Analysis of TIM2 retinal deficiency in healthy and during retinopathy and aging.

Funder

Organizational Unit

Publications

Unraveling the replication process of Toxoplasma gondii through the MOB1 protein

Publication . L. S. Delgado, Inês; Narciso, Sofia Bizarro Nolasco da Silva; Leitão, José Alexandre da Costa Perdigão e Cameira

ABSTRACT - MOB1 is a conserved protein that regulates cellular proliferation versus apoptosis, centrosome duplication and cellular differentiation in multicellular eukaryotes and also cytokinesis and division axis orientation in unicellular and multicellular eukaryotes. Toxoplasma gondii, an obligate intracellular parasite of veterinary and medical importance, presents one MOB1 protein. T. gondii interconverts between several cellular stages during its life cycle, namely between fast replicating tachyzoite and slow replicating bradyzoite stages during its asexual cycle, a key ability for its success as a parasite. Bradyzoites produce tissue cysts, establishing a chronic infection that enables recrudescence. Conversion is dependent on cell cycle regulation and involves cell differentiation and regulation of replication. This led us to select MOB1 as a strong candidate to be involved in the Toxoplasma replication process. We employed reverse genetics to assess the Mob1 function in T. gondii. In opposition to what was observed in other unicellular eukaryotes, as Tetrahymena and Trypanosoma, Mob1 knockout in T. gondii showed no cytokinesis impairment in its asexual cycle. Instead, we observed an increase in replication, a decrease in parasitophorous vacuole regularity and a significant loss in tachyzoite to bradyzoite conversion. Additionally, recombinant MOB1 accumulates in a midline between the daughter nuclei at the end of mitosis, suggesting MOB1 may be involved in this process. To elucidate how MOB1 acts in T. gondii, we employed a proximity biotinylation method and identified the MOB1 interactome. This analysis detected proteins related to several functional categories, indicating a multivalent role for MOB1 regulated by the ubiquitin proteasome system. We also verified that the Mob1 locus is transcribed from both genomic strands and gives rise to alternatively spliced variants. Our results indicate that MOB1 is tightly regulated along the cell cycle and along the life cycle of T. gondii, contributing to the control of replication and tachyzoite-bradyzoite differentiation.

2022-04-29Doctoral thesis

Open access

Analysis of TIM2 deficiency in the mouse retina

Publication . Valença, Andreia Barbosa; Ruberte París, Jesús; Jorge, Maria Luísa Mendes

Careful control of iron availability in the retina is central to maintenance of iron homeostasis, as its imbalance is associated with oxidative stress and progress of several retinopathies, such as diabetic retinopathy. Ferritin, known for its role in iron storage and detoxification, has also been proposed as an iron-transporter and can be regarded as a potential deliverer of a considerable large amount of iron to the retina compared to transferrin, the classical ironcarrier protein. Ferritin can bind to scavenger receptor class A member 5 (Scara5) and T-cell immunoglobulin and mucin-domain 2 (TIM2) receptors and is likely endocytosed. In this study, the presence of TIM2, which remained unknown in the retina, was investigated. Although no human ortholog for mouse TIM2 has been identified, human TIM1 and mouse TIM2 have similar functions. Our results revealed for the first time the presence of TIM2 receptors in the mouse retina, mainly expressed in Müller cells, unveiling new aspects of retinal iron metabolism regarding the putative role of TIM2 in this tissue. A knockout mouse for this membrane receptor was generated in order to better understand TIM2 functions in the retina. TIM2 deficiency affected retinal iron metabolism. Iron-loaded ferritin accumulation, probably due to increased ferritin uptake mediated by Scara5, and increased iron uptake by transferrin receptor 1 (TfR1)- transferrin binding led to retinal iron overload. Consequently, increased vascular permeability and blood-retinal barrier (BRB) breakdown were observed, inducing edema of the central retina. Paracellular and transcellular transports were impaired with tight junction integrity loss and increased caveolae number. Two mechanisms seem to be involved in this process: association of iron and ferritin overload with vascular endothelial growth factor (VEGF) overexpression and oxidative stress triggered by reactive oxygen species (ROS) overproduction generated by retinal iron overload. Altogether, these results point to TIM2 as a new key player in iron homeostasis in the mouse retina, possibly modulating cellular iron levels, and a potential target for the treatment of diabetic macular edema.

2019-05-28Doctoral thesis

Open access