Role of extracellular trafficking of neuroglobin in neurodegeneration and neuroprotection

Cellular survival relies on the regulation of growth, metabolism, and stress responses. Neurons, due to their post-mitotic nature, are particularly vulnerable and irreplaceable. In fact, in response to stress, they activate protective mechanisms, but excessive stress can lead to apoptosis. This progressive neuronal loss underlies neurodegeneration, contributing to aging and disorders such as Alzheimer’s, Parkinson’s, Huntington’s diseases and amyotrophic lateral sclerosis (Kole et al., 2013; Wilson III et al., 2023). Although the exact causes of these diseases remain unclear, they share common features including oxidative stress, mitochondrial dysfunction, and the accumulation of misfolded proteins, which induce endoplasmic reticulum (ER) stress and disrupt cellular homeostasis. Furthermore, neurodegenerative diseases are characterized by impaired autophagy, altered glucose metabolism, genetic mutations, and structural changes in neurons. Chronic inflammation exacerbates neuronal damage, accelerating disease progression. Given the rising prevalence of neurodegenerative diseases, largely driven by an aging population, there is an urgent need to identify new therapeutic targets. Current treatments are predominantly palliative, highlighting the importance of exploring alternative approaches (Marmolejo-Martìnez-Artesero et al., 2021; Wilson III et al., 2023). Consequently, recent research has focused on enhancing the intrinsic stress response mechanisms of neurons, with neuroglobin (NGB) emerging as a promising neuroprotective factor. NGB, a monomeric heme-globin, is primarily expressed in neurons of both the central and peripheral nervous systems (Burmester et al., 2000). Since its discovery in 2000, NGB has been associated with neuroprotective properties against various stressors linked to neuronal death, such as oxidative stress, hypoxia, ischemia, and oxygen/glucose deprivation (Fiocchetti et al., 2021). Intracellular NGB expression has been connected to several cell-autonomous neuroprotective mechanisms, influenced by both NGB expression levels and its intracellular distribution (Ascenzi et al., 2016). Furthermore, recent studies have identified NGB in astrocyte-derived exosomes (Venturini et al., 2019), suggesting a potential cytoprotective role beyond its intracellular effects. This supports the hypothesis that NGB may function as an intercellular resistance factor through non-cell-autonomous mechanisms. Previous research in our laboratory demonstrated the extracellular release of NGB in breast cancer models, showing that extracellular NGB could protect breast cancer cells from oxidative stress-induced apoptosis (Fiocchetti et al., 2020). However, the extracellular release of NGB and its potential neuroprotective effects on surrounding cells neuron like context remain unexplored. For this reason, the primary aim of this doctoral thesis is to investigate the extracellular release of NGB and assess its role in promoting neuronal cell resilience under stress and neurodegenerative conditions. The specific objectives of the thesis are as follows: (i) To characterize the extracellular release of NGB and identify potential regulatory mechanisms involved. (ii) To evaluate the functional significance of extracellular NGB in enhancing cellular resilience under stress conditions associated with neuropathologies in cells with neuronal characteristics and neurodegenerative phenotype. (iii) To investigate the potential influence of extracellular NGB on stress response pathways. REFERENCE: • Ascenzi P, di Masi A, Leboffe L, Fiocchetti M, Nuzzo MT, Brunori M, Marino M. Neuroglobin: From structure to function in health and disease. Mol Aspects Med. 2016 Dec;52:1-48. doi: 10.1016/j.mam.2016.10.004. Epub 2016 Nov 4. PMID: 27825818. • Burmester T, Weich B, Reinhardt S, Hankeln T. 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