Axonal Regeneration: Underlying Molecular Mechanisms and Potential Therapeutic Targets

Potential of ultrasound stimulation and sonogenetics in vision restoration: a narrative review

Vision restoration presents a considerable challenge in the realm of regenerative medicine, while recent progress in ultrasound stimulation has displayed potential as a non-invasive therapeutic approach. This narrative review offers a comprehensive overview of current research on ultrasound-stimulated neuromodulation, emphasizing its potential as a treatment modality for various nerve injuries. By examining of the efficacy of different types of ultrasound stimulation in modulating peripheral and optic nerves, we can delve into their underlying molecular mechanisms. Furthermore, the review underscores the potential of sonogenetics in vision restoration, which involves leveraging pharmacological and genetic manipulations to inhibit or enhance the expression of related mechanosensitive channels, thereby modulating the strength of the ultrasound response. We also address how methods such as viral transcription can be utilized to render specific neurons or organs highly responsive to ultrasound, leading to significantly improved therapeutic outcomes.

Pharmacological intervention for chronic phase of spinal cord injury

Spinal cord injury is an intractable traumatic injury. The most common hurdles faced during spinal cord injury are failure of axonal regrowth and reconnection to target sites. These also tend to be the most challenging issues in spinal cord injury. As spinal cord injury progresses to the chronic phase, lost motor and sensory functions are not recovered. Several reasons may be attributed to the failure of recovery from chronic spinal cord injury. These include factors that inhibit axonal growth such as activated astrocytes, chondroitin sulfate proteoglycan, myelin-associated proteins, inflammatory microglia, and fibroblasts that accumulate at lesion sites. Skeletal muscle atrophy due to denervation is another chronic and detrimental spinal cord injury-specific condition. Although several intervention strategies based on multiple outlooks have been attempted for treating spinal cord injury, few approaches have been successful. To treat chronic spinal cord injury, neural cells or tissue substitutes may need to be supplied in the cavity area to enable possible axonal growth. Additionally, stimulating axonal growth activity by extrinsic factors is extremely important and essential for maintaining the remaining host neurons and transplanted neurons. This review focuses on pharmacotherapeutic approaches using small compounds and proteins to enable axonal growth in chronic spinal cord injury. This review presents some of these candidates that have shown promising outcomes in basic research ( in vivo animal studies) and clinical trials: AA-NgR(310)ecto-Fc (AXER-204), fasudil, phosphatase and tensin homolog protein antagonist peptide 4, chondroitinase ABC, intracellular sigma peptide, (-)-epigallocatechin gallate, matrine, acteoside, pyrvate kinase M2, diosgenin, granulocyte-colony stimulating factor, and fampridine-sustained release. Although the current situation suggests that drug-based therapies to recover function in chronic spinal cord injury are limited, potential candidates have been identified through basic research, and these candidates may be subjects of clinical studies in the future. Moreover, cocktail therapy comprising drugs with varied underlying mechanisms may be effective in treating the refractory status of chronic spinal cord injury.

Basic Pathological Mechanisms in Peripheral Nerve Diseases

Pathological changes and the cellular and molecular mechanisms underlying axonopathy and myelinopathy are key to understanding a wide range of inherited and acquired peripheral nerve disorders. While the clinical indications for nerve biopsy have diminished over time, its diagnostic value remains significant in select conditions, offering a unique window into the pathophysiological processes of peripheral neuropathies. Evidence highlights the symbiotic relationship between axons and myelinating Schwann cells, wherein disruptions in axo-glial interactions contribute to neuropathogenesis. This review synthesizes recent insights into the pathological and molecular underpinnings of axonopathy and myelinopathy. Axonopathy encompasses Wallerian degeneration, axonal atrophy, and dystrophy. Although extensively studied in traumatic nerve injury, the mechanisms of axonal degeneration and Schwann cell-mediated repair are increasingly recognized as pivotal in non-traumatic disorders, including dying-back neuropathies. We briefly outline key transcription factors, signaling pathways, and epigenetic changes driving axonal regeneration. For myelinopathy, we discuss primary segmental demyelination and dysmyelination, characterized by defective myelin development. We describe paranodal demyelination in light of recent findings in nodopathies, emphasizing that it is not an exclusive indicator of demyelinating disorders. This comprehensive review provides a framework to enhance our understanding of peripheral nerve pathology and its implications for developing targeted therapies.

Strategies for promoting neurovascularization in bone regeneration

Bone tissue relies on the intricate interplay between blood vessels and nerve fibers, both are essential for many physiological and pathological processes of the skeletal system. Blood vessels provide the necessary oxygen and nutrients to nerve and bone tissues, and remove metabolic waste. Concomitantly, nerve fibers precede blood vessels during growth, promote vascularization, and influence bone cells by secreting neurotransmitters to stimulate osteogenesis. Despite the critical roles of both components, current biomaterials generally focus on enhancing intraosseous blood vessel repair, while often neglecting the contribution of nerves. Understanding the distribution and main functions of blood vessels and nerve fibers in bone is crucial for developing effective biomaterials for bone tissue engineering. This review first explores the anatomy of intraosseous blood vessels and nerve fibers, highlighting their vital roles in bone embryonic development, metabolism, and repair. It covers innovative bone regeneration strategies directed at accelerating the intrabony neurovascular system over the past 10 years. The issues covered included material properties (stiffness, surface topography, pore structures, conductivity, and piezoelectricity) and acellular biological factors [neurotrophins, peptides, ribonucleic acids (RNAs), inorganic ions, and exosomes]. Major challenges encountered by neurovascularized materials during their clinical translation have also been highlighted. Furthermore, the review discusses future research directions and potential developments aimed at producing bone repair materials that more accurately mimic the natural healing processes of bone tissue. This review will serve as a valuable reference for researchers and clinicians in developing novel neurovascularized biomaterials and accelerating their translation into clinical practice. By bridging the gap between experimental research and practical application, these advancements have the potential to transform the treatment of bone defects and significantly improve the quality of life for patients with bone-related conditions.

Mechanism and Application of Chinese Herb Medicine in Treatment of Peripheral Nerve Injury

Peripheral nerve injury (PNI) encompasses damage to nerves located outside the central nervous system, adversely affecting both motor and sensory functions. Although peripheral nerves possess an intrinsic capacity for self-repair, severe injuries frequently result in significant tissue loss and erroneous axonal junctions, thereby impeding complete recovery and potentially causing neuropathic pain. Various therapeutic strategies, including surgical interventions, biomaterials, and pharmacological agents, have been developed to enhance nerve repair processes. While preclinical studies in animal models have demonstrated the efficacy of certain pharmacological agents in promoting nerve regeneration and mitigating inflammation, only a limited number of these agents have been translated into clinical practice to expedite nerve regeneration. Chinese herb medicine (CHM) possesses a longstanding history in the treatment of various ailments and demonstrates potential efficacy in addressing PNI through its distinctive, cost-effective, and multifaceted methodologies. This review critically examines the advancements in the application of CHM for PNI treatment and nerve regeneration. In particular, we have summarized the most commonly employed and rigorously investigated CHM prescriptions, individual herbs, and natural products, elucidating their respective functions and underlying mechanisms in the context of PNI treatment. Furthermore, we have deliberated on the prospective development of CHM in both clinical practice and fundamental research.

