AMD and the alternative complement pathway: genetics and functional implications

Age-related macular degeneration (AMD) is an ocular neurodegenerative disorder and is the leading cause of legal blindness in Western societies, with a prevalence of up to 8 % over the age of 60, which continues to increase with age. AMD is characterized by the progressive breakdown of the macula (the central region of the retina), resulting in the loss of central vision including visual acuity. While its molecular etiology remains unclear, advances in genetics and genomics have illuminated the genetic architecture of the disease and have generated attractive pathomechanistic hypotheses. Here, we review the genetic architecture of AMD, considering the contribution of both common and rare alleles to susceptibility, and we explore the possible mechanistic links between photoreceptor degeneration and the alternative complement pathway, a cascade that has emerged as the most potent genetic driver of this disorder.     

Effects of myeloid differentiation primary response gene 88 (MyD88) activation on Helicobacter infection in vivo and induction of a Th17 response

Background:  Helicobacter pylori is a spiral‐shaped Gram‐negative microaerophilic bacterium associated with a number of gastrointestinal disorders, including gastritis, peptic ulcers, and gastric cancer. Several studies have implicated a Th17 response as a key to protective immunity against Helicobacter. Materials and Methods:  Wild type (WT) and MyD88‐deficient (MyD88^?/?) mice in the C57BL/6 background were infected with H. felis for 6 and 25 weeks and colonization density and host response evaluated. Real‐time PCR was used to determine the expression of cytokines and antimicrobial peptides in the gastric tissue of mice. Results:  mRNA expression levels of the Th17 cytokines interleukin‐17A (IL‐17A) and IL‐22 were markedly up‐regulated in WT compared with MyD88^?/? mice both at 6 and at 25 weeks in response to infection with H. felis, indicating that induction of Th17 responses depends on MyD88 signaling. Furthermore, reduction in the expression of Th17‐dependent intestinal antimicrobial peptide lipocalin‐2 was linked with increased bacterial burden in the absence of MyD88 signaling. Conclusion:  We provide evidence showing that MyD88‐dependent signaling is required for the host to induce a Th17 response for the control of Helicobacter infection.     

The t-SNARE Complex: A Close Up

The SNARE proteins, syntaxin, SNAP-25, and synaptobrevin have long been known to provide the driving force for vesicle fusion in the process of regulated exocytosis. Of particular interest is the initial interaction between SNAP-25 and syntaxin to form the t-SNARE heterodimer, an acceptor for subsequent synaptobrevin engagement. In vitro studies have revealed at least two different dynamic conformations of t-SNARE heterodimer defined by the degree of association of the C-terminal SNARE motif of SNAP-25 with syntaxin. At the plasma membrane, these proteins are organized into dense clusters of 50–60 nm in diameter. More recently, the t-SNARE interaction within these clusters was investigated in live cells at the molecular level, estimating each cluster to contain 35–70 t-SNARE molecules. This work reported the presence of both partially and fully zippered t-SNARE complex at the plasma membrane in agreement with the earlier in vitro findings. It also revealed a spatial segregation into distinct clusters containing predominantly one conformation apparently patterned by the surrounding lipid environment. The reason for this dynamic t-SNARE complex in exocytosis is uncertain; however, it does take us one step closer to understand the complex sequence of events leading to vesicle fusion, emphasizing the role of both membrane proteins and lipids.     

Patterns of Weight Change Associated With Long-Term Weight Change and Cardiovascular Disease Risk Factors in the Look AHEAD Study

This article provides an assessment of the associations that weight-loss patterns during the first year of an intensive lifestyle intervention have with 4-year maintenance and health outcomes. Two components described patterns of weight change during the first year of intervention: one reflected the typical pattern of weight loss over the 12 months, but distinguished those who lost larger amounts across the monthly intervals from those who lost less. The second component reflected the weight change trajectory, and distinguished a pattern of initial weight loss followed by regain vs. a more sustained pattern of weight loss. Two thousand four hundred and thirty eight individuals aged 45-76 years with type 2 diabetes mellitus, who enrolled in the weight-loss intervention of a randomized clinical trial, were assigned scores according to how their weight losses reflected these patterns. Relationships these scores had with weight losses and health outcomes (glycosolated hemoglobin-hemoglobin A1c (HbA1c); systolic blood pressure, high-density lipoprotein (HDL)-cholesterol, and triglycerides) over 4 years were described. When compared to those with lower scores on the two components, both individuals who had larger month-to-month weight losses in year 1 and whose weight loss was more sustained during the first year had better maintenance of weight loss over 4 years, independent of characteristics traditionally linked to weight loss success (P < 0.001). While relationships with year 4 weight loss were stronger, the pattern of larger monthly weight loss during year 1 was also independently predictive of year 4 levels of HbA1c, HDL-cholesterol, and systolic blood pressure.     

