RAR/RXR and PPAR/RXR Signaling in Spinal Cord Injury

A Narrative Review on Axonal Neuroprotection in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) resulting in demyelination and neurodegeneration. The therapeutic strategy is now largely based on reducing inflammation with immunosuppressive drugs. Unfortunately, when disease progression is observed, no drug offers neuroprotection apart from its anti-inflammatory effect. In this review, we explore current knowledge on the assessment of neurodegeneration in MS and look at putative targets that might prove useful in protecting the axon from degeneration. Among them, Bruton's tyrosine kinase inhibitors, anti-apoptotic and antioxidant agents, sex hormones, statins, channel blockers, growth factors, and molecules preventing glutamate excitotoxicity have already been studied. Some of them have reached phase III clinical trials and carry a great message of hope for our patients with MS.

The Diverse Manifestations of Regeneration and Why We Need to Study Them

For hundreds of years, the question of why some organisms can regenerate missing body parts while others cannot has remained poorly understood. This has been due in great part to the inability to genetically, molecularly, and cellularly dissect this problem for most of the history of the field. It has only been in the past 20-30 years that important mechanistic advances have been made in methodologies that introduce loss and gain of gene function in animals that can regenerate. However, we still have a very incomplete understanding of how broadly regenerative abilities may be dispersed across species and whether or not such properties share a common evolutionary origin, which may have emerged independently or both. Understanding regeneration, therefore, will require rigorously practiced fundamental, curiosity-driven, discovery research. Expanding the number of research organisms used to study regeneration allows us to uncover aspects of this problem we may not yet know exist and simultaneously increases our chances of solving this long-standing problem of biology.

Repurposing Peroxisome Proliferator-Activated Receptor Agonists in Neurological and Psychiatric Disorders

Common pathophysiological mechanisms have emerged for different neurological and neuropsychiatric conditions. In particular, mechanisms of oxidative stress, immuno-inflammation, and altered metabolic pathways converge and cause neuronal and non-neuronal maladaptative phenomena, which underlie multifaceted brain disorders. The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors modulating, among others, anti-inflammatory and neuroprotective genes in diverse tissues. Both endogenous and synthetic PPAR agonists are approved treatments for metabolic and systemic disorders, such as diabetes, fatty liver disease, and dyslipidemia(s), showing high tolerability and safety profiles. Considering that some PPAR-acting drugs permeate through the blood-brain barrier, the possibility to extend their scope from the periphery to central nervous system has gained interest in recent years. Here, we review preclinical and clinical evidence that PPARs possibly exert a neuroprotective role, thereby providing a rationale for repurposing PPAR-targeting drugs to counteract several diseases affecting the central nervous system.

Elucidating the Neuroprotective Role of PPARs in Parkinson's Disease: A Neoteric and Prospective Target

One of the utmost frequently emerging neurodegenerative diseases, Parkinson's disease (PD) must be comprehended through the forfeit of dopamine (DA)-generating nerve cells in the substantia nigra pars compacta (SN-PC). The etiology and pathogenesis underlying the emergence of PD is still obscure. However, expanding corroboration encourages the involvement of genetic and environmental factors in the etiology of PD. The destruction of numerous cellular components, namely oxidative stress, ubiquitin-proteasome system (UPS) dysfunction, autophagy-lysosome system dysfunction, neuroinflammation and programmed cell death, and mitochondrial dysfunction partake in the pathogenesis of PD. Present-day pharmacotherapy can alleviate the manifestations, but no therapy has been demonstrated to cease disease progression. Peroxisome proliferator-activated receptors (PPARs) are ligand-directed transcription factors pertaining to the class of nuclear hormone receptors (NHR), and are implicated in the modulation of mitochondrial operation, inflammation, wound healing, redox equilibrium, and metabolism of blood sugar and lipids. Numerous PPAR agonists have been recognized to safeguard nerve cells from oxidative destruction, inflammation, and programmed cell death in PD and other neurodegenerative diseases. Additionally, various investigations suggest that regular administration of PPAR-activating non-steroidal anti-inflammatory drugs (NSAIDs) (ibuprofen, indomethacin), and leukotriene receptor antagonists (montelukast) were related to the de-escalated evolution of neurodegenerative diseases. The present review elucidates the emerging evidence enlightening the neuroprotective outcomes of PPAR agonists in in vivo and in vitro models experiencing PD. Existing articles up to the present were procured through PubMed, MEDLINE, etc., utilizing specific keywords spotlighted in this review. Furthermore, the authors aim to provide insight into the neuroprotective actions of PPAR agonists by outlining the pharmacological mechanism. As a conclusion, PPAR agonists exhibit neuroprotection through modulating the expression of a group of genes implicated in cellular survival pathways, and may be a propitious target in the therapy of incapacitating neurodegenerative diseases like PD.

