Influence of age on regeneration in the peripheral nervous system

Treating amyotrophic lateral sclerosis with allogeneic Schwann cell-derived exosomal vesicles: a case report

Schwann cells are essential for the maintenance and function of motor neurons, axonal networks, and the neuromuscular junction. In amyotrophic lateral sclerosis, where motor neuron function is progressively lost, Schwann cell function may also be impaired. Recently, important signaling and potential trophic activities of Schwann cell-derived exosomal vesicles have been reported. This case report describes the treatment of a patient with advanced amyotrophic lateral sclerosis using serial intravenous infusions of allogeneic Schwann cell-derived exosomal vesicles, marking, to our knowledge, the first instance of such treatment. An 81-year-old male patient presented with a 1.5-year history of rapidly progressive amyotrophic lateral sclerosis. After initial diagnosis, the patient underwent a combination of generic riluzole, sodium phenylbutyrate for the treatment of amyotrophic lateral sclerosis, and taurursodiol. The patient volunteered to participate in an FDA-approved single-patient expanded access treatment and received weekly intravenous infusions of allogeneic Schwann cell-derived exosomal vesicles to potentially restore impaired Schwann cell and motor neuron function. We confirmed that cultured Schwann cells obtained from the amyotrophic lateral sclerosis patient via sural nerve biopsy appeared impaired (senescent) and that exposure of the patient's Schwann cells to allogeneic Schwann cell-derived exosomal vesicles, cultured expanded from a cadaver donor improved their growth capacity in vitro. After a period of observation lasting 10 weeks, during which amyotrophic lateral sclerosis Functional Rating Scale-Revised and pulmonary function were regularly monitored, the patient received weekly consecutive infusions of 1.54 × 10 12 (×2), and then consecutive infusions of 7.5 × 10 12 (×6) allogeneic Schwann cell-derived exosomal vesicles diluted in 40 mL of Dulbecco's phosphate-buffered saline. None of the infusions were associated with adverse events such as infusion reactions (allergic or otherwise) or changes in vital signs. Clinical lab serum neurofilament and cytokine levels measured prior to each infusion varied somewhat without a clear trend. A more sensitive in-house assay suggested possible inflammasome activation during the disease course. A trend for clinical stabilization was observed during the infusion period. Our study provides a novel approach to address impaired Schwann cells and possibly motor neuron function in patients with amyotrophic lateral sclerosis using allogeneic Schwann cell-derived exosomal vesicles. Initial findings suggest that this approach is safe.

Assessment of deep plane facelift combined with fascia lata graft for the static treatment of facial palsy: A preliminary report

Addressing facial palsy (FP) presents intricate challenges in achieving natural expressions. Although free functional muscle transfers (FFMT) offer effective smile restoration, age impacts their efficacy. The optimal FFMT age range of 5-55 years is limited by physical fitness, which extends beyond age boundaries. Unilateral FP demands vary; younger patients require dynamic solutions like FFMT, whereas older individuals prioritize public appearance due to baseline distortion. The aim of this study is to describe and to assess a new static technique combining deep plane facelift and fascia lata graft for FP treatment. We conducted a prospective pilot study enrolling unilateral FP patients aged >55 and declining FFMT. Exclusions encompassed prior FP surgery, recent injections, uncontrolled diabetes cognitive deficits, and patients unable to quit smoking. To evaluate this technique, the Glasgow Benefit Inventory (GBI), along with two objective scales, the Face- and Neck-Lift Objective Photo-Numerical Assessment Scale and the eFACE scale, were used. Interrater reliability and intrarater reliability were assessed. Fifteen patients (mean age: 60.9 years) underwent the procedure. Both static and dynamic symmetry significantly improved (p < 0.05), including check volume and position, oral commissure, and jawline. Notably, eye closure enhancement was observed. GBI scores also significantly increased (p < 0.05). Interrater reliability and intrarater reliability were minimal (p = 0.12 and p = 0.13). This combined approach offers a static FP treatment option, especially for the elderly or FFMT-ineligible patients. The relatively brief procedure yields immediate and satisfactory results, suggesting its potential value in FP management. Further comprehensive studies are encouraged to validate the technique's long-term efficacy and applicability across larger populations.

