Activation of Three Major Signaling Pathways After Endurance Training and Spinal Cord Injury

Influence of Tau on Neurotoxicity and Cerebral Vasculature Impairment Associated with Alzheimer's Disease

Alzheimer's disease is a fatal chronic neurodegenerative condition marked by a gradual decline in cognitive abilities and impaired vascular function within the central nervous system. This affliction initiates its insidious progression with the accumulation of two aberrant protein entities including Aβ plaques and neurofibrillary tangles. These chronic elements target distinct brain regions, steadily erasing the functionality of the hippocampus and triggering the erosion of memory and neuronal integrity. Several assumptions are anticipated for AD as genetic alterations, the occurrence of Aβ plaques, altered processing of amyloid precursor protein, mitochondrial damage, and discrepancy of neurotropic factors. In addition to Aβ oligomers, the deposition of tau hyper-phosphorylates also plays an indispensable part in AD etiology. The brain comprises a complex network of capillaries that is crucial for maintaining proper function. Tau is expressed in cerebral blood vessels, where it helps to regulate blood flow and sustain the blood-brain barrier's integrity. In AD, tau pathology can disrupt cerebral blood supply and deteriorate the BBB, leading to neuronal neurodegeneration. Neuroinflammation, deficits in the microvasculature and endothelial functions, and Aβ deposition are characteristically detected in the initial phases of AD. These variations trigger neuronal malfunction and cognitive impairment. Intracellular tau accumulation in microglia and astrocytes triggers deleterious effects on the integrity of endothelium and cerebral blood supply resulting in further advancement of the ailment and cerebral instability. In this review, we will discuss the impact of tau on neurovascular impairment, mitochondrial dysfunction, oxidative stress, and the role of hyperphosphorylated tau in neuron excitotoxicity and inflammation.

Osteopontin enhances the effect of treadmill training and promotes functional recovery after spinal cord injury

In this study, we examined the combined impact of osteopontin (OPN) and treadmill training on mice with spinal cord injury (SCI). OPN was overexpressed by injecting AAV9-SPP1-GFP into the sensorimotor cortex, followed by a left incomplete C5 crush injury two weeks later. Mice (Ex or Ex + OPN group) were trained at 50% maximum running speed for 8 weeks. To analyze the effects, we used biotinylated dextran amine (BDA) for tracing the corticospinal tract (CST) and performed Western blotting and immunohistochemical methods to assess the activation of the mammalian target of rapamycin (mTOR). We also examined axonal regeneration and conducted behavioral tests to measure functional recovery. The results demonstrated that treadmill training promoted the expression of neurotrophic factors such as brain-derived neurotrophic factor (BNDF) and insulin-like growth factor I (IGF-1) and activated mTOR signaling. OPN amplified the effect of treadmill training on activating mTOR signaling indicated by upregulated phosphorylation of ribosomal protein S6 kinase (S6). The combination of OPN and exercise further promoted functional recovery and facilitated limited CST axonal regeneration which did not occur with treadmill training and OPN treatment alone. These findings indicate that OPN enhances the effects of treadmill training in the treatment of SCI and offer new therapeutic insights for spinal cord injury.

Body Weight Support Treadmill Training Combined With Sciatic Nerve Electrical Stimulation Ameliorating Motor Function by Enhancing PI3K/Akt Proteins Expression via BDNF/TrkB Signaling Pathway in Rats with Spinal Cord Injury

OBJECTIVE

To investigate the effects of body weight support treadmill training (BWSTT) and sciatic nerve electrical stimulation (SNES) on motor function recovery in spinal cord injury (SCI) rats and its possible mechanism.

METHODS

Modified Allen's method was utilized for T10 incomplete SCI. The Basso-Beattie-Bresnahan (BBB) score and modified Tarlov score were applied to assess motor function. Pathologic alterations of the spinal cord and muscles were observed by hematoxylin and eosin (HE) staining. The positive staining region of collagen fibers was assessed with Masson staining. Immunofluorescence was applied to count the positive cells of brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B (TrkB). BDNF, TrkB, phosphatidylinositol-3-kinase (PI3K), and protein kinase B (Akt) relative mRNA and protein expressions were evaluated by reverse transcription polymerase chain reaction (RT-PCR) and Western blotting.

RESULTS

On the 21st day of the intervention, the motor scores in SNES and BWSTT + SNES groups were higher than that in SCI group (P < 0.05). Compared with SCI group, mRNA and protein expressions of BDNF/TrkB and PI3K/Akt were more significant on the 21st day of the intervention in SNES and BWSTT + SNES groups (P < 0.05), but there was no difference in BWSTT group (P > 0.05).

CONCLUSIONS

This experiment demonstrated that BWSTT combined with SNES contributed to alleviating spinal cord tissue injury, delaying muscle atrophy and improving locomotion. One of the possible mechanisms may be related to the regulation of the BDNF/TrkB signaling pathway, which changes the expression of PI3K/Akt protein. Furthermore, it was discovered that the ultra-early BWSTT may not be conducive to recovery.