Aspergillus fumigatus chsE: A Gene Related to CHS3 of Saccharomyces cerevisiae and Important for Hyphal Growth and Conidiophore Development but Not Pathogenicity

The Aspergillus fumigatus chsE (AfchsE) gene was isolated from an A. fumigatus DNA library on the basis of hybridization to a segment of Saccharomyces cerevisiae CHS3 (ScCHS3). The amino acid sequence derived from AfchsE is 28% identical with ScCHS3 and 80% identical with the product of Aspergillus nidulans chsD (AnchsD). A mutant strain constructed by disruption of AfchsE has reduced levels of mycelial chitin, periodic swellings along the length of hyphae, and a block in conidiation that can be partially restored by growth in osmotic stabilizer. This phenotype is different from that reported for an AnchsD mutant, in which germinating conidia and hyphal tips undergo lysis and the colonial growth rate is significantly reduced. Despite the defects associated with the AfchsE- strain, its virulence was not significantly reduced when compared with the wild-type parental strain in a mouse model of pulmonary aspergillosis.     

Helicobacter hepaticus HHGI1 is a pathogenicity island associated with typhlocolitis in B6.129-IL10 tm1Cgn mice

Helicobacter hepaticus strain 3B1 (H. hepaticus) contains a genomic island of approximately 71 kb, HHGI1, with some of the common features shared among known bacterial pathogenicity islands. In this study, we characterized the pathogenic potential of HHGI1 by infecting B6.129-IL10 tm1Cgn (IL10-/-) mice with an isogenic mutant (namely HhPAId1) lacking 19 predicted genes within HHGI1. In contrast to H. hepaticus (P<0.001), HhPAId1 did not cause typhlocolitis and hyperplasia in IL10-/- mice. Colonization levels of HhPAId1 were significantly higher in the cecum (P<0.007) and similar in the colon (P=0.27) when compared to H. hepaticus by 13 or 16 weeks post inoculation (WPI). The magnitude of the Th1-associated IgG2c response against HhPAId1 was less than that against H. hepaticus (P<0.004). There was no significant difference in Th2-associated IgG1 responses against these two strains. Cecal and colonic mRNA levels of proinflammatory cytokines IFN-gamma, TNF-alpha and IL-17a in the HhPAId1-infected mice were significantly lower than those in the H. hepaticus-infected mice (P<0.05) at 13 WPI. These results demonstrate that genes in the HHGI1 contribute to the pathogenicity of H. hepaticus, at least in part via up-regulation of proinflammatory mediators IFN-gamma, TNF-alpha and IL-17a.     

Apc tumor suppressor gene is the "zonation-keeper" of mouse liver

The molecular mechanisms by which liver genes are differentially expressed along a portocentral axis, allowing for metabolic zonation, are poorly understood. We provide here compelling evidence that the Wnt/beta-catenin pathway plays a key role in liver zonation. First, we show the complementary localization of activated beta-catenin in the perivenous area and the negative regulator Apc in periportal hepatocytes. We then analyzed the immediate consequences of either a liver-inducible Apc disruption or a blockade of Wnt signaling after infection with an adenovirus encoding Dkk1, and we show that Wnt/beta-catenin signaling inversely controls the perivenous and periportal genetic programs. Finally, we show that genes involved in the periportal urea cycle and the perivenous glutamine synthesis systems are critical targets of beta-catenin signaling, and that perturbations to ammonia metabolism are likely responsible for the death of mice with liver-targeted Apc loss. From our results, we propose that Apc is the liver "zonation-keeper" gene.     

Simultaneous multi-spectral,single-photon fluorescence imaging using a plasmonic colour filter array

We present the first realisation of simultaneous multi-spectral fluorescence imaging using a single-photon avalanche diode (SPAD) array, where the spectral unmixing is facilitated by a plasmonic metasurface mosaic colour filter array (CFA). A 64 × 64 pixel format silicon SPAD array is used to record widefield fluorescence and brightfield data from four biological samples. A plasmonic metasurface composed of an arrangement of circular and elliptical nanoholes etched into an aluminium thin film deposited on a glass substrate provides the high transmission efficiency CFA, enabling a bespoke spectral unmixing algorithm to reconstruct high fidelity, full colour images from as few as ∼3 photons per pixel. This approach points the way toward real-time, single-photon sensitive multi-spectral fluorescence imaging. Furthermore, this is possible without additional bulky components such as a filter wheel, prism or diffraction grating, nor the need for multiple sample exposures or multiple detectors.