Exercise preconditioning protects against spinal cord injury in rats by upregulating neuronal and astroglial heat shock protein 72

CircSmox knockdown alleviates PC12 cell apoptosis and inflammation in spinal cord injury by miR-340-5p/Smurf1 axis

BACKGROUND

Spinal cord injury (SCI) is a traumatic central nervous system disorder that leads to irreversible neurological dysfunction. Emerging evidence has shown that differentially expressed circular RNAs (circRNAs) after SCI is closely associated with the pathophysiological process. Herein, the potential function of circRNA spermine oxidase (circSmox) in functional recovery after SCI was investigated.

METHODS

Differentiated PC12 cells stimulated with lipopolysaccharide (LPS) were employed as an in vitro model for neurotoxicity research. Levels of genes and proteins were detected by quantitative real-time PCR and Western blot analysis. Cell viability and apoptosis were determined by CCK-8 assay and flow cytometry. Western blot analysis was used to detect the protein level of apoptosis-related markers. The levels of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α. Dual-luciferase reporter, RIP, and pull-down assays were used to confirm the target relationship between miR-340-5p and circSmox or Smurf1 (SMAD Specific E3 Ubiquitin Protein Ligase 1).

RESULTS

LPS elevated the levels of circSmox and Smurf1, but decreased the levels of miR-340-5p in PC12 cells in a dose-dependent manner. Functionally, circSmox silencing alleviated LPS-induced apoptosis and inflammation in PC12 cells in vitro. Mechanistically, circSmox directly sponged miR-340-5p, which targeted Smurf1. Rescue experiments showed that miR-340-5p inhibition attenuated the neuroprotective effect of circSmox siRNA in PC12 cells. Moreover, miR-340-5p suppressed LPS-triggered neurotoxicity in PC12 cells, which was reversed by Smurf1 overexpression.

CONCLUSION

CircSmox enhances LPS-induced apoptosis and inflammation via miR-340-5p/Smurf1 axis, providing an exciting view of the potential involvement of circSmox in SCI pathogenesis.

The Proteostasis Network: A Global Therapeutic Target for Neuroprotection after Spinal Cord Injury

Proteostasis (protein homeostasis) is critical for cellular as well as organismal survival. It is strictly regulated by multiple conserved pathways including the ubiquitin-proteasome system, autophagy, the heat shock response, the integrated stress response, and the unfolded protein response. These overlapping proteostasis maintenance modules respond to various forms of cellular stress as well as organismal injury. While proteostasis restoration and ultimately organism survival is the main evolutionary driver of such a regulation, unresolved disruption of proteostasis may engage pro-apoptotic mediators of those pathways to eliminate defective cells. In this review, we discuss proteostasis contributions to the pathogenesis of traumatic spinal cord injury (SCI). Most published reports focused on the role of proteostasis networks in acute/sub-acute tissue damage post-SCI. Those reports reveal a complex picture with cell type- and/or proteostasis mediator-specific effects on loss of neurons and/or glia that often translate into the corresponding modulation of functional recovery. Effects of proteostasis networks on such phenomena as neuro-repair, post-injury plasticity, as well as systemic manifestations of SCI including dysregulation of the immune system, metabolism or cardiovascular function are currently understudied. However, as potential interventions that target the proteostasis networks are expected to impact many cell types across multiple organ systems that are compromised after SCI, such therapies could produce beneficial effects across the wide spectrum of highly variable human SCI.

Mechanism Underlying Acupuncture Therapy in Spinal Cord Injury: A Narrative Overview of Preclinical Studies

Spinal cord injury (SCI) results from various pathogenic factors that destroy the normal structure and function of the spinal cord, subsequently causing sensory, motor, and autonomic nerve dysfunction. SCI is one of the most common causes of disability and death globally. It leads to severe physical and mental injury to patients and causes a substantial economic burden on families and the society. The pathological changes and underlying mechanisms within SCI involve oxidative stress, apoptosis, inflammation, etc. As a traditional therapy, acupuncture has a positive effect promoting the recovery of SCI. Acupuncture-induced neuroprotection includes several mechanisms such as reducing oxidative stress, inhibiting the inflammatory response and neuronal apoptosis, alleviating glial scar formation, promoting neural stem cell differentiation, and improving microcirculation within the injured area. Therefore, the recent studies exploring the mechanism of acupuncture therapy in SCI will help provide a theoretical basis for applying acupuncture and seeking a better treatment target and acupuncture approach for SCI patients.

