Dehydroepiandrosterone (DHEA) is expected to have a weight-reducing effect. In this study, we evaluated the effect of DHEA on genetically obese Otsuka Long Evans Fatty rats (OLETF) compared with Long-Evans Tokushima rats (LETO) as control. Feeding with 0.4% DHEA-containing food for 2 wk reduced the weight of sc, epididymal, and perirenal adipose tissue in association with decreased plasma leptin levels in OLETF. Adipose tissue from OLETF showed increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma) protein, which was prevented by DHEA treatment. Further, we examined the effect of DHEA on PPARgamma in primary cultured adipocytes and monolayer adipocytes differentiated from rat preadipocytes. PPARgamma protein level was decreased in a time- and concentration-dependent manner, and DHEA significantly reduced mRNA levels of PPARgamma, adipocyte lipid-binding protein, and sterol regulatory element-binding protein, but not CCAAT/enhancer binding protein alpha. DHEA-sulfate also reduced the PPARgamma protein, but dexamethasone, testosterone, or androstenedione did not alter its expression. In addition, treatment with DHEA for 5 d reduced the triglyceride content in monolayer adipocytes. These results suggest that DHEA down-regulates adiposity through the reduction of PPARgamma in adipocytes.

In vitro phosphorylation of 180-kDa protein, obtained by immunoprecipitation of adipocyte homogenate with anti-IRS-1 antibody was increased with the addition of conventional PKC in the presence of Ca2+, phosphatidylserine (PS) and diolein (DL). Human purified IRS-1 was phosphorylated by purified conventional PKC (cPKC) in the presence of Ca2+/PS/DL. These results suggest that PKC may have a role in the serine phosphorylation of IRS-1. In order to clarify the inhibitory effect of cPKC on glucose transport mechanism, we examined the overexpression of PKCbeta in cultured adipocytes. Overexpression of PKCbeta in adipocytes markedly induced mobility shift and serine phosphorylation of IRS-1, whereas overexpression of dominant negative PKCbeta (DNPKCbeta) blocked this mobility shift and serine phosphorylation of IRS-1. Insulin (10 nM) increased [3H]2-deoxyglucose (2-DOG) uptake to 200% from basal level (100%) in cultured adipocytes transfected with a vector alone. Overexpression of PKCbeta in adipocytes decreased insulin-induced 2-DOG uptake to 110%, whereas overexpression of DNPKCbeta increased it to 230%. These results suggest that PKCbeta negatively regulates glucose uptake via serine phosphorylation of IRS-1 in rat adipocytes.

No abstract

No abstract

SummaryPretreatment with glucocorticoids for 60 min depressed insulinstimulated uptake of 2-[ 3 H] deoxyglucose (2-DOG), an effect that neither cycloheximide, an inhibitor of protein synthesis, nor RU38486, a glucocorticoid receptor antagonist, could restore. Preincubation with conventional PKC inhibitors restored dexamethasone-induced insulin resistance. We also examined the dexamethasone-mediated inhibitory effect on insulin-induced 2-DOG uptake in adipocytes overexpressed with wild-type and dominant negative forms of PKCβ. The dexamethasonemediated inhibitory effect on insulin-induced 2-DOG uptake was abrogated in adipocytes overexpressed with dominant-negative PKCβ. These results indicate that PKCβ may play an important role in glucocorticoid-induced insulin resistance. IUBMB Life, 54: 365-370, 2002