Aging-Related Dysfunction of Striatal Cholinergic Interneurons Produces Conflict in Action Selection.

For goal-directed action to remain adaptive, new strategies are required to accommodate environmental changes, a process for which parafascicular thalamic modulation of cholinergic interneurons in the striatum (PF-to-CIN) appears critical. In the elderly, however, previously acquired experience frequently interferes with new learning, yet the source of this effect has remained unexplored. Here, combining sophisticated behavioral designs, cell-specific manipulation, and extensive neuronal imaging, we investigated the involvement of the PF-to-CIN pathway in this process. We found functional alterations of this circuit in aged mice that were consistent with their incapacity to update initial goal-directed learning, resulting in faulty activation of projection neurons in the striatum. Toxicogenetic ablation of CINs in young mice reproduced these behavioral and neuronal defects, suggesting that age-related deficits in PF-to-CIN function reduce the ability of older individuals to resolve conflict between actions, likely contributing to impairments in adaptive goal-directed action and executive control in aging. VIDEO ABSTRACT.

Sex hormone-related neurosteroids differentially rescue bioenergetic deficits induced by amyloid-ß or hyperphosphorylated tau protein.

Alzheimer's disease (AD) is an age-related neurodegenerative disease marked by a progressive cognitive decline. Metabolic impairments are common hallmarks of AD, and amyloid-ß (Aß) peptide and hyperphosphorylated tau protein--the two foremost histopathological signs of AD--have been implicated in mitochondrial dysfunction. Neurosteroids have recently shown promise in alleviating cognitive and neuronal sequelae of AD. The present study evaluates the impact of neurosteroids belonging to the sex hormone family (progesterone, estradiol, estrone, testosterone, 3α-androstanediol) on mitochondrial dysfunction in cellular models of AD: human neuroblastoma cells (SH-SY5Y) stably transfected with constructs encoding (1) the human amyloid precursor protein (APP) resulting in overexpression of APP and Aß, (2) wild-type tau (wtTau), and (3) mutant tau (P301L), that induces abnormal tau hyperphosphorylation. We show that while APP and P301L cells both display a drop in ATP levels, they present distinct mitochondrial impairments with regard to their bioenergetic profiles. The P301L cells presented a decreased maximal respiration and spare respiratory capacity, while APP cells exhibited, in addition, a decrease in basal respiration, ATP turnover, and glycolytic reserve. All neurosteroids showed beneficial effects on ATP production and mitochondrial membrane potential in APP/Aß overexpressing cells while only progesterone and estradiol increased ATP levels in mutant tau cells. Of note, testosterone was more efficient in alleviating Aß-induced mitochondrial deficits, while progesterone and estrogen were the most effective neurosteroids in our model of AD-related tauopathy. Our findings lend further support to the neuroprotective effects of neurosteroids in AD and may open new avenues for the development of gender-specific therapeutic approaches in AD.

FTD and ALS--translating mouse studies into clinical trials.

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are related neurodegenerative disorders, which are characterized by a rapid decline in cognitive and motor functions, and short survival. Although the clinical and neuropathological characterization of these diseases has progressed--in part--through animal studies of pathogenetic mechanisms, the translation of findings from rodent models to clinical practice has generally not been successful. This article discusses the gap between preclinical animal studies in mice and clinical trials in patients with FTD or ALS. We outline how to better design preclinical studies, and present strategies to improve mouse models to overcome the translational shortfall. This new approach could help identify drugs that are more likely to achieve a therapeutic benefit for patients.

Bio-orthogonal labeling as a tool to visualize and identify newly synthesized proteins in Caenorhabditis elegans.

