Protein kinase B is involved in Nogo-66 inhibiting neurite outgrowth in PC12 cells

LncRNA FTX Involves in the Nogo-66-Induced Inhibition of Neurite Outgrowth Through Regulating PDK1/PKB/GSK-3β Pathway

Nogo-66 can inhibit neurite outgrowth, while its regulation mechanisms have not been fully elucidated. Recent studies prove that lncRNAs are involved in neurite outgrowth. This study was aimed to investigate whether lncRNA FTX was involved in Nogo-66-induced inhibition of neurite outgrowth and explore the potential mechanism. The expression of relative genes was detected by qRT-PCR and western blot. The function of FTX was determined by overexpression and knockdown techniques. The interaction between FTX and PDK1 was evaluated by RIP and RNA pull-down assays. FTX expression was downregulated by Nogo-66 in PC12 cells. Nogo-66-induced inhibition of neurite outgrowth was relieved by FTX overexpression. FTX bound to PDK1 protein to disturb the interaction between PDK1 and E3 ubiquitin ligase RNF126, thereby blocked the ubiquitination degradation of PDK1 and elevated PDK1 protein level. Mechanically, FTX involved in the Nogo-66-induced inhibition of neurite outgrowth through the PDK1/PKB/GSK-3β pathway. In SCI rats, FTX knockdown inhibited neurite outgrowth induced by the receptor antagonist of Nogo-66. The present results suggested that FTX took part in Nogo-66-inhibited neurite outgrowth, and FTX exerted its function through regulating PDK1/PKB/GSK-3β pathway.

Extracellular Pgk1 enhances neurite outgrowth of motoneurons through Nogo66/NgR-independent targeting of NogoA

NogoA inhibits neurite outgrowth of motoneurons (NOM) through interaction with its receptors, Nogo66/NgR. Inhibition of Nogo receptors rescues NOM, but not to the extent exhibited by NogoA-knockout mice, suggesting the presence of other pathways. We found that NogoA-overexpressing muscle cells reduced phosphoglycerate kinase 1 (Pgk1) secretion, resulting in inhibiting NOM. Apart from its glycolytic role and independent of the Nogo66 pathway, extracellular Pgk1 stimulated NOM by triggering a reduction of p-Cofilin-S3, a growth cone collapse marker, through decreasing a novel Rac1-GTP/p-Pak1-T423/p-P38-T180/p-MK2-T334/p-Limk1-S323/p-Cofilin-S3 molecular pathway. Not only did supplementary Pgk1 enhance NOM in defective cells, but injection of Pgk1 rescued denervation in muscle-specific NogoA-overexpression of zebrafish and an Amyotrophic Lateral Sclerosis mouse model, SOD1 G93A. Thus, Pgk1 secreted from muscle is detrimental to motoneuron neurite outgrowth and maintenance.

Stereotactic injection of shrna GSK-3β-AAV promotes axonal regeneration after spinal cord injury

Evidence suggested that glycogen synthase kinase-3β (GSK-3β) is involved in Nogo-66 inhibiting axonal regeneration in vitro, but its effect in vivo was poorly understood. We showed that stereotactic injection of shRNA GSK-3β-adeno associated virus (GSK-3β-AAV) diminished syringomyelia and promoted axonal regeneration after spinal cord injury (SCI), using stereotactic injection of shRNA GSK-3β-AAV (tested with Western blotting and RT-PCR) into the sensorimotor cortex of rats with SCI and by the detection of biotin dextran amine (BDA)-labeled axonal regeneration. We also determined the right position to inject into the sensorimotor cortex. Our findings consolidate the hypothesis that downregulation of GSK-3β promotes axonal regeneration after SCI.

