Nitric oxide synthase in critically ischaemic muscle and alterations in isoform expression during revascularization surgery

BACKGROUND

Dysfunction of the nitric oxide pathway is implicated in peripheral arterial disease. Nitric oxide synthase (NOS) isoforms and NOS activity were studied in muscle from patients with critical leg ischaemia (CLI). Alterations in NOS during revascularization surgery were also assessed.

METHODS

Muscle biopsies were taken from patients with CLI undergoing amputation and also from patients undergoing femorodistal bypass at the start of surgery, after arterial clamping and following reperfusion. The presence of NOS within muscle sections was confirmed using reduced nicotinamide adenine dinucleotide phosphate diaphorase histochemistry. NOS isoform distribution was studied by immunohistochemistry. NOS mRNA and protein levels were measured using real-time reverse transcriptase-polymerase chain reaction and western blotting. NOS activity was assessed with the citrulline assay.

RESULTS

All three NOS isoforms were found in muscle, associated with muscle fibres and microvessels. NOS I and III protein expression was increased in CLI (P = 0.041). During revascularization, further ischaemia and reperfusion led to a rise in NOS III protein levels (P = 0.008). NOS activity was unchanged.

CONCLUSION

Alterations in NOS I and III occurred in muscle from patients with CLI and further changes occurred during bypass surgery.

Dysregulation of transforming growth factor beta signaling in scleroderma: overexpression of endoglin in cutaneous scleroderma fibroblasts

OBJECTIVE

As an initial approach to understanding the basis of the systemic sclerosis (SSc; scleroderma) phenotype, we sought to identify genes in the transforming growth factor beta (TGF beta) signaling pathway that are up-regulated in lesional SSc fibroblasts relative to their normal counterparts.

METHODS

We used gene chip, differential display, fluorescence-activated cell sorter, and overexpression analyses to assess the potential role of TGF beta signaling components in fibrosis. Fibroblasts were obtained by punch biopsy from patients with diffuse cutaneous SSc of 2-14 months' duration (mean 8 months) and from age- and sex-matched healthy control subjects.

RESULTS

Unexpectedly, we found that fibroblasts from SSc patients showed elevated expression of the endothelial cell-enriched TGF beta receptor endoglin. Endoglin is a member of the nonsignaling high-affinity TGF beta receptor type III family. The expression of endoglin increased with progression of disease. Transfection of endoglin in fibroblasts suppressed the TGF beta-mediated induction of connective tissue growth factor promoter activity.

CONCLUSION

SSc is characterized by overproduction of matrix; that is, genes that are targets of TGF beta signaling in normal fibroblasts. Our findings suggest that lesional SSc fibroblasts may overexpress endoglin as a negative feedback mechanism in an attempt to block further induction of profibrotic genes by TGF beta.

Fibroblast matrix gene expression and connective tissue remodeling: role of endothelin-1

This study examines endothelin-induced modulation of extracellular matrix synthesis and remodeling by fibroblasts, and its potential role in the pathogenesis of systemic sclerosis (scleroderma). Endothelin-1 promoted fibroblast synthesis of collagen types I and III, but not fibronectin, by a mechanism dependent upon both ETA and ETB receptors. Conversely, endothelin-1 inhibited both protein expression of matrix metalloproteinase 1 and zymographic activity exclusively via ETA receptors. A dual regulatory role for endothelin-1 in transcriptional regulation was suggested by the ability of endothelin-1 to enhance steady-state levels of collagen mRNA and activate the proalpha2(I) collagen (Col1a2) promoter, but in contrast to reduce matrix metalloproteinase 1 transcript expression and suppress transcription of a human matrix metalloproteinase 1 promoter reporter construct in transient transfection assays. Although endothelin-1 significantly enhanced remodeling of three-dimensional collagen lattices populated by normal fibroblasts, this was not observed for lattices populated by systemic sclerosis fibroblasts. Promotion of matrix remodeling was dependent upon ETA receptor expression and was blocked by specific inhibitors of tyrosine kinases or protein kinase C. Reverse transcriptase polymerase chain reaction, S1 nuclease, and functional cell surface binding studies showed that normal and systemic sclerosis fibroblasts express both ETA and ETB receptors (predominantly ETA), but that ETA receptor mRNA levels and ETA binding sites on fibroblasts cultured from systemic sclerosis skin biopsies are reduced by almost 50%. Endothelin-1 is thus able to induce a fibrogenic phenotype in normal fibroblasts that is similar to that of lesional systemic sclerosis fibroblasts. Moreover, reduced responsiveness to exogenous endothelin-1 in systemic sclerosis suggests that downstream pathways may have already been activated in vivo. These data further implicate dysregulated endothelin-receptor pathways in fibroblasts in the pathogenesis of connective tissue fibrosis.