The Influence of Neuron-Extrinsic Factors and Aging on Injury Progression and Axonal Repair in the Central Nervous System

In the aging western population, the average age of incidence for spinal cord injury (SCI) has increased, as has the length of survival of SCI patients. This places great importance on understanding SCI in middle-aged and aging patients. Axon regeneration after injury is an area of study that has received substantial attention and made important experimental progress, however, our understanding of how aging affects this process, and any therapeutic effort to modulate repair, is incomplete. The growth and regeneration of axons is mediated by both neuron intrinsic and extrinsic factors. In this review we explore some of the key extrinsic influences on axon regeneration in the literature, focusing on inflammation and astrogliosis, other cellular responses, components of the extracellular matrix, and myelin proteins. We will describe how each element supports the contention that axonal growth after injury in the central nervous system shows an age-dependent decline, and how this may affect outcomes after a SCI.

Age-Dependent Schwann Cell Phenotype Regulation Following Peripheral Nerve Injury

BACKGROUND

Schwann cells are integral to the regenerative capacity of the peripheral nervous system, which declines after adolescence. The mechanisms underlying this decline are poorly understood. This study sought to compare the protein expression of Notch, c-Jun, and Krox-20 after nerve crush injury in adolescent and young adult rats. We hypothesized that these Schwann cell myelinating regulatory factors are down-regulated after nerve injury in an age-dependent fashion.

METHODS

Adolescent (2 months old) and young adult (12 months old) rats (n = 48) underwent sciatic nerve crush injury. Protein expression of Notch, c-Jun, and Krox-20 was quantified by Western blot analysis at 1, 3, and 7 days post-injury. Functional recovery was assessed in a separate group of animals (n = 8) by gait analysis (sciatic functional index) and electromyography (compound motor action potential) over an 8-week post-injury period.

RESULTS

Young adult rats demonstrated a trend of delayed onset of the dedifferentiating regulatory factors, Notch and c-Jun, corresponding to the delayed functional recovery observed in young adult rats compared to adolescent rats. Compound motor action potential area was significantly greater in adolescent rats relative to young adult rats, while amplitude and velocity trended toward statistical significance.

CONCLUSIONS

The process of Schwann cell dedifferentiation following peripheral nerve injury shows different trends with age. These trends of delayed onset of key regulatory factors responsible for Schwann cell myelination may be one of many possible factors mediating the significant differences in functional recovery between adolescent and young adult rats following peripheral nerve injury.

Increased BACE1 activity inhibits peripheral nerve regeneration after injury

Axons of the peripheral nervous system possess the capacity to regenerate following injury. Previously, we showed that genetically knocking out Beta-Site APP-Cleaving Enzyme 1 (BACE1) leads to increased nerve regeneration. Two cellular components, macrophages and neurons, contribute to enhanced nerve regeneration in BACE1 knockout mice. Here, we utilized a transgenic mouse model that overexpresses BACE1 in its neurons to investigate whether neuronal BACE1 has an inverse effect on regeneration following nerve injury. We performed a sciatic nerve crush in BACE1 transgenic mice and control wild-type littermates, and evaluated the extent of both morphological and physiological improvements over time. At the earliest time point of 3days, we observed a significant decrease in the length of axonal sprouts growing out from the crush site in BACE1 transgenic mice. At later times (10 and 15days post-crush), there were significant reductions in the number of myelinated axons in the sciatic nerve and the percentage of re-innervated neuromuscular junctions in the gastrocnemius muscle. Transgenic mice had a functional electrophysiological delay in the recovery up to 8weeks post-crush compared to controls. These results indicate that BACE1 activity levels have an inverse effect on peripheral nerve repair after injury. The results obtained in this study provide evidence that neuronal BACE1 activity levels impact peripheral nerve regeneration. This data has clinical relevance by highlighting a novel drug target to enhance peripheral nerve repair, an area which currently does not have any approved therapeutics.

AlphaB-crystallin expression correlates with aging deficits in the peripheral nervous system

In an effort to identify factors that contribute to age-related deficits in the undamaged and injured peripheral nervous system (PNS), we noted that Brady and colleagues found that mice null for a small heat shock protein called alphaB-crystallin (αBC) developed abnormalities early in life that are reminiscent of aging pathologies. Because of our observation that αBC protein levels markedly reduce as wild-type mice age, we investigated whether the crystallin plays a role in modulating age-related deficits in the uninjured and damaged PNS. We show here that the presence of αBC correlates with maintenance of myelin sheath thickness, reducing macrophage presence, sustaining lipid metabolism, and promoting remyelination following peripheral nerve injury in an age-dependent manner. More specifically, animals null for αBC displayed a higher frequency of thinly myelinated axons, enhanced presence of Iba1+ macrophages, and fewer immunoreactive profiles of the cholesterol biosynthesis enzyme, squalene monooxygenase, before and after sciatic nerve crush injury. These findings thus suggest that αBC plays a protective and beneficial role in the aging PNS.

