Beat-by-Beat Cardiomyocyte T-Tubule Deformation Drives Tubular Content Exchange

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The sarcolemma of cardiomyocytes contains many proteins that are essential for electromechanical function in general, and excitation-contraction coupling in particular. The distribution of these proteins is nonuniform between the bulk sarcolemmal surface and membrane invaginations known as transverse tubules (TT). TT form an intricate network of fluid-filled conduits that support electromechanical synchronicity within cardiomyocytes. Although continuous with the extracellular space, the narrow lumen and the tortuous structure of TT can form domains of restricted diffusion. As a result of unequal ion fluxes across cell surface and TT membranes, limited diffusion may generate ion gradients within TT, especially deep within the TT network and at high pacing rates.

Advanced pathological study for definite diagnosis of mitochondrial cardiomyopathy

AIMS

Mitochondrial cardiomyopathy (MCM) is difficult to make a definite diagnosis because of various cardiovascular phenotypes and no diagnostic criteria in the pathology examination. We aim to add myocardial pathology to the diagnostic criteria for mitochondrial respiratory chain disorders.

METHODS

Quantitative analysis of mitochondria using electron microscopy and immunohistopathological analysis with respiratory chain enzyme antibodies were performed in 11 patients with hypertrophic or restrictive cardiomyopathy who underwent endomyocardial biopsy for possible MCM . Respiratory chain enzymatic assay in biopsied myocardium and genetic studies were also performed in all the subjects to define MCM.

RESULTS

Four patients were diagnosed with MCM according to the recent criteria of mitochondrial respiratory chain disorders. Using electron microscopy with quantitative analysis, the volume density of mitochondria within cardiac muscle cells was significantly increased in the MCM group compared with the non-MCM group (p=0.007). Immunohistopathological results were compatible with the result of the respiratory chain enzymatic assay.

CONCLUSIONS

Pathological diagnosis of MCM could be confirmed by a quantitative study of electron microscopy and immunohistopathological analysis using the mitochondrial respiratory chain enzyme subunit antibody.

Association of PTP4A3 expression and tumour size in functioning pituitary adenoma: a descriptive study

BACKGROUND

PTP4A3 is a subclass of a protein tyrosine phosphatase super family and is expressed in a range of epithelial neoplasms. We evaluated PTP4A3 expression and its association with clinicopathological parameters in different types of functioning pituitary adenomas.

METHODS

A total of 34 functioning pituitary adenomas samples were evaluated in this observational study. PTP4A3 expression was examined by immunohistochemical staining, and, possible correlations between PTP4A3 and some clinicopathological variables were investigated.

RESULTS

PTP4A3 was expressed in 19 out of 34 tumours (55%), at the cytoplasmic level of tumorous cells. Moreover, there was significant association (p=0.042) between PTP4A3 expression and tumorous size.

CONCLUSIONS

PTP4A3 was expressed in more than half of the tumours analysed, with there being a significant association with the tumorous size of functioning adenomas. This allows to speculate that PTP4A3 may regulate tumour growth, although further investigations are necessary to determine if this phosphatase can serve as a biomarker or used as a therapeutic target in pituitary macroadenomas.

[New inhibitors targeting bacterial RNA polymerase]

Rifamycins, a group of bacterial RNA polymerase inhibitors, are the firstline antimicrobial drugs to treat tuberculosis. In light of the emergence of rifamycinresistant bacteria, development of new RNA polymerase inhibitors that kill rifamycinresistant bacteria with high bioavailability is urgent. Structural analysis of bacterial RNA polymerase in complex with inhibitors by crystallography and cryo-EM indicates that RNA polymerase inhibitors function through five distinct molecular mechanisms:inhibition of the extension of short RNA; competition with substrates; inhibition of the conformational change of the'bridge helix'; inhibition of clamp opening;inhibition of clamp closure. This article reviews the research progress of these five groups of RNA polymerase inhibitors to provide references for the modification of existing RNA polymerase inhibitors and the discovery of new RNA polymerase inhibitors.

[Single-particle cryo-electron microscopy opens new avenues in structural biology of G protein-coupled receptor]

G protein-coupled receptors(GPCRs)represent the largest class of cell surface receptors,mediating wide range of cellular and physiological processes through their transducers,G proteins and the-arrestins participate in almost all pathological processes. Recent technological advances are revolutionizing the utility of cryo-electron microscopy(cryo-EM),leading to a tremendous progress in the structural studies of biological macromolecules and cryo-EM has played a leading role in the structural biology of GPCR signaling complex. New discoveries of high-resolution threedimensional structures of GPCR signaling complexes based on cryo-EM have emerged vigorously,which depict the common structural characteristics of intermolecular interaction between GPCR and G protein complex-the conformational changes of the transmembrane helix 6 of receptors,and also demonstrate the structural basis of G protein subtype selectivity. Single-particle cryo-EM becomes an efficient tool for identifying the molecular mechanism of receptor-ligand interaction,providing important information for understanding GPCR signaling and the structure-based drug design.

