Immunofluorescent study of heterogeneity in smooth muscle cells of human fetal vessels using antibodies to myosin, desmin, and vimentin

Tripartite factors leading to molecular divergence between human and murine smooth muscle

A large number of pre-clinical and developmental investigations involve experimental vertebrate animals, of which mice have emerged as a favored organism. Recognition of the differences between humans and mice is essential for assessment of the relevance of animal studies to humans. The primary purpose of this study was to gauge the conservation between human and mouse vascular smooth muscle cell (VSMC) proteins mined from an analysis of the Human Protein Atlas. Two comparison were made: a) immunohistochemistry for 16 proteins in brain, heart, esophagus, bladder, stomach, lung, kidney, and aorta enabled comparison between human and mouse of protein localization in VSMC and non-vascular SMC; and b) multi-species primary protein sequence analysis of an expanded set vascular molecules enabled comparison between VSMC sequences among vertebrate species. In total, three dimensions of diversity were uncovered. First, a significant number of factors show human/mouse differences in cellular expression; these differences occurred in both VSMC and non-vascular SMC in an organ and cell-type dependent fashion. Many markers demonstrated notable cell-to-cell and regional heterogeneity in VSMC of the aorta and non-vascular SMC of the esophagus, bladder, and stomach. Second, species specificity can arise by genetic deletions as exemplified by the human protein adipogenesis regulatory factor (ADIRF), which is not present due to a large sequence gap in mice. Third, we describe significant cross-species protein sequence divergence in selected VSMC proteins which may result in altered orthologue function. In a sample of 346 vascular molecules, 15% demonstrate incomplete vertebrate species gene conservation. Divergence of predicted human/mouse VSMC protein sequences is higher than for endothelial proteins in all species examined. In the future, each of these three cross-species differences could be neutralized using gene manipulation, resulting in improved translational potential of murine experimental models.

Immunohistochemical distribution of desmin in the human fetal heart

Desmin is a member of the intermediate filaments, which play crucial roles in the maturation, maintenance and recovery of muscle fibers. Its expression has been examined in human cardiac muscle, rat and chicken, but its spatial distribution in the human fetal heart has not been described. The present study investigated desmin expression in the human fetal heart and associated great vessels in 14 mid-term fetuses from 9 to 18 weeks of gestation. Immunoreactivity for myosin heavy chain (MHC) and alpha smooth muscle actin (α-SMA), as well as neuron-specific enolase (NSE), was also examined. Increased expression of desmin from 9 to 18 weeks was clearly localized in the atrial wall, the proximal portions of the pulmonary vein and vena cava, and around the atrioventricular node. Desmin-positive structures were also positive for MHC. Meanwhile, the great vessels were also positive for α-SMA. The distribution of desmin exhibited a pattern quite different from that described in previous studies of rat and chicken. Thus, desmin in the human fetal heart does not seem to play a general role in myocardial differentiation but rather a specific role closely related to the maturation of the α-isozyme of MHC. Desmin expression in the developing fetal heart also appeared to be induced by mechanical stress due to the involvement of venous walls against the atrium.

Placental Abnormalities in Ovine Somatic Cell Clones at Term: A Light and Electron Microscopic Investigation

To investigate the reasons for fetal losses after somatic cell nuclear transfer, an immunohistochemical and ultrastructural analysis of cloned placentae was performed. The main features observed were a marked reduction of villous vascularization, hypoplasia of trophoblastic epithelium, lack of binucleate cells, immaturity of placental vessels and reduced vasculogenesis. By means of transmission electron microscopy (TEM), a diffuse thickening and lamination of subtrophoblastic basement membrane (SBM) were noted in cloned placentae. These results led us to hypothesize, through an autoamplification model, that the abnormal vascularization, the ischaemia and the low development of an high specialized trophoblastic epithelium were the primary causes of the fetal loss occurring after somatic cells nuclear transfer.

