Probenecid protects against cerebral ischemia/reperfusion injury by inhibiting lysosomal and inflammatory damage in rats

Calpain: The regulatory point of cardiovascular and cerebrovascular diseases

Calpain, a key member of the Calpain cysteine protease superfamily, performs limited protein hydrolysis in a calcium-dependent manner. Its activity is tightly regulated due to the potential for non-specific cleavage of various intracellular proteins upon aberrant activation. A thorough review of the literature from 2010 to 2023 reveals 121 references discussing cardiovascular and cerebrovascular diseases. Dysregulation of the Calpain system is associated with various pathological phenomena, including lipid metabolism disorders, inflammation, apoptosis, and excitotoxicity. Although recent studies have revealed the significant role of Calpain in cardiovascular and cerebrovascular diseases, the precise mechanisms remain incompletely understood. Exploring the potential of Calpain inhibition as a therapeutic approach for the treatment of cardiovascular and cerebrovascular diseases may emerge as a compelling area of interest for future calpain research.

Astrocyte modulation in cerebral ischemia-reperfusion injury: A promising therapeutic strategy

Cerebral ischemia-reperfusion injury (CIRI) poses significant challenges for drug development due to its complex pathogenesis. Astrocyte involvement in CIRI pathogenesis has led to the development of novel astrocyte-targeting drug strategies. To comprehensively review the current literature, we conducted a thorough analysis from January 2012 to December 2023, identifying 82 drugs aimed at preventing and treating CIRI. These drugs target astrocytes to exert potential benefits in CIRI, and their primary actions include modulation of relevant signaling pathways to inhibit neuroinflammation and oxidative stress, reduce cerebral edema, restore blood-brain barrier integrity, suppress excitotoxicity, and regulate autophagy. Notably, active components from traditional Chinese medicines (TCM) such as Salvia miltiorrhiza, Ginkgo, and Ginseng exhibit these important pharmacological properties and show promise in the treatment of CIRI. This review highlights the potential of astrocyte-targeted drugs to ameliorate CIRI and categorizes them based on their mechanisms of action, underscoring their therapeutic potential in targeting astrocytes.

The underlying mechanism of calcium toxicity-induced autophagic cell death and lysosomal degradation in early stage of cerebral ischemia

Cerebral ischemia is the important cause of worldwide disability and mortality, that is one of the obstruction of blood vessels supplying to the brain. In early stage, glutamate excitotoxicity and high level of intracellular calcium (Ca2+) are the major processes which can promote many downstream signaling involving in neuronal death and brain tissue damaging. Moreover, autophagy, the reusing of damaged cell organelles, is affected in early ischemia. Under ischemic conditions, autophagy plays an important role to maintain energy of the brain and its function. In the other hand, over intracellular Ca2+ accumulation triggers excessive autophagic process and lysosomal degradation leading to autophagic process impairment which finally induce neuronal death. This article reviews the association between intracellular Ca2+ and autophagic process in acute stage of ischemic stroke.

Pannexin1 Channel-Mediated Inflammation in Acute Ischemic Stroke

Emerging evidence suggests that inflammation mediated by the pannexin1 channel contributes significantly to acute ischemic stroke. It is believed that the pannexin1 channel is key in initiating central system inflammation during the early stages of acute ischemic stroke. Moreover, the pannexin1 channel is involved in the inflammatory cascade to maintain the inflammation levels. Specifically, the interaction of pannexin1 channels with ATP-sensitive P2X7 purinoceptors or promotion of potassium efflux mediates the activation of the NLRP3 inflammasome, triggering the release of pro-inflammatory factors such as IL-1 and IL-18, exacerbating and sustaining inflammation of brain. Also, increased release of ATP induced by cerebrovascular injury activates pannexin1 in vascular endothelial cells. This signal directs peripheral leukocytes to migrate into ischemic brain tissue, leading to an expansion of the inflammatory zone. Intervention strategies targeting pannexin1 channels may greatly alleviate inflammation after acute ischemic stroke to improve this patient population's clinical outcomes. In this review, we sought to summarize relevant studies on inflammation mediated by the pannexin1 channel in acute ischemic stroke and discussed the possibility of using brain organoid-on-a-chip technology to screen miRNAs that exclusively target the pannexin1 channel to provide new therapeutic measures for targeted regulation of pannexin1 channel to reduce inflammation in acute ischemic stroke.

Probenecid ameliorates testosterone-induced benign prostatic hyperplasia: Implications of PGE-2 on ADAM-17/EGFR/ERK1/2 signaling cascade

Benign prostatic hyperplasia (BPH) is one of the most prevalent clinical disorders in the elderly. Probenecid (Prob) is a well-known FDA-approved therapy for gout owing to its uricosuric effect. The present study evaluated the use of Prob for BPH as a COX-2 inhibitor. Prob (100 and 200 mg/kg) was intraperitoneally injected into male Wistar rats daily for 3 weeks. In the second week, testosterone (3 mg/kg) was subcutaneously injected to induce BPH. Compared with BPH-induced rats, Prob treatment reduced prostate weight and index and improved histopathological architecture. The protease activity of ADAM-17/TACE and its ligands (TGF-α and TNF-α) were regulated by prob, which in turn abolished EGFR phosphorylation, and several inflammatory mediators (COX-2, PGE2, NF-κB (p65), and IL-6) were suppressed. By reducing the nuclear import of extracellular regulated kinase protein 1/2 (ERK1/2), Prob helped re-establish the usual equilibrium between antiapoptotic proteins like Bcl-2 and cyclin D1 and proapoptotic proteins like Bax. All of these data point to Prob as a promising treatment for BPH because of its ability to inhibit COX-2-syntheiszed PGE2 and control the ADAM-17/TGF-α-induced EGFR/ERK1/2 signaling cascade. These findings might help to repurpose Prob for the treatment of BPH.

Pannexin1: insight into inflammatory conditions and its potential involvement in multiple organ dysfunction syndrome

Sepsis represents a global health concern, and patients with severe sepsis are at risk of experiencing MODS (multiple organ dysfunction syndrome), which is associated with elevated mortality rates and a poorer prognosis. The development of sepsis involves hyperactive inflammation, immune disorder, and disrupted microcirculation. It is crucial to identify targets within these processes to develop therapeutic interventions. One such potential target is Panx1 (pannexin-1), a widely expressed transmembrane protein that facilitates the passage of molecules smaller than 1 KDa, such as ATP. Accumulating evidence has implicated the involvement of Panx1 in sepsis-associated MODS. It attracts immune cells via the purinergic signaling pathway, mediates immune responses via the Panx1-IL-33 axis, promotes immune cell apoptosis, regulates blood flow by modulating VSMCs' and vascular endothelial cells' tension, and disrupts microcirculation by elevating endothelial permeability and promoting microthrombosis. At the level of organs, Panx1 contributes to inflammatory injury in multiple organs. Panx1 primarily exacerbates injury and hinders recovery, making it a potential target for sepsis-induced MODS. While no drugs have been developed explicitly against Panx1, some compounds that inhibit Panx1 hemichannels have been used extensively in experiments. However, given that Panx1's role may vary during different phases of sepsis, more investigations are required before interventions against Panx1 can be applied in clinical. Overall, Panx1 may be a promising target for sepsis-induced MODS. Nevertheless, further research is needed to understand its complex role in different stages of sepsis fully and to develop suitable pharmaceutical interventions for clinical use.