Intramedullary clear cell ependymoma in the thoracic spinal cord: a case with its crush smear and ultrastructural findings

Clear cell ependymoma was included in the World Health Organization classification of the nervous system in 1993, and all the reported cases, except for two in the spinal cord, were located in the brain, mainly in the supratentorial compartment. Astrocytomas outnumber ependymomas in the spinal cord, and the two entities partly share cytologic findings such as long, bipolar glial processes and oval to round nuclei resembling those seen in pilocytic astrocytoma. Here, we report the first Korean case of intramedullary clear cell ependymoma of the spinal cord, which is the third case situated in the spinal cord in the literature. The crush smear revealed round-to-oval nuclei with occasional nuclear eosinophilic inclusion and rare nuclear grooves. Cytoplasm had fluffy eosinophilic glial processes, and acellular fibrillary zone. On hematoxylin-eosin stain, oval to round tumor cells had large central nuclei with indistinct nucleoli and a moderate amount of clear cytoplasm, i.e. perinuclear halo, mimicking oligodendroglioma. Perivascular pseudorosettes and ependymal clefts were rarely found. In retrospect, perinuclear halo was absent on crush smears. Ultrastructurally, they had extensive surface microvilli and edematous cytoplasm filled with abundant glial filaments and microlumens with or without microvilli. Intercellular long cell junctions of the zipper-like zonula adherens type were found.

Evidence for cyclooxygenase-2 association with caveolin-3 in primary cultured rat chondrocytes

The purpose of this study was to demonstrate the cellular localization of cyclooxygenase-2 (COX-2) and caveolin-3 (Cav-3) in primarily cultured rat chondrocytes. In normal rat chondrocytes, we observed relatively high levels of Cav-3 and a very low level of COX-2 mRNA and protein. Upon treating the chondrocytes with 5 microM of CdCl(2) (Cd) for 6 hr, the expressions of COX-2 mRNA and protein were increased with the decreased Cav-3 mRNA and protein expressions. The detergent insoluble caveolae-rich membranous fractions that were isolated from the rat chondrocytes and treated with Cd contained the both proteins of both COX-2 and Cav-3 in a same fraction. The immuno-precipitation experiments showed complex formation between the COX-2 and Cav-3 in the rat chondrocytes. Purified COX-2 with glutathione S-transferase-fused COX-2 also showed complex formation with Cav-3. Confocal and electron microscopy also demonstrated the co-localization of COX-2 and Cav-3 in the plasma membrane. The results from our current study show that COX-2 and Cav-3 are co-localized in the caveolae of the plasma membrane, and they form a protein-protein complex. The co-localization of COX-2 with Cav-3 in the caveolae suggests that the caveolins might play an important role for regulating the function of COX-2.

Ultrastructural studies of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the gastrointestinal tract (GIT). Although interstitial cells of Cajal has been suggested as origin of this tumor, the cytological and ultrastructural features of GISTs are heterogeneous and unclear. A total 10 cases of normal gastrointestinal tissue (control), 13 GISTs of the stomach (8), small intestine (3), mesocolon (1) and liver (1), and 2 gastrointestinal autonomic nervous tumor (GANT) of small intestine were ultrastructurally studied. Normal interstitial cells of Cajal (ICC) were abundantly present around the myenteric plexuses or individually scattered through the wall of GIT. ICC was characterized by slender cytoplasmic processes, well-developed endoplasmic reticulum (ER), mitochondria, Golgi apparatus, caveolae and intermediate filaments. The GISTs and GANTs had overlapping ultrastructures. The most common and important ultrastructural features of GISTs were rich villous cytoplasmic processes, dispersed intermediate filaments and abundant SER, and those of GANTs were neurosecretory granules and skenoid fibers. Compared with ICC, the GISTs and GANTs had remarkably reduced caveolae and gap junctions. Our study suggested that ultrastructural analysis gives much information to investigate lineage differentiation of neoplastic cells and make a differential diagnosis of these tumors from other mesenchymal tumors and between GISTs and GANTs.

Effects of tachyplesin on the morphology and ultrastructure of human gastric carcinoma cell line BGC-823

AIM: To investigate the morphological and ultrastructural changes in the human gastric carcinoma cell line BGC-823 after being treated with tachyplesin.

METHODS: Tachyplesin was isolated from acid extracts of Chinese horseshoe crab (Tachypleus tridentatus) hemocytes. BGC-823 cells and the cells treated with 2.0 mg/L tachyplesin were examined respectively under light microscope, scanning and transmission electron microscope.

RESULTS: BGC-823 cells had undergone the restorational alteration in morphology and ultrastructure after tachyplesin treatment. The changes were as follows: the shape of cells was unanimous, the volume enlarged and cells turned to be flat and spread, the nucleo-cytoplasmic ratio lessened and nuclear shape became rather regular, the number of nucleolus reduced and its volume lessened, heter-chromatin decreased while euchromatin increased in nucleus. In the cytoplasm, mitochondria grew in number with consistent structure relatively, Golgi complex turned to be typical and well-developed, rough endoplasmic reticulum increased and polyribosome decreased. The microvilli at cellular surface were rare and the filopodia reduced while lamellipodia increased at the cell edge.

CONCLUSION: Tachyplesin could alter the malignant morphological and ultrastructural characteristics of human gastric carcinoma cells effectively and have a certain inducing differen-tiation effect on human gastric carcinoma cells.