Neurodegenerative disorders are characterized by dysfunction and loss of specific neuronal populations in response to age-related, or toxic and traumatic events. Recently, it has become clear that astrocytic dysfunction plays a relevant role in neurodegenerative processes. In fact, astrocytes represent the main type of glia in the central nervous system (CNS) and constitute the principal element of the brain homeostatic system. Biochemical and structural changes of astrocytes during neuroinflammation represent a physiological response to CNS injury to minimize and repair the initial damage. Nevertheless, prolonged brain insults provide detrimental signals that can compromise astrocytic and neuronal functions and lead to chronic neuroinflammation. In fact, neuroinflammation is characterized by sustained glial activation (reactive astrogliosis) and the generation of an inflammatory loop, through the release of cytokines and other neurotoxic mediators that cause oxidative stress and limit functional repair of brain parenchyma. Another hallmark of neurodegenerative disorders is represented by mitochondrial dysfunction. Mitochondria are very dynamic organelles. In particular, mitochondrial dynamic processes (involving alternation of fission/fusion cycles and their axonal transport) and biogenesis are crucial for neuronal homeostasis and synaptic function. Moreover, alteration of the balance between fission and fusion can determine the fate of neuronal cells. This knowledge supports the hypothesis that alteration of mitochondrial function and metabolism plays an important role in the neurodegenerative process because neuronal cells require high levels of energy to perform their functions, such as during neuronal differentiation. So far, the correlation between neuroinflammation, mitochondrial dysfunction and neurodegeneration has been poorly investigated. In this study, we describe the effects of a number of natural anti-oxidants in rescuing astrocytic function and neuronal viability following glial activation. All tested dietary antioxidants were able to reduce astrocyte proliferation and restore astrocytic and neuronal survival and basal levels of reactive oxygen species (ROS), via differential modulation of NF-kB binding activity in cell cultures of neurons and astrocytes, suggesting that NF-kB plays a crucial role in the modulation of neuronal survival and anti-inflammatory responses. In addition, in a cellular model of neuronal NGF-induced differentiation, we demonstrated that this mechanism is accompanied by increased mitochondrial remodeling involving modulation of fission and fusion proteins, mitophagy and induction of proteins and transcription factors that regulate mitochondria biogenesis and metabolism to increase their efficiency and meet higher energy requirements. These data revealed a new NGF-dependent modulation of mitochondrial function that appear be important in both neurogenesis and nerve regeneration following brain injury. Overall, our data identify mitochondria as the “core” element of two relevant mechanisms underlying neurodegenerative disorders: neuroinflammation and neurogenesis. Moreover, we show that modulation of their morphology and activity can be achieved by a complex interplay of molecular events that can be controlled by both NGF and dietary factors. The relevance of mitochondrial dysfunction and its connection to neuroinflammation in neurodegenerative diseases is under investigation in the animal model of Parkinson based on 6-hydroxydopamine (6-OHDA) neurotoxicity. This model will be also used to assess the therapeutic potential of NGF and antioxidant molecules.

Le malattie neurodegenerative sono caratterizzate da disfunzione e perdita di specifiche popolazioni neuronali in risposta ad invecchiamento o eventi tossici o traumatici. Tuttavia, recentemente, è diventato chiaro che la disfunzione astrocitica ha un ruolo importante nei processi degenerativi. Infatti, gli astrociti rappresentano la popolazione cellulare maggiore del Sistema Nervoso Centrale (SNC) e costituiscono l’elemento principale per la sua omeostasi. Alterazioni biochimiche e strutturali degli astrociti durante la neuroinfiammazione rappresentano una risposta fisiologica a danni a carico del SNC per minimizzare e riparare il danno iniziale. Tuttavia, danni cerebrali prolungati forniscono segnali dannosi che possono compromettere le funzioni di astrociti e neuroni e causare neuroinfiammazione cronica. La neuroinfiammazione è un processo caratterizzato da attivazione gliale, che sottende ad un ciclo continuo di eventi infiammatori in cui si ha rilascio di citochine infiammatorie ed altri mediatori neurotossici che causano stress ossidativo e impediscono il ripristino funzionale del parenchima cerebrale. Un altro meccanismo implicato nelle malattie neurodegenerative è rappresentato dalla disfunzione mitocondriale. I mitocondri sono organelli dinamici. In particolare, i processi della dinamica mitocondriale (che coinvolgono cicli alternati di fissione/fusione e il loro trasporto assonale) e della biogenesi sono cruciali per l’omeostasi neuronale e la funzionalità sinaptica. Inoltre, un’alterazione dell’equilibrio tra processi di fissione e fusione può determinare il destino delle cellule neuronali. Queste informazioni supportano l’ipotesi che la disfunzione mitocondriale abbia un ruolo importante nel processo degenerativo, a causa dell’alta richiesta di energia da parte delle cellule neuronali per svolgere le loro funzioni, tra cui neurogenesi e differenziamento neuronale. Ad oggi, la correlazione tra neuroinfiammazione, disfunzione mitocondriale e neurodegenerazione è stata poco studiata. In questo lavoro, abbiamo descritto gli effetti di un certo numero di molecole antiossidanti naturali nel ripristinare la funzionalità astrocitica e la sopravvivenza neuronale in modelli in-vitro di astrogliosi reattiva. Tutte le molecole antiossidanti testate hanno rivelato la capacità di ridurre la proliferazione degli astrociti e ripristinare la sopravvivenza di astrociti e neuroni ed i livelli basali di specie reattive dell’ossigeno (ROS) mediante una differente modulazione di NF-kB in colture cellulari di astrociti e neuroni, suggerendo che NF-kB svolga un ruolo cruciale nel controllo della sopravvivenza neuronale e nelle risposte anti-infiammatorie. Inoltre, in un modello cellulare di differenziamento indotto da Nerve Growth Factor (NGF), abbiamo dimostrato che la differenziazione è accompagnata da un incremento del rimodellamento mitocondriale che richiede la modulazione di fissione/fusione e mitofagia, e l’induzione di proteine e fattori di trascrizione che regolano la biogenesi e il metabolismo mitocondriale, per aumentarne l’efficienza e soddisfare requisiti energetici più elevati. Questo studio ha rivelato un nuovo meccanismo di modulazione della funzionalità mitocondriale dipendente da NGF, importante nella neurogenesi e rigenerazione cerebrale. Nel complesso, i nostri dati identificano i mitocondri come elemento centrale a due meccanismi cruciali nel processo neurodegenerativo: neuroinfiammazione e neurogenesi. Inoltre, morfologia e attività mitocondriale possono essere modulate da un complesso crosstalk di eventi molecolari controllati da NGF o molecole antiossidanti. L’importanza della disfunzione mitocondriale e della sua correlazione a processi di neuroinfiammazione nella patologie neurodegenerative è attualmente oggetto di studio in un modello animale di Parkinson basato sulla neurotossicità di 6-OHDA, come anche il potenziale terapeutico di NGF e molecole antiossidanti.

