Mitochondrial Ca2+ Processing by a Unit of Mitochondrial Ca2+ Uniporter and Na+/Ca2+ Exchanger Supports the Neuronal Ca2+ Influx via Activated Glutamate Receptors

Neuronal Mitochondrial Calcium Uniporter (MCU) Deficiency Is Neuroprotective in Hyperexcitability by Modulation of Metabolic Pathways and ROS Balance

Epilepsy is one of the most common neurological disorders in the world. Common epileptic drugs generally affect ion channels or neurotransmitters and prevent the emergence of seizures. However, up to a third of the patients suffer from drug-resistant epilepsy, and there is an urgent need to develop new therapeutic strategies that go beyond acute antiepileptic (antiseizure) therapies towards therapeutics that also might have effects on chronic epilepsy comorbidities such as cognitive decline and depression. The mitochondrial calcium uniporter (MCU) mediates rapid mitochondrial Ca2+ transport through the inner mitochondrial membrane. Ca2+ influx is essential for mitochondrial functions, but longer elevations of intracellular Ca2+ levels are closely associated with seizure-induced neuronal damage, which are underlying mechanisms of cognitive decline and depression. Using neuronal-specific MCU knockout mice (MCU-/-ΔN), we demonstrate that neuronal MCU deficiency reduced hippocampal excitability in vivo. Furthermore, in vitro analyses of hippocampal glioneuronal cells reveal no change in total Ca2+ levels but differences in intracellular Ca2+ handling. MCU-/-ΔN reduces ROS production, declines metabolic fluxes, and consequently prevents glioneuronal cell death. This effect was also observed under pathological conditions, such as the low magnesium culture model of seizure-like activity or excitotoxic glutamate stimulation, whereby MCU-/-ΔN reduces ROS levels and suppresses Ca2+ overload seen in WT cells. This study highlights the importance of MCU at the interface of Ca2+ handling and metabolism as a mediator of stress-related mitochondrial dysfunction, which indicates the modulation of MCU as a potential target for future antiepileptogenic therapy.

Synergistic enhancing-memory effect of D-serine and RU360, a mitochondrial calcium uniporter blocker in rat model of Alzheimer's disease

BACKGROUND

Although Amyloid beta (Aβ) and N - methyl d- aspartate receptors (NMDARs are involved in Ca²⁺ neurotoxicity, the function of mitochondrial calcium uniporter in cognition deficit remain uncertain. Here, we examined the effect of mitochondrial calcium uniporter (MCU) blocker, together with NMDA receptor agonist d-cycloserine (DCS) on memory impairment in a rat model of AD.

METHODS

Forty adult male Wistar rats underwent stereotaxic cannulation for inducing AD by intracerebroventricular (ICV) injection of Aβ_1-42 (5 μg /8 μl/rat). Then animals were divided into 5 groups of: Saline + Saline, Aβ + Saline, Aβ + RU360, Aβ + DCS, Aβ + RU360 + DCS. Two weeks after the treatments, Morris Water Maze (MWM) and step through passive avoidance learning (SPL) were undertaken for evaluating of spatial and associative memories, respectively. Hippocampal level of cyclic-AMP response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF) were measured by western blot and ELISA.

RESULTS

Co - administration of RU360 and DCS significantly improved both acquisition and retrieval of spatial memory as evident by decreased escape latency and increased time spent in the target quadrant (TTS) in MWM, together with increase in step-through latency, but reduced time spent in the dark compartment in SPL. Furthermore, there was a significant rise in the hippocampal level of CREB and BDNF in comparison with Aβ + Saline.

CONCLUSION

The present study supports the idea that co- administration of RU360 and DCS ameliorate memory impairment induced by Aβ _1-42 probably via CREB / BDNF signaling.

