Characterization of PTPRG in Knockdown and Phosphatase-Inactive Mutant Mice and Substrate Trapping Analysis of PTPRG in Mammalian Cells

Receptor tyrosine phosphatase gamma (PTPRG, or RPTPγ) is a mammalian receptor-like tyrosine phosphatase which is highly expressed in the nervous system as well as other tissues. Its function and biochemical characteristics remain largely unknown. We created a knockdown (KD) line of this gene in mouse by retroviral insertion that led to 98–99% reduction of RPTPγ gene expression. The knockdown mice displayed antidepressive-like behaviors in the tail-suspension test, confirming observations by Lamprianou et al. 2006. We investigated this phenotype in detail using multiple behavioral assays. To see if the antidepressive-like phenotype was due to the loss of phosphatase activity, we made a knock-in (KI) mouse in which a mutant, RPTPγ C1060S, replaced the wild type. We showed that human wild type RPTPγ protein, expressed and purified, demonstrated tyrosine phosphatase activity, and that the RPTPγ C1060S mutant was completely inactive. Phenotypic analysis showed that the KI mice also displayed some antidepressive-like phenotype. These results lead to a hypothesis that an RPTPγ inhibitor could be a potential treatment for human depressive disorders. In an effort to identify a natural substrate of RPTPγ for use in an assay for identifying inhibitors, “substrate trapping” mutants (C1060S, or D1028A) were studied in binding assays. Expressed in HEK293 cells, these mutant RPTPγs retained a phosphorylated tyrosine residue, whereas similarly expressed wild type RPTPγ did not. This suggested that wild type RPTPγ might auto-dephosphorylate which was confirmed by an in vitro dephosphorylation experiment. Using truncation and mutagenesis studies, we mapped the auto-dephosphorylation to the Y1307 residue in the D2 domain. This novel discovery provides a potential natural substrate peptide for drug screening assays, and also reveals a potential functional regulatory site for RPTPγ. Additional investigation of RPTPγ activity and regulation may lead to a better understanding of the biochemical underpinnings of human depression.     

Protein τ-Mediated Effects on Rat Hippocampal Choline Transporters CHT1 and τ-Amyloid β Interactions

It is suggested that intracellular tau protein (τ), when released extracellularly upon neuron degeneration, could evoke direct toxic effects on the cholinergic neurotransmitter system through muscarinic receptors and thus contribute to the pathogenesis of Alzheimer’s disease. In this study, we evaluated the in vitro effects of six naturally occurring monomeric τ isoforms on rat hippocampal synaptosomal choline transporters CHT1 (large transmembrane proteins associated with high-affinity choline transport and vulnerable to actions of amyloid β peptides (Aβ) applied in vitro or in vivo). Some τ isoforms at nM concentrations inhibited choline transport in a dose- and time-dependent saturable manner (352 = 441 > 410 = 383 > 381 = 412) and effects were associated with changes in the Michaelis constant rather than in maximal velocity. Moreover, the actions of τ 352/441 were not influenced by previous depolarisation of synaptosomes or by previous depletion of membrane cholesterol. Specific binding of [3H]hemicholinium-3 was not significantly altered by τ 352/441 at higher nM concentrations. Results of in vitro tests on CHT1 transporters from cholesterol-depleted synaptosomes supported interactions between Aβ 1-40 and τ 352. In addition, we developed surface plasmon resonance biosensors to monitor complexes of Aβ 1-42 and τ 352 using a sandwich detection format. It seems, therefore, that protein τ, similar to Aβ peptides, can contribute to the pathogenesis of Alzheimer’s disease through its actions on CHT1 transporters. However, the interaction mechanisms are quite different (τ probably exerts its effects through direct interactions of microtubule binding repeats with extracellular portions of the CHT1 protein without influencing the choline recognition site, Aβ rather through lipid rafts in the surrounding membranes). An N-terminal insert of τ is not necessary but the N-terminal projection domain plays a role. The developed biosensor will be used to detect Aβ–τ complexes in cerebrospinal fluid in order to evaluate them as prospective biomarkers of Alzheimer′s disease.     

