Survival and Pulmonary Injury After Neonatal Sepsis: PD1/PDL1's Contributions to Mouse and Human Immunopathology

Morbidity and mortality associated with neonatal sepsis remains a healthcare crisis. PD1-/- neonatal mice endured experimental sepsis, in the form of cecal slurry (CS), and showed improved rates of survival compared to wildtype (WT) counterparts. End-organ injury, particularly of the lung, contributes to the devastation set forth by neonatal sepsis. PDL1-/- neonatal mice, in contrast to PD1-/- neonatal mice did not have a significant improvement in survival after CS. Because of this, we focused subsequent studies on the impact of PD1 gene deficiency on lung injury. Here, we observed that at 24 h post-CS (but not at 4 or 12 h) there was a marked increase in pulmonary edema (PE), neutrophil influx, myeloperoxidase (MPO) levels, and cytokine expression sham (Sh) WT mice. Regarding pulmonary endothelial cell (EC) adhesion molecule expression, we observed that Zona occludens-1 (ZO-1) within the cell shifted from a membranous location to a peri-nuclear location after CS in WT murine cultured ECs at 24hrs, but remained membranous among PD1-/- lungs. To expand the scope of this inquiry, we investigated human neonatal lung tissue. We observed that the lungs of human newborns exposed to intrauterine infection had significantly higher numbers of PD1+ cells compared to specimens who died from non-infectious causes. Together, these data suggest that PD1/PDL1, a pathway typically thought to govern adaptive immune processes in adult animals, can modulate the largely innate neonatal pulmonary immune response to experimental septic insult. The potential future significance of this area of study includes that PD1/PDL1 checkpoint proteins may be viable therapeutic targets in the septic neonate.

Improving Endothelial Explant Tissue Culture by Novel Thermoresponsive Cell Culture System

AIM

Studying cell migration of corneal endothelial cells in vitro is challenging because the capacity for cell migration needs to be maintained while at the same time the tissue must remain fixed on a rigid substrate. In this study, we report a thermoresponsive culture technique designed to maintain cellular viability, and to reduce tissue handling in order to analyze in vitro endothelial cell migration from corneal grafts.

MATERIALS AND METHODS

As a test tissue, fifteen Quarter-Descemet membrane endothelial keratoplasty (Q-DMEK) grafts were used that were embedded in a three-dimensional culture system using a temperature-reversible hydrogel and cultured over 2-3 weeks in a humidified atmosphere at 37°C and 5% CO₂.

RESULTS

All grafts could be successfully cultured inside the thermoresponsive polymer solution for periods of up to 21 days. Using this system, cell migration could be assessed by light microscopy at fixed time intervals. At the end of the culture period, the gel could be removed from all grafts and immunohistochemistry analysis showed that endothelial cells were able to maintain confluence, viability, and junctional integrity. Some problems were encountered when using the thermoresponsive cell culture system. These were mostly structural inconsistencies during the sol-to-gel transition phase that resulted in the formation of tiny bubbles in the matrix. Additionally, areas with different viscosity resulted in optical distortions showing up as folds throughout the matrix which can persist even after several cycles of culture medium exchange. These effects had impact on the imaging quality but did not affect the viability of the explant tissue.

CONCLUSION

This study proves that temperature-reversible hydrogel is a very useful matrix for studying in vitro corneal endothelial cell migration from explant grafts and allows for subsequent biological investigation after gel removal.

Increased endothelial shear stress improves insulin-stimulated vasodilatation in skeletal muscle

KEY POINTS

It has been postulated that increased blood flow-associated shear stress on endothelial cells is an underlying mechanism by which physical activity enhances insulin-stimulated vasodilatation. This report provides evidence supporting the hypothesis that increased shear stress exerts insulin-sensitizing effects in the vasculature and this evidence is based on experiments in vitro in endothelial cells, ex vivo in isolated arterioles and in vivo in humans. Given the recognition that vascular insulin signalling, and associated enhanced microvascular perfusion, contributes to glycaemic control and maintenance of vascular health, strategies that stimulate an increase in limb blood flow and shear stress have the potential to have profound metabolic and vascular benefits mediated by improvements in endothelial insulin sensitivity.

