5-HT4 receptor agonists treatment reduces tau pathology and behavioral deficit in the PS19 mouse model of tauopathy.

Background: Accumulation of tau in synapses in the early stages of Alzheimer's disease (AD) has been shown to cause synaptic damage, synaptic loss, and the spread of tau pathology through trans-synaptically connected neurons. Moreover, synaptic loss correlates with a decline in cognitive function, providing an opportunity to investigate therapeutic strategies to target synapses and synaptic tau to rescue or prevent cognitive decline in AD. One of the promising synaptic targets is the 5-HT4 serotonergic receptor present postsynaptically in the brain structures involved in the memory processes. 5-HT4R stimulation exerts synaptogenic and pro-cognitive effects involving synapse-to-nucleus signaling essential for synaptic plasticity. However, it is not known whether 5-HT4R activation has a therapeutic effect on tau pathology. Methods: The goal of this study was to investigate the impact of chronic stimulation of 5-HT4R by two agonists, prucalopride and RS-67333, in PS19 mice, a model of tauopathy. We utilized gradient assays to isolate pre- and post-synaptic compartments, followed by biochemical analyses for tau species and ubiquitinated proteins in the synaptic compartments and total brain tissue. Next, we performed kinetic assays to test the proteasome's hydrolysis capacity in treatment conditions. Moreover, behavioral tests such as the open field and non-maternal nest-building tests were used to evaluate anxiety-like behaviors and hippocampal-related cognitive functioning in the treatment paradigm. Results: Our results show that 5-HT4R agonism reduced tauopathy, reduced synaptic tau, increased proteasome activity, and improved cognitive functioning in PS19 mice. Our data suggest that enhanced proteasome activity by synaptic mediated signaling leads to the enhanced turnover of tau initially within synapses where the receptors are localized, and over time, the treatment attenuated the accumulation of tau aggregation and improved cognitive functioning of the PS19 mice. Conclusion: Therefore, stimulation of 5-HT4R offers a promising therapy to rescue synapses from the accumulation of toxic synaptic tau, evident in the early stages of AD.

Metabolism of Docosahexaenoic Acid (DHA) Induces Pyroptosis in BV-2 Microglial Cells.

DHA is one of the most abundant fatty acids in the brain, largely present in stores of membrane phospholipids. It is readily released by the action of phospholipase A2 and is known to induce anti-inflammatory and neurotrophic effects. It is not thought to contribute to proinflammatory processes in the brain. In this study, an immortalized murine microglia cell line (BV-2) was used to evaluate the effect of DHA on neuroinflammatory cells. Pretreatment of BV-2 cells with low concentrations of DHA (30 µM) attenuates lipopolysaccharide-mediated inflammatory cytokine gene expression, consistent with known anti-inflammatory effects. However, higher (but still physiologically relevant) concentrations of DHA (200 µM) induce profound cell swelling and a reduction of viability. This is accompanied by increases in the expressions of inflammatory cytokine and lipoxygenase genes, activation of caspase-1 activity, and release of IL1ß, indicating that cells were undergoing a proinflammatory cell death program known as pyroptosis. This process could be attenuated by pharmacological inhibition of 12-lipoxygenase (12-LOX, Alox12e), but not by inhibition of 5-LOX or 15-LOX. Cumulatively, these data demonstrate that DHA has an anti-inflammatory effect on microglial cells, but its metabolism by 12-LOX generates one or more products that activate a proinflammatory cell death program.

Lysophosphatidic acid and its receptor LPA1 mediate carrageenan induced inflammatory pain in mice.

Lysophosphatidic acid receptor 1 (LPA1) is one of six G protein-coupled receptors (GPCRs) activated by the bioactive lipid, lysophosphatidic acid (LPA). Previous studies have shown that LPA1 signaling plays a major role in the pathophysiology of neuropathic pain. It has also been shown that the inhibition of phospholipase A2, an enzyme upstream of LPA synthesis, reduces mechanical allodynia in experimental inflammatory orofacial pain. This suggests that the LPA-LPA1 axis may mediate inflammatory pain in addition to its known role in neuropathic pain, but this activity has not been reported. LPA1 signaling was disrupted in mice with both genetic and pharmacological approaches. Mice were then evaluated for behavioral and molecular characteristics of allodynia in a model for inflammatory orofacial pain. Pain behavior was significantly attenuated in LPA1 knockout mice relative to wild-type littermate controls. A similar significant attenuation in allodynia was observed when mice were treated with an LPA1 antagonist, AM095, following validation of its potency and selectivity. This was accompanied by a marked reduction in phosphorylated cAMP response element-binding protein (pCREB) labelling in the cerebral cortex. Interestingly, the reduction in allodynia was observed with central, but not systemic drug administration. Taken together, our findings indicate that LPA1 signaling in the central nervous system (CNS) plays a key role in mediating orofacial inflammatory pain, identifying LPA1 as a potential therapeutic target for treating inflammatory pain with a brain-penetrant drug.