Amyloid-β Inhibits No-cGMP Signaling in a CD36- and CD47-Dependent Manner

Amyloid-β interacts with two cell surface receptors, CD36 and CD47, through which the matricellular protein thrombospondin-1 inhibits soluble guanylate cyclase activation. Here we examine whether amyloid-β shares this inhibitory activity. Amyloid-β inhibited both drug and nitric oxide-mediated activation of soluble guanylate cyclase in several cell types. Known cGMP-dependent functional responses to nitric oxide in platelets and vascular smooth muscle cells were correspondingly inhibited by amyloid-β. Functional interaction of amyloid-β with the scavenger receptor CD36 was indicated by inhibition of free fatty acid uptake via this receptor. Both soluble oligomer and fibrillar forms of amyloid-β were active. In contrast, amyloid-β did not compete with the known ligand SIRPα for binding to CD47. However, both receptors were necessary for amyloid-β to inhibit cGMP accumulation. These data suggest that amyloid-β interaction with CD36 induces a CD47-dependent signal that inhibits soluble guanylate cyclase activation. Combined with the pleiotropic effects of inhibiting free fatty acid transport via CD36, these data provides a molecular mechanism through which amyloid-β can contribute to the nitric oxide signaling deficiencies associated with Alzheimer's disease

Condensed Mitotic Chromosome Structure at Nanometer Resolution Using PALM and EGFP- Histones

Photoactivated localization microscopy (PALM) and related fluorescent biological imaging methods are capable of providing very high spatial resolutions (up to 20 nm). Two major demands limit its widespread use on biological samples: requirements for photoactivatable/photoconvertible fluorescent molecules, which are sometimes difficult to incorporate, and high background signals from autofluorescence or fluorophores in adjacent focal planes in three-dimensional imaging which reduces PALM resolution significantly. We present here a high-resolution PALM method utilizing conventional EGFP as the photoconvertible fluorophore, improved algorithms to deal with high levels of biological background noise, and apply this to imaging higher order chromatin structure. We found that the emission wavelength of EGFP is efficiently converted from green to red when exposed to blue light in the presence of reduced riboflavin. The photon yield of red-converted EGFP using riboflavin is comparable to other bright photoconvertible fluorescent proteins that allow <20 nm resolution. We further found that image pre-processing using a combination of denoising and deconvolution of the raw PALM images substantially improved the spatial resolution of the reconstruction from noisy images. Performing PALM on Drosophila mitotic chromosomes labeled with H2AvD-EGFP, a histone H2A variant, revealed filamentous components of ∼70 nm. This is the first observation of fine chromatin filaments specific for one histone variant at a resolution approximating that of conventional electron microscope images (10–30 nm). As demonstrated by modeling and experiments on a challenging specimen, the techniques described here facilitate super-resolution fluorescent imaging with common biological samples

Serotonergic chemosensory neurons modify the <i>C. elegans</i> immune response by regulating G-protein signaling in epithelial cells

The nervous and immune systems influence each other, allowing animals to rapidly protect themselves from changes in their internal and external environment. However, the complex nature of these systems in mammals makes it difficult to determine how neuronal signaling influences the immune response. Here we show that serotonin, synthesized in Caenorhabditis elegans chemosensory neurons, modulates the immune response. Serotonin released from these cells acts, directly or indirectly, to regulate G-protein signaling in epithelial cells. Signaling in these cells is required for the immune response to infection by the natural pathogen Microbacterium nematophilum. Here we show that serotonin signaling suppresses the innate immune response and limits the rate of pathogen clearance. We show that C. elegans uses classical neurotransmitters to alter the immune response. Serotonin released from sensory neurons may function to modify the immune system in response to changes in the animal's external environment such as the availability, or quality, of food

Load-dependent release limits the processive stepping of the tetrameric Eg5 motor

