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.

Abstract 380: PDI and ERp57 Localization in Platelets Is Regulated by Actin Polymerization

Introduction: PDI and ERp57 are members of the thiol isomerase family of enzymes that are released to the platelet surface where they contribute to a range of platelet responses. PDI has been reported to be present in subcellular structures in resting platelets, although it is excluded from α - and δ -granules, and lysosomes. It was, however, recently shown to co-localise with TLR9 in T-granules, intracellular bodies underlying the plasma membrane. The subcellular localisation of other platelet thiol isomerases or their mechanisms of translocation to the cell surface have not been established.

Hypothesis and Methods: Using spinning disk confocal microscopy we sought to explore whether platelet thiol isomerases ERp57 and PDI are co-localised in resting and activated platelets and to test the hypothesis that translocation of thiol isomerases to the platelet surface is dependent on actin polymerization.

Results and Conclusions: In resting platelets, PDI and ERp57 were organized in punctate structures both on the platelet surface and in the cytoplasm. They did not colocalise with P-selectin consistent with them residing outside α -granules. In contrast to expectations, TLR9 did not colocalize with PDI and ERp57, suggesting their exclusion from T-granules. Partial colocalization was observed in resting platelets between PDI and ERp57 in granule-like structures. Upon platelet activation, this degree of co-distribution persisted with PDI and ERp57 migrating to the platelet surface. Latrunculin A, an inhibitor of actin polymerization, decreased P-selectin exposure on the platelet surface, as measured by flow cytometry, and agonist-stimulated platelets treated with this agent retained a rounded shape, as shown by tubulin staining. Importantly, latrunculin A also blocked the translocation of PDI and ERp57 from internal granule-like structures to the platelet surface. We conclude that in resting platelets PDI and ERp57 are organized, and partially co-localised, in punctuate structures unlikely to represent α- or T-granules. The polymerization of actin during platelet activation exerts a fundamental role in the relocalization of PDI and ERp57 from these cytoplasmic structures to the platelet surface.

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.

Endoscopic-assisted adenoidectomy

Adenoidectomy is a commonly performed procedure. The advent of endoscopic sinus surgery has popularized the use of endoscopes. Endoscopic-assisted adenoidectomy (EAA) is a natural progression of this technology to allow a more complete adenoidectomy. Two hundred thirty-six patients undergoing adenoidectomy were evaluated with an endoscopic technique. A routine transoral adenoidectomy was performed first. Then a 4-mm 0 degrees telescope was used transnasally, and residual adenoid tissue was removed from the anterior superior nasopharynx. Invariably, residual adenoid tissue was found after transoral adenoidectomy. The EAA technique is minimally invasive, adds less than 5 minutes to the procedure, and is not associated with excessive bleeding. Readily available telescope and endoscopic equipment is used. The EAA technique is advocated for use as an adjunct to a more complete adenoidectomy.

Going digital: image preparation for biomedical publishing

Authors are more often being held responsible for readying their own data figures for digital publication by scanning them at the proper resolution and preparing them for presentation in both print and on-line journals. In this manner, the visuals can be printed at the highest quality the publisher can provide and be ready for rapid electronic distribution on the Internet. Therefore, authors must become knowledgeable in the visual preparation process in order to generate electronic images that will be as true a representation of the original image as possible. Perfecting this procedure can be a learning experience and often requires some experimentation. When accomplished, the author will have more control of exactly how the images will look before they are published. In addition to the scan resolution, the type of digital scanner and software applications used are very important, and instruction manuals should be followed closely so as to understand the full potential of the digitizing equipment. Anat Rec (New Anat): 257:128-136, 1999.

Double outlet right ventricle in a cat

In a case of double outlet right ventricle in a cat, initial examination revealed a holosystolic murmur and right-sided heart enlargement, as deduced from electrocardiography and thoracic radiography. On cardiac catheterization, it was determined that pressure in the right ventricle equaled that of the left ventricle. Angiography revealed a large ventricular septal defect, with prodominant left-to-right shunt and some right-to-left component. The cat lived for 3 1/2 years. During this period, the cat would become cyanotic only under stressful situations. At necropsy, the diagnosis was further refined to that of a double outlet right ventricle, as both the aorta and pulmonary artery originated from the right ventricle.