Evaluation of the protective effects of cyclosporin a and FK506 on abnormal cytosolic and mitochondrial Ca²⁺ dynamics during ischemia and exposure to high glutamate concentration in mouse brain slice preparations

An unenhanced 3D-FLAIR sequence using long repetition time and constant flip angle to image endolymphatic hydrops

OBJECTIVES

To evaluate a three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) sequence using a long repetition time (TR) and constant flip angle (CFA) in differentiating between perilymph and endolymph in a phantom study, and unenhanced endolymphatic hydrops (EH) imaging in a patient study.

METHODS

Three solutions in similar ion and protein concentrations with endolymph, perilymph, and cerebrospinal fluid were prepared for variable flip angle (VFA) 3D-FLAIR (TR 10,000 ms) and CFA (120°) 3D-FLAIR using different TR (10,000, 16,000, and 20,000 ms). Fifty-two patients with probable or definite Meniere's disease received unenhanced CFA (120°) 3D-FLAIR using a long TR (20,000 ms) and 4-h-delay enhanced CFA (120°) 3D-FLAIR (TR 16,000 ms). Image quality, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of them were compared. Agreement in the evaluation of the EH degree between them was analyzed.

RESULTS

In the phantom study, CNRs between perilymphatic and endolymphatic samples of VFA 3D-FLAIR (TR 10,000 ms) and CFA 3D-FLAIR (TR 10,000, 16,000, and 20,000 ms) were 6.66 ± 1.30, 17.90 ± 2.76, 23.87 ± 3.09, and 28.22 ± 3.15 (p < 0.001). In patient study, average score (3.65 ± 0.48 vs. 4.19 ± 0.40), SNR (34.56 ± 9.80 vs. 51.40 ± 11.27), and CNR (30.66 ± 10.55 vs. 45.08 ± 12.27) of unenhanced 3D-FLAIR were lower than enhanced 3D-FLAIR (p < 0.001). Evaluations of the two sequences showed excellent agreement in the cochlear and vestibule (Kappa value: 0.898 and 0.909).

CONCLUSIONS

The CFA 3D-FLAIR sequence using a long TR could be used in unenhanced EH imaging with high accuracy.

CLINICAL RELEVANCE STATEMENT

Unenhanced imaging of endolymphatic hydrops is valuable in the diagnosis and follow-up of patients, especially those who cannot receive contrast-enhanced MRI.

KEY POINTS

Ion and protein concentration differences can be utilized in differentiating endolymph and perilymph on MRI. Endolymphatic and perilymphatic samples could be differentiated in vitro on this 3D-FLAIR sequence. This unenhanced 3D-FLAIR sequence is in excellent agreement with the enhanced constant flip angle 3D-FLAIR sequence.

High-resolution vasomotion analysis reveals novel arteriole physiological features and progressive modulation of cerebral vascular networks by stroke

Spontaneous cerebral vasomotion, characterized by ∼0.1 Hz rhythmic contractility, is crucial for brain homeostasis. However, our understanding of vasomotion is limited due to a lack of high-precision analytical methods to determine single vasomotion events at basal levels. Here, we developed a novel strategy that integrates a baseline smoothing algorithm, allowing precise measurements of vasodynamics and concomitant Ca2+ dynamics in mouse cerebral vasculature imaged by two-photon microscopy. We identified several previously unrecognized vasomotion properties under different physiological and pathological conditions, especially in ischemic stroke, which is a highly harmful brain disease that results from vessel occlusion. First, the dynamic characteristics between SMCs Ca2+ and corresponding arteriolar vasomotion are correlated. Second, compared to previous diameter-based estimations, our radius-based measurements reveal anisotropic vascular movements, enabling a more precise determination of the latency between smooth muscle cell (SMC) Ca2+ activity and vasoconstriction. Third, we characterized single vasomotion event kinetics at scales of less than 4 seconds. Finally, following pathological vasoconstrictions induced by ischemic stroke, vasoactive arterioles entered an inert state and persisted despite recanalization. In summary, we developed a highly accurate technique for analyzing spontaneous vasomotion, and our data suggested a potential strategy to reduce stroke damage by promoting vasomotion recovery.

Effects of TND1128 (a 5-deazaflavin derivative), with self-redox ability, as a mitochondria activator on the mouse brain slice and its comparison with β-NMN

We have no definitive treatment for dementia characterized by prolonged neuronal death due to the enormous accumulation of foreign matter, such as β-amyloid. Since Alzheimer's type dementia develops slowly, we may be able to delay the onset and improve neuronal dysfunction by enhancing the energy metabolism of individual neurons. TND1128, a derivative of 5-deazaflavin, is a chemical known to have an efficient self-redox ability. We expected TND1128 as an activator for mitochondrial energy synthesis. We used brain slices prepared from mice 22 ± 2 h pretreated with TND1128 or β-NMN. We measured Ca²⁺ concentrations in the cytoplasm ([Ca²⁺]_cyt) and mitochondria ([Ca²⁺]_mit) by using fluorescence Ca²⁺ indicators, Fura-4F, and X-Rhod-1, respectively, and examined the protective effects of drugs on [Ca²⁺]_cyt and [Ca²⁺]_mit overloading by repeating 80K exposure. TND1128 (0.01, 0.1, and 1 mg/kg s.c.) mitigates the dynamics of both [Ca²⁺]_cyt and [Ca²⁺]_mit in a dose-dependent manner. β-NMN (10, 30, and 100 mg/kg s.c.) also showed significant dose-dependent mitigating effects on [Ca²⁺]_cyt, but the effect on the [Ca²⁺]_mit dynamics was insignificant. We confirmed the mitochondria-activating potential of TND1128 in the present study. We expect TND1128 as a drug that rescues deteriorating neurons with aging or disease.

