Hsp27 and axonal growth in adult sensory neurons in vitro

A Charcot-Marie-Tooth-Causing Mutation in HSPB1 Decreases Cell Adaptation to Repeated Stress by Disrupting Autophagic Clearance of Misfolded Proteins

Charcot-Marie-Tooth (CMT) disease is the most common inherited neurodegenerative disorder with selective degeneration of peripheral nerves. Despite advances in identifying CMT-causing genes, the underlying molecular mechanism, particularly of selective degeneration of peripheral neurons remains to be elucidated. Since peripheral neurons are sensitive to multiple stresses, we hypothesized that daily repeated stress might be an essential contributor to the selective degeneration of peripheral neurons induced by CMT-causing mutations. Here, we mainly focused on the biological effects of the dominant missense mutation (S135F) in the 27-kDa small heat-shock protein HSPB1 under repeated heat shock. HSPB1S135F presented hyperactive binding to both α-tubulin and acetylated α-tubulin during repeated heat shock when compared with the wild type. The aberrant interactions with tubulin prevented microtubule-based transport of heat shock-induced misfolded proteins for the formation of perinuclear aggresomes. Furthermore, the transport of autophagosomes along microtubules was also blocked. These results indicate that the autophagy pathway was disrupted, leading to an accumulation of ubiquitinated protein aggregates and a significant decrease in cell adaptation to repeated stress. Our findings provide novel insights into the molecular mechanisms of HSPB1S135F-induced selective degeneration of peripheral neurons and perspectives for targeting autophagy as a promising therapeutic strategy for CMT neuropathy.

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.

Injury-Induced HSP27 Expression in Peripheral Nervous Tissue Is Not Associated with Any Alteration in Axonal Outgrowth after Immediate or Delayed Nerve Repair

We investigated injury-induced heat shock protein 27 (HSP27) expression and its association to axonal outgrowth after injury and different nerve repair models in healthy Wistar and diabetic Goto-Kakizaki rats. By immunohistochemistry, expression of HSP27 in sciatic nerves and DRG and axonal outgrowth (neurofilaments) in sciatic nerves were analyzed after no, immediate, and delayed (7-day delay) nerve repairs (7- or 14-day follow-up). An increased HSP27 expression in nerves and in DRG at the uninjured side was associated with diabetes. HSP27 expression in nerves and in DRG increased substantially after the nerve injuries, being higher at the site where axons and Schwann cells interacted. Regression analysis indicated a positive influence of immediate nerve repair compared to an unrepaired injury, but a shortly delayed nerve repair had no impact on axonal outgrowth. Diabetes was associated with a decreased axonal outgrowth. The increased expression of HSP27 in sciatic nerve and DRG did not influence axonal outgrowth. Injured sciatic nerves should appropriately be repaired in healthy and diabetic rats, but a short delay does not influence axonal outgrowth. HSP27 expression in sciatic nerve or DRG, despite an increase after nerve injury with or without a repair, is not associated with any alteration in axonal outgrowth.

Regional Differences in Heat Shock Protein 25 Expression in Brain and Spinal Cord Astrocytes of Wild-Type and SOD1 G93A Mice

Heterogeneity of glia in different CNS regions may contribute to the selective vulnerability of neuronal populations in neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS). Here, we explored regional variations in the expression of heat shock protein 25 in glia under conditions of acute and chronic stress. Hsp27 (Hsp27; murine orthologue: Hsp25) fulfils a number of cytoprotective functions and may therefore be a possible therapeutic target in ALS. We identified a subpopulation of astrocytes in primary murine mixed glial cultures that expressed Hsp25. Under basal conditions, the proportion of Hsp25-positive astrocytes was twice as high in spinal cord cultures than in cortical cultures. To explore the physiological role of the elevated Hsp25 expression in spinal cord astrocytes, we exposed cortical and spinal cord glia to acute stress, using heat stress and pro-inflammatory stimuli. Surprisingly, we observed no stress-induced increase in Hsp25 expression in either cortical or spinal cord astrocytes. Similarly, exposure to endogenous stress, as modelled in glial cultures from SOD1 G93A-ALS mice, did not increase Hsp25 expression above that observed in astrocytes from wild-type mice. In vivo, Hsp25 expression was greater under conditions of chronic stress present in the spinal cord of SOD1 G93A mice than in wild-type mice, although this increase in expression is likely to be due to the extensive gliosis that occurs in this model. Together, these results show that there are differences in the expression of Hsp25 in astrocytes in different regions of the central nervous system, but Hsp25 expression is not upregulated under acute or chronic stress conditions.

Facial nerve regeneration using silicone conduits filled with ammonia-functionalized graphene oxide and frankincense-embedded hydrogel

Background

Silicone tube (ST) conduits have been accepted as a therapeutic alternative to direct nerve suturing in the treatment of nerve injuries; however, the search for optimal adjuncts to maximize the outcomes is still ongoing. Frankincense (Fr) and graphene oxide (GO) have both been cited as neuroregenerative compounds in the literature. This study assesses the efficacy of these materials using a ST conduit in a rat facial nerve motor neuron axotomy model, distal to the stylomastoid foramen.

Methods

Ammonia-functionalized graphene oxide (NH2-GO) and/or Fr extract were embedded in a collagen-chitosan hydrogel and were injected inside a ST. The ST was inserted in the gap between the axotomized nerve stumps. Return of function in eye closure, blinking reflex, and vibrissae movements were assessed and compared to control groups through 30 days following axotomy. To assess the histological properties of regenerated nerves, biopsies were harvested distal to the axotomy site and were visualized through light and fluorescence microscopy using LFB and anti-MBP marker, respectively.

Results

There was no significant difference in behavioral test results between groups. Histological analysis of the nerve sections revealed increased number of regenerating axons and mean axon diameter in NH2-GO group and decreased myelin surface area in Fr group. Using both NH2-GO and Fr resulted in increased number of regenerated axons and myelin thickness compared to the hydrogel group.

Conclusions

The findings suggest a synergistic effect of the substances above in axon regrowth, notably in myelin regeneration, where Fr supposedly decreases myelin synthesis.

Heat shock response enhanced by cell culture treatment in mouse embryonic stem cell-derived proliferating neural stem cells

Cells have a regulatory mechanism known as heat shock (HS) response, which induces the expression of HS genes and proteins in response to heat and other cellular stresses. Exposure to moderate HS results in beneficial effects, such as thermotolerance and promotes survival, whereas excessive HS causes cell death. The effect of HS on cells depends on both exogenous factors, including the temperature and duration of heat application, and endogenous factors, such as the degree of cell differentiation. Neural stem cells (NSCs) can self-renew and differentiate into neurons and glial cells, but the changes in the HS response of symmetrically proliferating NSCs in culture are unclear. We evaluated the HS response of homogeneous proliferating NSCs derived from mouse embryonic stem cells during the proliferative phase and its effect on survival and cell death in vitro. The number of adherent cells and the expression ratios of HS protein (Hsp)40 and Hsp70 genes after exposure to HS for 20 min at temperatures above 43°C significantly increased with the extension of the culture period before exposure to HS. In contrast, caspase activity was significantly decreased by extension of the culture period before exposure to HS and suppressed the decrease in cell viability. These results suggest that the culture period before HS remarkably affects the HS response, influencing the expression of HS genes and cell survival of proliferating NSCs in culture.

