Somatostatin receptor-mediated suppression of gabaergic synaptic transmission in cultured rat retinal amacrine cells

Somatostatin (SRIF) modulates neurotransmitter release by activating the specific receptors (sst1-sst5). Our previous study showed that sst5 receptors are expressed in rat retinal GABAergic amacrine cells. Here, we investigated modulation of GABA release by SRIF in cultured amacrine cells, using patch-clamp techniques. The frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) in the amacrine cells was significantly reduced by SRIF, which was partially reversed by BIM 23056, an sst5 receptor antagonist, and was further rescued by addition of CYN-154806, an sst2 receptor antagonist. Both nimodipine, an L-type Ca2+ channel blocker, and ω-conotoxin GVIA, an N-type Ca2+ channel blocker, suppressed the sIPSC frequency, and in the presence of nimodipine and ω-conotoxin GVIA, SRIF failed to further suppress the sIPSC frequency. Extracellular application of forskolin, an activator of adenylate cyclase, increased the sIPSC frequency, while the membrane permeable protein kinase A (PKA) inhibitor Rp-cAMP reduced it, and in the presence of Rp-cAMP, SRIF did not change sIPSCs. However, SRIF persisted to suppress the sIPSCs in the presence of KT5823, a protein kinase G (PKG) inhibitor. Moreover, pre-incubation with Bis IV, a protein kinase C (PKC) inhibitor, or pre-application of xestospongin C, an inositol 1,4,5-trisphosphate receptor (IP3R) inhibitor, SRIF still suppressed the sIPSC frequency. All these results suggest that SRIF suppresses GABA release from the amacrine cells by inhibiting presynaptic Ca2+ channels, in part through activating sst5/sst2 receptors, a process that is mediated by the intracellular cAMP-PKA signaling pathway.

Association analysis of the IL2RA gene with alopecia areata in a Chinese population

BACKGROUND

Interleukin-2 receptor subunit alpha (IL2RA) is highly expressed on CD4+CD25+ regulatory T cells and is important for immune homeostasis and the suppression of autoimmune responses. It has been suggested that the single nucleotide polymorphism in IL2RA may affect the pathogenesis of alopecia areata (AA).

OBJECTIVE

Our aim was to investigate the link between IL2RA polymorphism and AA in a Chinese population.

METHODS

We examined 427 patients and 430 controls in this study. The rs3118470 polymorphism was evaluated using high-resolution melting analysis and direct sequencing.

RESULTS

The prevalence of the C/C, T/C and T/T genotypes was 16.2, 48.2 and 35.6%, respectively. The genotype distribution and allele frequencies were significantly different between AA and control subjects (p < 0.0001). The C allele frequency was significantly higher in the AA group (p < 0.0001), and the frequencies of C allele and C/C genotype were higher in the patients with family history (p = 0.034; p < 0.0001).

CONCLUSIONS

The rs3118470 single nucleotide polymorphism of IL2RA may be a genetic marker to assess the risk of AA in a Chinese population.

Suppression of outward K⁺ currents by WIN55212-2 in rat retinal ganglion cells is independent of CB1/CB2 receptors

Cannabinoid CB1 receptor (CB1R) signaling system is extensively distributed in the vertebrate retina. Activation of CB1Rs regulates a variety of functions of retinal neurons through modulating different ion channels. In the present work we studied effects of this receptor signaling on K(+) channels in retinal ganglion cells by patch-clamp techniques. The CB1R agonist WIN55212-2 (WIN) suppressed outward K(+) currents in acutely isolated rat retinal ganglion cells in a dose-dependent manner, with an IC50 of 4.7 μM. We further showed that WIN mainly suppressed the tetraethylammonium (TEA)-sensitive K(+) current component. While CB1Rs were expressed in rat retinal ganglion cells, the WIN effect on K(+) currents was not blocked by either AM251/SR141716, specific CB1R antagonists, or AM630, a selective CB2R antagonist. Consistently, cAMP-protein kinase A (PKA) and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling pathways were unlikely involved in the WIN-induced suppression of the K(+) currents because both PKA inhibitors H-89/Rp-cAMP and MAPK/ERK1/2 inhibitor U0126 failed to block the WIN effects. WIN-induced suppression of the K(+) currents was not observed when WIN was intracellularly applied. Furthermore, an endogenous ligand of the cannabinoid receptor anandamide, the specific CB1R agonist ACEA and the selective CB2R agonist CB65 also suppressed the K(+) currents, and the effects were not blocked by AM251/SR141716 or AM630 respectively. All these results suggest that the WIN-induced suppression of the outward K(+) currents in rat retinal ganglion cells, thereby regulating the cell excitability, were not through CB1R/CB2R signaling pathways.

