Silencing the enhancer of zeste homologue 2,Ezh2,represses axon regeneration of dorsal root ganglion neurons

Recovery from injury to the peripheral nervous system is different from that of the central nervous system in that it can lead to gene reprogramming that can induce the expression of a series of regeneration-associated genes.This eventually leads to axonal regeneration of injured neurons.Although some regeneration-related genes have been identified,the regulatory network underlying axon regeneration remains largely unknown.To explore the regulator of axon regeneration,we performed RNA sequencing of lumbar L4 and L5 dorsal root ganglion(DRG)neurons at different time points(0,3,6,12 hours,1,3 and 7 days)after rat sciatic nerve crush.The isolation of neurons was carried out by laser capture microscopy combined with NeuN immunofluorescence staining.We found 1228 differentially expressed genes in the injured sciatic nerve tissue.The hub genes within these differentially expressed genes include Atf3,Jun,Myc,Ngf,Fgf2,Ezh2,Gfap and Il6.We verified that the expression of the enhancer of zeste homologue 2 gene(Ezh2)was up-regulated in DRG neurons after injury,and this up-regulation differed between large-and small-sized dorsal root ganglion neurons.To investigate whether the up-regulation of Ezh2 impacts axonal regeneration,we silenced Ezh2 with siRNA in cultured DRG neurons and found that the growth of the newborn axons was repressed.In our investigation into the regulatory network of Ezh2 by interpretive phenomenal analysis,we found some regulators of Ezh2(including Erk,Il6 and Hif1a)and targets(including Atf3,Cdkn1a and Smad1).Our findings suggest that Ezh2,as a nerve regeneration-related gene,participates in the repair of the injured DRG neurons,and knocking down the Ezh2 in vitro inhibits the axonal growth of DRG neurons.All the experimental procedures approved by the Administration Committee of Experimental Animals of Jiangsu Province of China(approval No.S20191201-201)on March 21,2019.

Low-frequency electrical stimulation improves neurite outgrowth of dorsal root ganglion neurons in vitro via upregulating Ca^(2+)-mediated brain-derived neurotrophic factor expression

Short-term, low-frequency electrical stimulation of neural tissues significantly enhances axonal regeneration of peripheral nerves following injury. However, little is known about the mechanisms of electrical stimulation to induce neurite outgrowth. In the present study, short-term, low-frequency electrical stimulation, using identical stimulation parameters of in vivo experiments, was administered to in vitro dorsal root ganglion （DRG） neurons. Enhanced neurite outgrowth, as well as synthesis and release of brain-derived neurotrophic factor （BDNF）, were examined in electrical stimulation-treated DRG neuronal cultures. Because the effects of electrical stimulation on neuronal intracellular signaling molecules are less reported, classic calcium intracellular signals are directly or indirectly involved in electrical stimulation effects on neurons. Cultured DRG neurons were pretreated with the calcium channel blocker nifedipine, followed by electrical stimulation. Results suggested that electrical stimulation not only promoted in vitro neurite outgrowth, but also enhanced BDNF expression. However, nifedipine reduced electrical stimulation-enhanced neurite outgrowth and BDNF biosynthesis. These results suggest that the promoting effects of electrical stimulation on DRG neurite outgrowth could be associated with altered calcium influx, which is involved induction of neuronal BDNF expression and secretion.

Combination of Quercetin, Cinnamaldehyde and Hirudin Protects Rat Dorsal Root Ganglion Neurons against High Glucose-Induced Injury through Nrf-2/HO-1 Activation and NF-κB Inhibition

Objective： TO examine the effects of the combination of quercetin （Q）, cinnamaldehyde （C） and hirudin （H）, a Chinese medicine formula on high glucose （HG）-induced apoptosis of cultured dorsal root ganglion （DRG） neurons. Methods： DRG neurons exposed to HG （45 mmol/L） for 24 h were employed as an in vitro model of diabetic neuropathy. Cell viability, reactive oxygen species （ROS） level and apoptosis were determined. The expression of nuclear factor of Kappa B （NF- κB）, inhibitory kappa B α （IκBα ）, phosphorylated IκBα and Nf-E2 related factor 2 （Nrf2） were examined using reverse transcription-polymerase chain reaction （RT-PCR） and Western blot assay. The expression of hemeoxygenase-1 （HO-1）, interleukin-6 （IL-6）, tumor necrosis factor （TNF-α） and caspase-3 were also examined by RT-PCR and Western blot assay. Results： HG treatment markedly increased DRG neuron apoptosis via increasing intracellular ROS level and activating the NF- κB signaling pathway （P〈0.05）. Co-treatment with Q, C, H and their combination decreased HG-induced caspase-3 activation and apoptosis （P〈0.05 or P〈0.01）. The expressions of NF- κB, IL-6 and TNF-α were down- regulated, and Nrf2/HO-1 expression was up-regulated （P〈0.05 or P〈0.01）. QCH has better effect in scavenging ROS, activating Nrf-2/HO-1, and down-regulating the NF- κB pathway than other treatment group. Conclusions： DRG neurons＇ apoptosis was increased in diabetic conditions, which was reduced by QCH formula treatment. The possible reason could be activating Nrf-2/HO-1 pathway, scavenging ROS, and inhibition of NF- κB activation. The effect of QCH combination was better than each monomer or the combination of the two monomers.

