Molecular changes associated with spinal cord aging

Neuroprotective treatment with the nitrone compound OKN-007 mitigates age-related muscle weakness in aging mice

Despite the universal impact of sarcopenia on compromised health and quality of life in the elderly, promising pharmaceutical approaches that can effectively mitigate loss of muscle and function during aging have been limited. Our group and others have reported impairments in peripheral motor neurons and loss of muscle innervation as initiating factors in sarcopenia, contributing to mitochondrial dysfunction and elevated oxidative stress in muscle. We recently reported a reduction in α motor neuron loss in aging mice in response to the compound OKN-007, a proposed antioxidant and anti-inflammatory agent. In the current study, we asked whether OKN-007 treatment in wildtype male mice for 8-9 months beginning at 16 months of age can also protect muscle mass and function. At 25 months of age, we observed a reduction in the loss of whole-body lean mass, a reduced loss of innervation at the neuromuscular junction and well-preserved neuromuscular junction morphology in OKN-007 treated mice versus age matched wildtype untreated mice. The loss in muscle force generation in aging mice (~ 25%) is significantly improved with OKN-007 treatment. In contrast, OKN-007 treatment provided no protection in loss of muscle mass in aging mice. Mitochondrial function was improved by OKN-007 treatment, consistent with its potential antioxidative properties. Together, these exciting findings are the first to demonstrate that interventions through neuroprotection can be an effective therapy to counter aging-related muscle dysfunction.

Chronic pain in the elderly: Exploring cellular and molecular mechanisms and therapeutic perspectives

Chronic pain is a debilitating condition frequently observed in the elderly, involving numerous pathological mechanisms within the nervous system. Diminished local blood flow, nerve degeneration, variations in fiber composition, alterations in ion channels and receptors, accompanied by the sustained activation of immune cells and release of pro-inflammatory cytokines, lead to overactivation of the peripheral nervous system. In the central nervous system, chronic pain is strongly associated with the activation of glial cells, which results in central sensitization and increased pain perception. Moreover, age-related alterations in neural plasticity and disruptions in pain inhibitory pathways can exacerbate chronic pain in older adults. Finally, the environmental influences on the development of chronic pain in the elderly must be considered. An understanding of these mechanisms is essential for developing novel treatments for chronic pain, which can significantly improve the quality of life for this vulnerable population.

Autophagy markers LC3 and p62 in aging lumbar motor neurons

Autophagy is a ubiquitous process through which damaged cytoplasmic structures are recycled and degraded within cells. Aging can affect autophagy regulation in different steps leading to the accumulation of damaged organelles and proteins, which can contribute to cell dysfunction and death. Motor neuron (MN) loss and sarcopenia are prominent features of neuromuscular aging. Previous studies on phrenic MNs showed increased levels of the autophagy proteins LC3 and p62 in 24 month compared to 6 month old mice, consistent with the onset of diaphragm muscle sarcopenia. In the present study, we hypothesized that aging leads to increased expression of the autophagy markers LC3 and p62 in single lumbar MNs. Expression of LC3 and p62 in lumbar MNs (spinal levels L1-L6) was assessed using immunofluorescence and confocal imaging of male and female mice at 6, 18 and 24 months of age, reflecting 100 %, 90 % and 75 % survival, respectively. A mixed linear model with animal as a random effect was used to compare relative LC3 and p62 expression in choline acetyl transferase-positive MNs across age groups. Expression of LC3 and p62 decreased in the white matter of the lumbar spinal cord with aging, with ~29 % decrease in LC3 and ~ 7 % decrease in p62 expression at 24 months of age compared to 6 months of age. There was no change in LC3 or p62 expression in the gray matter with age. LC3 expression in MNs relative to white matter increased significantly with age, with 150 % increase at 24 months of age compared to 6 months of age. Similarly, p62 expression in MNs relative to white matter increased significantly with age, with ~14 % increase at 24 months of age compared to 6 months of age. No effect of sex or MN pool was observed in LC3 and p62 expression in MNs. Overall, these data suggest autophagy impairment during elongation (increased LC3) and degradation (increased p62) phases with aging in lumbar MNs.

