Monahan, C. | bioRxiv Science

bioRxiv2022

Interaction of an α-synuclein epitope with HLA-DRB1*15:01 initiates early enteric features of Parkinson's disease in humanized mice

Enteric symptoms, including constipation, are hallmarks of prodromal Parkinsons disease (PD) that can appear decades before the onset of motor symptoms and diagnosis. PD patients possess circulating T cells that recognize specific -synuclein-(-syn)-derived epitopes. One epitope, -syn32-46, binds with strong affinity to the HLA-DRB1*15:01 allele implicated in autoimmune diseases. We report that -syn32-46 immunization in a mouse expressing HLA-DRB1*15:01 triggers intestinal inflammation leading to loss of enteric neurons, damage of enteric dopaminergic neurons, constipation and weight loss. -Syn32-46 immunization activates innate and adaptive immune gene signatures in the gut and induces changes in CD4+ TH1/ TH17 transcriptome that resemble tissue resident memory cells found in mucosal barriers during inflammation. Depletion of CD4+, but not CD8+, T cells partially rescues enteric neurodegeneration. Therefore, interaction of -syn32-46 and HLA-DRB1*15:0 is critical for gut inflammation and CD4+ T cell-mediated loss of enteric neurons in humanized mice, suggesting potential mechanisms of prodromal enteric PD. HIGHLIGHTS AND eTOC BlurbO_LI-syn32-46 immunization of an HLA-DRB1*15:01 mouse triggers weight loss and constipation. C_LIO_LI-syn32-46 immunizations induce gut inflammation, loss of enteric neurons and damage to dopaminergic neurons. C_LIO_LI-syn32-46 immunization induces innate and adaptive immune responses in the gut. C_LIO_LIDepletion of CD4+, but not CD8+, T cells partially rescues enteric neural loss. C_LIO_LIAn interaction between -syn32-46 and HLA-DRB1*15:01 is critical for this model of prodromal PD. C_LI Parkinsons disease (PD) patients exhibit elevated number of circulating T cells that recognize -synuclein-(-syn)- epitopes, particularly during early disease stages. One epitope, -syn32-46, interacts with the HLA-DRB1*15:01; however, its role in PD pathogenesis remains unknown. Garretti et al. show that -syn32-46 immunization of a mouse expressing HLA-DRB1*15:01 triggers intestinal inflammation, a loss of enteric neurons, constipation and weight loss, suggesting a critical role for -syn autoimmunity in HLA-DRB1*15:01 carriers in prodromal PD.

neuroscience↗

bioRxiv2020

Functional assessment of the "two-hit" model for neurodevelopmental defects in Drosophila and X. laevis

We previously identified a deletion on chromosome 16p12.1 that is mostly inherited and associated with multiple neurodevelopmental outcomes, where severely affected probands carried an excess of rare pathogenic variants compared to mildly affected carrier parents. We hypothesized that the 16p12.1 deletion sensitizes the genome for disease, while "second-hits" in the genetic background modulate the phenotypic trajectory. To test this model, we examined how neurodevelopmental defects conferred by knockdown of individual 16p12.1 homologs are modulated by simultaneous knockdown of homologs of "second-hit" genes in Drosophila melanogaster and Xenopus laevis. We observed that knockdown of 16p12.1 homologs affect multiple phenotypic domains, leading to delayed developmental timing, seizure susceptibility, brain alterations, abnormal dendrite and axonal morphology, and cellular proliferation defects. Compared to genes within the 16p11.2 deletion, which has higher de novo occurrence, 16p12.1 homologs were less likely to interact with each other in Drosophila models or a human brain-specific interaction network, suggesting that interactions with "second-hit" genes may confer higher impact towards neurodevelopmental phenotypes. Assessment of 212 pairwise interactions in Drosophila between 16p12.1 homologs and 76 homologs of patient-specific "second-hit" genes (such as ARID1B and CACNA1A), genes within neurodevelopmental pathways (such as PTEN and UBE3A), and transcriptomic targets (such as DSCAM and TRRAP) identified genetic interactions in 63% of the tested pairs. In 11 out of 15 families, homologs of patient-specific "second-hits" enhanced or suppressed the phenotypic effects of one or many 16p12.1 homologs. In fact, homologs of SETD5 synergistically interacted with homologs of MOSMO in both Drosophila and X. laevis, leading to modified cellular and brain phenotypes, as well as axon outgrowth defects that were not observed with knockdown of either individual homolog. Our results suggest that several 16p12.1 genes sensitize the genome towards neurodevelopmental defects, and complex interactions with "second-hit" genes determine the ultimate phenotypic manifestation. Author SummaryCopy-number variants, or deletions and duplications in the genome, are associated with multiple neurodevelopmental disorders. The developmental delay-associated 16p12.1 deletion is mostly inherited, and severely affected children carry an excess of "second-hits" variants compared to mildly affected carrier parents, suggesting that additional variants modulate the clinical manifestation. We studied this "two-hit" model using Drosophila and Xenopus laevis, and systematically tested how homologs of "second-hit" genes modulate neurodevelopmental defects observed for 16p12.1 homologs. We observed that 16p12.1 homologs independently led to multiple neurodevelopmental features and weakly interacted with each other, suggesting that interactions with "second-hit" homologs potentially have a higher impact towards neurodevelopmental defects than interactions between 16p12.1 homologs. We tested 212 pairwise interactions of 16p12.1 homologs with "second-hit" homologs and genes within conserved neurodevelopmental pathways, and observed modulation of neurodevelopmental defects caused by 16p12.1 homologs in 11 out of 15 families, and 16/32 of these changes could be attributed to genetic interactions. Interestingly, we observed that SETD5 homologs interacted with homologs of MOSMO, which conferred additional neuronal phenotypes not observed with knockdown of individual homologs. We propose that the 16p12.1 deletion sensitizes the genome to multiple neurodevelopmental defects, and complex interactions with "second-hit" genes determine the clinical trajectory of the disorder.

genomics↗