytes, are irregular and leaky. We hypothesized that tumor cells can penetrate immature microvessels more easily than mature microvessels. In this study, we investigated the maturation of angiogenesis by the immunohistochemical staining of colorectal cancer specimens and determined the correlation between the microvessel count or the maturity of microvessels and clinicopathological variables.

METHODS

Ninety-two surgical specimens from our department were used. Double immunostaining of endothelial cells with anti-CD34 antibody and pericytes with anti-alpha-smooth muscle actin antibody was performed. The microvessel density (MVD) and microvessel pericyte coverage index (MPI) as an index of microvessel maturation were evaluated.

RESULTS

The MVD showed a significant positive correlation with tumor size, depth of invasion and Dukes' stage. The MPI showed a significant positive correlation with the histological differentiation of the tumor tissues and distant metastasis at the time of operation. The high MVD group (> or =26.0, n = 50) tended to have a poorer prognosis than the low MVD group (<26.0, n = 42) (p = 0.097). Next, the 50 patients in the high MVD group were classified into two subgroups of high MPI (> or =78.1%, n = 25) and low MPI (<78.1%, n = 25). MPI showed a significant negative correlation with hematogenous metastasis, and the low MPI group demonstrated a significantly poorer survival than the high MPI group (p = 0.040).

CONCLUSIONS

These findings demonstrate that immature neovascularization was observed in poorly differentiated tumors and was correlated with metastasis, resulting in a poorer prognosis. Taken together, not only microvessel density but also vascular maturation were crucial factors for colorectal cancer patients.

Differential arterial/venous expression of NG2 proteoglycan in perivascular cells along microvessels: identifying a venule-specific phenotype

OBJECTIVE

Similar to other vascular pericyte markers, including smooth muscle (SM) alpha-actin, desmin, and PDGF-beta-receptor, NG2 proteoglycan is not pericyte specific. Therefore, the use of NG2 as a pericyte marker, especially in cell lineage studies, in comparison to other nonspecific pericyte markers requires an understanding of how its expression varies spatially within a microvascular network. The objective of this study was to characterize NG2 expression along vessels within rat microvascular networks and compare this to SM alpha-actin expression.

METHODS

Mesenteric tissue, subcutaneous tissue, spinotrapezius muscle, and gracilis muscle were harvested from 250-g, female, Sprague-Dawley rats and stained for NG2 and SM alpha-actin. The distribution of NG2 expression was evaluated in mesenteric networks (n = 28) with complementary observations in subcutaneous tissue and skeletal muscle.

RESULTS

Perivascular cells, including mature smooth muscle cells (SMCs), immature SMCs, and pericytes, expressed NG2. Most importantly, NG2 expression was primarily confined to perivascular cells along arterioles and capillaries, and continuous expression was not observed along venules beyond the immediate postcapillary vessels. The differential expression of NG2 along the arteriolar side of microvascular networks was also observed in rat subcutaneous and skeletal muscle.

CONCLUSIONS

The results indicate that NG2 is expressed by all perivascular cells along arterioles, and its absence denotes a venule-specific phenotype. These results identify for the first time a marker that differentiates venous smooth muscle and pericytes from other capillary- and arteriole-associated perivascular cells.

Microarray analysis of in vitro pericyte differentiation reveals an angiogenic program of gene expression