Pharmacological Activation of RXR-α Promotes Hematoma Absorption via a PPAR-γ-dependent Pathway After Intracerebral Hemorrhage

Endogenously eliminating the hematoma is a favorable strategy in addressing intracerebral hemorrhage (ICH). This study sought to determine the role of retinoid X receptor-α (RXR-α) in the context of hematoma absorption after ICH. Our results showed that pharmacologically activating RXR-α with bexarotene significantly accelerated hematoma clearance and alleviated neurological dysfunction after ICH. RXR-α was expressed in microglia/macrophages, neurons, and astrocytes. Mechanistically, bexarotene promoted the nuclear translocation of RXR-α and PPAR-γ, as well as reducing neuroinflammation by modulating microglia/macrophage reprograming from the M1 into the M2 phenotype. Furthermore, all the beneficial effects of RXR-α in ICH were reversed by the PPAR-γ inhibitor GW9662. In conclusion, the pharmacological activation of RXR-α confers robust neuroprotection against ICH by accelerating hematoma clearance and repolarizing microglia/macrophages towards the M2 phenotype through PPAR-γ-related mechanisms. Our data support the notion that RXR-α might be a promising therapeutic target for ICH.

Inhibitory effect of retinoic acid receptor agonists on in vitro chondrogenic differentiation

Retinoic acid (RA), an active metabolite of vitamin A, plays pivotal roles in a wide variety of biological processes, such as body patterning, organ development, and cell differentiation and proliferation. RA signaling is mediated by nuclear retinoic acid receptors, α, β, and γ (RARα, RARβ, and RARγ). RA is a well-known regulator of cartilage and skeleton formation and RARs are also essential for skeletal growth and hypertrophic chondrocyte-specific gene expression. These important roles of RA and RARs in chondrogenesis have been widely investigated using in vivo mouse models. However, few reports are available on the function of each subtype of RARs on in vitro chondrocyte differentiation. Here, we examined the effect of specific agonists of RARs on chondrogenic differentiation of ATDC5 and C3H10T1/2 cells. Subtype-specific RAR agonists as well as RA decreased the expressions of chondrogenic differentiation marker genes and inhibited chondrogenic differentiation, which was accompanied with morphological change to spindle-shaped cells. Among RAR agonists, RARα and RARγ agonists revealed a strong inhibitory effect on chondrogenic differentiation. RARα and RARγ agonists also hampered viability of ATDC5 cells. These observations suggested that RARα and RARγ are dominant receptors of RA signaling that negatively regulate chondrogenic differentiation.

Retinoid X receptor α downregulation is required for tail and caudal spinal cord regeneration in the adult newt

Some adult vertebrate species, such as newts, axolotls and zebrafish, have the ability to regenerate their central nervous system (CNS). However, the factors that establish a permissive CNS environment for correct morphological and functional regeneration in these species are not well understood. Recent evidence supports a role for retinoid signaling in the intrinsic ability of neurons, in these regeneration-competent species, to regrow after CNS injury. Previously, we demonstrated that a specific retinoic acid receptor (RAR) subtype, RARβ, mediates the effects of endogenous retinoic acid (RA) on neuronal growth and guidance in the adult newt CNS after injury. Here, we now examine the expression of the retinoid X receptor RXRα (a potential heterodimeric transcriptional regulator with RARβ), in newt tail and spinal cord regeneration. We show that at 21 days post-amputation (dpa), RXRα is expressed at temporally distinct periods and in non-overlapping spatial domains compared to RARβ. Whereas RARβ protein levels increase, RXRα proteins level decrease by 21 dpa. A selective agonist for RXR, SR11237, prevents both this downregulation of RXRα and upregulation of RARβ and inhibits tail and caudal spinal cord regeneration. Moreover, treatment with a selective antagonist for RARβ, LE135, inhibits regeneration with the same morphological consequences as treatment with SR11237. Interestingly, LE135 treatment also inhibits the normal downregulation of RXRα in tail and spinal cord tissues at 21 dpa. These results reveal a previously unidentified, indirect regulatory feedback loop between these two receptor subtypes in regulating the regeneration of tail and spinal cord tissues in this regeneration-competent newt.