Impact of Endurance Training on Regeneration of Axons, Glial Cells, and Inhibitory Neurons after Spinal Cord Injury: A Link between Functional Outcome and Regeneration Potential within the Lesion Site and in Adjacent Spinal Cord Tissue

Endurance training prior to spinal cord injury (SCI) has a beneficial effect on the activation of signaling pathways responsible for survival, neuroplasticity, and neuroregeneration. It is, however, unclear which training-induced cell populations are essential for the functional outcome after SCI. Adult Wistar rats were divided into four groups: control, six weeks of endurance training, Th9 compression (40 g/15 min), and pretraining + Th9 compression. The animals survived six weeks. Training alone increased the gene expression and protein level of immature CNP-ase oligodendrocytes (~16%) at Th10, and caused rearrangements in neurotrophic regulation of inhibitory GABA/glycinergic neurons at the Th10 and L2 levels, known to contain the interneurons with rhythmogenic potential. Training + SCI upregulated markers for immature and mature (CNP-ase, PLP1) oligodendrocytes by ~13% at the lesion site and caudally, and increased the number of GABA/glycinergic neurons in specific spinal cord regions. In the pretrained SCI group, the functional outcome of hindlimbs positively correlated with the protein levels of CNP-ase, PLP1, and neurofilaments (NF-l), but not with the outgrowing axons (Gap-43) at the lesion site and caudally. These results indicate that endurance training applied before SCI potentiates the repair in damaged spinal cord, and creates a suitable environment for neurological outcome.

The neuroprotective effects of estrogen and estrogenic compounds in spinal cord injury

Spinal cord injury (SCI) occurs when the spinal cord is damaged from either a traumatic event or disease. SCI is characterised by multiple injury phases that affect the transmission of sensory and motor signals and lead to temporary or long-term functional deficits. There are few treatments for SCI. Estrogens and estrogenic compounds, however, may effectively mitigate the effects of SCI and therefore represent viable treatment options. This review systematically examines the pre-clinical literature on estrogen and estrogenic compound neuroprotection after SCI. Several estrogens were examined by the included studies: estrogen, estradiol benzoate, Premarin, isopsoralen, genistein, and selective estrogen receptor modulators. Across these pharmacotherapies, we find significant evidence that estrogens indeed offer protection against myriad pathophysiological effects of SCI and lead to improvements in functional outcomes, including locomotion. A STRING functional network analysis of proteins modulated by estrogen after SCI demonstrated that estrogen simultaneously upregulates known neuroprotective pathways, such as HIF-1, and downregulates pro-inflammatory pathways, including IL-17. These findings highlight the strong therapeutic potential of estrogen and estrogenic compounds after SCI.

Multimodal rehabilitation promotes axonal sprouting and functional recovery in a murine model of spinal cord injury (SCI)

Spinal cord injury (SCI) is a devastating neurological disorder affecting millions of people worldwide, resulting in severe and permanent disabilities that significantly impact the individual's life. Rehabilitation is a commonly accepted and effective clinical treatment modality for neurological disabilities. A single form of rehabilitation training is, however, limited. Indeed, recent studies have reported that a combination of various training strategies may be more promising in promoting functional recovery. However, few studies have focused on combining different forms of rehabilitative training. Here, we investigated the effect of combining treadmill training and single pellet grasping in a well-established model of murine SCI to assess whether combining rehabilitation approaches improve outcomes. In brief, one week following crush SCI, mice were subjected to the treadmill and single pellet grasping training (SPG) for a period of six weeks. Biotinylated dextran amine (BDA) was used to anterogradely trace corticospinal tract axons to assess functionally relevant axonal sprouting. Our results revealed that the combined training upregulated p-S6 expression, facilitated axonal sprouting, increased the formation of functional synaptic connections, and promoted functional recovery of the upper limb. Our study provides experimental evidence for the benefit of combining multiple modalities of rehabilitative strategies.

The Impact of Activity-Based Interventions on Neuropathic Pain in Experimental Spinal Cord Injury

Physical activity-based rehabilitative interventions represent the main treatment concept for people suffering from spinal cord injury (SCI). The role such interventions play in the relief of neuropathic pain (NP) states is emerging, along with underlying mechanisms resulting in SCI-induced NP (SCI-NP). Animal models have been used to investigate the benefits of activity-based interventions (ABI), such as treadmill training, wheel running, walking, swimming, and bipedal standing. These activity-based paradigms have been shown to modulate inflammatory-related alterations as well as induce functional and structural changes in the spinal cord gray matter circuitry correlated with pain behaviors. Thus far, the research available provides an incomplete picture of the cellular and molecular pathways involved in this beneficial effect. Continued research is essential for understanding how such interventions benefit SCI patients suffering from NP and allow the development of individualized rehabilitative therapies. This article reviews preclinical studies on this specific topic, goes over mechanisms involved in SCI-NP in relation to ABI, and then discusses the effectiveness of different activity-based paradigms as they relate to different forms, intensity, initiation times, and duration of ABI. This article also summarizes the mechanisms of respective interventions to ameliorate NP after SCI and provides suggestions for future research directions.

Glial-Neuronal Interactions in Pathogenesis and Treatment of Spinal Cord Injury

Traumatic spinal cord injury (SCI) elicits an acute inflammatory response which comprises numerous cell populations. It is driven by the immediate response of macrophages and microglia, which triggers activation of genes responsible for the dysregulated microenvironment within the lesion site and in the spinal cord parenchyma immediately adjacent to the lesion. Recently published data indicate that microglia induces astrocyte activation and determines the fate of astrocytes. Conversely, astrocytes have the potency to trigger microglial activation and control their cellular functions. Here we review current information about the release of diverse signaling molecules (pro-inflammatory vs. anti-inflammatory) in individual cell phenotypes (microglia, astrocytes, blood inflammatory cells) in acute and subacute SCI stages, and how they contribute to delayed neuronal death in the surrounding spinal cord tissue which is spared and functional but reactive. In addition, temporal correlation in progressive degeneration of neurons and astrocytes and their functional interactions after SCI are discussed. Finally, the review highlights the time-dependent transformation of reactive microglia and astrocytes into their neuroprotective phenotypes (M2a, M2c and A2) which are crucial for spontaneous post-SCI locomotor recovery. We also provide suggestions on how to modulate the inflammation and discuss key therapeutic approaches leading to better functional outcome after SCI.