Frontiers in Molecular Neuroscience最新文献

The accumulation of a disease-specific isoform of prion protein (PrP^Sc) and histopathological lesions, such as neuronal loss, are unevenly distributed in the brains of humans and animals affected with prion diseases. This distribution varies depending on the diseases and/or the combinations of prion strain and experimental animal. The brain region-dependent distribution of PrP^Sc and neuropathological lesions suggests a neuronal cell-type-dependent prion propagation and vulnerability to prion infection. However, the underlying mechanism is largely unknown. In this study, we provided evidence that the prion 22L strain propagates more efficiently in excitatory neurons than inhibitory neurons and that excitatory neurons in the thalamus are vulnerable to prion infection. PrP^Sc accumulation was less intense in the striatum, where GABAergic inhibitory neurons predominate, compared to the cerebral cortex and thalamus, where glutamatergic excitatory neurons are predominant, in mice intracerebrally or intraperitoneally inoculated with the 22L strain. PrP^Sc stains were observed along the needle track after stereotaxic injection into the striatum, whereas they were also observed away from the needle track in the thalamus. Consistent with inefficient prion propagation in the striatum, the 22L prion propagated more efficiently in glutamatergic neurons than GABAergic neurons in primary neuronal cultures. RNAscope in situ hybridization revealed a decrease in Vglut1- and Vglut2-expressing neurons in the ventral posterolateral nuclei of the thalamus in 22L strain-infected mice, whereas no decrease in Vgat-expressing neurons was observed in the adjacent reticular nucleus, mainly composed of Vgat-expressing interneurons. The excitatory neuron-prone prion propagation and excitatory neuronal loss in 22L strain-infected mice shed light on the neuropathological mechanism of prion diseases.

As many proteins prioritize functionality over constancy of structure, a proteome is the shortest stave in the Liebig's barrel of cell sustainability. In this regard, both prokaryotes and eukaryotes possess abundant machinery supporting the quality of the proteome in healthy and stressful conditions. This machinery, namely chaperones, assists in folding, refolding, and the utilization of client proteins. The functions of chaperones are especially important for brain cells, which are highly sophisticated in terms of structural and functional organization. Molecular chaperones are known to exert beneficial effects in many brain diseases including one of the most threatening and widespread brain pathologies, ischemic stroke. However, whether and how they exert the antioxidant defense in stroke remains unclear. Herein, we discuss the chaperones shown to fight oxidative stress and the mechanisms of their antioxidant action. In ischemic stroke, during intense production of free radicals, molecular chaperones preserve the proteome by interacting with oxidized proteins, regulating imbalanced mitochondrial function, and directly fighting oxidative stress. For instance, cells recruit Hsp60 and Hsp70 to provide proper folding of newly synthesized proteins-these factors are required for early ischemic response and to refold damaged polypeptides. Additionally, Hsp70 upregulates some dedicated antioxidant pathways such as FOXO3 signaling. Small HSPs decrease oxidative stress via attenuation of mitochondrial function through their involvement in the regulation of Nrf- (Hsp22), Akt and Hippo (Hsp27) signaling pathways as well as mitophagy (Hsp27, Hsp22). A similar function has also been proposed for the Sigma-1 receptor, contributing to the regulation of mitochondrial function. Some chaperones can prevent excessive formation of reactive oxygen species whereas Hsp90 is suggested to be responsible for pro-oxidant effects in ischemic stroke. Finally, heat-resistant obscure proteins (Hero) are able to shield client proteins, thus preventing their possible over oxidation.

KCC2 is CNS neuron-specific chloride extruder, essential for the establishment and maintenance of the transmembrane chloride gradient, thereby enabling synaptic inhibition within the CNS. Herein, we highlight KCC2 hypofunction as a fundamental and conserved pathology contributing to neuronal circuit excitation/inhibition (E/I) imbalances that underly epilepsies, chronic pain, neuro-developmental/-traumatic/-degenerative/-psychiatric disorders. Indeed, downstream of both acquired and genetic factors, multiple pathologies (e.g., hyperexcitability and inflammation) converge to impair KCC2-dependent inhibition in CNS. When KCC2 hypofunction occurs, affected neurons are disinhibited due to impaired inhibitory responses to GABA/glycine. This causes neuronal hyperexcitability, disinhibition within neuron circuits, and disrupted neurological functions. More recently, KCC2 was identified as a genetically-validated target for epilepsy, intellectual disability, and autism spectrum disorder, and pathogenic mutations in human SLC12A5 gene were linked to psychiatric/mood disorders. The broad therapeutic utility of KCC2-upmodulating drugs relates to its critical role in determining inhibitory activity of GABAergic neurotransmission, a mechanism widely targeted by several drugs. However, in cases of KCC2 hypofunction GABAergic neurotransmission can be depolarizing/excitatory, thereby impairing endogenous neuronal inhibition while also limiting the effectiveness of existing therapeutics targeting/requiring GABAergic pathway inhibition. Several preclinical reports have shown that KCC2 upmodulating treatments rescue and increase the efficacy of anti-seizure and analgesic medications. Thus, a first-in-class KCC2-potentiating therapy would provide a novel mechanism for restoring physiological CNS inhibition and addressing drug resistance in patients with E/I imbalance pathologies. Herein, we discuss progress toward and further work needed to develop the first-in-class KCC2 therapeutics to treat neurological disorder patients.

