Correlation between the distribution of smooth muscle or non muscle myosins and alpha-smooth muscle actin in normal and pathological soft tissues

Sudden coronary death in the young: Evidence of contractile phenotype of smooth muscle cells in the culprit atherosclerotic plaque

BACKGROUND

Culprit coronary atherosclerotic plaques (APs) from young sudden cardiac death (SCD) victims are mostly non-atheromatous, i.e., consisting of proliferative smooth muscle cells (SMCs). Coronary vasospasm has been advocated to explain plaque instability in the absence of thrombosis. Our aim was to characterize the SMC phenotype in the intima and media of coronary arteries from young SCD victims.

METHODS AND RESULTS

A total of 38 coronary artery segments were studied: (a) 18 APs from young (≤40 years old) SCD patients, (b) 9 APs from old (>40 years old) SCD patients, (c) 11 non-atherosclerotic coronary arteries from young patients (≤40 years old). Markers of differentiated SMCs such as α-smooth muscle actin (α-SMA), smooth muscle myosin heavy chains (SMMHCs), and heavy-caldesmon (h-CaD), were assessed in intima and media by immunohistochemistry and quantified morphometrically. In the intima, their expression was higher in non-atherosclerotic arteries (44.37 ± 3.03% for α-SMA, 14.21 ± 2.01% for SMMHCs, 8.90 ± 1.33% for h-CaD) and APs from young SCD victims (38.95 ± 2.29% for α-SMA, 11.92 ± 1.92% for SMMHCs, 8.93 ± 1.12% for h-CaD) compared with old patients (22.01 ± 3.56% for α-SMA, 6.39 ± 0.7% for SMMHCs, 3.00 ± 0.57% for h-CaD; all P statistically significant). The media of non-atherosclerotic arteries and APs from young SCD victims exhibited strong positivity for the differentiation markers unlike that of old patients.

CONCLUSIONS

SMCs of coronary APs as well as from the underlying media from young SCD victims exhibit strong contractile phenotype. In the setting of critical stenosis, both intima and media SMC contractility might contribute to transient coronary spasm leading to myocardial ischemia and SCD.

The myofibroblast, a key cell in normal and pathological tissue repair

Myofibroblasts are characterized by their expression of α-smooth muscle actin, their enhanced contractility when compared to normal fibroblasts and their increased synthetic activity of extracellular matrix proteins. Myofibroblasts play an important role in normal tissue repair processes, particularly in the skin where they were first described. During normal tissue repair, they appear transiently and are then lost via apoptosis. However, the chronic presence and continued activity of myofibroblasts characterize many fibrotic pathologies, in the skin and internal organs including the liver, kidney and lung. More recently, it has become clear that myofibroblasts also play a role in many types of cancer as stromal or cancer-associated myofibroblast. The fact that myofibroblasts are now known to be key players in many pathologies makes understanding their functions, origin and the regulation of their differentiation important to enable them to be regulated in normal physiology and targeted in fibrosis, scarring and cancer.

Myofibroblasts

Myofibroblasts are activated in response to tissue injury with the primary task to repair lost or damaged extracellular matrix. Enhanced collagen secretion and subsequent contraction - scarring - are part of the normal wound healing response and crucial to restore tissue integrity. Due to myofibroblasts ability to repair but not regenerate, accumulation of scar tissue is always associated with reduced organ performance. This is a fair price to pay by the body for not falling apart. Whereas myofibroblasts typically vanish after successful repair, dysregulation of the normal repair process can lead to persistent myofibroblast activation, for instance by chronic inflammation or mechanical stress in the tissue. Excessive repair leads to the accumulation of stiff collagenous ECM contractures - fibrosis - with dramatic consequences for organ function. The clinical need to terminate detrimental myofibroblast activities has stimulated researchers to answer a number of essential questions: where do myofibroblasts come from, what are the factors leading to their activation, how do we discriminate myofibroblasts from other cells, what is the molecular basis for their contractile activity, and how can we stop or at least control them? This article reviews the current state of the myofibroblast literature by emphasizing their role in ocular repair and fibrosis. It appears that although the eye is quite an extraordinary organ, ocular myofibroblasts behave or misbehave just like their siblings in other organs.

Fibroblasts and myofibroblasts in wound healing

(Myo)fibroblasts are key players for maintaining skin homeostasis and for orchestrating physiological tissue repair. (Myo)fibroblasts are embedded in a sophisticated extracellular matrix (ECM) that they secrete, and a complex and interactive dialogue exists between (myo)fibroblasts and their microenvironment. In addition to the secretion of the ECM, (myo)fibroblasts, by secreting matrix metalloproteinases and tissue inhibitors of metalloproteinases, are able to remodel this ECM. (Myo)fibroblasts and their microenvironment form an evolving network during tissue repair, with reciprocal actions leading to cell differentiation, proliferation, quiescence, or apoptosis, and actions on growth factor bioavailability by binding, sequestration, and activation. In addition, the (myo)fibroblast phenotype is regulated by mechanical stresses to which they are subjected and thus by mechanical signaling. In pathological situations (excessive scarring or fibrosis), or during aging, this dialogue between the (myo)fibroblasts and their microenvironment may be altered or disrupted, leading to repair defects or to injuries with damaged and/or cosmetic skin alterations such as wrinkle development. The intimate dialogue between the (myo)fibroblasts and their microenvironment therefore represents a fascinating domain that must be better understood in order not only to characterize new therapeutic targets and drugs able to prevent or treat pathological developments but also to interfere with skin alterations observed during normal aging or premature aging induced by a deleterious environment.

Post-transcriptional regulation of alpha-smooth muscle actin determines the contractile phenotype of Dupuytren's nodular cells

The objective was to study Dupuytren's myofibroblast cells in constrained collagen matrices in order to more closely emulate their in vivo environment and, to correlate their contractility with alpha-smooth muscle actin (alpha-SMA) expression and determine if dermal fibroblasts regulate Dupuytren's myofibroblast phenotype. Isotonic and isometric force contraction by cells isolated from Dupuytren's nodules, palmar and non-palmar skin fibroblasts was measured in collagen matrices. The effect of co-culturing nodule cells with dermal fibroblasts on isometric contraction was examined. Isometric contraction was correlated with levels of alpha-SMA mRNA by pcr and protein by Western blotting, and alpha-SMA distribution assessed by immunofluorescence. Dupuytren's nodule cells exhibited similar levels of isotonic contraction to both palmar and non-palmar dermal fibroblasts. However, nodule cells generated high levels of isometric force (mean: 3.5 dynes/h), which continued to increase over 24 h to a maximum of 173 dynes. In contrast, dermal fibroblasts initially exhibited low levels of contraction (mean: 0.5 dynes/h) and reached tensional homeostasis on average after 15 h (range: 4-20 h), with a maximum force of 52 dynes. Although all three cell types had similar alpha-SMA mRNA levels, increased levels of alpha-SMA protein were observed in nodule cells compared to dermal fibroblasts. alpha-SMA localised to stress fibres in 35% (range: 26-50%) of nodule cells compared to only 3% (range:0-6%) of dermal fibroblasts. Co-cultures of Dupuytren's cells and dermal fibroblasts showed no contractile differences. The contractile phenotype of Dupuytren's myofibroblasts is determined by increased alpha-SMA protein distributed in stress fibres, not by cellular mRNA levels. Dupuytren's cell contractility is not influenced by dermal fibroblasts.

Genetic inactivation of the laminin alpha5 chain receptor Lu/BCAM leads to kidney and intestinal abnormalities in the mouse

Lutheran blood group and basal cell adhesion molecule (Lu/BCAM) has been recognized as a unique receptor for laminin alpha5 chain in human red blood cells and as a coreceptor in epithelial, endothelial, and smooth muscle cells. Because limited information is available regarding the function of this adhesion glycoprotein in vivo, we generated Lu/BCAM-null mice and looked for abnormalities in red blood cells as well as in kidney and intestine, two tissues showing alteration in laminin alpha5 chain-deficient mice. We first showed that, in contrast to humans, wild-type murine red blood cells failed to express Lu/BCAM. Lu/BCAM-null mice were healthy and developed normally. However, although no alteration of the renal function was evidenced, up to 90% of the glomeruli from mutant kidneys exhibited abnormalities characterized by a reduced number of visible capillary lumens and irregular thickening of the glomerular basement membrane. Similarly, intestine analysis of mutant mice revealed smooth muscle coat thickening and disorganization. Because glomerular basement membrane and smooth muscle coat express laminin alpha5 chain and are in contact with cell types expressing Lu/BCAM in wild-type mice, these results provide evidence that Lu/BCAM, as a laminin receptor, is involved in vivo in the maintenance of normal basement membrane organization in the kidney and intestine.

