The general notion that functional platelets are important for successful hematogenous tumor metastasis has been inaugurated more than 4 decades ago and has since been corroborated in numerous experimental settings. Thorough IntroductionMetastasis is the main cause of cancer-related death and a major challenge in today's cancer management. Although many new therapies against malignant tumors have been developed over the last years, the prognosis of most malignancies remains unfavorable, once metastatic spread has occurred. This challenge underlines the importance of understanding the details of metastasis to develop specific therapies to impede tumor dissemination.The highly complex process of hematogenous tumor cell spreading includes detachment of cancer cells from the primary site, migration into and transport along the bloodstream, and, finally, tumor cell arrest and proliferation within the distant tissue. Thus, survival of the tumor cells within the bloodstream and adhesion in the vasculature at the metastatic sites are crucial for tumor cell dissemination. There is a plethora of studies indicating that the interaction of tumor cells with platelets within the bloodstream is essential during this early phase of metastasis and that agents directed against specific platelet receptors involved in this process may give rise to new therapies for patients with a high risk of metastasis or for minimizing the risk of cancer cell dissemination during antitumor surgery. Platelets in hematogenous metastasisThe involvement of platelets and coagulation factors in hematogenous tumor metastasis has long been recognized. A relationship between venous thromboembolism and cancer has been observed at least since 1865, 1 and more recent studies have shown that the risk of a diagnosis of cancer is clearly elevated after primary deep venous thromboembolism or pulmonary embolism. 2 As a more direct evidence of platelet involvement in the development of malignant tumors, a relationship between elevated platelet count and malignant tumors was reported by Reiss et al in 1872. 3 So far, thrombocytosis or even platelet counts that are within the upper normal range have been shown to be associated with advanced, often metastatic, stages of cancer and to be a negative prognostic marker for many different tumor entities, including endometrial carcinoma, 4,5 cervical cancer, 6 ovarian cancer, 7 gastric cancer, 8 or esophageal cancer. 9 Clearly, it is difficult to differentiate whether elevated platelet levels actually constitute a predisposition toward a more aggressive disease per se. To our knowledge, there are no prospective studies evaluating the possible development of cancer and aggressive metastatic disease in initially healthy people with elevated platelet levels compared with people with low platelet counts. Although animal models certainly show a role for platelets in cancer metastasis, in patients it is harder to distinguish between a mere correlation between thrombocytosis and cancer and an actual causality. It seems most p...

Neutrophilic granulocytes are able to release their own DNA as neutrophil extracellular traps (NETs) to capture and eliminate pathogens. DNA expulsion (NETosis) has also been documented for other cells and organisms, thus highlighting the evolutionary conservation of this process. Moreover, dysregulated NETosis has been implicated in many diseases, including cancer and inflammatory disorders. During NETosis, neutrophils undergo dynamic and dramatic alterations of their cellular as well as sub-cellular morphology whose biophysical basis is poorly understood. Here we investigate NETosis in real-time on the single-cell level using fluorescence and atomic force microscopy. Our results show that NETosis is highly organized into three distinct phases with a clear point of no return defined by chromatin status. Entropic chromatin swelling is the major physical driving force that causes cell morphology changes and the rupture of both nuclear envelope and plasma membrane. Through its material properties, chromatin thus directly orchestrates this complex biological process.

• PAD4-mediated chromatin decondensation and release by neutrophils exacerbate injury after MI/R. • Combining reduction of neutrophil recruitment with extracellular DNA cleavage could be a new approach to reduce cardiac damage after MI.Innate immune cells play a major role in the early response to myocardial ischemia/ reperfusion (MI/R) injury. Recombinant human ADAMTS13 (rhADAMTS13), cleaving von Willebrand factor (VWF), reduces leukocyte recruitment in mice. Death of cardiomyocytes and the possible formation of neutrophil extracellular traps (NETs) may result in chromatin release that is prothrombotic and cytotoxic. We investigated the pathophysiological role of extracellular chromatin during MI/R to evaluate the therapeutic potential of targeting extracellular DNA and VWF by using DNase I with/without rhADAMTS13. Finally, we examined the impact of histone citrullination and NETosis by peptidylarginine deiminase 4 (PAD4) on MI/R. We used a 24-hour MI/R mouse surgical model. MI/R injury caused an increase in plasma nucleosomes, abundant neutrophil infiltration, and the presence of citrullinated histone H3 at the site of injury. Both monotherapies and coadministration of DNase I and rhADAMTS13 revealed a cardioprotective effect, resulting in subsequent improvement of cardiac contractile function. PAD4 2/2 mice, which do not produce NETs, were also significantly protected from MI/R and DNase I treatment had no further beneficial effect. We demonstrate that extracellular chromatin released through NETosis exacerbates MI/R injury. Targeting both VWF-mediated leukocyte recruitment and chromatin removal may be a new therapeutic strategy to reduce ischemia-related cardiac damage. (Blood. 2014;123(1):141-148)

Peptidylarginine deiminase 4 (PAD4) citrullinates proteins. In neutrophils, it causes chromatin decondensation and release of NETs, which are injurious. Martinod et al. show in this study that NETs promote fibrosis in a cardiac model and that PAD4-deficient mice have reduced age-related organ fibrosis.