Amyloid beta-derived neuroplasticity in bone marrow-derived mesenchymal stem cells is mediated by NPY and 5-HT2B receptors via ERK1/2 signalling pathways

The Role of ERK1/2 Pathway in the Pathophysiology of Alzheimer's Disease: An Overview and Update on New Developments

Alzheimer's disease (AD) is the most common neurodegenerative disorder worldwide. Several findings suggest that correcting the dysregulated signaling pathways may offer a potential therapeutic approach in this disease. Extracellular signal-regulated kinase 1/2 (ERK1/2), a member of the mitogen-activated protein kinase family, plays a major role in regulation of cell proliferation, autophagy process, and protein synthesis. The available literature suggests dysregulated ERK1/2 in AD patients with potential implications in the multifaceted underlying pathologies of AD, including amyloid-β plaque formation, tau phosphorylation, and neuroinflammation. In this regard, in the current review, we aim to summarize the reports on the potential roles of ERK1/2 in AD pathophysiology.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Aβ inhibits mesenchymal stem cell-pericyte transition through MAPK pathway

Multiple independent reports have demonstrated pericyte loss in both the hippocampus and cortex in human Alzheimer's disease (AD). The differentiation and recruitment of pericytes are the essential steps in vasculature development. However, the role of amyloid beta (Aβ) in pericyte differentiation has not yet been fully elucidated. In this study, we investigated the interaction between Aβ and differentiation of mesenchymal stem cells (MSCs) toward pericytes in culture. Our results showed that mice overexpressing Aβ-precursor protein (APP/PS1) exhibited the loss of pericytes compared with the control group mice, evidenced by the lack of desmin expression in the cortex of 12-month-old mice. Interestingly, we further found that both Aβ40 and Aβ42 inhibited the expressions of pericyte markers (α-SMA, desmin, and PDGFRβ) in cultured MSCs which can be differentiated into mature pericytes. Mechanistically, the inhibitory effects of Aβs on MSC-pericyte transition is mediated by the activation of the ERK1/2 MAPK signal pathway. These new insights into the roles of Aβ in pericyte differentiation may help to develop more effective strategies for the treatment of AD.

Systemic Central Nervous System (CNS)-targeted Delivery of Neuropeptide Y (NPY) Reduces Neurodegeneration and Increases Neural Precursor Cell Proliferation in a Mouse Model of Alzheimer Disease

Neuropeptide Y (NPY) is one of the most abundant protein transmitters in the central nervous system with roles in a variety of biological functions including: food intake, cardiovascular regulation, cognition, seizure activity, circadian rhythms, and neurogenesis. Reduced NPY and NPY receptor expression is associated with numerous neurodegenerative disorders including Alzheimer disease (AD). To determine whether replacement of NPY could ameliorate some of the neurodegenerative and behavioral pathology associated with AD, we generated a lentiviral vector expressing NPY fused to a brain transport peptide (apoB) for widespread CNS delivery in an APP-transgenic (tg) mouse model of AD. The recombinant NPY-apoB effectively reversed neurodegenerative pathology and behavioral deficits although it had no effect on accumulation of Aβ. The subgranular zone of the hippocampus showed a significant increase in proliferation of neural precursor cells without further differentiation into neurons. The neuroprotective and neurogenic effects of NPY-apoB appeared to involve signaling via ERK and Akt through the NPY R1 and NPY R2 receptors. Thus, widespread CNS-targeted delivery of NPY appears to be effective at reversing the neuronal and glial pathology associated with Aβ accumulation while also increasing NPC proliferation. Overall, increased delivery of NPY to the CNS for AD might be an effective therapy especially if combined with an anti-Aβ therapeutic.

Towards clinical application of mesenchymal stem cells for treatment of neurological diseases of the central nervous system

The diagnosis of a neurological disease of the central nervous system (CNS) is often associated with the anticipation of an irreversible and untreatable disability. This is the case also of multiple sclerosis (MS) where approved treatments effectively modulate the autoimmune attack to myelin antigens, but poorly affect neurodegeneration and do not promote tissue repair. Thus, stem cell-based therapies are increasingly being considered a possible strategy for diseases of the CNS. Mesenchymal stem cells (MSC), the safety of which has been demonstrated in the last 20 years through clinical trials and case studies, are of particular interest in view not only of their neuroprotective, but also of their immunomodulatory properties. Here, we review the therapeutic features of MSC that make them relevant in the treatment of CNS illnesses and discuss the pioneer clinical experience with MSC-based therapy in neurological diseases.

Central hypotensive effects of neuropeptide Y are modulated by endothelial nitric oxide synthase after activation by ribosomal protein S6 kinase

BACKGROUND AND PURPOSE

Neuropeptide Y (NPY) is a 36-amino acid polypeptide found abundantly in the central and peripheral nervous systems. NPY exerts a potent depressor effect via the activation of both Y(1) and Y(2) receptors in the nucleus tractus solitarii (NTS) of rats. However, the precise mechanisms involved in this NPY-mediated action remained unclear.

