The proNGF-p75NTR-Sortilin Signalling Complex as New Target for the Therapeutic Treatment of Parkinsons Disease

Brain plasticity and neuroinflammatory protein biomarkers with circulating MicroRNAs as predictors of acute brain injury outcome - A prospective cohort study

BACKGROUND

Brain recovery mechanisms after injuries like aneurysmal subarachnoid hemorrhage (aSAH), ischemic stroke (IS), and traumatic brain injury (TBI) involve brain plasticity, synaptic regeneration, and neuroinflammation. We hypothesized that serum levels of the p75 neurotrophic receptor (p75NTR) and associated signaling proteins, as well as differentially expressed (DE) microRNAs, could predict recovery outcomes irrespective of injury type.

METHODS

A prospective patient cohort with ischemic stroke (IS, n = 30), aneurysmal subarachnoid hemorrhage (aSAH, n = 31), and traumatic brain injury (TBI, n = 13) were evaluated (total n = 74). Serum samples were collected at two post-injury intervals (early: 1-3 days, late: 4-8 days), and outcomes were assessed after three months using the modified Rankin Scale (mRS), categorizing outcomes as favorable (mRS 0-3) or unfavorable (mRS 4-6). Six proteins were measured using ELISAs: p75NTR, NGF, sortilin, IL1β, TNFα, and cyclophilin. DE microRNAs were identified using DESeq2, and their target genes were predicted. Serum molecules between patients with differing outcomes were compared using a Kolmogorov-Smirnov test, 2-tailed t-test and multivariate linear discriminant analysis (LDA).

RESULTS

Favorable (n = 46) and unfavorable (n = 28) outcome cohorts were balanced with age and sex (p = 0.25 and 0.63). None of the studied proteins correlated with age. Combinatory LDA of the six protein biomarkers indicated strong prognostic value for favorable outcomes (OR 2.09; AUC = 70.3%, p = 0.0058). MicroRNA expression changes over time were identified in the aSAH, TBI, and IS groups (p < 0.05, FDR corrected). Twenty-three microRNAs were commonly DE across all brain injury groups when comparing favorable and unfavorable outcomes (p < 0.05). LDA of four microRNAs targeting the studied proteins showed high prognostic accuracy (OR 11.7; AUC = 94.1%, p = 0.016).

CONCLUSIONS

The combined prognostic microRNA and protein biomarker models demonstrated accurate outcome prognostication across diverse injury types, implying the presence of a common recovery mechanism. DE microRNAs were found to target the studied molecules, suggesting a potential mechanistic role in recovery. Further investigation is warranted to study these molecules in prognostication, as well as therapeutic targets for enhancing recovery.

LM11a-31 Inhibits p75 Neurotrophin Receptor (p75 NTR ) Cleavage and is Neuroprotective in a Cell Culture Model of Parkinson's Disease

The p75 Neurotrophin Receptor (p75 NTR ) is a multifunctional transmembrane protein that mediates neuronal responses to pathological conditions in specific regions of the nervous system. In many biological contexts, p75 NTR signaling is initiated through sequential cleavage of the receptor by α- and γ-secretases, which releases receptor fragments for downstream signaling. Our previous work demonstrated that proteolytic processing of p75 NTR in this manner is stimulated by oxidative stress in Lund Human Mesencephalic (LUHMES) cells, a dopaminergic neuronal cell line derived from human mesencephalic tissue. Considering the vulnerability of dopaminergic neurons in the ventral mesencephalon to oxidative stress and neurodegeneration associated with Parkinson's disease (PD), we investigated the role of this signaling cascade in neurodegeneration and explored cellular processes that govern oxidative stress-induced p75 NTR signaling. In the present study, we provide evidence that oxidative stress induces cleavage of p75 NTR by promoting c-Jun N-terminal Kinase (JNK)-dependent internalization of p75 NTR from the cell surface. This activation of p75 NTR signaling is counteracted by tropomyosin-related kinase (Trk) receptor signaling; however, oxidative stress leads to Trk receptor downregulation, thereby enhancing p75 NTR processing. Importantly, we demonstrate that this pathway can be inhibited by LM11a-31, a small molecule modulator of p75 NTR , thereby conferring protection against neurodegeneration. Treatment with LM11a-31 significantly reduced p75 NTR cleavage and neuronal death associated with oxidative stress. These findings reveal novel mechanisms underlying activation of p75 NTR in response to oxidative stress, underscore a key role for p75 NTR in dopaminergic neurodegeneration, and highlight p75 NTR as a potential therapeutic target for reducing neurodegeneration in PD.

Sortilin is dispensable for secondary injury processes following traumatic brain injury in mice

Traumatic brain injury (TBI) is characterized by complex secondary injury processes involving the p75 neurotrophin receptor (p75NTR), which has been proposed as a possible therapeutic target. However, the pathogenic role of the p75NTR co-receptor sortilin in TBI has not been investigated. In this study, we examined whether sortilin contributes to acute and early processes of secondary injury using a murine controlled cortical impact (CCI) model of TBI. Initial expression analysis showed a down-regulation of sortilin mRNA levels 1 and 5 day post injury (dpi) and a reduced expression of sortilin protein 1 dpi. Next, a total of 40 SortilinΔExon14 loss-of-function mouse mutants (Sort1-/-) and wild-type (Sort1+/+) littermate mice were subjected to CCI and examined at 1 and 5 dpi. Neither sensorimotor deficits or brain lesion size nor CCI-induced cell death or calcium-dependent excitotoxicity as evaluated by TUNEL staining or Western blot analysis of alpha II spectrin breakdown products were different between Sort1-/- and Sort1+/+ mice. In addition, CCI induced the up-regulation of pro-inflammatory marker mRNA expression (Il6, Tnfa, Aif1, and Gfap) irrespectively of the genotype. Similarly, the mRNA expressions of neurotrophins (Bdnf, Ngf, Nt3), VPS10P domain receptors others than sortilin (Ngfr, Sorl1, Sorcs2), and the sortilin interactor progranulin were not affected by genotype. Our results suggest that sortilin is a modulatory rather than a critical factor in the acute and early brain tissue response after TBI.

The expression system affects the binding affinity between p75NTR and proNGF

ProNGF (nerve growth factor) is a precursor of NGF and a signaling peptide exerting opposite effects on neuronal cells, i.e., apoptotic or neuritogenic. The conflicting biological activity of proNGF depends on the relative levels of two membrane receptors, TrkA and p75NTR. The effect of proNGF depends on the expression levels of these receptor proteins and their affinity to proNGF. Since the affinity of proteins has been studied with various recombinant proteins, it is worth comparing the affinity of these proteins within one experiment with the same method. This study examined the affinity between a recombinant proNGF and p75NTR expressed in common systems: bacterial, insect, and mammalian cells. The extracellular domain of p75NTR expressed in the insect or mammalian systems bound to native mature NGF, with a higher affinity for the insect receptor. The uncleavable proNGF was expressed in the three systems and they showed neuritogenic activity in PC12 cells. These recombinant proteins were used to compare their binding affinity to p75NTR. The insect p75NTR showed a higher binding affinity to proNGF than the mammalian p75NTR. The insect p75NTR bound proNGF from the insect system with the highest affinity, then from the mammalian system, and the lowest from the bacterial system. Conversely, the mammalian p75NTR showed no such preference for proNGF. Because the recombinant proNGF and p75NTR from different expression systems are supposed to have the same amino acid sequences, these differences in the affinity depend likely on their post-translational modifications, most probably on their glycans. Each recombinant proNGF and p75NTR in various expression systems exhibited different mobilities on SDS-PAGE and reactivities with glycosidases and lectins.