Exercise Rehabilitation and/or Astragaloside Attenuate Amyloid-beta Pathology by Reversing BDNF/TrkB Signaling Deficits and Mitochondrial Dysfunction

We aim to investigate the mechanisms underlying the beneficial effects of exercise rehabilitation (ER) and/or astragaloside (AST) in counteracting amyloid-beta (Aβ) pathology. Aβ oligomers were microinjected into the bilateral ventricles to induce Aβ neuropathology in rats. Neurobehavioral functions were evaluated. Cortical and hippocampal expressions of both BDNF/TrkB and cathepsin D were determined by the western blotting method. The rat primary cultured cortical neurons were incubated with BDNF and/or AST and ANA12 followed by exposure to aggregated Aβ for 24 h. In vivo results showed that ER and/or AST reversed neurobehavioral disorders, downregulation of cortical and hippocampal expression of both BDNF/TrkB and cathepsin D, neural pathology, Aβ accumulation, and altered microglial polarization caused by Aβ. In vitro studies also confirmed that topical application of BDNF and/or AST reversed the Aβ-induced cytotoxicity, apoptosis, mitochondrial distress, and synaptotoxicity and decreased expression of p-TrkB, p-Akt, p-GSK3β, and β-catenin in rat cortical neurons. The beneficial effects of combined ER (or BDNF) and AST therapy in vivo and in vitro were superior to ER (or BDNF) or AST alone. Furthermore, we observed that any gains from ER (or BDNF) and/or AST could be significantly eliminated by ANA-12, a potent BDNF/TrkB antagonist. These results indicate that whereas ER (or BDNF) and/or AST attenuate Aβ pathology by reversing BDNF/TrkB signaling deficits and mitochondrial dysfunction, combining these two potentiates each other's therapeutic effects. In particular, AST can be an alternative therapy to replace ER.

Heat Shock Protein 70 in Penile Neurovascular Regeneration Requires Cystathionine Gamma-Lyase

Purpose

Diabetes mellitus, one of the major causes of erectile dysfunction, leads to a poor response to phosphodiesterase-5 inhibitors. Heat shock protein 70 (Hsp70), a ubiquitous molecular chaperone, is known to play a role in cell survival and neuroprotection. Here, we aimed to assess whether and how Hsp70 improves erectile function in diabetic mice.

Materials and Methods

Eight-week-old male C57BL/6 mice and Hsp70-Tg mice were used in this study. We injected Hsp70 protein into the penis of streptozotocin (STZ)-induced diabetic mice. Detailed mechanisms were evaluated in WT or Hsp70-Tg mice under normal and diabetic conditions. Primary MCECs, and MPG and DRG tissues were cultivated under normal-glucose and high-glucose conditions.

Results

Using Hsp70-Tg mice or Hsp70 protein administration, we demonstrate that elevated levels of Hsp70 restores erectile function in diabetic mice. We found that cystathionine gamma-lyase (Cse) is a novel target of Hsp70 in this process, showing that Hsp70-Cse acts through the SDF1/HO-1/PI3K/Akt/eNOS/NF-κB p65 pathway to exert its neurovascular regeneration-promoting effects. Coimmunoprecipitation and pull-down assays using mouse cavernous endothelial cells treated with Hsp70 demonstrated physical interactions between Hsp70 and Cse with a dissociation constant of 1.8 nmol/L.

Conclusions

Our findings provide novel and solid evidence that Hsp70 acts through a Cse-dependent mechanism to mediate neurovascular regeneration and restoration of erectile function under diabetic conditions.

Exosomes Derived from lncRNA TCTN2-Modified Mesenchymal Stem Cells Improve Spinal Cord Injury by miR-329-3p/IGF1R Axis