The vasculature consists of endothelial cells (ECs) lined by pericyte/vascular smooth muscle cells (vSMCs). Pericyte/vSMCs provide support to the mature vasculature but are also essential for normal blood vessel development. To determine how pericyte-EC communication influences vascular development, we used the well-established in vitro model of TGFbeta-stimulated differentiation of 10T1/2 cells into pericyte/vSMCs. Microarray analysis was performed to identify genes that were differentially expressed by induced vs. uninduced 10T1/2 cells. We discovered that these cells show an angiogenic program of gene expression, with up-regulation of several genes previously implicated in angiogenesis, including VEGF, IL-6, VEGF-C, HB-EGF, CTGF, tenascin C, integrin alpha5, and Eph receptor A2. Up-regulation of some genes was validated by Western blots and immunocytochemistry. We also examined the functional significance of these gene expression changes. VEGF and IL-6 alone and in combination were important in 10T1/2 cell differentiation. Furthermore, we used a coculture system of 10T1/2 and human umbilical vein ECs (HUVECs), resulting in the formation of cordlike structures by the HUVECs. This cordlike structure formation was disrupted when neutralizing antibodies to VEGF or IL-6 were added to the coculture system. The results of these studies show that factors produced by pericytes may be responsible for recruiting ECs and promoting angiogenesis. Therefore, a further understanding of the genes involved in pericyte differentiation could provide a novel approach for developing anti-angiogenic therapies.

Kinetics of vascular normalization by VEGFR2 blockade governs brain tumor response to radiation: role of oxygenation, angiopoietin-1, and matrix metalloproteinases

The recent landmark Phase III clinical trial with a VEGF-specific antibody suggests that antiangiogenic therapy must be combined with cytotoxic therapy for the treatment of solid tumors. However, there are no guidelines for optimal scheduling of these therapies. Here we show that VEGFR2 blockade creates a "normalization window"--a period during which combined radiation therapy gives the best outcome. This window is characterized by an increase in tumor oxygenation, which is known to enhance radiation response. During the normalization window, but not before or after it, VEGFR2 blockade increases pericyte coverage of brain tumor vessels via upregulation of Ang1 and degrades their pathologically thick basement membrane via MMP activation.

The human corpus luteum: which cells have progesterone receptors?

Studies comparing the regressing corpus luteum with the rescued corpus luteum have demonstrated that human chorionic gonadotrophin (hCG) has effects on cell types that do not express hCG receptors. As progesterone synthesis is hCG dependent and the corpus luteum has been shown to express genomic progesterone receptors, progesterone is a candidate molecule for these paracrine effects. This study aimed to define the cellular localisation of progesterone receptors in the human corpus luteum using dual-staining immunohistochemistry for genomic progesterone receptors and specific cellular markers. Well-characterised corpora lutea (n = 12) from different stages of the luteal phase were studied. The same distribution was observed in all corpora lutea examined. The steroidogenic cells (3β-hydroxysteroid dehydrogenase positive) and both thecalutein (17α-hydroxylase positive) and granulosalutein (aromatase positive) express progesterone receptors, as do stromal fibroblasts (vimentin positive, fibroblast antigen positive). Vascular endothelial cells (CD31 positive), pericytes (α-smooth muscle actin positive), macrophages (CD68 positive) and fibroblasts within the central clot do not express nuclear progesterone receptors. Progesterone is a candidate messenger molecule for the effects of hCG on the matrix metalloproteinase-producing stromal fibroblasts. Some of the effects of hCG on steroidogenic cells may be mediated by progesterone, but its effects on blood vessels and macrophages require alternate paracrine signalling mechanisms. In addition, there appears to be at least two fibroblast populations in the corpus luteum.

Differential expression of connective tissue growth factor in microglia and pericytes in the human diabetic retina

BACKGROUND/AIM

Connective tissue growth factor (CTGF) stimulates extracellular matrix formation, fibrosis, and angiogenesis. It has a role in the pathogenesis of diabetic nephropathy and possibly in diabetic retinopathy (DR): in cultured retinal vascular cells CTGF is induced by VEGF-A. To further characterise this role the authors investigated CTGF expression in normal and diabetic human retina.

METHODS

CTGF expression patterns were studied by immunohistochemistry in the retina of eyes of 36 diabetic persons and 18 non-diabetic controls and compared with markers of endothelial cells (CD31, PAL-E), pericytes (NG2), astrocytes (GFAP), and microglia (CD45).

