Faculty Bibliography

The use of nanoparticles for targeted drug delivery is often facilitated by specific conjugation of functional targeting molecules to the nanoparticle surface. We compared different biotin-binding proteins (avidin, streptavidin, or neutravidin) as crosslinkers to conjugate proteins to biodegradable nanoparticles prepared from poly(lactic-co-glycolic acid) (PLGA)-polyethylene glycol (PEG)-biotin polymers. Avidin gave the highest levels of overall protein conjugation, whereas neutravidin minimized protein non-specific binding to the polymer. The tetanus toxin C fragment (TTC), which is efficiently retrogradely transported in neurons and binds to neurons with high specificity and affinity, retained the ability to bind to neuroblastoma cells following amine group modifications. TTC was conjugated to nanoparticles using neutravidin, and the resulting nanoparticles were shown to selectively target neuroblastoma cells in vitro. TTC-conjugated nanoparticles have the potential to serve as drug delivery vehicles targeted to the central nervous system.

We present a model for olfactory coding based on spatial representation of glomerular responses. In this model distinct odorants activate specific subsets of glomeruli, dependent on the odorant's chemical identity and concentration. The glomerular response specificities are understood statistically, based on experimentally measured distributions of activation thresholds. A simple version of the model, in which glomerular responses are binary (the all-or-nothing model), allows us to account quantitatively for the following results of human/rodent olfactory psychophysics: 1) just noticeable differences in the perceived concentration of a single odor (Weber ratios) are as low as dC/C approximately 0.04; 2) the number of simultaneously perceived odors can be as high as 12; and 3) extensive lesions of the olfactory bulb do not lead to significant changes in detection or discrimination thresholds. We conclude that a combinatorial code based on a binary glomerular response is sufficient to account for several important features of the discrimination capacity of the mammalian olfactory system.

OBJECTIVE: Proton magnetic resonance spectroscopy ((1)H-MRS) has been increasingly used to examine striatal neurochemistry in adult major depressive disorder. This study extends the use of this modality to pediatric major depression to test the hypothesis that adolescents with major depression have elevated concentrations of striatal choline and creatine and lower concentrations of N-acetylaspartate. METHOD: Fourteen adolescents (ages 12-19 years, eight female) who had major depressive disorder for at least 8 weeks and a severity score of 40 or higher on the Children's Depression Rating Scale-Revised and 10 healthy comparison adolescents (six female) group-matched for gender, age, and handedness were enrolled. All underwent three-dimensional 3-T (1)H-MRS at high spatial resolution (0.75-cm(3) voxels). Relative levels of choline, creatine, and N-acetylaspartate in the left and right caudate, putamen, and thalamus were scaled into concentrations using phantom replacement, and levels were compared for the two cohorts. RESULTS: Relative to comparison subjects, adolescents with major depressive disorder had significantly elevated concentrations of choline (2.11 mM versus 1.56 mM) and creatine (6.65 mM versus 5.26 mM) in the left caudate. No other neurochemical differences were observed between the groups. CONCLUSIONS: These findings most likely reflect accelerated membrane turnover and impaired metabolism in the left caudate. The results are consistent with prior imaging reports of focal and lateralized abnormalities in the caudate in adult major depression

This review focuses on the current findings regarding interaction between amyloid beta peptide (Abeta) and receptor for advanced glycation endproducts (RAGE) and its roles in the pathogenesis of Alzheimer's disease (AD). As a ubiquitously expressed cell surface receptor, RAGE mediates the effects of Abeta on microglia, blood-brain barrier (BBB) and neurons through activating different signaling pathways. Data from autopsy brain tissues, in vitro cell cultures and transgenic mouse models suggest that Abeta-RAGE interaction exaggerates neuronal stress, accumulation of Abeta, impaired learning memory, and neuroinflammation. Blockade of RAGE protects against Abeta-mediated cellular perturbation. These findings may have an important therapeutic implication for neurodegenerative disorders relevant to AD.