Global Sensory Impairment in Older Adults in the United States

OBJECTIVES

To determine whether there may be a common mechanism resulting in global sensory impairment of the five classical senses (vision, smell, hearing, touch, and taste) in older adults.

DESIGN

Representative, population-based study.

SETTING

National Social Life, Health, and Aging Project.

PARTICIPANTS

Community-dwelling U.S. adults aged 57 to 85.

MEASUREMENTS

The frequency with which impairment co-occurred across the five senses was estimated as an integrated measure of sensory aging. It was hypothesized that multisensory deficits would be common and reflect global sensory impairment that would largely explain the effects of age, sex, and race on sensory dysfunction.

RESULTS

Two-thirds of subjects had two or more sensory deficits, 27% had just one, and 6% had none. Seventy-four percent had impairment in taste, 70% in touch, 22% in smell, 20% in corrected vision, and 18% in corrected hearing. Older adults, men, African Americans, and Hispanics had greater multisensory impairment (all P < .01). Global sensory impairment largely accounted for the effects of age, sex, and race on the likelihood of impairment in each of the five senses.

CONCLUSION

Multisensory impairment is prevalent in older U.S. adults. These data support the concept of a common process that underlies sensory aging across the five senses. Clinicians assessing individuals with a sensory deficit should consider further evaluation for additional co-occurring sensory deficits.

Facial nerve schwannomas presenting as occluding external auditory canal masses: a therapeutic dilemma

OBJECTIVE

To present a series of patients with facial nerve schwannomas (FNSs) presenting as occluding external auditory canal (EAC) masses.

STUDY DESIGN

Retrospective case series.

PATIENTS

Four patients were identified with mastoid segment FNSs occluding the EAC. Three patients presented with conductive hearing loss (CHL), and the fourth presented with facial paralysis, later developing CHL.

INTERVENTION

One patient underwent conservative debulking, removing the EAC component only. Two patients were managed nonoperatively with periodic cleaning of entrapped keratin. The fourth patient received radiation therapy.

MAIN OUTCOME MEASURES

Facial nerve function, canal cholesteatoma formation, and hearing.

RESULTS

Among the patients managed with serial cleaning of entrapped keratin, one maintained normal facial function and one worsened to House-Brackmann II/VI. Facial function worsened to House-Brackmann II/VI in the patient who underwent surgical debulking. The fourth patient, who received radiation, developed complete facial paralysis. All patients accumulated keratin medial to the tumor, and all had CHL.

CONCLUSION

When evaluating an EAC tumor, it is important to obtain imaging before biopsy because biopsy of a schwannoma can result in paralysis. EAC occlusion by a schwannoma presents a challenging management issue, particularly when cholesteatoma forms between the tumor and the tympanic membrane. The primary goal is maintaining normal facial function as long as possible and avoiding secondary ear canal complications. The presence of canal occlusion limits the choice of stereotactic radiation because this leads to a month-long period of tumor swelling and cutaneous sloughing. Resection and grafting are indicated when substantial facial weakness or twitch develops.

Aging profoundly delays functional recovery from gustatory nerve injury

The peripheral taste system remains plastic during adulthood. Sectioning the chorda tympani (CT) nerve, which sends sensory information from the anterior tongue to the central nervous system, causes degeneration of distal fibers and target taste buds. However, taste function is restored after about 40 days in young adult rodents. We tested whether aging impacts the reappearance of neural responses after unilateral CT nerve injury. Taste bud regeneration was minimal at day 50-65 after denervation, and most aged animals died before functional recovery could be assessed. A subset (n=3/5) of old rats exhibited normal CT responses at day 85 postsectioning, suggesting the potential for efficient recovery. The aged taste system is fairly resilient to sensory receptor loss and major functional changes in normal aging. However, injury to the taste system reveals a surprising vulnerability in old rodents. The gustatory system provides an excellent model to study mechanisms underlying delayed recovery from peripheral nerve injury. Strategies to accelerate recovery and restore normal function will be of interest, as the elderly population continues to grow.

The effects of treadmill training on young and mature rats after traumatic peripheral nerve lesion

The purpose of this study was to investigate the possible effects of a treadmill training program on regeneration in young (3-month-old) and mature (13-month-old) rats with sciatic nerve crush using functional, electrophysiological, and morphometric analyses. When compared to both the young and mature untrained injury groups, those groups that underwent a treadmill training showed improved sensorimotor function evaluated by narrow beam test (p<0.04 and p<0.001, respectively), while muscle action potential amplitude was only greater in the young group (p<0.02). The treadmill training program was able to reduce myelinated fiber density in the young group (p<0.001), which appeared to increase after nerve injury (poly-innervation), but decreased with training, which means that the innervation became more functional. The data indicate that treadmill training is able to promote functional, electrophysiological and morphological recovery in young animals. However, in mature animals, improvement was only seen in terms of functional recovery.

