Faculty Bibliography

Neurogenesis, the division, migration, and differentiation of new neurons, occurs throughout life. Brain derived neurotrophic factor (BDNF) has been identified as a potential signaling molecule regulating neurogenesis in the subventricular zone (SVZ), but its functional consequences in vivo have not been well defined. We report marked and unexpected deficits in survival but not proliferation of newly born cells of adult knock-in mice containing a variant form of BDNF [a valine (Val) to methionine (Met) substitution at position 66 in the prodomain of BDNF (Val66Met)], a genetic mutation shown to lead to a selective impairment in activity-dependent BDNF secretion. Utilizing knock-out mouse lines, we identified BDNF and tyrosine receptor kinase B (TrkB) as the critical molecules for the observed impairments in neurogenesis, with p75 knock-out mice showing no effect on cell proliferation or survival. We then localized the activated form of TrkB to a discrete population of cells, type A migrating neuroblasts, and demonstrate a decrease in TrkB phosphorylation in the SVZ of Val66Met mutant mice. With these findings, we identify TrkB signaling, potentially through activity dependent release of BDNF, as a critical step in the survival of migrating neuroblasts. Utilizing a behavioral task shown to be sensitive to disruptions in olfactory bulb neurogenesis, we identified specific impairments in spontaneous olfactory discrimination, but not general olfactory sensitivity or habituation to olfactory stimuli in BDNF mutant mice. Through these observations, we have identified novel links between genetic variant BDNF and adult neurogenesis in vivo, which may contribute to significant impairments in olfactory function

NMHC-IIa, a nonmuscle myosin heavy chain isoform encoded by MYH9, is expressed in sensory hair cells and its dysfunction is associated with syndromic and nonsyndromic hearing loss. In this study, we investigate the ultrastructural distribution of NMHC-IIa within murine hair cells to elucidate its potential role in hair cell function. Using previously characterized anti-mouse NMHC-IIa antibody detected with immunogold labelling, NMHC-IIa was observed in the stereocilia, in the cytosol along the plasma membrane, and within mitochondria. Within stereocilia, presence of NMHC-IIa is observed throughout its length along the actin core, from the center to the periphery and at its base in the cuticular plate, suggesting a potential role in structural support. Within the sensory hair cells, NMHC-IIa was distributed throughout the cytoplasm and along the plasma membrane. A novel finding of this study is the localization of NMHC-IIa within the mitochondria, with the majority of the label along its inner membrane folds. The presence of NMHC-IIa within heterogeneous areas of the hair cell suggests that it may play different functional roles in these distinct regions. Thus, mutant NMHC-IIa may cause hearing loss by affecting hair cell dysfunction through structural and or functional disruption of its stereocilia, plasma membrane, and/or mitochondria

Protein kinase A (PKA)-independent actions of adenosine 3',5'-cyclic monophosphate (cAMP) are mediated by Epac, a cAMP sensor expressed in pancreatic beta-cells. Evidence that Epac might mediate the cAMP-dependent inhibition of beta-cell ATP-sensitive K(+) channels (K(ATP)) was provided by one prior study of human beta-cells and a rat insulin-secreting cell line (INS-1 cells) in which it was demonstrated that an Epac-selective cAMP analogue (ESCA) inhibited a sulphonylurea-sensitive K(+) current measured under conditions of whole-cell recording. Using excised patches of plasma membrane derived from human beta-cells and rat INS-1 cells, we now report that 2'-O-Me-cAMP, an ESCA that activates Epac but not PKA, sensitizes single K(ATP) channels to the inhibitory effect of ATP, thereby reducing channel activity. In the presence of 2'-O-Me-cAMP (50 microM), the dose-response relationship describing ATP-dependent inhibition of K(ATP) channel activity (NP(o)) is left-shifted such that the concentration of ATP producing 50% inhibition (IC(50)) is reduced from 22 microM to 1 microM for human beta-cells, and from 14 microM to 4 microM for rat INS-1 cells. Conversely, when patches are exposed to a fixed concentration of ATP (10 microM), the administration of 2'-O-Me-cAMP inhibits channel activity in a dose-dependent and reversible manner (IC(50) 12 microM for both cell types). A cyclic nucleotide phosphodiesterase-resistant ESCA (Sp-8-pCPT-2'-O-Me-cAMPS) also inhibits K(ATP) channel activity, thereby demonstrating that the inhibitory actions of ESCAs reported here are unlikely to arise as a consequence of their hydrolysis to bioactive derivatives of adenosine. On the basis of such findings it is concluded that there exists in human beta-cells and rat INS-1 cells a novel form of ion channel modulation in which the ATP sensitivity of K(ATP) channels is regulated by Epac