Probenecid, an Old Drug with Potential New Uses for Central Nervous System Disorders and Neuroinflammation

Probenecid is an old uricosuric agent used in clinics to treat gout and reduce the renal excretion of antibiotics. In recent years, probenecid has gained attention due to its ability to interact with membrane proteins such as TRPV2 channels, organic anion transporters, and pannexin 1 hemichannels, which suggests new potential therapeutic utilities in medicine. Some current functions of probenecid include their use as an adjuvant to increase the bioavailability of several drugs in the Central Nervous System (CNS). Numerous studies also suggest that this drug has important neuroprotective, antiepileptic, and anti-inflammatory properties, as evidenced by their effect against neurological and neurodegenerative diseases. In these studies, the use of probenecid as a Panx1 hemichannel blocker to reduce neuroinflammation is highlighted since neuroinflammation is a major trigger for diverse CNS alterations. Although the clinical use of probenecid has declined over the years, advances in its use in preclinical research indicate that it may be useful to improve conventional therapies in the psychiatric field where the drugs used have a low bioavailability, either because of a deficient passage through the blood-brain barrier or a high efflux from the CNS or also a high urinary clearance. This review summarizes the history, pharmacological properties, and recent research uses of probenecid and discusses its future projections as a potential pharmacological strategy to intervene in neurodegeneration as an outcome of neuroinflammation.

Early urate-lowering therapy in gouty arthritis with acute flares: a double-blind placebo controlled clinical trial

BACKGROUND

Gouty arthritis (GA) is a chronic systemic disease with recurrent acute monoarthritis. In a previous study, a higher incidence of acute flares was observed during the initial marked decrease in serum urate level. Our study evaluated the effect of early urate-lowering therapy in patients with acute GA flares.

METHODS

This study included 40 patients with acute GA; of them, 20 received colchicine 0.5 mg colchicine twice daily, while 20 received probenecid 500 mg and colchicine 0.5 mg twice daily. We evaluated GA severity and laboratory data for 2 weeks after the initial therapy. Medians and interquartile ranges (IQRs) were calculated to evaluate clinical presentations between these two groups.

RESULTS

Rapidly decreasing median serum uric acid levels was found in the patients treated with probenecid and colchicine compared with the patients treated with colchicine alone on day 8 (- 1.9 [IQR, - 3.7 to 0] vs 0.8 [IQR, - 0.1-2.2]; P < 0.001). However, the median decrease in visual analog scale score did not differ significantly between the two groups (- 5.5 [IQR, - 8.0 to - 3.0] vs - 3.5 [IQR, - 5.9 to - 2.0]; P = 0.080).

CONCLUSION

No significant increase was noted in acute gout flare severity or duration among GA patients treated with early aggressive control of hyperuricemia using probenecid plus colchicine.

Effects of probenecid and brilliant blue G on rat enteric glial cells following intestinal ischemia and reperfusion

The P2X7 receptor participates in several intracellular events and acts with the pannexin-1 channel. This study examined the effects of probenecid (PB) and brilliant blue G (BBG), which are antagonists of the pannexin-1 channel and P2X7 receptor, respectively, on rat ileum enteric glial cells after on ischemia and reperfusion. The ileal vessels were occluded for 45 min with nontraumatic vascular tweezers, and reperfusion was performed for periods of 24 h and 14 and 28 days. After ischemia (IR groups), the animals were treated with BBG (BG group) or PB (PB group). The double-labeling results demonstrated the following: the P2X7 receptor was present in enteric glial cells (S100β) and enteric neurons positive for HuC/D; enteric glial cells exhibited different phenotypes; some enteric glial cells were immunoreactive to only S100β or GFAP; and the pannexin-1 channel was present in enteric glial cells (GFAP). Density (in cells/cm²) analyses showed that the IR group exhibited a decrease in the number of cells immunoreactive for the P2X7 receptor, pannexin-1, and HuC/D and that treatment with BBG or PB resulted in the recovery of the numbers of these cells. The number of glial cells (S100β and GFAP) was higher in the IR group, and the treatments decreased the number of these cells to the normal value. However, the PB group did not exhibit recovery of S100β-positive glia. The cell profile area (μm²) of S100β-positive enteric glial cells decreased to the normal value after BBG treatment, whereas no recovery was observed in the PB group. The ileum contractile activity was decreased in the IR group and returned to baseline in the BG and PB groups. BBG and PB can effectively induce the recovery of neurons and glia cells and are thus potential therapeutic agents in the treatment of gastrointestinal tract diseases.

Multi‑faceted roles of cathepsins in ischemia reperfusion injury (Review)

Cathepsins are one of the most abundant proteases within the lysosomes with diverse physiological effects ranging from immune responses, cell death and intracellular protein degradation. Cathepsins are involved in extracellular and systemic functions such as systemic inflammation and extracellular matrix degradation. Ischemia reperfusion (IR) injury is responsible for numerous diseases including myocardial infarction, acute kidney injury, stroke and acute graft failure after transplant surgery. Inflammation plays a major role in the reperfusion phase of IR injury and previous research has shown that cathepsins are key mediators of the inflammation cascade as well as apoptosis. Taken together, cathepsins modulation could provide potential therapeutic approaches to attenuate IR injury. The present review summarized the current understanding of various cathepsin subtypes, their major physiologic functions, their roles in multi‑organ IR injury and detailed selective cathepsin inhibitors with therapeutic potential.

The Long-Term Pannexin 1 Ablation Produces Structural and Functional Modifications in Hippocampal Neurons

Enhanced activity and overexpression of Pannexin 1 (Panx1) channels contribute to neuronal pathologies such as epilepsy and Alzheimer's disease (AD). The Panx1 channel ablation alters the hippocampus's glutamatergic neurotransmission, synaptic plasticity, and memory flexibility. Nevertheless, Panx1-knockout (Panx1-KO) mice still retain the ability to learn, suggesting that compensatory mechanisms stabilize their neuronal activity. Here, we show that the absence of Panx1 in the adult brain promotes a series of structural and functional modifications in the Panx1-KO hippocampal synapses, preserving spontaneous activity. Compared to the wild-type (WT) condition, the adult hippocampal neurons of Panx1-KO mice exhibit enhanced excitability, a more complex dendritic branching, enhanced spine maturation, and an increased proportion of multiple synaptic contacts. These modifications seem to rely on the actin-cytoskeleton dynamics as an increase in the actin polymerization and an imbalance between the Rac1 and the RhoA GTPase activities were observed in Panx1-KO brain tissues. Our findings highlight a novel interaction between Panx1 channels, actin, and Rho GTPases, which appear to be relevant for synapse stability.

Probenecid induces the recovery of renal ischemia/reperfusion injury via the blockade of Pannexin 1/P2X7 receptor axis

Renal ischemia/reperfusion injury (RI/RI) is one of the main driving causes of acute kidney injury. However, effective treatment to limit injury and promote recovery and/or survival is still unavailable. Probenecid (PBN), a drug indicated for refractory gout, exhibits protective activities against several preclinical diseases including cerebral and myocardial I/RI via Pannexin 1 (Panx1) and P2X7 receptors' (P2X7R) inhibition. However, its protective role against RI/RI has not been previously addressed. Accordingly, we subjected rats to bilateral RI/RI with/or without PBN treatment. Twenty-four hours post-reperfusion, PBN showed mild tubular injury and reduced serum nephrotoxicity indices, gene and protein expression levels of Panx 1 and P2X7R, and ATP and pro-inflammatory cytokines' levels. The nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome signaling was also downregulated, as demonstrated by reduced gene and protein expression of NLRP3 and caspase-1, along with suppressed IL-1β maturation. Furthermore, PBN enhanced Tregs activity as indicated by elevated FoxP3 gene expression, IL-10, and TGF-β renal levels. On day 5 post-reperfusion, PBN noticeably enhanced renal recovery, as demonstrated by intact tubular epithelium and restored nephrotoxicity indices, Panx 1 and P2X7R gene and protein expression levels, ATP and pro-inflammatory cytokine levels, and NLRP3 inflammasome signaling. Besides, renal Tregs activity was also significantly increased. Our study elaborates for the first time the effectiveness of PBN in recovering post-ischemic renal injury through synergistic inhibition in Panx1/P2X7R axis leading to inactivation of NLRP3 inflammasome signaling and activation of Tregs in ischemic renal tissues. Therefore, PBN can be considered a promising drug for RI/RI treatment.