Old age alters inflammation and autophagy signaling in the brain, leading to exacerbated neurological outcomes after spinal cord injury in male mice

Older patients with spinal cord injury (SCI) have different features with regard to neurological characteristics after injury. Recent large-scale longitudinal population-based studies showed that individuals with SCI are at a higher risk of developing dementia than non-SCI patients, indicating that SCI is a potential risk factor for dementia. Aging is known to potentiate inflammation and neurodegeneration at the injured site leading to impaired recovery from SCI. However, no research has been aimed at studying the mechanisms of SCI-mediated cognitive impairment in the elderly. The present study examined neurobehavioral and molecular changes in the brain and the underlying mechanisms associated with brain dysfunction in aged C57BL/6 male mice using a contusion SCI model. At 2 months post-injury, aged mice displayed worse performance in locomotor, cognitive and depressive-like behavioral tests compared to young adult animals. Histopathology in injured spinal cord tissue was exacerbated in aged SCI mice. In the brain, transcriptomic analysis with NanoString neuropathology panel identified activated microglia and dysregulated autophagy as the most significantly altered pathways by both age and injury. These findings were further validated by flow cytometry, which demonstrated increased myeloid and lymphocytes infiltration at both the injured site and brain of aged mice. Moreover, SCI in aged mice altered microglial function and dysregulated autophagy in microglia, resulting in worsened neurodegeneration. Taken together, our data indicate that old age exacerbates neuropathological changes in both the injured spinal cord and remote brain regions leading to poorer functional outcomes, at least in part, through altered inflammation and autophagy function.

Common synaptic inputs and persistent inward currents of vastus lateralis motor units are reduced in older male adults

Although muscle atrophy may partially account for age-related strength decline, it is further influenced by alterations of neural input to muscle. Persistent inward currents (PIC) and the level of common synaptic inputs to motoneurons influence neuromuscular function. However, these have not yet been described in the aged human quadriceps. High-density surface electromyography (HDsEMG) signals were collected from the vastus lateralis of 15 young (mean ± SD, 23 ± 5 y) and 15 older (67 ± 9 y) men during submaximal sustained and 20-s ramped contractions. HDsEMG signals were decomposed to identify individual motor unit discharges, from which PIC amplitude and intramuscular coherence were estimated. Older participants produced significantly lower knee extensor torque (p < 0.001) and poorer force tracking ability (p < 0.001) than young. Older participants also had lower PIC amplitude (p = 0.001) and coherence estimates in the alpha frequency band (p < 0.001) during ramp contractions when compared to young. Persistent inward currents and common synaptic inputs are lower in the vastus lateralis of older males when compared to young. These data highlight altered neural input to the clinically and functionally important quadriceps, further underpinning age-related loss of function which may occur independently of the loss of muscle mass.

Exploring the properties and potential of the neural extracellular matrix for next-generation regenerative therapies

The extracellular matrix (ECM) is a dynamic and complex network of proteins and molecules that surrounds cells and tissues in the nervous system and orchestrates a myriad of biological functions. This review carefully examines the diverse interactions between cells and the ECM, as well as the transformative chemical and physical changes that the ECM undergoes during neural development, aging, and disease. These transformations play a pivotal role in shaping tissue morphogenesis and neural activity, thereby influencing the functionality of the central nervous system (CNS). In our comprehensive review, we describe the diverse behaviors of the CNS ECM in different physiological and pathological scenarios and explore the unique properties that make ECM-based strategies attractive for CNS repair and regeneration. Addressing the challenges of scalability, variability, and integration with host tissues, we review how advanced natural, synthetic, and combinatorial matrix approaches enhance biocompatibility, mechanical properties, and functional recovery. Overall, this review highlights the potential of decellularized ECM as a powerful tool for CNS modeling and regenerative purposes and sets the stage for future research in this exciting field. This article is categorized under: Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Implantable Materials and Surgical Technologies > Nanomaterials and Implants.

