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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.

Arimoclomol is a hydroxylamine derivative, a group of compounds which have unique properties as co-inducers of heat shock protein expression, but only under conditions of cellular stress. Arimoclomol has been found to be neuroprotective in a number of neurodegenerative disease models, including Amyotrophic Lateral Sclerosis (ALS), and in mutant Superoxide Dismutase 1 (SOD1) mice that model ALS, Arimoclomol rescues motor neurons, improves neuromuscular function and extends lifespan. The therapeutic potential of Arimoclomol is currently under investigation in a Phase II clinical trial for ALS patients with SOD1 mutations. In this review we summarize the evidence for the neuroprotective effects of enhanced heat shock protein expression by Arimoclomol and other inducers of the Heat Shock Response. ALS is a complex, multifactorial disease affecting a number of cell types and intracellular pathways. Cells and pathways affected by ALS pathology and which may be targeted by a heat shock protein-based therapy are also discussed in this review. For example, protein aggregation is a characteristic pathological feature of neurodegenerative diseases including ALS. Enhanced heat shock protein expression not only affects protein aggregation directly, but can also lead to more effective clearance of protein aggregates via the unfolded protein response, the proteasome-ubiquitin system or by autophagy. However, compounds such as Arimoclomol have effects beyond targeting protein mis-handling and can also affect additional pathological mechanisms such as oxidative stress. Therefore, by targeting multiple pathological mechanisms, compounds such as Arimoclomol may be particularly effective in the development of a disease-modifying therapy for ALS and other neurodegenerative disorders., (© 2013.)

Spinal and bulbar muscular atrophy, also known as Kennedy's disease, is an adult-onset hereditary neurodegenerative disorder caused by an expansion of the polyglutamine repeat in the first exon in the androgen receptor gene. Pathologically, the disease is defined by selective loss of spinal and bulbar motor neurons causing bulbar, facial and limb weakness. Although the precise disease pathophysiology is largely unknown, it appears to be related to abnormal accumulation of the pathogenic androgen receptor protein within the nucleus, leading to disruption of cellular processes. Using a mouse model of spinal and bulbar muscular atrophy that exhibits many of the characteristic features of the human disease, in vivo physiological assessment of muscle function revealed that mice with the pathogenic expansion of the androgen receptor develop a motor deficit characterized by a reduction in muscle force, abnormal muscle contractile characteristics, loss of functional motor units and motor neuron degeneration. We have previously shown that treatment with arimoclomol, a co-inducer of the heat shock stress response, delays disease progression in the mutant superoxide dismutase 1 mouse model of amyotrophic lateral sclerosis, a fatal motor neuron disease. We therefore evaluated the therapeutic potential of arimoclomol in mice with spinal and bulbar muscular atrophy. Arimoclomol was administered orally, in drinking water, from symptom onset and the effects established at 18 months of age, a late stage of disease. Arimoclomol significantly improved hindlimb muscle force and contractile characteristics, rescued motor units and, importantly, improved motor neuron survival and upregulated the expression of the vascular endothelial growth factor which possess neurotrophic activity. These results provide evidence that upregulation of the heat shock response by treatment with arimoclomol may have therapeutic potential in the treatment of spinal and bulbar muscular atrophy and may also be a possible approach for the treatment of other neurodegenerative diseases.

According to the "membrane sensor" hypothesis, the membrane's physical properties and microdomain organization play an initiating role in the heat shock response. Clinical conditions such as cancer, diabetes and neurodegenerative diseases are all coupled with specific changes in the physical state and lipid composition of cellular membranes and characterized by altered heat shock protein levels in cells suggesting that these "membrane defects" can cause suboptimal hsp-gene expression. Such observations provide a new rationale for the introduction of novel, heat shock protein modulating drug candidates. Intercalating compounds can be used to alter membrane properties and by doing so normalize dysregulated expression of heat shock proteins, resulting in a beneficial therapeutic effect for reversing the pathological impact of disease. The membrane (and lipid) interacting hydroximic acid (HA) derivatives discussed in this review physiologically restore the heat shock protein stress response, creating a new class of "membrane-lipid therapy" pharmaceuticals. The diseases that HA derivatives potentially target are diverse and include, among others, insulin resistance and diabetes, neuropathy, atrial fibrillation, and amyotrophic lateral sclerosis. At a molecular level HA derivatives are broad spectrum, multi-target compounds as they fluidize yet stabilize membranes and remodel their lipid rafts while otherwise acting as PARP inhibitors. The HA derivatives have the potential to ameliorate disparate conditions, whether of acute or chronic nature. Many of these diseases presently are either untreatable or inadequately treated with currently available pharmaceuticals. Ultimately, the HA derivatives promise to play a major role in future pharmacotherapy.