Mesenchymal stem cells (MSCs)-derived exosomes play significant roles in alleviating spinal cord injury (SCI). Previous study showed that long non-coding RNA tectonic family member 2 (TCTN2) was able to relieve SCI. Herein, whether TCTN2 exerted its roles in functional recovery after SCI via exosomes derived from MSCs was explored. The SCI model was established in rats, and the neurological function was evaluated using the Basso, Beattie, and Bresnahan (BBB) scoring. Lipopolysaccharide (LPS)-induced differentiated PC12 cells were used as an in vitro model for neurotoxicity research. The expression of genes and proteins was detected by qRT-PCR and Western blot. Exosomes were isolated by ultracentrifugation and qualified by TEM and Western blot. In vitro assays were performed using CCK-8 assay, EdU assay, and flow cytometry, respectively. Dual-luciferase reporter assay and RIP assay were used to confirm the target relationship between miR-329-3p and TCTN2 or insulin-like growth factor1 receptor (IGF1R). TCTN2 expression was down-regulated in SCI model rat and lipopolysaccharide (LPS)-stimulated PC12 cells. MSCs produced exosomes and could package TCTN2 into secreted exosomes. Tail vein injection of TCTN2 exosomes into rats significantly improved functional recovery of SCI. Meanwhile, TCTN2 exosomes treatment alleviated LPS-induced neuronal apoptosis, inflammation, and oxidative stress in vitro. Additionally, TCTN2 targeted miR-329-3p and subsequently regulated the expression of its target IGF1R. Rescue assays suggested that miR-329-3p/IGF1R axis mediated the beneficial effects of TCTN2 exosomes on LPS-treated PC12 cells. In all, exosomes derived from TCTN2-modified MSCs could improve functional recovery of SCI in vivo and attenuate LPS-induced neuronal apoptosis, inflammation, and oxidative stress in vitro via miR-329-3p/IGF1R axis, suggesting a novel insight into the development of MSC-exosomes-based therapy for SCI.

Neuropathic pain after spinal cord injury and physical exercise in animal models: A systematic review and meta-analysis

The aim of this systematic review was to summarize the effects of physical exercise on neuropathic pain (NP) in animal models of SCI. The search was conducted in Medline and Science Direct to identify experimental preclinical studies involving animal models of SCI, physical exercise as an intervention and the assessment of NP. Fifteen articles met the eligibility criteria. The review shows that in studies of NP involving animal models of SCI, rodents are the most common species. Thoracic contusion is the most common injury and mechanical and thermal nociception are the most frequently assessed NP components. The benefits of physical exercise vary according to its starting period and total duration. In addition, there is considerable heterogeneity regarding the type and intensity of exercise capable of alleviating NP after SCI. Furthermore, physical exercise has beneficial effects on mechanical, thermal and cold nociception, and spontaneous pain. These results are weakened by the paucity of studies involving these pain outcomes. The review protocol is published for free access on the SyRF platform (http://syrf.org.uk/protocols/).

Overexpression of lncRNA TCTN2 protects neurons from apoptosis by enhancing cell autophagy in spinal cord injury

Neuronal apoptosis is the main pathological feature of spinal cord injury (SCI), while autophagy contributes to ameliorating neuronal damage via inhibition of apoptosis. Here, we investigated the role of tectonic family member 2 (TCTN2) long non-coding RNA on apoptosis and autophagy in SCI. TCTN2 was down-regulated in the spinal cord tissues of a rat model of SCI and in oxygen-glucose deprivation-induced hypoxic SY-SH-5Y cells, while microRNA-216b (miR-216b) was up-regulated. Overexpression of TCTN2 reduced neuron apoptosis by inducing autophagy, and TCTN2 was observed to negatively regulate miR-216b. Furthermore, TCTN2 promoted autophagy to repress apoptosis through the miR-216b-Beclin-1 pathway, and overexpression of TCTN2 improved neurological function in the SCI rat model. In summary, our data suggest that TCTN2 enhances autophagy by targeting the miR-216b-Beclin-1 pathway, thereby ameliorating neuronal apoptosis and relieving spinal cord injury.

Exercise Preconditioning Attenuates Neurological Injury by Preserving Old and Newly Formed HSP72-Containing Neurons in Focal Brain Ischemia Rats

