Evaluation of peripherin in biofluids of patients with motor neuron diseases

The potential therapeutic strategy in combating neurodegenerative diseases: Focusing on natural products

Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Huntington disease (HD), and Multiple sclerosis (MS), pose a significant global health challenge due to their intricate pathology and limited therapeutic interventions. Natural products represent invaluable reservoirs for combating these neurodegenerative diseases by targeting key pathological hallmarks such as protein aggregation, synaptic dysfunction, aberrant proteostasis, cytoskeletal abnormalities, altered energy homeostasis, inflammation, and neuronal cell death. This review provides an in-depth analysis of the mechanisms and therapeutic targets of natural products for their neuroprotective effects. Furthermore, it elucidates the current progress of clinical trials investigating the potential of natural products in delaying neurodegeneration. The objective of this review is to enhance the comprehension of natural products in the prevention and treatment of neurodegenerative diseases, offering new insights and potential avenues for future pharmaceutical research.

Ultrasensitive assay technology and fluid biomarkers for the evaluation of peripheral nerve disease

The field of biomarker discovery is rapidly expanding. The introduction of ultrasensitive immunoassays and the growing precision of genetic technologies are poised to revolutionise the assessment and monitoring of many diseases. Given the difficulties in imaging and tissue diagnosis, there is mounting interest in serum and cerebrospinal fluid biomarkers of peripheral neuropathy. Realised and potential fluid biomarkers of peripheral nerve disease include neuronal biomarkers of axonal degeneration, glial biomarkers for peripheral demyelinating disorders, immunopathogenic biomarkers (such as the presence and titre of antibodies or the levels of cytokines) and genetic biomarkers. Several are already starting to inform clinical practice, whereas others remain under evaluation as potential indicators of disease activity and treatment response. As more biomarkers become available for clinical use, it has become increasingly difficult for clinicians and researchers to keep up-to-date with the most recent discovery and interpretation. In this review, we aim to inform practising neurologists, neuroscientists and other clinicians about recent advances in fluid biomarker technology, with a focus on single molecule arrays (Simoa), chemiluminescent enzyme immunoassays (CLEIA), electrochemiluminescence (ECL), proximity extension assays (PEA), and microfluidic technology. We discuss established and emerging fluid biomarkers of peripheral neuropathy, their clinical applications, limitations and potential future developments.

The potential of blood neurofilament light as a marker of neurodegeneration for Alzheimer's disease

Over the past several years, there has been a surge in blood biomarker studies examining the value of plasma or serum neurofilament light (NfL) as a biomarker of neurodegeneration for Alzheimer's disease. However, there have been limited efforts to combine existing findings to assess the utility of blood NfL as a biomarker of neurodegeneration for Alzheimer's disease. In addition, we still need better insight into the specific aspects of neurodegeneration that are reflected by the elevated plasma or serum concentration of NfL. In this review, we survey the literature on the cross-sectional and longitudinal relationships between blood-based NfL levels and other, neuroimaging-based, indices of neurodegeneration in individuals on the Alzheimer's continuum. Then, based on the biomarker classification established by the FDA-NIH Biomarker Working group, we determine the utility of blood-based NfL as a marker for monitoring the disease status (i.e. monitoring biomarker) and predicting the severity of neurodegeneration in older adults with and without cognitive decline (i.e. a prognostic or a risk/susceptibility biomarker). The current findings suggest that blood NfL exhibits great promise as a monitoring biomarker because an increased NfL level in plasma or serum appears to reflect the current severity of atrophy, hypometabolism and the decline of white matter integrity, particularly in the brain regions typically affected by Alzheimer's disease. Longitudinal evidence indicates that blood NfL can be useful not only as a prognostic biomarker for predicting the progression of neurodegeneration in patients with Alzheimer's disease but also as a susceptibility/risk biomarker predicting the likelihood of abnormal alterations in brain structure and function in cognitively unimpaired individuals with a higher risk of developing Alzheimer's disease (e.g. those with a higher amyloid-β). There are still limitations to current research, as discussed in this review. Nevertheless, the extant literature strongly suggests that blood NfL can serve as a valuable prognostic and susceptibility biomarker for Alzheimer's disease-related neurodegeneration in clinical settings, as well as in research settings.

