The emerging role of neutrophils in neurodegeneration

Neutrophils are the first line of defense in the innate immune system, helping to maintain tissue homeostasis as well as eliminating pathogens and self-components. The traditional view of neutrophils as simple phagocytes has been revised over the last decade as new research reveals their unappreciated complexity. Neutrophils are phenotypically and functionally heterogeneous, allowing them to act as modulators of both inflammation and immune responses. During acute inflammation, neutrophils perform a variety of beneficial effector functions, but when inflammation is induced by injury (sterile inflammation) the benefits of neutrophils in tissue repair are more controversial. In several pathological conditions, including cancer and autoimmune diseases, neutrophils can trigger harmful tissue damage. Interestingly, neutrophils are also key players in neuroinflammatory disorders, during which they transmigrate in the central nervous system, acquire a toxic phenotype, home in on neurons, and release harmful molecules that compromise neuronal functions. In this review, we discuss recent data that redefine the cell biology and phenotype of neutrophils, focusing on the role of these cells in multiple sclerosis and Alzheimer's disease, both of which feature strong neuroinflammatory components

Editorial: Neurodegenerative Diseases: Looking Beyond the Boundaries of the Brain

Neurodegenerative Diseases: Looking Beyond the Boundaries of the Brai

In vitro Models of Neurodegenerative Diseases

Neurodegenerative diseases are progressive degenerative conditions characterized by the functional deterioration and ultimate loss of neurons. These incurable and debilitating diseases affect millions of people worldwide, and therefore represent a major global health challenge with severe implications for individuals and society. Recently, several neuroprotective drugs have failed in human clinical trials despite promising pre-clinical data, suggesting that conventional cell cultures and animal models cannot precisely replicate human pathophysiology. To bridge the gap between animal and human studies, three-dimensional cell culture models have been developed from human or animal cells, allowing the effects of new therapies to be predicted more accurately by closely replicating some aspects of the brain environment, mimicking neuronal and glial cell interactions, and incorporating the effects of blood flow. In this review, we discuss the relative merits of different cerebral models, from traditional cell cultures to the latest high-throughput three-dimensional systems. We discuss their advantages and disadvantages as well as their potential to investigate the complex mechanisms of human neurodegenerative diseases. We focus on in vitro models of the most frequent age-related neurodegenerative disorders, such as Parkinson\u2019s disease, Alzheimer\u2019s disease and prion disease, and on multiple sclerosis, a chronic inflammatory neurodegenerative disease affecting young adults

Common peripheral immunity mechanisms in multiple sclerosis and Alzheimer’s disease

Neurodegenerative diseases are closely related to inflammatory and autoimmune events, suggesting that the dysregulation of the immune system is a key pathological factor. Both multiple sclerosis (MS) and Alzheimer’s disease (AD) are characterized by infiltrating immune cells, activated microglia, astrocyte proliferation, and neuronal damage. Moreover, MS and AD share a common pro-inflammatory signature, characterized by peripheral leukocyte activation and transmigration to the central nervous system (CNS). MS and AD are both characterized by the accumulation of activated neutrophils in the blood, leading to progressive impairment of the blood–brain barrier. Having migrated to the CNS during the early phases of MS and AD, neutrophils promote local inflammation that contributes to pathogenesis and clinical progression. The role of circulating T cells inMS is well-established, whereas the contribution of adaptive immunity to AD pathogenesis and progression is a more recent discovery. Even so, blocking the transmigration of T cells to the CNS can benefit bothMS and AD patients, suggesting that common adaptive immunity mechanisms play a detrimental role in each disease. There is also growing evidence that regulatory T cells are beneficial during the initial stages of MS and AD, supporting the link between the modulatory immune compartments and these neurodegenerative disorders. The number of resting regulatory T cells declines in both diseases, indicating a common pathogenic mechanism involving the dysregulation of these cells, although their precise role in the control of neuroinflammation remains unclear. The modulation of leukocyte functions can benefit MS patients, so more insight into the role of peripheral immune cells may reveal new targets for pharmacological intervention in other neuroinflammatory and neurodegenerative diseases, including AD