Identification of key genes and pathways associated with spinal cord injury

The present study was designed to identify key genes or significant signaling pathways associated with spinal cord injury (SCI), and to clarify the underlying molecular mechanisms of SCI. Data from the GSE45550 array were downloaded from the Gene Expression Omnibus database. A total of 6 control samples, 6 samples at 3 days post‑SCI (SCI3d), 6 samples at 8 days post‑SCI (SCI8d) and 6 samples at 14 days post‑SCI (SCI14d) were included. The microarray data was preprocessed by the robust multi‑array average algorithm. The differentially expressed genes (DEGs) were identified using the limma package. The overlapping DEGs among groups were analyzed using the Venny 2.0 online tool. Modules enriched by DEGs were selected by weighted gene co‑expression network analysis. Gene Ontology annotation and the Kyoto Encyclopedia of Genes and Genomes pathways were identified for DEGs using the Database for Annotation, Visualization and Integrated Discovery. A total of 693 genes were obtained by combining the DEGs of the SCI3d, SCI8d and SCI14d groups. The pink module and green module with smaller P‑values obtained from weighted gene co‑expression network analysis module analyses of DEGs demonstrated a higher correlation with SCI. In addition, the peroxisome proliferator‑activated receptor (PPAR) signaling pathway that the cluster of differentiation 36 (CD36) was significantly enriched in, was one of the significant pathways in the pink module. The p53 signaling pathway that Caspase‑3 (Casp3) was significantly enriched in was one of the significant pathways in the green module. In conclusion, the results of the present study demonstrated that the PPAR and p53 signaling pathway may serve important roles in the progression of SCI. In addition, CD36 and Casp3 may be involved in the progression of SCI via the PPAR and p53 signaling pathways, respectively.

Role of Peroxisome Proliferator-Activated Receptor γ in Ocular Diseases

Peroxisome proliferator-activated receptor γ (PPAR γ), a member of the nuclear receptor superfamily, is a ligand-activated transcription factor that plays an important role in the control of a variety of physiological processes. The last decade has witnessed an increasing interest for the role played by the agonists of PPAR γ in antiangiogenesis, antifibrosis, anti-inflammation effects and in controlling oxidative stress response in various organs. As the pathologic mechanisms of major blinding diseases, such as age-related macular degeneration (AMD), diabetic retinopathy (DR), keratitis, and optic neuropathy, often involve neoangiogenesis and inflammation- and oxidative stress-mediated cell death, evidences are accumulating on the potential benefits of PPAR γ to improve or prevent these vision threatening eye diseases. In this paper we describe what is known about the role of PPAR γ in the ocular pathophysiological processes and PPAR γ agonists as novel adjuvants in the treatment of eye diseases.

Peroxisome proliferator-activated receptor agonists modulate neuropathic pain: a link to chemokines?

Chronic pain presents a widespread and intractable medical problem. While numerous pharmaceuticals are used to treat chronic pain, drugs that are safe for extended use and highly effective at treating the most severe pain do not yet exist. Chronic pain resulting from nervous system injury (neuropathic pain) is common in conditions ranging from multiple sclerosis to HIV-1 infection to type II diabetes. Inflammation caused by neuropathy is believed to contribute to the generation and maintenance of neuropathic pain. Chemokines are key inflammatory mediators, several of which (MCP-1, RANTES, MIP-1α, fractalkine, SDF-1 among others) have been linked to chronic, neuropathic pain in both human conditions and animal models. The important roles chemokines play in inflammation and pain make them an attractive therapeutic target. Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear receptors known for their roles in metabolism. Recent research has revealed that PPARs also play a role in inflammatory gene repression. PPAR agonists have wide-ranging effects including inhibition of chemokine expression and pain behavior reduction in animal models. Experimental evidence suggests a connection between the pain ameliorating effects of PPAR agonists and suppression of inflammatory gene expression, including chemokines. In early clinical research, one PPARα agonist, palmitoylethanolamide (PEA), shows promise in relieving chronic pain. If this link can be better established, PPAR agonists may represent a new drug therapy for neuropathic pain.

