Ultrastructure of early plexogenic pulmonary arteriopathy

A lung biopsy specimen from a young woman with the clinical features of primary pulmonary hypertension showed grade 2 plexogenic pulmonary arteriopathy. Electron microscopy revealed 'dark', electron-dense smooth muscle cells in the inner part of the media of muscular pulmonary arteries. Many of these transformed myocytes had migrated into the lumens of pulmonary arteries and arterioles which they occluded. This migration of smooth muscle cells was associated with a substantial increase in the number of pulmonary endocrine cells in the bronchioles containing bombesin and calcitonin.     

The histopathology of 36 cases of plexogenic pulmonary arteriopathy

A detailed histopathological study was made of the lungs of 36 cases of plexogenic pulmonary arteriopathy coming to combined heart-lung transplantation. It revealed two dissimilar processes involved in the pathogenesis of this disease. One comprised histological appearances consistent with constriction of muscular pulmonary arteries, a condition that would be likely to be reversed by pulmonary vasodilators. The other was the proliferation of myofibroblasts in the intima and lumen of pulmonary arteries, a disorder of growth unlikely to be influenced by this type of therapy. In previous ultrastructural studies we have shown that the source of these cells of muscular pedigree is muscle cells from the inner half of the media which migrate into the intima through gaps in the inner elastic lamina. In the present study we found a similar proliferation of myofibroblasts in the intima, not only of pulmonary arteries, but also of pulmonary veins, in plexogenic pulmonary arteriopathy. Arterial thrombi found were considered to be a complication rather than a cause of plexogenic pulmonary arteriopathy. Siderophages, cholesterol granulomas and focal fibrosis in the lung were considered to be a consequence of intrapulmonary haemorrhage early in the course of the disease. It is concluded that, while plexogenic pulmonary arteriopathy has an important vasoconstrictive element, it is also based on a disorder of growth of cells of muscular pedigree. This view has clear implications for the therapy of primary plexogenic pulmonary arteriopathy.     

Immunohistochemical study of endothelin-1 and matrix metalloproteinases in plexogenic pulmonary arteriopathy

The matrix metalloproteinases (MMPs) and endothelin-1, a potent vasoconstrictor and mitogen for smooth muscle cells, have been shown to be involved in the pathogenesis of various vascular disorders. However, the expression of endothelin-1 and the activation of MMPs have not been fully evaluated in plexogenic pulmonary arteriopathy (PPA). Immunohistochemical and confocal microscopic studies were conducted to evaluate the reactivity of lung tissue from six patients with pulmonary hypertension for alpha-smooth muscle actin (alpha-SMA), desmin, vimentin, factor VIII, endothelin-1, various types of MMPs (MMP-1, MMP-2, MMP-3, MMP-7 and MMP-9), membrane type-MMPs (MT-MMPs), tissue inhibitors of MMPs (TIMPs), and type IV collagen. Four major arterial morphological abnormalities were recognized in PPA: muscularization of pulmonary arterioles, onion-skin lesions, cellular and mature plexiform lesions, and atheromas in elastic pulmonary arteries. Reactivity for MMP-2 and MT-1-MMP was found in endothelial cells and, to a lesser extent, in myofibroblasts proliferating in various lesions of PPA. Increased expression of endothelin-1 was observed in the latter cells and in endothelial cells. Some myofibroblasts were positive for MMP-3 and MMP-7 in the vascular lesions except for mature plexiform lesions. MMP-1, MMP-9 and TIMP-2 tended to be positive only in the atheromatous lesions. Staining for type IV collagen showed focal thinning and discontinuities of the endothelial basement membrane in plexiform lesions. This study demonstrates colocalization of MMP-2 with MT-1-MMP and increased expression of endothelin-1 in various arterial lesions of PPA. These changes may play important roles in the remodeling of arterial structures, particularly of basement membranes, in this disorder.     

