The neuronal ceroid lipofuscinoses (NCLs) are a family of devastating neurodegenerative diseases resulting from mutations in as many as 14 different genes. Researchers have long sought a molecular link between various NCLs. Recent studies suggest a common NCL pathway associated specifically with membrane associated protein forms of the disease (CLN3, CLN6, CLN5, CLN8) may be intracellular transport via disrupted interaction with the cytoskeletal network. In support of this concept, we have identified a novel complex containing the ER-associated CLN6, whose mutation results in a variant late infantile NCL (vLINCL), the collapsin response mediator protein 2 (CRMP2), and the kinesin motor protein, KLC4. Acting through a network of protein interactions, CRMP2 regulates axonal/dendritic specification and extension during neurodevelopment and contributes to maintenance/regeneration in the mature brain. We hypothesize that the CRMP2/CLN6/KLC4 (CCK) complex utilizes CLN6 as a molecular tag on ER-vesicles for segregation of cargo to distal sites in dendrites and axons. Disruption of this signaling complex could contribute to the pathogenesis of vLINCL through altered neuronal process outgrowth and maintenance. To test this hypothesis, we propose aims that will 1) determine how the CCK complex regulates ER-vesicle transport development and maintenance of neurons; 2) define how CCK complex transport is linked to early events in neuronal differentiation and identify what cargo is transported by CLN6-tagged vesicles; and 3) determine if stabilization of CRMP2-associated complexes, independent of CLN6 rescue, could ameliorate neurological deficits in a pre- clinical NCL mouse model. These studies will expands our understanding of CLN6's contribution to crucial cellular processes and start to unravel the biological significance of the CCK complex in developing and mature neurons, as well as its role and the role of intracellular trafficking in neurological disorders such as the NCLs.
Within the brain, axons and dendrites serve unique functions to pass information between neurons and, depending on where they are connecting to and the information they are responsible for transmitting, the proteins that have to be shuttled to and from these cellular processes can vary dramatically. If the cell loses the ability to selectively send essential cargo to the proper dendrites and axons, the neurons will not be able to properly communicate and eventually die, a characteristic on many neurodevelopmental and neurodegenerative diseases. Thus, understanding the fundamental mechanisms that contribute to segregation of cargo within neuronal processes and these mechanisms role in the maintenance of neural processes in the brain is critical for finding a successful treatment for many neurological disorders. In this study, we look at a novel protein complex, composed of the CRMP2, KLC4, and CLN6 proteins, which we hypothesize allows for shipment of cellular cargo to the distal sites in axons and/or dendrites that is essential for the maintenance of these processes and without which the processes become unstable, synapses disappear, and the processes degenerate.
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