Diversity of CD97 in smooth muscle cells

CD97, an epidermal growth factor (EGF)-TM7 receptor, is not restricted to hematopoetic and carcinoma cells but is also found on smooth muscle cells (SMC). We have examined its location and biochemical structure in various normal and tumorigenic SMC-containing tissues. SMC of the urinary bladder, lung bronchi and bronchioles, myometrium, and gastrointestinal tract were immunohistologically stained by using monoclonal antibodies (mabs) to the CD97 stalk region (CD97(stalk)). Mabs directed against an N-glycosylation-dependent epitope within the EGF-domains (CD97(EGF)) did not bind to normal SMC. Vascular SMC, which was also CD97(EGF)-negative, showed further CD97 heterogeneity. Only a few, if any, SMC from the aorta or elastic arteries of the systemic circulation were positive for CD97 mRNA and therefore also for CD97(stalk). CD97(stalk)-positive SMC were slightly more numerous in muscular and peripheral arteries. In contrast, most venous SMC expressed CD97(stalk). A comparison with other SMC molecules revealed a similar but not identical staining pattern for CD97(stalk) and desmin. Further CD97 heterogeneity was observed during SMC transformation. All leiomyomas (n=5) and nine out of 21 leiomyosarcomas were positive for both CD97(stalk) and CD97(EGF). As expected, CD97(EGF)-positive SMC tumors expressed partly N-glycosylated CD97. Seven out of 21 leiomyosarcomas were completely devoid of CD97. Thus, CD97 showed variable expression in vascular and biochemical modification in tumorigenic SMC, suggesting that the function of the molecule is specific for the SMC subtype.

Mutations in a novel factor, glomulin, are responsible for glomuvenous malformations ("glomangiomas")

Glomuvenous malformations (GVMs) are cutaneous venous lesions characterized by the presence of smooth-muscle--like glomus cells in the media surrounding distended vascular lumens. We have shown that heritable GVMs link to a 4--6-cM region in chromosome 1p21-22. We also identified linkage disequilibrium that allowed a narrowing of this VMGLOM locus to 1.48 Mb. Herein, we report the identification of the mutated gene, glomulin, localized on the basis of the YAC and PAC maps. An incomplete cDNA sequence for glomulin had previously been designated "FAP48," for "FKBP-associated protein of 48 kD." The complete cDNA for glomulin contains an open reading frame of 1,785 nt encoding a predicted protein of 68 kD. The gene consists of 19 exons in which we identified 14 different germline mutations in patients with GVM. In addition, we found a somatic "second hit" mutation in affected tissue of a patient with an inherited genomic deletion. Since all but one of the mutations result in premature stop codons, and since the localized nature of the lesions could be explained by Knudson's two-hit model, GVMs are likely caused by complete loss of function of glomulin. The abnormal phenotype of vascular smooth-muscle cells (VSMCs) in GVMs suggests that glomulin plays an important role in differentiation of these cells--and, thereby, in vascular morphogenesis--especially in cutaneous veins.

Specific but variable expression of h-caldesmon in leiomyosarcomas: an immunohistochemical reassessment of a novel myogenic marker

h-Caldesmon is considered a novel specific marker for tumors with smooth muscle differentiation. To reassess its diagnostic use, the authors evaluated the immunohistochemical expression of h-caldesmon and other myogenic markers (calponin, alpha-smooth muscle actin, HHF35, and desmin) in 30 leiomyosarcomas (external soft tissues [15], retroperitoneum [8], uterus [5], other sites [2]), 26 myofibroblastic lesions, and 26 fibrohistiocytic tumors of varying biologic potential and histology. In contrast with previous data, h-caldesmon was expressed only in 11 (36%) of the 30 leiomyosarcomas analyzed, whereas they consistently expressed actins and frequently expressed calponin (86%) and desmin (76%). Leiomyosarcomas with the expression of h-caldesmon were well or moderately differentiated and primarily confined to the retroperitoneum or uterus. All but one leiomyosarcomas in the external soft tissues examined were negative for h-caldesmon, and the h-caldesmon-negative tumors showed moderately to poorly differentiated morphology. All myofibroblastic lesions examined were negative for h-caldesmon despite their constant expressions of at least one of the other markers. h-Caldesmon was not expressed in fibrohistiocytic tumors either, although focal positivity for the other markers was seen in subsets of the tumors. Thus, h-caldesmon can be regarded as a specific myogenic marker. However, one should be aware that the expression of h-caldesmon in leiomyosarcomas can be more variable according to their locations and/or extent of smooth muscle differentiation than considered previously.

