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Homeostasis of eukaryotic cells is largely dependent on dynamic compartmentalization of the endo-membrane system. The membrane trafficking linking different organelles is essential to maintain a proper composition of various compartments as well as to transport various molecules to appropriate compartments. Thus, the molecular machinery regulating properly the intracellular membrane trafficking has a key role in the maintenance of organelle functionality and cell viability. It is not surprising that alterations in membrane trafficking can result in different pathologies. Respect to other cell types nervous system is more sensitive to disturbances of the membrane trafficking. Hence, to understand how alterations of the intracellular trafficking could lead to neurodegeneration, we focused our attention on two nervous system disorders, Charcot-Marie Tooth disease 4J (CMT4J) and Parkinson disease (PD), both caused by mutations of an inositol phospahatase (Fig4 and Synj1, respectively). Together with specific kinases, the activity of phospahatases control, the levels of phosphoinosities (PI), a class of phospholipids that even more is emerging to be involved in the regulation of membrane trafficking. Numerous findings highlighted that the levels of PI might be finely regulated, in time and in the space, and are critical for membrane homeostasis. Specifically PI metabolism seems critical for nervous system functions. Aim of my PhD project was to explore the role of Fig4 and Synj1 in the membrane trafficking and neurodegenaration in CMT4J and Parkinson neuropathies.

Endosomal trafficking is essential for cellular homeostasis. At the crossroads of distinct intracellular pathways, the endolysosomal system is crucial to maintain critical functions and adapt to the environment. Alterations of endosomal compartments were observed in cells from adult individuals with Down syndrome (DS), suggesting that the dysfunction of the endosomal pathway may contribute to the pathogenesis of DS. However, the nature and the degree of impairment, as well as the timing of onset, remain elusive. Here, by applying imaging and biochemical approaches, we demonstrate that the structure and dynamics of early endosomes are altered in DS cells. Furthermore, we found that recycling trafficking is markedly compromised in these cells. Remarkably, our results in 18–20 week-old human fetal fibroblasts indicate that alterations in the endolysosomal pathway are already present early in development. In addition, we show that overexpression of the polyphosphoinositide phosphatase synaptojanin 1 (Synj1) recapitulates the alterations observed in DS cells, suggesting a role for this lipid phosphatase in the pathogenesis of DS, likely already early in disease development. Overall, these data strengthen the link between the endolysosomal pathway and DS, highlighting a dangerous liaison among Synj1, endosomal trafficking and DS.

Two analogues of the MS3 aptamer, which was previously shown to have an exquisite capability to selectively bind and modulate the activity of mutant huntingtin (mHTT), have been here designed and evaluated in their physicochemical and biological properties. Featured by a distinctive propensity to form complex G-quadruplex structures, including large multimeric aggregates, the original 36-mer MS3 has been truncated to give a 33-mer (here named MS3-33) and a 17-mer (here named MS3-17). A combined use of different techniques (UV, CD, DSC, gel electrophoresis) allowed a detailed physicochemical characterization of these novel G-quadruplex-forming aptamers, tested in vitro on SH-SY5Y cells and in vivo on a Drosophila Huntington’s disease model, in which these shorter MS3-derived oligonucleotides proved to have improved bioactivity in comparison with the parent aptamer.

A set of guanine-rich aptamers able to preferentially recognize full-length huntingtin with an expanded polyglutamine tract has been recently identified, showing high efficacy in modulating the functions of the mutated protein in a variety of cell experiments. We here report a detailed biophysical characterization of the best aptamer in the series, named MS3, proved to adopt a stable, parallel G-quadruplex structure and show high nuclease resistance in serum. Confocal microscopy experiments on HeLa and SH-SY5Y cells, as models of non-neuronal and neuronal cells, respectively, showed a rapid, dose-dependent uptake of fluorescein-labelled MS3, demonstrating its effective internalization, even in the absence of transfecting agents, with no general cytotoxicity. Then, using a well-established Drosophila melanogaster model for Huntington’s disease, which expresses the mutated form of human huntingtin, a significant improvement in the motor neuronal function in flies fed with MS3 was observed, proving the in vivo efficacy of this aptamer.