Peripherin is a biomarker of axonal damage in peripheral nervous system disease

Valid, responsive blood biomarkers specific to peripheral nerve damage would improve management of peripheral nervous system (PNS) diseases. Neurofilament light chain (NfL) is sensitive for detecting axonal pathology but is not specific to PNS damage, as it is expressed throughout the PNS and CNS. Peripherin, another intermediate filament protein, is almost exclusively expressed in peripheral nerve axons. We postulated that peripherin would be a promising blood biomarker of PNS axonal damage. We demonstrated that peripherin is distributed in sciatic nerve, and to a lesser extent spinal cord tissue lysates, but not in brain or extra-neural tissues. In the spinal cord, anti-peripherin antibody bound only to the primary cells of the periphery (anterior horn cells, motor axons and primary afferent sensory axons). In vitro models of antibody-mediated axonal and demyelinating nerve injury showed marked elevation of peripherin levels only in axonal damage and only a minimal rise in demyelination. We developed an immunoassay using single molecule array technology for the detection of serum peripherin as a biomarker for PNS axonal damage. We examined longitudinal serum peripherin and NfL concentrations in individuals with Guillain-Barré syndrome (GBS, n = 45, 179 time points), chronic inflammatory demyelinating polyradiculoneuropathy (CIDP, n = 35, 70 time points), multiple sclerosis (n = 30), dementia (as non-inflammatory CNS controls, n = 30) and healthy individuals (n = 24). Peak peripherin levels were higher in GBS than all other groups (median 18.75 pg/ml versus < 6.98 pg/ml, P < 0.0001). Peak NfL was highest in GBS (median 220.8 pg/ml) and lowest in healthy controls (median 5.6 pg/ml), but NfL did not distinguish between CIDP (17.3 pg/ml), multiple sclerosis (21.5 pg/ml) and dementia (29.9 pg/ml). While peak NfL levels were higher with older age (rho = +0.39, P < 0.0001), peak peripherin levels did not vary with age. In GBS, local regression analysis of serial peripherin in the majority of individuals with three or more time points of data (16/25) displayed a rise-and-fall pattern with the highest value within the first week of initial assessment. Similar analysis of serial NfL concentrations showed a later peak at 16 days. Group analysis of serum peripherin and NfL levels in GBS and CIDP patients were not significantly associated with clinical data, but in some individuals with GBS, peripherin levels appeared to better reflect clinical outcome measure improvement. Serum peripherin is a promising new, dynamic and specific biomarker of acute PNS axonal damage.

Transcriptional control of motor pool formation and motor circuit connectivity by the LIM-HD protein Isl2

The fidelity of motor control requires the precise positional arrangement of motor pools and the establishment of synaptic connections between them. During neural development in the spinal cord, motor nerves project to specific target muscles and receive proprioceptive input from these muscles via the sensorimotor circuit. LIM-homeodomain transcription factors are known to play a crucial role in successively restricting specific motor neuronal fates. However, their exact contribution to limb-based motor pools and locomotor circuits has not been fully understood. To address this, we conducted an investigation into the role of Isl2, a LIM-homeodomain transcription factor, in motor pool organization. We found that deletion of Isl2 led to the dispersion of motor pools, primarily affecting the median motor column (MMC) and lateral motor column (LMC) populations. Additionally, hindlimb motor pools lacked Etv4 expression, and we observed reduced terminal axon branching and disorganized neuromuscular junctions in Isl2-deficient mice. Furthermore, we performed transcriptomic analysis on the spinal cords of Isl2-deficient mice and identified a variety of downregulated genes associated with motor neuron (MN) differentiation, axon development, and synapse organization in hindlimb motor pools. As a consequence of these disruptions, sensorimotor connectivity and hindlimb locomotion were impaired in Isl2-deficient mice. Taken together, our findings highlight the critical role of Isl2 in organizing motor pool position and sensorimotor circuits in hindlimb motor pools. This research provides valuable insights into the molecular mechanisms governing motor control and its potential implications for understanding motor-related disorders in humans.

