1 Department of Biochemistry, Faculty of Medicine, Medical University of Lodz, 92-215 Lodz, Poland
2 High Performance Research Group in Physiopathology and Pharmacology of the Digestive System (NeuGut), Department of Basic Health Sciences, University Rey Juan Carlos, 28922 Alcorcón, Spain
3 Associated Unit to Institute of Medicinal Chemistry (Unidad Asociada I+D+i del Instituto de Química Médica, IQM), Spanish National Research Council (Consejo Superior de Investigaciones Científicas, CSIC), 28006 Madrid, Spain
4 Working Group of Basic Sciences in Pain and Analgesia of the Spanish Pain Society (Grupo de Trabajo de Ciencias Básicas en Dolor y Analgesia de la Sociedad Española del Dolor), 28046 Madrid, Spain
†These authors contributed equally.
Abstract
A nutraceutical is a food-derived molecule that provides medical or health benefits beyond its basic nutritional role, including the prevention and treatment of disease and its symptoms. In the peripheral nervous system, satellite glial cells are found in close relationship with neurons, mainly in peripheral sensory ganglia, but, compared with other glial cells, the relationship between these cells and nutraceuticals has received little attention. After describing satellite glial cells and their role and changes in physiology and pathology, we review the studies on the effects of nutraceuticals as modulators of their functions. Maybe due to the difficulties in selectively labeling these cells, only a few studies, performed mainly in rodent models, have analyzed nutraceutical effects, showing that N-acetylcysteine, curcumin, quercetin, osthole and resveratrol may palliate neuropathic pain through satellite glial cells-dependent pathways, namely antioxidant mechanisms and/or interference with purinergic signaling. Neither other conditions in which satellite glial cells are involved (visceral pain, nerve regeneration) nor other nutraceuticals or mechanisms of action have been studied. Although more preclinical and clinical research is needed, the available reports support the general notion that nutraceuticals may become interesting alternatives in the prevention and/or treatment of peripheral gliopathies and their associated conditions, including those affecting the satellite glial cells.
Keywords
- Satellite glial cells
- Nutraceuticals
- Resveratrol
- Curcumin
- Quercetin
- Diabetes mellitus
- Nerve injury
- Peripheral nervous system
The term “nutraceutical” was coined in 1989 by the Foundation for Innovation in Medicine (New York, NY, USA) as “any food substance or part of a food that provides specific medical or health benefits beyond their basic nutritional value” [1], including prevention and treatment of a wide variety of diseases such as cancer [2], cardiovascular diseases [3, 4, 5], obesity [6], diabetes [7, 8], Alzheimer’s and Parkinson’s diseases [9, 10, 11, 12] or eye disorders [13], among many others. Considering their preventive and therapeutic potential and the current globalization context, constantly in search for sustainable solutions for economy, environment and health [14, 15, 16], the number of studies reporting the modulating effects of nutraceuticals on the different functions of the body and, particularly, on the elements of the nervous system is rapidly increasing. Studies are mainly focused on neurons and glial cells [9, 11, 17, 18, 19, 20, 21].
Next to the neurons, glial cells constitute a second branch of the nervous system. They are present in both the central (CNS: astroglia, oligodendroglia and microglia) and peripheral nervous system (PNS: Schwann cells, olfactory ensheathing cells, satellite glial cells, enteric glial cells) [22]. At first, glia was considered structural support for neurons in the nervous system. Still, in recent years their functions have been more deeply investigated, and they turned out to be as important as nerve cells, because of their role in all aspects of neural functions [23]. Other glial cells, like microglia, Schwann cells or enteric glial cells have been intensely studied, even in aspects like the modulation of their functions by nutraceuticals [9, 11, 20, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35], but satellite glial cells (SCGs) have received less attention. However, SGCs are increasingly recognized for their essential roles in physiology and disease [36, 37].