Prenatal origins of human intrapulmonary arteries: formation and smooth muscle maturation

Recent studies on the morphogenesis of the pulmonary arteries have focused on nonhuman species such as the chick and the mouse. Using immunohistochemical techniques, we have studied 16 lungs from human embryos and fetuses from 28 d of gestation to newborn, using serial sections stained with a panel of antibodies specific for endothelium, smooth muscle, and extracellular matrix proteins. Cell replication was also assessed. Serial reconstruction showed a continuity of circulation between the heart and the capillary plexus from at least 38 d of gestation. The intrapulmonary arteries appeared to be derived from a continuous expansion of the primary capillary plexus that is from within the mesenchyme, by vasculogenesis. The arteries formed by continuous coalescence of endothelial tubes alongside the newly formed airway. Findings were consistent with the pulmonary arterial smooth muscle cells being derived from three sites in a temporally distinct sequence: the earliest from the bronchial smooth muscle, later from the mesenchyme surrounding the arteries, and last from the endothelial cells. Despite their different origins, all smooth muscle cells followed the same sequence of expression of smooth muscle-specific cytoskeletal proteins with increasing age. The order of appearance of these maturing proteins was from the subendothelial cells outward across the vessel wall and from hilum to periphery. The airways would seem to act as a template for pulmonary artery development. This study provides a framework for studying the signaling mechanisms controlling the various aspects of lung development.

Intraluminal pressure is essential for the maintenance of smooth muscle caldesmon and filamin content in aortic organ culture

Different forms of mechanical stimulation are among the physiological factors constantly acting on the vessel wall. We previously demonstrated that subjecting vascular smooth muscle cells (VSMCs) in culture to cyclic stretch increased the expression of high-molecular-weight caldesmon, a marker protein of a differentiated, contractile, VSMC phenotype. In the present work the effects of mechanical factors, in the form of circumferential stress and shear stress, on the characteristics of SM contractile phenotype were studied in an organ culture of rabbit aorta. Application of an intralumininal pressure of 80 mm Hg to aortic segments cultured in Dulbecco's modified Eagle's medium containing 20% fetal calf serum for 3 days prevented the decrease in high-molecular-weight caldesmon content (70+/-4% of initial level in nonpressurized vessel, 116+/-17% at 80 mm Hg) and filamin content (80+/-5% in nonpressurized vessel, 100+/-2% at 80 mm Hg). SM myosin and low-molecular-weight caldesmon contents showed no dependence on vessel pressurization. Neither endothelial denudation nor alteration of intraluminal flow rates affected marker protein content in 3-day vessel culture, thus excluding the possibility of any shear or endothelial effects. Maintenance of high high-molecular-weight caldesmon and filamin levels in the organ cultures of pressurized and stretched vessels demonstrates the positive role of mechanical factors in the control of the VSMC differentiated phenotype.

PDGF, TGF-beta, and heterotypic cell-cell interactions mediate endothelial cell-induced recruitment of 10T1/2 cells and their differentiation to a smooth muscle fate

We aimed to determine if and how endothelial cells (EC) recruit precursors of smooth muscle cells and pericytes and induce their differentiation during vessel formation. Multipotent embryonic 10T1/2 cells were used as presumptive mural cell precursors. In an under-agarose coculture, EC induced migration of 10T1/2 cells via platelet-derived growth factor BB. 10T1/2 cells in coculture with EC changed from polygonal to spindle-shaped, reminiscent of smooth muscle cells in culture. Immunohistochemical and Western blot analyses were used to examine the expression of smooth muscle (SM)-specific markers in 10T1/2 cells cultured in the absence and presence of EC. SM-myosin, SM22alpha, and calponin proteins were undetectable in 10T1/2 cells cultured alone; however, expression of all three SM-specific proteins was significantly induced in 10T1/2 cells cocultured with EC. Treatment of 10T1/2 cells with TGF-beta induced phenotypic changes and changes in SM markers similar to those seen in the cocultures. Neutralization of TGF-beta in the cocultures blocked expression of the SM markers and the shape change. To assess the ability of 10T1/2 cells to contribute to the developing vessel wall in vivo, prelabeled 10T1/2 cells were grown in a collagen matrix and implanted subcutaneously into mice. The fluorescently marked cells became incorporated into the medial layer of developing vessels where they expressed SM markers. These in vitro and in vivo observations shed light on the cell-cell interactions that occur during vessel development, as well as in pathologies in which developmental processes are recapitulated.