The role of neutrophils in the dysfunction of central nervous system barriers

Leukocyte migration into the central nervous system (CNS) represents a central process in the development of neurological diseases with a detrimental inflammatory component. Infiltrating neutrophils have been detected inside the brain of patients with several neuroinflammatory disorders, including stroke, multiple sclerosis and Alzheimer's disease. During inflammatory responses, these highly reactive innate immune cells can rapidly extravasate and release a plethora of pro-inflammatory and cytotoxic factors, potentially inducing significant collateral tissue damage. Indeed, several studies have shown that neutrophils promote blood-brain barrier damage and increased vascular permeability during neuroinflammatory diseases. Recent studies have shown that neutrophils migrate into the meninges and choroid plexus, suggesting these cells can also damage the blood-cerebrospinal fluid barrier (BCSFB). In this review, we discuss the emerging role of neutrophils in the dysfunction of brain barriers across different neuroinflammatory conditions and describe the molecular basis and cellular interplays involved in neutrophil-mediated injury of the CNS borders

Blockade of \u3b14 integrins reduces leukocyte-endothelial interactions in cerebral vessels and improves memory in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline associated with the deposition of amyloid-beta (A beta) plaques, hyperphosphorylation of tau protein, and neuronal loss. Vascular inflammation and leukocyte trafficking may contribute to AD pathogenesis, and a better understanding of these inflammation mechanisms could therefore facilitate the development of new AD therapies. Here we show that T cells extravasate in the proximity of cerebral VCAM-1(+) vessels in 3xTg-AD transgenic mice, which develop both A beta and tau pathologies. The counter-ligand of VCAM-1-alpha 4 beta 1 integrin, also known as very late antigen-4 (VLA-4) - was more abundant on circulating CD4(+) T cells and was also expressed by a significant proportion of blood CD8(+) T cells and neutrophils in AD mice. Intravital microscopy of the brain microcirculation revealed that alpha 4 integrins control leukocyte-endothelial interactions in AD mice. Therapeutic targeting of VLA-4 using antibodies that specifically block alpha 4 integrins improved the memory of 3xTg-AD mice compared to an isotype control. These antibodies also reduced neuropathological hallmarks of AD, including microgliosis, A beta load and tau hyperphosphorylation. Our results demonstrate that alpha 4 integrin-dependent leukocyte trafficking promotes cognitive impairment and AD neuropathology, suggesting that the blockade of alpha 4 integrins may offer a new therapeutic strategy in AD

LFA-1 Controls Th1 and Th17 Motility Behavior in the Inflamed Central Nervous System

Leukocyte trafficking is a key event during autoimmune and inflammatory responses. The subarachnoid space (SAS) and cerebrospinal fluid are major routes for the migration of encephalitogenic T cells into the central nervous system (CNS) during experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis, and are sites of T cell activation before the invasion of CNS parenchyma. In particular, autoreactive Th1 and Th17 cell trafficking and reactivation in the CNS are required for the pathogenesis of EAE. However, the molecular mechanisms controlling T cell dynamics during EAE are unclear. We used two-photon laser microscopy to show that autoreactive Th1 and Th17 cells display distinct motility behavior within the SAS in the spinal cords of mice immunized with the myelin oligodendrocyte glycoprotein peptide MOG(35-55). Th1 cells showed a strong directional bias at the disease peak, moving in a straight line and covering long distances, whereas Th17 cells exhibited more constrained motility. The dynamics of both Th1 and Th17 cells were strongly affected by blocking the integrin LFA-1, which interfered with the deformability and biomechanics of Th1 but not Th17 cells. The intrathecal injection of a blocking anti-LFA-1 antibody at the onset of disease significantly inhibited EAE progression and also strongly reduced neuro-inflammation in the immunized mice. Our results show that LFA-1 plays a pivotal role in T cell motility during EAE and suggest that interfering with the molecular mechanisms controlling T cell motility can help to reduce the pathogenic potential of autoreactive lymphocytes

An isoform of the giant protein titin is a master regulator of human T lymphocyte trafficking

Response to multiple microenvironmental cues and resilience to mechanical stress are essential features of trafficking leukocytes. Here, we describe unexpected role of titin (TTN), the largest protein encoded by the human genome, in the regulation of mechanisms of lymphocyte trafficking. Human T and B lymphocytes express five TTN isoforms, exhibiting cell-specific expression, distinct localization to plasma membrane microdomains, and different distribution to cytosolic versus nuclear compartments. In T lymphocytes, the LTTN1 isoform governs the morphogenesis of plasma membrane microvilli independently of ERM protein phosphorylation status, thus allowing selectin-mediated capturing and rolling adhesions. Likewise, LTTN1 controls chemokine-triggered integrin activation. Accordingly, LTTN1 mediates rho and rap small GTPases activation, but not actin polymerization. In contrast, chemotaxis is facilitated by LTTN1 degradation. Finally, LTTN1 controls resilience to passive cell deformation and ensures T lymphocyte survival in the blood stream. LTTN1 is, thus, a critical and versatile housekeeping regulator of T lymphocyte trafficking