Neuroinflammatory processes are augmented in mice overexpressing human heat-shock protein B1 following ethanol-induced brain injury

Background

Heat-shock protein B1 (HSPB1) is among the most well-known and versatile member of the evolutionarily conserved family of small heat-shock proteins. It has been implicated to serve a neuroprotective role against various neurological disorders via its modulatory activity on inflammation, yet its exact role in neuroinflammation is poorly understood. In order to shed light on the exact mechanism of inflammation modulation by HSPB1, we investigated the effect of HSPB1 on neuroinflammatory processes in an in vivo and in vitro model of acute brain injury.

Methods

In this study, we used a transgenic mouse strain overexpressing the human HSPB1 protein. In the in vivo experiments, 7-day-old transgenic and wild-type mice were treated with ethanol. Apoptotic cells were detected using TUNEL assay. The mRNA and protein levels of cytokines and glial cell markers were examined using RT-PCR and immunohistochemistry in the brain. We also established primary neuronal, astrocyte, and microglial cultures which were subjected to cytokine and ethanol treatments. TNFα and hHSPB1 levels were measured from the supernates by ELISA, and intracellular hHSPB1 expression was analyzed using fluorescent immunohistochemistry.

Results

Following ethanol treatment, the brains of hHSPB1-overexpressing mice showed a significantly higher mRNA level of pro-inflammatory cytokines (Tnf, Il1b), microglia (Cd68, Arg1), and astrocyte (Gfap) markers compared to wild-type brains. Microglial activation, and 1 week later, reactive astrogliosis was higher in certain brain areas of ethanol-treated transgenic mice compared to those of wild-types. Despite the remarkably high expression of pro-apoptotic Tnf, hHSPB1-overexpressing mice did not exhibit higher level of apoptosis. Our data suggest that intracellular hHSPB1, showing the highest level in primary astrocytes, was responsible for the inflammation-regulating effects. Microglia cells were the main source of TNFα in our model. Microglia isolated from hHSPB1-overexpressing mice showed a significantly higher release of TNFα compared to wild-type cells under inflammatory conditions.

Conclusions

Our work provides novel in vivo evidence that hHSPB1 overexpression has a regulating effect on acute neuroinflammation by intensifying the expression of pro-inflammatory cytokines and enhancing glial cell activation, but not increasing neuronal apoptosis. These results suggest that hHSPB1 may play a complex role in the modulation of the ethanol-induced neuroinflammatory response.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02070-2.

Spinal heat shock protein 27 participates in PDGFRβ-mediated morphine tolerance through PI3K/Akt and p38 MAPK signalling pathways

BACKGROUND AND PURPOSE

The development of antinociceptive morphine tolerance is a clinically intractable problem. Earlier work has demonstrated the pivotal roles of PDGF and its receptor PDGFRβ in morphine tolerance. Here, we have investigated the role of spinal heat shock protein 27 (HSP27) in morphine tolerance and its relationship with PDGFRβ activation.

EXPERIMENTAL APPROACH

Rats were treated with morphine for 9 days, and its anti-nociceptive effect against thermal pain was evaluated by a tail-flick latency test. Western blot, real-time PCR, immunofluorescent staining, and various antagonists, agonists, and siRNA lentiviral vectors elucidated the roles of HSP27, PDGFRβ, and related signalling pathways in morphine tolerance.

KEY RESULTS

Chronic morphine administration increased expression and phosphorylation of HSP27 in the spinal cord. Down-regulating HSP27 attenuated the development of morphine tolerance. PDGFRβ antagonism inhibited HSP27 activation and attenuated and reversed morphine tolerance. PDGFRβ induction increased HSP27 expression and activation and partly decreased morphine analgesia. PDGFRβ inhibition reduced Akt and p38 MAPK activity in morphine tolerance. PI3K and p38 inhibitors reversed morphine tolerance and suppressed morphine-induced HSP27 phosphorylation.

CONCLUSION AND IMPLICATIONS

This study demonstrated for the first time that spinal HSP27 participates in PDGFRβ-mediated morphine tolerance via the PI3K/Akt and p38 MAPK signalling pathways. These findings suggest a potential clinical strategy for prolonging the antinociceptive effects of opioids during long-term pain control.

Heat Shock Proteins Regulatory Role in Neurodevelopment

Heat shock proteins (Hsps) are a large family of molecular chaperones that are well-known for their roles in protein maturation, re-folding and degradation. While some Hsps are constitutively expressed in certain regions, others are rapidly upregulated in the presence of stressful stimuli. Numerous stressors, including hyperthermia and hypoxia, can induce the expression of Hsps, which, in turn, interact with client proteins and co-chaperones to regulate cell growth and survival. Such interactions must be tightly regulated, especially at critical points during embryonic and postnatal development. Hsps exhibit specific patterns of expression consistent with a spatio-temporally regulated role in neurodevelopment. There is also growing evidence that Hsps may promote or inhibit neurodevelopment through specific pathways regulating cell differentiation, neurite outgrowth, cell migration, or angiogenesis. This review will examine the regulatory role that these individual chaperones may play in neurodevelopment, and will focus specifically on the signaling pathways involved in the maturation of neuronal and glial cells as well as the underlying vascular network.

HSP90 is a chaperone for DLK and is required for axon injury signaling

Peripheral nerve injury induces a robust proregenerative program that drives axon regeneration. While many regeneration-associated genes are known, the mechanisms by which injury activates them are less well-understood. To identify such mechanisms, we performed a loss-of-function pharmacological screen in cultured adult mouse sensory neurons for proteins required to activate this program. Well-characterized inhibitors were present as injury signaling was induced but were removed before axon outgrowth to identify molecules that block induction of the program. Of 480 compounds, 35 prevented injury-induced neurite regrowth. The top hits were inhibitors to heat shock protein 90 (HSP90), a chaperone with no known role in axon injury. HSP90 inhibition blocks injury-induced activation of the proregenerative transcription factor cJun and several regeneration-associated genes. These phenotypes mimic loss of the proregenerative kinase, dual leucine zipper kinase (DLK), a critical neuronal stress sensor that drives axon degeneration, axon regeneration, and cell death. HSP90 is an atypical chaperone that promotes the stability of signaling molecules. HSP90 and DLK show two hallmarks of HSP90-client relationships: (i) HSP90 binds DLK, and (ii) HSP90 inhibition leads to rapid degradation of existing DLK protein. Moreover, HSP90 is required for DLK stability in vivo, where HSP90 inhibitor reduces DLK protein in the sciatic nerve. This phenomenon is evolutionarily conserved in Drosophila Genetic knockdown of Drosophila HSP90, Hsp83, decreases levels of Drosophila DLK, Wallenda, and blocks Wallenda-dependent synaptic terminal overgrowth and injury signaling. Our findings support the hypothesis that HSP90 chaperones DLK and is required for DLK functions, including proregenerative axon injury signaling.

