Academic literature on the topic 'Motoneuron, HSP70'

Motoneuron diseases (MNDs) are neurodegenerative conditions associated with death of upper and/or lower motoneurons (MNs). Proteostasis alteration is a pathogenic mechanism involved in many MNDs and is due to the excessive presence of misfolded and aggregated proteins. Protein misfolding may be the product of gene mutations, or due to defects in the translation process, or to stress agents; all these conditions may alter the native conformation of proteins making them prone to aggregate. Alternatively, mutations in members of the protein quality control (PQC) system may determine a loss of function of the proteostasis network. This causes an impairment in the capability to handle and remove aberrant or damaged proteins. The PQC system consists of the degradative pathways, which are the autophagy and the proteasome, and a network of chaperones and co-chaperones. Among these components, Heat Shock Protein 70 represents the main factor in substrate triage to folding, refolding, or degradation, and it is assisted in this task by a subclass of the chaperone network, the small heat shock protein (sHSPs/HSPBs) family. HSPBs take part in proteostasis by bridging misfolded and aggregated proteins to the HSP70 machinery and to the degradative pathways, facilitating refolding or clearance of the potentially toxic proteins. Because of its activity against proteostasis alteration, the chaperone system plays a relevant role in the protection against proteotoxicity in MNDs. Here, we discuss the role of HSPBs in MNDs and which HSPBs may represent a valid target for therapeutic purposes.

A prominent clinical feature of ALS is muscle weakness due to dysfunction, denervation and degeneration of motoneurons (MNs). While MN degeneration is a late stage event in the ALS mouse model, muscle denervation occurs significantly earlier in the disease. Strategies to prevent this early denervation may improve quality of life by maintaining muscle control and slowing disease progression. The precise cause of MN dysfunction and denervation is not known, but several mechanisms have been proposed that involve potentially toxic intra- and extracellular changes. Many cells confront these changes by mounting a stress response that includes increased expression of heat shock protein 70 (Hsp70). MNs do not upregulate Hsp70, and this may result in a potentially increased vulnerability. We previously reported that recombinant human hsp70 (rhHsp70) injections delayed symptom onset and increased lifespan in SOD1G93Amice. The exogenous rhHsp70 was localized to the muscle and not to spinal cord or brain suggesting it modulates peripheral pathophysiology. In the current study, we focused on earlier administration of Hsp70 and its effect on initial muscle denervation. Injections of the protein appeared to arrest denervation with preserved large myelinated peripheral axons, and reduced glial activation.

Motoneurons are made in excess throughout development. Initial analysis of the mechanisms that lead to apoptotic cell death during later stages of development and the early postnatal period led to the discovery of neurotrophic factors. These factors comprise different families acting through different tyrosine kinase receptors. Intracellular signalling cascades that lead to the survival of neurons are, on the one hand, the Ras/Raf (Ras-activated factor)/MAPK (mitogen-activated protein kinase) pathway and, on the other, the PI3K (phosphoinositide 3-kinase)/Akt (protein kinase B) pathway. The initial thought of these factors acting as single molecules in separate cascades has been converted into a model in which the dynamics of interaction of these pathways and the subcellular diverse functions of the key regulators have been taken into account. Bag1 (Bcl-2-associated athanogene 1), a molecule that was originally found to act as a co-chaperone of Hsp70 (heat-shock protein 70), also interacts with B-Raf, C-Raf and Akt to phosphorylate Bad (Bcl-2/Bcl-XL-antagonist, causing cell death), a pro-apoptotic member of the Bcl-2 family, and leads to specific subcellular distribution of phosphorylated Akt and B-Raf. These functions lead to survival of embryonic neural stem cells and therefore serve as a key event to regulate the viability of these cells.

AbstractPharmacological 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.