Next-generation small RNA sequencing for microRNAs profiling in Apis mellifera: comparison between nurses and foragers

MicroRNAs (miRNAs) are endogenous small non-coding RNAs regulating gene expression in animals and plants. To find some differentially expressed miRNAs that may be associated with age-dependent behavioural changes in honey bees (Apis mellifera), we applied next-generation high-throughput sequencing technology to detect small RNAs in nurses and foragers. Our results showed that both nurses and foragers had a complicated small RNA population, and the length of small RNAs varied, 22 nucleotides being the predominant length. Combining deep sequencing and bioinformatic analysis, we discovered that nine known miRNAs were significantly different between nurses and foragers (P < 0.01; absolute value of fold-change ≥ 1). Some of their target genes were related to neural function. Moreover, 67 novel miRNAs were identified in nurses and foragers. Ame-miR-31a and ame-miR-13b were further validated using quantitative reverse-transcription PCR assays. The present study provides new information on the miRNA abundance of honey bees, and enhances our understanding of miRNA function in the regulation of honey bee development.

Vasohibin 2 is transcriptionally activated and promotes angiogenesis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) typically relies on angiogenesis for its malignant behavior, including growth and metastasis. Vasohibin 2 (VASH2) was previously identified as an angiogenic factor, but its role in tumorigenesis is unknown. Using quantitative PCR and western blot analyses, we found that VASH2 is overexpressed in HCC cells and tissues. Using chromatin immunoprecipitation, we detected histone modifications at the putative VASH2 promoter, with increased H3K4 trimethylation and H3 acetylation and decreased H3K27 trimethylation, suggesting that epigenetic mechanisms are responsible for the deregulated VASH2 transcription in HCC. Knockdown of VASH2 via siRNA inhibited the proliferation of the hepatoma cell lines by delaying cell cycle progression and increasing apoptosis. Importantly, we found VASH2 secreted in the culture supernatant, and co-expression of its secretory chaperone small vasohibin-binding protein (SVBP) further enhanced VASH2 secretion. The supernatant from HepG2 cells expressing VASH2 enhanced the proliferation, migration and tube formation of human umbilical vein endothelial cells, and knockdown of VASH2 significantly inhibited these effects. In an in vivo study using a nude mouse model, we found that exogenous VASH2 significantly contributed to tumor growth, microvessel density and hemoglobin concentration in the tumors. Further analyses showed that the VASH2-mediated increase in the transcription of fibroblast growth factor-2, vascular endothelial growth factor and vasohibin 1 may be the mechanism underlying these effects. Taken together, these data indicate that VASH2 is abnormally expressed in HCC cells as a result of histone modifications and that VASH2 contributes to the angiogenesis in HCC via an SVBP-mediated paracrine mechanism. These results indicate a novel and important role for VASH2 in HCC angiogenesis and malignant transformation.