Connexins, Pannexins and Gap Junctions in Perinatal Brain Injury

Perinatal brain injury secondary to hypoxia-ischemia and/or infection/inflammation remains a major cause of disability. Therapeutic hypothermia significantly improves outcomes, but in randomized controlled trials nearly half of infants still died or survived with disability, showing that additional interventions are needed. There is growing evidence that brain injury spreads over time from injured to previously uninjured regions of the brain. At least in part, this spread is related to opening of connexin hemichannels and pannexin channels, both of which are large conductance membrane channels found in many brain cells. Opening of these membrane channels releases adenosine triphosphate (ATP), and other neuroactive molecules, into the extracellular space. ATP has an important role in normal signaling, but pathologically can trigger the assembly of the multi-protein inflammasome complex. The inflammasome complex promotes activation of inflammatory caspases, and release of inflammatory cytokines. Overall, the connexin hemichannel appears to play a primary role in propagation of injury and chronic disease, and connexin hemichannel blockade has been shown to be neuroprotective in multiple animal models. Thus, there is potential for some blockers of connexin or pannexin channels to be developed into targeted interventions that could be used in conjunction with or separate to therapeutic hypothermia.

Mechanisms of SARS-CoV-2 and Male Infertility: Could Connexin and Pannexin Play a Role?

The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on male infertility has lately received significant attention. SARS-CoV-2, the virus that causes coronavirus disease (COVID-19) in humans, has been shown to impose adverse effects on both the structural components and function of the testis, which potentially impact spermatogenesis. These adverse effects are partially explained by fever, systemic inflammation, oxidative stress, and an increased immune response leading to impaired blood-testis barrier. It has been well established that efficient cellular communication via gap junctions or functional channels is required for tissue homeostasis. Connexins and pannexins are two protein families that mediate autocrine and paracrine signaling between the cells and the extracellular environment. These channel-forming proteins have been shown to play a role in coordinating cellular communication in the testis and epididymis. Despite their role in maintaining a proper male reproductive milieu, their function is disrupted under pathological conditions. The involvement of these channels has been well documented in several physiological and pathological conditions and their designated function in infectious diseases. However, their role in COVID-19 and their meaningful contribution to male infertility remains to be elucidated. Therefore, this review highlights the multivariate pathophysiological mechanisms of SARS-CoV-2 involvement in male reproduction. It also aims to shed light on the role of connexin and pannexin channels in disease progression, emphasizing their unexplored role and regulation of SARS-CoV-2 pathophysiology. Finally, we hypothesize the possible involvement of connexins and pannexins in SARS-CoV-2 inducing male infertility to assist future research ideas targeting therapeutic approaches.

Possible role of pannexin 1 channels and purinergic receptors in the pathogenesis and mechanism of action of SARS-CoV-2 and therapeutic potential of targeting them in COVID-19

Identifying signaling pathways and molecules involved in SARS-CoV-2 pathogenesis is pivotal for developing new effective therapeutic or preventive strategies for COVID-19. Pannexins (PANX) are ATP-release channels in the plasma membrane essential in many physiological and immune responses. Activation of pannexin channels and downstream purinergic receptors play dual roles in viral infection, either by facilitating viral replication and infection or inducing host antiviral defense. The current review provides a hypothesis demonstrating the possible contribution of the PANX1 channel and purinergic receptors in SARS-CoV-2 pathogenesis and mechanism of action. Moreover, we discuss whether targeting these signaling pathways may provide promising preventative therapies and treatments for patients with progressive COVID-19 resulting from excessive pro-inflammatory cytokines and chemokines production. Several inhibitors of this pathway have been developed for the treatment of other viral infections and pathological consequences. Specific PANX1 inhibitors could be potentially included as part of the COVID-19 treatment regimen if, in future, studies demonstrate the role of PANX1 in COVID-19 pathogenesis. Of note, any ATP therapeutic modulation for COVID-19 should be carefully designed and monitored because of the complex role of extracellular ATP in cellular physiology.

Pannexin-1 channel opening is critical for COVID-19 pathogenesis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly rampaged worldwide, causing a pandemic of coronavirus disease (COVID -19), but the biology of SARS-CoV-2 remains under investigation. We demonstrate that both SARS-CoV-2 spike protein and human coronavirus 229E (hCoV-229E) or its purified S protein, one of the main viruses responsible for the common cold, induce the transient opening of Pannexin-1 (Panx-1) channels in human lung epithelial cells. However, the Panx-1 channel opening induced by SARS-CoV-2 is greater and more prolonged than hCoV-229E/S protein, resulting in an enhanced ATP, PGE₂, and IL-1β release. Analysis of lung lavages and tissues indicate that Panx-1 mRNA expression is associated with increased ATP, PGE₂, and IL-1β levels. Panx-1 channel opening induced by SARS-CoV-2 spike protein is angiotensin-converting enzyme 2 (ACE-2), endocytosis, and furin dependent. Overall, we demonstrated that Panx-1 channel is a critical contributor to SARS-CoV-2 infection and should be considered as an alternative therapy.

Pannexin 1 plays a pro-survival role by attenuating P2X7 receptor-mediated Ca2+ influx

Extracellular ATP works as an autocrine and/or paracrine signaling molecule by activating plasma membrane-localized purinergic receptors. Stimulation of purinergic P2X7 receptor (P2X7R) increases cytosolic Ca²⁺ ([Ca²⁺]_c), which in turn activates Pannexin 1 (Panx1) channel. In earlier studies, Panx1 and P2X7R have been shown to interact physically. Also, both the channels have been implicated in similar pathophysiological processes. In this study, we investigated the effect of Panx1 on P2X7R-mediated Ca²⁺influx. Panx1 attenuated P2X7R-mediated [Ca²⁺]_c rise in CHO-K1 and HEK-293 cells. [Ca²⁺]_c rise was higher in Panx1 knockdown astrocytes. The inhibitory effect was unaffected in the presence of Panx1 blocker, carbenoxolone. The region between 350th and 386th amino acid residues in the carboxyl terminus (CT) of Panx1 was found to be crucial for inhibiting P2X7R. Like full-length Panx1, the CT (350th to 426th amino acids) alone was able to attenuate the [Ca²⁺]_c rise. Further, CT prevented cell death caused by P2X7R overactivation. Based on our results, we propose a novel pro-survival role of Panx1 exerted by modulating P2X7R.