Interferon-alpha does not improve outcome at one year in patients with diffuse cutaneous scleroderma: results of a randomized, double-blind, placebo-controlled trial

OBJECTIVE

To determine whether interferon-alpha (IFNalpha) reduces the severity of skin involvement in early (<3 years) diffuse scleroderma.

METHODS

In a randomized, placebo-controlled, double-blind trial, 35 patients with early scleroderma received subcutaneous injections of either IFNalpha (13.5 x 10(6) units per week in divided doses) or indistinguishable placebo. Outcomes assessed were the modified Rodnan skin score, as determined by a single observer at baseline, 6 months, and 12 months, as well as data on renal, cardiac, and lung function. Pre- and posttreatment skin biopsy samples were analyzed and blood was obtained for assessment of procollagen peptide levels.

RESULTS

There were 11 withdrawals from the IFNalpha group and 3 from the placebo group due to either toxicity, lack of efficacy, or death. In the intent-to-treat analysis, there was a greater improvement in the skin score in the placebo group between 0 and 12 months (mean change IFNalpha -4.7 versus placebo -7.5; P = 0.36). There was also a greater deterioration in lung function in patients receiving active therapy, as assessed by either the forced vital capacity (mean change IFNalpha -8.2 versus placebo +1.3; P = 0.01) or the diffusing capacity for carbon monoxide (mean change IFNalpha -9.3 versus placebo +4.7; P = 0.002). Skin biopsy showed no significant decrease in collagen synthesis in the IFNalpha group, and no significant differences in the levels of procollagen peptides were seen between the 2 groups.

CONCLUSION

This study suggests that IFNalpha is of no value in the treatment of scleroderma, and that it may in fact be deleterious.

Scleroderma fibroblasts promote migration of mononuclear leucocytes across endothelial cell monolayers

Perivascular infiltrates of inflammatory cells are a hallmark of lesional skin in scleroderma. We have explored the potential for scleroderma fibroblasts to modulate mononuclear leucocyte migration across endothelial cell monolayers in tissue culture, and to regulate expression of endothelial cell adhesion molecules. Fibroblasts were grown from skin biopsies of eight patients with active diffuse cutaneous scleroderma and from four healthy controls. Co-culture and conditioned medium transfer experiments examined the effect of soluble fibroblast products on mononuclear leucocyte (U937) cell migration across endothelial cell (1E-7) monolayers grown on tissue culture inserts. Co-culture of scleroderma, but not control fibroblasts, promoted transendothelial migration of U937 cells. Scleroderma fibroblast-conditioned medium had qualitatively similar effects and equivalent results were obtained using Jurkat-6 (T lymphocyte) cells, and with peripheral blood mononuclear cells from a patient with diffuse cutaneous scleroderma. Promotion of leucocyte migration does not appear to result from increased endothelial adhesion molecule expression, since fibroblast-conditioned medium did not up-regulate endothelial cell expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) or E-selectin. Moreover, leucocyte migration across cytokine-activated endothelial cell layers in co-culture with fibroblasts was less than across resting cells, although the selective effect of scleroderma fibroblast co-culture persisted. Recombinant monocyte chemoattractant protein-1 (MCP-1) or IL-8 increased passage of mononuclear leucocytes across endothelial cell monolayers, whilst anti-MCP-1, but not anti-IL-8 antibodies, significantly reduced the effect of fibroblast conditioned medium. These data suggest that systemic sclerosis (SSc) fibroblasts promote leucocyte migration across endothelial cell monolayers in tissue culture via an MCP-1-dependent mechanism. These findings may be relevant to the perivascular mononuclear leucocyte infiltrates characteristic of early SSc lesions.

