2-Arachidonylglycerol Protects Primary Astrocytes Exposed to Oxygen-Glucose Deprivation Through a Blockade of NDRG2 Signaling and STAT3 Phosphorylation

Hormetic effects of a cannabinoid system component, 2-arachidonoyl glycerol, on cell viability and expression profile of growth factors in cultured mouse Sertoli cells: Friend or foe of male fertility?

The generally undesired effects of exocannabinoids on male reproduction include alterations in testicular cell proliferation and function, as well as apoptosis induction. However, this paradigm has been challenged by the ability of endocannabinoids to regulate reproductive function. The present study addresses these paradoxical facts by investigating the effects of the endocannabinoid 2-arachidonoyl glycerol (2-AG) on mouse Sertoli cells' survival and apoptosis, with a mechanistic insight into Sertoli cell-based growth factors' production. The Mus musculus Sertoli cell line (TM4) was exposed to different concentrations of 2-AG, and cell viability was evaluated using MTT assay. Growth factors' gene and protein expressions were analyzed through RT-PCR and western blotting. 2-AG concentration dependently increased TM4 viability, with a slight increase starting at 0.0001 µM, a peak of 190% of the control level at 1 µM, and a decrease at 3 µM. Moreover, 2-AG paradoxically altered mRNA expression of caspase-3 and growth factors. Caspase-3 mRNA expression was down-regulated, and growth factors mRNA and protein expression were up-regulated when using a low concentration of 2-AG (1 μM). Opposite effects were observed by a higher concentration of 2-AG (3 μM). These paradoxical effects of 2-AG can be explained through the concept of hormesis. The results indicate the pivotal role of 2-AG in mediating Sertoli cell viability and apoptosis, at least in part, through altering growth factors secretion. Furthermore, they suggest the involvement of endocannabinoids in Sertoli cell-based physiological and pathological conditions and reflect the ability of abnormally elevated 2-AG to mimic the actions of exocannabinoids in reproductive dysfunction.

NDRG2 alleviates photoreceptor apoptosis by regulating the STAT3/TIMP3/MMP pathway in mice with retinal degenerative disease

Photoreceptor apoptosis is the main pathological feature of retinal degenerative diseases; however, the underlying molecular mechanism has not been elucidated. Recent studies have shown that N-myc downstream regulated gene 2 (NDRG2) exerts a neuroprotective effect on the brain and spinal cord. In addition, our previous studies have confirmed that NDRG2 is expressed in mouse retinal photoreceptors and counteracts N-methyl-N-nitrosourea (MNU)-induced apoptosis. However, the underlying molecular mechanism remains unclear. In this study, we observed that the expression of NDRG2 was not only significantly inhibited in photoreceptors after MNU treatment but also after hydrogen peroxide treatment, and photoreceptor apoptosis was alleviated or aggravated after overexpression or knockdown of NDRG2 in the 661W photoreceptor cell line, respectively. The apoptosis inhibitor Z-VAD-FMK rescued photoreceptor apoptosis induced by MNU after NDRG2 knockdown. Next, we screened and identified tissue inhibitor of metalloproteinases 3 (TIMP3) as the downstream molecule of NDRG2 in 661W cells by using quantitative real-time polymerase chain reaction. TIMP3 exerts a neuroprotective effect by inhibiting the expression of matrix metalloproteinases (MMPs). Subsequently, we found that signal transducer and activator of transcription 3 (STAT3) mediated the NDRG2-associated regulation of TIMP3. Finally, we overexpressed NDRG2 in mouse retinal tissues by intravitreally injecting an adeno-associated virus with mouse NDRG2 in vivo. Results showed that NDRG2 upregulated the expression of phospho-STAT3 (p-STAT3) and TIMP3, while suppressing MNU-induced photoreceptor apoptosis and MMP expression. Our findings revealed how NDRG2 regulates the STAT3/TIMP3/MMP pathway and uncovered the molecular mechanism underlying its neuroprotective effect on mouse retinal photoreceptors.

Endocannabinoid signaling in astrocytes

The study of the astrocytic contribution to brain functions has been growing in popularity in the neuroscience field. In the last years, and especially since the demonstration of the involvement of astrocytes in synaptic functions, the astrocyte field has revealed multiple functions of these cells that seemed inconceivable not long ago. In parallel, cannabinoid investigation has also identified different ways by which cannabinoids are able to interact with these cells, modify their functions, alter their communication with neurons and impact behavior. In this review, we will describe the expression of different endocannabinoid system members in astrocytes. Moreover, we will relate the latest findings regarding cannabinoid modulation of some of the most relevant astroglial functions, namely calcium (Ca²⁺ ) dynamics, gliotransmission, metabolism, and inflammation.

