RhoA/Rho kinase signaling in the spinal cord and diabetic painful neuropathy

[CASE REPORT] Homozygous N-terminal missense variant in PLEKHG5 associated with intermediate CMT: a case report

Mutations in PLEKHG5, a pleckstrin homology domain containing member of the GEF family, are associated with distal spinal muscular atrophy and intermediate Charcot-Marie-Tooth disease. Here, we describe an isolated case with distal intermediate neuropathy with scapular winging. By whole exome sequencing, we identified the homozygous PLEKHG5 Arg97Gln missense mutation, located in the N-terminal region of the protein. This mutation resides between a zinc-finger motif and a RBD domain, involved in binding rnd3, a RhoA effector protein. We conclude that based on the characteristic phenotype presented by the patient and the supportive genetic findings, the PLEKHG5 mutation is the causative variant.

Neurobiological Opportunities in Diabetic Polyneuropathy

This review highlights a selection of potential translational directions for the treatment of diabetic polyneuropathy (DPN) currently irreversible and without approved interventions beyond pain management. The list does not include all diabetic targets that have been generated over several decades of research but focuses on newer work. The emphasis is firstly on approaches that support the viability and growth of peripheral neurons and their ability to withstand a barrage of diabetic alterations. We include a section describing Schwann cell targets and finally how mitochondrial damage has been a common element in discussing neuropathic damage. Most of the molecules and pathways described here have not yet reached clinical trials, but many trials have been negative to date. Nonetheless, these failures clear the pathway for new thoughts over reversing DPN.

Exosomes Derived From Schwann Cells Ameliorate Peripheral Neuropathy in Type 2 Diabetic Mice

Schwann cell-derived exosomes communicate with dorsal root ganglia (DRG) neurons. The current study investigated the therapeutic effect of exosomes derived from healthy Schwann cells (SC-Exos) on diabetic peripheral neuropathy (DPN). We found that intravenous administration of SC-Exos to type 2 diabetic db/db mice with peripheral neuropathy remarkably ameliorated DPN by improving sciatic nerve conduction velocity and increasing thermal and mechanical sensitivity. These functional improvements were associated with the augmentation of epidermal nerve fibers and remyelination of sciatic nerves. Quantitative RT-PCR and Western blot analysis of sciatic nerve tissues showed that SC-Exo treatment reversed diabetes-reduced mature form of miRNA (miR)-21, -27a, and -146a and diabetes-increased semaphorin 6A (SEMA6A); Ras homolog gene family, member A (RhoA); phosphatase and tensin homolog (PTEN); and nuclear factor-κB (NF-κB). In vitro data showed that SC-Exos promoted neurite outgrowth of diabetic DRG neurons and migration of Schwann cells challenged by high glucose. Collectively, these novel data provide evidence that SC-Exos have a therapeutic effect on DPN in mice and suggest that SC-Exo modulation of miRs contributes to this therapy.

Involvement of inhibition of RhoA/Rho kinase signaling in simvastatin-induced amelioration of neuropathic pain

Small molecular G-protein plays a key role in several diseases. This study was designed to reveal the role of RhoA signaling in the pathophysiology of neuropathic pain in mice. Partial sciatic nerve injury caused thermal hyperalgesia, mechanical allodynia, and increased plasma membrane translocation of RhoA in the lumber spinal cord. GFAP-immunoreactivity (ir), Iba-1-ir, and Rho kinase 2 (ROCK2-ir) was also increased in the ipsilateral spinal dorsal horn of nerve-ligated mice. Moreover, partial nerve ligation increased the expression of phosphorylated myristoylated alanine-rich protein kinase C substrate (MARCKS)-ir in the ipsilateral spinal dorsal horn. Daily intrathecal administration of simvastatin, beginning 3days before nerve injury, completely blocked all these changes in nerve-ligated mice. Pharmacological inhibition of ROCK also attenuated the increased expression of GFAP-ir and phosphorylated MARCKS-ir. Together, it is suggested that astrogliosis initiated by the activation of RhoA/ROCK signaling results in MARCKS phosphorylation in nerve terminals, which leads to hyperalgesia in neuropathic pain. Furthermore, simvastatin exerts antihyperalgesic and antiallodynic effects through the inhibition of spinal RhoA activation.

