Platelets are critical for hemostasis, thrombosis, and inflammatory responses1,2, yet the events leading to mature platelet production remain incompletely understood3. The bone marrow (BM) is proposed to be a major site of platelet production although indirect evidence points towards a potential pulmonary contribution to platelet biogenesis4-7. By directly imaging the lung microcirculation in mice8, we discovered that a large number of megakaryocytes (MKs) circulate through the lungs where they dynamically release platelets. MKs releasing platelets in the lung are of extrapulmonary origin, such as the BM, where we observed large MKs migrating out of the BM space. The lung contribution to platelet biogenesis is substantial with approximately 50% of total platelet production or 10 million platelets per hour. Furthermore, we identified populations of mature and immature MKs along with hematopoietic progenitors that reside in the extravascular spaces of the lung. Under conditions of thrombocytopenia and relative stem cell deficiency in the BM9, these progenitors can migrate out of the lung, repopulate the BM, completely reconstitute blood platelet counts, and contribute to multiple hematopoietic lineages. These results position the lung as a primary site of terminal platelet production and an organ with considerable hematopoietic potential.

• Neutrophil-platelet aggregates are dynamically formed in the lung in response to injury and are regulated by aspirin-triggered lipoxin.• The therapeutic effect of aspirin in acute lung injury is in large part mediated by the production of pro-resolving lipid mediators.Evidence is emerging that platelets are major contributors to innate immune responses in conditions such as acute lung injury (ALI). Platelets form heterotypic aggregates with neutrophils, and we hypothesized that lipoxin mediators regulate formation of neutrophilplatelet aggregates (NPA) and that NPA significantly contribute to ALI. Lipopolysaccharide (LPS)-induced lung injury was accompanied by platelet sequestration, activation, intra-alveolar accumulation, and NPA formation within both blood and alveolar compartments. Using lung intravital microscopy, we observed the dynamic formation of NPA during physiologic conditions, which sharply increased with ALI. Aspirin (ASA) treatment significantly reduced lung platelet sequestration and activation, NPA formation, and lung injury. ASA treatment increased levels of ASA-triggered lipoxin (ATL; 15-epi-lipoxin A 4 ), and blocking the lipoxin A 4 receptor (ALX) with a peptide antagonist (Boc2) or using ALX knockouts (Fpr2/3 2/2 ) reversed this protection. LPS increased NPA formation in vitro, which was reduced by ATL, and engagement of ALX by ATL on both neutrophils and platelets was necessary to prevent aggregation. In a model of transfusion-related acute lung injury (TRALI), Boc2 also reversed ASA protection, and treatment with ATL in both LPS and TRALI models protected from ALI. We conclude that ATL regulates neutrophil-platelet aggregation and that platelet-neutrophil interactions are a therapeutic target in lung injury. (Blood. 2014;124(17):2625-2634

NETs accumulate in the lung in both experimental and clinical PGD. In experimental PGD, NET formation is platelet-dependent, and disruption of NETs with DNaseI reduces lung injury. These data are the first description of a pathogenic role for NETs in solid organ transplantation and suggest that NETs are a promising therapeutic target in PGD.

Activation of Janus kinase/signal transducers and activators of transcription (JAK/STAT) is an important mechanism by which hyperglycemia contributes to renal damage, suggesting that modulation of this pathway may prevent renal and vascular complications of diabetes. Here, we investigated the involvement of suppressors of cytokine signaling (SOCS) as intracellular negative regulators of JAK/STAT activation in diabetic nephropathy. In a rat model, inducing diabetes resulted in JAK/STAT activation and increased expression of SOCS1 and SOCS3. In humans, we observed increased expression of glomerular and tubulointerstitial SOCS proteins in biopsies of patients with diabetic nephropathy. In vitro, high concentrations of glucose activated JAK/STAT/SOCS in human mesangial and tubular cells. Overexpression of SOCS reversed the glucose-induced activation of the JAK/STAT pathway, expression of STATdependent genes (chemokines, growth factors, and extracellular matrix proteins), and cell proliferation. In vivo, intrarenal delivery of adenovirus expressing SOCS1 and SOCS3 to diabetic rats significantly improved renal function and reduced renal lesions associated with diabetes, such as mesangial expansion, fibrosis, and influx of macrophages. SOCS gene delivery also decreased the activation of STAT1 and STAT3 and the expression of proinflammatory and profibrotic proteins in the diabetic kidney. In summary, these results provide direct evidence for a link between the JAK/STAT/SOCS axis and hyperglycemia-induced cell responses in the kidney. Suppression of the JAK/STAT pathway by increasing intracellular SOCS proteins may have therapeutic potential in diabetic nephropathy.

Objective-Suppressors of cytokine signaling (SOCS) proteins are intracellular regulators of receptor signal transduction, mainly Janus kinase/signal transducers and activators of transcription (JAK/STAT). We investigated the effects of SOCS modulation on the JAK/STAT-dependent responses in vascular cells, and their implication in atherosclerotic plaque development. Methods and Results-Immunohistochemistry in human plaques revealed a high expression of SOCS1 and SOCS3 by vascular smooth muscle cells (VSMCs) and macrophages in the inflammatory region of the shoulders, when compared to the fibrous area. SOCS were also increased in aortic lesions from apoE Ϫ/Ϫ mice. In cultured VSMCs, endothelial cells, and monocytes, SOCS1 and SOCS3 were transiently induced by proinflammatory cytokines, proatherogenic lipoproteins, and immune molecules. Furthermore, overexpression of SOCS suppressed STAT activation and reduced inflammatory gene expression and cell growth, whereas SOCS knockdown increased these cell responses. In vivo, antisense oligodeoxynucleotides targeting SOCS3 exacerbated the atherosclerotic process in apoE Ϫ/Ϫ mice by increasing the size, leukocyte content, and chemokine expression in the lesions. Key Words: atherosclerosis Ⅲ inflammation Ⅲ signal transduction Ⅲ proliferation Ⅲ chemokines A therosclerosis is a chronic inflammatory disease that involves a complex interaction of the artery wall and its cellular components, lipoproteins, and circulating blood elements. 1 Leukocyte invasion and vascular smooth muscle cell (VSMC) proliferation are key early events in lesion development. 2 Low-density lipoproteins (LDL) and cytokines, such as interferon ␥ (IFN␥) and interleukin-6 (IL-6), influence the dynamics of vascular cell function and are main mediators of inflammation during atherogenesis. 2,3 Native and modified forms of LDL induce a variety of biological properties, including cytokine expression, changes in monocyte/macrophages motility and arterial vasomotricity, and VSMC mitogenesis. 4,5 IFN␥ is expressed in human and experimental plaques, and induces the expression of major histocompatibility complex-II, downregulates scavenger receptors, and modulates vascular cell proliferation. 2,6 IL-6 is secreted from endothelial cells (ECs), VSMCs, and leukocytes, and has multiple biological activities, including lymphocyte activation, acute-phase proteins induction, and proliferation. 7,8 Evidence supports the involvement of cellular and humoral immune responses in atherosclerosis, from its initiation to its thrombotic complication. 9 Elevated levels of LDL-containing immune complexes (ICs) and their IgG Fc receptors (Fc␥R) have been found in atherosclerotic patients. 10 Furthermore, Fc␥R mediates the clearance of ICs containing LDL and foam cell formation, 10 and Fc␥R activation in vascular cells is critical for atherosclerosis development in mice. 11 The Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway is an essential intracellular mechanism of cytokines and other stimuli tha...