Spinal cord injury induced changes of nuclear receptors PPARα and LXRβ and modulation with oleic acid/albumin treatment

In previous studies with animal models of spinal cord injury (SCI) pharmacological activation of peroxisome proliferator activated receptors (PPAR) and liver X receptors (LXR) were used to reduce tissue damage and promote behavioral recovery in animal models. We have studied the endogenous expression of the transcription factors PPARα and LXRβ in the chronic stage after SCI in rats. The immunohistochemical investigation revealed a long lasting increase in the level of PPARα in white matter in the vicinity of the lesion site. The source of this signal was identified in a subpopulation of astrocytes outside of the glial scar area. Intrathecal injections of oleic acid/albumin reduced the lesion-induced PPARα immunoreactivity. In addition, ependymal cells displayed a prominent PPARα signal in the non-injured spinal cord, and continued to express the receptor as they proliferated and migrated within the damaged tissue. The nuclear receptor LXRβ was detected at similar levels after SCI as in sham operated animals. We found high levels of immunoreactivity in the gray matter, while in the white matter it was present in subpopulations of astrocytes and oligodendrocytes. Macrophages that had accumulated within the center of the lesion contained LXRβ in their cell nuclei. Possible endogenous functions of PPARα and LXRβ after SCI are discussed, specifically the control of fatty acid and cholesterol metabolism and the regulation of inflammatory reactions.

Gene expression profiling of liver X receptor α and Bcl-2-associated X protein in experimental transection spinal cord-injured rats

BACKGROUND

Study of molecular responses to central nervous system injury would be helpful for controlling the harmful pathways post-injury and triggering the useful pathways required for the treatment of injury.

OBJECTIVE

To investigate the expression level of liver X receptor α (LXRα) which has anti-inflammatory effects and pro-apoptotic Bcl-2-associated X protein (Bax) upon spinal cord injury (SCI).

DESIGN

To induce SCI, transection was carried out at T9 level of male Wister rats. Approximately 8 mm of rostral, caudal, and epicenter tissues of injured sites in treated rats were chosen for quantitative real-time polymerase chain reaction at the 6, 24, and 72 hours, and 7 and 10 days post-surgery.

RESULTS

Our results showed a complicated temporal and spatial pattern of alteration in LXRα and Bax mRNA expression levels after SCI. LXRα expression level followed a homologues pattern (additive and subtractive wave) with a difference in time at three areas of studied. Rostral, caudal, and epicenter expression patterns of Bax were dissimilar in these areas. Gradual increase in the expression of Bax without any decrease at the rostral area was observed, presumably indicating the active transcription process of this gene, regardless of its protein situation.

CONCLUSION

A time lapse significant change in Bax expression level was observed only in the epicenter of injury, emphasizing that apoptotic responses are limited to this area. Furthermore, an increase in LXRα transcription level was observed first in rostral area and then extended to epicentral and caudal areas, implying that inflammation responses extended from rostral to caudal areas.

New insights into the role of peroxisome proliferator-activated receptors in regulating the inflammatory response after tissue injury

Major trauma results in a strong inflammatory response in injured tissue. This posttraumatic hyperinflammation has been implied in the adverse events leading to a breakdown of host defense mechanisms and ultimately to delayed organ failure. Ligands to peroxisome proliferator-activated receptors (PPARs) have recently been identified as potent modulators of inflammation in various acute and chronic inflammatory conditions. The main mechanism of action mediated by ligand binding to PPARs is the inhibition of the nuclear transcription factor NF-κB, leading to downregulation of downstream gene transcription, such as for genes encoding proinflammatory cytokines. Pharmacological PPAR agonists exert strong anti-inflammatory properties in various animal models of tissue injury, including central nervous system trauma, ischemia/reperfusion injury, sepsis, and shock. In addition, PPAR agonists have been shown to induce wound healing process after tissue trauma. The present review was designed to provide an up-to-date overview on the current understanding of the role of PPARs in the pathophysiology of the inflammatory response after major trauma. Therapeutic options for using recombinant PPAR agonists as pharmacological agents in the management of posttraumatic inflammation will be discussed.

Peroxisome proliferator-activated receptors: "key" regulators of neuroinflammation after traumatic brain injury

Traumatic brain injury is characterized by neuroinflammatory pathological sequelae which contribute to brain edema and delayed neuronal cell death. Until present, no specific pharmacological compound has been found, which attenuates these pathophysiological events and improves the outcome after head injury. Recent experimental studies suggest that targeting peroxisome proliferator-activated receptors (PPARs) may represent a new anti-inflammatory therapeutic concept for traumatic brain injury. PPARs are “key” transcription factors which inhibit NFκB activity and downstream transcription products, such as proinflammatory and proapoptotic cytokines. The present review outlines our current understanding of PPAR-mediated neuroprotective mechanisms in the injured brain and discusses potential future anti-inflammatory strategies for head-injured patients, with an emphasis on the putative beneficial combination therapy of synthetic cannabinoids (e.g., dexanabinol) with PPARα agonists (e.g., fenofibrate).

