Impact of aging on inflammatory and immune responses during elastin peptide-induced murine emphysema.

Deterioration of lung functions and degradation of elastin fibers with age are accelerated during chronic obstructive pulmonary disease (COPD). Excessive genesis of soluble elastin peptides (EP) is a key factor in the pathophysiology of COPD. We have previously demonstrated that 6-wk-old mice exhibited emphysematous structural changes associated with proinflammatory immune response after EP instillation. In this study, we investigated the consequences of aging on inflammatory, immune, and histological criteria associated with murine emphysema progression after EP exposure. Young (6 wk old) and elderly (15 mo old) C57BL/6J mice were endotracheally instilled with EP, and, at various time points after treatment, the inflammatory cell profiles from bronchoalveolar lavage fluids (BALF) and the T-lymphocyte phenotypes, at local and systemic levels, were analyzed by flow cytometry. Lungs were also prepared to allow morphological and histological analysis by confocal microscopy. Elderly mice exhibited an earlier development of pulmonary emphysema, characterized by an increase of the inflammatory and lymphocytic infiltrates, extracellular matrix breakdown, and airspace enlargement compared with young mice. This age-dependent parenchymal tissue remodeling was associated with an increase of the matrix metalloproteinase expressions and desmosine levels in BALF and/or sera of EP-treated mice. In addition, both the proportion of CD4+CD28- and CD8+CD28- T cells in the tissues of EP-treated mice and the interferon-γ levels in the EP-specific memory T-cell clones were significantly higher in elderly versus younger mice. This study demonstrates that aging accelerates emphysema development and that this effect is linked to increased EP production and their effects on inflammatory and immune response.

Induction and regulation of murine emphysema by elastin peptides.

Emphysema is the major component of chronic obstructive pulmonary disease (COPD). During emphysema, elastin breakdown in the lung tissue originates from the release of large amounts of elastase by inflammatory cells. Elevated levels of elastin-derived peptides (EP) reflect massive pulmonary elastin breakdown in COPD patients. Only the EP containing the GXXPG conformational motif with a type VIII ß-turn are elastin receptor ligands inducing biological activities. In addition, the COOH-terminal glycine residue of the GXXPG motif seems a prerequisite to the biological activity. In this study, we endotracheally instilled C57BL/6J mice with GXXPG EP and/or COOH-terminal glycine deleted-EP whose sequences were designed by molecular dynamics and docking simulations. We investigated their effect on all criteria associated with the progression of murine emphysema. Bronchoalveolar lavages were recovered to analyze cell profiles by flow cytometry and lungs were prepared to allow morphological and histological analysis by immunostaining and confocal microscopy. We observed that exposure of mice to EP elicited hallmark features of emphysema with inflammatory cell accumulation associated with increased matrix metalloproteinases and desmosine expression and of remodeling of parenchymal tissue. We also identified an inactive COOH-terminal glycine deleted-EP that retains its binding-activity to EBP and that is able to inhibit the in vitro and in vivo activities of emphysema-inducing EP. This study demonstrates that EP are key actors in the development of emphysema and that they represent pharmacological targets for an alternative treatment of emphysema based on the identification of EP analogous antagonists by molecular modeling studies.

Role of the amino acid sequence in domain swapping of the B1 domain of protein G.

