Agricultural activities and risk of Alzheimer's disease: the TRACTOR project, a nationwide retrospective cohort study

Data regarding Alzheimer's disease (AD) occurrence in farming populations is lacking. This study aimed to investigate whether, among the entire French farm manager (FM) workforce, certain agricultural activities are more strongly associated with AD than others, using nationwide data from the TRACTOR (Tracking and monitoring occupational risks in agriculture) project. Administrative health insurance data (digital electronic health/medical records and insurance claims) for the entire French agricultural workforce, over the period 2002-2016, on the entire mainland France were used to estimate the risk of AD for 26 agricultural activities with Cox proportional hazards model. For each analysis (one for each activity), the exposed group included all FMs that performed the activity of interest (e.g. crop farming), while the reference group included all FMs who did not carry out the activity of interest (e.g. FMs that never farmed crops between 2002 and 2016). There were 5067 cases among 1,036,069 FMs who worked at least one year between 2002 and 2016. Analyses showed higher risks of AD for crop farming (hazard ratio (HR) = 3.72 [3.47-3.98]), viticulture (HR = 1.29 [1.18-1.42]), and fruit arboriculture (HR = 1.36 [1.15-1.62]). By contrast, lower risks of AD were found for several animal farming types, in particular for poultry and rabbit farming (HR = 0.29 [0.20-0.44]), ovine and caprine farming (HR = 0.50 [0.41-0.61]), mixed dairy and cow farming (HR = 0.46 [0.37-0.57]), dairy farming (HR = 0.67 [0.61-0.73]), and pig farming (HR = 0.30 [0.18-0.52]). This study shed some light on the association between a wide range of agricultural activities and AD in the entire French FMs population.

Stimulation of synaptic activity promotes TFEB-mediated clearance of pathological MAPT/Tau in cellular and mouse models of tauopathies

Synapses represent an important target of Alzheimer disease (AD), and alterations of their excitability are among the earliest changes associated with AD development. Synaptic activation has been shown to be protective in models of AD, and deep brain stimulation (DBS), a surgical strategy that modulates neuronal activity to treat neurological and psychiatric disorders, produced positive effects in AD patients. However, the molecular mechanisms underlying the protective role(s) of brain stimulation are still elusive. We have previously demonstrated that induction of synaptic activity exerts protection in mouse models of AD and frontotemporal dementia (FTD) by enhancing the macroautophagy/autophagy flux and lysosomal degradation of pathological MAPT/Tau. We now provide evidence that TFEB (transcription factor EB), a master regulator of lysosomal biogenesis and autophagy, is a key mediator of this cellular response. In cultured primary neurons from FTD-transgenic mice, synaptic stimulation inhibits MTORC1 signaling, thus promoting nuclear translocation of TFEB, which, in turn, induces clearance of MAPT/Tau oligomers. Conversely, synaptic activation fails to promote clearance of toxic MAPT/Tau in neurons expressing constitutively active RRAG GTPases, which sequester TFEB in the cytosol, or upon TFEB depletion. Activation of TFEB is also confirmed in vivo in DBS-stimulated AD mice. We also demonstrate that DBS reduces pathological MAPT/Tau and promotes neuroprotection in Parkinson disease patients with tauopathy. Altogether our findings indicate that stimulation of synaptic activity promotes TFEB-mediated clearance of pathological MAPT/Tau. This mechanism, underlying the protective effect of DBS, provides encouraging support for the use of synaptic stimulation as a therapeutic treatment against tauopathies.Abbreviations: 3xTg-AD: triple transgenic AD mice; AD: Alzheimer disease; CSA: cyclosporine A; DBS: deep brain stimulation; DIV: days in vitro; EC: entorhinal cortex; FTD: frontotemporal dementia; gLTP: glycine-induced long-term potentiation; GPi: internal segment of the globus pallidus; PD: Parkinson disease; STN: subthalamic nucleus; TFEB: transcription factor EB.