Grading of pulmonary vascular lesions-a reappraisal

Grading of pulmonary vascular alterations, introduced by Heath & Edwards (1958), has been widely used for assessment of the severity of hypertensive pulmonary vascular disease. Two factors call for a reappraisal of the grading principle: an increasing awareness of the complexity of the vascular lesions and an increasing use of lung biopsies for the pre-operative evaluation of the operability of an underlying cardiac defect. We suggest that the grading system, as well as the previously proposed variations of it, no longer fulfil the requirements of unambiguous assessment of the severity of vascular disease. The degree and extent of the various lesions, the different types of intimal fibrosis, and the eventual decrease in number and size of vessels should all be assessed, not only for arteries but also for other vessels. Careful consideration and weighing of all these features are necessary in order to form an opinion on diagnosis and prognosis. This cannot be achieved by using a single grade.     

The ultrastructure of the various forms of pulmonary arterial intimal fibrosis

Summary Intimal fibrosis of muscular pulmonary arteries may present in various forms and in varying degrees of severity according to the underlying condition. In patients with pulmonary hypertension, the type of intimal fibrosis is often significant with regard to prognosis and reversibility. For these reasons we have studied the ultrastructure of the thickened intimal layer in aged individuals, where intimal fibrosis occurs as a normal age change, and in patients with pulmonary hypertension associated with fibrosis of the lungs, mitral stenosis, chronic pulmonary thromboembolism and plexogenic pulmonary arteriopathy (either primary or secondary to congenital cardiac defects). In all these forms of intimal fibrosis, the cellular component of the subendothelial intimal layer was apparently almost exclusively the smooth muscle cell.These cells usually had a haphazard arrangement. In primary and secondary plexogenic pulmonary arteriopathy, however, there was a more regular circumferential arrangement. The ultrastructural evidence suggested that the intimal cells were derived from medial smooth muscle cells.     

Onset and evolution of pulmonary vascular disease in young children: abnormal postnatal remodelling studied in lung biopsies.

Pulmonary arterial structure was examined in lung biopsies from 26 children with severe pulmonary hypertensive congenital heart disease, aged 2 months-18 years, in whom the mean pulmonary arterial pressure was 55 (range 35-105) mmHg, using light, transmission, and scanning electron microscopy. Qualitative and quantitative techniques were applied and findings compared with those in age-matched controls. At 2 months, the smooth muscle cells showed hyperplasia, hypertrophy (mean cell diameter increased, P less than 0.001), and accelerated differentiation. In all pulmonary hypertensive cases aged less than 6 months, the contractile myofilament concentration was similar to the normal concentration at 6 months. Medial connective tissue was excessive for age. Smooth muscle cells within the intima (intimal proliferation) were first seen at 7 months, lying beneath a new internal elastic lamina. They showed a reduction in myofilament concentration in the more fibrotic lesions. In all cases, endothelial cells were abnormally thick (P less than 0.001) and elongated. Cytoskeletal remodelling was indicated by an increase in micro- and intermediate filament volume density (P less than 0.05 for both). The severity of endothelial damage was related to vessel size and position in the arterial pathway. These findings indicate that pulmonary vascular disease begins at or soon after birth with abnormal pulmonary vascular remodelling which leads to obliterative pulmonary vascular disease.     

Computerized morphometry of the pulmonary vasculature over a range of intravascular pressures

Recent availability of computerized image analysis has fostered hope that barium injection and landmarking of pulmonary arteries would be unnecessary for morphometric assessment when using this technique. We reasoned that if barium injection altered morphometric variables, it would do so in a linear fashion correlating with incremental increases in injection pressure of the barium. The two goals of the present study were to determine whether barium injection into arteries affected morphometric measurements and to determine whether incremental increases in injection pressure correlated with alterations in morphometric measurements in a linear fashion. Computerized image analysis was used to measure the internal elastic lamina (IEL) and external elastic lamina (EEL). Medial area (MA), luminal area (LA), percentage of medial thickness, IEL√MA. and idealized LA were calculated. Barium injection did not alter morphometric variables in a linear fashion correlating with incremental increases in injection pressure of the barium except the percentage of arteries that filled with barium. Maximum recruitment for pre-acinar arteries occurred at 40 mmHg pressure and 60 mmHg distending pressure for intra-acinar arteries. Incremental increases in injection pressure did not affect IEL, EEL, or calculated morphometric variables. However, IEL, medial thickness, and MA were all smaller in injected vessels than in uninjected vessels. IEL√MA and the ratio of measured vs. idealized LA were both increased in injected lungs. We suspect that vascular injection selects for evaluation, a population of smaller, thin-walled vessels, which in the uninjected lungs are collapsed and hence excluded from analysis. Anat. Rec. 252:92–101, 1998. © 1998 Wiley-Liss, Inc.     