Differentiation of smooth muscle cells in human blood vessels as defined by smoothelin, a novel marker for the contractile phenotype

Smoothelin is a constituent of the cytoskeleton specific for smooth muscle cells (SMCs) in a broad range of species. It has been postulated that smoothelin represents a marker of highly differentiated, contractile SMCs. Here, we present data on the presence of smoothelin in the human vascular system that support this hypothesis. For this purpose, smoothelin distribution was studied (1) during vasculogenesis of the placenta, (2) in normal adult blood vessels, and (3) in atherosclerotic lesions. Smoothelin was first observed in placental tissue at approximately week 10 to 11 of gestation. In full-term placenta, it was found in the SMCs of vessels in the large stem villi and in the chorionic plate. Furthermore, it was present in the fetal arteries of smaller stem villi, but it was not found in the veins. In adult blood vessels, a small population of aortic (approximately 10%) and large muscular artery (approximately 30% to 50%) SMCs was positive for smoothelin. In general, smoothelin and desmin were coexpressed in the same SMCs, but expression of desmin appeared to be less abundant. However, the majority of SMCs in these blood vessels were smoothelin- and desmin negative but expressed vimentin, whereas alpha-smooth muscle actin (alpha-SMA) was present in all SMCs. The SMCs in the media of small muscular arteries were positive for smoothelin and desmin (> 95%), whereas the vimentin-positive SMC type was scarce. Smoothelin was absent in capillaries, pericytic venules, and small veins but was occasionally observed in the SMCs of large veins. Thus, the distribution of smoothelin in the SMCs of the vascular system appears to be limited to blood vessels that are capable of pulsatile contraction. In atherosclerotic femoral arteries, smoothelin-positive cells were detected in the media, the atheromatous plaque, and the intimal thickening. Smoothelin-positive cells were present primarily at the luminal portion of advanced lesions. The presence of a considerable number of such smoothelin-positive cells at that location may indicate that these plaques are no longer expanding.

Smoothelin, a novel cytoskeletal protein specific for smooth muscle cells

The characterization of a novel 59-kD cytoskeletal protein is described. It is exclusively observed in smooth muscle cells by Northern blotting and immunohistochemical analysis and therefore designated "smoothelin." A human smooth muscle cDNA library was screened with the monoclonal antibody R4A, and a full-size cDNA of the protein was selected. The cDNA was sequenced and appeared to contain a 1,113-bp open reading frame. Based on the cDNA sequence, the calculated molecular weight of the polypeptide was 40 kD and it was demonstrated to contain two N-glycosylation sites. Computer assisted analysis at the protein level revealed a 56-amino acid domain with homologies of approximately 40% with a sequence bordering the actin-binding domains of dystrophin, utrophin, beta-spectrin and alpha-actinin. In situ hybridization demonstrated that human smoothelin is encoded by a single copy gene which is located on chromosome 22. Immunohistochemistry and Western blotting revealed synthesis of smoothelin in smooth muscle of species evolutionarily as far apart as human and teleost. Northern blotting indicated that sequence as well as size of the mRNA (approximately 1,500 bases) are conserved among vertebrates. Cell fractionation studies and differential centrifugation showed that the protein cannot be extracted with Triton X-100, which indicates that it is a part of the cytoskeleton. Transfection of the human cDNA into smooth muscle cells and COS7 cells produced a protein of 59 kD, which assembled into a filamentous network. However, in rat heart-derived myoblasts association with stress fibers was most prominent. Smoothelin was not detected in primary or long term smooth muscle cell cultures. Also, transcription of smoothelin mRNA was almost instantly halted in smooth muscle tissue explants. We conclude that smoothelin is a new cytoskeletal protein that is only found in contractile smooth muscle cells and does not belong to one of the classes of structural proteins presently known.