Telomere shortening induces aging-associated phenotypes in hiPSC-derived neurons and astrocytes

Telomere shortening is a well-established hallmark of cellular aging. Telomerase reverse transcriptase (TERT) plays a crucial role in maintaining the length of telomeres, which are specialised protective caps at the end of chromosomes. The lack of in vitro aging models, particularly for the central nervous system (CNS), has impeded progress in understanding aging and age-associated neurodegenerative diseases. In this study, we aimed to explore the possibility of inducing aging-associated features in cell types of the CNS using hiPSC (human induced pluripotent stem cell) technology. To achieve this, we utilised CRISPR/Cas9 to generate hiPSCs with a loss of telomerase function and shortened telomeres. Through directed differentiation, we generated motor neurons and astrocytes to investigate whether telomere shortening could lead to age-associated phenotypes. Our findings revealed that shortened telomeres induced age-associated characteristics in both motor neurons and astrocytes including increased cellular senescence, heightened inflammation, and elevated DNA damage. We also observed cell-type specific age-related morphology changes. Additionally, our study highlighted the fundamental role of TERT and telomere shortening in neural progenitor cell (NPC) proliferation and neuronal differentiation. This study serves as a proof of concept that telomere shortening can effectively induce aging-associated phenotypes, thereby providing a valuable tool to investigate age-related decline and neurodegenerative diseases.

Contrast-enhanced ultrasound imaging detects anatomical and functional changes in rat cervical spine microvasculature with normal aging

Normal aging is associated with significant deleterious cerebrovascular changes; these have been implicated in disease pathogenesis and increased susceptibility to ischemic injury. While these changes are well documented in the brain, few studies have been conducted in the spinal cord. Here, we utilize specialized contrast-enhanced ultrasound (CEUS) imaging to investigate age-related changes in cervical spinal vascular anatomy and hemodynamics in male Fisher 344 rats, a common strain in aging research. Aged rats (24-26 mo., N=6) exhibited significant tortuosity in the anterior spinal artery and elevated vascular resistance compared to adults (4-6 mo., N=6; tortuosity index 2.20±0.15 vs 4.74±0.45, p<0.05). Baseline blood volume was lower in both larger vessels and the microcirculation in the aged cohort, specifically in white matter (4.44e14±1.37e13 vs 3.66e14±2.64e13 CEUS bolus AUC, p<0.05). To elucidate functional differences, animals were exposed to a hypoxia challenge; whereas adult rats exhibited significant functional hyperemia in both gray and white matter (GM: 1.13±0.10-fold change from normoxia, p<0.05; WM: 1.16±0.13, p<0.05), aged rats showed no response. Immunohistochemistry revealed reduced pericyte coverage and activated microglia behavior in aged rats, which may partially explain the lack of vascular response. This study provides the first in vivo description of age-related hemodynamic differences in the cervical spinal cord.

Molecular hallmarks of ageing in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal, severely debilitating and rapidly progressing disorder affecting motor neurons in the brain, brainstem, and spinal cord. Unfortunately, there are few effective treatments, thus there remains a critical need to find novel interventions that can mitigate against its effects. Whilst the aetiology of ALS remains unclear, ageing is the major risk factor. Ageing is a slowly progressive process marked by functional decline of an organism over its lifespan. However, it remains unclear how ageing promotes the risk of ALS. At the molecular and cellular level there are specific hallmarks characteristic of normal ageing. These hallmarks are highly inter-related and overlap significantly with each other. Moreover, whilst ageing is a normal process, there are striking similarities at the molecular level between these factors and neurodegeneration in ALS. Nine ageing hallmarks were originally proposed: genomic instability, loss of telomeres, senescence, epigenetic modifications, dysregulated nutrient sensing, loss of proteostasis, mitochondrial dysfunction, stem cell exhaustion, and altered inter-cellular communication. However, these were recently (2023) expanded to include dysregulation of autophagy, inflammation and dysbiosis. Hence, given the latest updates to these hallmarks, and their close association to disease processes in ALS, a new examination of their relationship to pathophysiology is warranted. In this review, we describe possible mechanisms by which normal ageing impacts on neurodegenerative mechanisms implicated in ALS, and new therapeutic interventions that may arise from this.

