Regulation of the pannexin-1 promoter in the rat epididymis

Role of Pannexin 1, P2X7, and CFTR in ATP Release and Autocrine Signaling by Principal Cells of the Epididymis

Extracellular adenosine triphosphate (ATP) is a signaling molecule that acts as a paracrine and autocrine modulator of cell function. Here, we characterized the role of luminal ATP in the regulation of epithelial principal cells (PCs) in the epididymis, an understudied organ that plays crucial roles in male reproduction. We previously showed that ATP secretion by PCs is part of a complex communication system that ensures the establishment of an optimal luminal acidic environment in the epididymis. However, the molecular mechanisms regulating ATP release and the role of ATP-mediated signaling in PCs acidifying functions are not fully understood. In other cell types, pannexin 1 (PANX-1) has been associated with ATP-induced ATP release through the interaction with the purinergic P2X7 receptor. Here, we show that PANX-1 and P2X7 are located in the apical membrane of PCs in the mouse epididymis. Functional analysis using the immortalized epididymal PC cell line (DC2) and the mouse epididymis perfused in vivo showed that (1) PANX-1 and P2X7 participate in ATP release by DC2 cells, together with cystic fibrosis transmembrane conductance regulator (CFTR); (2) several ATP-activated P2Y and P2X purinergic receptors are expressed in DC2 cells; (3) the nonhydrolyzable ATP analog ATPγS induces a dose-dependent increase in intracellular Ca2+ concentration in DC2 cells, a process that is mainly mediated by P2X7; and (4) perfusion of the epididymal lumen in vivo with ATPγS induces the internalization of apical sodium-hydrogen exchanger 3 (NHE3) in PCs. Altogether, this study shows that luminal ATP, regulated by CFTR, PANX-1, and P2X7, modulates sodium-proton exchange in PCs in an autocrine manner through activation of purinergic receptor-mediated intracellular calcium signaling.

Molecular Pathways Implicated in the Differentiation and Function of Epididymal Basal Cells

The postnatal development of the epididymis is a complex and poorly understood process. Our recent studies have shown that undifferentiated primitive small columnar cells are stem cells and can differentiate in vitro into basal and principal cells. This process represents a key aspect of early epididymal development. As such, the genes and signaling pathways implicated in the differentiation of stem cells are critical. In the rat, epididymal development has been subdivided into three phases consisting of an undifferentiated epithelium (birth to day 14), differentiation (days 14 to 44), and expansion (day 45 to adult). During this period, changes in gene expression in the epididymis are the most significant, as almost 1500 genes are differentially expressed between epididymides of 7 and 18 days of age. In the adult rat, basal cells appear to represent a quiescent adult stem cell population that can be cultured under 3D conditions and can differentiate into principal cells. Gene expression in basal cells of adults compared with epididymides from day 7 rats reveals approximately 400 genes that are common to both. Analyses of these genes predict multiple signaling pathways and master regulator genes. Their roles in early epididymal development suggest that the process is complex and involves multiple regulators, cell surface factors, signaling pathways, and hormones that are interconnected and which promote the differentiation of epididymal basal cells into other epididymal cell types.

Pannexin1 deletion in lymphatic endothelium affects lymphatic function in a sex-dependent manner

The lymphatic network of capillaries and collecting vessels ensures tissue fluid homeostasis, absorption of dietary fats and trafficking of immune cells. Pannexin1 (Panx1) channels allow for the passage of ions and small metabolites between the cytosol and extracellular environment. Panx1 channels regulate the pathophysiological function of several tissues in a sex-dependent manner. Here, we studied the role of Panx1 in lymphatic function, and potential sex-dependent differences therein, in Prox1-CreERT2Panx1fl/fl and Panx1fl/fl control mice. Panx1 expression was higher in lymphatic endothelial cells (LECs) of male mice. Lymphatic vessel morphology was not affected in Prox1-CreERT2Panx1fl/fl male and female mice. Lymphatic drainage was decreased by 25% in male Prox1-CreERT2Panx1fl/fl mice, but was similar in females of both genotypes. Accordingly, only male Prox1-CreERT2Panx1fl/fl mice exhibited tail swelling, pointing to interstitial fluid accumulation in males upon Panx1 deletion in LECs. Moreover, serum triglyceride and free fatty acid levels raised less in Prox1-CreERT2Panx1fl/fl mice of both sexes in an oral lipid tolerance test. Finally, the percentage of migratory dendritic cells arriving in draining lymph nodes was increased in Prox1-CreERT2Panx1fl/fl female mice, but was comparable between male mice of both genotypes. Our results point to a LEC-specific role for Panx1 in the functions of the lymphatic system.