The TRACTOR Project: TRACking and MoniToring Occupational Risks in Agriculture Using French Insurance Health Data (MSA)

OBJECTIVES

A vast data mining project called 'TRACking and moniToring Occupational Risks in agriculture' (TRACTOR) was initiated in 2017 to investigate work-related health events among the entire French agricultural workforce. The goal of this work is to present the TRACTOR project, the challenges faced during its implementation, to discuss its strengths and limitations and to address its potential impact for health surveillance.

METHODS

Three routinely collected administrative health databases from the National Health Insurance Fund for Agricultural Workers and Farmers (MSA) were made available for the TRACTOR project. Data management was required to properly clean and prepare the data before linking together all available databases.

RESULTS

After removing few missing and aberrant data (4.6% values), all available databases were fully linked together. The TRACTOR project is an exhaustive database of agricultural workforce (active and retired) from 2002 to 2016, with around 10.5 million individuals including seasonal workers and farm managers. From 2012 to 2016, a total of 6 906 290 individuals were recorded. Half of these individuals were active and 46% had at least one health event (e.g. declared chronic disease, reimbursed drug prescription) during this 5-year period.

CONCLUSIONS

The assembled MSA databases available in the TRACTOR project are regularly updated and represent a promising and unprecedent dataset for data mining analysis dedicated to the early identification of current and emerging work-related illnesses and hypothesis generation. As a result, this project could help building a prospective integrated health surveillance system for the benefit of agricultural workers.

Deep Brain Stimulation of the Medial Septal Nucleus Induces Expression of a Virally Delivered Reporter Gene in Dentate Gyrus

Background

Mechanisms of deep brain stimulation (DBS) remain controversial, and spatiotemporal control of brain-wide circuits remains elusive. Adeno-associated viral (AAV) vectors have emerged as vehicles for spatiotemporal expression of exogenous transgenes in several tissues, including specific nuclei in the brain. Coupling DBS with viral vectors to modulate exogenous transgene expression remains unexplored.

Objective

This study examines whether DBS of the medial septal nucleus (MSN) can regulate gene expression of AAV-transduced neurons in a brain region anatomically remote from the stimulation target: the hippocampal dentate gyrus.

Methods

Rats underwent unilateral hippocampal injection of an AAV vector with c-Fos promoter-driven expression of TdTomato (TdT), followed by MSN electrode implantation. Rodents received no stimulation, 7.7 Hz (theta), or 130 Hz (gamma) DBS for 1 h one week after surgery. In a repeat stimulation experiment, rodents received either no stimulation, or two 1 h MSN DBS over 2 weeks.

Results

No significant differences in hippocampal TdT expression between controls and acute MSN DBS were found. With repeat DBS we found c-Fos protein expression was induced and we could detect increased TdT with either gamma or theta stimulation.

Conclusion

We demonstrate that viral vector-mediated gene expression can be regulated spatially and temporally using DBS. Control of gene expression by DBS warrants further investigation into stimulation-responsive promoters for clinical applications.

Anatomy and function of the fornix in the context of its potential as a therapeutic target

The fornix is a white matter bundle located in the mesial aspect of the cerebral hemispheres, which connects various nodes of a limbic circuitry and is believed to play a key role in cognition and episodic memory recall. As the most prevalent cause of dementia, Alzheimer's disease (AD) dramatically impairs the quality of life of patients and imposes a significant societal burden on the healthcare system. As an established treatment for movement disorders, deep brain stimulation (DBS) is currently being investigated in preclinical and clinical studies for treatment of memory impairment in AD by modulating fornix activity. Optimal target and stimulation parameters to potentially rescue memory deficits have yet to be determined. The aim of this review is to consolidate the structural and functional aspects of the fornix in the context of neuromodulation for memory deficits. We first present an anatomical and functional overview of the fibres and structures interconnected by the fornix. Recent evidence from preclinical models suggests that the fornix is subdivided into two distinct functional axes: a septohippocampal pathway and a subiculothalamic pathway. Each pathway's target and origin structures are presented, followed by a discussion of their oscillatory dynamics and functional connectivity. Overall, neuromodulation of each pathway of the fornix is discussed in the context of evidence-based forniceal DBS strategies. It is not yet known whether driving fornix activity can enhance cognition-optimal target and stimulation parameters to rescue memory deficits have yet to be determined.