Pannexin 1 channels facilitate communication between T cells to restrict the severity of airway inflammation

Allergic airway inflammation is driven by type-2 CD4⁺ T cell inflammatory responses. We uncover an immunoregulatory role for the nucleotide release channel, Panx1, in T cell crosstalk during airway disease. Inverse correlations between Panx1 and asthmatics and our mouse models revealed the necessity, specificity, and sufficiency of Panx1 in T cells to restrict inflammation. Global Panx1^-/- mice experienced exacerbated airway inflammation, and T-cell-specific deletion phenocopied Panx1^-/- mice. A transgenic designed to re-express Panx1 in T cells reversed disease severity in global Panx1^-/- mice. Panx1 activation occurred in pro-inflammatory T effector (Teff) and inhibitory T regulatory (Treg) cells and mediated the extracellular-nucleotide-based Treg-Teff crosstalk required for suppression of Teff cell proliferation. Mechanistic studies identified a Salt-inducible kinase-dependent phosphorylation of Panx1 serine 205 important for channel activation. A genetically targeted mouse expressing non-phosphorylatable Panx1^S205A phenocopied the exacerbated inflammation in Panx1^-/- mice. These data identify Panx1-dependent Treg:Teff cell communication in restricting airway disease.

Pannexin-1 Channels as Mediators of Neuroinflammation

Neuroinflammation is a major component of central nervous system (CNS) injuries and neurological diseases, including Alzheimer’s disease, multiple sclerosis, neuropathic pain, and brain trauma. The activation of innate immune cells at the damage site causes the release of pro-inflammatory cytokines and chemokines, which alter the functionality of nearby tissues and might mediate the recruitment of leukocytes to the injury site. If this process persists or is exacerbated, it prevents the adequate resolution of the inflammation, and ultimately enhances secondary damage. Adenosine 5′ triphosphate (ATP) is among the molecules released that trigger an inflammatory response, and it serves as a chemotactic and endogenous danger signal. Extracellular ATP activates multiple purinergic receptors (P2X and P2Y) that have been shown to promote neuroinflammation in a variety of CNS diseases. Recent studies have shown that Pannexin-1 (Panx1) channels are the principal conduits of ATP release from dying cells and innate immune cells in the brain. Herein, we review the emerging evidence that directly implicates Panx-1 channels in the neuroinflammatory response in the CNS.

Purinergic signaling in nervous system health and disease: Focus on pannexin 1

Purinergic signaling encompasses the cycle of adenosine 5' triphosphate (ATP) release and its metabolism into nucleotide and nucleoside derivatives, the direct release of nucleosides, and subsequent receptor-triggered downstream intracellular pathways. Since the discovery of nerve terminal and glial ATP release into the neuropil, purinergic signaling has been implicated in the modulation of nervous system development, function, and disease. In this review, we detail our current understanding of the roles of the pannexin 1 (PANX1) ATP-release channel in neuronal development and plasticity, glial signaling, and neuron-glial-immune interactions. We additionally provide an overview of PANX1 structure, activation, and permeability to orientate readers and highlight recent research developments. We identify areas of convergence between PANX1 and purinergic receptor actions. Additional highlights include data on PANX1's participation in the pathophysiology of nervous system developmental, degenerative, and inflammatory disorders. Our aim in combining this knowledge is to facilitate the movement of our current understanding of PANX1 in the context of other nervous system purinergic signaling mechanisms one step closer to clinical translation.

Differential Action of Connexin Hemichannel and Pannexin Channel Therapeutics for Potential Treatment of Retinal Diseases

Dysregulation of retinal function in the early stages of light-induced retinal degeneration involves pannexins and connexins. These two types of proteins may contribute to channels that release ATP, leading to activation of the inflammasome pathway, spread of inflammation and retinal dysfunction. However, the effect of pannexin channel block alone or block of both pannexin channels and connexin hemichannels in parallel on retinal activity in vivo is unknown. In this study, the pannexin channel blocker probenecid and the connexin hemichannel blocker tonabersat were used in the light-damaged rat retina. Retinal function was evaluated using electroretinography (ERG), retinal structure was analyzed using optical coherence tomography (OCT) imaging and the tissue response to light-induced injury was assessed immunohistochemically with antibodies against glial fibrillary acidic protein (GFAP), Ionized calcium binding adaptor molecule 1 (Iba-1) and Connexin43 (Cx43). Probenecid did not further enhance the therapeutic effect of connexin hemichannel block in this model, but on its own improved activity of certain inner retina neurons. The therapeutic benefit of blocking connexin hemichannels was further evaluated by comparing these data against results from our previously published studies that also used the light-damaged rat retina model. The analysis showed that treatment with tonabersat alone was better than probenecid alone at restoring retinal function in the light-damaged retina model. The results assist in the interpretation of the differential action of connexin hemichannel and pannexin channel therapeutics for potential treatment of retinal diseases.

Exercise combined with trimetazidine improves anti-fatal stress capacity through enhancing autophagy and heat shock protein 70 of myocardium in mice

Background: Anti-stress capacity is important to resist the occurrence of adverse events. To observe the effects of exercise, trimetazidine alone or combined on the anti-stress capacity of mice, and further explore its potential mechanism. Methods: Forty-four C57BL/6 male mice aged 8 weeks were randomly divided into four groups (n=11 for each group): control group (group C), exercise group (group E), trimetazidine group (group T), exercise combined with trimetazidine group (group TE). After the intervention, each group was randomly subdivided into the exhaustive exercise (EE, n=6) and the non-EE (n=5) subgroups. The mice in the EE-subgroup underwent EE. Mice were sacrificed 12 hours later after EE. The myocardial ultrastructure and autophagosomes were observed under an electron microscope. The expression of autophagy-related proteins: BNIP3, LC3-II, and P62 were analyzed and the heat shock protein 70 mRNA transcription and protein expression were also investigated. Results: Exercise or trimetazidine increased the expression of BNIP3, LC3-II, and heat shock protein 70, decreased the expression of P62 pre- and post-EE while the combination has the synergistic effect. Conclusion: Exercise and trimetazidine, alone or combined enhanced the anti-stress capacity of mice significantly. The underlying mechanism may be associated with the promotion of autography and the expression of heat shock protein 70.

The Role of Connexin 43 and Pannexin 1 During Acute Inflammation

During acute inflammation, the recruitment of leukocytes from the blood stream into the inflamed tissue is a well-described mechanism encompassing the interaction of endothelial cells with leukocytes allowing leukocytes to reach the site of tissue injury or infection where they can fulfill their function such as phagocytosis. This process requires a fine-tuned regulation of a plethora of signaling cascades, which are still incompletely understood. Here, connexin 43 (Cx43) and pannexin 1 (Panx1) are known to be pivotal for the correct communication of endothelial cells with leukocytes. Pharmacological as well as genetic approaches provide evidence that endothelial Cx43-hemichannels and Panx1-channels release signaling molecules including ATP and thereby regulate vessel function and permeability as well as the recruitment of leukocytes during acute inflammation. Furthermore, Cx43 hemichannels and Panx1-channels in leukocytes release signaling molecules and can mediate the activation and function of leukocytes in an autocrine manner. The focus of the present review is to summarize the current knowledge of the role of Cx43 and Panx1 in endothelial cells and leukocytes in the vasculature during acute inflammation and to discuss relevant molecular mechanisms regulating Cx43 and Panx1 function.