CHIT1-positive microglia drive motor neuron ageing in the primate spinal cord

Ageing is a critical factor in spinal-cord-associated disorders1, yet the ageing-specific mechanisms underlying this relationship remain poorly understood. Here, to address this knowledge gap, we combined single-nucleus RNA-sequencing analysis with behavioural and neurophysiological analysis in non-human primates (NHPs). We identified motor neuron senescence and neuroinflammation with microglial hyperactivation as intertwined hallmarks of spinal cord ageing. As an underlying mechanism, we identified a neurotoxic microglial state demarcated by elevated expression of CHIT1 (a secreted mammalian chitinase) specific to the aged spinal cords in NHP and human biopsies. In the aged spinal cord, CHIT1-positive microglia preferentially localize around motor neurons, and they have the ability to trigger senescence, partly by activating SMAD signalling. We further validated the driving role of secreted CHIT1 on MN senescence using multimodal experiments both in vivo, using the NHP spinal cord as a model, and in vitro, using a sophisticated system modelling the human motor-neuron-microenvironment interplay. Moreover, we demonstrated that ascorbic acid, a geroprotective compound, counteracted the pro-senescent effect of CHIT1 and mitigated motor neuron senescence in aged monkeys. Our findings provide the single-cell resolution cellular and molecular landscape of the aged primate spinal cord and identify a new biomarker and intervention target for spinal cord degeneration.

Considerable effects of lateralization and aging in intracortical excitation and inhibition

Introduction

Findings based on the use of transcranial magnetic stimulation and electromyography (TMS-EMG) to determine the effects of motor lateralization and aging on intracortical excitation and inhibition in the primary motor cortex (M1) are inconsistent in the literature. TMS and electroencephalography (TMS-EEG) measures the excitability of excitatory and inhibitory circuits in the brain cortex without contamination from the spine and muscles. This study aimed to investigate the effects of motor lateralization (dominant and non-dominant hemispheres) and aging (young and older) and their interaction effects on intracortical excitation and inhibition within the M1 in healthy adults, measured using TMS-EMG and TMS-EEG.

Methods

This study included 21 young (mean age = 28.1 ± 3.2 years) and 21 older healthy adults (mean age = 62.8 ± 4.2 years). A battery of TMS-EMG measurements and single-pulse TMS-EEG were recorded for the bilateral M1.

Results

Two-way repeated-measures analysis of variance was used to investigate lateralization and aging and the lateralization-by-aging interaction effect on neurophysiological outcomes. The non-dominant M1 presented a longer cortical silent period and larger amplitudes of P60, N100, and P180. Corticospinal excitability in older participants was significantly reduced, as supported by a larger resting motor threshold and lower motor-evoked potential amplitudes. N100 amplitudes were significantly reduced in older participants, and the N100 and P180 latencies were significantly later than those in young participants. There was no significant lateralization-by-aging interaction effect in any outcome.

Conclusion

Lateralization and aging have independent and significant effects on intracortical excitation and inhibition in healthy adults. The functional decline of excitatory and inhibitory circuits in the M1 is associated with aging.

The Brain and Spinal Microvasculature in Normal Aging

Changes in the brain and spinal cord microvasculature during normal aging contribute to the "sensitive" nature of aged central nervous system tissue to ischemic insults. In this review, we will examine alterations in the central nervous system microvasculature during normal aging, which we define as aging without a dominant pathology such as neurodegenerative processes, vascular injury or disease, or trauma. We will also discuss newer technologies to improve the study of central nervous system microvascular structure and function. Microvasculature within the brain and spinal cord will be discussed separately as anatomy and physiology differ between these compartments. Lastly, we will identify critical areas for future studies as well as key unanswered questions.

Aging alters mechanisms underlying voluntary movements in spinal motor neurons of mice, primates, and humans

Spinal motor neurons have been implicated in the loss of motor function that occurs with advancing age. However, the cellular and molecular mechanisms that impair the function of these neurons during aging remain unknown. Here, we show that motor neurons do not die in old female and male mice, rhesus monkeys, and humans. Instead, these neurons selectively and progressively shed excitatory synaptic inputs throughout the soma and dendritic arbor during aging. Thus, aged motor neurons contain a motor circuitry with a reduced ratio of excitatory to inhibitory synapses that may be responsible for the diminished ability to activate motor neurons to commence movements. An examination of the motor neuron translatome (ribosomal transcripts) in male and female mice reveals genes and molecular pathways with roles in glia-mediated synaptic pruning, inflammation, axonal regeneration, and oxidative stress that are upregulated in aged motor neurons. Some of these genes and pathways are also found altered in motor neurons affected with amyotrophic lateral sclerosis (ALS) and responding to axotomy, demonstrating that aged motor neurons are under significant stress. Our findings show mechanisms altered in aged motor neurons that could serve as therapeutic targets to preserve motor function during aging.

