Date Published: April 5, 2017
Publisher: Public Library of Science
Author(s): Daniel I. Bromage, Stasa Taferner, Mahesh Pillai, Derek M. Yellon, Sean M. Davidson, Shree Ram Singh.
Stromal derived factor-1α (SDF-1α/CXCL12) is a chemokine that is up-regulated in diseases characterised by tissue hypoxia, including myocardial infarction, ischaemic cardiomyopathy and remote ischaemic conditioning (RIC), a technique of cyclical, non-injurious ischaemia applied remote from the heart that protects the heat from lethal ischaemia-reperfusion injury. Accordingly, there is considerable interest in SDF-1α as a potential biomarker of such conditions. However, SDF-1α is rapidly degraded and inactivated by dipeptidyl peptidase 4 and other peptidases, and the kinetics of intact SDF-1α remain unknown.
To facilitate investigation of full-length SDF-1α we established an ELISA using a novel recombinant human antibody we developed called HCI.SDF1. HCI.SDF1 is specific to the N-terminal sequence of all isoforms of SDF-1 and has a comparable KD to commercially available antibodies. Together with a detection antibody specific to the α-isoform, HCI.SDF1 was used to specifically quantify full-length SDF-1α in blood for the first time. Using RIC applied to the hind limb of Sprague-Dawley rats or the arms of healthy human volunteers, we demonstrate an increase in SDF-1α using a commercially available antibody, as previously reported, but an unexpected decrease in full-length SDF-1α after RIC in both species.
We report for the first time the development of a novel recombinant antibody specific to full-length SDF-1. Applied to RIC, we demonstrate a significant decrease in SDF-1α that is at odds with the literature and suggests a need to investigate the kinetics of full-length SDF-1α in conditions characterised by tissue hypoxia.
Stromal derived factor-1α (SDF-1α/CXCL12) is a CXC chemokine that is expressed in several tissues in response to hypoxia, via up-regulation of hypoxia inducible fator-1α (HIF-1α).[1–5] For example, SDF-1α is up-regulated in experimental and clinical studies of acute myocardial infarction (MI), wherein it is thought to mitigate adverse ventricular remodelling. Its mechanism of action is reportedly as a chemo-attractant for a variety of cell types expressing its cognate G protein-coupled receptor, CXCR4, including mesenchymal stem cells (MSCs), adipose-derived regenerative cells, c-kit+ endogenous cardiac stem cells and T lymphocytes,[6–9] which subsequently have beneficial paracrine effects. It has also been implicated in acute cardioprotection via its binding to myocardial CXCR4 and subsequent activation of the reperfusion injury salvage kinase pathway.[11, 12]
Several studies have associated increased SDF-1α with both increased risk of incident cardiovascular events and subsequent adverse outcome. For example, in Framingham Heart Study patients, circulating SDF-1α was significantly associated with both new-onset heart failure and all-cause mortality in a multi-variable regression model. SDF-1α was not associated with MI in this study, although genome-wide association studies (GWAS) have identified SDF-1α as a risk locus for both coronary artery disease and MI. Furthermore, in patients with chronic kidney disease, who are at high risk for cardiovascular events, SDF-1α was significantly associated with MI and all-cause mortality. Circulating SDF-1α has also been associated with worse left ventricular (LV) function in patients hospitalised with heart failure.
SDF-1α is ostensibly increased by RIC, a manoeuvre that has been associated with acute and chronic cardioprotection. However, by using an antibody specific to the intact, active form of SDF-1α we have shown that RIC reduces circulating SDF-1α, which we hypothesise is due to its cleavage, a finding we replicated in both rats and humans. This has implications for the increasing number of studies exploring the potential of SDF-1α as a biomarker in a range of cardiovascular contexts. Further studies are necessary to fully elucidate the value of HCI.SDF1 as a biomarker in relation to clinical phenotypes.