Variations in structural protein expression and endothelial cell proliferation in relation to clinical manifestations of cerebral cavernous malformations

OBJECTIVE

Cerebral cavernous malformations (CCMs) are associated with hemorrhagic proliferation of endothelial-lined vascular caverns, resulting in hemorrhagic stroke, epilepsy, and other neurological manifestations. We hypothesize that structural protein expression and endothelial cell proliferation markers within CCM lesions are different in the setting of various clinical manifestations.

METHODS

The percentage of immunohistochemically stained caverns positive for collagen IV, fibronectin, laminin, alpha-smooth muscle actin, myosin, and smoothelin and the percentage of dividing endothelial cells within caverns were determined in 36 excised CCM surgical specimens. These were compared in CCMs with different multiplicity, location, and size in patients of different age, sex, seizure status, and hemorrhage status.

RESULTS

Comparisons of seven lesion features and clinical manifestations with the fraction of caverns containing the structural proteins studied and endothelial cell proliferation demonstrated no significant differences. A possible exception was the difference (P < 0.05) in the fraction (mean +/- standard deviation) of positively stained caverns for collagen IV between adult (0.63 +/- 0.39) and pediatric patients (0.87 +/- 0.21) as well as fewer caverns with laminin expression in older patients. These trends did not sustain significance with Bonferroni's correction for multiple comparisons.

CONCLUSION

The fraction of caverns containing the particular structural proteins studied and endothelial cell proliferation within caverns are not correlated with particular lesion features and clinical manifestations that were investigated in CCMs. The possible fewer fractions of caverns containing collagen IV and laminin in adult lesions compared with pediatric lesions may have implications for lesion regression and quiescence with age.

Phenotypic Modulation of Intima and Media Smooth Muscle Cells in Fatal Cases of Coronary Artery Lesion

OBJECTIVE

Characterize the phenotypic features of media and intima coronary artery smooth muscle cells (SMCs) in mildly stenotic plaques, erosions, stable plaques, and in-stent restenosis.

METHODS AND RESULTS

Expression of alpha-smooth muscle actin (alpha-SMA), smooth muscle myosin heavy chains (SMMHCs), and smoothelin was investigated by immunohistochemistry followed by morphometric quantification. The cross-sectional area and the expression of cytoskeletal proteins in the media were lower in restenotic lesions and, to a lesser extent, in stable plaques compared with mildly stenotic plaques and erosions. An important expression of alpha-SMA was detected in the intima of the different lesions; moreover, alpha-SMA staining was significantly larger in erosions compared with all other conditions. In the same location, a striking decrease of SMMHCs and a disappearance of smoothelin were observed in all situations.

CONCLUSIONS

Medial atrophy is prevalent in restenotic lesions and stable plaques compared with mildly stenotic plaques and erosions. Intimal SMCs of all situations exhibit a phenotypic profile, suggesting that they have modulated into myofibroblasts (MFs). The high accumulation of alpha-SMA-positive MFs in erosions compared with stable plaques correlates with the higher appearance of thrombotic complications in this situation.

Focal adhesion size controls tension-dependent recruitment of alpha-smooth muscle actin to stress fibers

Expression of α-smooth muscle actin (α-SMA) renders fibroblasts highly contractile and hallmarks myofibroblast differentiation. We identify α-SMA as a mechanosensitive protein that is recruited to stress fibers under high tension. Generation of this threshold tension requires the anchoring of stress fibers at sites of 8–30-μm-long “supermature” focal adhesions (suFAs), which exert a stress approximately fourfold higher (∼12 nN/μm²) on micropatterned deformable substrates than 2–6-μm-long classical FAs. Inhibition of suFA formation by growing myofibroblasts on substrates with a compliance of ≤11 kPa and on rigid micropatterns of 6-μm-long classical FA islets confines α-SMA to the cytosol. Reincorporation of α-SMA into stress fibers is established by stretching 6-μm-long classical FAs to 8.1-μm-long suFA islets on extendable membranes; the same stretch producing 5.4-μm-long classical FAs from initially 4-μm-long islets is without effect. We propose that the different molecular composition and higher phosphorylation of FAs on supermature islets, compared with FAs on classical islets, accounts for higher stress resistance.

Phenotypic heterogeneity influences the behavior of rat aortic smooth muscle cells in collagen lattice

Phenotypic modulation of vascular smooth muscle cells (SMCs) in atherosclerosis and restenosis involves responses to the surrounding microenvironment. SMCs obtained by enzymatic digestion from tunica media of newborn, young adult (YA) and old rats and from the thickened intima (TI) and underlying media of young adult rat aortas 15 days after ballooning were entrapped in floating populated collagen lattice (PCL). TI-SMCs elongated but were poor at PCL contraction and remodeling and expressed less alpha2 integrin compared to other SMCs that appeared more dendritic. During early phases of PCL contraction, SMCs showed a marked decrease in the expression of alpha-smooth muscle actin and myosin. SMCs other than TI-SMCs required 7 days to re-express alpha-smooth muscle actin and myosin. Only TI-SMCs in PCL were able to divide in 48 h, with a greater proportion in S and G2-M cell cycle phases compared to other SMCs. Anti-alpha2 integrin antibody markedly inhibited contraction but not proliferation in YA-SMC-PLCs; anti-alpha1 and anti-alpha2 integrin antibodies induced a similar slight inhibition in TI-SMC-PCLs. Finally, TI-SMCs rapidly migrated from PCL on plastic reacquiring their epithelioid phenotype. Heterogeneity in proliferation and cytoskeleton as well the capacity to remodel the extracellular matrix are maintained, when SMCs are suspended in PCLs.

The N-terminal Ac-EEED sequence plays a role in alpha-smooth-muscle actin incorporation into stress fibers

We have previously shown that the N-terminal sequence AcEEED of alpha-smooth-muscle actin causes the loss of alpha-smooth-muscle actin from stress fibers and a decrease in cell contractility when introduced in myofibroblasts as a cell-penetrating fusion peptide. Here, we have investigated the function of this sequence on stress fiber organization in living cells, using enhanced green fluorescent protein (EGFP)-tagged alpha-smooth-muscle actin. The fusion peptide provokes the gradual disappearance of EGFP fluorescence of alpha-smooth-muscle actin from stress fibers and the formation of hitherto unknown rod-like structures. In addition to alpha-smooth-muscle actin, these structures contain cytoplasmic actins, gelsolin and cofilin but not other major actin-binding proteins. These rod-like structures are also visible in wild-type fibroblasts during normal cell spreading, suggesting that they represent a physiological step in the organization of alpha-smooth-muscle actin in stress fibers. Fluorescence-recovery-after-photobleaching experiments suggest that the fusion peptide reduces the dynamics of alpha-smooth-muscle actin and its incorporation in stress fibers. Here, we propose a new mechanism of how alpha-smooth-muscle actin is incorporated in stress fibers involving the sequence Ac-EEED.

Expression of histone deacetylase 8, a class I histone deacetylase, is restricted to cells showing smooth muscle differentiation in normal human tissues

Histone deacetylases (HDACs) were originally identified as nuclear enzymes involved in gene transcription regulation. Until recently, it was thought that their activity was restricted within the nucleus, with histones as unique substrates. The demonstration that specific HDACs deacetylate nonhistone proteins, such as p53 and alpha-tubulin, broadened the field of activity of these enzymes. HDAC8, a class I HDAC, is considered to be ubiquitously expressed, as suggested by results of Northern blots performed on tissue RNA extracts, and transfection experiments using various cell lines have indicated that this enzyme may display a prominent nuclear localization. Using immunohistochemistry, we unexpectedly found that, in normal human tissues, HDAC8 is exclusively expressed by cells showing smooth muscle differentiation, including visceral and vascular smooth muscle cells, myoepithelial cells, and myofibroblasts, and is mainly detected in their cytosol. These findings were confirmed in vitro by nucleo-cytoplasmic fractionation and immunoblot experiments performed on human primary smooth muscle cells, and by the cytosolic detection of epitope-tagged HDAC8 overexpressed in fibroblasts. Immunocytochemistry strongly suggested a cytoskeleton-like distribution of the enzyme. Further double-immunofluorescence staining experiments coupled with confocal microscopy analysis showed that epitope-tagged HDAC8 overexpressed in murine fibroblasts formed cytoplasmic stress fiber-like structures that co-localized with the smooth muscle cytoskeleton protein smooth muscle alpha-actin. Our works represent the first demonstration of the restricted expression of a class I HDAC to a specific cell type and indicate that HDAC8, besides being a novel marker of smooth muscle differentiation, may play a role in the biology of these contractile cells.