Deletion of Sod1 in Motor Neurons Exacerbates Age-Related Changes in Axons and Neuromuscular Junctions in Mice

Whole-body knock-out of Cu,Zn superoxide dismutase (Sod1KO) results in accelerated, age-related loss of muscle mass and function associated with neuromuscular junction (NMJ) breakdown similar to sarcopenia. In order to determine whether altered redox in motor neurons underlies this phenotype, an inducible neuron-specific deletion of Sod1 (i-mnSod1KO) was compared with wild-type (WT) mice of different ages (adult, mid-age, and old) and whole-body Sod1KO mice. Nerve oxidative damage, motor neuron numbers and structural changes to neurons and NMJ were examined. Tamoxifen-induced deletion of neuronal Sod1 from two months of age. No specific effect of a lack of neuronal Sod1 was seen on markers of nerve oxidation (electron paramagnetic resonance of an in vivo spin probe, protein carbonyl, or protein 3-nitrotyrosine contents). i-mnSod1KO mice showed increased denervated NMJ, reduced numbers of large axons and increased number of small axons compared with old WT mice. A large proportion of the innervated NMJs in old i-mnSod1KO mice displayed a simpler structure than that seen in adult or old WT mice. Thus, previous work showed that neuronal deletion of Sod1 induced exaggerated loss of muscle in old mice, and we report that this deletion leads to a specific nerve phenotype including reduced axonal area, increased proportion of denervated NMJ, and reduced acetyl choline receptor complexity. Other changes in nerve and NMJ structure seen in the old i-mnSod1KO mice reflect aging of the mice.

Aging-accelerated differential production and aggregation of STAT3 protein in neuronal cells and neural stem cells in the male mouse spinal cord

Aging-affected cellular compositions of the spinal cord are diverse and region specific. Age leads to the accumulation of abnormal protein aggregates and dysregulation of proteostasis. Dysregulated proteostasis and protein aggregates result from dysfunction of the ubiquitin-proteasome system (UPS) and autophagy. Understanding the molecular mechanisms of spinal cord aging is essential and important for scientists to discover new therapies for rejuvenation. We found age-related increases in STAT3 and decreases in Tuj1 in aging mouse spinal cords, which was characterized by increased expression of P16. Coaggregation of lysine-48 and lysine-63 ubiquitin with STAT3 was revealed in aging mouse spinal cords. STAT3-ubiquitin aggregates formed via lysine-48 and lysine-63 linkages were increased significantly in the aging spinal cords but not in central canal ependymal cells or neural stem cells in the spinal cord. These results highlight the increase in STAT3 and its region-specific aggregation and ubiquitin-conjugation during spinal cord aging.

Neuronal deletion of MnSOD in mice leads to demyelination, inflammation and progressive paralysis that mimics phenotypes associated with progressive multiple sclerosis

Neuronal oxidative stress has been implicated in aging and neurodegenerative disease. Here we investigated the impact of elevated oxidative stress induced in mouse spinal cord by deletion of Mn-Superoxide dismutase (MnSOD) using a neuron specific Cre recombinase in Sod2 floxed mice (i-mn-Sod2 KO). Sod2 deletion in spinal cord neurons was associated with mitochondrial alterations and peroxide generation. Phenotypically, i-mn-Sod2 KO mice experienced hindlimb paralysis and clasping behavior associated with extensive demyelination and reduced nerve conduction velocity, axonal degeneration, enhanced blood brain barrier permeability, elevated inflammatory cytokines, microglia activation, infiltration of neutrophils and necroptosis in spinal cord. In contrast, spinal cord motor neuron number, innervation of neuromuscular junctions, muscle mass, and contractile function were not altered. Overall, our findings show that loss of MnSOD in spinal cord promotes a phenotype of demyelination, inflammation and progressive paralysis that mimics phenotypes associated with progressive multiple sclerosis.