Satellite glial cells are present in sensory ganglia (dorsal root ganglia, DRG, trigeminal ganglia, TG) and sympathetic and parasympathetic ganglia. Their main features are summarized in Table 1. We will focus on the sensory neurons and surrounding glial cells present in the DRG and TG, because, on the one hand, data concerning SGCs physiology in the autonomic nervous system is limited, and, on the other hand, data regarding the modulatory effects of nutraceuticals on SGCs are almost only available for DRG and TG.
| Feature | Satellite glial cells |
| Morphology | Laminar, normally devoid of processes |
| Subtypes | Not recognized |
| Location | Dorsal root ganglia, trigeminal ganglia, other peripheral ganglia |
| Proposed markers | GFAP |
| Kir4.1 | |
| Cadherin 19 | |
| GS | |
| SK3 | |
| Adjacent cells coupling | Gap junction coupling |
| Activation | Able to release pro-inflammatory cytokines (i.e., IL-1 |
| Activation of MAPK pathways, i.e., phosphorylation of p38 and ERK | |
| Enhanced expression of glial cells markers | |
| Involved in | Chronic pain (inflammatory, neuropathic, visceral) |
| Abbreviations: ERK, extracellular signal-regulated kinase; GFAP, glial
fibrillary acidic protein; GS, glutamine synthetase; IL, interleukin; Kir4.1,
inwardly rectifying potassium channel, type 4.1; MAPK, mitogen-activated protein
kinase; SK3, small conductance calcium-activated potassium channel;
TNF- | |
Satellite glial cells share similarities with Schwann cells, as they are derived from the neural crest and occur in the PNS. Nevertheless, SGCs also exhibit common features with astrocytes, as like these cells, they express several proteins recognized as glial cell markers: glial fibrillary acidic protein (GFAP), and glutamine synthetase (GS). Furthermore, SGCs are coupled by gap junctions similarly to glia in the CNS and the enteric nervous system (ENS) [36, 38]. However, unlike astrocytes, SGCs have laminar-shaped cell bodies and lack processes. A unique function of SGCs is that they wrap around and compose envelopes around the neural cell bodies. Neural cells and surrounding SGCs constitute a distinct functional unit (neuron-glial unit). Usually, a single neuron is enveloped by a few SGCs, but there may be exceptions: occasionally in the DRG, two neurons share a common SGCs envelope, creating a ‘cluster’. The extracellular space between the neuron and SGCs measures only 20 nm enabling rapid bi-directional communication [38].
Studies on the role of SCGs in physiology and pathophysiology are limited due to the lack of specific molecular tools. They were recognized mainly according to their morphology and location. Several markers of SGCs were distinguished: i.e., GFAP [39], inwardly rectifying potassium channel (Kir4.1) [40], cadherin 19 [41], GS [42], calcium activated potassium channel (SK3; small conductance calcium-activated potassium channel 3) [43, 44]. It remains extremely difficult to purify SGCs and investigate their biology at the molecular level, because all above markers do not appear specific to SGCs. For example, GS at the immunostaining level seems specific. Still, it does not label all SGCs, while at messenger ribonucleic acid (RNA) expression level, in the DRG, GS is expressed by many cell types, not only SGCs [45].
There is emerging evidence that the morphology and function of SGCs change under the influence of harmful factors, such as nerve injury or inflammation [46, 47, 48, 49]. The response of SGCs to peripheral nerve injury is rapid and takes place within 4 hours. This reaction peaks at 1 week and begins to alleviate after 3 weeks [48, 49, 50].
Activated SGCs synthesize and release pro-inflammatory cytokines (i.e.,
interleukin (IL)-1
The family of MAPK includes extracellular signal-regulated kinase 1 and 2 (ERK1 and ERK2), p38, and c-Jun N-terminal kinases (JNK). MAPK signaling pathway maintains an important role in intracellular signaling in neurons during persistent pain. In several studies, it was evidenced that nerve fiber injury results in augmented phosphorylation (activation) of p38 in SGCs of DRG [52, 53], while the peripheral inflammation of temporomandibular joint results in increased activation of this pathway in SGCs of TG [54]. Noteworthy, axonal injury leads to the phosphorylation of ERK in SGCs in DRG [55], whereas the inflammation of the temporomandibular joint promotes activation of ERK in SGCs of TG [54]. MAPK pathways are inactivated by phosphatases (MAPK phosphatase 1, 2, 3, MKP). It was assessed that the expression of MKP1, MKP2 and MKP3 rapidly increases in SCGs of TG during inflammation [54].
Following nerve injury, SGCs proliferation increases, and these cells display
increased expression of GFAP [56] and enhanced production of cytokines
(IL-1
Finally, besides previously mentioned changes, adenosine triphosphate (ATP) sensitivity increases and purinergic signaling is altered.
