Mass spectrometry identifies tau C-terminal phosphorylation cluster during neuronal hyperexcitation.

Tau is a microtubule-associated protein implicated in Alzheimer's disease (AD) and other neurodegenerative disorders termed tauopathies. Pathological, aggregated forms of tau form neurofibrillary tangles (NFTs), impairing its ability to stabilize microtubules and promoting neurotoxicity. Indeed, NFTs correlate with neuronal loss and cognitive impairment. Hyperphosphorylation of tau is seen in all tauopathies and mirrors disease progression, suggesting an essential role in pathogenesis. However, hyperphosphorylation remains a generic and ill-defined term, obscuring the functional importance of specific sites in different physiological or pathological settings. Here, we focused on global mapping of tau phosphorylation specifically during conditions of neuronal hyperexcitation. Hyperexcitation is a property of AD and other tauopathies linked to human cognitive deficits and increased risk of developing seizures and epilepsy. Moreover, hyperexcitation promotes extracellular secretion and trans-synaptic propagation of tau. Using unbiased mass spectrometry, we identified a novel phosphorylation signature in the C-terminal domain of tau detectable only during neuronal hyperactivity in primary cultured rat hippocampal neurons. These sites influenced tau localization to dendrites as well as the size of excitatory postsynaptic sites. These results demonstrate novel physiological tau functions at synapses and the utility of comprehensive analysis of tau phosphorylation during specific signaling contexts.

Plk2 promotes synaptic destabilization through disruption of N-cadherin adhesion complexes during homeostatic adaptation to hyperexcitation.

Synaptogenesis in the brain is highly organized and orchestrated by synaptic cellular adhesion molecules (CAMs) such as N-cadherin and amyloid precursor protein (APP) that contribute to the stabilization and structure of synapses. Although N-cadherin plays an integral role in synapse formation and synaptic plasticity, its function in synapse dismantling is not as well understood. Synapse weakening and loss are prominent features of neurodegenerative diseases, and can also be observed during homeostatic compensation to neuronal hyperexcitation. Previously, we have shown that during homeostatic synaptic plasticity, APP is a target for cleavage triggered by phosphorylation by Polo-like kinase 2 (Plk2). Here, we found that Plk2 directly phosphorylates N-cadherin, and during neuronal hyperexcitation Plk2 promotes N-cadherin proteolytic processing, degradation, and disruption of complexes with APP. We further examined the molecular mechanisms underlying N-cadherin degradation. Loss of N-cadherin adhesive function destabilizes excitatory synapses and promotes their structural dismantling as a prerequisite to eventual synapse elimination. This pathway, which may normally help to homeostatically restrain excitability, could also shed light on the dysregulated synapse loss that occurs in cognitive disorders.

Central Cholinergic Synapse Formation in Optimized Primary Septal-Hippocampal Co-cultures.

Septal innervation of basal forebrain cholinergic neurons to the hippocampus is critical for normal learning and memory and is severely degenerated in Alzheimer's disease. To understand the molecular events underlying physiological cholinergic synaptogenesis and remodeling, as well as pathological loss, we developed an optimized primary septal-hippocampal co-culture system. Hippocampal and septal tissue were harvested from embryonic Sprague-Dawley rat brain and cultured together at varying densities, cell ratios, and in the presence of different growth factors. We identified conditions that produced robust septal-hippocampal synapse formation. We used confocal microscopy with primary antibodies and fluorescent ligands to validate that this system was capable of generating developmentally mature cholinergic synapses. Such synapses were comprised of physiological synaptic partners and mimicked the molecular composition of in vivo counterparts. This co-culture system will facilitate the study of the formation, plasticity, and dysfunction of central mammalian cholinergic synapses.

CK-MM Polymorphism is Associated With Physical Fitness Test Scores in Military Recruits.

OBJECTIVE: Muscle-specific creatine kinase is thought to play an integral role in maintaining energy homeostasis by providing a supply of creatine phosphate. The genetic variant, rs8111989, contributes to individual differences in physical performance, and thus the purpose of this study was to determine if rs8111989 variant is predictive of Physical Fitness Test (PFT) scores in male, military infantry recruits. METHODS: DNA was extracted from whole blood, and genotyping was performed in 176 Marines. Relationships between PFT measures (run, sit-ups, and pull-ups) and genotype were determined. RESULTS: Participants with 2 copies of the T allele for rs8111989 variant had higher PFT scores for run time, pull-ups, and total PFT score. Specifically, participants with 2 copies of the TT allele (variant) (n = 97) demonstrated an overall higher total PFT score as compared with those with one copy of the C allele (n = 79) (TT: 250 ± 31 vs. CC/CT: 238 ± 31; p = 0.02), run score (TT: 82 ± 10 vs. CC/CT: 78 ± 11; p = 0.04) and pull-up score (TT: 78 ± 11 vs. CC/CT: 65 ± 21; p = 0.04) or those with the CC/CT genotype. CONCLUSION: These results demonstrate an association between physical performance measures and genetic variation in the muscle-specific creatine kinase gene (rs8111989).