Traumatic brain injury metabolome and mitochondrial impact after early stage Ru360 treatment

Ru360, a mitochondrial Ca²⁺ uptake inhibitor, was tested in a unilateral fluid percussion TBI model in developing rats (P31). Vehicle and Ru360 treated TBI rats underwent sensorimotor behavioral monitoring between 24 and 72 h, thereafter which 185 brain metabolites were analyzed postmortem using LC/MS. Ru360 treatment after TBI improved sensorimotor behavioral recovery, upregulated glycolytic and pentose phosphate pathways, mitigated oxidative stress and prevented NAD⁺ depletion across both hemispheres. While neural viability improved ipsilaterally, it reduced contralaterally. Ru360 treatment, overall, had a global impact with most benefit near the strongest injury impact areas, while perturbing mitochondrial oxidative energetics in the milder TBI impact areas.

Intracerebroventricular streptozotocin administration impairs mitochondrial calcium homeostasis and bioenergetics in memory-sensitive rat brain regions

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with cardinal manifestation of cognitive dysfunction. The limitation to avail a successful drug candidate encourages researchers to establish an appropriate animal model in the novel anti-AD drug discovery process. In this context, the mechanism of mitochondrial dysfunction in cognitive deficit animals is yet to be established for intracerebroventricular injection of streptozotocin (ICV-STZ). Experimental dementia was induced in male rats by ICV-STZ on day-1 (D-1) of the experimental protocol at a sub-diabetogenic dose (3 mg/kg) twice at an interval of 48 h into both rat lateral ventricles. ICV-STZ caused cognitive decline in terms of increase in the escape latency on D-14 to D-17 and, decrease in the time spent and percentage of distance travelled in the target quadrant during Morris water maze and decrease in the spontaneous alteration behavior during Y-maze tests in rats. Further, ICV-STZ decreased the level of acetylcholine and activity of choline acetyltransferase and increased the activity of acetylcholinesterase in rat hippocampus, pre-frontal cortex and amygdala. Interestingly, ICV-STZ increased the mitochondrial calcium in addition to decrease in the mitochondrial function, integrity and bioenergetics in all rat brain regions. Further, ICV-STZ enhanced the levels of expression of NR1 subunit of N-methyl-D-aspartate receptor, mitochondrial calcium uniporter and sodium-calcium exchanger in these rat brain regions. Thus, NR1-dependent mitochondrial calcium accumulation could be considered as a major attribute to the animal model of ICV-STZ-induced AD-like manifestations. Further, drugs targeting to manage mitochondrial calcium homeostasis could best be studied in this animal model.

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.

Mitochondria-coupled glucose phosphorylation develops after birth to modulate H2 O2 release and calcium handling in rat brain

The adult brain is a high-glucose and oxygen-dependent organ, with an extremely organized network of cells and large energy-consuming synapses. To reach this level of organization, early stages in development must include an efficient control of cellular events and regulation of intracellular signaling molecules and ions such as hydrogen peroxide (H₂ O₂ ) and calcium (Ca²⁺ ), but in cerebral tissue, these mechanisms of regulation are still poorly understood. Hexokinase (HK) is the first enzyme in the metabolism of glucose and, when bound to mitochondria (mtHK), it has been proposed to have a role in modulation of mitochondrial H₂ O₂  generation and Ca²⁺ handling. Here, we have investigated how mtHK modulates these signals in the mitochondrial context during postnatal development of the mouse brain. Using high-resolution respirometry, western blot analysis, spectrometry and resorufin, and Calcium Green fluorescence assays with brain mitochondria purified postnatally from day 1 to day 60, we demonstrate that brain HK increases its coupling to mitochondria and to oxidative phosphorylation to induce a cycle of ADP entry/ATP exit of the mitochondrial matrix that leads to efficient control over H₂ O₂ generation and Ca²⁺ uptake during development until reaching plateau at day 21. This contrasts sharply with the antioxidant enzymes, which do not increase as mitochondrial H₂ O₂ generation escalates. These results suggest that, as its use of glucose increases, the brain couples HK to mitochondria to improve glucose metabolism, redox balance and Ca²⁺ signaling during development, positioning mitochondria-bound hexokinase as a hub for intracellular signaling control.