The multifaceted role of extracellular ATP in sperm function: From spermatogenesis to fertilization

Extracellular adenosine 5'-triphosphate (ATP) is a vital signaling molecule involved in various physiological processes within the body. In recent years, studies have revealed its significant role in male reproduction, particularly in sperm function. This review explores the multifaceted role of extracellular ATP in sperm function, from spermatogenesis to fertilization. We discuss the impact of extracellular ATP on spermatogenesis, sperm maturation and sperm-egg fusion, highlighting the complex regulatory mechanisms and potential clinical applications in the context of male infertility. By examining the latest research, we emphasize the crucial role of extracellular ATP in sperm function and propose future research directions to further.

Pannexin1 channels in the liver: an open enemy

Pannexin1 proteins form communication channels at the cell plasma membrane surface, which allow the transfer of small molecules and ions between the intracellular compartment and extracellular environment. In this way, pannexin1 channels play an important role in various cellular processes and diseases. Indeed, a plethora of human pathologies is associated with the activation of pannexin1 channels. The present paper reviews and summarizes the structure, life cycle, regulation and (patho)physiological roles of pannexin1 channels, with a particular focus on the relevance of pannexin1 channels in liver diseases.

Role of transcription factors in apoptotic cells clearance

The human body generates 10-100 billion cells every day, and the same number of cells die to maintain homeostasis. The genetically controlled, autonomously ordered cell death mainly proceeds by apoptosis. Apoptosis is an important way of programmed cell death in multicellular organisms, timely and effective elimination of apoptotic cells plays a key role in the growth and development of organisms and the maintenance of homeostasis. During the clearance of apoptotic cells, transcription factors bind to specific target promoters and act as activators or repressors to regulate multiple genes expression, how transcription factors regulate apoptosis is an important and poorly understood aspect of normal development. This paper summarizes the regulatory mechanisms of transcription factors in the clearance of apoptotic cells to date.

Impact of quercetin, carnosine, and ozone in the cryopreservation on Nellore (Bos indicus) semen

The objective of this study was to reduce the effects of cryoinjury caused in bovine semen by cryopreservation. Ejaculates were collected from Nellore bulls and subjected to freezing in C (control), ozone (15, 30, and 60 µg mL^-1 of ozone), quercetin (25, 50, and 100 µg mL^-1 of quercetin), and carnosine groups (100, 200, and 300 ng mL^-1 of carnosine). Samples were evaluated post-thaw (M0) and post-rapid thermoresistance test (M30) for sperm kinetics (total motility, progressive motility, curvilinear speed, linearity and amplitude of lateral head displacement) and cell structure viability (plasma membrane integrity, acrosomal integrity, mitochondrial potential, membrane fluidity, and lipid peroxidation). There were no differences (P > 0.05) between the control, quercetin, and carnosine-treated groups for the parameters evaluated at M0 and M30. In turn, supplementation with ozone resulted in lower values for sperm kinetics (P < 0.05) and lower mitochondrial potential at M30 (P < 0.05). Quercetin and carnosine at the concentrations used did not promote significant gains in frozen semen, nor did they demonstrate cytotoxicity. We expected to obtain positive results with the use of ozone. Nonetheless, the addition was harmful to the parameters of sperm kinetics, and its effect was not observed as a possible pro-antioxidant. We believe that the fact that the gas did not harm the sperm structure opens avenues for tests with lower dosages, since, by reducing its concentration, we could minimize the damage to sperm kinetics.

Sex-dependent role of Pannexin 1 in regulating skeletal muscle and satellite cell function

The development and regeneration of skeletal muscle are mediated by satellite cells (SCs), which ensure the efficient formation of myofibers while repopulating the niche that allows muscle repair following injuries. Pannexin 1 (Panx1) channels are expressed in SCs and their levels increase during differentiation in vitro, as well as during skeletal muscle development and regeneration in vivo. Panx1 has recently been shown to regulate muscle regeneration by promoting bleb-based myoblast migration and fusion. While skeletal muscle is largely influenced in a sex-specific way, the sex-dependent roles of Panx1 in regulating skeletal muscle and SC function remain to be investigated. Here, using global Panx1 knockout (KO) mice, we demonstrate that Panx1 loss reduces muscle fiber size and strength, decreases SC number, and alters early SC differentiation and myoblast fusion in male, but not in female mice. Interestingly, while both male and female Panx1 KO mice display an increase in the number of regenerating fibers following acute injury, the newly formed fibers in male Panx1 KO mice are smaller. Overall, our results demonstrate that Panx1 plays a significant role in regulating muscle development, regeneration, and SC number and function in male mice and reveal distinct sex-dependent functions of Panx1 in skeletal muscle.