Sortilin Expression Levels and Peripheral Immunity: A Potential Biomarker for Segregation between Parkinson's Disease Patients and Healthy Controls

Parkinson's disease (PD) is characterized by substantial phenotypic heterogeneity that limits the disease prognosis and patient's counseling, and complicates the design of further clinical trials. There is an unmet need for the development and validation of biomarkers for the prediction of the disease course. In this study, we utilized flow cytometry and in vitro approaches on peripheral blood cells and isolated peripheral blood mononuclear cell (PBMC)-derived macrophages to characterize specific innate immune populations in PD patients versus healthy donors. We found a significantly lower percentage of B lymphocytes and monocyte populations in PD patients. Monocytes in PD patients were characterized by a higher CD40 expression and on-surface expression of the type I membrane glycoprotein sortilin, which showed a trend of negative correlation with the age of the patients. These results were further investigated in vitro on PBMC-derived macrophages, which, in PD patients, showed higher sortilin expression levels compared to cells from healthy donors. The treatment of PD-derived macrophages with oxLDL led to higher foam cell formation compared to healthy donors. In conclusion, our results support the hypothesis that surface sortilin expression levels on human peripheral monocytes may potentially be utilized as a marker of Parkinson's disease and may segregate the sporadic versus the genetically induced forms of the disease.

The NONRATT023402.2/rno-miR-3065-5p/NGFR axis affects levodopa-induced dyskinesia in a rat model of Parkinson's disease

Levodopa-induced dyskinesia (LID) is a common motor complication in Parkinson's disease. However, few studies have focused on the pathogenesis of LID at the transcriptional level. NONRATT023402.2, a long non-coding RNA (lncRNA) that may be related to LID was discovered in our previous study and characterized in rat models of LID. In the present study, NONRATT023402.2 was overexpressed by injection of adeno-associated virus (AAV) in striatum of LID rats, and 48 potential target genes, including nerve growth factor receptor (NGFR) were screened using next-generation sequencing and target gene predictions. The NONRATT023402.2/rno-miR-3065-5p/NGFR axis was verified using a dual luciferase reporter gene. Overexpression of NONRATT023402.2 significantly increased the abnormal involuntary movements (AIM) score of LID rats, activated the PI3K/Akt signaling pathway, and up-regulated c-Fos in the striatum. NGFR knockdown by injection of ShNGFR-AAV into the striatum of LID rats resulted in a significant decrease in the PI3K/Akt signaling pathway and c-Fos expression. The AIM score of LID rats was positively correlated with the expressions of NONRATT023402.2 and NGFR. A dual luciferase reporter assay showed that c-Fos, as a transcription factor, bound to the NONRATT023402.2 promoter and activated its expression. Together, the results showed that NONRATT023402.2 regulated NGFR expression via a competing endogenous RNA mechanism, which then activated the PI3K/Akt pathway and promoted c-Fos expression. This suggested that c-Fos acted as a transcription factor to activate NONRATT023402.2 expression, and form a positive feedback regulation loop in LID rats, thus, aggravating LID symptoms. NONRATT023402.2 is therefore a possible novel therapeutic target for LID.

Novel therapeutic targets to halt the progression of Parkinson's disease: an in-depth review on molecular signalling cascades

Recent research has focused mostly on understanding and combating the neurodegenerative mechanisms and symptoms of Parkinson's disease (PD). Moreover, developing novel therapeutic targets to halt the progression of PD remains a key focus for researchers. As yet, no agents have been found to have unambiguous evidence of disease-modifying actions in PD. The primary objective of this review is to summarize the promising targets that have recently been uncovered which include histamine 4 receptors, beta2 adrenergic receptor, phosphodiesterase 4, sphingosine-1-phosphate receptor subtype 1, angiotensin receptors, high-mobility group box 1, rabphilin-3A, purinergic 2Y type 12 receptor, colony-stimulating factor-1 receptor, transient receptor potential vanilloid 4, alanine-serine-cysteine transporter 2, G protein-coupled oestrogen receptor, a mitochondrial antiviral signalling protein, glucocerebrosidase, indolamine-2,3-dioxygenase-1, soluble epoxy hydroxylase and dual specificity phosphatase 6. We have also reviewed the molecular signalling cascades of those novel targets which cause the initiation and progression of PD and gathered some emerging disease-modifying agents that could slow the progression of PD. These approaches will assist in the discovery of novel target molecules, for curing disease symptoms and may provide a glimmer of hope for the treatment of PD. As of now, there is no drug available that will completely prevent the progression of PD by inhibiting the pathogenesis involved in PD, and thus, the newer targets and their inhibitors or activators are the major focus for researchers to suppress PD symptomatology. And the major limitations of these targets are the lack of clinical data and less number pre-clinical data, as we have majorly discussed the different targets which all have well reported for other disease pathogenesis. Thus, finding the disease-drug interactions, the molecular mechanisms, and the major side effects will be major challenges for the researchers.

Similarities and differences between nigral and enteric dopaminergic neurons unravel distinctive involvement in Parkinson's disease

In addition to the well-known degeneration of midbrain dopaminergic neurons, enteric neurons can also be affected in neurodegenerative disorders such as Parkinson's disease (PD). Dopaminergic neurons have recently been identified in the enteric nervous system (ENS). While ENS dopaminergic neurons have been shown to degenerate in genetic mouse models of PD, analyses of their survival in enteric biopsies of PD patients have provided inconsistent results to date. In this context, this review seeks to highlight the distinctive and shared factors and properties that control the evolution of these two sets of dopaminergic neurons from neuronal precursors to aging neurons. Although their cellular sources and developmental times of origin differ, midbrain and ENS dopaminergic neurons express many transcription factors in common and their respective environments express similar neurotrophic molecules. For example, Foxa2 and Sox6 are expressed by both populations to promote the specification, differentiation, and long-term maintenance of the dopaminergic phenotype. Both populations exhibit sustained patterns of excitability that drive intrinsic vulnerability over time. In disorders such as PD, colon biopsies have revealed aggregation of alpha-synuclein in the submucosal plexus where dopaminergic neurons reside and lack blood barrier protection. Thus, these enteric neurons may be more susceptible to neurotoxic insults and aggregation of α-synuclein that spreads from gut to midbrain. Under sustained stress, inefficient autophagy leads to neurodegeneration, GI motility dysfunction, and PD symptoms. Recent findings suggest that novel neurotrophic factors such as CDNF have the potential to be used as neuroprotective agents to prevent and treat ENS symptoms of PD.

Fading memories in aging and neurodegeneration: Is p75 neurotrophin receptor a culprit?

