Contributions of extracellular-signal regulated kinase 1/2 activity to the memory trace

Effects of miR-204-5p and Target Gene EphB2 on Cognitive Impairment Induced by Aluminum Exposure in Rats

Aluminum is a common environmental neurotoxin. Aluminum ions can cross the blood-brain barrier and accumulate in different brain regions, damage brain tissue, and cause cognitive impairment, but the molecular mechanism of aluminum neurotoxicity is not precise. This study investigated the effects of miR-204-5p, target gene EphB2, and downstream signaling pathway NMDAR-ERK-CREB-Arc on cognitive dysfunction induced by aluminum exposure. The results showed that the learning and memory of the rats were impaired in behavior. The accumulation of aluminum in the hippocampus resulted in the damage of nerve cell morphology in the CA1 region of the hippocampus. The expression level of miR-204-5p was increased, and the mRNA and protein expressions of EphB2, NMDAR2B, ERK1/2, CREB, and Arc were decreased. The results indicated that the mechanism of impaired learning and memory induced by aluminum exposure might promote the expression of miR-204-5P and further inhibit the expression of the target gene EphB2 and its downstream signaling pathway NMDAR-ERK-CREB-Arc.

Beyond PDE4 inhibition: A comprehensive review on downstream cAMP signaling in the central nervous system

Cyclic adenosine monophosphate (cAMP) is a key second messenger that regulates signal transduction pathways pivotal for numerous biological functions. Intracellular cAMP levels are spatiotemporally regulated by their hydrolyzing enzymes called phosphodiesterases (PDEs). It has been shown that increased cAMP levels in the central nervous system (CNS) promote neuroplasticity, neurotransmission, neuronal survival, and myelination while suppressing neuroinflammation. Thus, elevating cAMP levels through PDE inhibition provides a therapeutic approach for multiple CNS disorders, including multiple sclerosis, stroke, spinal cord injury, amyotrophic lateral sclerosis, traumatic brain injury, and Alzheimer's disease. In particular, inhibition of the cAMP-specific PDE4 subfamily is widely studied because of its high expression in the CNS. So far, the clinical translation of full PDE4 inhibitors has been hampered because of dose-limiting side effects. Hence, focusing on signaling cascades downstream activated upon PDE4 inhibition presents a promising strategy, offering novel and pharmacologically safe targets for treating CNS disorders. Yet, the underlying downstream signaling pathways activated upon PDE(4) inhibition remain partially elusive. This review provides a comprehensive overview of the existing knowledge regarding downstream mediators of cAMP signaling induced by PDE4 inhibition or cAMP stimulators. Furthermore, we highlight existing gaps and future perspectives that may incentivize additional downstream research concerning PDE(4) inhibition, thereby providing novel therapeutic approaches for CNS disorders.

Brain-targeted Tet-1 peptide-PLGA nanoparticles for berberine delivery against STZ-induced Alzheimer's disease in a rat model: Alleviation of hippocampal synaptic dysfunction, Tau pathology, and amyloidogenesis

Alzheimer's disease (AD) is an age-related neurodegenerative disorder that causes severe dementia and memory loss. Surface functionalized poly(lactic-co-glycolic acid) nanoparticles have been reported for better transport through the blood-brain barrier for AD therapy. This study investigated the improved therapeutic potential of berberine-loaded poly(lactic-co-glycolic acid)/Tet-1 peptide nanoparticles (BBR/PLGA-Tet NPs) in a rat model of sporadic AD. BBR was loaded into the PLGA-Tet conjugate. BBR/PLGA-Tet NPs were physicochemically and morphologically characterized. AD was achieved by bilateral intracerebroventricular (ICV) injection of streptozotocin (STZ). Cognitively impaired rats were divided into STZ, STZ + BBR, STZ + BBR/PLGA-Tet NPs, and STZ + PLGA-Tet NPs groups. Cognitive improvement was assessed using the Morris Water Maze. Brain acetylcholinesterase and monoamine oxidase activities, amyloid β42 (Aβ42), and brain glycemic markers were estimated. Further, hippocampal neuroplasticity (BDNF, pCREB, and pERK/ERK), Tau pathogenesis (pGSK3β/GSK3β, Cdk5, and pTau), inflammatory, and apoptotic markers were evaluated. Finally, histopathological changes were monitored. ICV-STZ injection produces AD-like pathologies evidenced by Aβ42 deposition, Tau hyperphosphorylation, impaired insulin signaling and neuroplasticity, and neuroinflammation. BBR and BBR/PLGA-Tet NPs attenuated STZ-induced hippocampal damage, enhanced cognitive performance, and reduced Aβ42, Tau phosphorylation, and proinflammatory responses. BBR/PLGA-Tet NPs restored neuroplasticity, cholinergic, and monoaminergic function, which are critical for cognition and brain function. BBR/PLGA-Tet NPs may have superior therapeutic potential in alleviating sporadic AD than free BBR due to their bioavailability, absorption, and brain uptake.

NF-κB and JAK/STAT Signaling Pathways as Crucial Regulators of Neuroinflammation and Astrocyte Modulation in Spinal Cord Injury

Spinal cord injury (SCI) leads to significant functional impairments below the level of the injury, and astrocytes play a crucial role in the pathophysiology of SCI. Astrocytes undergo changes and form a glial scar after SCI, which has traditionally been viewed as a barrier to axonal regeneration and functional recovery. Astrocytes activate intracellular signaling pathways, including nuclear factor κB (NF-κB) and Janus kinase-signal transducers and activators of transcription (JAK/STAT), in response to external stimuli. NF-κB and STAT3 are transcription factors that play a pivotal role in initiating gene expression related to astrogliosis. The JAK/STAT signaling pathway is essential for managing secondary damage and facilitating recovery processes post-SCI: inflammation, glial scar formation, and astrocyte survival. NF-κB activation in astrocytes leads to the production of pro-inflammatory factors by astrocytes. NF-κB and STAT3 signaling pathways are interconnected: NF-κB activation in astrocytes leads to the release of interleukin-6 (IL-6), which interacts with the IL-6 receptor and initiates STAT3 activation. By modulating astrocyte responses, these pathways offer promising avenues for enhancing recovery outcomes, illustrating the crucial need for further investigation into their mechanisms and therapeutic applications in SCI treatment.

Apple Pomace Extract Improves MK-801-Induced Memory Impairment in Mice

Alzheimer's disease (AD) is a neurodegenerative disease that involves progressive cognitive decline accompanied by synaptic degeneration and impaired neurotransmission. Recent studies revealed that apple pomace, a waste byproduct of the apple processing industry, has beneficial health properties, but its potential to prevent and treat AD has not been determined. Herein, we examined the effects of apple pomace extract on N-methyl-D-aspartate receptor antagonist MK-801-induced memory impairment in mice. Repeated treatment with apple pomace extract for 7 days reversed the MK-801-induced impairment of associative memory and recognition memory. RNA sequencing revealed that repeated treatment with apple pomace extract altered the gene expression profile in the hippocampus of mice. Real-time PCR showed that apple pomace extract induced upregulation of the mRNA expression for Zfp125 and Gstp1. Furthermore, gene sets related to synapse and neurotransmission were upregulated by apple pomace extract. These findings indicate that apple pomace extract may be useful for the prevention and treatment of AD.