Progranulin regulates neuronal outgrowth independent of sortilin.
BACKGROUND
Progranulin (PGRN), a widely secreted growth factor, is involved in multiple biological functions, and mutations located within the PGRN gene (GRN) are a major cause of frontotemporal lobar degeneration with TDP-43-positive inclusions (FLTD-TDP). In light of recent reports suggesting PGRN functions as a protective neurotrophic factor and that sortilin (SORT1) is a neuronal receptor for PGRN, we used a Sort1-deficient (Sort1-/-) murine primary hippocampal neuron model to investigate whether PGRN's neurotrophic effects are dependent on SORT1. We sought to elucidate this relationship to determine what role SORT1, as a regulator of PGRN levels, plays in modulating PGRN's neurotrophic effects.


RESULTS
As the first group to evaluate the effect of PGRN loss in Grn knockout primary neuronal cultures, we show neurite outgrowth and branching are significantly decreased in Grn-/- neurons compared to wild-type (WT) neurons. More importantly, we also demonstrate that PGRN overexpression can rescue this phenotype. However, the recovery in outgrowth is not observed following treatment with recombinant PGRN harboring missense mutations p.C139R, p.P248L or p.R432C, indicating that these mutations adversely affect the neurotrophic properties of PGRN. In addition, we also present evidence that cleavage of full-length PGRN into granulin peptides is required for increased neuronal outgrowth, suggesting that the neurotrophic functions of PGRN are contained within certain granulins. To further characterize the mechanism by which PGRN impacts neuronal morphology, we assessed the involvement of SORT1. We demonstrate that PGRN induced-outgrowth occurs in the absence of SORT1 in Sort1-/- cultures.


CONCLUSIONS
We demonstrate that loss of PGRN impairs proper neurite outgrowth and branching, and that exogenous PGRN alleviates this impairment. Furthermore, we determined that exogenous PGRN induces outgrowth independent of SORT1, suggesting another receptor(s) is involved in PGRN induced neuronal outgrowth.
Department of Neuroscience, Mayo Clinic College of Medicine, Jacksonville, FL, USA.
Jennifer
J
Gass
Wing C
WC
Lee
Casey
C
Cook
Nicole
N
Finch
Caroline
C
Stetler
Karen
K
Jansen-West
Jada
J
Lewis
Christopher D
CD
Link
Rosa
R
Rademakers
Anders
A
Nykjær
Leonard
L
Petrucelli
D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D049109:Cell Proliferation; D004797:Enzyme-Linked Immunosorbent Assay; D057174:Frontotemporal Lobar Degeneration / Q000235:genetics / Q000378:metabolism; D000077155:Granulins; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D016501:Neurites / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009924:Organ Culture Techniques; D000077153:Progranulins; D000099183:Sortilin
D033942:Adaptor Proteins, Vesicular Transport; D000077155:Granulins; D036341:Intercellular Signaling Peptides and Proteins; D000077153:Progranulins; D000099183:Sortilin; C120204:Grn protein, mouse