Chronic pain and impaired glial glutamate transporter function in lupus-prone mice are ameliorated by blocking macrophage colony-stimulating factor-1 receptors

The sexually dimorphic expression of glutamate transporters and their implication in pain after spinal cord injury

JOURNAL/nrgr/04.03/01300535-202511000-00033/figure1/v/2024-12-20T164640Z/r/image-tiff In addition to the loss of motor function, ~ 60% of patients develop pain after spinal cord injury. The cellular-molecular mechanisms are not well understood, but the data suggests that plasticity within the rostral, epicenter, and caudal penumbra of the injury site initiates a cellular-molecular interplay that acts as a rewiring mechanism leading to central neuropathic pain. Sprouting can lead to the formation of new connections triggering abnormal sensory transmission. The excitatory glutamate transporters are responsible for the reuptake of extracellular glutamate which makes them a critical target to prevent neuronal hyperexcitability and excitotoxicity. Our previous studies showed a sexually dimorphic therapeutic window for spinal cord injury after treatment with the selective estrogen receptor modulator tamoxifen. In this study, we investigated the anti-allodynic effects of tamoxifen in male and female rats with spinal cord injury. We hypothesized that tamoxifen exerts anti-allodynic effects by increasing the expression of glutamate transporters, leading to reduced hyperexcitability of the secondary neuron or by decreasing aberrant sprouting. Male and female rats received a moderate contusion to the thoracic spinal cord followed by subcutaneous slow-release treatment of tamoxifen or matrix pellets as a control (placebo). We used von Frey monofilaments and the "up-down method" to evaluate mechanical allodynia. Tamoxifen treatment decreased allodynia only in female rats with spinal cord injury revealing a sex-dependent effect. The expression profile of glutamatergic transporters (excitatory amino acid transporter 1/glutamate aspartate transporter and excitatory amino acid transporter 2/glutamate transporter-1) revealed a sexual dimorphism in the rostral, epicenter, and caudal areas of the spinal cord with a pattern of expression primarily on astrocytes. Female rodents showed a significantly higher level of excitatory amino acid transporter-1 expression while male rodents showed increased excitatory amino acid transporter-2 expression compared with female rodents. Analyses of peptidergic (calcitonin gene-related peptide-α) and non-peptidergic (isolectin B4) fibers outgrowth in the dorsal horn after spinal cord injury showed an increased calcitonin gene-related peptide-α/ isolectin B4 ratio in comparison with sham, suggesting increased receptive fields in the dorsal horn. Although the behavioral assay shows decreased allodynia in tamoxifen-treated female rats, this was not associated with overexpression of glutamate transporters or alterations in the dorsal horn laminae fibers at 28 days post-injury. Our findings provide new evidence of the sexually dimorphic expression of glutamate transporters in the spinal cord. The dimorphic expression revealed in this study provides a therapeutic opportunity for treating chronic pain, an area with a critical need for treatment.

Animal models of neuropsychiatric systemic lupus erythematosus: deciphering the complexity and guiding therapeutic development

Systemic lupus erythematosus (SLE) poses formidable challenges due to its multifaceted etiology while impacting multiple tissues and organs and displaying diverse clinical manifestations. Genetic and environmental factors contribute to SLE complexity, with relatively limited approved therapeutic options. Murine models offer insights into SLE pathogenesis but do not always replicate the nuances of human disease. This review critically evaluates spontaneous and induced animal models, emphasizing their validity and relevance to neuropsychiatric SLE (NPSLE). While these models undoubtedly contribute to understanding disease pathophysiology, discrepancies persist in mimicking some NPSLE intricacies. The lack of literature addressing this issue impedes therapeutic progress. We underscore the urgent need for refining models that truly reflect NPSLE complexities to enhance translational fidelity. We encourage a comprehensive, creative translational approach for targeted SLE interventions, balancing scientific progress with ethical considerations to eventually improve the management of NPSLE patients. A thorough grasp of these issues informs researchers in designing experiments, interpreting results, and exploring alternatives to advance NPSLE research.