Removal of uracil by uracil DNA glycosylase limits pemetrexed cytotoxicity: overriding the limit with methoxyamine to inhibit base excision repair

Uracil DNA glycosylase (UDG) specifically removes uracil bases from DNA, and its repair activity determines the sensitivity of the cell to anticancer agents that are capable of introducing uracil into DNA. In the present study, the participation of UDG in the response to pemetrexed-induced incorporation of uracil into DNA was studied using isogenic human tumor cell lines with or without UDG (UDG(+/+)/UDG(-/-)). UDG(-/-) cells were very sensitive to pemetrexed. Cell killing by pemetrexed was associated with genomic uracil accumulation, stalled DNA replication, and catastrophic DNA strand breaks. By contrast, UDG(+/+) cells were >10 times more resistant to pemetrexed due to the rapid removal of uracil from DNA by UDG and subsequent repair of the resultant AP sites (abasic sites) via the base excision repair (BER). The resistance to pemetrexed in UDG(+/+) cells could be reversed by the addition of methoxyamine (MX), which binds to AP sites and interrupts BER pathway. Furthermore, MX-bound AP sites induced cell death was related to their cytotoxic effect of dual inactivation of UDG and topoisomerase IIα, two genes that are highly expressed in lung cancer cells in comparison with normal cells. Thus, targeting BER-based therapy exhibits more selective cytotoxicity on cancer cells through a synthetic lethal mechanism.

Simulating microbial systems: addressing model uncertainty/incompleteness via multiscale and entropy methods

Most systems of interest in the natural and engineering sciences are multiscale in character. Typically available models are incomplete or uncertain. Thus, a probabilistic approach is required. We present a deductive multiscale approach to address such problems, focusing on virus and cell systems to demonstrate the ideas. There is usually an underlying physical model, all factors in which (e.g., particle masses, charges, and force constants) are known. For example, the underlying model can be cast in terms of a collection of N-atoms evolving via Newton's equations. When the number of atoms is 10(6) or more, these physical models cannot be simulated directly. However, one may only be interested in a coarse-grained description, e.g., in terms of molecular populations or overall system size, shape, position, and orientation. The premise of this chapter is that the coarse-grained equations should be derived from the underlying model so that a deductive calibration-free methodology is achieved. We consider a reduction in resolution from a description for the state of N-atoms to one in terms of coarse-grained variables. This implies a degree of uncertainty in the underlying microstates. We present a methodology for modeling microbial systems that integrates equations for coarse-grained variables with a probabilistic description of the underlying fine-scale ones. The implementation of our strategy as a general computational platform (SimEntropics™) for microbial modeling and prospects for developments and applications are discussed.

Clinical correlates of white matter blood flow perfusion changes in Sturge-Weber syndrome: a dynamic MR perfusion-weighted imaging study

BACKGROUND AND PURPOSE

Low brain tissue perfusion due to abnormal venous drainage is thought to be a central mechanism of brain damage in SWS. Here, HR-PWI was used to quantify WM perfusion abnormalities and to correlate these with brain atrophy and clinical variables.

MATERIALS AND METHODS

Fourteen children (age range, 0.8-10.0 years) with unilateral SWS underwent MR imaging examinations, including HR-PWI. rCBV, rCBF, and MTT in the affected WM and in contralateral homotopic WM were measured. AI for each perfusion parameter was correlated with age, brain atrophy, and motor and seizure variables as well as IQ.

RESULTS

Increased perfusion was seen in the affected hemisphere in 5 children and decreased perfusion in 9 children. Brain atrophy was more severe in the low-perfusion group (P = .01) and was related to both CBF-AI and CBV-AI (r = -0.69, P = .007; r = -0.64, P = .014, respectively). Older children had lower CBV values on the affected side (r = -0.62, P = .02). Longer duration of epilepsy was related to lower CBF (more negative CBF-AI, r = -0.58, P = .03) and low CBV (r = -0.55, P = .04) on the affected side. Lower perfusion was associated with more frequent seizures (rCBF-AI: r = -0.56, P = .04; rCBV-AI: r = -0.63, P = .02).

CONCLUSIONS

Increased perfusion in the affected cerebral WM may indicate an early stage of SWS without severe brain atrophy. Decreased perfusion is associated with frequent seizures, long duration of epilepsy, and brain atrophy.