Modulation of human dendritic cells funtional activity by M. tuberculosis

Mycobacterium tuberculosis (Mtb) \ue8 in grado di interferire sulle funzionalit\ue0 delle cellule dendritiche (DC) e quindi di influenzare la risposta acquisita dei linfociti T. In questa tesi noi mostriamo che Mtb \ue8 in grado di alterare il differenziamento dei monociti a DC con la formazione di cellule esprimenti alti livelli di CD14 e bassi livelli di CD1a e CD1c. Queste cellule sono in grado di produrre TNF-\u3b1 cos\uec come piccole quantit\ue0 di IL-1\u3b2, IL-6 e IL-23, ma non secernono misurabili quantit\ue0 di IL-12 nei sopranatanti di coltura. Probabilmente da questa incapacit\ue0 di secernere citochine deriva la sostanziale mancanza di una risposta dei linfociti T CD4+ incubati con tali DC, che sono infatti incapaci di sintetizzare significative quantit\ue0 di IFN-\u3b3 o IL-17. Al contrario, DC ottenute dal normale differenziamento dei monociti e successivamente trattate con Mtb presentano un fenotipo maturo e sono in grado di secernere alti quantitativi di IL-1\u3b2, IL-6, IL-23 e TNF-\u3b1. Questa combinazione di citochine contribuisce alla polarizzazione di linfociti T CD4+ verso una popolazione mista caratterizzata da fenotipi Th1, Th17 e Th1/17, in grado di produrre IFN-\u3b3 e IL-17. Il rilascio di TNF-\u3b1, IL-1\u3b2, IL-23 e IL-6 da parte delle DC \ue8 dovuto al legame del recettore dectin-1 da parte del Mtb, mentre il TLR2 sembra non essere coinvolto in questo meccanismo. Altri dati da noi ottenuti utilizzando il glucano, che \ue8 un agonista solubile del dectin-1, ci hanno permesso di confermare una specifica polarizzazione Th1/Th17 indipendente dal coinvolgimento del TLR2. Questi risultati indicano che il dectin-1 potrebbe essere il recettore pi\uf9 importante nell\u2019induzione di una risposta acquisita di tipo Th1/Th17. In aggiunta abbiamo riportato che il coinvolgimento di DC-SIGN o CD206 nel legame con Mtb porta ad una diminuita secrezione di TNF-\u3b1, IL-1\u3b2, IL-23 e IL-6 da parte delle DC. Questo effetto \ue8 probabilmente dovuto ad interferenza da parte di CD206 e DC-SIGN sulla cascata di segnali attivati dal dectin-1, come suggerito dagli esperimenti effettuati con gli agonisti solubili dei recettori. Infatti, la stimolazione simultanea di dectin-1 e CD206 o DC-SIGN porta ad un diminuito rilascio di citochine da parte delle DC. Inoltre abbiamo effettuato altri esperimenti utilizzando antigeni secreti dal Mtb. L\u2019antigene HspX \ue8 risultato essere il pi\uf9 interessante, infatti il contemporaneo trattamento di cellule dendritiche con HspX e Mtb porta ad una significativa diminuzione di IL-23 ed a una aumentata sintesi di TNF-\u3b1, IL-1\u3b2 e IL-6. Queste cellule inoltre sono in grado di cambiare la polarizzazione Th1/Th17 risultante dalla stimolazione con il solo Mtb, verso una risposta principalmente Th1 con diminuito rilascio di IL-17 e aumentata secrezione di IFN-\u3b3 da parte dei linfociti T CD4+. E\u2019 inoltre interessante notare che il trattamento con HspX durante la maturazione indotta da Mtb \ue8 in grado di aumentare l\u2019espressione di superficie di CD206 e DC-SIGN e diminuire quella di dectin-1, se paragonata a quella ottenuta con la sola maturazione indotta da Mtb. Questi risultati suggeriscono che l\u2019antigene HspX potrebbe influenzare il riarrangiamento dei recettori sulla superficie delle DC, modificando quindi il diretto contatto con il Mtb. I nostri risultati indicano che Mtb pu\uf2 modulare la polarizzazione funzionale dei linfociti T interferendo con il differenziamento delle DC o con il rilascio di citochine, attraverso meccanismi che coinvolgono l\u2019interazione del patogeno con i recettori dectin-1, DC-SIGN e CD206.Mycobacterium tuberculosis (Mtb) subverts the functional activity of dendritic cells (DC) and influences T cell-mediated immune responses. Here we show that Mtb alters monocytes differentiation into DC with formation of CD14+ cells showing decreased CD1a and CD1c acquisition and producing TNF-\u3b1, little amounts of IL-1\u3b2, IL-6, IL-23 and no IL-12. These cells are unable to induce substantial IFN-\u3b3 or IL-17 production in CD4+ lymphocytes. The treatment of conventionally differentiated monocyte-derived DC with Mtb elicits the formation of mature DC producing high amounts of IL-1\u3b2, IL-6, IL-23 and TNF-\u3b1, stimulating the secretion of IFN-\u3b3 and IL-17 by CD4+ lymphocytes. Here we also show that TNF-\u3b1, IL-1\u3b2, IL-23, and IL-6 secretion is mainly due to dectin-1 receptor engagement by Mtb, whereas TLR2 does not play an essential role in the release of these cytokines. Accordingly, DC stimulation with the dectin-1 agonist glucan triggers Th1/Th17 polarization independently of TLR2 engagement. These findings indicate that dectin-1 could be the most important receptor involved in induction of Th1/Th17 generation. Here we also report that DC-SIGN or CD206 engagement leads to a decrease of Mtb-dependent TNF-\u3b1, IL-1\u3b2, IL-23, and IL-6 production by DC. These effects are probably due to an interference of CD206 and DC-SIGN on dectin-1-activated signals, as suggested by the experiments performed with soluble receptor agonists, in which simultaneous addition of the specific dectin-1 agonist and CD206 or DC-SIGN ligands results in depressed cytokine release. Moreover, some soluble secreted antigens from Mtb have been tested. Among them, HspX gave the most interesting results. In fact, it significantly decreased IL-23 and increased TNF-\u3b1, IL-1\u3b2, IL-6 secretion by DC in response to Mtb. We also found that HspX switched Mtb-dependent Th1/Th17 polarization towards the Th1 response, with decreased IL-17 and enhanced IFN-\u3b3 production by CD4+ T cells, probably as a consequence of the above-mentioned changes of cytokine expression. Interestingly, HspX treatment during the Mtb-induced maturation process increased CD206 and DC-SIGN, and decreased dectin-1 expression as compared to Mtb-matured DC. These results suggest that antigen HspX could limit the receptor arrangements induced by the direct contacts between Mtb and DC. Our results indicate that Mtb could modulates the functional polarization of T lymphocytes by affecting DC differentiation and cytokine release through mechanisms involving interactions of the pathogen with dectin-1, DC-SIGN and CD206

Induction of Th1/Th17 immune response by Mycobacterium tuberculosis: role of dectin-1, mannose receptor, and DC-SIGN

Mtb influences DC activity and T cell-mediated immune responses. We show that the treatment of immature monocyte-derived DC with Mtb elicited the formation of mature DC, producing TNF-\u3b1, IL-1\u3b2, IL-6, and IL-23 and instructing CD4+ cells to secrete IFN-\u3b3 and IL-17. Mtb-induced cytokine release by DC depended on dectin-1 receptor engagement, whereas MR or DC-SIGN stimulation inhibited this process. A selective dectin-1 binding by the receptor agonist glucan was sufficient to enable DC to generate Th1/Th17 lymphocytes, showing features comparable with those induced by Mtb-treated DC. Interestingly, DC-SIGN or MR engagement inhibited Th17 and increased Th1 generation by glucan- or Mtb-treated DC. Our results indicate that Mtb modulates the lymphocyte response by affecting DC maturation and cytokine release. Dectin-1 engagement by Mtb enables DC to promote a Th1/Th17 response, whereas DC-SIGN and MR costimulation limits dectin-1-dependent Th17 generation and favors a Th1 response, probably by interfering with release of cytokines