Abstract 225: SDF1α Preconditions the Heart: Role for a Functional Cardiac SDF1α-CXCR4 Axis
The chemokine, stromal cell derived factor-1α (SDF), and its receptor CXCR4 are well known for their role in stem cell biology; however, nothing is known regarding their role in the heart. We performed expression profiling studies to define novel genes involved in pharmacologic preconditioning (PC) in mice. SDF was found to be significantly upregulated. At 6 h after pharmacologic PC with the NO donor DETANO, SDF was increased 1.7 fold (verified by real time PCR, P<0.05, n=5– 6). Next, studies to demonstrate that SDF and CXCR4 are present and functional in the heart were performed in isolated adult mouse cardiac myocytes (CM) and in vivo. Both CM and non- myocytes expressed SDF and CXCR4 mRNA by RT-PCR, and protein was detected in both CM and non-myocytes by immunoprecipitation (IP) and immunoblotting (IB). Radioligand binding showed 125I SDF specific binding in intact CM. CM expressed a functional CXCR4 receptor that, when activated with 25 nM SDF, resulted in increased levels of both p-Akt and p-ERK (P<0.05 SDF vs control, n=3) while decreasing levels of p-p38 and p-JNK (P<0.05 SDF vs. control, n=3). SDF increased p-ERK was dose-dependent. In hypoxia - reoxygenation experiments, cultured CM treated with 25 nM SDF for 5 min were resistant to reoxygenation damage, demonstrated by decreased trypan blue staining, LDH release, and TUNEL positive CM (P<0.05 SDF vs. control, n=3) suggesting an anti-apoptotic mechanism. The CXCR4 specific antagonist AMD3100 blocked the SDF-induced decrease in trypan blue staining, LDH release, and TUNEL positive cells. SDF was increased after 1 and 4 h hypoxia in CM homogenates (ELISA; P<0.05 n=3) and by IP and IB. In vivo, LV infusion of 35 ug/kg/min SDF for 5 min ending 10 minutes before a 30-min coronary occlusion and 4 h of reperfusion in mice decreased infarct size (29.4 +/− 3.9 % of region at risk, n=8 vs. 63.3 +/− 2.2 % in controls, n=15, P<0.05 ). These findings demonstrate, for the first time, that a SDF-CXCR4 axis resides in the heart within myocytes but also in non-myocytes, and that this axis is activated by ischemia, promotes an antiapoptotic signaling program, and is capable of preconditioning cardiac myocytes. The results suggest that the cardiac SDF-CXCR4 axis may serve a paracrine function to protect the myocardium from ischemic stress.