The effect of neonatal nerve injury on the expression of heat shock proteins in developing rat motoneurones

Heat-shock chaperone HSPB1 regulates cytoplasmic TDP-43 phase separation and liquid-to-gel transition

While acetylated, RNA-binding-deficient TDP-43 reversibly phase separates within nuclei into complex droplets (anisosomes) comprised of TDP-43-containing liquid outer shells and liquid centres of HSP70-family chaperones, cytoplasmic aggregates of TDP-43 are hallmarks of multiple neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Here we show that transient oxidative stress, proteasome inhibition or inhibition of the ATP-dependent chaperone activity of HSP70 provokes reversible cytoplasmic TDP-43 de-mixing and transition from liquid to gel/solid, independently of RNA binding or stress granules. Isotope labelling mass spectrometry was used to identify that phase-separated cytoplasmic TDP-43 is bound by the small heat-shock protein HSPB1. Binding is direct, mediated through TDP-43's RNA binding and low-complexity domains. HSPB1 partitions into TDP-43 droplets, inhibits TDP-43 assembly into fibrils, and is essential for disassembly of stress-induced TDP-43 droplets. A decrease in HSPB1 promotes cytoplasmic TDP-43 de-mixing and mislocalization. HSPB1 depletion was identified in spinal motor neurons of patients with ALS containing aggregated TDP-43. These findings identify HSPB1 to be a regulator of cytoplasmic TDP-43 phase separation and aggregation.

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.

Extracellular heat shock proteins in neurodegenerative diseases: New perspectives

One pathological hallmark of neurodegenerative diseases and CNS trauma is accumulation of insoluble, hydrophobic molecules and protein aggregations found both within and outside cells. These may be the consequences of an inadequate or overburdened cellular response to stresses resulting from potentially toxic changes in extra- and intracellular environments. The upregulated expression of heat shock proteins (HSPs) is one example of a highly conserved cellular response to both internal and external stress. Intracellularly these proteins act as chaperones, playing vital roles in the folding of nascent polypeptides, the translocation of proteins between subcellular locations, and the disaggregation of misfolded or aggregated proteins in an attempt to maintain cellular proteostasis during both homeostatic and stressful conditions. While the predominant study of the HSPs has focused on their intracellular chaperone functions, it remains unclear if all neuronal populations can mount a complete stress response. Alternately, it is now well established that some members of this family of proteins can be secreted by nearby, non-neuronal cells to act in the extracellular environment. This review addresses the current literature detailing the use of exogenous and extracellular HSPs in the treatment of cellular and animal models of neurodegenerative disease. These findings offer a new measure of therapeutic potential to the HSPs, but obstacles must be overcome before they can be efficiently used in a clinical setting.

Expression of the protein chaperone, clusterin, in spinal cord cells constitutively and following cellular stress, and upregulation by treatment with Hsp90 inhibitor

Clusterin, a protein chaperone found at high levels in physiological fluids, is expressed in nervous tissue and upregulated in several neurological diseases. To assess relevance to amyotrophic lateral sclerosis (ALS) and other motor neuron disorders, clusterin expression was evaluated using long-term dissociated cultures of murine spinal cord and SOD1(G93A) transgenic mice, a model of familial ALS. Motor neurons and astrocytes constitutively expressed nuclear and cytoplasmic forms of clusterin, and secreted clusterin accumulated in culture media. Although clusterin can be stress inducible, heat shock failed to increase levels in these neural cell compartments despite robust upregulation of stress-inducible Hsp70 (HspA1) in non-neuronal cells. In common with HSPs, clusterin was upregulated by treatment with the Hsp90 inhibitor, geldanamycin, and thus could contribute to the neuroprotection previously identified for such compounds in disease models. Clusterin expression was not altered in cultured motor neurons expressing SOD1(G93A) by gene transfer or in presymptomatic SOD1(G93A) transgenic mice; however, clusterin immunolabeling was weakly increased in lumbar spinal cord of overtly symptomatic mice. More striking, mutant SOD1 inclusions, a pathological hallmark, were strongly labeled by anti-clusterin. Since secreted, as well as intracellular, mutant SOD1 contributes to toxicity, the extracellular chaperoning property of clusterin could be important for folding and clearance of SOD1 and other misfolded proteins in the extracellular space. Evaluation of chaperone-based therapies should include evaluation of clusterin as well as HSPs, using experimental models that replicate the control mechanisms operant in the cells and tissue of interest.

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.