Laminin alpha5 chain is required for intestinal smooth muscle development

Laminins (comprised of alpha, beta, and gamma chains) are heterotrimeric glycoproteins integral to all basement membranes. The function of the laminin alpha5 chain in the developing intestine was defined by analysing laminin alpha5(-/-) mutants and by grafting experiments. We show that laminin alpha5 plays a major role in smooth muscle organisation and differentiation, as excessive folding of intestinal loops and delay in the expression of specific markers are observed in laminin alpha5(-/-) mice. In the subepithelial basement membrane, loss of alpha5 expression was paralleled by ectopic or accelerated deposition of laminin alpha2 and alpha4 chains; this may explain why no obvious defects were observed in the villous form and enterocytic differentiation. This compensation process is attributable to mesenchyme-derived molecules as assessed by chick/mouse alpha5(-/-) grafted associations. Lack of the laminin alpha5 chain was accompanied by a decrease in epithelial alpha3beta1 integrin receptor expression adjacent to the epithelial basement membrane and of Lutheran blood group glycoprotein in the smooth muscle cells, indicating that these receptors are likely mediating interactions with laminin alpha5-containing molecules. Taken together, the data indicate that the laminin alpha5 chain is essential for normal development of the intestinal smooth muscle and point to possible mesenchyme-derived compensation to promote normal intestinal morphogenesis when laminin alpha5 is absent.

Asp1424Asn MYH9 mutation results in an unstable protein responsible for the phenotypes in May-Hegglin anomaly/Fechtner syndrome

May-Hegglin anomaly (MHA), Fechtner syndrome (FTNS), Sebastian syndrome (SBS), and Epstein syndrome (EPS) are a group of rare, autosomal dominant disorders characterized by thrombocytopenia, giant platelets, and Döhle-like inclusion bodies, together with variable manifestations of Alport-like symptoms that include high-tone sensorineural deafness, cataracts, and nephritis. These disorders result from mutations in the MYH9 gene, which encodes for the nonmuscle myosin heavy chain A protein (also known as NMMHC-A). To date 20 different mutations have been characterized for this gene, but no clear phenotype-genotype correlation has been established, and very little is known regarding the molecular pathogenesis of this group of diseases. Here, we describe 2 new families with MHA/FTNS phenotypes that have been characterized in terms of their mutations, protein localization in megakaryocytes, protein expression, and mRNA stability. Our findings suggest that, at least for the Asp1424Asn mutation in the MYH9 gene, the phenotypes result from a highly unstable protein. No abnormalities in protein localization or mRNA stability were observed. We hypothesize that haploinsufficiency of the MYH9 results in a failure to properly reorganize the cytoskeleton in megakaryocytes as required for efficient platelet production.

Heterogeneity of smooth muscle cell populations cultured from pig coronary artery

OBJECTIVE

Heterogeneous smooth muscle cell (SMC) populations have been described in the arteries of several species. We have investigated whether SMC heterogeneity is present in the porcine coronary artery, which is widely used as a model of restenosis.

METHODS AND RESULTS

By using 2 isolation methods, distinct medial populations were identified: spindle-shaped SMCs (S-SMCs) after enzymatic digestion, with a "hill-and-valley" growth pattern, and rhomboid SMCs (R-SMCs) after explantation, which grow as a monolayer. Moreover, the intimal thickening that was induced after stent implantation yielded a large proportion of R-SMCs. R-SMCs exhibited high proliferative and migratory activities and high urokinase activity and were poorly differentiated compared with S-SMCs. Heparin and transforming growth factor-beta2 inhibited proliferation and increased differentiation in both populations, whereas fibroblast growth factor-2 and platelet-derived growth factor-BB had the opposite effect. In addition, S-SMCs treated with fibroblast growth factor-2 or platelet-derived growth factor-BB or placed in coculture with coronary artery endothelial cells acquired a rhomboid phenotype. This change was reversible and was also observed with S-SMC clones, suggesting that it depends on phenotypic modulation rather than on selection.

CONCLUSIONS

Our results show that 2 distinct SMC subpopulations can be recovered from the pig coronary artery media. The study of these subpopulations will be useful for understanding the mechanisms of restenosis.

Mechanical tension controls granulation tissue contractile activity and myofibroblast differentiation

We have examined the role of mechanical tension in myofibroblast differentiation using two in vivo rat models. In the first model, granulation tissue was subjected to an increase in mechanical tension by splinting a full-thickness wound with a plastic frame. Myofibroblast features, such as stress fiber formation, expression of ED-A fibronectin and alpha-smooth muscle actin (alpha-SMA) appeared earlier in splinted than in unsplinted wounds. Myofibroblast marker expression decreased in control wounds starting at 10 days after wounding as expected, but persisted in splinted wounds. In the second model, granuloma pouches were induced by subcutaneous croton oil injection; pouches were either left intact or released from tension by evacuation of the exudate at 14 days. The expression of myofibroblast markers was reduced after tension release in the following sequence: F-actin (2 days), alpha-SMA (3 days), and ED-A fibronectin (5 days); cell density was not affected. In both models, isometric contraction of tissue strips was measured after stimulation with smooth muscle agonists. Contractility correlated always with the level of alpha-SMA expression, being high when granulation tissue had been subjected to tension and low when it had been relaxed. Our results support the assumption that mechanical tension is crucial for myofibroblast modulation and for the maintenance of their contractile activity.

Alpha-smooth muscle actin expression upregulates fibroblast contractile activity

To evaluate whether alpha-smooth muscle actin (alpha-SMA) plays a role in fibroblast contractility, we first compared the contractile activity of rat subcutaneous fibroblasts (SCFs), expressing low levels of alpha-SMA, with that of lung fibroblasts (LFs), expressing high levels of alpha-SMA, with the use of silicone substrates of different stiffness degrees. On medium stiffness substrates the percentage of cells producing wrinkles was similar to that of alpha-SMA-positive cells in each fibroblast population. On high stiffness substrates, wrinkle production was limited to a subpopulation of LFs very positive for alpha-SMA. In a second approach, we measured the isotonic contraction of SCF- and LF-populated attached collagen lattices. SCFs exhibited 41% diameter reduction compared with 63% by LFs. TGFbeta1 increased alpha-SMA expression and lattice contraction by SCFs to the levels of LFs; TGFbeta-antagonizing agents reduced alpha-SMA expression and lattice contraction by LFs to the level of SCFs. Finally, 3T3 fibroblasts transiently or permanently transfected with alpha-SMA cDNA exhibited a significantly higher lattice contraction compared with wild-type 3T3 fibroblasts or to fibroblasts transfected with alpha-cardiac and beta- or gamma-cytoplasmic actin. This took place in the absence of any change in smooth muscle or nonmuscle myosin heavy-chain expression. Our results indicate that an increased alpha-SMA expression is sufficient to enhance fibroblast contractile activity.

Alpha-smooth muscle actin-positive myofibroblasts in endometrial stroma are not a reliable criterion for the diagnosis of well differentiated endometrioid adenocarcinoma in small tissue samples

Although a desmoplastic stromal reaction in well-differentiated endometrioid adenocarcinoma is considered a major criterion in the differential diagnosis with atypical hyperplasia, this histologic feature has not met with universal approval. Since alpha-smooth muscle (alpha-SM) actin positive myofibroblasts characterize the desmoplastic stromal response in a variety of neoplasms, the present study was undertaken in order to establish whether these cells are also prominent in the stroma of endometrioid carcinoma and if present could be used as a valid criterion in the differential diagnosis between benign and malignant lesions. The present study of 100 endometrial samples showed focal desmoplastic stromal reaction with alpha-SM actin positive myofibroblasts in 30% of small samples and in 50% of hysterectomy specimens with endometrioid carcinoma. In normal endometrium and in benign lesions lacking a desmoplastic reaction, focal stromal alpha-SM actin positivity was a very common finding. Stromal alpha-SM actin-positive cells were also frequently seen in nondesmoplastic stroma of endometrioid carcinoma. Thus the common presence of alpha-SM actin-positive myofibroblasts in normal endometrial stroma and in benign and malignant lesions precludes its usefulness in the diagnosis of well differentiated endometrioid adenocarcinoma, especially in small tissue samples.

