Browsing by Author "Ahmed, Shehab"

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    The Effectors of the Transient Receptor Vanilloid Potential Type 4 in the Choroid Plexus
    (Office of the Vice Chancellor for Research, 2016-04-08) Otun, Ayodamola; Ahmed, Shehab; Joyner, Michael; Simpson, Stephanie; Blazer-Yost, Bonnie L.
    Hydrocephalus is a deadly disease that affects 1-2 births in 1000. When severe, this disease can result in irreversible brain damage. There are no drugs to treat hydrocephalus and the standard therapy is to surgically implant shunts to drain the excess cerebrospinal fluid (CSF) into other parts of the body. However this approach often results in a less than optimal outcomes. Shunt failures due to blockage, infection, and other causes are as high as 50% even in major medical centers which specialize in these procedures. Our laboratory is using a Meckel-Gruber syndrome rat model to study the development of severe hydrocephalus. Immunohistochemistry has been used to show the overexpression of Transient Receptor Vanilloid Potential Type 4, TRPV4 on the choroid plexus epithelial membrane. Because the choroid plexus is responsible for the majority of the cerebrospinal fluid that contributes to the progression of hydrocephalus, the TRPV4 calcium channel is a potential target that could contribute to the disease development. The endogenous activators of this channel in the choroid plexus are yet to be determined. Consequently, the current study is using a cultured choroid plexus cell line to identify endogenous activators of this channel. Potential activators include homovanillic acid (HVA), lysophosphatidic acid, and arachidonic acid. In addition, the introduction of novel compounds that act as sensitizers of the channel led to a set of experiments that were conducted to confirm the existence and identification of the sensitizers such as inflammatory cytokines. The effect of these compounds on the activation of the TRPV4 channel are being investigated using electrophysiological techniques in a porcine choroid plexus cell line with the characteristics of the in vivo choroid plexus. This cell line exhibits a robust increase in ion transport in response to a TRPV4 agonist. . The determination of the endogenous TRPV4 activators and sensitizers will provide important information in the development of a drug that can be used to treat hydrocephalus with minimal side effects by altering the activity of TRPV4.
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    Identification of elongated cilia and chiral malformation in TMEM67 mutant brains
    (Office of the Vice Chancellor for Research, 2015-04-17) Shim, Joon W.; Territo, Paul R.; Maue, Ellen; Ahmed, Shehab; Watson, John C.; Fulkerson, Dan; Blazer-Yost, Bonnie L.
    Transmembrane protein 67 (TMEM67) is encoded by one of four syndromic encephalocele genes. In humans a mutation in TMEM67 causes Meckel Gruber Syndrome, type 3 (MKS3) which is characterized by severe encephalocele and cystic kidneys and is usually fatal in the neonatal period. MKS3 is one of a spectrum of diseases known as ciliopathies because the proteins responsible for the disease are found in cells with the primary cilia. Primary cilia are a single, hair-like organelle that is found on the apical membrane of polarized cells and is thought to be involved in formation of left-right asymmetry during development as well as mechano- and chemo-reception. Here we characterize previously unreported details of cerebral phenotype in the Wistar polycystic kidney (Wpk) rats with a TMEM67 mutation. In choroid plexus (CP) epithelia of wild type animals, TMEM67 localizes to the plasma membrane and to a region close to the basal side of CP primary cilia. In a choroid plexus cell line that forms an epithelial sheet, the TMEM67 is found intracellularly but also localizes to the junctional complexes as evidenced by β catenin co-localization. Absence of normal TMEM67 leads to elongation of primary cilia in the ependymal cells lining the cerebral ventricles of the TMEM67-/- animals indicating that this protein is involved in the regulation of cilia length. Reduced aqueduct, bilateral dilatation with fusion of lateral ventricles, swelling of the hippocampus, and altered hindbrain histoarchitecture are noted in the TMEM67-/- rats. In the heterozygous animals mild asymmetric ventriculomegaly primarily on the left side is observed during early postnatal periods and continues into adulthood. These results suggest that TMEM67 is required for cilia length control and normal development of cerebral midline that maintains the symmetry of the left and right hemispheres. The Wpk rat model, orthologous to human MKS3, provides a unique model in which to study the development of both severe (TMEM67-/-) and mild (TMEM67+/-) hydrocephalus and other developmental abnormalities that are commonly found in human patients with ciliopathies.
