Forkhead transcription factors (FoxOs) promote apoptosis of insulin-resistant macrophages during cholesterol-induced endoplasmic reticulum stress.
OBJECTIVE
Endoplasmic reticulum stress increases macrophage apoptosis, contributing to the complications of atherosclerosis. Insulin-resistant macrophages are more susceptible to endoplasmic reticulum stress-associated apoptosis probably contributing to macrophage death and necrotic core formation in atherosclerotic plaques in type 2 diabetes. However, the molecular mechanisms of increased apoptosis in insulin-resistant macrophages remain unclear.


METHODS
The studies were performed in insulin-resistant macrophages isolated from insulin receptor knockout or ob/ob mice. Gain- or loss-of-function approaches were used to evaluate the roles of forkhead transcription factors (FoxOs) in endoplasmic reticulum stress-associated macrophage apoptosis.


RESULTS
Insulin-resistant macrophages showed attenuated Akt activation and increased nuclear localization of FoxO1 during endoplasmic reticulum stress induced by free cholesterol loading. Overexpression of active FoxO1 or FoxO3 failed to induce apoptosis in unchallenged macrophages but exacerbated apoptosis in macrophages with an active endoplasmic reticulum stress response. Conversely, macrophages with genetic knockouts of FoxO1, -3, and -4 were resistant to apoptosis in response to endoplasmic reticulum stress. FoxO1 was shown by chromatin immunoprecipitation and promoter expression analysis to induce inhibitor of kappaBepsilon gene expression and thereby to attenuate the increase of nuclear p65 and nuclear factor-kappaB activity during endoplasmic reticulum stress, with proapoptotic and anti-inflammatory consequences.


CONCLUSIONS
Decreased Akt and increased FoxO transcription factor activity during the endoplasmic reticulum stress response leads to increased apoptosis of insulin-resistant macrophages. FoxOs may have a dual cellular function, resulting in either proapoptotic or anti-inflammatory effects in an endoplasmic reticulum stress-modulated manner. In the complex plaque milieu, the ultimate effect is likely to be an increase in macrophage apoptosis, plaque inflammation, and destabilization.
Senokuchi
Takafumi
T
Department of Medicine, Columbia University, New York, New York, USA. senokuchi@fc.kuh.kumamoto-u.ac.jp
Liang
Chien-Ping
CP
Seimon
Tracie A
TA
Han
Seongah
S
Matsumoto
Michihiro
M
Banks
Alexander S
AS
Paik
Ji-Hye
JH
DePinho
Ronald A
RA
Accili
Domenico
D
Tabas
Ira
I
Tall
Alan R
AR
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002784:Cholesterol / Q000494:pharmacology; D047369:Chromatin Immunoprecipitation; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007333:Insulin Resistance / Q000235:genetics; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011972:Receptor, Insulin / Q000235:genetics / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects; D051996:Transcription Factor RelA / Q000378:metabolism; D014162:Transfection
D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; C467200:Foxo1 protein, mouse; D011993:Recombinant Fusion Proteins; C498144:Rela protein, mouse; D051996:Transcription Factor RelA; D049452:Green Fluorescent Proteins; D002784:Cholesterol; D011972:Receptor, Insulin