The heat shock protein 70 (HSP70) is a key component of the stress response induced by various noxious conditions such as heat, oxygen stress, trauma and infection. In present study we have assessed the consequences of the compression of lower lumbar and sacral nerve roots caused by a multiple cauda equina constrictions (MCEC) on HSP70 immunoreactivity (HSP70-IR) in the dog. Our data indicate that constriction of central processes evokes HSP70 up-regulation in the spinal cord (L7, S1-Co3) as well as in the corresponding dorsal root ganglion cells (DRGs) (L7-S1) two days following injury. A limited number of bipolar or triangular HSP-IR neurons were found in the lateral collateral pathway (LCP) as well as in the pericentral region (lamina X) of the spinal cord. In contrast, a high number of HSP70 exhibiting motoneurons with fine processes appeared in the ventral horn (laminae VIII-IX) of lumbosacral segments. Concomitantly, close to them a few lightly HSP70-positive neuronal somata or cell bodies lacking the HSP70-IR occurred. In the DRGs, HSP70 expression was mildly up-regulated in small and medium-sized neurons and in satellite cells. On the contrary, DRGs from intact or sham-operated dogs did not reveal HSP70 specific neuronal staining. In conclusion, we have demonstrated that the MCEC in dogs mimicking the cauda equina syndrome in clinical settings evokes expression of HSP70 synthesis in specific neurons of the lumbo-sacro-coccygeal spinal cord segments and in small and medium sized neurons of corresponding DRGs. This suggests that HSP70 may play an active role in neuroprotective processes partly by maintaining intracellular protein integrity and preventing the neuronal degeneration in this experimental paradigm.

Excitotoxicity is the major contributor to the pathophysiological damage after acute spinal cord injury which is often incomplete, yet it produces paralysis with uncertain outcome for gait recovery despite early intensive care support. Neuroprotecting the spinal cord during the early phase of injury is an important goal to determine a favourable outcome to suppress delayed pathological events that extend the primary damage and amplify the loss of motor function often with irreversible consequences. While intensive care and neurosurgical intervention remain mainstay treatments, effective neuroprotection requires further focused experimental studies under controlled conditions. To better understand the pathophysiological mechanism of spinal lesion an in vitro model of rat spinal cord has been developed by our laboratory whereby injury is mimicked by a moderate excitotoxic insult. Such an injury suppresses the locomotor networks together with partial loss of motoneuronal population. The present thesis explores if the volatile general anesthetic methoxyflurane can protect spinal locomotor networks from kainate induced excitotoxicity and whether motoneuronal survival after excitotoxicity relies on cell expression of heat shock protein 70 (HSP70), a cytosolic neuroprotective protein binding and sequestering metabolic distress-generated proteins. The protocols involved 1 h excitotoxic stimulation on day 1 followed by electrophysiological and immunohistochemical testing after 24 h. A time-limited (1 h), single administration of methoxyfluorane together with kainate (or with 30 min or 60 min delay), prevented any depression of spinal reflexes, loss of motoneuron excitability, and histological damage. Methoxyfluorane per se temporarily decreased synaptic transmission and motoneuron excitability. These effects were readily reversible on washout. When methoxyfluorane was applied with or after kainate, spinal locomotor activity recorded as alternating electrical discharges from lumbar motor pools was fully preserved after 24 h. Furthermore to test the second hypothesis, the motoneurons were investigated for their expression of apoptosis inducing factor (AIF; a known biomarker of cell death) which became preferentially localized to the nucleus in pyknotic cells after excitotoxicity. The surviving motoneurons showed strong expression of HSP70 with no nuclear AIF. The sham preparations did not show any AIF nuclear translocation whereas the preparations treated with kainate (100 µM) were the most affected. VER155008, a pharmacological inhibitor of HSP70, per se induced neurotoxicity comparable to that of kainate. Electrophysiological recording indicated depression of motoneuron field potential with strong decrease in excitability and impaired synaptic transmission following kainate or VER155008. Their combined application elicited more intense neurotoxicity. Interestingly, motoneurons in the spinal cord (24 h in vitro) showed large expression of HSP70 compared to freshly dissected tissue, suggesting that HSP70 up-regulation was critical for spinal cord preparation survival in vitro. These data suggest that a volatile general anesthetic could provide strong electrophysiological and histological neuroprotection that enabled retention of locomotor network activity even one day after the excitotoxic challenge. Our study also showed that HSP70 is important for motoneuronal survival. It is hypothesized that the benefits of early neurosurgery for acute SCI might be enhanced if, in addition to injury decompression and stabilization, the protective role of general anesthesia is maximized. Another potential future strategy to neuroprotect motoneurons could be the upregulation of HSP70 activity by either using its pharmacological enhancers or by inducing its over-expression.