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The extensive use of organophosphates (OPs) is an ongoing environmental health concern due to multiple reports of OP-related neurologic abnormalities. The mechanism of the acute toxicity of OPs has been attributed to inhibition of acetylcholinesterase (AChE), but there is growing evidence that this may not account for all the long-term neurotoxic effects of OPs. In previous experiments (using ex vivo and in vitro model systems) we observed that the insecticide OP chlorpyrifos impaired the movements of vesicles and mitochondria in axons. Here, using a time-lapse imaging technique, we evaluated the OP-nerve agent diisopropylfluorophosphate (DFP) across a wide range of concentrations (subnanomolar to micromolar) for effects on fast axonal transport of membrane-bound organelles (MBOs) that contain the amyloid precursor protein (APP) tagged with the fluorescent marker Dendra2 (APPDendra2). Both 1 and 24 hours of exposure to DFP and a positive control compound, colchicine, resulted in a decrease in the velocity of anterograde and retrograde movements of MBOs and an increase in the number of stationary MBOs. These effects occurred at picomolar (100 pM) to low nanomolar (0.1 nM) concentrations that were not associated with compromised cell viability or cytoskeletal damage. Moreover, the effects of DFP on axonal transport occurred at concentrations that did not inhibit AChE activity, and they were not blocked by cholinergic receptor antagonists. Given the fundamental importance of axonal transport to neuronal function, these observations may explain some of the long-term neurologic deficits that have been observed in humans who have been exposed to OPs.

The cellular mechanisms underlying the exceptional vulnerability of the basal forebrain ( BF) cholinergic neurons during pathological aging have remained elusive. Here we employed an adeno-associated viral vector-based RNA interference ( AAV- RNAi) strategy to suppress the expression of tropomyosin-related kinase A (trk A) receptors by cholinergic neurons in the nucleus basalis of Meynert/substantia innominata ( nMB/ SI) of adult and aged rats. Suppression of trk A receptor expression impaired attentional performance selectively in aged rats. Performance correlated with trk A levels in the nMB/ SI. trk A knockdown neither affected nMB/ SI cholinergic cell counts nor the decrease in cholinergic cell size observed in aged rats. However, trk A suppression augmented an age-related decrease in the density of cortical cholinergic processes and attenuated the capacity of cholinergic neurons to release acetylcholine ( ACh). The capacity of cortical synapses to release ACh in vivo was also lower in aged/trk A- AAV-infused rats than in aged or young controls, and it correlated with their attentional performance. Furthermore, age-related increases in cortical pro NGF and p75 receptor levels interacted with the vector-induced loss of trk A receptors to shift NGF signaling toward p75-mediated suppression of the cholinergic phenotype, thereby attenuating cholinergic function and impairing attentional performance. These effects model the abnormal trophic regulation of cholinergic neurons and cognitive impairments in patients with early Alzheimer's disease. This rat model is useful for identifying the mechanisms rendering aging cholinergic neurons vulnerable as well as for studying the neuropathological mechanisms that are triggered by disrupted trophic signaling. [ABSTRACT FROM AUTHOR]