Na+ /Ca2+ exchanger 1 is a key mechanosensitive molecule of the esophageal myenteric neurons

AIM

Our earlier studies showed that mechanical stretch activates inhibitory motor neurons of the oesophagus; however, the underlying molecular mechanisms are unclear. Here, we sought to examine if Na⁺ /Ca²⁺ exchanger 1 (NCX1) is responsible for the mechanosensitivity in the esophageal myenteric neurons (EMN) of rats and humans.

METHODS

The function of NCX1 in primary culture of neurons was determined using calcium imaging, and mechanosensitivity was tested using osmotic stretch and direct mechanical stretch. Axial stretch-induced relaxation of the lower esophageal sphincter (LES) was also studied in vivo in rats.

RESULTS

The expression and co-localization of NCX1 with nNOS were identified in the EMN from both rats and humans. The extracellular Ca²⁺ entry caused by ATP through purinergic signalling in the rat EMN was significantly inhibited by selective NCX blockers. Removal of extracellular Na⁺ to activate the Ca²⁺ entry mode of NCX1 induced an increase in the cytoplasmic calcium ([Ca²⁺ ]_cyt ), which was attenuated by NCX blockers. Osmotic stretch and mechanical stretch-induced [Ca²⁺ ]_cyt signalling in the rat and human EMN were attenuated by NCX blockers as well as specific NCX1 knockdown. Osmotic stretch and mechanical stretch also induced [Ca²⁺ ]_cyt signalling in the Chinese hamster ovary (CHO) cells with NCX1 over-expression, which was attenuated by NCX blockers. Finally, NCX blockade inhibited axial stretch-activated LES relaxation in vivo experiments in the rats.

CONCLUSIONS

We demonstrate a novel NCX1/Ca²⁺ pathway in the mechanosensitive neurons of rat and human oesophagus, which may provide a potential therapeutic target for the treatment of oesophageal motility disorders.

IP3R-Grp75-VDAC1-MCU calcium regulation axis antagonists protect podocytes from apoptosis and decrease proteinuria in an Adriamycin nephropathy rat model

BACKGROUND

The mechanism of podocyte apoptosis is not fully understood. In addition, the role of the inositol 1,4,5-triphosphate receptor (IP₃R)/glucose-regulated protein 75 (Grp75)/voltage-dependent anion channel 1 (VDAC1)/mitochondrial calcium uniporter (MCU) calcium regulation axis, which is located at sites of endoplasmic reticulum (ER) mitochondria coupling, in the mechanism of podocyte apoptosis is unclear. This study aimed to understand the roles of this axis in podocyte apoptosis and explore potential targets for podocyte protection.

METHODS

The expression of IP₃R, Grp75, VDAC1, and MCU and mitochondrial Ca²⁺ were analyzed during Adriamycin- or angiotensin II-induced apoptosis in cultured mouse podocytes. The interaction between IP₃R, Grp75, and VDAC1 was investigated using co-immunoprecipitation experiments. The effects of IP₃R, Grp75, and MCU agonists and antagonists on mitochondrial Ca²⁺ and apoptosis were investigated in cultured podocytes. The podocyte-protective effects of an MCU inhibitor were further investigated in rats with Adriamycin-induced nephropathy.

RESULTS

Increased expression of IP₃R, Grp75, VDAC1 and MCU, enhanced interaction among the IP₃R-Grp75-VDAC1 complex, mitochondrial Ca²⁺ overload, and increased active caspase-3 levels were confirmed during Adriamycin- or angiotensin II-induced mouse podocyte apoptosis. Agonists of this axis facilitated mitochondrial Ca²⁺ overload and podocyte apoptosis, whereas specific antagonists against IP₃R, Grp75, or MCU prevented mitochondrial Ca²⁺ overload and podocyte apoptosis. A specific MCU inhibitor prevented Adriamycin-induced proteinuria and podocyte foot process effacement in rats.