Cultured arterial smooth muscle cells maintain distinct phenotypes when implanted into carotid artery

Cultured arterial smooth muscle cells (SMCs) with distinct phenotypic features have been described by several laboratories; however, it is not presently known whether this phenotypic heterogeneity can be maintained within an in vivo environment. To answer this question, we have seeded into the intima of denuded rat carotid artery 2 SMC populations with well-established distinct biological features, ie, spindle-shaped, not growing in the absence of serum, and well differentiated versus epithelioid, growing in the absence of serum, and relatively undifferentiated, derived from the aortic media of newborn rats (aged 4 days) and old rats (aged >18 months), respectively. We show that these 2 populations maintain their distinct biochemical features (ie, expression of alpha-smooth muscle actin, smooth muscle myosin heavy chains, and cellular retinol binding protein-1) in the in vivo environment. The old rat media-derived SMCs continue to produce cellular retinol binding protein-1 but little alpha-smooth muscle actin and smooth muscle myosin heavy chains, whereas the newborn rat media-derived SMCs continue to express alpha-smooth muscle actin and smooth muscle myosin heavy chains but no cellular retinol binding protein-1. Our results reinforce the notion of arterial SMC phenotypic heterogeneity and suggest that in our model, heterogeneity is controlled genetically and not by the local environment.

Establishment and characterization of a spontaneously immortalized myofibroblast cell line derived from a human liver angiosarcoma

BACKGROUND/AIM

Fibrosis and/or cirrhosis are present in the precursor stages of most liver cancers. However, little is known about the reciprocal interactions of fibroblasts, mainly responsible for fibrosis, and the other liver cells. We report here the isolation of a new liver myofibroblast cell line from a human liver angiosarcoma and its characterization.

METHODS

The cells were isolated by the explant technique and characterization was performed, on one hand, using immunohistochemical and ultrastructural analysis and, in the other hand, by determining their karyotype, ras and p53 status and their tumorigenic properties.

RESULTS

To date, the cells have undergone approximately 170 population doublings and are still proliferating. Immunohistochemically, they were negative for desmin, smooth muscle myosin, cytokeratin 19 and von Willebrand factor, positive for vimentin and alpha-smooth muscle actin, with an important deposition of fibronectin around the cells. Ultrastructure showed particularly cytoplasmic microfilament bundles. Their chromosome number ranged from 38 to 168 with a bimodal population, near diploid and hypotetraploid. No mutations were found in codons 12, 13 or 61 of Ha-, Ki- and N-ras genes but a homozygous missense mutation in codon 179 (CAT-->CTT) was detected in the p53 gene. They were unable to form foci in soft agar or tumors in nude mice.

CONCLUSIONS

Taken together, these results show that these cells, called BM 2.2.1, exhibited typical myofibroblast-like features. Although they contained a karyotype suggestive of tumoral cells and a homozygous mutated p53 gene, they were not tumorigenic. The nature of these cells and the abnormalities of the p53 gene and the karyotype, suggest that: i) they were a component of the tumor stroma, and ii) they could have been involved in angiosarcoma development. Thus, this cell line may be valuable for the study of cellular interactions in liver carcinogenesis.

Cardiac and smooth muscle cell contribution to the formation of the murine pulmonary veins

Previous studies have demonstrated that the primordial pulmonary veins originate as an outgrowth of the atrial cells and anastomosis with the pulmonary venous plexus. As a consequence of this embryologic origin the tunica media of these vessels is composed of cardiac cells that express atrial specific markers (Lyons et al. [1990] J Cell Biol 111:2427-2436; Jones et al. [1994] Dev Dyn 200:117-128). We used transgenic mice for the cardiac troponin I (cTNI) gene and smooth muscle (SM) myosin heavy chain as differentiation markers, to analyze how cardiac and SM cells contribute to the formation and structural remodeling of the pulmonary veins during development. We show here that the tunica media of the adult mouse pulmonary veins contains an outer layer of cardiac cells and an intermediate SM cell compartment lining down on the inner endothelium. This structural organization is well expressed in the intrapulmonary veins from the beginning of vasculogenesis, with cardiac cells accumulating over preexisting roots of endothelial and SM cells and extending to the third bifurcation of the pulmonary branches without reaching the more distal tips of the vessels. On the other hand, SM cells, which are widely distributed in the intrapulmonary veins from the embryonic stage E16, accumulate also in the extrapulmonary branches and reach the posterior wall of the left atrium, including the orifices of the pulmonary veins. This event takes place around birth when the pulmonary blood flow starts to function properly. A model for the development of the pulmonary veins is presented, based upon our analysis.

Inducible expression of basic transcription element-binding protein 2 in proliferating smooth muscle cells at the vascular anastomotic stricture

OBJECTIVE

The proliferation of vascular smooth muscle cells surrounding a suture line is an important factor in the development of anastomotic stricture that is frequently seen after coronary artery bypass grafting. The aim of this study was to investigate the time course of intimal thickening and to examine the expression of the molecular marker of smooth muscle cell activation surrounding the suture line.

METHODS

Longitudinal aortotomy was performed in the abdominal aorta of rats. The rats were put to death 1, 2, 4, and 8 weeks after aortotomy, and the percentage of the lumen occluded by intimal thickening was calculated. All tissues were stained with antibodies against basic transcription element- binding protein 2, human cyclin-dependent kinase (cdk4), and Sp1 for immunohistochemistry. Basic transcription element-binding protein 2 is a transcription factor that is involved in phenotypic modulation of vascular smooth muscle cells. Cdk4 represents a marker for G(1) phase of the cell cycle. Sp1 is a transcription factor known to be expressed in a variety of tissues. Basic transcription element-binding protein 2 messenger RNA expression was confirmed by means of reverse transcriptase-polymerase chain reaction.

RESULTS

We noted significant thickening of the intimal layer 1 week after aortotomy. Immunohistochemistry demonstrated that smooth muscle cells in the neointima were strongly positive for basic transcription element-binding protein 2 and human cyclin-dependent kinase 4, which peaked 2 weeks after aortotomy. Basic transcription element-binding protein 2 expression was closely associated with human cyclin-dependent kinase 4 expression in the neointima, although Sp1 was not. Basic transcription element-binding protein 2 messenger RNA levels were significantly up-regulated early after aortotomy.

CONCLUSION

The experimental rat aortotomy model is useful to investigate the proliferation of vascular smooth muscle cells around the suture line. Moreover, our results suggest the possible role of basic transcription element-binding protein 2 in the development of vascular anastomotic strictures.

Vascular smooth muscle differentiation of murine stroma: a sequential model

Previous studies by our group showed that stromal cells from human long-term marrow cultures were mesenchymal cells following a vascular smooth muscle pathway. The present study using 58 immortalized stromal lines from different hematopoietic sites was conducted to verify whether this hypothesis also held true for murine stroma. Principal components analysis performed using cytoskeletal and extracellular matrix proteins allowed the segregation of five factors explaining more than 70% of the variance. Factor I, including osteopontin and vimentin, and factor II, laminins and fibronectins, were representative of the mesenchyme. The remaining three factors were representative of vascular smooth muscle: factor III, including alphaSM actin, SM alpha actinin, SM22alpha, EDa+ fibronectin, and thrombospondin-1; factor IV, metavinculin and h-caldesmon; and factor V, smooth muscle myosin SM1 and desmin. All lines expressed factors I and II; 53 lines expressed factor III, 35 lines expressed factor IV; and 11 lines expressed factor V. A second principal components analysis including membrane antigens indicated the cosegregration of vascular cell adhesion molecule-1 with osteopontin and that of Ly6A/E with vimentin, whereas CD34 and Thy-1 appeared to be independent factors. The heterogeneity of vascular smooth muscle markers expression suggests that harmonious maintenance of hematopoiesis depends on the cooperation between different stromal cell clones.

