Intracellular Trafficking, Localization, and Mobilization of Platelet-Borne Thiol Isomerases.

OBJECTIVE: Thiol isomerases facilitate protein folding in the endoplasmic reticulum, and several of these enzymes, including protein disulfide isomerase and ERp57, are mobilized to the surface of activated platelets, where they influence platelet aggregation, blood coagulation, and thrombus formation. In this study, we examined the synthesis and trafficking of thiol isomerases in megakaryocytes, determined their subcellular localization in platelets, and identified the cellular events responsible for their movement to the platelet surface on activation. APPROACH AND RESULTS: Immunofluorescence microscopy imaging was used to localize protein disulfide isomerase and ERp57 in murine and human megakaryocytes at various developmental stages. Immunofluorescence microscopy and subcellular fractionation analysis were used to localize these proteins in platelets to a compartment distinct from known secretory vesicles that overlaps with an inner cell-surface membrane region defined by the endoplasmic/sarcoplasmic reticulum proteins calnexin and sarco/endoplasmic reticulum calcium ATPase 3. Immunofluorescence microscopy and flow cytometry were used to monitor thiol isomerase mobilization in activated platelets in the presence and absence of actin polymerization (inhibited by latrunculin) and in the presence or absence of membrane fusion mediated by Munc13-4 (absent in platelets from Unc13d(Jinx) mice). CONCLUSIONS: Platelet-borne thiol isomerases are trafficked independently of secretory granule contents in megakaryocytes and become concentrated in a subcellular compartment near the inner surface of the platelet outer membrane corresponding to the sarco/endoplasmic reticulum of these cells. Thiol isomerases are mobilized to the surface of activated platelets via a process that requires actin polymerization but not soluble N-ethylmaleimide-sensitive fusion protein attachment receptor/Munc13-4-dependent vesicular-plasma membrane fusion.

EphB2 regulates contact-dependent and contact-independent signaling to control platelet function.

The Eph kinases, EphA4 and EphB1, and their ligand, ephrinB1, have been previously reported to be present in platelets where they contribute to thrombus stability. Although thrombus formation allows for Eph-ephrin engagement and bidirectional signaling, the importance specifically of Eph kinase or ephrin signaling in regulating platelet function remained unidentified. In the present study, a genetic approach was used in mice to establish the contribution of signaling orchestrated by the cytoplasmic domain of EphB2 (a newly discovered Eph kinase in platelets) in platelet activation and thrombus formation. We conclude that EphB2 signaling is involved in the regulation of thrombus formation and clot retraction. Furthermore, the cytoplasmic tail of this Eph kinase regulates initial platelet activation in a contact-independent manner in the absence of Eph-ephrin ligation between platelets. Together, these data demonstrate that EphB2 signaling not only modulates platelet function within a thrombus but is also involved in the regulation of the function of isolated platelets in a contact-independent manner.

How do malaria parasites activate dendritic cells?

Evaluation of: Wu X, Gowda NM, Kumar S, Gowda S: Protein-DNA complex is the exclusive malaria parasite component that activates dendritic cells and triggers innate immune responses. J. Immunol. 184(8), 4338-4348 (2010). Malaria parasites induce strong proinflammatory immune responses upon infection. These responses, driven largely by CD4+ Th1 cells, help the body to control malaria parasitemia. When excessive, inflammatory responses contribute to the pathology observed in malaria infection. Dendritic cells (DCs) are innate immune cells that activate Th1 cells in malaria infection via the secretion of the cytokine IL-12. It remains unclear precisely which components of malaria-infected red blood cells are responsible for activating DCs. In this study, Wu et al. set out to deconstruct malaria-infected red blood cells to determine the immunogenic components that induce production of the proinflammatory cytokines IL-12 and TNF-alpha from DCs. The authors suggest that parasite DNA complexed with protein is the main trigger for activation of DCs in malaria-infected red blood cells.

Models of maternal-infant attachment: a role for nurses.

Two models of maternal-infant attachment, one related to full-term newborns (Goulet, Bell, St-Cyr Tribble, Paul, & Lang, 1998), and one including premature infants (Bialoskurski, Cox, & Hayes, 1999), are examined. The elements of both models are integrated into a more comprehensive model. Implicit organizational components are made explicit, and a discussion regarding the possibility of fit for the extremely low-birth-weight (ELBW) group is offered. This integrated model can serve as a basis for neonatal nurses to improve care for newly emerging families and especially those of the premature/low birth weight group.

Facial nerve in parotidectomy: a topographical analysis.

OBJECTIVE: Establish normative data concerning parotidectomy and facial nerve dissection and determine the relationship between the length of the facial nerve dissected during parotidectomy and subsequent facial nerve paresis. STUDY DESIGN: Prospective mapping of facial nerve during parotidectomy and comparison with postoperative facial nerve function. METHODS: A prospective observational study of 78 patients who underwent 79 parotidectomy procedures. During each procedure, various topographical measurements were recorded. These measurements included the distance from the tragal pointer to the main trunk of the facial nerve, the distance to the pes anserinus, and length of each segmental branch dissected. In addition, a designation of the patient's tumor location was made by drawing a line from the ear canal to the nasal spine. Tumors above this line were designated anatomic zone A and those below the line were designated anatomic zone B. Finally, facial nerve function was quantified at a 1-week follow-up visit using the House-Brackmann Scale. RESULTS: The distance from the main trunk of the facial nerve to the tragal pointer was significantly (P < .000) less than the previously accepted standard of 1 cm. The cervical and marginal mandibular branches had more nerve dissected, whereas the eye and forehead branches were the least dissected. Results of an independent t test and logistic regression (P = .01, both) indicated that patients with temporary facial nerve paresis had a significantly greater amount of nerve dissected than patients without temporary facial nerve paresis. Patients with short-term facial nerve dysfunction had significantly (P < .01) more total nerve dissected (136.73 mm vs. 94.73 mm) than patients without short-term facial nerve dysfunction. Patients with nerve dissection lengths at the third quartile (130.0 mm) were 3.8 times more likely to experience temporary facial nerve paresis than patients with nerve dissection lengths at the first quartile (64.5 mm). CONCLUSIONS: The axiom that the main trunk of the facial nerve is located 1 cm from the tragal pointer may need to be modified to less than 1 cm. The cervical and marginal mandibular branches had more nerve dissected, whereas the eye and forehead branches were the least dissected. Facial nerve paresis after parotidectomy is associated with the length of the facial nerve dissected during the procedure. The greater the length of facial nerve dissected, the higher the chance of facial nerve paresis, albeit temporarily, in this particular series of patients.