Faculty Bibliography

Reports an error in "Epac2-dependent mobilization of intracellular Ca2+ by glucagon-like peptide-1 receptor agonist exendin-4 is disrupted in beta -cells of phospholipase C-epsilon knockout mice" by Igor Dzhura, Oleg G. Chepurny, Grant G. Kelley, Colin A. Leech, Michael W. Roe, Elvira Dzhura, Parisa Afshari, Sundeep Malik, Michael J. Rindler, Xin Xu, Youming Lu, Alan V. Smrcka and George G. Holz (The Journal of Physiology, 2010[Dec][15], Vol 588[24], 4871-4889). In the original article, there was an error in the Methods section entitled 'Generation of Epac2 knockout mice' on page 4873. The first sentence of that section should read 'Epac2 KO mice with global disruption of RAPGEF4 gene expression (NCBI GeneID 56508) were generated by the Texas A&M Institute for Genomic Medicine through customized service for Dr. Lu at Louisiana State University Health Sciences Center'. (The following abstract of the original article appeared in record 2011-11969-007). Calcium can be mobilized in pancreatic beta -cells via a mechanism of Ca2+-induced Ca2+ release (CICR), and cAMP-elevating agents such as exendin-4 facilitate CICR in beta -cells by activating both protein kinase A and Epac2. Here we provide the first report that a novel phosphoinositide-specific phospholipase C-epsilon (PLC-epsilon ) is expressed in the islets of Langerhans, and that the knockout (KO) of PLC-epsilon gene expression in mice disrupts the action of exendin-4 to facilitate CICR in the beta -cells of these mice. Thus, in the present study, in which wild-type (WT) C57BL/6 mouse beta -cells were loaded with the photolabile Ca2+ chelator NP-EGTA, the UV flash photolysis-catalysed uncaging of Ca2+ generated CICR in only 9% of the beta -cells tested, whereas CICR was generated in 82% of the beta -cells pretreated with exendin-4. This action of exendin-4 to facilitate CICR was reproduced by cAMP analogues that activate protein kinase A(6-Bnz-cAMP-AM)orEpac2 (8-pCPT-2'-O-Me-cAMP-AM)selectively. However, in beta -cells of PLC-epsilon KO mice, and also Epac2 KO mice, these test substances exhibited differential efficacies in the CICR assay such that exendin-4 was partly effective, 6-Bnz-cAMP-AM was fully effective, and 8-pCPT-2'-O-Me-cAMP-AM was without significant effect. Importantly, transduction of PLC-epsilon KO beta -cells with recombinant PLC-epsilon rescued the action of 8-pCPT-2'-O-Me-cAMP-AM to facilitate CICR, whereas a K2150E PLC-epsilon with amutated Ras association (RA) domain, or a H1640L PLC-epsilon that is catalytically dead, were both ineffective. Since 8-pCPT-2'-O-Me-cAMP-AM failed to facilitate CICR in WT beta -cells transduced with a GTPase activating protein (RapGAP) that downregulates Rap activity, the available evidence indicates that a signal transduction 'module' comprised of Epac2, Rap and PLC-epsilon exists in beta -cells, and that the activities of Epac2 and PLC-epsilon are key determinants of CICR in this cell type.

the molecular characterization of melanoma has ex- panded to include studies of microRNA (miRNA) ex- pression. As miR-16 has been utilized as a normalizer in serum-based miRNA studies in several cancers, we evaluated miR-16 expression as a potential reference for normalization of serum miRNA expression in melanoma patients. Methods: 143 primary cutaneous melanoma patients who presented to New York Uni- versity (NYU) Langone Medical Center for surgical resection of AJCC stage I-III disease were studied. In addition, sera samples from 60 control subjects were utilized including 22 healthy volunteers, 13 rheuma- toid arthritis patients, 20 non-melanoma cancer pa- tients (10 renal cell carcinoma and 10 bladder cancer), and 5 Atypical Mole Syndrome patients. The Kruskal- Wallis test (k = 6) or Wilcoxon test (k = 2) with Bon- ferroni correction was used for analyses of miR-16 expression in melanoma patients compared to various control groups, using raw Ct values directly. The Kruskal-Wallis test was used to compare miR-16 ex- pression across stages of melanoma. The equivalence test for independent samples was used to test the equivalence of miR-16 expression among different groups. Results: No significant differential expression of miR-16 was observed between melanoma patients and healthy volunteers (Wilcoxon test, p = 0.37). How- ever, miR-16 did show a significant difference in ex- pression as it related to stage of melanoma (p = 0.015). Additionally, the equivalence test was unable to con- firm equivalent expression of miR-16 in any melanoma versus control group pair. Conclusion: Our data in- dicate that miR-16 cannot be used as a universal normalizer in sera studies of melanoma patients