Quercetin induces pannexin 1 expression via an alternative transcript with a translationally active 5' leader in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a deadly cancer of skeletal muscle origin. Pannexin 1 (PANX1) is down-regulated in RMS and increasing its levels drastically inhibits RMS progression. PANX1 upregulation thus represents a prospective new treatment strategy for this malignancy. However, the mechanisms regulating PANX1 expression, in RMS and other contexts, remain largely unknown. Here we show that both RMS and normal skeletal muscle express a comparable amount of PANX1 mRNAs, but surprisingly the canonical 5′ untranslated region (5′ UTR) or 5′ leader of the transcript is completely lost in RMS. We uncover that quercetin, a natural plant flavonoid, increases PANX1 protein levels in RMS by inducing re-expression of a 5′ leader-containing PANX1 transcript variant that is efficiently translated. This particular PANX1 mRNA variant is also present in differentiated human skeletal muscle myoblasts (HSMM) that highly express PANX1. Mechanistically, abolishing ETV4 transcription factor binding sites in the PANX1 promoter significantly reduced the luciferase reporter activities and PANX1 5′ UTR levels, and both quercetin treatment in RMS cells and induction of differentiation in HSMM enriched the binding of ETV4 to its consensus element in the PANX1 promoter. Notably, quercetin treatment promoted RMS differentiation in a PANX1-dependent manner. Further showing its therapeutic potential, quercetin treatment prevented RMS in vitro tumor formation while inducing complete regression of established spheroids. Collectively, our results demonstrate the tumor-suppressive effects of quercetin in RMS and present a hitherto undescribed mechanism of PANX1 regulation via ETV4-mediated transcription of a translationally functional 5′ leader-containing PANX1 mRNA.

Endothelial Pannexin 1 Channels Control Inflammation by Regulating Intracellular Calcium

The proinflammatory cytokine IL-1β is a significant risk factor in cardiovascular disease that can be targeted to reduce major cardiovascular events. IL-1β expression and release are tightly controlled by changes in intracellular Ca²⁺ ([Ca²⁺]_i), which has been associated with ATP release and purinergic signaling. Despite this, the mechanisms that regulate these changes have not been identified. The pannexin 1 (Panx1) channels have canonically been implicated in ATP release, especially during inflammation. We examined Panx1 in human umbilical vein endothelial cells following treatment with the proinflammatory cytokine TNF-α. Analysis by whole transcriptome sequencing and immunoblot identified a dramatic increase in Panx1 mRNA and protein expression that is regulated in an NF-κB-dependent manner. Furthermore, genetic inhibition of Panx1 reduced the expression and release of IL-1β. We initially hypothesized that increased Panx1-mediated ATP release acted in a paracrine fashion to control cytokine expression. However, our data demonstrate that IL-1β expression was not altered after direct ATP stimulation in human umbilical vein endothelial cells. Because Panx1 forms a large pore channel, we hypothesized it may permit Ca²⁺ diffusion into the cell to regulate IL-1β. High-throughput flow cytometric analysis demonstrated that TNF-α treatments lead to elevated [Ca²⁺]_i, corresponding with Panx1 membrane localization. Genetic or pharmacological inhibition of Panx1 reduced TNF-α-associated increases in [Ca²⁺]_i, blocked phosphorylation of the NF-κB-p65 protein, and reduced IL-1β transcription. Taken together, the data in our study provide the first evidence, to our knowledge, that [Ca²⁺]_i regulation via the Panx1 channel induces a feed-forward effect on NF-κB to regulate IL-1β synthesis and release in endothelium during inflammation.