Background: Exercise preconditioning (EP⁺) is a useful and important procedure for the prevention of stroke. We aimed to ascertain whether EP⁺ protects against ischemic brain injury by preserving heat shock protein (HSP) 72-containing neurons in ischemic brain tissues. Methods: Adult male Sprague-Dawley rats (n=240) were used to assess the contribution of HSP72-containing neurons to the neuroprotective effects of EP⁺ on ischemic brain injury caused by transient middle cerebral artery occlusion. Results: Significant (P<0.05) increases in the percentages of both old HSP72-containing neurons (NeuN+HSP72 double positive cells) (18~20% vs. 40~50%) and newly formed HSP72-containing neurons (BrdU+NeuN+HSP72 triple positive cells); (2~3% vs. 16~20%) after 3 weeks of exercise coincided with significant (P<0.05) reductions in brain ischemia volume (250 mm³ vs. 100 mm³), brain edema (78% vs. 74% brain water content), blood-brain barrier disruption (1.5 μg/g vs. 0.7 μg/g tissue Evans Blue dye extravasation) and neurological motor deficits (neurological severity scores of 12 vs. 6 and maximal angles of 60° vs. 20°) in brain ischemia rats. Reductions in the percentages of both old (from 40~50% to 10~12%) and newly formed (from 18~20% to 5~7%) HSP72-containing neurons by gene silencing with an intracerebral injection of pSUPER small interfering RNA showed a significant (P<0.05) reversal in the neuroprotective outcomes. Our data provide an inverse correlation between the EP⁺-mediated increases in both old and newly formed HSP72-containing neurons and the extent of cerebral ischemic injury. Conclusions: The percentages of both old and newly formed HSP72-containing neurons are inversely correlated with the outcomes of ischemic brain injury. Additionally, preischemic treadmill exercise improves the outcomes of ischemic brain injury by preserving both the old and newly formed HSP72-containing neurons in rats.

Exercise attenuates neurological deficits by stimulating a critical HSP70/NF-κB/IL-6/synapsin I axis in traumatic brain injury rats

Background

Despite previous evidence for a potent inflammatory response after a traumatic brain injury (TBI), it is unknown whether exercise preconditioning (EP) improves outcomes after a TBI by modulating inflammatory responses.

Methods

We performed quantitative real-time PCR (qPCR) to quantify the genes encoding 84 cytokines and chemokines in the peripheral blood and used ELISA to determine both the cerebral and blood levels of interleukin-6 (IL-6). We also performed the chromatin immunoprecipitation (ChIP) assay to evaluate the extent of nuclear factor kappa-B (NF-κB) binding to the DNA elements in the IL-6 promoter regions. Also, we adopted the Western blotting assay to measure the cerebral levels of heat shock protein (HSP) 70, synapsin I, and β-actin. Finally, we performed both histoimmunological and behavioral assessment to measure brain injury and neurological deficits, respectively.

Results

We first demonstrated that TBI upregulated nine pro-inflammatory and/or neurodegenerative messenger RNAs (mRNAs) in the peripheral blood such as CXCL10, IL-18, IL-16, Cd-70, Mif, Ppbp, Ltd, Tnfrsf 11b, and Faslg. In addition to causing neurological injuries, TBI also upregulated the following 14 anti-inflammatory and/or neuroregenerative mRNAs in the peripheral blood such as Ccl19, Ccl3, Cxcl19, IL-10, IL-22, IL-6, Bmp6, Ccl22, IL-7, Bmp7, Ccl2, Ccl17, IL-1rn, and Gpi. Second, we observed that EP inhibited both neurological injuries and six pro-inflammatory and/or neurodegenerative genes (Cxcl10, IL-18, IL-16, Cd70, Mif, and Faslg) but potentiated four anti-inflammatory and/or neuroregenerative genes (Bmp6, IL-10, IL-22, and IL-6). Prior depletion of cerebral HSP70 with gene silence significantly reversed the beneficial effects of EP in reducing neurological injuries and altered gene profiles after a TBI. A positive Pearson correlation exists between IL-6 and HSP70 in the peripheral blood or in the cerebral levels. In addition, gene silence of cerebral HSP70 significantly reduced the overexpression of NF-κB, IL-6, and synapsin I in the ipsilateral brain regions after an EP in rats.

Conclusions

TBI causes neurological deficits associated with stimulating several pro-inflammatory gene profiles but inhibiting several anti-inflammatory gene profiles of cytokines and chemokines. Exercise protects against neurological injuries via stimulating an anti-inflammatory HSP70/NF-κB/IL-6/synapsin I axis in the injured brains.

D-β-hydroxybutyrate promotes functional recovery and relieves pain hypersensitivity in mice with spinal cord injury

BACKGROUND AND PURPOSE

Spinal cord injury (SCI) leads to severe motor and sensory dysfunction and significantly reduces the quality of life. The aim of the present work was to investigate the effect of administration of exogenous D-β-hydroxybutyrate (DBHB) on functional recovery and neuropathic pain in spinal cord-injured mice.

EXPERIMENTAL APPROACH

Mice were given a moderate-severe thoracic spinal contusion injury at the T_9-10 level and treated with exogenous DBHB.