RESULTS

In the retina, distinct and specific staining of CTGF was observed in microglia, situated around or in close vicinity of retinal capillaries. In the control cases, sporadic staining of pericytes was also observed within the vascular wall. In contrast, in the retina of people with diabetes, CTGF staining in microglia was decreased and staining in pericytes was increased. This pattern of predominantly pericyte staining was observed in 20 out of 36 diabetic cases and in one out of 18 controls. The altered CTGF staining patterns in the diabetic cases did not correlate to staining of PAL-E, a marker of retinal vascular leakage associated with DR.

CONCLUSIONS

The study shows that CTGF is expressed in microglia in the normal retina whereas in a large subset of diabetic persons, CTGF expression shifts to microvascular pericytes. This altered CTGF expression pattern appears unrelated to manifest DR and may therefore represent a preclinical retinal change caused by diabetes. The results suggest a distinct, but as yet unidentified, role of CTGF in the pathogenesis of diabetic retinopathy.

Two-photon imaging of brain pericytes in vivo using dextran-conjugated dyes

Pericytes in the central nervous system (CNS) are hypothesized to be involved in important circulatory functions, including local blood flow regulation, angiogenesis, immune reaction, and regulation of blood-brain barrier. Despite these putative functions, functional correlates of pericytes in vivo are scarce. We have labeled CNS pericytes using the dextran-conjugated fluorescent calcium indicator Calcium Green I and imaged them in somatosensory cortex of the mouse in vivo. Intracellular calcium concentration in pericytes showed spontaneous surges lasting for several seconds. Furthermore, population bursts of neuronal activity were associated with increased Ca(2+) signal in a portion of the pericytes. Selective in vivo labeling of pericytes with functional markers may help reveal their physiological function in neuronal activity-associated regulation of local cerebral blood flow.

VEGF coordinates interaction of pericytes and endothelial cells during vasculogenesis and experimental angiogenesis

Biological activities of vascular endothelial growth factor (VEGF) have been studied extensively in endothelial cells (ECs), but few data are available regarding its effects on pericytes. In murine embryoid body cultures, VEGF-induced expression of desmin and alpha-smooth muscle actin (alpha-SMA) in CD-31+ cells. The number of CD-31+/desmin+ vascular chords increased with VEGF treatment time and peaked during a differentiation window between 6 and 9 days after plating. In vivo, VEGF-induced elongation and migration of desmin-positive pericytes and coverage of angiogenic capillaries, as revealed by analysis of Sambucus nigra lectin-stained vascular beds of the chick chorioallantoic membrane. VEGF also caused significant decrease of intercapillary spaces, an indicator for intussusceptive vascular growth. These VEGF-mediated effects point at a more intricate interaction between ECs and pericytes cells than previously demonstrated and suggest that pericytes may be derived from EC progenitors in vitro and not only stabilize capillaries but also participate in vascular remodeling in vivo.

Circulating anti-pericyte autoantibodies are present in Type 2 diabetic patients and are associated with non-proliferative retinopathy

AIMS/HYPOTHESIS

This study aims to determine the prevalence of anti-pericyte autoantibodies in Type 2 diabetes and to characterize these autoantibodies as new markers of disease activity in diabetic retinopathy.

METHODS

A total of 299 patients with Type 2 diabetes participated in this study. Retinopathy was assessed by 7-field stereo fundus photography and was graded according to the ETDRS scale. Serum anti-pericyte autoantibodies were detected by immunofluorescence on tissue cultured bovine retinal pericytes.

RESULTS

The prevalence of anti-pericyte autoantibodies in Type 2 diabetic patients was 54% and was approximately equal in men and women. The prevalence was approximately 55% with retinopathy at grades from 10 to 53. At grades above 53 the prevalence declined to 23% ( p<0.0001). The highest prevalence by duration of diabetes, 70%, was found at 0 to 5 years and the lowest, 25% at more than 25 years duration ( p<0.0001).