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    TRPV4 and cAMP Mediated Ion Transport in the Porcine Choroid Plexus
    (2016-12-01) Ahmed, Shehab; Blazer-Yost, Bonnie
    Hydrocephalus is a medical condition characterized by a buildup of cerebrospinal fluid which causes hydrostatic pressure to increase resulting neuronal destruction and can ultimately cause death. Hydrocephalus is seen in both the pediatric population and adults. Treatment of hydrocephalus usually involves surgical placement of a relocation system to drain the fluid into the abdominal cavity. Hydrocephalus may be caused by mechanical obstruction of the outflow of CSF from the ventricles or by faulty reabsorption. It can be also caused by CSF overproduction by the choroid plexus found in the lateral, third, and fourth ventricles of the brain. The choroid plexus is composed of a high resistance monolayer epithelium which surrounds a network of capillaries. Its primary function is to regulate transport of ions and water that control the production and movement of CSF. Therefore it is important to understand the mechanism of CSF production by the choroid plexus. Recently, a stable porcine choroid plexus (PCP-R) epithelial cell line with a high transepithelial resistance (TER) was developed that provides an important model to study regulation of CSF production. Ussing style electrophysiology was used to measure short circuit current (SCC) to characterize stimulated transepithelial ion transport in confluent PCP-R cells. GSK1016790, a TRPV4 agonist, was used to understand the role of TRPV4 in CSF production by the choroid plexus using PCP-R cell model. TRPV4 activation produces a sustained ion transport response that is consistent with an increase in cation secretion and/or anion absorption which is accompanied by a reversible decrease in TER. The effect of the agonist on both SCC and TER was blocked by HC067047, a TRPV4 antagonist, showing that the sustained ion transport and TER change is TRPV4 specific. TRPV4 mediated ion flux was inhibited by CFTR inhibitor II GlyH-101, a cell permeable inhibitor of the cAMP activated chloride channel CFTR, when added on either side of the membrane and was not accompanied by a TER reversal which showed that CFTR is activated by TRPV4 mediated ion flux. TMEM16A, a calcium activated chloride channel, was speculated to be located in that basal membrane as T16Ainh-AO1, a membrane permeable TMEM16A inhibitor, reversed the TRPV4 mediated ion flux when added on either side of the membrane. Slight reversal in TER was observed when T16Ainh-AO1 was added on the apical side. Apamin, a differential inhibitor of calcium activated small conductance potassium channel 1, 2 and 3 (SK1, SK2 and SK3) had no effect on the TRPV4 mediated ion flux. Whereas, fluoxetine, a membrane permeable inhibitor of SK1, SK2 and SK3 channel, inhibited the TRPV4 mediated ion flux and TER change. Bumetanide, an inhibitor of the sodium-potassium-chloride cotransporter reversed TRPV4 mediated ion flux when added on the apical membrane but not on the basal membrane indicating a possible K+ secretion via SK1 and/or SK4/IK channels and Cl- absorption through CFTR and TMEM16A channels. Acetazolamide, a carbonic anhydrase inhibitor and a compound used to treat hydrocephalus had no effect on the TRPV4 mediated ion flux. cAMP is an intracellular mediator involved in neuromodulator effects, inflammatory responses and other regulatory mechanisms and is constitutively activated by forskolin. In PCP-R cells, forskolin stimulated an increase in transepithelial ion flux that is consistent with an increase in cation absorption and/or anion secretion. Forskolin mediated ion transport was inhibited by CFTR inhibitor II GlyH-101 when added on either side of the membrane. No change in TER was observed. No effect on forskolin mediated ion flux was observed when T16Ainh-A01, apamin or fluoxetine were added. Forskolin stimulated transport is partially inhibited by 1 mM BaCl2. Barium chloride is a general inhibitor of K+ channels. No change in TER was observed.