Role of sensory stimulation in amelioration of obstructive sleep apnea

Obstructive sleep apnea (OSA), characterized by recurrent upper airway (UA) collapse during sleep, is associated with significant morbidity and disorders. Polysomnogram is employed in the evaluation of OSA and apnea-hypopnea number per hour reflects severity. For normal breathing, it is essential that the collapsible UA is patent. However, obstruction of the UA is quite common in adults and infants. Normally, important reflex mechanisms defend against the UA collapse. The muscle activity of UA dilators, including the genioglossus, tensor palatini (TP), and pharyngeal constrictors, is due to the integrated mechanism of afferent sensory input → to motor function. Snoring is harsh breathing to prevent UA obstruction. Unfortunately, snoring vibrations, pharyngeal suction collapse, negative pressure, and hypoxia cause pathological perturbations including dysfunctional UA afferent sensory activity. The current paper posits that peripheral sensory stimulation paradigm, which has been shown to be efficacious in improving several neurological conditions, could be an important therapeutic strategy in OSA also.

Aging and partial body weight support affects gait variability

Background

Aging leads to increases in gait variability which may explain the large incidence of falls in the elderly. Body weight support training may be utilized to improve gait in the elderly and minimize falls. However, before initiating rehabilitation protocols, baseline studies are needed to identify the effect of body weight support on elderly gait variability. Our purpose was to determine the kinematic variability of the lower extremities in young and elderly healthy females at changing levels of body weight support during walking.

Methods

Ten young and ten elderly females walked on a treadmill for two minutes with a body weight support (BWS) system under four different conditions: 1 g, 0.9 g, 0.8 g, and 0.7 g. Three-dimensional kinematics was captured at 60 Hz with a Peak Performance high speed video system. Magnitude and structure of variability of the sagittal plane angular kinematics of the right lower extremity was analyzed using both linear (magnitude; standard deviations and coefficient of variations) and nonlinear (structure; Lyapunov exponents) measures. A two way mixed ANOVA was used to evaluate the effect of age and BWS on variability.

Results

Linear analysis showed that the elderly presented significantly more variability at the hip and knee joint than the young females. Moreover, higher levels of BWS presented increased variability at all joints as found in both the linear and nonlinear measures utilized.

Conclusion

Increased levels of BWS increased lower extremity kinematic variability. If the intent of BWS training is to decrease variability in gait patterns, this did not occur based on our results. However, we did not perform a training study. Thus, it is possible that after several weeks of training and increased habituation, these initial increased variability values will decrease. This assumption needs to be addressed in future investigation with both "healthy" elderly and elderly fallers. In addition, it is possible that BWS training can have a positive transfer effect by bringing overground kinematic variability to healthy normative levels, which also needs to be explored in future studies.

Influence of Aging on Regeneration in End-to-Side Neurorrhaphy

Aging profoundly affects the structural and functional characteristics of the peripheral nervous system. Although several experiments have investigated the effect of aging on nerve regeneration after crush and transection nerve injuries, little is known about the influence of age on end-to-side nerve repairs. It was hypothesized that decreased terminal and collateral sprouting in older animals would be associated with less robust regeneration through end-to-side nerve repairs. In this study, 27 Lewis rats underwent end-to-side repair at ages 2 weeks, 3 months, or 1 year. Histomorphometric assessments at 12 weeks demonstrated increased fiber width, percent neural tissue, and neural density in animals undergoing nerve reconstruction at the age of 2 weeks (P < 0.05). A trend toward further decline in regeneration was noted at ages 1 year versus 3 months. After end-to-side nerve repair, younger animals exhibit a more robust regenerative response, consistent with prior experience in other nerve injury models.

Effect of deficits in laryngeal sensation on laryngeal muscle biochemistry

Swallowing deficits in elderly people are significant clinical problems and may be associated with impaired pharyngolaryngeal sensation. However, the extent to which sensory innervation affects the motor system is unclear. Our purpose was to examine differences in biochemical properties of laryngeal muscles following sensory nerve ablation. We used sodium dodecyl sulfate-polyacrylamide gel electrophoresis to evaluate laryngeal muscles of young and old Fischer 344/Brown Norway rats, and rats that underwent sensory ablation via bilateral section of the superior laryngeal nerve, internal branch (SLNi), or mixed sensory-motor nerve ablation via left-sided recurrent laryngeal nerve (RLN) section. In lateral thyroarytenoid muscle, a reduction was found in the proportion of the most rapidly contracting myosin heavy chain isoform (type 2B) with SLNi section, RLN section, and aging. Section of the SLNi did not alter the proportion of any myosin heavy chain isoform within the lateral cricoarytenoid or posterior cricoarytenoid muscles, but RLN section resulted in a reduction in the proportion of type 2B. Accordingly, alteration in biochemical properties of the lateral thyroarytenoid muscle alone was demonstrated following sensory ablation. We conclude that sensory changes may affect properties of laryngeal muscles, and may thus have an impact on motor control during critical functions, such as airway protection during swallowing.

