Characteristics of joint involvement and relationships with systemic inflammation in systemic sclerosis: results from the EULAR Scleroderma Trial and Research Group (EUSTAR) database

OBJECTIVE

To determine the prevalence of and independent factors associated with joint involvement in a large population of patients with systemic sclerosis (SSc).

METHODS

This study was cross-sectional, based on data collected on patients included in the European League Against Rheumatism (EULAR) Scleroderma Trials and Research (EUSTAR) registry. We queried this database to extract data regarding global evaluation of patients with SSc and the presence of any clinical articular involvement: synovitis (tender and swollen joints), tendon friction rubs (rubbing sensation detected as the tendon was moved), and joint contracture (stiffness of the joints that decreased their range of motion). Overall joint involvement was defined by the occurrence of synovitis and/or joint contracture and/or tendon friction rubs.

RESULTS

We recruited 7286 patients with SSc; their mean age was 56 +/- 14 years, disease duration 10 +/- 9 years, and 4210 (58%) had a limited cutaneous disease subset. Frequencies of synovitis, tendon friction rubs, and joint contractures were 16%, 11%, and 31%, respectively. Synovitis, tendon friction rubs, and joint contracture were more prevalent in patients with the diffuse cutaneous subset and were associated together and with severe vascular, muscular, renal, and interstitial lung involvement. Moreover, synovitis had the highest strength of association with elevated acute-phase reactants taken as the dependent variable.

CONCLUSION

Our results highlight the striking level of articular involvement in SSc, as evaluated by systematic examination in a large cohort of patients with SSc. Our data also show that synovitis, joint contracture, and tendon friction rubs are associated with a more severe disease and with systemic inflammation.

Multistate equilibrium unfolding of Escherichia coli dihydrofolate reductase: thermodynamic and spectroscopic description of the native, intermediate, and unfolded ensembles

The thermodynamic and spectroscopic properties of a cysteine-free variant of Escherichia coli dihydrofolate reductase (AS-DHFR) were investigated using the combined effects of urea and temperature as denaturing agents. Circular dichroism (CD), absorption, and fluorescence spectra were recorded during temperature-induced unfolding at different urea concentrations and during urea-induced unfolding at different temperatures. The first three vectors obtained by singular-value decomposition of each set of unfolding spectra were incorporated into a global analysis of a unique thermodynamic model. Although individual unfolding profiles can be described as a two-state process, a simultaneous fit of 99 vectors requires a three-state model as the minimal scheme to describe the unfolding reaction along both perturbation axes. The model, which involves native (N), intermediate (I), and unfolded (U) states, predicts a maximum apparent stability, DeltaG degrees (NU), of 6 kcal mol(-)(1) at 15 degrees C, an apparent m(NU) value of 2 kcal mol(-)(1) M(-)(1), and an apparent heat capacity change, DeltaC(p)()(-NU), of 2.5 kcal mol(-)(1) K(-)(1). The intermediate species has a maximum stability of approximately 2 kcal mol(-)(1) and a compactness closer to that of the native than to that of the unfolded state. The population of the intermediate is maximal ( approximately 70%) around 50 degrees C and falls below the limits of detection of > or =2 M urea or at temperatures of <35 or >65 degrees C. The fluorescence properties of the equilibrium intermediate resemble those of a transient intermediate detected during refolding from the urea-denatured state, suggesting that a tryptophan-containing hydrophobic cluster in the adenosine-binding domain plays a key role in both the equilibrium and kinetic reactions. The CD spectroscopic properties of the native state reveal the presence of two principal isoforms that differ in ligand binding affinities and in the packing of the adenosine-binding domain. The relative populations of these species change slightly with temperature and do not depend on the urea concentration, implying that the two native isoforms are well-structured and compact. Global analysis of data from multiple spectroscopic probes and several methods of unfolding is a powerful tool for revealing structural and thermodynamic properties of partially and fully folded forms of DHFR.

Global analysis of the acid-induced and urea-induced unfolding of staphylococcal nuclease and two of its variants

We have studied the equilibrium unfolding staphylococcal nuclease and two of its variants, V66W and V66W', over two perturbation axes (acid-induced unfolding as a function of urea concentration and urea-induced unfolding as a function of pH). The transitions were monitored by simultaneous measurements of circular dichroism and fluorescence. With this multidimensional array of data (2 perturbation axes and 2 signals), we present a strategy of performing a global analysis, over as many as 12 individual data sets, to test various models for the unfolding process, to determine with greater confidence the pertinent thermodynamic parameters, and to characterize unfolding intermediates. For example, wildtype nuclease shows a cooperative two-state transition with either urea or pH as denaturant, but the global fits are improved when the model is expanded to include a pH dependence of the urea m value or when two distinct classes of protonic groups are considered. The best fit for wild-type nuclease is with delta G degree 0,UN = 6.4 kcal/mol at pH 7, with the acid-induced unfolding being triggered by protonation of three to five carboxylate groups (with possible contribution from His121), and with the urea m = 2.5 kcal mol-1 M-1. V66W' lacks the last 13 amino acids on the C-terminus, has a tryptophan at position 66, has a predominantly beta-sheet structure, and is less stable than the wild type. For V66W', delta G degree 0,UN = 1.6 kcal/mol, m = 1.2 kcal mol-1 M-1, and there are two or three groups responsible for acid unfolding. V66W, a full-length mutant with two tryptophan residues, unfolds via a three-state mechanism: native reversible intermediate reversible unfolded. It appears that its beta-barrel subdomain retains structure in the intermediate state. Assuming that the unfolding of V66W' and the beta-barrel subdomain of V66W can be described by the same thermodynamic parameters, a global analysis enabled a description of the alpha subdomain of V66W with delta G degree 0,IN = 2.7 kcal/mol, mIN = 1.1 kcal mol-1 M-1, and with the acid unfolding being triggered by protonation of a single group. This group has a pKa around 6 in the unfolded state, suggesting that the state of protonation of a histidine residue may contribute significantly to the stability of V66W.