Emerging Molecular and Synaptic Targets for the Management of Chronic Pain Caused by Systemic Lupus Erythematosus

Patients with systemic lupus erythematosus (SLE) frequently experience chronic pain due to the limited effectiveness and safety profiles of current analgesics. Understanding the molecular and synaptic mechanisms underlying abnormal neuronal activation along the pain signaling pathway is essential for developing new analgesics to address SLE-induced chronic pain. Recent studies, including those conducted by our team and others using the SLE animal model (MRL/lpr lupus-prone mice), have unveiled heightened excitability in nociceptive primary sensory neurons within the dorsal root ganglia and increased glutamatergic synaptic activity in spinal dorsal horn neurons, contributing to the development of chronic pain in mice with SLE. Nociceptive primary sensory neurons in lupus animals exhibit elevated resting membrane potentials, and reduced thresholds and rheobases of action potentials. These changes coincide with the elevated production of TNFα and IL-1β, as well as increased ERK activity in the dorsal root ganglion, coupled with decreased AMPK activity in the same region. Dysregulated AMPK activity is linked to heightened excitability in nociceptive sensory neurons in lupus animals. Additionally, the increased glutamatergic synaptic activity in the spinal dorsal horn in lupus mice with chronic pain is characterized by enhanced presynaptic glutamate release and postsynaptic AMPA receptor activation, alongside the reduced activity of glial glutamate transporters. These alterations are caused by the elevated activities of IL-1β, IL-18, CSF-1, and thrombin, and reduced AMPK activities in the dorsal horn. Furthermore, the pharmacological activation of spinal GPR109A receptors in microglia in lupus mice suppresses chronic pain by inhibiting p38 MAPK activity and the production of both IL-1β and IL-18, as well as reducing glutamatergic synaptic activity in the spinal dorsal horn. These findings collectively unveil crucial signaling molecular and synaptic targets for modulating abnormal neuronal activation in both the periphery and spinal dorsal horn, offering insights into the development of analgesics for managing SLE-induced chronic pain.

Deficient AMPK activity contributes to hyperexcitability in peripheral nociceptive sensory neurons and thermal hyperalgesia in lupus mice

Patients with systemic lupus erythematosus (SLE) often suffer from chronic pain. Little is known about the peripheral mechanisms underlying the genesis of chronic pain induced by SLE. The aim of this study was to investigate whether and how membrane properties in nociceptive neurons in the dorsal root ganglions (DRGs) are altered by SLE. We found elevation of resting membrane potentials, smaller capacitances, lower action potential thresholds and rheobases in nociceptive neurons in the DRGs from MRL/lpr mice (an SLE mouse model) with thermal hyperalgesia. DRGs from MRL/lpr mice had increased protein expressions in TNFα, IL-1β, and phosphorylated ERK but suppressed AMPK activity, and no changes in sodium channel 1.7 protein expression. We showed that intraplantar injection of Compound C (an AMPK inhibitor) induced thermal hyperalgesia in normal mice while intraplantar injection of AICAR (an AMPK activator) reduced thermal hyperalgesia in MRL/Lpr mice. Upon inhibition of AMPK membrane properties in nociceptive neurons from normal control mice could be rapidly switched to those found in SLE mice with thermal hyperalgesia. Our study indicates that increased excitability in peripheral nociceptive sensory neurons contributes to the genesis of thermal hyperalgesia in mice with SLE, and AMPK regulates membrane properties in nociceptive sensory neurons as well as thermal hyperalgesia in mice with SLE. Our study provides a basis for targeting signaling pathways regulating membrane properties of peripheral nociceptive neurons as a means for conquering chronic pain caused by SLE.