Do PPAR-Gamma Agonists Have a Future in Parkinson's Disease Therapy?

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor (PPAR)-γ agonists commonly used as insulin-sensitizing drugs for the treatment of type 2 diabetes. In the last decade, PPAR-γ agonists have received increasing attention for their neuroprotective properties displayed in a variety of neurodegenerative diseases, including Parkinson's disease (PD), likely related to the anti-infammatory activity of these compounds. Recent studies indicate that neuroinflammation, specifically reactive microglia, plays important roles in PD pathogenesis. Moreover, after the discovery of infiltrating activated Limphocytes in the substantia nigra (SN) of PD patients, most recent research supports a role of immune-mediated mechanisms in the pathological process leading to chronic neuroinflammation and dopaminergic degeneration. PPAR-γ are highly expressed in cells of both central and peripheral immune systems, playing a pivotal role in microglial activation as well as in monocytes and T cells differentiation, in which they act as key regulators of immune responses. Here, we review preclinical evidences of PPAR-γ-induced neuroprotection in experimental PD models and highlight relative anti-inflammatory mechanisms involving either central or peripheral immunomodulatory activity. Specific targeting of immune functions contributing to neuroinflammation either directly (central) or indirectly (peripheral) may represent a novel therapeutic approach for disease modifying therapies in PD.

Inflammatory chemokine release of astrocytes in vitro is reduced by all-trans retinoic acid

The production of chemokines by astrocytes constitutes an important component of neuroinflammatory processes in the brain. As the transcriptional activator retinoic acid (RA), used for chemotherapy and dermatological applications, exerts anti-inflammatory effects on monocytes and lymphocytes, we have tested whether the physiologically occurring isomer, all-trans RA, affects chemokine expression by astrocytes. Under control conditions, primary cultures of murine cortical astrocytes expressed no or very low levels of CCL and CXCL chemokines. After treatment with bacterial lipopolysaccharides to simulate inflammation in vitro, we detected a strong increase in the release of CCL2 (to > 4 ng/mL in cell culture supernatant), CCL3 (> 20 ng/mL), CCL5 (> 25 ng/mL), CXCL1 (> 30 ng/mL) and CXCL2 (> 20 ng/mL). Although simultaneous exposure to RA did not significantly affect this response, 12 h pre-treatment with 0.1 microM all-trans RA strongly suppressed mRNA expression and protein release of all chemokines. The anti-inflammatory activity of RA engaged RA and retinoid X receptors and correlated with a decreased expression of the lipopolysaccharides co-receptor CD14. A minor reduction of nuclear NF-kappaB was observed but not significant, activation of Jun amino-terminal kinase, p38 and signal transducer and activator of transcription 3 were not altered by RA. The results suggest that retinoids should be further investigated as candidates for the treatment of neuroinflammation.

[Technology of analysis of epigenetic and structural changes of epithelial tumors genome with NotI-microarrays by the example of human chromosome]

New comparative genome hybridization technology on NotI-microarrays is presented (Karolinska Institute International Patent WO02/086163). The method is based on comparative genome hybridization of NotI-probes from tumor and normal genomic DNA with the principle of new DNA NotI-microarrays. Using this method 181 NotI linking loci from human chromosome 3 were analyzed in 200 malignant tumor samples from different organs: kidney, lung, breast, ovary, cervical, prostate. Most frequently (more than in 30%) aberrations--deletions, methylation,--were identified in NotI-sites located in MINT24, BHLHB2, RPL15, RARbeta1, ITGA9, RBSP3, VHL, ZIC4 genes, that suggests they probably are involved in cancer development. Methylation of these genomic loci was confirmed by methylation-specific PCR and bisulfite sequencing. The results demonstrate perspective of using this method to solve some oncogenomic problems.