Cellular junctions in the epididymis, a critical parameter for understanding male reproductive toxicology

Epididymal sperm maturation is a critical aspect of male reproduction in which sperm acquire motility and the ability to fertilize an ovum. Sperm maturation is dependent on the creation of a specific environment that changes along the epididymis and which enables the maturation process. The blood-epididymis barrier creates a unique luminal micro-environment, different from blood, by limiting paracellular transport and forcing receptor-mediated transport of macromolecules across the epididymal epithelium. Direct cellular communication between cells allows coordinated function of the epithelium. A limited number of studies have directly examined the effects of toxicants on junctional proteins and barrier function in the epididymis. Effects on the integrity of the blood-epididymis barrier have resulted in decreased fertility and, in some cases, the development of sperm granulomas. Studies have shown that in addition to tight junctions, proteins implicated in the maintenance of adherens junctions and gap junctions alter epididymal functions. This review will provide an overview of the types and roles of cellular junctions in the epididymis, and how these are targeted by different toxicants.

Revisiting multimodal activation and channel properties of Pannexin 1

Pannexin 1 (Panx1) forms plasma membrane ion channels that are widely expressed throughout the body. Panx1 activation results in the release of nucleotides such as adenosine triphosphate and uridine triphosphate. Thus, these channels have been implicated in diverse physiological and pathological functions associated with purinergic signaling, such as apoptotic cell clearance, blood pressure regulation, neuropathic pain, and excitotoxicity. In light of this, substantial attention has been directed to understanding the mechanisms that regulate Panx1 channel expression and activation. Here we review accumulated evidence for the various activation mechanisms described for Panx1 channels and, where possible, the unitary channel properties associated with those forms of activation. We also emphasize current limitations in studying Panx1 channel function and propose potential directions to clarify the exciting and expanding roles of Panx1 channels.

Transcriptional and post-translational regulation of pannexins

Pannexins are a 3-membered family of proteins that form large pore ion and metabolite channels in vertebrates. The impact of pannexins on vertebrate biology is intricately tied to where and when they are expressed, and how they are modified, once produced. The purpose of this review is therefore to outline our current understanding of transcriptional and post-translational regulation of pannexins. First, we briefly summarize their discovery and characteristics. Next, we describe several aspects of transcriptional regulation, including cell and tissue-specific expression, dynamic expression over development and disease, as well as new insights into the underlying molecular machinery involved. Following this, we delve into the role of post-translational modifications in the regulation of trafficking and channel properties, highlighting important work on glycosylation, phosphorylation, S-nitrosylation and proteolytic cleavage. Embedded throughout, we also highlight important knowledge gaps and avenues of future research. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Parental vitamin D deficiency during pregnancy is associated with increased blood pressure in offspring via Panx1 hypermethylation

Vitamin D deficiency is one of the most common nutritional deficiencies worldwide. Maternal vitamin D deficiency is associated with increased susceptibility to hypertension in offspring, but the reasons for this remain unknown. The aim of this study was to determine if parental vitamin D deficiency leads to altered DNA methylation in offspring that may relate to hypertension. Male and female Sprague-Dawley rats were fed a standard or vitamin D-depleted diet. After 10 wk, nonsibling rats were mated. The conceived pups received standard chow. We observed an increased systolic and diastolic blood pressure in the offspring from depleted parents (F1-depl). Genome-wide methylation analyses in offspring identified hypermethylation of the promoter region of the Pannexin-1 (Panx1) gene in F1-depl rats. Panx1 encodes a hemichannel known to be involved in endothelial-dependent relaxation, and we demonstrated that in F1-depl rats the increase in blood pressure was associated with impaired endothelial relaxation of the large vessels, suggesting an underlying biological mechanism of increased blood pressure in children from parents with vitamin deficiency. Parental vitamin D deficiency is associated with epigenetic changes and increased blood pressure levels in offspring.

Pannexin1 as mediator of inflammation and cell death

Pannexins form channels at the plasma membrane surface that establish a pathway for communication between the cytosol of individual cells and their extracellular environment. By doing so, pannexin signaling dictates several physiological functions, but equally underlies a number of pathological processes. Indeed, pannexin channels drive inflammation by assisting in the activation of inflammasomes, the release of pro-inflammatory cytokines, and the activation and migration of leukocytes. Furthermore, these cellular pores facilitate cell death, including apoptosis, pyroptosis and autophagy. The present paper reviews the roles of pannexin channels in inflammation and cell death. In a first part, a state-of-the-art overview of pannexin channel structure, regulation and function is provided. In a second part, the mechanisms behind their involvement in inflammation and cell death are discussed.