CONCLUSION/INTERPRETATION

Anti-pericyte autoantibodies are present at high prevalence in Type 2 diabetes. Their presence during earlier stages of retinopathy could be due to a reaction with antigens expressed by "activated" pericytes. The decline in antibody prevalence in advanced retinopathy could mark pericyte loss and progression to an angiogenic retinal milieu.

Expression of the cytokine leukemia inhibitory factor and pro-apoptotic insulin-like growth factor binding protein-3 in Alzheimer's disease

Amyloid-beta (Abeta) deposition in cerebral blood vessel walls is one of the key features of Alzheimer's disease (AD). Abeta(1-40) carrying the "Dutch" mutation (DAbeta(1-40)) induces rapid degeneration of cultured human brain pericytes (HBP). To study the mechanisms of this Abeta-induced toxicity, a comparative cDNA expression array was performed to detect differential gene expression of Abeta-treated versus untreated HBP. Messenger RNA expression of leukemia inhibitory factor (LIF) and insulin-like growth factor binding protein 3 (IGFBP-3) was increased in DAbeta(1-40)-treated HBP, whereas early growth response factor-1 (Egr-1) expression was decreased. Corresponding protein expression was investigated in AD and control brains. In all AD cases examined, LIF expression was observed in senile plaques and cerebral amyloid angiopathy, whereas IGFBP-3 expression in these lesions was only observed in a subset of cases. LIF and IGFBP-3 were also expressed in neurofibrillary tangles, as well as in neurons in AD and control brains. Egr-1 was predominantly expressed in astrocytes. Given its known involvement in both neuronal and immune responses to injury, the cytokine LIF may be a mediator of the inflammatory reaction seen in AD. IGFBP-3 is known to inhibit cell proliferation and induce apoptosis and may therefore contribute to neuronal degeneration in AD.

Intravascular myopericytoma

BACKGROUND

Myopericytoma is a benign tumor composed of cells that show apparent differentiation towards putative perivascular myoid cells called myopericytes. It arises most commonly in the dermis or subcutaneous tissue of the extremities in adults.

METHODS

We describe a myopericytoma that was unusual in its intravascular location.

RESULTS

A 54-year-old man presented with a 10-year history of a painful slowly growing 1.5-cm nodule in the subcutaneous tissue of the thigh. Histologic examination of the excised lesion showed that is was entirely contained within the lumen of a vein. It was composed of a proliferation of myoid-appearing spindle cells, which were arranged in a striking concentric pattern around numerous blood vessels, in a manner that accentuated the vessel walls. This pattern is characteristic of myopericytoma. In some areas, fascicles of spindle cells, embedded in a myxoid stroma, bulged into the lumina of lesional vessels, reminiscent of myofibroma/myofibromatosis. Lesional spindle cells were diffusely positive for smooth muscle actin, focally positive for CD34 and were negative for desmin, cytokeratin, S100 protein, HMB-45 and CD31.

CONCLUSION

This case illustrates that myopericytoma can be entirely intravascular in its location.

NG2 proteoglycan is expressed exclusively by mural cells during vascular morphogenesis

Immunofluorescence mapping demonstrates that the NG2 proteoglycan is invariably expressed by the mural cell component of mouse neovascular structures. This pattern is independent of the developmental mechanism responsible for formation of the vasculature (vasculogenesis or angiogenesis). Thus, NG2 is expressed in the embryonic heart by cardiomyocytes, in developing macrovasculature by smooth muscle cells, and in nascent microvessels by vascular pericytes. Due to the scarcity of proven markers for developing pericytes, NG2 is especially useful for identification of this cell type. The utility of NG2 as a pericyte marker is illustrated by two observations. First, pericytes are associated with endothelial tubes at an early point in microvessel development. This early interaction between pericytes and endothelial cells has important implications for the role of pericytes in the development and stabilization of microvascular tubes. Second, the pericyte to endothelial cell ratio in developing capillaries varies from tissue to tissue. Because the extent of pericyte investment is likely to affect the physical properties of the vessel in question, it is important to understand the mechanisms that control this process. Additional insight into these and other aspects of vascular morphogenesis should be possible through use of NG2 as a mural cell marker.