MicroRNA-124 regulates cell pyroptosis during cerebral ischemia-reperfusion injury by regulating STAT3

Cerebral ischemia-reperfusion injury (CIRI) is the observed continuation and deterioration of ischemic injury, and currently, there are no effective treatment strategies for the condition. It has been reported that microRNAs (miRNAs) serve an important role in CIRI by regulating pyroptosis. The present study demonstrated that miRNA-124 regulated CIRI by regulating STAT3. To explore the relationship between miRNA-124/STAT3 and pyroptosis in CIRI, CIRI was simulated using a middle cerebral artery occlusion model. Subsequently, miRNA-124 expression levels were altered via the intracerebroventricular injection of miRNA-124 agonist or antagonist. The degree of brain tissue injury was assessed by conducting TTC staining and neurological function scoring. Relative miRNA-124 expression levels were determined via reverse transcription-quantitative PCR. A luciferase reporter gene system verified the targeted binding of miRNA-124 to STAT3. The expression levels of key proteins and proinflammatory cytokines associated with pyroptosis [caspase-1, gasdermin D, interleukin (IL)-18 and IL-1β] were detected via western blotting and immunohistochemistry. The increased expression levels of pyroptosis-associated proteins and proinflammatory cytokines in the I/R groups compared with the control group, indicated that pyroptosis intensified over time during CIRI, and miRNA-124 agonist significantly abrogated pyroptosis and improved neurological function compared with the control group. Furthermore, miRNA-124 inhibited STAT3 activation in a targeted manner, which also decreased the extent of pyroptosis. However, miRNA-124 antagonist reversed miR-124 agonist-mediated effects. Therefore, the present study indicated that miRNA-124 may provide neuroprotection against pyroptosis during CIRI, potentially via inhibition of the STAT3 signaling pathway.

Soluble uric acid induces myocardial damage through activating the NLRP3 inflammasome

Uric acid crystal is known to activate the NLRP3 inflammasome and to cause tissue damages, which can result in many diseases, such as gout, chronic renal injury and myocardial damage. Meanwhile, soluble uric acid (sUA), before forming crystals, is also related to these diseases. This study was carried out to investigate whether sUA could also activate NLRP3 inflammasome in cardiomyocytes and to analyse the mechanisms. The cardiomyocyte activity was monitored, along with the levels of mature IL-1β and caspase-1 from H9c2 cells following sUA stimulus. We found that sUA was able to activate NLRP3 inflammasome, which was responsible for H9c2 cell apoptosis induced by sUA. By elevating TLR6 levels and then activating NF-κB/p65 signal pathway, sUA promoted NLRP3, pro-caspase 1 and pro-IL-1β production and provided the first signal of NLRP3 inflammasome activation. Meanwhile, ROS production regulated by UCP2 levels also contributed to NLRP3 inflammasome assembly and subsequent caspase 1 activation and mature IL-1β secretion. In addition, the tlr6 knockdown rats suffering from hyperuricemia showed the lower level of IL-1β and an ameliorative cardiac function. These findings suggest that sUA activates NLRP3 inflammasome in cardiomyocytes and they may provide one therapeutic strategy for myocardial damage induced by sUA.

Regulation of JNK signaling pathway and RIPK3/AIF in necroptosis-mediated global cerebral ischemia/reperfusion injury in rats

Receptor-interacting protein kinase 3 (RIPK3) regulates a newly discovered cell death form called necroptosis. RIPK3 nuclear translocation and inflammatory factor release are involved in necroptosis after rat global cerebral ischemia/reperfusion (I/R) injury. The purpose of this study was to investigate the effects of interactions between the RIPK3 and apoptosis-inducing factor (AIF) necroptosis pathway and the JNK-mediated inflammatory pathway. Rats were subjected to 4-vessel occlusion and reperfusion injury. RIPK3 inhibitor GSK872, RIPk3 recombinant adeno-associated virus (rAAV) and JNK-specific inhibitor SP600125 were intracerebroventricular injected before I/R. Hippocampus CA1 tissue were obtained and RIPK3, AIF, p-JNK, IL-6 were determined by western blot analysis. The RIPK3 and AIF interaction were also analyzed by immunofluorescence and immunoprecipitation. The expression of endogenous RIPK3, AIF, p-JNK and IL-6 was increased in hippocampus CA1 in I/R group. In addition, RIPK3 was increased in both the total protein and nuclear protein. GSK872 administration reduced the number of neuron deaths and the expression of RIPK3, p-JNK and IL-6. GSK872 also improve the rat neurobehavior. While use RIPk3 rAAV treatment to overexpress RIPK3, it appeared lower neuron survival. Immunofluorescence staining demonstrated that RIPK3 and AIF formed as a novel complex in the cytoplasm first, and then nuclear translocation. GSK872 pretreatment decreased the number of RIPK3-positive cells and related to the generation of RIPK3-AIF complex in nuclear. Moreover, the production of inflammatory factors levels was found to be significantly elevated after I/R. We further use SP600125 to attenuate inflammation cascade. It not only inhibits the expression of inflammatory factors p-JNK and IL-6, but also inhibits RIPK3 and AIF in the cytoplasm. Collectively, the results of our study indicate that RIPK3-mediated necroptosis interacts with the JNK-mediated inflammatory signaling pathway to participate in global cerebral I/R injury. JNK-regulated inflammatory mediators may promote the necroptosis initiation.

Upregulation of pannexin-1 hemichannels explains the apparent death of the syncytiotrophoblast during human placental explant culture

BACKGROUND

It has been reported that during the culture of human placental explants, the syncytiotrophoblast dies between 3 and 24 h and is then replaced within 48 h by a new syncytiotrophoblast layer formed by the fusion of underlying cytotrophoblasts. Most frequently the death of the syncytiotrophoblast is indicated by the uptake of nuclear stains such as propidium iodide (PI). This process is reportedly similar in both early and late gestation placental explants.

METHODS

We cultured first trimester placental explants for up to 48 h and tested membrane intactness by exposure to PI. Connexin and pannexin mRNAs were quantified by RT-PCR and protein levels determined by immunofluorescence. The syncytiotrophoblast membrane leak was determined by culturing explants in the presence of hemichannel blockers. Extrusion of extracellular vesicles from the syncytiotrophoblast was quantified.

RESULTS

Nuclei of the syncytiotrophoblast were stained with PI following approximately 4 h of culture and this was prevented by culturing the explants with pannexin-1 blockers. Expression of pannexin-1 hemichannels increased during explant culture (p = 0.0027). Extracellular vesicles were most abundantly extruded from the explants during the first 3 h of culture and the temporal pattern of extrusion was unaltered by blocking hemichannels.

DISCUSSION

We show the mechanism of uptake of nuclear non-viability stains into the syncytiotrophoblast during explant culture is via upregulation of pannexin 1 hemichannels. Contrary to suggestions by some, the production of extracellular vesicles from cultured placental explants is not an in vitro artefact resulting from the apparent death of the syncytiotrophoblast in explant cultures.

Acute Pannexin 1 Blockade Mitigates Early Synaptic Plasticity Defects in a Mouse Model of Alzheimer's Disease

Synaptic loss induced by soluble oligomeric forms of the amyloid β peptide (sAβos) is one of the earliest events in Alzheimer’s disease (AD) and is thought to be the major cause of the cognitive deficits. These abnormalities rely on defects in synaptic plasticity, a series of events manifested as activity-dependent modifications in synaptic structure and function. It has been reported that pannexin 1 (Panx1), a nonselective channel implicated in cell communication and intracellular signaling, modulates the induction of excitatory synaptic plasticity under physiological contexts and contributes to neuronal death under inflammatory conditions. Here, we decided to study the involvement of Panx1 in functional and structural defects observed in excitatory synapses of the amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (Tg) mice, an animal model of AD. We found an age-dependent increase in the Panx1 expression that correlates with increased Aβ levels in hippocampal tissue from Tg mice. Congruently, we also observed an exacerbated Panx1 activity upon basal conditions and in response to glutamate receptor activation. The acute inhibition of Panx1 activity with the drug probenecid (PBN) did not change neurodegenerative parameters such as amyloid deposition or astrogliosis, but it significantly reduced excitatory synaptic defects in the AD model by normalizing long-term potentiation (LTP) and depression and improving dendritic arborization and spine density in hippocampal neurons of the Tg mice. These results suggest a major contribution of Panx1 in the early mechanisms leading to the synaptopathy in AD. Indeed, PBN induced a reduction in the activation of p38 mitogen-activated protein kinase (MAPK), a kinase widely implicated in the early neurotoxic signaling in AD. Our data strongly suggest that an enhanced expression and activation of Panx1 channels contribute to the Aβ-induced cascades leading to synaptic dysfunction in AD.