CONCLUSIONS

This study identified a novel pathway in which the IP₃R-Grp75-VDAC1-MCU calcium regulation axis mediated podocyte apoptosis by facilitating mitochondrial Ca²⁺ overload. Antagonists that inhibit Ca²⁺ transfer from ER to mitochondria protected mouse podocytes from apoptosis. An MCU inhibitor protected podocytes and decreased proteinuria in rats with Adriamycin-induced nephropathy. Therefore, antagonists to this pathway have promise as novel podocyte-protective drugs.

KB-R7943 reduces 4-aminopyridine-induced epileptiform activity in adult rats after neuronal damage induced by neonatal monosodium glutamate treatment

BACKGROUND

Neonatal monosodium glutamate (MSG) treatment triggers excitotoxicity and induces a degenerative process that affects several brain regions in a way that could lead to epileptogenesis. Na+/Ca2+ exchangers (NCX1-3) are implicated in Ca2+ brain homeostasis; normally, they extrude Ca2+ to control cell inflammation, but after damage and in epilepsy, they introduce Ca2+ by acting in the reverse mode, amplifying the damage. Changes in NCX3 expression in the hippocampus have been reported immediately after neonatal MSG treatment. In this study, the expression level of NCX1-3 in the entorhinal cortex (EC) and hippocampus (Hp); and the effects of blockade of NCXs on the seizures induced by 4-Aminopyridine (4-AP) were analysed in adult rats after neonatal MSG treatment. KB-R7943 was applied as NCXs blocker, but is more selective to NCX3 in reverse mode.

METHODS

Neonatal MSG treatment was applied to newborn male rats at postnatal days (PD) 1, 3, 5, and 7 (4 g/kg of body weight, s.c.). Western blot analysis was performed on total protein extracts from the EC and Hp to estimate the expression level of NCX1-3 proteins in relative way to the expression of β-actin, as constitutive protein. Electrographic activity of the EC and Hp were acquired before and after intracerebroventricular (i.c.v.) infusion of 4-AP (3 nmol) and KB-R7943 (62.5 pmol), alone or in combination. All experiments were performed at PD60. Behavioural alterations were also recorder.

RESULTS

Neonatal MSG treatment significantly increased the expression of NCX3 protein in both studied regions, and NCX1 protein only in the EC. The 4-AP-induced epileptiform activity was significantly higher in MSG-treated rats than in controls, and KB-R7943 co-administered with 4-AP reduced the epileptiform activity in more prominent way in MSG-treated rats than in controls.

CONCLUSIONS

The long-term effects of neonatal MSG treatment include increases on functional expression of NCXs (mainly of NCX3) in the EC and Hp, which seems to contribute to improve the control that KB-R7943 exerted on the seizures induced by 4-AP in adulthood. The results obtained here suggest that the blockade of NCXs could improve seizure control after an excitotoxic process; however, this must be better studied.

mRNA changes in nucleus accumbens related to methamphetamine addiction in mice

Methamphetamine (METH) is a highly addictive psychostimulant that elicits aberrant changes in the expression of microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) in the nucleus accumbens of mice, indicating a potential role of METH in post-transcriptional regulations. To decipher the potential consequences of these post-transcriptional regulations in response to METH, we performed strand-specific RNA sequencing (ssRNA-Seq) to identify alterations in mRNA expression and their alternative splicing in the nucleus accumbens of mice following exposure to METH. METH-mediated changes in mRNAs were analyzed and correlated with previously reported changes in non-coding RNAs (miRNAs and lncRNAs) to determine the potential functions of these mRNA changes observed here and how non-coding RNAs are involved. A total of 2171 mRNAs were differentially expressed in response to METH with functions involved in synaptic plasticity, mitochondrial energy metabolism and immune response. 309 and 589 of these mRNAs are potential targets of miRNAs and lncRNAs respectively. In addition, METH treatment decreases mRNA alternative splicing, and there are 818 METH-specific events not observed in saline-treated mice. Our results suggest that METH-mediated addiction could be attributed by changes in miRNAs and lncRNAs and consequently, changes in mRNA alternative splicing and expression. In conclusion, our study reported a methamphetamine-modified nucleus accumbens transcriptome and provided non-coding RNA-mRNA interaction networks possibly involved in METH addiction.