Phenotypic Screening of Small-Molecule Inhibitors: Implications for Therapeutic Discovery and Drug Target Development in Traumatic Brain Injury

The inability of central nervous system (CNS) neurons to regenerate damaged axons and dendrites following traumatic brain injury (TBI) creates a substantial obstacle for functional recovery. Apoptotic cell death, deposition of scar tissue, and growth-repressive molecules produced by glia further complicate the problem and make it challenging for re-growing axons to extend across injury sites. To date, there are no approved drugs for the treatment of TBI, accentuating the need for relevant leads. Cell-based and organotypic bioassays can better mimic outcomes within the native CNS microenvironment than target-based screening methods and thus should speed the discovery of therapeutic agents that induce axon or dendrite regeneration. Additionally, when used to screen focused chemical libraries such as small-molecule protein kinase inhibitors, these assays can help elucidate molecular mechanisms involved in neurite outgrowth and regeneration as well as identify novel drug targets. Here, we describe a phenotypic cellular (high content) screening assay that utilizes brain-derived primary neurons for screening small-molecule chemical libraries.

Dealing with Danger in the CNS: The Response of the Immune System to Injury

Fighting pathogens and maintaining tissue homeostasis are prerequisites for survival. Both of these functions are upheld by the immune system, though the latter is often overlooked in the context of the CNS. The mere presence of immune cells in the CNS was long considered a hallmark of pathology, but this view has been recently challenged by studies demonstrating that immunological signaling can confer pivotal neuroprotective effects on the injured CNS. In this review, we describe the temporal sequence of immunological events that follow CNS injury. Beginning with immediate changes at the injury site, including death of neural cells and release of damage-associated molecular patterns (DAMPs), and progressing through innate and adaptive immune responses, we describe the cascade of inflammatory mediators and the implications of their post-injury effects. We conclude by proposing a revised interpretation of immune privilege in the brain, which takes beneficial neuro-immune communications into account.

Function of Nogo-A/Nogo-A receptor in Alzheimer's disease

Nogo-A is a protein inhibiting axonal regeneration, which is considered a major obstacle to nerve regeneration after injury in mammals. Rapid progress has been achieved in new physiopathological function of Nogo-A in Alzheimer's disease in the past decade. Recent research shows that through binding to Nogo-A receptor, Nogo-A plays an important role in Alzheimer's disease (AD) pathogenesis. Particularly, Nogo-A/Nogo-A receptors modulate the generation of amyloid β-protein (Aβ), which is thought to be a major cause of AD. This review describes the recent development of Nogo-A, Nogo-A receptor, and downstream signaling involved in AD and pharmacological basis of therapeutic drugs. We concluded the Nogo-A/Nogo-A receptor provide new insight into potential mechanisms and promising therapy strategies in AD.

GSK-3β activation mediates Nogo-66-induced inhibition of neurite outgrowth in N2a cells

The axons of the adult mammalian brain and spinal cord fail to regenerate after injury, and it has been suggested that Nogo-66 could prevent CNS axon repair. However, the mechanism of Nogo-66 inhibiting neurite outgrowth remains unknown. Our previous results indicated that protein kinase B (PKB) is involved in the inhibition of the neurite outgrowth by Nogo-66. Glycogen synthase kinase-3β (GSK-3β) is implicated in many processes in the nervous system, including differentiation, specification, polarity, plasticity and axon growth. In addition, GSK-3β is one of the most important molecules downstream of PKB. In the present study, we report on the role of GSK-3β signaling on Nogo-66-treated mouse neuroblastoma N2a cells. Nogo-66 reduced the phosphorylation of GSK-3β at Ser9 in N2a cells. In contrast, pretreatment with SB216763, a specific inhibitor of GSK-3β, resulted in an amelioration of neurite outgrowth by Nogo-66, compared with the Nogo-66 alone group (P<0.05). Moreover, we performed RNA interference experiments to knock down GSK-3β expression levels in N2a cells via transient transfection of shRNA plasmids. The inhibition of neurite outgrowth by Nogo-66 was subdued in shRNA cells, compared to the non-RNAi cells (P<0.05). Taken together, these data suggest that GSK-3β is involved in the inhibition by Nogo-66 of neurite outgrowth in N2a cells.