KEY RESULTS

Treatment of SCI mice with DBHB markedly improved locomotor function and relieved SCI-induced hypersensitivities to mechanical and thermal stimulation. DBHB treatment partly prevented the SCI-induced loss of motor neurons and suppressed microglial and glial activation. DBHB treatment enhanced histone acetylation and up-regulated expression of the transcription factor FOXO3a, catalase and SOD2 in injured region of SCI mice. DBHB treatment suppressed SCI-induced NLRP3 inflammasome activation and reduced protein expression of IL-1β and IL-18. In addition, DBHB treatment improved mitochondrial function and abated oxidative stress following SCI.

CONCLUSIONS AND IMPLICATIONS

DBHB promoted functional recovery and relieved pain hypersensitivity in mice with SCI, possibly through inhibition of histone deacetylation and NLRP3 inflammasome activation and preservation of mitochondrial function. DBHB could thus be envisaged as a potential use of interventions for SCI but remains to be tested in humans.

Chaperone Proteins in the Central Nervous System and Peripheral Nervous System after Nerve Injury

Injury to axons of the central nervous system (CNS) and the peripheral nervous system (PNS) is accompanied by the upregulation and downregulation of numerous molecules that are involved in mediating nerve repair, or in augmentation of the original damage. Promoting the functions of beneficial factors while reducing the properties of injurious agents determines whether regeneration and functional recovery ensues. A number of chaperone proteins display reduced or increased expression following CNS and PNS damage (crush, transection, contusion) where their roles have generally been found to be protective. For example, chaperones are involved in mediating survival of damaged neurons, promoting axon regeneration and remyelination and, improving behavioral outcomes. We review here the various chaperone proteins that are involved after nervous system axonal damage, the functions that they impact in the CNS and PNS, and the possible mechanisms by which they act.

Effects of voluntary exercise on apoptosis and cortisol after chronic restraint stress in mice

[Purpose]

To determine whether voluntary exercise (wheel running) has the potential of relieving stress.

[Methods]

In this study, restraint stress with or without voluntary wheel running was performed for mice housed in individual cages. A total of 21 ICR male mice were assigned into control (CON), restraint stress with voluntary exercise (RSVE), or restraint stress (RS) without voluntary exercise groups (n = 7 each).

[Results]

No significant difference in body weight increase was found among the three groups, although CON and RS groups had a tendency of having smaller body weight increase compared to the RSVE group. No significant difference in the expression level of liver heat shock protein 70, Bcl-2, or p53 was found among the three groups. However, caspase-3 protein level in RS group was significantly higher than that in the other two groups. Blood cortisol concentration in RS was higher (p < 0.05) than that in RSVE or CON group. It was the lowest (p < 0.05) in the RSVE group.

[Conclusion]

Our findings suggest that apoptosis caused by chronic restraint stress might be suppressed by voluntary exercise in mice.

Exercise-induced ROS in heat shock proteins response

Cells have evolved multiple and sophisticated stress response mechanisms aiming to prevent macromolecular (including proteins, lipids, and nucleic acids) damage and to maintain or re-establish cellular homeostasis. Heat shock proteins (HSPs) are among the most highly conserved, ubiquitous, and abundant proteins in all organisms. Originally discovered more than 50 years ago through heat shock stress, they display multiple, remarkable roles inside and outside cells under a variety of stresses, including also oxidative stress and radiation, recognizing unfolded or misfolded proteins and facilitating their restructuring. Exercise consists in a combination of physiological stresses, such as metabolic disturbances, changes in circulating levels of hormones, increased temperature, induction of mild to severe inflammatory state, increased production of reactive oxygen and nitrogen species (ROS and RNS). As a consequence, exercise is one of the main stimuli associated with a robust increase in different HSPs in several tissues, which appears to be also fundamental in facilitating the cellular remodeling processes related to the training regime. Among all factors involved in the exercise-related modulation of HSPs level, the ROS production in the contracting muscle or in other tissues represents one of the most attracting, but still under discussion, mechanism. Following exhaustive or damaging muscle exercise, major oxidative damage to proteins and lipids is likely involved in HSP expression, together with mechanically induced damage to muscle proteins and the inflammatory response occurring several days into the recovery period. Instead, the transient and reversible oxidation of proteins by physiological concentrations of ROS seems to be involved in the activation of stress response following non-damaging muscle exercise. This review aims to provide a critical update on the role of HSPs response in exercise-induced adaptation or damage in humans, focusing on experimental results where the link between redox homeostasis and HSPs expression by exercise has been addressed. Further, with the support of in vivo and in vitro studies, we discuss the putative molecular mechanisms underlying the ROS-mediated modulation of HSP expression and/or activity during exercise.

