Tspan18 is a novel regulator of the Ca2+ channel Orai1 and von Willebrand factor release in endothelial cells.

Ca2+ entry via Orai1 store-operated Ca2+ channels in the plasma membrane is critical to cell function, and Orai1 loss causes severe immunodeficiency and developmental defects. The tetraspanins are a superfamily of transmembrane proteins that interact with specific 'partner proteins' and regulate their trafficking and clustering. The aim of this study was to functionally characterize tetraspanin Tspan18. We show that Tspan18 is expressed by endothelial cells at several-fold higher levels than most other cell types analyzed. Tspan18-knockdown primary human umbilical vein endothelial cells have 55-70% decreased Ca2+ mobilization upon stimulation with the inflammatory mediators thrombin or histamine, similar to Orai1-knockdown. Tspan18 interacts with Orai1, and Orai1 cell surface localization is reduced by 70% in Tspan18-knockdown endothelial cells. Tspan18 overexpression in lymphocyte model cell lines induces 20-fold activation of Ca2+ -responsive nuclear factor of activated T cell (NFAT) signaling, in an Orai1-dependent manner. Tspan18-knockout mice are viable. They lose on average 6-fold more blood in a tail-bleed assay. This is due to Tspan18 deficiency in non-hematopoietic cells, as assessed using chimeric mice. Tspan18-knockout mice have 60% reduced thrombus size in a deep vein thrombosis model, and 50% reduced platelet deposition in the microcirculation following myocardial ischemia-reperfusion injury. Histamine- or thrombin-induced von Willebrand factor release from endothelial cells is reduced by 90% following Tspan18-knockdown, and histamine-induced increase of plasma von Willebrand factor is reduced by 45% in Tspan18-knockout mice. These findings identify Tspan18 as a novel regulator of endothelial cell Orai1/Ca2+ signaling and von Willebrand factor release in response to inflammatory stimuli.

Identification of Tspan9 as a novel platelet tetraspanin and the collagen receptor GPVI as a component of tetraspanin microdomains.

Platelets are essential for wound healing and inflammatory processes, but can also play a deleterious role by causing heart attack and stroke. Normal platelet activation is dependent on tetraspanins, a superfamily of glycoproteins that function as 'organisers' of cell membranes by recruiting other receptors and signalling proteins into tetraspanin-enriched microdomains. However, our understanding of how tetraspanin microdomains regulate platelets is hindered by the fact that only four of the 33 mammalian tetraspanins have been identified in platelets. This is because of a lack of antibodies to most tetraspanins and difficulties in measuring mRNA, due to low levels in this anucleate cell. To identify potentially platelet-expressed tetraspanins, mRNA was measured in their nucleated progenitor cell, the megakaryocyte, using serial analysis of gene expression and DNA microarrays. Amongst 19 tetraspanins identified in megakaryocytes, Tspan9, a previously uncharacterized tetraspanin, was relatively specific to these cells. Through generating the first Tspan9 antibodies, Tspan9 expression was found to be tightly regulated in platelets. The relative levels of CD9, CD151, Tspan9 and CD63 were 100, 14, 6 and 2 respectively. Since CD9 was expressed at 49000 cell surface copies per platelet, this suggested a copy number of 2800 Tspan9 molecules. Finally, Tspan9 was shown to be a component of tetraspanin microdomains that included the collagen receptor GPVI (glycoprotein VI) and integrin alpha6beta1, but not the von Willebrand receptor GPIbalpha or the integrins alphaIIbbeta3 or alpha2beta1. These findings suggest a role for Tspan9 in regulating platelet function in concert with other platelet tetraspanins and their associated proteins.

Out-of-Hospital Perimortem Cesarean Section as Resuscitative Hysterotomy in Maternal Posttraumatic Cardiac Arrest.

The optimal treatment of a severe hemodynamic instability from shock to cardiac arrest in late term pregnant women is subject to ongoing studies. However, there is an increasing evidence that early "separation" between the mother and the foetus may increase the restoration of the hemodynamic status and, in the cardiac arrest setting, it may raise the likelihood of a return of spontaneous circulation (ROSC) in the mother. This treatment, called Perimortem Cesarean Section (PMCS), is now termed as Resuscitative Hysterotomy (RH) to better address the issue of an early Cesarean section (C-section). This strategy is in contrast with the traditional treatment of cardiac arrest characterized by the maintenance of cardiopulmonary resuscitation (CPR) maneuvers without any emergent surgical intervention. We report the case of a prehospital perimortem delivery by Caesarean (C) section of a foetus at 36 weeks of gestation after the mother's traumatic cardiac arrest. Despite the negative outcome of the mother, the choice of performing a RH seems to represent up to date the most appropriate intervention to improve the outcome in both mother and foetus.