Satellite glial cells (SGCs) closely envelop cell bodies of neurons in sensory, sympathetic and parasympathetic ganglia. This unique organization is not found elsewhere in the nervous system. SGCs in ...sensory ganglia are activated by numerous types of nerve injury and inflammation. The activation includes upregulation of glial fibrillary acidic protein, stronger gap junction-mediated SGC-SGC and neuron-SGC coupling, increased sensitivity to ATP, downregulation of Kir4.1 potassium channels and increased cytokine synthesis and release. There is evidence that these changes in SGCs contribute to chronic pain by augmenting neuronal activity and that these changes are consistent in various rodent pain models and likely also in human pain. Therefore, understanding these changes and the resulting abnormal interactions of SGCs with sensory neurons could provide a mechanistic approach that might be exploited therapeutically in alleviation and prevention of pain. We describe how SGCs are altered in rodent models of four common types of pain: systemic inflammation (sickness behaviour), post-surgical pain, diabetic neuropathic pain and post-herpetic pain.
•Gap junctions increase in sensory ganglia and spinal cord after painful injury.•Gap junctions in sensory ganglia are found between neurons, between Satellite Glial cells and between neurons and ...glia.•Pannexin1 is increased in pain models and it deletion leads to hyposensitivity.
Enhanced expression and function of gap junctions and pannexin (Panx) channels have been associated with both peripheral and central mechanisms of pain sensitization. At the level of the sensory ganglia, evidence includes augmented gap junction and pannexin1 expression in glial cells and neurons in inflammatory and neuropathic pain models and increased synchrony and enhanced cross-excitation among sensory neurons by gap junction-mediated coupling. In spinal cord and in suprapinal areas, evidence is largely limited to increased expression of relevant proteins, although in several rodent pain models, hypersensitivity is reduced by treatment with gap junction/Panx1 channel blocking compounds. Moreover, targeted modulation of Cx43 expression was shown to modulate pain thresholds, albeit in somewhat contradictory ways, and mice lacking Panx1 expression globally or in specific cell types show depressed hyperalgesia. We here review the evidence for involvement of gap junctions and Panx channels in a variety of animal pain studies and then discuss ways in which gap junctions and Panx channels may mediate their action in pain processing. This discussion focusses on spread of signals among satellite glial cells, in particular intercellular Ca2+ waves, which are propagated through both gap junction and Panx1-dependent routes and have been associated with the phenomenon of spreading depression and the malady of migraine headache with aura.
Glioblastoma multiforme (GBM), classified as World Health Organization grade IV astrocytoma, is the deadliest adult cancer of the central nervous system. An important contributing factor to poor ...survival rates in GBM is extensive invasion, which decreases the efficacy of resection and subsequent adjuvant therapies. These treatments could be markedly improved with increased resolution of the genetic and molecular initiators and effectors of invasion. Connexin 43 (Cx43) is the principal astrocytic gap junction (GJ) protein. Despite the heterogeneity of GBM, a subpopulation of cells in almost all GBM tumors express Cx43. Functional GJs between GBM cells and astrocytes at the tumor edge are of critical interest for understanding invasion. In this study, we find that both
and in
slice cultures, GBM is substantially less invasive when placed in a Cx43-deficient astrocyte environment. Furthermore, when Cx43 is deleted in GBM, the invasive phenotype is recovered. These data strongly suggest that there are opposing roles for Cx43 in GBM migration. We find that Cx43 is localized to the tumor edge in our
model, suggesting that GBM-astrocyte GJ communication at the tumor border is a driving force for invasion. Finally, we find that by a Cx43-dependent mechanism, but likely not direct channel-mediated diffusion, miRNAs associated with cell-matrix adhesion are transferred from GBM to astrocytes and miR-19b promotes invasion, revealing a role for post-transcriptional manipulation of astrocytes in fostering an invasion-permissive peritumoral niche. IMPLICATIONS: Cx43-mediated communication, specifically miRNA transfer, profoundly impacts glioblastoma invasion and may enable further therapeutic insight.
Primary sensory neurons in the DRG play an essential role in initiating pain by detecting painful stimuli in the periphery. Tissue injury can sensitize DRG neurons, causing heightened pain ...sensitivity, often leading to chronic pain. Despite the functional importance, how DRG neurons function at a population level is unclear due to the lack of suitable tools. Here we developed an imaging technique that allowed us to simultaneously monitor the activities of >1,600 neurons/DRG in live mice and discovered a striking neuronal coupling phenomenon that adjacent neurons tend to activate together following tissue injury. This coupled activation occurs among various neurons and is mediated by an injury-induced upregulation of gap junctions in glial cells surrounding DRG neurons. Blocking gap junctions attenuated neuronal coupling and mechanical hyperalgesia. Therefore, neuronal coupling represents a new form of neuronal plasticity in the DRG and contributes to pain hypersensitivity by “hijacking” neighboring neurons through gap junctions.
•Tissue injury induces DRG neuronal coupling that adjacent neurons activate together•The coupled activation is mediated by an injury-induced upregulation of gap junctions•DRG neuronal coupling contributes to pain hypersensitivity•Inhibiting gap-junction-mediated coupling may provide a way to relieve chronic pain
Using in vivo DRG imaging, Kim et al. discovered a neuronal coupling phenomenon that adjacent neurons tend to activate together following tissue injury. This coupled activation, mediated by an upregulation of gap junctions in the DRG, contributes to pain hypersensitivity.