Activation of Protease-Activated Receptor-1 Causes Chronic Pain in Lupus-Prone Mice Via Suppressing Spinal Glial Glutamate Transporter Function and Enhancing Glutamatergic Synaptic Activity

Systemic lupus erythematosus (SLE) is an unpredictable autoimmune disease where the body's immune system mistakenly attacks healthy tissues in many parts of the body. Chronic pain is one of the most frequently reported symptoms among SLE patients. We previously reported that MRL lupus prone (MRL/lpr) mice develop hypersensitivity to mechanical and heat stimulation. In the present study, we found that the spinal protease-activated receptor-1(PAR1) plays an important role in the genesis of chronic pain in MRL/lpr mice. Female MRL/lpr mice with chronic pain had activation of astrocytes, over-expression of thrombin and PAR1, enhanced glutamatergic synaptic activity, as well as suppressed activity of adenosine monophosphate-activated protein kinase (AMPK) and glial glutamate transport function in the spinal cord. Intrathecal injection of either the PAR1 antagonist, or AMPK activator attenuated heat hyperalgesia and mechanical allodynia in MRL/lpr mice. Furthermore, we also identified that the enhanced glutamatergic synaptic activity and suppressed activity of glial glutamate transporters in the spinal dorsal horn of MRL/lpr mice are caused by activation of the PAR1 and suppression of AMPK signaling pathways. These findings suggest that targeting the PAR1 and AMPK signaling pathways in the spinal cord may be a useful approach for treating chronic pain caused by SLE. PERSPECTIVE: Our study provides evidence suggesting activation of PAR1 and suppression of AMPK in the spinal cord induces thermal hyperalgesia and mechanical allodynia in a lupus mouse model. Targeting signaling pathways regulating the PAR1 and AMPK could potentially provide a novel approach to the management of chronic pain caused by SLE.

Emerging roles of GPR109A in regulation of neuroinflammation in neurological diseases and pain

Neuroinflammation plays a critical role in the pathological process of multiple neurological disorders and pathological pain conditions. GPR109A, a Gi protein-coupled receptor, has emerged as an important therapeutic target for controlling inflammation in various tissues and organs. In this review, we summarized current data about the role of GPR109A in neuroinflammation. Specifically, we focused on the pharmacological features of GPR109A and signaling pathways used by GPR109A to ameliorate neuroinflammation and symptoms in Alzheimer's disease, Parkinson's disease, multiple sclerosis, stroke, and pathological pain conditions.

Phytohormone abscisic acid ameliorates neuropathic pain via regulating LANCL2 protein abundance and glial activation at the spinal cord

Spinal neuroinflammation plays a critical role in the genesis of neuropathic pain. Accumulating data suggest that abscisic acid (ABA), a phytohormone, regulates inflammatory processes in mammals. In this study, we found that reduction of the LANCL2 receptor protein but not the agonist ABA in the spinal cord is associated with the genesis of neuropathic pain. Systemic or intrathecal administration of ABA ameliorates the development and pre-existence of mechanical allodynia and heat hyperalgesia in animals with partial sciatic nerve ligation (pSNL). LANCL2 is expressed only in microglia in the spinal dorsal horn. Pre-emptive treatment with ABA attenuates activation of microglia and astrocytes, ERK activity, and TNFα protein abundance in the dorsal horn in rats with pSNL. These are accompanied by restoration of spinal LANCL2 protein abundance. Spinal knockdown of LANCL2 gene with siRNA recapitulates the behavioral and spinal molecular changes induced by pSNL. Activation of spinal toll-like receptor 4 (TLR4) with lipopolysaccharide leads to activation of microglia, and over production of TNFα, which are concurrently accompanied by suppression of protein levels of LANCL2 and peroxisome proliferator activated-receptor γ. These changes are ameliorated when ABA is added with LPS. The anti-inflammatory effects induced by ABA do not requires G_i protein activity. Our study reveals that the ABA/LANCL2 system is a powerful endogenous system regulating spinal neuroinflammation and nociceptive processing, suggesting the potential utility of ABA as the management of neuropathic pain.

Activation of microglial GPR109A alleviates thermal hyperalgesia in female lupus mice by suppressing IL-18 and glutamatergic synaptic activity

