Jürgen Zezula

Immunohistochemical localization of the α1, α2 and α3 subunit of the GABAA receptor in the rat brain

Abstract The immunohistochemical distribution of the α 1 , α 2 and α 3 subunit of the γ-aminobutyric acid-A (GABA A ) receptor was investigated in the rat brain using affinity-purified antibodies against unique parts of the amino acid sequence of the respective subunits. The distribution of the 3 subunits differed markedly from each other indicating heterogeneity of the GABA A -receptor composition in different brain regions and at various receptive compartments (dendrites or somata) of neuronal cells.

A single allele of Hdac2 but not Hdac1 is sufficient for normal mouse brain development in the absence of its paralog

The histone deacetylases HDAC1 and HDAC2 are crucial regulators of chromatin structure and gene expression, thereby controlling important developmental processes. In the mouse brain, HDAC1 and HDAC2 exhibit different developmental stage- and lineage-specific expression patterns. To examine the individual contribution of these deacetylases during brain development, we deleted different combinations of Hdac1 and Hdac2 alleles in neural cells. Ablation of Hdac1 or Hdac2 by Nestin-Cre had no obvious consequences on brain development and architecture owing to compensation by the paralog. By contrast, combined deletion of Hdac1 and Hdac2 resulted in impaired chromatin structure, DNA damage, apoptosis and embryonic lethality. To dissect the individual roles of HDAC1 and HDAC2, we expressed single alleles of either Hdac1 or Hdac2 in the absence of the respective paralog in neural cells. The DNA-damage phenotype observed in double knockout brains was prevented by expression of a single allele of either Hdac1 or Hdac2. Strikingly, Hdac1-/-Hdac2+/- brains showed normal development and no obvious phenotype, whereas Hdac1+/-Hdac2-/- mice displayed impaired brain development and perinatal lethality. Hdac1+/-Hdac2-/- neural precursor cells showed reduced proliferation and premature differentiation mediated by overexpression of protein kinase C, delta, which is a direct target of HDAC2. Importantly, chemical inhibition or knockdown of protein kinase C delta was sufficient to rescue the phenotype of neural progenitor cells in vitro. Our data indicate that HDAC1 and HDAC2 have a common function in maintaining proper chromatin structures and show that HDAC2 has a unique role by controlling the fate of neural progenitors during normal brain development.

Allosteric modulation of [3H]flunitrazepam binding to recombinant GABAA receptors.

The allosteric modulation of [3H]flunitrazepam binding by gamma-aminobutyric acid (GABA), pentobarbital, (+)-etomidate, etazolate, alphaxalone, propofol and chlormethiazole was investigated in cerebellar membranes and membranes from human embryonic kidney (HEK) 193 cells transfected with alpha 1 beta 3 gamma 2 or alpha 1 gamma 2 subunits. Results obtained indicate that [3H]flunitrazepam binding to recombinant GABAA receptors consisting of alpha 1 beta 3 gamma 2 subunits could be modulated by these compounds in a way and with a potency similar to that observed in cerebellar membranes. In addition, it was demonstrated that not only receptors consisting of alpha 1 beta 3 gamma 3, but also those consisting of alpha 1 gamma 2 subunits exhibited [3H]flunitrazepam binding which could be stimulated by GABA. In contrast to alpha 1 beta 3 gamma 2 receptors, however, [3H]flunitrazepam binding to recombinant alpha 1 gamma 2 receptors was inhibited by pentobarbital, (+)-etomidate, etazolate, alphaxalone, propofol and chlormethiazole. This seems to indicate that binding sites for these compounds are present on alpha 1 gamma 2 receptors, but that their allosteric interaction with [3H]flunitrazepam binding sites is different from that of alpha 1 beta 3 gamma 2 receptors.

[3H]Propyl-6-azido-β-carboline-3-carboxylate: a new photoaffinity label for the GABAA-benzodiazepine receptor

[3H]Propyl-6-azido-beta-carboline-3-carboxylate ([3H]ACCP) exhibited a high affinity for GABAA receptors affinity purified from the brains of adult rats, and binding of this compound could be inhibited by several ligands of the benzodiazepine binding site of GABAA receptors. On irradiation with UV light, [3H]ACCP, similarly to [3H]flunitrazepam, irreversibly labeled a protein with an apparent molecular weight of 51 kDa in affinity-purified GABAA receptors, and this labeling could be inhibited in the presence of diazepam. These data indicate that [3H]ACCP can be used as a photoaffinity label for GABAA receptors.

Restricted collision coupling of the adenosine A2A receptor is due to its agonist-induced confinement in the membrane

Background The A2A adenosine receptor is of interest because of several reasons. (i) It is a frequently blocked pharmacological target, because it is the site of action of caffeine. (ii) It has a long C-terminus that provides a docking site for several proteins, which direct the fate of the receptor from its synthesis to its lysosomal degradation. (iii) The A2A receptor can only promote activation of a limited number of available Gs molecules. This coupling mode was termed restricted collision coupling. (iv) Most G protein-coupled receptors carry one or several cysteine residues in their C-terminus which is subject to palmitoylation to anchor and stabilize the amphipathic helix 8; the A2A receptor lacks this palmitoylation site. We explored the hypothesis that there is a causal link between the absence of a palmitoyl moiety and restricted collision coupling.

Tracking the A2A adenosine receptor

Background The A2A adenosine receptor has become a drug target in the treatment of Parkinson’s disease, psychotic behavior and dementia. In addition, targeted deletion of this receptor in mice leads to hypertension, increased platelet aggregation, male aggressiveness and decreased susceptibility to ischemic brain damage. The potential clinical relevance of this receptor is obvious. The A2A adenosine receptor, a prototypical GPCR, is known to signal via restricted collision coupling with Gs. In addition, it is able to stimulate MAP kinase/ERK in a Gs-independent way but dependent on the lipid microenvironment of the membrane. Hence, we characterized the mobility and the targeting of the A2A receptor in nerve cells.

Receptor G protein coupling and the cytoskeleton

The A2A adenosine receptor is a prototypical Gs proteincoupled receptor; it has been proposed as a drug target in the treatment of Parkinsons disease, because there is a mutual antagonism between D2 dopamine and A2A receptors in striatal neurons. Because of their ability to stimulate endothelial cell proliferation, A2A agonists are in clinical development for diabetic ulcers. Several modes of coupling have been proposed to account for the interaction of receptor and G proteins; these have been termed precoupling, restricted collision coupling etc. Here, we investigated the mode of coupling of the A2A receptor by visualizing agonist-induced changes in mobility of the YFP-tagged receptor by FRAP (fluorescence recovery after photobleaching) microscopy. Agonist stimulation did not affect the mobility of the A2A receptor; in contrast, agonist challenge induced a decrease in the mobility of the D2 receptor. When coexpressed in the same cell, the A2A receptor precluded the agonist-induced change in D2 receptor mobility. Thus, the A2A receptor does not only undergo restricted collision coupling but it also restricts the mobility of the D2 receptor. Restricted mobility is not due to tethering to the actin cytoskeleton but is, in part, related to the cholesterol content of the membrane. Depletion of cholesterol increases receptor mobility, but blunts activation of adenylyl cyclase. We conclude that signalling of the A2A receptor takes place in cholesterolrich domains of the membrane. from 13th Scientific Symposium of the Austrian Pharmacological Society (APHAR). Joint Meeting with the Austrian Society of Toxicology (ASTOX) and the Hungarian Society for Experimental and Clinical Pharmacology (MFT) Vienna, Austria. 22–24 November 2007