Embryonic smooth muscle myosin heavy chain SMemb is expressed in pressure-overloaded cardiac fibroblasts

Left ventricular hypertrophy (LVH) is a secondary adaptation to increased external load. Various qualitative and quantitative changes in myocytes and extracellular components occur during the development of LVH. It has recently been demonstrated that alpha-smooth muscle actin (alpha-SMA)-expressing myofibroblasts appear in the interstitium of the heart subjected to increased workload suggesting that cardiac fibroblasts as well as myocytes alter their phenotype in response to pressure overload. In the present study, to explore the load-induced response and phenotypic modulation of cardiac fibroblasts, the localization of embryonic smooth muscle myosin heavy chain (SMemb) and alpha-SMA in thoracic aorta-constricted rat hearts was investigated by immunohistochemistry, and the morphology of the SMemb-expressing cells was examined by electron microscopy. In addition, to clarify the mechanisms by which SMemb is induced in pressure-overloaded hearts, mRNA expression of SMemb in aorta-constricted rat hearts and in transforming growth factor-beta1 (TGF-beta1)-treated or mechanically-stretched cultured cardiac fibroblasts was investigated. Enhanced staining of SMemb and alpha-SMA was detected in the interstitial spindle-shaped cells in the fibrotic lesions of the pressure-overloaded left ventricles by immunohistochemistry. These cells were demonstrated by electron microscopy to have features specific for activated fibroblasts such as serrated nuclei or prominent rough endoplasmic reticulum. These cells also had characteristic features of myofibroblasts, i.e. irregularly arranged actin filaments and scattered dense bodies. Northern blot analysis revealed increased mRNA levels of SMemb both in aorta-constricted rat hearts and in cultured cardiac fibroblasts stimulated by TGF-beta1 or by mechanical stretch. These results suggest that SMemb may be a molecular marker both for the detection of activated cardiac fibroblasts that may play important roles in the remodeling of pressure-overloaded cardiac interstitium, and for the identification of the regu latory mechanisms that control the phenotypic modulation of cardiac fibroblasts in response to pressure overload.

Cultured porcine coronary artery smooth muscle cells. A new model with advanced differentiation

Arterial intimal thickening after endothelial injury induced in rodents has proven to be a relatively unreliable model of restenosis for testing clinically useful compounds. The same has been found for cultured rat or rabbit vascular smooth muscle cells (SMCs). To test alternative possibilities, we have studied several differentiation features of porcine coronary artery SMCs, cultured up to the 5th passage after enzymatic digestion of the media. The effects of heparin, transforming growth factor (TGF)-beta1 or TGF-beta2, and all-trans-retinoic acid (tRA) on proliferation, migration, and differentiation of these cells also were examined. Porcine arterial SMCs in culture not only express high levels of alpha-smooth muscle (SM) actin but, contrary to rodent SMCs, also maintain an appreciable expression of SM myosin heavy chain isoforms 1 and 2, desmin, and smoothelin, a recently described late differentiation marker of vascular SMCs. We demonstrate for the first time that smoothelin is colocalized with alpha-SM actin in these cells. Finally, we show that in the porcine model, heparin is more potent than TGF-beta1 or TGF-beta2 and tRA in terms of inhibition of proliferation and migration and of increasing the expression of differentiation markers. This model should be a useful complement to in vivo studies of SMC differentiation and of pathological situations such as restenosis and atheromatosis.

Periacinar collagenization in patients with chronic alcoholism

To examine the development of pancreatic fibrosis in alcoholics, the fibrosis types grouped according to Martin's classification were examined by immunohistochemistry using an antibody against alpha-smooth muscle actin (alpha-SMA). The initial stage of periacinar collagenization was also investigated by electron microscopy. The total incidence of pancreatic fibrosis at autopsy of the 29 alcoholics was significantly higher than that of the 40 non-alcoholics. Intralobular sclerosis was observed to be the most frequent type of fibrosis regardless of alcohol intake. No differences in the enhancement of alpha-SMA expression in each type of fibrosis were found between the alcoholics and non-alcoholics. Electron microscopically, myofibroblasts were found around acini in the early stage of periacinar collagenization, and were accompanied by numerous fine filaments (8-15 nm in diameter). The various changes in zymogen granules (ZG), lysosomes and lipid droplets were augmented in the acinar cells of alcoholics. Medium-density materials were also found in dilated rough endoplasmic reticulum (RER). The contents of ZG and RER occasionally leaked out. In conclusion, pancreatic fibrosis was increased in alcoholics; myofibroblasts may play an important role in the initial stage of periacinar collagenization; and the intracellular transport blockage of protein as represented by abnormalities of ZG, ER and lysosomes may contribute to the development of periacinar collagenization.

Expression of sarcomeric proteins and assembly of myofibrils in the putative myofibroblast cell line BHK-21/C13

The expression and organization patterns of several myofibrillar proteins were analysed in the putative myofibroblast cell line BHK-21/C13. Although this cell line originates from renal tissue, the majority of the cells express titin. In these cells, titin is, under standard culture conditions, detected in myofibril-like structures (MLSs), where it alternates with non-muscle myosin (NMM). Expression of sarcomeric myosin heavy chain (sMyHC) is observed in a small minority of cells, while other sarcomeric proteins, such as nebulin, myosin binding protein C (MyBP-C), myomesin and M-protein are not expressed at all. By changing the culture conditions in a way equal to conditions that induce differentiation of skeletal muscle cells, a process reminiscent of sarcomerogenesis in vitro is induced. Within one day after the switch to a low-nutrition medium, myofibrillar proteins can be detected in a subset of cells, and after two to five days, all myofibrillar proteins examined are organized in typical sarcomeric patterns. Frequently, cross-striations are visible with phase contrast optics. Transfection of these cells with truncated myomesin fragments showed that a specific part of the myomesin molecule, known to contain a titin-binding site, binds to MLSs, whereas other parts do not. These results demonstrate that this cell line could serve as a powerful model to study the assembly of myofibrils. At the same time, its transfectability offers an invaluable tool for in vivo studies concerning binding properties of sarcomeric proteins.

Subepithelial fibroblast cell lines from different levels of gut axis display regional characteristics

The intestine is characterized by morphofunctional differences along the proximodistal axis. The aim of this study was to derive mesenchymal cell lines representative of the gut axis. We isolated and cloned rat intestinal subepithelial myofibroblasts raised from 8-day proximal jejunum, distal ileum, and proximal colon lamina propria. Two clonal cell lines from each level of the gut were characterized. They 1) express the specific markers vimentin, smooth muscle alpha-actin, and smooth muscle myosin heavy chain, revealed by immunofluorescence microscopy and 2) distinctly support endodermal cell growth in a coculture model, depending on their regional origin, and 3) the clones raised from the various proximodistal regions maintain the same pattern of morphogenetic and growth and/or differentiation factor gene expression as in vivo: hepatocyte growth and/or scatter factor and transforming growth factor-beta 1 mRNAs analyzed by RT-PCR were more abundant, in the colon and ileal clones and mucosal connective tissue, respectively. In addition, epimorphin mRNA studied by Northern blot was also the highest in one ileal clone, in which it was selectively upregulated by all-trans retinoic acid (RA) treatment. Epimorphin expression in isolated 8-day intestinal lamina propria was higher in the distal small intestine and proximal colon than in the proximal small intestine. In conclusion, we isolated and characterized homogeneous cell subtypes that can now be used to approach the molecular regulation of the epithelium-mesenchyme-dependent regional specificity along the gut.

Sarcomeric gene expression and contractility in myofibroblasts

Myofibroblasts are unusual cells that share morphological and functional features of muscle and nonmuscle cells. Such cells are thought to control liver blood flow and kidney glomerular filtration rate by having unique contractile properties. To determine how these cells achieve their contractile properties and their resemblance to muscle cells, we have characterized two myofibroblast cell lines. Here, we demonstrate that myofibroblast cell lines from kidney mesangial cells (BHK) and liver stellate cells activate extensive programs of muscle gene expression including a wide variety of muscle structural proteins. In BHK cells, six different striated myosin heavy chain isoforms and many thin filament proteins, including troponin T and tropomyosin are expressed. Liver stellate cells express a limited subset of the muscle thick filament proteins expressed in BHK cells. Although these cells are mitotically active and do not morphologically differentiate into myotubes, we show that MyoD and myogenin are expressed and functional in both cell types. Finally, these cells contract in response to endothelin-1 (ET-1); and we show that ET-1 treatment increases the expression of sarcomeric myosin.

