Mutations in the Progranulin (PGRN) gene have been linked to two distinct neurodegenerative diseases, frontotemporal lobar degeneration (FTLD) and neuronal ceroid lipofuscinosis (NCL). Accumulating evidence suggests a critical role of PGRN in the lysosome. However how PGRN regulates lysosomal function and protects against neurodegeneration remains elusive. We have identified prosaposin (PSAP), the precursor of saposin peptides essential for lysosomal glycosphingolipid degradation, as a PGRN binding partner. We further showed that PGRN facilitates PSAP lysosomal trafficking from the extracellular space via the neuronal trafficking receptor sortilin. We found reduced neuronal levels of PSAP and saposins in PGRN deficient mice and in FTLD patients due to PGRN mutations. Moreover, we showed that PGRN forms a complex with PSAP and lysosomal proteases cathepsin B and D. Cathepsin D deficiency has been reported to cause FTLD related pathology and our preliminary studies showed that impaired PSAP function also leads to FTLD related phenotypes in mice. Thus we hypothesize that PGRN is critical for proper PSAP and cathepsin B and D functions and impaired PSAP and cathepsin functions is one key disease mechanism of FTLD-PGRN. To test this hypothesis, we propose three specific aims.
In Aim1, we will examine the role of PGRN in regulating PSAP function. PSAP trafficking, processing and glycosphingolipid metabolism will be assayed in WT and PGRN-/- cells and tissues as well as control and FTLD-PGRN patient samples.
In Aim2, we will determine the role of PGRN in cathepsin B and D trafficking and activation by examining WT and PGRN-/- cells and tissues as well as control and FTLD-PGRN patient samples.
In Aim3, we will assay FTLD like phenotypes in mice with different levels of PSAP or cathepsin B or D to determine whether partial loss of PSAP or cathepsin function could contribute to FTLD disease progression. Furthermore, PSAP or cathepsin B or D will be overexpressed via adeno associated viruses (AAV) to determine whether PSAP or cathepsin overexpression can rescue phenotypes associated with PGRN loss in mice. In summary, these proposed studies will shed light on how PGRN regulates lysosomal function and provide novel insights into the disease mechanism of FTLD. We expect the results from our studies to facilitate therapeutic development for FTLD-PGRN as well other neurodegenerative diseases with a reported role of PGRN, such as Alzheimer?s disease.

Public Health Relevance

We aim to determine lysosomal function of progranulin, loss of function of which results in frontotemporal lobar degeneration (FTLD) and neuronal ceroid lipofuscinosis, and dissect molecular mechanism of FTLD due to progranulin mutations. The regulation of lysosomal proteins, prosaposin and cathepsin B and D, by progranulin and its implication for FTLD will be investigated.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS095954-02
Application #
9537693
Study Section
Cellular and Molecular Biology of Neurodegeneration Study Section (CMND)
Program Officer
Sutherland, Margaret L
Project Start
2017-08-01
Project End
2022-05-31
Budget Start
2018-06-01
Budget End
2019-05-31
Support Year
2
Fiscal Year
2018
Total Cost
Indirect Cost
Name
Cornell University
Department
Miscellaneous
Type
Organized Research Units
DUNS #
872612445
City
Ithaca
State
NY
Country
United States
Zip Code
14850
Zhou, Xiaolai; Sullivan, Peter M; Sun, Lirong et al. (2017) The interaction between progranulin and prosaposin is mediated by granulins and the linker region between saposin B and C. J Neurochem 143:236-243