Many patients with systemic lupus erythematosus (SLE) live with chronic pain despite advances in medical management in reducing mortality related to SLE. Few animal studies have addressed mechanisms and treatment for chronic pain caused by SLE. In this study, we provide the first evidence for the analgesic effects of a GPR109A specific agonist (MK1903) and its action mechanisms in thermal hyperalgesia in female MRL/lpr mice, an SLE mouse model. Specifically, we show that MRL/lpr mice had a higher sensitivity to thermal stimuli at age 11-16 weeks, which was accompanied with significantly microglial and astrocytic activation, increases in p38 MAPK and glutamatergic synaptic activities in the spinal dorsal horn. We demonstrate that thermal hyperalgesia in MRL/lpr mice was significantly attenuated by intrathecal injection of MK1903. GPR109A was expressed in spinal microglia but not astrocytes or neurons. Its expression was significantly increased in MRL/lpr mice with thermal hyperalgesia. Activation of GPR109A receptors in microglia attenuated glutamatergic synaptic activity via suppressing production of interleukin-18 (IL-18). We provide evidence that activation of GPR109A attenuated thermal hyperalgesia in the SLE animal model via suppressing p38 MAPK activity and production of IL-18. Our study suggests that targeting the microglial GPR109A is a potent approach for reversing spinal neuroinflammation, abnormal excitatory synaptic activity, and management of thermal hyperalgesia caused by SLE.

Smek1 deficiency exacerbates experimental autoimmune encephalomyelitis by activating proinflammatory microglia and suppressing the IDO1-AhR pathway

BACKGROUND

Experimental autoimmune encephalomyelitis (EAE) is an animal disease model of multiple sclerosis (MS) that involves the immune system and central nervous system (CNS). However, it is unclear how genetic predispositions promote neuroinflammation in MS and EAE. Here, we investigated how partial loss-of-function of suppressor of MEK1 (SMEK1), a regulatory subunit of protein phosphatase 4, facilitates the onset of MS and EAE.

METHODS

C57BL/6 mice were immunized with myelin oligodendrocyte glycoprotein 35-55 (MOG35-55) to establish the EAE model. Clinical signs were recorded and pathogenesis was investigated after immunization. CNS tissues were analyzed by immunostaining, quantitative polymerase chain reaction (qPCR), western blot analysis, and enzyme-linked immunosorbent assay (ELISA). Single-cell analysis was carried out in the cortices and hippocampus. Splenic and lymph node cells were evaluated with flow cytometry, qPCR, and western blot analysis.

RESULTS

Here, we showed that partial Smek1 deficiency caused more severe symptoms in the EAE model than in controls by activating myeloid cells and that Smek1 was required for maintaining immunosuppressive function by modulating the indoleamine 2,3-dioxygenase (IDO1)-aryl hydrocarbon receptor (AhR) pathway. Single-cell sequencing and an in vitro study showed that Smek1-deficient microglia and macrophages were preactivated at steady state. After MOG35-55 immunization, microglia and macrophages underwent hyperactivation and produced increased IL-1β in Smek1-/+ mice at the peak stage. Moreover, dysfunction of the IDO1-AhR pathway resulted from the reduction of interferon γ (IFN-γ), enhanced antigen presentation ability, and inhibition of anti-inflammatory processes in Smek1-/+ EAE mice.

CONCLUSIONS

The present study suggests a protective role of Smek1 in autoimmune demyelination pathogenesis via immune suppression and inflammation regulation in both the immune system and the central nervous system. Our findings provide an instructive basis for the roles of Smek1 in EAE and broaden the understanding of the genetic factors involved in the pathogenesis of autoimmune demyelination.

Perineural high-mobility group box 1 induces mechanical hypersensitivity through activation of spinal microglia: Involvement of glutamate-NMDA receptor dependent mechanism in spinal dorsal horn

High mobility box 1 (HMGB1), a damage-associated molecular pattern, has crucial roles in induction of neuropathic pain. Upregulation of HMGB1 around the injured sciatic nerve contributes to mechanical hypersensitivity following partial sciatic nerve ligation (PSNL) of mice. However, central mechanisms mediating perineural HMGB1-induced nociceptive hypersensitivity, especially within the spinal dorsal horn, have not been determined. The current study shows that perineural treatment of naïve mice with recombinant HMGB1, which mimics increased HMGB1 around the injured sciatic nerve of PSNL mice, significantly induced activation of microglia, but not astrocytes, in the spinal dorsal horn. Intraperitoneal injection of minocycline, a microglial inhibitor, ameliorated perineural rHMGB1-induced mechanical hypersensitivity. In addition, blockade of spinal N-methyl-D-aspartate (NMDA) receptors significantly prevented perineural rHMGB1-induced mechanical hypersensitivity and microglial activation. In contrast, non-NMDA receptors, neurokinin 1 receptor, colony-stimulating factor 1 receptor and P2Y₁₂ receptor were not involved in perineural rHMGB1-induced mechanical hypersensitivity. Furthermore, repeated perineural treatment with an anti-HMGB1 antibody blocked activation of spinal microglia in PSNL mice. Collectively, the current findings demonstrate that increased HMGB1 around injured sciatic nerve might induce nociceptive hypersensitivity through activation of spinal microglia. Thus, HMGB1-dependent mechanisms between the injured sciatic nerve and spinal dorsal horn could be crucial in induction of neuropathic pain.