Differential processes of vascular smooth muscle cell differentiation within elastic and muscular arteries of rats and rabbits: an immunofluorescence study of desmin and vimentin distribution

Two main populations of smooth muscle cells exist in the arterial media of adult mammals with respect to expression of two intermediate filament proteins: vimentin-positive/desmin-negative cells (V+/D-) and vimentin-positive/desmin-positive ones (V+/D+). However, it is still not understood how this phenotypic diversity is established. Since the proportion and the distribution patterns of the two muscle cell populations depend both on the type of blood vessel and the species examined, the aim of the present study was to determine and to compare their developmental origin in various artery segments from two different species. Using confocal scanning laser microscopy and sections stained by means of immunofluorescence, the distribution patterns of desmin and vimentin were compared in transverse sections of thoracic and abdominal aortas (elastic arteries) and of the femoral artery (muscular artery) of newborn and adult rats (n = 12) and rabbits (n = 12). The comparison of sections labelled with specific antibodies showed the existence of a subpopulation of smooth muscle cells in the aortas, but not in the femoral artery, which expressed desmin in newborns but not in adults. These data suggest that the phenotype of smooth muscle cells in elastic arteries but not in muscular arteries is modulated during development.

Contractile proteins in human fetoplacental vessels

OBJECTIVE

Our purpose was to compare the protein isoform composition of the contractile apparatus at different levels of the fetoplacental vessel musculature at term.

STUDY DESIGN

Umbilical, chorionic, and stem villi vessel protein extracts were run on one- and two-dimensional gel electrophoresis; previously characterized human myometrium proteins were used as the smooth muscle proteins of reference.

RESULTS

Fetoplacental vessel musculature exhibited a high actin/myosin ratio. The presence, in varying quantities, of myosin heavy chain and actin isoforms of smooth muscle type in the different vessels reflected their degree of differentiation. The presence of nonmuscle protein isoforms, particularly in stem villi vessels, indicated a certain degree of immaturity.

CONCLUSIONS

The presence of smooth muscle contractile protein isoforms indicates that fetoplacental vessel musculature is highly differentiated. Regional modulation of fetoplacental blood flow could be, in part, the result of local differences in contractile apparatus protein composition.

The monoclonal antibody GB 42--a useful marker for the differentiation of myofibroblasts

The expression patterns of a variety of cytoskeletal antigens were studied in normal human tissues (placenta, umbilical cord, myometrium, colon, mammary gland, testis, skeletal muscle, myocardium) as well as in abnormal human tissues (palmar fibromatosis, fibrocystic disease of the mammary gland, mammary carcinoma). The immunohistochemical binding patterns of the monoclonal antibody GB 42 were compared to those of commercial antibodies directed against vimentin, desmin, smooth muscle myosin, pan actin, alpha-smooth muscle actin and gamma-smooth muscle actin. Methods applied comprised immunohistochemistry on cryostat sections and paraffin sections. Immunogold immunocytochemistry was performed on Lowicryl sections. The patterns of GB 42-binding were confirmed biochemically by SDS-PAGE and Western-blotting, and quantitative amino acid analysis. Our data suggest that the monoclonal antibody GB 42 recognizes an actin isoform which is identical to, or closely related to, gamma-smooth muscle actin. Unlike the commercially available antibody against gamma-smooth muscle actin, GB 42 does not cross-react with alpha-skeletal or alpha-cardiac actins. The GB 42-antigen is expressed in smooth muscle cells, myoepithelial cells and in later stages of differentiation of myofibroblasts, in all the tissues investigated. Throughout the development of smooth muscle cells and myofibroblasts, the appearance of the GB 42-antigen occurs after the expression of vimentin, desmin and alpha-smooth muscle actin, but prior to the expression of smooth muscle myosin. GB 42 is a reliable marker for higher stages of differentiation of smooth muscle cells and myofibroblasts.

