Wnt-5a/Ca2+ pathway modulates endogenous current and oocyte structure of Xenopus laevis.

Wnt signaling plays an essential role in cellular processes like development, maturation, and function maintenance. Xenopus laevis oocytes are a suitable model to study not only the development but also the function of different receptors expressed in their membranes, like those receptors expressed in the central nervous system (CNS) including Frizzled 7. Here, using frog oocytes and recordings of endogenous membrane currents in a two-electrode path configuration along with morphological observations, we evaluated the role of the non-canonical Wnt-5a ligand in oocytes. We found that acute application of Wnt-5a generated changes in endogenous calcium-dependent currents, entry oscillatory current, the membrane's outward current, and induced membrane depolarization. The incubation of oocytes with Wnt-5a caused a reduction of the membrane potential, potassium outward current, and protected the ATP current in the epithelium/theca removed (ETR) model. The oocytes exposed to Wnt-5a showed increased viability and an increase in the percentage of the germinal vesicle breakdown (GVBD), at a higher level than the control with progesterone. Altogether, our results suggest that Wnt-5a modulates different aspects of oocyte structure and generates calcium-dependent endogenous current alteration and GVDB process with a change in membrane potential at different concentrations and times of the exposition. These results help to understand the cellular effect of Wnt-5a and present the use of Xenopus oocytes to explore the mechanism that could impact the activation of Wnt signaling.

Episodic Binge-like Ethanol Reduces Skeletal Muscle Strength Associated with Atrophy, Fibrosis, and Inflammation in Young Rats.

Binge Drinking (BD) corresponds to episodes of ingestion of large amounts of ethanol in a short time, typically ≤2 h. BD occurs across all populations, but young and sports-related people are especially vulnerable. However, the short- and long-term effects of episodic BD on skeletal muscle function have been poorly explored. Young rats were randomized into two groups: control and episodic Binge-Like ethanol protocol (BEP) (ethanol 3 g/kg IP, 4 episodes of 2-days ON-2-days OFF paradigm). Muscle function was evaluated two weeks after the last BEP episode. We found that rats exposed to BEP presented decreased muscle strength and increased fatigability, compared with control animals. Furthermore, we observed that skeletal muscle from rats exposed to BEP presented muscle atrophy, evidenced by reduced fiber size and increased expression of atrophic genes. We also observed that BEP induced fibrotic and inflammation markers, accompanied by mislocalization of nNOSµ and high levels of protein nitration. Our findings suggest that episodic binge-like ethanol exposure alters contractile capacity and increases fatigue by mechanisms involving atrophy, fibrosis, and inflammation, which remain for at least two weeks after ethanol clearance. These pathological features are common to several neuromuscular diseases and might affect muscle performance and health in the long term.

Building a Bridge Between NMDAR-Mediated Excitotoxicity and Mitochondrial Dysfunction in Chronic and Acute Diseases.

Glutamate is the major excitatory neurotransmitter in the brain, and it is widely accepted to play a role in synaptic plasticity and excitotoxic cell death. Glutamate binds to several receptors, including ionotropic N-methyl-D-Aspartate receptor (NMDAR), which is essential in synaptic plasticity and excitotoxicity. This receptor is a calcium channel that is located in synaptic and extrasynaptic sites, triggering different signalling cascades in each case. The calcium entry through extrasynaptic NMDARs is linked to calcium overload in the mitochondria in neurons in vitro. The mitochondria, besides their role in ATP production in the cell, participate in calcium homeostasis, acting as a buffering organelle. Disruption of mitochondrial calcium homeostasis has been linked to neuronal death either by triggering apoptosis or driven by the opening of the mitochondrial transition pore. These cell-death mechanisms contribute to the pathophysiology of diverse diseases such as neurodegenerative Alzheimer's disease or Parkinson's disease, and acute neuropathological conditions such as stroke or traumatic brain injury. In this review, we will address the available evidence that positions the mitochondria as an essential organelle in the control of calcium-mediated toxicity, highlighting its role from the perspective of specific NMDAR signalling microdomains at the level of the central synapse.

Alcohol consumption during adolescence alters the hippocampal response to traumatic brain injury.