Prospective midbrain and cerebellum formation are coordinated by FGF ligands produced by the isthmic organizer. Previous studies have suggested that midbrain and cerebellum development require different levels of FGF signaling. However, little is known about the extent to which specific regions within these two parts of the brain differ in their requirement for FGF signaling during embryogenesis. Here, we have explored the effects of inhibiting FGF signaling within the embryonic mouse midbrain (mesencephalon) and cerebellum (rhombomere 1) by misexpressing sprouty2 (Spry2) from an early stage. We show that such Spry2 misexpression moderately reduces FGF signaling, and that this reduction causes cell death in the anterior mesencephalon, the region furthest from the source of FGF ligands. Interestingly, the remaining mesencephalon cells develop into anterior midbrain, indicating that a low level of FGF signaling is sufficient to promote only anterior midbrain development. Spry2 misexpression also affects development of the vermis, the part of the cerebellum that spans the midline. We found that, whereas misexpression of Spry2 alone caused loss of the anterior vermis, reducing FGF signaling further, by decreasing Fgf8 gene dose, resulted in loss of the entire vermis. Our data suggest that cell death is not responsible for vermis loss, but rather that it fails to develop because reducing FGF signaling perturbs the balance between vermis and roof plate development in rhombomere 1. We suggest a molecular explanation for this phenomenon by providing evidence that FGF signaling functions to inhibit the BMP signaling that promotes roof plate development

Cystinuria is an inherited disorder characterized by the impaired reabsorption of cystine in the proximal tubule of the nephron and the gastrointestinal epithelium. The only clinically significant manifestation is recurrent nephrolithiasis secondary to the poor solubility of cystine in urine. Although cystinuria is a relatively common disorder, it accounts for no more than 1% of all urinary tract stones. Thus far, mutations in 2 genes, SLC3A1 and SLC7A9, have been identified as being responsible for most cases of cystinuria by encoding defective subunits of the cystine transporter. With the discovery of mutated genes, the classification of patients with cystinuria has been changed from one based on phenotypes (I, II, III) to one based on the affected genes (I and non-type I; or A and B). Most often this classification can be used without gene sequencing by determining whether the affected individual's parents have abnormal urinary cystine excretion. Clinically, insoluble cystine precipitates into hexagonal crystals that can coalesce into larger, recurrent calculi. Prevention of stone formation is the primary goal of management and includes hydration, dietary restriction of salt and animal protein, urinary alkalinization, and cystine-binding thiol drugs

This report summarizes the recommendations of the Frontotemporal Dementia (FTD) Working Group on FTD Drug Discovery that was part of an international FTD Workshop held on January 18 and 19, 2007, in Miami, Florida. The workshop was sponsored by the National Institute of Neurological Disorders and Stroke (NINDS) and the National Institute on Aging (NIA) of the National Institutes of Health (NIH) and the Association for Frontotemporal Dementia (AFTD) with the express purpose of defining opportunities to improve the diagnosis and treatment of patients affected by a neurodegenerative disorder classified as one of the many variants of FTD. The recognition that almost all forms of FTD are due to TDP-43 proteinopathies and tauopathies creates new opportunities for FTD drug discovery targeting pathways of TDP-43 and tau-mediated neurodegeneration

OBJECTIVE: The susceptibility to suffer neurally mediated syncope and loss of consciousness varies markedly. In addition to vasodilatation and bradycardia, hyperventilation precedes loss of consciousness. The resultant hypocapnia causes cerebral vasoconstriction and peripheral vasodilatation. We postulate that more pronounced cerebral and peripheral vascular responses to reductions in arterial CO(2) levels underlie greater susceptibility to neurally mediated syncope. METHODS: We compared vascular responses to CO(2) among 31 patients with histories of recurrent neurally mediated syncope and low orthostatic tolerance and 14 age- and sex-matched control subjects with no history of syncope and normal orthostatic tolerance. Vascular responses to CO(2) were calculated after all subjects had fully recovered and their blood pressures and heart rates were stable. We measured blood flow velocity in the middle cerebral artery (transcranial Doppler) and in the left brachial artery (brachial Doppler), and end-tidal CO(2) during voluntary hyperventilation and hypoventilation (end-tidal CO(2) from 21-45mm Hg), and determined the slopes of the relations. RESULTS: Hypocapnia produced a significantly greater reduction in cerebral blood flow velocity and in forearm vascular resistance in patients with neurally mediated syncope than in control subjects. Opposite changes occurred in response to hypercapnia. In all subjects, the changes in cerebral blood flow velocity and forearm vasodilatation were inversely related with orthostatic tolerance. INTERPRETATION: Susceptibility to neurally mediated syncope can be explained, at least in part, by enhanced cerebral vasoconstriction and peripheral vasodilatation in response to hypocapnia. This may have therapeutic implications. Ann Neurol 2007