Transcriptional regulation of small HSP-HSF1 and beyond

The members of the small heat shock protein (sHSP) family are molecular chaperones that play major roles in development, stress responses, and diseases, and have been envisioned as targets for therapy, particularly in cancer. The molecular mechanisms that regulate their transcription, in normal, stress, or pathological conditions, are characterized by extreme complexity and subtlety. Although historically linked to the heat shock transcription factors (HSFs), the stress-induced or developmental expression of the diverse members, including HSPB1/Hsp27/Hsp25, αA-crystallin/HSPB4, and αB-crystallin/HSPB5, relies on the combinatory effects of many transcription factors. Coupled with remarkably different cis-element architectures in the sHsp regulatory regions, they confer to each member its developmental expression or stress-inducibility. For example, multiple regulatory pathways coordinate the spatio-temporal expression of mouse αA-, αB-crystallin, and Hsp25 genes during lens development, through the action of master genes, like the large Maf family proteins and Pax6, but also HSF4. The inducibility of Hsp27 and αB-crystallin transcription by various stresses is exerted by HSF-dependent mechanisms, by which concomitant induction of Hsp27 and αB-crystallin expression is observed. In contrast, HSF-independent pathways can lead to αB-crystallin expression, but not to Hsp27 induction. Not surprisingly, deregulation of the expression of sHSP is associated with various pathologies, including cancer, neurodegenerative, or cardiac diseases. However, many questions remain to be addressed, and further elucidation of the developmental mechanisms of sHsp gene transcription might help to unravel the tissue- and stage-specific functions of this fascinating class of proteins, which might prove to be crucial for future therapeutic strategies. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

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.

Activation of the heat shock response in a primary cellular model of motoneuron neurodegeneration-evidence for neuroprotective and neurotoxic effects

Pharmacological up-regulation of heat shock proteins (hsps) rescues motoneurons from cell death in a mouse model of amyotrophic lateral sclerosis. However, the relationship between increased hsp expression and neuronal survival is not straightforward. Here we examined the effects of two pharmacological agents that induce the heat shock response via activation of HSF-1, on stressed primary motoneurons in culture. Although both arimoclomol and celastrol induced the expression of Hsp70, their effects on primary motoneurons in culture were significantly different. Whereas arimoclomol had survival-promoting effects, rescuing motoneurons from staurosporin and H₂O₂ induced apoptosis, celastrol not only failed to protect stressed motoneurons from apoptosis under same experimental conditions, but was neurotoxic and induced neuronal death. Immunostaining of celastrol-treated cultures for hsp70 and activated caspase-3 revealed that celastrol treatment activates both the heat shock response and the apoptotic cell death cascade. These results indicate that not all agents that activate the heat shock response will necessarily be neuroprotective.

MHC class I upregulation is not sufficient to rescue neonatal alpha motoneurons after peripheral axotomy

Associated with neuronal death, profound synaptic changes occur in the spinal cord during the apoptotic process triggered after axotomy in neonatal rats. With respect to this, the major histocompatibility complex of class I (MHC class I) has recently emerged as a new mechanism related to synaptic stripping and plasticity. The present study investigated the impact of upregulating MHC class I expression by treatment with beta interferon (beta INF) on motoneuron survival, synaptic plasticity and astrogliosis after neonatal sciatic nerve injury. P2 rats were subjected to unilateral axotomy followed by three days of beta INF treatment. The results were analyzed by counting Nissl stained motoneurons, immunohistochemistry (anti-synaptophysin, MHC class I, GFAP and Iba-1) and transmission electron microscopy. INF treatment induced an increased expression of MHC class I, which resulted in a stronger synaptic elimination process in the spinal cord, as seen by the synaptophysin labeling. GFAP and Iba-1 upregulation were not significantly altered by the INF treatment, displaying the same degree of enhanced reactivity as compared to the placebo group. The ultrastructural analysis showed that, apart from the overall reduction of inputs in the neuropil, no statistical differences were present when comparing the INF and placebo treated animals. Also, neuronal survival was not altered by cytokine administration. The present results provide evidence that MHC class I upregulation after neonatal injury does not change the fate of lesioned motoneurons. In this way, the lack of neurotrophic support may cause broader synaptic loss, which superposes the more subtle effects of the upregulation of MHC class I.

