Genetic and functional evidence for gp130/IL6ST-induced transient receptor potential ankyrin 1 upregulation in uninjured but not injured neurons in a mouse model of neuropathic pain.

ABSTRACT: Peripheral nerve injuries result in pronounced alterations in dorsal root ganglia, which can lead to the development of neuropathic pain. Although the polymodal mechanosensitive transient receptor potential ankyrin 1 (TRPA1) ion channel is emerging as a relevant target for potential analgesic therapies, preclinical studies do not provide unequivocal mechanistic insight into its relevance for neuropathic pain pathogenesis. By using a transgenic mouse model with a conditional depletion of the interleukin-6 (IL-6) signal transducer gp130 in Nav1.8 expressing neurons (SNS-gp130-/-), we provide a mechanistic regulatory link between IL-6/gp130 and TRPA1 in the spared nerve injury (SNI) model. Spared nerve injury mice developed profound mechanical hypersensitivity as indicated by decreased withdrawal thresholds in the von Frey behavioral test in vivo, as well as a significant increase in mechanosensitivity of unmyelinated nociceptive primary afferents in ex vivo skin-nerve recordings. In contrast to wild type and control gp130fl/fl animals, SNS-gp130-/- mice did not develop mechanical hypersensitivity after SNI and exhibited low levels of Trpa1 mRNA in sensory neurons, which were partially restored by adenoviral gp130 re-expression in vitro. Importantly, uninjured but not injured neurons developed increased responsiveness to the TRPA1 agonist cinnamaldehyde, and neurons derived from SNS-gp130-/- mice after SNI were significantly less responsive to cinnamaldehyde. Our study shows for the first time that TRPA1 upregulation is attributed specifically to uninjured neurons in the SNI model, and this depended on the IL-6 signal transducer gp130. We provide a solution to the enigma of TRPA1 regulation after nerve injury and stress its significance as an important target for neuropathic pain disorders.

Role of IL-6 in the regulation of neuronal development, survival and function.

The pleiotropic cytokine interleukin-6 (IL-6) is emerging as a molecule with both beneficial and destructive potentials. It can exert opposing actions triggering either neuron survival after injury or causing neurodegeneration and cell death in neurodegenerative or neuropathic disorders. Importantly, neurons respond differently to IL-6 and this critically depends on their environment and whether they are located in the peripheral or the central nervous system. In addition to its hub regulator role in inflammation, IL-6 is recently emerging as an important regulator of neuron function in health and disease, offering exciting possibilities for more mechanistic insight into the pathogenesis of mental, neurodegenerative and pain disorders and for developing novel therapies for diseases with neuroimmune and neurogenic pathogenic components.

Prokineticin Receptor Inhibition With PC1 Protects Mouse Primary Sensory Neurons From Neurotoxic Effects of Chemotherapeutic Drugs in vitro.

Neurotoxicity is a common side effect of chemotherapeutics that often leads to the development of chemotherapy-induced peripheral neuropathy (CIPN). The peptide Prokineticin 2 (PK2) has a key role in experimental models of CIPN and can be considered an insult-inducible endangering mediator. Since primary afferent sensory neurons are highly sensitive to anticancer drugs, giving rise to dysesthesias, the aim of our study was to evaluate the alterations induced by vincristine (VCR) and bortezomib (BTZ) exposure in sensory neuron cultures and the possible preventive effect of blocking PK2 signaling. Both VCR and BTZ induced a concentration-dependent reduction of total neurite length that was prevented by the PK receptor antagonist PC1. Antagonizing the PK system also reduced the upregulation of PK2, PK-R1, TLR4, IL-6, and IL-10 expression induced by chemotherapeutic drugs. In conclusion, inhibition of PK signaling with PC1 prevented the neurotoxic effects of chemotherapeutics, suggesting a promising strategy for neuroprotective therapies against the sensory neuron damage induced by exposure to these drugs.

Impaired mechanical, heat, and cold nociception in a murine model of genetic TACE/ADAM17 knockdown.

TNF-α-converting enzyme, a member of the ADAM (A disintegrin and metalloproteinase) protease family and also known as ADAM17, regulates inflammation and regeneration in health and disease. ADAM17 targets are involved in pain development and hypersensitivity in animal models of inflammatory and neuropathic pain. However, the role of ADAM17 in the pain pathway is largely unknown. Therefore, we used the hypomorphic ADAM17 (ADAM17ex/ex) mouse model to investigate the importance of ADAM17 in nociceptive behavior, morphology, and function of primary afferent nociceptors. ADAM17ex/ex mice were hyposensitive to noxious stimulation, showing elevated mechanical thresholds as well as impaired heat and cold sensitivity. Despite these differences, skin thickness and innervation were comparable to controls. Although dorsal root ganglia of ADAM17ex/ex mice exhibited normal morphology of peptidergic and nonpeptidergic neurons, a small but significant reduction in the number of isolectin ß-4-positive neurons was observed. Functional electrical properties of unmyelinated nociceptors showed differences in resting membrane potential, afterhyperpolarization, and firing patterns in specific subpopulations of sensory neurons in ADAM17ex/ex mice. However, spinal cord morphology and microglia activity in ADAM17ex/ex mice were not altered. Our data suggest that ADAM17 contributes to the processing of painful stimuli, with a complex mode of action orchestrating the function of neurons along the pain pathway.-Quarta, S., Mitric, M., Kalpachidou, T., Mair, N., Schiefermeier-Mach, N., Andratsch, M., Qi, Y., Langeslag, M., Malsch, P., Rose-John, S., Kress, M. Impaired mechanical, heat, and cold nociception in a murine model of genetic TACE/ADAM17 knockdown.

