Axotomy increases the expression of glucose-regulated protein 78 kDa in rat facial nucleus

Cell-Permeable HSP70 Protects Neurons and Astrocytes Against Cell Death in the Rotenone-Induced and Familial Models of Parkinson's Disease

Heat shock protein 70 (HSP70) is activated under stress response. Its involvement in cell protection, including energy metabolism and quality control makes it a promising pharmacological target. A strategy to increase HSP70 levels inside the cells is the application of recombinant HSP70. However, cell permeability and functionality of these exogenously applied proteins inside the cells is still disputable. Here, using fluorescence- labeled HSP70, we have studied permeability and distribution of HSP70 inside primary neurons and astrocytes, and how exogenous HSP70 changes mitochondrial metabolism and mitophagy. We have found that exogenous recombinant HSP70 can penetrate the neurons and astrocytes and distributes in mitochondria, lysosomes and in lesser degree in the endoplasmic reticulum. HSP70 increases mitochondrial membrane potential in control neurons and astrocytes, and in fibroblasts of patients with familial Parkinson´s disease (PD) with PINK1 and LRRK2 mutations. Increased mitochondrial membrane potential was associated with higher mitochondrial ROS production and activation of mitophagy. Importantly, preincubation of the cells with HSP70 protected neurons and astrocytes against cell death in a toxic model of PD induced by rotenone, and in the PINK1 and LRRK2 PD human fibroblasts. Thus, exogenous recombinant HSP70 is cell permeable, and acts as endogenous HSP70 protecting cells in the case of toxic model and familial forms of Parkinson's Disease.

Exogenous Hsp70 exerts neuroprotective effects in peripheral nerve rupture model

Hsp70 is the main molecular chaperone responsible for cellular proteostasis under normal conditions and for restoring the conformation or utilization of proteins damaged by stress. Increased expression of endogenous Hsp70 or administration of exogenous Hsp70 is known to exert neuroprotective effects in models of many neurodegenerative diseases. In this study, we have investigated the effect of exogenous Hsp70 on recovery from peripheral nerve injury in a model of sciatic nerve transection in rats. It was shown that recombinant Hsp70 after being added to the conduit connecting the ends of the nerve at the site of its extended severance, migrates along the nerve into the spinal ganglion and is retained there at least three days. In animals with the addition of recombinant Hsp70 to the conduit, a decrease in apoptosis in the spinal ganglion cells after nerve rupture, an increase in the level of PTEN-induced kinase 1 (PINK1), an increase in markers of nerve tissue regeneration and a decrease in functional deficit were observed compared to control animals. The obtained data indicate the possibility of using recombinant Hsp70 preparations to accelerate the recovery of patients after neurotrauma.

Effects of sciatic nerve transection on glucose uptake in the presence and absence of lactate in the frog dorsal root ganglia and spinal cord

Frogs have been used as an alternative model to study pain mechanisms because the simplicity of their nervous tissue and the phylogenetic aspect of this question. One of these models is the sciatic nerve transection (SNT), which mimics the clinical symptoms of “phantom limb”, a condition that arises in humans after amputation or transverse spinal lesions. In mammals, the SNT increases glucose metabolism in the central nervous system, and the lactate generated appears to serve as an energy source for nerve cells. An answerable question is whether there is elevated glucose uptake in the dorsal root ganglia (DRG) after peripheral axotomy. As glucose is the major energy substrate for frog nervous tissue, and these animals accumulate lactic acid under some conditions, bullfrogs Lithobates catesbeianus were used to demonstrate the effect of SNT on DRG and spinal cord 1-[14C] 2-deoxy-D-glucose (14C-2-DG) uptake in the presence and absence of lactate. We also investigated the effect of this condition on the formation of 14CO2 from 14C-glucose and 14C-L-lactate, and plasmatic glucose and lactate levels. The 3-O-[14C] methyl-D-glucose (14C-3-OMG) uptake was used to demonstrate the steady-state tissue/medium glucose distribution ratio under these conditions. Three days after SNT, 14C-2-DG uptake increased, but 14C-3-OMG uptake remained steady. The increase in 14C-2-DG uptake was lower when lactate was added to the incubation medium. No change was found in glucose and lactate oxidation after SNT, but lactate and glucose levels in the blood were reduced. Thus, our results showed that SNT increased the glucose metabolism in the frog DRG and spinal cord. The effect of lactate on this uptake suggests that glucose is used in glycolytic pathways after SNT.

Induced expressions of Rab24 GTPase and LC3 in nerve-injured motor neurons

Rab24 is a member of the Rab GTPase family, but its function is unclear. Here, we demonstrated increase in Rab24 mRNA in nerve-injured hypoglossal motor neurons of rats. Expression of Rab24 mRNA was also induced in differentiated PC12 cells following proteasome inhibitor (MG132) treatment. MG132 treatment further induced expression of microtubule-associated protein light chain 3 (LC3), and accumulation of LC3-II, a processed form of LC3 and the most reliable marker for autophagy. Induction of LC3 mRNA and accumulation of LC3-II were also observed in nerve-injured hypoglossal motor neurons, and partial co-localization of Rab24 and LC3 was demonstrated by immunohistochemistry. The present data suggest that nerve injury promotes autophagy-like events, and this may be an important response for degradation of unnecessary and misfolded proteins to recycle limited amino acids, and synthesize new proteins that are necessary for survival and nerve regeneration responses.

