Neuroinflammation and protein accumulation in experimental Mucopolysaccharidosis type II (MPSII) animal models

Mucopolysaccharidosis type II (MPS II or Hunter syndrome) is a rare X-linked recessive lysosomal storage disease (LSD) caused by a deficiency in the iduronate-2-sulfatase (IDS) enzyme, which is involved in the first step of the degradative pathway of glycosaminoglycans (GAGs), specifically heparan (HS) and dermatan sulphate (DS). Consequently, GAGs accumulate in almost every cell type, causing a broad array of clinical symptoms such as cardio-respiratory impairment, skeletal deformities, growth retardation, and, for the majority of patients, neurological decline. Indeed, the central nervous system (CNS) seems to be extremely vulnerable to impaired lysosomal function and as such severe neuroinflammation and glial activation is a consistent finding in MPSs. Among glial cells, astrocytes play a key role in maintaining brain health and provide critical neurotrophic support. However, when turning into reactive, they change their molecular signature and trigger a neuroinflammatory response which chronic activation may be counterproductive. Key hallmarks of astrocyte reactivity include increased expression of intermediate filament proteins, such as Glial Fibrillary Acidic Protein (GFAP) and Vimentin, along with functional and morphological changes. Accordingly, my research aimed to characterize CNS alterations at early and late stages of MPS II pathology exploiting the stable ids mutant zebrafish line (herein referred as 〖ids〗^(-/-)), with a focus on the astroglia population. Indeed, a robust in vitro protocol for the primary co-culture of zebrafish neurons and astrocytes was successfully established which served as highly refined tool to dissect cell-autonomous changes and crosstalk between these two cell types. Specifically, my work focused on identifying alterations within the lysosomal compartment, notably its acidification in wild-type versus ids mutant fish-derived primary co-culture. Furthermore, I aimed at understanding the long-term consequences of lysosomal alterations in the adult zebrafish brain. In particular, I evaluated by western blot the levels of key protein markers associated with autophagy, proteasomal degradation, and protein accumulation on two years old mutant and control fish-derived midbrain samples. Additionally, to further support these findings, I performed a preliminary characterization of autophagic, proteasomal, and lysosomal markers in the midbrain and forebrain regions of MPSII and wild-type mice at early disease stages (1 month). Collectively, my preliminary results allowed me to assess cell-specific pathogenic mechanisms underlying lysosomal dysfunction in astrocytes and neurons, and how these defects may have an impact in different stages of the disease across different experimental MPSII models.