The value of serum creatinine as biomarker of disease progression in spinal and bulbar muscular atrophy (SBMA)

Serum creatinine has been indicated as a potential marker of motor function in SBMA and results form previous longitudinal studies pointed to its decline over time. This is a longitudinal retrospective study investigating creatinine changes over a 36-month-period in 73 patients with SBMA. Severity and progression of the disease was assessed according to serum creatine kinase (CK) values, manual muscle testing (MMT), SBMA functional rating scale (SBMAFRS) score, 6-min-walk test (6MWT) value, and spirometry (forced vital capacity, fVC%) obtained at the baseline and at each of the annual follow-up visits. Baseline serum creatinine concentrations positively correlated with 6MWT, the MMT megascore score of both the upper (ULM) and lower (LLM) limbs and SBMAFRS. No correlation was found with CK or fVC% values. Similar correlation results were achieved at all the subsequent time points. Longitudinal assessments conducted by the generalized estimating equations (GEE) method returned significant changes for SBMAFRS (- 1.41 points per year, p < 0.001), ULM and LLM (- 0.69, p = 0.01; and - 1.07, p < 0.001, respectively), 6MWT (- 47 m, p < 0.001) but not for creatinine (- 0.82, p > 0.05). We also observed that creatinine levels at baseline did not correlate with changes in the other measures from baseline at each annual visit. Our data do not support a role for serum creatinine as sensitive biomarker of disease progression, and possibily prognosis, in SBMA.

Intermediate filament proteins are reliable immunohistological biomarkers to help diagnose multiple tissue-specific diseases

Cytoskeletal networks are proteins that effectively maintain cell integrity and provide mechanical support to cells by actively transmitting mechanical signals. Intermediate filaments, which are from the cytoskeleton family and are 10 nanometres in diameter, are unlike actin and microtubules, which are highly dynamic cytoskeletal elements. Intermediate filaments are flexible at low strain, harden at high strain and resist breaking. For this reason, these filaments fulfil structural functions by providing mechanical support to the cells through their different strain-hardening properties. Intermediate filaments are suitable in that cells both cope with mechanical forces and modulate signal transmission. These filaments are composed of fibrous proteins that exhibit a central α-helical rod domain with a conserved substructure. Intermediate filament proteins are divided into six groups. Type I and type II include acidic and basic keratins, type III, vimentin, desmin, peripheralin and glial fibrillary acidic protein (GFAP), respectively. Type IV intermediate filament group includes neurofilament proteins and a fourth neurofilament subunit, α-internexin proteins. Type V consists of lamins located in the nucleus, and the type VI group consists of lens-specific intermediate filaments, CP49/phakinin and filen. Intermediate filament proteins show specific immunoreactivity in differentiating cells and mature cells of various types. Various carcinomas such as colorectal, urothelial and ovarian, diseases such as chronic pancreatitis, cirrhosis, hepatitis and cataract have been associated with intermediate filaments. Accordingly, this section reviews available immunohistochemical antibodies to intermediate filament proteins. Identification of intermediate filament proteins by methodological methods may contribute to the understanding of complex diseases.

Peripherin: A proposed biomarker of traumatic axonal injury triggered by mechanical force

Traumatic axonal injury (TAI) is one of the most common pathological features of severe traumatic brain injury (TBI). Our previous study using proteomics suggested that peripherin (PRPH) should be a potential candidate as a biomarker for TAI diagnosis. This study is to further elucidate the role and association of PRPH with TAI. In the animal study, we performed immunohistochemistry, ELISA and morphological analysis to evaluate PRPH level and distribution following a severe impact. PRPH-positive regions were widely distributed in the axonal tract throughout the whole brain. Axonal injuries with PRPH inclusion were observed post-TBI. Besides, PRPH was significantly increased in both cerebral spinal fluid and plasma at the early phase post-TBI. Colocalization analysis based on microscopy revealed that PRPH represents an immunohistological biomarker in the neuropathological diagnosis of TAI. Brain samples from patients with TBI were included to further test whether PRPH is feasible in the real practice of neuropathology. Immunohistochemistry of PRPH, NFH, APP and NFL on human brain tissues further confirmed PRPH as an immunohistological biomarker that could be applied in practice. Collectively, we conclude that PRPH mirrors the cytoskeleton injury of axons and could represent a neuropathological biomarker for TAI.