Epigenetic profiling reveals a developmental decrease in promoter accessibility during cortical maturation in vivo

Axon regeneration in adult central nervous system (CNS) is limited in part by a developmental decline in the ability of injured neurons to re-express needed regeneration associated genes (RAGs). Adult CNS neurons may lack appropriate pro-regenerative transcription factors, or may display chromatin structure that restricts transcriptional access to RAGs. Here we performed epigenetic profiling around the promoter regions of key RAGs, and found progressive restriction across a time course of cortical maturation. These data identify a potential intrinsic constraint to axon growth in adult CNS neurons. Neurite outgrowth from cultured postnatal cortical neurons, however, proved insensitive to treatments that improve axon growth in other cell types, including combinatorial overexpression of AP1 factors, overexpression of histone acetyltransferases, and pharmacological inhibitors of histone deacetylases. This insensitivity could be due to intermediate chromatin closure at the time of culture, and highlights important differences in cell culture models used to test potential pro-regenerative interventions.

HspB5/αB-crystallin increases dendritic complexity and protects the dendritic arbor during heat shock in cultured rat hippocampal neurons

The small heat shock protein ΗspΒ5 (αB-crystallin) exhibits generally cytoprotective functions and possesses powerful neuroprotective capacity in the brain. However, little is known about the mode of action of ΗspΒ5 or other members of the HspB family particularly in neurons. To get clues of the neuronal function of HspBs, we overexpressed several HspBs in cultured rat hippocampal neurons and investigated their effect on neuronal morphology and stress resistance. Whereas axon length and synapse density were not affected by any HspB, dendritic complexity was enhanced by HspB5 and, to a lesser extent, by HspB6. Furthermore, we could show that this process was dependent on phosphorylation, since a non-phosphorylatable mutant of HspB5 did not show this effect. Rarefaction of the dendritic arbor is one hallmark of several neurodegenerative diseases. To investigate if HspB5, which is upregulated at pathophysiological conditions, might be able to protect dendrites during such situations, we exposed HspB5 overexpressing neuronal cultures to heat shock. HspB5 prevented heat shock-induced rarefaction of dendrites. In conclusion, we identified regulation of dendritic complexity as a new function of HspB5 in hippocampal neurons.

Astrocytes release HspB1 in response to amyloid-β exposure in vitro

Although heat shock proteins are thought to function primarily as intracellular chaperones, the release and potential extracellular functions of heat shock proteins have been the focus of an increasing number of studies. Our particular interest is HspB1 (Hsp25/27) and as astrocytes are an in vivo source of HspB1 it is a reasonable possibility they could release HspB1 in response to local stresses. Using primary cultures of rat cortical astrocytes, we investigated the extracellular release of HspB1 with exposure to amyloid-β (Aβ). In order to assess potential mechanisms of release, we cotreated the cells with compounds that can modulate protein secretion including Brefeldin A, Methyl β-cyclodextrin, and MAP kinase inhibitors. Exposure to Aβ (0.1, 1.0, 2.0 μM) for 24-48 h resulted in a selective release of HspB1 that was insensitive to BFA treatment; none of the other inhibitors had any detectable influence. Protease protection assays indicated that some of the released HspB1 was associated with a membrane bound fraction, and analysis of exosomal preparations indicated the presence of HspB1 in exosomes. Finally, immunoprecipitation experiments demonstrated that the extracellular HspB1 was able to interact with extracellular Aβ. In summary, Aβ can stimulate release of HspB1 from astrocytes, this release is insensitive to Golgi or lipid raft disruption, and HspB1 can be found either free in the medium or associated with exosomes. This release suggests that there is a potential for extracellular HspB1 to be able to bind and sequester extracellular Aβ.

Autophagy inhibition in endogenous and nutrient-deprived conditions reduces dorsal root ganglia neuron survival and neurite growth in vitro

Peripheral neuropathies can result in cytoskeletal changes in axons, ultimately leading to Wallerian degeneration and cell death. Recently, autophagy has been studied as a potential target for improving axonal survival and growth during peripheral nerve damage. This study investigates the influence of autophagy on adult dorsal root ganglia (DRG) neuron survival and axonal growth under control and nutrient deprivation conditions. Constitutive autophagy was modulated with pharmacological activators (rapamycin; Rapa) and inhibitors (3-methyladenine, bafilomycin A1) in conjunction with either a nutrient-stable environment (standard culture medium) or a nutrient-deprived environment (Hank's balanced salt solution + Ca(2+) /Mg(2+) ). The results demonstrated that autophagy inhibition decreased cell viability and reduced neurite growth and branching complexity. Although autophagy was upregulated with nutrient deprivation compared with the control, it was not further activated by rapamycin, suggesting a threshold level of autophagy. Overall, both cellular and biochemical approaches combined to show the influence of autophagy on adult DRG neuron survival and growth. © 2016 Wiley Periodicals, Inc.

Induction of neurite outgrowth in PC12 cells treated with temperature-controlled repeated thermal stimulation

To promote the functional restoration of the nervous system following injury, it is necessary to provide optimal extracellular signals that can induce neuronal regenerative activities, particularly neurite formation. This study aimed to examine the regulation of neuritogenesis by temperature-controlled repeated thermal stimulation (TRTS) in rat PC12 pheochromocytoma cells, which can be induced by neurotrophic factors to differentiate into neuron-like cells with elongated neurites. A heating plate was used to apply thermal stimulation, and the correlation of culture medium temperature with varying surface temperature of the heating plate was monitored. Plated PC12 cells were exposed to TRTS at two different temperatures via heating plate (preset surface temperature of the heating plate, 39.5°C or 42°C) in growth or differentiating medium for up to 18 h per day. We then measured the extent of growth, neuritogenesis, or acetylcholine esterase (AChE) activity (a neuronal marker). To analyze the mechanisms underlying the effects of TRTS on these cells, we examined changes in intracellular signaling using the following: tropomyosin-related kinase A inhibitor GW441756; p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580; and MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor U0126 with its inactive analog, U0124, as a control. While a TRTS of 39.5°C did not decrease the growth rate of cells in the cell growth assay, it did increase the number of neurite-bearing PC12 cells and AChE activity without the addition of other neuritogenesis inducers. Furthermore, U0126, and SB203580, but not U0124 and GW441756, considerably inhibited TRTS-induced neuritogenesis. These results suggest that TRTS can induce neuritogenesis and that participation of both the ERK1/2 and p38 MAPK signaling pathways is required for TRTS-dependent neuritogenesis in PC12 cells. Thus, TRTS may be an effective technique for regenerative neuromedicine.