(2020). Mitochondria as the core of neuroinflammation and neurodegeneration in models of neuronal and astrocytic dysfunction. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2020).

Mitochondria as the core of neuroinflammation and neurodegeneration in models of neuronal and astrocytic dysfunction

MARTORANA, FRANCESCA
2020

Abstract

Neurodegenerative disorders are characterized by dysfunction and loss of specific neuronal populations in response to age-related, or toxic and traumatic events. Recently, it has become clear that astrocytic dysfunction plays a relevant role in neurodegenerative processes. In fact, astrocytes represent the main type of glia in the central nervous system (CNS) and constitute the principal element of the brain homeostatic system. Biochemical and structural changes of astrocytes during neuroinflammation represent a physiological response to CNS injury to minimize and repair the initial damage. Nevertheless, prolonged brain insults provide detrimental signals that can compromise astrocytic and neuronal functions and lead to chronic neuroinflammation. In fact, neuroinflammation is characterized by sustained glial activation (reactive astrogliosis) and the generation of an inflammatory loop, through the release of cytokines and other neurotoxic mediators that cause oxidative stress and limit functional repair of brain parenchyma. Another hallmark of neurodegenerative disorders is represented by mitochondrial dysfunction. Mitochondria are very dynamic organelles. In particular, mitochondrial dynamic processes (involving alternation of fission/fusion cycles and their axonal transport) and biogenesis are crucial for neuronal homeostasis and synaptic function. Moreover, alteration of the balance between fission and fusion can determine the fate of neuronal cells. This knowledge supports the hypothesis that alteration of mitochondrial function and metabolism plays an important role in the neurodegenerative process because neuronal cells require high levels of energy to perform their functions, such as during neuronal differentiation. So far, the correlation between neuroinflammation, mitochondrial dysfunction and neurodegeneration has been poorly investigated. In this study, we describe the effects of a number of natural anti-oxidants in rescuing astrocytic function and neuronal viability following glial activation. All tested dietary antioxidants were able to reduce astrocyte proliferation and restore astrocytic and neuronal survival and basal levels of reactive oxygen species (ROS), via differential modulation of NF-kB binding activity in cell cultures of neurons and astrocytes, suggesting that NF-kB plays a crucial role in the modulation of neuronal survival and anti-inflammatory responses. In addition, in a cellular model of neuronal NGF-induced differentiation, we demonstrated that this mechanism is accompanied by increased mitochondrial remodeling involving modulation of fission and fusion proteins, mitophagy and induction of proteins and transcription factors that regulate mitochondria biogenesis and metabolism to increase their efficiency and meet higher energy requirements. These data revealed a new NGF-dependent modulation of mitochondrial function that appear be important in both neurogenesis and nerve regeneration following brain injury. Overall, our data identify mitochondria as the “core” element of two relevant mechanisms underlying neurodegenerative disorders: neuroinflammation and neurogenesis. Moreover, we show that modulation of their morphology and activity can be achieved by a complex interplay of molecular events that can be controlled by both NGF and dietary factors. The relevance of mitochondrial dysfunction and its connection to neuroinflammation in neurodegenerative diseases is under investigation in the animal model of Parkinson based on 6-hydroxydopamine (6-OHDA) neurotoxicity. This model will be also used to assess the therapeutic potential of NGF and antioxidant molecules.
GRANUCCI, FRANCESCA
COLANGELO, ANNA MARIA
mitocondri; astrociti; neuroinfiammazione; neurodegenerazione; neurogenesi
mitochondria; astrocytes; neuroinflammation; neurodegeneration; neurogenesi
BIO/10 - BIOCHIMICA
English
21-gen-2020
MEDICINA TRASLAZIONALE E MOLECOLARE - DIMET - 76R
32
2018/2019
open
(2020). Mitochondria as the core of neuroinflammation and neurodegeneration in models of neuronal and astrocytic dysfunction. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2020).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/259338
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