Physiopathology of pain in systemic erythematosus lupus

Systemic lupus erythematosus is an autoimmune disease that promotes chronic inflammation, with periods of activation and remission. Pain is commonly one of the first symptoms reported by patients with lupus. It interferes with patients' quality of life, leading to a decrease in strength and difficulty in performing daily activities. Given the chronic nature of the disease, the high prevalence of pain and its negative impact on the quality of life of patients with lupus, the present literature review study aims to explain the pathophysiology of pain in systemic lupus erythematosus and the implications of the chronic process and contributing factors. During periods of systemic lupus erythematosus activity, pain is a significant symptom. Despite this, several studies show that severe pain can occur in patients with in mild to moderate disease activity. Also, in the early stages of the disease, the pain may be accentuated by the greater activity of the disease. However, even when advanced disease is under control, there can be comorbidities and accumulated damage that can also cause high levels of pain. This sensitivity is due to the overlap of primary, secondary, and tertiary pain pathologies, which feedback and make this symptom one of the main concerns of patients with lupus. Understanding the pathophysiology of pain in systemic lupus erythematosus, as well as its chronification and contribution factors, is essential to identify effective therapeutic alternatives in these patients at each stage of pain pathology (primary, secondary, and tertiary).

Epigenetic reduction of miR-214-3p upregulates astrocytic colony-stimulating factor-1 and contributes to neuropathic pain induced by nerve injury

Emerging evidence has indicated that colony-stimulating factor-1 (CSF1) modulates neuroinflammation in the central nervous system and the development of neuropathic pain, while the underlying mechanism remains unknown. Here, we identified the increased expression of CSF1 derived from activated astrocytes in the ipsilateral dorsal horn in rats with spinal nerve ligation (SNL). Suppression of CSF1 expression alleviated neuroinflammation, neuronal hyperexcitability, and glutamatergic receptor subunit upregulation in the dorsal horn and improved SNL-induced pain behavior. We also found reduced miR-214-3p expression in the ipsilateral dorsal horn following an SNL procedure; miR-214-3p directly bound to the 3'-UTR of CSF1 mRNA and negatively regulated CSF1 expression. Intrathecal delivery of miR-214-3p mimic reversed the enhanced expression of CSF1 and astrocyte overactivity and alleviated the IL-6 upregulation and pain behavior induced by SNL. Moreover, suppression of spinal miR-214-3p increased astrocyte reactivity, promoted CSF1 and IL-6 production, and induced pain hypersensitivity in naive animals. Furthermore, SNL induced the expression of DNA methyltransferase 3a (DNMT3a) that was associated with the hypermethylation of the miR-214-3p promoter, leading to reduced miR-214-3p expression in the model rodents. Treatment with the DNMT inhibitor zebularine significantly reduced cytosine methylation in the miR-214-3p promoter; this reduced methylation consequently increased the expression of miR-214-3p and decreased the content of CSF1 in the ipsilateral dorsal horn and, further, attenuated IL-6 production and pain behavior in rats with SNL. Together, our data indicate that the DNMT3a-mediated epigenetic suppression of miR-214-3p enhanced CSF1 production in astrocytes, which subsequently induced neuroinflammation and pain behavior in SNL model rats.