Over-expression of Hsp27 does not influence disease in the mutant SOD1(G93A) mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a chronic, adult-onset neurodegenerative disorder characterized by the selective loss of upper and lower motor neurons, resulting in severe atrophy of muscles and death. Although the exact pathogenic mechanism of mutant superoxide dismutase 1 (SOD1) causing familial ALS is still elusive, toxic protein aggregation leading to insufficiency of chaperones is one of the main hypotheses. In this study, we investigated the effect of over-expressing one of these chaperones, heat shock protein 27 (Hsp27), in ALS. Mice over-expressing the human, mutant SOD1(G93A) were crossed with mice that ubiquitously over-expressed human Hsp27. Even though the single transgenic hHsp27 mice showed protection against spinal cord ischemia, the double transgenic SOD1(G93A)/hHsp27 mice did not live longer, and did not show a significant delay in the onset of disease compared to their SOD1(G93A) littermates. There was no protective effect of hHsp27 over-expression on the motor neurons and on the mutant SOD1 aggregates in the double transgenic SOD1(G93A)/hHsp27 mice. In conclusion, despite the protective action against acute motor neuron injury, Hsp27 alone is not sufficient to protect against the chronic motor neuron injury due to the presence of mutant SOD1.

Heat shock protein 27 rescues motor neurons following nerve injury and preserves muscle function

Heat shock proteins (HSPs) are a family of ubiquitously expressed proteins that are up-regulated in response to a range of stresses and play an important role in cellular defence mechanisms. In previous studies, we demonstrated that overexpression of heat shock protein 27 (HSP27) in transgenic mice has significant cytoprotective properties in vivo, reducing caspase-3-mediated cell death in the hippocampus associated with limbic seizures and reducing infarct size in cardiac ischaemia. In motor neurons, HSP27 is also implicated as a survival promoting factor; however, it remains to be established whether HSP27 is able to exert long-term neuroprotective effects following neonatal nerve injury. We now show that, following neonatal nerve crush, HSP27 overexpression in vivo provides a substantial rescue of motor neurons 5-6 months following nerve injury. Furthermore, in vivo isometric tension recordings demonstrate that surviving motor neurons were able to regenerate, resulting in a 90% improvement (P < 0.0005) in motor unit number in HSP27 mice. Moreover, this increase in motor unit number was associated with improved muscle weight, muscle force, contractile speeds, and histochemical markers of muscle activity. These properties of HSP27 therefore have considerable potential for improving long-term muscle function in motor neuron disorders.

Increased sensory neuron apoptotic death 2 weeks after peripheral axotomy in C57BL/6J mice compared to A/J mice

Peripheral nerve transection results in a disconnection of the neuron from its target. As a result, a series of metabolic changes occur in the cell body that may cause neuronal death, mainly by apoptotic mechanisms. Although neurons from neonatal animals are the most susceptible, peripheral, lesion-induced, neuronal loss also occurs in adults, and is particularly evident in mouse sensory neurons. However, differences in genetic background cause particular isogenic strains of mice to react unevenly to peripheral nerve lesion. In this work, we investigated the occurrence of apoptosis as well as the ultrastructural changes in the dorsal root ganglion sensory neurons and satellite cells of C57BL/6J and A/J mice 2 weeks after ipsilateral sciatic nerve transection at the mid-thigh level. C57BL/6J mice displayed a stronger sensory neuron chromatolytic reaction that resulted in an increased loss of neurons when compared with isogenic A/J mice (p<0.01). Additionally, most of the degenerating neurons displayed the classic features of apoptosis. These findings reinforced previous data obtained by the terminal-deoxynucleotidyl transferase nick-end labeling (TUNEL) technique.

Use of c-fos to identify activity-dependent spinal neurons after stepping in intact adult rats

STUDY DESIGN

An investigation of c-fos activation pattern in spinal neurons of intact adult rats after acute bouts of treadmill locomotion.

OBJECTIVES

To map spinal neurons that are involved in quadrupedal treadmill stepping of intact adult rats by using c-fos as a marker.

SETTINGS

Los Angeles, CA, USA.

METHODS

Spinal cord sections of rats that were not stepped (n = 4) were used to map the FOS-positive (+) neurons under basal conditions. The stepped group (n = 16) was placed on a treadmill to step quadrupedally for varying durations to induce c-fos activity. Spinal cord sections of thoracic and lumbar segments of Stp and Nstp rats were processed using a c-fos antibody, choline acetyl transferase and heat shock protein 27 for identifying motoneurons.

RESULTS

Stepping induced a greater number of FOS+ neurons than was observed in rats that did not step on the treadmill. There was a rostrocaudal and a dorsoventral gradient of FOS labeled neurons. The number of FOS+ neurons increased with the duration of treadmill stepping. Significant increases in FOS+ neurons were in the most medial parts of laminae IV, V, and VII. FOS+ motoneurons increased with treadmill stepping, particularly in large motoneurons (> or = 700 microm2).