Refinement of Protein Extraction Protocols for Human Peripheral Nerve Tissue

Our aim was to establish an effective method for protein extraction from freshly frozen human peripheral nerves, determine the minimum amount required for consistent protein extraction outcomes, and assess which method produced the highest number of protein identities. Five extraction methods were compared using 8 M urea and Ripa buffer using either the Bullet Blender or Bioruptor. Out of the total 2619 identified proteins, protein extraction using the Ripa buffer combined with either Bioruptor or Bullet Blender resulted in the identification of 1582 (60%) and 1615 (62%) proteins, respectively. In contrast, using 8 M urea and Bioruptor for protein extraction resulted in 1022 proteins (39%), whereas employing Bullet Blender yielded 1446 proteins (55%). Sample amounts, ranging from 0.6 to 10 mg, were prepared with consistent protein extraction outcome obtained for samples ≥1.2 mg. Combining Ripa and 8 M urea with Bullet Blender increased protein identification to 2126 (81%). Proteins were classified by their cell components, molecular functions, and biological processes. Furthermore, a subclassification of proteins involved in the extracellular matrix (ECM) was introduced. We recommend the use of Ripa buffer, in combination with 8 M urea and Bullet Blender for extracting proteins from fresh-frozen human nerves weighing ≥1.2 mg.

Exploring the cellular and molecular basis of nerve growth factor in cerebral ischemia recovery

Vascular obstruction often causes inadequate oxygen and nutrient supply to the brain. This deficiency results in cerebral ischemic injury, which significantly impairs neurological function. This review aimed to explore the neuroprotective and regenerative effects of nerve growth factor (NGF) in cerebral ischemic injury. NGF, a crucial neurotrophic factor, could inhibit neuronal apoptosis, reduce inflammatory responses, and promote axon regeneration and angiogenesis through its interaction with TrkA, a high-affinity receptor. These functions were closely related to the activation of Phosphatidylinositol 3-kinase/Protein kinase B (PI3K/AKT) and Mitogen-Activated Protein Kinase (MAPK) pathways. Moreover, the mechanisms of NGF in the acute and recovery phases, along with the strategies to enhance its therapeutic effects using delivery systems (such as intranasal administration, nanovesicles, and gene therapy) were also summarized. Although NGF shows great potential for clinical application, its delivery efficiency and long-term safety still need more research and improvements. Future research should focus on exploring the specific action mechanism of NGF, optimizing the delivery strategy, and evaluating its long-term efficacy and safety to facilitate its clinical transformation in cerebral ischemic stroke.

Neurons Are Not All the Same: Diversity in Neuronal Populations and Their Intrinsic Responses to Spinal Cord Injury

Functional recovery following spinal cord injury will require the regeneration and repair of damaged neuronal pathways. It is well known that the tissue response to injury involves inflammation and the formation of a glial scar at the lesion site, which significantly impairs the capacity for neuronal regeneration and functional recovery. There are initial attempts by both supraspinal and intraspinal neurons to regenerate damaged axons, often influenced by the neighboring tissue pathology. Many experimental therapeutic strategies are targeted to further stimulate the initial axonal regrowth, with little consideration for the diversity of the affected neuronal populations. Notably, recent studies reveal that the neuronal response to injury is variable, based on multiple factors, including the location of the injury with respect to the neuronal cell bodies and the affected neuronal populations. New insights into regenerative mechanisms have shown that neurons are not homogenous but instead exhibit a wide array of diversity in their gene expression, physiology, and intrinsic responses to injury. Understanding this diverse intrinsic response is crucial, as complete functional recovery requires the successful coordinated regeneration and reorganization of various neuron pathways.

Maternal Bisphenol A Exposure Induces Hippocampal-Dependent Learning and Memory Deficits Through the PI3K/Akt/mTOR Pathway in Male Offspring Rats

Bisphenol A (BPA), an environmental endocrine disrupting chemical, is one of the most widely used chemicals in the world and is widely distributed in the external environment, specifically in food, water, dust, and soil. BPA exposure is associated with abnormal cognitive behaviors. However, the underlying mechanism remains unclear. In this study, pregnant female Sprague Dawley rats were orally exposed to BPA at a low dose of 0, 0.04, 0.4, or 4 mg per kg·of body weight per day from embryonic Day 0 (ED 0) to postnatal Day 21 (PND 21). Spatial learning and memory were measured via a Morris water maze test on PND 22. PI3K/Akt/mTOR signaling pathway protein expression was detected in the hippocampi of male offspring using a western blot. The water maze test demonstrated that BPA exposure considerably reduced the learning and memory capacities of the male offspring exposure groups when compared to the control group. The male offspring rats' latency to escape increased significantly, the time taken to traverse a platform reduced, and latency to find a hidden platform showed an increasing trend. Meanwhile, maternal exposure to BPA downregulated the expression of PI3K/Akt/mTOR/p70S6K pathway in the hippocampi of the offspring. Moreover, BPA exposure improved the GSK3β and phosphorylated tau protein (T231) levels, increased malondialdehyde levels, and activated caspase-3 expression in the hippocampi of the male offspring rats. Taken together, these findings indicate that maternal exposure to BPA causes learning and memory impairment and that the PI3K/Akt/mTOR pathway participates in the mechanism of BPA-induced neurocognitive decline.

Salidroside exerts neuroprotective effects on retrograde neuronal death following neonatal axotomy via activation of PI3K/Akt pathway and deactivation of p38 MAPK pathway

Salidroside, a glucoside of tyrosol, is a powerful active ingredient extracted from the Chinese herb medicine Rhodiola rosea L.. As a neuroprotective agent, the application of salidroside in combination with neural tissue engineering has recently attracted much attention in peripheral nerve repair and reconstruction. However, the cellular and molecular mechanisms by which salidroside promotes nerve regeneration remain to be elucidated. We aim to evaluate the long-term neuroprotective potential of salidroside in an experimental rat model of neonatal sciatic nerve crush injury, with a focus on target-deprived neuronal death and the mechanisms involved. Behavioral analysis showed that salidroside dose-dependently improved voluntary hindlimb behavior and rod rotation ability following neonatal axotomy during an 8-week observation period. According to electrophysiology, Fluoro-Gold retrograde tracing, histological and immunohistochemical analyses, salidroside significantly improved nerve regeneration and reinnervation. Nissle and TUNEL staining, as well as caspase-3 activation assay indicated a beneficial effect of salidroside on retrograde loss and apoptosis of motoneurons within 2 weeks after axotomy. qPCR, ELISA and oxidative stress experiments revealed that salidroside improved the imbalance of spinal microenvironment, including oxidative stress and down-regulation of neurotrophic factors. Western blotting analysis showed that salidroside enhanced the activation of PI3K/Akt and inhibited the p38 MAPK signaling pathway following axotomy. The oxidative stress and axonal disconnection/regeneration models of primary motoneurons in vitro further confirmed the involvement of these two pathways in the neuroprotective effects of salidroside. These data provide a theoretical basis for the application of salidroside in peripheral nerve repair and reconstruction.