Substitution of four amino acid residues (L5V,F30V, Y33F,A34F) in the B1 domain of the immunoglobulin G binding protein (GB1) leads to the formation of a swapped dimer, shown to be in equilibrium with a native-like monomeric state of the protein (Byeon et al., J Mol Biol 2003;333:141-152). In this study, we employ protein design calculations and molecular dynamics simulations to investigate the role of these substitutions in fostering the swapping reaction. DESIGNER, a fully automatic procedure for computing the amino acid sequences likely to stabilize a given backbone structure is used to investigate the effect of the four substitutions on the stability of the wild type native monomeric conformation. Results indicate that at least three of these substitutions (L5V,F30V, A34F) have a destabilizing effect. The L5V forms destabilizing interactions with surrounding residues, whereas F30V causes local strain due to unfavorable interactions with its own backbone. A dual role in the swapping reaction is played by A34F. It destabilizes the monomer conformation while stabilizing the swapped dimer. Our calculations find an energetically favorable conformation for the 34F side chain in the core of the monomer, but only at the expense of forcing the wild type W43 side chain into a highly strained rotamer, and forming unfavorable interactions with both W43 and V54. Although detailed calculations could not be performed on the swapped dimer, due to the lower accuracy of the model, analysis revealed that the 34F side chain from both subunits are tightly packed against each other in the dimer core, suggesting that their replacement by the smaller Ala, as in the wild type, would be highly destabilizing through the creation of a large internal cavity possibly accompanied by a substantial conformational change. Analysis of room temperature molecular dynamics (MD) simulations of the wild type and the modeled quadruple mutant structures reveals that the latter structure fluctuates more than its wild type counterpart. In addition, its C-terminal beta-hairpin, which is exchanged in the swapping reaction, undergoes a conformation change, which pushes it further away from the remainder of the protein. Simulations at higher temperature (450 K) show that the quadruple mutant unfolds earlier and more completely than the wild type following a sequence of events that is compatible with the description of the highly fluctuating monomeric state of this mutant observed by NMR. Our findings thus support the notion that domain swapping in GB1 is fostered by three main factors: a decrease in stability and increased flexibility of the monomer conformation, concomitant with stabilization of the swapped dimer conformation through new interactions that have no counterparts in the monomer.

Structural characterization of human elastin derived peptides containing the GXXP sequence.

The degradation of elastin, the insoluble biopolymer of tropoelastin, can lead to the production of small peptides. These elastin-derived peptides (EDPs) are playing a key role in cellular behavior within the extracellular matrix, showing a great variety of biological effects such as chemotaxis, stimulation of cell proliferation, ion flux modifications, vasorelaxation, and inflammatory enzymes secretion. It has also been demonstrated recently that EDPs containing the GXXPG motif could induce pro-MMP1 and pro-MMP3 upregulation. Elastolysis could then cause collagen degradation and play an important role in the aging process. Many experimental studies have been devoted to EDPs, but their structure/activity relationships are not well elucidated yet. However, the assumption that their active conformation is a type VIII beta-turn on GXXP was highly suggested on the basis of predictive statistical calculations. Investigation of the EDPs three-dimensional (3D) structure would provide useful information for drug-design strategies to propose specific inhibitors. The work presented here reports theoretical results obtained from molecular dynamics simulations performed over 128 human EDPs containing the GXXP motif. We show that all the peptides, for which the central residues are not glycines, adopt a canonical (or very close to) type VIII beta-turn structure on the GXXP sequence. Amino acids surrounding this motif are also important for the structural behavior. Any residue located before the GXXP motif (XGXXP) increases the beta-turn stabilization, whereas the residue located after GXXP (GXXPX) has no significant structural effect. Moreover, we show their biological activity can be correlated with their ability to exhibit a type VIII beta-turn conformation.

Structural characterization of VGVAPG, an elastin-derived peptide.

Elastic fibers are an important component of the extracellular matrix, providing elasticity and resilience to tissues that require the ability to deform repetitively and reversibly. Among the elastin-derived peptides, the Val-Gly-Val-Ala-Pro-Gly (VGVAPG) hexapeptide is known for its chemotactic activity and metalloproteinases upregulation properties. As other elastin-derived peptides, having homologous similar sequences, do not exhibit any biological activity, the following question arises: Does the peptide-receptor interaction need a specific active conformation? Previous experimental studies including NMR and CD spectroscopies did not clearly identify the conformations adopted by the VGVAPG peptide in solution. However, structural predictions made on VGVAPG and related XGXXPG peptides suggested a folded beta-turn conformation. So we undertook a theoretical and experimental study of the VGVAPG peptide. The work presented here, which gives an overall structural description of VGVAPG behavior in water, also provides an additional insight into its structure-activity relationship. Both theoretical and experimental results suggest the existence of an ensemble of rather extended and folded conformations in solution. All the folded structures obtained exhibit a type VIII beta-turn spanning the GVAP sequence. In the lack of any structural information concerning the elastin receptor, these results suggest that such a conformation could be relevant for the peptide-receptor interaction and thus for biological activity.