Thus far, the possible modulatory role of nutraceuticals on SGCs has only been evaluated for a few compounds, whose key properties are shown in Table 2. Furthermore, their effects have only been analyzed in animal models and cell cultures in a few reports (see Table 3 (Ref. [60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70]) and the text below for references).
| Nutraceutical | Characteristics | Structure | Source | Properties |
| Vitamin E | Fat-soluble vitamin |  |
Plant-derived oils, nuts, seeds, fruits, and vegetables | Antioxidant |
| Available as a dietary supplement | Modulation of proliferation | |||
| N-acetylcysteine | Amino acid derivative |  |
Supplement form of cysteine | Antioxidant, mucolytic |
| Curcumin | Flavonoid polyphenol |  |
Produced by plants of the Curcuma longa species | Anti-inflammatory, antioxidant, anticancer, antiapoptotic |
| Quercetin | Flavonoid polyphenol |  |
Fruits and vegetables | Anti-oxidant, anti-inflammatory, and anti-nociceptive |
| Available as a dietary supplement | ||||
| Osthole | O-methylated coumarin |  |
Found in a variety of plants | Anti-inflammatory and antioxidant |
| Available as a dietary supplement | ||||
| Resveratrol | Non-flavonoid polyphenol |  |
Concentrated mostly in the skins and seeds of grapes and berries | Anti-inflammatory and anti-nociceptive |
| Available as a dietary supplement | ||||
| Molecules were made using http://biomodel.uah.es/en/DIY/JSME/draw.es.htm. | ||||
| Nutraceutical | Species | Pathology | Key findings | References |
| Vitamin E | Sprague-Dawley rats | Vitamin E deficiency | Vitamin E-deficient rats present a faster turnover in SGCs | [60] |
| Control of SGCs proliferation | ||||
| Rhesus monkeys | Vitamin E deficiency | Neuropathologic lesions in DRG | [61] | |
| N-acetylcysteine | Sprague-Dawley rats | Postoperative hyperalgesia | Attenuates mechanical allodynia and thermal hyperalgesia | [62] |
| Suppresses MMP-9 activation | ||||
| Inhibits the cleavage of IL-1 | ||||
| Sprague-Dawley rats | Nerve injury | Neuroprotection | [63] | |
| Mitochondrial preservation in SGCs | ||||
| Curcumin | Sprague-Dawley rats | Sciatic nerve crush | Neuroprotective effects on the DRG, prevents SGC loss | [64] |
| STZ treated Sprague-Dawley rats | Diabetes mellitus | Prevents mechanical and thermal hyperalgesia | [65] | |
| Prevents upregulation of P2Y12 receptor on SGC | ||||
| Quercetin | Sprague-Dawley rats and C6 rat glioma cell line | Spared nerve injury | Attenuates neuropathic pain | [66] |
| GFAP inhibition in the L5 DRGs | ||||
| STZ-treated Sprague-Dawley rats | Diabetes mellitus | Attenuates neuropathic pain | [67] | |
| Inhibits P2X4 receptor‐mediated p38MAPK activation | ||||
| Osthole | STZ treated Sprague-Dawley rats and HEK293 cells transfected with P2X4 plasmid | Diabetes Mellitus | Alleviates mechanical and thermal hyperalgesia through P2X4 receptor | [68] |
| Reduces up-regulation of IL-1 | ||||
| Enhance the down-regulation of IL-10 | ||||
| Resveratrol | Gp 120 treated Sprague-Dawley rats and HEK293 cells transfected with P2X7 plasmid | HIV-associated neuropathic pain | Relieves mechanical hyperalgesia inhibiting the P2X7 receptor on SGCs | [69] |
| Sprague-Dawley rats | Chronic constriction injury | Suppresses the transmission of neuropathic pain mediated by the P2X7 receptor in SGCs of DRG | [70] | |
| Abbreviations: BDNF, brain derived neurotrophic factor; DRG, dorsal root ganglia; GFAP, glial fibrillary acidic protein; L5, lumbar 5; MAPK, mitogen-activated protein kinase; MMP, matrix metalloprotease; HEK, Human embryonic kidney; HIV, human immunodeficiency virus; IL, interleukin; P2, purinergic receptor; SGCs, satellite glial cells; TNF, tumor necrosis factor. | ||||
In 1999 it was observed that vitamin E deficiency in rats caused the proliferation of SGCs, shown by immunohistochemical methods [60]. Vitamin E deficiency causes neurodegenerative processes in the DRG [61] that would induce a response in SGCs. Taking this into account, it was postulated that vitamin E could function as an exogenous control for this proliferation in pathological conditions. Further research using disease models is needed to clarify if administering vitamin E would have a beneficial role and whether, in addition to proliferation, other mechanisms (purinergic signaling, nitric oxide or cytokine release…) are involved in the suggested beneficial effect of vitamin E.
