Interleukin-6 Reduces NMDA-Induced Ca2+Overload via Prevention of Ca2+Release From Intracellular Store

The Neuroimmune System and the Cerebellum

The recognition that there is an innate immune system of the brain, referred to as the neuroimmune system, that preforms many functions comparable to that of the peripheral immune system is a relatively new concept and much is yet to be learned. The main cellular components of the neuroimmune system are the glial cells of the brain, primarily microglia and astrocytes. These cell types preform many functions through secretion of signaling factors initially known as immune factors but referred to as neuroimmune factors when produced by cells of the brain. The immune functions of glial cells play critical roles in the healthy brain to maintain homeostasis that is essential for normal brain function, to establish cytoarchitecture of the brain during development, and, in pathological conditions, to minimize the detrimental effects of disease and injury and promote repair of brain structure and function. However, dysregulation of this system can occur resulting in actions that exacerbate or perpetuate the detrimental effects of disease or injury. The neuroimmune system extends throughout all brain regions, but attention to the cerebellar system has lagged that of other brain regions and information is limited on this topic. This article is meant to provide a brief introduction to the cellular and molecular components of the brain immune system, its functions, and what is known about its role in the cerebellum. The majority of this information comes from studies of animal models and pathological conditions, where upregulation of the system facilitates investigation of its actions.

Impaired endoplasmic reticulum-mitochondrial signaling in ataxia-telangiectasia

There is evidence that ATM mutated in ataxia-telangiectasia (A-T) plays a key role in protecting against mitochondrial dysfunction, the mechanism for which remains unresolved. We demonstrate here that ATM-deficient cells are exquisitely sensitive to nutrient deprivation, which can be explained by defective cross talk between the endoplasmic reticulum (ER) and the mitochondrion. Tethering between these two organelles in response to stress was reduced in cells lacking ATM, and consistent with this, Ca2+ release and transfer between ER and mitochondria was reduced dramatically when compared with control cells. The impact of this on mitochondrial function was evident from an increase in oxygen consumption rates and a defect in mitophagy in ATM-deficient cells. Our findings reveal that ER-mitochondrial connectivity through IP3R1-GRP75-VDAC1, to maintain Ca2+ homeostasis, as well as an abnormality in mitochondrial fusion defective in response to nutrient stress, can account for at least part of the mitochondrial dysfunction observed in A-T cells.

Neutrophil depletion after subarachnoid hemorrhage improves memory via NMDA receptors

Cognitive deficits after aneurysmal subarachnoid hemorrhage (SAH) are common and disabling. Patients who experience delayed deterioration associated with vasospasm are likely to have cognitive deficits, particularly problems with executive function, verbal and spatial memory. Here, we report neurophysiological and pathological mechanisms underlying behavioral deficits in a murine model of SAH. On tests of spatial memory, animals with SAH performed worse than sham animals in the first week and one month after SAH suggesting a prolonged injury. Between three and six days after experimental hemorrhage, mice demonstrated loss of late long-term potentiation (L-LTP) due to dysfunction of the NMDA receptor. Suppression of innate immune cell activation prevents delayed vasospasm after murine SAH. We therefore explored the role of neutrophil-mediated innate inflammation on memory deficits after SAH. Depletion of neutrophils three days after SAH mitigates tissue inflammation, reverses cerebral vasoconstriction in the middle cerebral artery, and rescues L-LTP dysfunction at day 6. Spatial memory deficits in both the short and long-term are improved and associated with a shift of NMDA receptor subunit composition toward a memory sparing phenotype. This work supports further investigating suppression of innate immunity after SAH as a target for preventative therapies in SAH.

