Tay-Sachs Disease: Mechanisms of Neuropathology and Potential Therapeutic Strategies Utilizing Human Lysosomal Sialidase

Abstract

<p>GM2 gangliosidoses encompass a group of chronic neurodegenerative disorders characterized by metabolic defects in ganglioside catabolism and marked intralysosomal accumulation of GM2 in central nervous system (CNS)-resident neurons. Included in this group are Tay-Sachs and Sandhoff disease. Human cases of Tay-Sachs and Sandhoff disease present with devastating neurological deterioration; however, murine models display drastically divergent phenotypes. Tay-Sachs mice avoid pathology via a sialidase-mediated bypass of β-hexosaminidase A (HEXA) deficiency, though the precise mechanism of avoidance is not fully elucidated. The following work aimed to: i) determine if the murine sialidase-mediated bypass could be potentiated in human cells, and ii) help clarify the mechanism of disease avoidance in Tay-Sachs animals.</p> <p>Adenoviral overexpression of truncated CCAAT displacement protein (CDP^831-1505) in human Tay-Sachs neuroglia augmented neuraminidase 1/lysosomal sialidase (NEU1) protein levels, which reduced intralysosomal GM2 accumulations. Chromatin immunoprecipitation revealed binding of CDP^831-1505 to the human <em>NEU1</em> promoter in Tay-Sachs neuroglia. These results provide mechanistic and functional evidence supporting therapeutic exploitation of <em>NEU1</em> for Tay-Sachs disease.</p> <p>Comparison of immunological responses of bone marrow-derived macrophages (BMDMs) to pathogen associated molecular patterns (PAMPs) or GM2 demonstrated that Sandhoff macrophages secrete increased TNF and reduced IL-10 following lipopolysaccharide stimulation. GM2 treatment failed to stimulate an immune response. Such behaviour occurred in the absence of clearly observable intralysosomal ganglioside accumulations. Altered LAMP2 protein size, potentially due to aberrant glycosylation, is hypothesized to disrupt autophagosomal/lysosomal fusion. Subsequent autophagosomal accumulation could result in inherent macrophage hypersensitivity and immunologic irritability. Downstream interleukin-10 (IL-10)/signal transducer and activator of transcription 3 (Stat3) axis, mitogen activated protein kinase (MAPK), and glycogen synthase kinase 3-beta (GSK3β) signaling pathways were affected in Sandhoff BMDMs. These data indicate inherent differences in immunological responses of BMDMs from Sandhoff mice, presumably related to their β-hexosaminidase B (HEXB) deficiency.</p> <p>Data presented here provides evidence to suggest a paradigm shift in the neurodegenerative model of Tay-Sachs and Sandhoff Diseases towards one that places immune cells as an initiating factor for widespread neuroinflammation.</p>