The macroscopic volume-regulated anion current (VRAC) is regulated by both intracellular and extracellular ATP, which has important implications in signaling and regulation of cellular excitability. The outwardly rectifying Cl(-) channel (ORCC) is a major contributor to the VRAC. This study investigated the effects of intracellular and extracellular ATP on the ORCCs expressed in the human cardiovascular system. With inside-out single-channel patch-clamp techniques, ORCCs were recorded from myocytes isolated from human atrium and septal ventricle and from primary cells originating from human coronary artery endothelium and human coronary artery smooth muscle. ORCCs from all of these tissues had similar biophysical properties, i.e., they were outwardly rectifying in symmetrical Cl(-) solutions, exhibited a slope conductance of approximately 90-100 pS at positive potentials and approximately 22 pS at negative potentials, and had a high open probability that was independent of voltage or time. The presence of ATP at the cytosolic face of the membrane increased the number of patches that contained functional ORCC but had no effect on gating. In contrast, 'extracellular' ATP (in pipette solution) had no effect on the proportion of patches in which ORCC was detected but strongly reduced the open probability by increasing the closed dwell time. The potency order for nucleotides to affect gating was ATPgammaS > ATP = UTP > ADP > AMP, which suggests that a negatively charged phosphate group is involved in ORCC block. Our findings are consistent with a role of ORCC in the human cardiovasculature (atrium, ventricle, and coronary arteries). Regulation of ORCC by extracellular ATP suggests that this channel may have an important role in maintaining electrical activity and membrane potential under conditions in which extracellular ATP levels are elevated, such as with ATP release from nerve endings or during pathophysiological conditions

Agrin activates MuSK, a receptor tyrosine kinase expressed in skeletal muscle, leading to tyrosine phosphorylation of the acetylcholine receptor (AChR) beta-subunit and clustering of AChRs. The importance of AChR beta-subunit tyrosine phosphorylation in clustering AChRs and regulating synaptic differentiation is poorly understood. We generated mice with targeted mutations in the three intracellular tyrosines of the AChR beta-subunit (AChR-beta(3F/3F)). Mice lacking AChR beta-subunit tyrosine phosphorylation thrive postnatally and have no overt behavioral defects, indicating that AChR beta-subunit tyrosine phosphorylation is not essential for the formation of neuromuscular synapses. Nonetheless, the size of synapses and the density of synaptic AChRs are reduced in AChR- beta(3F/3F) mutant mice. Moreover, synapses are structurally simplified and the organization of postjunctional folds is aberrant in mice lacking tyrosine phosphorylation of the AChR beta-subunit. Furthermore, mutant AChRs cluster poorly in response to agrin and are readily extracted from the cell surface of cultured myotubes by non-ionic detergent. These data indicate that tyrosine phosphorylation of the AChR beta-subunit has an important role in organizing AChRs and regulating synaptic differentiation

Autophagy allows cell survival during starvation through the bulk degradation of proteins and organelles by lysosomal enzymes. However, the mechanisms responsible for the induction and regulation of the autophagy program are poorly understood. Here we show that the FoxO3 transcription factor, which plays a critical role in muscle atrophy, is necessary and sufficient for the induction of autophagy in skeletal muscle in vivo. Akt/PKB activation blocks FoxO3 activation and autophagy, and this effect is not prevented by rapamycin. FoxO3 controls the transcription of autophagy-related genes, including LC3 and Bnip3, and Bnip3 appears to mediate the effect of FoxO3 on autophagy. This effect is not prevented by proteasome inhibitors. Thus, FoxO3 controls the two major systems of protein breakdown in skeletal muscle, the ubiquitin-proteasomal and autophagic/lysosomal pathways, independently. These findings point to FoxO3 and Bnip3 as potential therapeutic targets in muscle wasting disorders and other degenerative and neoplastic diseases in which autophagy is involved

Neurons in posterior parietal cortex (PPC) may serve both proprioceptive and exteroceptive functions during prehension, signaling hand actions and object properties. To assess these roles, we used digital video recordings to analyze responses of 83 hand-manipulation neurons in area 5 as monkeys grasped and lifted objects that differed in shape (round and rectangular), size (large and small spheres), and location (identical rectangular blocks placed lateral and medial to the shoulder). The task contained seven stages -- approach, contact, grasp, lift, hold, lower, relax -- plus a pretrial interval. The four test objects evoked similar spike trains and mean rate profiles that rose significantly above baseline from approach through lift, with peak activity at contact. Although representation by the spike train of specific hand actions was stronger than distinctions between grasped objects, 34% of these neurons showed statistically significant effects of object properties or hand postures on firing rates. Somatosensory input from the hand played an important role as firing rates diverged most prominently on contact as grasp was secured. The small sphere -- grasped with the most flexed hand posture -- evoked the highest firing rates in 43% of the population. Twenty-one percent distinguished spheres that differed in size and weight, and 14% discriminated spheres from rectangular blocks. Location in the workspace modulated response amplitude as objects placed across the midline evoked higher firing rates than positions lateral to the shoulder. We conclude that area 5 neurons, like those in area AIP, integrate object features, hand actions, and grasp postures during prehension