The Anti‐Inflammatory Peptide Ac‐SDKP is Released from Thymosin β4 by Meprin α and Prolyl Oligopeptidase

N‐acetyl‐seryl‐aspartyl‐lysyl‐proline (Ac‐SDKP) is a natural tetrapeptide with anti‐inflammatory and anti‐fibrotic properties. We have previously shown that prolyl oligopeptidase (POP) is involved in the Ac‐SDKP release from thymosin β4 (Tβ4). However, POP can only hydrolyze peptides shorter than 30 amino acids and Tβ4 is 43 amino acids long. This suggests that Tβ4 must be hydrolyzed by another peptidase that releases N‐terminal intermediate peptide(s) <30 amino acids before POP hydrolysis takes place. Our search in peptidase database for potential candidate(s) gave high score for meprin α metalloprotease. Therefore, we hypothesize that Tβ4 is hydrolyzed by meprin α prior to POP hydrolysis. To test this, in vitro and in vivo studies were performed. In vitro, we found that the incubation of Tβ4 with both, meprin α and POP releases Ac‐SDKP, whereas it failed when Tβ4 is incubated with either meprin α or POP alone. Incubation of Tβ4 with rat kidney homogenate increases Ac‐SDKP, which is blocked by actinonin (meprin α inhibitor). In addition, kidney from meprin α knockout mice showed a significantly lower Ac‐SDKP as compared to its wild type control. In vivo , we observed that rat treated with captopril (ACE inhibitor) increased plasma concentrations of Ac‐SDKP, which is inhibited by the co‐administration of actinonin (vehicle 3.1±0.22 nmol/L; captopril 15.1±0.7 nmol/L; captopril + actinonin 6.1±0.3 nmol/L; vehicle versus captopril, P <0.002; captopril versus captopril + actinonin, P< 0.002). Similar results were obtained with urinary Ac‐SDKP excretion. We conclude that Ac‐SDKP is released from Tβ4 by the successive action of meprin α and POP. Support or Funding Information This work is supported by National Institute Health Grant HL028982