The expression of NMDA receptor and pCREB in the visual cortex of monocularly-deprived rats

N-methyl-D-aspartate receptor subunit 1 (NMDAR1) and cAMP response element binding protein (CREB) play a role in vision plasticity. However, the correlation between their expression and vision plasticity is not clear. The present study aimed to examine the expression of NMDAR1 and phosphorylated CREB (pCREB) in the visual cortex of monocularly-deprived (MD) rats in the developmental phase. Eighty healthy Sprague Dawley rats were randomly divided into 4 groups (n=20); normal, MD, KN-93 (MD rats treated with KN-93, a calmodulin kinase IV inhibitor) and saline (MD rats treated with saline as control). All rats were reared for 45 days in a naturally lit environment. The expression of NMDAR1 and pCREB in the hibateral visual cortex of rats from each group was detected by immunohistochemistry and western blot analysis. The results demonstrate that, compared with the normal group, the expression of NMDAR1 and pCREB was increased in deprived and decreased in the non-deprived-side visual cortex in MD. Compared with the saline group, no significant difference was identified in NMDAR1 expression while pCREB expression was decreased in the deprived-side visual cortex in KN‑93. No significant difference in the expression of NMDAR1 and pCREB in the non-deprived-side visual cortex between the KN-93 and saline groups was observed. The results indicate that NMDAR1 and CREB are involved in the ocular dominance forming process and play a role in vision plasticity.

The calcium signaling pathway regulates leydig cell steroidogenesis through a transcriptional cascade involving the nuclear receptor NR4A1 and the steroidogenic acute regulatory protein

In the gonads and adrenal glands, the transient increase in steroidogenesis after hormonal stimulation requires modulation of steroidogenic acute regulatory protein (Star) expression and activity in a tightly regulated process involving cAMP and Ca(2+). In Leydig cells, the cAMP and Ca(2+) pathways account for most if not all of LH-induced steroidogenesis. Although the cAMP-activated molecular network has been well characterized in Leydig cells, little is known about the molecular cascade triggered by the Ca(2+) signaling pathway and the transcription factors responsible for mediating the genomic response. It is established that LH induces an increase in cytoplasmic Ca(2+) from the endoplasmic reticulum primarily through the ryanodine receptors. Previous reports also suggested a role of the Ca(2+) signaling pathway in Star expression based on the fact that inhibition of the Ca(2+)/calmodulin (CaM) protein kinase pathway greatly impaired Star expression in Leydig and adrenal cells. In this study, we used ryanodine receptors and CaM antagonists to show that the increase in intracellular Ca(2+) level is an essential modulator of progesterone synthesis through the regulation of Star gene expression in MA-10 Leydig cells. Furthermore, we mapped a Ca(2+)/CaM-sensitive element in the Star promoter, which led to the identification of the nuclear receptor 4A1 (NR4A1) as a key mediator of the Ca(2+)/CaM signaling pathway in these cells. These data provide new insights into the Ca(2+) molecular pathway essential for steroidogenesis in Leydig cells.

Effects of NaF on the expression of intracellular Ca2+ fluxes and apoptosis and the antagonism of taurine in murine neuron

Sodium fluoride (NaF) has been shown to be cytotoxic and produces inflammatory responses in humans. However, the cellular mechanisms underlying the neurotoxicity of fluoride are unclear. The present study aims to define a possible mechanism of NaF-induced neurotoxicity with respect to apoptosis and intracellular Ca(2+) fluxes. Meanwhile, the cytoprotective role of taurine in intervention, the toxic effects of NaF on neurons, is also investigated. The primary mouse hippocampal neurons were incubated with 5.0, 10.0, 15.0, 20.0, and 40.0 mg NaF/L in vitro and Kunming mice were exposed to 0.7, 2.8, and 11.2 mg NaF/kg and 7.5 and 15.0 mg taurine/kg in vivo. Intracellular Ca(2+) fluxes and apoptosis were assayed. Compared with the control, the significant differences of intracellular Ca(2+) concentration and apoptotic peaks were found in 5.0-40.0 mg NaF/L groups in vitro (p < 0.01) and in the groups of 0.7-11.2 mg NaF/kg in vivo (p < 0.01). Instantaneously, taurine can minimize F-induced neurotoxicity significantly at doses of 7.5 and 15.0 mg/kg (p < 0.01). The present study herein suggested that NaF could increase intercellular Ca(2+) concentration leading to apoptosis. Meanwhile, taurine could minimize neurotoxicity caused by fluoride through decreasing intercellular Ca(2+) concentration and cell apoptosis.