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Letters to the Editor
Human platelets are a source of collagen I
Platelets are involved in primary hemostasis but also affect or modulate inflammatory and immune responses as well as angiogenesis1 and cancer metastasis.2 Activated platelets can affect the function of other cells either through direct cell-cell interaction or through the release of soluble factors and microparticles. Moreover, despite being anucleate, platelets contain mRNA and are able to synthesize proteins.3 However, the platelet protein land-
scape has not been fully explored and there is evidence of dynamic changes in the platelet proteome upon activa- tion. To investigate potential mechanisms underlying platelet hyper-reactivity, platelets from healthy subjects and patients with polycystic ovary syndrome (PCOS) were studied. The latter syndrome is a common endocrinopathy affecting women of reproductive age and is associated with abnormal platelet responses.4 Here we report, for the first time, that human platelets express pro-collagen I mRNA and protein, which is secreted in response to platelet activation and processed by throm-
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Figure 1. Hydroxyproline and collagen levels in human platelets. (A) Hydroxyproline levels in platelets from healthy donors (H) and polycystic ovary syndrome (PCOS) subjects, n=9-13 (Student’s t-test, ***P<0.001). (B) Collagen levels in platelets from healthy donors (H) and from PCOS subjects, n=10 (Student’s t-test, *P<0.05). (C) Expression of mRNA encoding collagen I a1 and β2 in platelets from healthy donors and PCOS patients, n=7-8 (ANOVA, Tukey’s multiple comparisons post test, P>0.1). (D) Representative blots (upper panel) and quantification (lower panel) showing collagen I a1 subunit in platelets from H and PCOS subjects, n=5-7 (Student’s t-test, *P<0.05). (E) Representative blots (upper panel) and quantification (lower panel) showing collagen I a1 expression in platelet lysates from PCOS subjects treated with solvent or collagenase (ColG), n=4 (Student’s t-test, ***P<0.001). (F) Representative images (left panel) and quantification (right panel) of collagen I (red) and Gp1b (green) in unstimulated non-permeabilized platelets from H or PCOS subjects; bar = 10 mm; n=6 (Student’s t-test, ***P<0.001).
haematologica | 2021; 106(3)
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