Abstract P289: Cardio-protective Peptide Ac-SDKP is Highly Concentrated in Lymph Nodes

Abstract

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a natural peptide released from its precursor Thymosin β4 (Tβ4) by meprin-α and the prolyl oligopeptidase enzymes (POP) in sequential steps. Ac-SDKP is hydrolyzed by the angiotensin converting enzyme (ACE). Ac-SDKP has anti-inflammatory and anti-fibrotic effects in heart, aorta and kidney and part of the beneficial effects of ACE inhibitors has been ascribed to the increased levels of Ac-SDKP. Ac-SDKP is present in spleen and thymus, however, the presence of Ac-SDKP in the lymph node has not been studied. We hypothesized that Tβ4, Ac-SDKP and its releasing enzymes are present in lymph node. Ac-SDKP concentration was evaluated in Sprague-Dawley (SD) rat tissues. Tβ4 as well as Meprin-α and POP enzymes were measured in the lymph node, thymus, spleen and other tissues obtained from SD rats. Additionally, Ac-SDKP content was measured in different cell populations of lymph node obtained through cell sorting. Lymph node showed the highest Ac-SDKP concentration (181±18.3 ng/mg of protein), followed by the testis (104.3±6.5, thymus (54.2±1.8) and spleen (44.9±4.7) in SD rats (P<0.001 lymph node vs. testis, thymus and spleen). Meprin-α and POP activity were present in lymph node, spleen and thymus. Tβ4 and Meprin-α immunostaining were found to be positive in multinucleated giant cells in the cortical region of lymph node and along the septums; it was also found in the follicular region and germinal center. POP staining was found positive in the cortical region. In the lymph node, Ac-SDKP concentration was higher in Macrophages (CD45+CD68+) in comparison with T lymphocytes (CD45+CD3+) (150±110 pmol/100,000 cell vs. 0.3±0.1pmol/100,000cell, respectively). We conclude that in lymph node, Ac-SDKP is highly concentrated and that all the components of Tβ4/Ac-SDKP system are present. Macrophages could be the main source of Ac-SDKP in lymph node. The presence of Ac-SDKP in lymph node may have important implications in understanding inflammation and target organ damage in cardiovascular diseases.