Monomeric structure of the cardioprotective chemokine SDF‐1/CXCL12

Abstract

The chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) directs leukocyte migration, stem cell homing, and cancer metastasis through activation of CXCR4, which is also a coreceptor for T-tropic HIV-1. Recently, SDF-1 was shown to play a protective role after myocardial infarction, and the protein is a candidate for development of new anti-ischemic compounds. SDF-1 is monomeric at nanomolar concentrations but binding partners promote self-association at higher concentrations to form a typical CXC chemokine homodimer. Two NMR structures have been reported for the SDF-1 monomer, but only one matches the conformation observed in a series of dimeric crystal structures. In the other model, the C-terminal helix is tilted at an angle incompatible with SDF-1 dimerization. Using a rat heart explant model for ischemia/ reperfusion injury, we found that dimeric SDF-1 exerts no cardioprotective effect, suggesting that the active species is monomeric. To resolve the discrepancy between existing models, we solved the NMR structure of the SDF-1 monomer in different solution conditions. Irrespective of pH and buffer composition, the C-terminal helix remains tilted at an angle with no evidence for the perpendicular arrangement. Furthermore, we find that phospholipid bicelles promote dimerization that necessarily shifts the helix to the perpendicular orientation, yielding dipolar couplings that are incompatible with the NOE distance constraints. We conclude that interactions with the alignment medium biased the previous structure, masking flexibility in the helix position that may be essential for the distinct functional properties of the SDF-1 monomer.

Cardiac myocyte-specific overexpression of human GTP cyclohydrolase I protects against acute cardiac allograft rejection

“…This recruitment may serve as an adaptive response to repair damaged myocardium. Indeed, treatment with mesenchymal stromal cells improves cardiac function and decreases infarct size following myocardial ischemia (10,27). Likewise under certain conditions, hematopoietic stem cells prolong cardiac allograft survival (32).…”

Heparin Oligosaccharides Inhibit Chemokine (CXC Motif) Ligand 12 (CXCL12) Cardioprotection by Binding Orthogonal to the Dimerization Interface, Promoting Oligomerization, and Competing with the Chemokine (CXC Motif) Receptor 4 (CXCR4) N Terminus

“…Hearts perfused continuously for 245 min served as nonischemic controls. Administration of the perfusion sequence, monitoring of cardiac function, and analysis of infarcted tissue was performed as previously described (19,33,34). Each dosage group consisted of four replicates.…”

“…CXCL12 possesses cardioprotective properties when administered either pre-or post-ischemia including reduced infarct zone, decreased scar tissue, increased angiogenesis, resistance to hypoxia/reoxygenation damage, and improved cardiac function (12)(13)(14)(15)(16)(17)(18)(19). Despite functional analyses in vitro and in vivo, the mechanism of CXCL12-induced cardioprotection is disputed: CXCL12 may act through direct activation of growth and survival signaling pathways in cardiomyocytes (12,13) and/or enhance cardiac regeneration by recruiting hematopoietic stem and endothelial progenitor cells into the heart (18, 20 -24).…”

“…In each case, CXCL12 treatment is effective, but variations in protection may be related to stability, dosage, or drug interactions. We recently demonstrated that CXCL12 is cardioprotective over a narrow concentration range, whereas a constitutively dimeric form of the chemokine exerts little to no effect (19). Because heparin is commonly administered in response to myocardial infarctions (2) and induces CXCL12 dimerization (25,26), we hypothesized that the protective properties of CXCL12 may be attenuated by interactions with soluble heparin in a modern clinical setting.…”

Chemokine (C-X-C Motif) Receptor 4 and Atypical Chemokine Receptor 3 Regulate Vascular α1-Adrenergic Receptor Function

“…Human CXCL11 was cloned into previously described pQE30 vectors that incorporate an N-terminal His6 and Saccharomyces cervisiae small ubiquitin-related modifier (SUMO) protein (Smt3) fusion tag (28)(29)(30) to be used for purification. The final, purified CXCL11 construct has a native N-terminal sequence vital for proper function.…”