Anti-RNA polymerases and other autoantibody specificities in systemic sclerosis

Sera from 735 patients with systemic sclerosis were classified according to antinuclear antibody (ANA) pattern as follows: centromere (25%), homogeneous (26%), fine speckled (21%), fine speckled with nucleolar (14%), coarse speckled (7%), nucleolar only (3%) and cytoplasmic only (3%). Immunoprecipitations using 35S-labelled HeLa cell antigen extract were performed using sera from 374 of these patients to detect the systemic sclerosis-specific antibodies to RNA polymerases I and III. The sera were selected to represent each ANA group, but focused on those giving fine speckled nucleoplasmic staining (with or without nucleolar staining) where all 86 sera positive for these antibodies were concentrated. Immunoprecipitates from a further 93 sera from patients with ANA-positive autoimmune diseases other than systemic sclerosis did not precipitate RNA polymerases. In addition, all sera were tested for antibodies to the extractable nuclear antigens topoisomerase I, nRNP, Ro, La and PM-Scl. Sera positive for antibodies to these antigens gave clear correlations with ANA patterns but, of the examples tested, none contained antibodies precipitating RNA polymerase I or III. Thus, sera containing antibodies to RNA polymerases I and III were exclusive of both anticentromere and anti-topoisomerase I, and formed a major serological subgroup (11.7%). Clinically, 77% were patients with diffuse cutaneous disease reflected by higher skin scores and a significantly higher incidence of renal involvement (33%) than patients with antibodies to topoisomerase I (3%).

Scleroderma lung fibroblasts exhibit elevated and dysregulated type I collagen biosynthesis

OBJECTIVE

To examine whether scleroderma lung fibroblasts show a pattern of aberrant type I collagen (CI) biosynthesis similar to that observed previously in studies of dermal fibroblasts in this disease.

METHODS

CI secretion and steady-state pro alpha1(I) collagen messenger RNA (mRNA) levels and COL1A2 gene activation were examined in fibroblasts grown from lung biopsy specimens obtained from 16 scleroderma patients with lung fibrosis and from 10 histologically normal lung specimens (controls). The effect of culture in a 3-dimensional (3-D) CI gel matrix culture on CI mRNA levels was also examined.

RESULTS

The mean (+/- SEM) collagen secretion in monolayer culture for scleroderma lung fibroblasts was 90.9 +/- 56 ng/ml/10(6) cells, significantly greater (P < 0.05) than controls (40.2 +/- 17.5). Pro alpha1(I) collagen mRNA levels in monolayer cultures were higher in scleroderma (mean +/- SEM collagen:GAPDH ratio 3.7 +/- 0.9) compared with control (1.9 +/- 0.8) lung fibroblasts. Transient expression assays confirmed that genes coding for CI are transcriptionally activated in scleroderma lung fibroblasts compared with control strains. Although all lung fibroblasts induced equivalent contraction of 3-D CI gel matrices, scleroderma strains failed to show a reduction in steady-state pro alpha1(I) collagen mRNA levels in gel culture.

CONCLUSION

We have demonstrated elevated CI biosynthesis and impaired mRNA down-regulation for CI by scleroderma lung fibroblasts. These properties are likely to be highly relevant to the pathogenesis of scleroderma-associated lung fibrosis.

Expression and shedding of intercellular adhesion molecule 1 and lymphocyte function-associated antigen 3 by normal and scleroderma fibroblasts. Effects of interferon-gamma, tumor necrosis factor alpha, and estrogen

OBJECTIVE

To examine intercellular adhesion molecule 1 (ICAM-1) and lymphocyte function-associated antigen 3 (LFA-3) in cultures of normal and systemic sclerosis (SSc) dermal fibroblasts.

METHODS

The surface and soluble forms of ICAM-1 and LFA-3 were measured by flow cytometry and capture enzyme-linked immunosorbent assay, respectively.

RESULTS

Surface ICAM-1 was significantly higher on SSc fibroblasts compared with normal controls. Beta-estradiol did not directly enhance ICAM-1 or LFA-3 expression in either normal or SSc cells, but significantly augmented the cytokine-induced increase in ICAM-1. Soluble ICAM-1 (sICAM-1) and sLFA-3 were detected in fibroblast cultures. While no difference was found in the level of sLFA-3, the shedding of sICAM-1 was significantly increased (P < 0.001) in cells from SSc patients.

CONCLUSION

SSc fibroblasts express intrinsically elevated levels of surface ICAM-1 and release higher levels of sICAM-1 in vitro. Increased expression of ICAM-1 by interferon-gamma and tumor necrosis factor alpha alone, and the further induction in combination with beta-estradiol may underlie an aspect of fibroblast dysfunction in SSc and the female predisposition to the disease.