Tetrameric motor proteins of the Kinesin-5 family are essential for eukaryotic cell division. The microscopic mechanism by which Eg5, the vertebrate Kinesin-5, drives bipolar mitotic spindle formation remains unknown. Here we show in optical trapping experiments that full-length Eg5 moves processively and stepwise along microtubule bundles. Interestingly, the force produced by individual Eg5 motors typically reached only ∼2 pN, one-third of the stall force of Kinesin-1. Eg5 typically detached from microtubules before stalling. This behavior may reflect a regulatory mechanism important for the role of Eg5 in the mitotic spindle. © 2007 EBSA

Superior odontoid migration in the Klippel–Feil patient

Klippel–Feil syndrome (KFS) is an uncommon condition noted primarily as congenital fusion of two or more cervical vertebrae. Superior odontoid migration (SOM) has been noted in various skeletal deformities and entails an upward/vertical migration of the odontoid process into the foramen magnum with depression of the cranium. Excessive SOM could potentially threaten neurologic integrity. Risk factors associated with the amount of SOM in the KFS patient are based on conjecture and have not been addressed in the literature. Therefore, this study evaluated the presence and extent of SOM and the various risk factors and clinical manifestations associated therein in patients with KFS. Twenty-seven KFS patients with no prior history of surgical intervention of the cervical spine were included for a prospective radiographic and retrospective clinical review. Radiographically, McGregor’s line was utilized to evaluate the degree of SOM. Anterior and posterior atlantodens intervals (AADI/PADI), number of fused segments (C1–T1), presence of occipitalization, classification-type, and lateral and coronal cervical alignments were also evaluated. Clinically, patient demographics and presence of cervical symptoms were assessed. Radiographic and clinical evaluations were conducted by two independent blinded observers. There were 8 males and 19 females with a mean age of 13.5 years at the time of radiographic and clinical assessment. An overall mean SOM of 5.0 mm (range = −1.0 to 19.0 mm) was noted. C2–C3 (74.1%) was the most commonly fused segment. A statistically significant difference was not found between the amount of SOM to age, sex-type, classification-type, AADI, PADI, and lateral cervical alignment (P > 0.05). A statistically significant greater amount of SOM was found as the number of fused segments increased (r = 0.589; P = 0.001) and if such levels included occipitalization (r = 0.616; P = 0.001). A statistically significant greater amount of SOM was also found with an increase in coronal cervical alignment (r = 0.413; P = 0.036). Linear regression modeling further supported these findings as the strongest predictive variables contributing to an increase in SOM. A 7.20 crude relative risk (RR) ratio [95% confidence interval (CI) = 1.05–49.18; risk differences (RD) = 0.52] was noted in contributing to a SOM greater than 4.5 mm if four or more segments were fused. Adjusting for coronal cervical alignment greater than 10°, five or more fused segments were found to significantly increase the RR of a SOM greater than 4.5 mm (RR = 4.54; 95% CI = 1.07–19.50; RD = 0.48). The RR of a SOM greater than 4.5 mm was more pronounced in females (RR = 1.68; 95% CI = 0.45–6.25; RD = 0.17) than in males. Eight patients (29.6%) were symptomatic, of which symptoms in two of these patients stemmed from a traumatic event. However, a statistically significant difference was not found between the presence of symptoms to the amount of SOM and other exploratory variables (P > 0.05). A mean SOM of 5.0 mm was found in our series of KFS patients. In such patients, increases in the number of congenitally fused segments and in the degree of coronal cervical alignment were strongly associated risk factors contributing to an increase in SOM. Patients with four or greater congenitally fused segments had an approximately sevenfold increase in the RR in developing SOM greater than 4.5 mm. A higher RR of SOM more than 4.5 mm may be associated with sex-type. However, 4.5 mm or greater SOM is not synonymous with symptoms in this series. Furthermore, the presence of symptoms was not statistically correlated with the amount of SOM. The treating physician should be cognizant of such potential risk factors, which could also help to indicate the need for further advanced imaging studies in such patients. This study suggests that as motion segments diminish and coronal cervical alignment is altered, the odontoid orientation is located more superiorly, which may increase the risk of neurologic sequelae