Aging and age-related neurodegenerative diseases have become one of the major concerns in modern times as cognitive abilities tend to decline when we get older. It is well known that the main cause of this age-related cognitive deficit is due to aberrant changes in cellular, molecular circuitry and signaling pathways underlying synaptic plasticity and neuronal connections. The p75 neurotrophin receptor (p75^NTR) is one of the important mediators regulating the fate of the neurons in the nervous system. Its importance in neuronal apoptosis is well documented. However, the mechanisms involving the regulation of p75^NTR in synaptic plasticity and cognitive function remain obscure, although cognitive impairment has been associated with a higher expression of p75^NTR in neurons. In this review, we discuss the current understanding of how neurons are influenced by p75^NTR function to maintain normal neuronal synaptic strength and connectivity, particularly to support learning and memory in the hippocampus. We then discuss the age-associated alterations in neurophysiological mechanisms of synaptic plasticity and cognitive function. Furthermore, we also describe current evidence that has begun to elucidate how p75^NTR regulates synaptic changes in aging and age-related neurodegenerative diseases, focusing on the hippocampus. Elucidating the role that p75^NTR signaling plays in regulating synaptic plasticity will contribute to a better understanding of cognitive processes and pathological conditions. This will in turn provide novel approaches to improve therapies for the treatment of neurological diseases in which p75^NTR dysfunction has been demonstrated.

Neutralizing antibody to proNGF rescues erectile function by regulating the expression of neurotrophic and angiogenic factors in a mouse model of cavernous nerve injury

BACKGROUND

Radical prostatectomy induces some degree of cavernous nerve injury (CNI) and causes denervation-induced pathologic changes in cavernous vasculature, regardless of the advances in surgical techniques and robotic procedures. The precursor for nerve growth factor (proNGF) is known to be involved in neuronal cell apoptosis and microvascular dysfunction through its receptor p75NTR .

OBJECTIVES

To determine the expression of proNGF/p75NTR and the efficacy of proNGF neutralizing antibody (anti-proNGF-Ab) in a mouse model of ED induced by CNI.

MATERIALS AND METHODS

Age-matched 12-week-old C57BL/6 mice were distributed into three groups: sham group and bilateral CNI group treated with intracavernous injections of PBS (20 μL) or of anti-proNGF-Ab (20 µg in 20 μL of PBS) on days -3 and 0. Two weeks after treatment, erectile function was measured by electrical stimulation of cavernous nerve. Penis tissues from a separate group of animals were harvested for further analysis. We also determined the efficacy of anti-proNGF-Ab on neural preservation in major pelvic ganglion (MPG) ex vivo.

RESULTS

We observed increased penile expression of proNGF and p75NTR after CNI. Intracavernous administration of anti-proNGF-Ab increased nNOS and neurofilament expression probably by enhancing the production of neurotrophic factors, such as neurotrophin-3, NGF, and brain-derived neurotrophic factor. Anti-proNGF-Ab preserved the integrity of cavernous sinusoids, such as pericytes, endothelial cells, and endothelial cell-to-cell junctions, possibly by controlling angiogenic factors (angiopoietin-1, angiopoietin-2, and vascular endothelial growth factor) and induced endogenous eNOS phosphorylation in CNI mice. And finally, treatment with anti-proNGF-Ab rescued erectile function in CNI mice. Anti-proNGF-Ab also enhanced neurite sprouting from MPG exposed to lipopolysaccharide.

DISCUSSION AND CONCLUSION

The preservation of damaged cavernous neurovasculature through inhibition of the proNGF/p75NTR pathway may be a novel strategy to treat radical prostatectomy-induced erectile dysfunction.

Nerve Growth Factor is a Potential Treated Target in Tg(SOD1*G93A)1Gur Mice

Nerve growth factor (NGF) is a protective factor of neural cells; the possible relationship between the NGF and the pathogenesis of amyotrophic lateral sclerosis (ALS) hasn't been completely known. In this study, we observed and analyzed the expression and distribution of NGF, as well as the possible relationship between the NGF expression and distribution and the neural cell death in both SOD1 wild-type (WT) and Tg(SOD1*G93A)1Gur (TG) mice applying the fluorescence immunohistochemistry method. The results showed that the expression and distribution of NGF in the anterior horn (AH), the lateral horn (LH), and the surrounding central canal (CC) significantly increased at the supper early stage of ALS (Pre-onset stage) and the early stage (Onset stage), but the NGF expression and distribution in the AH, the LH, and the surrounding CC significantly reduced at the progression stage. The astrocyte, neuron, and oligodendrocyte produced the NGF and the neural precursor cells (NPCs) produced the NGF. The neural cell death gradually increased accompanying with the reduction of NGF expression and distribution. Our data suggested that the NGF was a protective factor of neural cells, because the neural cells in the AH, the LH, and the surrounding CC produced more NGF at the supper early and early stage of ALS; moreover, the NPCs produced the NGF. It implied that the NGF exerted the protective effect of neural cells, prevented from the neural cell death and aroused the potential of self-repair in the development of ALS.

Oral Administration of the p75 Neurotrophin Receptor Modulator, LM11A-31, Improves Erectile Function in a Mouse Model of Cavernous Nerve Injury

BACKGROUND

Radical prostatectomy for prostate cancer can not only induce cavernous nerve injury (CNI), but also causes cavernous hypoxia and cavernous structural changes, which lead to a poor response to phosphodiesterase 5 inhibitors.

AIM

To investigate the therapeutic effect of oral administration of LM11A-31, a small molecule p75 neurotrophin receptor (p75^NTR) ligand and proNGF antagonist, in a mouse model of bilateral CNI, which mimics nerve injury-induced erectile dysfunction after radical prostatectomy.

METHODS

8-week-old male C57BL/6 mice were divided into sham operation and CNI groups. Each group was divided into 2 subgroups: phosphate-buffered saline and LM11A-31 (50 mg/kg/day) being administered once daily starting 3 days before CNI via oral gavage. 2 weeks after CNI, we measured erectile function by electrical stimulation of the bilateral cavernous nerve. The penis was harvested for histologic examination and Western blot analysis. The major pelvic ganglia was harvested and cultured for assays of ex vivo neurite outgrowth.

OUTCOMES

Intracavernous pressure, neurovascular regeneration in the penis, in vivo or ex vivo functional evaluation, and cell survival signaling were measured.

RESULTS

Erectile function was decreased in the CNI group (44% of the sham operation group), while administration of LM11A-31 led to a significant improvement of erectile function (70% of the sham operation group) in association with increased neurovascular content, including cavernous endothelial cells, pericytes, and neuronal processes. Immunohistochemical and Western blot analyses showed significantly increased p75^NTR expression in the dorsal nerve of CNI mice, which was attenuated by LM11A-31 treatment. Protein expression of active PI3K, AKT, and endothelial nitric oxide synthase was increased, and cell death and c-Jun N-terminal kinase signaling was significantly attenuated after LM11A-31 treatment. Furthermore, LM11A-31 promoted neurite sprouting in cultured major pelvic ganglia after lipopolysaccharide exposure.

CLINICAL IMPLICATIONS

LM11A-31 may be used as a strategy to treat erectile dysfunction after radical prostatectomy or in men with neurovascular diseases.

STRENGTHS & LIMITATIONS

Unlike biological therapeutics, such as proteins, gene therapies, or stem cells, the clinical application of LM11A-31 would likely be relatively less complex and low cost. Our study has some limitations. Future studies will assess the optimal dosing and duration of the compound. Given its plasma half-life of approximately 1 hour, it is possible that dosing more than once per day will provide added efficacy.

CONCLUSION

Specific inhibition of the proNGF-p75^NTR degenerative signaling via oral administration of LM11A-31 represents a novel therapeutic strategy for erectile dysfunction induced by nerve injury. Yin GN, Ock J, Limanjaya A, et al. Oral Administration of the p75 Neurotrophin Receptor Modulator, LM11A-31, Improves Erectile Function in a Mouse Model of Cavernous Nerve Injury. J Sex Med 2021;18:17-28.

