HIG1, a novel regulator of mitochondrial γ-secretase, maintains normal mitochondrial function.

The γ-secretase complex (which contains presenilins, nicastrin, anterior pharynx defective-1, and presenilin enhancer-2) cleaves type I transmembrane proteins, including Notch and amyloid precursor protein. Dysregulated γ-secretase activity has been implicated in the pathogenesis of Alzheimer's disease, stroke, atherosclerosis, and cancer. Tight regulation of γ-secretase activity is required for normal physiology. Here, we isolated HIG1 (hypoxia inducible gene 1, domain member 1A) from a functional screen of γ-secretase inhibitory genes. HIG1 was highly expressed in the brain. Interestingly, HIG1 was localized to the mitochondria and was directly bound to γ-secretase components on the mitochondrial membrane in SK-N-SH neuroblastoma cells. Overexpresssion of HIG1 attenuated hypoxia-induced γ-secretase activation on the mitochondrial membrane and the accumulation of intracellular amyloid ß. This accumulation was accompanied by hypoxia-induced mitochondrial dysfunction. The latter half domain of HIG1 was required for binding to the γ-secretase complex and suppression of γ-secretase activity. Moreover, depletion of HIG1 increased γ-secretase activation and enhanced hypoxia-induced mitochondrial dysfunction. In summary, HIG1 is a novel modulator of the mitochondrial γ-secretase complex, and may play a role in the maintenance of normal mitochondrial function.

Assembly mechanism of FCT region type 1 pili in serotype M6 Streptococcus pyogenes.

The human pathogen Streptococcus pyogenes produces diverse pili depending on the serotype. We investigated the assembly mechanism of FCT type 1 pili in a serotype M6 strain. The pili were found to be assembled from two precursor proteins, the backbone protein T6 and ancillary protein FctX, and anchored to the cell wall in a manner that requires both a housekeeping sortase enzyme (SrtA) and pilus-associated sortase enzyme (SrtB). SrtB is primarily required for efficient formation of the T6 and FctX complex and subsequent polymerization of T6, whereas proper anchoring of the pili to the cell wall is mainly mediated by SrtA. Because motifs essential for polymerization of pilus backbone proteins in other Gram-positive bacteria are not present in T6, we sought to identify the functional residues involved in this process. Our results showed that T6 encompasses the novel VAKS pilin motif conserved in streptococcal T6 homologues and that the lysine residue (Lys-175) within the motif and cell wall sorting signal of T6 are prerequisites for isopeptide linkage of T6 molecules. Because Lys-175 and the cell wall sorting signal of FctX are indispensable for substantial incorporation of FctX into the T6 pilus shaft, FctX is suggested to be located at the pilus tip, which was also implied by immunogold electron microscopy findings. Thus, the elaborate assembly of FCT type 1 pili is potentially organized by sortase-mediated cross-linking between sorting signals and the amino group of Lys-175 positioned in the VAKS motif of T6, thereby displaying T6 and FctX in a temporospatial manner.

Pili of oral Streptococcus sanguinis bind to salivary amylase and promote the biofilm formation.

Streptococcus sanguinis is a member of oral streptococci and one of the most abundant species found in oral biofilm called dental plaque. Colonization of the oral streptococci on the tooth surface depends on the adhesion of bacteria to salivary components adsorbed to the tooth surface. Recently, we identified unique cell surface long filamentous structures named pili in this species. Herein, we investigated the role of S. sanguinis pili in biofilm formation. We found that pili-deficient mutant, in which the genes encoding the three pilus proteins PilA, PilB and PilC have been deleted, showed an impaired bacterial accumulation on saliva-coated surfaces. Confocal microscopic observations suggested that the mutant was incapable of producing typical three-dimensional layer of biofilm. Ligand blot analysis showed that the ancillary pilus proteins PilB and PilC bound to human whole saliva. Additional analysis demonstrated that PilC bound to multiple salivary components, and one of which was found to be salivary α-amylase. These results indicate that pilus proteins are members of saliva-binding proteins of oral S. sanguinis, and suggest the involvement of pili in its colonization on saliva-coated tooth surfaces and in the human oral cavity.

Inefficient phagosome maturation in infant macrophages.

The quantitative and qualitative differences between the immune systems of infants and adults have been extensively investigated in the context of adaptive immunity. Here, we demonstrate that the infantile innate immune system is immature and weak against bacterial infections. Upon infection by Escherichia coli, macrophages from infantile mice showed a lower performance in killing the bacteria. In infant macrophages, bacteria were taken up relatively normally and delivered into lysosomal compartments, but not efficiently digested. The inefficient bacterial killing in infant macrophages was correlated with impaired acidification of the lysosomal compartments and reduced lysosomal recruitment of Rab7, an essential component of the acidification process. The acidification defect was not intrinsic to the cells, and was rescued by pretreatment with interferon-gamma. Thus, we propose that the limited capacity of phagosome maturation is one of the major causes of the high sensitivity to infectious microorganisms during infancy and that the specific cytokine milieu shapes the nature of infantile innate immunity.