Physical modulation and peripheral nerve regeneration: a literature review

Peripheral nerve injury (PNI) usually causes severe motor, sensory and autonomic dysfunction. In addition to direct surgical repair, rehabilitation exercises, and traditional physical stimuli, for example, electrical stimulation, have been applied in promoting the clinical recovery of PNI for a long time but showed low efficiency. Recently, significant progress has been made in new physical modulation to promote peripheral nerve regeneration. We hereby review current progress on the mechanism of peripheral nerve regeneration after injury and summarize the new findings and evidence for the application of physical modulation, including electrical stimulation, light, ultrasound, magnetic stimulation, and mechanical stretching in experimental studies and the clinical treatment of patients with PNI.

Molecular mechanisms of neurofilament alterations and its application in assessing neurodegenerative disorders

Neurofilaments are intermediate filaments present in neurons. These provide structural support and maintain the size and shape of the neurons. Dysregulation, mutation, and aggregation of neurofilaments raise the levels of these proteins in the blood and cerebrospinal fluid (CSF), which are characteristic features of axonal damage and certain rare neurological diseases, such as Giant Axonal Neuropathy and Charcot-Mare-Tooth disease. Understanding the structure, dynamics, and function of neurofilaments has been greatly enhanced by a diverse range of biochemical and preclinical investigations conducted over more than four decades. Recently, there has been a resurgence of interest in post-translational modifications of neurofilaments, such as phosphorylation, aggregation, mutation, oxidation, etc. Over the past twenty years, several rare disorders have been studied from structural alterations of neurofilaments. These disorders are monitored by fluid biomarkers such as neurofilament light chains. Currently, there are many tools, such as Enzyme-Linked Immunosorbent Assay, Electrochemiluminescence Assay, Single-Molecule Array, Western/immunoblotting, etc., in use to assess the neurofilament proteins in Blood and CSF. However, all these techniques utilize expensive, non-specific, or antibody-based methods, which make them unsuitable for routine screening of neurodegenerative disorders. This provides room to search for newer sensitive, cost-effective, point-of-care tools for rapid screening of the disease. For a long time, the molecular mechanisms of neurofilaments have been poorly understood due to insufficient research attempts, and a deeper understanding of them remains elusive. Therefore, this review aims to highlight the available literature on molecular mechanisms of neurofilaments and the function of neurofilaments in axonal transport, axonal conduction, axonal growth, and neurofilament aggregation, respectively. Further, this review discusses the role of neurofilaments as potential biomarkers for the identification of several neurodegenerative diseases in clinical laboratory practice.

c-Myc and FOXO3a-The Everlasting Decision Between Neural Regeneration and Degeneration

The transcription factors c-Myc and FoxO3a play significant roles in neurodegenerative processes, yet their interaction in neurological disorders remains largely unexplored. In contrast, much of the available information about their relationship comes from cancer research. While it is well-established that FoxO3a inhibits c-Myc activity, this interaction represents only a basic understanding of a far more complex dynamic, which includes exceptions under specific conditions and the involvement of additional regulatory factors. Given the critical need to address this gap for the treatment and prevention of neurodegenerative disorders, this review consolidates current knowledge on the joint roles of these two factors in neuropathology. It also highlights their conformational flexibility, post-translational modifications, and outlines potential directions for future research.

Quercetin Alleviates Diabetic Peripheral Neuropathy by Regulating Axon Guidance Factors and Inhibiting the Rho/ROCK Pathway in vivo and in vitro

Purpose

The axon guidance factors and Rho/ROCK pathway play crucial roles in axon protection and nerve repair and has been implicated in the development of diabetic peripheral neuropathy (DPN). This study investigates the protective effects of quercetin against DPN, focusing on axon guidance factors and Rho/ROCK pathway.

Methods

DPN was induced by intraperitoneal injection of streptozotocin (STZ) to Sprague-Dawley rats. The DPN model rats were allocated into three groups and administered quercetin at two different doses (30 mg/kg/day and 60 mg/kg/day) or a placebo. Concurrently, healthy rats were divided into two groups and administered either a placebo or quercetin (60 mg/kg/day). Administration was initiated 8 weeks post-STZ injection and continued for a duration of six weeks. To assess quercetin's neuroprotective effects, biochemical analyses, neurological function tests (mechanical threshold, thermal response latency, motor nerve conduction velocity), and morphological assessments via transmission electron microscopy were conducted. Immunofluorescence and immunohistochemical assays were performed on sciatic nerve tissue and high glucose-induced RSC96 rat Schwann cells to explore quercetin's pharmacological effects on DPN.

Results

Quercetin exhibited neuroprotective effects on both DPN rats and RSC96 cells exposed to high-glucose. A six-week administration of quercetin at both doses significantly improved the peripheral neurological functions and alleviated the pathological changes in sciatic nerve of DPN rats (P<0.05). Mechanistically, quercetin markedly upregulated the expressions of axonal growth factors, Slit-2 and Netrin-1 in vivo and in vitro (P<0.05), while inhibiting the aberrant activation of Rho/ROCK signaling pathway in the sciatic nerve of DPN rats.

Conclusion

Our findings suggest that quercetin improves DPN through a novel mechanism, indicating its potential as a therapeutic agent for DPN therapy.

Excitotoxic spinal damage induced by kainic acid impairs locomotion, alters nociception, and reduces CREB nuclear translocation

Our previous in vitro studies showed that excitotoxicity evoked by glutamate analogue kainate (KA) significantly decreased the number of rat spinal neurons and triggered high release of glutamate leading to locomotor network block. Our current objective was to assess the role of CREB as a predictive marker of damage following chemically-induced spinal cord injury by using in vivo and in vitro models. Thus, in vivo excitotoxicity in Balb/c adult mice was induced by KA intraspinal injection, while in vitro spinal cord excitotoxicity was produced by bath-applied KA. KA application evoked significant neuronal loss, deterioration in hindlimb motor coordination and thermal allodynia. In addition, immunohistochemical analysis showed that KA application resulted in decreased number of CREB positive nuclei in the ventral horn and in dorsal layers III-IV. Our data suggests that excitotoxic-induced neuronal loss may be potentially predicted by altered CREB nuclear translocation.