Hepatocyte growth factor promotes long-term survival and axonal regeneration of retinal ganglion cells after optic nerve injury: comparison with CNTF and BDNF

AIMS

Different trophic factors are known to promote retinal ganglion cell survival and regeneration, but each had their own limitations. We report that hepatocyte growth factor (HGF) confers distinct advantages in supporting ganglion cell survival and axonal regeneration, when compared to two well-established trophic factors ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF).

METHODS

Ganglion cells in adult hamster were injured by cutting the optic nerve. HGF, CNTF, or BDNF was injected at different dosages intravitreally after injury. Ganglion cell survival was quantified at 7, 14, or 28 days postinjury. Peripheral nerve (PN) grafting to the cut optic nerve of the growth factor-injected eye was performed either immediately after injury or delayed until 7 days post-injury. Expression of heat-shock protein 27 and changes in microglia numbers were quantified in different growth factor groups. The cellular distribution of c-Met in the retina was examined by anti-c-Met immunostaining.

RESULTS

Hepatocyte Growth Factor (HGF) was equally potent as BDNF in promoting short-term survival (up to 14 days post-injury) and also supported survival at 28 days post-injury when ganglion cells treated by CNTF or BDNF failed to be sustained. When grafting was performed without delay, HGF stimulated twice the number of axons to regenerate compared with control but was less potent than CNTF. However, in PN grafting delayed for 7 days after optic nerve injury, HGF maintained a better propensity of ganglion cells to regenerate than CNTF. Unlike CNTF, HGF application did not increase HSP27 expression in ganglion cells. Microglia proliferation was prolonged in HGF-treated retinas compared with CNTF or BDNF. C-Met was localized to both ganglion cells and Muller cells, suggesting HGF could be neuroprotective via interacting with both neurons and glia.

CONCLUSION

Compared with CNTF or BDNF, HGF is advantageous in sustaining long-term ganglion cell survival and their propensity to respond to favorable stimuli.

HspB1 silences translation of PDZ-RhoGEF by enhancing miR-20a and miR-128 expression to promote neurite extension

HspB1 is a small heat shock protein implicated in neuronal survival and neurite growth; mutations in HspB1 have been identified in hereditary motor neuronopathies and Charcot Marie Tooth Type 2 neuropathies. In cortical neurons we found that expression of HspB1 decreased RhoA activity and RhoA-GTP protein, and reversed the inhibition of neurite extension induced by NogoA. HspB1 decreased PDZ-RhoGEF, a RhoA specific guanine nucleotide exchange factor, while other regulators of RhoA activity were unchanged. The decrease in PDZ-RhoGEF was independent of proteasomal or lysosomal degradation pathways and was not associated with changes in PDZ-RhoGEF mRNA. We sequenced the 3'UTR of rat PDZ-RhoGEF and found binding sites for miRNAs miR-20a, miR-128 and miR-132. Expression of these microRNAs was substantially increased in cortical neurons transfected with HspB1. Co-transfection of HspB1 with specific inhibitors of miR-20a or miR-128 prevented the decrease in PDZ-RhoGEF and blocked the neurite growth promoting effects of HspB1. Using the 3'UTR of PDZ-RhoGEF mRNA in a luciferase reporter construct we observed that HspB1, miR-20a and miR-128 each inhibited luciferase expression. We conclude that HspB1 regulates RhoA activity through modulation of PDZ-RhoGEF levels achieved by translational control through enhanced expression of specific miRNAs (miR-20a and miR-128). Regulation of RhoA activity by translational silencing of PDZ-RhoGEF may be the mechanism through which HspB1 is involved in regulation of neurite growth. As RhoA-GTPase plays a regulatory role in the organization and stability of cytoskeletal networks through its downstream effectors, the results suggest a possible mechanism linking HspB1 mutations and axonal cytoskeletal pathology.

FE65 interacts with ADP-ribosylation factor 6 to promote neurite outgrowth

FE65 is an adaptor protein that binds to the amyloid precursor protein (APP). As such, FE65 has been implicated in the pathogenesis of Alzheimer's disease. In addition, evidence suggests that FE65 is involved in brain development. It is generally believed that FE65 participates in these processes by recruiting various interacting partners to form functional complexes. Here, we show that via its first phosphotyrosine binding (PTB) domain, FE65 binds to the small GTPase ADP-ribosylation factor 6 (ARF6). FE65 preferentially binds to ARF6-GDP, and they colocalize in neuronal growth cones. Interestingly, FE65 stimulates the activation of both ARF6 and its downstream GTPase Rac1, a regulator of actin dynamics, and functions in growth cones to stimulate neurite outgrowth. We show that transfection of FE65 and/or ARF6 promotes whereas small interfering RNA knockdown of FE65 or ARF6 inhibits neurite outgrowth in cultured neurons as compared to the mock-transfected control cells. Moreover, knockdown of ARF6 attenuates FE65 stimulation of neurite outgrowth and defective neurite outgrowth seen in FE65-deficient neurons is partially corrected by ARF6 overexpression. Notably, the stimulatory effect of FE65 and ARF6 on neurite outgrowth is abrogated either by dominant-negative Rac1 or knockdown of Rac1. Thus, we identify FE65 as a novel regulator of neurite outgrowth via controlling ARF6-Rac1 signaling.

Cell stress promotes the association of phosphorylated HspB1 with F-actin

Previous studies have suggested that the small heat shock protein, HspB1, has a direct influence on the dynamics of cytoskeletal elements, in particular, filamentous actin (F-actin) polymerization. In this study we have assessed the influence of HspB1 phosphorylation on its interaction(s) with F-actin. We first determined the distribution of endogenous non-phosphorylated HspB1, phosphorylated HspB1 and F-actin in neuroendocrine PC12 cells by immunocytochemistry and confocal microscopy. We then investigated a potential direct interaction between HspB1 with F-actin by precipitating F-actin directly with biotinylated phalloidin followed by Western analyses; the reverse immunoprecipitation of HspB1 was also carried out. The phosphorylation influence of HspB1 in this interaction was investigated by using pharmacologic inhibition of p38 MAPK. In control cells, HspB1 interacts with F-actin as a predominantly non-phosphorylated protein, but subsequent to stress there is a redistribution of HspB1 to the cytoskeletal fraction and a significantly increased association of pHspB1 with F-actin. Our data demonstrate HspB1 is found in a complex with F-actin both in phosphorylated and non-phosphorylated forms, with an increased association of pHspB1 with F-actin after heat stress. Overall, our study combines both cellular and biochemical approaches to show cellular localization and direct demonstration of an interaction between endogenous HspB1 and F-actin using methodolgy that specifically isolates F-actin.