Inhibition of the Rho/Rho kinase pathway prevents lipopolysaccharide-induced hyperalgesia and the release of TNF-α and IL-1β in the mouse spinal cord

Administration of lipopolysaccharide (LPS) by various routes produces profound inflammatory pain hypersensitivity. However, the molecular events that induce this response remain largely uncharacterized. In the present study, we sought to elucidate the role of the Rho/Rho kinase (ROCK) pathway in the release of tumor necrosis factor-α (TNF-α) and interleukin 1β (IL-1β) following injection of LPS into the mouse paw, which is associated with nociceptive behavior. The spinal cord of LPS-treated mice showed increased active GTP-bound RhoA and upregulation of ROCK2 and c-fos compared to the normal saline group. Furthermore, the inflammation-related cytokines TNF-α and IL-1β were markedly increased in the spinal dorsal horn after intraplantar injection of LPS. However, the latter effects were prevented by prophylactic intrathecal administration of the Rho inhibitor (C3 exoenzyme) or the ROCK inhibitor (Y27632). Collectively, our results suggest that the Rho/ROCK signaling pathway plays a critical role in LPS-induced inflammatory pain and that this pathway is coincident with the release of the pro-nociceptive cytokines TNF-α and IL-1β, which produces hyperalgesia.

Dendritic spine dysgenesis in neuropathic pain

The failure of neuropathic pain to abate even years after trauma suggests that adverse changes to synaptic function must exist in a chronic pathological state in nociceptive pathways. The chronicity of neuropathic pain therefore underscores the importance of understanding the contribution of dendritic spines--micron-sized postsynaptic structures that represent modifiable sites of synaptic contact. Historically, dendritic spines have been of great interest to the learning and memory field. More recent evidence points to the exciting implication that abnormal dendritic spine structure following disease or injury may represent a "molecular memory" for maintaining chronic pain. Dendritic spine dysgenesis in dorsal horn neurons contributes to nociceptive hyperexcitability associated with neuropathic pain, as demonstrated in multiple pain models, i.e., spinal cord injury, peripheral nerve injury, diabetic neuropathy, and thermal burn injury. Because of the relationship between dendritic spine structure and neuronal function, a thorough investigation of dendritic spine behavior in the spinal cord is a unique opportunity to better understand the mechanisms of sensory dysfunction after injury or disease. At a conceptual level, a spinal memory mechanism that engages dendritic spine remodeling would also contribute to a broad range of intractable neurological conditions. Molecules involved in regulating dendritic spine plasticity may offer novel targets for the development of effective and durable therapies for neurological disease.

[Effect of repeated oral treatment with etoposide on the expression of intestinal P-glycoprotein and oral morphine analgesia]

Currently, the World Health Organization recommends oral administration of opioid analgesics for patients with cancer to treat cancer-related pain from the initial stage of treatment. Furthermore, many anticancer drugs have been newly-developed and approved as oral form. Because of this trend, the chances of drug-drug interactions between anticancer drugs and opioid analgesics during absorption process from the intestine are likely to increase. To investigate these possible drug-drug interactions, we have focused on intestinal P-glycoprotein (P-gp) which regulates the absorption of various substrate drugs administered orally. Previously, we have found that repeated oral treatment with etoposide (ETP), an anticancer drug, attenuates analgesia of oral morphine, a substrate drug for P-gp, by increasing the expression and activity of intestinal P-gp. However, the mechanism by which ETP treatment increases the intestinal P-gp expression and decreases oral morphine analgesia remains unclear. RhoA, a small G-protein, and ROCK, an effector of RhoA, pathway has been attracted attention with regard to their involvement in the regulatory mechanism of the expression and activity of P-gp. Interestingly, this pathway is activated in response to various signaling induced by some anticancer drugs. Furthermore, it has been reported that ezrin/radixin/moesin (ERM) play a key role in the plasma membrane localization of P-gp, and that RhoA/ROCK pathway regulates the activation process of ERM. This review article introduces the result of our previous research as well as recent findings on the involvement of ERM via activation of RhoA/ROCK in the increased expression of intestinal P-gp and decreased oral morphine analgesia induced by repeated oral treatment with ETP.

