Synergic interaction between amyloid precursor protein and neural cell adhesion molecule promotes neurite outgrowth

Swimming alters some proteins of skeletal muscle tissue in rats with Alzheimer-like phenotype

OBJECTIVES

Exercise training plays a significant role in preventing the destruction of central nerve neurons and muscle atrophy. The purpose of the present study was to investigate the effect of a period of swimming training on the expression of Neural cell adhesion molecule (NCAM), Semaphorin 3A (SEMA3A), and Profilin-1 (PFN1) proteins in the gastrocnemius muscle of Alzheimer-like phenotype rats.

METHODS & MATERIALS

32 Wistar males were (6 weeks of age) divided into four groups: Healthy Control (HC), Alzheimer-like phenotype's Control (AC), Healthy Training (HT), and Alzheimer-like phenotype's Training (AT). Alzheimer-like phenotypes were induced by beta-amyloid injection in the hippocampus. The training program consisted of 20 swimming sessions. Gastrocnemius muscle was removed after the intervention, and NCAM, SEMA3A, and PFN1 proteins were measured by the immunohistoflorescent method.

RESULTS

The results showed that SEMA3A was increased (p = 0.001), and NCAM (p = 0.001), and PFN1 (p = 0.001) were decreased in AC compared to the HC group. Also, the results showed that NCAM (p = 0.001) and Pfn1 (p = 0.002) increased in the HT group compared to HC, and the NCAM (p = 0.001) and Pfn1 (p = 0.002) in AT group compared to AC (p = 0.001) increased significantly, while SEMA3A was reduced in the HT group compared to HC (p = 0.001) and AT group compared to AC (p = 0.001) CONCLUSION: Swimming effectively improves axon regeneration and neuronal formation in motor neurons and, therefore, can be an effective intervention to prevent and control the complications of Alzheimer-like phenotype.

Amyloid precursor protein (APP) and amyloid β (Aβ) interact with cell adhesion molecules: Implications in Alzheimer’s disease and normal physiology

Alzheimer’s disease (AD) is an incurable neurodegenerative disorder in which dysfunction and loss of synapses and neurons lead to cognitive impairment and death. Accumulation and aggregation of neurotoxic amyloid-β (Aβ) peptides generated via amyloidogenic processing of amyloid precursor protein (APP) is considered to play a central role in the disease etiology. APP interacts with cell adhesion molecules, which influence the normal physiological functions of APP, its amyloidogenic and non-amyloidogenic processing, and formation of Aβ aggregates. These cell surface glycoproteins also mediate attachment of Aβ to the neuronal cell surface and induce intracellular signaling contributing to Aβ toxicity. In this review, we discuss the current knowledge surrounding the interactions of cell adhesion molecules with APP and Aβ and analyze the evidence of the critical role these proteins play in regulating the processing and physiological function of APP as well as Aβ toxicity. This is a necessary piece of the complex AD puzzle, which we should understand in order to develop safe and effective therapeutic interventions for AD.

Proximity Interactome Map of the Vac14-Fig4 Complex Using BioID

Conversion between phosphatidylinositol-3-phosphate and phosphatidylinositol-3,5-bisphosphate on endosomal membranes is critical for the maturation of early endosomes to late endosomes/lysosomes and is regulated by the PIKfyve-Vac14-Fig4 complex. Despite the importance of this complex for endosomal homeostasis and vesicular trafficking, there is little known about how its activity is regulated or how it interacts with other cellular proteins. Here, we screened for the cellular interactome of Vac14 and Fig4 using proximity-dependent biotin labeling (BioID). After independently screening the interactomes of Vac14 and Fig4, we identified 89 high-confidence protein hits shared by both proteins. Network analysis of these hits revealed pathways with known involvement of the PIKfyve-Vac14-Fig4 complex, including vesicular organization and PI3K/Akt signaling, as well as novel pathways including cell cycle and mitochondrial regulation. We also identified subunits of coatomer complex I (COPI), a Golgi-associated complex with an emerging role in endosomal dynamics. Using proximity ligation assays, we validated the interaction between Vac14 and COPI subunit COPB1 and between Vac14 and Arf1, a GTPase required for COPI assembly. In summary, this study used BioID to comprehensively map the Vac14-Fig4 interactome, revealing potential roles for these proteins in diverse cellular processes and pathways, including preliminary evidence of an interaction between Vac14 and COPI. Data are available via ProteomeXchange with the identifier PXD027917.

