532 nm low-power laser irradiation recovers γ-secretase inhibitor-mediated cell growth suppression and promotes cell proliferation via Akt signaling.
OBJECTIVE
The γ-secretase inhibitor (GSI) has been shown to inhibit expression of amyloid beta (Aβ), but GSI also has a side effect of reducing cell survival. Since low-power laser irradiation (LLI) has been known to promote cell survival, we examined whether 532 nm LLI can rescue the GSI side effect or not.


METHODS
The human-derived glioblastoma cells (A-172) were cultured in 35 mm culture dishes or 96-well plate. The center of dish or selected wells was irradiated with 532 nm laser (Nd:YVO4, CW, 60 mW) for 20, 40 and 60 min, respectively. The irradiated cells were photographed at immediately after, 24 and 48 h later and counted. GSI was supplemented in medium 3 h before LLI. The MTT assay was also used to estimate viable cells at 48 h after irradiation. The expression of phosphorylated Akt (p-Akt) or phosphorylated PTEN (p-PTEN) was examined by immunofluorescent staining and measured by fluorescence intensity using the software (BZ-9000, KEYENCE, Japan).


RESULTS
GSI application depressed cell proliferation as well as cell survival compared to control. GSI down-regulated Aβ but up-regulated p-PTEN and suppressed p-Akt. Application of 532 nm LLI in the presence of GSI significantly recovered the GSI-mediated effects, i.e., LLI could decrease elevated p-PTEN, while increased p-Akt expression with keeping Aβ suppression. The LLI effects had a dose-dependency.


CONCLUSIONS
We confirmed that GSI potently suppressed intracellular Aβ and decreased cell survival. We conclude that a combination of GSI application and 532 nm LLI can increase cell proliferation via Akt activation while keeping PTEN and Aβ suppressed.
Department of Bioinformatics, Graduate School of Engineering, Soka University, Hachioji, Tokyo, Japan.
Yumi
Y
Fukuzaki
Haruna
H
Sugawara
Banri
B
Yamanoha
Shinichi
S
Kogure
D000255:Adenosine Triphosphate / Q000378:metabolism; D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects* / Q000528:radiation effects*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005455:Fluorescent Antibody Technique; D006801:Humans; D028022:Low-Level Light Therapy; D009842:Oligopeptides / Q000494:pharmacology*; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects
D009842:Oligopeptides; C523462:benzyloxycarbonyl-leucyl-leucyl-norleucinal; D000255:Adenosine Triphosphate; D051057:Proto-Oncogene Proteins c-akt; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D053829:Amyloid Precursor Protein Secretases