Evaluating developmental shape changes in Homo antecessor subadult facial morphology

The fossil ATD6-69 from Atapuerca, Spain, dated to ca. 900 ka (thousands of years ago) has been suggested to mark the earliest appearance of modern human facial features. However, this specimen is a subadult and the interpretation of its morphology remains controversial, because it is unclear how developmental shape changes would affect the features that link ATD6-69 to modern humans. Here we analyze ATD6-69 in an evolutionary and developmental context. Our modern human sample comprises cross-sectional growth series from four populations. The fossil sample covers human specimens from the Pleistocene to the Upper Paleolithic, and includes several subadult Early Pleistocene humans and Neanderthals. We digitized landmarks and semilandmarks on surface and CT scans and analyzed the Procrustes shape coordinates using multivariate statistics. Ontogenetic allometric trajectories and developmental simulations were employed in order to identify growth patterns and to visualize potential adult shapes of ATD6-69. We show that facial differences between modern and archaic humans are not exclusively allometric. We find that while postnatal growth further accentuates the differences in facial features between Neanderthals and modern humans, those features that have been suggested to link ATD6-69's morphology to modern humans would not have been significantly altered in the course of subsequent development. In particular, the infraorbital depression on this specimen would have persisted into adulthood. However, many of the facial features that ATD6-69 shares with modern humans can be considered to be part of a generalized pattern of facial architecture. Our results present a complex picture regarding the polarity of facial features and demonstrate that some modern human-like facial morphology is intermittently present in Middle Pleistocene humans. We suggest that some of the facial features that characterize recent modern humans may have developed multiple times in human evolution.     

The genetic basis of triple A (Allgrove) syndrome in a Greek family

Triple A (or Allgrove) syndrome is an autosomal recessive genetic disorder. Patients typically suffer from chronic adrenal insufficiency due to resistance to ACTH (Addison's disease), achalasia of the cardia, and defective tear formation (alacrima). The syndrome is caused by mutations in the AAAS gene which encodes the protein ALADIN, a constituent of eukaryotic nuclear pore complexes. The multi-systemic nature and variable manifestations of the triple A syndrome often confound its diagnosis and limit our understanding of its exact pathogenesis. We performed mutational screening of the AAAS gene in a Greek family of four individuals, including an affected propositus with typical symptoms of late-onset triple A syndrome. Our results are consistent with an autosomal recessive pattern of inheritance within the family, caused by a functional c.43C > A mutation in exon 1 of the AAAS gene. All members of the family were also homozygous for a silent c.855C > T nucleotide change within exon 9 of the AAAS gene, representing a common single nucleotide polymorphism. The compromising c.43C > A mutation is predicted to cause a p.Gln15Lys amino acid substitution in the ALADIN protein. However, it has been suggested that the functional impact of this mutation may be more severe, causing a shift in the reading frame of AAAS gene via formation of an aberrant premature donor splice site within exon 1. We propose that mutational analysis of the AAAS gene should be considered in adult patients with one or more clinical signs of the disease, as diagnosis of late-onset cases can be ambiguous.     

Synthesis and evaluation of carbamoylmethylene linked prodrugs of BMS-582949, a clinical p38α inhibitor

A series of carbamoylmethylene linked prodrugs of 1 (BMS-582949), a clinical p38α inhibitor, were synthesized and evaluated. Though the phosphoryloxymethylene carbamates (3, 4, and 5) and α-aminoacyloxymethylene carbamates (22, 23, and 26) were found unstable at neutral pH values, fumaric acid derived acyloxymethylene carbamates (2, 28, and 31) were highly stable under both acidic and neutral conditions. Prodrugs 2 and 31 were also highly soluble at both acidic and neutral pH values. At a solution dose of 14.2 mpk (equivalent to 10 mpk of 1), 2 gave essentially the same exposure of 1 compared to dosing 10 mpk of 1 itself. At a suspension dose of 142 mpk (equivalent to 100 mpk of 1), 2 demonstrated that it could overcome the solubility issue associated with 1 and provide a much higher exposure of 1. To our knowledge, the unique type of prodrugs like 2, 28, and 31 was not reported in the past and could represent a novel prodrug approach for secondary amides, a class of molecules frequently identified as drug candidates.