Background: SARS‐CoV‐2 the causative agent of COVID‐19 displays a broad range of pathophysiology. Cytokine storms associated with COVID‐19 damage the blood‐brain barrier (BBB) and allow pro‐inflammatory factors to invade the brain, further promoting neurodegeneration. While SARS‐CoV‐2 viral RNA and proteins have been detected in brain tissues, the mechanisms of neuroinvasion remain unknown. COVID‐19 has had a disproportionate impact on those suffering from neurodegenerative disorders such as Alzheimer's disease (AD). Understanding the mechanisms of SARS‐CoV‐2 neuroinvasion is crucial to study the long‐term neurocognitive effects of COVID‐19 on AD pathology. Viruses can infiltrate the brain through the meninges via infected immune cells. The meninges regulate the immune surveillance of the brain and play a key role in the efflux of pathogens from the brain. Meningeal dysfunction has been demonstrated to exacerbate amyloid‐beta pathogenesis. In this study, we explore the neuroinvasion pathway of SARS‐CoV‐2 through the meninges and its effect on AD pathology. Method: 5x FAD x hACE2 mice were inoculated intranasally with a sublethal dose of SARS‐CoV‐2. The mice were maintained for 2 weeks. Mouse brains and meninges were harvested. The tissue was stained and immunofluorescence imaging was conducted to study viral proliferation and immune responses. Histo‐cytometry was conducted for quantitative imaging analysis. Gene expression studies were done using Nanostring assays. All experiments involving the SARS‐Cov‐2 virus were carried out in a BSL3 facility. Result: This ongoing study demonstrates the proliferation of the SARS‐CoV‐2 virus in the brain via meningeal lymphatics. SARS‐CoV‐2 infection resulted in increased neuroinflammation. Additionally, inflammatory responses induced meningeal dysfunction resulting in increased amyloid‐beta pathology and cerebrospinal fluid drainage. Conclusion: Given the increasing evidence for a viral hypothesis of Alzheimer's Disease it is extremely important to study the neurodegenerative effects of COVID‐19 which has affected millions worldwide. We demonstrate that SARS‐CoV‐2 infiltrates the brain via the meninges promoting neuroinflammation. Furthermore, amyloid‐beta pathologies are exacerbated by COVID‐19 in animal models providing preclinical evidence of the long‐term neurodegenerative effects of COVID‐19. [ABSTRACT FROM AUTHOR]

The chemicals known as the organophosphates (OPs) are found in hundreds of useful agricultural, industrial, and commercial products; however, they have also been associated with a variety of adverse health effects in humans and other non-target organisms. The acute toxicity of OPs is attributed to the inhibition of the enzyme acetylcholinesterase; however, this mechanism is inadequate to explain all of the long-term adverse effects of OPs. In both live imaging studies in primary neuronal culture as well as in manganese-enhanced magnetic resonance imaging (MEMRI) studies of the brains of living rats, we have observed impairments in axonal transport (AXT) associated with both the insecticide OP chlorpyrifos and the nerve agent OP diisopropylfluorophosphate. These observations may be important since AXT is an essential process that is responsible for the movement of a variety of important macromolecules to and from a neuron's cell body. In this presentation, a brief overview of the results of these neuronal culture (trafficking) and MEMRI experiments will be provided. In addition, the results of experiments conducted to date to identify specific molecular targets of OPs that might negatively influence axonal transport will be summarized. These targets include post-translational modifications of structural proteins that affect AXT through the regulation of microtubule dynamics and stability (e.g., Tau phosphorylation, Tubulin Acetylation), and specific signaling kinases (e.g., ERK GSKIIIß) that are known to regulate various components of the AXT process. These experiments are expected to help us begin to develop novel therapeutic strategies to improve the neuronal deficits associated with OPs. [ABSTRACT FROM AUTHOR]

G protein-coupled receptors (GPCRs) are important modulators of synaptic functions. A fundamental but poorly addressed question in neurobiology is how targeted GPCR trafficking is achieved. Rab GTPases are the master regulators of vesicle-mediated membrane trafficking, but their functions in the synaptic presentation of newly synthesized GPCRs are virtually unknown. Here, we investigate the role of Rab43, via dominant-negative inhibition and CRISPR-Cas9-mediated KO, in the export trafficking of α2-adrenergic receptor (α2-AR) and muscarinic acetylcholine receptor (mAChR) in primary neurons and cells. We demonstrate that Rab43 differentially regulates the overall surface expression of endogenous α2-AR and mAChR, as well as their signaling, in primary neurons. In parallel, Rab43 exerts distinct effects on the dendritic and postsynaptic transport of specific α2B-AR and M3 mAChR subtypes. More interestingly, the selective actions of Rab43 toward α2B-AR and M3 mAChR are neuronal cell specific and dictated by direct interaction. These data reveal novel, neuronspecific functions for Rab43 in the dendritic and postsynaptic targeting and sorting of GPCRs and imply multiple forward delivery routes for different GPCRs in neurons. Overall, this study provides important insights into regulatory mechanisms of GPCR anterograde traffic to the functional destination in neurons. [ABSTRACT FROM AUTHOR]