In this protocol we describe the incorporation of bio-orthogonal amino acids as a versatile method for visualizing and identifying de novo-synthesized proteins in the roundworm Caenorhabditis elegans. This protocol contains directions on implementing three complementary types of analysis: 'click chemistry' followed by western blotting, click chemistry followed by immunofluorescence, and isobaric tags for relative and absolute quantification (iTRAQ) quantitative mass spectrometry. The detailed instructions provided herein enable researchers to investigate the de novo proteome, an analysis that is complicated by the fact that protein molecules are chemically identical to each other, regardless of the timing of their synthesis. Our protocol circumvents this limitation by identifying de novo-synthesized proteins via the incorporation of the chemically modifiable azidohomoalanine instead of the natural amino acid methionine in the nascent protein, followed by facilitating the visualization of the resulting labeled proteins in situ. It will therefore be an ideal tool for studying de novo protein synthesis in physiological and pathological processes including learning and memory. The protocol requires 10 d for worm growth, liquid culture and synchronization; 1-2 d for bio-orthogonal labeling; and, with regard to analysis, 3-4 d for western blotting, 5-6 d for immunofluorescence or ~3 weeks for mass spectrometry.

Granulovacuolar degeneration and unfolded protein response in mouse models of tauopathy and Aß amyloidosis.

Histopathological studies on the brains of tauopathy cases including cases with Alzheimer's disease (AD) demonstrate that neurons with hyperphosphorylated protein tau display granulovacuolar degeneration (GVD), as evidenced by vacuolar lesions harboring a central granule, together with markers of the activated unfolded protein response (UPR). In order to examine whether this hallmark is reproduced in animal models we studied the presence of GVD and the activated UPR in two complementary mouse models, pR5 mice with a tau pathology and APPSLxPS1mut mice with an amyloid plaque pathology. Neither GVD nor a significant activation of the UPR was found in both APPSLxPS1mut mice and in those regions in the pR5 brain where only neurons with an early stage of tau hyperphosphorylation were present. In contrast, those neurons that displayed a tau phospho-epitope signature that only appeared in old pR5 mice and also correlated with Gallyas-positive tangle staining harbored granulovacuolar lesions that were labeled with the GVD markers casein kinases 1δ and 1ε. Granulovacuolar lesions in pR5 mice were also labeled with the UPR markers phosphorylated PKR-like endoplasmic reticulum kinase, phosphorylated inositol-requiring enzyme 1α and phosphorylated eukaryotic initiation factor 2α. However, GVD was rarely observed in neurons bearing mature neurofibrillary tangles as evidenced by Congo red staining. Our results suggest that NFT-formation activates the UPR in pR5 mice and that it is the early stages of neurofibrillary tangle formation that are accompanied by GVD, in line with observations from studies on human autopsy cases.

The herbal compound geniposide rescues formaldehyde-induced apoptosis in N2a neuroblastoma cells.

The herbal medicine Tong Luo Jiu Nao (TLJN) contains geniposide (GP) and ginsenoside Rg1 at a molar ratio of 10:1. Rg1 is the major component of another herbal medicine, panax notoginseng saponin (PNS). TLJN has been shown to strengthen brain function in humans, and in animals it improves learning and memory. We have previously shown that TLJN reduces amyloidogenic processing in Alzheimer's disease (AD) mouse models. Together this suggests TLJN may be a potential treatment for patients with dementia. Because chronic damage of the central nervous system by formaldehyde (FA) has been presented as a risk factor for age-associated cognitive dysfunction, in the present study we investigated the protective effect of both TLJN and GP in neuron-like cells exposed to FA. FA-exposed murine N2a neuroblastoma cells were incubated with TLJN, its main ingredient GP, as well as PNS, to measure cell viability and morphology, the rate of apoptosis and expression of genes encoding Akt, FOXO3, Bcl2 and p53. The CCK-8 assay, cytoskeletal staining and flow cytometry were used to test cell viability, morphology and apoptosis, respectively. Fluorescent quantitative real-time PCR (qRT-PCR) was used to monitor changes in gene expression, and HPLC to determine the rate of FA clearance. Treatment of N2a cells with 0.09 mmol L(-1) FA for 24 h significantly reduced cell viability, changed cell morphology and promoted apoptosis. Both TLJN and GP conferred neuroprotection to FA-treated N2a cells, whereas PNS, which had to be used at lower concentrations because of its toxicity, did not. Our data demonstrate that TLJN can rescue neuronal damage caused by FA and that its main ingredient, GP, has a major role in this efficacy. This presents purified GP as a drug or lead compound for the treatment of AD.