The other nutraceuticals whose effects on SGCs from DRG and TG have been described seem to do so through antioxidant mechanisms or interference with purinergic signaling. These will be summarized in the following sections.
Nutraceuticals with antioxidant capacities have been evaluated in several studies. Indeed, some diseases exert damaging effects on SGCs due to free radicals and nutraceuticals seem to exert beneficial effects in these conditions.
One such antioxidant compound is N-acetylcysteine (NAC), a safe and commonly
used drug in the clinics, also present in some fruits and vegetables [71]. The
main antioxidant effect is due to the ability of NAC to act as a reduced
glutathione (GSH) precursor; GSH is a well-known direct antioxidant and a
substrate of several antioxidant enzymes. Moreover, in some conditions where a
significant depletion of endogenous cysteine (Cys) and GSH occurs, NAC can act as
a direct antioxidant for some oxidant species such as NO
An investigation on postoperative hyperalgesia induced by remifentanil in
Sprague-Dawley rats focused on the usefulness of NAC in modulating the action of
MMP-9 metalloproteases, which were up-regulated and activated by remifentanil in
the DRGs [62]. Matrix metalloproteases are a group of calcium-dependent enzymes
responsible for the cleavage of extracellular matrix proteins and cytokines [74].
The excessive proteolytic activity of MMP-9 damages DRGs and may increase
neuronal transmission and produce neuropathic pain by stimulating the activation
of microglia [75]. MMP-9 is mainly expressed in neurons that co-express mu opioid
receptors (MOR) [76] and causes maturation of pro-inflammatory cytokines through
the cleavage of IL-1
In Sprague-Dawley rats, Hart et al. [63] investigated the effects of systemic NAC upon cell death within DRG, which characterizes many peripheral neuropathies, particularly those of traumatic etiology. NAC was applied after peripheral nerve injury, and its neuroprotective potential was analyzed. Specifically, the effect of treatment upon cell survival was quantified using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), a method for detecting apoptotic deoxyribonucleic acid (DNA) fragmentation, widely used to identify and quantify apoptotic cells [77]. TUNEL positive cells were more numerous in axotomized ganglia, and NAC application provoked a reduction in the number of TUNEL positive glial cells. Additionally, mitochondrial architecture, usually damaged in this kind of neuropathies, was preserved. In vivo treatment with NAC might therefore increase glial glutathione production, potentially protecting glia not only directly but indirectly, through neuroprotection secondary to increased neuronal glutathione levels.
Curcumin, a spice obtained from the rhizome of turmeric, is another compound with antioxidant action, well-known to act as a free radical scavenger [78, 79]. Pathological processes such as sciatic nerve crush lead to poor function of the affected limb and induce histological changes including neuronal loss, as already mentioned. Norafshan et al. [64] studied this process in Sprague-Dawley rats and found a reduction in the number of SGCs in the lumbar 5 (L5) DRG. The damaging insult produces a period of ischemia with the release of chemical mediators, an increase in vascular permeability and a deficiency in the blood-nerve barrier [80], with edema, inflammation and metabolic disability in the cells [81, 82]. All these events favor the production of toxic oxygen metabolites such as superoxide anions, hydrogen peroxide and hydroxyl radicals due to the infiltration of polymorphonuclear leukocytes into the lesioned areas. These free radicals and cytokines released by neutrophils are responsible for cell damage. SGCs damage (measured histologically in the DRG and the associated signs of painful neuropathy (measured in vivo) were less intense with curcumin treatment, probably due to the reduction of toxic oxygen-derived metabolites, although this mechanism was not directly evaluated.
Curcumin may also act through purinergic receptors. Specifically, this mechanism
of action has been shown for curcumin in the field of diabetes mellitus and the
neuropathic pain that it entails. Jia et al. [65] used the classical
type 1 diabetes mellitus model, induced by streptozotocin (STZ) injection, in
adult Sprague-Dawley rats, where they tested the effect of curcumin-loaded
nanoparticles, since the low in vivo metabolic stability of this
compound and its low bioavailability make it necessary to find more efficient
forms of administration [83]. The G protein-coupled type 2 (P2) purinergic
receptor P2Y12 is expressed in SGCs and plays an important role in transmitting
pain signals. These P2Y12 receptors are increased in SGCs of animals with
diabetes that suffer thermal hyperalgesia, associated with increased production
of the pro-inflammatory cytokine IL-1
Inhibition of other types of purinergic receptors 2 (P2X4 and P2X7) appears to be the mechanism of action by which other nutraceuticals such as quercetin, resveratrol, and osthole exert their effects on SGCs.