The role of transcriptional and epigenetic modifications in astrogliogenesis

Astrocytes are widely distributed and play a critical role in the central nervous system (CNS) of the human brain. During the development of CNS, astrocytes provide essential nutritional and supportive functions for neural cells and are involved in their metabolism and pathological processes. Despite the numerous studies that have reported on the regulation of astrogliogenesis at the transcriptional and epigenetic levels, there is a paucity of literature that provides a comprehensive summary of the key factors influencing this process. In this review, we analyzed the impact of transcription factors (e.g., NFI, JAK/STAT, BMP, and Ngn2), DNA methylation, histone acetylation, and noncoding RNA on astrocyte behavior and the regulation of astrogliogenesis, hope it enhances our comprehension of the mechanisms underlying astrogliogenesis and offers a theoretical foundation for the treatment of patients with neurological diseases.

IGF-1 and Glucocorticoid Receptors Are Potential Target Proteins for the NGF-Mimic Effect of β-Cyclocitral from Lavandula angustifolia Mill. in PC12 Cells

In the present study, the PC12 cells as a bioassay system were used to screen the small molecules with nerve growth factor (NGF)- mimic effect from Lavandula angustifolia Mill. The β-Cyclocitral (β-cyc) as an active compound was discovered, and its chemical structure was also determined. Furthermore, we focused on the bioactive and action mechanism of this compound to do an intensive study with specific protein inhibitors and Western blotting analysis. The β-cyc had novel NGF-mimic and NGF-enhancer effects on PC12 cells, while the insulin-like growth factor-1 receptor (IGF-1R)/phosphatidylinositol 3 kinase, (PI3K)/serine/threonine-protein kinase (AKT), and glucocorticoid receptor (GR)/phospholipase C (PLC)/protein kinase C (PKC) signaling pathways were involved in the bioactivity of β-cyc. In addition, the important role of the rat sarcoma (Ras)/protooncogene serine-threonine protein kinase (Raf) signaling pathway was observed, although it was independent of tyrosine kinase (Trk) receptors. Moreover, the non-label target protein discovery techniques, such as the cellular thermal shift assay (CETSA) and drug affinity responsive target stability (DARTS), were utilized to make predictions of its target protein. The stability of IGF-R and GR, proteins for temperature and protease, was dose-dependently increased after treatment of β-cyc compared with control groups, respectively. These findings indicated that β-cyc promoted the neuron differentiation of PC12 cells via targeting IGF-1R and GR and modification of downstream signaling pathways.

Nerve Regeneration Potential of Antioxidant-Modified Black Phosphorus Quantum Dots in Peripheral Nerve Injury

Peripheral nerve injury is a major societal concern. Black phosphorus (BP) has inherent advantages over cell-based therapies in regenerative medicine. However, controlling spontaneous degradation and size-dependent cytotoxicity remains challenging and poses difficulties for clinical translation. In this study, we constructed zero-dimensional BP quantum dots (QDs) modified with antioxidant β-carotene and comprehensively investigated them in Schwann cells (SCs) to elucidate their potential for peripheral nerve repair. In vitro experiments demonstrated that BPQD@β-carotene has an inappreciable toxicity and good biocompatibility, favoring neural regrowth, angiogenesis, and inflammatory regulation of SCs. Furthermore, the PI3K/Akt and Ras/ERK1/2 signaling pathways were activated in SCs at the genetic, protein, and metabolite levels. The BPQD@β-carotene-embedded GelMA/PEGDA scaffold enhanced functional recovery by promoting axon remyelination and regeneration and facilitating intraneural angiogenesis in peripheral nerve injury models of rats and beagle dogs. These results contribute to advancing knowledge of BP nanomaterials in tissue regeneration and show significant potential for application in translational medicine.

Neuroscience of cancer: Research progress and emerging of the field

Cancer cells immediately expand and penetrate adjoining tissues, as opposed to metastasis, that is the spread of cancer cells through the circulatory or lymphatic systems to more distant places via the invasion process. We found that a lack of studies discussed tumor development with the nervous system, by the aspects of cancer-tissue invasion (biological) and chemical modulation of growth that cascades by releasing neural-related factors from the nerve endings via chemical substances known as neurotransmitters. In this review, we aimed to carefully demonstrate and describe the cancer invasion and interaction with the nervous system, as well as reveal the research progress and the emerging neuroscience of cancer. An initial set of 160 references underwent systematic review and summarization. Through a meticulous screening process, these data were refined, ultimately leading to the inclusion of 98 studies that adhered to predetermined criteria. The outcomes show that one formidable challenge in the realm of cancer lies in its intrinsic heterogeneity and remarkable capacity for rapid adaptation. Despite advancements in genomics and precision medicine, there is still a need to identify new molecular targets. Considering cancer within its molecular and cellular environment, including neural components, is crucial for addressing this challenge. In conclusion, this review provides good referential data for direct, indirect, biological, and chemical interaction for nerve tissue-tumor interaction, suggesting the establishment of new therapy techniques and mechanisms by controlling and modifying neuron networks that supply signals to tumors.

Transplantation of Predegenerated Peripheral Nerves after Complete Spinal Cord Transection in Rats: Effect of Neural Precursor Cells and Pharmacological Treatment with the Sulfoglycolipid Tol-51

Following spinal cord injury (SCI), the regenerative capacity of the central nervous system (CNS) is severely limited by the failure of axonal regeneration. The regeneration of CNS axons has been shown to occur by grafting predegenerated peripheral nerves (PPNs) and to be promoted by the transplantation of neural precursor cells (NPCs). The introduction of a combinatorial treatment of PPNs and NPCs after SCI has to address the additional problem of glial scar formation, which prevents regenerating axons from leaving the implant and making functional connections. Previously, we discovered that the synthetic sulfoglycolipid Tol-51 inhibits astrogliosis. The objective was to evaluate axonal regeneration and locomotor function improvement after SCI in rats treated with a combination of PPN, NPC, and Tol-51. One month after SCI, the scar tissue was removed and replaced with segments of PPN or PPN+Tol-51; PPN+NPC+Tol-51. The transplantation of a PPN segment favors regenerative axonal growth; in combination with Tol-51 and NPC, 30% of the labeled descending corticospinal axons were able to grow through the PPN and penetrate the caudal spinal cord. The animals treated with PPN showed significantly better motor function. Our data demonstrate that PPN implants plus NPC and Tol-51 allow successful axonal regeneration in the CNS.