HSPB1 facilitates the formation of non-centrosomal microtubules

The remodeling capacity of microtubules (MT) is essential for their proper function. In mammals, MTs are predominantly formed at the centrosome, but can also originate from non-centrosomal sites, a process that is still poorly understood. We here show that the small heat shock protein HSPB1 plays a role in the control of non-centrosomal MT formation. The HSPB1 expression level regulates the balance between centrosomal and non-centrosomal MTs. The HSPB1 protein can be detected specifically at sites of de novo forming non-centrosomal MTs, while it is absent from the centrosomes. In addition, we show that HSPB1 binds preferentially to the lattice of newly formed MTs in vitro, suggesting that its function occurs by stabilizing MT seeds. Our findings open new avenues for the understanding of the role of HSPB1 in the development, maintenance and protection of cells with specialized non-centrosomal MT arrays.

Remote ischemic postconditioning promotes the survival of retinal ganglion cells after optic nerve injury

Ischemic conditioning, the application of a mild ischemic stimulus to an ischemia-sensitive structure like the heart or brain either before (preconditioning) or after (postconditioning) its exposure to a lethal ischemic insult, is known to switch on endogenous protective mechanisms. However, most studies of its neuroprotective effect in the central nervous system (CNS) have focused on ischemic damage or related conditions like hypoxia, while its potential in treating other neural diseases remains uncertain. In particular, the recent discovery of remote ischemic postconditioning whereby mild ischemia applied to a region remote from the target after the main ischemic insult also confers protection offers an attractive paradigm to study its potential in other types of neural injury. Retinal ganglion cells damaged by optic nerve transection undergo extensive cell death. However, application of a series of mild ischemic/reperfusion cycles to the hind limb (limb remote ischemic postconditioning) at 10 min or 6 h after optic nerve cut was found to promote ganglion cell survival at 7 days post-injury, with the 10 min postconditioning still exerting protection at 14 days post-injury. Concomitant with the increased ganglion cell survival, 51 % more ganglion cells expressed the small heat shock protein HSP27, when remote ischemic postconditioning was performed at 10 min post-injury, as compared to the sham conditioning group. Our results highlight the potential of using remote ischemic postconditioning as a noninvasive neuroprotective strategy in different CNS disorders like spinal cord and traumatic brain injury.

Transcriptional insights on the regenerative mechanics of axotomized neurons in vitro

Axotomized neurons have the innate ability to undergo regenerative sprouting but this is often impeded by the inhibitory central nervous system environment. To gain mechanistic insights into the key molecular determinates that specifically underlie neuronal regeneration at a transcriptomic level, we have undertaken a DNA microarray study on mature cortical neuronal clusters maintained in vitro at 8, 15, 24 and 48 hrs following complete axonal severance. A total of 305 genes, each with a minimum fold change of ±1.5 for at least one out of the four time points and which achieved statistical significance (one-way ANOVA, P < 0.05), were identified by DAVID and classified into 14 different functional clusters according to Gene Ontology. From our data, we conclude that post-injury regenerative sprouting is an intricate process that requires two distinct pathways. Firstly, it involves restructuring of the neurite cytoskeleton, determined by compound actin and microtubule dynamics, protein trafficking and concomitant modulation of both guidance cues and neurotrophic factors. Secondly, it elicits a cell survival response whereby genes are regulated to protect against oxidative stress, inflammation and cellular ion imbalance. Our data reveal that neurons have the capability to fight insults by elevating biological antioxidants, regulating secondary messengers, suppressing apoptotic genes, controlling ion-associated processes and by expressing cell cycle proteins that, in the context of neuronal injury, could potentially have functions outside their normal role in cell division. Overall, vigilant control of cell survival responses against pernicious secondary processes is vital to avoid cell death and ensure successful neurite regeneration.

Charcot-Marie-Tooth disease and intracellular traffic

Mutations of genes whose primary function is the regulation of membrane traffic are increasingly being identified as the underlying causes of various important human disorders. Intriguingly, mutations in ubiquitously expressed membrane traffic genes often lead to cell type- or organ-specific disorders. This is particularly true for neuronal diseases, identifying the nervous system as the most sensitive tissue to alterations of membrane traffic. Charcot-Marie-Tooth (CMT) disease is one of the most common inherited peripheral neuropathies. It is also known as hereditary motor and sensory neuropathy (HMSN), which comprises a group of disorders specifically affecting peripheral nerves. This peripheral neuropathy, highly heterogeneous both clinically and genetically, is characterized by a slowly progressive degeneration of the muscle of the foot, lower leg, hand and forearm, accompanied by sensory loss in the toes, fingers and limbs. More than 30 genes have been identified as targets of mutations that cause CMT neuropathy. A number of these genes encode proteins directly or indirectly involved in the regulation of intracellular traffic. Indeed, the list of genes linked to CMT disease includes genes important for vesicle formation, phosphoinositide metabolism, lysosomal degradation, mitochondrial fission and fusion, and also genes encoding endosomal and cytoskeletal proteins. This review focuses on the link between intracellular transport and CMT disease, highlighting the molecular mechanisms that underlie the different forms of this peripheral neuropathy and discussing the pathophysiological impact of membrane transport genetic defects as well as possible future ways to counteract these defects.

Tuning the orchestra: transcriptional pathways controlling axon regeneration

Trauma in the adult mammalian central nervous system leads to irreversible structural and functional impairment due to failed regeneration attempts. In contrast, neurons in the peripheral nervous system exhibit a greater regenerative ability. It has been proposed that an orchestrated sequence of transcriptional events controlling the expression of specific sets of genes may be the underlying basis of an early cell-autonomous regenerative response. Understanding whether transcriptional fine tuning, in parallel with strategies aimed at counteracting extrinsic impediments promotes axon re-growth following central nervous system injuries represents an exciting challenge for future studies. Transcriptional pathways controlling axon regeneration are presented and discussed in this review.

Heat shock protein 27 is associated with better nerve function and fewer signs of neuropathy

AIMS/HYPOTHESIS

High levels of serum heat shock protein 27 (sHSP27) have been associated with distal symmetric polyneuropathy in patients with type 1 diabetes. Our objective was to investigate the association between sHSP27, neuropathic signs and nerve function in individuals with normal glucose tolerance (NGT), impaired glucose tolerance (IGT) and type 2 diabetes.

METHODS

Participants were recruited consecutively from the population-based Västerbotten Intervention Program (NGT, n = 39, IGT, n = 29, and type 2 diabetes, n = 51) and were matched for age and sex. sHSP27 levels were measured and nerve conduction studies were performed (peroneal and sural nerves). z Scores for each nerve conduction measure were calculated and compiled into a composite z score for the leg. Neuropathy disability score (NDS) was used to assess neuropathic signs.

RESULTS

Patients with diabetes had significantly lower sHSP27 levels (geometric mean sHSP27 206 pg/ml, 95% CI 142, 299) than those with IGT (geometric mean sHSP27 455 pg/ml, 95% CI 319, 650, p < 0.05) and controls (geometric mean sHSP27 361 pg/ml, 95% CI 282, 461, p < 0.05). Participants with few signs of neuropathy (first tertile, NDS ≤2) had significantly higher sHSP27 levels (geometric mean sHSP27 401 pg/ml, 95% CI 310, 520) than participants with many signs (third tertile, NDS ≥7) (geometric mean sHSP27 192 pg/ml, 95% CI 128, 288, p = 0.007). The highest sHSP27 tertile was associated with better nerve function, adjusted for age, sex, statin medication and HbA(1c) (OR 2.51, 95% CI 1.25, 5.05, p < 0.05).