EXPERIMENTAL APPROACH

Effects of a selective antagonist of Y(1) receptors, a PKC inhibitor, a PI3 kinase inhibitor, a NOS inhibitor, an endothelial NOS (eNOS)-selective inhibitor, a neuronal NOS (nNOS)-specific inhibitor or a MAPK inhibitor, on responses to microinjection of NPY into the NTS of Wistar-Kyoto rats were studied to determine the underlying mechanisms. Blood pressure and heart rate were measured and, in NTS, protein phosphorylation assessed by immunohistochemical techniques.

KEY RESULTS

Unilateral microinjection of exogenous NPY (4.65pmol/60nL) into the NTS of urethane-anesthetized Wistar-Kyoto rats markedly decreased blood pressure and heart rate. Microinjection of the Y(1) receptor antagonist BIBP3226 or the G(i) /G(o) -protein inhibitor, Pertussis toxin, into the NTS attenuated these NPY-induced hypotensive effects. A selective Y(1) receptor agonist increased expression of ERK1/2, ribosomal protein S6 kinase (RSK) and the phosphorylation of eNOS. RSK also bound directly to eNOS and induced its phosphorylation at Ser(1177) . Pretreatment of the NTS with an eNOS inhibitor, but not a nNOS inhibitor, attenuated the NPY-induced hypotensive effects.

CONCLUSIONS AND IMPLICATIONS

Together, these results suggested that NPY-induced depressor effects were mediated by activating NPY Y(1) receptor-PKC-ERK-RSK-eNOS and Ca(2+) -eNOS signalling pathways, which are involved in regulation of blood pressure in the NTS.

Human adipose tissue-derived mesenchymal stem cells secrete functional neprilysin-bound exosomes

Alzheimer's disease (AD) is characterized by the accumulation of β-amyloid peptide (Aβ) in the brain because of an imbalance between Aβ production and clearance. Neprilysin (NEP) is the most important Aβ-degrading enzyme in the brain. Thus, researchers have explored virus-mediated NEP gene delivery. However, such strategies may entail unexpected risks, and thus exploration of a new possibility for NEP delivery is also required. Here, we show that human adipose tissue-derived mesenchymal stem cells (ADSCs) secrete exosomes carrying enzymatically active NEP. The NEP-specific activity level of 1 μg protein from ADSC-derived exosomes was equivalent to that of ~ 0.3 ng of recombinant human NEP. Of note, ADSC-derived exosomes were transferred into N2a cells, and were suggested to decrease both secreted and intracellular Aβ levels in the N2a cells. Importantly, these characteristics were more pronounced in ADSCs than bone marrow-derived mesenchymal stem cells, suggesting the therapeutic relevance of ADSC-derived exosomes for AD.

Involvement of neuropeptide Y and its Y1 and Y5 receptors in maintaining self-renewal and proliferation of human embryonic stem cells

Neuropeptide Y (NPY) and NPY receptors are widely expressed in various organs and cell types and have been shown to have pleiotropic functions. However, their presence or role in human embryonic stem cells (hESCs) remains unknown. We now show that undifferentiated hESCs primarily express NPY and its Y1 and Y5 receptors. Inhibition of NPY signalling using either the selective NPY Y1 or Y5 receptor antagonist reduces the maintenance of self-renewal and proliferation of undifferentiated hESCs. We also provide compelling evidence that exogenous NPY supports the long-term growth of undifferentiated hESCs in the absence of feeder cell factors using only knockout serum replacement media. Further, NPY facilitates the use of chemically defined medium made up of N2/B27 supplement and basic fibroblast growth factor (bFGF) for hESC feeder-free culture. Our results indicate that both Y1 and Y5 receptors appear to be involved in the NPY-mediated activation of AKT/protein kinase B and extracellular signal-regulated kinase 1/2 (ERK1/2) in hESCs. Notably, only Y1 receptor, but not Y5 receptor, is responsible for the NPY-induced activation of cAMP-response element binding (CREB) in hESCs. These results provide the first evidence that NPY and its Y1 and Y5 receptors have potential role in maintaining hESC self-renewal and pluripotency. We demonstrate the underlying importance of NPY signalling and its usefulness in the development of a defined and xeno-free culture condition for the large-scale propagation of undifferentiated hESCs.

Degeneration and repair in central nervous system disease

Divergent disease triggers in neurodegeneration may induce convergent endogenous pathways in neuronal, glial and vascular elements as the central nervous system (CNS) attempts to compensate, remodel and recover. Dissecting these multicellular mechanisms and the integrative responses in cerebral blood flow and metabolism may allow us to understand the balance between injury and repair, validate new targets and define therapeutic time windows for neurodegeneration.