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Expression of palmitoyl protein thioesterase in neurons
O Heinonen1, A Kyttälä, E Lehmus
1Department of Human Molecular Genetics, National Public Health Institute, Helsinki, 00300, Finland. Outi.Heinonen@ktl.fi
Insights
Infantile neuronal ceroid lipofuscinosis (INCL) is a childhood neurodegenerative disease. Research shows the palmitoyl protein thioesterase (PPT) enzyme is secreted by neurons and found at synapses, suggesting a role beyond lysosomal function.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Infantile neuronal ceroid lipofuscinosis (INCL) is a severe childhood neurodegenerative disorder.
- Mutations in the palmitoyl protein thioesterase (PPT) gene cause INCL, leading to cortical neuron loss.
Purpose of the Study:
- To investigate the intracellular processing and localization of the PPT enzyme in neuronal cells.
- To determine if PPT has functions beyond its known lysosomal role.
Main Methods:
- Adenovirus-mediated delivery of PPT into mouse primary neurons and PC-12 cells.
- Immunofluorescence analysis to visualize PPT localization and colocalization with synaptic markers (SV2, synaptophysin).
Main Results:
- Neuronal PPT processing is similar to peripheral cells, with significant secretion.
- PPT localizes to neuronal shafts and synaptic terminals, colocalizing with SV2 and synaptophysin.
- Endogenous PPT distribution in the mouse brain mirrors these in vitro findings.
Conclusions:
- PPT is targeted to neuritic shafts and nerve terminals, suggesting a role in synaptic function maintenance.
- The secretion of PPT by neurons implies potential extracellular substrates and functions.
- PPT may not be exclusively a lysosomal hydrolase.
Abstract:
Infantile neuronal ceroid lipofuscinosis (INCL) is a severe neurodegenerative disorder in childhood that is caused by mutations in the gene encoding lysosomal palmitoyl protein thioesterase (PPT). INCL is characterized by massive and selective loss of cortical neurons. Here we have analyzed the intracellular processing and localization of adenovirus-mediated PPT in mouse primary neurons and NGF-induced PC-12 cells. The neuronal processing of PPT was found to be similar to that observed in peripheral cells, and a significant amount of the PPT enzyme was secreted in the primary neurons. Immunofluorescence analysis of the neuronal cells infected with wild-type PPT showed a granular staining pattern in the cell soma and neuronal shafts. Interestingly, PPT was also found in the synaptic ends of the neuronal cells and the staining pattern of the enzyme colocalized to a significant extent with the synaptic markers SV2 and synaptophysin. These in vitro data correspond with the distribution of endogeneous PPT in mouse brain and suggest that PPT may not solely be a lysosomal hydrolase. The specific targeting of PPT into the neuritic shafts and nerve terminals indicates that PPT may be associated with the maintenance of synaptic function. Furthermore, since a substantial amount of PPT is secreted by neurons, it is tempting to speculate that the enzyme could also have an extracellular substrate.