Pathway-based metabolomics study of sarcopenia-related traits in two US cohorts

We aimed to validate two metabolites, aspartic acid and glutamic acid, which were associated with sarcopenia-related traits, muscle mass and strength, in our previous untargeted metabolomics study and to identify novel metabolites from five metabolic pathways involving these two metabolites. We included a discovery cohort of 136 white women aged 20-40 years (used for the previous untargeted metabolomics analysis) and a validation cohort of 174 subjects aged ≥ 60 years, including men and women of white and black. A targeted LC-MS assay successfully detected 12 important metabolites from these pathways. Aspartic acid was associated with muscle mass and strength in the discovery cohort, but not in the validation cohort. However, glutamic acid was associated with these sarcopenia traits in both cohorts. Additionally, N-acetyl-L-aspartic acid and carnosine were the newly identified metabolites that were associated with muscle strength in the discovery and validation cohorts, respectively. We did not observe any significant sex and race differences in the associations of these metabolites with sarcopenia traits in the validation cohort. Our findings indicated that glutamic acid might be consistently associated with sarcopenia-related traits across age, sex, and race. They also suggested that age-specific metabolites and metabolic pathways might be involved in muscle regulation.

A New Framework for Investigating the Biological Basis of Degenerative Cervical Myelopathy [AO Spine RECODE-DCM Research Priority Number 5]: Mechanical Stress, Vulnerability and Time

STUDY DESIGN

Literature Review (Narrative).

OBJECTIVE

To propose a new framework, to support the investigation and understanding of the pathobiology of DCM, AO Spine RECODE-DCM research priority number 5.

METHODS

Degenerative cervical myelopathy is a common and disabling spinal cord disorder. In this perspective, we review key knowledge gaps between the clinical phenotype and our biological models. We then propose a reappraisal of the key driving forces behind DCM and an individual's susceptibility, including the proposal of a new framework.

RESULTS

Present pathobiological and mechanistic knowledge does not adequately explain the disease phenotype; why only a subset of patients with visualized cord compression show clinical myelopathy, and the amount of cord compression only weakly correlates with disability. We propose that DCM is better represented as a function of several interacting mechanical forces, such as shear, tension and compression, alongside an individual's vulnerability to spinal cord injury, influenced by factors such as age, genetics, their cardiovascular, gastrointestinal and nervous system status, and time.

CONCLUSION

Understanding the disease pathobiology is a fundamental research priority. We believe a framework of mechanical stress, vulnerability, and time may better represent the disease as a whole. Whilst this remains theoretical, we hope that at the very least it will inspire new avenues of research that better encapsulate the full spectrum of disease.

Pharmacologic treatment with OKN-007 reduces alpha-motor neuron loss in spinal cord of aging mice

Aging is associated with molecular and functional declines in multiple physiologic systems. We have previously reported age-related changes in spinal cord that included a decline in α-motor neuron numbers, axonal loss, and demyelination associated with increased inflammation and blood-spinal cord barrier (BSCB) permeability. These changes may influence other pathologies associated with aging, in particular loss of muscle mass and function (sarcopenia), which we and others have shown is accompanied by neuromuscular junction disruption and loss of innervation. Interventions to protect and maintain motor neuron viability and function in aging are currently lacking and could have a significant impact on improving healthspan. Here we tested a promising compound, OKN-007, that has known antioxidant, anti-inflammatory and neuroprotective properties, as a potential intervention in age-related changes in the spinal cord. OKN-007 is a low molecular weight disulfonyl derivative of (N-tert Butyl-α-phenylnitrone) (PBN) that can easily cross the blood-brain barrier. We treated middle age (16 month) wild-type male mice with OKN-007 in drinking water at a dose of 150 mg/kg/day until 25 months of age. OKN-007 treatment exerted a number of beneficial effects in the aging spinal cord, including a 35% increase in the number of lumbar α-motor neurons in OKN-treated old mice compared to age-matched controls. Brain spinal cord barrier permeability, which is increased in aging spinal cord, was also blunted by OKN-007 treatment. Age-related changes in microglia proliferation and activation are blunted by OKN-007, while we found no effect on astrocyte proliferation. Transcriptome analysis identified expression changes in a number of genes that are involved in neuronal structure and function and revealed a subset of genes whose changes in response to aging are reversed by OKN-007 treatment. Overall, our findings suggest that OKN-007 exerts neuroprotective and anti-inflammatory effects on the aging spinal cord and support OKN-007 as a potential therapeutic to improve α-motor neuron health.