BDNF-TrkB and proBDNF-p75NTR/Sortilin Signaling Pathways are Involved in Mitochondria-Mediated Neuronal Apoptosis in Dorsal Root Ganglia after Sciatic Nerve Transection

Background:

Brain-Derived Neurotrophic Factor (BDNF) plays critical roles during development of the central and peripheral nervous systems, as well as in neuronal survival after injury. Although proBDNF induces neuronal apoptosis after injury in vivo, whether it can also act as a death factor in vitro and in vivo under physiological conditions and after nerve injury, as well as its mechanism of inducing apoptosis, is still unclear.

Objective:

In this study, we investigated the mechanisms by which proBDNF causes apoptosis in sensory neurons and Satellite Glial Cells (SGCs) in Dorsal Root Ganglia (DRG) After Sciatic Nerve Transection (SNT).

Methods:

SGCs cultures were prepared and a scratch model was established to analyze the role of proBDNF in sensory neurons and SGCs in DRG following SNT. Following treatment with proBDNF antiserum, TUNEL and immunohistochemistry staining were used to detect the expression of Glial Fibrillary Acidic Protein (GFAP) and Calcitonin Gene-Related Peptide (CGRP) in DRG tissue; immunocytochemistry and Cell Counting Kit-8 (CCK8) assay were used to detect GFAP expression and cell viability of SGCs, respectively. RT-qPCR, western blot, and ELISA were used to measure mRNA and protein levels, respectively, of key factors in BDNF-TrkB, proBDNF-p75NTR/sortilin, and apoptosis signaling pathways.

Results:

proBDNF induced mitochondrial apoptosis of SGCs and neurons by modulating BDNF-TrkB and proBDNF-p75NTR/sortilin signaling pathways. In addition, neuroprotection was achieved by inhibiting the biological activity of endogenous proBDNF protein by injection of anti-proBDNF serum. Furthermore, the anti-proBDNF serum inhibited the activation of SGCs and promoted their proliferation.

Conclusion:

proBDNF induced apoptosis in SGCs and sensory neurons in DRG following SNT. The proBDNF signaling pathway is a potential novel therapeutic target for reducing sensory neuron and SGCs loss following peripheral nerve injury.

hNGF Peptides Elicit the NGF-TrkA Signalling Pathway in Cholinergic Neurons and Retain Full Neurotrophic Activity in the DRG Assay

In the last decade, Nerve Growth Factor (NGF)-based clinical approaches have lacked specific and efficient Tyrosine Kinase A (TrkA) agonists for brain delivery. Nowadays, the characterization of novel small peptidomimetic is taking centre stage in preclinical studies, in order to overcome the main size-related limitation in brain delivery of NGF holoprotein for Central Nervous System (CNS) pathologies. Here we investigated the NGF mimetic properties of the human NGF 1–14 sequence (hNGF1–14) and its derivatives, by resorting to primary cholinergic and dorsal root ganglia (DRG) neurons. Briefly, we observed that: 1) hNGF1–14 peptides engage the NGF pathway through TrkA phosphorylation at tyrosine 490 (Y490), and activation of ShcC/PI3K and Plc-γ/MAPK signalling, promoting AKT-dependent survival and CREB-driven neuronal activity, as seen by levels of the immediate early gene c-Fos, of the cholinergic marker Choline Acetyltransferase (ChAT), and of Brain Derived Neurotrophic Factor (BDNF); 2) their NGF mimetic activity is lost upon selective TrkA inhibition by means of GW441756; 3) hNGF1–14 peptides are able to sustain DRG survival and differentiation in absence of NGF. Furthermore, the acetylated derivative Ac-hNGF1–14 demonstrated an optimal NGF mimetic activity in both neuronal paradigms and an electrophysiological profile similar to NGF in cholinergic neurons. Cumulatively, the findings here reported pinpoint the hNGF1–14 peptide, and in particular its acetylated derivative, as novel, specific and low molecular weight TrkA specific agonists in both CNS and PNS primary neurons.

Reactive astrocytes increase expression of proNGF in the mouse model of contused spinal cord injury

Astrocytes are major glial cells critically in maintaining stability of the central nervous system and functional activation of astrocytes occurs rapidly in various diseased or traumatic events. We are interested in functional changes of astrocytes during the spinal cord injury, and studied expression of nerve growth factor (NGF) in activated astrocytes by mouse model of contused spinal cord injury and cell culture experiment. It revealed that the spinal cord injury resulted in apparent activation of astrocytes and microglial cells and decreased BMS scores. A larger number of astrocytes showed immunoreactivity to proNGF in the injured spinal cord areas, and proNGF expression increased and remained high level at 7 to 14dpi, which was coincided with upregulation of glial fibrillary acidic protein. The proNGF was clearly localized in both exosome-like vesicles and cytoplasm of astrocytes in culture. Electron microscopy confirmed exosome-like vesicles with proNGF-immunoreactivity in diameter sizes of 50-100 nm. Finally, cell culture with lipopolysaccharide (LPS) experiment indicated increasing expression and release of proNGF in the astrocytes with LPS exposure. This study demonstrated that reactive astrocytes increased proNGF expression after spinal cord injury, also suggesting involvement of exosome-like proNGF transport or release in triggering neuronal apoptosis and aggravating progression of spinal cord injury.

Genetic Association Between NGFR, ADAM17 Gene Polymorphism, and Parkinson's Disease in the Chinese Han Population

Parkinson's disease (PD) is a common neurodegenerative disease characterized by neuronal loss in the substantia nigra. The p75 neurotrophin receptor (p75NTR, encoded by NGFR) was found to play an important role in the selective neuronal death of dopamine neurons in the substantia nigra, as well as the pathogenesis and development of PD. To assess the association between NGFR gene polymorphism and the susceptibility of PD, this case-control study consisting of 414 PD patients and 623 age- and sex-matched controls in a Chinese Han cohort was conducted. Twelve tag-single nucleotide polymorphisms (tag-SNPs) were selected from the NGFR gene through the construction of linkage disequilibrium blocks. One tag-SNP from the ADAM17 gene was also selected owing to its function of encoding tumor necrosis factor α-converting enzyme, which is responsible for the shedding of the extracellular domain of p75NTR. A multiplex polymerase chain reaction-ligase detection reaction (PCR-LDR) method was applied for genotyping. The associations between tag-SNPs and the risk of PD with the adjustment for age and sex were analyzed by unconditional logistic regression, and five genetic models including codominant, dominant, recessive, over-dominant, and additive models were applied. The results showed that among the 13 tag-SNPs, rs741073 was associated with a reduced risk of PD in the codominant (OR = 0.71, 95% CI = 0.54-0.93, P = 0.037), dominant (OR = 0.76, 95% CI = 0.58-0.98, P = 0.033), and over-dominant models (OR = 0.71, 95% CI = 0.54-0.92, P = 0.010), and rs1804011 was also associated with a reduced risk of PD in the codominant (OR = 0.69, 95% CI = 0.50-0.95, P = 0.049), dominant (OR = 0.69, 95% CI = 0.50-0.93, P = 0.014), over-dominant (OR = 0.70, 95% CI = 0.51-0.96, P = 0.025), and additive models (OR = 0.72, 95% CI = 0.54-0.94, P = 0.016). However, these associations did not retain after Bonferroni correction. Conclusively, our study failed to reveal the association between the selected tag-SNPs within NGFR, ADAM17, and the susceptibility of PD. The role of p75NTR and its gene polymorphisms in the pathogenesis of PD needs to be further studied.

