1. The document summarizes research on CLN7 disease, which is caused by mutations in the CLN7 gene encoding a lysosomal membrane protein. 2. A mouse model of CLN7 disease was generated that recapitulates some neuropathological features seen in human patients, including accumulation of autofluorescent storage material in the brain. 3. The researchers aim to identify the pathomechanisms of CLN7 disease, develop biomarkers, analyze the function of the CLN7 protein, and understand how mutations impact its localization and function to inform potential therapies.

1. Variant Infantile Batten Disease
Laura Brandenstein 1, Markus Damme 4, Susanne Fehr 2, M. Schweizer 2, U. Bartsch 3, Irm Hermans-Borgmeyer 2, and Stephan Storch 1
1 Children’s Hospital Biochemistry, 2 Center for Molecular Neurobiology Hamburg, 3 Department of Ophthalmology , University Medical Center Hamburg-Eppendorf,
Hamburg, Germany, 20246; 4 Department of Biochemistry, University of Kiel, 24118 Kiel, Germany. Contact: storch@uke.de
INTRODUCTION
CLN7 disease , variant late infantile phenotype, is
caused by mutations in the CLN7 gene which
encodes a lysosomal membrane protein of unknown
function. Based on its localization and sequence
homologies with the major facilitator superfamily
CLN7 is predicted to be a lysosomal transporter.
Mutations/sequence variations in the CLN7 gene (X)
lead to the biosynthesis of an altered CLN7 protein
with substitutions of single amino acids (;; ■; *) or
the loss of many amino acids. The altered CLN7
proteins are expressed in all cells and tissues of the
organism, also in the brain.
KEY PROJECTS
WHAT THIS MEANS
FOR THERAPY
Biochemistry
Cell Biology
Molecular Biology
Immunohisto
chemistry
Methods applied in the laboratory to analyze cell
and mouse models of CLN7 disease.
Aims
1. Identification of pathomechanisms
in a mouse model for CLN7 disease
2. Identification of specific bio-markers
for CLN7 disease
3. Analyzing the physiological function
of the CLN7 membrane protein
4. Impact of pathogenic mutations on
localization and function of CLN7
Our expertise
Mass Spectrometry
Live time
imaging
Confocal Laser
Scan Microscopy
I. Analysis of intracellular trafficking
of the CLN7 protein to lysosomes
Lysosomal membrane proteins carry a lysosomal
targeting code (LTC) code in their amino acid
sequence which directs them from their site of
synthesis to their final destination, the lysosome.
We could identify two key residues in the CLN7
protein sequence which constitute the LTC for
specific delivery to lysosomes (Steenhuis et al.,
2010). The correct intracellular transport of CLN7
to lysosomes is important for its function.
CLN7 with altered lysosomal targeting code (LTC) is
mislocalized at the cell surface (A; green, CS),
whereas wild-type CLN7 reaches lysosomes (B;
yellow, LYS).
II. Analysis of spatial and temporal
expression of CLN7 in the brain.
Since CLN7 is not highly expressed in the brain
and specific antibodies detecting endogenous
CLN7 protein are lacking we use a lacZ-reporter
gene mouse model for expression analyses.
III. Analysis of a mouse model for
CLN7 disease
Histochemical detection of b-galactosidase activity
reveals high CLN7 expression in two regions of the
brain of adult mice, the hippocampus (HC, A and B)
and the cortex (Ctx, A and C).
We have generated a mouse model for CLN7
disease which recapitulates partially the
neuropathological changes observed in human
CLN7 patients (Damme et al., 2014). Analyses
revealed (A) accumulation of autofluorescent
material in the brain of CLN7 mice which was not
observed in wild type mice , (B) accumulation of
storage material (db) in neurons shown by electron
microscopy, (C) increased amounts of subunit c of
mitochondrial ATP synthase (brown, SCMAS) shown
by immunhistochemistry and (D) localization of
SCMAS (green) in neuronal cells (red) of the
cerebellum.
In the CLN7 mouse model early degeneration of
photoreceptors in the eyes was observed.
Open questions:
Which pathomechanisms contribute to
progression of CLN7 disease (impaired
autophagy, lysosomal dysfunction, altered
Ca2+ homöostasis) ?
What is/are the substrate (s) of the putative
lysosomal transporter CLN7 ?
The function of CLN7 is unknown. One goal of our
research is to analyze its putative transporter function
and to identify its substrate (s). This knowledge is
required as a basis for designing and testing experimental
therapies.
Acknowledgements:
We thank Prof. T. Braulke, Prof. A. Kohlschütter and the
research group at the UKE for continuous scientific
support of the projects. Financial support from the
German Research Foundation (DFG), from the Research
Training Group 1459 (GRK1459) and BDSRA is
acknowledged.
*
*
A
B
*
*
A) Schematic representation of the CLN7 protein.
CLN7 is a membrane protein of unknown function
localized mainly inside cells in lysosomal
membranes.
B) GFP-CLN7 (green) co-localizes with LAMP-2
(red) in lysosomes (yellow). * denote GFP-CLN7
expressing cells.
Recent publications:
Steenhuis, P., Herder, S., Gelis, S., Braulke, T., Storch, S. (2010) Lysosomal targeting of the CLN7 membrane protein and transport via the plasma membrane require a dileucine motif. Traffic, 11:987-1000.
Steenhuis, P., Froemming, J., Reinheckel, T., Storch, S. (2012) Proteolytic cleavage of the disease-related lysosomal membrane protein CLN7. Biochim. Biophys. Acta, 822:1617-1628.
Damme, M., Brandenstein, L., Fehr, S., Jankowiak, A., Bartsch, U., Hermans-Borgmeyer, I., Storch, S. (2014) Gene disruption of Mfsd8 in mice provides the first animal model for CLN7 disease. Neurobio. Dis. 65:12-24.