Early-onset impairment of the ubiquitin-proteasome system in dopaminergic neurons caused by α-synuclein

Parkinson's disease is a progressive neurodegenerative disorder characterised by the accumulation of misfolded α-synuclein in selected brain regions, including the substantia nigra pars compacta (SNpc), where marked loss of dopaminergic neurons is also observed. Yet, the relationship between misfolded α-synuclein and neurotoxicity currently remains unclear. As the principal route for degradation of misfolded proteins in mammalian cells, the ubiquitin-proteasome system (UPS) is critical for maintenance of cellular proteostasis. Misfolded α-synuclein impairs UPS function and contributes to neuronal death in vitro. Here, we examine its effects in vivo using adeno-associated viruses to co-express A53T α-synuclein and the ubiquitinated reporter protein Ub^G76V-GFP in rat SNpc. We found that α-synuclein over-expression leads to early-onset catalytic impairment of the 26S proteasome with associated UPS dysfunction, preceding the onset of behavioural deficits and dopaminergic neurodegeneration. UPS failure in dopaminergic neurons was also associated with selective accumulation of α-synuclein phosphorylated at the serine 129 residue, which has previously been linked to increased neurotoxicity. Our study highlights a role for α-synuclein in disturbing proteostasis which may contribute to neurodegeneration in vivo.

Full-field swept-source optical coherence tomography and neural tissue classification for deep brain imaging

Optical coherence tomography can differentiate brain regions with intrinsic contrast and at a micron scale resolution. Such a device can be particularly useful as a real-time neurosurgical guidance tool. We present, to our knowledge, the first full-field swept-source optical coherence tomography system operating near a wavelength of 1310 nm. The proof-of-concept system was integrated with an endoscopic probe tip, which is compatible with deep brain stimulation keyhole neurosurgery. Neuroimaging experiments were performed on ex vivo brain tissues and in vivo in rat brains. Using classification algorithms involving texture features and optical attenuation, images were successfully classified into three brain tissue types.

Transcranial direct current stimulation does not improve memory deficits or alter pathological hallmarks in a rodent model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive and debilitating degenerative disorder for which there are currently no effective therapeutic options. Non-invasive neuromodulation, including transcranial direct current stimulation (tDCS), has been investigated for the treatment of cognitive symptoms in AD. Results from clinical and preclinical studies, however, have been somewhat controversial. We investigate whether tDCS delivered to triple transgenic (3xTg) AD mice improves memory deficits and mitigates the development of AD-type neuropathology. 3xTg AD mice and controls were implanted with paddle electrodes over the skull. The cathode was anterior to bregma and the anode anterior to lamda. tDCS was delivered for 20 min/day, 5 days/week over three weeks at 50 μA. Though this amplitude was lower than the one used in the preclinical literature, it generated a high current density compared to the clinical scenario. Memory testing was conducted during treatment weeks 2 and 3. Post-mortem pathological AD markers were studied. Our results show that performance of 3xTg mice in the novel object recognition and Morris water maze tests was significantly impaired compared to that of controls. In addition, AD transgenics had an increased expression of tau, phosphorylated-tau and amyloid precursor protein in the hippocampus. tDCS did not improve behavioural deficits or mitigated the development of AD neuropathology in 3xTg animals. In summary, we found that tDCS at the settings selected in our study was largely ineffective in improving memory performance or altering the expression of AD pathological hallmarks in a validated mouse model.

Chronic deep brain stimulation in an Alzheimer's disease mouse model enhances memory and reduces pathological hallmarks

BACKGROUND

Alzheimer's disease (AD) is a progressive degenerative disorder that currently remains extremely disabling. Recent work has shown that deep brain stimulation (DBS) has promising effects in AD patients. In parallel to the clinical trials, we investigated the impact of chronic DBS in 3xTg mice, a well-established animal model of AD.

METHODS

AD mice were assigned to control (Cont), non-stimulation (NS) and stimulation (DBS) groups, along with age matched wild type controls (WT-Cont). Bilateral electrodes were implanted in the entorhinal cortex to deliver chronic high frequency stimulation for 25 days. Animals were tested in memory behavioral tasks, with post-mortem measurements of pathological markers.