Unique primed status of microglia under the systemic autoimmune condition of lupus-prone mice

BACKGROUND

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of various autoantibodies. This disease causes disabling neuropsychiatric symptoms even in the absence of apparent inflammation in the central nervous system (CNS), but the mechanisms involved remain unknown. Innate immune-mediated inflammation has attracted attention as a pathogenic mechanism in neuropsychiatric diseases.

METHODS

We investigated the CNS of lupus-prone mice focusing on innate immunity. Three strains of lupus-prone mice, FcγRIIB^-/-Yaa, an F1 hybrid of NZB and NZW (NZB/NZW) mice, and MRL/Fas^lpr (MRL/lpr) mice were used to analyze CNS immunopathology.

RESULTS

Flow cytometry analysis demonstrated the numbers of brain CD45⁺ cells were increased compared with controls in lupus-prone mice. Upregulation of MHC class I and PDCA1 was observed in microglia and CD11b⁺ myeloid cells of lupus-prone mice, indicating they were activated in response to interferons (IFN). Microglial gene expression analysis of FcγRIIB^-/-Yaa mice revealed the upregulation of IFN-responsive genes and inflammation-related genes including Axl, Clec7a, and Itgax, which were previously reported in neurodegenerative conditions and primed conditions. Upregulated chemokine gene expressions including Ccl5 and Cxcl10 were concurrent with increased numbers of T cells and monocytes, especially Ly6C^lo monocytes in the CNS. Upregulation of Axl, Clec7a, Itgax, Ccl5, and Cxcl10 was also observed in NZB/NZW mice, indicating common lupus pathology. The primed status of microglia in FcγRIIB^-/-Yaa mice was also demonstrated by morphological changes such as enlarged cell bodies with hypertrophic processes, and hyperreactivity to lipopolysaccharide. Immunohistochemistry of FcγRIIB^-/-Yaa mice indicated reactive responses of astrocytes and vascular endothelium. Behavioral studies of FcγRIIB^-/-Yaa mice revealed depressive-like behavior and heat hyperalgesia in the forced swim test and the tail-flick test, respectively.

CONCLUSIONS

Our data indicated that microglia in lupus exhibit a unique primed phenotype characterized by the upregulated expressions of neurodegeneration-related genes and IFN-responsive genes. Interaction with peripheral cells and brain resident cells was presumed to orchestrate neuroinflammation. Targeting innate immune cells, such as microglia and monocytes, may be a promising therapeutic approach for neuropsychiatric SLE.

Macrophage-derived insulin-like growth factor-1 is a key neurotrophic and nerve-sensitizing factor in pain associated with endometriosis

Endometriosis is a common incurable inflammatory disorder that is associated with debilitating pelvic pain in women. Macrophages are central to the pathophysiology of endometriosis: they dictate the growth and vascularization of endometriosis lesions and more recently have been shown to promote lesion innervation. The aim of this study was to determine the mechanistic role of macrophages in producing pain associated with endometriosis. Herein, we show that macrophage depletion in a mouse model of endometriosis can reverse abnormal changes in pain behavior. We identified that disease-modified macrophages exhibit increased expression of IGF-1 in an in vitro model of endometriosis-associated macrophages and confirmed expression by lesion-resident macrophages in mice and women. Concentrations of IGF-1 were elevated in peritoneal fluid from women with endometriosis and positively correlate with their pain scores. Mechanistically, we demonstrate that macrophage-derived IGF-1 promotes sprouting neurogenesis and nerve sensitization in vitro. Finally, we show that the Igf-1 receptor inhibitor linsitinib reverses the pain behavior observed in mice with endometriosis. Our data support a role for macrophage-derived IGF-1 as a key neurotrophic and sensitizing factor in endometriosis, and we propose that therapies that modify macrophage phenotype may be attractive therapeutic options for the treatment of women with endometriosis-associated pain.-Forster, R., Sarginson, A., Velichkova, A., Hogg, C., Dorning, A., Horne, A. W., Saunders, P. T. K., Greaves, E. Macrophage-derived insulin-like growth factor-1 is a key neurotrophic and nerve-sensitizing factor in pain associated with endometriosis.