Increased serum potassium affects renal outcomes: a post hoc analysis of the Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan (RENAAL) trial

AIMS/HYPOTHESIS

To assess the effect of an angiotensin receptor blocker (ARB) on serum potassium and the effect of a serum potassium change on renal outcomes in patients with type 2 diabetes and nephropathy.

METHODS

We performed a post hoc analysis in patients with type 2 diabetes participating in the Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan (RENAAL) study. Renal outcomes were defined as a composite of doubling of serum creatinine or end-stage renal disease.

RESULTS

At month 6, 259 (38.4%) and 73 (10.8%) patients in the losartan group and 151 (22.8%) and 34 (5.1%) patients in the placebo group had serum potassium ≥5.0 mmol/l and ≥5.5 mmol/l, (p < 0.001), respectively. Losartan was an independent predictor for serum potassium ≥5.0 mmol/l at month 6 (OR 2.8; 95% CI 2.0-3.9). Serum potassium at month 6 ≥ 5.0 mmol/l was in turn associated with increased risk for renal events (HR 1.22; 95% CI 1.00-1.50), independent of other risk factors. Adjustment of the overall treatment effects for serum potassium augmented losartan's renoprotective effect from 21% (6-34%) to 35% (20-48%), suggesting that the renoprotective effects of losartan are offset by its effect on serum potassium.

CONCLUSIONS/INTERPRETATION

In this study, we found that treatment with the ARB losartan is associated with a high risk of increased serum potassium levels, which is in turn associated with an increased risk of renal outcomes in patients with diabetes and nephropathy. Whether additional management of high serum potassium would further increase the renal protective properties of losartan is an important clinical question.

Melatonin inhibits tetraethylammonium-sensitive potassium channels of rod ON type bipolar cells via MT2 receptors in rat retina

By challenging specific receptors, melatonin synthesized and released by photoreceptors regulates various physiological functions in the vertebrate retina. Here, we studied modulatory effects of melatonin on K+ currents of rod-dominant ON type bipolar cells (Rod-ON-BCs) in rat retinal slices by patch-clamp techniques. Double immunofluorescence experiments conducted in isolated cell and retinal section preparations showed that the melatonin MT₂ receptor was expressed in somata, dendrites and axon terminals of rat Rod-ON-BCs. Electrophysiologically, application of melatonin selectively inhibited the tetraethylammonium (TEA)-sensitive K+ current component, but did not show any effect on the 4-aminopyridine (4-AP)-sensitive component. Consistent with the immunocytochemical result, the melatonin effect was blocked by co-application of 4-phenyl-2-propionamidotetralin (4-P-PDOT), a specific MT₂ receptor antagonist. Neither protein kinase A (PKA) nor protein kinase G (PKG) seemed to be involved because both the PKA inhibitor Rp-cAMP and the PKG inhibitor KT5823 did not block the melatonin-induced suppression of the K+ currents. In contrast, application of the phospholipase C (PLC) inhibitor U73122 or the protein kinase C (PKC) inhibitor bisindolylmaleimide IV (Bis IV) eliminated the melatonin effect, and when the Ca²+ chelator BAPTA-containing pipette was used, melatonin failed to inhibit the K+ currents. These results suggest that suppression of the TEA-sensitive K+ current component via activation of MT₂ receptors expressed on rat Rod-ON-BCs may be mediated by a Ca²+-dependent PLC/inositol 1,4,5-trisphosphate (IP₃/PKC signaling pathway.

