Investigating TTYH3 and Its Relation to CLN3 Batten Disease

About This Grant

PROJECT SUMMARY CLN3 disease is a rare lysosomal disease affecting approximately 1 in 100,000 live born children. It is caused by recessive mutations in the CLN3 gene, which encodes a transmembrane protein that primarily localizes to the lysosome. Affected children suffer from progressive blindness, seizures, psychosis, and cognitive and motor failure, and the disease is invariably fatal. CLN3 is implicated in various cellular processes including endolysosomal trafficking and lipid metabolism, but the primary function remains incompletely resolved. Interestingly, immune system changes have been described in CLN3 patients and animal models including early neuroinflammation in brain regions that later see the first neuronal cell dropout, suggesting the neuroimmune system plays a role in the neurodegenerative disease process. In a proteomics study of CLN3- deficient microglia, we recently discovered a dramatic elevation in the levels of the Tweety homolog protein, TTYH3, which was over 10-fold elevated in microglia isolated from presymptomatic mice, and over 20-fold elevated in microglia from symptomatic mice, suggesting TTYH3 elevation is a relatively early disease event and that it progresses with disease severity. Indeed, we also identified TTYH3 elevation in a neuronal progenitor cell model of CLN3 disease, indicating TTYH3 levels increase in response to loss of CLN3 function in both neurons and microglia. In this proposal, which is responsive to the NOFO for research projects of understudied proteins linked to rare disease (NOFO PAR-25-122), we aim to develop important tools to study the TTYH3 protein in the context of CLN3 disease. We hypothesize that TTYH3 is a novel lysosomal lipid transporter, and we will test this hypothesis by studying TTYH3 subcellular localization and by establishing Ttyh3/TTYH3 knockout mouse and human induced pluripotent stem (iPS) cell-based models that will be phenotyped to evaluate lysosomal function. Finally, we will evaluate whether modulation of TTYH3 impacts CLN3 disease pathophysiology, setting the stage for future work to fully uncover TTYH3 function and whether targeting TTYH3 in CLN3 disease holds therapeutic promise.