Microglial proliferation and monocyte infiltration contribute to microgliosis following status epilepticus

Microglial activation has been recognized as a major contributor to inflammation of the epileptic brain. Seizures are commonly accompanied by remarkable microgliosis and loss of neurons. In this study, we utilize the CX3CR1^GFP/+ CCR2^RFP/+ genetic mouse model, in which CX3CR1⁺ resident microglia and CCR2⁺ monocytes are labeled with GFP and RFP, respectively. Using a combination of time-lapse two-photon imaging and whole-cell patch clamp recording, we determined the distinct morphological, dynamic, and electrophysiological characteristics of infiltrated monocytes and resident microglia, and the evolution of their behavior at different time points following kainic acid-induced seizures. Seizure activated microglia presented enlarged somas with less ramified processes, whereas, infiltrated monocytes were smaller, highly motile cells that lacked processes. Moreover, resident microglia, but not infiltrated monocytes, proliferate locally in the hippocampus after seizure. Microglial proliferation was dependent on the colony-stimulating factor 1 receptor (CSF-1R) pathway. Pharmacological inhibition of CSF-1R reduced seizure-induced microglial proliferation, which correlated with attenuation of neuronal death without altering acute seizure behaviors. Taken together, we demonstrated that proliferation of activated resident microglia contributes to neuronal death in the hippocampus via CSF-1R after status epilepticus, providing potential therapeutic targets for neuroprotection in epilepsy.

CSF-1 in Inflammatory and Arthritic Pain Development

Pain is one of the most debilitating symptoms in many diseases for which there is inadequate management and understanding. CSF-1, also known as M-CSF, acts via its receptor (CSF-1R, c-Fms) to regulate the development of the monocyte/macrophage lineage and to act locally in tissues to control macrophage numbers and function. It has been implicated in the control of neuropathic pain via a central action on microglia. We report in this study that systemic administration of a neutralizing anti-CSF-1R or CSF-1 mAb inhibits the development of inflammatory pain induced by zymosan, GM-CSF, and TNF in mice. This approach also prevented but did not ameliorate the development of arthritic pain and optimal disease driven by the three stimuli in mice, suggesting that CSF-1 may only be relevant when the driving inflammatory insults in tissues are acute and/or periodic. Systemic CSF-1 administration rapidly induced pain and enhanced the arthritis in an inflamed mouse joint, albeit via a different pathway(s) from that used by systemic GM-CSF and TNF. It is concluded that CSF-1 can function peripherally during the generation of inflammatory pain and hence may be a target for such pain and associated disease, including when the clinically important cytokines, TNF and GM-CSF, are involved. Our findings have ramifications for the selection and design of anti-CSF-1R/CSF-1 trials.

Interaction between astrocytic colony stimulating factor and its receptor on microglia mediates central sensitization and behavioral hypersensitivity in chronic post ischemic pain model

Accumulation of microglia occurs in the dorsal horn in the rodent model of chronic post ischemic pain (CPIP), while the mechanism how microglia affects the development of persistent pain largely remains unknown. Here, using a rodent model of CPIP induced by ischemia-reperfusion (IR) injury in the hindpaw, we observed that microglial accumulation occurred in the ipsilateral dorsal horn after ischemia 3h, and in ipsilateral and contralateral dorsal horn in the rats with ischemia 6h. The accumulated microglia released BDNF, increased neuronal excitability in dorsal horn, and produced pain behaviors in the modeled rodents. We also found significantly increased signaling mediated by astrocytic colony-stimulating factor-1 (CSF1) and microglial CSF1 receptor (CSF1R) in dorsal horn in the ischemia 6h modeled rats. While exogenous M-CSF induced microglial activation and proliferation, BDNF production, neuronal hyperactivity in dorsal horn and behavioral hypersensitivity in the naïve rats, inhibition of astrocytic CSF1/microglial CSF1R signaling by fluorocitric or PLX3397 significantly suppressed microglial activation and proliferation, BDNF upregulation, and neuronal activity in dorsal horn, as well as the mechanical allodynia and thermal hyperalgesia, in the rats with ischemia 6h. Collectively, these results demonstrated that glial CSF1/CSF1R pathway mediated the microglial activation and proliferation, which facilitated the nociceptive output and contributed to the chronic pain induced by IR injury.