In Vivo Evidence for Lysosome Depletion and Impaired Autophagic Clearance in Hereditary Spastic Paraplegia Type SPG11.
Hereditary spastic paraplegia (HSP) is characterized by a dying back degeneration of corticospinal axons which leads to progressive weakness and spasticity of the legs. SPG11 is the most common autosomal-recessive form of HSPs and is caused by mutations in SPG11. A recent in vitro study suggested that Spatacsin, the respective gene product, is needed for the recycling of lysosomes from autolysosomes, a process known as autophagic lysosome reformation. The relevance of this observation for hereditary spastic paraplegia, however, has remained unclear. Here, we report that disruption of Spatacsin in mice indeed causes hereditary spastic paraplegia-like phenotypes with loss of cortical neurons and Purkinje cells. Degenerating neurons accumulate autofluorescent material, which stains for the lysosomal protein Lamp1 and for p62, a marker of substrate destined to be degraded by autophagy, and hence appears to be related to autolysosomes. Supporting a more generalized defect of autophagy, levels of lipidated LC3 are increased in Spatacsin knockout mouse embryonic fibrobasts (MEFs). Though distinct parameters of lysosomal function like processing of cathepsin D and lysosomal pH are preserved, lysosome numbers are reduced in knockout MEFs and the recovery of lysosomes during sustained starvation impaired consistent with a defect of autophagic lysosome reformation. Because lysosomes are reduced in cortical neurons and Purkinje cells in vivo, we propose that the decreased number of lysosomes available for fusion with autophagosomes impairs autolysosomal clearance, results in the accumulation of undegraded material and finally causes death of particularly sensitive neurons like cortical motoneurons and Purkinje cells in knockout mice.
Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany; Institute of Clinical Chemistry, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Rita-Eva
RE
Varga
Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Mukhran
M
Khundadze
Biochemical Institute, University of Kiel, Kiel, Germany.
Markus
M
Damme
Electron Microscopy Center, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Sandor
S
Nietzsche
Biomolecular Photonics Group, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Birgit
B
Hoffmann
Leibniz-Institut für Molekulare Pharmakologie (FMP) und Max-Delbrück Centrum für Molekulare Medizin (MDC), Berlin, Germany.
Tobias
T
Stauber
Institute of Biochemistry I, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Nicole
N
Koch
Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
J Christopher
JC
Hennings
Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Patricia
P
Franzka
Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Antje K
AK
Huebner
Institute of Biochemistry I, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Michael M
MM
Kessels
Biomolecular Photonics Group, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Christoph
C
Biskup
Leibniz-Institut für Molekulare Pharmakologie (FMP) und Max-Delbrück Centrum für Molekulare Medizin (MDC), Berlin, Germany.
Thomas J
TJ
Jentsch
Institute of Biochemistry I, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Britta
B
Qualmann
Department of Biochemistry, Children's Hospital, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Thomas
T
Braulke
Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Ingo
I
Kurth
Institute of Clinical Chemistry, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Christian
C
Beetz
Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany.
Christian A
CA
Hübner
D000818:Animals; D001343:Autophagy; D002478:Cells, Cultured; D002531:Cerebellum / Q000473:pathology; D005260:Female; D008247:Lysosomes / Q000502:physiology*; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009044:Motor Cortex / Q000473:pathology; D011506:Proteins / Q000235:genetics*; D011689:Purkinje Cells / Q000473:pathology; D015419:Spastic Paraplegia, Hereditary / Q000235:genetics / Q000473:pathology*
D011506:Proteins; C000597153:SPG11 protein, mouse