Vlahakis, Nicholas E.

Abstract Chemokine receptors are essential for triggering chemotaxis to immune cells; however, a number of them can also mediate death when engaged by nonchemokine ligands. When the chemokine receptor CXCR4 is engaged by stromal cell-derived factor (SDF1)α, it triggers cells to chemotax, and in some cell types such as neurons, causes cell death. To elucidate this dual and opposing receptor function, we have investigated whether CXCR4 activation by its chemokine SDF1α could lead to the simultaneous activation of both anti- and proapoptotic signaling pathways; the balance ultimately influencing cell survival. CXCR4 activation in CD4 T cells by SDF1α led to the activation of the prosurvival second messengers, Akt and extracellular signal-regulated protein kinase. Selective inhibition of each signal demonstrated that extracellular signal-regulated protein kinase is essential for mediating SDF1α-triggered chemotaxis but does not confer an antiapoptotic state. In contrast, Akt activation through CXCR4 by SDF1α interactions is necessary to confer resistance to apoptosis. The proapoptotic signaling pathway triggered by SDF1α-CXCR4 interaction involves the Giα protein-independent activation of the proapoptotic MAPK (p38). Furthermore, other chemokines and chemokine receptors also signal chemotaxis and proapoptotic effects via similar pathways. Thus, Giα protein-coupled chemokine receptors can function as death prone receptors and the balance between the above signaling pathways will ultimately mandate the fate of the activated cell.

Background: Safe and effective glucose control in the intensive care unit (ICU) continues to be actively pursued. Large clinical trials have examined the safety and efficacy of insulin infusion protocols in medical and surgical ICUs. We report experiences of a single-center standardized nurse-driven insulin infusion protocol in three ICUs in an observational quality-improvement study. Method: We analyzed the hourly point-of-care arterial blood glucose obtained during ICU insulin infusion protocol (protocol A) with a glucose target of 80–130 mg/dl in medical and surgical ICUs in February 2009. Following Normoglycemia in Intensive Care Evaluation and Survival Using Glucose Algorithm Regulation (NICE-SUGAR) study results, the protocol was amended (protocol B) to achieve target glucose of 110–150 mg/dl. The performance of protocol B was assessed in the ICUs in May 2010 and compared with protocol A with respect to glucose concentrations and rates of severe (<40 mg/dl) and moderate (40–60 mg/dl) hypoglycemia. Results: With protocol A, in medical ( n = 44) and surgical ( n = 164) ICUs taken together, median glucose was 119 mg/dl, with severe and moderate hypoglycemia rates 1.4% (3/208) and 7.7% (16/208), respectively, which were significantly lower than those reported by the NICE-SUGAR and the Leuven studies. With protocol B, in medical ( n = 44) and surgical ( n = 167) ICUs taken together, median glucose was 132 mg/dl, with severe and moderate hypoglycemia of 0 % (0/211) and 0.5% (1/211), respectively. Conclusion: The current ICU insulin infusion protocol (protocol B) reduces severe and moderate hypoglycemia without compromising glucose control when compared with protocol A. This could potentially impact patient-important outcomes.

Integrins are important mediators of cell adhesion and migration, which in turn are essential for diverse biological functions, including wound healing and cancer metastasis. The integrin α9β1 is expressed on numerous mammalian tissues and can mediate accelerated cell migration. As the molecular signaling mechanisms that transduce this effect are poorly defined, we investigated the pathways by which activated integrin α9β1 signals migration. We found for the first time that specific ligation of integrin α9β1 rapidly activates Src tyrosine kinase, with concomitant tyrosine phosphorylation of p130Cas and activation of Rac-1. Furthermore, activation of integrin α9β1 also enhanced NO production through activation of inducible nitric oxide synthase (iNOS). Inhibition of Src tyrosine kinase or NOS decreased integrin-α9β1-dependent cell migration. Src appeared to function most proximal in the signaling cascade, in a FAK-independent manner to facilitate iNOS activation and NO-dependent cell migration. The cytoplasmic domain of integrin α9 was crucial for integrin-α9β1-induced Src activation, subsequent signaling events and cell migration. When taken together, our results describe a novel and unique mechanism of coordinated interactions of the integrin α9 cytoplasmic domain, Src tyrosine kinase and iNOS to transduce integrin-α9β1-mediated cell migration.

Abstract The clinical and experimental literature has unequivocally established that mechanical ventilation with large tidal volumes is injurious to the lung. However, uncertainty about the micromechanics of injured lungs and the numerous degrees of freedom in ventilator settings leave many unanswered questions about the biophysical determinants of lung injury. In this review we focus on experimental evidence for lung cells as injury targets and the relevance of these studies for human ventilator-associated lung injury. In vitro, the stress-induced mechanical interactions between matrix and adherent cells are important for cellular remodeling as a means for preventing compromise of cell structure and ultimately cell injury or death. In vivo, these same principles apply. Large tidal volume mechanical ventilation results in physical breaks in alveolar epithelial and endothelial plasma membrane integrity and subsequent triggering of proinflammatory signaling cascades resulting in the cytokine milieu and pathologic and physiologic findings of ventilator-associated lung injury. Importantly, though, alveolar cells possess cellular repair and remodeling mechanisms that in addition to protecting the stressed cell provide potential molecular targets for the prevention and treatment of ventilator-associated lung injury in the future.

Abstract Cells experience plasma membrane stress failure when the matrix to which they adhere undergoes large deformations. In the lung, such a mechanism might explain mechanical ventilation–associated cell injury. We have previously shown that in alveolar epithelial cells, deformation induces lipid trafficking to the plasma membrane, thereby accommodating the required increase in the cell surface area. We now show that cell wounding is strain amplitude and rate dependent and that under conditions of impaired exocytosis strain-induced cell wounding is significantly increased. In addition, the susceptibility of cells to mechanical injury was not correlated with changes in cell stiffness. Using a dual-labeling technique, we differentiated between cell populations that were reversibly and irreversibly injured and showed that interventions that impair deformation-induced lipid trafficking also reduce the likelihood of plasma membrane resealing. Our findings suggest that cell plasticity and remodeling responses such as deformation-induced lipid trafficking are more important for cytoprotection from strain injury than are the innate mechanical properties of the cell. We also conclude that in deformation experiments, tests of cell membrane integrity cannot be interpreted as tests of cell viability because an intact plasma membrane after deformation does not mean that no injury had occurred.