Targeted melanoma imaging and therapy with radiolabeled alpha-melanocyte stimulating hormone peptide analogues

Radiolabeled alpha-melanocyte stimulating hormone (a-MSH) analogues have been used to define the expression, affinity and function of the melanocortin-1 receptor (MC1-R). The MC1-R is one of a family of five G-protein linker receptors, which is primarily involved in regulation of skin pigmentation. Over-expression of the MC1-R on melanoma tumor cells has made it an attractive target for the development of a-MSH peptide based imaging and therapeutic agents. Initially, the native a-MSH peptide was radiolabeled directly, but it suffered from low specific activity and poor stability. The addition of non-natural amino acids yielded a-MSH analogues with greater MC-1R affinity and stability. Furthermore, peptide cyclization via disulfide and lactam bond formation as well as site-specific metal coordination resulted in additional gains in receptor affinity and peptide stability in vitro and in vivo. Radiochemical stability of the a-MSH analogues was improved through the conjugation of metal chelators to the peptide's N-terminus or lysine residues for radionuclide coordination. In vitro cell binding studies demonstrated that the radiolabeled a-MSH analogues had low to subnanomolar affinities for the MC1-R. Biodistribution and imaging studies in the B16 mouse melanoma modeled showed rapid tumor uptake of the radiolabeled peptides, with the cyclic peptides demonstrating prolonged tumor retention. Cyclic a-MSH analogues labeled with beta and alpha emitting radionuclides demonstrated melanoma therapeutic efficacy in the B16 melanoma mouse model. Strong pre-clinical imaging and therapy data highlight the clinical potential use of radiolabeled a-MSH peptides for melanoma imaging and treatment of disseminated disease.

Iron stores and cerebral veins in MS studied by susceptibility weighted imaging

AIM

In this paper, we seek to determine whether the iron deposition as seen by susceptibility weighted imaging (SWI) in the basal ganglia and thalamus of patients with multiple sclerosis is greater than the iron content measured in normal subjects (individuals unaffected by multiple sclerosis). As increased iron content may result from increased venous pressure, such information would add credence to the concept of Zamboni et al (1) that MS is caused by chronic cerebrospinal venous insufficiency.

METHODS

Fourteen MS patients were recruited for this study with a mean age of 38 years ranging from 19 to 66 year-old. A velocity compensated 3D gradient echo sequence was used to generate SW images with a high sensitivity to iron content. We evaluated iron in the following structures: substantia nigra, red nucleus, globus pallidus, putamen, caudate nucleus, thalamus and pulvinar thalamus. Each structure was broken into two parts, a high iron content region and a low iron content region. The measured values were compared to previously established baseline iron content in these structures as a function of age.

RESULTS

Twelve of fourteen patients had an increase in iron above normal levels and with a particular pattern of iron deposition in the medial venous drainage system that was associated with the confluence of the veins draining that structure.

CONCLUSION

Iron may serve as a biomarker of venous vascular damage in multiple sclerosis. The backward iron accumulation pattern seen in the basal ganglia and thalamus of most MS patients is consistent with the hypothesis of venous hypertension.

Self-assembly of nanocomponents into composite structures: derivation and simulation of Langevin equations

The kinetics of the self-assembly of nanocomponents into a virus, nanocapsule, or other composite structure is analyzed via a multiscale approach. The objective is to achieve predictability and to preserve key atomic-scale features that underlie the formation and stability of the composite structures. We start with an all-atom description, the Liouville equation, and the order parameters characterizing nanoscale features of the system. An equation of Smoluchowski type for the stochastic dynamics of the order parameters is derived from the Liouville equation via a multiscale perturbation technique. The self-assembly of composite structures from nanocomponents with internal atomic structure is analyzed and growth rates are derived. Applications include the assembly of a viral capsid from capsomers, a ribosome from its major subunits, and composite materials from fibers and nanoparticles. Our approach overcomes errors in other coarse-graining methods, which neglect the influence of the nanoscale configuration on the atomistic fluctuations. We account for the effect of order parameters on the statistics of the atomistic fluctuations, which contribute to the entropic and average forces driving order parameter evolution. This approach enables an efficient algorithm for computer simulation of self-assembly, whereas other methods severely limit the timestep due to the separation of diffusional and complexing characteristic times. Given that our approach does not require recalibration with each new application, it provides a way to estimate assembly rates and thereby facilitate the discovery of self-assembly pathways and kinetic dead-end structures.