Semaphorin 7A is protective during inflammatory peritonitis through integrin receptor signaling.

Introduction: The study explores the role of endothelial Semaphorin 7A (SEMA7A) in inflammatory processes. SEMA7A is known for enhancing inflammation during tissue hypoxia and exhibiting anti-inflammatory properties in the intestinal system during colitis. This research extends the understanding of SEMA7A's function by examining its role in inflammatory peritonitis and intestinal inflammation. Methods: The research involved inducing peritonitis in SEMA7A knockout (SEMA7A-/-) and wild-type (WT) animals through Zymosan A (ZyA) injection. The inflammatory response was assessed by measuring cell count and cytokine release. In parallel, the study investigated the expression of SEMA7A in intestinal epithelial cells under inflammatory stimuli and its impact on interleukin 10 (IL-10) production using an in vitro co-culture model of monocytes and epithelial cells. Additionally, the distribution of SEMA7A target receptors, particularly ITGAV/ITGB1 (CD51/CD29), was analyzed in WT animals. Results: The results revealed that SEMA7A-/- animals exhibited increased inflammatory peritonitis compared to the WT animals. Inflammatory conditions in intestinal epithelial cells led to the induction of SEMA7A. The co-culture experiments demonstrated that SEMA7A induced IL-10 production, which depended on integrin receptors and was independent of PLXNC1 expression. Furthermore, ITGAV/ITGB1 emerged as the predominant SEMA7A receptor in the intestinal area of WT animals. Discussion: These findings underscore the multifaceted role of SEMA7A in inflammatory processes. The differential responses in peritonitis and intestinal inflammation suggest that SEMA7A's function is significantly influenced by the expression and distribution of its target receptors within different organ systems. The study highlights the complex and context-dependent nature of SEMA7A in mediating inflammatory responses.

Phosphorylation of vasodilator-stimulated phosphoprotein contributes to myocardial ischemic preconditioning.

Ischemic preconditioning (IP) is a well-known strategy to protect organs against cell death following ischemia. The previous work has shown that vasodilator-stimulated phosphoprotein (VASP) is involved in cytoskeletal reorganization and that it holds significant importance for the extent of myocardial ischemia reperfusion injury. Yet, the role of VASP during myocardial IP is, to date, not known. We report here that VASP phosphorylation at serine157 and serine239 is induced during hypoxia in vitro and during IP in vivo. The preconditioning-induced VASP phosphorylation inactivates the GP IIb/IIIa integrin receptor on platelets, which results in the reduced formation of organ compromising platelet neutrophil complexes. Experiments in chimeric mice confirmed the importance of VASP phosphorylation during myocardial IP. When studying this in VASP-/- animals and in an isolated heart model, we were able to confirm the important role of VASP on myocardial IP. In conclusion, we were able to show that IP-induced VASP phosphorylation in platelets is a protective mechanism against the deleterious effects of ischemia.

Gαi2- and Gαi3-deficient mice display opposite severity of myocardial ischemia reperfusion injury.

G-protein-coupled receptors (GPCRs) are the most abundant receptors in the heart and therefore are common targets for cardiovascular therapeutics. The activated GPCRs transduce their signals via heterotrimeric G-proteins. The four major families of G-proteins identified so far are specified through their α-subunit: Gαi, Gαs, Gαq and G12/13. Gαi-proteins have been reported to protect hearts from ischemia reperfusion injury. However, determining the individual impact of Gαi2 or Gαi3 on myocardial ischemia injury has not been clarified yet. Here, we first investigated expression of Gαi2 and Gαi3 on transcriptional level by quantitative PCR and on protein level by immunoblot analysis as well as by immunofluorescence in cardiac tissues of wild-type, Gαi2-, and Gαi3-deficient mice. Gαi2 was expressed at higher levels than Gαi3 in murine hearts, and irrespective of the isoform being knocked out we observed an up regulation of the remaining Gαi-protein. Myocardial ischemia promptly regulated cardiac mRNA and with a slight delay protein levels of both Gαi2 and Gαi3, indicating important roles for both Gαi isoforms. Furthermore, ischemia reperfusion injury in Gαi2- and Gαi3-deficient mice exhibited opposite outcomes. Whereas the absence of Gαi2 significantly increased the infarct size in the heart, the absence of Gαi3 or the concomitant upregulation of Gαi2 dramatically reduced cardiac infarction. In conclusion, we demonstrate for the first time that the genetic ablation of Gαi proteins has protective or deleterious effects on cardiac ischemia reperfusion injury depending on the isoform being absent.

The uncoordinated-5 homolog B (UNC5B) receptor increases myocardial ischemia-reperfusion injury.

The UNC5 receptor family are chemorepulsive neuronal guidance receptors with additional functions outside the central nervous system. Previous studies have implicated that the UNC5B receptor influences the migration of leukocytes into sites of tissue inflammation. Given that this process is a critical step during the pathophysiology of myocardial ischemia followed by reperfusion (IR) we investigated the role of UNC5B during myocardial IR. In initial in-vitro experiments, the functional inhibition of UNC5B resulted in a significant reduction of chemotactic migration of neutrophils. In-vivo, using a model of acute myocardial ischemia in UNC5B(+/-) and wild type (WT) animals, we found a significant reduction of infarct sizes in UNC5B(+/-) animals. This was associated with significantly reduced levels of troponin-I and IL-6 in UNC5B(+/-) mice. The repression of UNC5B using siRNA and the functional inhibition of UNC5B significantly dampened the extent of myocardial IR injury. Following depletion of neutrophils, we were not able to observe any further reduction in infarct size through functional inhibition of UNC5B in WT and UNC5B(+/-) mice. In summary our studies demonstrate an important role for UNC5B during myocardial IR injury, and that UNC5B might be a potential therapeutic target to control reperfusion injury in the future.

Repression of the equilibrative nucleoside transporters dampens inflammatory lung injury.

Acute lung injury (ALI) is a devastating disorder of the lung that is characterized by hypoxemia, overwhelming pulmonary inflammation, and a high mortality in the critically ill. Adenosine has been implicated as an anti-inflammatory signaling molecule, and previous studies showed that extracellular adenosine concentrations are increased in inflamed tissues. Adenosine signaling is terminated by the uptake of adenosine from the extracellular into the intracellular compartment via equilibrative nucleoside transporters (ENTs). However, their role in controlling adenosine signaling during pulmonary inflammation remains unknown. After inflammatory in vitro experiments, we observed a repression of ENT1 and ENT2 that was associated with an attenuation of extracellular adenosine uptake. Experiments using short, interfering RNA silencing confirmed a significant contribution of ENT repression in elevating extracellular adenosine concentrations during inflammation. Furthermore, an examination of the ENT2 promoter implicated NF-κB as a key regulator for the observed ENT repression. Additional in vivo experiments using a murine model of inflammatory lung injury showed that the pharmacological inhibition of ENT1 and ENT2 resulted in improved pulmonary barrier function and reduced signs of acute inflammation of the lung. Whereas experiments on Ent1(-/-) or Ent2(-/-) mice revealed lung protection in LPS-induced lung injury, an examination of bone marrow chimeras for ENTs pointed to the nonhematopoetic expression of ENTs as the underlying cause of dampened pulmonary inflammation during ALI. Taken together, these findings reveal the transcriptional repression of ENTs as an innate protective response during acute pulmonary inflammation. The inhibition of ENTs could be pursued as a therapeutic option to ameliorate inflammatory lung injury.