A Potential Route to Reduce Ischemia/Reperfusion Injury in Organ Preservation

The pathophysiological process of ischemia and reperfusion injury (IRI), an inevitable step in organ transplantation, causes important biochemical and structural changes that can result in serious organ damage. IRI is relevant for early graft dysfunction and graft survival. Today, in a global context of organ shortages, most organs come from extended criteria donors (ECDs), which are more sensitive to IRI. The main objective of organ preservation solutions is to protect against IRI through the application of specific, nonphysiological components, under conditions of no blood or oxygen, and then under conditions of metabolic reduction by hypothermia. The composition of hypothermic solutions includes osmotic and oncotic buffering components, and they are intracellular (rich in potassium) or extracellular (rich in sodium). However, above all, they all contain the same type of components intended to protect against IRI, such as glutathione, adenosine and allopurinol. These components have not changed for more than 30 years, even though our knowledge of IRI, and much of the relevant literature, questions their stability or efficacy. In addition, several pharmacological molecules have been the subjects of preclinical studies to optimize this protection. Among them, trimetazidine, tacrolimus and carvedilol have shown the most benefits. In fact, these drugs are already in clinical use, and it is a question of repositioning them for this novel use, without additional risk. This new strategy of including them would allow us to shift from cold storage solutions to cold preservation solutions including multitarget pharmacological components, offering protection against IRI and thus protecting today's more vulnerable organs.

A biomimetic triple-layered biocomposite with effective multifunction for dura repair

Dura mater defect and subsequent cerebrospinal fluid (CSF) leakage usually appear in trauma or neurosurgical procedures and are followed by a series of serious complications and even death. The use of a qualified dura mater substitute with multifunction of leakage blockade, adhesion prevention, and dura reconstruction is one of the promising treatment methods. However, even though some products have been used in the clinic, none of the substitutes achieved the required multifunction. In this study, we aimed to design and fabricate a dura repair composite with the ideal multifunction. By biomimicking the structure and component of natural dura, we applied poly(L-lactic acid) (PLLA), chitosan (CS), gelatin, and acellular small intestinal submucosa (SIS) powders to successfully prepare a triple-layered composite. Then, a series of specific devices and techniques were developed to investigate the performance. The results revealed that satisfactory structural stability could be realized under good synergistic interactions among the components. In addition, all the findings suggested that the bionic triple-layered composite showed satisfactory multifunction of leakage blockade, adhesion prevention, antibacterial property, and dura reconstruction potential, and thus, it might be a promising candidate for dura repair. STATEMENT OF SIGNIFICANCE: Developing qualified dura mater substitutes with multifunction of leakage blockade, adhesion prevention, and dura reconstruction is crucial for treating dura mater defect and subsequent cerebrospinal fluid (CSF) leakage that appear in trauma or neurosurgical procedures. In this study, we designed and fabricated a triple-layered dura repair biocomposite with satisfactory structural stability and desired multifunction based on biomimicking of the structure and component of natural dura. Moreover, a series of specific devices and techniques were developed to investigate the relevant performance. Overall, the developed hydrogel electrospinning system exhibited excellent advantages in achieving multifunction and could be applied widely in the future to achieve multifunctional tissue repair materials.

Transient Oxygen/Glucose Deprivation Causes a Delayed Loss of Mitochondria and Increases Spontaneous Calcium Signaling in Astrocytic Processes

Recently, mitochondria have been localized to astrocytic processes where they shape Ca(2+) signaling; this relationship has not been examined in models of ischemia/reperfusion. We biolistically transfected astrocytes in rat hippocampal slice cultures to facilitate fluorescent confocal microscopy, and subjected these slices to transient oxygen/glucose deprivation (OGD) that causes delayed excitotoxic death of CA1 pyramidal neurons. This insult caused a delayed loss of mitochondria from astrocytic processes and increased colocalization of mitochondria with the autophagosome marker LC3B. The losses of neurons in area CA1 and mitochondria in astrocytic processes were blocked by ionotropic glutamate receptor (iGluR) antagonists, tetrodotoxin, ziconotide (Ca(2+) channel blocker), two inhibitors of reversed Na(+)/Ca(2+) exchange (KB-R7943, YM-244769), or two inhibitors of calcineurin (cyclosporin-A, FK506). The effects of OGD were mimicked by NMDA. The glutamate uptake inhibitor (3S)-3-[[3-[[4-(trifluoromethyl)benzoyl]amino]phenyl]methoxy]-l-aspartate increased neuronal loss after OGD or NMDA, and blocked the loss of astrocytic mitochondria. Exogenous glutamate in the presence of iGluR antagonists caused a loss of mitochondria without a decrease in neurons in area CA1. Using the genetic Ca(2+) indicator Lck-GCaMP-6S, we observed two types of Ca(2+) signals: (1) in the cytoplasm surrounding mitochondria (mitochondrially centered) and (2) traversing the space between mitochondria (extramitochondrial). The spatial spread, kinetics, and frequency of these events were different. The amplitude of both types was doubled and the spread of both types changed by ∼2-fold 24 h after OGD. Together, these data suggest that pathologic activation of glutamate transport and increased astrocytic Ca(2+) through reversed Na(+)/Ca(2+) exchange triggers mitochondrial loss and dramatic increases in Ca(2+) signaling in astrocytic processes.

