Figure 8. TSP-deficient platelets release higher amounts of SDF-1 after stimulation.

(A) SDF-1 levels in carefully collected platelet-poor plasma were measured. However, most samples contained SDF-1 below detection level. An average concentration of less than 250 pg/ml was calculated for both WT and TSP-DKO animals (n = 6). (B) Retro-orbital blood from the same animals as in A was collected and incubated for clot formation, and serum was harvested after centrifugation. SDF-1 in the serum was higher in TSP-DKO than in WT blood. However, this difference did not reach a level of significance (2.3 ng/ml in WT versus 2.8 ng/ml in TSP-DKO serum; P = 0.08) but reflected the elevated platelet levels found in TSP-DKO mice. Importantly, these results strongly suggest that platelets are the major source of serum SDF-1. (C) PRP underwent analysis by aggregometry, and SDF-1 released upon stimulation with different platelet agonists was examined. Stimulation of 10 μg/ml collagen followed by 10 μmol adenosine resulted in the strongest aggregation. Interestingly, TSP-DKO platelets secreted twice as much total SDF-1 as WT platelets under these conditions (5 pg/ml in WT versus 11.5 pg/ml in TSP-DKO). PRP was pooled from n = 3–4 animals, experiment was repeated 3 times, *P < 0.05.