Tracking Innate Immune Activation in a Mouse Model of Parkinson's Disease Using TREM1 and TSPO PET Tracers.

Parkinson's disease (PD) is associated with aberrant innate immune responses, including microglial activation and infiltration of peripheral myeloid cells into the central nervous system (CNS). Methods to investigate innate immune activation in PD are limited and have not yet elucidated key interactions between neuroinflammation and peripheral inflammation. Translocator protein 18 kDa (TSPO) PET is a widely evaluated imaging approach for studying activated microglia and peripheral myeloid lineage cells in vivo but has yet to be fully explored in PD. Here, we investigate the utility of TSPO PET in addition to PET imaging of triggering receptor expressed on myeloid cells 1 (TREM1)-a novel biomarker of proinflammatory innate immune cells-for detecting innate immune responses in the 6-hydroxydopamine mouse model of dopaminergic neuron degeneration. Methods: C57/BL6J and TREM1 knockout mice were stereotactically injected with 6-hydroxydopamine in the left striatum; control mice were injected with saline. At day 7 or 14 after surgery, mice were administered 18F-GE-180, 64Cu-TREM1 monoclonal antibody (mAb), or 64Cu-isotype control mAb and imaged by PET/CT. Ex vivo autoradiography was performed to obtain high-resolution images of tracer binding within the brain. Immunohistochemistry was conducted to verify myeloid cell activation and dopaminergic cell death, and quantitative polymerase chain reaction and flow cytometry were completed to assess levels of target in the brain. Results: PET/CT images of both tracers showed elevated signal within the striatum of 6-hydroxydopamine-injected mice compared with those injected with saline. Autoradiography afforded higher-resolution brain images and revealed significant TSPO and TREM1 tracer binding within the ipsilateral striatum of 6-hydroxydopamine mice compared with saline mice at both 7 and 14 d after toxin. Interestingly, 18F-GE-180 enabled detection of inflammation in the brain and peripheral tissues (blood and spleen) of 6-hydroxydopamine mice, whereas 64Cu-TREM1 mAb appeared to be more sensitive and specific for detecting neuroinflammation, in particular infiltrating myeloid cells, in these mice, as demonstrated by flow cytometry findings and higher tracer binding signal-to-background ratios in brain. Conclusion: TSPO and TREM1 PET tracers are promising tools for investigating different cell types involved in innate immune activation in the context of dopaminergic neurodegeneration, thus warranting further investigation in other PD rodent models and human postmortem tissue to assess their clinical potential.

Author Correction: Engineering monocyte/macrophage-specific glucocerebrosidase expression in human hematopoietic stem cells using genome editing.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Engineering monocyte/macrophage-specific glucocerebrosidase expression in human hematopoietic stem cells using genome editing.

Gaucher disease is a lysosomal storage disorder caused by insufficient glucocerebrosidase activity. Its hallmark manifestations are attributed to infiltration and inflammation by macrophages. Current therapies for Gaucher disease include life-long intravenous administration of recombinant glucocerebrosidase and orally-available glucosylceramide synthase inhibitors. An alternative approach is to engineer the patient's own hematopoietic system to restore glucocerebrosidase expression, thereby replacing the affected cells, and constituting a potential one-time therapy for this disease. Here, we report an efficient CRISPR/Cas9-based approach that targets glucocerebrosidase expression cassettes with a monocyte/macrophage-specific element to the CCR5 safe-harbor locus in human hematopoietic stem and progenitor cells. The targeted cells generate glucocerebrosidase-expressing macrophages and maintain long-term repopulation and multi-lineage differentiation potential with serial transplantation. The combination of a safe-harbor and a lineage-specific promoter establishes a universal correction strategy and circumvents potential toxicity of ectopic glucocerebrosidase in the stem cells. Furthermore, it constitutes an adaptable platform for other lysosomal enzyme deficiencies.