Maladaptive dendritic spine remodeling contributes to diabetic neuropathic pain

Diabetic neuropathic pain imposes a huge burden on individuals and society, and represents a major public health problem. Despite aggressive efforts, diabetic neuropathic pain is generally refractory to available clinical treatments. A structure-function link between maladaptive dendritic spine plasticity and pain has been demonstrated previously in CNS and PNS injury models of neuropathic pain. Here, we reasoned that if dendritic spine remodeling contributes to diabetic neuropathic pain, then (1) the presence of malformed spines should coincide with the development of pain, and (2) disrupting maladaptive spine structure should reduce chronic pain. To determine whether dendritic spine remodeling contributes to neuropathic pain in streptozotocin (STZ)-induced diabetic rats, we analyzed dendritic spine morphology and electrophysiological and behavioral signs of neuropathic pain. Our results show changes in dendritic spine shape, distribution, and shape on wide-dynamic-range (WDR) neurons within lamina IV-V of the dorsal horn in diabetes. These diabetes-induced changes were accompanied by WDR neuron hyperexcitability and decreased pain thresholds at 4 weeks. Treatment with NSC23766 (N(6)-[2-[[4-(diethylamino)-1-methylbutyl]amino]-6-methyl-4-pyrimidinyl]-2-methyl-4,6-quinolinediamine trihydrochloride), a Rac1-specific inhibitor known to interfere with spine plasticity, decreased the presence of malformed spines in diabetes, attenuated neuronal hyperresponsiveness to peripheral stimuli, reduced spontaneous firing activity from WDR neurons, and improved nociceptive mechanical pain thresholds. At 1 week after STZ injection, animals with hyperglycemia with no evidence of pain had few or no changes in spine morphology. These results demonstrate that diabetes-induced maladaptive dendritic spine remodeling has a mechanistic role in neuropathic pain. Molecular pathways that control spine morphogenesis and plasticity may be promising future targets for treatment.

Effects of exogenous galanin on neuropathic pain state and change of galanin and its receptors in DRG and SDH after sciatic nerve-pinch injury in rat

A large number of neuroanatomical, neurophysiologic, and neurochemical mechanisms are thought to contribute to the development and maintenance of neuropathic pain. However, mechanisms responsible for neuropathic pain have not been completely delineated. It has been demonstrated that neuropeptide galanin (Gal) is upregulated after injury in the dorsal root ganglion (DRG) and spinal dorsal horn (SDH) where it plays a predominantly antinociceptive role. In the present study, sciatic nerve-pinch injury rat model was used to determine the effects of exogenous Gal on the expression of the Gal and its receptors (GalR1, GalR2) in DRG and SDH, the alterations of pain behavior, nerve conduction velocity (NCV) and morphology of sciatic nerve. The results showed that exogenous Gal had antinociceptive effects in this nerve-pinch injury induced neuropathic pain animal model. It is very interesting that Gal, GalR1 and GalR2 change their expression greatly in DRG and SDH after nerve injury and intrathecal injection of exougenous Gal. Morphological investigation displays a serious damage after nerve-pinch injury and an amendatory regeneration after exogenous Gal treatment. These findings imply that Gal, via activation of GalR1 and/or GalR2, may have neuroprotective effects in reducing neuropathic pain behaviors and improving nerve regeneration after nerve injury.