Investigating contributions of late endosomal and lysosomal chloride/proton antiporter dysfunction to neuronal storage - Project Summary/Abstract
Progressive neurodegenerative disorders such as Alzheimer’s and Parkinson’s are characterized by
inappropriate accumulation of proteinaceous matter within neurons, and are accompanied by a constellation of
symptoms, including gradual degeneration of movement and dementia. Accumulation of matter in lysosomes,
an intracellular compartment that degrades obsolete protein, also characterizes lysosomal storage disorders
(LSDs). The CLCN6 and CLCN7 genes encode CLC-6 and CLC-7. CLC-6, and CLC-7 in combination with an
accessory subunit, OSTM1 (CLC-7/OSTM1), are proteins that function to transport chloride and protons across
membranes defining contiguous intracellular compartments—late endosomes and lysosomes, respectively.
Variants causing CLC-6 and CLC-7 loss of function (LoF) associate with accumulation of matter within these
compartments, characteristic of LSDs. The LSDs associated with CLC-6 and CLC-7/OSTM1 LoF have distinct
differences, in onset as well as disease severity. Interestingly, variants producing CLC-6 and CLC-7/OSTM1
gain of function (GoF) associate with distinct profound neurodegenerative disease. Presently, knowledge
regarding their mechanism of function points to general similarities, as well as subtle regulatory differences.
Greater understanding about the precise transport mechanism of wild type transporters, as well as both LoF and
GoF disease-associated variants, is important for understanding disease etiologies, but also requires additional
and deeper functional analysis. To gain this needed insight, Aim 1 combines biophysical, electrophysiological,
and computational modeling approaches to extract and compare the detailed biophysical parameters regulating
function of wild-type and disease variants of CLC-6 and CLC-7. Aim 2 proposes initially to generate human iPSC-
derived CLCN6 gene-edited, differentiated neuronal lines to study early changes in compartmental homeostasis
hypothesized to precipitate disease, and aims to monitor progressive dysfunction. Time-permitting, similar
development of CLCN7 gene-edited lines can proceed. In summary, measurement, analysis, and detailed
modeling of CLC-6 and CLC-7/OSTM1 transport function offer needed insight into functional disruption in
disease-associated, transporter variants. Moreover, the proposed work provides unique neuronal cell models for
monitoring disease progression at refined resolution. Forthcoming foundational knowledge informs strategies
toward treatment of a plethora of devastating neurodegenerative diseases, thereby exerting sustained impact.