SIGNIFICANCE STATEMENT

Astrocytes, the most abundant cell type in the brain, are vital integrators of signaling and metabolism. Each astrocyte consists of many long, thin branches, called processes, which ensheathe vasculature and thousands of synapses. Mitochondria occupy the majority of each process. This occupancy is decreased by ∼50% 24 h after an in vitro model of ischemia/reperfusion injury, due to delayed fragmentation and mitophagy. The mechanism appears to be independent of neuropathology, instead involving an extended period of high glutamate uptake into astrocytes. Our data suggest that mitochondria serve as spatial buffers, and possibly even as a source of calcium signals in astrocytic processes. Loss of mitochondria resulted in drastically altered calcium signaling that could disrupt neurovascular coupling and gliotransmission.

Neuroprotective effects of the immunomodulatory drug FK506 in a model of HIV1-gp120 neurotoxicity

Background

HIV-associated neurocognitive disorders (HAND) continue to be a common morbidity associated with chronic HIV infection. It has been shown that HIV proteins (e.g., gp120) released from infected microglial/macrophage cells can cause neuronal damage by triggering inflammation and oxidative stress, activating aberrant kinase pathways, and by disrupting mitochondrial function and biogenesis. Previous studies have shown that FK506, an immunophilin ligand that modulates inflammation and mitochondrial function and inhibits calcineurin, is capable of rescuing the neurodegenerative pathology in models of Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease. In this context, the main objective of this study was to evaluate if FK506 could rescue the neuronal degeneration and mitochondrial alterations in a transgenic (tg) animal model of HIV1-gp120 neurotoxicity.

Methods

GFAP-gp120 tg mice were treated with FK506 and analyzed for neuropathology, behavior, mitochondrial markers, and calcium flux by two-photon microscopy.

Results

We found that FK506 reduced the neuronal cell loss and neuro-inflammation in the gp120 tg mice. Moreover, while vehicle-treated gp120 tg mice displayed damaged mitochondria and increased neuro-inflammatory markers, FK506 rescued the morphological mitochondrial alterations and neuro-inflammation while increasing levels of optic atrophy 1 and mitofusin 1. By two-photon microscopy, calcium levels were not affected in the gp120 tg mice and no effects of FK506 were detected. However, at a functional level, FK506 ameliorated the gp120 tg mice hyperactivity in the open field.

Conclusions

Together, these results suggest that FK506 might be potentially neuroprotective in patients with HAND by mitigating inflammation and mitochondrial alterations.

Hypothermia protects against oxygen-glucose deprivation-induced neuronal injury by down-regulating the reverse transport of glutamate by astrocytes as mediated by neurons

Glutamate is the major mediator of excitotoxic neuronal death following cerebral ischemia. Under severe ischemic conditions, glutamate transporters can functionally reverse to release glutamate, thereby inducing further neuronal injury. Hypothermia has been shown to protect neurons from brain ischemia. However, the mechanism(s) involved remain unclear. Therefore, the aim of this study was to investigate the mechanism(s) mediating glutamate release during brain ischemia-reperfusion injury under hypothermic conditions. Neuron/astrocyte co-cultures were exposed to oxygen-glucose deprivation (OGD) at various temperatures for 2h, and cell viability was assayed 12h after reoxygenation. PI and MAP-2 staining demonstrated that hypothermia significantly decreased neuronal injury. Furthermore, [(3)H]-glutamate uptake assays showed that hypothermia protected rat primary cortical cultures against OGD reoxygenation-induced injury. Protein levels of the astrocytic glutamate transporter, GLT-1, which is primarily responsible for the clearance of extracellular glutamate, were also found to be reduced in a temperature-dependent manner. In contrast, expression of GLT-1 in astrocyte-enriched cultures was found to significantly increase following the addition of neuron-conditioned medium maintained at 37 °C, and to a lesser extent with neuron-conditioned medium at 33 °C. In conclusion, the neuroprotective effects of hypothermia against brain ischemia-reperfusion injury involve down-regulation of astrocytic GLT-1, which mediates the reverse transport of glutamate. Moreover, this process may be regulated by molecules secreted by stressed neurons.