A transcriptomic study of probenecid on injured spinal cords in mice

Background

Recent studies have found that probenecid has neuroprotective and reparative effects on central nervous system injuries. However, its effect on genome-wide transcription in acute spinal cord injury (SCI) remains unknown. In the present study, RNA sequencing (RNA-Seq) is used to analyze the effect of probenecid on the local expression of gene transcription 8 h after spinal injury.

Methods

An Infinite Horizon impactor was used to perform contusive SCI in mice. The SCI model was made by using a rod (1.3 mm diameter) with a force of 50 Kdynes. Sham-operated mice only received a laminectomy without contusive injury. The injured mice were randomly assigned into either the control (SCI_C) or probenecid injection (SCI_P) group. In the latter group, the probenecid drug was intraperitoneally injected (0.5 mg/kg) immediately following injury. Eight hours after the injury or laminectomy, the spinal cords were removed from the mice in both groups. The total RNAs were extracted and purified for library preparation and transcriptome sequencing. Differential gene expressions (DEGs) of the three groups-sham, SCI_C and SCI_P-were analyzed using a DESeq software. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of DEGs were performed using a GOseq R package and KOBAS software. Real-time quantitative reverse-transcriptase polymerase chain reaction was used to validate RNA-Seq results.

Results

RNA-Seq showed that, compared to the SCI_C group, the number of DEGs was 641 in the SCI_P group (286 upregulated and 355 downregulated). According to GO analysis, DEGs were most enriched in extracellular matrix (ECM), collagen trimer, protein bounding and sequence specific DNA binding. KEGG analysis showed that the most enriched pathways included: cell adhesion molecules, Leukocyte transendothelial migration, ECM-receptor interactions, PI3K-Akt signaling pathways, hematopoietic cell lineages, focal adhesions, the Rap1 signaling pathway, etc. The sequence data have been deposited into the Sequence Read Archive (https://www.ncbi.nlm.nih.gov/sra/PRJNA554464).

Probenecid Relieves Cerebral Dysfunction of Sepsis by Inhibiting Pannexin 1-Dependent ATP Release

Acute brain dysfunction and the following neurological manifestation are common complications in septic patients, which are associated with increased morbidity and mortality. However, the therapeutic strategy of this disorder remains a major challenge. Given the emerging role of a clinically approved drug, probenecid (PRB) has been recently identified as an inhibitor of pannexin 1 (PANX1) channel, which restrains extracellular ATP release-induced purinergic pathway activation and inflammatory response contributing to diverse pathological processes. In this study, we explored whether PRB administration attenuated neuroinflammatory response and cognitive impairment during sepsis. In mice suffered from cecal ligation and puncture (CLP)-induced sepsis, treatment with PRB improved memory retention and lessened behavioral deficits. This neuroprotective effect was coupled with restricted overproduction of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and interleukin (IL)-1β in the hippocampus. Since this damped neuroinflammation was replicated by inhibition of ATP release, it suggested that PANX1 channel modulates a purinergic-related pathway contributing to the neurohistological damage. Therefore, we identified PRB could be a promising therapeutic approach for the therapy of cerebral dysfunction of sepsis.

Dispelling myths about connexins, pannexins and P2X7 in hypoxic-ischemic central nervous system

In membrane physiology, as in other fields, myths or speculations may be repeated so often and so widely that they are perceived as facts. To some extent, this has occurred with regard to gap junctions, hemichannels, pannexin channels and P2X7 (ionotropic receptors), especially concerning the interpretation of the individual role of these channels in hypoxic-ischemic CNS since these channels may be closed by the same pharmacological blockers. Significance of existing controversial data are highlighted and contradictory views from different groups are critically discussed herein.

The Role of Connexin and Pannexin Channels in Perinatal Brain Injury and Inflammation

Perinatal brain injury remains a major cause of death and life-long disability. Perinatal brain injury is typically associated with hypoxia-ischemia and/or infection/inflammation. Both hypoxia-ischemia and infection trigger an inflammatory response in the brain. The inflammatory response can contribute to brain cell loss and chronic neuroinflammation leading to neurological impairments. It is now well-established that brain injury evolves over time, and shows a striking spread from injured to previously uninjured regions of the brain. There is increasing evidence that this spread is related to opening of connexin hemichannels and pannexin channels, both of which are large conductance membrane channels found in almost all cell types in the brain. Blocking connexin hemichannels within the first 3 h after hypoxia-ischemia has been shown to improve outcomes in term equivalent fetal sheep but it is important to also understand the downstream pathways linking membrane channel opening with the development of injury in order to identify new therapeutic targets. Open membrane channels release adenosine triphosphate (ATP), and other neuroactive molecules, into the extracellular space. ATP has an important physiological role, but has also been reported to act as a damage-associated molecular pattern (DAMP) signal mediated through specific purinergic receptors and so act as a primary signal 1 in the innate immune system inflammasome pathway. More crucially, extracellular ATP is a key inflammasome signal 2 activator, with purinergic receptor binding triggering the assembly of the multi-protein inflammasome complex. The inflammasome pathway and complex formation contribute to activation of inflammatory caspases, and the release of inflammatory cytokines, including interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-18, and vascular endothelial growth factor (VEGF). We propose that the NOD-like receptor protein-3 (NLRP3) inflammasome, which has been linked to inflammatory responses in models of ischemic stroke and various inflammatory diseases, may be one mechanism by which connexin hemichannel opening especially mediates perinatal brain injury.

Ferulic Acid Exerts Anti-apoptotic Effects against Ischemic Injury by Activating HSP70/Bcl-2- and HSP70/Autophagy-Mediated Signaling after Permanent Focal Cerebral Ischemia in Rats

This study assessed the anti-apoptotic effects of the administration of ferulic acid (FrA) in rats 30 min before middle cerebral artery occlusion (MCAo) followed by 3 d of ischemia and the involvement of 70 kDa heat shock protein (HSP70)-mediated signaling in the penumbral cortex. Our results demonstrated that FrA pretreatment at doses of 80 mg/kg (FrA-80 mg) and 100 mg/kg (FrA-100 mg) effectively ameliorated neurological functions and reduced the numbers of cytochrome c-, cleaved caspase-3-, and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive cells in the penumbral cortex 3 d after ischemia. Moreover, FrA-80 mg and FrA-100 mg pretreatment markedly upregulated cytosolic HSP70, Beclin-1, microtubule-associated protein 1 light chain 3 (LC3) A/B-II and autophagy-related protein 5 (Atg5) expression; cytosolic and mitochondrial X-linked inhibitor of apoptosis (XIAP) expression and the Bcl-2/Bax ratio. FrA pretreatment downregulated cytosolic cytochrome c, apoptosis-inducing factor (AIF), procathepsin B, and cathepsin B expression and mitochondrial and cytosolic second mitochondria-derived activator of caspase/direct inhibitor of apoptosis protein-binding protein with a low isoelectric point (Smac/DIABLO) expression in the penumbral cortex. Pretreatment with VER155008, a HSP70 family inhibitor, significantly inhibited the effects of FrA-100 mg on the expression of the aforementioned proteins expression in the penumbral cortex. FrA-80 mg and FrA-100 mg pretreatment exerts neuroprotective effects against caspase-dependent and -independent apoptosis through activating HSP70/Bcl-2- and HSP70/autophagy-induced signaling pathways. Furthermore, the HSP70/Bcl-2- and HSP70/autophagy-induced anti-apoptotic effects of FrA pretreatment can be attributed to the regulation of Bax/cytochrome c/Smac/DIABLO/XIAP/ caspase-3- (or Bax/AIF-) and Beclin-1/LC3A/B-II/Atg5-mediated signaling, respectively, in the penumbral cortex 3 d after permanent MCAo.