Divergent transcriptional regulation of astrocyte reactivity across disorders

Astrocytes respond to injury and disease in the central nervous system with reactive changes that influence the outcome of the disorder1-4. These changes include differentially expressed genes (DEGs) whose contextual diversity and regulation are poorly understood. Here we combined biological and informatic analyses, including RNA sequencing, protein detection, assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) and conditional gene deletion, to predict transcriptional regulators that differentially control more than 12,000 DEGs that are potentially associated with astrocyte reactivity across diverse central nervous system disorders in mice and humans. DEGs associated with astrocyte reactivity exhibited pronounced heterogeneity across disorders. Transcriptional regulators also exhibited disorder-specific differences, but a core group of 61 transcriptional regulators was identified as common across multiple disorders in both species. We show experimentally that DEG diversity is determined by combinatorial, context-specific interactions between transcriptional regulators. Notably, the same reactivity transcriptional regulators can regulate markedly different DEG cohorts in different disorders; changes in the access of transcriptional regulators to DNA-binding motifs differ markedly across disorders; and DEG changes can crucially require multiple reactivity transcriptional regulators. We show that, by modulating reactivity, transcriptional regulators can substantially alter disorder outcome, implicating them as therapeutic targets. We provide searchable resources of disorder-related reactive astrocyte DEGs and their predicted transcriptional regulators. Our findings show that transcriptional changes associated with astrocyte reactivity are highly heterogeneous and are customized from vast numbers of potential DEGs through context-specific combinatorial transcriptional-regulator interactions.

Neuroprotective and Immunomodulatory Action of the Endocannabinoid System under Neuroinflammation

Endocannabinoids (eCBs) are lipid-based retrograde messengers with a relatively short half-life that are produced endogenously and, upon binding to the primary cannabinoid receptors CB_1/2, mediate multiple mechanisms of intercellular communication within the body. Endocannabinoid signaling is implicated in brain development, memory formation, learning, mood, anxiety, depression, feeding behavior, analgesia, and drug addiction. It is now recognized that the endocannabinoid system mediates not only neuronal communications but also governs the crosstalk between neurons, glia, and immune cells, and thus represents an important player within the neuroimmune interface. Generation of primary endocannabinoids is accompanied by the production of their congeners, the N-acylethanolamines (NAEs), which together with N-acylneurotransmitters, lipoamino acids and primary fatty acid amides comprise expanded endocannabinoid/endovanilloid signaling systems. Most of these compounds do not bind CB_1/2, but signal via several other pathways involving the transient receptor potential cation channel subfamily V member 1 (TRPV1), peroxisome proliferator-activated receptor (PPAR)-α and non-cannabinoid G-protein coupled receptors (GPRs) to mediate anti-inflammatory, immunomodulatory and neuroprotective activities. In vivo generation of the cannabinoid compounds is triggered by physiological and pathological stimuli and, specifically in the brain, mediates fine regulation of synaptic strength, neuroprotection, and resolution of neuroinflammation. Here, we review the role of the endocannabinoid system in intrinsic neuroprotective mechanisms and its therapeutic potential for the treatment of neuroinflammation and associated synaptopathy.

Astrocytic NDRG2 is critical in the maintenance of neuropathic pain

Activation of astrocytes and abnormal synaptic glutamate metabolism are closely associated with the induction and maintenance of neuropathic pain (NP), but the exact mechanism underlying this association remains unclear. N-myc downstream-regulated gene 2 (NDRG2), a novel tumor-suppressor protein and stress-response gene, is involved in the pathogenesis of several neurodegenerative diseases. However, its role in nociceptive transduction has rarely been investigated. Here, we found that NDRG2, which was mainly expressed in the astrocytes in the central nervous system (CNS), was increased in the spinal cord of a spinal nerve ligation (SNL) rat model for NP. Suppression of NDRG2 by intrathecal injection of an NDRG2-RNAi-adenovirus significantly alleviated SNL-induced mechanical and thermal hypersensitivity, as well as elevated astrocytic glutamate transporter 1 (GLT-1) expression and downregulated pro-inflammatory cytokine levels, in the spinal dorsal horn of rats on Day 10 after SNL. Furthermore, in lipopolysaccharide (LPS)-stimulated primary astrocytic cultures derived from neonatal rats, inhibition of NDRG2 significantly reversed both the LPS-induced activation of astrocytes and decreased expression of GLT-1. By contrast, overexpression of NDRG2 by an adenoviral vector carrying NDRG2 resulted in astrocytic activation, aberrant glutamatergic neurotransmission, and spontaneous nociceptive responses in rats. Intrathecal injection of AG490, which is an inhibitor of the Janus tyrosine kinase and signal transducer and activator of the transcription 3 (JAK/STAT3) signaling pathway, significantly attenuated both mechanical and thermal hyperalgesia, as well as inhibited reactive astrocytes and restored normal expression levels of astrocytic GLT-1, in the spinal dorsal horn of NDRG2-overexpression rats. In conclusion, spinal astrocytic NDRG2 is critical in the maintenance of NP. Moreover, NDRG2 modulates astrocytic activation and inflammatory responses via regulating GLT-1 expression through the JAK/STAT3 signaling pathway. Our findings suggested that NDRG2 could be a novel therapeutic target for the treatment of NP.