Nuclear import mechanism of neurofibromin for localization on the spindle and function in chromosome congression.

Neurofibromatosis type-1 (NF-1) is caused by mutations in the tumor suppressor gene NF1; its protein product neurofibromin is a RasGTPase-activating protein, a property that has yet to explain aneuploidy, most often observed in astrocytes in NF-1. Here, we provide a mechanistic model for the regulated nuclear import of neurofibromin during the cell cycle and for a role in chromosome congression. Specifically, we demonstrate that neurofibromin, phosphorylated on Ser2808, a residue adjacent to a nuclear localization signal in the C-terminal domain (CTD), by Protein Kinase C-epsilon (PKC-ε), accumulates in a Ran-dependent manner and through binding to lamin in the nucleus at G2 in glioblastoma cells. Furthermore, we identify CTD as a tubulin-binding domain and show that a phosphomimetic substitution of its Ser2808 results in a predominantly nuclear localization. Confocal analysis shows that endogenous neurofibromin localizes on the centrosomes at interphase, as well as on the mitotic spindle, through direct associations with tubulins, in glioblastoma cells and primary astrocytes. More importantly, analysis of mitotic phenotypes after siRNA-mediated depletion shows that acute loss of this tumor suppressor protein leads to aberrant chromosome congression at the metaphase plate. Therefore, neurofibromin protein abundance and nuclear import are mechanistically linked to an error-free chromosome congression. Concerned with neurofibromin's, a tumor suppressor, mechanism of action, we demonstrate in astrocytic cells that its synthesis, phosphorylation by Protein Kinase C-ε on Ser2808 (a residue adjacent to a nuclear localization sequence), and nuclear import are cell cycle-dependent, being maximal at G2. During mitosis, neurofibromin is an integral part of the spindle, while its depletion leads to aberrant chromosome congression, possibly explaining the development of chromosomal instability in Neurofibromatosis type-1. Read the Editorial Highlight for this article on page 11. Cover Image for this issue: doi: 10.1111/jnc.13300.

Exposure to a mildly aversive early life experience leads to prefrontal cortex deficits in the rat.

Aversive early life experiences in humans have been shown to result in deficits in the function of the prefrontal cortex (PFC). In an effort to elucidate possible neurobiological mechanisms involved, we investigated in rats, the effects of a mildly aversive early experience on PFC structure and function. The early experience involved exposure of rat pups during postnatal days (PND) 10-13 to a T-maze in which they search for their mother, but upon finding her are prohibited contact with her, thus being denied the expected reward (DER). We found that the DER experience resulted in adulthood in impaired PFC function, as assessed by two PFC-dependent behavioral tests [attention set-shifting task (ASST) and fear extinction]. In the ASST, DER animals showed deficits specifically in the intra-dimensional reversal shifts and a lower activation-as determined by c-Fos immunohistochemistry-of the medial orbital cortex (MO), a PFC subregion involved in this aspect of the task. Furthermore, the DER experience resulted in decreased glutamatergic neuron and dendritic spine density in the MO and infralimbic cortex (IL) in the adult brain. The decreased neuronal density was detected as early as PND12 and was accompanied by increased micro- and astroglia-density in the MO/IL.

Rat dams exposed repeatedly to a daily brief separation from the pups exhibit increased maternal behavior, decreased anxiety and altered levels of receptors for estrogens (ERα, ERß), oxytocin and serotonin (5-HT1A) in their brain.

In the present study we investigated the neurobiological mechanisms underlying expression of maternal behavior. Increased maternal behavior was experimentally induced by a brief 15-min separation between the mother and the pups during postnatal days 1 to 22. On postnatal days (PND) 12 and 22, we determined in experimental and control dams levels of anxiety in the elevated plus maze (EPM) as well as the levels of receptors for estrogens (ERα, ERß), oxytocin (OTR) and serotonin (5-HT1AR) in areas of the limbic system (prefrontal cortex-PFC, hippocampus, lateral septum-SL, medial preoptic area-MPOA, shell of nucleus accumbens-nAc-Sh, central-CeA and basolateral-BLA amygdala), involved in the regulation of maternal behavior. Experimental dams, which showed increased maternal behavior towards their offspring, displayed reduced anxiety in the EPM on both PND12 and PND22. These behavioral differences could be attributed to neurochemical alterations in their brain: On both PND12 and PND22, experimental mothers had higher levels of ERα and OTRs in the PFC, hippocampus, CeA, SL, MPOA and nAc-Sh. The experimental manipulation-induced increase in ERß levels was less widespread, being localized in PFC, the hippocampal CA2 area, MPOA and nAc-Sh. In addition, 5-HT1ARs were reduced in the PFC, hippocampus, CeA, MPOA and nAc-Sh of the experimental mothers. Our results show that the experience of the daily repeated brief separation from the pups results in increased brain ERs and OTRs, as well as decreased 5-HT1ARs in the dam's brain; these neurochemical changes could underlie the observed increase in maternal behavior and the reduction of anxiety.