Mutant superoxide dismutase disrupts cytoplasmic dynein in motor neurons

Cytoplasmic dynein and dynactin drive retrograde axonal transport in neurons, and mutations in dynein/dynactin cause motor neuron degeneration. To test whether defects in dynein/dynactin function are involved in the neurodegenerative disease amyotrophic lateral sclerosis, we examined neurotracer transport from muscle to motor neuron in a transgenic mouse model of amyotrophic lateral sclerosis. Significant inhibition was observed, which was temporally correlated with declines in muscle strength. No decrease in dynein/dynactin expression was observed, but immunohistochemistry suggests that dynein associates with aggregates of mutant Cu/Zn superoxide dismutase 1. Expression of mutant Cu/Zn superoxide dismutase 1 in primary motor neurons altered the cellular localization of dynein, suggesting an inhibition of dynein/dynactin function. Thus, inhibition of dynein/dynactin function may have a role in motor neuron degeneration in amyotrophic lateral sclerosis.

Sciatic nerve axotomy in aged rats: response of motoneurons and the effect of GM1 ganglioside treatment

The number, size, and staining intensity of choline acetyltransferase (ChAT)-immunopositive cells in the retrodorsal lateral nucleus (RDLN) of the spinal cord were studied in young (3-5 months old) and aged (22-24 months old) rats following left sciatic nerve distal transection (axotomy) and treatment with GM1 ganglioside. The cell size and the ChAT immunostaining density were decreased in the RDLN of non-manipulated as well as in the contralateral intact side of axotomized aged rats. Axotomy had no effect on the number of RDLN motoneurons in both aged and young rats. In the young rats, there was a decrease in the size of motoneurons 7 days post-axotomy and a partial spontaneous recovery occurred by 21 days. Axotomy did not reduce further the size of aged motoneurons, however. The ChAT staining intensity of the axotomized RDLN declined in both age groups after 7 days, and there was spontaneous near normal recovery by 21 days. In the aged rats, GM1 administration for 7 days corrected the cell size and ChAT immunoreactivity of the contralateral intact RDLN. With regard to axotomized RDLN neurons, 7 days of GM1 restored the cell size but not the ChAT immunostaining in young animals. The same treatment schedule, however, corrected both cell size and staining in aged rats. Administration of GM1 for 21 days had no further effect on the morphometric parameters of the axotomized motoneurons in aged rats, but slightly enhanced the recovery of ChAT immunostaining in young rats. Thus, it appears that GM1 facilitates the phenotypic recovery of RDLN motoneurons during aging and after axotomy.

Neural control of aging skeletal muscle

Functional and structural decline in the neuromuscular system with aging has been recognized as a cause of impairment in physical performance and loss of independence in the elderly. Alterations in spinal cord motor neurones and at the neuromuscular junction have been identified as evidence of denervation in skeletal muscles from aging mammals, including humans. However, the reciprocal influences of neurones on gene expression in muscle and of muscle on age-related neurodegeneration are poorly understood, and, as a result, interventions aimed at delaying or preventing degeneration of the neural component in aging muscle have been largely unsuccessful. The present article discusses the evidence for neural influence on age-related impairments of skeletal muscle, including a role in excitation-contraction uncoupling. The role of nerves in regulating the trophic actions of insulin-like growth factor-1 (IGF-1) and other neurotrophic factors is considered as a novel influence on the effects of aging on the neuromuscular junction. A better understanding of nerve-muscle interactions will allow for more rational interventions in the aging neuromuscular system.

Differential schwann cell migration in adult and old mice: an in vitro study

The influence of aging on Schwann cell (SC) proliferation, migration and viability was studied in vitro. SCs were cultured in Ham F-10 medium enriched with 20% fetal calf serum (FCS), 40% FCS or collagen I gel plus 20% FCS. The migration of adult mice derived SCs was stimulated with FCS and collagen. With aging, SC migration, multiplication and viability decreased, indicating that ideal culturing conditions should be adjusted.