Vascular smooth muscle cells and pericytes express MMP-1, MMP-9, TIMP-1 and type I procollagen in inflammatory bowel disease

AIMS

Matrix metalloproteinases (MMPs) are involved in tissue remodelling, which is one of the important aspects of inflammatory disease. To assess the balance between the matrix degradation and production, we analysed the in situ expression of MMP-1, -3, -8 and -9, tissue inhibitor of metalloproteinases (TIMP)-1 and -2, and type I procollagen (PC-I) in inflammatory bowel disease.

METHODS AND RESULTS

Immunohistochemistry using frozen sections was performed in 17 patients with ulcerative colitis (UC) and 16 with Crohn's disease (CD). In both UC and CD, MMPs and TIMPs were expressed by inflammatory cells as well as by fibroblastic cells most prominently in actively inflamed areas in ulcer bases, but sparsely in intact inflamed mucosa in both UC and CD. In UC, inflamed mucosa with erosions expressed these substances focally. Fibroblasts also expressed PC-I. We identified that vascular smooth muscle cells of venules in ulcer bases expressed MMP-1 and -9, TIMP-1 and PC-I. These venules also expressed E-selectin, a cell adhesion molecule to facilitate the leucocyte extravasation, and vascular endothelial growth factor (VEGF) receptor 2, consistent with their property of newly formed vessels.

CONCLUSIONS

Our results suggest that MMPs are involved in the tissue remodelling, angiogenesis and promotion of leucocyte extravasation in the actively inflamed area in the ulcer base in both UC and CD. MMP-1 expression in the mucosa may be related to the initial step of ulceration in UC. Therapeutic manipulation of extracellular matrix turnover would be an effective therapy to alleviate active inflammation and accelerate ulcer healing.

Human dermal pericytes express 3G5 ganglioside--a new approach for microvessel histology in the skin

BACKGROUND

Pericytes cover the abluminal surface of microvessels and play an important role in capillary regulation and pathology. Studies on pericytes have been hindered by the lack of specific markers with which to facilitate microscopic identification of this cell type. Expression of the cell surface 3G5 ganglioside antigen has been reported in cultured retinal and cardiac pericytes. The objective of this study was to determine the usefulness of monoclonal antibody 3G5 as a pericyte marker in human skin.

METHODS

Cryosections of 21 skin biopsies were examined by direct fluorescence technique with anti-3G5, anti-von Willebrand factor, anti-alpha-smooth muscle actin or DNA fluorochrome.

RESULTS

In human dermis, 3G5 expression is limited to pericytes discriminating this cell type from all other cells including smooth muscle cells, myofibroblasts and myoepithelial cells. We found a pericyte: endothelial cell ratio of 1:12.4 (+/-7.1), and a difference of alpha-smooth muscle actin expression between the subpapillary plexus and the microvessels of the Stratum reticulare.

CONCLUSIONS

3G5 mAB is an excellent and so far the only reported tool for identification of dermal pericytes by fluorescent light microscopy. Moreover, this is the first report of the application of 3G5 technique to the microvasculature in tissue sections at the light microscopic level.

t-Butyl hydroperoxide and oxidized low density lipoprotein enhance phospholipid hydrolysis in lipopolysaccharide-stimulated retinal pericytes