Cytoskeletal features of immature pulmonary vascular smooth muscle cells: the influence of pulmonary hypertension on normal development

Using an immunohistochemical technique, the development of the cytoskeletal proteins desmin, vimentin, and actin (using alpha isotype and non-isotype specific antibodies) was assessed using a semi-quantitative grading system in the pulmonary vascular smooth muscle of nine normal pigs and 19 normal humans at different ages, and in 13 children with pulmonary hypertensive congenital heart disease. In the normal of both species, immunostaining for vimentin decreased after birth and then increased gradually while immunostaining for desmin and alpha actin increased steadily with age. In pulmonary hypertension, immunostaining for alpha actin and vimentin showed an accelerated increase at between 2 and 8 months. Also, the media showed regional differences in immunostaining which preceded the development of intimal proliferation. The inner media showed less immunoreactivity for all cytoskeletal proteins studied than did the outer media. Within areas of intimal proliferation many cells were immunonegative. These results suggest that the cytoskeletal features of medial smooth muscle cells are remodelled in the normal infant; that this process is altered from at least 2 months in the pulmonary hypertensive infant; and that the smooth muscle cells immediately beneath the internal elastic lamina are remodelled before migrating to form intimal proliferation. Changes in cytoskeletal composition can be related to the previously described postnatal maturation of pulmonary vascular smooth muscle cells.     

Fatal pulmonary arterial occlusive vascular disease following chemotherapy in a 9-month-old infant

Fatal pulmonary hypertension developed in an infant during the 7-month period in which he received, via a central venous catheter, combination chemotherapy for stage IV neuroblastoma as well as intermittent parenteral feeding. In a lung biopsy and at autopsy, small pulmonary arteries showed diffuse medial hypertrophy and peripheral muscularization, very extensive concentric intimal fibrosis, and focal eccentric fibrosis evolving from organizing thrombi. Pulmonary veins were normal. Hypothetically, chemotherapeutic drug therapy (possibly potentiated either by the parenteral nutrition or simply by the vehicular fluids causing volume loading of the pulmonary circulation) could cause occlusive pulmonary arterial disease by several mechanisms, but the association has not been described previously, although use of such drugs has been reported with pulmonary veno-occlusive disease.     

Ca2+ and ion channels in hypoxia-mediated pulmonary hypertension

Alveolar hypoxia, a consequence of many lung diseases, can have adverse effects on the pulmonary vasculature. The changes that occur in the pulmonary circulation with exposure to chronic hypoxia include reductions in the diameter of the pulmonary arteries due to structural remodeling of the vasculature. Although the structural and functional changes that occur in the development of pulmonary hypertension have been well investigated, less is known about the cellular and molecular mechanisms of this process. This review will discuss the role of several potassium and calcium channels in hypoxic pulmonary vasoconstriction, both in elevating calcium influx into pulmonary artery smooth muscle cells (PASMCs). In addition to other signal transduction pathways, Ca²⁺ signaling in PASMCs plays an important role in the development and progression of pulmonary hypertension due to its central roles in vasoconstriction and vascular remodeling. This review will focus on the effect of chronic hypoxia on ion channels and the potential pathogenic role of Ca²⁺ signaling and regulation in the progression of pulmonary hypertension.     

Histopathology of pulmonary hypertensive diseases

The spectrum of histopathological lesions of pulmonary hypertensive vascular disease is extraordinarily varied. A number of distinct patterns can be recognized, and these correlate with aetiological factors and clinical data. Recent research has yielded important new insights on the pathogenesis of pulmonary hypertension at the molecular and cellular level, and various key mechanisms are emerging. These include induction and maintenance of vasoconstriction, endothelial activation and proliferation, and thrombosis. In the light of these developments, a re-evaluation of lesions at the histopathological level is receiving a new level of significance, as histological data complement those from research based on non-morphological techniques. We review the main histopathological features of hypertensive pulmonary vascular disease in this perspective.     