Binge drinking is the consumption of large volumes of alcohol in short periods and exerts its effects on the central nervous system, including the hippocampus. We have previously shown that binge drinking alters mitochondrial dynamics and induces neuroinflammation in the hippocampus of adolescent rats. Mild traumatic brain injury (mTBI), is regularly linked to alcohol consumption and share mechanisms of brain damage. In this context, we hypothesized that adolescent binge drinking could prime the development of brain damage generated by mTBI. We found that alcohol binge drinking induced by the "drinking in the dark" (DID) paradigm increases oxidative damage and astrocyte activation in the hippocampus of adolescent mice. Interestingly, adolescent animals submitted to DID showed decreased levels of mitofusin 2 that controls mitochondrial dynamics. When mTBI was evaluated as a second challenge, hippocampi from animals previously submitted to DID showed a reduction in dendritic spine number and a different spine profile. Mitochondrial performance could be compromised by alterations in mitochondrial fission in DID-mTBI animals. These data suggest that adolescent alcohol consumption can modify the progression of mTBI pathophysiology. We propose that mitochondrial impairment and oxidative damage could act as priming factors, modifying predisposition against mTBI effects.

Age-related NMDA signaling alterations in SOD2 deficient mice.

Oxidative stress affects the survival and function of neurons. Hence, they have a complex and highly regulated machinery to handle oxidative changes. The dysregulation of this antioxidant machinery is associated with a wide range of neurodegenerative conditions. Therefore, we evaluated signaling alterations, synaptic properties and behavioral performance in 2 and 6-month-old heterozygous manganese superoxide dismutase knockout mice (SOD2+/- mice). We found that their low antioxidant capacity generated direct oxidative damage in proteins, lipids, and DNA. However, only 6-month-old heterozygous knockout mice presented behavioral impairments. On the other hand, synaptic plasticity, synaptic strength and NMDA receptor (NMDAR) dependent postsynaptic potentials were decreased in an age-dependent manner. We also analyzed the phosphorylation state of the NMDAR subunit GluN2B. We found that while the levels of GluN2B phosphorylated on tyrosine 1472 (synaptic form) remain unchanged, we detected increased levels of GluN2B phosphorylated on tyrosine 1336 (extrasynaptic form), establishing alterations in the synaptic/extrasynaptic ratio of GluN2B. Additionally, we found increased levels of two phosphatases associated with dephosphorylation of p-1472: striatal-enriched protein tyrosine phosphatase (STEP) and phosphatase and tensin homolog deleted on chromosome Ten (PTEN). Moreover, we found decreased levels of p-CREB, a master transcription factor activated by synaptic stimulation. In summary, we describe mechanisms by which glutamatergic synapses are altered under oxidative stress conditions. Our results uncovered new putative therapeutic targets for conditions where NMDAR downstream signaling is altered. This work also contributes to our understanding of processes such as synapse formation, learning, and memory in neuropathological conditions.

Intracellular effects of lithium in aging neurons.

Lithium therapy received approval during the 1970s, and it has been used for its antidepressant, antimanic, and anti-suicidal effects for acute and long-term prophylaxis and treatment of bipolar disorder (BPD). These properties have been well established; however, the molecular and cellular mechanisms remain controversial. In the past few years, many studies demonstrated that at the cellular level, lithium acts as a regulator of neurogenesis, aging, and Ca2+ homeostasis. At the molecular level, lithium modulates aging by inhibiting glycogen synthase kinase-3ß (GSK-3ß), and the phosphatidylinositol (PI) cycle; latter, lithium specifically inhibits inositol production, acting as a non-competitive inhibitor of inositol monophosphatase (IMPase). Mitochondria and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) have been related to lithium activity, and its regulation is mediated by GSK-3ß degradation and inhibition. Lithium also impacts Ca2+ homeostasis in the mitochondria modulating the function of the lithium-permeable mitochondrial Na+-Ca2+exchanger (NCLX), affecting Ca2+ efflux from the mitochondrial matrix to the endoplasmic reticulum (ER). A close relationship between the protease Omi, GSK-3ß, and PGC-1α has also been established. The purpose of this review is to summarize some of the intracellular mechanisms related to lithium activity and how, through them, neuronal aging could be controlled.

Mild Traumatic Brain Injury Induces Mitochondrial Calcium Overload and Triggers the Upregulation of NCLX in the Hippocampus.