Free radicals induced by organic peroxides or oxidized low density lipoprotein (oxLDL) play a critical role in the development of atherosclerosis. In investigating this process, and the concomitant inflammatory response, the role of pericytes, cells supporting the endothelial ones in blood vessels, has received little attention. In this study we tested the hypothesis that tert-butyl hydroperoxide (t-BuOOH) and oxLDL, administered in sublethal doses to the culture medium of retinal pericytes, function as prooxidant signals to increase the stimulation of the peroxidation process induced by lipopolysaccharide (LPS). Confluent cell monolayers were exposed to t-BuOOH (25-400 microM), native LDL or oxLDL (3.4-340 nmol hydroperoxides/mg protein, 1-100 micro). LPS (1 microg/ml), t-BuOOH (200 microM), and oxLDL (100 microM), but not native LDL, incubated for 24 h with cells, markedly increased lipid peroxidation, cytosolic phospholipase A2 (cPLA2) activity and arachidonic acid (AA) release in a time- and dose-dependent manner. AACOCF(3), a potent cPLA2 inhibitor, and the antioxidant alpha-tocopherol strongly inhibited the prooxidant-stimulated AA release. Long-term exposure to maximal concentrations of t-BuOOH (400 microM) or oxLDL (100 microM) had a sharp cytotoxic effect on the cells, described by morphological and biochemical indices. The presence of t-BuOOH or oxLDL at the same time, synergistically increased phospholipid hydrolysis induced by LPS alone. 400 microM t-BuOOH or 100 microM oxLDL had no significant effect on the stimulation of an apoptosis process estimated by DNA laddering and light and electron microscopy. The results indicate that (i) pericytes may be the target of extensive oxidative damage; (ii) activation of cPLA2 mediates AA liberation; (iii) as long-term regulatory signals, organic peroxide and specific constituents of oxLDL increase the pericyte ability to degrade membrane phospholipids mediated by LPS which was used, in the present study, to simulate in vitro an inflammatory burst in the retinal capillaries.

[Effects of DDPH on proliferation and immunophenotypes of the pulmonary vascular pericytes]

OBJECTIVE

To study the effects of 1-(2, 6-dimethylphenoxy)-2-(3, 4-dimethoxyphenylethylamino) propane hydrochloride (DDPH) on proliferation and immunophenotypes of newborn rat pulmonary vascular pericytes (PCs) induced by hypoxic endothelial cell conditioned medium (HECCM) from porcine pulmonary arteries.

METHODS

The PCs were divided into 4 groups according to the endothelial cell conditioned medium (ECCM): normoxic ECCM (NECCM) group, NECCM + DDPH group, HECCM group and HECCM + DDPH group. Cell culture, immunocytochemical staining, image analysis and flow cytometry were used to investigate the effects of HECCM and DDPH on the expression of alpha-smooth muscle actin (alpha-SM-actin) and proliferating cell nuclear antigen (PCNA) and cell cycle in PCs.

RESULTS

The alpha-SM-actin antigen in the PCs in HECCM group was more positively expressed than that in the other three groups, but CD(34) antigen and S-100 antigen were negatively expressed. The expression of alpha-SM-actin antigen, CD(34) and S-100 was positive in the groups of NECCM, NECCM + DDPH and HECCM + DDPH. The expression of alpha-SM-actin and PCNA in HECCM group was 1.32 times (F = 11.09, P = 0.000 1) and 1.24 times (F = 2.89, P = 0.025 7) that in NECCM group, 1.30 times (F = 3.65, P = 0.007 0) and 1.21 times (F = 2.63, P = 0.041 4) that in HECCM + DDPH group, respectively; The percentage of the cells in the G(0)-G(1) phase in the HECCM group was lower by 11.7% and 9.1%, in S phase higher by 5.6% and 4.2%, in G(2)-M phase higher by 6.1% and 4.9% than that in the groups of NECCM, HECCM + DDPH, respectively. The inhibitory rates of DDPH on the increased alpha-SM-actin and PCNA syntheses in PCs induced by HECCM were 23.4% and 17.1% respectively. The inhibitory rate on the increased PCs from G(0)-G(1) phase to S phase was 8.3%.

CONCLUSION

DDPH might directly inhibit PCs from proliferation and immunophenotypical transformation of smooth muscle-like cells induced by HECCM.