Transfected muscle and non-muscle actins are differentially sorted by cultured smooth muscle and non-muscle cells

We have analyzed by immunolabeling the fate of exogenous epitope-tagged actin isoforms introduced into cultured smooth muscle and non-muscle (i.e. endothelial and epithelial) cells by transfecting the corresponding cDNAs in transient expression assays. Exogenous muscle actins did not produce obvious shape changes in transfected cells. In smooth muscle cells, transfected striated and smooth muscle actins were preferentially recruited into stress fibers. In non-muscle cells, exogenous striated muscle actins were rarely incorporated into stress fibers but remained scattered within the cytoplasm and frequently appeared organized in long crystal-like inclusions. Transfected smooth muscle actins were incorporated into stress fibers of epithelial cells but not of endothelial cells. Exogenous non-muscle actins induced alterations of cell architecture and shape. All cell types transfected by non-muscle actin cDNAs showed an irregular shape and a poorly developed network of stress fibers. beta- and gamma-cytoplasmic actins transfected into muscle and non-muscle cells were dispersed throughout the cytoplasm, often accumulated at the cell periphery and rarely incorporated into stress fibers. These results show that isoactins are differently sorted: not only muscle and non-muscle actins are differentially distributed within the cell but also, according to the cell type, striated and smooth muscle actins can be discriminated for. Our observations support the assumption of isoactin functional diversity.

Enhanced proliferation and migration and altered cytoskeletal proteins in early passage smooth muscle cells from young and old rat aortic explants

Smooth muscle cell (SMC) proliferation, migration, and cytoskeletal protein expression were studied in cultured cells obtained from the aortic explants of young (6-month) and old (30-month) Fischer 344XNB rats. Second-passage SMC were cultured on coverslips, and cytoskeletal fibers were examined by immunofluorescence microscopy using antibodies specific for smooth muscle myosin, alpha-smooth muscle actin, vimentin, desmin, and tubulin. The cytoskeletal fiber density was quantified as fluorescence intensity by confocal microscopy. The proliferation of SMC was analyzed from the growth curve of cells grown in culture from 0 to 14 days, and a Boyden chamber assay was used to quantify the SMC migration rate. The diameter of fresh SMC digested enzymatically from old rat aortae was 52.4% larger than that of the cells from young animals (20.0 +/- 3 microm vs 13.1 +/- 2 microm, P < 0.05). In SMC cultured from old animals, the intensities of smooth muscle myosin, alpha-smooth muscle actin, and vimentin decreased by 59.6, 41.2, and 54.8%, respectively; desmin and tubulin increased by 46.1 and 65.1% (all P < 0.001). Compared to SMC isolated from young rat aortae, the number of SMC cultured (second passage) from the old rat aorta was increased by 48.4, 27.2, and 26.9%, respectively, at Days 3, 7, and 14 in culture (P < 0.05, P < 0.01, and P < 0.001). The migration rate of SMC cultured from old rats was 59.3% higher than that of the cells obtained from young rats. These data show that alterations of the SMC cytoskeleton occur concomitantly with changes in SMC proliferation and migration rate during aging, suggesting that the age-associated changes in cytoskeletal proteins may play a role in remodeling of the aortic wall during aging.

Phenotypic characterization of human smooth muscle cells derived from atherosclerotic tibial and peroneal arteries

PURPOSE

The vascular smooth muscle cell plays a pivotal role in the development of atherosclerosis. The objectives of this study were to characterize smooth muscle cells from the human atherosclerotic tibial artery to determine their phenotypic properties and to examine the contractile reactions of these cells to physiologic and pharmacologic stimuli.

METHODS

After below-knee amputations were performed, vascular smooth muscle cells were harvested and cultivated from tibioperoneal source. Characterization was done with transmission electron microscopy and immunocytochemistry. The contractile properties were determined by observing the response to various stimuli. In addition, segments of vessels harvested were submitted to electron microscopy studies for comparison with the cultured cells.

RESULTS

Immunofluorescent labeling was positive for alpha-smooth muscle actin. Electron microscopy revealed the presence of a thickened basal laminae and large intracellular lipid vacuoles. The earlier passages revealed cells with a large number of microfilaments characteristic of a contractile cell. As later passages were examined, there was a notable change in character with an increasing amount of rough endoplasmic reticulum and Golgi complexes. The increased thickness of the basal lamina in the cultured cells resembled that found in vessel segments studied by electron microscopy. A rapid contraction response was seen when the cells were incubated with angiotensin II, bradykinin, or endothelin. No response was seen with the addition of isoproterenol, nitroglycerin, or nitroprusside, known smooth-muscle relaxants.

CONCLUSION

This model demonstrates the apparent inability of these smooth muscle cells from atherosclerotic tibial arteries to relax to pharmacologic and physiologic stimuli. In addition, as seen by transmission electron microscopy, these cells maintain their atherosclerotic phenotype after multiple passages.

Nonmuscle and smooth muscle myosin heavy chain expression in rejected cardiac allografts. A study in rat and monkey models

BACKGROUND

Diagnosis of acute rejection and graft arteriosclerosis (chronic rejection) is critical to the success of cardiac transplantation, but accurate diagnosis is often difficult. We have reported that there are three types of vascular myosin heavy chain (MHC) isoforms: SM1, SM2, and SMemb. SM2 is specifically expressed in differentiated smooth muscle cells (SMCs). SMemb is a nonmuscle-type MHC abundantly expressed in SMCs of fetal aorta.

METHODS AND RESULTS

To evaluate the usefulness of MHC expression for diagnosis and analysis of acute and chronic rejection, heterotopic cardiac transplantation was performed in rats and monkeys. Immunohistochemistry, electron microscopy, and Northern blot assay were performed to evaluate MHC expression. SMemb was expressed in spindle-shaped cells located in acutely rejected myocardium in the rats and monkeys. These cells were also observed in areas lacking cellular infiltration. These SMemb-positive cells were activated fibroblasts or myofibroblasts. SMemb mRNA was enhanced parallel to the progression of acute rejection. In the coronary arteries of chronically rejected allografts, enhanced SMemb and reduced SM2 expression was observed in both thickened intima and media. The reduced medial SM2 expression was observed before the intimal thickening occurred. These cells were phenotypically modulated SMCs.

CONCLUSIONS

Altered expression of MHC isoforms is a sensitive indicator in the diagnosis of acute and chronic cardiac rejection. The pathophysiology of this alteration in MHC isoform expression should be studied further to elucidate the pathogenesis of cardiac rejection.

Placental villous stroma as a model system for myofibroblast differentiation

Different subtypes of myofibroblasts have been described according to their cytoskeletal protein patterns. It is quite likely that these different subtypes represent distinct steps of differentiation. We propose the human placental stem villi as a particularly suitable model to study this differentiation process. During the course of pregnancy, different types of placental villi develop by differentiation of the mesenchymal stroma surrounding the fetal blood vessels. In order to characterise the differentiation of placental stromal cells in the human placenta, the expression patterns of the cytoskeletal proteins vimentin, desmin, alpha- and gamma-smooth muscle actin, pan-actin, smooth muscle myosin, and the monoclonal antibody GB 42, a marker of myofibroblasts, were investigated on placental tissue of different gestational age (7th-40th week of gestation). Proliferation patterns were assessed with the proliferation markers MIB 1 and PCNA. Additionally, dipeptidyl peptidase IV distribution was studied in term placenta and the ultrastructure of placental stromal cells was assessed by electron microscopy. Different subpopulations of extravascular stromal cells were distinguished according to typical co-expression patterns of cytoskeletal proteins. Around the fetal stem vessels in term placental villi they were arranged as concentric layers with increasing stage of differentiation. A variable layer of extravascular stromal cells lying beneath the trophoblast expressed vimentin (V) or vimentin and desmin (VD). They were mitotically active. The next layer co-expressed vimentin, desmin, and alpha-smooth muscle actin (VDA). More centrally towards the fetal vessels, extravascular stromal cells co-expressed vimentin, desmin, alpha- and gamma-smooth muscle actin, and GB 42 (VDAG). Cells close to the fetal vessels additionally co-expressed smooth muscle myosin (VDAGM). Ultrastructurally, V cells resembled typical mesenchymal cells. VD cells corresponded to fibroblasts, while VDA and VDAG cells developed features of myofibroblasts. Cells of the VDAGM-type revealed a smooth muscle cell-related ultrastructure. In earlier stages of pregnancy, stromal cell types with less complex expression patterns prevailed. The media smooth muscle cells of the fetal vessels showed a mixture of different co-expression patterns. These cells were separated from extravascular stromal cells by a layer of collagen fibres. The results obtained indicate a clearly defined spatial differentiation gradient with increasing cytoskeletal complexity in human placental stromal cells from the superficial trophoblast towards the blood vessels in the centre of the stem villi. The spatial distribution of the various stages of differentiation suggests that human placental villi could be a useful model for the study of the differentiation of myofibroblasts.