Identification of plasma proteins relating to brain neurodegeneration and vascular pathology in cognitively normal individuals

INTRODUCTION

This study aims to first discover plasma proteomic biomarkers relating to neurodegeneration (N) and vascular (V) damage in cognitively normal individuals and second to discover proteins mediating sex-related difference in N and V pathology.

METHODS

Five thousand and thirty-two plasma proteins were measured in 1061 cognitively normal individuals (628 females and 433 males), nearly 90% of whom had magnetic resonance imaging measures of hippocampal volume (as N) and white matter hyperintensities (as V).

RESULTS

Differential protein expression analysis and co-expression network analysis revealed different proteins and modules associated with N and V, respectively. Furthermore, causal mediation analysis revealed four proteins mediated sex-related difference in N and one protein mediated such difference in V damage.

DISCUSSION

Once validated, the identified proteins could help to select cognitively normal individuals with N and V pathology for Alzheimer's disease clinical trials and provide targets for further mechanistic studies on brain sex differences, leading to sex-specific therapeutic strategies.

Molecular mechanisms of altered adult hippocampal neurogenesis in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia globally. AD is a progressive neurodegenerative disorder, eventually manifesting as severe cognitive impairment. Adult hippocampal neurogenesis (AHN) occurs throughout adulthood and plays an important role in hippocampus-dependent learning and memory. The stages of AHN, predominantly comprising the proliferation, differentiation, survival, and maturation of newborn neurons, are affected to varying degrees in AD. However, the exact molecular mechanisms remain to be elucidated. Recent evidence suggests that the molecules involved in AD pathology contribute to the compromised AHN in AD. Notably, various interventions may have common signaling pathways that, once identified, could be harnessed to enhance adult neurogenesis. This in turn could putatively rescue cognitive deficits associated with impaired neurogenesis as observed in animal models of AD. In this manuscript, we review the current knowledge concerning AHN under normal physiological and AD pathological conditions and highlight the possible role of specific molecules in AHN alteration in AD. In addition, we summarize in vivo experiments with emphasis on the effect of the activation of certain key signalings on AHN in AD rodent models. We propose that these signaling targets and corresponding interventions should be considered when developing novel therapies for AD.

Bottom up proteomics identifies neuronal differentiation pathway networks activated by cathepsin inhibition treatment in neuroblastoma cells that are enhanced by concurrent 13-cis retinoic acid treatment

Neuroblastoma is the second most common pediatric cancer involving the peripheral nervous system in which stage IVS metastatic tumors regress due to spontaneous differentiation. 13-cis retinoic acid (13-cis RA) is currently used in the clinic for its differentiation effects and although it improves outcomes, relapse is seen in half of high-risk patients. Combinatorial therapies have been shown to be more effective in oncotherapy and since cathepsin inhibition reduces tumor growth, we explored the potential of coupling 13-cis RA with a cathepsin inhibitor (K777) to enhance therapeutic efficacy against neuroblastoma. Shotgun proteomics was used to identify proteins affected by K777 and dual (13-cis RA/K777) treatment in neuroblastoma SK-N-SH cells. Cathepsin inhibition was more effective in increasing proteins involved in neuronal differentiation and neurite outgrowth than 13-cis RA alone, but the combination of both treatments enhanced the neuronal differentiation effect. SIGNIFICANCE: As neuroblastoma can spontaneously differentiate, determining which proteins are involved in differentiation can guide development of more accurate diagnostic markers and more effective treatments. In this study, we established a differentiation proteomic map of SK-N-SH cells treated with a cathepsin inhibitor (K777) and K777/13-cis RA (dual). Bioinformatic analysis revealed these treatments enhanced neuronal differentiation and axonogenesis pathways. The most affected proteins in these pathways may become valuable biomarkers of efficacy of drugs designed to enhance differentiation of neuroblastoma [1].