Heat shock proteins (Hsps) have been studied for many years and there is now a large body of evidence that demonstrates the role of Hsp upregulation in tissue and cell protection in a wide variety of stress conditions. Oxidative stress is known to be involved in a number of pathological conditions, including neurodegeneration, cardiovascular disease and stroke, and even plays a role in natural aging. In this review we summarize the current understanding of the role of Hsps and the heat shock response (HSR) in these pathological conditions and discuss the therapeutic potential of an Hsp therapy for these disorders. However, although an Hsp based therapy appears to be a promising approach for the treatment of diseases that involve oxidative damage, there are some significant hurdles that must be overcome before this approach can be successful. For example, to be effective an Hsp based therapy will need to ensure that the upregulation of Hsps occurs in the right place (i.e. be cell specific), at the right time and to a level and specificity that ensures that all the important binding partners, namely the co-chaperones, are also present at the appropriate levels. It is therefore unlikely that strategies that involve genetic modifications that result in overexpression of specific Hsps will achieve such sophisticated and coordinated effects. Similarly, it is likely that some pharmaceutical inducers of Hsps may be too generic to achieve the desired specific effects on Hsp expression, or may simply fail to reach their target cells due to delivery problems. However, if these difficulties can be overcome, it is clear that an effective Hsp based therapy would be of great benefit to the wide range of depilating conditions in which oxidative stress plays a critical role.

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.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition in which motoneurons of the spinal cord and motor cortex die, resulting in progressive paralysis. This condition has no cure and results in eventual death, usually within 1-5 years of diagnosis. Although the specific etiology of ALS is unknown, 20% of familial cases of the disease carry mutations in the gene encoding Cu/Zn superoxide dismutase-1 (SOD1). Transgenic mice overexpressing human mutant SOD1 have a phenotype and pathology that are very similar to that seen in human ALS patients. Here we show that treatment with arimoclomol, a coinducer of heat shock proteins (HSPs), significantly delays disease progression in mice expressing a SOD1 mutant in which glycine is substituted with alanine at position 93 (SOD1(G93A)). Arimoclomol-treated SOD1(G93A) mice show marked improvement in hind limb muscle function and motoneuron survival in the later stages of the disease, resulting in a 22% increase in lifespan. Pharmacological activation of the heat shock response may therefore be a successful therapeutic approach to treating ALS, and possibly other neurodegenerative diseases.

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.

The expression of the heat shock proteins hsp27 and hsp70 was examined in the spinal cord and sciatic nerves of developing rats. Using immunohistochemistry, we found that hsp27 is present in many motoneurones at birth. With development, the intensity of staining increases, reaching adult levels by 21 days, when all sciatic motoneurones express hsp27. In the sciatic nerve, hsp27 is strongly expressed throughout postnatal development. In contrast, hsp70 immunoreactivity in motoneurones and the sciatic nerve is weak at birth and does not change with development. The expression of heat shock proteins has been shown to increase in cells under conditions of stress, where they have beneficial effects on cell survival. The effect of neonatal nerve injury on hsp27 and hsp70 expression was also examined in this study. Four days after injury, staining for hsp27 increases in motoneurones, whereas hsp70 does not change. However, there is a significant increase in hsp70 staining in glial cells surrounding the injured motor pool, predominantly in astrocytes. Since neonatal nerve injury induces apoptotic motoneurone death, we also studied the co-expression of hsp27 with markers of apoptosis. No hsp27-positive motoneurones were found to be apoptotic, as assessed by both TUNEL and caspase-3 immunoreactivity. Therefore, it is possible that the upregulation of hsp27 observed in injured motoneurones may play a role in protecting motoneurones from apoptotic cell death following nerve injury.