Roles of Semaphorins in Neurodegenerative Diseases

Semaphorins are secreted and transmembrane proteins that bind plexin/neuropilin or integrin receptors, providing paracrine axonal guidance signals and ultimately leading to a functional and developed neuronal network. Following semaphorin’s initial discovery, their relevance in the central nervous system (CNS) soon intrigued researchers about the possible links between semaphorins, their receptors and signaling mechanisms and different neurodegenerative diseases. Here, we explore the current knowledge of semaphorin’s function and signaling in Alzheimer’s disease (AD), Parkinson’s disease (PD), Charcot-Marie-Tooth disease (CMT), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and Human T-cell lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We focus on the effects of the most known semaphorin subclasses 3A and 4D, yet extending our discussion to other semaphorins that have been found involved in specific neuropathologies and the potential effect of semaphorins modulating the immune system in disorders with inflammatory components. Molecular, cellular, and genetic evidences are reviewed, highlighting the relevance of semaphorins on each disease etiology, pathophysiology, and progression. The newly discovered semaphorin functions in neurological disorders even suggest alternative therapies that may be highly valuable in diseases that have no current cure

Endolysosomal degradation of Tau and its role in glucocorticoid-driven hippocampal malfunction

Emerging studies implicate Tau as an essential mediator of neuronal atrophy and cognitive impairment in Alzheimer's disease (AD), yet the factors that precipitate Tau dysfunction in AD are poorly understood. Chronic environmental stress and elevated glucocorticoids (GC), the major stress hormones, are associated with increased risk of AD and have been shown to trigger intracellular Tau accumulation and downstream Tau-dependent neuronal dysfunction. However, the mechanisms through which stress and GC disrupt Tau clearance and degradation in neurons remain unclear. Here, we demonstrate that Tau undergoes degradation via endolysosomal sorting in a pathway requiring the small GTPase Rab35 and the endosomal sorting complex required for transport (ESCRT) machinery. Furthermore, we find that GC impair Tau degradation by decreasing Rab35 levels, and that AAV-mediated expression of Rab35 in the hippocampus rescues GC-induced Tau accumulation and related neurostructural deficits. These studies indicate that the Rab35/ESCRT pathway is essential for Tau clearance and part of the mechanism through which GC precipitate brain pathology.work was supported by NIH grants R01NS080967and R21MH 104803 to C.L.W., Portuguese Foundation for Science & Technology (FCT) PhD fellowships to J. Vaz-Silva and T. Meira (PD/BD/105938/2014; PD/BD/113700/2015, respectively), and the following grants to I.S.: FCT Investigator grant IF/01799/2013, the Portuguese North Regional Operational Program (ON.2) under the National Strategic Reference Framework (QREN), through the European Regional Development Fund (FEDER), the Project Estratégico co-funded by FCT (PEst-C/SAU/LA 0026/2013) and the European Regional Development Fund COMPETE (FCOMP-01 -0124-FEDER-037298) as well as the project NORTE- 01-0145-FEDER-000013, supported by the Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (FEDER)info:eu-repo/semantics/publishedVersio

Physiological and Pathological Roles of Rab-Dynein-Dynactin Binding Adaptors

Transport of different organelles along the Microtubule cytoskeleton is carried out mainly by motor proteins Dynein and Kinesin. The tubulin monomers in Microtubules are organized in such a way that the generate polarity (a minus and a plus end) that is recognized by Motor proteins. Dynein usually acts with a binding partner, Dynactin, and is in charge of moving cargoes to the minus end of microtubules (mainly towards the center of the cell). There are different kinesins, the most studied is Kinesin-1, which moves cargoes towards the plus end of microtubules. In order to fulfil their function Motors usually bind to their cargoes indirectly through adaptor proteins. Chapter 1 explains the general concepts related to a group of Adaptors that recognize the small GTP-ases, Rabs, in cargoes that need to be transported under certain physiological circumstances and help recruiting the Dynein/Dynactin complexes to them so they can move in the minus end direction. This family of Adaptors is called Rab-Dynein-Dynactin (RDD) adaptors and in this project I focused on two of them: BicD2 and RILP. In chapter 2, I will focus on BicD2 and its role in Golgi morphology. BicD2 is an RDD adaptor that mediates binding of Dynein/Dynactin to Rab6-positive vesicles. Some mutations in BicD2 have been associated to Golgi apparatus morphology disruption, but the mechanism is unclear. It has been suggested that mutated BicD2 abnormally binds Dynein/Dynactin, sequestering this motor complex, producing Golgi disruption indirectly since this organelle depends heavily on minus-directed transport to maintain its localization and structure. I test this hypothesis and conclude that even when most pathological mutations disrupt the Golgi, a Dynein/Dynactin-mediated mechanisms is probably true only to some of them, proposing alternatives mechanisms such as Rab6 abnormal accumulation and non-Golgi related mechanisms of pathogenesis. In chapter 3, I will focus on RILP and its role in autophagosome movement. RILP is an RDD adaptor that mediates binding of Dynein/Dynactin to Rab7-positive vesicles such as Lysosomes. During autophagy, autophagosomes (which are LC3-positive) are formed mainly in the ER and mature to finally fuse with the Late Endosomes or Lysosomes (both acidic) in the center of the cell. It has been described by our lab that RILP can transport LC3-vesicles in axons. Nevertheless, these vesicles are acidic, which suggest these LC3-vesicles are already fused with either Lysosomes or Late endosomes. I will work under the Hypothesis that RILP can move autophagosomes in early stages (before fusion with Lysosomes or Late endosomes) in non-neuronal cells. I show that RILP can move autophagosomes to the center and FYCO1 (a Kinesin-1 adaptor) can move them to the periphery. RILP-mediated movement of autophagosomes depends on Rab7 activation status and seems to be controlled by PKA. I proposed a phosphorylation in Rab7 as a control mechanism. Finally, the discovery of 3 LC3 interacting regions (LIRs) in the RILP molecule is discussed and their contribution to autophagosome movement is analyzed. My results highlight the relevance of RDD proteins in physiological and pathological context

Tax posttranslational modifications and interaction with calreticulin in MT-2 cells and human peripheral blood mononuclear cells of human t cell lymphotropic virus type-i-Associated myelopathy/tropical spastic paraparesis patients

The human retrovirus human T cell lymphotropic virus type-I (HTLV-1) is the etiologic agent of HTLV-1-Associated myelopathy/tropical spastic paraparesis (HAM/TSP). Axonal degeneration in HAM/TSP patients occurs without neuron infection, with the secreted viral Tax protein proposed to be involved. We previously found that Tax secreted into the culture medium of MT-2 cells (HTLV-1-infected cell line) produced neurite retraction in neuroblastoma cells differentiated to neuronal type. To assess the relevance of Tax posttranslational modifications on this effect, we addressed the question of whether Tax secreted by MT-2 cells and peripheral blood mononuclear cells (PBMCs) of HTLV-1-infected subjects is modified. The interaction of Tax with calreticulin (CRT) that modulates intracellular Tax localization and secretion has been described. We studied Tax localization and modifications in MT-2 cells and its interaction with CRT. Intracellular Tax in MT-2 cells was assessed by flow cytometry, c