CONCLUSION

These data suggest that FOS can be used to identify activity-dependent neuronal pathways in the spinal cord that are associated with treadmill stepping, specifically in lamina VII and in alpha motoneurons.

SPONSORSHIP

NIH NS16333, NS40917, and the Christopher Reeve Paralysis Foundation (CRPF VEC 2002).

Extracellular heat shock protein 70: a critical component for motoneuron survival

The dependence of developing spinal motoneuron survival on a soluble factor(s) from their target, muscle tissue is well established both in vivo and in vitro. Considering this apparent dependence, we examined whether a specific component of the stress response mediates motoneuron survival in trophic factor-deprived environments. We demonstrate that, although endogenous expression of heat shock protein 70 (HSP70) did not change during trophic factor deprivation, application of e-rhHsp70 (exogenous recombinant human Hsp70) promoted motoneuron survival. Conversely, depletion of HSP70 from chick muscle extract (MEx) potently reduces the survival-promoting activity of MEx. Additionally, exogenous treatment with or spinal cord overexpression of Hsp70 enhances motoneuron survival in vivo during the period of naturally occurring cell death [programmed cell death (PCD)]. Hindlimb muscle cells and lumbar spinal astrocytes readily secrete HSP70 in vitro, suggesting potential physiological sources of extracellular Hsp70 for motoneurons. However, in contrast to exogenous treatment with or overexpression of Hsp70 in vivo, muscle-targeted injections of this factor in an ex vivo preparation fail to attenuate motoneuron PCD. These data (1) suggest that motoneuron survival requirements may extend beyond classical trophic factors to include HSP70, (2) indicate that the source of this factor is instrumental in determining its trophic function, and (3) may therefore influence therapeutic strategies designed to increase motoneuron Hsp70 signaling during disease or injury.

Molecular chaperones as therapeutic targets in amyotrophic lateral sclerosis

Neurodegenerative diseases are characterized by a number of common hallmarks, such as the presence of intracellular aggregates and activation of the apoptotic cell-death pathway. Intracellular chaperones, responsible for protein integrity and structural repair, may play a crucial role in the progression of a disease. In this paper, we aim to summarize our understanding of the role and potential of a particular family of chaperones, the heat-shock proteins, in neurodegeneration, by focusing our discussion on models of motoneuron death.

Administration of Hsp70 in vivo inhibits motor and sensory neuron degeneration

The induction of heat shock proteins (Hsps) serves not only as a marker for cellular stress but also as a promoter of cell survival, which is especially important in the nervous system. We examined the regulation of the constitutive and stress-induced 70-kD Hsps (Hsc70 and Hsp70, respectively) after sciatic nerve (SN) axotomy in the neonatal mouse. Additionally, the prevention of axotomy-induced SN cell death by administration of several preparations of exogenous Hsc70 and Hsp70 was tested. Immunohistochemistry and Western blot analyses showed that endogenous levels of Hsc70 and Hsp70 did not increase significantly in lumbar motor neurons or dorsal root ganglion sensory neurons up to 24 hours after axotomy. When a variety of Hsc70 and Hsp70 preparations at doses ranging from 5 to 75 microg were applied to the SN stump after axotomy, the survival of both motor and sensory neurons was significantly improved. Thus, it appears that motor and sensory neurons in the neonatal mouse do not initiate a typical Hsp70 response after traumatic injury and that administration of exogenous Hsc/Hsp70 can remedy that deficit and reduce the subsequent loss of neurons by apoptosis.

Motoneuron degeneration after facial nerve avulsion is exacerbated in presymptomatic transgenic rats expressing human mutant Cu/Zn superoxide dismutase

We investigated motoneuron degeneration after proximal nerve injury in presymptomatic transgenic (tg) rats expressing human mutant Cu/Zn superoxide dismutase (SOD1). The right facial nerves of presymptomatic tg rats expressing human H46R or G93A SOD1 and their non-tg littermates were avulsed, and facial nuclei were examined at 2 weeks postoperation. Nissl-stained cell counts revealed that facial motoneuron loss after avulsion was exacerbated in H46R- and G93A-tg rats compared with their non-tg littermates. The loss of motoneurons in G93A-tg rats after avulsion was significantly greater than that in H46R-tg rats. Intense cytoplasmic immunolabeling for SOD1 in injured motoneurons after avulsion was demonstrated in H46R- and G93A-tg rats but not in their littermates. Facial axotomy did not induce significant motoneuron loss nor enhance SOD1 immunoreactivity in these tg rats and non-tg littermates at 2 weeks postoperation, although both axotomy and avulsion elicited intense immunolabeling for activating transcription factor-3, phosphorylated c-Jun, and phosphorylated heat shock protein 27 in injured motoneurons of all these animals. The present data indicate the increased vulnerability of injured motoneurons after avulsion in the presymptomatic mutant SOD1-tg rats.

