Sex-dimorphic neuroprotective effect of CD163 in an alpha-synuclein mouse model of Parkinson's disease
Alpha-synuclein (a-syn) aggregation and immune activation represent hallmark pathological events in Parkinson's disease (PD). The PD-associated immune response encompasses both brain and peripheral immune cells, although little is known about the immune proteins relevant for such response. We propose that the upregulation of CD163 observed in blood monocytes and in the responsive microglia in the PD patients is a protective mechanism in the disease.  To investigate this, we used the PD model based on intrastriatal injections of murine a-syn pre-formed fibrils (PFF) in CD163 knockout (KO) mice and wild-type littermates. CD163KO females revealed an impaired and differential early immune response to a-syn pathology as revealed by immunohistochemical and transcriptomic analysis. After 6 months, CD163KO females showed an exacerbated immune response and a-syn pathology, which ultimately led to a dopaminergic neurodegeneration of greater magnitude. These findings support a novel, sex-dimorphic neuroprotective role for CD163 during a-syn-induced neurodegeneration. Overall design: To generate a PD model, murine alpha-synuclein pre-formed fibrils (a-syn PFF) were used due to their higher seeding efficiency in mice compared to human a-syn PFF. In parallel, phosphate buffered saline (PBS) was used as an absolute control, and murine monomeric a-syn (MONO) was used as a control for a-syn pathology, based on its reported lack of seeding capacity in vitro and in vivo. For whole population RNA sequencing, a third and fourth group of mice (batch 1 and batch 2) received bilateral intrastriatal injection of a-syn MONO (Males WT n=7 & CD163KO n=4*; Females WT n=7 &CD163KO n=5), and a-syn PFF (Males WT n=7, & CD163KO n =5; Females WT n=7 & CD163KO n=5). Triplicates were used for sequencing. Mice were sacrificed 2 months post-surgery, their brains dissected and the immune cells (microglia & macrophages) isolated and FACS sorted for RNA purification and subsequent SMART-seq2 sequencing. *CD163KO-MONO males were excluded from the analysis due to inconsistencies in the technical replicates. For the in vitro experiment, bone-marrow derived macrophages (BMDM) were isolated from CD163KO and WT C57BL/6N male and female mice, aged 6-12 weeks (n=5 per group).