Involvement of integrin β1/FAK signaling in the analgesic effects induced by glial cell line-derived neurotrophic factor in neuropathic pain

Interplay of BDNF and GDNF in the Mature Spinal Somatosensory System and Its Potential Therapeutic Relevance

The growth factors BDNF and GDNF are gaining more and more attention as modulators of synaptic transmission in the mature central nervous system (CNS). The two molecules undergo a regulated secretion in neurons and may be anterogradely transported to terminals where they can positively or negatively modulate fast synaptic transmission. There is today a wide consensus on the role of BDNF as a pro-nociceptive modulator, as the neurotrophin has an important part in the initiation and maintenance of inflammatory, chronic, and/or neuropathic pain at the peripheral and central level. At the spinal level, BDNF intervenes in the regulation of chloride equilibrium potential, decreases the excitatory synaptic drive to inhibitory neurons, with complex changes in GABAergic/glycinergic synaptic transmission, and increases excitatory transmission in the superficial dorsal horn. Differently from BDNF, the role of GDNF still remains to be unraveled in full. This review resumes the current literature on the interplay between BDNF and GDNF in the regulation of nociceptive neurotransmission in the superficial dorsal horn of the spinal cord. We will first discuss the circuitries involved in such a regulation, as well as the reciprocal interactions between the two factors in nociceptive pathways. The development of small molecules specifically targeting BDNF, GDNF and/or downstream effectors is opening new perspectives for investigating these neurotrophic factors as modulators of nociceptive transmission and chronic pain. Therefore, we will finally consider the molecules of (potential) pharmacological relevance for tackling normal and pathological pain.

Glial cell line-derived neurotrophic factors (GFLs) and small molecules targeting RET receptor for the treatment of pain and Parkinson's disease

Rearranged during transfection (RET), in complex with glial cell line-derived (GDNF) family receptor alpha (GFRα), is the canonical signaling receptor for GDNF family ligands (GFLs) expressed in both central and peripheral parts of the nervous system and also in non-neuronal tissues. RET-dependent signaling elicited by GFLs has an important role in the development, maintenance and survival of dopamine and sensory neurons. Both Parkinson's disease and neuropathic pain are devastating disorders without an available cure, and at the moment are only treated symptomatically. GFLs have been studied extensively in animal models of Parkinson's disease and neuropathic pain with remarkable outcomes. However, clinical trials with recombinant or viral vector-encoded GFL proteins have produced inconclusive results. GFL proteins are not drug-like; they have poor pharmacokinetic properties and activate multiple receptors. Targeting RET and/or GFRα with small molecules may resolve the problems associated with using GFLs as drugs and can result in the development of therapeutics for disease-modifying treatments against Parkinson's disease and neuropathic pain.

Natural Selection Equally Supports the Human Tendencies in Subordination and Domination: A Genome-Wide Study With in silico Confirmation and in vivo Validation in Mice

We proposed the following heuristic decision-making rule: "IF {an excess of a protein relating to the nervous system is an experimentally known physiological marker of low pain sensitivity, fast postinjury recovery, or aggressive, risk/novelty-seeking, anesthetic-like, or similar agonistic-intolerant behavior} AND IF {a single nucleotide polymorphism (SNP) causes overexpression of the gene encoding this protein} THEN {this SNP can be a SNP marker of the tendency in dominance} WHILE {underexpression corresponds to subordination} AND vice versa." Using this decision-making rule, we analyzed 231 human genes of neuropeptidergic, non-neuropeptidergic, and neurotrophinergic systems that encode neurotrophic and growth factors, interleukins, neurotransmitters, receptors, transporters, and enzymes. These proteins are known as key factors of human social behavior. We analyzed all the 5,052 SNPs within the 70 bp promoter region upstream of the position where the protein-coding transcript starts, which were retrieved from databases Ensembl and dbSNP using our previously created public Web service SNP_TATA_Comparator (http://beehive.bionet.nsc.ru/cgi-bin/mgs/tatascan/start.pl). This definition of the promoter region includes all TATA-binding protein (TBP)-binding sites. A total of 556 and 552 candidate SNP markers contributing to the dominance and the subordination, respectively, were uncovered. On this basis, we determined that 231 human genes under study are subject to natural selection against underexpression (significance p < 0.0005), which equally supports the human tendencies in domination and subordination such as the norm of a reaction (plasticity) of the human social hierarchy. These findings explain vertical transmission of domination and subordination traits previously observed in rodent models. Thus, the results of this study equally support both sides of the century-old unsettled scientific debate on whether both aggressiveness and the social hierarchy among humans are inherited (as suggested by Freud and Lorenz) or are due to non-genetic social education, when the children are influenced by older individuals across generations (as proposed by Berkowitz and Fromm).

Analgesic effects of TLR4/NF-κB signaling pathway inhibition on chronic neuropathic pain in rats following chronic constriction injury of the sciatic nerve

OBJECTIVE

Chronic neuropathic pain (CNP) is attributed to a lesion or disease of the somatosensory system, may be derived from the peripheral and central system. Recent study revealed that spinal cord stimulation attenuated CNP by inhibiting TLR4/NF-κB signaling pathway. The present study focuses on the potential analgesic effects of TLR4/NF-κB signaling pathway on CNP in a rat model of chronic constriction injury (CCI).

METHODS

We successfully established the rat model of CCI by Bennett method, and then inhibited the TLR4/NF-κB signaling pathway in rat models. Next, we measured the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) 0D, 2D, 6D, 8D and 12D after operation respectively. MTS510 100 mg/kg, an inhibitor of TLR4, was intrathecal injected into rats after 6D, 8D and 12D after operation. The experiment lasted for 12 days, and then the rats were sacrificed to collect the spinal cord tissues. Protein and mRNA expression levels of toll-like receptor 4 (TLR4), nuclear factor-kappaB (NF-κB), glial cell line-derived neurotrophic factor (GDNF), glial fibrillary acidic protein (GFAP) and nerve growth factor (NGF) were detected by western blot analysis and RT-qPCR, respectively. Immunohistochemistry was performed to detect GDNF, GFAP and NGF expression.

RESULTS

With the prolongation of MTS510 treatment time, MWT and TWL were increased and finally, the MWT and TWL were close to the baseline level. The levels of TLR4, NF-κB, GDNF, and GFAP as well as NGF increased in rats treated with CCI + Immunoglobulin G1 (IgG1) or CCI + MTS510, suggesting the model establishment was successful. Besides, with the prolongation of MTS510 treatment time, the protein level and mRNA expression of NF-kB, GDNF, GFAP and NGF decreased in rats treated with CCI + IgG1 or CCI + MTS510. Moreover, the GDNF, GFAP and NGF expression in spinal cord tissue in rats treated with CCI + IgG1 or CCI + MTS510 increased obviously, while the GDNF, GFAP and NGF expression decreased in spinal cord tissue in rats treated with CCI + IgG1 or CCI + MTS510 after MTS510 treatment.

CONCLUSIONS

Collectively, this study defines the role of TLR4 and NF-κB, and inhibition of TLR4/NF-κB signaling pathway might contribute to the alleviation of CNP and improvement of MWT and TWL in a rat model of CCI. Additionally, the results obtained from the study provided a promising basis that could aid as an experimental basis for the potential treatment of TLR4/NF-κB signaling pathway.