Protecting against ischaemic stroke in rats by heat shock protein 20-mediated exercise

BACKGROUND

Exercise preconditioning (EP(+) ) has been widely accepted as a being of safe and effective preventive measure for stroke. The purpose of this study was to investigate whether EP(+) improves outcomes of ischaemic stroke by promoting neuronal and glial expression of heat shock protein (HSP) 20.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats (288 in number) were used to investigate the contribution of HSP20-containing neurons and HSP20-containing glial cells in the exercise-mediated neuroprotection in the stroke condition using middle cerebral artery occlusion.

RESULTS

Exercise preconditioning, in addition to increasing the numbers of both the HSP20-containg neurons (88 ± 8 vs. 43 ± 4; n = 8 each group; P < 0·05) and the HSP20-containg astrocytes (102 ± 10 vs. 56 ± 5; n = 8; P < 0·05) significantly attenuated stroke-induced brain infarct (140 ± 9 vs. 341 ± 20 mm(3) ; n = 8 per group; P < 0·01), neuronal apoptosis (20 ± 5 vs. 87 ± 7; n = 8 per group; n = 8; P < 0·01), glial apoptosis (29 ± 5 vs. 101 ± 4; n = 8; P < 0·01), and neurological deficits (6·6 ± 0·3 vs. 11·7 ± 0·8; n = 8 per group; P < 0·01). Reducing the numbers of both HSP20-containing neurons and HSP20-contaiing glia by intracerebral injection of pSUPER small interfering RNAί expressing HSP20 significantly reversed the beneficial effects of EP(+) in attenuating stroke-induced cerebral infarct, neuronal and glial apoptosis, and neurological deficits.

CONCLUSIONS

The numbers of both the HSP20-containing neurons and the HSP20-containing glia inversely correlated with the outcomes of ischaemic stroke. In addition, preischaemic treadmill exercise improves outcomes of ischaemic stroke by increasing the numbers of both the HSP20-containing neurons and the HSP20-containing glia.

Decreasing or increasing heat shock protein 72 exacerbates or attenuates heat-induced cell death, respectively, in rat hypothalamic cells

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Mild heat preconditioning up-regulated HSP72 expression in cultured hypothalamic cells.

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siRNA-HSP72 pretreatment down-regulated HSP72 expression.

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Mild heat preconditioning attenuated heat-induced cell loss.

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siRNA-HSP72 pre-treatment exacerbated heat-induced cell loss.

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A positive correlation between HSP72 expression and heat tolerance might exist in hypothalamic cells.

Heat shock protein (HSP) 72 in serum was decreased to a greater degree in patients with serious heat stroke than in those with mild heat stroke. Thus, increased levels of HSP72 appeared to correlate with a better outcome for the patient. Nevertheless, the function of HSP72 in the heat-induced hypothalamic cell death has not been assessed. In this study, we found that increasing HSP72 levels with mild heat preconditioning or decreasing HSP72 levels with pSUPER plasmid expressing HSP72 small interfering RNA significantly attenuated or exacerbated heat-induced cell death in cultured primary hypothalamic cells, respectively. Our findings suggest that HSP72 plays a pivotal role in heat-induced cell death and may be associated with heat tolerance.

Exercise promotes motor functional recovery in rats with corticospinal tract injury: anti-apoptosis mechanism

Studies have shown that exercise interventions can improve functional recovery after spinal cord injury, but the mechanism of action remains unclear. To investigate the mechanism, we established a unilateral corticospinal tract injury model in rats by pyramidotomy, and used a single pellet reaching task and horizontal ladder walking task as exercise interventions postoperatively. Functional recovery of forelimbs and forepaws in the rat models was noticeably enhanced after the exercises. Furthermore, TUNEL staining revealed significantly fewer apoptotic cells in the spinal cord of exercised rats, and western blot analysis showed that spinal cord expression of the apoptosis-related protein caspase-3 was significantly lower, and the expression of Bcl-2 was significantly higher, while the expression of Bax was not signifiantly changed after exercise, compared with the non-exercised group. Expression of these proteins decreased with time after injury, towards the levels observed in sham-operated rats, however at 4 weeks postoperatively, caspase-3 expression remained significantly greater than in sham-operated rats. The present findings indicate that a reduction in apoptosis is one of the mechanisms underlying the improvement of functional recovery by exercise interventions after corticospinal tract injury.