Altered Brain Expression of Insulin and Insulin-Like Growth Factors in Frontotemporal Lobar Degeneration: Another Degenerative Disease Linked to Dysregulation of Insulin Metabolic Pathways

BACKGROUND

Frontotemporal lobar degeneration (FTLD) is the third most common dementing neurodegenerative disease with nearly 80% having no known etiology.

OBJECTIVE

Growing evidence that neurodegeneration can be linked to dysregulated metabolism prompted us to measure a panel of trophic factors, receptors, and molecules that modulate brain metabolic function in FTLD.

METHODS

Postmortem frontal (Brodmann's area [BA]8/9 and BA24) and temporal (BA38) lobe homogenates were used to measure immunoreactivity to Tau, phosphorylated tau (pTau), ubiquitin, 4-hydroxynonenal (HNE), transforming growth factor-beta 1 (TGF-β1) and its receptor (TGF-β1R), brain-derived neurotrophic factor (BDNF), nerve growth factor, neurotrophin-3, neurotrophin-4, tropomyosin receptor kinase, and insulin and insulin-like growth factor-1 (IGF-1) and insulin-like growth factor-2 (IGF-2) and their receptors by direct-binding enzyme-linked immunosorbent assay.

RESULTS

FTLD brains had significantly elevated pTau, ubiquitin, TGF-β1, and HNE immunoreactivity relative to control. In addition, BDNF and neurotrophin-4 were respectively reduced in BA8/9 and BA38, while neurotrophin-3 and nerve growth factor were upregulated in BA38, and tropomyosin receptor kinase was elevated in BA24. Lastly, insulin and insulin receptor expressions were elevated in the frontal lobe, IGF-1 was increased in BA24, IGF-1R was upregulated in all three brain regions, and IGF-2 receptor was reduced in BA24 and BA38.

CONCLUSIONS

Aberrantly increased levels of pTau, ubiquitin, HNE, and TGF-β1, marking neurodegeneration, oxidative stress, and neuroinflammation, overlap with altered expression of insulin/IGF signaling ligand and receptors in frontal and temporal lobe regions targeted by FTLD. Dysregulation of insulin-IGF signaling networks could account for brain hypometabolism and several characteristic neuropathologic features that characterize FTLD but overlap with Alzheimer's disease, Parkinson's disease, and Dementia with Lewy Body Disease.

Neurotrophic factors hold promise for the future of Parkinson's disease treatment: is there a light at the end of the tunnel?

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is characterized by a spectrum of clinicopathologic signs and a complex etiology. PD results from the degeneration of dopaminergic (DAergic) neurons in the substantia nigra. Current therapies for PD are only able to alleviate symptoms without stopping disease progression. In addition, the available therapeutic strategies do not have long-lasting effects. Furthermore, these therapies cause different ranges of adverse side effects. There is great interest in neurotrophic factors (NTFs) due to their ability to promote the survival of different neural cells. These factors are divided into four families: neurotrophins, neurokines, the glial cell line-derived NTF family of ligands, and the newly recognized cerebral DA NTF/mesencephalic astrocyte-derived NTF family. The protective and therapeutic effects of these factors on DAergic neurons make them suitable for the prevention of progressive cell loss in PD. Based on the above premise, we focus on the protective effects of NTFs, especially CDNF and MANF, on nigrostriatal DAergic neurons in PD.

proBDNF inhibits the proliferation and migration of OLN‑93 oligodendrocytes

In contrast with mature brain-derived neurotrophic factor (mBDNF), proBDNF induces cell apoptosis. However, the function of proBDNF in oligodendrocytes remains unclear. In the present study, the OLN-93 oligodendroglia cell line was utilized as an in vitro model to analyse the functions of proBDNF in oligodendroglia. p75NTR, sortilin and proBDNF were expressed in cultured OLN-93 cells. It was indicated that proBDNF inhibited OLN-93 cell proliferation in a dose-dependent manner as determined using the MTT assay and BrdU staining. Furthermore, proBDNF suppressed the migration of OLN-93 cells as demonstrated using the scratch assay. proBDNF also decreased cell viability and promoted apoptosis as indicated by activated cysteine-aspartic acid protease-3 (caspase-3) immunocytochemistry. Notably, anti-proBDNF treatment neutralized the effect of proBDNF and resulted in increased cell proliferation and migration and decreased apoptosis. However, these effects were not observed in the presence of recombinant p75NTR extracellular domain-human FC fusion protein and p75NTR antibody, indicating that proBDNF imparts its inhibitory effects on oligodendrocytes through the p75NTR signal pathway.

The lysosomal function of progranulin, a guardian against neurodegeneration

Progranulin (PGRN), encoded by the GRN gene in humans, is a secreted growth factor implicated in a multitude of processes ranging from regulation of inflammation to wound healing and tumorigenesis. The clinical importance of PGRN became especially evident in 2006, when heterozygous mutations in the GRN gene, resulting in haploinsufficiency, were found to be one of the main causes of frontotemporal lobar degeneration (FTLD). FTLD is a clinically heterogenous disease that results in the progressive atrophy of the frontal and temporal lobes of the brain. Despite significant research, the exact function of PGRN and its mechanistic relationship to FTLD remain unclear. However, growing evidence suggests a role for PGRN in the lysosome-most striking being that homozygous GRN mutation leads to neuronal ceroid lipofuscinosis, a lysosomal storage disease. Since this discovery, several links between PGRN and the lysosome have been established, including the existence of two independent lysosomal trafficking pathways, intralysosomal processing of PGRN into discrete functional peptides, and direct and indirect regulation of lysosomal hydrolases. Here, we summarize the cellular functions of PGRN, its roles in the nervous system, and its link to multiple neurodegenerative diseases, with a particular focus dedicated to recent lysosome-related mechanistic developments.

Pro-BDNF Contributes to Hypoxia/Reoxygenation Injury in Myocardial Microvascular Endothelial Cells: Roles of Receptors p75NTR and Sortilin and Activation of JNK and Caspase 3

The aim of this study was to identify the role of the precursor of the brain-derived neurotrophic factor (pro-BDNF) in myocardial hypoxia/reoxygenation injury (H/R) and to address the underlying mechanisms. For this purpose, myocardial microvascular endothelial cells (MMECs) exposed to a high concentration of glucose (30 mM) for 48 h were subjected to 4 h of hypoxia followed by 2 h of reoxygenation. Terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining and flow-cytometric analysis were performed to detect apoptosis. Cell scratch and capillary-like-structure formation assays were employed to evaluate cell function. The levels of apoptosis-related proteins were evaluated by Western blotting and immunofluorescence assays. Our results showed that H/R resulted in MMEC injury, as indicated by significant increases in TUNEL-positive cell numbers and a reduction in MMEC migration and in capillary-like-structure formation coupled with increased pro-BDNF protein expression. In addition, overexpression of pro-BDNF in MMECs via a viral vector led to increased pro-BDNF expression, and this upregulation induced apoptosis. Mechanistic experiments revealed that H/R did not influence BDNF, JNK, and caspase 3 expression, but upregulated pro-BDNF, p75^NTR, sortilin, phospho-JNK, and cleaved caspase 3 protein levels. In contrast, neutralization of endogenous pro-BDNF with an antibody significantly attenuated H/R-induced upregulation of pro-BDNF, p75^NTR, sortilin, p-JNK, and cleaved caspase 3 protein levels, indicating that p75^NTR-sortilin signaling and activation of JNK and caspase 3 may be involved in these effects. In conclusion, H/R-induced injury may be mediated by pro-BDNF, at least in part through the regulation of p75^NTR-sortilin signaling and activation of JNK and caspase 3.