Neuronal NOS deficiency promotes apoptotic cell death of spinal cord neurons after peripheral nerve transection

To study the role of endogenous NO in survival and recovery of spinal cord neurons after nerve lesions, wild type mice were compared to knock-out mice lacking neuronal, endothelial or inducible NO synthase (NOS) after sciatic nerve transection. The NO-generating capacities were assessed by NOS immunohistochemistry and NADPH-diaphorase staining. The feature of affected neurons was evaluated following Nissl- and TUNEL-staining, by immunocytochemical demonstration of cytochrome c-translocation, and by ultrastructural examination. Time point of cell loss was found to be independent of the mice type and occurred only at later post-axotomy states. The extent of neuronal degeneration, however, depended on the NO supply. Whereas a lack of endothelial or inducible NOS was well tolerated, deficiency of neuronal NOS enhanced the competence-to-die and led to a substantial apoptotic cell death of spinal cord neurons. Thus, NO supply turned out to be essential for cell survival and recovery with reference to the neuronal NOS isoform.

The effect of treatment with BRX-220, a co-inducer of heat shock proteins, on sensory fibers of the rat following peripheral nerve injury

In this study, we examined the effect BRX-220, a co-inducer of heat shock proteins, in injury-induced peripheral neuropathy. Following sciatic nerve injury in adult rats and treatment with BRX-220, the following features of the sensory system were studied: (a) expression of calcitonin gene-related peptide (CGRP); (b) binding of isolectin B4 (IB4) in dorsal root ganglia (DRG) and spinal cord; (c) stimulation-evoked release of substance P (SP) in an in vitro spinal cord preparation and (d) nociceptive responses of partially denervated rats. BRX-220 partially reverses axotomy-induced changes in the sensory system. In vehicle-treated rats there is a decrease in IB4 binding and CGRP expression in injured neurones, while in BRX-220-treated rats these markers were better preserved. Thus, 7.0 +/- 0.6% of injured DRG neurones bound IB4 in vehicle-treated rats compared to 14.4 +/- 0.9% in BRX-220-treated animals. Similarly, 4.5 +/- 0.5% of DRG neurones expressed CGRP in the vehicle-treated group, whereas 9.0 +/- 0.3% were positive in the BRX-220-treated group. BRX-220 also partially restored SP release from spinal cord sections to electrical stimulation of primary sensory neurones. Behavioural tests carried out on partially denervated animals showed that BRX-220 treatment did not prevent the emergence of mechanical or thermal hyperalgesia. However, oral treatment for 4 weeks lead to reduced pain-related behaviour suggesting either slowly developing analgesic actions or enhancement of recovery processes. Thus, the morphological improvement seen in sensory neurone markers was accompanied by restored functional activity. Therefore, treatment with BRX-220 promotes restoration of morphological and functional properties in the sensory system following peripheral nerve injury.

Upregulation of heat shock proteins rescues motoneurones from axotomy-induced cell death in neonatal rats

Heat shock proteins (hsps) are induced in a variety of cells following periods of stress, where they promote cell survival. In this study, we examined the effect of upregulating hsp expression by treatment with BRX-220, a co-inducer of hsps, on the survival of injured motoneurones. Following sciatic nerve crush at birth, rat pups were treated daily with BRX-220. The expression of hsp70 and hsp90, motoneurone survival, and muscle function was examined at various intervals later and the number of functional motor units was assessed by in vivo isometric tension recordings. Fourteen days after injury, significantly more motoneurones survived in the BRX-220-treated group (39 +/- 2.8%) compared to the saline-treated group (21 +/- 1.7%). Moreover, in the BRX-220-treated group no further loss of motoneurones occurred, so that at 10 weeks 42 +/- 2.1% of motoneurones survived compared to 15 +/- 0.6% in the untreated group. There were also more functional motor units in the hindlimb muscles of BRX-220-treated animals. In addition, treatment with BRX-220 resulted in a significant increase in the expression of hsp70 and hsp90 in glia and neurones. Thus, treatment with BRX-220, a co-inducer of hsps, protects motoneurones from axotomy-induced cell death.