RESULTS

We found that chronic DBS in AD mice normalized their impaired performance in the Morris water maze task to that of the WT group in the probe test. In the novel object and novel place preference tasks, AD-DBS mice spent more time at the novel object and novice location compared to AD-NS mice. These cognitive improvements in AD-DBS mice were associated with DBS induced increased neurogenesis in the dentate gyrus, a significant reduction in β-amyloid plaques, a reduction in CA-1 cellular β-amyloid-42 levels, decreased cortical total-tau and phosphorylated-tau, along with decreased hippocampal total-tau.

CONCLUSION

Overall, we show that chronic DBS of the entorhinal cortex in AD mice improves both memory and AD specific pathological markers. These results support further testing of DBS as a potential treatment in AD patients.

Rapid Modulation of Protein Expression in the Rat Hippocampus Following Deep Brain Stimulation of the Fornix

BACKGROUND

The forniceal area is currently being evaluated as a target for deep brain stimulation (DBS) to improve cognitive function in patients with Alzheimer's disease. The molecular changes at downstream targets within the stimulated circuit are unknown.

OBJECTIVE

To analyze the modulation of hippocampal protein expression following 1 h of fornix DBS in the rat.

METHODS

Animals underwent bilateral forniceal DBS for 1 h and sacrificed at different time-points after the initiation of the stimulation (1 h, 2.5 h, 5 h, 25 h). Bilateral hippocampi were isolated for western blot analyses.

RESULTS

Forniceal DBS led to a dramatic elevation of cFos post-stimulation, suggesting that forniceal DBS activates the hippocampus. There was also a significant increase in candidate proteins including several trophic factors, such as brain derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) but not glial cell-derived neurotrophic factor (GDNF). There was in addition, increased expression of the synaptic markers growth associated protein 43 (GAP-43), synaptophysin and α-synuclein. No changes were observed at the studied time-points in Alzheimer's-related proteins including amyloid precursor protein (APP), tau, phosphorylated tau (ptau), or selected chaperone proteins (HSP40, HSP70 and CHIP).

CONCLUSIONS

Forniceal DBS triggers hippocampal activity and rapidly modulate the expression of neurotrophic factors and markers of synaptic plasticity known to play key roles in memory processing. The clinical effects of DBS of the fornix may, in part, be mediated by producing changes in the expression of these proteins.

Enhanced histaminergic neurotransmission and sleep-wake alterations, a study in histamine H3-receptor knock-out mice

Long-term abolition of a brain arousal system impairs wakefulness (W), but little is known about the consequences of long-term enhancement. The brain histaminergic arousal system is under the negative control of H3-autoreceptors whose deletion results in permanent enhancement of histamine (HA) turnover. In order to determine the consequences of enhancement of the histaminergic system, we compared the cortical EEG and sleep-wake states of H3-receptor knockout (H3R-/-) and wild-type mouse littermates. We found that H3R-/-mice had rich phenotypes. On the one hand, they showed clear signs of enhanced HA neurotransmission and vigilance, i.e., a higher EEG θ power during spontaneous W and a greater extent of W or sleep restriction during behavioral tasks, including environmental change, locomotion, and motivation tests. On the other hand, during the baseline dark period, they displayed deficient W and signs of sleep deterioration, such as pronounced sleep fragmentation and reduced cortical slow activity during slow wave sleep (SWS), most likely due to a desensitization of postsynaptic histaminergic receptors as a result of constant HA release. Ciproxifan (H3-receptor inverse agonist) enhanced W in wild-type mice, but not in H3R-/-mice, indicating a functional deletion of H3-receptors, whereas triprolidine (postsynaptic H1-receptor antagonist) or α-fluoromethylhistidine (HA-synthesis inhibitor) caused a greater SWS increase in H3R-/- than in wild-type mice, consistent with enhanced HA neurotransmission. These sleep-wake characteristics and the obesity phenotypes previously reported in this animal model suggest that chronic enhancement of histaminergic neurotransmission eventually compromises the arousal system, leading to sleep-wake, behavioral, and metabolic disorders similar to those caused by voluntary sleep restriction in humans.