Stretch affects phenotype and proliferation of vascular smooth muscle cells

The exertion of periodic dynamic strain on the arterial wall is hypothesized to be relevant to smooth muscle cell morphology and function. This study has investigated the effect of cyclic mechanical stretching on rabbit aortic smooth muscle cell proliferation and expression of contractile phenotype protein markers. Cells were cultured on flexible-bottomed dishes and cyclic stretch was applied (frequency 30 cycles/min, 15% elongation) using a Flexercell Strain unit. Cyclic stretch potentiated smooth muscle cell proliferation in serum-activated cultures but not in cultures maintained in 0.5% fetal calf serum. Stretching induced a serum-independent increase of h-caldesmon expression and this effect was reversible following termination of mechanical stimulation. Strain was without effect on smooth muscle myosin or calponin expression. In cells grown on laminin stretch-induced h-caldesmon expression was more prominent than in cells cultured on collagen types I and IV, poly-L-lysine and gelatin. These data suggest that cyclic mechanical stimulation possesses dual effect on vascular smooth muscle cell phenotype characteristics since it: 1) potentiates proliferation, an attribute of a dedifferentiated phenotype; and 2) increases expression of h-caldesmon considered a marker of a differentiated smooth muscle cell state.

Identification and classification of interstitial cells in the canine proximal colon by ultrastructure and immunocytochemistry

The ultrastructure and immunocytochemistry of interstitial cells (ICs) in the canine proximal colon were investigated. Three types of ICs were found within the tunica muscularis. (1) ICs were located along the submucosal surface of the circular muscle (IC-SM). These cells shared many features of smooth muscle cells, including myosin thick filaments and immunoreactivity to smooth muscle gamma actin, myosin light chain, and calponin antibodies. IC-SM were clearly different from smooth muscle cells in that contractile filaments were less abundant and intermediate filaments consisted of vimentin instead of desmin. (2) ICs in the region of the myenteric plexus (IC-MY) were similar to IC-SM, but these cells had no thick filaments or immunoreactivity to smooth muscle gamma actin or calponin antibodies. (3) The fine structures and immunoreactivity of ICs within the muscle layers (IC-BU) were similar to IC-MY, but IC-BU lacked a definite basal lamina and membrane caveolae. IC-BU and IC-MY were both immunopositive for vimentin. Since all ICs were immunopositive for vimentin, vimentin antibodies may be a useful tool for distinguishing between ICs and smooth muscle cells. Each class of ICs was closely associated with nerve fibers, made specialized contacts with smooth muscle cells, and formed multicellular networks. A combination of ultrastructural and immunocytochemical techniques helps the identification and classification of ICs by revealing the fine structures and determining the "chemical coding" of each class of ICs.

Immunohistochemical localization of extracellular matrix in perivillous fibrinoid of normal human term placenta

The extracellular matrix of perivillous fibrinoid in normal human term placenta was investigated by means of the indirect immunofluorescent technique. Polyclonal antibodies to collagen types I, III, IV, V, fibronectin, fibrinogen, laminin, entactin and heparan sulphate proteoglycan and monoclonal antibodies BC-1, IST-9 and IST-4 to human fibronectin were used. The antigens can be grouped according to their presence in fibrinoid as abundant (fibrinogen, fibronectin, heparan sulphate proteoglycan, basement membrane collagen types IV and V), absent (laminin) and variable between fibrinoids (interstitial collagen types I and III, entactin). Our results also demonstrate that fibronectin in fibrinoid originates from placental cells (presumably cytotrophoblast). Monoclonal antibodies BC-1 and IST-9 specific to tissue fibronectin do not stain neighbouring placental extracellular matrix but do bind to fibrinoids on the same sections. Work by other authors has presented evidence that fibrin actually originates from maternal blood and even makes an attempt to substitute the term "fibrinoid" for "fibrin deposition". Our data on the composition of perivillous fibrinoids and the abundance of extracellular matrix components do not support this view and suggest that fibrinoid is a more relevant term for this interesting phenomenon, which deserves further investigation.