The relevance of BDNF for neuroprotection and neuroplasticity in multiple sclerosis

Background

Neuroplasticity as a mechanism to overcome central nervous system injury resulting from different neurological diseases has gained increasing attention in recent years. However, deficiency of these repair mechanisms leads to the accumulation of neuronal damage and therefore long-term disability. To date, the mechanisms by which remyelination occurs and why the extent of remyelination differs interindividually between multiple sclerosis patients regardless of the disease course are unclear. A member of the neurotrophins family, the brain-derived neurotrophic factor (BDNF) has received particular attention in this context as it is thought to play a central role in remyelination and thus neuroplasticity, neuroprotection, and memory.

Objective

To analyse the current literature regarding BDNF in different areas of multiple sclerosis and to provide an overview of the current state of knowledge in this field.

Conclusion

To date, studies assessing the role of BDNF in patients with multiple sclerosis remain inconclusive. However, there is emerging evidence for a beneficial effect of BDNF in multiple sclerosis, as studies reporting positive effects on clinical as well as MRI characteristics outweighed studies assuming detrimental effects of BDNF. Furthermore, studies regarding the Val66Met polymorphism have not conclusively determined whether this is a protective or harmful factor in multiple sclerosis, but again most studies hypothesized a protective effect through modulation of BDNF secretion and anti-inflammatory effects with different effects in healthy controls and patients with multiple sclerosis, possibly due to the pro-inflammatory milieu in patients with multiple sclerosis. Further studies with larger cohorts and longitudinal follow-ups are needed to improve our understanding of the effects of BDNF in the central nervous system, especially in the context of multiple sclerosis.

Progress in Research on the Role of the Thioredoxin System in Chemical Nerve Injury

(1) Background: Various factors, such as oxidative stress, mitochondrial dysfunction, tumors, inflammation, trauma, immune disorders, and neuronal toxicity, can cause nerve damage. Chemical nerve injury, which results from exposure to toxic chemicals, has garnered increasing research attention. The thioredoxin (Trx) system, comprising Trx, Trx reductase, nicotinamide adenine dinucleotide phosphate, and Trx-interacting protein (TXNIP; endogenous Trx inhibitor), helps maintain redox homeostasis in the central nervous system. The dysregulation of this system can cause dementia, cognitive impairment, nerve conduction disorders, movement disorders, and other neurological disorders. Thus, maintaining Trx system homeostasis is crucial for preventing or treating nerve damage. (2) Objective: In this review study, we explored factors influencing the homeostasis of the Trx system and the involvement of its homeostatic imbalance in chemical nerve injury. In addition, we investigated the therapeutic potential of the Trx system-targeting active substances against chemical nerve injury. (3) Conclusions: Chemicals such as morphine, metals, and methylglyoxal interfere with the activity of TXNIP, Trx, and Trx reductase, disrupting Trx system homeostasis by affecting the phosphatidylinositol-3-kinase/protein kinase B, extracellular signal-regulated kinase, and apoptotic signaling-regulated kinase 1/p38 mitogen-activated protein kinase pathways, thereby leading to neurological disorders. Active substances such as resveratrol and lysergic acid sulfide mitigate the symptoms of chemical nerve injury by regulating the Ras/Raf1/extracellular signal-regulated kinase pathway and the miR-146a-5p/TXNIP axis. This study may guide the development of Trx-targeting modulators for treating neurological disorders and chemical nerve injuries.

Regeneration of Propriospinal Axons in Rat Transected Spinal Cord Injury through a Growth-Promoting Pathway Constructed by Schwann Cells Overexpressing GDNF

Unsuccessful axonal regeneration in transected spinal cord injury (SCI) is mainly attributed to shortage of growth factors, inhibitory glial scar, and low intrinsic regenerating capacity of severely injured neurons. Previously, we constructed an axonal growth permissive pathway in a thoracic hemisected injury by transplantation of Schwann cells overexpressing glial-cell-derived neurotrophic factor (SCs-GDNF) into the lesion gap as well as the caudal cord and proved that this novel permissive bridge promoted the regeneration of descending propriospinal tract (dPST) axons across and beyond the lesion. In the current study, we subjected rats to complete thoracic (T11) spinal cord transections and examined whether these combinatorial treatments can support dPST axons' regeneration beyond the transected injury. The results indicated that GDNF significantly improved graft-host interface by promoting integration between SCs and astrocytes, especially the migration of reactive astrocyte into SCs-GDNF territory. The glial response in the caudal graft area has been significantly attenuated. The astrocytes inside the grafted area were morphologically characterized by elongated and slim process and bipolar orientation accompanied by dramatically reduced expression of glial fibrillary acidic protein. Tremendous dPST axons have been found to regenerate across the lesion and back to the caudal spinal cord which were otherwise difficult to see in control groups. The caudal synaptic connections were formed, and regenerated axons were remyelinated. The hindlimb locomotor function has been improved.

Immunoregulation of Glia after spinal cord injury: a bibliometric analysis

Objective

Immunoregulation is a complex and critical process in the pathological process of spinal cord injury (SCI), which is regulated by various factors and plays an important role in the functional repair of SCI. This study aimed to explore the research hotspots and trends of glial cell immunoregulation after SCI from a bibliometric perspective.

Methods

Data on publications related to glial cell immunoregulation after SCI, published from 2004 to 2023, were obtained from the Web of Science Core Collection. Countries, institutions, authors, journals, and keywords in the topic were quantitatively analyzed using the R package "bibliometrix", VOSviewer, Citespace, and the Bibliometrics Online Analysis Platform.

Results

A total of 613 papers were included, with an average annual growth rate of 9.39%. The papers came from 36 countries, with the United States having the highest output, initiating collaborations with 27 countries. Nantong University was the most influential institution. We identified 3,177 authors, of whom Schwartz, m, of the Weizmann Institute of Science, was ranked first regarding both field-specific H-index (18) and average number of citations per document (151.44). Glia ranked first among journals with 2,574 total citations. The keywords "microglia," "activation," "macrophages," "astrocytes," and "neuroinflammation" represented recent hot topics and are expected to remain a focus of future research.

Conclusion

These findings strongly suggest that the immunomodulatory effects of microglia, astrocytes, and glial cell interactions may be critical in promoting nerve regeneration and repair after SCI. Research on the immunoregulation of glial cells after SCI is emerging, and there should be greater cooperation and communication between countries and institutions to promote the development of this field and benefit more SCI patients.