Cellular Trafficking of Amyloid Precursor Protein in Amyloidogenesis Physiological and Pathological Significance

The accumulation of excess intracellular or extracellular amyloid beta (Aβ) is one of the key pathological events in Alzheimer's disease (AD). Aβ is generated from the cleavage of amyloid precursor protein (APP) by beta secretase-1 (BACE1) and gamma secretase (γ-secretase) within the cells. The endocytic trafficking of APP facilitates amyloidogenesis while at the cell surface, APP is predominantly processed in a non-amyloidogenic manner. Several adaptor proteins bind to both APP and BACE1, regulating their trafficking and recycling along the secretory and endocytic pathways. The phosphorylation of APP at Thr668 and BACE1 at Ser498, also influence their trafficking. Neurotrophins and proneurotrophins also influence APP trafficking through their receptors. In this review, we describe the molecular trafficking pathways of APP and BACE1 that lead to Aβ generation, the involvement of different signaling molecules or adaptor proteins regulating APP and BACE1 subcellular localization. We have also discussed how neurotrophins could modulate amyloidogenesis through their receptors.

Decreased serum proNGF concentration in patients with Parkinson's disease

Parkinson's disease (PD), a progressive and age-related neurodegenerative condition, is a common neurodegenerative disorder. However, no validated biomarkers for PD have been identified to date. Accumulating evidence supports the role of proNGF-p75NTR-sortilin signaling in the neurodegeneration and pathogenesis of PD. The aim of our study was to investigate alterations in serum proNGF concentrations in PD patients and related anxiety. Seventy-seven consecutive PD patients and 39 healthy controls were enrolled, and clinical data were collected. Modified Hoehn-Yahr Staging Scale, Unified Parkinson's Disease Rating Scale (UPDRS), and Hamilton Anxiety (HAMA) Scale scores were assessed upon admission. Serum proNGF concentration was compared between that of PD patients and healthy controls. Pearson correlation coefficients were determined to explore the relationship between proNGF concentration and UPDRS, Hoehn-Yahr, and HAMA scores. Received operating characteristic (ROC) curves and proNGF optimal cutoff point were used to distinguish PD and related anxiety. The median concentration of proNGF was significantly lower (p = 0.000) in PD patients (94.91 ng/L, range 85.92-118.06 ng/L) compared with that of healthy controls (106.67 ng/L, range 102.39-122.06 ng/L). The optimal proNGF cutoff point for distinguishing PD patients was 102.29 ng/L, and the sensitivity and specificity values were 87.0 and 100%, respectively. proNGF concentration positively correlated with UPDRS (r = 0.281, p = 0.013), Hoehn-Yahr (r = 0.260, p = 0.023), and HAMA (r = 0.276, p = 0.015) scores. Our results indicate that serum proNGF concentration may represent a biomarker for PD and its role in the pathogenesis of PD thus warrants further investigation.

ProNGF-p75NTR axis plays a proinflammatory role in inflamed joints: a novel pathogenic mechanism in chronic arthritis

Objective

To identify the role of mature nerve growth factor (mNGF), its immature form proNGF and their receptors in arthritis inflammation.

Methods

Real-time PCR, western blot and ELISA were performed to evaluate NGF, proNGF, their receptor and cytokine expression in synovial tissue and cells of patients with juvenile idiopathic arthritis (JIA) and rheumatoid arthritis (RA), and controls.

Results

proNGF and not mNGF is the prevalent form measured in synovial fluids of patients with JIA and RA with synovial fibroblasts as a major source of proNGF in the inflamed synoviae. p75NTR, the specific receptor for proNGF, is the NGF receptor most expressed in mononuclear cells of patients with JIA, while TrkA is the prevalent receptor in healthy donors. In ex vivo experiments the effects of proNGF differ from those of mNGF, suggesting that the balance of p75NTR and TrkA expression represents a critical factor in regulating mNGF/proNGF functions, determining which intracellular pathways and biological activities are triggered. Contrary to NGF, proNGF administration increased inflammatory cytokines but not interleukin (IL)-10 expression, inducing a stronger activation of p38 and JNK pathways. proNGF effects depend on its binding to p75NTR, as inhibition of p75NTR with neutralising antibodies or LM11A-31 abolished proNGF-induced production of IL-6 in patients’ mononuclear cells, while inhibition of TrkA did not. There is a correlation in patients with arthritis between high p75NTR levels and severity of clinical symptoms.

Conclusions

Our data suggest that an active proNGF-p75NTR axis promotes proinflammatory mechanisms contributing to chronic tissue inflammation, and that the use of p75NTR inhibitors may represent a new therapeutic approach in chronic arthritis.

Neurotrophin receptor agonists and antagonists as therapeutic agents: An evolving paradigm

Neurodegenerative disorders are prevalent, complex and devastating conditions, with very limited treatment options currently available. While they manifest in many forms, there are commonalities that link them together. In this review, we will focus on neurotrophins - a family of related factors involved in neuronal development and maintenance. Neurodegenerative diseases often present with a neurotrophin imbalance, in which there may be decreases in trophic signaling through Trk receptors for example, and/or increases in pro-apoptotic activity through p75. Clinical trials with neurotrophins have continuously failed due to their poor pharmacological properties as well as the unavoidable activation of p75. Thus, there is a need for drugs without such setbacks. Small molecule neurotrophin mimetics are favorable options since they can selectively activate Trks or inactivate p75. In this review, we will initially present a brief outline of how these molecules are synthesized and their mechanisms of action; followed by an update in the current state of neurotrophins and small molecules in major neurodegenerative diseases. Although there has been significant progress in the development of potential therapeutics, more studies are needed to establish clear mechanisms of action and target specificity in order to transition from animal models to the assessment of safety and use in humans.

Mice with Sort1 deficiency display normal cognition but elevated anxiety-like behavior

Exposure to stressful life events plays a central role in the development of mood disorders in vulnerable individuals. However, the mechanisms that link mood disorders to stress are poorly understood. Brain-derived neurotrophic factor (BDNF) has long been implicated in positive regulation of depression and anxiety, while its precursor (proBDNF) recently showed an opposing effect on such mental illnesses. P75(NTR) and sortilin are co-receptors of proBDNF, however, the role of these receptors in mood regulation is not established. Here, we aimed to investigate the role of sortilin in regulating mood-related behaviors and its role in the proBDNF-mediated mood abnormality in mice. We found that sortilin was up-regulated in neocortex (by 78.3%) and hippocampus (by 111%) of chronically stressed mice as assessed by western blot analysis. These changes were associated with decreased mobility in the open field test and increased depression-like behavior in the forced swimming test. We also found that sortilin deficiency in mice resulted in hyperlocomotion in the open field test and increased anxiety-like behavior in both the open field and elevated plus maze tests. No depression-like behavior in the forced swimming test and no deficit in spatial cognition in the Morris water maze test were found in the Sort1-deficient mice. Moreover, the intracellular and extracellular levels of mature BDNF and proBDNF were not changed when sortilin was absent in vivo and in vitro. Finally, we found that both WT and Sort1-deficient mice injected with proBDNF in lateral ventricle displayed increased depression-like behavior in the forced swimming test but not anxiety-like behaviors in the open field and elevated plus maze tests. The present study suggests that sortilin functions as a negative regulator of mood performance and can be a therapeutic target for the treatment of mental illness.

