Elaboration of type-1 plasminogen activator inhibitor from adipocytes. A potential pathogenetic link between obesity and cardiovascular disease.
BACKGROUND
Obesity is known to predispose to attenuated fibrinolysis attributable to increased concentrations in plasma of type-1 plasminogen activator inhibitor (PAI-1), the primary physiological inhibitor of endogenous fibrinolysis. PAI-1 is present in neointimal vascular smooth muscle cells and lipid-laden macrophages.


RESULTS
The present study was designed to determine whether PAI-1 expression occurs in adipose tissue as well, thereby potentially contributing to increased cardiovascular risk associated with obesity. 3T3-L1 preadipocytes were differentiated into adipocytes by exposing them to isobutylxanthine (0.5 mmol/L) and dexamethasone (0.25 mumol/L) over 7 days and incubated for 24 hours with transforming growth factor-beta (TGF-beta), known to augment PAI-1 synthesis in several cell types and to be released from platelets when they are activated. TGF-beta increased PAI-1 activity in the conditioned media of the 3T3-L1-derived cells in a concentration-dependent fashion without significantly affecting cell proliferation. Western blotting and immunoprecipitation of 35S-labeled PAI-1 showed that the increased PAI-1 activity paralleled increased PAI-1 protein. Northern blotting showed that increased PAI-1 mRNA preceded increased accumulation of PAI-1 activity and protein in the conditioned media. Furthermore, TGF-beta (10 ng/g body wt) administered in vivo increased PAI-1 activity in mouse plasma and PAI-1 mRNA expression in mouse adipose tissue.


CONCLUSIONS
Increased plasma PAI-1 activity in obese human subjects may result from PAI-1 release from an increased mass of adipose tissue, particularly in association with thrombosis and elaboration of TGF-beta from platelet alpha-granules into the circulation. The increased PAI-1 may exacerbate vascular disease by shifting the balance between thrombosis and thrombolysis toward thrombosis and consequently exposing luminal surfaces of vessels to mitogens associated with microthrombi over protracted intervals.
Lundgren
C H
CH
Cardiovascular Division, Washington University School of Medicine, St Louis, MO, USA.
Brown
S L
SL
Nordt
T K
TK
Sobel
B E
BE
Fujii
S
S
D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D002318:Cardiovascular Diseases / Q000209:etiology / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D051379:Mice; D009765:Obesity / Q000150:complications / Q000378:metabolism*; D017395:Plasminogen Activator Inhibitor 1 / Q000096:biosynthesis* / Q000097:blood; D012333:RNA, Messenger / Q000096:biosynthesis; D012307:Risk Factors; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D017395:Plasminogen Activator Inhibitor 1; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta