TNiK is required for postsynaptic and nuclear signaling pathways and cognitive function.

Traf2 and NcK interacting kinase (TNiK) contains serine-threonine kinase and scaffold domains and has been implicated in cell proliferation and glutamate receptor regulation in vitro. Here we report its role in vivo using mice carrying a knock-out mutation. TNiK binds protein complexes in the synapse linking it to the NMDA receptor (NMDAR) via AKAP9. NMDAR and metabotropic receptors bidirectionally regulate TNiK phosphorylation and TNiK is required for AMPA expression and synaptic function. TNiK also organizes nuclear complexes and in the absence of TNiK, there was a marked elevation in GSK3ß and phosphorylation levels of its cognate phosphorylation sites on NeuroD1 with alterations in Wnt pathway signaling. We observed impairments in dentate gyrus neurogenesis in TNiK knock-out mice and cognitive testing using the touchscreen apparatus revealed impairments in pattern separation on a test of spatial discrimination. Object-location paired associate learning, which is dependent on glutamatergic signaling, was also impaired. Additionally, TNiK knock-out mice displayed hyperlocomotor behavior that could be rapidly reversed by GSK3ß inhibitors, indicating the potential for pharmacological rescue of a behavioral phenotype. These data establish TNiK as a critical regulator of cognitive functions and suggest it may play a regulatory role in diseases impacting on its interacting proteins and complexes.

Arc Requires PSD95 for Assembly into Postsynaptic Complexes Involved with Neural Dysfunction and Intelligence.

Arc is an activity-regulated neuronal protein, but little is known about its interactions, assembly into multiprotein complexes, and role in human disease and cognition. We applied an integrated proteomic and genetic strategy by targeting a tandem affinity purification (TAP) tag and Venus fluorescent protein into the endogenous Arc gene in mice. This allowed biochemical and proteomic characterization of native complexes in wild-type and knockout mice. We identified many Arc-interacting proteins, of which PSD95 was the most abundant. PSD95 was essential for Arc assembly into 1.5-MDa complexes and activity-dependent recruitment to excitatory synapses. Integrating human genetic data with proteomic data showed that Arc-PSD95 complexes are enriched in schizophrenia, intellectual disability, autism, and epilepsy mutations and normal variants in intelligence. We propose that Arc-PSD95 postsynaptic complexes potentially affect human cognitive function.

Analysis of human Nav1.8 expressed in SH-SY5Y neuroblastoma cells.

The tetrodotoxin-resistant voltage-gated sodium channel alpha-subunit Nav1.8 is expressed in nociceptors and has been implicated in chronic pain. Difficulties of heterologous expression have so far precluded analysis of the pharmacological properties of human Nav1.8. To address this we have introduced human Nav1.8 in neuroblastoma SH-SY5Y cells. Voltage-clamp analysis showed that human Nav1.8 generated an inward tetrodotoxin-resistant sodium current with an activating threshold around -50 mV, half maximal activation at -11+/-3 mV and a reversal potential of 67+/-4 mV. These properties closely match those of the endogenous rat tetrodotoxin-resistant sodium current in dorsal root ganglia suggesting that the expressed human channel is in a near physiological conformation. Human Nav1.8 was resistant to tetrodotoxin and activated by the pyrethroid toxin deltamethrin. Both voltage-activated and deltamethrin-activated human Nav1.8 were inhibited by the sodium channel blockers BIII 890 CL, NW-1029, and mexiletine. Inhibition of Nav1.8 by these compounds may underlie their known analgesic effects in animal models.

Dendritic cell-based proliferative assays of peripheral T cell responses to tetanus toxoid.

Antigen-specific proliferative responses of peripheral blood T cells are widely used in humans to study the T cell compartment. However, responses to autoantigens are often weak and poorly reproducible. Here we show, using a test recall antigen (tetanus toxoid), that absolute levels of proliferation, minimally detectable antigen doses, and/or ability to detect statistically significant responses can be enhanced using in vitro-generated autologous dendritic cells as antigen presenting cells.

Humoral and cellular immune responses to proinsulin in adults with newly diagnosed type 1 diabetes.

BACKGROUND: Type 1 diabetes (T1D) is an autoimmune disease characterized by immunity against pancreatic islet-derived proteins. The object of this study was to measure antibody and T-cell responses against proinsulin (PI), an islet-derived protein, and to map its dominant T-cell epitopes. METHODS: Antibody responses to proinsulin, insulin, glutamic acid decarboxylase (GAD), protein tyrosine phosphatase IA-2 and islet-cell antigen were measured in 116 newly diagnosed diabetic subjects aged 16 to 40 years. T-cell proliferative responses to proinsulin and proinsulin peptides were measured in 33 of these diabetic subjects and in 21 healthy control subjects. RESULTS: 22% of diabetic subjects but no control subjects expressed antibodies to proinsulin. A strong correlation existed between antibody levels to proinsulin and insulin within diabetic subjects. Similar proportions of diabetic (12%) and healthy (9.5%) subjects displayed T-cell responses to proinsulin. There was no correlation between antibody and T-cell responses to proinsulin within subjects. Amino acid region 56 to 72 was identified as the major T-cell epitope of proinsulin, though significant responses to region 14 to 37 were also present. CONCLUSION: Elevated proinsulin autoantibodies in diabetic subjects confirm proinsulin is an important autoantigen in type 1 diabetes. Though elevated cellular immunity to proinsulin protein was not detected, two dominant T-cell epitopes of proinsulin were identified that span the C-peptide and insulin junctions. Immunity to proinsulin was lower than that reported for childhood-onset type 1 diabetes and we propose that, like insulin, proinsulin may be targeted less frequently in adulthood.

Dendritic cell-based assays, but not mannosylation of antigen, improves detection of T-cell responses to proinsulin in type 1 diabetes.

In vitro detection of T-cell responses to autoantigens in type 1 diabetes is recognized as being technically challenging. We aimed to accurately measure cellular responses to proinsulin in patients with diabetes, and speculated that presentation of antigen by dendritic cells (DCs) would enhance the sensitivity of the peripheral blood assay. Antigen was mannosylated to facilitate uptake through DC surface mannose receptors to further improve the assay. Whole proinsulin, as well as mannosylated peptides of proinsulin, were combined with peripheral T cells and autologous immature DCs in a proliferative assay in a panel of newly diagnosed type 1 diabetic patients. The DC-based assay detected responses to proinsulin in five of 15 diabetic patients compared to one of 15 diabetic patients detected using the standard mononuclear cell assay. When the results of all patients were combined, the DC assay, but not the mononuclear cell assay, had a proinsulin response that was significantly higher than background (P < 0.001). The DC assay was, however, associated with high autologous mixed lymphocyte reactions that possibly masked responses in individual patients. Mannosylated antigen was taken up in larger quantities than non-mannosylated antigen, but not presented any more powerfully. Our data suggest that autologous DC-based assays are more powerful than standard peripheral blood mononuclear cell assays. However, they are compromised by high autologous mixed lymphocyte reactions and this requires addressing before they can be used as a routine readout of in vitro peripheral T-cell responses.