Contractile proteins in pericytes at the blood-brain and blood-retinal barriers

Evidence from a variety of sources suggests that pericytes have contractile properties and may therefore function in the regulation of capillary blood flow. However, it has been suggested that contractility is not a ubiquitous function of pericytes, and that pericytes surrounding true capillaries apparently lack the machinery for contraction. The present study used a variety of techniques to investigate the expression of contractile proteins in the pericytes of the CNS. The results of immunocytochemistry on cryosections of brain and retina, retinal whole-mounts and immunoblotting of isolated brain capillaries indicate strong expression of the smooth muscle isoform of actin (alpha-SM actin) in a significant number of mid-capillary pericytes. Immunogold labelling at the ultrastructural level showed that alpha-SM actin expression in capillaries was exclusive to pericytes, and endothelial cells were negative. Compared to alpha-SM actin, non-muscle myosin was present in lower concentrations. By contrast, smooth muscle myosin isoforms, were absent. Pericytes were strongly positive for the intermediate filament protein vimentin, but lacked desmin which was consistently found in vascular smooth muscle cells. These results add support for a contractile role in pericytes of the CNS microvasculature, similar to that of vascular smooth muscle cells.

[Ultrastructural and immunohistochemical characteristics of pericytes during neovascularization in breast carcinoma]

OBJECTIVE

To study the morphology of pericyte, the relationship between pericytes and neovascularization of breast carcinoma.

METHODS

Ultrastructural, immunohistochemical and quantitative morphology analysis techniques were used to study 89 cases of human breast carcinoma. 4 human granulation tissues cases were used as control.

RESULTS

The positive cells for FVIIIRAg were endothelial cells situated inside the vascular wall with abundant cytoplasm containing caveolae and Weibel-palade bodies. The positive cells for alpha-SMA were pericytes with cytoplasm containing abundant myofilament, and connections with endothelial cells. The pericyte-endothelial junctions can be found. Quantitative morphological analysis showed that the number of pericytes in the low-microvascular density areas are much higher than that in the high- microvascular density areas (P < 0.0005).

CONCLUSION

Ultrastructural observation and immunohistochemical staining of alpha-SMA are useful in identifying pericytes. The results of this study imply that pericytes may possibly inhibit angiogenesis.

Activation of microvascular pericytes in autoimmune Raynaud's phenomenon and systemic sclerosis

OBJECTIVE

To determine the temporal and spatial relationship between platelet-derived growth factor beta (PDGFbeta) receptors, PDGF-AB/BB, and activated pericytes across the Raynaud's phenomenon (RP) and systemic sclerosis (SSc; scleroderma) disease spectrum.

METHODS

Monoclonal antibodies against PDGFbeta receptors, PDGF-AB/BB, and high molecular weight-melanoma-associated antigen (HMW-MAA), a marker for activated pericytes, were used to immunohistochemically analyze serial sections of skin biopsy tissue from patients with RP and from scleroderma patients. To delineate cell-specific PDGFbeta receptor expression, double immunofluorescence-stained sections were analyzed using computer-aided image analysis and confocal microscopy.

RESULTS

PDGFbeta receptor-expressing cells and HMW-MAA-expressing pericytes were found in biopsy samples from autoimmune RP patients and in both early fibrotic and early nonfibrotic scleroderma skin, but not in normal or primary RP or late-stage scleroderma skin. PDGF-AB/BB was expressed within the epidermis, at the epidermal/dermal junction, and by dermal macrophages. Analysis of juxtaposed serial sections revealed an increased frequency of receptor expression in microvessels from autoimmune RP and early scleroderma skin (P < 0.01). Double-labeling studies using confocal microscopy showed that, in vivo, PDGFbeta receptors were predominantly expressed by microvascular pericytes from both autoimmune RP and early scleroderma skin.

CONCLUSION

PDGFbeta receptors are expressed by activated microvascular pericytes in patients with autoimmune RP and in early SSc patients, but not in those with primary RP or late-stage scleroderma. These findings suggest that features of autoimmune RP are distinct from those of primary RP, and that microvascular pericytes may be an important link between chronic microvascular damage and fibrosis.