Astrocyte-specific NDRG2 gene: functions in the brain and neurological diseases

In recent years, the roles of astrocytes of the central nervous system in brain function and neurological disease have drawn increasing attention. As a member of the N-myc downstream-regulated gene (NDRG) family, NDRG2 is principally expressed in astrocytes of the central nervous system. NDRG2, which is involved in cell proliferation and differentiation, is commonly regarded as a tumor suppressor. In astrocytes, NDRG2 affects the regulation of apoptosis, astrogliosis, blood-brain barrier integrity, and glutamate clearance. Several preclinical studies have revealed that NDRG2 is implicated in the pathogenesis of many neurological diseases not limited to tumors (mostly glioma in the nervous system), such as stroke, neurodegeneration (Alzheimer's disease and Parkinson's disease), and psychiatric disorders (depression and attention deficit hyperactivity disorder). This review summarizes the biological functions of NDRG2 under physiological and pathological conditions, and further discusses the roles of NDRG2 during the occurrence and development of neurological diseases.

Opposite Effects of Neuroprotective Cannabinoids, Palmitoylethanolamide, and 2-Arachidonoylglycerol on Function and Morphology of Microglia

Various studies performed in cultured cells and in in vivo models of neuronal damage showed that cannabinoids exert a neuroprotective effect. The increase in cannabinoids and cannabinoid like substances after stroke has been postulated to limit the content of neuronal injury. As well-accepted, inflammation, and neuronal damage are coupled processes and microglial cells as the main intrinsic immunological effector within the brain play a central role in their regulation. Treatment with the endocannabinoid, 2-arachidonoylglycerol (2-AG) or the endocannabinoid-like substance, palmitoylethanolamide (PEA) affected microglial cells and led to a decrease in the number of damaged neurons after excitotoxical lesion in organotypic hippocampal slice cultures (OHSC). 2-AG activated abnormal cannabidiol (abn-CBD) receptor, PEA was shown to mediate neuroprotection via peroxisome proliferator-activated receptor (PPAR)α. Despite the known neuroprotective and anti-inflammatory properties, the potential synergistic effect, namely possible entourage effect after treatment with the combination of these two protective cannabinoids has not been examined yet. After excitotoxical lesion OHSC were treated with PEA, 2-AG or a combination of both and the number of damaged neurons was evaluated. To investigate the role of microglial cells in PEA and 2-AG mediated protection, primary microglial cell cultures were treated with lipopolysaccharide (LPS) and 2-AG, PEA or a combination of those. Thereafter, we measured NO production, ramification index, proliferation and PPARα distribution in microglial cells. While PEA or 2-AG alone were neuroprotective, their co-application vanished the protective effect. This behavior was independent of microglial cells. Furthermore, PEA and 2-AG had contrary effects on ramification index and on NO production. No significant changes were observed in the proliferation rate of microglial cells after treatment. The expression of PPARα was not changed upon stimulation with PEA or 2-AG, but the distribution was significantly altered. 2-AG and PEA mediated neuroprotection was abolished when co-applied. Both cannabinoids exert contrary effects on morphology and function of microglial cells. Co-application of both cannabinoids with different targets did not lead to a positive additive effect as expected, presumably due to the contrary polarization of microglial cells.

Kappa opioid receptor agonists improve postoperative cognitive dysfunction in rats via the JAK2/STAT3 signaling pathway

Postoperative cognitive dysfunction (POCD) is a common and well‑known complication following surgery, particularly cardiopulmonary bypass (CPB) surgery. There are currently no suitable treatments for POCD, which is associated with increased illness and mortality rates. The present study aimed to identify a novel treatment for POCD. The protective effect of kappa opioid receptor (KOR) agonists on POCD in rats following CPB was determined and the regulatory mechanism of the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway was examined. The rats were randomly divided into five groups: Sham operation (Sham group), CPB operation (CPB group), KOR agonist + CPB (K group), KOR agonist + norbinaltorphimine (nor‑BNI) + CPB (NK group), and KOR agonist + JAK2‑STAT3 specific pathway inhibitor + CPB (AG group). A water maze test and neurological function scores were used to evaluate POCD. Hematoxylin and eosin staining was used to observe hippocampal neurons. ELISA was used to detect the levels of inflammatory factors, oxidative stress factors and brain injury markers. Immunofluorescence was used to visualize the neurons. TUNEL staining and western blotting were used to detect neuronal apoptosis, and western blotting was also used to detect JAK2/STAT3 pathway‑related proteins. The KOR agonists significantly improved POCD. S‑100β and NSE detection revealed that KOR agonists alleviated brain damage in CPB rats, and this result was reversed by KOR antagonists. The KOR agonists led to a significantly reduced inflammatory response and oxidative stress, as determined by ELISA detection, and attenuated hippocampal neuronal apoptosis, as revealed by TUNEL staining and western blotting, compared with the results in the CPB group. Finally, the KOR agonists inhibited the expression levels of phosphorylated (p‑)JAK2 and p‑STAT3, rather than total JAK2 and STAT3, compared with levels in the CPB group. Taken together, KOR agonists improved POCD in rats with CPB by inhibiting the JAK2/STAT3 signaling pathway.