Homozygous SLC6A17 Mutations Cause Autosomal-Recessive Intellectual Disability with Progressive Tremor,Speech Impairment,and Behavioral Problems

We report on Dutch and Iranian families with affected individuals who present with moderate to severe intellectual disability and additional phenotypes including progressive tremor, speech impairment, and behavioral problems in certain individuals. A combination of exome sequencing and homozygosity mapping revealed homozygous mutations c.484G>A (p.Gly162Arg) and c.1898C>G (p.Pro633Arg) in SLC6A17. SLC6A17 is predominantly expressed in the brain, encodes a synaptic vesicular transporter of neutral amino acids and glutamate, and plays an important role in the regulation of glutamatergic synapses. Prediction programs and 3D modeling suggest that the identified mutations are deleterious to protein function. To directly test the functional consequences, we investigated the neuronal subcellular localization of overexpressed wild-type and mutant variants in mouse primary hippocampal neuronal cells. Wild-type protein was present in soma, axons, dendrites, and dendritic spines. p.Pro633Arg altered SLC6A17 was found in soma and proximal dendrites but did not reach spines. p.Gly162Arg altered SLC6A17 showed a normal subcellular distribution but was associated with an abnormal neuronal morphology mainly characterized by the loss of dendritic spines. In summary, our genetic findings implicate homozygous SLC6A17 mutations in autosomal-recessive intellectual disability, and their pathogenic role is strengthened by genetic evidence and in silico and in vitro functional analyses.     

Characterization of Rhinitis According to the Asthma Status in Adults Using an Unsupervised Approach in the EGEA Study

Background

The classification of rhinitis in adults is missing in epidemiological studies.

Objective

To identify phenotypes of adult rhinitis using an unsupervised approach (data-driven) compared with a classical hypothesis-driven approach.

Methods

983 adults of the French Epidemiological Study on the Genetics and Environment of Asthma (EGEA) were studied. Self-reported symptoms related to rhinitis such as nasal symptoms, hay fever, sinusitis, conjunctivitis, and sensitivities to different triggers (dust, animals, hay/flowers, cold air…) were used. Allergic sensitization was defined by at least one positive skin prick test to 12 aeroallergens. Mixture model was used to cluster participants, independently in those without (Asthma-, n = 582) and with asthma (Asthma+, n = 401).

Results

Three clusters were identified in both groups: 1) Cluster A (55% in Asthma-, and 22% in Asthma+) mainly characterized by the absence of nasal symptoms, 2) Cluster B (23% in Asthma-, 36% in Asthma+) mainly characterized by nasal symptoms all over the year, sinusitis and a low prevalence of positive skin prick tests, and 3) Cluster C (22% in Asthma-, 42% in Asthma+) mainly characterized by a peak of nasal symptoms during spring, a high prevalence of positive skin prick tests and a high report of hay fever, allergic rhinitis and conjunctivitis. The highest rate of polysensitization (80%) was found in participants with comorbid asthma and allergic rhinitis.

Conclusion

This cluster analysis highlighted three clusters of rhinitis with similar characteristics than those known by clinicians but differing according to allergic sensitization, and this whatever the asthma status. These clusters could be easily rebuilt using a small number of variables.     

Rapid synthesis of the X-linked mental retardation protein OPHN1 mediates mGluR-dependent LTD through interaction with the endocytic machinery

Activation of group I metabotropic glutamate receptors leads to long-term depression (mGluR-LTD). Alterations in this form of plasticity have been linked to drug addiction and cognitive disorders. A key characteristic of mGluR-LTD is its dependence on rapid protein synthesis; however, the identities of the proteins mediating LTD remain elusive. Here, we identify the X-linked mental retardation protein OPHN1 as a molecule essential for mGluR-LTD in the hippocampus. mGluR-LTD induction elicits rapid dendritic OPHN1 synthesis, which is dependent on mGluR1 activation and independent of fragile X mental retardation protein (FMRP). This response is essential for mGluR-LTD, as acute blockade of OPHN1 synthesis impedes LTD. mGluR-induced OPHN1 mediates LTD and associated persistent decreases in surface AMPARs via interactions with endophilin A2/3. Importantly, this role of OPHN1 is separable from its effects on basal synaptic strength, which require OPHN1's Rho-GAP activity and interaction with Homer1b/c. Thus, our data establish a role for rapid OPHN1 synthesis in mGluR-LTD. VIDEO ABSTRACT:     

Investigation of a potential zoonotic transmission of orthoreovirus associated with acute influenza-like illness in an adult patient

Bats are increasingly being recognized as important reservoir hosts for a large number of viruses, some of them can be highly virulent when they infect human and livestock animals. Among the new bat zoonotic viruses discovered in recent years, several reoviruses (respiratory enteric orphan viruses) were found to be able to cause acute respiratory infections in humans, which included Melaka and Kampar viruses discovered in Malaysia, all of them belong to the genus Orthoreovirus, family Reoviridae. In this report, we describe the isolation of a highly related virus from an adult patient who suffered acute respiratory illness in Malaysia. Although there was no direct evidence of bat origin, epidemiological study indicated the potential exposure of the patient to bats before the onset of disease. The current study further demonstrates that spillover events of different strains of related orthoreoviruses from bats to humans are occurring on a regular basis, which calls for more intensive and systematic surveillances to fully assess the true public health impact of these newly discovered bat-borne zoonotic reoviruses.     