Background: Reductions in brain-derived neurotrophic factor (BDNF) have been implicated in the pathophysiology of Alzheimer's disease (AD). Nevertheless, the factors influencing central and peripheral BDNF levels are still poorly understood. Cerebral microvascular endothelial cells are known to be a major source of BDNF with a rate of production by far exceeding that of cortical neurons. Exposure of these cells to amyloid beta (Ab), results in cell death or injury with significant reductions in BDNF secretion. Moreover, in rodents, infusion of Ab40 into the carotid resulted in a disruption of endothelial cells, which was not observed with Ab42. Plasma Ab40 levels have also been associated with white matter hyperintense lesions (WMHI) on MRI scans in AD, an effect that may be mediated by the toxic effects of soluble Ab40 on small cerebral blood vessels and endothelial cells. Therefore, we hypothesized that concentrations of plasma Ab40, but not Ab42, would have a negative effect on plasma BDNF and on measures of white matter integrity as determined by Diffusion Tensor Imaging (DTI). Methods: To test this hypothesis, we examined BDNF and Ab levels in plasma from 119 subjects with intact cognition (no dementia and a Mini-Mental State Exam score of at least 28) and no gross MRI abnormalities other than white matter hyperintensities. Of these, 88 subjects also had BDNF in plasma determined. Results: Consistent with our prediction, Ab40 was inversely correlated with BDNF concentrations (P <.001), whereas Ab42 was independent (P = .231). Fractional anisotropy (FA; a measure of white matter integrity in DTI) was also inversely correlated with Ab40 (P = .001) and so was performance in delayed recall (P = .029). Conclusions: In cognitively intact individuals, circulating Ab40 results in reduction in plasma BDNF, white matter integrity (FA), and memory performance. As such, it may have prognostic significance

Homeostatic scaling of synaptic strengths is essential for maintenance of network "gain", but also poses a risk of losing the distinctions among relative synaptic weights, which are possibly cellular correlates of memory storage. Multiplicative scaling of all synapses has been proposed as a mechanism that would preserve the relative weights among them, because they would all be proportionately adjusted. It is crucial for this hypothesis that all synapses be affected identically, but whether or not this actually occurs is difficult to determine directly. Mathematical tests for multiplicative synaptic scaling are presently carried out on distributions of miniature synaptic current amplitudes, but the accuracy of the test procedure has not been fully validated. We now show that the existence of an amplitude threshold for empirical detection of miniature synaptic currents limits the use of the most common method for detecting multiplicative changes. Our new method circumvents the problem by discarding the potentially distorting subthreshold values after computational scaling. This new method should be useful in assessing the underlying neurophysiological nature of a homeostatic synaptic scaling transformation, and therefore in evaluating its functional significance.

Tauopathy in the brain of patients with Alzheimer's disease starts in the entorhinal cortex (EC) and spreads anatomically in a defined pattern. To test whether pathology initiating in the EC spreads through the brain along synaptically connected circuits, we have generated a transgenic mouse model that differentially expresses pathological human tau in the EC and we have examined the distribution of tau pathology at different timepoints. In relatively young mice (10-11 months old), human tau was present in some cell bodies, but it was mostly observed in axons within the superficial layers of the medial and lateral EC, and at the terminal zones of the perforant pathway. In old mice (>22 months old), intense human tau immunoreactivity was readily detected not only in neurons in the superficial layers of the EC, but also in the subiculum, a substantial number of hippocampal pyramidal neurons especially in CA1, and in dentate gyrus granule cells. Scattered immunoreactive neurons were also seen in the deeper layers of the EC and in perirhinal and secondary somatosensory cortex. Immunoreactivity with the conformation-specific tau antibody MC1 correlated with the accumulation of argyrophilic material seen in old, but not young mice. In old mice, axonal human tau immunoreactivity, especially at the endzones of the perforant pathway, was greatly reduced. Relocalization of tau from axons to somatodendritic compartments and propagation of tauopathy to regions outside of the EC correlated with mature tangle formation in neurons in the EC as revealed by thioflavin-S staining. Our data demonstrate propagation of pathology from the EC and support a trans-synaptic mechanism of spread along anatomically connected networks, between connected and vulnerable neurons. In general, the mouse recapitulates the tauopathy that defines the early stages of AD and provides a model for testing mechanisms and functional outcomes associated with disease progression.