Role of the Intermediate Filament Protein Peripherin in Health and Disease

Intermediate filaments are the most heterogeneous class among cytoskeletal elements. While some of them have been well-characterized, little is known about peripherin. Peripherin is a class III intermediate filament protein with a specific expression in the peripheral nervous system. Epigenetic modifications are involved in this cell-type-specific expression. Peripherin has important roles in neurite outgrowth and stability, axonal transport, and axonal myelination. Moreover, peripherin interacts with proteins involved in vesicular trafficking, signal transduction, DNA/RNA processing, protein folding, and mitochondrial metabolism, suggesting a role in all these processes. This review collects information regarding peripherin gene regulation, post-translational modifications, and functions and its involvement in the onset of a number of diseases.

Phosphorylated CRMP1, axon guidance protein, is a component of spheroids and is involved in axonal pathology in amyotrophic lateral sclerosis

In amyotrophic lateral sclerosis (ALS), neurodegeneration is characterized by distal axonopathy that begins at the distal axons, including the neuromuscular junctions, and progresses proximally in a “dying back” manner prior to the degeneration of cell bodies. However, the molecular mechanism for distal axonopathy in ALS has not been fully addressed. Semaphorin 3A (Sema3A), a repulsive axon guidance molecule that phosphorylates collapsin response mediator proteins (CRMPs), is known to be highly expressed in Schwann cells near distal axons in a mouse model of ALS. To clarify the involvement of Sema3A–CRMP signaling in the axonal pathogenesis of ALS, we investigated the expression of phosphorylated CRMP1 (pCRMP1) in the spinal cords of 35 patients with sporadic ALS and seven disease controls. In ALS patients, we found that pCRMP1 accumulated in the proximal axons and co-localized with phosphorylated neurofilaments (pNFs), which are a major protein constituent of spheroids. Interestingly, the pCRMP1:pNF ratio of the fluorescence signal in spheroid immunostaining was inversely correlated with disease duration in 18 evaluable ALS patients, indicating that the accumulation of pCRMP1 may precede that of pNFs in spheroids or promote ALS progression. In addition, overexpression of a phospho-mimicking CRMP1 mutant inhibited axonal outgrowth in Neuro2A cells. Taken together, these results indicate that pCRMP1 may be involved in the pathogenesis of axonopathy in ALS, leading to spheroid formation through the proximal progression of axonopathy.

Neurofilament Proteins as Biomarkers to Monitor Neurological Diseases and the Efficacy of Therapies

Biomarkers of neurodegeneration and neuronal injury have the potential to improve diagnostic accuracy, disease monitoring, prognosis, and measure treatment efficacy. Neurofilament proteins (NfPs) are well suited as biomarkers in these contexts because they are major neuron-specific components that maintain structural integrity and are sensitive to neurodegeneration and neuronal injury across a wide range of neurologic diseases. Low levels of NfPs are constantly released from neurons into the extracellular space and ultimately reach the cerebrospinal fluid (CSF) and blood under physiological conditions throughout normal brain development, maturation, and aging. NfP levels in CSF and blood rise above normal in response to neuronal injury and neurodegeneration independently of cause. NfPs in CSF measured by lumbar puncture are about 40-fold more concentrated than in blood in healthy individuals. New ultra-sensitive methods now allow minimally invasive measurement of these low levels of NfPs in serum or plasma to track disease onset and progression in neurological disorders or nervous system injury and assess responses to therapeutic interventions. Any of the five Nf subunits - neurofilament light chain (NfL), neurofilament medium chain (NfM), neurofilament heavy chain (NfH), alpha-internexin (INA) and peripherin (PRPH) may be altered in a given neuropathological condition. In familial and sporadic Alzheimer's disease (AD), plasma NfL levels may rise as early as 22 years before clinical onset in familial AD and 10 years before sporadic AD. The major determinants of elevated levels of NfPs and degradation fragments in CSF and blood are the magnitude of damaged or degenerating axons of fiber tracks, the affected axon caliber sizes and the rate of release of NfP and fragments at different stages of a given neurological disease or condition directly or indirectly affecting central nervous system (CNS) and/or peripheral nervous system (PNS). NfPs are rapidly emerging as transformative blood biomarkers in neurology providing novel insights into a wide range of neurological diseases and advancing clinical trials. Here we summarize the current understanding of intracellular NfP physiology, pathophysiology and extracellular kinetics of NfPs in biofluids and review the value and limitations of NfPs and degradation fragments as biomarkers of neurodegeneration and neuronal injury.