Combating Proteins with Proteins: Engineering Cell-Penetrating Peptide Antagonists of Amyloid-β Aggregation and Associated Neurotoxicity

A central event that underlies the etiology of Alzheimer's disease (AD) is the self-assembly of the amyloid-β (Aβ) peptide into aggregates termed amyloids. Increasing evidence implicates soluble prefibrillar Aβ oligomers in the neurodegeneration and synaptic dysfunction in AD. Recently we introduced a new class of highly promising antagonists of Aβ amyloidogenesis: designed cell-penetrating peptides (CPPs). These CPPs combine the attractive intrinsic properties of peptides (high target specificity and selectivity, biocompatibility, biodegradability, and ease and low cost of production) with potent therapeutic effects (inhibition of Aβ oligomerization, fiber formation, and neurotoxicity) and highly efficient delivery (to target cells and subcellular organelles).

Pericyte loss leads to circulatory failure and pleiotrophin depletion causing neuron loss

Pericytes are positioned between brain capillary endothelial cells, astrocytes and neurons. They degenerate in multiple neurological disorders. However, their role in the pathogenesis of these disorders remains debatable. Here we generate an inducible pericyte-specific Cre line and cross pericyte-specific Cre mice with iDTR mice carrying Cre-dependent human diphtheria toxin receptor. After pericyte ablation with diphtheria toxin, mice showed acute blood-brain barrier breakdown, severe loss of blood flow, and a rapid neuron loss that was associated with loss of pericyte-derived pleiotrophin (PTN), a neurotrophic growth factor. Intracerebroventricular PTN infusions prevented neuron loss in pericyte-ablated mice despite persistent circulatory changes. Silencing of pericyte-derived Ptn rendered neurons vulnerable to ischemic and excitotoxic injury. Our data demonstrate a rapid neurodegeneration cascade that links pericyte loss to acute circulatory collapse and loss of PTN neurotrophic support. These findings may have implications for the pathogenesis and treatment of neurological disorders that are associated with pericyte loss and/or neurovascular dysfunction.

Amyloid Precursor Protein (APP) and GABAergic Neurotransmission

The amyloid precursor protein (APP) is the parent polypeptide from which amyloid-beta (Aβ) peptides, key etiological agents of Alzheimer's disease (AD), are generated by sequential proteolytic processing involving β- and γ-secretases. APP mutations underlie familial, early-onset AD, and the involvement of APP in AD pathology has been extensively studied. However, APP has important physiological roles in the mammalian brain, particularly its modulation of synaptic functions and neuronal survival. Recent works have now shown that APP could directly modulate γ-aminobutyric acid (GABA) neurotransmission in two broad ways. Firstly, APP is shown to interact with and modulate the levels and activity of the neuron-specific Potassium-Chloride (K+-Cl-) cotransporter KCC2/SLC12A5. The latter is key to the maintenance of neuronal chloride (Cl-) levels and the GABA reversal potential (EGABA), and is therefore important for postsynaptic GABAergic inhibition through the ionotropic GABAA receptors. Secondly, APP binds to the sushi domain of metabotropic GABAB receptor 1a (GABABR1a). In this regard, APP complexes and is co-transported with GABAB receptor dimers bearing GABABR1a to the axonal presynaptic plasma membrane. On the other hand, secreted (s)APP generated by secretase cleavages could act as a GABABR1a-binding ligand that modulates presynaptic vesicle release. The discovery of these novel roles and activities of APP in GABAergic neurotransmission underlies the physiological importance of APP in postnatal brain function.