Phenotypic heterogeneity of rat arterial smooth muscle cell clones. Implications for the development of experimental intimal thickening

It is well accepted that smooth muscle cells (SMCs) cultured from normal rat arterial media have different morphological and biological features compared with SMCs cultured from experimental intimal thickening (IT) 15 days after endothelial injury. It is not known, however, whether the phenotypic modulation producing IT cells occurs in any medial SMCs or only in a particular SMC subpopulation. To distinguish among these possibilities, the phenotypic features of SMC clones derived from normal adult media and the IT 15 days after endothelial lesion were analyzed according to morphological appearance, replicative activity in the presence and absence of fetal calf serum, and [3H]thymidine incorporation and motile activity; these features were compared with those of the respective SMC parental populations. Two categories of SMC clones predominated: spindle clones, with morphological features similar to those of the parental population from the normal media, and epithelioid clones, with morphological features similar to those of the IT parental population. Both categories were present among clones produced from normal media and IT; however, spindle was more common among normal media clones, and epithelioid, among IT clones. The behavior in vitro was distinct for each category of clones and did not depend on their origin. Our results are compatible with the possibility that the SMC population of IT in vivo derives mainly from SMCs belonging to the category exhibiting epithelioid features in vitro.

Differentiated properties and proliferation of arterial smooth muscle cells in culture

The smooth muscle cell is the sole cell type normally found in the media of mammalian arteries. In the adult, it is a terminally differentiated cell that expresses cytoskeletal marker proteins like smooth muscle alpha-actin and smooth muscle myosin heavy chains, and contracts in response to chemical and mechanical stimuli. However, it is able to revert to a proliferative and secretory active state equivalent to that seen during vasculogenesis in the fetus, and this is a prerequisite for the involvement of the smooth muscle cell in the formation of atherosclerotic and restenotic lesions. A similar transition from a contractile to a synthetic phenotype occurs when smooth muscle cells are established in culture. Accordingly, an in vitro system has been used extensively to study the regulation of differentiated properties and proliferation of these cells. During the first few days after seeding, the cells are reorganized structurally with a loss of myofilaments and formation of a widespread endoplasmic reticulum and a prominent Golgi complex. In parallel, they lose their contractility and instead become competent to divide in response to a large variety of mitogens, including platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). After entering the cell cycle, they start to produce these and other mitogens on their own, and continue to replicate in the absence of exogenous stimuli for a restricted number of generations. Furthermore, they start to secrete extracellular matrix components such as collagen, elastin, and proteoglycans. The mechanisms that control this change in morphology and function of the smooth muscle cells are still poorly understood. Adhesive proteins such as fibronectin and laminin apparently have an important role in determining the basic phenotypic state of the cells and exert their effects via integrin receptors. The proliferative and secretory activities of the cells are influenced by a multitude of growth factors, cytokines, and other molecules. Although much work remains before an integrated view of this regulatory machinery can be achieved, there is no doubt that the cell culture technique has contributed substantially to our knowledge of smooth muscle differentiation and growth. At the same time, it has been crucial in exploring the role of these cells in vascular disease and developing new therapeutic strategies to cope with major causes of human death and disability.

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.

A retinoic acid-induced clonal cell line derived from multipotential P19 embryonal carcinoma cells expresses smooth muscle characteristics

Despite intense interest in understanding the differentiation of vascular smooth muscle, very little is known about the cellular and molecular mechanisms that control differentiation of this cell type. Progress in this field has been hampered by the lack of an inducible in vitro system for study of the early steps of smooth muscle differentiation. In this study, we describe a model system in which multipotential mouse P19 embryonal carcinoma cells (P19s) can be induced to express multiple characteristics of differentiated smooth muscle. Treatment of P19s with retinoic acid was associated with profound changes in cell morphology and with the appearance at high frequency of smooth muscle alpha-actin-positive cells that were absent or present at extremely low frequency in parental P19s. A clonal line derived from retinoic acid-treated P19s (9E11G) stably expressed multiple characteristics of differentiated smooth muscle, including smooth muscle-specific isoforms of alpha-actin and myosin heavy chain, as well as functional responses to the contractile agonists phenylephrine, angiotensin II, ATP, bradykinin, histamine, platelet-derived growth factor (PDGF)-AA, and PDGF-BB. Additionally, 9E11G cells expressed transcripts for MHox, a muscle homeobox gene expressed in smooth, cardiac, and skeletal muscles, but not the skeletal muscle-specific regulatory factors, MyoD and myogenin. Results demonstrate that retinoic acid treatment of multipotential P19 cells is associated with formation of cell lines that stably express multiple properties of differentiated smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

The origin of the myofibroblasts in breast cancer. Recapitulation of tumor environment in culture unravels diversity and implicates converted fibroblasts and recruited smooth muscle cells

The origin of myofibroblasts in stromal reaction has been a subject of controversy. To address this question definitively, we developed techniques for purification and characterization of major stromal cell types. We defined a panel of markers that could, in combination, unequivocally distinguish these cell types by immunocytochemistry, iso-electric focusing, immunoblotting, and two-dimensional gel electrophoresis. We then devised an assay to recapitulate in culture, within two weeks of incubation, critical aspects of the microenvironment in vivo including the typical tissue histology and stromal reaction. When confronted with tumor cells in this assay, fibroblasts readily converted into a graded pattern of myogenic differentiation, strongest in the immediate vicinity of tumor cells. Vascular smooth muscle cells (VSMC), in contrast, did not change appreciably and remained coordinately smooth muscle differentiated. Midcapillary pericytes showed only a slight propensity for myogenic differentiation. Analysis of ten primary tumors implicated converted fibroblasts (10/10), vascular smooth muscle cells (4/10), and pericytes (1/10) in the stromal reaction. Tumor cells were shown to specifically denude the venules both in culture and in vivo, explaining the VSMC phenotype in the stroma. The establishment of this assay and clarification of the origin of these cells pave the way for further analysis of the mechanisms of conversion, and of the consequence of such heterogeneity for diagnosis and treatment.

Modulation of fibroblastic cytoskeletal features during wound healing and fibrosis

Fibroblast heterogeneity within normal tissues and the subsequent modulation in pathological settings are reflected by ultrastructural criteria and expression patterns of cytoskeletal proteins. The temporal or permanent expression of alpha-smooth muscle (sm) actin in fibroblastic cells is generally related to the development of structural features typical of myofibroblasts. There is evidence of site specific subtypes of myofibroblasts and even of a histogenetic diversity. While granulation tissues myofibroblasts are derived from local fibroblasts, other cell types may also have the potential to acquire a myofibroblastic phenotype. Myofibroblast phenotype can be modulated by several agents such as cytokines (e.g. GM-CSF and gamma-interferon) and extracellular matrix components.

Characterization of rat aortic smooth muscle cells resistant to the antiproliferative activity of heparin following long-term heparin treatment

Vascular smooth muscle cells (SMC) do not represent a homogeneous population (Schwartz et al., 1990, Am. J. Pathol. 136: 1417-1428). Cellular clones resistant to the antiproliferative activity of heparin were isolated from rat aortic SMC cultures (Pukac et al., 1990, Cell Regul., 1:435-443; San Antonio et al., 1993, Arterioscler. Thromb., 13:748-757) and from explant of human arterial restenotic lesions (Chan et al., 1993, Lancet, 341:341-342). We have shown in the present study that long-term treatment (growth medium supplemented with 200 micrograms/ml heparin, from the second to the tenth passage) of rat aortic SMC, without cell cloning, resulted in a significant loss of sensitivity to the growth inhibition by heparin and its derivatives. The heparin resistance was stable after growing cells for two passages in heparin-free medium, suggesting the selection of a particular phenotype. We tried to characterize these cells and to determine the causes of the resistance to the growth inhibition by heparin. Heparin-treated SMC (HT-SMC) were smaller than their control culture at the same passage, expressed less alpha-SM actin, and did not overgrow after reaching confluence. As in the heparin-resistant clones (San Antonio et al., 1993, Cell Regul., 1:435-443) expression of alpha-SM actin could be increased in HT-SMC by heparin addition before Western blotting. Heparin resistance was associated with a tenfold decrease in [3H]-heparin binding capacity (Bmax = 1.9 x 10(6) sites per cell) compared to control cultures (Bmax = 1.7 x 10(7) sites per cell), which was irreversible after growing the cells for two additional passages in heparin-free medium. We also investigated protein kinase C (PKC) in HT-SMC in terms of both enzymatic activity and protein expression (evaluated by [3H]-staurosporine and [3H]-phorbol-12,13-dibutyrate binding). We found that HT-SMC had only half the PKC activity and expression as control SMC. Therefore, long-term treatment of rat aortic SMC with heparin allowed the selection of a less differentiated subpopulation of cells, exhibiting low sensitivity to the growth inhibition by heparin, which could be related to the low capacity of binding heparin and to a lower PKC activity and/or expression.