Blood-Spinal Cord Barrier: Its Role in Spinal Disorders and Emerging Therapeutic Strategies

The blood-spinal cord barrier (BSCB) has been long thought of as a functional equivalent to the blood-brain barrier (BBB), restricting blood flow into the spinal cord. The spinal cord is supported by various disc tissues that provide agility and has different local immune responses compared to the brain. Though physiologically, structural components of the BSCB and BBB share many similarities, the clinical landscape significantly differs. Thus, it is crucial to understand the composition of BSCB and also to establish the cause–effect relationship with aberrations and spinal cord dysfunctions. Here, we provide a descriptive analysis of the anatomy, current techniques to assess the impairment of BSCB, associated risk factors and impact of spinal disorders such as spinal cord injury (SCI), amyotrophic lateral sclerosis (ALS), peripheral nerve injury (PNI), ischemia reperfusion injury (IRI), degenerative cervical myelopathy (DCM), multiple sclerosis (MS), spinal cavernous malformations (SCM) and cancer on BSCB dysfunction. Along with diagnostic and mechanistic analyses, we also provide an up-to-date account of available therapeutic options for BSCB repair. We emphasize the need to address BSCB as an individual entity and direct future research towards it.

Region-specific vulnerability in neurodegeneration: lessons from normal ageing

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Why neurodegenerative disease pathology is regionally restricted remains elusive.

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Regions selectively prone to neurodegeneration are also vulnerable to normal ageing.

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Nervous system tissue, cellular and molecular ageing may determine regional vulnerability.

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Differential ageing can conceptually extend from an individual to subcellular scale.

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An understanding of region-specific vulnerability might guide therapeutic advances.

A number of age-associated neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS), possess a shared characteristic of region-specific neurodegeneration. However, the mechanisms which determine why particular regions within the nervous system are selectively vulnerable to neurodegeneration, whilst others remain relatively unaffected throughout disease progression, remain elusive. Here, we review how regional susceptibility to the ubiquitous physiological phenomenon of normal ageing might underlie the vulnerability of these same regions to neurodegeneration, highlighting three regions archetypally associated with AD, PD and ALS (the hippocampus, substantia nigra pars compacta and ventral spinal cord, respectively), as especially prone to age-related alterations. Placing particular emphasis on these three regions, we comprehensively explore differential regional susceptibility to nervous system tissue, cellular and molecular level ageing to provide an integrated perspective on why age-related neurodegenerative diseases exhibit region-selective vulnerability. Combining these principles with increasingly recognised differences between chronological and biological ageing (termed differential or ‘delta’ ageing) might ultimately guide therapeutic approaches for these devastating neurodegenerative diseases, for which a paucity of disease modifying and/or life promoting treatments currently exist.

Rapamycin restores brain vasculature, metabolism, and blood-brain barrier in an inflammaging model

Rapamycin (RAPA) is found to have neuro-protective properties in various neuroinflammatory pathologies, including brain aging. With magnetic resonance imaging (MRI) techniques, we investigated the effect of RAPA in a lipopolysaccharide (LPS)-induced inflammaging model in rat brains. Rats were exposed to saline (control), or LPS alone or LPS combined with RAPA treatment (via food over 6 weeks). Arterial spin labeling (ASL) perfusion imaging was used to measure relative cerebral blood flow (rCBF). MR spectroscopy (MRS) was used to measure brain metabolite levels. Contrast-enhanced MRI (CE-MRI) was used to assess blood-brain barrier (BBB) permeability. Immunohistochemistry (IHC) was used to confirm neuroinflammation. RAPA restored NF-κB and HIF-1α to normal levels. RAPA was able to significantly restore rCBF in the cerebral cortex post-LPS exposure (p < 0.05), but not in the hippocampus. In the hippocampus, RAPA was able to restore total creatine (Cr) acutely, and N-acetyl aspartate (NAA) at 6 weeks, post-LPS. Myo-inositol (Myo-Ins) levels were found to decrease with RAPA treatment acutely post-LPS. RAPA was also able to significantly restore the BBB acutely post-LPS in both the cortex and hippocampus (p < 0.05 for both). RAPA was found to increase the percent change in BOLD signal in the cortex at 3 weeks, and in the hippocampus at 6 weeks post-LPS, compared to LPS alone. RAPA treatment also restored the neuronal and macro-vascular marker, EphB2, back to normal levels. These results indicate that RAPA may play an important therapeutic role in inhibiting neuroinflammation by normalizing brain vascularity, BBB, and some brain metabolites, and has a high translational capability.

