Exploring the Pathogenic Mechanisms of Batten's disease MFSD8 mutations using patient iPSC derived neurons.

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Mutations in the MFSD8 gene cause CLN7 Batten’s disease (BD), a rare neurodegenerative lysosomal storage disorder characterized by the accumulation of a lipopigment called ceroid in the brain. Furthermore, MFSD8 mutations were recently associated with frontotemporal dementia (FTD), and other BD-associated genes are linked to Parkinson’s disease (ATP13A2) and other subtypes of FTD (GRN, CTSD). CLN7 BD falls within a broader category of pediatric diseases called neuronal ceroid lipofuscinoses (NCL) that share common histopathology of ceroid accumulation in neurons and neurological symptoms including dementia, blindness, seizures, and premature death. The MFSD8 gene encodes the CLN7 protein, a membrane protein of unknown function that is localized to lysosomes. Mutations that cause CLN7 BD are loss of function and many of the known mutations result in premature stops or point mutations that destabilize the protein. Our previous studies in patient fibroblasts demonstrated that loss of CLN7 reduces lysosomal hydrolase activity, autophagic flux, and the accumulation of autofluorescent material. While these studies contributed to our understanding of how CLN7 leads to disease, the mechanisms that lead to neurodegeneration are not known. Furthermore, there are no studies done in relevant patient-derived neuronal models. Here, we propose to explore the mechanisms of neurotoxicity caused by CLN7 mutations, using a several iPSC-lines derived from distinct BD patients. Our preliminary data indicates that CLN7 BD lines can develop into cortical neurons in vitro, but demonstrate lysosomal phenotypes and reduced neurite extensions. In aim 1, we plan to use this established neuronal model to determine how loss of CLN7 influences the stability of the proteome and protein solubility to discover novel pathways and generate hypotheses for how cell death occurs in CLN7 BD. In aim 2, we will assess rescue mechanisms that aim to restore protein homeostasis in CLN7 neurons, as well as co-culturing wild-type astrocytes with CLN7-BD neurons to assess the role of glia cells in dementia. Since almost no mechanistic information is known about how CLN7 causes neurological dysfunction, our studies have the potential to uncover novel therapeutic pathways for CLN7 BD and other NCLs that share similar pathologies. Beyond NCLs, mutations in MFSD8 are associated with FTD, an age-related neurodegenerative disorder, and therefore our studies may be relevant to more common age-related neurodegeneration. Since there is accumulating evidence for lysosomal dysfunction common sporadic diseases including Parkinson’s disease and other synucleinopathies, our studies may have a broad impact on the field.