Probenecid arrests the progression of pronounced clinical symptoms in a mouse model of multiple sclerosis

While it has been established that Probenecid (PBN) prevents the onset of experimental autoimmune encephalomyelitis (EAE) in mice, it is not clear whether it has any effect on already manifest EAE. The aim of this study was therefore to analyze the therapeutic effect of PBN in pronounced EAE. Mice with manifest clinical symptoms of EAE were either treated with PBN or solvent for 20 days, or they were left untreated. The clinical symptoms were monitored daily. Inflammation, demyelination and oligodendrocyte numbers were determined in the spinal cord. We were able to demonstrate that PBN not only significantly prolonged survival but also prevented the progression of clinical symptoms in the EAE model of multiple sclerosis. In addition, we were able to show that PBN reduced inflammation, T cell infiltration and oligodendrocyte cell loss. PBN was previously shown to inhibit – among other targets – pannexin channels. As pannexin channels provide conduits for ATP, are associated with the inflammasome, and act as “find me-signals” in the process of apoptosis, inhibition of pannexins via PBN might contribute to the PBN-effects observed in this study. The beneficial and therapeutic effects of PBN in the context of EAE demonstrate an intriguing link between PBN and neuroinflammation, which might foster translational interest.

Inhibitors of connexin and pannexin channels as potential therapeutics

While gap junctions support the exchange of a number of molecules between neighboring cells, connexin hemichannels provide communication between the cytosol and the extracellular environment of an individual cell. The latter equally holds true for channels composed of pannexin proteins, which display an architecture reminiscent of connexin hemichannels. In physiological conditions, gap junctions are usually open, while connexin hemichannels and, to a lesser extent, pannexin channels are typically closed, yet they can be activated by a number of pathological triggers. Several agents are available to inhibit channels built up by connexin and pannexin proteins, including alcoholic substances, glycyrrhetinic acid, anesthetics and fatty acids. These compounds not always strictly distinguish between gap junctions, connexin hemichannels and pannexin channels, and may have effects on other targets as well. An exception lies with mimetic peptides, which reproduce specific amino acid sequences in connexin or pannexin primary protein structure. In this paper, a state-of-the-art overview is provided on inhibitors of cellular channels consisting of connexins and pannexins with specific focus on their mode-of-action and therapeutic potential.

Pannexin1 links lymphatic function to lipid metabolism and atherosclerosis

Extracellular ATP is a central signaling molecule in inflammatory responses. Pannexin1 (Panx1) channels release ATP in a controlled manner and have been implicated in various inflammatory pathologies, but their role in atherogenesis remains elusive. Using atherosclerosis-susceptible mouse models with ubiquitous deletion of Panx1 (Panx1^−/−Apoe^−/−) or with Cre recombinase-mediated deletion of Panx1 in endothelial cells and monocytes (Tie2-Cre^TgPanx1^fl/flApoe^−/−; Panx1^delApoe^−/−), we identified a novel role for Panx1 in the lymphatic vasculature. Atherosclerotic lesion development in response to high-cholesterol diet was enhanced in Panx1^delApoe^−/− mice, pointing to an atheroprotective role for Panx1 in endothelial and/or monocytic cells. Unexpectedly, atherogenesis was not changed in mice with ubiquitous Panx1 deletion, but Panx1^−/−Apoe^−/− mice displayed reduced body weight, serum cholesterol, triglycerides and free fatty acids, suggesting altered lipid metabolism in these Panx1-deficient mice. Mechanistically, Panx1^−/−Apoe^−/− mice showed impairment of lymphatic vessel function with decreased drainage of interstitial fluids and reduced dietary fat absorption. Thus, the detrimental effect of Panx1 deletion in endothelial and/or monocytic cells during atherogenesis is counterbalanced by an opposite effect resulting from impaired lymphatic function in ubiquitous Panx1-deficient mice. Collectively, our findings unveil a pivotal role of Panx1 in linking lymphatic function to lipid metabolism and atherosclerotic plaque development.

Regulation of pannexin channels in the central nervous system by Src family kinases

Pannexins form single membrane channels that regulate the passage of ions, small molecules and metabolites between the intra- and extracellular compartments. In the central nervous system, these channels are integrated into numerous signaling cascades that shape brain physiology and pathology. Post-translational modification of pannexins is complex, with phosphorylation emerging as a prominent form of functional regulation. While much is still not known regarding the specific kinases and modified amino acids, recent reports support a role for Src family tyrosine kinases (SFK) in regulating pannexin channel activity. This review outlines the current evidence supporting SFK-dependent pannexin phosphorylation in the CNS and examines the importance of these modifications in the healthy and diseased brain.

Rufinamide pretreatment attenuates ischemia-reperfusion injury in the gerbil hippocampus

OBJECTIVES

Rufinamide, a voltage-gated sodium channel (VGSC) blocker, is widely used for the clinical treatment of seizures associated with Lennox-Gastaut syndrome. Previous studies have demonstrated that VGSC blockers have neuroprotective properties against ischemic damage following experimental cerebral ischemia. However, protective effects of rufinamide against cerebral ischemic insults have not been addressed. Therefore, in the present study, we firstly examined neuroprotective effects of rufinamide using a gerbil model of transient global cerebral ischemia.

METHODS

Gerbils were established by the occlusion of common carotid arteries for 5 min. The gerbils were divided into vehicle-treated sham-operated group, vehicle-treated ischemia-operated group, 50 and 100 mg/kg rufinamide-treated sham-operated groups, and 50 and 100 mg/kg rufinamide-treated ischemia-operated groups. Rufinamide was administrated intraperitoneally once daily for 3 days before ischemic surgery. To examine neuroprotective effects of rufinamide, we carried out cresyl violet staining, neuronal nuclear antigen immunohistochemistry and Fluoro-Jade B histofluorescence staining. In addition, we examined gliosis using immunohistochemistry for glial fibrillary acidic protein (a marker for astrocytes) and ionized calcium-binding adapter molecule 1 (a marker for microglia).

RESULTS

We found that pre-treatment with 100 mg/kg of rufinamide effectively protected pyramidal neurons in the hippocampal cornus ammonis 1 (CA1) area after transient global cerebral ischemia. In addition, pre-treatment with 100 mg/kg of rufinamide significantly attenuated activations of astrocytes and microglia in the ischemic CA1 area.

DISCUSSION

These findings suggest that rufinamide can display neuroprotective effect against cerebral ischemic insults and that its neuroprotective effect may involve the attenuation of ischemia-induced glial activation.