Pannexin 1 is required for full activation of insulin-stimulated glucose uptake in adipocytes

Objective

Defective glucose uptake in adipocytes leads to impaired metabolic homeostasis and insulin resistance, hallmarks of type 2 diabetes. Extracellular ATP-derived nucleotides and nucleosides are important regulators of adipocyte function, but the pathway for controlled ATP release from adipocytes is unknown. Here, we investigated whether Pannexin 1 (Panx1) channels control ATP release from adipocytes and contribute to metabolic homeostasis.

Methods

We assessed Panx1 functionality in cultured 3T3-L1 adipocytes and in adipocytes isolated from murine white adipose tissue by measuring ATP release in response to known activators of Panx1 channels. Glucose uptake in cultured 3T3-L1 adipocytes was measured in the presence of Panx1 pharmacologic inhibitors and in adipocytes isolated from white adipose tissue from wildtype (WT) or adipocyte-specific Panx1 knockout (AdipPanx1 KO) mice generated in our laboratory. We performed in vivo glucose uptake studies in chow fed WT and AdipPanx1 KO mice and assessed insulin resistance in WT and AdipPanx1 KO mice fed a high fat diet for 12 weeks. Panx1 channel function was assessed in response to insulin by performing electrophysiologic recordings in a heterologous expression system. Finally, we measured Panx1 mRNA in human visceral adipose tissue samples by qRT-PCR and compared expression levels with glucose levels and HOMA-IR measurements in patients.

Results

Our data show that adipocytes express functional Pannexin 1 (Panx1) channels that can be activated to release ATP. Pharmacologic inhibition or selective genetic deletion of Panx1 from adipocytes decreased insulin-induced glucose uptake in vitro and in vivo and exacerbated diet-induced insulin resistance in mice. Further, we identify insulin as a novel activator of Panx1 channels. In obese humans Panx1 expression in adipose tissue is increased and correlates with the degree of insulin resistance.

Conclusions

We show that Panx1 channel activity regulates insulin-stimulated glucose uptake in adipocytes and thus contributes to control of metabolic homeostasis.

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Adipocytes express Pannexin 1 channels that can be activated to release ATP.

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Inhibition of Pannexin 1 decreased insulin-induced glucose uptake in adipocytes.

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Adipocyte Pannexin 1 knockout mice are more insulin resistant on high fat diet.

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We identify insulin as a novel activator of Pannexin 1 channels.

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Pannexin 1 expression in human adipose tissue correlates with insulin resistance.

Estrogen receptor ESR1 mediates activation of ERK1/2, CREB, and ELK1 in the corpus of the epididymis

Expression of the estrogen receptor ESR1 is higher in the corpus than it is in the initial segment/caput and cauda of the epididymis. ESR1 immunostaining in the corpus has been localized not only in the nuclei but also in the cytoplasm and apical membrane, which indicates that ESR1 plays a role in membrane-initiated signaling. The present study investigated whether ESR1 mediates the activation of rapid signaling pathways by estradiol (E2) in the epididymis. We investigated the effect of E2 and the ESR1-selective agonist (4,4',4''-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT) on the activation of extracellular signal-regulated protein kinases (ERK1/2), CREB protein, and ETS oncogene-related protein (ELK1). Treatment with PPT did not affect ERK1/2 phosphorylation in the cauda, but it rapidly increased ERK1/2 phosphorylation in the initial segment/caput and corpus of the epididymis. PPT also activated CREB and ELK1 in the corpus of the epididymis. The PPT-induced phosphorylation of ERK1/2, CREB, and ELK1 was blocked by the ESR1-selective antagonist MPP and by pretreatment with a non-receptor tyrosine kinase SRC inhibitor, an EGFR kinase inhibitor, an MEK1/2 inhibitor, and a phosphatidylinositol-3-kinase inhibitor. In conclusion, these results indicate that the corpus, which is a region with high expression of the estrogen receptor ESR1, is a major target in the epididymis for the activation of rapid signaling by E2. The sequence of events that follow E2 interaction with ESR1 includes the SRC-mediated transactivation of EGFR and the phosphorylation of ERK1/2, CREB, and ELK1. This rapid estrogen signaling may modulate gene expression in the corpus of the epididymis, and it may play a role in the dynamic microenvironment of the epididymal lumen.