Anti-inflammatory effect of retinoic acid on prostaglandin synthesis in cultured cortical astrocytes

Prostanoids are important mediators of inflammation and pain signaling. Although it is now well accepted that astrocytes participate in inflammatory reactions in the CNS, the molecular regulation of this activity is still largely unknown. Specifically, the regulation of prostanoid synthesis by this type of glia remains to be resolved. Recent evidence suggests that the transcriptional regulator retinoic acid (RA) is involved in regulation of the immune response. We have investigated the expression pattern of the enzymes that catalyze prostanoid and leukotriene synthesis in cultured cortical astrocytes, their stimulation by lipopolysaccharides (LPS) and their regulation by RA. The data indicate that astrocytes are an important source of prostaglandins (PGs) and that RA reduces their inflammatory biosynthesis. LPS treatment induced the expression of enzymes for the production of arachidonic acid and PGs but caused down-regulation of a PG degrading enzyme and of leukotriene synthesizing enzymes that compete with PG synthesis. Consequently, the secretion of the PGE(2) was highly increased after LPS exposure. RA counteracted the inflammatory regulation of cyclooxygenase (COX)-2 mRNA and protein in astrocytes and thereby reduced the synthesis of PGE(2) by approximately 60%. In the absence of LPS, RA enhanced the expression of COX-1 mRNA. In conclusion, RA might be effective in suppressing inflammatory processes in the brain by inhibiting PG synthesis.

RAR/RXR and PPAR/RXR signaling in neurological and psychiatric diseases

Retinoids are important signals in brain development. They regulate gene transcription by binding to retinoic acid receptors (RAR) and, as was discovered recently, a peroxisome proliferator-activated receptor (PPAR). Traditional ligands of PPAR are best known for their functions in lipid metabolism and inflammation. RAR and PPAR are ligand-activated transcription factors, which share members of the retinoid X receptor (RXR) family as heterodimeric partners. Both signal transduction pathways have recently been implicated in the progression of neurodegenerative and psychiatric diseases. Since inflammatory processes contribute to various neurodegenerative diseases, the anti-inflammatory activity of retinoids and PPARgamma agonists recommends them as potential therapeutic targets. In addition, genetic linkage studies, transgenic mouse models and experiments with vitamin A deprivation provide evidence that retinoic acid signaling is directly involved in physiology and pathology of motoneurons, of the basal ganglia and of cognitive functions. The activation of PPAR/RXR and RAR/RXR transcription factors has therefore been proposed as a therapeutic strategy in disorders of the central nervous system.

Intrathecal rosiglitazone acts at peroxisome proliferator-activated receptor-gamma to rapidly inhibit neuropathic pain in rats

In this report, we demonstrate the transcription, expression, and DNA-binding properties of the peroxisome proliferator-activated receptor (PPAR)-gamma subtype of the peroxisome proliferator-activated nuclear receptor family to the spinal cord with real-time PCR, Western blot, and electrophoretic mobility shift assay. To test the hypothesis that activation of spinal PPAR-gamma decreases nerve injury-induced allodynia, we intrathecally administered PPAR-gamma agonists and/or antagonists in rats after transection of the tibial and common peroneal branches of the sciatic nerve. Single injection of either a natural (15-deoxy-prostaglandin J2, 15d-PGJ2) or synthetic (rosiglitazone) PPAR-gamma agonist dose-dependently decreased mechanical and cold hypersensitivity. These effects were maximal at a dose of 100 microg and peaked at approximately 60 minutes after injection, a rapid time course suggestive of transcription-independent mechanisms of action. Concurrent administration of a PPAR-gamma antagonist (bisphenol A diglycidyl ether, BADGE) reversed the effects of 15d-PGJ2 and rosiglitazone, further indicating a receptor-mediated effect. In animals without nerve injury, rosiglitazone did not alter motor coordination, von Frey threshold, or withdrawal response to a cool stimulus. Intraperitoneal and intracerebroventricular administration of PPAR-gamma agonists (100 microg) did not decrease mechanical and cold hypersensitivity, arguing against effects subsequent to diffusion from the intrathecal space. We conclude that ligand-induced activation of spinal PPAR-gamma rapidly reverses nerve injury-induced mechanical allodynia. New or currently available drugs targeted at spinal PPAR-gamma may yield important therapeutic effects for the management of neuropathic pain.

PERSPECTIVE

PPAR-gamma receptor agonists such as rosiglitazone and pioglitazone are approved as insulin sensitizers by the United States Food and Drug Administration. We demonstrate PPAR-gamma expression in the spinal cord and report that activation of these receptors inhibits allodynia. BBB-permeant PPAR-gamma agonists may yield important therapeutic effects for the management of neuropathic pain.