Paeoniflorin attenuates monocrotaline-induced pulmonary arterial hypertension in rats by suppressing TAK1-MAPK/NF-κB pathways

Pulmonary arterial hypertension (PAH) characterized by pulmonary vascular remodeling is a lethal disease. Paeoniflorin (PF) is a monoterpene glycoside with numerous beneficial functions, such as vasodilation, anti-inflammation and immunomodulation. This study aims to investigate the effects of PF on monocrotaline (MCT)-induced PAH rats. Our data showed that both prophylactic or therapeutic administration of PF alleviated MCT-induced increasing of right ventricular systolic pressure (RVSP), prevented right ventricle hypertrophy and pulmonary arterial remodeling, as well as inhibited inflammatory cell infiltration around pulmonary arteries. Meanwhile, PF blocked MCT-induced endothelial-mesenchymal transition (EndMT) as indicated by the restored expression of endothelial markers in lung. Moreover, PF inhibited MCT-induced down-regulation of bone morphogenetic protein receptor 2 (BMPR2) and suppressed MCT-induced phosphorylation of transforming growth factor-β (TGFβ) activated kinase 1 (TAK1) in vivo. In vitro studies indicated that PF prevented human pulmonary arterial smooth muscle cells (PASMCs) from platelet-derived growth factor-BB (PDGF-BB)-stimulated proliferation and migration. PF also partially reversed TGFβ1, interleukin-1β (IL-1β) and tumor necrosis factor (TNF-α) co-stimulated endothelial-to-mesenchymal transition (EndMT) in cultured human pulmonary artery endothelial cells (HPAECs). Signaling pathway analysis demonstrated that the underlying mechanism might be associated with the inhibition of TAK1-MAPK/NF-κB pathways. Taken together, our results suggested that PF could be a potential drug for the treatment of PAH.     

Remodelling of the pulmonary arteries during recovery from pulmonary hypertension induced by neonatal hypoxia

Little is understood of the mechanisms involved in reducing pulmonary arterial wall thickness on recovery from pulmonary hypertension and the present study sought to clarify the events that occur. Piglets were exposed to hypobaric hypoxia for 3 days, either from birth or from 3 days of age, and others were exposed for 11 days starting at 3 days. All recovered in room air for up to 6 days. Using light and electron microscopy, the pulmonary artery wall thickness, the relative contribution of smooth muscle and matrix, smooth muscle cell replication, and apoptosis were assessed after hypoxic exposure and during recovery from hypoxic exposure. In elastic arteries, after 6 days' recovery in room air, a reduction in wall thickness to normal was associated with a similar reduction in proportional area of smooth muscle cells and matrix (p < 0.05), increased apoptosis (p < 0.05), and an abnormally low replication rate (p < 0.05). In peripheral muscular arteries, an increase in external diameter, and wall thinning on recovery, was achieved by smooth muscle cell remodelling and a reduction in cell replication (p < 0.05). Apoptosis did not contribute. Thus, different mechanisms are involved in recovery from hypoxia-induced pulmonary hypertension in elastic and muscular pulmonary arteries. Recovery is slower in animals exposed from birth rather than from 3 days of age.     

Variable expression of tenascin‐C,osteopontin and fibronectin in inflammatory myofibroblastic tumour of the lung