CAPS1 RNA Editing Promotes Dense Core Vesicle Exocytosis.

Calcium-dependent activator protein for secretion 1 (CAPS1) plays a distinct role in the priming step of dense core vesicle (DCV) exocytosis. CAPS1 pre-mRNA is known to undergo adenosine-to-inosine RNA editing in its coding region, which results in a glutamate-to-glycine conversion at a site in its C-terminal region. However, the physiological significance of CAPS1 RNA editing remains elusive. Here, we created mutant mice in which edited CAPS1 was solely expressed. These mice were lean due to increased energy expenditure caused by physical hyperactivity. Electrophysiological and biochemical analyses demonstrated that the exocytosis of DCVs was upregulated in the chromaffin cells and neurons of these mice. Furthermore, we showed that edited CAPS1 bound preferentially to the activated form of syntaxin-1A, a component of the exocytotic fusion complex. These findings suggest that RNA editing regulates DCV exocytosis in vivo, affecting physical activity.

A Development of Nucleic Chromatin Measurements as a New Prognostic Marker for Severe Chronic Heart Failure.

BACKGROUND: Accurate prediction of both mortality and morbidity is of significant importance, but it is challenging in patients with severe heart failure. It is especially difficult to detect the optimal time for implanting mechanical circulatory support devices in such patients. We aimed to analyze the morphometric ultrastructure of nuclear chromatin in cardiomyocytes by developing an original clinical histopathological method. Using this method, we developed a biomarker to predict poor outcome in patients with dilated cardiomyopathy (DCM). METHODS AND RESULTS: As a part of their diagnostic evaluation, 171 patients underwent endomyocardial biopsy (EMB). Of these, 63 patients diagnosed with DCM were included in this study. We used electron microscopic imaging of cardiomyocyte nuclei and an automated image analysis software program to assess whether it was possible to detect discontinuity of the nuclear periphery. Twelve months after EMB, all patients with a discontinuous nuclear periphery (Group A, n = 11) died from heart failure or underwent left ventricular assist device (VAD) implantation. In contrast, in patients with a continuous nuclear periphery (Group N, n = 52) only 7 patients (13%) underwent VAD implantation and there were no deaths (p<0.01). We then evaluated chromatin particle density (Nuc-CS) and chromatin thickness in the nuclear periphery (Per-CS) in Group N patients; these new parameters were able to identify patients with poor prognosis. CONCLUSIONS: We developed novel morphometric methods based on cardiomyocyte nuclear chromatin that may provide pivotal information for early prediction of poor prognosis in patients with DCM.

High-efficacy site-directed drug delivery system using sialyl-Lewis X conjugated liposome.

The aim of this study was to evaluate the new developed sialyl-Lewis X conjugated liposome (sLe XL) as a site-directed delivery system to activated endothelial cells in vivo using a murine experimental autoimmune uveoretinitis (EAU) model. Four types of nanoparticles were prepared using this liposome: fluorescein isothiocyanate (FITC) labeled sLe XL (F-sLe XL) and its vehicle (F-L), sLe XL containing dexamethasone (d-sLe XL) and liposome without sLe X containing dexamethasone (d-L). First, after a bolus injection of F-sLe XL or F-L into EAU mice, sequential tissue accumulation of FITC was examined by confocal laser scanning microscopy. Second, anti-E-selectin antibody, as a blocking antibody, was given intravenously to EAU mice prior to the injection of F-sLe XL in order to investigate the effect of the antibody on inhibition of the accumulation of F-sLe XL. Third, concentration of dexamethasone in several organs after the injection of d-sLe XL (total dexamethasone 2 microg) or free dexamethasone solution (1mg) was measured by radioimmunoassay. Accumulation of FITC was only observed in F-sLe XL treated EAU mice. F-sLe XL accumulated on the activated endothelial cells within 5 min; accumulation then was inhibited using anti-E-selectin antibody. The FITC color was dispersed sequentially to the entire retina. d-sLe XL showed selective targeting to the inflamed eye, where an approximately two-fold higher dexamethasone concentration was achieved compared with 1mg free dexamethasone. sLe XL can be a highly efficacious site-directed system in vivo. Using sLe XL as a vehicle for drug delivery, substantial pharmacologic effects with minimum side effects in inflammatory diseases should be achieved.