Rat aortic smooth muscle cells isolated from different layers and at different times after endothelial denudation show distinct biological features in vitro

Endothelial denudation by balloon injury of the rat aorta induces the development of a neointima as a consequence of the migration and proliferation of smooth muscle cells (SMCs). Initially, intimal SMCs show a dedifferentiated phenotype, which reverts to a normal differentiated phenotype after endothelial cells have resurfaced the vessel lumen. We investigated in vitro the proliferative and phenotypic features of SMCs from different layers of rat aorta isolated 15 and 60 days after endothelial denudation. Freshly isolated intimal cells 15 days after balloon injury (IT-15) appeared rounded and showed a decreased content of alpha-smooth muscle actin, smooth muscle myosin, and desmin compared with intimal cells isolated 60 days after balloon injury (IT-60). No morphological and cytoskeletal differences were observed among freshly isolated IT-60 cells and other medial populations, which included medial SMCs that underlie the intimal thickening. In culture, IT-15 cells showed increased proliferative activity both in monolayers and in free-floating collagen lattices. Decreased expression of alpha-smooth muscle actin and smooth muscle myosin was documented in IT-15 cells compared with IT-60 cells and other medial SMC populations in monolayer. Moreover, IT-15 cells suspended in collagen lattices were poor at contracting these collagen lattices compared with IT-60 and control SMCs. IT-60 cells were equivalent to control SMCs at lattice contraction except for a temporary delay at day 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Phenotypic and functional features of myofibroblasts in sheep fetal wounds

The myofibroblast is a mesenchymal cell with functional and structural characteristics in common with fibroblasts and smooth muscle cells. These cells play a critical role in wound closure and in the pathologic sequelae of healing. It has been shown in adult humans and experimental animals that the myofibroblast expresses alpha -smooth muscle actin (ASMA) temporarily during wound contraction and more persistently during fibrocontractive diseases; however, it is unclear whether this cell makes any contribution to tissue repair in utero. Experimental work in fetal animal models has demonstrated that wound repair in fetal skin occurs by reconstitution of epidermal appendages and organized restoration of the dermal collagen network. Fetal lamb wound healing studies have shown that a transition from scarless tissue repair to healing with scar formation occurs late in gestation. In this study we examined the ontogeny of myofibroblasts in fetal lamb wounds at early through late gestation, using transmission electron microscopy (TEM) and ASMA immunohistochemistry. Dramatic differences were observed in ASMA content of early as compared to late gestation fetal wound granulation tissue: ASMA was absent in wounds made at 75 days gestation but was present in progressively greater amounts in wounds made at 100 and 120 days gestation (term = 145 days). TEM studies also demonstrated progressive development and organization of microfilament bundles. Early in development microfilament bundles were sparse and disorganized, but as gestation progressed the bundles became more prevalent and formed tightly parallel arrangements. The organization of microfilament bundles was also accompanied by fibronexus formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical identification and characterization of a special type of desmin-producing stromal cells in human placenta and other fetal tissues

An unusual type of stromal cells has been found to be abundantly present in chorionic villi of human placenta of gestational weeks 6, 17, 35-42 and in tissues of early stages of fetal development (gestational weeks 16-21). These mesenchymal cells are loosely arranged throughout the villous interior and contain the intermediate filament (IF) proteins vimentin and desmin; however the smooth muscle (sm) markers sm-alpha-actin and sm-myosin are absent. Typical myoid stromal cells that are positive for both desmin and sm-alpha-actin also occur in this tissue but are restricted to certain dispersed cell clusters associated with blood vessels. Similar disperse desmin-positive, sm-alpha-actin-negative stromal cells have also been identified, although more sparsely, in the chorionic plate of the placenta and in other diverse fetal tissues such as the interstitium of the kidney, of testis and epididymis, and in cells surrounding Hassall bodies of thymus. The biological nature of these desmin-containing but sm-alpha-actin-negative stromal cells is discussed in relation to myoid cell differentiation. It is emphasized that despite their synthesis of considerable amounts of desmin they cannot be considered myogenic as the occurrence of desmin in the cells may represent an isolated expression of an individual IF protein gene, independent of the synthesis of other muscle proteins.

Beta-actin specific monoclonal antibody

Using a synthetic peptide mimicking the NH2-terminus of beta-actin we have raised a monoclonal antibody specific for this cytoplasmic actin isoform. Specificity of the antibody was demonstrated by its labelling of the actin polypeptide only in tissues containing the beta isoform, by its exclusive recognition of the synthetic beta-actin peptide amongst those mimicking all six vertebrate isoactins, and by its selective recognition of the beta-actin spot in two-dimensional electrophoresis gels of smooth muscle extracts. The antibody bound to actin filaments in both living and fixed fibroblasts where it labelled the stress fiber bundles and, more predominantly, the peripheral actin rich lamellipodia. The characteristics of the antibody indicate that it should serve as a useful tool for studying isoactin distribution and function.

Arterial smooth muscle cell phenotype in stroke-prone spontaneously hypertensive rats

The aim of this study was to determine the phenotype of smooth muscle cells in the arteries of chronically hypertensive animals and to analyze the effects of treatments known to increase the survival of the animal without a clear effect on its hypertensive state. Stroke-prone spontaneously hypertensive rats (SHRSP) kept on a 1% sodium drinking solution were untreated or treated with one of two diuretics, indapamide (3 mg/kg per day) or hydrochlorothiazide (20 mg/kg per day), from 6 to 13 weeks of age. Phenotype was characterized by the immunolabeling of arteries with antibodies raised against a cellular form (EIIIA) of fibronectin, alpha-smooth muscle actin, and nonmuscle myosin. We demonstrated that phenotypes of smooth muscle cells of the SHRSP differ from those found in Wistar-Kyoto rats. The difference in phenotype is specific for the vessel type: ie, an increased expression of nonmuscle myosin in the aorta and of both EIIIA fibronectin and nonmuscle myosin in the coronary arteries. The two diuretics (1) had no effect on blood pressure, (2) prevented or did not prevent the increase in medial thickness, and (3) prevented changes in both smooth muscle cell phenotype and ischemic tissular lesions. Taken together, the results suggest that in SHRSP the changes in the phenotype of smooth muscle cells and the thickness of arteries are unrelated events. We propose that the maintenance of the contractile phenotype of the arterial smooth muscle cells could be an essential parameter involved in the prevention of the deleterious consequences characteristic of a severe hypertensive state.

Targeting gene expression to specific cardiovascular cell types in transgenic mice

Transgenic techniques, which allow the introduction of exogenous genes into the genome of experimental animals, promise to bridge the gap between the in vitro observations made by molecular and cellular biologists on cardiac and vascular cells in tissue culture and the physiology and pathology of the whole organ system. One such application of these techniques is tissue targeting: by genetic manipulation to direct expression of a protein--such as a signaling peptide, a growth factor receptor, or an oncogene involved in cell growth--to a tissue where it normally would not be expressed (or where expression is tightly controlled) by fusing it to the transcriptional control sequences of another gene normally expressed in that tissue. In the cardiovascular system, regulatory sequences for cardiomyocyte-specific proteins, vascular endothelium-specific proteins, and smooth muscle-specific proteins can be used to target heterologous genes to their respective tissues in transgenic animals. The effects that such perturbations have on organ physiology and intracellular and intercellular communication can be observed by applying established physiological and molecular approaches. In this review, we highlight some tissue-specific genes from cardiac and vascular cell types whose regulatory sequences may be used to target heterologous proteins; we discuss neutral "reporter" proteins and signal transduction components as paradigms for the application of this technique; and we briefly touch on the potentials and pitfalls of transgenic approaches to molecular physiology.