Neuronal death in the dorsal root ganglion after sciatic nerve injury does not depend on sortilin

Injury to the sciatic nerve induces loss of sensory neurons in the affected dorsal root ganglia (DRGs). Previous studies have suggested the involvement of the neurotrophin receptors p75 neurotrophin receptor (p75(NTR)) and sortilin, proposing that sensory neuron subpopulations undergo proneurotrophin-induced apoptosis in a similar manner to what can be observed in the CNS following injury. To further investigate this hypothesis we induced sciatic nerve injury in sortilin-deficient mice, thereby preventing apoptotic signaling of proneurotrophins via the sortilin-p75(NTR) receptor complex. Using an unbiased stereological approach we found that loss of sortilin did not prevent the injury-induced loss of DRG neurons. This result demonstrates that previous findings linking p75(NTR) and proneurotrophins to loss of sensory neurons need to involve sortilin-independent pathways and suggests that proneurotrophins may elicit different functions in the CNS and PNS.

Adipose-derived Stem Cell Conditioned Media Extends Survival time of a mouse model of Amyotrophic Lateral Sclerosis

Adipose stromal cells (ASC) secrete various trophic factors that assist in the protection of neurons in a variety of neuronal death models. In this study, we tested the effects of human ASC conditional medium (ASC-CM) in human amyotrophic lateral sclerosis (ALS) transgenic mouse model expressing mutant superoxide dismutase (SOD1^G93A). Treating symptomatic SOD1^G93A mice with ASC-CM significantly increased post-onset survival time and lifespan. Moreover, SOD1^G93A mice given ASC-CM treatment showed high motor neuron counts, less activation of microglia and astrocytes at an early symptomatic stage in the spinal cords under immunohistochemical analysis. SOD1^G93A mice treated with ASC-CM for 7 days showed reduced levels of phosphorylated p38 (pp38) in the spinal cord, a mitogen-activated protein kinase that is involved in both inflammation and neuronal death. Additionally, the levels of α-II spectrin in spinal cords were also inhibited in SOD1^G93A mice treated with ASC-CM for 3 days. Interestingly, nerve growth factor (NGF), a neurotrophic factor found in ASC-CM, played a significant role in the protection of neurodegeneration inSOD1^G93A mouse. These results indicate that ASC-CM has the potential to develop into a novel and effective therapeutic treatment for ALS.

Imbalance of the nerve growth factor and its precursor as a potential biomarker for diabetic retinopathy

Our previous studies have demonstrated that diabetes-induced oxidative stress alters homeostasis of retinal nerve growth factor (NGF) resulting in accumulation of its precursor, proNGF, at the expense of NGF which plays a critical role in preserving neuronal and retinal function. This imbalance coincided with retinal damage in experimental diabetes. Here we test the hypothesis that alteration of proNGF and NGF levels observed in retina and vitreous will be mirrored in serum of diabetic patients. Blood and vitreous samples were collected from patients (diabetic and nondiabetic) undergoing vitrectomy at Georgia Regents University under approved IRB. Levels of proNGF, NGF, and p75^NTR shedding were detected using Western blot analysis. MMP-7 activity was also assayed. Diabetes-induced proNGF expression and impaired NGF expression were observed in vitreous and serum. Vitreous and sera from diabetic patients (n = 11) showed significant 40.8-fold and 3.6-fold increases, respectively, compared to nondiabetics (n = 9). In contrast, vitreous and sera from diabetic patients showed significant 44% and 64% reductions in NGF levels, respectively, compared to nondiabetics. ProNGF to NGF ratios showed significant correlation between vitreous and serum. Further characterization of diabetes-induced imbalance in the proNGF to NGF ratio will facilitate its utility as an early biomarker for diabetic complications.

Dynamic nature of the p75 neurotrophin receptor in response to injury and disease

Neurotrophins and their respective tropomyosin related kinase (Trk) receptors (TrkA, TrkB, and TrkC) and the p75 neurotrophin receptor (p75(NTR)) play a fundamental role in the development and maintenance of the nervous system making them important targets for treatment of neurodegenerative diseases. Whereas Trk receptors are directly activated by specific neurotrophins, the p75(NTR) is a multifunctional receptor that exerts its effects via heterodimeric interactions with TrkA, TrkB, TrkC, sortilin or the Nogo receptor to regulate a wide array of cellular functions. By partnering with different receptors the p75(NTR) regulates binding of mature versus pro-neurotrophins and activation of different signaling pathways with outcomes ranging from growth and survival to cell death. While the developmental downregulation of the p75(NTR) has raised questions regarding its role in the mature nervous system, recent data have revealed widespread expression of low levels, a role in synaptic plasticity and adult neurogenesis and upregulation in response to injury or disease. Studies are needed to better understand these processes, particularly in the damaged nervous system, but will be complicated by expression of p75(NTR) on immune cells including macrophages and microglia that are intimately involved in disease and repair processes. Recent approaches that regulate p75(NTR) function with small non-peptide ligands have demonstrated potent neuroprotection in models of injury and neurodegenerative diseases that highlight the importance of the p75(NTR) as a therapeutic target. Future studies hold the promise of revealing a wealth of information on the multifaceted actions of the p75(NTR) that will inform the design of new neurotrophin-based therapies.

Sorting receptor sortilin-a culprit in cardiovascular and neurological diseases

Sortilin is a sorting receptor that directs target proteins, such as growth factors, signaling receptors, and enzymes, to their destined location in secretory or endocytic compartments of cells. The activity of sortilin is essential for proper function of not only neurons but also non-neuronal cell types, and receptor (dys)function emerges as a major cause of malignancies, including hypercholesterolemia, retinal degeneration, neuronal cell loss in stroke and spinal cord injury, or Alzheimer's disease and other neurodegenerative disorders. In this article, we describe the molecular mechanisms of sortilin action in protein sorting and signaling and how modulation of receptor function may offer novel therapeutic strategies for treatment of common diseases of the cardiovascular and nervous systems.

LPS-induced proNGF synthesis and release in the N9 and BV2 microglial cells: a new pathway underling microglial toxicity in neuroinflammation

Purpose

While aberrant activation of microglial cells was evidently involved in neuroinflammation and neurotoxicity in the neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, objective of study was to address if activated microglias deliver their effect by releasing pro-neurotrophins.

Materials and methods

By in vitro culture of N9 and BV2 cell lines and lipopolysaccharide (LPS) stimulation model, generation and release of proNGF, proBDNF and MMP-9 was studied in the activated microglial cells by immunocytochemistry, western blotting and bioassay methods.

Results

Activation of microglial cells was observed with obvious increasing iba1-immunoreactivity following LPS stimulation in cell culture. Synthesis and up-regulation of proNGF protein significantly occurred in N9 and BV2 cells 12h-48h after LPS exposure, whereas no significant changes of proBDNF and MMP9 were observed in these microglial cell lines with LPS insult. More interestingly, extracellular release or secretion of proNGF molecule was also detected in culture medium of N9 cells after LPS stimulation. Finally, bioassay using MTT, Hoechst/PI and TUNEL staining in SH-SY5Y cells further confirmed that proNGF treatment could result in apoptotic cell death but it did not significantly influence cell viability of SH-SY5Y cells.