CONCLUSIONS/INTERPRETATION

High sHSP27 levels were associated with better nerve function and fewer neuropathic signs in NGT, IGT and type 2 diabetes.

Recent Advances on the Possible Neuroprotective Activities of Epstein-Barr Virus Oncogene BARF1 Protein in Chronic Inflammatory Disorders of Central Nervous System

Multiple sclerosis and neurodegenerative diseases in which cells of the central nervous system (CNS) are lost or damaged are rapidly increasing in frequency, and there is neither effective treatment nor cure to impede or arrest their destructive course. The Epstein-Barr virus is a human gamma-herpesvirus that infects more than 90% of the human population worldwide and persisting for the lifetime of the host. It is associated with numerous epithelial cancers, principally undifferentiated nasopharyngeal carcinoma and gastric carcinoma. Individuals with a history of symptomatic primary EBV infection, called infectious mononucleosis, carry a moderately higher risk of developing multiple sclerosis (MS). It is not known how EBV infection potentially promotes autoimmunity and central nervous system (CNS) tissue damage in MS. Recently it has been found that EBV isolates from different geographic regions have highly conserved BARF1 epitopes. BARF1 protein has the neuroprotective and mitogenic activity, thus may be useful to combat and overcome neurodegenerative disease. BARF1 protein therapy can potentially be used to enhance the neuroprotective activities by combinational treatment with anti-inflammatory antagonists and neuroprotectors in neural disorders.

NeuroD6 genomic signature bridging neuronal differentiation to survival via the molecular chaperone network

During neurogenesis, expression of the basic helix-loop-helix NeuroD6/Nex1/MATH-2 transcription factor parallels neuronal differentiation and is maintained in differentiated neurons in the adult brain. To dissect NeuroD6 differentiation properties further, we previously generated a NeuroD6-overexpressing stable PC12 cell line, PC12-ND6, which displays a neuronal phenotype characterized by spontaneous neuritogenesis, accelerated NGF-induced differentiation, and increased regenerative capacity. Furthermore, we reported that NeuroD6 promotes long-term neuronal survival upon serum deprivation. In this study, we identified the NeuroD6-mediated transcriptional regulatory pathways linking neuronal differentiation to survival, by conducting a genome-wide microarray analysis using PC12-ND6 cells and serum deprivation as a stress paradigm. Through a series of filtering steps and a gene-ontology analysis, we found that NeuroD6 promotes distinct but overlapping gene networks, consistent with the differentiation, regeneration, and survival properties of PC12-ND6 cells. By using a gene-set-enrichment analysis, we provide the first evidence of a compelling link between NeuroD6 and a set of heat shock proteins in the absence of stress, which may be instrumental in conferring stress tolerance on PC12-ND6 cells. Immunocytochemistry results showed that HSP27 and HSP70 interact with cytoskeletal elements, consistent with their roles in neuritogenesis and preserving cellular integrity. HSP70 also colocalizes with mitochondria located in the soma, growing neurites, and growth cones of PC12-ND6 cells prior to and upon stress stimulus, consistent with its neuroprotective functions. Collectively, our findings support the notion that NeuroD6 links neuronal differentiation to survival via the network of molecular chaperones and endows the cells with increased stress tolerance.

HSP27: mechanisms of cellular protection against neuronal injury

The heat shock protein (HSP) family has long been associated with a generalized cellular stress response, particularly in terms of recognizing and chaperoning misfolded proteins. While HSPs in general appear to be protective, HSP27 has recently emerged as a particularly potent neuroprotectant in a number of diverse neurological disorders, ranging from ALS to stroke. Although its robust protective effect on a number of insults has been recognized, the mechanisms and regulation of HSP27's protective actions are still undergoing intense investigation. On the basis of recent studies, HSP27 appears to have a dynamic and diverse range of function in cellular survival. This review provides a forum to compare and contrast recent literature exploring the protective mechanism and regulation of HSP27, focusing on neurological disorders in particular, as they represent a range from protein aggregate-associated diseases to acute stress.

Local application of olprinone for promotion of peripheral nerve regeneration

BACKGROUND

Olprinone was applied locally to the sciatic nerves of rats, and nerve regeneration activity was examined in relation to heat shock protein (HSP)27 expression.

METHODS

Adult rat sciatic nerves were locally exposed to olprinone, physiological saline, or a mixture of saline and HCl and underwent crush injury. HSP27 protein levels were assessed by Western blotting and immunohistochemistry. Nerve regeneration was assessed by sciatic function index (SFI) and by morphological evaluation.

RESULTS

Olprinone was detected in ipsilateral L4-L6 dorsal root ganglion (DRG) and sciatic nerve proximal to the site of crush injury. Western blot analysis of the DRG 24 h postsurgery and the sciatic nerve 7 days postsurgery showed a marked increase in HSP27 protein levels in the olprinone-treated group. Immunohistochemical analysis was consistent with the Western blot analysis. SFI was significantly better for the olprinone-treated group than for either the saline- or HCl-treated groups at 7, 22, and 25 days, respectively, after application. The packing density and the number of myelinated axons 21 days after the crush injury in the olprinone-treated group were significantly greater in comparison to the other groups.

CONCLUSION

The local application of olprinone to the sciatic nerve increases HSP27 protein levels in DRG in the early stage and in the sciatic nerve 1 week thereafter. The results from this crush model indicate that increasing levels of HSP27 appear to result in therapeutic effects.

Activation of gene transcription by heat shock protein 27 may contribute to its neuronal protection

Heat shock proteins are up-regulated as a physiological response to stressful stimuli and generally function as molecular chaperones for improperly folded protein substrates. The small heat shock protein HSP27 (or HSPB1) has multiple cytoplasmic roles. HSP27 also can translocate to the nucleus in response to stress, but the functional significance of this nuclear distribution has not been elucidated. We have previously implicated HSP27 as a genetic modifier of spinocerebellar ataxia 17 (SCA17), a neurological disease caused by a polyglutamine expansion in the TATA-binding protein (TBP). Altered expression of HSP27 is also found in cell models of other polyglutamine diseases, including Huntington disease as well as SCA3 and SCA7. Here, we show that Hsp27, unlike Hsp70, is not detected in mutant TBP aggregates in primary cerebellar granule neurons from transgenic SCA17 mice. Although HSP27 overexpression does not reduce the aggregation of cotransfected mutant TBP containing 105 glutamines, it potentiates activated transcription from both TATA-containing and TATA-lacking promoters. Neither HSP40 nor HSP70 elicits the same transcriptional effect. Moreover, HSP27 interacts with the transcription factor SP1, and coexpression of SP1 and nuclear localization signal-tagged HSP27 synergistically activates reporter constructs for the SP1-responsive neurotrophic receptor genes Ngfr(p75) and TRKA. Overexpression of nuclear localization signal-tagged HSP27 also rescues mutant TBP-mediated down-regulation of TrkA in a PC12 cell model of SCA17. These results indicate that nuclear HSP27 can modulate SP1-dependent transcriptional activity to promote neuronal protection.