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.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Cloning and characterization of a novel GRP78-binding protein in the rat brain

The full-length cDNA clone of a novel GRP78-binding protein (GBP) was isolated from rat brain using PCR-selected cDNA subtraction. GBP was predominantly expressed in neuronal cells among various brain tissues. GBP mRNA was already detected in the E12 brain and then gradually increased to reach a peak within P0-2 weeks after birth. GBP expression in the brain decreased age-dependently to approximately 30% of the postnatal level at 12 months. GBP encoded 1021 amino acids and was predicted to have two transmembrane regions and glutamic acid- and proline-rich regions. Because the sequence of GBP offered few clues to the possible function, we performed a GST-tagged GBP pull-down assay in PC12 lysates and identified GRP78, one of the heat shock proteins, as a counterpart. Observation of COS7 cells expressing green fluorescent protein- or Myc-tagged GBP showed that GBP was localized in the endoplasmic reticulum-Golgi domain where BODIPY 558/568 (4,4-difluro-5-(2-thienyl)-4-bora-3alpha,4alpha-diaza-S-indacene)-labeled brefeldin A accumulated. To investigate a biological role for GBP, we established Neuro2a cells stably expressing Myc-tagged GBP. Overexpression of GBP did not affect cell growth or morphological features but attenuated the time-dependent decrease in cell viability caused by serum deprivation compared with control cells. After 48 h of serum starvation, Neuro2a cells overexpressing GBP were resistant to the cell death induced by serum withdrawal. These results suggest that GBP would have a relevant functional role in embryonic and postnatal development of the brain.

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

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.

Gene expression in the brain across the sleep-waking cycle

Sleep and waking differ significantly in terms of behavior, metabolism, and neuronal activity. Recent evidence indicates that sleep and waking also differ with respect to the expression of certain genes. To systematically investigate such changes, we used mRNA differential display and cDNA microarrays to screen approximately 10000 transcripts expressed in the cerebral cortex of rats after 8 h of sleep, spontaneous waking, or sleep deprivation. We found that 44 genes had higher mRNA levels after waking and/or sleep deprivation relative to sleep, while 10 were upregulated after sleep. Known genes that were upregulated in waking and sleep deprivation can be grouped into the following categories: immediate early genes/transcription factors (Arc, CHOP, IER5, NGFI-A, NGFI-B, N-Ras, Stat3), genes related to energy metabolism (glucose type I transporter Glut1, Vgf), growth factors/adhesion molecules (BDNF, TrkB, F3 adhesion molecule), chaperones/heat shock proteins (BiP, ERP72, GRP75, HSP60, HSP70), vesicle- and synapse-related genes (chromogranin C, synaptotagmin IV), neurotransmitter/hormone receptors (adrenergic receptor alpha(1A) and beta(2), GABA(A) receptor beta(3), glutamate NMDA receptor 2A, glutamate AMPA receptor GluR2 and GluR3, nicotinic acetylcholine receptor beta(2), thyroid hormone receptor TRbeta), neurotransmitter transporters (glutamate/aspartate transporter GLAST, Na(+)/Cl(-) transporter NTT4/Rxt1), enzymes (aryl sulfotransferase, c-jun N-terminal kinase 1, serum/glucocorticoid-induced serine/threonine kinase), and a miscellaneous group (calmodulin, cyclin D2, LMO-4, metallothionein 3). Several other genes that were upregulated in waking and all the genes upregulated in sleep, with the exception of the one coding for membrane protein E25, did not match any known sequence. Thus, significant changes in gene expression occur across behavioral states, which are likely to affect basic cellular functions such as RNA and protein synthesis, neural plasticity, neurotransmission, and metabolism.

The endoplasmic reticulum stress-responsive protein GRP78 protects neurons against excitotoxicity and apoptosis: suppression of oxidative stress and stabilization of calcium homeostasis

The 78-kDa glucose-regulated protein (GRP78) is localized in the endoplasmic reticulum (ER), and its expression is increased by environmental stressors in many types of nonneuronal cells. We report that levels of GRP78 are increased in cultured rat hippocampal neurons exposed to glutamate and oxidative insults (Fe2+ and amyloid beta-peptide) and that treatment of cultures with a GRP78 antisense oligodeoxynucleotide increases neuronal death following exposure to each insult. GRP78 antisense treatment enhanced apoptosis of differentiated PC12 cells following NGF withdrawal or exposure to staurosporine. Pretreatment of hippocampal cells with 2-deoxy-d-glucose, a potent inducer of GRP78 expression, protected neurons against excitotoxic and oxidative injury. GRP78 expression may function to suppress oxidative stress and stabilize calcium homeostasis because treatment with GRP78 antisense resulted in increased levels of reactive oxygen species and intracellular calcium following exposure to glutamate and oxidative insults in hippocampal neurons. Dantrolene (a blocker of ER calcium release), uric acid (an antioxidant), and zVAD-fmk (a caspase inhibitor) each protected neurons against the death-enhancing action of GRP78 antisense. The data suggest that ER stress plays a role in neuronal cell death induced by an array of insults and that GRP78 serves a neuroprotective function.