Berberine improves cognitive impairment by alleviating brain atrophy and promoting white matter reorganization in diabetic db/db mice: a magnetic resonance imaging-based study

Diabetic cognitive impairment is a common complication in type 2 diabetes. Berberine (BBR) is an isoquinoline alkaloid that has been shown to have neuroprotective effects against diabetes. This study aimed to investigate the effect of BBR on the gray and white matter of the brain by using magnetic resonance imaging (MRI) and to explore the underlying mechanisms. The study used diabetic db/db mice and administered BBR (50 and 100 mg/kg) intragastrically for twelve weeks. Morris water maze was applied to examine cognitive function. T2-weighted imaging (T2WI) was performed to assess brain atrophy, and diffusion tensor imaging (DTI) combined with fiber tracking was conducted to monitor the structural integrity of the white matter, followed by histological immunostaining. Furthermore, the protein expressions of the phosphatidylinositol 3-kinase (PI3K)/ protein kinase B (AKT)/ glycogen synthase kinase-3β (GSK-3β) were detected. The results revealed that BBR significantly improved the spatial learning and memory of the db/db mice. T2WI exhibited ameliorated brain atrophy in the BBR-treated db/db mice, as evidenced by reduced ventricular volume accompanied by increased hippocampal volumes. DTI combined with fiber tracking revealed that BBR increased FA, fiber density and length in the corpus callosum/external capsule of the db/db mice. These imaging findings were confirmed by histological immunostaining. Notably, BBR significantly enhanced the protein levels of phosphorylated AKT at Ser473 and GSK-3β at Ser9. Collectively, this study demonstrated that BBR significantly improved the cognitive function of the diabetic db/db mice through ameliorating brain atrophy and promoting white matter reorganization via AKT/GSK-3β pathway.

Repurposing development genes for axonal regeneration following injury: Examining the roles of Wnt signaling

In this review, we explore the connections between developmental embryology and axonal regeneration. Genes that regulate embryogenesis and central nervous system (CNS) development are discussed for their therapeutic potential to induce axonal and cellular regeneration in adult tissues after neuronal injury. Despite substantial differences in the tissue environment in the developing CNS compared with the injured CNS, recent studies have identified multiple molecular pathways that promote axonal growth in both scenarios. We describe various molecular cues and signaling pathways involved in neural development, with an emphasis on the versatile Wnt signaling pathway. We discuss the capacity of developmental factors to initiate axonal regrowth in adult neural tissue within the challenging environment of the injured CNS. Our discussion explores the roles of Wnt signaling and also examines the potential of other embryonic genes including Pax, BMP, Ephrin, SOX, CNTF, PTEN, mTOR and STAT3 to contribute to axonal regeneration in various CNS injury model systems, including spinal cord and optic crush injuries in mice, Xenopus and zebrafish. Additionally, we describe potential contributions of Müller glia redifferentiation to neuronal regeneration after injury. Therefore, this review provides a comprehensive summary of the state of the field, and highlights promising research directions for the potential therapeutic applications of specific embryologic molecular pathways in axonal regeneration in adults.

Mesenchymal stem cells' "garbage bags" at work: Treating radial nerve injury with mesenchymal stem cell-derived exosomes

Unlike central nervous system injuries, peripheral nerve injuries (PNIs) are often characterized by more or less successful axonal regeneration. However, structural and functional recovery is a senile process involving multifaceted cellular and molecular processes. The contemporary treatment options are limited, with surgical intervention as the gold-standard method; however, each treatment option has its associated limitations, especially when the injury is severe with a large gap. Recent advancements in cell-based therapy and cell-free therapy approaches using stem cell-derived soluble and insoluble components of the cell secretome are fast-emerging therapeutic approaches to treating acute and chronic PNI. The recent pilot study is a leap forward in the field, which is expected to pave the way for more enormous, systematic, and well-designed clinical trials to assess the therapeutic efficacy of mesenchymal stem cell-derived exosomes as a bio-drug either alone or as part of a combinatorial approach, in an attempt synergize the best of novel treatment approaches to address the complexity of the neural repair and regeneration.

Iridoids rich fraction from Valeriana jatamansi Jones promotes axonal regeneration and motor functional recovery after spinal cord injury through activation of the PI3K/Akt signaling pathway

Valeriana jatamansi Jones (VJJ), renowned for its extensive history in traditional Chinese medicine and ethnomedicine within China, is prevalently utilized to alleviate ailments such as epigastric distension and pain, gastrointestinal disturbances including food accumulation, diarrhea, and dysentery, as well as insomnia and other diseases. Moreover, the Iridoid-rich fraction derived from Valeriana jatamansi Jones (IRFV) has demonstrated efficacy in facilitating the recuperation of motor functions after spinal cord injury (SCI). This study is aimed to investigate the therapeutic effect of IRFV on SCI and its underlying mechanism. Initially, a rat model of SCI was developed to assess the impact of IRFV on axonal regeneration. Subsequently, employing the PC12 cell model of oxidative damage, the role and mechanism of IRFV in enhancing axonal regeneration were explored using the phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway inhibitor LY294002. Ultimately, the same inhibitor was administered to SCI rats to confirm the molecular mechanism through which IRFV promotes axonal regeneration by activating the PI3K/Akt signaling pathway. The results showed that IRFV significantly enhanced motor function recovery, reduced pathological injury, and facilitated axonal regeneration in SCI rats. In vitro experiments revealed that IRFV improved PC12 cell viability, augmented axonal regeneration, and activated the PI3K/Akt signaling pathway. Notably, the inhibition of this pathway negated the therapeutic benefits of IRFV in SCI rats. In conclusion, IRFV promote promotes axonal regeneration and recovery of motor function after SCI through activation of the PI3K/Akt signaling pathway.

Advances in electroactive bioscaffolds for repairing spinal cord injury

Spinal cord injury (SCI) is a devastating neurological disorder, leading to loss of motor or somatosensory function, which is the most challenging worldwide medical problem. Re-establishment of intact neural circuits is the basis of spinal cord regeneration. Considering the crucial role of electrical signals in the nervous system, electroactive bioscaffolds have been widely developed for SCI repair. They can produce conductive pathways and a pro-regenerative microenvironment at the lesion site similar to that of the natural spinal cord, leading to neuronal regeneration and axonal growth, and functionally reactivating the damaged neural circuits. In this review, we first demonstrate the pathophysiological characteristics induced by SCI. Then, the crucial role of electrical signals in SCI repair is introduced. Based on a comprehensive analysis of these characteristics, recent advances in the electroactive bioscaffolds for SCI repair are summarized, focusing on both the conductive bioscaffolds and piezoelectric bioscaffolds, used independently or in combination with external electronic stimulation. Finally, thoughts on challenges and opportunities that may shape the future of bioscaffolds in SCI repair are concluded.