Recently, a new form of autosomal recessive early-onset parkinsonism (PARK20), due to mutations in the gene encoding the phosphoinositide phosphatase, Synaptojanin 1 (Synj1), has been reported. Several genes responsible for hereditary forms of Parkinson’s disease are implicated in distinct steps of the endolysosomal pathway. However, the nature and the degree of endocytic membrane trafficking impairment in early-onset parkinsonism remains elusive. Here, we show that depletion of Synj1 causes drastic alterations of early endosomes, which become enlarged and more numerous, while it does not affect the morphology of late endosomes both in non-neuronal and neuronal cells. Moreover, Synj1 loss impairs the recycling of transferrin, while it does not alter the trafficking of the epidermal growth factor receptor. The ectopic expression of Synj1 restores the functions of early endosomes, and rescues these trafficking defects in depleted cells. Importantly, the same alterations of early endosomal compartments and trafficking defects occur in fibroblasts of PARK20 patients. Our data indicate that Synj1 plays a crucial role in regulating the homeostasis and functions of early endosomal compartments in different cell types, and highlight defective cellular pathways in PARK20. In addition, they strengthen the link between endosomal trafficking and Parkinson’s disease.

Homeostasis of eukaryotic cells is largely dependent on dynamic com-partmentalization of the endo-membrane system. The membrane traf-ficking linking different organelles is essential to maintain a proper composition of various compartments as well as to transport various molecules to appropriate compartments. Respect to other cell types nervous system is more sensitive to alterations of the membrane traf-ficking. In the last years, we studied the role of endosomal trafficking in neurodegeneration focusing on two nervous system disorders, Charcot-Marie Tooth disease 4 J (CMT4 J) and a new form of autosomal recessive early-onset parkinsonism (PARK20), both caused by muta-tions of an inositol phosphatase (Fig 4 and Synj1, respectively). Our recent investigations show that:1. Synj1 plays a crucial role in regulating the homeostasis and func-tions of early endosomal compartments in different cell types and in fibroblasts of PARK20 patients;2. the loss of Fig 4 drastically alters the whole endo-lysosome axis (lysosomes, but also late and early endosomes result enlarged and more numerous) implying its essential role for the homeostasis and function of these compartments.All together, our data provide evidence for the implication of endo-somal pathway in neurodegeneration, emphasising the link between endosomal trafficking and neurodegenerative diseases.

Resveratrol, a dietary polyphenol, is under consideration as chemopreventive and chemotherapeutic agent for several diseases, including cancer. However, its mechanisms of action and its effects on non-tumor cells, fundamental to understand its real efficacy as chemopreventive agent, remain largely unknown. Proline-rich tyrosine kinase 2 (PYK2), a non-receptor tyrosine kinase acting as signaling mediator of different stimuli, behaves as tumor-suppressor in prostate. Since, PYK2 and RSV share several fields of interaction, including oxidative stress, we have investigated their functional relationship in human non-transformed prostate EPN cells and in their tumor-prone counterpart EPN-PKM, expressing a PYK2 dead-kinase mutant. We show that RSV has a strong biological activity in both cell lines, decreasing ROS production, inducing morphological changes and reversible growth arrest, and activating autophagy but not apoptosis. Interestingly, the PYK2 mutant increases basal ROS and autophagy levels, and modulates the intensity of RSV effects. In particular, the anti-oxidant effect of RSV is more potent in EPN than in EPN-PKM, whereas its anti-proliferative and pro-autophagic effects are more significant in EPN-PKM. Consistently, PYK2 depletion by RNAi replicates the effects of the PKM mutant. Taken together, our results reveal that PYK2 and RSV act on common cellular pathways and suggest that RSV effects on prostate cells may depend on mutational-state or expression levels of PYK2 that emerges as a possible mediator of RSV mechanisms of action. Moreover, the observation that resveratrol effects are reversible and not associated to apoptosis in tumor-prone EPN-PKM cells suggests caution for its use in humans.