Retinal membrane guanylyl cyclase (RetGC), regulated by guanylyl cyclase activating proteins (GCAPs) via negative calcium-feedback, is one of the most critically important enzymes in vertebrate rod and cone physiology, enabling their sensitivity to light. It was also reported that, similarly to olfactory receptor guanylyl cyclase, bicarbonate anion directly stimulates RetGC activity in photoreceptors as a novel phototransduction-linked regulating factor. We directly tested whether or not RetGC is a bicarbonate-activated enzyme using recombinant human RetGC expressed in HEK293 cells and the native RetGC in mouse retinas. Whereas RetGC in all cases was activated by GCAPs, we found no evidence indicating that bicarbonate can produce direct stimulating effect on RetGC catalytic activity, either basal or GCAP-activated, even at concentrations as high as 100 mM. Instead, near-physiological concentrations of bicarbonate only slightly reduced RetGC activity, whereas concentrations substantially exceeding physiological levels caused a more pronounced reduction of RetGC activity measured in mouse retinas. Our results argue that photoreceptor guanylyl cyclase is not a bicarbonate-stimulated enzyme and rule out the possibility that effects of bicarbonate on photoreceptor physiology are mediated by a direct stimulation of retinal guanylyl cyclase by HCO₃ ^-.

Background: Retinal degeneration is a major cause of irreversible blindness. Stimulation with controlled low-level electrical fields, such as transcorneal electrical stimulation (TES), has recently been postulated as a therapeutic strategy. With promising results, there is a need for detailed molecular characterization of the therapeutic effects of TES.

Methods: Controlled, non-invasive TES was delivered using a custom contact lens electrode to the retinas of Royal College of Surgeons (RCS) rats, a model of retinal degeneration. DNA methylation in the retina, brain and cell-free DNA in plasma was assessed by reduced representation bisulfite sequencing (RRBS) and gene expression by RNA sequencing.

Results: TES induced DNA methylation and gene expression changes implicated in neuroprotection in the retina of RCS rats. We devised an epigenomic-based retinal health score, derived from DNA methylation changes observed with disease progression in RCS rats, and showed that TES improved the epigenomic health of the retina. TES also induced DNA methylation changes in the superior colliculus: the brain which is involved in integrating visual signaling. Lastly, we demonstrated that TES-induced retinal DNA methylation changes were detectable in cell-free DNA derived from plasma.

Conclusion: TES induced DNA methylation changes with therapeutic effects, which can be measured in circulation. Based on these changes, we were able to devise a liquid biopsy biomarker for retinal health. These findings shed light on the therapeutic potential and molecular underpinnings of TES, and provide a foundation for the further development of TES to improve the retinal health of patients with degenerative eye diseases.

Copper (Cu) is essential for brain development and function, yet its overload induces neuronal damage and contributes to neurodegeneration and other neurological disorders. Multiple studies demonstrated that Cu neurotoxicity is associated with mitochondrial dysfunction, routinely assessed by reduction of mitochondrial membrane potential. Nonetheless, the role of alterations of mitochondrial dynamics in brain mitochondrial dysfunction induced by Cu exposure is still debatable. Therefore, the objective of the present narrative review was to discuss the role of mitochondrial dysfunction in Cu-induced neurotoxicity with special emphasis on its influence on brain mitochondrial fusion and fission, as well as mitochondrial clearance by mitophagy. Existing data demonstrate that, in addition to mitochondrial electron transport chain inhibition, membrane damage, and mitochondrial reactive oxygen species (ROS) overproduction, Cu overexposure inhibits mitochondrial fusion by down-regulation of Opa1, Mfn1, and Mfn2 expression, while promoting mitochondrial fission through up-regulation of Drp1. It has been also demonstrated that Cu exposure induces PINK1/Parkin-dependent mitophagy in brain cells, that is considered a compensatory response to Cu-induced mitochondrial dysfunction. However, long-term high-dose Cu exposure impairs mitophagy, resulting in accumulation of dysfunctional mitochondria. Cu-induced inhibition of mitochondrial biogenesis due to down-regulation of PGC-1α further aggravates mitochondrial dysfunction in brain. Studies from non-brain cells corroborate these findings, also offering additional evidence that dysregulation of mitochondrial dynamics and mitophagy may be involved in Cu-induced damage in brain. Finally, Cu exposure induces cuproptosis in brain cells due mitochondrial proteotoxic stress, that may also contribute to neuronal damage and pathogenesis of certain brain diseases. Based on these findings, it is assumed that development of mitoprotective agents, specifically targeting mechanisms of mitochondrial quality control, would be useful for prevention of neurotoxic effects of Cu overload.