Peripheral sensory axon growth: from receptor binding to cellular signaling

Regeneration following axonal injury of the adult peripheral sensory nervous system is heavily influenced by factors located in a neuron's extracellular environment. These factors include neurotrophins, such as Nerve Growth Factor (NGF) and the extracellular matrix, such as laminin. The presence of these molecules in the peripheral nervous system (PNS) is a major contributing factor for the dichotomy between regenerative capacities of central vs. peripheral neurons. Although PNS neurons are capable of spontaneous regeneration, this response is critically dependent on many different factors including the type, location and severity of the injury. In this article, we will focus on the plasticity of adult dorsal root ganglion (DRG) sensory neurons and how trophic factors and the extracellular environment stimulate the activation of intracellular signaling cascades that promote axonal growth in adult dorsal root ganglion neurons.

Heat shock protein 27 in neuronal survival and neurite outgrowth

The small heat shock protein 27 (Hsp27) is well documented to promote neuronal survival in neurodegenerative diseases and following nerve injury. It can directly inhibit apoptotic pathways, and as a chaperone it can ameliorate the toxic effects of misfolded proteins. More recently, Hsp27 has been implicated to also play a role in neurite outgrowth. Thus, Hsp27 is situated at the intersection of neuronal survival and differentiation and, as such, it has dual potential as a key therapeutic target for neuroregeneration.

Proteomics of neural stem cells

The isolation of neural stem cells from fetal and adult mammalian CNS and the demonstration of functional neurogenesis in adult CNS have offered perspectives for treatment of many devastating hereditary and acquired neurological diseases. Due to this enormous potential, neural stem cells are a subject of extensive molecular profiling studies with a search for new markers and regulatory pathways governing their self-renewal as opposed to differentiation. Several in-depth proteomic studies have been conducted on primary or immortalized cultures of neural stem cells and neural progenitor cells, and yet more remains to be done. Additionally, neurons and glial cells have been obtained from embryonic stem cells and mesenchymal stem cells, and proteins associated with the differentiation process have been characterized to a certain degree with a view to further investigations. This review summarizes recent findings relevant to the proteomics of neural stem cells and discusses major proteins significantly regulated during neural stem cell differentiation with a view to their future use in cell-based regenerative and reparative therapy.

Pituitary adenylate cyclase-activating polypeptide 38-mediated Rin activation requires Src and contributes to the regulation of HSP27 signaling during neuronal differentiation

Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38) is a potent neuropeptide that acts through G-protein-coupled receptors. While it is well established that PACAP mediates both neurotrophic and neurodevelopmental effects, the signaling cascades that underlie these diverse actions remain incompletely characterized. Here we show that the Ras-related Rin GTP-binding protein, a GTPase that is expressed predominantly in neurons, is regulated by PACAP38 signaling, and loss-of-function analysis demonstrates that Rin makes an essential contribution to PACAP38-mediated pheochromocytoma cell differentiation. Rin is activated following stimulation of both Gsalpha and Gialpha cascades but does not rely upon cyclic AMP (cAMP)-, Ca(2+)-, or Epac-dependent signaling pathways. Instead, Rin is activated in a Src kinase-dependent manner. Surprisingly, Rin knockdown significantly inhibits PACAP38-mediated neurite outgrowth, without affecting mitogen-activated protein kinase signaling cascades. Instead, Rin loss attenuates PACAP38-mediated HSP27 activation by disrupting a cAMP-protein kinase A cascade. RNA interference-mediated HSP27 silencing suppresses both PACAP38- and Rin-mediated neurite outgrowth, while expression of a constitutively active Rin mutant increases both HSP27 protein and phospho-HSP27 levels, supporting a role for Rin-HSP27 signaling in neuronal differentiation. Together, these observations identify an unsuspected role for Rin in neuronal PACAP signaling and establish a novel Galpha-Src-Rin-HSP27 signal transduction pathway as a critical element in PACAP38-mediated neuronal differentiation signaling.

Heat shock enhances NGF-induced neurite elongation which is not mediated by Hsp25 in PC12 cells

Neuronal differentiation and neurite outgrowth are key processes during development of the nervous system. Understanding the regulation of neurite outgrowth stimulated by neurotrophins is crucial to developing therapies to promote axon regeneration after injury or in neurodegenerative diseases. Treatment of PC12 cells with nerve growth factor (NGF) stimulates them to extend neurites and differentiate into a sympathetic neuron-like phenotype. In this study we found that exposure of PC12 cells to 42 degrees C for 1 h significantly enhanced NGF-induced neurite elongation, but not branching. This heat shock treatment led to induction of heat shock protein 25 (Hsp25) and Hsp70. The morphological changes induced by NGF were accompanied by increased Hsp25 mRNA levels, in addition to elevation in Hsp25 protein expression and phosphorylation, without a concomitant increase in Hsp70. A possible role for Hsp25 in NGF-stimulated neurite outgrowth was investigated. However, quantification of NGF-induced neurite elongation and branching revealed that neither of these features were altered in PC12 cells which stably overexpressed human Hsp27 (to mimic heat shock induction of Hsp25). Similarly, knockdown of Hsp25 using siRNA had no effect on NGF-induced neurite outgrowth. Inhibition of p38 MAPK signalling with SB202190 blocked phosphorylation of Hsp25 without affecting NGF-induced neurite outgrowth or the heat shock-dependent enhancement of elongation. These findings indicate that Hsp25 is not required for NGF-induced neurite outgrowth in PC12 cells and is not responsible for the heat shock-enhancement of NGF-induced neurite elongation. Instead, inhibition of MEK1/2 with U0126 partially reduced the heat shock-enhancement of NGF-stimulated neurite elongation.