IP(3)-mediated Ca(2+) signals in human neuroblastoma SH-SY5Y cells with exogenous overexpression of type 3 IP(3) receptor

Human neuroblastoma SH-SY5Y cells, predominantly expressing type 1 inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R), were stably transfected with IP(3)R type 3 (IP(3)R3) cDNA. Immunocytochemistry experiments showed a homogeneous cytoplasmic distribution of type 3 IP(3)Rs in transfected and selected high expression cloned cells. Using confocal Ca(2+) imaging, carbachol (CCh)-induced Ca(2+) release signals were studied. Low CCh concentrations (< or = 750 nM) evoked baseline Ca(2+) oscillations. Transfected cells displayed a higher CCh responsiveness than control or cloned cells. Ca(2+) responses varied between fast, large Ca(2+) spikes and slow, small Ca(2+) humps, while in the clone only Ca(2+) humps were observed. Ca(2+) humps in the transfected cells were associated with a high expression level of IP(3)R3. At high CCh concentrations (10 microM) Ca(2+) transients in transfected and cloned cells were similar to those in control cells. In the clone exogenous IP(3)R3 lacked the C-terminal channel domain but IP(3)-binding capacity was preserved. Transfected cells mainly expressed intact type 3 IP(3)Rs but some protein degradation was also observed.We conclude that in transfected cells expression of functional type 3 IP(3)Rs causes an apparent higher affinity for IP(3). In the clone, the presence of degraded receptors leads to an efficient cellular IP(3) buffer and attenuated IP(3)-evoked Ca(2+) release.     

Inhibition of CFTR channels by a peptide toxin of scorpion venom

Peptide toxins have been valuable probes in efforts to identify amino acid residues that line the permeation pathway of cation-selective channels. However, no peptide toxins have been identified that interact with known anion-selective channels such as the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR channels are expressed in epithelial cells and are associated with several genetic disorders, including cystic fibrosis and polycystic kidney disease. Several organic inhibitors have been used to investigate the structure of the Cl^– permeation pathway in CFTR. However, investigations of the wider cytoplasmic vestibule have been hindered by the lack of a high-affinity blocker that interacts with residues in this area. In this study we show that venom of the scorpion Leiurus quinquestriatus hebraeus reversibly inhibits CFTR, in a voltage-independent manner, by decreasing single-channel mean burst duration and open probability only when applied to the cytoplasmic surface of phosphorylated channels. Venom was able to decrease burst duration and open probability even when CFTR channels were locked open by treatment with either vanadate or adenosine 5'-(,-imido)triphosphate, and block was strengthened on reduction of extracellular Cl^– concentration, suggesting inhibition by a pore-block mechanism. Venom had no effect on ATP-dependent macroscopic opening rate in channels studied by inside-out macropatches. Interestingly, the inhibitory activity was abolished by proteinase treatment. We conclude that a peptide toxin contained in the scorpion venom inhibits CFTR channels by a pore-block mechanism; these experiments provide the first step toward isolation of the active component, which would be highly valuable as a probe for CFTR structure and function. cystic fibrosis; anion channel; cystic fibrosis transmembrane conductance regulator; ion channel block     

Late systolic onset of regional LV relaxation demonstrated in three-dimensional space by MRI tissue tagging

Left ventricular (LV) relaxation entails myocardial deformation that induces LV filling. Yet, the precise mechanisms of the earliest changes in tissue properties that characterize myocardial relaxation remain incompletely understood. Ten healthy volunteers (seven males), 25-43 yr, underwent tagged and cine MRI with high temporal resolution (25-35 ms). Normal strains including radial (E(rr)), circumferential (E(cc)), and longitudinal (E(ll)) strains, shear strains including E(cl) (circumferential-longitudinal), E(cr) (circumferential-radial), and E(rl) (radial-longitudinal), and principal strains (E(1), E(2), and E(3)) were calculated using a displacement field-fitting method. Temporal changes in angular strains indicative of shear and torsion release and normal strains were studied during late systole and early relaxation. The onset of individual relaxation strains was heterogeneous relative to LV filling. Shear strains (E(cr), E(rl), and E(cl)) and radial thinning were first to develop. Times of onset of E(cr), E(rl), E(cl), and E(rr) occurred 108, 93, 67, and 73 ms before aortic valve closure, respectively. E(ll), E(cc), and LV volume change commenced significantly later after the onset of diastolic shear strains and radial thinning. The onset of E(cc), E(ll), and LV volume change was noted 38 ms before aortic valve closure (P < or = 0.05 relative to the onset of shear strains and E(rr)). Myocardial relaxation is characterized by a three-dimensional unfolding deformation that includes release of torsion, shear, and radial thinning beginning before aortic valve closure. This unfolding pattern precedes longitudinal and circumferential elongation and may facilitate early diastolic filling.     

CFTR: a cysteine at position 338 in TM6 senses a positive electrostatic potential in the pore

We investigated the accessibility to protons and thiol-directed reagents of a cysteine substituted at position 338 in transmembrane segment 6 (TM6) of CFTR to test the hypothesis that T338 resides in the pore. Xenopus oocytes expressing T338C CFTR exhibited pH-dependent changes in gCl and I-V shape that were specific to the substituted cysteine. The apparent pKa of T338C CFTR was more acidic than that expected for a cysteine or similar simple thiols in aqueous solution. The pKa was shifted toward alkaline values when a nearby positive charge (R334) was substituted with neutral or negatively charged residues, consistent with the predicted influence of the positive charge of R334, and perhaps other residues, on the titration of a cysteine at 338. The relative rates of chemical modification of T338C CFTR by MTSET+ and MTSES- were also altered by the charge at 334. These observations support a model for CFTR that places T338 within the anion conduction path. The apparent pKa of a cysteine substituted at 338 and the relative rates of reaction of charged thiol-directed reagents provide a crude measure of a positive electrostatic potential that may be due to R334 and other residues near this position in the pore.