[This corrects the article DOI: 10.3389/fnmol.2024.1394932.].

Stressful experiences form stronger memories due to enhanced neural plasticity mechanisms linked to glucocorticoid hormones (cortisol in humans, corticosterone in rats). Among other neural structures, the dorsal striatum plays a role in the corticosterone-induced consolidation of stressful memories, particularly in the cued water maze task. Neural plasticity is related to mitochondrial activity due to the relevance of energy production and signaling mechanisms for functional and morphological neuronal adaptations. Corticosterone has been shown to enhance brain mitochondrial activity by activating glucocorticoid receptors. In this context, striatum functions are susceptible to change in relation to mitochondrial responses. Based on this evidence, we hypothesized that training in the cued water maze would induce an increase in corticosterone levels and mitochondrial activity (mitochondrial membrane potential and calcium content) in the dorsal striatum, and that these adaptations might be related to memory consolidation of the task. We used an ELISA assay to evaluate plasma and striatal corticosterone levels; mitochondrial activity was determined with the florescent probes MitoTracker Red (mitochondrial membrane potential) and Rhod-2 (calcium content) in brain slices containing the dorsal striatum of rats trained in the cued water maze and euthanized at different times after training (0.5, 1.5, or 6.0 h). We also analyzed the effect of post-training inhibition of striatal mitochondrial activity by OXPHOS complex 1 inhibitor rotenone, on the consolidation of the cued water maze task. We found that cued water maze training induced an increase in corticosterone levels and a time-dependent elevation of mitochondrial membrane potential and mitochondrial calcium content in the dorsal striatum. Unexpectedly, rotenone administration facilitated the retention test. Altogether, our results suggest that enhanced mitochondrial activity in the dorsal striatum is relevant for cued water maze consolidation. The increase in mitochondrial activity was contextually associated with an elevation of corticosterone in plasma and the dorsal striatum. Additionally, our swimming groups also showed an increase in mitochondrial activity in the dorsal striatum, but with a different pattern, which could suggest a differential functional adaptation in this structure.

Neuronal radial migration is a fundamental process for cortical development, the disruption of which causes neurological and psychiatric dysfunctions. SLIT2 plays diverse functions in brain development and is a well-known axon guidance molecule. In this study, we investigated the radial migration of projection neurons in the developing cerebral cortex by in utero knockdown (KD) of Slit2 in mice. KD of Slit2 did not interfere with the neurogenesis and fate-determination but led to the accumulation of the transfected cells in the intermediate zone (IZ), suggesting that the expression of Slit2 is crucial for the radial migration of the cortical neurons. KD of Slit2 hindered the transition of cells from a multipolar to a bipolar shape, which is necessary for glia-guided locomotion. Interestingly, reducing Slit2 did not affect the migration of neighboring untransfected cells, indicating a cell-autonomous action by SLIT2. In addition, the action of SLIT2 KD was mimicked by a dominant negative mutant of ROBO2, a canonical membrane receptor of SLIT2, supporting that SLIT2 acted locally as a secretory molecule. Our results suggest that SLIT2 is indispensable for the radial migration of cortical neurons through an autocrine signaling mechanism.

Sleep deprivation (SD) contributes to cognitive impairment. Astrocytic cholesterol biosynthesis is crucial for brain cholesterol homeostasis and cognitive function. However, the underlying mechanism of astrocytic cholesterol metabolism in SD-induced cognitive impairment has not been fully explored. Trimethylamine N-oxide (TMAO), a product of liver flavin-containing monooxygenase-3 (FMO3), has been shown to be increased in the urine of sleep-deprived humans and implicated with peripheral cholesterol metabolism. Nevertheless, how TMAO affects brain cholesterol metabolism remains unclear. In our study, increased FMO3 and brain TMAO levels were observed in the SD mice, and elevated levels of TMAO were confirmed to lead to SD-induced cognitive dysfunction. In addition, we found that the expression of sterol regulatory element-binding protein 2 (SREBP2) is decreased in the brain of SD mice, resulting in the reduction in brain cholesterol content, which in turn causes synaptic damage. Moreover, we demonstrated that TMAO inhibits the expression of SREBP2. In contrast, FMO3 inhibitor 3,3'-diindolylmethane (DIM) alleviates SD-induced cognitive impairment by targeting the liver-brain axis. In conclusion, our study revealed that the TMAO pathway is involved in memory impairment in SD mice through deregulating astrocytic cholesterol metabolism.