Traumatic brain injury (TBI) is brain damage due to external forces. Mild TBI (mTBI) is the most common form of TBI, and repeated mTBI is a risk factor for developing neurodegenerative diseases. Several mechanisms of neuronal damage have been described in the cortex and hippocampus, including mitochondrial dysfunction. However, up until now, there have been no studies evaluating mitochondrial calcium dynamics. Here, we evaluated mitochondrial calcium dynamics in an mTBI model in mice using isolated hippocampal mitochondria for biochemical studies. We observed that 24 h after mTBI, there is a decrease in mitochondrial membrane potential and an increase in basal matrix calcium levels. These findings are accompanied by increased mitochondrial calcium efflux and no changes in mitochondrial calcium uptake. We also observed an increase in NCLX protein levels and calcium retention capacity. Our results suggest that under mTBI, the hippocampal cells respond by incrementing NCLX levels to restore mitochondrial function.

Traumatic Brain Injury: Mechanisms of Glial Response.

Traumatic brain injury (TBI) is a heterogeneous disorder that involves brain damage due to external forces. TBI is the main factor of death and morbidity in young males with a high incidence worldwide. TBI causes central nervous system (CNS) damage under a variety of mechanisms, including synaptic dysfunction, protein aggregation, mitochondrial dysfunction, oxidative stress, and neuroinflammation. Glial cells comprise most cells in CNS, which are mediators in the brain's response to TBI. In the CNS are present astrocytes, microglia, oligodendrocytes, and polydendrocytes (NG2 cells). Astrocytes play critical roles in brain's ion and water homeostasis, energy metabolism, blood-brain barrier, and immune response. In response to TBI, astrocytes change their morphology and protein expression. Microglia are the primary immune cells in the CNS with phagocytic activity. After TBI, microglia also change their morphology and release both pro and anti-inflammatory mediators. Oligodendrocytes are the myelin producers of the CNS, promoting axonal support. TBI causes oligodendrocyte apoptosis, demyelination, and axonal transport disruption. There are also various interactions between these glial cells and neurons in response to TBI that contribute to the pathophysiology of TBI. In this review, we summarize several glial hallmarks relevant for understanding the brain injury and neuronal damage under TBI conditions.

Glutamatergic Receptor Trafficking and Delivery: Role of the Exocyst Complex.

Cells comprise several intracellular membrane compartments that allow them to function properly. One of these functions is cargo movement, typically proteins and membranes within cells. These cargoes ride microtubules through vesicles from Golgi and recycling endosomes to the plasma membrane in order to be delivered and exocytosed. In neurons, synaptic functions employ this cargo trafficking to maintain inter-neuronal communication optimally. One of the complexes that oversee vesicle trafficking and tethering is the exocyst. The exocyst is a protein complex containing eight subunits first identified in yeast and then characterized in multicellular organisms. This complex is related to several cellular processes, including cellular growth, division, migration, and morphogenesis, among others. It has been associated with glutamatergic receptor trafficking and tethering into the synapse, providing the molecular machinery to deliver receptor-containing vesicles into the plasma membrane in a constitutive manner. In this review, we discuss the evidence so far published regarding receptor trafficking and the exocyst complex in both basal and stimulated levels, comparing constitutive trafficking and long-term potentiation-related trafficking.

Effect of Alcohol on Hippocampal-Dependent Plasticity and Behavior: Role of Glutamatergic Synaptic Transmission.

Problematic alcohol drinking and alcohol dependence are an increasing health problem worldwide. Alcohol abuse is responsible for approximately 5% of the total deaths in the world, but addictive consumption of it has a substantial impact on neurological and memory disabilities throughout the population. One of the better-studied brain areas involved in cognitive functions is the hippocampus, which is also an essential brain region targeted by ethanol. Accumulated evidence in several rodent models has shown that ethanol treatment produces cognitive impairment in hippocampal-dependent tasks. These adverse effects may be related to the fact that ethanol impairs the cellular and synaptic plasticity mechanisms, including adverse changes in neuronal morphology, spine architecture, neuronal communication, and finally an increase in neuronal death. There is evidence that the damage that occurs in the different brain structures is varied according to the stage of development during which the subjects are exposed to ethanol, and even much earlier exposure to it would cause damage in the adult stage. Studies on the cellular and cognitive deficiencies produced by alcohol in the brain are needed in order to search for new strategies to reduce alcohol neuronal toxicity and to understand its consequences on memory and cognitive performance with emphasis on the crucial stages of development, including prenatal events to adulthood.