Connexins and Pannexins in cerebral ischemia

A common cause of mortality and long-term adult disability, cerebral ischemia or brain ischemia imposes a significant health and financial burden on communities worldwide. Cerebral ischemia is a condition that arises from a sudden loss of blood flow and consequent failure to meet the high metabolic demands of the brain. The lack of blood flow initiates a sequelae of cell death mechanisms, including the activation of the inflammatory pathway, which can ultimately result in irreversible brain tissue damage. In particular, Connexins and Pannexins are non-selective channels with a large pore that have shown to play time-dependent roles in the perpetuation of ischaemic injury. This review highlights the roles of Connexin and Pannexin channels in cell death mechanisms as a promising therapeutic target in cerebral ischemia, and in particular connexin hemichannels which may contribute most of the ATP release as a result of ischemia as well as during reperfusion. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Pannexin channel and connexin hemichannel expression in vascular function and inflammation

Control of blood flow distribution and tissue homeostasis depend on the tight regulation of and coordination between the microvascular network and circulating blood cells. Channels formed by connexins or pannexins that connect the intra- and extracellular compartments allow the release of paracrine signals, such as ATP and prostaglandins, and thus play a central role in achieving fine regulation and coordination of vascular function. This review focuses on vascular connexin hemichannels and pannexin channels. We review their expression pattern within the arterial and venous system with a special emphasis on how post-translational modifications by phosphorylation and S-nitrosylation of these channels modulate their function and contribute to vascular homeostasis. Furthermore, we highlight the contribution of these channels in smooth muscle cells and endothelial cells in the regulation of vasomotor tone as well as how these channels in endothelial cells regulate inflammatory responses such as during ischemic and hypoxic conditions. In addition, this review will touch on recent evidence implicating a role for these proteins in regulating red blood cell and platelet function.

Tanshinone IIA increases levels of NeuN, protein disulfide isomerase, and Na+/K+-ATPase and decreases evidence of microglial activation after cerebral ischemic injury

This study was designed to clarify the neuroprotective effects of tanshinone IIA (TSA) following cerebral ischemic insult. Adult Sprague-Dawley rats were operated upon to achieve a middle cerebral artery occlusion to cause transient focal cerebral ischemia, which were then randomly divided into the sham-operated control group and cerebral ischemia/reperfusion (I/R) groups receiving a 2 h occlusion. The treatment groups received daily intraperitoneal injections of high or low doses of TSA, for 7 or 15 days. NeuN immunostaining revealed neuronal loss following I/R, which was partially prevented with subsequent TSA dosing. Protein disulfide isomerase and adenosine triphosphatase (Na(+)/K(+)-ATPase) levels were all depressed by means of I/R. TSA treatment markedly reversed the depression of all indices examined. The intensity of microglial activation, as evidenced with CD11b staining, was increased by means of cerebral artery occlusion, but this was partially reversed with subsequent TSA treatment. TSA may affect neuroprotection by way of minimizing deficits in energy metabolism and reduction of the extent of cell death within affected regions.

Probenecid protects against oxygen-glucose deprivation injury in primary astrocytes by regulating inflammasome activity

Inflammation is extremely important in the development of cerebral ischemia/reperfusion injury. Pannexin 1 (Panx1) channel has been reported to activate inflammasome in astrocytes and be involved in ischemic injury, but this damage effect is reversed by a Panx1 inhibitor-probenecid. However, the mechanism of probenecid protects against cerebral ischemia/reperfusion injury remains unclear. In present study, we hypothesized that probenecid protected astrocytes from ischemia/reperfusion injury in vitro by modulating the inflammasome. Primary cultured neocortical astrocytes were exposed to oxygen-glucose deprivation/reoxygenation (OGD/RX) and probenecid was added in this model. Viability and nuclear morphology of astrocytes, production of reactive oxygen species (ROS), protein expressions of NLRP3 (NOD-like receptor protein 3), caspase-1, and AQP4 (Aquaporins 4), as well as release of cellular HMGB1 and IL-1β were observed to evaluate the effect and mechanisms of probenecid on OGD/reoxygenated astrocytes. Probenecid did not affect cell viability at concentrations of 1, 5, 10, and 100μM but induced significant astrocytes death at 500μM. Probenecid inhibited cell death and ROS generation in astrocytes subjected to 6h of OGD and 24h of reoxygenation. The expression levels of NLRP3, caspase-1, and AQP4 increased after 6h of OGD, but probenecid treatment attenuated this increase. Moreover, the extracellular release of IL-1β and HMGB1 from OGD/reoxygenated astrocytes increased significantly. However, treatment by probenecid resulted in substantial reduction of these proteins levels in extracellular space. In conclusion, The Panx1 inhibitor, probenecid, which was administered before OGD, provided protective effects on the OGD/reoxygenation model of cultured astrocytes by modulating inflammasome activity and downregulating AQP4 expression.

Probenecid and N-Acetylcysteine Prevent Loss of Intracellular Glutathione and Inhibit Neuronal Death after Mechanical Stretch Injury In Vitro

Probenecid and N-acetylcysteine (NAC) can preserve intracellular levels of the vital antioxidant glutathione (GSH) via two distinct biochemical pathways. Probenecid inhibits transporter-mediated GSH efflux and NAC serves as a cysteine donor for GSH synthesis. We hypothesized that probenecid and NAC alone would maintain intracellular GSH concentrations and inhibit neuronal death after traumatic stretch injury, and that the drugs in combination would produce additive effects. Sex-segregated rat primary cortical neurons were treated with probenecid (100 μM) and NAC (50 μM), alone and in combination (Pro-NAC), then subjected to mechanical stretch (10s^-1 strain rate, 50% membrane deformation). At 24 h, both probenecid and NAC inhibited trauma-induced intracellular GSH depletion, lactate dehydrogenase (LDH) release, and propidium iodide (PI) uptake in both XY- and XX-neurons. Combined Pro-NAC treatment was superior to probenecid or NAC alone in maintenance of intracellular GSH and neuronal death assessed by PI uptake. Interestingly, caspase 3 activity 24 h after mechanical trauma was more prominent in XX-neurons, and treatment effects (probenecid, NAC, and Pro-NAC) were observed in XX- but not XY-neurons; however, XY-neurons were ultimately more vulnerable to mechanical stretch-induced injury than their XX counterparts, as was evidenced by more neuronal death detected by LDH release and PI uptake. In addition, after stretch injury in HT22 hippocampal cells, both NAC and probenecid were highly effective at reducing oxidative stress detected by dichlorofluorescein fluorescence. These in vitro data support further testing of this drug combination in models of traumatic neuronal injury in vivo.

ATP stimulates pannexin 1 internalization to endosomal compartments

The ubiquitous pannexin 1 (Panx1) ion- and metabolite-permeable channel mediates the release of ATP, a potent signalling molecule. In the present study, we provide striking evidence that ATP, in turn, stimulates internalization of Panx1 to intracellular membranes. These findings hold important implications for understanding the regulation of Panx1 when extracellular ATP is elevated. In the nervous system, this includes phenomena such as synaptic plasticity, pain, precursor cell development and stroke; outside of the nervous system, this includes things like skeletal and smooth muscle activity and inflammation. Within 15 min, ATP led to significant Panx1-EGFP internalization. In a series of experiments, we determined that hydrolysable ATP is the most potent stimulator of Panx1 internalization. We identified two possible mechanisms for Panx1 internalization, including activation of ionotropic purinergic (P2X) receptors and involvement of a putative ATP-sensitive residue in the first extracellular loop of Panx1 (Trp(74)). Internalization was cholesterol-dependent, but clathrin, caveolin and dynamin independent. Detailed analysis of Panx1 at specific endosome sub-compartments confirmed that Panx1 is expressed in endosome membranes of the classical degradation pathway under basal conditions and that elevation of ATP levels diverts a sub-population to recycling endosomes. This is the first report detailing endosome localization of Panx1 under basal conditions and the potential for ATP regulation of its surface expression. Given the ubiquitous expression profile of Panx1 and the importance of ATP signalling, these findings are of critical importance for understanding the role of Panx1 in health and disease.