Macpherson P, Ahn B, Piekarz KM, Staunton CA, Brown JL, Qaisar R, Vasilaki A, Richardson A, McArdle A, Jackson MJ, Brooks SV, Van Remmen H. Neuron-specific deletion of CuZnSOD leads to an advanced sarcopenic phenotype in older mice

Age-associated loss of muscle mass and function (sarcopenia) has a profound effect on the quality of life in the elderly. Our previous studies show that CuZnSOD deletion in mice (Sod1-/- mice) recapitulates sarcopenia phenotypes, including elevated oxidative stress and accelerated muscle atrophy, weakness, and disruption of neuromuscular junctions (NMJs). To determine whether deletion of Sod1 initiated in neurons in adult mice is sufficient to induce muscle atrophy, we treated young (2- to 4-month-old) Sod1flox/SlickHCre mice with tamoxifen to generate i-mn-Sod1KO mice. CuZnSOD protein was 40-50% lower in neuronal tissue in i-mn-Sod1KO mice. Motor neuron number in ventral spinal cord was reduced 28% at 10 months and more than 50% in 18- to 22-month-old i-mn-Sod1KO mice. By 24 months, 22% of NMJs in i-mn-Sod1KO mice displayed a complete lack of innervation and deficits in specific force that are partially reversed by direct muscle stimulation, supporting the loss of NMJ structure and function. Muscle mass was significantly reduced by 16 months of age and further decreased at 24 months of age. Overall, our findings show that neuronal-specific deletion of CuZnSOD is sufficient to cause motor neuron loss in young mice, but that NMJ disruption, muscle atrophy, and weakness are not evident until past middle age. These results suggest that loss of innervation is critical but may not be sufficient until the muscle reaches a threshold beyond which it cannot compensate for neuronal loss or rescue additional fibers past the maximum size of the motor unit.

Molecular changes in transcription and metabolic pathways underlying muscle atrophy in the CuZnSOD null mouse model of sarcopenia

Mice lacking the superoxide anion scavenger CuZn superoxide dismutase (Sod1^-/- mice) develop a number of age-related phenotypes, including an early progression of muscle atrophy and weakness (sarcopenia) associated with loss of innervation. The purpose of this study was to delineate the early development of sarcopenia in the Sod1^-/- mice and to measure changes in the muscle transcriptome, proteome, and eicosanoid profile at the stage when sarcopenia is markedly induced in this model (7-9 months of age). We found a strong correlation between muscle atrophy and mitochondrial state 1 hydroperoxide production, which was 40% higher in isolated mitochondria from Sod1^-/- mouse gastrocnemius muscle by 2 months of age. The primary pathways showing altered gene expression in Sod1^-/- mice identified by RNA-seq transcriptomic analysis are protein ubiquitination, synaptic long-term potentiation, calcium signaling, phospholipase C signaling, AMPK, and TWEAK signaling. Targeted proteomics shows elevated expression of mitochondrial proteins, fatty acid metabolism enzymes, tricarboxylic acid (TCA) cycle enzymes, and antioxidants, while enzymes involved in carbohydrate metabolism are downregulated in Sod1^-/- mice. LC-MS analysis of lipids in gastrocnemius muscle detected 78 eicosanoids, of which 31 are significantly elevated in muscle from Sod1^-/- mice. These data suggest that mitochondrial hydroperoxide generation is elevated prior to muscle atrophy and may be a potential driving factor of changes in the transcriptome, proteome, and eicosanoid profile of the Sod1^-/- mice. Together, these analyses revealed important molecular events that occur during muscle atrophy, which will pave the way for future studies using new approaches to treat sarcopenia.