Physiological relevance of soma secretion in dorsal root ganglion neurons

Dorsal root ganglion (DRG) cells are primary sensory neurons and are important in pain. Recently, a distinct type of exocytosis, Ca2+ independent but voltage-dependent, is found

Effects of Hirudin on High Glucose-Induced Oxidative Stress and Inflammatory Pathway in Rat Dorsal Root Ganglion Neurons

Objective:To investigate protective effects of hirudin on oxidative stress and apoptosis of spinal dorsal root ganglion cells in high-glucose rats at the cellular and molecular level.Methods:Dorsal root ganglion neurons(DRGn)were harvested from embryonic day in 15 SD rats,purified and identificated after primary culture.They were divided into the normal control group,high-glucose(HG)group,positive control(alpha-lipoic acid,ALA)group,low-dose hirudin group(H1),medium-dose hirudin group(H2)and high-dose hirudin group(H3).The control group was cultured by neuron specific culture medium,while the HG group was cultured by neuron specific culture medium and 20 mmol/L glucose(HG medium).The hirudin groups were cultured by HG medium+0.25 IU/mL hirudin(H1),HG medium+0.5 IU/mL hirudin(H2)and HG medium+1 IU/mL hirudin(H3).The ALA group was cultured by HG medium +100μmol/L ALA.3-(4,5-dimethylthiazol-2-yl)-2,5-diphenylt etrazolium bromide(MTT)assay was used to explore the optimum concentration and intervention time.Flow cytometry assay was used to detect the level of reactive oxygen series(ROS).Western blot and quantificational realtime polymerase chain reaction(qRT-PCR)were used to detect the expression of protein and mRNA of nuclear factor erythroid 2-related factor 2(Nrf-2),hemeoxygence-1(HO-1),nuclear factor-κB(NF-κB)and Caspase-3.TUNEL assay was used to test the apoptosis rate of different groups.Results:After 24 h of culture,the cell activity of hirudin and ALA groups were higher than that of HG group,and there was a statistical difference between the H1 group and HG group(P<0.05).In hirudin groups,the apoptosis rate of cells,the expression of activated Caspase-3 protein and Caspase-3 mRNA were lower than those of HG group(P<0.01),higher than those of ALA group(P<0.01 or P<0.05).The ROS level of hirudin groups was higher than that of ALA group(P<0.01),lower than that of HG group(P<0.01 or P<0.05).The expression of NF-κB(P65)protein in H3 group were lower than those of HG group(P<0.05).The expression of Nrf-2 protein in hirudin groups was higher than that of HG group(P<0.01),lower than that of ALA group(P<0.01 or P<0.05).The expression of HO-1 protein in hirudin groups was lower than that of ALA group(P<0.01 or P<0.05),higher than that of HG group(P<0.01 or P<0.05).Conclusions:The activity of DRGn cells can be promoted by hirudin under HG conditions.The effects of hirudin on the inhibition of HG on DRGn cells damage mainly include scavenging ROS,up-regulating Nrf-2/HO-1 pathway,inhibiting activation of NF-κB pathway,down-regulating the expression of and Caspase-3 and reducing DRGn cell apoptosis.

Pulsed electrical stimulation protects neurons in the dorsal root and anterior horn of the spinal cord after peripheral nerve injury

Most studies on peripheral nerve injury have focused on repair at the site of injury, but very few have examined the effects of repair strategies on the more proximal neuronal cell bodies. In this study, an approximately 10-mm-long nerve segment from the ischial tuberosity in the rat was transected and its proximal and distal ends were inverted and sutured. The spinal cord was subjected to pulsed electrical stimulation at T10 and L3, at a current of 6.5 m A and a stimulation frequency of 15 Hz, 15 minutes per session, twice a day for 56 days. After pulsed electrical stimulation, the number of neurons in the dorsal root ganglion and anterior horn was increased in rats with sciatic nerve injury. The number of myelinated nerve fibers was increased in the sciatic nerve. The ultrastructure of neurons in the dorsal root ganglion and spinal cord was noticeably improved. Conduction velocity of the sciatic nerve was also increased. These results show that pulsed electrical stimulation protects sensory neurons in the dorsal root ganglia as well as motor neurons in the anterior horn of the spinal cord after peripheral nerve injury, and that it promotes the regeneration of peripheral nerve fibers.