Cyclic strain-induced HSP27 phosphorylation modulates actin filaments in airway smooth muscle cells

Mechanical stress (cyclic deformational strain) increases proteins of cytoskeletal and contractile domains in airway smooth muscle (ASM) cells in a manner that increases cell contractility. Here we studied the role of HSP27 in strain-induced microfilament formation and stability. Cultured ASM cells showed rapid phosphorylation of HSP27 upon cyclic strain within a few minutes that continued for 30 to 40 minutes. Such increases in HSP27 phosphorylation were abolished with SB 202190, a specific inhibitor of p38 mitogen-activated protein kinase (MAPK), but not by PD 98059 (an inhibitor of extracellular regulated kinase), GF109203X (an inhibitor of protein kinase C), or Y27632 (an inhibitor of Rho kinase). Direct activation of RhoA by GTPgammaS did not alter the level of HSP27 phosphorylation. Confocal microscopy revealed that cells pre-incubated with SB 202190, and/or Y27632 resulted in disorganization of stress fibers upon strain, unlike PD 98059 and GF 1092030X, suggesting that both p38 MAPK and Rho kinase were necessary for strain-induced microfilament formation. To determine the relationship between HSP27 and RhoA in strain-induced microfilament formation, cells were transfected with various isoforms of HSP27 and RhoA before strain. Co-expression of inactive HSP27 (3A-HSP27) with constitutively active EGF-RhoA (RhoV14) caused diminution of microfilaments compared with constitutive active EGFP-RhoA (RhoV14) alone, suggesting that HSP27 is necessary for microfilament stability. Similarly, expression of phosphomimicking HSP27 (3D-HSP27) was sufficient for retaining microfilament formation even when co-expressed with the dominant-negative RhoA (EGFP-RhoN17). Thus, HSP27 activation is necessary for microfilament stability independently of RhoA activation.

Timing of surgery in cauda equina syndrome with urinary retention: meta-analysis of observational studies

Object

The authors performed exploratory meta-analyses of observational cohort studies, evidence level III, examining whether earlier surgery makes a difference in outcome in terms of urinary function once cauda equina syndrome (CES) from a herniated lumbar disc has progressed to urinary retention (CESR).

Methods

Literature search identified 27 studies of CESR patients with clear definition of surgical timing. Relative risk (RR) could not be calculated in 11 studies, leaving 16 for meta-analysis. Urinary retention related to surgical timing at 5 breakpoints: 12, 24, 36, 48, or 72 hours. Urinary outcome was classified as Normal, Fair, or Poor. Meta-analysis was performed for “Event = Fair/Poor” or “Event = Poor.” Eight studies allowed separation into CESR and incomplete CES (CESI), and 5 of these had enough data for meta-analysis to compare CESR and CESI. A random effects meta-analysis model was used because of heterogeneity across the studies. A best-evidence synthesis was performed for the 4 largest studies that had 24- and 48-hour breakpoints.

Results

For “Event = Fair/Poor,” meta-analyses using the 5 breakpoints predicted a more likely Fair/Poor outcome for later surgery (RR range 1.77–2.19). The RR for later timing of surgery was statistically significant for 24-and 72-hour breakpoints and was elevated but not statistically significant for the other 3. For “Event = Poor,” the RR range was 1.09–5.82, statistically significant for the 36 hour breakpoint only. Meta-analysis comparing CESR patients with CESI patients predicted a Fair/Poor result for CESR (RR 2.58, 95% confidence interval 0.59–11.31). The best-evidence synthesis did not disclose reasons for differences in the results of the 4 studies.

Conclusions

This study supports early surgery for CES and indicates that CESR and CESI cases should not be analyzed together.

Blockade of hexokinase activity and binding to mitochondria inhibits neurite outgrowth in cultured adult rat sensory neurons

Hexokinase is known as the first enzyme and rate-limiting step in glycolysis. The role of hexokinase activity and localization in regulating the rate of axonal regeneration was studied in cultured adult sensory neurons of dorsal root ganglia (DRG). Immunofluorescent staining of DRG demonstrated that small-medium neurons and satellite cells exhibited high levels of expression of hexokinase I. Large neurons had negative staining for hexokinase I. Intracellular localization and biochemical studies in cultured adult rat sensory neurons revealed that hexokinase I was almost exclusively found in the mitochondrial compartment. The hypothesis that neurotrophic factor dependent activation of Akt would regulate hexokinase association with the mitochondria was tested and quantitative Western blotting showed no effect of blockade of the phosphoinositide 3-kinase (PI 3-kinase)/Akt pathway using the inhibitor LY294002, indicating this interaction of hexokinase with mitochondria was not neurotrophic factor or Akt-dependent. Finally, pharmacological blockade of hexokinase activity and inhibition of localization to the mitochondrial compartment with hexokinase II VDAC binding domain (Hxk2VBD) peptide caused a significant inhibition of neurotrophic factor-directed axon outgrowth. The results support a key role for hexokinase activity and/or localization to the mitochondria in the regulation of neurite outgrowth in cultured adult sensory neurons.

Polyglutamine domain modulates the TBP-TFIIB interaction: implications for its normal function and neurodegeneration

Expansion of the polyglutamine (polyQ) tract in human TATA-box binding protein (TBP) causes the neurodegenerative disease spinocerebellar ataxia 17 (SCA17). It remains unclear how the polyQ tract regulates normal protein function and induces selective neuropathology in SCA17. We generated transgenic mice expressing polyQ-expanded TBP. These mice showed weight loss, progressive neurological symptoms and neurodegeneration before early death. Expanded polyQ tracts reduced TBP dimerization but enhanced the interaction of TBP with the general transcription factor IIB (TFIIB). In SCA17 transgenic mice, the small heat shock protein HSPB1, a potent neuroprotective factor, was downregulated, and TFIIB occupancy of the Hspb1 promoter was decreased. Overexpression of HSPB1 or TFIIB alleviated mutant TBP-induced neuritic defects. These findings implicate the polyQ domain of TBP in transcriptional regulation and provide insight into the molecular pathogenesis of SCA17.

Src and FAK are key early signalling intermediates required for neurite growth in NGF-responsive adult DRG neurons

Axonal regeneration is influenced by factors in the extracellular environment, including neurotrophins, such as NGF, and adhesion molecules, such as laminin. The provision of both NGF and a permissive substrate to cultured adult NGF-responsive DRG neurons results in enhanced levels of neurite growth not achievable by either factor alone. In this study, we have investigated the early signalling events that contribute to NGF and laminin-induced neurite growth. Adult NGF-responsive DRG neurons were plated on poly-d-lysine for 2 h then stimulated with NGF, laminin, or laminin plus NGF for 10 min, 1 h, or 6 h. Signalling pathways were subsequently analysed using Western blotting and pharmacological inhibition of specific signalling components. While activation of the various signalling intermediates (Src, FAK, Akt, MAPK) could be detected as early as 10 min-1 h after stimulation, significant neurite growth was observed mainly at the 6 h time point. The results of the time course experiments showed differential activation of the signalling intermediates. Src was activated by all treatments (NGF, laminin and the combination) at the earliest time point analysed, 10 min. NGF stimulation also resulted in detectable activation of FAK, Akt and MAPK by 10 min. However, laminin stimulation alone did not result in detectable activation of FAK, Akt or MAPK until the 1 h time point. Inhibition of either Src or FAK activity attenuated both laminin and/or NGF-induced PI 3-K/Akt and MEK/MAPK signalling pathways, as well as neurite growth. Downstream inhibition of Akt by Akt knockdown also blocked observed neurite growth, while inhibition of MEK/MAPK had no significant effect. Together, these results demonstrate that signalling underlying neurite growth can be detected within minutes of stimulation and provide a mechanism for the observed enhancement of neurite growth when both NGF and the permissive substrate, laminin, are provided.