ABSTRACT

The vasodilator actions of insulin contribute to glucose uptake by skeletal muscle, and previous studies have demonstrated that acute and chronic physical activity improves insulin-stimulated vasodilatation and glucose uptake. Because this effect of exercise primarily manifests in vascular beds highly perfused during exercise, it has been postulated that increased blood flow-associated shear stress on endothelial cells is an underlying mechanism by which physical activity enhances insulin-stimulated vasodilatation. Accordingly, herein we tested the hypothesis that increased shear stress, in the absence of muscle contraction, can acutely render the vascular endothelium more insulin-responsive. To test this hypothesis, complementary experiments were conducted using (1) cultured endothelial cells, (2) isolated and pressurized skeletal muscle arterioles from swine, and (3) humans. In cultured endothelial cells, 1 h of increased shear stress from 3 to 20 dynes cm^-2 caused a significant shift in insulin signalling characterized by greater activation of eNOS relative to MAPK. Similarly, isolated arterioles exposed to 1 h of intraluminal shear stress (20 dynes cm^-2 ) subsequently exhibited greater insulin-induced vasodilatation compared to arterioles kept under no-flow conditions. Finally, we found in humans that increased leg blood flow induced by unilateral limb heating for 1 h subsequently augmented insulin-stimulated popliteal artery blood flow and muscle perfusion. In aggregate, these findings across models (cells, isolated arterioles and humans) support the hypothesis that elevated shear stress causes the vascular endothelium to become more insulin-responsive and thus are consistent with the notion that shear stress may be a principal mechanism by which physical activity enhances insulin-stimulated vasodilatation.

Alterations in cell cycle dynamics in human endothelium cell culture infected with influenza virus

The cell cycle of endothelium EAhy 926 cell culture infected with influenza virus has been studied. Cytometric analysis of cell culture synchronized by contact inhibition revealed the elongation of the S phase of the cell cycle in EAhy 926 cells under the influence of influenza virus. This result was shown in an EAhy 926 culture infected with influenza virus and treated with nocodazole. Comparison of a lung carcinoma A549 cell line in which influenza virus causes G₀/G₁ arrest and of an endothelial EAhy 926 cell line in which the same infection leads to S-phase elongation allows it to be suggested that different effects of influenza virus on cell cycle dynamics depend on the origin of infected cells.

Imbalance between the endothelial cell-derived contracting factors prostacyclin and angiotensin II and nitric oxide/cyclic GMP in human primary varicosis

1. The role of the endothelium in the vasomotor control of human veins in the lower extremity is little understood. We tested the hypothesis that the production of relaxing and contracting factors is altered in endothelial cells from varicose saphenous veins which may predispose to the decreased vessel tone observed in primary varicosis. 2. We determined the intracellular accumulation of guanosine 3':5'-cyclic monophosphate cyclic GMP; a measure of nitric oxide production and the release of endothelin and prostacyclin (measured as its stable metabolite 6-keto-prostaglandin F1alpha) from cultured cells derived from the long saphenous veins of patients with primary varicosis (Varicose saphena group, n = 27) or from patients undergoing coronary artery bypass surgery (Healthy saphena group, n = 22). In addition, levels of endothelin, angiotensin II, bradykinin, cyclic GMP and cyclic AMP in plasma from patients with primary varicosis and healthy volunteers (n = 8-11 in each group) were determined. 3. Although basal cyclic GMP levels were similar, more cyclic GMP accumulated in response to histamine (1-100 micromol l[-1]) in cells from varicose saphenous veins (0.75 +/- 0.1 pmol per well) than in cells from veins without varicosis (0.27 +/- 0.05 pmol per well). Furthermore, the relaxant potency of nitroprusside (1 nmol l(-1) - 300 micromol l[-1]) in vitro was higher for varicose veins (mean EC50 = 5.9 micromol l(-1); n = 8) than healthy veins (mean EC50 = 20.0 micromol l(-1); n = 7). 4. The production of prostacyclin was significantly less in cells from varicose than healthy saphenous veins (66 +/- 8.7 and 121 +/- 20.1 nmol g(-1) protein), but the production of endothelin was similar in both groups. Prostacyclin (3 nmol l(-1) 30 micromol l[-1]) consistently contracted rings of varicose saphenous vein in vitro with a mean EC50 value of 10-20 micromol l(-1) (n = 7); the maximum tension generated was approximately 50% of that of a completely depolarizing solution of K+ (120 mmol l[-1]). 5. In plasma from patients with varicose veins, levels of cyclic GMP were higher than in healthy controls (9.2 +/- 0.03 and 7.2 +/- 0.02 nmol l[-1]), levels of angiotensin II were lower (81 +/- 11.5 and 147 +/- 21.7 pmol l[-1]), and levels of endothelin, cyclic AMP, and bradykinin were not different. 6. It is concluded that endothelial cells from diseased saphenous veins secrete less constrictor mediators than cells from healthy veins and that in diseased veins the nitric oxide/cyclic GMP system is up-regulated which may shift the balance of vasoactive factors towards vasodilatation and contribute to the development of primary varicosis.