Circulating APP, NCAM and Aβ serve as biomarkers for Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease and the early diagnosis and intervention are important for valid treatment of AD. However, there are few biomarkers for the diagnosis and monitoring of AD. In the present study, circulating APP, NCAM, Aβ40, and Aβ42 were measured in order to identify which marker or combination of markers could be useful, cost-effective and noninvasive biomarkers for diagnosing and continuously monitoring AD. The results showed that circulating APP, NCAM, Aβ40, and Aβ42 were different between the AD group and the control group. Importantly, the combination of the four biomarkers had the highest AUC (0.997) with the highest sensitivity (98.5). Therefore, circulating APP, NCAM, Aβ40, and Aβ42 can be used as desirable biomarkers for AD diagnosis and monitoring.

Deoxynivalenol induces structural alterations in epidermoid carcinoma cells A431 and impairs the response to biomechanical stimulation

Morphology together with the capability to respond to surrounding stimuli are key elements governing the spatial interaction of living cells with the environment. In this respect, biomechanical stimulation can trigger significant physiological cascades that can potentially modulate toxicity. Deoxynivalenol (DON, vomitoxin) is one of the most prevalent mycotoxins produced by Fusarium spp. and it was used to explore the delicate interaction between biomechanical stimulation and cytotoxicity in A431 cells. In fact, in addition of being a food contaminant, DON is a relevant toxin for several organ systems. The combination between biomechanical stimulation and the mycotoxin revealed how DON can impair crucial functions affecting cellular morphology, tubulin and lysosomes at concentrations even below those known to be cytotoxic in routine toxicity studies. Sub-toxic concentrations of DON (0.1-1 μM) impaired the capability of A431 cells to respond to a biomechanical stimulation that normally sustains trophic effects in these cells. Moreover, the effects of DON (0.1-10 μM) were partially modulated by the application of uniaxial stretching (0.5 Hz, 24 h, 15% deformation). Ultimately, proteomic analysis revealed the potential of DON to alter several proteins necessary for cell adhesion and cytoskeletal modulation suggesting a molecular link between biomechanics and the cytotoxic potential of the mycotoxin.

Decreased Motor Neuron Support by SMA Astrocytes due to Diminished MCP1 Secretion

Spinal muscular atrophy (SMA) is an autosomal-recessive disorder characterized by severe, often fatal muscle weakness due to loss of motor neurons. SMA patients have deletions and other mutations of the survival of motor neuron 1 (SMN1) gene, resulting in decreased SMN protein. Astrocytes are the primary support cells of the CNS and are responsible for glutamate clearance, metabolic support, response to injury, and regulation of signal transmission. Astrocytes have been implicated in SMA as in in other neurodegenerative disorders. Astrocyte-specific rescue of SMN protein levels has been shown to mitigate disease manifestations in mice. However, the mechanism by which SMN deficiency in astrocytes may contribute to SMA is unclear and what aspect of astrocyte activity is lacking is unknown. Therefore, it is worthwhile to identify defects in SMN-deficient astrocytes that compromise normal function. We show here that SMA astrocyte cultures derived from mouse spinal cord of both sexes are deficient in supporting both WT and SMN-deficient motor neurons derived from male, female, and mixed-sex sources and that this deficiency may be mitigated with secreted factors. In particular, SMN-deficient astrocytes have decreased levels of monocyte chemoactive protein 1 (MCP1) secretion compared with controls and MCP1 restoration stimulates outgrowth of neurites from cultured motor neurons. Correction of MCP1 deficiency may thus be a new therapeutic approach to SMA.SIGNIFICANCE STATEMENT Spinal muscular atrophy (SMA) is caused by the loss of motor neurons, but astrocyte dysfunction also contributes to the disease in mouse models. Monocyte chemoactive protein 1 (MCP1) has been shown to be neuroprotective and is released by astrocytes. Here, we report that MCP1 levels are decreased in SMA mice and that replacement of deficient MCP1 increases differentiation and neurite length of WT and SMN-deficient motor-neuron-like cells in cell culture. This study reveals a novel aspect of astrocyte dysfunction in SMA and indicates a possible approach for improving motor neuron growth and survival in this disease.