Kaarteenaho R, Sormunen R, Pääkkö P. Variable expression of tenascin‐C, osteopontin and fibronectin in inflammatory myofibroblastic tumour of the lung. APMIS 2010; 118: 91–100. The aim of this study was to analyse the expression of tenascin‐C, osteopontin and fibronectin in inflammatory myofibroblastic tumour of the lung, which is a rare tumour of unknown aetiology. Nine patients with an inflammatory myofibroblastic tumour of lung were studied by immunohistochemistry for the presence of tenascin‐C, osteopontin, fibronectin and alpha‐smooth muscle actin, which is a common marker for myofibroblasts. The ultrastructure of myofibroblasts was confirmed by transmission electron microscopy. The expression of tenascin‐C, osteopontin, fibronectin and alpha‐smooth muscle actin was also studied by immunoelectron microscopy. All cases displayed all of the studied extracellular matrix proteins and also alpha‐smooth muscle actin‐positive spindle‐shaped fibroblastic cells that were undoubtedly myofibroblasts. The immunoelectron microscopic studies demonstrated labelling for alpha‐smooth muscle actin in intracellular filament bundles within myofibroblasts, for fibronectin in the extracellular filaments of the fibronexus and for tenascin‐C extracellularly often adjacent to myofibroblasts. Labels for osteopontin were observed within myofibroblasts and plasma cells. These results demonstrate that tenascin‐C, osteopontin and fibronectin were expressed in all three kinds of subtypes of inflammatory myofibroblastic tumours of the lung and further, variable amounts of myofibroblasts could be observed by light and transmission electron microscopy as well as by immunoelectron microscopic techniques.     

Pulmonary vascular disease in 57 necropsy cases of total anomalous pulmonary venous connection

In a semi-quantitative necropsy study, total anomalous pulmonary venous connection (TAPVC) was an isolated anomaly in 35 cases and was associated with asplenia and either pulmonary stenosis or pulmonary atresia in 22 cases. A comparison of the two groups showed pulmonary venous obstruction (26% vs. 4%), a small interatrial communication (51% vs. 4%), a patent ductus arteriosus or operative shunt (40% vs. 64%), medial hypertrophy of muscular pulmonary arteries (80 vs. 23%), muscularization of arterioles (80% vs. 23%), capillary engorgement (60% vs. 27%) alveolar wall thickening (29% vs. 0%), interlobular septal oedema (34% vs. 14%), dilated lymphatics (80% vs. 45%), arterialization of pulmonary veins (86% vs. 68%), medial hypertrophy of veins (26% vs. 0%), and venous dilatation (74% vs. 50%). Only one patient, a 5-year-old girl with isolated TAPVC, had severe plexogenic pulmonary arteriopathy. In the remainder, the pulmonary lesions were those generally associated with reversible pulmonary venous hypertension; they were most striking in patients with pulmonary venous obstruction, and were least prominent in patients with pulmonary stenosis or puimonary atresia.     

Distribution and Quantity of Contractile Tissue in Postnatal Development of Rat Alveolar Interstitium

Alpha–smooth muscle actin (α‐SMA) ‐expressing cells are important participants in lung remodeling, during both normal postnatal ontogeny and after injury. Developmental dysregulation of these contractile cells contributes to bronchopulmonary dysplasia in newborns, and aberrant recapitulation in adults of the normal ontogeny of these cells has been speculated to underlie disease and repair in mature lungs. The significance of airway smooth muscle has been widely investigated, but contractile elements within the pulmonary parenchyma, although also of structural and functional consequence in developing and mature lungs, are relatively unstudied and little quantitative information exists. Here, we quantify the areal density of α‐SMA expression in lung parenchyma and assess changes in its spatiotemporal distribution through postnatal ontogeny. Using an antibody against α‐SMA, we immunofluorescently labeled contractile elements in lung sections from a postnatal growth series of rats. Images were segmented using thresholded pixel intensity. Alpha‐SMA areal density in the alveolar interstitium was calculated by dividing the area of α‐SMA–positive staining by the tissue area. The areal density of α‐SMA in 2‐day neonates was 3.7%, almost doubled, to 7.2% by 21 days, and decreased to 3% in adults. Neonates had large, elongate concentrations of α‐SMA, and α‐SMA localized both at septal tips and within the interstitium. In adults, individual areas of α‐SMA expression were smaller and more round, and located predominately in alveolar ducts, at alveolar ends and bends. The results are consistent with increasing α‐SMA expression during the period of peak myofibroblast activity, corresponding to the phase of rapid alveolarization in the developing lung. Anat Rec, 291:83–93, 2007. © 2007 Wiley‐Liss, Inc.