The role of kinases in peripheral nerve regeneration: mechanisms and implications

Peripheral nerve injury disease is a prevalent traumatic condition in current medical practice. Despite the present treatment approaches, encompassing surgical sutures, autologous nerve or allograft nerve transplantation, tissue engineering techniques, and others, an effective clinical treatment method still needs to be discovered. Exploring novel treatment methods to improve peripheral nerve regeneration requires more effort in investigating the cellular and molecular mechanisms involved. Many factors are associated with the regeneration of injured peripheral nerves, including the cross-sectional area of the injured nerve, the length of the nerve gap defect, and various cellular and molecular factors such as Schwann cells, inflammation factors, kinases, and growth factors. As crucial mediators of cellular communication, kinases exert regulatory control over numerous signaling cascades, thereby participating in various vital biological processes, including peripheral nerve regeneration after nerve injury. In this review, we examined diverse kinase classifications, distinct nerve injury types, and the intricate mechanisms involved in peripheral nerve regeneration. Then we stressed the significance of kinases in regulating autophagy, inflammatory response, apoptosis, cell cycle, oxidative processes, and other aspects in establishing conductive microenvironments for nerve tissue regeneration. Finally, we briefly discussed the functional roles of kinases in different types of cells involved in peripheral nerve regeneration.

Programmed cell death 4 blocks autophagy and promotes dopaminergic neuronal injury in Parkinson's disease

Dysregulation of autophagy has previously been associated with the formation of toxic proteins, such as α-synuclein, in patients with Parkinson's disease (PD). In addition, it has been indicated that programmed cell death 4 (PDCD4) can inhibit autophagy in certain conditions, such as diabetic nephropathy, atherosclerosis and cardiac hypertrophy. Therefore, the hypothesis that PDCD4 can promote dopaminergic neuron damage through autophagy was proposed. To explore this hypothesis, the present study treated human neuroblastoma SK-N-SH cells with 1-methyl-4-phenylpyridinium (MPP+) to establish an in vitro model of PD. The potential effects of PDCD4 knockdown on lactate dehydrogenase (LDH) release, cell apoptosis, inflammatory response, oxidative stress and autophagy were then evaluated in this model of PD using an LDH assay kit, flow cytometry, western blotting, ELISA and immunofluorescence. The autophagy inhibitor 3-methyladenine (3-MA) was also applied to treat these cells, and its effects on these aforementioned parameters following PDCD4 knockdown were assessed. MPP+ was shown to increase the expression levels of PDCD4 in SK-N-SH cells. PDCD4 knockdown was revealed to suppress LDH release, cell apoptosis, secretion of inflammatory factors and oxidative stress. In addition, PDCD4 knockdown was demonstrated to enhance autophagy in cells treated with MPP+. By contrast, 3-MA treatment reversed the aforementioned effects of PDCD4 knockdown on cells, suggesting autophagy to be among the processes regulated by PDCD4 in SK-N-SH cells. The results of the present study suggested the existence of regulatory effects mediated by PDCD4 on autophagy in MPP+-induced SK-N-SH cells, offering potential future targets for PD therapy.

Blockade of Rho-associated kinase prevents inhibition of axon regeneration of peripheral nerves induced by anti-ganglioside antibodies

Anti-ganglioside antibodies are associated with delayed/poor clinical recovery in Guillain-Barrè syndrome, mostly related to halted axon regeneration. Cross-linking of cell surface gangliosides by anti-ganglioside antibodies triggers inhibition of nerve repair in in vitro and in vivo paradigms of axon regeneration. These effects involve the activation of the small GTPase RhoA/ROCK signaling pathways, which negatively modulate growth cone cytoskeleton, similarly to well stablished inhibitors of axon regeneration described so far. The aim of this work was to perform a proof of concept study to demonstrate the effectiveness of Y-27632, a selective pharmacological inhibitor of ROCK, in a mouse model of axon regeneration of peripheral nerves, where the passive immunization with a monoclonal antibody targeting gangliosides GD1a and GT1b was previously reported to exert a potent inhibitory effect on regeneration of both myelinated and unmyelinated fibers. Our results demonstrate a differential sensitivity of myelinated and unmyelinated axons to the pro-regenerative effect of Y-27632. Treatment with a total dosage of 9 mg/kg of Y-27632 resulted in a complete prevention of anti-GD1a/GT1b monoclonal antibody-mediated inhibition of axon regeneration of unmyelinated fibers to skin and the functional recovery of mechanical cutaneous sensitivity. In contrast, the same dose showed toxic effects on the regeneration of myelinated fibers. Interestingly, scale down of the dosage of Y-27632 to 5 mg/kg resulted in a significant although not complete recovery of regenerated myelinated axons exposed to anti-GD1a/GT1b monoclonal antibody in the absence of toxicity in animals exposed to only Y-27632. Overall, these findings confirm the in vivo participation of RhoA/ROCK signaling pathways in the molecular mechanisms associated with the inhibition of axon regeneration induced by anti-GD1a/GT1b monoclonal antibody. Our findings open the possibility of therapeutic pharmacological intervention targeting RhoA/Rock pathway in immune neuropathies associated with the presence of anti-ganglioside antibodies and delayed or incomplete clinical recovery after injury in the peripheral nervous system.

Astroglial Cells: Emerging Therapeutic Targets in the Management of Traumatic Brain Injury

Traumatic Brain Injury (TBI) represents a significant health concern, necessitating advanced therapeutic interventions. This detailed review explores the critical roles of astrocytes, key cellular constituents of the central nervous system (CNS), in both the pathophysiology and possible rehabilitation of TBI. Following injury, astrocytes exhibit reactive transformations, differentiating into pro-inflammatory (A1) and neuroprotective (A2) phenotypes. This paper elucidates the interactions of astrocytes with neurons, their role in neuroinflammation, and the potential for their therapeutic exploitation. Emphasized strategies encompass the utilization of endocannabinoid and calcium signaling pathways, hormone-based treatments like 17β-estradiol, biological therapies employing anti-HBGB1 monoclonal antibodies, gene therapy targeting Connexin 43, and the innovative technique of astrocyte transplantation as a means to repair damaged neural tissues.

New insights into glycogen synthase kinase-3: A common target for neurodegenerative diseases

Glycogen synthase kinase 3 (GSK-3) is a highly conserved protein serine/threonine kinase that plays a central role in a wide variety of cellular processes to coordinate catabolic and anabolic pathways and regulate cell growth and fate. There is increasing evidence showing that abnormal glycogen synthase kinase 3 (GSK-3) is associated with the pathogenesis and progression of many disorders, such as cancer, diabetes, psychiatric diseases, and neurodegenerative diseases. In this review, we summarize recent findings about the regulatory role of GSK-3 in the occurrence and development of multiple neurodegenerative diseases, mainly focusing on Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. The aim of this study is to provide new insight into the shared working mechanism of GSK-3 as a therapeutic target of multiple neurodegenerative diseases.