Quercetin is a flavonoid widely distributed in fruits and vegetables such as
onions, blueberries, or apples with antioxidant, anti-inflammatory and
antinociceptive properties [84]. It is also a supplement for the alternative
treatment of allergies, asthma, arthritis, hypertension, or neurodegenerative
disorders [85, 86, 87, 88]. Using a rat model that developed neuropathic pain as a
consequence of spared nerve injury, it was found that the administration of
quercetin before surgery attenuated mechanical allodynia and inhibited GFAP
expression (measured by Western blot) and labeling (measured
immunohistochemically) in L5 DRG [66]. After the peripheral nerve damage, SGCs
changed their number and function, revealing an increase in gap junctions that
enhanced intercellular coupling of the SGCs and decreased their membrane
resistance, causing pain. In addition, SGCs upregulated the production of
pro-inflammatory cytokines such as TNF-
Using STZ-induced diabetic Sprague-Dawley rats, the mechanism of action of quercetin was studied in depth [67]. Thus, combining real-time reverse-transcription polymerase chain reaction (RT-PCR) for P2X4 receptor, Western blot for P2X4 and p38 MAPK, immunofluorescence for P2X4 and GFAP and molecular docking techniques (computer simulation tools used to predict the binding mode of a ligand in the active site of a protein), quercetin appeared to act through the inhibition of P2X4 receptors located on SGCs. Upregulation of these nociceptive ion channels contributes to developing and maintaining pain-related symptoms of diabetes mellitus induced by STZ. These studies showed the ability of quercetin to bind the P2X4 receptor, effectively decreasing its upregulation in DRG SGCs, and consequently inhibiting the activation of p38 MAPK mediated by this receptor, which led to thermal and mechanical hyperalgesia alleviation in diabetic rats.
The P2X4 receptor also appears to be behind the beneficial effects of osthole, a
component extracted from the seeds of the Cnidium monnieri (L) cusson
plant with anti-inflammatory and antioxidant properties in the diabetic
neuropathy that was induced in male Sprague-Dawley rats after STZ injection [68].
Again, different techniques were used, including RT-PCR for P2X4 detection,
Western blot analysis of GFAP, P2X4, p38 MAPK, p-P38 MAPK and brain-derived
neurotrophic factor (BDNF), and immunofluorescence labeling of P2X4 receptor and
GFAP. Osthole decreased the upregulation of this receptor and the activation of
SGCs in the DRGs that occurs during diabetes mellitus, followed by downregulation
of BDNF, IL-1
As already mentioned, resveratrol is a naturally occurring polyphenolic compound
found in peanuts, blackberries, grapes, and red wine with antinociceptive and
anti-inflammatory effects [89]. Two studies using Sprague-Dawley rats have
analyzed its mechanism of action in two different animal models: a chronic pain
model caused by administration of gp120, derived from the human immunodeficiency
virus (HIV) [69]; and a neuropathic pain model caused by chronic constriction
injury [70]. In both cases, resveratrol seemed to act through the inhibition of
P2X7 purinergic receptors located on SGCs of DRG, which are related to the
induction and maintenance of neuropathic and inflammatory pain. In both animal
models, treatment with resveratrol reduced pain transmission, suppressing the
expression of the P2X7 receptor and preventing an elevation of the pain
threshold. The mechanism by which it relieves pain includes the inhibition of
P2X7 and GFAP in SCGs and the consequent reduction in the release of cytokines
such as TNF-
Here, we have reviewed the physiopathological roles of satellite glial cells, a relatively understudied type of peripheral glial cells, as well as the research evaluating the effects of different nutraceuticals and food components on them (Tables 2,3), and the mechanisms involved (Fig. 1).