Purinergic signaling plays distinct and important roles in the CNS, including the transmission of calcium signals between astrocytes. Gap junction hemichannels are among the mechanisms proposed by ...which astrocytes might release ATP; however, whether the gap junction protein connexin43 (Cx43) forms these "hemichannels" remains controversial. Recently, a new group of proteins, the pannexins, have been shown to form nonselective, high-conductance plasmalemmal channels permeable to ATP, thereby offering an alternative for the hemichannel protein. Here, we provide strong evidence that, in cultured astrocytes, pannexin1 (Panx1) but not Cx43 forms hemichannels. Electrophysiological and fluorescence microscope recordings performed in wild-type and Cx43-null astrocytes did not reveal any differences in hemichannel activity, which was mostly eliminated by treating Cx43-null astrocytes with Panx1-short interfering RNA Panx1-knockdown (Panx1-KD). Moreover, quantification of the amount of ATP released from wild-type, Cx43-null, and Panx1-KD astrocytes indicates that downregulation of Panx1, but not of Cx43, prevented ATP release from these cells.
Pannexins are ubiquitously expressed in human and mouse tissues. Pannexin 1 (Panx1), the most thoroughly characterized member of this family, forms plasmalemmal membrane channels permeable to ...relatively large molecules, such as ATP. Although human and mouse Panx1 amino acid sequences are conserved in the presently known regulatory sites involved in trafficking and modulation of the channel, differences are reported in the N- and C-termini of the protein, and the mechanisms of channel activation by different stimuli remain controversial. Here we used a neuroblastoma cell line to study the activation properties of endogenous mPanx1 and exogenously expressed hPanx1. Dye uptake and electrophysiological recordings revealed that in contrast to mouse Panx1, the human ortholog is insensitive to stimulation with high extracellular K+ but responds similarly to activation of the purinergic P2X7 receptor. The two most frequent Panx1 polymorphisms found in the human population, Q5H (rs1138800) and E390D (rs74549886), exogenously expressed in Panx1-null N2a cells revealed that regarding P2X7 receptor mediated Panx1 activation, the Q5H mutant is a gain of function whereas the E390D mutant is a loss of function variant. Collectively, we demonstrate differences in the activation between human and mouse Panx1 orthologs and suggest that these differences may have translational implications for studies where Panx1 has been shown to have significant impact.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Peripheral sensory ganglia contain the somata of neurons mediating mechanical, thermal, and painful sensations from somatic, visceral, and oro‐facial organs. Each neuronal cell body is closely ...surrounded by satellite glial cells (SGCs) that have properties and functions similar to those of central astrocytes, including expression of gap junction proteins and functional dye coupling. As shown in other pain models, after systemic pain induction by intra‐peritoneal injection of lipopolysaccharide, dye coupling among SGCs in intact trigeminal ganglion was enhanced. Moreover, neuron–neuron and neuron–SGC coupling was also detected. To verify the presence of gap junction‐mediated coupling between SGCs and sensory neurons, we performed dual whole cell patch clamp recordings from both freshly isolated and short term cultured cell pairs dissociated from mouse trigeminal ganglia. Bidirectional gap junction mediated electrical responses were frequently recorded between SGCs, between neurons and between neurons and SGCs. Polarization of SGC altered neuronal excitability, providing evidence that gap junction‐mediated interactions between neurons and glia within sensory ganglia may contribute to integration of peripheral sensory responses, and to the modulation and coordinaton of neuronal activity.
Main Points
Voltage clamp recordings revealed that satellite glial cells in trigeminal ganglia are mutually coupled, sensory neurons are also mutually coupled, and are coupled to glia. Glial electrical polarization can depress or enhance neuronal excitability.
Astrocytes support the energy demands of synaptic transmission and plasticity. Enduring changes in synaptic efficacy are highly sensitive to stress, yet whether changes to astrocyte bioenergetic ...control of synapses contributes to stress-impaired plasticity is unclear. Here we show in mice that stress constrains the shuttling of glucose and lactate through astrocyte networks, creating a barrier for neuronal access to an astrocytic energy reservoir in the hippocampus and neocortex, compromising long-term potentiation. Impairing astrocytic delivery of energy substrates by reducing astrocyte gap junction coupling with dominant negative connexin 43 or by disrupting lactate efflux was sufficient to mimic the effects of stress on long-term potentiation. Furthermore, direct restoration of the astrocyte lactate supply alone rescued stress-impaired synaptic plasticity, which was blocked by inhibiting neural lactate uptake. This gating of synaptic plasticity in stress by astrocytic metabolic networks indicates a broader role of astrocyte bioenergetics in determining how experience-dependent information is controlled.
OBJECTIVE—Recent publications questioned the validity of endothelial cell (EC) culture studies of glycocalyx (GCX) function because of findings that GCX in vitro may be substantially thinner than GCX ...in vivo. The assessment of thickness differences is complicated by GCX collapse during dehydration for traditional electron microscopy. We measured in vitro GCX thickness using rapid freezing/freeze substitution (RF/FS) transmission electron microscopy (TEM), taking advantage of the high spatial resolution provided by TEM and the capability to stably preserve the GCX in its hydrated configuration by RF/FS.
METHODS AND RESULTS—Bovine aortic EC (BAEC) and rat fat pad EC were subjected to conventional or RF/FS-TEM. Conventionally preserved BAEC GCX was ≈0.040 μm in thickness. RF/FS-TEM revealed impressively thick BAEC GCX of ≈11 μm and rat fat pad EC GCX of ≈5 μm. RF/FS-TEM also discerned GCX structure and thickness variations due to heparinase III enzyme treatment and extracellular protein removal, respectively. Immunoconfocal studies confirmed that the in vitro GCX is several micrometers thick and is composed of extensive and well-integrated heparan sulfate, hyaluronic acid, and protein layers.
CONCLUSION—New observations by RF/FS-TEM reveal substantial GCX layers on cultured EC, supporting their continued use for fundamental studies of GCX and its function in the vasculature.
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