Rab27a/Slp2-a complex is involved in Schwann cell myelination

Myelination of Schwann cells in the peripheral nervous system is an intricate process involving myelin protein trafficking. Recently, the role and mechanism of the endosomal/lysosomal system in myelin formation were emphasized. Our previous results demonstrated that a small GTPase Rab27a regulates lysosomal exocytosis and myelin protein trafficking in Schwann cells. In this present study, we established a dorsal root ganglion （DRG） neuron and Schwann cell co-culture model to identify the signals associated with Rab27a during myelination. First, Slp2-a, as the Rab27a effector, was endogenously expressed in Schwann cells. Second, Rab27a expression significantly increased during Schwann cell myelination. Finally, Rab27a and Slp2-a silencing in Schwann cells not only reduced myelin protein expression, but also impaired formation of myelin-like membranes in DRG neuron and Schwann cell co-cultures. Our findings suggest that the Rab27a/ Slp2-a complex affects Schwann cell myelination in vitro.

Potentiation of PIEZO2 mechanically-activated currents in sensory neurons mediates vincristine-induced mechanical hypersensitivity

Vincristine,a widely used chemotherapeutic agent for treating different cancer,often induces severe peripheral neuropathic pain.A common symptom of vincristine-induced peripheral neuropathic pain is mechanical allodynia and hyperalgesia.However,mechanisms underlying vincristine-induced mechanical allodynia and hyperalgesia are not well understood.In the present study,we show with behavioral assessment in rats that vincristine induces mechanical allodynia and hyperalgesia in a PIEZO2 channel-dependent manner since gene knockdown or pharmacological inhibition of PIEZO2 channels alleviates vincristine-induced mechanical hypersensitivity.Electrophysiological results show that vincristine potentiates PIEZO2 rapidly adapting(RA)mechanically-activated(MA)currents in rat dorsal root ganglion(DRG)neurons.We have found that vincristine-induced potentiation of PIEZO2 MA currents is due to the enhancement of static plasma membrane tension(SPMT)of these cells following vincristine treatment.Reducing SPMT of DRG neurons by cytochalasin D(CD),a disruptor of the actin filament,abolishes vincristine-induced potentiation of PIEZO2 MA currents,and suppresses vincristine-induced mechanical hypersensitivity in rats.Collectively,enhancing SPMT and subsequently potentiating PIEZO2 MA currents in primary afferent neurons may be an underlying mechanism responsible for vincristineinduced mechanical allodynia and hyperalgesia in rats.Targeting to inhibit PIEZO2 channels may be an effective analgesic method to attenuate vincristine-induced mechanical hypersensitivity.

End-to-side neurorrhaphy repairs peripheral nerve injury：sensory nerve induces motor nerve regeneration

End-to-side neurorrhaphy is an option in the treatment of the long segment defects of a nerve.It involves suturing the distal stump of the disconnected nerve（recipient nerve） to the side of the intimate adjacent nerve（donor nerve）.However,the motor-sensory specificity after end-to-side neurorrhaphy remains unclear.This study sought to evaluate whether cutaneous sensory nerve regeneration induces motor nerves after end-to-side neurorrhaphy.Thirty rats were randomized into three groups：（1） end-to-side neurorrhaphy using the ulnar nerve（mixed sensory and motor） as the donor nerve and the cutaneous antebrachii medialis nerve as the recipient nerve;（2） the sham group：ulnar nerve and cutaneous antebrachii medialis nerve were just exposed;and（3） the transected nerve group：cutaneous antebrachii medialis nerve was transected and the stumps were turned over and tied.At 5 months,acetylcholinesterase staining results showed that 34% ± 16% of the myelinated axons were stained in the end-to-side group,and none of the myelinated axons were stained in either the sham or transected nerve groups.Retrograde fluorescent tracing of spinal motor neurons and dorsal root ganglion showed the proportion of motor neurons from the cutaneous antebrachii medialis nerve of the end-to-side group was 21% ± 5%.In contrast,no motor neurons from the cutaneous antebrachii medialis nerve of the sham group and transected nerve group were found in the spinal cord segment.These results confirmed that motor neuron regeneration occurred after cutaneous nerve end-to-side neurorrhaphy.