Fig. 1.Nutraceuticals and their mechanisms of action on the satellite
glial cells. Vitamin E controls the proliferation of SGCs, but further
research is needed to elucidate the exact mechanism of its action (1). NAC
modulates the action of MMP-9, expressed on neurons in DRG, inhibits IL-1B
cleavage and enhances the mitochondrial preservation in SGCs (2). The P2Y12
receptor, IL-1B and Cx43 (gap junctions building component),
following nerve injury, are up-regulated. The proposed mechanism of
action of curcumin involves the prevention from P2Y12 receptor up-regulation,
resulting in the decrease of IL-1B production and excessive SGCs activation
associated with the increment of the number of gap junctions connecting adjacent
SGCs. Curcumin also exerts antioxidant effects by ROS scavenging (3). Quercetin
decreases the up-regulation of GFAP and P2X4 receptors on the surface of SGCs
(which results from SGCs activation), and consequently, blocks the activation of
p38 MAPK (4). Osthole downregulates the P2X4 receptors and thus inhibits the
activation of SGCs (5). Finally, resveratrol relieves mechanical hyperalgesia and
suppresses the transmission of neuropathic pain through the inhibition of P2X7
receptor and ERK1/2 and inhibits GFAP up-regulation (6). Abbreviations:
Cx43—connexin 43; ERK—extracellular signal-regulated kinase; GFAP—glial
fibrillary acidic protein; IL-1B—interleukin 1B; MMP-9—matrix
metallopeptidase; NAC—N-acetylcysteine; P2X7R, P2X4R, P2Y12R—purinergic
receptors 2; P38 MAPK—p38 mitogen-activated protein kinases; ROS—reactive
oxygen species; SGC—satellite glial cell; TNF-
In general, reports on nutraceuticals’ modulatory effects on these glial cells are relatively scarce. They might be somehow biased since only a few research groups have been actively involved in these studies (i.e., the same Chinese group from Nanchang University performed 5 out of 11 studies), in part due to the technical difficulties in reliably identifying these cells. The findings, mainly obtained in rodent models, seem to indicate that compounds like NAC, curcumin, quercetin, osthole, and resveratrol may exert beneficial effects in the treatment of neuropathic pain associated with different pathologies as varied as traumatic injury, diabetes, HIV infection, in which alterations of satellite glial cells occur. Furthermore, antioxidant mechanisms and interference with purinergic signaling were identified as underlying the effects on these cells of the nutraceuticals studied.
Although the results obtained thus far are encouraging, the research in this field is clearly in its infancy. The modulatory role of other nutraceuticals on satellite glial cell activity and their mechanisms of action need to be investigated. Among these, one important but neglected issue is the possible role of intestinal microbiota, which, on the one hand, release microbial-associated molecular patterns with potential systemic effects, and, on the other, actively metabolize nutritional components and drugs in the intestines, adding complexity to the effects food-derived nutraceuticals and their metabolites can cause both in the gut and distantly, after absorption. This has been previously addressed for other glial cell types (for example, [91, 92] illustrate the relevance of the glia-microbiota-nervous system axis) and should also be done in this case. Furthermore, the effects of nutraceuticals and their mechanisms of action need to be evaluated in additional preclinical models (i.e., chemotherapy-induced neuropathic pain, visceral pain, nerve regeneration…), and the results from these studies should be validated in robust clinical trials.
Hopefully, further research will soon define the connections between nutraceuticals and satellite glial cells as a possible target to treat, prevent or reduce their alterations associated with the different disorders in which they are involved, particularly chronic pain.
ATP, adenosine triphosphate; BDNF, brain derived neurotrophic factor; bFGF, basic fibroblast growth factor; CNS, central nervous system; Cx43, connexin 43; Cys, cysteine; DNA deoxyribonucleic acid; DRG, dorsal root ganglion, dorsal root ganglia; ENS, enteric nervous system; ERK, extracellular signal-regulated kinase; GFAP, glial fibrillary acidic protein; GS, glutamine synthetase; GSH, reduced glutathione; HIV, human immunodeficiency virus; IL, interleukin; JNK, c-Jun N-terminal kinases; Kir, inwardly rectifying potassium channel; L5, lumbar 5; MAPK, mitogen-activated protein kinase; MKPs, MAPK phosphatases; MMP, matrix metalloproteinase; MOR, mu opioid receptors; NAC, N-acetylcysteine; P2, purinergic receptor 2; PNS, peripheral nervous system; RNA, ribonucleic acid; SGC, satellite glial cell; RT-PCR, real-time reverse-transcription polymerase chain reaction; SK3, small conductance calcium-activated potassium channel 3; STZ, streptozotocin; TG, trigeminal ganglia; TNF, tumor necrosis factor; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling.
Conceptualization: RA. Writing—original draft preparation: LLG, AS, MZ. Writing—review and editing RA. All authors have read and agreed to the published version of the manuscript.
Not applicable.
Not applicable.
This research was funded by Ministerio de Ciencia, Innovación y Universidades (grant number PID2019-111510RB-I00 to RA) and by National Science Center–SONATA 15 (number UMO-2019/35/D/NZ7/02830 to MZ).
The authors declare no conflict of interest.