The Dynamics of Nerve Degeneration and Regeneration in a Healthy Milieu and in Diabetes

Appropriate animal models, mimicking conditions of both health and disease, are needed to understand not only the biology and the physiology of neurons and other cells under normal conditions but also under stress conditions, like nerve injuries and neuropathy. In such conditions, understanding how genes and different factors are activated through the well-orchestrated programs in neurons and other related cells is crucial. Knowledge about key players associated with nerve regeneration intended for axonal outgrowth, migration of Schwann cells with respect to suitable substrates, invasion of macrophages, appropriate conditioning of extracellular matrix, activation of fibroblasts, formation of endothelial cells and blood vessels, and activation of other players in healthy and diabetic conditions is relevant. Appropriate physical and chemical attractions and repulsions are needed for an optimal and directed regeneration and are investigated in various nerve injury and repair/reconstruction models using healthy and diabetic rat models with relevant blood glucose levels. Understanding dynamic processes constantly occurring in neuropathies, like diabetic neuropathy, with concomitant degeneration and regeneration, requires advanced technology and bioinformatics for an integrated view of the behavior of different cell types based on genomics, transcriptomics, proteomics, and imaging at different visualization levels. Single-cell-transcriptional profile analysis of different cells may reveal any heterogeneity among key players in peripheral nerves in health and disease.

Comparative evaluation of ethyl acetate and n-Hexane extracts of Cannabis sativa L. leaves for muscle function restoration after peripheral nerve lesion

Peripheral nerve injuries are one of those complex medical conditions for which a highly effective first-line treatment is currently missing. The use of natural compound as medicines to treat various disorders has a long history. Our previous research explored that crude Cannabis sativa L. accelerated the recovery of sensorimotor functions following nerve injury. The purpose of the current study was to investigate the effects of n-Hexane and ethyl acetate extracts of C. sativa L. leaves on the muscle function restoration in a mouse model after sciatic nerve injury. For this purpose, albino mice (n = 18) were equally divided into control and two treatment groups. The control group was fed on a plain diet while treatment groups were given a diet having n-Hexane (treatment 1) and ethyl acetate (treatment 2) extracts of C. sativa L. (10 mg/kg body weight), respectively. The hot plate test (M = 15.61, SD = 2.61, p = .001), grip strength (M = 68.32, SD = 3.22, p < .001), and sciatic functional index (SFI) (M = 11.59, SD = 6.54, p = .012) assessment indicated significant amelioration in treatment 1 as compared to treatment 2 group. Furthermore, muscle fiber cross-sectional area revealed a noticeable improvement (M = 182,319, SD = 35.80, p = .013) in treatment 1 while muscle mass ratio of Gastrocnemius (M = 0.64, SD = 0.08, p = .427) and Tibialis anterior (M = 0.57, SD = 0.04, p = .209) indicated nonsignificant change. A prominent increase in total antioxidant capacity (TAC) (M = 3.76, SD = 0.38, p < .001) and momentous decrease in total oxidant status (TOS) (M = 11.28, SD = 5.71, p < .001) along with blood glucose level indicated significant difference (M = 105.5, SD = 9.12, p < 0.001) in treatment 1 group. These results suggest that treatment 1 has the ability to speed up functional recovery after a peripheral nerve lesion. Further research is necessary, nevertheless, to better understand the extract's actual curative properties and the mechanisms that improve functional restoration.

Abnormal intraepidermal nerve fiber density in disease: A scoping review

Background

Intraepidermal nerve fiber density (IENFD) has become an important biomarker for neuropathy diagnosis and research. The consequences of reduced IENFD can include sensory dysfunction, pain, and a significant decrease in quality of life. We examined the extent to which IENFD is being used as a tool in human and mouse models and compared the degree of fiber loss between diseases to gain a broader understanding of the existing data collected using this common technique.

Methods

We conducted a scoping review of publications that used IENFD as a biomarker in human and non-human research. PubMed was used to identify 1,004 initial articles that were then screened to select articles that met the criteria for inclusion. Criteria were chosen to standardize publications so they could be compared rigorously and included having a control group, measuring IENFD in a distal limb, and using protein gene product 9.5 (PGP9.5).

Results

We analyzed 397 articles and collected information related to publication year, the condition studied, and the percent IENFD loss. The analysis revealed that the use of IENFD as a tool has been increasing in both human and non-human research. We found that IENFD loss is prevalent in many diseases, and metabolic or diabetes-related diseases were the most studied conditions in humans and rodents. Our analysis identified 73 human diseases in which IENFD was affected, with 71 reporting IENFD loss and an overall average IENFD change of -47%. We identified 28 mouse and 21 rat conditions, with average IENFD changes of -31.6% and -34.7%, respectively. Additionally, we present data describing sub-analyses of IENFD loss according to disease characteristics in diabetes and chemotherapy treatments in humans and rodents.

Interpretation

Reduced IENFD occurs in a surprising number of human disease conditions. Abnormal IENFD contributes to important complications, including poor cutaneous vascularization, sensory dysfunction, and pain. Our analysis informs future rodent studies so they may better mirror human diseases impacted by reduced IENFD, highlights the breadth of diseases impacted by IENFD loss, and urges exploration of common mechanisms that lead to substantial IENFD loss as a complication in disease.

Abnormal Intraepidermal Nerve Fiber Density in Disease: A Scoping Review

Background

Intraepidermal nerve fiber density (IENFD) has become an important biomarker for neuropathy diagnosis and research. The consequences of reduced IENFD can include sensory dysfunction, pain, and a significant decrease in quality of life. We examined the extent to which IENFD is being used as a tool in human and mouse models and compared the degree of fiber loss between diseases to gain a broader understanding of the existing data collected using this common technique.

Methods

We conducted a scoping review of publications that used IENFD as a biomarker in human and non-human research. PubMed was used to identify 1,004 initial articles that were then screened to select articles that met the criteria for inclusion. Criteria were chosen to standardize publications so they could be compared rigorously and included having a control group, measuring IENFD in a distal limb, and using protein gene product 9.5 (PGP9.5).

Results

We analyzed 397 articles and collected information related to publication year, the condition studied, and the percent IENFD loss. The analysis revealed that the use of IENFD as a tool has been increasing in both human and non-human research. We found that IENFD loss is prevalent in many diseases, and metabolic or diabetes-related diseases were the most studied conditions in humans and rodents. Our analysis identified 74 human diseases in which IENFD was affected, with 71 reporting IENFD loss and an overall average IENFD change of -47%. We identified 28 mouse and 21 rat conditions, with average IENFD changes of -31.6 % and - 34.7% respectively. Additionally, we present data describing sub-analyses of IENFD loss according to disease characteristics in diabetes and chemotherapy treatments in humans and rodents.

Interpretation

Reduced IENFD occurs in a surprising number of human disease conditions. Abnormal IENFD contributes to important complications, including poor cutaneous vascularization, sensory dysfunction, and pain. Our analysis informs future rodent studies so they may better mirror human diseases impacted by reduced IENFD, highlights the breadth of diseases impacted by IENFD loss, and urges exploration of common mechanisms that lead to substantial IENFD loss as a complication in disease.