Conclusions

This in vitro study revealed LPS-stimulated proNGF synthesis and release in activated N9/BV2 microglial cell lines, also suggesting that proNGF may appeal a new pathway or possible mechanism underlying microglial toxicity in the neuroinflammation and a potential target for therapeutic manipulation of the neurodegenerative diseases.

Presence of proNGF-sortilin signaling complex in nigral dopamine neurons and its variation in relation to aging, lactacystin and 6-OHDA insults

Growing evidence has shown that proNGF-p75NTR-sortilin signaling might be a crucial factor in neurodegeneration, but it remains unclear if it may function in nigral neurons under aging and disease. The purpose of this study is to examine and quantify proNGF and sortilin expression in the substantia nigra and dynamic changes of aging in lactacystin and 6-hydroxydopamine (6-OHDA) rat models of Parkinson’s disease using immunofluorescence, electronic microscopy, western blot and FLIVO staining methods. The expression of proNGF and sortilin was abundantly and selectively identified in tyrosine hydroxylase (TH)-containing dopamine neurons in the substantia nigra. These proNGF/TH, sortilin/TH-positive neurons were densely distributed in the ventral tier, while they were less distributed in the dorsal tier, where calbindin-D28K-containing neurons were numerously located. A correlated decrease of proNGF, sortilin and TH was also detected during animal aging process. While increase of proNGF, sortilin and cleaved (active) caspase-3 expression was found in the lactacystin model, dynamic proNGF and sortilin changes along with dopamine neuronal loss were demonstrated in the substantia nigra of both the lactacystin and 6-OHDA models. This study has thus revealed the presence of the proNGF-sortilin signaling complex in nigral dopamine neurons and its response to aging, lactacystin and 6-OHDA insults, suggesting that it might contribute to neuronal apoptosis or neurodegeneration during pathogenesis and disease progression of Parkinson’s disease; the underlying mechanism and key signaling pathways involved warrant further investigation.

Sortilin participates in light-dependent photoreceptor degeneration in vivo

Both proNGF and the neurotrophin receptor p75 (p75^NTR) are known to regulate photoreceptor cell death caused by exposure of albino mice to intense illumination. ProNGF-induced apoptosis requires the participation of sortilin as a necessary p75^NTR co-receptor, suggesting that sortilin may participate in the photoreceptor degeneration triggered by intense lighting. We report here that light-exposed albino mice showed sortilin, p75^NTR, and proNGF expression in the outer nuclear layer, the retinal layer where photoreceptor cell bodies are located. In addition, cone progenitor-derived 661W cells subjected to intense illumination expressed sortilin and p75^NTR and released proNGF into the culture medium. Pharmacological blockade of sortilin with either neurotensin or the “pro” domain of proNGF (pro-peptide) favored the survival of 661W cells subjected to intense light. In vivo, the pro-peptide attenuated retinal cell death in light-exposed albino mice. We propose that an auto/paracrine proapoptotic mechanism based on the interaction of proNGF with the receptor complex p75^NTR/sortilin participates in intense light-dependent photoreceptor cell death. We therefore propose sortilin as a putative target for intervention in hereditary retinal dystrophies.

Chopper is prodeath regardless of the effect of p75ICD on sensitivity to oxidative stress

BACKGROUND

The intracellular domain (ICD) of the neurotrophin receptor, p75NTR, exhibits variably pro- and antiapoptotic activity and has been implicated in neurodegenerative and neurodestructive disease. The molecular determinants of these cellular effects are not completely understood. The "Chopper" domain of p75ICD has been shown to be proapoptotic in in vitro systems in which p75ICD is proapoptotic. The effects of Chopper in systems in which p75ICD is antiapoptotic and, therefore, whether or not Chopper accounts for the variability of the cellular effects of p75ICD are not known. We therefore examined the effects of deletion of Chopper on the effects of p75ICD on in vitro cell culture systems in which p75ICD is pro- or antiapoptotic, respectively.

RESULTS

In HN33.11 murine neuroblastoma-hippocampal neuron hybrid cells, p75ICD is antiapoptotic. In NIH 3T3 cells, p75ICD is proapoptotic. In both cell lines deletion of the Chopper domain from p75ICD decreases the incidence of apoptosis resulting from oxidative stress. Thus, irrespective of the nature of the effects of p75ICD on the cell, its Chopper domain is proapoptotic.

CONCLUSIONS

Expression of p75ICD can enhance or attenuate oxidative induction of apoptosis. Variability of the effects of p75ICD is not related to variability of the effects of its Chopper domain.

The TrkB-positive dopaminergic neurons are less sensitive to MPTP insult in the substantia nigra of adult C57/BL mice

Tyrosine kinase receptors TrkB and TrkC mediate neuroprotective effects of the brain-derived neurotrophic factor (BDNF) and neurotrophins in the dopaminergic nigro-striatal system, but it is obscure about their responses or expression changes in the injured substantia nigra under Parkinson's disease. In present study, immunofluorescence, Fluoro-Jade staining and laser scanning confocal microscopy were applied to investigate distribution and changes of TrkB and TrkC in the dopamine neurons of the substantia nigra by comparison of control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. It revealed that TrkB and TrkC-immunoreactivities were substantially localized in cytoplasm and cell membrane of the substantia nigra neurons of control adults. While neurons double-labeled with tyrosine hydroxylase (TH)/TrkB, or TH/TrkC were distributed in a large numbers in the substantia nigra of controls, they apparently went down at 36.2-65.7% of normal level, respectively following MPTP insult. In MPTP model, cell apoptosis or degeneration of nigral neurons were confirmed by caspase-3 and Fluoro-Jade staining. More interestingly, TH/TrkB-positive neurons survived more in cell numbers in comparison with that of TH/TrkC-positive ones in the MPTP model. This study has indicated that TrkB-containing dopamine neurons are less sensitive in the substantia nigra of MPTP mouse model, suggesting that specific organization of Trks may be involved in neuronal vulnerability to MPTP insult, and BDNF-TrkB signaling may play more important role in protecting dopamine neurons and exhibit therapeutic potential for Parkinson's disease.

Understanding proneurotrophin actions: Recent advances and challenges

Neurotrophins are initially synthesized as larger precursors (proneurotrophins), which undergo proteolytic cleavage to yield mature forms. Although the functions of the mature neurotrophins have been well established during neural development and in the adult nervous system, roles for the proneurotrophins in developmental and injury-induced cell death, as well as in synaptic plasticity, have only recently been appreciated. Interestingly, both mature neurotrophins and proneurotrophins utilize dual-receptor complexes to mediate their actions. The mature neurotrophin coreceptors consist of the Trk receptor tyrosine kinases and p75(NTR), wherein Trk transduces survival and differentiative signaling, and p75(NTR) modulates the affinity and selectivity of Trk activation. On the other hand, proneurotrophins engage p75(NTR) and the structurally distinct coreceptor sortilin, to initiate p75(NTR)-dependent signal transduction cascade. Although the specificity of mature neurotrophins vs. proneurotrophins actions is due in part to the formation of distinct coreceptor complexes, a number of recent studies highlight how different p75(NTR)-mediated cellular actions are modulated. Here, we review emerging evidence for a novel transmembrane mechanism for ligand-specific p75(NTR) activation and several mechanisms by which p75(NTR)-dependent apoptotic and nonapoptotic responses can be selective activated.