Alcohol impairs hippocampal function: From NMDA receptor synaptic transmission to mitochondrial function.

Many studies have reported that alcohol produces harmful effects on several brain structures, including the hippocampus, in both rodents and humans. The hippocampus is one of the most studied areas of the brain due to its function in learning and memory, and a lot of evidence suggests that hippocampal failure is responsible for the cognitive loss present in individuals with recurrent alcohol consumption. Mitochondria are organelles that generate the energy needed for the brain to maintain neuronal communication, and their functional failure is considered a mediator of the synaptic dysfunction induced by alcohol. In this review, we discuss the mechanisms of how alcohol exposure affects neuronal communication through the impairment of glutamate receptor (NMDAR) activity, neuroinflammatory events and oxidative damage observed after alcohol exposure, all processes under the umbrella of mitochondrial function. Finally, we discuss the direct role of mitochondrial dysfunction mediating cognitive and memory decline produced by alcohol exposure and their consequences associated with neurodegeneration.

Correction to: Adolescent Binge Alcohol Exposure Affects the Brain Function Through Mitochondrial Impairment.

The authors declare that the original version of this article contained a mistake in the data of the Figure 2, particularly in the LTP data.

Adolescent Binge Alcohol Exposure Affects the Brain Function Through Mitochondrial Impairment.

In the young population, binge drinking is a pattern of problematic alcohol consumption, characterized by a short period of heavy drinking followed by abstinence which is frequently repeated over time. This drinking pattern is associated with mental problems, use of other drugs, and an increased risk of excessive alcohol intake during adulthood. However, little is known about the effects of binge drinking on brain function in adolescents and its neurobiological impact during the adulthood. In the present study, we evaluated the effects of alcohol on hippocampal memory, synaptic plasticity, and mitochondrial function in adolescent rats after a binge drinking episode in vivo. These effects were analyzed at 1, 3, or 7 weeks post alcohol exposure. Our results showed that binge-like ethanol pre-treated (BEP) rats exhibited early alterations in learning and memory tests accompanied by an impairment of synaptic plasticity that was total and partially compensated, respectively. These changes could be attributed to a rapid increase in oxidative damage and a late inflammatory response induced by post ethanol exposure. Additionally, BEP alters the regulation of mitochondrial dynamics and modifies the expression of mitochondrial permeability transition pore (mPTP) components, such as cyclophilin D (Cyp-D) and the voltage-dependent anion channel (VDAC). These mitochondrial structural changes result in the impairment of mitochondrial bioenergetics, decreasing ATP production progressively until adulthood. These results strongly suggest that teenage alcohol binge drinking impairs the function of the adult hippocampus including memory and synaptic plasticity as a consequence of the mitochondrial damage induced by alcohol and that the recovery of hippocampal function could implicate the activation of alternative pathways that fail to reestablish mitochondrial function.

Alcohol consumption during adolescence: A link between mitochondrial damage and ethanol brain intoxication.

Adolescence is a period of multiple changes where social behaviors influence interpersonal-relations. Adolescents live new experiences, including alcohol consumption which has become an increasing health problem. The age of onset for consumption has declined in the last decades, and additionally, the adolescents now uptake greater amounts of alcohol per occasion. Alcohol consumption is a risk factor for accidents, mental illnesses or other pathologies, as well as for the appearance of addictions, including alcoholism. An interesting topic to study is the damage that alcohol induces on the central nervous system (CNS) in the young population. The brain undergoes substantial modifications during adolescence, making brain cells more vulnerable to the ethanol toxicity. Over the last years, the brain mitochondria have emerged as a cell organelle which is particularly susceptible to alcohol. Mitochondria suffer severe alterations which can be exacerbated if the amount of alcohol or the exposure time is increased. In this review, we focus on the changes that the adolescent brain undergoes after drinking, placing particular emphasis on mitochondrial damage and their consequences against brain function. Finally, we propose the mitochondria as an important mediator in alcohol toxicity and a potential therapeutic target to reduce or treat brain conditions associated with excessive alcohol consumption.